Multi-layer co-extrusion thermoplastic plastic composite pipe and preparation method thereof

Abstract

The invention belongs to the technical field of non-metal pipe products, and relates to a multi-layer co-extrusion thermoplastic plastic composite pipe and a preparation method thereof, and the composite pipe comprises a modified fluoroplastic layer, a PA layer, a bonding resin layer and a PE layer from inside to outside in the radial direction in sequence; the modified fluoroplastic contains an anhydride group, a reaction functional group with a bonding effect, and a polymer containing an imide bond structure unit generated by reacting with an amide group on a molecular chain of PA, and the imide group has relatively high bond energy, has excellent high temperature resistance and chemical medium corrosion resistance, and meets the requirements of conveying media; bonding of PA and PE is achieved through bonding resin, the bonding resin is anhydride modified polyolefin resin, amino at the tail end of a PA molecular chain and an active anhydride group grafted on a bonding resin molecular chain are subjected to a chemical reaction to form a closed-loop imino functional group, and therefore bonding force between phase interfaces is obtained through covalent bonds; and the C-C bond on the bonding resin is organically combined with the C-C bond on the PE on the outer layer.

Description

Technical Field

[0001] The invention belongs to the technical field of non-metallic pipe products, and in particular relates to a multi-layer co-extruded thermoplastic composite pipe and a preparation method thereof. Background Art

[0002] At present, there are many types of multi-layer co-extruded composite pipe products. Most of the product types are high-performance thermoplastics in contact with the conveying medium, ordinary thermoplastics on the outside, and hot melt adhesives in the middle. The characteristics of this pipe are that the thickness of high-performance thermoplastics is about 2mm, which plays the role of isolating the medium and temperature, while the thickness of ordinary thermoplastics is about 5mm-10mm, which meets the requirements of pressure-bearing strength, and better achieves the purpose of reducing costs and increasing efficiency. For example, the current patent documents CN202756779U, CN 107166112B, CN108017818B, etc. describe related multi-layer co-extruded products. However, due to the problems that still exist in multi-layer co-extruded composite pipes, they have not been widely promoted and applied. There are mainly two problems: the bonding performance of high-performance fluoroplastics and ordinary polyethylene plastics is poor; the application range of multi-layer co-extruded composite pipes prepared based on low-performance plastics is limited, and cannot meet the transportation of high temperature (≥65℃) and highly corrosive media (including H2S and CO2, etc.). Details are as follows:

[0003] At present, the existing patent technology is to use adhesive resin to bond anhydride-modified fluoroplastics to PP. The modified ETFE molecular chain contains anhydride, which will react with the epoxy group in the hot melt adhesive molecular chain under high temperature conditions to generate esters (-COOR), thereby achieving bonding with polypropylene, as described in patent document CN 202756779U. As the service time increases, the esters generated by the reaction are prone to chain dissociation, resulting in a decrease in bonding performance and a huge risk of failure.

[0004] Therefore, how to improve the bonding performance between fluoroplastics and ordinary polypropylene has become a bottleneck in existing technology. Summary of the invention

[0005] The purpose of the present invention is to provide a multi-layer co-extruded thermoplastic composite pipe and a preparation method thereof, which solves the problem of poor bonding performance between current fluoroplastic pipes and ordinary polypropylene.

[0006] The present invention is achieved through the following technical solutions:

[0007] A multi-layer co-extruded thermoplastic composite pipe, the multi-layer co-extruded thermoplastic composite pipe comprising a modified fluoroplastic layer, a PA layer, an adhesive resin layer and a PE layer sequentially connected from inside to outside in radial direction;

[0008] The multi-layer co-extruded thermoplastic composite pipe is prepared by a multi-layer co-extrusion process;

[0009] Modified fluoroplastics use anhydride-modified fluoroplastics, containing anhydride groups R-CO-O-CO-R;

[0010] The adhesive resin layer uses an anhydride-modified polyolefin resin.

[0011] Furthermore, the material of the fluoroplastic is polyvinylidene fluoride or ethylene-tetrafluoroethylene copolymer.

[0012] Furthermore, the material used for the PA layer is PA6, PA11 or PA12.

[0013] Furthermore, the material used for the polyolefin resin is ethylene-vinyl acetate copolymer or low-density polyethylene polymer.

[0014] Furthermore, the material used for the PE layer is low-density polyethylene, medium-density polyethylene, high-density polyethylene or heat-resistant polyethylene.

[0015] Furthermore, the thickness of the modified fluoroplastic layer is 1 mm to 5 mm.

[0016] Furthermore, the thickness of the PA layer is 1 mm to 5 mm.

[0017] Furthermore, the thickness of the adhesive resin layer is 0.1 to 0.6 mm.

[0018] Furthermore, the thickness of the PE layer is 3 mm to 8 mm.

[0019] The present invention also discloses a method for preparing a multi-layer co-extruded thermoplastic composite pipe, comprising the following steps:

[0020] 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;

[0021] Step 2, preparing materials for the modified fluoroplastic layer, the PA layer, the adhesive resin layer and the PE layer;

[0022] Step 3: Complete the co-extrusion operation of the modified fluoroplastic layer, the PA layer, the adhesive resin layer and the PE layer in sequence from the inside to the outside.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects:

[0024] The invention discloses a composite pipe prepared by a multi-layer co-extrusion process. The composite pipe has a radial structure of 4 layers, which are a modified fluoroplastic layer, a PA layer, an adhesive resin layer and a PE layer from the inside to the outside. Molecular-level bonding is achieved between the layers, effectively ensuring the quality reliability of the composite pipe during long-term service. Among them, the modified fluoroplastic contains anhydride groups (R-CO-O-CO-R), which are reactive functional groups for bonding, and reacts with amide groups (CONH) on the molecular chain of PA to generate a polymer containing an amide bond (R-CO-NH-CO-R) structural unit. The amide group has a high bond energy and has excellent high temperature resistance and chemical medium corrosion resistance, meeting the requirements of the conveying medium. The bonding of PA and PE is achieved by an adhesive resin, which is an anhydride-modified polyolefin resin. The amine group at the end of the PA molecular chain reacts chemically with the active anhydride group grafted on the molecular chain of the adhesive resin to form a closed-loop amide functional group, thereby obtaining the bonding force between the phase interfaces through covalent bonds. The CC bond on the adhesive resin is organically combined with the CC bond on the outer layer of PE.

[0025] Fluoroplastic has excellent medium and temperature resistance, but its disadvantage is that it is relatively expensive, about 20 to 30 times that of ordinary polyethylene. The inner layer is fluoroplastic, the outer layer is ordinary polyethylene material, and the two are compounded by appropriate technology, which will achieve the dual goals of improving the pipe transportation performance and reducing costs. In addition, the outermost layer is PE layer, which is cheaper than PP material, which can reduce costs.

[0026] The invention discloses a method for preparing a composite pipe by a multi-layer co-extrusion process, which has a simple process and is easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic structural diagram of a multi-layer co-extruded thermoplastic composite pipe of the present invention.

[0028] Among them, 1. modified fluoroplastic layer; 2. PA layer; 3. adhesive resin layer; 4. PE layer. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the present invention more clear, the following is further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the embodiments described are only part of the embodiments of the present invention, not all embodiments.

[0030] The components described and shown in the drawings and embodiments of the present invention may be arranged and designed in various configurations. Therefore, the detailed description of the embodiments of the present invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely represents a selected embodiment of the present invention. Based on the drawings and embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0031] It should be noted that the terms "comprises", "includes" or any other variations are intended to cover non-exclusive inclusion, so that a process, element, method, article or equipment that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to the process, element, method, article or equipment.

[0032] The features and performances of the present invention are further described in detail below in conjunction with the embodiments.

[0033] The present invention discloses a method for preparing a multi-layer co-extruded thermoplastic composite pipe, comprising the following steps:

[0034] Step 1: Determine the extrusion wall thickness of each layer according to the process design and adjust the relevant parameters of the extruder;

[0035] Step 2: Prepare thermoplastic plastics for co-extrusion of each layer as required, mainly including modified fluoroplastics, and the available materials include polyvinylidene fluoride (PVDF) or ethylene-tetrafluoroethylene copolymer (ETFE), etc.; PA, the available materials include PA6, PA11 and PA12, etc.; adhesive resin, the available materials include anhydride-modified ethylene-vinyl acetate copolymer, anhydride-modified linear low-density polyethylene polymer, etc.; PE layer 3, the available materials include low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE) and heat-resistant polyethylene (PE-RT), etc.;

[0036] Step 3: Complete the multi-layer lining co-extrusion operation, from inside to outside, the modified fluoroplastic layer 1, the PA layer 2, the adhesive resin layer 3 and the PE layer 3.

[0037] Example 1

[0038] The present invention discloses a method for preparing a multi-layer co-extruded thermoplastic composite pipe in which PVDF is used as the innermost layer, comprising the following steps:

[0039] Step 1: According to the process design, determine the extrusion wall thickness of each layer, where the wall thickness of the modified fluoroplastic layer 1 is 2 mm, the thickness of the PA layer 2 is 2 mm, the thickness of the adhesive resin layer 3 is 0.5 mm, and the thickness of the PE layer 3 is 4 mm, and adjust the relevant parameters of the extruder;

[0040] Step 2: Prepare thermoplastic plastics for co-extrusion of each layer as required, select anhydride-modified polyvinylidene fluoride PVDF for fluoroplastics, select PA12 for PA layer 2, select anhydride-modified ethylene-vinyl acetate copolymer for adhesive resin layer 3, and select HDPE for PE layer 3;

[0041] Step 3: Complete the multi-layer co-extrusion operation, from inside to outside, the modified fluoroplastic layer 1, the PA layer 2, the adhesive resin layer 3 and the PE layer 3.

[0042] Evaluation of bonding effect: The peel strength of three samples obtained from the whole pipe was measured to characterize the bonding effect in accordance with the provisions of GB / T 2791. The peel strength values ​​tested were 67N / cm, 62N / cm and 68N / cm, respectively, which are much higher than the peel strength requirements (15N / cm) in the relevant standards (GB / T 32439-2015 "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 skeleton reinforced polyethylene composite pipes").

[0043] Example 2

[0044] The invention discloses a method for preparing a multi-layer co-extruded thermoplastic composite pipe in which ETFE is used as the innermost layer, comprising the following steps:

[0045] Step 1: According to the process design, determine the extrusion wall thickness of each layer, where the wall thickness of the modified fluoroplastic layer 1 is 1.5 mm, the thickness of the PA layer 2 is 2 mm, the thickness of the adhesive resin layer 3 is 0.5 mm, and the thickness of the PE layer 3 is 4 mm, and adjust the relevant parameters of the extruder;

[0046] Step 2: Prepare thermoplastic plastics for co-extrusion of each layer as required, select anhydride-modified ETFE for fluoroplastic, select PA6 for PA layer 2, select anhydride-modified linear low-density polyethylene polymer for adhesive resin layer 3, and select PE-RT for PE layer 3;

[0047] Step 3: Complete the multi-layer lining co-extrusion operation, from inside to outside, the modified fluoroplastic layer 1, the PA layer 2, the adhesive resin layer 3 and the PE layer 3.

[0048] Evaluation of bonding effect: The peel strength of three samples obtained from the whole pipe was measured to characterize the bonding effect in accordance with the provisions of GB / T 2791. The peel strength values ​​tested were 64N / cm, 66N / cm and 63N / cm, respectively, which are much higher than the peel strength requirements (15N / cm) in the relevant standards (GB / T 32439-2015 "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 skeleton reinforced polyethylene composite pipes").

[0049] Example 3

[0050] The invention discloses a method for preparing a multi-layer co-extruded thermoplastic composite pipe in which ETFE is used as the innermost layer, comprising the following steps:

[0051] Step 1: According to the process design, determine the extrusion wall thickness of each layer, where the wall thickness of the modified fluoroplastic layer 1 is 5 mm, the thickness of the PA layer 2 is 5 mm, the thickness of the adhesive resin layer 3 is 0.6 mm, and the thickness of the PE layer 3 is 8 mm, and adjust the relevant parameters of the extruder;

[0052] Step 2: Prepare thermoplastic plastics for co-extrusion of each layer as required, select anhydride-modified ETFE for fluoroplastic, select PA11 for PA layer 2, select anhydride-modified linear low-density polyethylene polymer for adhesive resin layer 3, and select heat-resistant polyethylene for PE layer 3;

[0053] Step 3: Complete the multi-layer lining co-extrusion operation, from inside to outside, the modified fluoroplastic layer 1, the PA layer 2, the adhesive resin layer 3 and the PE layer 3.

[0054] Evaluation of bonding effect: The peel strength of three samples obtained from the whole pipe was measured to characterize the bonding effect in accordance with the provisions of GB / T 2791. The peel strength values ​​tested were 69N / cm, 68N / cm and 71N / cm, respectively, which are much higher than the peel strength requirements (15N / cm) in the relevant standards (GB / T 32439-2015 "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 skeleton reinforced polyethylene composite pipes").

[0055] Example 4

[0056] The invention discloses a method for preparing a multi-layer co-extruded thermoplastic composite pipe in which ETFE is used as the innermost layer, comprising the following steps:

[0057] Step 1: According to the process design, determine the extrusion wall thickness of each layer, where the wall thickness of the modified fluoroplastic layer 1 is 1 mm, the thickness of the PA layer 2 is 1 mm, the thickness of the adhesive resin layer 3 is 0.1 mm, and the thickness of the PE layer 3 is 3 mm, and adjust the relevant parameters of the extruder;

[0058] Step 2: Prepare thermoplastic plastics for co-extrusion of each layer as required, select anhydride-modified ETFE for fluoroplastic, select PA11 for PA layer 2, select anhydride-modified linear low-density polyethylene polymer for adhesive resin layer 3, and select low-density polyethylene for PE layer 3;

[0059] Step 3: Complete the multi-layer lining co-extrusion operation, from inside to outside, the modified fluoroplastic layer 1, the PA layer 2, the adhesive resin layer 3 and the PE layer 3.

[0060] Evaluation of bonding effect: The peel strength of three samples obtained from the whole pipe was measured to characterize the bonding effect in accordance with the provisions of GB / T 2791. The peel strength values ​​tested were 58N / cm, 54N / cm and 56N / cm, respectively, which are much higher than the peel strength requirements (15N / cm) in the relevant standards (GB / T 32439-2015 "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 skeleton reinforced polyethylene composite pipes").

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does 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 multi-layer co-extruded thermoplastic composite pipe comprises a modified fluoroplastic layer (1), a PA layer (2), an adhesive resin layer (3) and a PE layer (4) which are sequentially connected from the inside to the outside in the radial direction; The multi-layer co-extruded thermoplastic composite pipe is prepared by a multi-layer co-extrusion process; Modified fluoroplastics use anhydride-modified fluoroplastics, containing anhydride groups R-CO-O-CO-R; The adhesive resin layer (3) is made of anhydride-modified polyolefin resin.

2. A multi-layer co-extruded thermoplastic composite pipe according to claim 1, characterized in that: The material of fluoroplastic is polyvinylidene fluoride or ethylene-tetrafluoroethylene copolymer.

3. The multi-layer co-extruded thermoplastic composite pipe according to claim 1, characterized in that: The material used for the PA layer (2) is PA6, PA11 or PA12.

4. The multi-layer co-extruded thermoplastic composite pipe according to claim 1, characterized in that: The material used for the polyolefin resin is ethylene-vinyl acetate copolymer or low-density polyethylene polymer.

5. The multi-layer co-extruded thermoplastic composite pipe according to claim 1, characterized in that: The material used for the PE layer (4) is low-density polyethylene, medium-density polyethylene, high-density polyethylene or heat-resistant polyethylene.

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

7. The multi-layer co-extruded thermoplastic composite pipe according to claim 1, characterized in that: The thickness of the PA layer (2) is 1 mm to 5 mm.

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

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

10. The method for preparing a multi-layer co-extruded thermoplastic composite pipe according to any one of claims 1 to 9, characterized in that: The following steps are involved: 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: preparing materials for the modified fluoroplastic layer (1), the PA layer (2), the adhesive resin layer (3) and the PE layer (4); Step 3: Complete the co-extrusion operation of the modified fluoroplastic layer (1), the PA layer (2), the adhesive resin layer (3) and the PE layer (4) in sequence from the inside to the outside.

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