Preparation process of integrated temperature-locked PPR pipe

Abstract

The application relates to a preparation process of an integrated temperature-locking PPR pipe with high production efficiency, and the prepared integrated temperature-locking PPR pipe has high structural strength and good heat preservation effect. 1) outer layer raw materials, middle layer raw materials and inner layer raw materials are respectively configured; 2) the prepared outer layer raw materials, middle layer raw materials and inner layer raw materials in step 1) are respectively put into high-speed mixers to prepare outer layer master batches, middle layer master batches and inner layer master batches; 3) the prepared outer layer master batches, middle layer master batches and inner layer master batches in step 2) are respectively added into corresponding hoppers of a three-layer co-extrusion machine, and after being heated, melted and plasticized, the outer layer master batches, the middle layer master batches and the inner layer master batches are co-extruded through a mold, vacuum sizing, spraying cooling and traction cutting are carried out, and the integrated temperature-locking PPR pipe is prepared.

Description

Technical Field

[0001] This invention relates to a manufacturing process for an integrated thermal lock-in PPR tube. Background Technology

[0002] Pipes are components of pipeline systems used to transport fluids, gases, or solids. They are commonly found in construction, industry, agriculture, mining, and other fields. These pipes can be classified into various types based on their application, materials, and manufacturing processes. Common pipe types include metal pipes (steel, copper, aluminum, galvanized), plastic pipes (PVC, PE, PPR, PP, composite pipes, glass, ceramic, and carbon fiber composite pipes). These pipes have different characteristics and applications, and selecting the appropriate pipe requires consideration of project requirements, environmental conditions, and the transported medium. Currently, PPR pipes are widely used in water supply systems. PPR pipes, also known as type 3 polypropylene pipes or random copolymer polypropylene, are made from random copolymer polypropylene, which can be extruded into pipes or injection molded into fittings. Ethylene is the most commonly used monomer, causing changes in the physical properties of polypropylene. Compared to PP homopolymer, random copolymers improve optical properties, enhance impact resistance, increase flexibility, and lower melting temperature, thus reducing the heat fusion temperature. Meanwhile, they maintain essentially the same chemical stability, water vapor barrier properties, and organ-sensory properties as homopolymers. With social development and technological advancements, people are increasingly pursuing higher quality of life, leading to greater functional requirements for plastic pipes used in households. Consequently, manufacturers are adopting composite-structured plastic pipes.

[0003] For example, Chinese patent application CN201320581585.1 discloses a heat-insulating polyethylene pipe, comprising an outer adhesive layer, a fiberglass layer, a fire-resistant insulation layer, and a polyethylene layer. The fiberglass layer is bonded to the inner side of the outer adhesive layer, and the outer adhesive layer and the fiberglass layer are cross-linked and bonded together by an adhesive. The fiberglass can greatly increase the ductility and tensile strength of the polyethylene pipe, thereby increasing its service life. The fire-resistant insulation layer is disposed between the fiberglass layer and the polyethylene layer, and the inner and outer sides of the fire-resistant insulation layer are bonded tightly to the fiberglass layer and the polyethylene layer by an adhesive. The fire-resistant insulation layer has excellent heat insulation effect. However, the method of bonding the fire-resistant insulation layer to the fiberglass layer and the polyethylene layer with an adhesive requires that the outer adhesive layer, fiberglass layer, and polyethylene layer be formed separately during the production process, and then the fire-resistant insulation layer is bonded together with adhesive. This makes the structure of the layered pipe unstable, prone to delamination under large external forces, and results in low pipe production efficiency and poor insulation effect. Summary of the Invention

[0004] Therefore, in view of the above problems, the present invention provides a manufacturing process for an integrated thermally insulating PPR tube with high production efficiency, and the resulting integrated thermally insulating PPR tube has high structural strength and good insulation effect.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A manufacturing process for an integrated thermal lock-in PPR tube includes the following steps: 1) Prepare outer layer raw materials, middle layer raw materials, and inner layer raw materials separately. The outer layer raw materials, by weight, include: 100 parts polyethylene, 5-10 parts UV-resistant masterbatch, and 0.2-0.5 parts antioxidant; the middle layer raw materials, by weight, include: 100 parts polypropylene resin, 15-25 parts thermal insulation cotton granules, 3-8 parts compatibilizer, 0.5-2 parts chemical foaming agent, and 0.1-0.5 parts nucleating agent; the inner layer raw materials, by weight, include: 100 parts PPR resin, 2-5 parts antibacterial agent, and 3-6 parts cold-resistant modifier. 2) The outer layer raw material, middle layer raw material and inner layer raw material prepared in step 1) are put into a high-speed mixer and mixed evenly. Then, they are put into a twin-screw extruder for melt mixing, extrusion, cooling and pelletizing to obtain outer layer masterbatch, middle layer masterbatch and inner layer masterbatch respectively. 3) The outer layer masterbatch, middle layer masterbatch, and inner layer masterbatch obtained in step 2) are respectively added to the corresponding hoppers of a three-layer co-extrusion extruder. After heating, melting, and plasticizing, they are co-extruded through a die. After vacuum sizing, spray cooling, and traction cutting, an integrated heat-locking PPR pipe is obtained. The die is a three-layer co-extrusion die, consisting of an outer layer melt, a middle layer melt, and an inner layer melt. The outer layer melt, middle layer melt, and inner layer melt are combined in the die and then extruded. The extrusion temperature is controlled at 190℃-230℃. The integrated heat-locking PPR pipe includes a pipe body, which includes an outer layer, a middle insulation layer, and an inner layer, which are integrally structured from the outside to the inside. The thickness of the outer layer accounts for 10%-20% of the total thickness of the pipe body, the thickness of the middle insulation layer accounts for 40%-60% of the total thickness of the pipe body, the middle insulation layer has irregular pores, and the thickness of the inner layer accounts for 30%-40% of the total thickness of the pipe body.

[0006] Furthermore, in step 1), the method for preparing the thermal insulation cotton granules is as follows: after surface modification treatment, fibrous thermal insulation cotton is mixed with polypropylene resin and extruded and granulated by a twin-screw extruder; the length of the thermal insulation cotton granules is 0.5-2mm and the diameter is 1-3mm.

[0007] Furthermore, the surface modification process of the fibrous thermal insulation cotton includes the following steps: 11) Cut the fibrous insulation cotton to a length of 5-10mm, and then dry it at 100-120℃ for 2-4 hours until its moisture content is below 0.5%; 12) Mix the silane coupling agent with anhydrous ethanol at a weight ratio of 1:10-1:20 and stir for 30 minutes to form a homogeneous treatment solution; 13) Put the pretreated insulation cotton from step 11) into a high-speed mixer. At a speed of 800-1200 rpm and a temperature of 80-100℃, spray the treatment solution prepared in step 12) evenly onto the surface of the insulation cotton and continue stirring and reacting for 30-60 minutes. 14) Dry the thermal insulation cotton that has undergone the reaction in step 13) at 100-110℃ for 1-2 hours to remove residual solvent and obtain surface-modified thermal insulation cotton.

[0008] Furthermore, in step 1), the UV-resistant masterbatch in the outer layer raw material is either carbon black masterbatch or UV absorber masterbatch.

[0009] Furthermore, in step 1), the antioxidant is a compound of hindered phenolic antioxidants and phosphite antioxidants.

[0010] Furthermore, in step 1), the antibacterial agent in the inner layer material is a nano silver ion antibacterial agent or a zinc oxide antibacterial agent.

[0011] Furthermore, in step 1), the cold-resistant modifier is a polyolefin elastomer or an ethylene-vinyl acetate copolymer.

[0012] Furthermore, the intermediate insulation layer forms a structure with irregular pores after extrusion molding. The specific control of extrusion temperature in its preparation process is as follows: In step 3), the temperature of the intermediate barrel of the three-layer co-extrusion extruder is controlled by gradient cooling. The temperature near the feeding section is 200℃-210℃, and the temperature near the die section is reduced to 175℃-185℃. The temperature difference is used to control the matching of the decomposition rate of the chemical foaming agent with the melt viscosity, so that an irregular microporous structure with a pore size of 50-200μm is formed inside the intermediate insulation layer.

[0013] Furthermore, the chemical foaming agent is one or more of azodicarbonamide, barium azodicarbonate, or 4,4'-oxobisbenzenesulfonyl hydrazine.

[0014] Furthermore, the nucleating agent is one or more of talc, nano-calcium carbonate, or citric acid.

[0015] By adopting the aforementioned technical solution, the beneficial effects of this invention are as follows: The manufacturing process of this integrated heat-locking PPR pipe involves using a three-layer co-extrusion mold to fuse the outer layer, intermediate insulation layer, and inner layer in a molten state before integral extrusion molding, directly forming a tightly composite pipe body from the outside to the inside. This eliminates the need for subsequent adhesive bonding processes, significantly improving production efficiency. Simultaneously, the outer layer, intermediate insulation layer, and inner layer form a molecularly fused integrated structure, eliminating the need for traditional adhesive interfaces and effectively avoiding the risk of interlayer separation under external forces, thus greatly enhancing the structural strength of the pipe. The intermediate insulation layer accounts for 40%-% of the total thickness of the pipe body. With 60% irregular pores, and a specific thickness ratio of 10%-20% for the outer layer and 30%-40% for the inner layer, sufficient insulation space and heat insulation effect are ensured while maintaining the overall mechanical properties of the pipe. The outer layer uses polyethylene base material and is compounded with anti-ultraviolet masterbatch and antioxidants, which makes the pipe excellent in terms of weather resistance and anti-aging ability. The inner layer uses PPR resin as the matrix and adds antibacterial agents and cold-resistant modifiers to ensure the safety of drinking water contact and low-temperature impact resistance, thus achieving integrated heat lock while providing synergistic improvement in antibacterial, anti-aging and cold resistance. Attached Figure Description

[0016] Figure 1 This is a cross-sectional structural diagram of the pipe body in an embodiment of the present invention. Detailed Implementation

[0017] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments.

[0018] The embodiments of the present invention are as follows: Example 1

[0019] refer to Figure 1 As shown, the manufacturing process of an integrated thermal lock-in PPR tube includes the following steps: 1) Prepare outer layer raw materials, middle layer raw materials and inner layer raw materials respectively. The outer layer raw materials include, by weight, 100 parts of polyethylene, 5 parts of UV-resistant masterbatch, and 0.2 parts of antioxidant. The middle layer raw materials include, by weight, 100 parts of polypropylene resin, 15 parts of thermal insulation cotton granules, 3 parts of compatibilizer, 0.5 parts of chemical foaming agent, and 0.1 parts of nucleating agent. The compatibilizer is maleic anhydride-grafted polypropylene. The inner layer raw materials include, by weight, 100 parts of PPR resin, 2 parts of antibacterial agent, and 3 parts of cold-resistant modifier. 2) The outer layer raw material, middle layer raw material and inner layer raw material prepared in step 1) are put into a high-speed mixer and mixed evenly. Then, they are put into a twin-screw extruder for melt mixing, extrusion, cooling and pelletizing to obtain outer layer masterbatch, middle layer masterbatch and inner layer masterbatch respectively. 3) The outer layer masterbatch, middle layer masterbatch, and inner layer masterbatch obtained in step 2) are respectively added to the corresponding hoppers of a three-layer co-extrusion extruder. After heating, melting, and plasticizing, they are co-extruded through a die. After vacuum sizing, spray cooling, and traction cutting, an integral heat-locking PPR pipe is obtained. The die is a three-layer co-extrusion die, consisting of an outer layer melt, a middle layer melt, and an inner layer melt. The outer layer melt, middle layer melt, and inner layer melt are combined in the die and then extruded. The extrusion temperature is controlled. The temperature range is 190℃-230℃. The integrated heat-locking PPR pipe includes a pipe body 1, which consists of an outer layer 11, a middle insulation layer 12, and an inner layer 13, arranged in an integral structure from the outside to the inside. The outer layer 11 has a thickness of 10% of the total thickness of the pipe body 1, the middle insulation layer 13 has a thickness of 50% of the total thickness of the pipe body 1, the middle insulation layer 12 has irregular pores 2, and the inner layer 13 has a thickness of 40% of the total thickness of the pipe body 1.

[0020] The manufacturing process of this integrated thermal insulation PPR pipe involves using a three-layer co-extrusion mold to fuse the outer layer 11, the intermediate insulation layer 12, and the inner layer 13 in a molten state before integral extrusion molding. This directly forms a tightly composite pipe body 1 from the outside in, eliminating the need for subsequent adhesive bonding processes and significantly improving production efficiency. Furthermore, the outer layer 11, the intermediate insulation layer 12, and the inner layer 13 form a molecular-level fused integral structure, eliminating the need for traditional adhesive interfaces. This effectively avoids the risk of interlayer separation under external forces, greatly enhancing the structural strength of the pipe. The intermediate insulation layer 13 accounts for 40%-60% of the total thickness of the pipe body 1 and possesses… The irregular pores, combined with the specific thickness ratio of the outer layer 11 (10%-20% of the total thickness of the pipe body 1) and the inner layer 13 (30%-40% of the total thickness of the pipe body 1), ensure sufficient insulation space and heat insulation effect while maintaining the overall mechanical properties of the pipe. The outer layer uses polyethylene base material and is compounded with anti-ultraviolet masterbatch and antioxidants, which makes the pipe excellent in terms of weather resistance and anti-aging ability. The inner layer uses PPR resin as the matrix and adds antibacterial agents and cold-resistant modifiers to ensure the safety of drinking water contact and low-temperature impact resistance, thus achieving integrated heat lock while providing synergistic improvement in antibacterial, anti-aging and cold resistance.

[0021] Furthermore, in step 1), the preparation method of the thermal insulation cotton granules is as follows: after surface modification treatment, fibrous thermal insulation cotton is mixed with polypropylene resin and extruded and granulated by a twin-screw extruder; the length of the thermal insulation cotton granules is 0.5-2mm and the diameter is 1-3mm, so that the thermal insulation cotton is evenly dispersed in the intermediate layer masterbatch and the size is appropriate, which avoids the extrusion blockage or melt rupture caused by excessively large particles, and also prevents the thermal insulation performance from decreasing due to excessively small particles; the granules can be well compatible with the polypropylene melt in the subsequent co-extrusion process, which is conducive to the formation of stable and evenly distributed irregular pores in the intermediate layer during the foaming process, thereby enhancing the thermal insulation uniformity and structural consistency of the thermal insulation layer.

[0022] Furthermore, the surface modification process of the fibrous thermal insulation cotton includes the following steps: 11) Cut the fibrous thermal insulation cotton to a length of 5mm, and then dry it at 100℃ for 4 hours until its moisture content is below 0.5%; 12) Mix the silane coupling agent with anhydrous ethanol at a weight ratio of 1:10 and stir for 30 minutes to form a uniform treatment solution. The silane coupling agent is γ-aminopropyltriethoxysilane. 13) Put the pretreated insulation cotton from step 11) into a high-speed mixer. At a speed of 800 rpm and a temperature of 80°C, spray the treatment solution prepared in step 12) evenly onto the surface of the insulation cotton and continue stirring and reacting for 30-60 minutes. 14) Dry the thermal insulation cotton that has undergone the reaction in step 13) at 100°C for 2 hours to remove residual solvent and obtain surface-modified thermal insulation cotton.

[0023] Through a series of surface modification processes including shearing, drying, silane coupling agent treatment, and secondary drying, the surface of the fibrous insulation cotton is transformed from hydrophilic to oleophilic to hydrophobic, significantly improving its interfacial bonding with polypropylene resin. Optimization of the treatment solution ratio (1:10-1:20) and spray reaction conditions (800-1200 rpm, 80-100℃, and 30-60 minutes of stirring time) ensures uniform coating of the insulation cotton fibers with the coupling agent, preventing agglomeration. This allows the insulation cotton to be effectively embedded in polypropylene during extrusion granulation, improving the processing flowability of the intermediate masterbatch and the structural uniformity of the final insulation layer. Drying to a moisture content below 0.5% prevents moisture vaporization during high-temperature extrusion, which could lead to uneven melt bubbles or surface defects.

[0024] In this embodiment, in step 1), the UV-resistant masterbatch in the outer layer raw material is either carbon black masterbatch or UV absorber masterbatch, preferably carbon black masterbatch. Carbon black masterbatch can effectively shield ultraviolet rays and also has a light-shielding effect, delaying the photo-oxidative aging of the outer polyethylene layer. UV absorber masterbatch can convert harmful ultraviolet light energy into heat energy and release it, protecting the inner PPR layer from ultraviolet radiation damage. The two options can be flexibly combined according to the pipe's usage environment, expanding the product's applicable scenarios, while ensuring the color stability and mechanical retention rate of the outer layer under long-term use.

[0025] Furthermore, in step 1), the antioxidant is a compound of hindered phenolic antioxidants and phosphite antioxidants. The preferred hindered phenolic antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the preferred phosphite antioxidant is tris[2,4-di-tert-butylphenyl]phosphite. Hindered phenols can capture free radicals to terminate the oxidation chain reaction, and phosphites can decompose hydrogen peroxide. The synergistic effect of the two produces an antioxidant effect, which is more effective than a single antioxidant in inhibiting the thermo-oxidative degradation of the outer polyethylene layer during processing and long-term use, significantly extending the service life of the pipe, and maintaining good mechanical properties, especially under high-temperature transport media conditions.

[0026] Furthermore, in step 1), the antibacterial agent in the inner layer material is either a nano-silver ion antibacterial agent or a zinc oxide antibacterial agent, preferably a nano-silver ion antibacterial agent. Nano-silver ions have broad-spectrum and long-lasting bactericidal properties and have a significant inhibitory effect on common waterborne bacteria, such as Escherichia coli and Staphylococcus aureus. Zinc oxide antibacterial agent has both safety and heat resistance, making it suitable for the high-temperature use environment of PPR pipes. Both can be well dispersed with PPR resin, enabling the inner layer surface to maintain antibacterial function, effectively preventing the growth of biofilm on the inner wall of the pipe, ensuring the safety of drinking water, and meeting the health requirements of high-quality domestic water.

[0027] Furthermore, in step 1), the cold-resistant modifier is a polyolefin elastomer or an ethylene-vinyl acetate copolymer, whose flexible molecular chains can be embedded in the PPR matrix to toughen and resist impact at low temperatures, significantly reducing the embrittlement temperature of the pipe and preventing inner layer cracking or freezing cracking in low-temperature winter environments. At the same time, this type of modifier has good compatibility with PPR and does not affect the chemical stability and hygienic properties of the inner layer, so that the pipe still has reliable applicability in cold regions or winter construction conditions.

[0028] In this embodiment, the intermediate insulation layer forms a structure with irregular pores after extrusion molding. The specific control of extrusion temperature in its preparation process is as follows: In step 3), the temperature of the intermediate barrel of the three-layer co-extrusion extruder is controlled by gradient cooling. The temperature near the feeding section is 200℃-210℃, and the temperature near the die section is reduced to 175℃-185℃. The temperature difference is used to control the matching between the decomposition rate of the chemical foaming agent and the melt viscosity, so that an irregular microporous structure with a pore size of 50-200μm is formed inside the intermediate insulation layer.

[0029] Gradient cooling control is adopted during the intermediate layer extrusion process, namely 200℃-210℃ in the feeding section and 175℃-185℃ in the die section. The temperature difference is used to precisely adjust the matching relationship between the decomposition rate of the chemical foaming agent and the viscosity of the polypropylene melt. This allows the foaming agent to fully decompose and generate gas in the high-temperature section, and "freeze" the gas in the matrix when the melt viscosity increases in the low-temperature section. This results in the formation of an irregular microporous structure with a pore size of 50-200μm inside the intermediate insulation layer. This microporous size range optimizes the insulation performance, and the irregular pores are more conducive to scattering heat radiation than regular spherical pores, further improving the insulation efficiency. At the same time, it avoids large bubbles or pore defects caused by uncontrolled foaming.

[0030] Furthermore, the chemical foaming agent is one or a mixture of azodicarbonamide, barium azodicarbonate, or 4,4'-oxobisbenzenesulfonyl hydrazine, preferably azodicarbonamide. These foaming agents have a suitable decomposition temperature window within the PPR processing temperature range. The nitrogen, carbon dioxide, and other gases produced during decomposition are non-toxic and do not corrode equipment, and the decomposition residue has little impact on the performance of polypropylene. When multiple compoundings are used, the decomposition temperature range can be adjusted to adapt to different extrusion temperature gradients, making the foaming process more stable and controllable, and ensuring the uniformity and reproducibility of the microporous structure of the intermediate layer.

[0031] Furthermore, the nucleating agent is one or more of talc, nano-calcium carbonate, or citric acid, preferably talc. It can provide a large number of heterogeneous nucleation sites in the intermediate layer melt, promoting the formation of microbubble nuclei at these sites by the gas decomposed from the chemical foaming agent, thereby obtaining more, finer, and more distributed microporous structures. Nano-calcium carbonate and talc can also play a certain role in reinforcement and dimensional stability, while citric acid is both environmentally friendly and easy to dispersible. The addition of the nucleating agent effectively avoids excessive growth or merging of bubbles, so that the final micropore size is concentrated in the target range of 50-200μm, improving the closed-cell rate and thermal insulation stability of the insulation layer, while reducing the amount of material used, reducing the linear density of the pipe, and facilitating transportation and installation.

[0032] In this embodiment, the structure of the die of the three-layer co-extrusion extruder is disclosed in the patent application No. 202111651353.4 filed by the applicant on December 30, 2021, entitled "A Three-Layer High-Strength Antibacterial Tube Extrusion Die", which will not be elaborated further here. Example 2

[0033] The difference between this embodiment and Embodiment 1 lies in the adjustment of the distribution ratio of each group and the process parameters: Outer layer raw materials: 100 parts polyethylene, 8 parts UV absorber masterbatch (UV absorber masterbatch is selected), 0.3 parts antioxidant (hindered phenolic antioxidant and phosphite antioxidant are compounded in a 2:1 ratio).

[0034] Intermediate layer raw materials: 100 parts polypropylene resin, 20 parts thermal insulation cotton granules, 5 parts compatibilizer, 1.0 part chemical foaming agent (4,4'-oxobisbenzenesulfonyl hydrazine), and 0.3 parts nucleating agent (nano calcium carbonate).

[0035] Inner layer raw materials: 100 parts PPR resin, 3 parts antibacterial agent (zinc oxide antibacterial agent is selected), and 4 parts cold-resistant modifier (ethylene-vinyl acetate copolymer, EVA is selected).

[0036] In the preparation of thermal insulation cotton granules, fibrous thermal insulation cotton is cut to a length of 8 mm and dried at 110℃ for 3 hours; silane coupling agent and anhydrous ethanol are mixed at a weight ratio of 1:15, and the treatment reaction is carried out at 900 rpm and 90℃ for 45 minutes, and the drying temperature is 105℃ for 1.5 hours.

[0037] In three-layer co-extrusion molding, the outer layer accounts for 15% of the total thickness of the pipe body, the middle insulation layer accounts for 55%, and the inner layer accounts for 30%. The barrel temperature of the middle layer is 205℃ in the feeding section and 180℃ in the die section. Example 3

[0038] The difference between this embodiment and Embodiment 1 lies in the adjustment of the distribution ratio of each group and the process parameters: Outer layer raw materials: 100 parts polyethylene, 10 parts UV-resistant masterbatch (carbon black masterbatch and UV absorber masterbatch mixed at a ratio of 1:1), and 0.5 parts antioxidant (hindered phenolic antioxidant and phosphite antioxidant compounded at a ratio of 1:2).

[0039] Intermediate layer raw materials: 100 parts polypropylene resin, 25 parts thermal insulation cotton granules, 8 parts compatibilizer, 2.0 parts chemical foaming agent (azodicarbonamide and barium azodicarbonate mixed in a 1:1 ratio), and 0.5 parts nucleating agent (citric acid).

[0040] Inner layer raw materials: 100 parts PPR resin, 5 parts antibacterial agent (nano silver ion antibacterial agent and zinc oxide antibacterial agent mixed in a 1:1 ratio), 6 parts cold-resistant modifier (polyolefin elastomer and ethylene-vinyl acetate copolymer mixed in a 1:1 ratio).

[0041] In the preparation of thermal insulation cotton granules, fibrous thermal insulation cotton is cut to a length of 10 mm and dried at 120℃ for 2 hours; silane coupling agent and anhydrous ethanol are mixed at a weight ratio of 1:20, and the treatment reaction is carried out at 1200 rpm and 100℃ for 30 minutes, and the drying temperature is 110℃ for 1 hour.

[0042] In three-layer co-extrusion molding, the outer layer accounts for 20% of the total thickness of the pipe body, the middle insulation layer accounts for 45%, and the inner layer accounts for 35%. The barrel temperature of the middle layer is 200℃ in the feeding section and 175℃ in the die section.

[0043] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0044] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0045] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0046] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.

Claims

1. A manufacturing process for an integrated thermally locked PPR tube, characterized in that: Includes the following steps: 1) Prepare outer layer raw materials, middle layer raw materials, and inner layer raw materials separately. The outer layer raw materials, by weight, include: 100 parts polyethylene, 5-10 parts UV-resistant masterbatch, and 0.2-0.5 parts antioxidant; the middle layer raw materials, by weight, include: 100 parts polypropylene resin, 15-25 parts thermal insulation cotton granules, 3-8 parts compatibilizer, 0.5-2 parts chemical foaming agent, and 0.1-0.5 parts nucleating agent; the inner layer raw materials, by weight, include: 100 parts PPR resin, 2-5 parts antibacterial agent, and 3-6 parts cold-resistant modifier. 2) The outer layer raw material, middle layer raw material and inner layer raw material prepared in step 1) are put into a high-speed mixer and mixed evenly. Then, they are put into a twin-screw extruder for melt mixing, extrusion, cooling and pelletizing to obtain outer layer masterbatch, middle layer masterbatch and inner layer masterbatch respectively. 3) The outer layer masterbatch, middle layer masterbatch, and inner layer masterbatch obtained in step 2) are respectively added to the corresponding hoppers of a three-layer co-extrusion extruder. After heating, melting, and plasticizing, they are co-extruded through a die. After vacuum sizing, spray cooling, and traction cutting, an integrated heat-locking PPR pipe is obtained. The die is a three-layer co-extrusion die, consisting of an outer layer melt, a middle layer melt, and an inner layer melt. The outer layer melt, middle layer melt, and inner layer melt are combined in the die and then extruded. The extrusion temperature is controlled at 190℃-230℃. The integrated heat-locking PPR pipe includes a pipe body, which includes an outer layer, a middle insulation layer, and an inner layer, which are integrally structured from the outside to the inside. The thickness of the outer layer accounts for 10%-20% of the total thickness of the pipe body, the thickness of the middle insulation layer accounts for 40%-60% of the total thickness of the pipe body, the middle insulation layer has irregular pores, and the thickness of the inner layer accounts for 30%-40% of the total thickness of the pipe body.

2. The manufacturing process of the integrated temperature-locking PPR tube according to claim 1, characterized in that: In step 1), the method for preparing the thermal insulation cotton granules is as follows: after surface modification treatment, fibrous thermal insulation cotton is mixed with polypropylene resin and extruded and granulated by a twin-screw extruder; the length of the thermal insulation cotton granules is 0.5-2mm and the diameter is 1-3mm.

3. The manufacturing process of the integrated temperature-locking PPR tube according to claim 2, characterized in that: The surface modification process of the fibrous thermal insulation cotton includes the following steps: 11) Cut the fibrous insulation cotton to a length of 5-10mm, and then dry it at 100-120℃ for 2-4 hours until its moisture content is below 0.5%; 12) Mix the silane coupling agent with anhydrous ethanol at a weight ratio of 1:10-1:20 and stir for 30 minutes to form a homogeneous treatment solution; 13) Put the pretreated insulation cotton from step 11) into a high-speed mixer. At a speed of 800-1200 rpm and a temperature of 80-100℃, spray the treatment solution prepared in step 12) evenly onto the surface of the insulation cotton and continue stirring and reacting for 30-60 minutes. 14) Dry the thermal insulation cotton that has undergone the reaction in step 13) at 100-110℃ for 1-2 hours to remove residual solvent and obtain surface-modified thermal insulation cotton.

4. The manufacturing process of the integrated thermally locked PPR tube according to claim 1, characterized in that: In step 1), the UV-resistant masterbatch in the outer layer raw material is either carbon black masterbatch or UV absorber masterbatch.

5. The manufacturing process of the integrated thermally locked PPR tube according to claim 1, characterized in that: In step 1), the antioxidant is a compound of hindered phenolic antioxidants and phosphite antioxidants.

6. The manufacturing process of the integrated thermally locked PPR tube according to claim 1, characterized in that: In step 1), the antibacterial agent in the inner layer material is a nano silver ion antibacterial agent or a zinc oxide antibacterial agent.

7. The manufacturing process of the integrated temperature-locking PPR tube according to claim 1, characterized in that: In step 1), the cold-resistant modifier is a polyolefin elastomer or an ethylene-vinyl acetate copolymer.

8. The manufacturing process of the integrated thermally locked PPR tube according to any one of claims 1 to 7, characterized in that: The intermediate insulation layer forms a structure with irregular pores after extrusion molding. The specific control of extrusion temperature in its preparation process is as follows: In step 3), the temperature of the intermediate barrel of the three-layer co-extrusion extruder is controlled by gradient cooling. The temperature near the feeding section is 200℃-210℃, and the temperature near the die section is reduced to 175℃-185℃. The temperature difference is used to control the matching between the decomposition rate of the chemical foaming agent and the melt viscosity, so that an irregular microporous structure with a pore size of 50-200μm is formed inside the intermediate insulation layer.

9. The manufacturing process of the integrated thermally locked PPR tube according to claim 8, characterized in that: The chemical foaming agent is one or a mixture of azodicarbonamide, barium azodicarbonate, or 4,4'-oxobisbenzenesulfonyl hydrazine.

10. The manufacturing process of the integrated temperature-locking PPR tube according to claim 9, characterized in that: The nucleating agent is one or more of talc, nano-calcium carbonate, or citric acid.

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