A multilayer coextruded thermoplastic composite pipe and a method for making the same

Abstract

The present application belongs to the technical field of non-metal pipe products, and relates to a multilayer co-extrusion thermoplastic plastic composite pipe and a preparation method. The composite pipe comprises, from inside to outside in the radial direction, a modified fluoroplastic layer, a PA layer, an adhesive resin layer and a PE layer. The modified fluoroplastic contains anhydride groups, which are reactive functional groups for adhesion and react with amide groups on the molecular chain of PA to form a polymer containing imide bond structural units. The imide groups have high bond energy and excellent high-temperature resistance and chemical medium corrosion resistance, meeting the requirements for medium transportation. The adhesion between PA and PE is realized through the adhesive resin, which is an anhydride-modified polyolefin resin. The amine groups at the end of the molecular chain of PA chemically react with the active anhydride groups grafted on the molecular chain of the adhesive resin to form a closed-loop imido functional group, thereby obtaining the adhesion between the interfaces through covalent bonds. The C-C bonds on the adhesive resin and the C-C bonds on the outer PE layer are organically combined.

Description

Technical Field

[0001] This invention belongs to the field of non-metallic pipe product technology, and specifically relates to a multi-layer co-extruded thermoplastic composite pipe and its preparation method. Background Technology

[0002] Currently, there are many types of multilayer co-extruded composite pipes. Most of these pipes use high-performance thermoplastic plastic in contact with the transported medium, with a common thermoplastic plastic exterior, bonded together with hot melt adhesive. The characteristic of this type of pipe is that the high-performance thermoplastic plastic is about 2mm thick, serving to isolate the medium and control temperature, while the common thermoplastic plastic is about 5mm-10mm thick, meeting the pressure resistance requirements, thus achieving a good balance between cost reduction and efficiency. For example, patent documents CN202756779U, CN 107166112B, and CN108017818B describe related multilayer co-extruded products. However, due to existing problems, multilayer co-extruded composite pipes have not been widely adopted. The main problems are twofold: poor adhesion between high-performance fluoroplastics and common polyethylene plastics; and the limited application range of multilayer co-extruded composite pipes based on low-performance plastics, which cannot meet the requirements for transporting high-temperature (≥65℃) and highly corrosive media (including H2S and CO2). Details are as follows: Current patented technologies involve bonding anhydride-modified fluoroplastics to polypropylene using adhesive resins. The modified ETFE molecular chains contain anhydrides, which react with epoxy groups in the hot melt adhesive molecular chains under high-temperature conditions to generate esters (-COOR), thereby achieving adhesion to polypropylene, as described in patent document CN 202756779U. However, with prolonged service life, the generated esters are prone to chain decomposition, leading to decreased adhesive performance and a significant risk of failure.

[0003] Therefore, improving the bonding performance between fluoroplastics and ordinary polypropylene has become a bottleneck in current technology. Summary of the Invention

[0004] The purpose of this invention is to provide a multilayer co-extruded thermoplastic composite pipe and its preparation method, which solves the problem of poor adhesion between fluoroplastic pipes and ordinary polypropylene.

[0005] This invention is achieved through the following technical solution: A multilayer co-extruded thermoplastic composite pipe, the multilayer co-extruded thermoplastic composite pipe comprising a modified fluoroplastic layer, a PA layer, an adhesive resin layer and a PE layer connected in sequence from the inside to the outside in the radial direction; The multi-layer co-extruded thermoplastic composite pipe is manufactured using a multi-layer co-extrusion process. Modified fluoroplastics are anhydride-modified fluoroplastics containing anhydride groups R-CO-O-CO-R; The adhesive resin layer is made of an anhydride-modified polyolefin resin.

[0006] Furthermore, the material of fluoroplastics is polyvinylidene fluoride or ethylene-tetrafluoroethylene copolymer.

[0007] Furthermore, the PA layer is made of PA6, PA11, or PA12.

[0008] Furthermore, the polyolefin resin is made of ethylene-vinyl acetate copolymer or low-density polyethylene polymer.

[0009] Furthermore, the PE layer is made of low-density polyethylene, medium-density polyethylene, high-density polyethylene, or heat-resistant polyethylene.

[0010] Furthermore, the thickness of the modified fluoroplastic layer is 1mm to 5mm.

[0011] Furthermore, the thickness of the PA layer is 1mm to 5mm.

[0012] Furthermore, the thickness of the adhesive resin layer is 0.1~0.6mm.

[0013] Furthermore, the thickness of the PE layer is 3mm to 8mm.

[0014] This invention also discloses a method for preparing a multilayer co-extruded thermoplastic composite pipe, comprising the following steps: Step 1: Determine the extrusion wall thickness of each layer according to the process design, and adjust the extrusion parameters of each layer according to the wall thickness; Step 2: Prepare the materials for the modified fluoroplastic layer, PA layer, adhesive resin layer, and PE layer; Step 3: Complete the co-extrusion of the modified fluoroplastic layer, PA layer, adhesive resin layer and PE layer from the inside out.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a multi-layer co-extrusion process for preparing composite pipes. The composite pipe has a radial four-layer structure, consisting of a modified fluoroplastic layer, a PA layer, an adhesive resin layer, and a PE layer from the inside out. Molecular-level bonding is achieved between the layers, effectively ensuring the reliability of the composite pipe during long-term service. The modified fluoroplastic contains anhydride groups (R-CO-O-CO-R), which are reactive functional groups for bonding. These react with the amide groups (CONH) on the PA molecular chain to form a polymer containing imide bond (R-CO-NH-CO-R) structural units. The imide groups have high bond energy and excellent high-temperature resistance and chemical corrosion resistance, meeting the requirements for transporting media. The bonding between PA and PE is achieved through the adhesive resin, which is an anhydride-modified polyolefin resin. The amine groups at the ends of the PA molecular chain react chemically with the active anhydride groups grafted onto the adhesive resin molecular chain to form closed-ring imide functional groups, thereby achieving interfacial adhesion through covalent bonds. The CC bonds on the adhesive resin are organically combined with the CC bonds on the outer PE layer.

[0016] Fluoroplastics possess excellent resistance to various media and temperatures, but their main drawback is their high price, approximately 20 to 30 times that of ordinary polyethylene. A composite material consisting of an inner fluoroplastic layer and an outer ordinary polyethylene layer, using a suitable process, can simultaneously achieve the dual goals of improving pipe conveying performance and reducing costs. Furthermore, using a PE layer for the outermost layer, which is cheaper than PP, further reduces costs.

[0017] This invention discloses a method for preparing composite pipes using a multilayer co-extrusion process. The process is simple and easy to promote. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a multilayer co-extruded thermoplastic composite pipe according to the present invention.

[0019] The layers are: 1. Modified fluoroplastic layer; 2. PA layer; 3. Adhesive resin layer; 4. PE layer. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0021] The components described and illustrated in the accompanying drawings and embodiments of this invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the accompanying drawings and embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0022] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, element, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, element, method, article, or apparatus.

[0023] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0024] This invention discloses a method for preparing a multilayer co-extruded thermoplastic composite pipe, comprising the following steps: Step 1: Based on the process design, determine the extrusion wall thickness of each layer and adjust the relevant parameters of the extruder; Step 2: Prepare the thermoplastics for each co-extrusion layer as needed, mainly including modified fluoroplastics, such as polyvinylidene fluoride (PVDF) or ethylene-tetrafluoroethylene copolymer (ETFE); PA, such as PA6, PA11, and PA12; adhesive resin, such as anhydride-modified ethylene-vinyl acetate copolymer and anhydride-modified linear low-density polyethylene polymer; and PE layer 4, such as low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), and heat-resistant polyethylene (PE-RT). Step 3: Complete the multi-layer co-extrusion process, from the inside out: modified fluoroplastic layer 1, PA layer 2, adhesive resin layer 3, and PE layer 4.

[0025] Example 1 This invention discloses a method for preparing a multilayer co-extruded thermoplastic composite pipe with PVDF as the innermost layer, comprising the following steps: Step 1: According to the process design, determine the extrusion wall thickness of each layer, where the wall thickness of modified fluoroplastic layer 1 is 2mm, the thickness of PA layer 2 is 2mm, the thickness of adhesive resin layer 3 is 0.5mm, the thickness of PE layer 4 is 4mm, and adjust the relevant parameters of the extruder. Step 2: Prepare thermoplastic plastics for each co-extrusion layer as needed. For fluoroplastics, use anhydride-modified polyvinylidene fluoride (PVDF); for PA layer 2, use PA12; for adhesive resin layer 3, use anhydride-modified ethylene-vinyl acetate copolymer; and for PE layer 4, use HDPE. Step 3: Complete the multi-layer co-extrusion process, from the inside out: modified fluoroplastic layer 1, PA layer 2, adhesive resin layer 3, and PE layer 4.

[0026] Bonding effect evaluation: The peel strength of three samples obtained from the entire pipe was measured to characterize the bonding effect, according to GB / T 2791. The tested peel strength values ​​were 67 N / cm, 62 N / cm, and 68 N / cm, respectively, which are significantly higher than the peel strength requirements (15 N / cm) in relevant standards (GB / T 32439-2015 "Steel Wire Mesh Reinforced Polyethylene Composite Pipes for Water Supply" and SY / T 6662.1-2022 "Non-metallic Composite Pipes for Petroleum and Natural Gas Industry Part 1: Steel Reinforced Polyethylene Composite Pipes").

[0027] Example 2 This invention discloses a method for preparing a multilayer co-extruded thermoplastic composite pipe with ETFE as the innermost layer, comprising the following steps: Step 1: According to the process design, determine the extrusion wall thickness of each layer, where the wall thickness of modified fluoroplastic layer 1 is 1.5mm, the thickness of PA layer 2 is 2mm, the thickness of adhesive resin layer 3 is 0.5mm, the thickness of PE layer 4 is 4mm, and adjust the relevant parameters of the extruder. Step 2: Prepare thermoplastic plastics for co-extrusion as needed. For fluoroplastics, use anhydride-modified ETFE; for PA layer 2, use PA6; for adhesive resin layer 3, use anhydride-modified linear low-density polyethylene polymer; and for PE layer 4, use PE-RT. Step 3: Complete the multi-layer co-extrusion process, from the inside out: modified fluoroplastic layer 1, PA layer 2, adhesive resin layer 3, and PE layer 4.

[0028] Bonding effect evaluation: The peel strength of three samples obtained from the entire pipe was measured to characterize the bonding effect, according to GB / T 2791. The tested peel strength values ​​were 64 N / cm, 66 N / cm, and 63 N / cm, respectively, which are significantly higher than the peel strength requirements (15 N / cm) in relevant standards (GB / T 32439-2015 "Steel Wire Mesh Reinforced Polyethylene Composite Pipes for Water Supply" and SY / T 6662.1-2022 "Non-metallic Composite Pipes for Petroleum and Natural Gas Industry Part 1: Steel Reinforced Polyethylene Composite Pipes").

[0029] Example 3 This invention discloses a method for preparing a multilayer co-extruded thermoplastic composite pipe with ETFE as the innermost layer, comprising the following steps: Step 1: According to the process design, determine the extrusion wall thickness of each layer, where the wall thickness of modified fluoroplastic layer 1 is 5mm, the thickness of PA layer 2 is 5mm, the thickness of adhesive resin layer 3 is 0.6mm, the thickness of PE layer 4 is 8mm, and adjust the relevant parameters of the extruder. Step 2: Prepare thermoplastic plastics for each co-extrusion layer as needed. Fluoroplastics are selected from anhydride-modified ETFE, PA layer 2 is selected from PA11, adhesive resin layer 3 is selected from anhydride-modified linear low-density polyethylene polymer, and PE layer 4 is selected from heat-resistant polyethylene. Step 3: Complete the multi-layer co-extrusion process, from the inside out: modified fluoroplastic layer 1, PA layer 2, adhesive resin layer 3, and PE layer 4.

[0030] Bonding effect evaluation: The peel strength of three samples obtained from the entire pipe was measured to characterize the bonding effect, according to GB / T 2791. The tested peel strength values ​​were 69 N / cm, 68 N / cm, and 71 N / cm, respectively, which are significantly higher than the peel strength requirements (15 N / cm) in relevant standards (GB / T 32439-2015 "Steel Wire Mesh Reinforced Polyethylene Composite Pipes for Water Supply" and SY / T 6662.1-2022 "Non-metallic Composite Pipes for Petroleum and Natural Gas Industry Part 1: Steel Reinforced Polyethylene Composite Pipes").

[0031] Example 4 This invention discloses a method for preparing a multilayer co-extruded thermoplastic composite pipe with ETFE as the innermost layer, comprising the following steps: Step 1: According to the process design, determine the extrusion wall thickness of each layer, where the wall thickness of modified fluoroplastic layer 1 is 1mm, the thickness of PA layer 2 is 1mm, the thickness of adhesive resin layer 3 is 0.1mm, the thickness of PE layer 4 is 3mm, and adjust the relevant parameters of the extruder. Step 2: Prepare thermoplastic plastics for co-extrusion as needed. For fluoroplastics, use anhydride-modified ETFE; for PA layer 2, use PA11; for adhesive resin layer 3, use anhydride-modified linear low-density polyethylene polymer; and for PE layer 4, use low-density polyethylene. Step 3: Complete the multi-layer co-extrusion process, from the inside out: modified fluoroplastic layer 1, PA layer 2, adhesive resin layer 3, and PE layer 4.

[0032] Bonding effect evaluation: The peel strength of three samples obtained from the entire pipe was measured to characterize the bonding effect, according to GB / T 2791. The tested peel strength values ​​were 58 N / cm, 54 N / cm, and 56 N / cm, respectively, which are significantly higher than the peel strength requirements (15 N / cm) in relevant standards (GB / T 32439-2015 "Steel Wire Mesh Reinforced Polyethylene Composite Pipes for Water Supply" and SY / T 6662.1-2022 "Non-metallic Composite Pipes for Petroleum and Natural Gas Industry Part 1: Steel Reinforced Polyethylene Composite Pipes").

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A multi-layer co-extruded thermoplastic composite pipe, characterized in that, The multilayer co-extruded thermoplastic composite pipe includes a modified fluoroplastic layer (1), a PA layer (2), an adhesive resin layer (3), and a PE layer (4) connected in the radial direction from the inside to the outside. The multi-layer co-extruded thermoplastic composite pipe is manufactured using a multi-layer co-extrusion process. Modified fluoroplastics are anhydride-modified fluoroplastics containing anhydride groups R-CO-O-CO-R; The adhesive resin layer (3) is made of an anhydride-modified polyolefin resin; The anhydride groups of modified fluoroplastics react with the amide groups on the PA molecular chain to generate polymers containing imide bond structural units; the amine groups at the ends of the PA molecular chain react chemically with the active anhydride groups grafted onto the adhesive resin molecular chain to form closed-ring imide functional groups. Fluoroplastics are made of polyvinylidene fluoride or ethylene-tetrafluoroethylene copolymers. The material used for the PA layer (2) is PA6, PA11 or PA12; The polyolefin resin is made of ethylene-vinyl acetate copolymer or low-density polyethylene polymer.

2. The multilayer co-extruded thermoplastic composite pipe according to claim 1, characterized in that, The PE layer (4) is made of low-density polyethylene, medium-density polyethylene, high-density polyethylene or heat-resistant polyethylene.

3. The multilayer co-extruded thermoplastic composite pipe according to claim 1, characterized in that, The thickness of the modified fluoroplastic layer (1) is 1mm to 5mm.

4. The multilayer co-extruded thermoplastic composite pipe according to claim 1, characterized in that, The thickness of PA layer (2) is 1mm~5mm.

5. A multilayer co-extruded thermoplastic composite pipe according to claim 1, characterized in that, The thickness of the adhesive resin layer (3) is 0.1~0.6mm.

6. The multilayer co-extruded thermoplastic composite pipe according to claim 1, characterized in that, The thickness of the PE layer (4) is 3mm~8mm.

7. A method for preparing the multilayer co-extruded thermoplastic composite pipe according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Determine the extrusion wall thickness of each layer according to the process design, and adjust the extrusion parameters of each layer according to the wall thickness; Step 2: Prepare the materials for the modified fluoroplastic layer (1), PA layer (2), adhesive resin layer (3) and PE layer (4); Step 3: Complete the co-extrusion of the modified fluoroplastic layer (1), PA layer (2), adhesive resin layer (3) and PE layer (4) from the inside out.

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