A structurally stable plastic-lined composite steel pipe and its preparation method

Abstract

This invention discloses a structurally stable plastic-lined composite steel pipe and its preparation method, comprising a steel pipe and a plastic pipe, wherein the steel pipe is sleeved on the plastic pipe, and the plastic pipe includes a PE pipe and an adhesive layer. The adhesive layer is disposed on the outer wall of the PE pipe, and the side of the adhesive layer away from the PE pipe is fixedly connected to the steel pipe. The adhesive layer is obtained by melting hot melt adhesive particles, which are made from the following raw materials in parts by weight: 40-60 parts of ethylene-vinyl acetate copolymer; 10-30 parts of modified polyglycerol fatty acid ester; 10-20 parts of styrene-butadiene rubber; 5-15 parts of hydrogenated castor oil; 20-30 parts of furan resin; and 1-5 parts of antioxidant. The modified polyglycerol fatty acid ester includes polyglycerol fatty acid ester, zinc chloride, isopropyl myristate, tara gum, and a surfactant. This application has the effect of making the bonding between the steel pipe and the plastic pipe more stable.

Description

Technical Field

[0001] This invention relates to the field of plastic-lined steel pipes, and in particular to a structurally stable plastic-lined composite steel pipe and its preparation method. Background Technology

[0002] Plastic-lined composite steel pipe is a steel-plastic composite pipe with a three-layer structure of steel, hot melt adhesive, and plastic, formed by bonding a thin-walled plastic pipe to the inner wall of a steel pipe with hot melt adhesive. Using ordinary steel pipe as the base material and a chemically stable thermoplastic pipe as the inner lining, it combines the mechanical properties of steel pipe with the chemical corrosion resistance and smooth inner wall of plastic pipe, making it an ideal pipeline for transporting media such as acids, alkalis, salts, and corrosive gases. Currently, most plastic-lined steel pipes use EVA hot melt adhesive to bond the steel and plastic pipes together.

[0003] Regarding the aforementioned technologies, the inventors believe that EVA adhesives generally suffer from low bonding strength, resulting in a low production qualification rate for plastic-lined steel pipes. Summary of the Invention

[0004] In order to prepare an adhesive that can bond steel pipes and plastic pipes more stably, this application provides a structurally stable plastic-lined composite steel pipe and its preparation method.

[0005] Firstly, this application provides a structurally stable plastic-lined composite steel pipe using the following technical solution:

[0006] A structurally stable plastic-lined composite steel pipe includes a steel pipe and a plastic pipe, wherein the steel pipe is sleeved on the plastic pipe, and the plastic pipe includes a PE pipe and an adhesive layer. The adhesive layer is disposed on the outer wall of the PE pipe, and the side of the adhesive layer away from the PE pipe is fixedly connected to the steel pipe. The adhesive layer is obtained by heating and extruding hot melt adhesive particles, and the hot melt adhesive particles are made of the following raw materials in parts by weight: 40-60 parts of ethylene-vinyl acetate copolymer; 10-30 parts of modified polyglycerol fatty acid ester; 10-20 parts of styrene-butadiene rubber; 5-15 parts of hydrogenated castor oil; 20-30 parts of furan resin; and 1-5 parts of antioxidant. The modified polyglycerol fatty acid ester includes polyglycerol fatty acid ester, zinc chloride, isopropyl myristate, tara gum, and surfactant.

[0007] By adopting the above technical solution, ethylene-vinyl acetate copolymer is used as the base material of the adhesive. The hot melt adhesive granules prepared by mixing it with various raw materials such as modified polyglycerol fatty acid ester, styrene-butadiene rubber, hydrogenated castor oil, and furan resin are used as the adhesive to bond steel pipes and PE pipes. Hydrogenated castor oil can improve the wettability of the adhesive layer on the inner wall of the steel pipe, so that when the adhesive layer melts, the steel pipe is tightly bonded to the PE pipe through the adhesive layer, thereby improving the bonding strength of the adhesive layer to the steel pipe. Modified polyglycerol fatty acid ester and furan resin are added to the hot melt adhesive as fillers. Hydrogenated castor oil makes the modified polyglycerol fatty acid ester and furan resin more compatible with ethylene-vinyl acetate copolymer, thereby improving the bonding strength of the hot melt adhesive to the PE pipe. At the same time, this application modifies the polyglycerol fatty acid ester, which improves the dispersibility of the polyglycerol fatty acid ester in the system, improves the interaction force between styrene-butadiene rubber and ethylene-vinyl acetate copolymer, and increases the bonding performance of the hot melt adhesive granules.

[0008] Preferably, the modified polyglycerol fatty acid ester is prepared by heating and stirring 5-10 parts by weight of zinc chloride and 20-40 parts by weight of polyglycerol fatty acid ester, then adding 10-20 parts by weight of isopropyl myristate and 10-20 parts by weight of tara gum and continuing to stir, then adding 1-3 parts by weight of surfactant to obtain the modified polyglycerol fatty acid ester. The weight ratio of zinc chloride, polyglycerol fatty acid ester, isopropyl myristate and tara gum is (0.45-0.6):(2.1-2.4):1:(0.8-1).

[0009] By adopting the above technical solution, in the process of modifying polyglycerol fatty acid esters, zinc chloride, isopropyl myristate, tara gum, and surfactants are used to modify polyglycerol fatty acid esters. Zinc chloride is introduced to adhere to the surface of polyglycerol fatty acid esters, modifying the surface of polyglycerol fatty acid esters. Tara gum improves the compatibility of isopropyl myristate with xylitol fatty acid esters, increasing the cohesive strength of xylitol fatty acid esters. Isopropyl myristate and tara gum improve the bonding strength of polyglycerol fatty acid esters. When zinc chloride, polyglycerol fatty acid esters, isopropyl myristate, and tara gum are mixed in the same proportion, the fluidity of polyglycerol fatty acid esters is increased, allowing zinc chloride to be uniformly dispersed on the surface of polyglycerol fatty acid esters. The resulting modified polyglycerol fatty acid esters can accelerate the removal of air bubbles in the adhesive layer, reduce the presence of air bubbles on the inner wall of the resulting plastic-lined composite steel pipe, and thus improve the connection strength between the steel pipe and the plastic pipe in the plastic-lined composite steel pipe.

[0010] Preferably, the hydrogenated castor oil is a modified hydrogenated castor oil, which is made from the following raw materials in parts by weight: 5-15 parts hydrogenated castor oil; 10-20 parts carrageenan; and 8-16 parts nano-silica.

[0011] Preferably, the modified hydrogenated castor oil is prepared by heating and stirring hydrogenated castor oil and carrageenan, keeping it at a constant temperature, and then adding nano-silica and stirring to disperse it evenly to obtain the modified hydrogenated castor oil; the weight ratio of hydrogenated castor oil, carrageenan and nano-silica is (0.4-0.6):1:(0.6-0.7).

[0012] By adopting the above technical solution, hydrogenated castor oil, a vegetable oil, is commonly used as a lubricant after being catalytically hydrogenated under high pressure. In this application, hydrogenated castor oil is modified by carrageenan and nano-silica. Carrageenan uniformly disperses nano-silica on the hydrogenated castor oil. After mixing and stirring with nano-silica, the hydrophobicity of the nano-silica surface is improved, thereby improving the dispersibility of the modified hydrogenated castor oil and the bonding performance of the hot melt adhesive. When hydrogenated castor oil, carrageenan, and nano-silica are in a specific ratio, the peel strength of the resulting adhesive is greatly improved.

[0013] Preferably, the weight ratio of the modified polyglycerol fatty acid ester, styrene-butadiene rubber, hydrogenated castor oil and furan resin is (1.6-1.9):1:(0.8-1):(1.4-1.6).

[0014] By adopting the above technical solution, when modified polyglycerol fatty acid ester, styrene-butadiene rubber, hydrogenated castor oil and furan resin are in a specific weight ratio, the bonding ability of the adhesive layer made of hot melt adhesive particles can be improved, while reducing the generation of air bubbles at both ends of the plastic-lined composite steel pipe.

[0015] Preferably, the surfactant comprises one of sodium lauryl sulfate, sodium lignosulfonate, and sodium octadecyl sulfate.

[0016] Preferably, the antioxidant includes one of ascorbic acid and tea polyphenols.

[0017] By adopting the above technical solutions, the use of appropriate surfactants can improve the effect of modified polyglycerol fatty acid esters, and the selection of appropriate antioxidants can extend the service life of lined composite pipes.

[0018] Preferably, the thickness of the adhesive layer is 0.5-1 mm.

[0019] By adopting the above technical solution, the thickness range of the adhesive layer can be controlled. If the adhesive layer is too thin, the bonding stability between the plastic pipe and the steel pipe will be low, and the steel pipe and the plastic pipe will easily separate.

[0020] Secondly, this application provides a method for preparing a structurally stable plastic-lined composite steel pipe using the following technical solution:

[0021] A method for preparing a structurally stable plastic-lined composite steel pipe includes the following steps:

[0022] S1. Ethylene-vinyl acetate copolymer is heated and mixed with styrene-butadiene rubber and hydrogenated castor oil to obtain a premix; the premix is ​​mixed with modified polyglycerol fatty acid ester, furan resin and antioxidant for 1-2 hours, then dried and granulated to obtain the hot melt adhesive granules;

[0023] S2. PE granules and hot melt adhesive granules are extruded together into a PE pipe and an adhesive layer attached to the PE pipe to obtain a plastic pipe;

[0024] S3. The steel pipe is placed on the plastic pipe, the adhesive layer is melted by heating, and then water is sprayed to cool it, thus obtaining the plastic-lined composite steel pipe.

[0025] By adopting the above technical solution, the hot melt adhesive granules and PE granules are mixed and extruded together, and the outer wall of the PE pipe is coated with an adhesive layer. After the plastic pipe is inserted into the steel pipe, it is heat-treated to melt the adhesive layer and then spray water to cool the steel pipe, so that the plastic pipe and the steel pipe are in closer contact, thus improving the bonding performance between the plastic liner and the steel pipe.

[0026] In summary, this application has the following beneficial effects:

[0027] 1. Ethylene-vinyl acetate copolymer is used as the base material of the adhesive. Hot melt adhesive granules prepared by mixing it with various raw materials such as modified polyglycerol fatty acid ester, styrene-butadiene rubber, hydrogenated castor oil, and furan resin serve as the adhesive for bonding steel pipes and PE pipes. Hydrogenated castor oil improves the wettability of the adhesive layer on the inner wall of the steel pipe, allowing the steel pipe to bond tightly to the PE pipe through the adhesive layer when it melts, thus increasing the bonding strength of the adhesive layer to the steel pipe. Modified polyglycerol fatty acid ester and furan resin are added to the hot melt adhesive as fillers. Hydrogenated castor oil improves the compatibility of the modified polyglycerol fatty acid ester and furan resin with the ethylene-vinyl acetate copolymer, further enhancing the bonding strength of the hot melt adhesive to the PE pipe. Simultaneously, this application modifies the polyglycerol fatty acid ester, improving its dispersibility in the system and increasing the interaction force between styrene-butadiene rubber and the ethylene-vinyl acetate copolymer, thereby enhancing the bonding performance of the hot melt adhesive granules.

[0028] 2. In the process of modifying polyglycerol fatty acid esters, zinc chloride, isopropyl myristate, tara gum, and surfactants are used to modify the polyglycerol fatty acid esters. Zinc chloride is introduced to adhere to the surface of the polyglycerol fatty acid esters, modifying the surface of the polyglycerol fatty acid esters. Tara gum improves the compatibility between isopropyl myristate and xylitol fatty acid esters, increasing the cohesive strength of xylitol fatty acid esters. Isopropyl myristate and tara gum improve the bonding strength of polyglycerol fatty acid esters. When zinc chloride, polyglycerol fatty acid esters, isopropyl myristate, and tara gum are mixed in the same proportion, the fluidity of polyglycerol fatty acid esters is increased, allowing zinc chloride to be uniformly dispersed on the surface of polyglycerol fatty acid esters. The resulting modified polyglycerol fatty acid esters can accelerate the removal of air bubbles in the adhesive layer, reduce the presence of air bubbles on the inner wall of the resulting plastic-lined composite steel pipe, and thus improve the connection strength between the steel pipe and the plastic pipe in the plastic-lined composite steel pipe. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of this application.

[0030] Explanation of reference numerals in the attached figures:

[0031] 1. Steel pipe; 2. Plastic pipe; 3. Adhesive layer. Detailed Implementation

[0032] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0033] Preparation Example

[0034] Preparation Example 1

[0035] A method for preparing modified hydrogenated castor oil:

[0036] 5 kg of hydrogenated castor oil and 10 kg of carrageenan were added to a reaction vessel, heated to 100°C, stirred for 20 min at 300 r / min, and kept at 80°C for 3 h. Then, 8 kg of nano-silica was added and stirred and dispersed at 1200 r / min for 1 h. After uniform dispersion, modified hydrogenated castor oil was obtained.

[0037] Preparation Example 2

[0038] A method for preparing modified hydrogenated castor oil:

[0039] 15 kg of hydrogenated castor oil and 20 kg of carrageenan were added to a reactor and heated to 100°C. The mixture was stirred for 20 min at 300 r / min and then kept at 80°C for 3 h. 16 kg of nano-silica was then added and stirred and dispersed at 1200 r / min for 1 h. After uniform dispersion, modified hydrogenated castor oil was obtained.

[0040] Preparation Example 3

[0041] A method for preparing modified hydrogenated castor oil differs from Preparation Example 1 in that the amount of hydrogenated castor oil added is 6 kg, the amount of carrageenan added is 15 kg, and the amount of nano-silica added is 9 kg.

[0042] Preparation Example 4

[0043] A method for preparing modified hydrogenated castor oil differs from Preparation Example 1 in that the amount of hydrogenated castor oil added is 8 kg, the amount of carrageenan added is 15 kg, and the amount of nano-silica added is 10 kg.

[0044] Example

[0045] Example 1

[0046] A structurally stable plastic-lined composite steel pipe, with reference to Figure 1 The system includes steel pipes and plastic pipes. In this embodiment, the steel pipe has a wall thickness of 30mm, and the plastic pipe has a wall thickness of 1.5mm. The steel pipe is fitted onto the plastic pipe, and the outer wall of the plastic pipe is bonded to the inner wall of the steel pipe. The plastic pipe includes a PE pipe and an adhesive layer. The adhesive layer is disposed on the outer wall of the PE pipe, with one side bonded to the PE pipe and the other side bonded to the inner wall of the steel pipe. The adhesive layer can bond the PE pipe and the steel pipe tightly, thereby giving the inner wall of the steel pipe good rust and corrosion resistance. The adhesive layer is made of hot melt adhesive particles and has a thickness of 1mm.

[0047] A method for preparing a structurally stable plastic-lined composite steel pipe:

[0048] S1. Preparation of hot melt adhesive granules: 40 kg of ethylene-vinyl acetate copolymer, 10 kg of styrene-butadiene rubber, and 5 kg of hydrogenated castor oil were added to a stirred tank and mixed together at 60°C for 1 h to obtain a premix; the premix was then mixed and stirred with 10 kg of modified polyglycerol fatty acid ester, 20 kg of furan resin, and 1 kg of ascorbic acid at 80°C for 2 h, stirred for 10 min, dried, and granulated to obtain hot melt adhesive granules.

[0049] The ethylene-vinyl acetate copolymer has a melting temperature of 85℃ and a density of 0.91 g / cm³. 3 The furan resin has a high temperature resistance of 150℃ and a density of 1.12 g / cm³. 3 The density of hydrogenated castor oil is 1.06 g / mL; the styrene-butadiene rubber selected is Kraton D1116AIM.

[0050] The preparation method of modified polyglycerol fatty acid ester is as follows:

[0051] 5 kg of zinc chloride and 20 kg of polyglycerol fatty acid ester were added to a mixer and heated to 60°C. The mixture was stirred for 30 min at a speed of 70 r / min. Then, 10 kg of isopropyl myristate and 10 kg of tara gum were added and stirred for another 30 min. Finally, 1 kg of sodium lauryl sulfate surfactant was added to obtain the modified polyglycerol fatty acid ester.

[0052] S2. Hot melt adhesive granules and PE granules are fed into a screw extruder with a weight ratio of 1:3. The PE pipe and the adhesive layer bonded to the PE pipe are extruded to obtain a plastic pipe.

[0053] S3. The steel pipe is fitted onto the plastic pipe, with the inner diameter of the steel pipe being larger than the outer diameter of the plastic pipe. The plastic pipe is heated to 215°C using a composite machine, causing it to soften and expand, melting the adhesive layer between the plastic and steel pipes, thus tightly fixing them together to obtain a plastic-lined composite pipe. After the composite process is completed, the plastic-lined composite pipe is cooled by water cooling. Water is sprayed onto the plastic-lined composite pipe to cool it to room temperature, completing the cooling process.

[0054] Example 2

[0055] A method for preparing a structurally stable plastic-lined composite steel pipe differs from Example 1 in that, in step S1, the process of preparing hot melt adhesive granules involves: adding 60 kg of ethylene-vinyl acetate copolymer, 20 kg of styrene-butadiene rubber, and 15 kg of hydrogenated castor oil into a stirred tank and mixing them together at 60°C for 1 hour to obtain a premix; then mixing the premix with 30 kg of modified polyglycerol fatty acid ester, 30 kg of furan resin, and 5 kg of ascorbic acid at 80°C for 2 hours, stirring for 10 minutes, drying, and granulating to obtain hot melt adhesive granules.

[0056] Example 3

[0057] A method for preparing a structurally stable plastic-lined composite steel pipe differs from Example 1 in that, in step S1, the process of preparing hot melt adhesive granules involves: adding 50 kg of ethylene-vinyl acetate copolymer, 15 kg of styrene-butadiene rubber, and 10 kg of hydrogenated castor oil to a stirred tank and mixing them together at 60°C for 1 hour to obtain a premix; then mixing the premix with 20 kg of modified polyglycerol fatty acid ester, 25 kg of furan resin, and 3 kg of ascorbic acid at 80°C for 2 hours, stirring for 10 minutes, drying, and granulating to obtain hot melt adhesive granules.

[0058] Example 4

[0059] A method for preparing a structurally stable plastic-lined composite steel pipe differs from Example 3 in that the preparation method of the modified polyglycerol fatty acid ester is different:

[0060] 10 kg of zinc chloride and 40 kg of polyglycerol fatty acid ester were added to a mixer and heated to 60°C. The mixture was stirred for 30 min at a speed of 70 r / min. Then, 20 kg of isopropyl myristate and 20 kg of tara gum were added and stirred for another 30 min. Finally, 3 kg of surfactant was added to obtain the modified polyglycerol fatty acid ester.

[0061] Example 5

[0062] A method for preparing a structurally stable plastic-lined composite steel pipe differs from Example 4 in that the amount of raw materials used in preparing the modified polyglycerol fatty acid ester is different. Specifically, the amount of zinc chloride is 7 kg, the amount of polyglycerol fatty acid ester is 32 kg, the amount of isopropyl myristate is 15 kg, and the amount of tara rubber is 12 kg.

[0063] Example 6

[0064] A method for preparing a structurally stable plastic-lined composite steel pipe differs from Example 4 in that the amount of raw materials used in preparing the modified polyglycerol fatty acid ester is different. Specifically, the amount of zinc chloride is 9 kg, the amount of polyglycerol fatty acid ester is 36 kg, the amount of isopropyl myristate is 15 kg, and the amount of tara rubber is 15 kg.

[0065] Example 7

[0066] A method for preparing a structurally stable plastic-lined composite steel pipe differs from Example 6 in that the hydrogenated castor oil in step S1 is replaced in an equal amount with the modified castor oil obtained in Preparation Example 1.

[0067] Example 8

[0068] A method for preparing a structurally stable plastic-lined composite steel pipe differs from Example 6 in that the hydrogenated castor oil in step S1 is replaced in an equal amount with the modified castor oil obtained in Preparation Example 2.

[0069] Example 9

[0070] A method for preparing a structurally stable plastic-lined composite steel pipe differs from Example 6 in that the hydrogenated castor oil in step S1 is replaced in an equal amount with the modified castor oil obtained in Preparation Example 3.

[0071] Example 10

[0072] A method for preparing a structurally stable plastic-lined composite steel pipe differs from Example 6 in that the hydrogenated castor oil in step S1 is replaced in an equal amount with the modified castor oil obtained in Preparation Example 4.

[0073] Example 11

[0074] A method for preparing a structurally stable plastic-lined composite steel pipe differs from Example 6 in that, in step S1, the amount of modified polyglycerol fatty acid ester added is 25 kg, the amount of styrene-butadiene rubber added is 15 kg, the amount of hydrogenated castor oil added is 12 kg, and the amount of furan resin added is 21 kg.

[0075] Example 12

[0076] A method for preparing a structurally stable plastic-lined composite steel pipe differs from Example 10 in that, in step S1, the amount of modified polyglycerol fatty acid ester added is 25 kg, the amount of styrene-butadiene rubber added is 15 kg, the amount of modified hydrogenated castor oil added in Preparation Example 4 is 12 kg, and the amount of furan resin added is 21 kg.

[0077] Example 13

[0078] A method for preparing a structurally stable plastic-lined composite steel pipe differs from Example 10 in that, in step S1, the amount of modified polyglycerol fatty acid ester added is 28 kg, the amount of styrene-butadiene rubber added is 15 kg, the amount of modified hydrogenated castor oil added in Preparation Example 4 is 15 kg, and the amount of furan resin added is 24 kg.

[0079] Comparative Example

[0080] Comparative Example 1

[0081] A method for preparing a structurally stable plastic-lined composite steel pipe differs from Example 1 in that, in step S1, the modified polyglycerol fatty acid ester is replaced with an equal amount of polyglycerol fatty acid ester.

[0082] Comparative Example 2

[0083] A method for preparing a structurally stable plastic-lined composite steel pipe differs from Example 1 in that, in step S1, furan resin is replaced with an equal amount of polyvinyl alcohol.

[0084] Comparative Example 3

[0085] A method for preparing a structurally stable plastic-lined composite steel pipe differs from Example 1 in that the adhesive layer bonded to the PE pipe is a commercially available hot melt adhesive granule, wherein the commercially available hot melt adhesive granule is selected from Doton 770C hot melt adhesive granules.

[0086] Performance testing:

[0087] Stability of plastic-lined composite steel pipes: Observe whether air bubbles appear at both ends of the plastic-lined composite steel pipes prepared in Examples 1-13 and Comparative Examples 1-3.

[0088] The hot melt adhesive granules from Examples 1-13 and Comparative Examples 1-3 were pressed into 1mm thick films in a hot press at 160°C. The films were then cut into 25×150mm pieces. The cut films were placed between two aluminum sheets (25×200mm) and hot-pressed for 2 minutes at 160°C with a pressure of 4MPa. The films were then left to stand for 24 hours under the test conditions to obtain the test films.

[0089] Bond strength test: The bond strength of the adhesive sheets prepared by hot melt adhesives in Examples 1-13 and Comparative Examples 1-3 was determined by a universal testing machine according to ASTM D1002.

[0090] Peel strength test: The peel strength of the films made from the hot melt adhesives prepared in Examples 1-13 and Comparative Examples 1-3 was determined according to GB / T 2791-1995 standard.

[0091] Stability of plastic-lined composite steel pipe Bond strength / MPa Peel strength / N / cm Example 1 No layering, few air bubbles 25.4 12.1 Example 2 No layering, few air bubbles 25.6 11.7 Example 3 No layering, few air bubbles 25.6 12.2 Example 4 No layering, few air bubbles 25.5 12.0 Example 5 No layering, no obvious bubbles 27.1 12.4 Example 6 No layering, no obvious bubbles 26.9 12.6 Example 7 No layering, no obvious bubbles 27.2 15.4 Example 8 No layering, no obvious bubbles 27.1 15.1 Example 9 No layering, no obvious bubbles 28.8 15.7 Example 10 No layering, no obvious bubbles 29.0 15.9 Example 11 No layering, no obvious bubbles 27.3 12.1 Example 12 No layering, no obvious bubbles 31.2 18.2 Example 13 No layering, no obvious bubbles 31.3 18.4 Comparative Example 1 Layered, with many air bubbles 18.4 5.8 Comparative Example 2 Layered, with many air bubbles 20.5 8.2 Comparative Example 3 Layered, with a large number of bubbles 16.9 7.7

[0092] Based on the data comparison of Examples 1-4 and Comparative Examples 1-3, it can be seen that the ethylene-vinyl acetate copolymer, as the base material of the adhesive, is mixed with various raw materials such as modified polyglycerol fatty acid ester, styrene-butadiene rubber, hydrogenated castor oil, and furan resin to prepare hot melt adhesive granules, which are used to bond steel pipes and PE pipes. Hydrogenated castor oil can improve the wettability of the adhesive layer on the inner wall of the steel pipe, so that when the adhesive layer melts, the steel pipe is tightly bonded to the PE pipe through the adhesive layer, thereby improving the bonding strength of the adhesive layer to the steel pipe. Modified polyglycerol fatty acid ester and furan resin are added to the hot melt adhesive as fillers. Hydrogenated castor oil makes the modified polyglycerol fatty acid ester and furan resin more compatible with the ethylene-vinyl acetate copolymer, thereby improving the bonding strength of the hot melt adhesive to the PE pipe. At the same time, the present application modifies the polyglycerol fatty acid ester, which improves the dispersibility of the polyglycerol fatty acid ester in the system, improves the interaction force between styrene-butadiene rubber and ethylene-vinyl acetate copolymer, and increases the bonding performance of the hot melt adhesive granules.

[0093] According to the data comparison of Examples 4-6, when zinc chloride, polyglycerol fatty acid ester, isopropyl myristate, and tarara are mixed in the same proportion, the fluidity of polyglycerol fatty acid ester is increased, so that zinc chloride can be evenly dispersed on the surface of polyglycerol fatty acid ester. The modified polyglycerol fatty acid ester can accelerate the discharge of air bubbles in the adhesive layer, reduce the presence of air bubbles on the inner wall of the plastic-lined composite steel pipe, and thus improve the connection strength between the steel pipe and the plastic pipe in the plastic-lined composite steel pipe.

[0094] Based on the data comparison of Examples 6-10, it can be seen that this application modifies hydrogenated castor oil by using carrageenan and nano-silica. Carrageenan uniformly disperses nano-silica on the hydrogenated castor oil, and after mixing and stirring with nano-silica, the hydrophobicity of the nano-silica surface is improved, thereby improving the dispersibility of the modified hydrogenated castor oil and the bonding performance of the hot melt adhesive. When hydrogenated castor oil, carrageenan, and nano-silica are in a specific ratio, the peel strength of the resulting adhesive is greatly improved.

[0095] According to the data comparison of Examples 11-13, when modified polyglycerol fatty acid ester, styrene-butadiene rubber, hydrogenated castor oil and furan resin are in a specific weight ratio, the bonding ability of the adhesive layer made of hot melt adhesive particles can be improved, while reducing the generation of air bubbles at both ends of the plastic-lined composite steel pipe.

[0096] The specific embodiments are merely explanations of this application and are not intended to limit it. Those skilled in the art can make modifications to these embodiments without contributing any inventive step after reading this specification, but such modifications are protected by patent law as long as they are within the scope of the claims of this application.

Claims

1. A structurally stable plastic-lined composite steel pipe, characterized in that: The device includes a steel pipe and a plastic pipe, wherein the steel pipe is sleeved on the plastic pipe, and the plastic pipe includes a PE pipe and an adhesive layer. The adhesive layer is disposed on the outer wall of the PE pipe, and the side of the adhesive layer away from the PE pipe is fixedly connected to the steel pipe. The adhesive layer is obtained by heating and extruding hot melt adhesive granules, which are made from the following raw materials in parts by weight: 40-60 parts of ethylene-vinyl acetate copolymer; 10-30 parts of modified polyglycerol fatty acid ester; 10-20 parts of styrene-butadiene rubber; 5-15 parts of hydrogenated castor oil; 20-30 parts of furan resin; and 1-5 parts of antioxidant. The modified polyglycerol fatty acid ester includes polyglycerol fatty acid ester, zinc chloride, isopropyl myristate, tara gum, and surfactant.

2. The structurally stable plastic-lined composite steel pipe according to claim 1, characterized in that: The modified polyglycerol fatty acid ester is prepared by heating and stirring 5-10 parts by weight of zinc chloride and 20-40 parts by weight of polyglycerol fatty acid ester, then adding 10-20 parts by weight of isopropyl myristate and 10-20 parts by weight of tara gum and continuing to stir, then adding 1-3 parts by weight of surfactant to obtain the modified polyglycerol fatty acid ester.

3. The structurally stable plastic-lined composite steel pipe according to claim 1, characterized in that: The hydrogenated castor oil is a modified hydrogenated castor oil, which is made from the following raw materials in parts by weight: 5-15 parts hydrogenated castor oil; 10-20 parts carrageenan; 8-16 parts of nano-silica.

4. The structurally stable plastic-lined composite steel pipe according to claim 3, characterized in that: The modified hydrogenated castor oil is prepared by heating and stirring hydrogenated castor oil and carrageenan, keeping it at a constant temperature, and then adding nano-silica and stirring to disperse it evenly to obtain the modified hydrogenated castor oil; the weight ratio of hydrogenated castor oil, carrageenan and nano-silica is (0.4-0.6):1:(0.6-0.7).

5. The structurally stable plastic-lined composite steel pipe according to claim 1, characterized in that: The weight ratio of the modified polyglycerol fatty acid ester, styrene-butadiene rubber, hydrogenated castor oil and furan resin is (1.6-1.9):1:(0.8-1):(1.4-1.6).

6. The structurally stable plastic-lined composite steel pipe according to claim 1, characterized in that: The surfactant includes one of sodium lauryl sulfate, sodium lignosulfonate, and sodium octadecyl sulfate.

7. The structurally stable plastic-lined composite steel pipe according to claim 1, characterized in that: The antioxidants include one of ascorbic acid and tea polyphenols.

8. The structurally stable plastic-lined composite steel pipe according to claim 1, characterized in that: The thickness of the adhesive layer is 0.5-1 mm.

9. A method for preparing a structurally stable plastic-lined composite steel pipe, characterized in that, The method for preparing a structurally stable plastic-lined composite steel pipe according to any one of claims 1-8 includes the following steps: S1. Ethylene-vinyl acetate copolymer is heated and mixed with styrene-butadiene rubber and hydrogenated castor oil to obtain a premix; the premix is ​​mixed with modified polyglycerol fatty acid ester, furan resin and antioxidant for 1-2 hours, then dried and granulated to obtain the hot melt adhesive granules; S2. PE granules and hot melt adhesive granules are extruded together into a PE pipe and an adhesive layer attached to the PE pipe to obtain a plastic pipe; S3. The steel pipe is sleeved on the plastic pipe, the adhesive layer is melted by heating, and then water is sprayed to cool it, thus obtaining the plastic-lined composite steel pipe.

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