Peroxide crosslinked polyethylene pipe as well as preparation method and preparation system thereof

Abstract

The invention provides a peroxide crosslinked polyethylene pipe as well as a preparation method and a preparation system thereof, and belongs to the technical field of polyethylene pipes. According to the peroxide crosslinked polyethylene pipe disclosed by the invention, the high-density polyethylene and the ultra-low-density polyethylene are adopted, and the antioxidant and the lubricant are combined, so that the heat resistance, the flexibility, the creep resistance, the environmental stress cracking resistance, the radiation resistance and the oxidation resistance of the peroxide crosslinked polyethylene pipe are improved; meanwhile, a polymer containing boric acid ester bonds is added into the assistant crosslinking agent, so that the crosslinking uniformity, radiation resistance, heat resistance, durability, aging resistance and mechanical properties of the peroxide polyethylene pipe are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of polyethylene pipes, and particularly relates to a peroxide cross-linked polyethylene pipe, a preparation method thereof, and a preparation system thereof. Background Art

[0002] Peroxide cross-linked polyethylene (PE-Xa) pipes are mainly made of high-density polyethylene. Through the action of a cross-linking agent, the linear macromolecular structure is transformed into a three-dimensional network structure, which well compensates for the disadvantages of ordinary polyethylene pipes such as low heat distortion temperature, insufficient creep resistance and rigidity. It has good heat resistance, pressure resistance, environmental stress cracking resistance and other properties, and is widely used in many fields. However, there are many deficiencies in the existing preparation technologies of peroxide cross-linked polyethylene pipes. The cross-linking reaction is difficult to precisely control, which easily leads to uneven cross-linking, resulting in unstable local properties of the pipes and affecting the overall service life and reliability. At the same time, traditional preparation methods rely on specific equipment, with high energy consumption and large costs. Moreover, in a long-term high-temperature and high-pressure environment, the cross-linked structure of some pipes is easily damaged and the performance drops significantly. Summary of the Invention

[0003] The purpose of the present disclosure is to overcome the deficiencies of the prior art and provide a peroxide cross-linked polyethylene pipe, a preparation method thereof, and a preparation system thereof.

[0004] To achieve the above purpose, the technical solutions adopted in the present disclosure are as follows: In the first aspect, a peroxide cross-linked polyethylene pipe is provided, which comprises the following components in parts by weight: 99-101 parts of polyethylene resin, 0.7-1.6 parts of peroxide cross-linking agent, 0.4-1.3 parts of co-cross-linking agent, 0.25-0.6 parts of antioxidant and 0.15-0.35 parts of lubricant; The polyethylene resin comprises high-density polyethylene and ultra-low density polyethylene, and the density of the high-density polyethylene is 0.955-0.970 g / cm 3 , and the density of the ultra-low density polyethylene is 0.860-0.900 g / cm 3 ; The co-cross-linking agent is a polymer containing a borate bond, N,N'-m-phenylene bismaleimide and trimethylolpropane trimethacrylate.

[0005] In some embodiments, the mass ratio of the high-density polyethylene to the ultra-low density polyethylene is (7-9):(1-3); In some embodiments, the melt index of the high-density polyethylene is 0.6-1.8 g / 10 min; In some embodiments, the melt index of the ultra-low density polyethylene is 1.2-3.5 g / 10 min.

[0006] In some embodiments, the mass ratio of the polymer containing a borate ester bond, N,N'-m-phenylene bismaleimide, and trimethylolpropane trimethacrylate is (0.5 - 1.2):(1 - 1.5):(1 - 1.5).

[0007] In some embodiments, the method for preparing the polymer containing a borate ester bond is as follows: React a polyol, an unsaturated acid, and an acidic catalyst at a temperature of 80 - 120°C for 4 - 8 h under an inert atmosphere to obtain an esterification product; After cooling the esterification product to 60 - 80°C, add a boron-containing compound and a complexing agent, react at a temperature of 80 - 100°C for 2 - 4 h, and then remove impurities to obtain the polymer containing a borate ester bond.

[0008] In some embodiments, the molar ratio of the polyol to the unsaturated acid is 1:(3 - 4.5).

[0009] In some embodiments, the mass of the acidic catalyst is 0.5 - 2% of the total mass of the polyol and the unsaturated acid.

[0010] In some embodiments, the molar ratio of the polyol to the boron-containing compound is 1:(0.8 - 1.2).

[0011] In some embodiments, the molar ratio of the polyol to the complexing agent is 1:(0.9 - 1.1).

[0012] In some embodiments, the polyol is at least one of pentaerythritol, dipentaerythritol, polyethylene glycol, and trimethylolpropane; In some embodiments, the unsaturated acid is at least one of acrylic acid, methacrylic acid, maleic anhydride, and itaconic acid; In some embodiments, the boron-containing compound is at least one of boric acid, borax, and phenylboronic acid; In some embodiments, the acidic catalyst is p-toluenesulfonic acid; In some embodiments, the complexing agent is at least one of ethanolamine and triethanolamine.

[0013] In some embodiments, the peroxide crosslinking agent is at least one of benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane; In some embodiments, the antioxidant is at least one of hindered amine antioxidants and thioester antioxidants; In some embodiments, the lubricant is at least one of low molecular weight esters, metal soaps, stearic acid composite esters, and amides.

[0014] In some embodiments, the peroxide crosslinking agent is benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and the mass ratio of benzoyl peroxide to 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane is (1 - 1.5):(1 - 1.5).

[0015] In some embodiments, the antioxidant is a hindered amine antioxidant and a thioester antioxidant, and the mass ratio of the hindered amine antioxidant to the thioester antioxidant is (2 - 2.5):(1 - 1.5).

[0016] In some embodiments, the lubricant is ethylene bisstearamide and silicone powder, and the mass ratio of ethylene bisstearamide to silicone powder is (1 - 1.5):(1 - 1.5).

[0017] Second, a method for preparing the peroxide crosslinked polyethylene pipe as described above is provided, comprising the following steps: Mix each component evenly according to the ratio to obtain a premix; Add the premix into a screw extruder for melt extrusion to obtain a pipe blank; Subject the pipe blank to pre-crosslinking treatment and main crosslinking treatment in sequence under infrared irradiation, and cool and post-treat the obtained crosslinked pipe to obtain a peroxide crosslinked polyethylene pipe.

[0018] In some embodiments, the parameters of the mixing satisfy at least one of the following: the temperature is below 38°C, the rotation speed is 1000 - 1400 r / min, and the time is 15 - 25 min.

[0019] In some embodiments, the parameters of the melt extrusion satisfy at least one of the following: the screw length-diameter ratio is 28 - 30:1, the temperature is 140 - 180°C, the screw rotation speed is 30 - 40 r / min, and the feeding speed is 150 - 200 kg / h.

[0020] In some embodiments, the temperature of the pre-crosslinking treatment is 185 - 230°C, and the time is 9 - 15 s.

[0021] In some embodiments, the temperature of the main crosslinking treatment is 230 - 280°C, and the time is 9 - 15 s.

[0022] In some embodiments, the end temperature of the cooling is 20 - 30°C, and the cooling rate is 5 - 10°C / min.

[0023] In some embodiments, the temperature of the post-treatment is 70 - 100°C, and the time is 20 - 30 h.

[0024] In some embodiments, when performing melt extrusion, the set temperatures of the screw extruder from the feeding port to the head are as follows: the temperature of zone 1 is 140 - 150 °C, the temperature of zone 2 is 150 - 160 °C, the temperature of zone 3 is 160 - 170 °C, the temperature of zone 4 is 150 - 160 °C, the temperature of zone 5 is 160 - 170 °C, and the temperature of zone 6 is 160 - 180 °C; In some embodiments, the pre-crosslinking treatment includes a first pre-crosslinking treatment, a second pre-crosslinking treatment, and a third pre-crosslinking treatment performed in sequence. Among them, the temperature of the first pre-crosslinking treatment is 185 - 195 °C, the temperature of the second pre-crosslinking treatment is 195 - 205 °C, and the temperature of the third pre-crosslinking treatment is 205 - 230 °C; the time of the first pre-crosslinking treatment, the second pre-crosslinking treatment, and the third pre-crosslinking treatment are each independently 3 - 5 s, and the heating rate is each independently 5 - 10 °C / s; In some embodiments, the main crosslinking treatment includes a first main crosslinking treatment, a second main crosslinking treatment, and a third main crosslinking treatment performed in sequence. Among them, the temperature of the first main crosslinking treatment is 240 - 250 °C, the temperature of the second main crosslinking treatment is 260 - 280 °C, and the temperature of the third main crosslinking treatment is 230 - 245 °C; the time of the first main crosslinking treatment, the second main crosslinking treatment, and the third main crosslinking treatment are each independently 3 - 5 s; In some embodiments, the cooling includes a first cooling treatment, a second cooling treatment, and a third cooling treatment performed in sequence. Among them, the end temperature of the first cooling treatment is 70 - 85 °C, the end temperature of the second cooling treatment is 40 - 55 °C, and the end temperature of the third cooling treatment is 20 - 30 °C.

[0025] In a third aspect, a preparation system for the peroxide crosslinked polyethylene pipe as described above is provided, including a twin-screw extruder, a feeding and discharging system, a crosslinking infrared furnace, a vacuum tank, a cooling water tank, a tractor, and a coiler; the discharging end of the feeding and discharging system is connected to the feeding end of the twin-screw extruder, and the twin-screw extruder, the crosslinking infrared furnace, the vacuum tank, the cooling water tank, the tractor, and the coiler are connected in sequence; The crosslinking infrared furnace includes a pre-crosslinking mechanism and a main crosslinking mechanism connected in sequence; the pre-crosslinking mechanism is used for performing pre-crosslinking treatment, and the main crosslinking mechanism is used for performing main crosslinking treatment; The pipe blank extruded from the twin-screw extruder passes through the crosslinking infrared furnace, the vacuum tank, and the cooling water tank in sequence through the traction mechanism of the tractor, and is wound by the coiler.

[0026] Compared with the prior art, the beneficial effects of the present disclosure are: The present invention uses high-density polyethylene and ultra-low density polyethylene, combined with antioxidants and lubricants, to improve the heat resistance, flexibility, creep resistance, environmental stress cracking resistance, radiation resistance and antioxidant properties of peroxide cross-linked polyethylene pipes, enabling peroxide polyethylene pipes to adapt to more demanding usage environments; in addition, a specific co-crosslinking agent is used to improve the cross-linking uniformity of peroxide polyethylene pipes, effectively avoiding differences in local cross-linking, significantly improving the stability of peroxide polyethylene pipes, extending the service life of peroxide polyethylene pipes, and at the same time, the polymer containing borate bonds can also endow peroxide polyethylene pipes with certain radiation resistance. The B-O-C bond in the polymer containing borate bonds endows the co-crosslinking agent with dynamic reversible cross-linking ability, enhancing the self-healing ability of the cross-linking network in peroxide polyethylene pipes, and significantly improving heat resistance, durability, anti-aging properties and mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a system diagram for the preparation of the peroxide cross-linked polyethylene pipe of the present invention; Figure 2 is a schematic structural diagram of the twin-screw extruder and the feeding and discharging system in the embodiment of the present invention; Figure 3 is a schematic structural diagram of the cross-linking infrared furnace in the embodiment of the present invention; Figure 4 is a schematic structural diagram of the vacuum tank in the embodiment of the present invention; Figure 5 is a schematic structural diagram of the cooling water tank in the embodiment of the present invention; Figure 6 is a schematic structural diagram of the tractor and the coiler in the embodiment of the present invention; Figures 1-6 In the figure, 100 is the twin-screw extruder, 101 is the feeding and discharging system, 102 is the cross-linking infrared furnace, 103 is the vacuum tank, 104 is the cooling water tank, 105 is the tractor, 106 is the coiler, 107 is the peroxide cross-linked polyethylene pipe, 200 is the pre-crosslinking mechanism, 201 is the first heating element, 202 is the second heating element, 203 is the third heating element, 300 is the main cross-linking mechanism, 301 is the fourth heating element, 302 is the fifth heating element, 303 is the sixth heating element; Figure 7 is a cross-sectional view of the peroxide cross-linked polyethylene pipe in Example 1; Figure 8 is a cross-sectional view of the peroxide cross-linked polyethylene pipe in Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0028] For ease of understanding the present disclosure, the present disclosure will be described more comprehensively below. However, the present disclosure may be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided so that the understanding of the disclosure content of the present disclosure is more thorough and comprehensive.

[0029] As used herein, the terms: "prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing" or any other variation thereof used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article or apparatus containing the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article or apparatus.

[0030] The conjunctive "consisting of" excludes any unstated element, step or component. If used in a claim, this phrase will render the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the claim body rather than immediately following the subject, it only limits the elements described in that clause; other elements are not excluded from the claim as a whole.

[0031] When an equivalent, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood to specifically disclose all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is separately disclosed. For example, when the range "1-5" is disclosed, the described range should be interpreted to include the ranges "1-4", "1-3", "1-2", "1-2 and 4-5", "1-3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range.

[0032] In these embodiments, unless otherwise specified, the parts and percentages are by mass.

[0033] "parts by mass" refers to the basic measurement unit representing the mass ratio relationship of multiple components. 1 part can represent any unit mass, such as 1 g or 2.689 g, etc. Suppose we say that the mass part of component A is a parts and the mass part of component B is b parts, then it represents the mass ratio of component A to component B as a:b. Or, it represents that the mass of component A is aK and the mass of component B is bK (K is any number representing a multiple factor). It should not be misunderstood that, different from the number of mass parts, the sum of the mass parts of all components is not limited to 100 parts.

[0034] "And / or" is used to indicate that one or both of the described situations may occur. For example, A and / or B includes (A and B) and (A or B).

[0035] To further illustrate the present invention, the peroxide cross-linked polyethylene pipe provided by the present invention, its preparation method and application will be described in detail below in conjunction with the accompanying drawings and embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0036] In the first aspect, a peroxide cross-linked polyethylene pipe is provided, which comprises the following components in parts by weight: 99 - 101 parts of polyethylene resin, 0.7 - 1.6 parts of peroxide cross-linking agent, 0.4 - 1.3 parts of co-cross-linking agent, 0.25 - 0.6 parts of antioxidant and 0.15 - 0.35 parts of lubricant; The polyethylene resin includes high-density polyethylene and ultra-low density polyethylene. The density of the high-density polyethylene is 0.955 - 0.970 g / cm 3 , and the density of the ultra-low density polyethylene is 0.860 - 0.900 g / cm 3 ; The co-cross-linking agent is a polymer containing a borate ester bond, N,N'-m-phenylene bismaleimide (HVA-2) and trimethylolpropane trimethacrylate (TMPTMA).

[0037] Specifically, the parts by weight of the peroxide cross-linking agent can be, but are not limited to, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, 1.5 parts, 1.6 parts; Specifically, the parts by weight of the co-cross-linking agent can be, but are not limited to, 0.4 parts, 0.45 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 1.1 parts, 1.2 parts, 1.3 parts; Specifically, the parts by weight of the antioxidant can be, but are not limited to, 0.25 parts, 0.3 parts, 0.35 parts, 0.4 parts, 0.45 parts, 0.5 parts, 0.55 parts, 0.6 parts; Specifically, the parts by weight of the lubricant can be, but are not limited to, 0.15 parts, 0.17 parts, 0.2 parts, 0.23 parts, 0.25 parts, 0.27 parts, 0.3 parts, 0.33 parts, 0.35 parts.

[0038] The present invention uses high-density polyethylene and ultra-low density polyethylene, combined with antioxidants and lubricants, to improve the heat resistance, flexibility, creep resistance, environmental stress cracking resistance, radiation resistance and antioxidant properties of peroxide cross-linked polyethylene pipes, enabling peroxide polyethylene pipes to adapt to more demanding usage environments; in addition, a specific co-crosslinking agent is used to improve the cross-linking uniformity of peroxide polyethylene pipes, effectively avoiding differences in local cross-linking, significantly improving the stability of peroxide polyethylene pipes, extending the service life of peroxide polyethylene pipes, and at the same time, the polymer containing borate bonds can also endow peroxide polyethylene pipes with certain radiation resistance. The B-O-C bond in the polymer containing borate bonds endows the co-crosslinking agent with dynamic reversible cross-linking ability, enhancing the self-healing ability of the cross-linking network in peroxide polyethylene pipes, and significantly improving heat resistance, durability, anti-aging properties and mechanical properties.

[0039] In some embodiments, the mass ratio of the high-density polyethylene to the ultra-low density polyethylene is (7-9):(1-3); for example, it can be but not limited to 7:3, 8:2, 9:1, 7:1, 8:3. In some embodiments, the melt index of the high-density polyethylene is 0.6-1.8 g / 10 min; for example, it can be but not limited to 0.6 g / 10 min, 0.8 g / 10 min, 1.2 g / 10 min, 1.6 g / 10 min, 1.8 g / 10 min; its test method is ASTM D1238-20, and the test conditions are 190°C / 5 kg.

[0040] In some embodiments, the melt index of the ultra-low density polyethylene is 1.2-3.5 g / 10 min, for example, it can be but not limited to 1.2 g / 10 min, 1.5 g / 10 min, 1.8 g / 10 min, 2.1 g / 10 min, 2.4 g / 10 min, 2.7 g / 10 min, 3 g / 10 min, 3.3 g / 10 min, 3.5 g / 10 min. Its test method is ASTM D1238-20, and the test conditions are 190°C / 2.16 kg.

[0041] When the melt indices of the high-density polyethylene and the low-density polyethylene and the mass ratio between the two are within the above ranges, the comprehensive performance of the peroxide cross-linked polyethylene pipes is improved.

[0042] In some embodiments, the mass ratio of the polymer containing a borate ester bond, N,N'-m-phenylene bismaleimide, and trimethylolpropane trimethacrylate is (0.5 - 1.2):(1 - 1.5):(1 - 1.5); for example, it can be but is not limited to 0.8:1:1, 0.8:1.2:1, 0.8:1.5:1, 0.8:1:1.2, 0.8:1:1.5, 1:1:1, 0.5:1:1.5, 1:1.2:1.2, 0.8:1.5:1; preferably (0.8 - 1):(1 - 1.5):(1 - 1.5).

[0043] When the mass ratio of the polymer containing a borate ester bond, N,N'-m-phenylene bismaleimide, and trimethylolpropane trimethacrylate is within the above range, the comprehensive properties of the peroxide crosslinked polyethylene pipe are improved.

[0044] In some embodiments, the preparation method of the polymer containing a borate ester bond is as follows: React polyol, unsaturated acid, and an acidic catalyst at a temperature of 80 - 120°C for 4 - 8 h in an inert atmosphere to obtain an esterification product; After cooling the esterification product to 60 - 80°C, add a boron-containing compound and a complexing agent, react at a temperature of 80 - 100°C for 2 - 4 h, and then remove impurities to obtain a polymer containing a borate ester bond.

[0045] In the present invention, the hydroxyl group in the esterification product undergoes a complexation reaction with the boron-containing compound to form a B - O - C bond, endowing the polymer containing a borate ester bond with dynamic reversible crosslinking ability.

[0046] In the present invention, the end point of the complexation reaction is determined by detecting the formation rate and content of the B - O characteristic peak in the polymer containing a borate ester bond by FT - IR.

[0047] In some embodiments, the molar ratio of the polyol to the unsaturated acid is 1:(3 - 4.5), for example, it can be but is not limited to 1:3, 1:3.3, 1:3.5, 1:3.8, 1:4, 1:4.3, 1:4.5; In some embodiments, the mass of the acidic catalyst is 0.5 - 2% of the total mass of the polyol and the unsaturated acid; for example, it can be but is not limited to 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%; In some embodiments, the molar ratio of the polyol to the boron-containing compound is 1:(0.8 - 1.2); In some embodiments, the molar ratio of the polyol to the complexing agent is 1:(0.9 - 1.1); In some embodiments, the polyol is at least one of pentaerythritol, dipentaerythritol, polyethylene glycol, trimethylolpropane; preferably, the polyol is pentaerythritol; a functionality of the polyol ≥3 can increase the number of active sites in the esterification product, facilitating the formation of more B-O-C bonds, thereby enhancing the crosslinking efficiency of the peroxide polyethylene pipe.

[0048] In some embodiments, the unsaturated acid is at least one of acrylic acid, methacrylic acid, maleic anhydride, itaconic acid; preferably, the unsaturated acid is acrylic acid; acrylic acid has high reactivity, which is beneficial for the esterification reaction with the polyol.

[0049] In some embodiments, the boron-containing compound is at least one of boric acid, borax, phenylboronic acid; preferably, the boron-containing compound is boric acid.

[0050] In some embodiments, the acidic catalyst is p-toluenesulfonic acid.

[0051] In some embodiments, the complexing agent is at least one of ethanolamine, triethanolamine.

[0052] In some embodiments, the peroxide crosslinking agent is at least one of benzoyl peroxide (BPO), 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane (DBPH); In some embodiments, the antioxidant is at least one of hindered amine antioxidants, thioester antioxidants. In some embodiments, the lubricant is at least one of low molecular weight esters, metal soaps, stearic acid composite esters, amides.

[0053] In some embodiments, the peroxide crosslinking agent is benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and the mass ratio of benzoyl peroxide to 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane is (1 - 1.5):(1 - 1.5); for example, it can be but not limited to 1:1.5, 1.2:1.3, 1.3:1.2, 1.5:1; when the mass ratio of benzoyl peroxide to 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane is within the above range, the comprehensive performance of the peroxide crosslinked polyethylene pipe is improved.

[0054] In some embodiments, the antioxidant is a hindered amine antioxidant and a thioester antioxidant, and the mass ratio of the hindered amine antioxidant to the thioester antioxidant is (2 - 2.5):(1 - 1.5); for example, it can be but is not limited to 2:1.5, 2.2:1.3, 2.4:1.1, 2.5:1; the combined use of the hindered amine antioxidant and the thioester antioxidant can play an antioxidant role at different stages and effectively inhibit the oxidative degradation of peroxide polyethylene pipes during processing and use.

[0055] In some embodiments, the lubricant is ethylene bisstearamide (EBS) and silicone powder, and the mass ratio of the ethylene bisstearamide to the silicone powder is (1 - 1.5):(1 - 1.5); for example, it can be but is not limited to 1:1.5, 1.2:1.3, 1.3:1.2, 1.5:1. The combined use of ethylene bisstearamide and silicone powder can better reduce the friction between the material and the equipment and improve the smoothness of extrusion molding.

[0056] Second, a method for preparing the peroxide cross-linked polyethylene pipe is provided, including the following steps: Mix each component evenly according to the ratio to obtain a premix; Add the premix into a screw extruder for melt extrusion to obtain a pipe blank; Subject the pipe blank to pre-crosslinking treatment and main crosslinking treatment successively under infrared irradiation, and cool and post-treat the obtained cross-linked pipe to obtain a peroxide cross-linked polyethylene pipe.

[0057] By subjecting the pipe blank to pre-crosslinking treatment and main crosslinking treatment, the present invention is conducive to improving the crosslinking uniformity and stability of the peroxide polyethylene pipe.

[0058] In some embodiments, the parameters of the mixing at least meet one of the following: the temperature is below 38 °C, the rotation speed is 1000 - 1400 r / min, and the time is 15 - 25 min; the above mixing conditions can ensure that each component is fully and evenly mixed and improve the crosslinking effect of the peroxide polyethylene pipe.

[0059] In some embodiments, the parameters of the melt extrusion at least meet one of the following: the screw length-diameter ratio is 28 - 30:1, the temperature is 140 - 180 °C, the screw rotation speed is 30 - 40 r / min, and the feeding speed is 150 - 200 kg / h.

[0060] Specifically, when performing melt extrusion, the set temperatures of the screw extruder from the feeding port to the die head are as follows: the temperature of zone 1 is 140 - 150 °C, the temperature of zone 2 is 150 - 160 °C, the temperature of zone 3 is 160 - 170 °C, the temperature of zone 4 is 150 - 160 °C, the temperature of zone 5 is 160 - 170 °C, and the temperature of zone 6 is 160 - 180 °C.

[0061] Appropriate screw length - diameter ratio, screw speed, feeding speed, and the temperature of multi - stage melt extrusion can ensure that the material is fully plasticized and uniformly mixed during the extrusion process, improving the forming quality of the pipe.

[0062] In some embodiments, the temperature of the pre - crosslinking treatment is 185 - 230 °C, and the time is 9 - 15 s; Specifically, the pre - crosslinking treatment includes a first pre - crosslinking treatment, a second pre - crosslinking treatment, and a third pre - crosslinking treatment carried out in sequence. Among them, the temperature of the first pre - crosslinking treatment is 185 - 195 °C, the temperature of the second pre - crosslinking treatment is 195 - 205 °C, and the temperature of the third pre - crosslinking treatment is 205 - 230 °C; the time of the first pre - crosslinking treatment, the second pre - crosslinking treatment, and the third pre - crosslinking treatment are each independently 3 - 5 s, and the heating rate is each independently 5 - 10 °C / s; In some embodiments, the temperature of the main crosslinking treatment is 230 - 280 °C, and the time is 9 - 15 s; The main crosslinking treatment includes a first main crosslinking treatment, a second main crosslinking treatment, and a third main crosslinking treatment carried out in sequence. Among them, the temperature of the first main crosslinking treatment is 240 - 250 °C, the temperature of the second main crosslinking treatment is 260 - 280 °C, and the temperature of the third main crosslinking treatment is 230 - 245 °C; the time of the first main crosslinking treatment, the second main crosslinking treatment, and the third main crosslinking treatment are each independently 3 - 5 s.

[0063] The present invention adopts a multi - stage variable - temperature treatment process for pre - crosslinking treatment and main crosslinking treatment. The combination of the two makes the crosslinking reaction more controllable and uniform, effectively avoiding local crosslinking differences and significantly improving the stability of the overall performance of peroxide - crosslinked polyethylene pipes; specifically, the first pre - crosslinking treatment makes the peroxide crosslinking agent start to decompose slowly, initiating partial crosslinking reactions and forming a small number of crosslinking points; the second pre - crosslinking treatment further promotes the progress of the crosslinking reaction and increases the number of crosslinking points; the third pre - crosslinking treatment makes the crosslinking structure initially stable and reduces stress concentration; the first main crosslinking treatment makes the crosslinking reaction proceed rapidly, forming a large number of crosslinking points and starting to connect into a crosslinking network structure; the second main crosslinking treatment further improves the crosslinking network structure and increases the crosslinking degree of peroxide - crosslinked polyethylene pipes; the third main crosslinking treatment ensures that the crosslinking reaction is fully completed, forming a uniform and firm three - dimensional crosslinking network.

[0064] Specifically, during the pre-crosslinking treatment and the crosslinking treatment, the temperature difference between adjacent stages is 10-20°C; The precise temperature difference and the heating and cooling rates can effectively control the process and uniformity of the crosslinking reaction, making the network crosslinked structure in the peroxide crosslinked polyethylene pipe more dense and stable.

[0065] In some embodiments, the end temperature of the cooling is 20-30°C, and the cooling rate is 5-10°C / min; Specifically, the cooling includes a first cooling treatment, a second cooling treatment, and a third cooling treatment carried out in sequence, wherein the end temperature of the first cooling treatment is 70-85°C, the end temperature of the second cooling treatment is 40-55°C, and the end temperature of the third cooling treatment is 20-30°C.

[0066] Specifically, the time of the first cooling treatment, the second cooling treatment, and the third cooling treatment are each independently 3-5 min.

[0067] The cooling rate and the multi-stage cooling treatment method can ensure the dimensional stability and the internal structure uniformity of the peroxide crosslinked polyethylene pipe. Specifically, the first cooling treatment can rapidly cool the peroxide crosslinked polyethylene pipe while avoiding internal stress caused by rapid cooling; the second cooling treatment further reduces the temperature of the peroxide crosslinked polyethylene pipe and stabilizes the crosslinked structure; the third cooling treatment brings the peroxide crosslinked polyethylene pipe to room temperature and completes the cooling and shaping.

[0068] Specifically, before cooling, a vacuum shaping treatment is also included. By evacuating the vacuum tank to form a negative pressure, the pipe blank can be rapidly shaped before cooling, avoiding deformation caused by gravity or thermal expansion; the vacuum pressure makes the pipe blank closely adhere to the shaping mold, ensuring the uniformity of the outer diameter and wall thickness of the pipe, and at the same time eliminating surface defects (such as bubbles and wrinkles) after melt extrusion, improving the surface smoothness of the pipe. Further, the vacuum shaping treatment can also assist in cooling, reducing the internal stress concentration of the pipe blank and improving the structural density of the pipe.

[0069] In some embodiments, the temperature of the post-treatment is 70-100°C, and the time is 20-30 h.

[0070] Within the above parameter range of the post-treatment, the residual internal stress of the peroxide crosslinked polyethylene pipe can be eliminated, and at the same time, moderate secondary crosslinking is carried out, improving the performance stability of the peroxide crosslinked polyethylene pipe; in addition, the post-treatment can also eliminate the residual peroxide, reaction by-products, and odors, ensuring the hygienic performance.

[0071] In order to avoid the influence of moisture and volatile impurities, before the raw material mixing, the polyethylene resin needs to be dried, and the drying temperature is 90-100°C, and the time is 6-8 h.

[0072] In a third aspect, as Figures 1-6 shown, a preparation system for the peroxide cross-linked polyethylene pipe as described above is provided, including a twin-screw extruder 100, a loading and unloading system 101, a cross-linking infrared furnace 102, a vacuum tank 103, a cooling water tank 104, a tractor 105, and a winding machine 106; the unloading end of the loading and unloading system 101 is connected to the feeding end of the twin-screw extruder 100, and the twin-screw extruder 100, the cross-linking infrared furnace 102, the vacuum tank 103, the cooling water tank 104, the tractor 105, and the winding machine 106 are connected in sequence; The interior of the cross-linking infrared furnace includes a pre-cross-linking mechanism 200 and a main cross-linking mechanism 300 connected in sequence; the pre-cross-linking mechanism 200 is used for pre-cross-linking treatment, and the main cross-linking mechanism 300 is used for main cross-linking treatment; The pipe blank extruded from the twin-screw extruder 100 passes through the cross-linking infrared furnace 102, the vacuum tank 103, and the cooling water tank 104 in sequence through the traction mechanism of the tractor 105, and is wound by the winding machine 106.

[0073] Specifically, the pre-cross-linking mechanism 200 includes a first chamber, a second chamber, and a third chamber connected in sequence through a through hole; the first chamber, the second chamber, and the third chamber are isolated from each other so that the first chamber, the second chamber, and the third chamber can be maintained at respective preset temperatures. The through hole is for the pipe to pass through, and the pipe blank passes through the through hole and passes through the first chamber, the second chamber, and the third chamber in sequence. A first heating element 201 is connected in the first chamber, a second heating element 202 is connected in the second chamber, and a third heating element 203 is connected in the third chamber; the first heating element 201 is used to adjust the temperature of the first pre-cross-linking treatment, the second heating element 202 is used to adjust the temperature of the second pre-cross-linking treatment, and the third heating element 203 is used to adjust the temperature of the third pre-cross-linking treatment.

[0074] Specifically, the main cross-linking mechanism 300 includes a fourth chamber, a fifth chamber, and a sixth chamber connected in sequence through a through hole. The fourth chamber, the fifth chamber, and the sixth chamber are isolated from each other so that the fourth chamber, the fifth chamber, and the sixth chamber can be maintained at respective preset temperatures. The through hole is for the pipe to pass through, and the pipe blank passes through the through hole and passes through the fourth chamber, the fifth chamber, and the sixth chamber in sequence. A fourth heating element 301 is connected in the fourth chamber, a fifth heating element 302 is connected in the fifth chamber, and a sixth heating element 303 is connected in the sixth chamber; the fourth heating element 301 is used to adjust the temperature of the first main cross-linking treatment, the fifth heating element 302 is used to adjust the temperature of the second main cross-linking treatment, and the sixth heating element 303 is used to adjust the temperature of the third main cross-linking treatment.

[0075] In the present invention, the cross-linking infrared furnace has a plurality of heating elements. Through the plurality of heating elements, the temperatures and times of the pre-cross-linking reaction and the main cross-linking reaction can be independently controlled respectively, and the process of the cross-linking reaction of the peroxide cross-linked polyethylene pipe can be accurately controlled. Among them, the pre-cross-linking mechanism realizes the stepwise temperature-rising pre-cross-linking reaction, and the main cross-linking mechanism adopts a three-stage temperature control of high temperature - temperature rising - temperature decreasing to realize the high-temperature main cross-linking reaction and temperature decreasing and curing, so that the peroxide cross-linked polyethylene pipe forms a dynamic cross-linking network; the problem of uneven cross-linking of the peroxide cross-linked polyethylene pipe in the traditional technology is solved, and the heat resistance and mechanical properties of the peroxide cross-linked polyethylene pipe are significantly improved.

[0076] Specifically, the cooling water tank 104 includes a first cooling element, a second cooling element and a third cooling element connected in sequence. The first cooling element is used to control the temperature of the first cooling treatment, the second cooling element is used to control the temperature of the second cooling treatment, and the third cooling element is used to control the temperature of the third cooling treatment.

[0077] The pipe after passing through the cross-linking infrared furnace sequentially passes through vacuum sizing (vacuum tank) and three-stage gradient temperature reduction cooling (cooling water tank) to avoid stress concentration of the peroxide cross-linked polyethylene pipe and improve the overall performance of the peroxide cross-linked polyethylene pipe.

[0078] Specifically, a method for preparing a peroxide cross-linked polyethylene pipe by using the preparation system of the peroxide cross-linked polyethylene pipe includes the following steps: After mixing each component evenly, the obtained premix is conveyed to the twin-screw extruder 100 through the discharging end of the feeding and discharging system 101 for melting and plasticizing extrusion to obtain a pipe blank. The pipe blank enters the pre-cross-linking mechanism 200 through the traction mechanism of the tractor 105 for pre-cross-linking treatment, then enters the main cross-linking mechanism 300 for main cross-linking treatment, then enters the vacuum tank 103 for vacuum sizing, then enters the cooling water tank 104 for cooling and sizing, and then is wound by the winding machine 106 to obtain a semi-finished product. The obtained semi-finished product is post-treated to obtain the peroxide cross-linked polyethylene pipe 107.

[0079] The raw materials used in the examples and comparative examples are described as follows, but are not limited to these materials: High-density polyethylene A: The density is 0.953 g / cm³, and the melt index at 190 °C and 5 kg is 0.7 g / 10 min, Lupolen 5461B Q471 B (Basell); High-density polyethylene B: The density is 0.965 g / cm³, and the melt index at 190 °C and 5 kg is 1.2 g / 10 min, ExxonMobil HDPE HDZ-100 (ExxonMobil); Ultra-low density polyethylene A: density is 0.880 g / cm³, melt index is 2.0 g / 10 min at 190 °C and 2.16 kg, Dow ATTANE™ 4203 (Dow Chemical); Ultra-low density polyethylene B: density is 0.890 g / cm³, melt index is 2.5 g / 10 min at 190 °C and 2.16 kg, Mitsui ULDPE SP0540 (Mitsui Chemicals); Linear low density polyethylene: density is 0.920 g / cm³, melt index is 1.0 g / 10 min at 190 °C and 2.16 kg, ExxonMobil LLDPE LL 1001 (ExxonMobil); The polymer containing borate bond is self-made, and its preparation method is as follows: Add pentaerythritol and acrylic acid with a molar ratio of 1:3 into the reaction kettle, and at the same time add p-toluenesulfonic acid, and the mass of p-toluenesulfonic acid is 1% of the total mass of pentaerythritol and acrylic acid; Then under the protection of nitrogen, heat up to 100 °C, stir for esterification reaction, and remove the water generated by the esterification reaction through a water separator. When the acid value in the reaction product ≤ 5 mg KOH / g, terminate the esterification reaction to obtain an esterification product; Cool the esterification product to 80 °C, add boric acid, then dropwise add triethanolamine at a dropping rate of 1 mL / min, react at 80 °C for 4 h. After the obtained reaction product removes low-boiling substances by vacuum distillation, dissolve it with acetone, and filter and dry the obtained solution to obtain a polymer A containing borate bond; Among them, the molar ratio of triethanolamine to boric acid is 1:1.

[0080] Hindered amine antioxidant: the polymer of succinic acid and (4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol), abbreviated as antioxidant GW-622, commercially available; Thioester antioxidant: dilauryl thiodipropionate, abbreviated as antioxidant DLTP, commercially available; Hindered phenol antioxidant: pentaerythritol tetra(3,5-di-tert-butyl-4-hydroxyhydrocinnamate), commercially available; Except for the above specific descriptions, each parallel example and comparative example use the same commercially available or self-made variety for a certain component (such as high density polyethylene, peroxide crosslinking aid, antioxidant, lubricant, etc.).

[0081] Examples 1-13 and Comparative Examples 1-5 The composition components of the peroxide crosslinked polyethylene pipes described in Examples 1-13 and Comparative Examples 1-5 are shown in Tables 1 and 2; The preparation method of the peroxide crosslinked polyethylene pipe described in Example 1 includes the following steps: Add each component into a high-speed mixer according to the parts by weight in Table 1, and stir at a speed of 1200 r / min at a temperature of 25 °C for 20 min to obtain a premix; Transport the premix to a co-rotating twin-screw extruder through a loading and unloading system at a feeding speed of 150 kg / h for melt extrusion to obtain a pipe blank; wherein, the length-diameter ratio of the twin-screw is 30:1, the screw speed is 35 r / min. During melt extrusion, the set temperatures of the co-rotating twin-screw extruder from the feeding port to the die head are as follows: the temperature of zone 1 is 140 - 150 °C, the temperature of zone 2 is 150 - 160 °C, the temperature of zone 3 is 160 - 170 °C, the temperature of zone 4 is 150 - 160 °C, the temperature of zone 5 is 160 - 170 °C, and the temperature of zone 6 is 160 - 180 °C; Add the pipe blank into a pre-crosslinking mechanism to perform the first pre-crosslinking treatment, the second pre-crosslinking treatment, and the third pre-crosslinking treatment in sequence to obtain a pre-crosslinked pipe. Among them, the temperature of the first pre-crosslinking treatment is 195 °C and the time is 5 s; the temperature of the second pre-crosslinking treatment is 200 °C, the time is 5 s, and the heating rate is 5 °C / s; the temperature of the third pre-crosslinking treatment is 230 °C, the time is 5 s, and the heating rate is 30 °C / s; Add the pre-crosslinked pipe into a main crosslinking mechanism to perform the first main crosslinking treatment, the second main crosslinking treatment, and the third main crosslinking treatment in sequence to obtain a crosslinked pipe; among them, the temperature of the first main crosslinking treatment is 245 °C and the time is 5 s; the temperature of the second main crosslinking treatment is 275 °C, the time is 5 s, and the heating rate is 30 °C / s; the temperature of the third main crosslinking treatment is 235 °C, the time is 5 s, and the cooling rate is 30 °C / s; Add the crosslinked pipe into a vacuum tank for vacuum shaping, and add the obtained pipe into a cooling water tank to perform the first cooling treatment, the second cooling treatment, and the third cooling treatment in sequence, and then draw it through a drawing machine and collect it with a winding machine to obtain a semi-finished product; among them, the end temperature of the first cooling treatment is 75 °C and the time is 5 min; the end temperature of the second cooling treatment is 50 °C, the time is 5 min, and the cooling rate is 10 °C / min. The end temperature of the third cooling treatment is 25 °C and the time is 5 min, and the cooling rate is 10 °C / min; Place the semi-finished product in a hot air circulation oven and heat-treat it at a temperature of 85 °C for 24 h to obtain a peroxide crosslinked polyethylene pipe.

[0082] The preparation method of the peroxide crosslinked polyethylene pipe described in Example 2 includes the following steps: Add each component into a high-speed mixer according to the parts by weight in Table 1, and stir at a speed of 1200 r / min at a temperature of 25 °C for 20 min to obtain a premix; The premix is conveyed into a co-rotating twin-screw extruder through a loading and unloading system at a feeding speed of 150 kg / h for melt extrusion to obtain a pipe blank; wherein, the ratio of the length to the diameter of the twin-screw is 30:1, the screw rotation speed is 35 r / min, and when melt extruding, the set temperatures of the co-rotating twin-screw extruder from the feeding port to the die head are as follows: the temperature of zone 1 is 140 - 150 °C, the temperature of zone 2 is 150 - 160 °C, the temperature of zone 3 is 160 - 170 °C, the temperature of zone 4 is 150 - 160 °C, the temperature of zone 5 is 160 - 170 °C, and the temperature of zone 6 is 160 - 180 °C; The pipe blank is added into a pre-crosslinking mechanism to carry out the first pre-crosslinking treatment, the second pre-crosslinking treatment and the third pre-crosslinking treatment in sequence to obtain a pre-crosslinked pipe; wherein, the temperature of the first pre-crosslinking treatment is 200 °C and the time is 5 s; the temperature of the second pre-crosslinking treatment is 205 °C, the time is 5 s, and the heating rate is 5 °C / s; the temperature of the third pre-crosslinking treatment is 240 °C, the time is 5 s, and the heating rate is 35 °C / s; The pre-crosslinked pipe is added into a main crosslinking mechanism to carry out the first main crosslinking treatment, the second main crosslinking treatment and the third main crosslinking treatment in sequence to obtain a main crosslinked pipe; wherein, the temperature of the first crosslinking treatment is 250 °C and the time is 5 s; the temperature of the second crosslinking treatment is 280 °C, the time is 5 s, and the heating rate is 30 °C / s; the temperature of the third crosslinking treatment is 240 °C, the time is 5 s, and the cooling rate is 40 °C / s; The crosslinked pipe is added into a vacuum tank for vacuum shaping, and the obtained pipe is added into a cooling water tank to carry out the first cooling treatment, the second cooling treatment and the third cooling treatment in sequence, and then is drawn by a drawing machine and collected by a coiling machine to obtain a semi-finished product; wherein, the end temperature of the first cooling treatment is 75 °C and the time is 5 min; the end temperature of the second cooling treatment is 50 °C, the time is 5 min, and the cooling rate is 10 °C / min, and the end temperature of the third cooling treatment is 25 °C, the time is 5 min, and the cooling rate is 10 °C / min; The semi-finished product is placed in a hot air circulation oven and heat-treated at a temperature of 85 °C for 24 h to obtain a peroxide crosslinked polyethylene pipe.

[0083] The preparation method of the peroxide crosslinked polyethylene pipes in Examples 3 - 13 and Comparative Examples 1 - 5 includes the following steps: Each component is added into a high-speed mixer according to the parts by weight in Table 1 and Table 2, and stirred at a rotation speed of 1200 r / min at a temperature of 25 °C for 20 min to obtain a premix; The premix is conveyed into a co-rotating twin-screw extruder through a loading and unloading system at a feeding speed of 150 kg / h for melt extrusion to obtain a pipe blank; wherein, the length-diameter ratio of the twin-screws is 30:1, the screw speed is 35 r / min, and during melt extrusion, the set temperatures of the twin-screw extruder from the feeding port to the die head are as follows: the temperature of zone 1 is 140 - 150 °C, the temperature of zone 2 is 150 - 160 °C, the temperature of zone 3 is 160 - 170 °C, the temperature of zone 4 is 150 - 160 °C, the temperature of zone 5 is 160 - 170 °C, and the temperature of zone 6 is 160 - 180 °C; The pipe blank is added into a pre-crosslinking mechanism to successively carry out the first pre-crosslinking treatment, the second pre-crosslinking treatment, and the third pre-crosslinking treatment to obtain a pre-crosslinked pipe; wherein, the temperature of the first pre-crosslinking treatment is 195 °C and the time is 5 s; the temperature of the second pre-crosslinking treatment is 200 °C, the time is 5 s, and the heating rate is 5 °C / s; the temperature of the third pre-crosslinking treatment is 230 °C, the time is 5 s, and the heating rate is 30 °C / s; The pre-crosslinked pipe is added into a main crosslinking mechanism to successively carry out the first main crosslinking treatment, the second main crosslinking treatment, and the third main crosslinking treatment to obtain a crosslinked pipe; wherein, the temperature of the first main crosslinking treatment is 245 °C and the time is 5 s; the temperature of the second main crosslinking treatment is 275 °C, the time is 5 s, and the heating rate is 30 °C / s; the temperature of the third main crosslinking treatment is 235 °C, the time is 5 s, and the cooling rate is 30 °C / s; The crosslinked pipe is added into a vacuum tank for vacuum sizing, and the obtained pipe is added into a cooling water tank to successively carry out the first cooling treatment, the second cooling treatment, and the third cooling treatment, and then is drawn by a drawing machine and collected by a winding machine to obtain a semi-finished product; wherein, the end temperature of the first cooling treatment is 75 °C and the time is 5 min; the end temperature of the second cooling treatment is 50 °C, the time is 5 min, and the cooling rate is 10 °C / min, and the end temperature of the third cooling treatment is 25 °C, the time is 5 min, and the cooling rate is 10 °C / min; The semi-finished product is placed in a hot air circulation oven and heat-treated at a temperature of 85 °C for 24 h to obtain a peroxide crosslinked polyethylene pipe.

[0084] Table 1 Table 2 Example 14 The composition of the peroxide crosslinked polyethylene pipe in this example is the same as that in Example 1.

[0085] The preparation method of the peroxide cross-linked polyethylene pipe in this example is only different from the preparation method of the peroxide cross-linked polyethylene pipe in Example 1 in that: the pre-crosslinking treatment step in the preparation method is different. The pre-crosslinking treatment steps in this example are as follows: adding the pipe blank into the pre-crosslinking mechanism to successively carry out the first pre-crosslinking treatment, the second pre-crosslinking treatment, and the third pre-crosslinking treatment to obtain the pre-crosslinked pipe. Among them, the temperatures of the first pre-crosslinking treatment, the second pre-crosslinking treatment, and the third pre-crosslinking treatment are all 210 °C, and the time is all 5 s.

[0086] Example 15 The composition of the peroxide cross-linked polyethylene pipe in this example is the same as that in Example 1.

[0087] The preparation method of the peroxide cross-linked polyethylene pipe in this example is only different from the preparation method of the peroxide cross-linked polyethylene pipe in Example 1 in that: the main cross-linking treatment step in the preparation method is different. The main cross-linking treatment steps in this example are as follows: adding the pre-crosslinked pipe into the main cross-linking mechanism to successively carry out the first main cross-linking treatment, the second main cross-linking treatment, and the third main cross-linking treatment to obtain the cross-linked pipe; among them, the temperatures of the first cross-linking treatment, the second cross-linking treatment, and the third cross-linking treatment are all 250 °C, and the time is all 5 s.

[0088] Example 16 The composition of the peroxide cross-linked polyethylene pipe in this example is the same as that in Example 1.

[0089] The preparation method of the peroxide cross-linked polyethylene pipe in this example is only different from the preparation method of the peroxide cross-linked polyethylene pipe in Example 1 in that: the cooling and shaping step in the preparation method is different. The cooling and shaping steps in this example are as follows: adding the cross-linked pipe into the vacuum tank for vacuum shaping, adding the obtained pipe into the cooling water tank for cooling treatment, and then passing through the drawing machine for drawing and the coiling machine for collection to obtain the semi-finished product; among them, the end temperature of cooling is 25 °C, the time is 15 min, and the cooling rate is 10 °C / min.

[0090] Performance test Perform performance tests on the peroxide cross-linked polyethylene pipes obtained in the examples and comparative examples. The test methods are as follows: (1) Crosslinking degree: ASTM D2765-16 (2024) (xylene extraction method), calculate the mass fraction of insoluble matter; (2) Tensile strength: ISO6529-2:2020, test speed 50 mm / min, dumbbell-shaped specimen; (3) Heat distortion temperature: ISO 75-2:2013, temperature when the load is 0.45 MPa and the deformation is 2 mm; (4)Environmental stress cracking resistance time: ASTM D1693-15, a solution of polyoxyethylene (9) nonylphenyl ether (CAS No. 68412-54-4) with a mass-volume concentration of 50 g / mL, Type A specimen, notch depth of 0.3 mm, record the cracking time at 80 °C; (5)Radiation resistance: ASTM D1879-06(2023), irradiated with cobalt-60 γ-rays, dose rate of 5 kGy / h, total absorbed dose of 200 kGy, test the tensile strength retention rate and surface morphology change after irradiation; (6)Antioxidant performance: ISO 11346:2014 (oxidation induction time method, OIT), test conditions: 200 °C, oxygen flow rate of 50 mL / min, record the oxidation induction time (minutes) to reflect the antioxidant ability of the material.

[0091] The test results are shown in Table 3.

[0092] Table 3 It can be seen from the experimental data in Table 3 that the crosslinking degree of the peroxide-crosslinked polyethylene of the present invention is greater than or equal to 70%, the tensile strength is greater than or equal to 23 MPa, the heat distortion temperature is greater than or equal to 105 °C, the environmental stress cracking resistance time is greater than or equal to 500 h. After radiation, the tensile strength retention rate is greater than or equal to 85%, and the antioxidant performance is greater than or equal to 35 min.

[0093] From the experimental data of Example 1 and Examples 4-5, it can be known that the peroxide crosslinking agent is benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane. The crosslinking degree of the obtained peroxide-crosslinked polyethylene is greater than or equal to 85%, the tensile strength is greater than or equal to 28 MPa, the heat distortion temperature is greater than or equal to 120 °C, the environmental stress cracking resistance time is ≥800 h. After radiation, the tensile strength retention rate is greater than or equal to 95%, and the antioxidant performance is greater than or equal to 45 min. This shows that the compound use of benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane can improve the overall performance of peroxide-crosslinked polyethylene.

[0094] From the comparison of Example 1 and Examples 6-8, it can be known that the antioxidants are hindered amine antioxidants and thioester antioxidants; the crosslinking degree of the obtained peroxide-crosslinked polyethylene is greater than or equal to 85%, the tensile strength is greater than or equal to 28 MPa, the heat distortion temperature is greater than or equal to 120 °C, the environmental stress cracking resistance time is greater than or equal to 800 h. After radiation, the tensile strength retention rate is greater than or equal to 95%, and the antioxidant performance is greater than or equal to 45 min. This shows that the compound use of hindered amine antioxidants and thioester antioxidants can improve the overall performance of peroxide-crosslinked polyethylene.

[0095] From the experimental data of Example 1 and Examples 9 - 10, it can be seen that the lubricants are ethylene bisstearamide and silicone powder; the crosslinking degree of the obtained peroxide crosslinked polyethylene is greater than or equal to 85%, the tensile strength is greater than or equal to 28 MPa, the heat distortion temperature is greater than or equal to 120 °C, the environmental stress cracking resistance time is greater than or equal to 800 h. After radiation, the tensile strength retention rate is greater than or equal to 95%, and the antioxidant performance is greater than or equal to 45 min, indicating that the compound use of ethylene bisstearamide and silicone powder can improve the overall performance of peroxide crosslinked polyethylene.

[0096] From the experimental data of Example 1 and Examples 11 - 13, it can be seen that when the mass ratio of the borate - bond - containing polymer, N,N'-m - phenylene dimaleimide and trimethylolpropane trimethacrylate is (0.8 - 1):(1 - 1.5):(1 - 1.5), the crosslinking degree of the obtained peroxide crosslinked polyethylene is greater than or equal to 84%, the tensile strength is greater than or equal to 27 MPa, the heat distortion temperature is greater than or equal to 119 °C, the environmental stress cracking resistance time is greater than or equal to 770 h. After radiation, the tensile strength retention rate is greater than or equal to 93%, and the antioxidant performance is greater than or equal to 43 min, indicating that when the mass ratio of the borate - bond - containing polymer, N,N'-m - phenylene dimaleimide and trimethylolpropane trimethacrylate is (0.8 - 1):(1 - 1.5):(1 - 1.5), it can improve the overall performance of peroxide crosslinked polyethylene.

[0097] Comparing Example 1 with Examples 14 - 16, it can be seen that using single - temperature treatment for pre - crosslinking treatment, main crosslinking treatment or cooling treatment will all lead to a decrease in the overall performance of peroxide crosslinked polyethylene, indicating that using multi - stage variable - temperature treatment for pre - crosslinking treatment, main crosslinking treatment and cooling treatment, the multi - stage variable - temperature process controls the crosslinking rate in stages, avoids local stress concentration, improves material uniformity, and enhances the overall performance of peroxide crosslinked polyethylene.

[0098] Comparing Example 1 with Comparative Examples 1 - 4, it can be seen that when using a single co - crosslinking agent, the crosslinking degree of the obtained peroxide crosslinked polyethylene is less than or equal to 70%, the tensile strength is less than or equal to 20 MPa, the heat distortion temperature is less than or equal to 100 °C, the environmental stress cracking resistance time is less than or equal to 300 h. After radiation, the tensile strength retention rate is less than or equal to 50%, and the antioxidant performance is less than or equal to 8 min, indicating that there is a synergistic effect between N,N'-m - phenylene dimaleimide, trimethylolpropane trimethacrylate and the borate - bond - containing polymer. The three components synergistically enhance the dynamic reversibility and self - healing ability of the crosslinking network, effectively improving the overall performance of peroxide crosslinked polyethylene pipes.

[0099] Comparing Example 1 and Comparative Example 5, it can be seen that when linear low-density polyethylene is used to replace ultra-low-density polyethylene, the crosslinking degree of the obtained peroxide-crosslinked polyethylene is 65%, the tensile strength is 18 MPa, the heat distortion temperature is 95 °C, the environmental stress cracking resistance time is 150 h. After radiation, the tensile strength retention rate is 40%, and the antioxidant performance is 5 min. This shows that only ultra-low-density polyethylene can improve the overall performance of peroxide polyethylene pipes.

[0100] The fracture morphologies of the peroxide-crosslinked polyethylene pipes obtained in the examples and comparative examples were observed using a scanning electron microscope, and the results are as Figures 7-8 shown. It can be seen from Figures 7-8 that the cross-section of the peroxide-crosslinked polyethylene pipe obtained in Example 1 presents a uniform dimple structure, indicating that the crosslinking network is uniformly dispersed; obvious cracks and voids exist in the cross-section of the peroxide-crosslinked polyethylene pipe obtained in Comparative Example 3, indicating that defects are caused by uneven crosslinking.

[0101] Finally, it should be noted that the above examples are used to illustrate the technical solutions of the present disclosure rather than to limit the protection scope of the present disclosure. Although the present disclosure has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present disclosure can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present disclosure.

Claims

1. A peroxide cross-linked polyethylene pipe, characterized in that: The invention comprises the following components in parts by weight: 99-101 parts of polyethylene resin, 0.7-1.6 parts of peroxide crosslinking agent, 0.4-1.3 parts of auxiliary crosslinking agent, 0.25-0.6 parts of antioxidant and 0.15-0.35 parts of lubricant; The polyethylene resin includes high-density polyethylene and ultra-low-density polyethylene, and the density of the high-density polyethylene is 0.955-0.970 g / cm 3 The density of the ultra-low density polyethylene is 0.860-0.900 g / cm 3 ; The auxiliary cross-linking agent is a polymer containing a borate ester bond, N,N'-m-phenylene bismaleimide and trimethylolpropane trimethacrylate.

2. The peroxide cross-linked polyethylene pipe according to claim 1, characterized in that: The mass ratio of the high-density polyethylene to the ultra-low-density polyethylene is (7-9): (1-3); And / or, the melt index of the high-density polyethylene is 0.6-1.8 g / 10 min; And / or, the ultra-low density polyethylene has a melt index of 1.2-3.5 g / 10 min; And / or, the mass ratio of the borate ester bond-containing polymer, N,N'-m-phenylene bismaleimide and trimethylolpropane trimethacrylate is (0.5 - 1.2): (1 - 1.5): (1 - 1.5).

3. The peroxide cross-linked polyethylene pipe according to claim 1, characterized in that: The preparation method of the borate ester bond-containing polymer is as follows: The polyol, the unsaturated acid and the acid catalyst are reacted in an inert atmosphere at a temperature of 80-120° C. for 4-8 hours to obtain an esterification product; After cooling the esterification product to 60-80° C., adding a boron-containing compound and a complexing agent, reacting at a temperature of 80-100° C. for 2-4 hours, removing impurities, and obtaining a polymer containing a boric acid ester bond.

4. The peroxide cross-linked polyethylene pipe according to claim 3, characterized in that: The molar ratio of the polyol to the unsaturated acid is 1:(3-4.5); and / or, the mass of the acidic catalyst is 0.5-2% of the total mass of the polyol and the unsaturated acid; and / or, the molar ratio of the polyol to the boron-containing compound is 1:(0.8-1.2); and / or, the molar ratio of the polyol to the complexing agent is 1:(0.9-1.1); And / or, the polyol is at least one of pentaerythritol, dipentaerythritol, polyethylene glycol, and trimethylolpropane; And / or, the unsaturated acid is at least one of acrylic acid, methacrylic acid, maleic anhydride and itaconic acid; And / or, the boron-containing compound is at least one of boric acid, borax, and phenylboric acid; And / or, the acidic catalyst is p-toluenesulfonic acid; And / or, the complexing agent is at least one of ethanolamine and triethanolamine.

5. The peroxide cross-linked polyethylene pipe according to claim 1, characterized in that: The peroxide crosslinking agent is at least one of benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane; And / or, the antioxidant is at least one of a hindered amine antioxidant and a thioester antioxidant; And / or, the lubricant is at least one of low molecular weight esters, metal soaps, stearic acid complex esters, and amides.

6. The peroxide cross-linked polyethylene pipe according to claim 5, characterized in that: The peroxide crosslinking agent is benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and the mass ratio of the benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane is (1 - 1.5): (1 - 1.5); And / or, the antioxidant is a hindered amine antioxidant and a thioester antioxidant, and the mass ratio of the hindered amine antioxidant to the thioester antioxidant is (2 - 2.5): (1 - 1.5); And / or, the lubricant is ethylene bisstearamide and silicone powder, and the mass ratio of ethylene bisstearamide to silicone powder is (1-1.5):(1-1.5).

7. A method for preparing a peroxide cross-linked polyethylene pipe according to any one of claims 1 to 6, characterized in that: The following steps are involved: Mix the components uniformly according to the proportion to obtain a premix; The premix is ​​added into a screw extruder for melt extrusion to obtain a pipe blank; The pipe blank is subjected to a pre-crosslinking treatment and a main crosslinking treatment in sequence under infrared irradiation, and the obtained crosslinked pipe is cooled and post-treated to obtain a peroxide crosslinked polyethylene pipe.

8. The method for preparing a peroxide cross-linked polyethylene pipe according to claim 7, characterized in that: The mixing parameters satisfy at least one of the following: temperature below 38°C, rotation speed 1000-1400r / min, time 15-25min; And / or, the melt extrusion parameters satisfy at least one of the following: screw aspect ratio of 28-30:1, temperature of 140-180°C, screw speed of 30-40r / min, and feed rate of 150-200kg / h; And / or, the pre-crosslinking treatment is performed at a temperature of 185-230° C. and for a time of 9-15 seconds; And / or, the temperature of the main cross-linking treatment is 230-280° C. and the time is 9-15 seconds; And / or, the cooling end point temperature is 20-30°C, and the cooling rate is 5-10°C / min; And / or, the post-treatment temperature is 70-100° C. and the time is 20-30 h.

9. The method for preparing a peroxide cross-linked polyethylene pipe according to claim 7, characterized in that: During the melt extrusion, the setting temperatures of the screw extruder from the feed port to the die are: the temperature of zone 1 is 140-150°C, the temperature of zone 2 is 150-160°C, the temperature of zone 3 is 160-170°C, the temperature of zone 4 is 150-160°C, the temperature of zone 5 is 160-170°C, and the temperature of zone 6 is 160-180°C; And / or, the pre-crosslinking treatment includes a first pre-crosslinking treatment, a second pre-crosslinking treatment and a third pre-crosslinking treatment performed in sequence, wherein the temperature of the first pre-crosslinking treatment is 185-195°C, the temperature of the second pre-crosslinking treatment is 195-205°C, and the temperature of the third pre-crosslinking treatment is 205-230°C; the time of the first pre-crosslinking treatment, the second pre-crosslinking treatment and the third pre-crosslinking treatment is independently 3-5s, and the heating rate is independently 5-10°C / s; And / or, the main cross-linking treatment includes a first main cross-linking treatment, a second main cross-linking treatment and a third main cross-linking treatment performed in sequence, wherein the temperature of the first main cross-linking treatment is 240-250° C., the temperature of the second main cross-linking treatment is 260-280° C., and the temperature of the third main cross-linking treatment is 230-245° C.; the time of the first main cross-linking treatment, the second main cross-linking treatment and the third main cross-linking treatment is independently 3-5s; And / or, the cooling includes a first cooling treatment, a second cooling treatment and a third cooling treatment performed in sequence, wherein the terminal temperature of the first cooling treatment is 70-85°C, the terminal temperature of the second cooling treatment is 40-55°C, and the terminal temperature of the third cooling treatment is 20-30°C.

10. A system for preparing a peroxide cross-linked polyethylene pipe according to any one of claims 1 to 6, characterized in that: The invention comprises a twin-screw extruder (100), a loading and unloading system (101), a cross-linking infrared furnace (102), a vacuum tank (103), a cooling water tank (104), a tractor (105) and a winder (106); the unloading end of the loading and unloading system (101) is connected to the feeding end of the twin-screw extruder (100), and the twin-screw extruder (100), the cross-linking infrared furnace (102), the vacuum tank (103), the cooling water tank (104), the tractor (105) and the winder (106) are connected in sequence; The cross-linking infrared furnace comprises a pre-cross-linking mechanism (200) and a main cross-linking mechanism (300) which are connected in sequence; the pre-cross-linking mechanism (200) is used to perform a pre-cross-linking treatment, and the main cross-linking mechanism (300) is used to perform a main cross-linking treatment; The tube blank extruded from the twin-screw extruder (100) passes through a cross-linking infrared furnace (102), a vacuum tank (103), and a cooling water tank (104) in sequence through a traction mechanism of a traction machine (105), and is wound up through a winder (106).

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