Production process of environment-friendly high-strength corrosion-resistant PE pipe

Abstract

The invention relates to the technical field of pipes, and discloses an environment-friendly high-strength corrosion-resistant PE pipe production process which comprises the following steps: raw material pretreatment: mixing high-density polyethylene, low-density polyethylene, borate, polyvinylidene fluoride, epoxidized soybean oil and an antioxidant in proportion, and performing melting pretreatment to form a uniform mixture; dynamic cross-linking extrusion molding: carrying out dynamic cross-linking extrusion on the pretreated mixture in a three-zone temperature control extruder, wherein three zones are respectively a dynamic bond activation zone, a chain orientation induction zone and a dynamic locking zone; and carrying out on-line molecular chain orientation stretching: heating the extruded semi-cured pipe, and carrying out one-way or two-way stretching under a constant-temperature condition. Through a dynamic boron-oxygen cross-linked network extrusion process, an on-line molecular chain orientation stretching technology, a partitioned cooling process and a synergistic effect of a polyvinylidene fluoride thin layer coated on the surface, high strength, toughness and balanced inner and outer layer performance of the pipe are effectively realized.

Description

Technical Field

[0001] The invention relates to the technical field of pipes, and in particular to a production process of environmentally friendly high-strength and corrosion-resistant PE pipes. Background Art

[0002] Polyethylene (PE) pipes are widely used in chemical transportation, water supply and drainage, gas transportation and other fields due to their excellent mechanical properties, chemical corrosion resistance and good processing performance. However, with the continuous improvement of modern industry's requirements for pipe performance, the performance bottleneck of traditional PE pipes in the existing technology has gradually emerged, especially in terms of high strength, corrosion resistance and long-term stability, there are still many shortcomings, which limits its further promotion in harsh application environments.

[0003] The production of traditional PE pipes usually adopts static cross-linking technology or completely relies on the molecular chain structure of the material itself. Although static cross-linking methods (such as peroxide cross-linking or radiation cross-linking) can improve certain mechanical properties, the cross-linking process is irreversible, which causes the material to break easily at the stress concentration site and lose ductility. At the same time, the uniformity of static cross-linking is difficult to control, and the material performance is unevenly distributed. Although PE pipes that do not use cross-linking technology maintain a certain degree of flexibility, the strength is limited due to insufficient interaction between the molecular chains, and the disordered distribution of the molecular chains makes it more susceptible to aging under long-term stress or chemical environment, and the performance gradually decays. In addition, mechanical enhancement in traditional processes is mostly achieved through material modification, such as filling rigid particles or adding toughening agents, but these methods often lead to a decrease in material processing performance and even introduce other defects.

[0004] In terms of corrosion resistance, although PE material itself has a certain tolerance to certain chemical media, its molecular structure is easily corroded by chemical media when exposed to strong acid, strong alkali or salt spray environment for a long time, showing problems such as cracking, aging or significant performance degradation of the material surface. Some existing technologies have improved the material by increasing the crystallinity of the material or adding corrosion-resistant fillers, but the effect is not ideal due to the unevenness of the material microstructure and the limitations of the filler dispersion. The surface coating process in the existing technology is mostly a thin layer treatment with poor durability, which cannot meet the needs of long-term complex chemical transportation.

[0005] In addition, the traditional pipe cooling process mainly relies on rapid cooling, and lacks a zoning design for the cooling rate inside and outside, resulting in uneven stress distribution between the inner and outer layers, accumulation of residual stress in the inner layer, and loose structure of the outer layer. This process has an adverse effect on the pressure resistance and long-term stability of the pipe, making it easy for the pipe to rupture or deform due to stress concentration during use, further limiting its application in high-pressure or complex environments.

[0006] Faced with the above problems, existing technologies have not yet achieved a comprehensive balance between high strength, corrosion resistance and long-term stability of PE pipes. Some technical solutions attempt to improve by adding material modification steps or adopting more complex processing techniques, but these methods often increase manufacturing costs or processing difficulties and are limited in practicality. Therefore, how to solve the problems of insufficient strength, poor corrosion resistance and lack of long-term stability of traditional pipes by dynamically regulating the molecular structure, improving chemical resistance and optimizing the cooling process while maintaining the basic advantages of PE pipes has become a technical problem that needs to be solved urgently. Summary of the invention

[0007] In view of the deficiencies in the prior art, the present invention provides an environmentally friendly, high-strength, corrosion-resistant PE pipe production process to solve the problems of the existing polyethylene pipes being insufficient in mechanical strength, corrosion resistance and long-term stability.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions: an environmentally friendly high-strength corrosion-resistant PE pipe production process, comprising the following steps: Raw material pretreatment: high-density polyethylene, low-density polyethylene, borate, polyvinylidene fluoride, epoxidized soybean oil, and antioxidant are mixed in proportion and melt-pretreated to form a uniform mixture; Dynamic cross-linking extrusion molding: The pre-treated mixture is dynamically cross-linked and extruded in a three-zone temperature-controlled extruder, the three zones being the dynamic bond activation zone, the chain orientation induction zone, and the dynamic locking zone; Online molecular chain orientation stretching: the extruded semi-cured pipe is heated and stretched unidirectionally or bidirectionally under constant temperature conditions; Partition cooling: The pipe is cooled by using fast cooling and slow cooling partition cooling methods; Annealing treatment: annealing the cooled pipe in a protective gas environment; Surface treatment: Polyvinylidene fluoride coating is applied on the surface of the pipe.

[0009] Preferably, the mass ratio of high-density polyethylene, low-density polyethylene, borate, polyvinylidene fluoride, epoxidized soybean oil and antioxidant in the raw material pretreatment step is as follows: 70-85 parts of high-density polyethylene, 10-20 parts of low-density polyethylene, 8-12 parts of borate, 5-10 parts of polyvinylidene fluoride, 3-6 parts of epoxidized soybean oil and 0.5-1 part of antioxidant.

[0010] Preferably, the temperature of the melt pretreatment is 80-100°C and the time is 10-20 minutes.

[0011] Preferably, the dynamic cross-linking extrusion molding step is specifically as follows: Dynamic bond activation: The raw material is fed into the dynamic bond activation zone of the extruder through the feed port. The temperature is controlled at 180-200°C and the screw speed is 300-500rpm. The material is melted under the action of the screw and the dynamic boron-oxygen bond of the borate ester is broken and reorganized to initially form a dynamic cross-linking network. The material stays in this zone for 60-120S. Chain orientation induction: The molten material enters the chain orientation induction zone, the temperature rises to 200-220°C, the screw speed is 400-600rpm, and the polyethylene molecular chains are induced to stretch and arrange along the flow direction through high shearing action. At the same time, the dynamic cross-linking network is further evenly distributed. The material stays in this zone for 90-150S; Dynamic locking: The material enters the dynamic locking zone, the temperature drops to 170-190°C, the screw speed is adjusted to 200-300rpm, and the dynamic cross-linking network structure is locked by controlling the temperature and shear rate to ensure the stable arrangement of the molecular chains. The material stays in this zone for 60-120S; Extrusion molding: The material after dynamic cross-linking is transported to the die head, the die head temperature is 150-170℃, the melt is extruded through the die head at a speed of 1-5m / min to form a pipe, and enters the initial cooling stage.

[0012] Preferably, the online molecular chain orientation stretching step comprises the following operations: The extruded semi-cured pipe enters the online constant temperature stretching device, and the device temperature is controlled at 120-140℃; The stretching ratio is controlled at 3-6 times; The stretching speed is 10-50mm / s, and the stretching tension range is controlled to be 30-80MPa by real-time tension adjustment; The stretching method is unidirectional stretching or bidirectional stretching.

[0013] Preferably, the zone cooling step comprises the following operations: The external cooling zone adopts rapid cooling, the cooling medium is cooling water, the water temperature is controlled at 5-15℃, and the cooling rate is 15-30℃ / S; The inner cooling zone adopts slow cooling, the cooling medium is warm water or air, the temperature is controlled at 30-50℃, and the cooling rate is 2-10℃ / S; the outer cooling zone and the inner cooling zone independently control the cooling rate, and the cooling medium flow rates are 0.5-2m / s and 0.1-0.5m / s respectively.

[0014] Preferably, the annealing step comprises the following operations: The cooled pipe is placed in an annealing device at a temperature of 95-105°C; Annealing time is 4-8h; The annealing environment is filled with nitrogen or other inert gases, with a gas flow rate of 0.1-0.5m 3 / h; After annealing, it was cooled naturally to room temperature.

[0015] Preferably, the surface treatment step comprises the following operations: The surface of the pipe is cleaned with deionized water to remove surface impurities and oil stains; Use spraying or dipping technology to coat the surface of the pipe with polyvinylidene fluoride solution, and the concentration of the solution is controlled at 5-15%; After coating, it is naturally dried at room temperature for 24 hours, and the coating thickness is 0.05-0.1mm.

[0016] Preferably, in the online molecular chain orientation stretching step, the uniaxial stretching ratio and the biaxial stretching ratio are respectively: the uniaxial stretching ratio is 3-5 times, and the biaxial stretching ratio is 4-6 times.

[0017] Preferably, the annealing environment in the annealing treatment stage uses nitrogen with a purity of not less than 99.99%.

[0018] The present invention provides an environmentally friendly, high-strength, corrosion-resistant PE pipe production process, which has the following beneficial effects: 1. The present invention adopts the extrusion process of dynamic boron-oxygen cross-linking network, and realizes the efficient cross-linking and uniform distribution of polyethylene molecular chains through three-zone temperature control and dynamic cross-linking density regulation, thereby achieving the effect of improving the strength and chemical corrosion resistance of the pipe. Compared with the technical solution of single cross-linking using static cross-linking agent in the prior art, the present invention overcomes the problems of insufficient cross-linking uniformity and uneven distribution of mechanical properties.

[0019] 2. The present invention uses online molecular chain orientation stretching technology, which significantly improves the orderly arrangement of polyethylene molecular chains, enhances the tensile strength and toughness of the pipe, and controls the distribution of the dynamic cross-linking network. Compared with the traditional melt stretching process, the present invention solves the problem of insufficient tensile strength of the material and susceptibility to external stress damage caused by the disordered arrangement of molecular chains.

[0020] 3. The present invention adopts a zoned cooling process, and through the precise control of the internal and external cooling rates, the performance of the inner and outer layers of the pipe is balanced, achieving the technical effect of enhancing the toughness of the inner layer and improving the corrosion resistance of the outer layer. The single cooling method commonly used in the prior art easily leads to uneven distribution of internal and external stresses. The present invention effectively avoids the shortcomings of pipe structure deformation and performance degradation during long-term use.

[0021] 4. The present invention imparts excellent chemical inertness and weather resistance to the pipe by coating a thin layer of polyvinylidene fluoride, and enhances resistance to acid, alkali and ultraviolet rays. Compared with the traditional PE pipe without surface reinforcement, the present invention further solves the problem of pipe surface aging and function loss caused by environmental corrosion. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the method flow of the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Please see attached Figure 1 The embodiment of the present invention provides an environmentally friendly high-strength corrosion-resistant PE pipe production process, comprising the following steps: S1. Raw material pretreatment: high-density polyethylene, low-density polyethylene, borate, polyvinylidene fluoride, epoxidized soybean oil, and antioxidant are mixed in proportion and melt-pretreated to form a uniform mixture; S2, dynamic cross-linking extrusion molding: the pretreated mixture is dynamically cross-linked and extruded in a three-zone temperature-controlled extruder, wherein the three zones are a dynamic bond activation zone, a chain orientation induction zone, and a dynamic locking zone; S3, online molecular chain orientation stretching: the extruded semi-cured pipe is heated and stretched unidirectionally or bidirectionally under constant temperature conditions; S4, zone cooling: The pipe is cooled by using a zone cooling method of fast cooling and slow cooling; S5. Annealing treatment: annealing the cooled pipe in a protective gas environment; S6. Surface treatment: Apply polyvinylidene fluoride coating on the surface of the pipe.

[0025] The mass ratio of high-density polyethylene, low-density polyethylene, borate, polyvinylidene fluoride, epoxidized soybean oil and antioxidant in the raw material pretreatment step is as follows: 70-85 parts of high-density polyethylene, 10-20 parts of low-density polyethylene, 8-12 parts of borate, 5-10 parts of polyvinylidene fluoride, 3-6 parts of epoxidized soybean oil and 0.5-1 part of antioxidant.

[0026] The temperature of the melt pretreatment is 80-100°C and the time is 10-20 minutes.

[0027] The dynamic cross-linking extrusion molding steps are as follows: Dynamic bond activation: The raw material is fed into the dynamic bond activation zone of the extruder through the feed port. The temperature is controlled at 180-200°C and the screw speed is 300-500rpm. The material is melted under the action of the screw and the dynamic boron-oxygen bond of the borate ester is broken and reorganized to initially form a dynamic cross-linking network. The material stays in this zone for 60-120S. Chain orientation induction: The molten material enters the chain orientation induction zone, the temperature rises to 200-220°C, the screw speed is 400-600rpm, and the polyethylene molecular chains are induced to stretch and arrange along the flow direction through high shearing action. At the same time, the dynamic cross-linking network is further evenly distributed. The material stays in this zone for 90-150S; Dynamic locking: The material enters the dynamic locking zone, the temperature drops to 170-190°C, the screw speed is adjusted to 200-300rpm, and the dynamic cross-linking network structure is locked by controlling the temperature and shear rate to ensure the stable arrangement of the molecular chains. The material stays in this zone for 60-120S; Extrusion molding: The material after dynamic cross-linking is transported to the die head, the die head temperature is 150-170℃, the melt is extruded through the die head at a speed of 1-5m / min to form a pipe, and enters the initial cooling stage.

[0028] The online molecular chain orientation stretching step includes the following operations: The extruded semi-cured pipe enters the online constant temperature stretching device, and the device temperature is controlled at 120-140℃; The stretching ratio is controlled at 3-6 times; The stretching speed is 10-50mm / s, and the stretching tension range is controlled to be 30-80MPa by real-time tension adjustment; The stretching method is unidirectional stretching or bidirectional stretching.

[0029] The zone cooling step includes the following operations: The external cooling zone adopts rapid cooling, the cooling medium is cooling water, the water temperature is controlled at 5-15℃, and the cooling rate is 15-30℃ / S; The inner cooling zone adopts slow cooling, the cooling medium is warm water or air, the temperature is controlled at 30-50℃, and the cooling rate is 2-10℃ / S; the outer cooling zone and the inner cooling zone independently control the cooling rate, and the cooling medium flow rates are 0.5-2m / s and 0.1-0.5m / s respectively.

[0030] The annealing step includes the following operations: The cooled pipe is placed in an annealing device at a temperature of 95-105°C; Annealing time is 4-8h; The annealing environment is filled with nitrogen or other inert gases, with a gas flow rate of 0.1-0.5m 3 / h; After annealing, it was cooled naturally to room temperature.

[0031] The surface preparation steps include the following operations: The surface of the pipe is cleaned with deionized water to remove surface impurities and oil stains; Use spraying or dipping technology to coat the surface of the pipe with polyvinylidene fluoride solution, and the concentration of the solution is controlled at 5-15%; After coating, it is naturally dried at room temperature for 24 hours, and the coating thickness is 0.05-0.1mm.

[0032] In the online molecular chain orientation stretching step, the uniaxial stretching ratio and the biaxial stretching ratio are respectively: the uniaxial stretching ratio is 3-5 times, and the biaxial stretching ratio is 4-6 times.

[0033] The annealing environment in the annealing treatment stage uses nitrogen with a purity of not less than 99.99%.

[0034] Example 1: Preparation of high-strength corrosion-resistant PE pipe using dynamic boron-oxygen cross-linked network Raw material preparation and pretreatment: Take 80 parts of high-density polyethylene, 15 parts of low-density polyethylene, 10 parts of borate, 7 parts of polyvinylidene fluoride, 5 parts of epoxidized soybean oil and 0.7 parts of antioxidant in mass proportion. Add all raw materials to a high-speed mixer, set the speed to 1500rpm, mix for 12 minutes to ensure uniform dispersion. Then transfer the mixture to a twin-screw extruder, set the melt temperature to 90°C, and pretreat for 15 minutes to form pellets for use.

[0035] Dynamic cross-linking extrusion molding: The pellets are fed into the three-zone temperature-controlled extruder through a feeding device: The temperature of the dynamic bond activation zone was set at 190 °C, the screw speed was set at 400 rpm, and the residence time was 90 s to preliminarily activate the boron-oxygen bonds in the borate ester and form a dynamic cross-linking network; The temperature of the chain orientation induction zone was set at 210 °C, and the screw speed was increased to 500 rpm to induce the orderly arrangement of the polyethylene molecular chains through high shearing action, with a residence time of 120 s; The temperature of the dynamic locking zone was set at 180 °C, and the screw speed was reduced to 250 rpm. The dynamic cross-linked network structure was locked by gradually lowering the temperature, and the residence time was 90 s. The extrusion die temperature was set at 160°C, the pipe extrusion speed was 2 m / min, and the pipe was sent to the next process after preliminary cooling.

[0036] Online molecular chain orientation stretching: The extruded semi-cured pipe passes through an online constant temperature stretching device at a temperature of 130°C. The pipe is stretched unidirectionally with a stretching ratio of 4 times, a stretching speed of 30 mm / s, and a tension of 50 MPa to keep the molecular chain of the pipe oriented along the stretching direction.

[0037] Partition cooling: The pipe first enters the outer cooling zone, where the cooling medium is 10℃ cooling water and the cooling rate is 20℃ / S, and the outer layer is quickly solidified. Then it enters the inner cooling zone, where the cooling medium is 40℃ warm water and the cooling rate is 5℃ / S, and the residual stress of the inner layer is gradually released.

[0038] Annealing treatment: The cooled pipe is placed in an annealing device, the temperature is set to 100°C, the protective gas is nitrogen, and the gas flow rate is 0.3m 3 / h, the annealing time is 6h, and then it is naturally cooled to room temperature.

[0039] Surface treatment: The surface of the pipe is cleaned with deionized water, sprayed with a 10% concentration of polyvinylidene fluoride solution, and naturally dried at 25°C for 24 hours after coating. The coating thickness is 0.08mm.

[0040] Example 2: Optimizing the stretching process to prepare high-pressure resistant PE pipes Raw material pretreatment: Take 75 parts of high-density polyethylene, 20 parts of low-density polyethylene, 9 parts of borate, 8 parts of polyvinylidene fluoride, 4 parts of epoxidized soybean oil and 0.5 parts of antioxidant. Mix them in proportion, set the mixer speed to 1600 rpm, and the mixing time is 10 minutes. Then melt them in an extruder at 95°C for 12 minutes to form uniform pellets.

[0041] Dynamic cross-linking extrusion molding: The three-zone temperature control parameters of the extruder are as follows: The temperature of the dynamic bond activation zone was 185 °C, the screw speed was 350 rpm, and the residence time was 80 s to activate the borate ester; The temperature of the chain orientation induction zone was 205°C, the screw speed was 450 rpm, the residence time was 110 s, and the high shear conditions induced the orientation of the molecular chains; The temperature of the dynamic locking zone is 175°C, the screw speed is 220 rpm, the residence time is 85S, and the dynamic cross-linking structure is locked; the extrusion die temperature is set to 165°C, and the extrusion speed is 3m / min.

[0042] Online biaxial stretching: The extruded tube is sent to a constant temperature stretching device at 135°C, and axial and radial stretching are performed simultaneously. The axial stretching ratio is 3.5 times, the radial stretching ratio is 4.5 times, the stretching speed is 20mm / s, and the tension is controlled at 60MPa.

[0043] Cooling and annealing: The pipe is first cooled quickly, with the cooling medium being 5°C cooling water and the rate being 25°C / S, and the outer layer is quickly solidified. Then it is cooled slowly, with the cooling medium being 35°C warm water and the rate being 6°C / S, to reduce the residual stress of the inner layer. After cooling, annealing is performed at 95°C for 5 hours, and the gas is 99.99% pure nitrogen.

[0044] Surface treatment: The surface of the pipe is coated with polyvinylidene fluoride solution by dip coating, with a concentration of 12% and a coating thickness of 0.1mm, and then dried naturally for 24 hours.

[0045] Example 3: Corrosion-resistant PE pipes for chemical transportation scenarios Raw material pretreatment: Take 85 parts of high-density polyethylene, 10 parts of low-density polyethylene, 12 parts of borate, 10 parts of polyvinylidene fluoride, 3 parts of epoxidized soybean oil, and 1 part of antioxidant in mass proportion. Set the speed of the high-speed mixer to 1400 rpm and the mixing time to 15 minutes. Control the melt pretreatment temperature at 85°C for 18 minutes to prepare pellets.

[0046] Dynamic cross-linking extrusion molding: The temperature of the dynamic bond activation zone was 195°C, the screw speed was 450 rpm, and the residence time was 90 s; The temperature of the chain orientation induction zone was 215 °C, the screw speed was 500 rpm, and the residence time was 130 s; The temperature of the dynamic locking zone was 185°C, the screw speed was 300 rpm, and the residence time was 100 s; the extrusion die temperature was set to 155°C, and the extrusion speed was 2.5 m / min.

[0047] Online molecular chain orientation stretching: The extruded pipe is uniaxially stretched at a constant temperature of 130°C, the ratio is controlled at 4 times, the stretching speed is 40 mm / s, and the tension is 70 MPa.

[0048] Cooling and annealing: The cooling medium in the outer cooling zone is 8℃ cooling water, the rate is 25℃ / S; the cooling medium in the inner cooling zone is 40℃ warm water, the rate is 5℃ / S. The annealing temperature is 100℃, the time is 7h, the inert gas is nitrogen, and the flow rate is 0.4m 3 / h.

[0049] Surface treatment: The surface of the pipe is coated with a 15% concentration of PVDF solution using a spraying process with a coating thickness of 0.08 mm and dried at room temperature.

[0050] Comparative Example 1: Traditional crosslinking method without dynamic boron-oxygen crosslinking network Raw material pretreatment: Use 85 parts of high-density polyethylene, 15 parts of low-density polyethylene, and 0.7 parts of antioxidant. Omit boric acid ester and polyvinylidene fluoride, and the raw material only relies on the mixing of high-density polyethylene and low-density polyethylene to improve toughness and strength. Mix in a high-speed mixer according to the above proportions, with a speed of 1500rpm and mixing for 10 minutes. The mixture is pretreated by a twin-screw extruder, the temperature is controlled at 100℃, the time is 15 minutes, and the pellets are formed for use.

[0051] Extrusion molding: Using traditional static cross-linking extrusion technology, the extruder temperature zone is divided into two sections: The first stage (melting zone): the temperature is set to 200°C, the screw speed is 400rpm, and the material is melted under the action of the screw; The second stage (molding zone): the temperature is set to 190°C, the screw speed is 250rpm, the die temperature is 160°C, and the extrusion speed is 2m / min. No dynamic cross-linking network is used, and the strength is obtained only by the distribution of the molecular chain of the material itself.

[0052] Stretching process: No online molecular chain orientation stretching is performed, and the product is directly cooled and formed after extrusion.

[0053] Cooling: Single rapid cooling method, the cooling medium is 10℃ cooling water, the cooling rate is 20℃ / S, and there is no distinction between inner and outer cooling layers.

[0054] Surface treatment: No polyvinylidene fluoride coating was applied, and the surface was only simply cleaned.

[0055] Comparative Example 2: No molecular chain orientation stretching Raw material pretreatment: The raw material ratio is the same as that in Example 1: 80 parts of high-density polyethylene, 15 parts of low-density polyethylene, 10 parts of borate, 7 parts of polyvinylidene fluoride, 5 parts of epoxidized soybean oil and 0.7 parts of antioxidant. Mix and melt pretreatment in the same manner as in Example 1 to form uniform pellets.

[0056] Dynamic cross-linking extrusion molding: Extrusion was performed according to the dynamic crosslinking process of Example 1: The temperature of the dynamic bond activation zone is 190°C, the screw speed is 400 rpm, and the residence time is 90 s; The temperature of the chain orientation induction zone was 210 °C, the screw speed was 500 rpm, and the residence time was 120 s; The temperature of the dynamic locking zone was 180°C, the screw speed was 250 rpm, and the residence time was 90 s; The extrusion die temperature was 160°C and the extrusion speed was 2 m / min.

[0057] Cooling: The cooling method is the same as that in Example 1, using external cooling zone and internal cooling zone for zone cooling.

[0058] Stretching process: No online molecular chain orientation stretching is performed, the extruded tube directly enters the cooling stage, and the molecular chains are disorderly distributed.

[0059] Surface treatment: Surface coating treatment was performed according to Example 1, with a 10% concentration of polyvinylidene fluoride solution being coated, and the coating thickness was 0.08 mm.

[0060] Comparative Example 3: No zone cooling, only rapid cooling Raw material pretreatment: The raw material ratio is the same as that in Example 2: 75 parts of high-density polyethylene, 20 parts of low-density polyethylene, 9 parts of borate, 8 parts of polyvinylidene fluoride, 4 parts of epoxidized soybean oil and 0.5 parts of antioxidant. According to the mixing and pretreatment method of Example 2, pellets are formed.

[0061] Dynamic cross-linking extrusion molding: Extrusion was performed according to the dynamic crosslinking process of Example 2: The temperature of the dynamic bond activation zone is 185°C, the screw speed is 350 rpm, and the residence time is 80 s; The temperature of the chain orientation induction zone was 205 °C, the screw speed was 450 rpm, and the residence time was 110 s; The temperature of the dynamic locking zone was 175°C, the screw speed was 220 rpm, and the residence time was 85 s; The extrusion die temperature was 165°C and the extrusion speed was 3 m / min.

[0062] Stretching process: biaxial stretching process was carried out according to Example 2: axial stretching ratio was 3.5 times, radial stretching ratio was 4.5 times, stretching speed was 20 mm / s, and tension was 60 MPa.

[0063] Cooling: Cooling adopts single rapid cooling method. The cooling medium is 8℃ cooling water, the cooling rate is 25℃ / S, and there is no slow cooling in the inner cooling zone.

[0064] Surface treatment: Surface treatment was performed according to Example 2, by dip coating with a 12% concentration of polyvinylidene fluoride solution, with a coating thickness of 0.1 mm.

[0065] Comparative Example 4: Surface treatment without PVDF coating Raw material pretreatment: The raw material ratio is the same as that in Example 3: 85 parts of high-density polyethylene, 10 parts of low-density polyethylene, 12 parts of borate, 10 parts of polyvinylidene fluoride, 3 parts of epoxidized soybean oil and 1 part of antioxidant. According to the mixing and pretreatment method of Example 3, pellets are formed.

[0066] Dynamic cross-linking extrusion molding: Extrusion was performed according to the dynamic crosslinking process of Example 3: The temperature of the dynamic bond activation zone is 195°C, the screw speed is 450 rpm, and the residence time is 90 s; The temperature of the chain orientation induction zone was 215 °C, the screw speed was 500 rpm, and the residence time was 130 s; The temperature of the dynamic locking zone was 185°C, the screw speed was 300 rpm, and the residence time was 100 s; The extrusion die temperature was 155°C and the extrusion speed was 2.5 m / min.

[0067] Stretching process: The uniaxial stretching process was carried out according to Example 3: the stretching ratio was 4 times, the stretching speed was 40 mm / s, and the tension was 70 MPa.

[0068] Cooling and annealing: The cooling method is the same as that in Example 3, using a zone cooling process. The annealing temperature is 100° C., the time is 7 hours, and the inert gas is nitrogen.

[0069] Surface treatment: No PVDF coating was performed, the surface was only cleaned with deionized water, and no protective layer was applied.

[0070] Experiment 1: Tensile strength and elongation at break test Experimental description: Purpose: To verify the effect of improving the mechanical properties of the pipe by the dynamic boron-oxygen cross-linking network and molecular chain orientation stretching technology in the embodiments of the present invention, and to compare with the control examples that do not use these technologies.

[0071] Experimental equipment: The test was carried out using an INSTRON universal material testing machine, the equipment model is Instron5969, equipped with a 10kN tensile sensor.

[0072] Sample preparation: Standard test strips were cut from the tubes of Example 1, Example 2, Example 3, and Comparative Example 2, with a size of 100 mm×10 mm and a thickness consistent with the tube wall thickness.

[0073] Both ends of the sample are polished to ensure flatness, in line with GB / T1040.2-2006 standards.

[0074] Five specimens were prepared for each group of samples.

[0075] Experimental steps: Fix the test strip in the test machine fixture and adjust the fixture spacing to 50 mm.

[0076] Set the stretching rate to 50 mm / min, start the testing machine, and begin stretching the sample until it breaks.

[0077] The tensile strength (maximum stress at break) and elongation at break (percent elongation at break) of each sample were recorded.

[0078] After the test is completed, take the average and standard deviation.

[0079] Experimental data: Table 1: Tensile strength and elongation at break test data Summary: The dynamic boron-oxygen cross-linked network and molecular chain orientation stretching technology used in the present invention show significant advantages in experimental data. Through the action of the dynamic cross-linked network, the interaction force between the polyethylene molecular chains is enhanced, the overall strength is improved, and the molecular chains are arranged more orderly. This technical path combining chemistry and physics makes the example sample far superior to comparative example 2 in tensile strength. Because comparative example 2 was not stretched, the molecular chains were arranged in disorder, and the material showed lower tensile strength.

[0080] The elongation at break of the example samples is relatively high, especially Example 1 and Example 2, which show good flexibility. This is closely related to the reversibility of the dynamic network structure. During the stretching process, the breaking and reorganization of the dynamic boron-oxygen bond absorbs part of the external force, allowing the material to maintain a certain ductility under stress. However, due to the lack of dynamic adjustment ability of cross-linking, the force is concentrated on a few molecular chains, resulting in a significantly low elongation at break in Comparative Example 2.

[0081] Through data analysis, it can be found that the tensile strength of Example 1 and Example 3 is higher, which is closely related to the uniformity of molecular chain orientation and the balanced release of stress in the inner and outer layers during cooling. In particular, in Example 3, the precise regulation of its dynamic locking process enables the molecular chain arrangement to reach the optimal state. In contrast, due to the lack of molecular chain orientation stretching treatment, there are obvious microscopic stress concentration points inside the material in Comparative Example 2, which makes it easier to break under external force. This defect reflects the shortcomings of traditional technology in optimizing the mechanical properties of materials.

[0082] Experiment 2: Corrosion resistance test Experimental description: Purpose: To test the corrosion resistance of the embodiments and comparative examples in acidic, alkaline and salt spray environments, to compare the advantages of the present invention in terms of dynamic cross-linking network and PVDF coating, and to verify its corrosion resistance in chemical application scenarios.

[0083] Experimental equipment: constant temperature and humidity test chamber, gravimetric analytical balance (accuracy 0.001g), tensile testing machine (same equipment as in Experiment 1).

[0084] Sample preparation: Samples of Example 1, Example 3, Comparative Example 1 (no borate and PVDF coating) and Comparative Example 4 (no PVDF coating) were selected.

[0085] The samples were cut into sheets of 50 mm × 50 mm × tube wall thickness.

[0086] Each group of samples had 5 pieces, which were washed with deionized water and dried before recording the initial mass.

[0087] Experimental steps: Soaking treatment: The samples were immersed in the following solutions: 10 wt % sulfuric acid, 10 wt % sodium hydroxide, and 3 wt % sodium chloride solution.

[0088] The soaking temperature was set at 60°C and the soaking time was 7 days.

[0089] Take out the samples every day, clean the surface with deionized water to remove any residual substances that may be attached, wipe them dry, and record the appearance and weight changes of the samples.

[0090] Subsequent performance test: After immersion for 7 days, the samples were subjected to a tensile strength test (the method was the same as in Experiment 1), and the tensile strength residual rate was recorded.

[0091] Recording and analysis: Record the mass change rate (Δm%) and appearance changes of the samples during the immersion process according to the standard; The residual tensile strength after immersion was calculated to verify the retention of corrosion resistance.

[0092] Experimental data: Table 2: Corrosion resistance test data of different samples in chemical media Summary: The experimental data clearly reveal the key role of the dynamic cross-linking network and PVDF coating in improving the corrosion resistance of the pipe. The example samples showed an extremely low mass loss rate during the immersion process, which indicates that the borate dynamic cross-linking network significantly inhibits the penetration of the chemical medium into the material matrix. In contrast, due to the lack of dynamic cross-linking and corrosion-resistant components, the mass change rate of Comparative Example 1 is significantly high, showing a strong swelling effect. The erosion of this chemical medium is a typical manifestation of the lack of intermolecular bonding and loose structure in traditional pipes.

[0093] In the strong corrosive environment of sulfuric acid and sodium hydroxide, the tensile strength residual rates of Example 1 and Example 3 exceeded 92% and 93% respectively, demonstrating the stability of the material under the dynamic cross-linked network. The barrier effect of the PVDF coating further enhances the corrosion resistance. Due to the lack of coating protection, although dynamic cross-linking has a certain effect, the residual rate of Comparative Example 4 is still lower than that of the embodiment, indicating the necessity of the synergistic effect of dynamic cross-linking and surface coating.

[0094] In the sodium chloride environment, the performance of the example samples is particularly outstanding, which may be related to the excellent barrier properties of the PVDF coating. The fluorine element in the PVDF molecular structure provides extremely low chemical activity, blocking the corrosion of chloride ions in salt spray. However, Comparative Examples 1 and 4 show obvious strength attenuation in this environment, proving that the salt resistance in their material systems is far from the level of the examples. These results once again emphasize that the combination of dynamic cross-linked networks and surface coatings is a key technical path to achieve high durability of chemical transportation pipes.

[0095] Experiment 3: Stress Tolerance Test Experimental description: Objective: To test the deformation behavior of pipes under external loads, compare the effects of zoned cooling process on the compressive properties of pipes, and verify the optimization effect of the difference in cooling rates between inner and outer layers on mechanical properties.

[0096] Experimental equipment: pipe compression testing machine (model: Instron 3385H); digital measuring caliper for recording sample deformation; data recorder for measuring compression load and deformation curve.

[0097] Sample preparation: The samples were cut from the pipes prepared in Example 2, Example 3, and Comparative Example 3 (zone cooling was not adopted), and the lengths were all 200 mm, and the diameters remained the original pipe size.

[0098] The end surface of the sample was polished with sandpaper to ensure smoothness.

[0099] Experimental steps: Initial Measurement: Use a digital caliper to measure the outside diameter and wall thickness of the tubing and record the initial dimensions.

[0100] Loading process: Place the sample vertically between the compression tester platens to ensure uniform force; Set the compression speed to 10 mm / min; Continue loading and record the radial deformation (mm) when the load reaches 50 MPa; Continue to apply the load until the sample fails in compression and record the failure load value (N).

[0101] Experimental data record: Each group of samples was tested 3 times and the average value was taken; The deformation and failure load of the samples were compared.

[0102] Experimental data: Table 3: Compressive performance test data of different samples Summary: The experimental results show that the zoned cooling process significantly improves the compressive resistance of the pipe, especially in the coordination of the performance distribution of the inner and outer layers. The radial deformation of the samples in the embodiment is generally small, and the failure load is significantly higher than that of the comparative example 3. This is directly related to the slow cooling of the inner cooling zone, which slowly releases the residual stress of the inner layer and avoids the stress concentration problem caused by traditional rapid cooling. Comparative example 3 has the same cooling rate inside and outside, resulting in stress accumulation in the inner layer, which is easy to become unstable under external compression load.

[0103] The contribution of the dynamic boron-oxygen cross-linked network is also fully reflected in the failure load test. The dynamic cross-linking process in Example 3 ensures that the material can still maintain the coordinated deformation of the molecular chain under high pressure, showing a higher compression failure load. However, due to the lack of dynamic adjustment ability of the molecular chain, the comparative sample is concentrated on certain segments, which eventually leads to instability and failure of the pipe under lower loads. This difference directly reflects the technical advantages of the present invention.

[0104] When the load reaches 50MPa, the radial deformation of Examples 2 and 3 is significantly better than that of Comparative Example 3, which verifies the reinforcing effect of zoned cooling on the outer layer structure. In particular, the rapid cooling of the outer cold zone effectively improves the crystallinity of the outer layer, thereby enhancing the resistance of the pipe to external compressive stress. However, the rapid cooling in Comparative Example 3 causes the inner and outer layers to solidify at the same time, resulting in insufficient performance of the outer layer, and the pipe is prone to plastic deformation during the compression process. The above phenomenon shows that the technical path of the present invention in structural regulation and optimization of the performance of the inner and outer layers is reasonable and efficient.

[0105] Experiment 4: Long-term aging performance test Experimental description: Purpose: To test the long-term mechanical property stability of pipes under high temperature and high humidity environment, compare the effects of dynamic boron-oxygen cross-linking network and annealing treatment on the anti-aging ability of pipes, and verify the superiority of the present invention under long-term use conditions.

[0106] Experimental equipment: high temperature aging box (temperature control accuracy ±0.5°C); tensile testing equipment (same as Experiment 1); digital balance (accuracy 0.001g).

[0107] Sample preparation: The samples are selected from Example 1, Example 3, Comparative Example 1 (dynamic boron-oxygen crosslinking is not adopted) and Comparative Example 2 (no annealing treatment is performed).

[0108] The samples were cut into test strips of 100 mm × 10 mm with smooth edges and no burrs. Five samples were prepared for each group.

[0109] Experimental steps: Initial performance testing: The initial tensile strength and elongation at break of each sample were recorded (according to the test method of Experiment 1).

[0110] Aging treatment: Place the sample in a high temperature aging box with the aging environment set to 80°C and 90% humidity; The aging time is 1000h. Samples are taken out every 200h, the surface is cleaned, and performance tests are performed after drying.

[0111] Subsequent performance testing: Test the tensile strength and elongation at break of the samples, and record the changes in performance during aging; Calculate the performance retention rate (tensile strength retention rate and elongation at break retention rate) after aging.

[0112] Experimental data: Table 4: Performance retention of different samples under long-term aging conditions Summary: In the long-term aging experiment, the samples of the examples showed significant performance retention capabilities, especially the introduction of the dynamic boron-oxygen cross-linking network, which significantly delayed the performance degradation of the material under high temperature and high humidity environments. The tensile strength retention rates of Examples 1 and 3 were both higher than 92%, while the elongation at break remained above 88%, indicating that the dynamic cross-linking network effectively absorbed the molecular chain breakage energy caused by the external environment through a reversible fracture and recombination mechanism. In contrast, Comparative Example 1 showed a significant performance degradation due to the lack of dynamic cross-linking technology, with a tensile strength retention rate of only about 70% and an even lower elongation at break, showing a tendency for the material to rapidly degrade during aging.

[0113] Annealing also plays an important role in improving the long-term stability of the material, and the performance of Example 3 is particularly outstanding. This is mainly due to the release of residual stress during the annealing process, and at the same time, the uniformity and stability of the dynamic cross-linked network are improved by rearranging the molecular chains. Since Comparative Example 2 was not annealed, its internal residual stress was gradually released during the aging process, resulting in loose molecular chains and decreased structural stability. It can be seen from the experiment that the residual rate of elongation at break is only about 65%, which is much lower than that of the example samples.

[0114] In the aging test, the performance retention rate of Example 3 is slightly higher than that of Example 1, which may be related to the more balanced regulation of the dynamic crosslinking density and the cooling stage. The partition design of internal and external cooling enables a better combination of the inner layer toughness and outer layer strength of the pipe, showing stronger adaptability under long-term stress and environmental corrosion. The performance degradation of Comparative Examples 1 and 2 highlights the shortcomings of traditional technologies in aging tolerance, and verifies the necessity of combining dynamic crosslinking with annealing processes to improve the long-term performance of pipes.

[0115] Experiment 5: Chemical transportation scenario simulation experiment Experimental description: Purpose: To simulate the chemical transportation environment, test the corrosion resistance and mechanical stability of the pipe in continuous transportation in acid and alkali media, and verify the adaptability of the dynamic boron-oxygen cross-linked network and PVDF coating to chemical transportation application scenarios.

[0116] Experimental equipment: chemical transportation simulation system (circulation pump + temperature control transportation pipeline); digital balance (accuracy 0.001g); tensile testing machine (same as experiment 1); 10wt% sulfuric acid solution and 10wt% sodium hydroxide solution.

[0117] Sample preparation: The samples were selected from Example 3, Comparative Example 1 (dynamic crosslinking and PVDF coating not used), and Comparative Example 4 (PVDF coating not applied); Each group of samples is 1 meter long, with the ends sealed and connected to the conveying equipment.

[0118] Experimental steps: Connecting chemical delivery system: Connect the sample tube to the delivery system to ensure it is leak-proof. The chemical medium is 10wt% sulfuric acid and 10wt% sodium hydroxide solution, the delivery temperature is set at 50°C, and the medium flow rate is 2m / s; The circulation time was set to 500 h, and the changes in sample appearance were recorded every 100 h.

[0119] Performance Testing: After the delivery, the sample was removed, washed with deionized water and dried naturally; Test the mass change of the sample (record according to the initial mass) and the tensile strength residual rate (test the tensile strength according to the method of Experiment 1); record whether the sample surface has cracks, blistering or peeling.

[0120] Analysis and Recording: Compare the corrosion resistance and strength retention capabilities of the embodiments and comparative examples under chemical transportation conditions.

[0121] Experimental data: Table 5: Performance test data of different samples under chemical transportation conditions Summary: The experimental data clearly demonstrate the actual effect of the dynamic boron-oxygen cross-linking network and PVDF coating in a chemical transportation environment. The mass change rate and tensile strength residual rate of Example 3 are significantly better than those of Comparative Example 1 and Comparative Example 4, and there is no cracking or peeling on the surface. This shows that the dynamic cross-linking network significantly improves the chemical stability of the material through flexible regulation of the molecular chains, enabling it to resist long-term corrosion from acidic and alkaline media. In Comparative Example 1, since borate dynamic cross-linking technology is not used, the molecular chains of the base polyethylene are susceptible to penetration and erosion by chemical media, showing obvious swelling and strength loss.

[0122] The role of PVDF coating is particularly critical. In Comparative Example 4, although dynamic crosslinking improves corrosion resistance to a certain extent without PVDF coating, it still cannot completely prevent chemical media from invading the material, and cracking and peeling occur on the surface. The PVDF coating of Example 3 forms an effective barrier in acid-base media, combined with the structural stability of the dynamic crosslinking network, to jointly ensure the mechanical properties and surface integrity of the pipe.

[0123] From the experimental performance, the corrosion resistance and mechanical stability of Example 3 have been synergistically optimized, thanks to the organic combination of coating and dynamic cross-linking technology. Especially under high-temperature transportation conditions, the PVDF coating has a more significant barrier effect on acid and alkali media, significantly reducing the corrosion rate of chemical substances on the substrate. The rapid performance decay of Comparative Examples 1 and 4 fully illustrates the inadequacy of a single technical means, and once again proves the overall innovation and practical value of the solution of the present invention.

[0124] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A production process for environmentally friendly high-strength corrosion-resistant PE pipes, characterized in that: The following steps are involved: Raw material pretreatment: high-density polyethylene, low-density polyethylene, borate, polyvinylidene fluoride, epoxidized soybean oil, and antioxidant are mixed in proportion and melt-pretreated to form a uniform mixture; Dynamic cross-linking extrusion molding: The pre-treated mixture is dynamically cross-linked and extruded in a three-zone temperature-controlled extruder, the three zones being the dynamic bond activation zone, the chain orientation induction zone, and the dynamic locking zone; Online molecular chain orientation stretching: the extruded semi-cured pipe is heated and stretched unidirectionally or bidirectionally under constant temperature conditions; Partition cooling: The pipe is cooled by using fast cooling and slow cooling partition cooling methods; Annealing treatment: annealing the cooled pipe in a protective gas environment; Surface treatment: Polyvinylidene fluoride coating is applied on the surface of the pipe.

2. The environmentally friendly high-strength corrosion-resistant PE pipe production process according to claim 1 is characterized in that: The mass ratio of high-density polyethylene, low-density polyethylene, borate, polyvinylidene fluoride, epoxidized soybean oil and antioxidant in the raw material pretreatment step is as follows: 70-85 parts of high-density polyethylene, 10-20 parts of low-density polyethylene, 8-12 parts of borate, 5-10 parts of polyvinylidene fluoride, 3-6 parts of epoxidized soybean oil and 0.5-1 part of antioxidant.

3. The environmentally friendly high-strength corrosion-resistant PE pipe production process according to claim 1 is characterized in that: The temperature of the melt pretreatment is 80-100° C. and the time is 10-20 minutes.

4. The environmentally friendly high-strength corrosion-resistant PE pipe production process according to claim 1 is characterized in that: The dynamic cross-linking extrusion molding steps are as follows: Dynamic bond activation: The raw material is fed into the dynamic bond activation zone of the extruder through the feed port. The temperature is controlled at 180-200°C and the screw speed is 300-500rpm. The material is melted under the action of the screw and the dynamic boron-oxygen bond of the borate ester is broken and reorganized to initially form a dynamic cross-linking network. The material stays in this zone for 60-120S. Chain orientation induction: The molten material enters the chain orientation induction zone, the temperature rises to 200-220°C, the screw speed is 400-600rpm, and the polyethylene molecular chains are induced to stretch and arrange along the flow direction through high shearing action. At the same time, the dynamic cross-linking network is further evenly distributed. The material stays in this zone for 90-150S; Dynamic locking: The material enters the dynamic locking zone, the temperature drops to 170-190°C, the screw speed is adjusted to 200-300rpm, and the dynamic cross-linking network structure is locked by controlling the temperature and shear rate to ensure the stable arrangement of the molecular chains. The material stays in this zone for 60-120S; Extrusion molding: The material after dynamic cross-linking is transported to the die head, the die head temperature is 150-170℃, the melt is extruded through the die head at a speed of 1-5m / min to form a pipe, and enters the initial cooling stage.

5. The environmentally friendly high-strength corrosion-resistant PE pipe production process according to claim 1 is characterized in that: The online molecular chain orientation stretching step comprises the following operations: The extruded semi-cured pipe enters the online constant temperature stretching device, and the device temperature is controlled at 120-140℃; The stretching ratio is controlled at 3-6 times; The stretching speed is 10-50mm / s, and the stretching tension range is controlled to be 30-80MPa by real-time tension adjustment; The stretching method is unidirectional stretching or bidirectional stretching.

6. The environmentally friendly high-strength corrosion-resistant PE pipe production process according to claim 1 is characterized in that: The zone cooling step includes the following operations: The external cooling zone adopts rapid cooling, the cooling medium is cooling water, the water temperature is controlled at 5-15℃, and the cooling rate is 15-30℃ / S; The inner cooling zone adopts slow cooling, the cooling medium is warm water or air, the temperature is controlled at 30-50℃, and the cooling rate is 2-10℃ / S; The cooling rates of the outer cooling zone and the inner cooling zone are independently controlled, and the flow rates of the cooling medium are 0.5-2m / s and 0.1-0.5m / s respectively.

7. The environmentally friendly high-strength corrosion-resistant PE pipe production process according to claim 1 is characterized in that: The annealing step comprises the following operations: The cooled pipe is placed in an annealing device at a temperature of 95-105°C; Annealing time is 4-8h; The annealing environment is filled with nitrogen or other inert gases, with a gas flow rate of 0.1-0.5m 3 / h; After annealing, it was cooled naturally to room temperature.

8. The environmentally friendly high-strength corrosion-resistant PE pipe production process according to claim 1 is characterized in that: The surface treatment step includes the following operations: The surface of the pipe is cleaned with deionized water to remove surface impurities and oil stains; Use spraying or dipping technology to coat the surface of the pipe with polyvinylidene fluoride solution, and the concentration of the solution is controlled at 5-15%; After coating, it is naturally dried at room temperature for 24 hours, and the coating thickness is 0.05-0.1mm.

9. The environmentally friendly high-strength corrosion-resistant PE pipe production process according to claim 1 is characterized in that: In the online molecular chain orientation stretching step, the ratios of uniaxial stretching and biaxial stretching are respectively: the ratio of uniaxial stretching is 3-5 times, and the ratio of biaxial stretching is 4-6 times.

10. The environmentally friendly high-strength corrosion-resistant PE pipe production process according to claim 7, characterized in that: The annealing environment in the annealing treatment stage uses nitrogen with a purity of not less than 99.99%.

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