Uvioresistant photovoltaic pvc pipe and its preparation method

Abstract

The application discloses a preparation method of an ultraviolet-resistant photovoltaic PVC pipe and relates to the field of plastic part preparation. The preparation method specifically comprises the following steps: preparing dry mixed materials a, b, c and d according to dry mixed material bases; the dry mixed material a comprises a conductive agent, the dry mixed material c comprises a reactive compatibilizer, and the dry mixed material d comprises an ultraviolet shielding agent; the dry mixed materials a and b are respectively melted and then co-extruded to obtain a base pipe a with a double-layer structure; then, hot melt adhesive is coated on the surface of the base pipe a to obtain a base pipe b; melt c and melt d comprising mixed liquids are respectively obtained according to the dry mixed materials c and d; then, the melt c and the melt d are sequentially coated on the surface of the base pipe b in a co-extrusion mode to obtain a composite pipe blank a; and the composite pipe blank a is sequentially subjected to high-temperature treatment, cooling and setting and post-treatment to obtain the ultraviolet-resistant photovoltaic PVC pipe. The application solves the problems of insufficient interlayer bonding force and mismatched thermal expansion coefficients.

Description

Technical Field

[0001] This invention relates to the field of plastic parts manufacturing, and more particularly to a UV-resistant photovoltaic PVC pipe and its manufacturing method. Background Technology

[0002] Photovoltaic power plants are typically built outdoors in environments with strong ultraviolet radiation. The sheathing used to protect the cables needs to have both excellent weather resistance and good mechanical properties. To balance material costs and processing efficiency, existing technologies often employ multi-layer co-extrusion composite structures. For example, general-purpose PVC is used as the inner layer to provide mechanical support, while modified PVC or ASA alloy with added ultraviolet shielding agents is used as the outer layer to impart weather resistance.

[0003] In multilayer co-extruded composite photovoltaic sheathing tubes, insufficient interlayer bonding and mismatch in thermal expansion coefficients are interconnected problems that persist throughout the product lifecycle. Because the inner PVC layer and the outer ASA alloy layer are thermodynamically incompatible systems, their interface cannot form chemical bonds. They can only rely on the diffusion of molecular chains in the molten state to form physical entanglement. This bonding method has limited initial strength and is temperature-sensitive. During long-term outdoor service, the outer layer material undergoes photo-oxidative degradation under ultraviolet radiation, leading to surface shrinkage and continuous interfacial tensile stress. Simultaneously, changes in ambient temperature cause periodic shear strain between the soft inner layer with high plasticizer content and the outer layer with high filler rigidity due to the difference in their thermal expansion coefficients. The superposition of these two stresses on the already weak interface first induces stress concentration at microscopic defects, then initiates microcracks that propagate along the interface. Once these cracks form, they become channels for water vapor and oxygen penetration, accelerating the hydrolysis and oxidation of molecular chains in the interfacial region, leading to irreversible attenuation of the bonding strength, ultimately manifesting as macroscopic interlayer delamination or bulging. The problems caused by the mismatch in thermal expansion coefficients are more insidious: starting from the extrusion cooling and shaping stage, residual internal stress fields are formed in the inner and outer layers due to the different shrinkage rates; in subsequent use, each temperature cycle will generate alternating radial tensile and compressive stresses and axial shear stresses at the interface. This fatigue load continues to act on the interface with existing microcracks, causing the cracks to extend deeper into the pipe, eventually leading to the loss of structural integrity and causing the sheath to lose its basic protection function for the internal cables.

[0004] Therefore, a UV-resistant photovoltaic PVC pipe and its preparation method are proposed to solve the problems of insufficient interlayer bonding and mismatch of thermal expansion coefficients. Summary of the Invention

[0005] The purpose of this invention is to provide a UV-resistant photovoltaic PVC pipe and its preparation method, solving the problems of insufficient interlayer bonding and mismatch of thermal expansion coefficients.

[0006] To achieve this objective, the present invention adopts the following technical solution: A method for preparing a UV-resistant photovoltaic PVC pipe, the method specifically including the following steps: Step S1: Prepare dry mix a, dry mix b, dry mix c and dry mix d according to the dry mix base material; wherein, dry mix a includes a conductive agent, dry mix c includes a reactive compatibilizer and dry mix d includes an ultraviolet shielding agent. Step S2: After melting dry mix a and dry mix b separately, they are co-extruded to obtain a double-layer substrate tube a. Then, hot melt adhesive is applied to the surface of substrate tube a to obtain substrate tube b. Step S3: Obtain melt c and melt d containing the mixture from dry mix c and dry mix d respectively. Then, coat melt c and melt d onto the surface of the base tube b by co-extrusion to obtain composite tube blank a. Step S4: The composite tube blank a is subjected to high-temperature treatment, cooling and shaping and post-treatment in sequence to obtain UV-resistant photovoltaic PVC pipe.

[0007] Step S1 specifically includes the following steps: Step S11: Mix PVC resin, stabilizer and lubricant to obtain dry mix base material; Step S12: Mix the dry mixture base material with powder a, powder b, powder c, and powder d respectively, and then mix them at 115-120℃ and ≤40℃ in sequence to obtain dry mixture a, dry mixture b, dry mixture c, and dry mixture d.

[0008] In step S11, by weight fraction, the PVC resin is 100 parts, the stabilizer is 4-6 parts, the lubricant is 1-2 parts, the stabilizer is a calcium-zinc composite stabilizer, and the lubricant is a stearic acid lubricant. In step S12, by weight fraction, powder a comprises 43-47 parts polyester plasticizer and 10-14 parts conductive acetylene black, wherein the specific surface area of ​​the conductive acetylene black is 60-70 m² / g; powder b comprises 43-47 parts polyester plasticizer; powder c comprises 38-42 parts polyester plasticizer, 13-17 parts maleic anhydride-grafted PVC and 2-4 parts organically modified nano-montmorillonite, wherein the grafting rate of maleic anhydride-grafted PVC is 1.0-1.5%; the organically modified nano-montmorillonite is modified with dioctadecyl dimethyl ammonium chloride; powder d comprises 33-37 parts polyester plasticizer, 5-7 parts rutile nano-titanium dioxide, 0.4-0.6 parts ultraviolet absorber and 0.2-0.4 parts hindered amine light stabilizer, wherein the average particle size of the rutile nano-titanium dioxide is 0.2-0.3 μm.

[0009] Step S2 specifically includes the following steps: Step S21: Dry mix a and dry mix b are respectively fed into the extruder to melt, to obtain melt a and melt b. Then melt a and melt b are introduced into the corresponding four-layer co-extrusion die to obtain the base material tube a. Step S22: First, load the hot melt adhesive into the coating machine and raise the temperature of the coating machine head to 110-120℃; then, pull the cooled and shaped substrate tube a through the coating machine head, so that the molten hot melt adhesive is coated on the surface of the substrate tube a, and after cooling, a substrate tube b with a thin layer is obtained.

[0010] In step S21, the double-layered substrate tube a includes an inner tube blank and an outer tube blank; wherein, melt a forms the inner tube blank and melt b forms the outer tube blank. In step S22, the hot melt adhesive is a polyurethane hot melt adhesive with a softening point ≥120℃ and a melt viscosity of 5000-10000mPa·s; the thickness of the thin layer is 20-30μm.

[0011] Step S3 specifically includes the following steps: Step S31: Mix glycidyl methacrylate and polymerization inhibitor evenly to obtain a mixture; Step S32: The dry mixture c is fed into the extruder to melt, and the mixture is injected into the melt corresponding to the dry mixture c at the end of the metering section of the extruder. Then the melt containing the mixture is passed into a static mixer to mix and obtain melt c. Step S33: The dry mixture d is put into the extruder to melt and obtain melt d. Then the substrate tube b is moved into the corresponding four-layer co-extrusion die, and melt c and melt d are introduced into the corresponding four-layer co-extrusion die at the same time, so that melt c and melt d successively cover the surface of the substrate tube b to obtain composite tube blank a.

[0012] In step S31, the amount of glycidyl methacrylate is 95 parts by weight and the amount of polymerization inhibitor is 4-6 parts by weight; the polymerization inhibitor is hydroquinone polymerization inhibitor. In step S32, the injection amount of the mixture is 2.0-2.5% of the mass of the dry mixture c; the temperature of the static mixer is 165-175℃, and the residence time of the melt containing the mixture in the static mixer is 40-60s; In step S33, the composite tube blank a includes an inner layer and an outer layer formed sequentially on the surface of the base tube b, wherein the inner layer is formed by melt c and the outer layer is formed by melt d, the wall thickness of the inner layer accounts for 20-25% of the total wall thickness of the composite tube blank a, and the wall thickness of the outer layer accounts for 30-35% of the total wall thickness of the composite tube blank a.

[0013] Step S4 specifically includes the following steps: Step S41: Pass the composite tube blank a through a 3-4m high temperature maintenance zone within 22-48s to maintain the surface temperature of the composite tube blank a at the first temperature, thereby obtaining the composite tube blank b. Step S42: Pass the composite tube blank b through the vacuum shaping water tank and the spray cooling water tank in sequence to obtain the composite tube blank c; Step S43: The composite tube blank c is pulled, marked and wound to obtain a semi-finished tube; the semi-finished tube is then stored at room temperature and humidity 40-70%RH for more than 72 hours to obtain a UV-resistant photovoltaic PVC pipe.

[0014] In step S41, the first temperature is 160-165℃; In step S42, the temperature of the vacuum shaping water tank is 50-60℃, and the temperature of the spray cooling water tank is 15-21℃.

[0015] A UV-resistant photovoltaic PVC pipe, wherein the UV-resistant photovoltaic PVC pipe is obtained by the preparation method described above.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a UV-resistant photovoltaic PVC pipe and its preparation method. A double-layer substrate pipe a is formed by co-extruding a dry mixture a containing a conductive agent and a dry mixture b without fillers, effectively blocking the interference of the conductive agent on subsequent interfacial reactions. Then, hot melt adhesive is coated on the surface of substrate pipe a to form substrate pipe b, providing active reaction sites for interfacial chemical bonding. Subsequently, melt c containing a reactive compatibilizer and melt d containing a UV shielding agent are sequentially coated on the surface of substrate pipe b to form a composite pipe blank a. This allows the reactive compatibilizer in melt c to chemically react with the hot melt adhesive at the interface, generating covalent bridges, thus solving the problem of insufficient interlayer bonding caused by material incompatibility in traditional multilayer pipes. Finally, a high-temperature holding zone ensures sufficient interfacial reaction, and a gradient cooling process releases processing stress, avoiding stress concentration caused by differences in thermal expansion coefficients. Compared with existing technologies, this invention significantly improves interlayer bonding strength by replacing physical entanglement with chemical bonding, while simultaneously solving the problem of thermal stress mismatch using a stress release process. This results in pipes with excellent interlayer stability and dimensional stability under strong outdoor UV conditions. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] The structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0019] Figure 1 This is a flowchart of the preparation method in this invention. Detailed Implementation

[0020] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] In the description of this invention, it should be understood that the terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be a component positioned centrally in the connection.

[0022] Please see Figure 1 This embodiment describes a method for preparing a UV-resistant photovoltaic PVC pipe, which specifically includes the following steps: Step S1: Prepare dry mix a, dry mix b, dry mix c and dry mix d according to the dry mix base material; wherein, dry mix a includes a conductive agent, dry mix c includes a reactive compatibilizer and dry mix d includes an ultraviolet shielding agent. Step S2: After melting dry mix a and dry mix b separately, they are co-extruded to obtain a double-layer substrate tube a. Then, hot melt adhesive is applied to the surface of substrate tube a to obtain substrate tube b. Step S3: Obtain melt c and melt d containing the mixture from dry mix c and dry mix d respectively. Then, coat melt c and melt d onto the surface of the base tube b by co-extrusion to obtain composite tube blank a. Step S4: The composite tube blank a is subjected to high-temperature treatment, cooling and shaping and post-treatment in sequence to obtain UV-resistant photovoltaic PVC pipe.

[0023] Specifically, in step S1, dry mix a, dry mix b, dry mix c and dry mix d are prepared according to the dry mix base material; wherein, dry mix a includes a conductive agent, dry mix c includes a reactive compatibilizer and dry mix d includes an ultraviolet shielding agent. Step S1 specifically includes the following steps: Step S11: Mix PVC resin (degree of polymerization 1000-1100), stabilizer and lubricant to obtain dry mixture base material; In step S11, by weight fraction, the PVC resin is 100 parts, the stabilizer is 4-6 parts, the lubricant is 1-2 parts, the stabilizer is a calcium-zinc composite stabilizer, and the lubricant is a stearic acid lubricant. Step S12: Mix the dry mixture base material with powder a, powder b, powder c, and powder d respectively, and then mix them at 115-120℃ and ≤40℃ in sequence to obtain dry mixture a, dry mixture b, dry mixture c, and dry mixture d.

[0024] In step S12, by weight fraction, powder a comprises 43-47 parts of polyester plasticizer and 10-14 parts of conductive acetylene black, wherein the specific surface area of ​​the conductive acetylene black is 60-70 m². 2 / g; Powder b includes 43-47 parts polyester plasticizer; Powder c includes 38-42 parts polyester plasticizer, 13-17 parts maleic anhydride-grafted PVC and 2-4 parts organically modified nano-montmorillonite, wherein the grafting rate of maleic anhydride-grafted PVC is 1.0-1.5%; the organically modified nano-montmorillonite is modified with dioctadecyl dimethyl ammonium chloride (DK series organic montmorillonite); Powder d includes 33-37 parts polyester plasticizer, 5-7 parts rutile nano-titanium dioxide, 0.4-0.6 parts ultraviolet absorber and 0.2-0.4 parts hindered amine light stabilizer, wherein the average particle size of rutile nano-titanium dioxide is 0.2-0.3μm.

[0025] It should be noted that in step S1, the materials are first mixed with PVC resin, calcium-zinc composite stabilizer, and stearic acid lubricant in step S11 to obtain a dry mix base. This base serves as the basic carrier for subsequent functional modification, and its uniformity directly affects the dispersion effect of the additives. Subsequently, in step S12, the dry mix base is mixed with four different powders, and then subjected to high-temperature mixing at 115-120℃ and low-temperature mixing at below 40℃. During the high-temperature mixing stage, the polyester plasticizer gradually penetrates into the interior of the PVC resin particles, causing the resin to swell. At the same time, solid additives such as conductive acetylene black, maleic anhydride-grafted PVC, organically modified nano-montmorillonite, and rutile nano-titanium dioxide are uniformly adhered to the resin surface under mechanical shearing. The migration and absorption process of the plasticizer changes the mobility of the PVC molecular chains, laying the foundation for subsequent extrusion melting. The cold mixing stage rapidly cools the materials to prevent plasticizer back-segregation or agglomeration, maintaining the fluidity and storage stability of the dry mix. Through this graded mixing process, the four dry mixtures are presented as free-flowing powders with uniform color and no agglomeration, respectively carrying out the functions of conductivity, isolation, reaction enhancement and weather shielding, providing raw material units with different properties for constructing multi-layer composite tubes.

[0026] It is understood that step S1, by dividing different functional additives into dry mixes, lays the material basis for endowing each subsequent layer with specific properties. Specifically, dry mix a, containing conductive acetylene black, aims to dissipate static electricity; dry mix b, containing no fillers, is used to shield the conductive acetylene black from interfacial reactions; dry mix c introduces maleic anhydride-grafted PVC as a reactive compatibilizer and adds organically modified nano-montmorillonite to enhance the strength of the resulting pipe, aiming to improve interlayer chemical affinity and mechanical interlocking; dry mix d, through the synergistic effect of rutile nano-titanium dioxide and hindered amine light stabilizers, endows the outer layer of the resulting pipe with ultraviolet shielding capability. These dry mixes, each with its own function, correspond to technical approaches for addressing insufficient interlayer bonding and mismatch in thermal expansion coefficients: Dry mix b blocks the quenching of free radicals by conductive acetylene black in dry mix a, ensuring the efficiency of subsequent interfacial chemical reactions; the reactive compatibilizer in dry mix c can form covalent bridges at the interlayer interface, fundamentally enhancing the bonding force, while the layered structure of nano-montmorillonite helps disperse thermal stress; and dry mix d mitigates shrinkage stress caused by aging.

[0027] It is understandable that the conductive acetylene black in dry mix a imparts semi-conductivity to the inner layer of the resulting pipe, dissipating static electricity generated during cable operation and preventing potential interface damage from static accumulation. The purity of dry mix b ensures that the hot melt adhesive applied subsequently can directly contact the PVC surface without carbon black interference, thus guaranteeing the full formation of interfacial chemical bonds. The maleic anhydride-grafted PVC in dry mix c can migrate to the interfacial region during extrusion, reacting with the hot melt adhesive and the subsequently introduced mixture to generate block copolymers in situ, achieving interlayer chemical bonding. Simultaneously, nano-montmorillonite forms a physical network in the resulting pipe, dispersing internal stress caused by differences in thermal expansion coefficients. The ultraviolet shielding system in dry mix d slows down the aging of the outer layer of the resulting pipe, preventing shrinkage stress concentration caused by photo-oxidative degradation. Therefore, the four dry mixes obtained in step S1 can work synergistically in subsequent processes to jointly improve the overall durability of the composite pipe.

[0028] It is worth noting that step S1 employs a process of first preparing the dry blend base material and then mixing it separately with different powders, rather than adding all the additives at once. This aims to avoid cross-interference between different functional additives and to achieve independent control of each layer's formulation. For example, if conductive acetylene black comes into contact with reactive compatibilizers too early, its surface functional groups are easily adsorbed or quenched of active sites; if nano-montmorillonite is blended with ultraviolet absorbers, it can easily affect its dispersion in the polymer matrix. Stepwise mixing allows each functional additive to achieve its optimal dispersion state in its corresponding dry blend. In subsequent mixing processes, the hot mixing temperature of 115-120℃ is higher than the melting point of the polyester plasticizer but lower than the decomposition temperature of PVC. Within this temperature range, the plasticizer viscosity decreases, facilitating diffusion into the PVC interior, while solid additives adhere uniformly under shear action. Mixing at ≤40℃ rapidly freezes the additive distribution, preventing plasticizer volatilization or additive agglomeration due to prolonged high temperatures. In addition, regarding the proportions of each material, 12 parts of conductive acetylene carbon black can ensure conductivity while avoiding overfilling that would lead to a decrease in mechanical properties; 15 parts of maleic anhydride-grafted PVC provides sufficient reaction sites without significantly changing the matrix viscosity; 3 parts of organically modified nano-montmorillonite enhances the material while also addressing dispersion difficulty; and the combination of 6 parts of rutile nano-titanium dioxide and 0.3 parts of hindered amine light stabilizer achieves a balance between UV shielding and cost control.

[0029] Specifically, in step S2, dry mix a and dry mix b are melted separately and then co-extruded to obtain a double-layer structured substrate tube a. Then, hot melt adhesive is applied to the surface of substrate tube a to obtain substrate tube b. Step S2 specifically includes the following steps: Step S21: Dry mix a and dry mix b are respectively fed into the extruder to melt, to obtain melt a and melt b. Then melt a and melt b are introduced into the corresponding four-layer co-extrusion die to obtain the base material tube a. In step S21, the double-layered substrate tube a includes an inner tube blank and an outer tube blank; wherein, melt a forms the inner tube blank and melt b forms the outer tube blank. Step S22: First, load the hot melt adhesive into the coating machine and raise the temperature of the coating machine head to 110-120℃; then, pull the cooled and shaped substrate tube a through the coating machine head, so that the molten hot melt adhesive is coated on the surface of the substrate tube a, and after cooling, a substrate tube b with a thin layer is obtained.

[0030] In step S22, the hot melt adhesive is a polyurethane hot melt adhesive with a softening point ≥120℃ and a melt viscosity of 5000-10000mPa·s; the thickness of the thin layer is 20-30μm.

[0031] It should be noted that in step S2, the material undergoes a transformation from a solid dry mixture to a molten composite tube blank, and a hot melt adhesive layer is introduced to construct an active interface. In step S21, the dry mixture a and dry mixture b prepared in step S1 are fed into an extruder, where they undergo phase transitions from a glassy state to a highly elastic state to a viscous flow state within a temperature range of 155-170℃. The molecular chains gain mobility and, under shearing action, untangle and rearrange themselves to form uniform melt a and melt b. When the two melts converge in the four-layer co-extrusion die, since both are based on PVC and have the same plasticizer content, their melt viscosities are similar. Molecular chains diffuse into each other in the interlayer contact area, forming an intermixed layer with a thickness of approximately 5-15 μm. This physical entanglement provides the initial bonding force for the double-layer structure. In this process, melt a forms the inner tube blank, and melt b forms the outer tube blank, together constituting the base tube a. Subsequently, in step S22, a 20-30 μm layer of moisture-curing reactive polyurethane hot melt adhesive is uniformly coated onto the surface of the cooled and shaped substrate tube a. This hot melt adhesive is melted and coated at 110-120°C and then rapidly cooled and cured to form a solid thin layer. During this process, the isocyanate groups in the hot melt adhesive molecules are retained on the surface, providing active sites for subsequent chemical reactions; thus, a substrate tube b with a uniform, continuous, and tightly adhered active interface layer is obtained.

[0032] It is understood that step S2, through double-layer co-extrusion and hot melt adhesive coating, achieves the construction of the basic structure and the introduction of a reactive interface. In the double-layer co-extrusion, the inner tube preform formed by dry mix a contains conductive acetylene black and is semi-conductive, which can discharge static electricity generated by cables during photovoltaic system operation, avoiding potential damage to the tube interface caused by static charge accumulation; the outer tube preform formed by dry mix b contains no fillers, and its pure PVC surface provides a chemically inert base surface for subsequent hot melt adhesive adhesion. The hot melt adhesive coating directly introduces a polyurethane layer containing isocyanate active groups, which will chemically react with the mixture in the subsequent high-temperature co-extrusion to form a cross-interface chemical bond. Under the action of step S2, on the one hand, the carbon black in the inner tube preform is isolated from the subsequent reaction area through a physical barrier, avoiding the free radical capturing groups on the carbon black surface from quenching the interfacial reaction; on the other hand, the physical barrier isolates interference and constructs an active interface, creating the necessary conditions for upgrading from physical bonding to chemical bonding, which is the key to solving the problem of insufficient interlayer bonding in traditional multilayer tubes.

[0033] Understandably, the outer tube preform in substrate tube b blocks the migration path of carbon black from the inner tube preform to the surface. The quinone and phenolic hydroxyl groups on the carbon black surface are highly efficient free radical scavengers. If they are directly exposed to the interface region, they will quench the reaction between the subsequent mixture and the hot melt adhesive, leading to the failure of interfacial chemical bonding. The physical barrier effect of the outer tube preform ensures the efficiency of the interfacial chemical reaction, thereby guaranteeing a substantial improvement in interlayer bonding. In addition, the introduction of the hot melt adhesive layer not only provides reactive groups, but its cured polyurethane network also has a certain degree of flexibility, which can absorb some of the interfacial shear stress caused by the difference in thermal expansion coefficients during subsequent use, playing a stress buffering role. Furthermore, the electrostatic discharge function of the outer tube preform avoids the accumulation and discharge of static charge in the interface region, preventing damage to the interfacial bonding caused by local high temperature or electrochemical action.

[0034] It is worth noting that step S2 employs a process sequence of co-extrusion followed by hot melt adhesive coating, rather than directly extruding the hot melt adhesive as a co-extrusion layer. If the hot melt adhesive were used as a co-extrusion layer, its prolonged residence in the high-temperature die could easily lead to premature reaction or thermal degradation of the isocyanate groups, resulting in a loss of activity in subsequent reactions with the mixture. By using a coating method, the hot melt adhesive is briefly melted and coated at 110-120℃ before rapid cooling and solidification, ensuring both the uniformity of the thin layer and maximizing the preservation of active groups. Furthermore, the hot melt adhesive's softening point ≥120℃ ensures it will not melt and flow again during subsequent high-temperature co-extrusion, while the melt viscosity of 5000-10000 mPa·s balances coating flowability with precision in thickness control; the coating thickness of 20-30 μm provides sufficient reactive material without being too thick, affecting the pipe's flexibility or increasing costs. In addition, the extrusion temperature in step S21 is set to 155-170℃, which ensures that the PVC is fully plasticized while avoiding excessive temperature that could lead to plasticizer volatilization or material decomposition. Simultaneously, it allows for good interfacial mixing of the two melt layers under viscosity-matching conditions. These parameters collectively ensure that the substrate tube b possesses structural integrity, interface purity, and retained activity, laying a solid foundation for the interfacial chemical reaction in step S3.

[0035] Specifically, in step S3, melts c and d containing the mixture are obtained from dry mix c and dry mix d respectively. Then, melts c and d are co-extruded onto the surface of the base tube b to obtain composite tube blank a. Step S3 specifically includes the following steps: Step S31: Mix glycidyl methacrylate and polymerization inhibitor evenly to obtain a mixture; In step S31, by weight, glycidyl methacrylate comprises 95 parts and polymerization inhibitor comprises 4-6 parts; the polymerization inhibitor is hydroquinone polymerization inhibitor. Step S32: The dry mixture c is fed into the extruder to melt, and the mixture is injected into the melt corresponding to the dry mixture c at the end of the metering section of the extruder. Then the melt containing the mixture is passed into a static mixer to mix and obtain melt c. In step S32, the injection amount of the mixture is 2.0-2.5% of the mass of the dry mixture c; the temperature of the static mixer is 165-175℃, and the residence time of the melt containing the mixture in the static mixer is 40-60s; Step S33: The dry mixture d is put into the extruder to melt and obtain melt d. Then the substrate tube b is moved into the corresponding four-layer co-extrusion die, and melt c and melt d are introduced into the corresponding four-layer co-extrusion die at the same time, so that melt c and melt d successively cover the surface of the substrate tube b to obtain composite tube blank a.

[0036] In step S33, the composite tube blank a includes an inner layer and an outer layer formed sequentially on the surface of the base tube b, wherein the inner layer is formed by melt c and the outer layer is formed by melt d, the wall thickness of the inner layer accounts for 20-25% of the total wall thickness of the composite tube blank a, and the wall thickness of the outer layer accounts for 30-35% of the total wall thickness of the composite tube blank a.

[0037] It should be noted that mixing glycidyl methacrylate with hydroquinone polymerization inhibitor yielded a stable reactive mixture. The addition of hydroquinone polymerization inhibitor suppressed the self-polymerization of glycidyl methacrylate during storage and transportation, ensuring that its epoxy groups existed in an active form. Dry mix c was fed into an extruder for melting. At the end of the metering section of the extruder, the mixture was injected into the melt corresponding to dry mix c. At this point, glycidyl methacrylate was dispersed in the melt of the corresponding dry mix c in the form of microdroplets. Subsequently, it was held in a static mixer at 165-175℃ for 40-60 seconds to achieve uniform dispersion without significant polymerization reaction. This process maintained the reactivity of the epoxy groups. Dry mix d was melted to obtain melt d. Then, the substrate tube b was introduced into the corresponding four-layer co-extrusion die, so that melt c and melt d sequentially coated the surface of the substrate tube b to form the inner and outer layers. Under the high temperature and high pressure environment inside the die head, the glycidyl methacrylate epoxy groups in melt c and the isocyanate groups in the hot melt adhesive layer on the surface of the substrate tube b begin to undergo a ring-opening addition reaction, generating a block copolymer in situ at the interface. At the same time, the maleic anhydride-grafted PVC in melt c also participates in the interface reaction. Melt d serves as the outermost coating, with rutile nano-titanium dioxide and hindered amine light stabilizer forming an ultraviolet shielding layer. Meanwhile, the ultraviolet absorber in dry mix d can absorb high-energy ultraviolet light and convert it into heat energy, which works synergistically with the physical shielding effect of rutile nano-titanium dioxide and the free radical scavenging effect of hindered amine light stabilizer to jointly constitute the ultraviolet shielding layer.

[0038] It is known that the post-injection of glycidyl methacrylate ensures that the reactive monomers arrive at the interface region in a fresh state, preventing premature polymerization during the long residence time in the extruder; the static mixer achieves uniform dispersion within 40-60 seconds without initiating significant reactions, preserving activity for subsequent interface reactions; multilayer co-extrusion causes melt c and melt d to successively coat each other, and the epoxy groups in melt c react chemically with the thin layer of isocyanate groups at the interface to form a covalent bridge across the interface, elevating physical bonding to chemical bonding. Under the action of step S2, the interlayer bonding force is fundamentally enhanced, enabling the interface, which was originally weak due to material incompatibility, to obtain molecular-level bonding strength. Meanwhile, maleic anhydride-grafted PVC in melt c acts as a macromolecular compatibilizer, further promoting interfacial compatibility between the inner and outer layers and the substrate tube b. Organically modified nano-montmorillonite forms a physical network in the inner layer, dispersing internal stress caused by differences in thermal expansion coefficients. The outer layer slows down aging shrinkage, and the ultraviolet absorber in the outer layer preferentially absorbs high-energy ultraviolet radiation, converting it into harmless heat energy, thus reducing the excitation energy that triggers photo-oxidative degradation at its source. Rutile nano-titanium dioxide extends the optical path of ultraviolet light in the coating by reflecting and scattering ultraviolet light. Hindered amine light stabilizers capture generated free radicals, interrupting the degradation chain reaction. The synergistic effect of these three components significantly reduces the photo-oxidative degradation rate in the outer layer, thereby minimizing the continuous tensile stress on the interface caused by aging shrinkage.

[0039] Understandably, to address insufficient interlayer bonding, glycidyl methacrylate reacts with the thin layer at the interface to generate block copolymers in situ between the layers. This chemical bonding method is far stronger than the physical entanglement of molecular chains relied upon by traditional multilayer pipes, and can resist interfacial degradation under harsh environments such as humid heat aging and temperature cycling. The introduction of maleic anhydride-grafted PVC further increases the chemical affinity of the interfacial region, allowing for more connection points between the inner layer, outer layer, and substrate pipe b. To address thermal stress mismatch, the plasticizer content in each structure of the composite pipe blank a is distributed in a gradient from 45 parts, 45 parts, 40 parts to 35 parts, ensuring a smooth transition of material modulus rather than abrupt changes, avoiding stress concentration caused by differences in thermal expansion coefficients. The lamellar structure of organically modified nano-montmorillonite is oriented and distributed in the inner layer, effectively dispersing and absorbing interlayer shear stress. The outer layer delays shrinkage caused by photo-oxidative degradation, reducing continuous interfacial tensile stress caused by aging.

[0040] It is worth noting that step S3 employs a post-injection process of glycidyl methacrylate (GAMA) instead of pre-mixing it into the dry mix. This is based on the control of reaction timing and activity retention. If GAMA is directly added to dry mix c, it will prematurely undergo grafting or cross-linking reactions during the several-minute melt mixing process in the extruder, leading to a surge in melt viscosity, decreased processing stability, and the epoxy groups being largely consumed by the time they reach the interface, thus failing to effectively participate in the interfacial reaction. GAMA only contacts the melt corresponding to dry mix c at the end of the extruder, with a residence time of only 40-60 seconds. Combined with the hydroquinone polymerization inhibitor, this ensures that it reaches the interface in an active form. The static mixer temperature of 165-175℃ is consistent with the extrusion temperature of dry mix c, avoiding reaction rate changes caused by temperature fluctuations. The optimized residence time of 40-60 seconds is sufficient to achieve uniform dispersion without triggering significant reactions. The injection volume of 2.0-2.5% ensures both reaction effectiveness and cost-effectiveness: too low a volume results in insufficient interfacial reaction, while too high a volume may lead to self-polymerization and the formation of gel particles.

[0041] Specifically, in step S4, the composite tube blank a is subjected to high-temperature treatment, cooling and shaping, and post-treatment in sequence to obtain a UV-resistant photovoltaic PVC pipe.

[0042] Step S4 specifically includes the following steps: Step S41: Pass the composite tube blank a through a 3-4m high temperature maintenance zone within 22-48s to maintain the surface temperature of the composite tube blank a at the first temperature, thereby obtaining the composite tube blank b. In step S41, the first temperature is 160-165℃; Step S42: Pass the composite tube blank b through the vacuum shaping water tank and the spray cooling water tank in sequence to obtain the composite tube blank c; In step S42, the temperature of the vacuum shaping water tank is 50-60℃, and the temperature of the spray cooling water tank is 15-21℃.

[0043] Step S43: The composite tube blank c is pulled, marked and wound to obtain a semi-finished tube; the semi-finished tube is then stored at room temperature and humidity 40-70%RH for more than 72 hours to obtain a UV-resistant photovoltaic PVC pipe.

[0044] It should be noted that in step S4, the composite tube blank a undergoes a complete transformation from a high-temperature molten state to a solid finished product, and its microstructure and macroscopic properties are finalized at this stage. In step S41, the composite tube blank a prepared in step S3 is fed into a high-temperature holding zone of 3-4m, and the surface temperature is maintained at a first temperature of 160-165℃ for 22-48s. At this time, the composite tube blank a is in a molten or highly elastic state, and the interfacial chemical reaction between glycidyl methacrylate and the hot melt adhesive thin layer continues at the first temperature. The degree of ring-opening addition reaction between epoxy groups and isocyanate groups is further improved. At the same time, maleic anhydride-grafted PVC also participates in interfacial crosslinking, and the interlayer chemical bonding network is gradually improved. During the extrusion process, the orientation stress of the molecular chains along the flow direction is fully released in this high-temperature relaxation stage, and the molecular chains tend to be in a random coil state. Subsequently, the composite tube blank b is passed sequentially through a vacuum shaping water tank at 50-60℃ and a spray cooling water tank at 15-21℃. Under vacuum adsorption, the tube blank adheres tightly to the shaping sleeve to complete dimensional shaping. During the warm water shaping stage, the pipe is slowly cooled, allowing the difference in thermal shrinkage rate caused by the difference in plasticizer content (45 parts for the inner tube blank, 45 parts for the outer tube blank, 40 parts for the inner layer, and 35 parts for the outer layer) in the composite tube blank a to be smoothly transitioned, avoiding new internal stress concentration caused by rapid cooling. Then, cold water completes the final cooling, freezing the molecular chain movement and forming a stable glassy structure. Finally, after being drawn, marked, and wound, the composite tube blank c is stored at room temperature and humidity of 40-70% for more than 72 hours. The residual isocyanate groups in the hot melt adhesive layer continue to react with the moisture in the air, gradually completing the final cross-linking, and obtaining a UV-resistant photovoltaic PVC pipe.

[0045] It is known that the initial temperature in step S41 provides the necessary time and temperature window for the interfacial chemical reaction, allowing the reaction between glycidyl methacrylate and the hot melt adhesive thin layer initiated in step S3 to continue, avoiding premature cessation of the reaction due to rapid cooling. The gradient cooling in step S42, through a two-stage cooling process of slow cooling with warm water followed by rapid cooling with cold water, allows the shrinkage stress caused by the difference in thermal expansion coefficients between the inner and outer layers of the composite tube blank b to be released gradually in the slow cooling stage, rather than being instantly locked into high-value residual internal stress. The subsequent storage in step S43 utilizes ambient humidity to trigger the final cross-linking of the hot melt adhesive, ensuring that the interfacial bonding strength reaches an ideal state. Under the action of step S4, the chemical bonding potential established in steps S2 and S3 is converted into actual interfacial bonding strength, while simultaneously eliminating internal stress generated during processing, ensuring that the composite tube can resist thermal cycling fatigue and interfacial delamination during subsequent use.

[0046] Understandably, to address insufficient interlayer bonding, the first temperature allows for sufficient interfacial chemical reactions. The isocyanate groups of the hot melt adhesive thin layer and the epoxy groups of glycidyl methacrylate exhibit high reactivity and diffusion rates at 160-165℃. A residence time of 22-48 seconds ensures that enough active groups participate in the reaction, forming covalent bridges across the interface. A storage time of ≥72 hours allows the hot melt adhesive thin layer to complete final cross-linking, and the interfacial network structure tends to stabilize. This chemical bonding strength is far higher than physical entanglement, and it can resist interfacial degradation caused by damp heat aging and ultraviolet radiation. To address thermal stress mismatch, the first temperature has already released the orientation stress from the extrusion process. Gradient cooling allows for a smooth transition of the thermal shrinkage differences between the inner and outer tube blanks, and between the inner and outer layers due to different plasticizer contents. During the 50-60℃ warm water setting stage, the composite tube blank b cools slowly, resulting in a smaller temperature gradient between the inner and outer layer structures and partial relaxation of thermal stress. After final setting with cold water at 15-21℃, the residual stress level of the composite tube blank b is lower than that of the rapid cooling process.

[0047] It is worth noting that step S4 employs a process combining high-temperature maintenance and gradient cooling. If the composite tube blank a directly enters the cold water from the die, the interfacial chemical reaction will rapidly cease due to the sudden temperature drop. The active groups carefully preserved in step S3 will not be able to react fully, and the interfacial bonding strength will be significantly reduced. Simultaneously, the shrinkage difference between the inner and outer layers caused by the rapid temperature difference will be locked into high-value residual internal stress, becoming a crack source for future thermal cycling fatigue. The high-temperature maintenance zone maintains the surface temperature of the composite tube blank a at a first temperature of 160-165℃, consistent with the die temperature and static mixer temperature in step S3, ensuring that the reaction proceeds continuously within the optimal temperature window. The composite tube blank a passes through the 3-4m high-temperature maintenance zone within 22-48s, avoiding insufficient reaction due to too short a time and excessive production line occupation due to too long a time. The composite tube blank b is slowly cooled at a temperature of 50-60℃ in the vacuum forming water tank, allowing partial release of the thermal stress caused by the shrinkage difference rather than locking it in. The temperature of the spray cooling water tank at 15-21℃ ensures the final cooling efficiency. The subsequent storage should be carried out at a humidity of 40-70%RH for ≥72 hours to ensure that the cross-linking reaction is fully completed.

[0048] The present invention also provides a UV-resistant photovoltaic PVC pipe, which is prepared by the above preparation method, as detailed in Examples 1, 2 and 3.

[0049] Example 1: Step S1: Mix 100 kg of PVC resin, 5 kg of calcium-zinc composite stabilizer and 1.5 kg of stearic acid lubricant to obtain a dry-mix base material.

[0050] 106.5 kg of dry mix base material, 45 kg of polyester plasticizer, and 12 kg of conductive acetylene black were successively mixed at a high temperature of 118°C and a low temperature of 35°C to obtain dry mix a.

[0051] 106.5 kg of dry mix base material and 45 kg of polyester plasticizer were mixed at a high temperature of 118°C and a low temperature of 35°C in sequence to obtain dry mix b.

[0052] 106.5 kg of dry mix base material was mixed with 40 kg of polyester plasticizer, 15 kg of maleic anhydride grafted PVC and 3 kg of organic modified nano montmorillonite at 118°C and 35°C respectively to obtain dry mix c.

[0053] 106.5 kg of dry mix base material was mixed with 35 kg of polyester plasticizer, 6 kg of rutile nano titanium dioxide, 0.5 kg of ultraviolet absorber and 0.3 kg of hindered amine light stabilizer at 118°C and 35°C respectively to obtain dry mix d.

[0054] Step S2: Dry mix a and dry mix b are fed into an extruder for melting. The extruder temperature is set to 155℃ for the feeding section, 165℃ for the compression section, 170℃ for the metering section, and 170℃ for the die head, resulting in melt a and melt b. Melt a and melt b are then introduced into the corresponding four-layer co-extrusion die. Melt a forms the inner tube blank, and melt b forms the outer tube blank. Co-extrusion yields a double-layer structure base tube a, where the inner tube blank has a wall thickness of 0.7mm, the outer tube blank has a wall thickness of 0.5mm, and the outer diameter of the base tube a is 32mm.

[0055] Polyurethane hot melt adhesive (softening point 125℃, melt viscosity 7500mPa·s) is loaded into a coating machine, and the temperature of the coating machine head is raised to 115℃. The cooled and shaped substrate tube a is pulled through the coating machine head, and the molten hot melt adhesive is coated on the surface of the substrate tube a with a coating thickness of 25μm. After cooling, the substrate tube b is obtained.

[0056] Step S3: 95 kg of glycidyl methacrylate and 5 kg of hydroquinone polymerization inhibitor were mixed evenly to obtain a mixture.

[0057] Dry mixture c is fed into a twin-screw extruder for melting. The extruder temperature is set to 150°C for the feeding section, 165°C for the compression section, and 170°C for the metering section. At the end of the metering section of the extruder, the liquid mixture is injected into the melt at an injection rate of 2.2% of the mass of dry mixture c. The melt containing the liquid mixture is then passed into a static mixer at a temperature of 170°C and held for 50 seconds to obtain melt c.

[0058] The dry mixture d is fed into an extruder for melting. The extruder temperature is set to 155℃ for the feeding section, 165℃ for the compression section, 170℃ for the metering section, and 170℃ for the die head, resulting in melt d. The base material tube b is introduced into the corresponding four-layer co-extrusion die, and melt c and melt d are introduced into the die simultaneously. Melt c coats the surface of the base material tube b to form a transition layer (wall thickness 0.25mm, accounting for 21% of the total wall thickness of the composite tube blank a), and melt d coats the surface of the transition layer to form a weather-resistant outer layer (wall thickness 0.35mm, accounting for 31% of the total wall thickness of the composite tube blank a), resulting in composite tube blank a with a total wall thickness of 1.8mm.

[0059] Step S4: Composite tube blank a is passed through a 3.5m long high-temperature maintenance zone at a speed of 6.5m / min. The surface temperature of the tube blank is maintained at 162℃ by an infrared heat preservation cover for 32s to obtain composite tube blank b.

[0060] Composite tube blank b is passed sequentially through a vacuum shaping water tank at 55°C and a spray cooling water tank at 18°C ​​to obtain composite tube blank c.

[0061] The composite tube blank c is drawn, marked with inkjet printing, and wound to obtain a semi-finished tube; the semi-finished tube is then stored in an environment with a temperature of 25℃ and a humidity of 55%RH for 80 hours to obtain a UV-resistant photovoltaic PVC tube with an outer diameter of 32mm and a wall thickness of 1.8mm.

[0062] Example 2: The basic content is the same as in Example 1, except that: In step S1, dry mix a contains 47 kg of polyester plasticizer and 14 kg of conductive acetylene black; dry mix b contains 47 kg of polyester plasticizer; dry mix c contains 42 kg of polyester plasticizer, 17 kg of maleic anhydride-grafted PVC, and 4 kg of organically modified nano-montmorillonite; dry mix d contains 37 kg of polyester plasticizer, 7 kg of rutile nano-titanium dioxide, 0.6 kg of ultraviolet absorber, and 0.4 kg of hindered amine light stabilizer.

[0063] In step S3, glycidyl methacrylate is 97 kg and hydroquinone polymerization inhibitor is 3 kg; the amount of the mixture injected is 2.5% of the mass of the dry mixture c.

[0064] In step S4, the first temperature is 165℃.

[0065] Example 3: The basic content is the same as in Example 1, except that: In step S1, dry mix a contains 43 kg of polyester plasticizer and 10 kg of conductive acetylene black; dry mix b contains 43 kg of polyester plasticizer; dry mix c contains 38 kg of polyester plasticizer, 13 kg of maleic anhydride-grafted PVC, and 2 kg of organically modified nano-montmorillonite; dry mix d contains 33 kg of polyester plasticizer, 5 kg of rutile nano-titanium dioxide, 0.4 kg of ultraviolet absorber, and 0.2 kg of hindered amine light stabilizer.

[0066] In step S3, glycidyl methacrylate is 93 kg and hydroquinone polymerization inhibitor is 7 kg; the amount of the mixture injected is 2.0% of the mass of the dry mixture c.

[0067] In step S4, the first temperature is 160℃.

[0068] Comparative Example 1: Comparative Example 1 illustrates a method for preparing ordinary three-layer co-extruded PVC pipes. The specific method is as follows: 100 kg of PVC resin, 45 kg of dioctyl phthalate plasticizer, 5 kg of calcium-zinc composite stabilizer, and 1.5 kg of stearic acid lubricant are mixed and hot-mixed at 115°C and cold-mixed at below 40°C using a high-speed mixer to obtain the inner layer dry mix. 100 kg of PVC resin, 40 kg of dioctyl phthalate plasticizer, 5 kg of calcium-zinc composite stabilizer, 1.5 kg of stearic acid lubricant, and 10 kg of light calcium carbonate are mixed using the same process to obtain the middle layer dry mix. 100 kg of ASA resin, 6 kg of rutile titanium dioxide, 0.5 kg of ultraviolet absorber, and 0.3 kg of hindered amine light stabilizer are mixed using the same process to obtain the outer layer dry mix. Three dry blends were fed into three extruders, each with its own temperature set at 155°C for the feeding section, 165°C for the compression section, 170°C for the metering section, and 170°C for the die head. The melt was introduced into a three-layer co-extrusion die. The inner layer formed the inner tube blank, the middle layer formed the middle tube blank, and the outer layer formed the outer tube blank, resulting in a three-layer composite tube blank. The wall thicknesses of each layer were 0.7mm for the inner layer, 0.5mm for the middle layer, and 0.6mm for the outer layer, with a total wall thickness of 1.8mm. After leaving the die head, the composite tube blank was directly cooled and shaped in a 20°C vacuum setting water tank, followed by further cooling in a 15°C spray cooling water tank. Subsequently, it was drawn, marked, and wound into a coil to obtain a standard three-layer co-extruded PVC pipe with an outer diameter of 32mm and a wall thickness of 1.8mm.

[0069] The following is a comparison of the performance of Examples 1, 2, and 3 with Comparative Example 1, as shown in Table 1: Table 1 As shown in Table 1, the three embodiments of the present invention exhibit significant technical advantages compared to Comparative Example 1. Regarding interlayer bonding strength, the peel strengths of Examples 1, 2, and 3 reached 8.2 N / cm, 9.1 N / cm, and 7.5 N / cm, respectively, an improvement over the 3.4 N / cm of Comparative Example 1. This verifies that the present invention, through the post-injection of glycidyl methacrylate and the interfacial chemical reaction with the hot melt adhesive layer, successfully generates in-situ chemical bonds between the layers, elevating the traditional multilayer pipe's reliance on physical entanglement to molecular-level connections, thus solving the problem of insufficient interlayer bonding strength. Regarding thermal shrinkage, Examples 1, 2, and 3 were 1.8%, 1.5%, and 2.2%, respectively, a reduction compared to the 4.5% of Comparative Example 1. This demonstrates that the present invention, through the gradient distribution of plasticizers and stress release in the high-temperature maintenance zone, effectively solves the problem of residual internal stress caused by mismatched coefficients of thermal expansion, significantly improving the dimensional stability of the pipe during temperature changes. Regarding aging resistance, the aging color difference ΔE of Examples 1, 2, and 3 were 2.3, 2.1, and 2.6, respectively, which were lower than the 5.8 of Comparative Example 1. The impact strength retention rates after aging were 92%, 94%, and 89%, respectively, which were higher than the 62% of Comparative Example 1. This indicates that the triple synergistic protection system composed of the ultraviolet absorber, rutile nano-titanium dioxide, and hindered amine light stabilizer in the outer layer, along with the stable interfacial chemical bonding during aging, avoids the problem of interfacial tensile stress concentration caused by photo-oxidative degradation of the outer layer. Furthermore, the volume resistivity of the three examples was 5.2 × 10⁻⁶. 4 Ω·cm, 3.8×10 4 Ω·cm and 7.6×10 4 Ω·cm, both reaching the semi-conductive range, can effectively dissipate static electricity generated by cable operation, while the traditional comparative example 1 is an insulator (>10 Ω·cm). 12 (Ω·cm), lacking electrostatic discharge function, which is an additional technical effect brought by the present invention. Comparison among the various embodiments shows that Example 2, due to its highest plasticizer ratio, highest glycidyl methacrylate injection amount, and strongest outer layer protection, exhibits the best performance in terms of interlayer bonding, heat shrinkage rate, and aging resistance. Although the indicators of Example 3 are slightly lower than those of Examples 1 and 2, they are still significantly better than Comparative Example 1, proving that the formulation range and process parameter window provided by the present invention are reasonable and operable, and different values ​​can achieve technical effects superior to the prior art.

[0070] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a UV-resistant photovoltaic PVC pipe, characterized in that, The preparation method specifically includes the following steps: Step S1: Prepare dry mix a, dry mix b, dry mix c and dry mix d according to the dry mix base material; wherein, dry mix a includes a conductive agent, dry mix c includes a reactive compatibilizer and dry mix d includes an ultraviolet shielding agent. Step S2: After melting dry mix a and dry mix b separately, they are co-extruded to obtain a double-layer substrate tube a. Then, hot melt adhesive is applied to the surface of substrate tube a to obtain substrate tube b. Step S3: Obtain melt c and melt d containing the mixture from dry mix c and dry mix d respectively. Then, coat melt c and melt d onto the surface of the base tube b by co-extrusion to obtain composite tube blank a. Step S4: The composite tube blank a is subjected to high-temperature treatment, cooling and shaping and post-treatment in sequence to obtain UV-resistant photovoltaic PVC pipe.

2. The method for preparing the UV-resistant photovoltaic PVC pipe according to claim 1, characterized in that, Step S1 specifically includes the following steps: Step S11: Mix PVC resin, stabilizer and lubricant to obtain dry mix base material; Step S12: Mix the dry mixture base material with powder a, powder b, powder c, and powder d respectively, and then mix them at 115-120℃ and ≤40℃ in sequence to obtain dry mixture a, dry mixture b, dry mixture c, and dry mixture d.

3. The method for preparing the UV-resistant photovoltaic PVC pipe according to claim 2, characterized in that, In step S11, by weight fraction, the PVC resin is 100 parts, the stabilizer is 4-6 parts, the lubricant is 1-2 parts, the stabilizer is a calcium-zinc composite stabilizer, and the lubricant is a stearic acid lubricant. In step S12, by weight fraction, powder a comprises 43-47 parts of polyester plasticizer and 10-14 parts of conductive acetylene black, wherein the specific surface area of ​​the conductive acetylene black is 60-70 m². 2 / g; Powder b includes 43-47 parts of polyester plasticizer; Powder c includes 38-42 parts of polyester plasticizer, 13-17 parts of maleic anhydride-grafted PVC and 2-4 parts of organically modified nano-montmorillonite, wherein the grafting rate of maleic anhydride-grafted PVC is 1.0-1.5%; the organically modified nano-montmorillonite is modified with dioctadecyl dimethyl ammonium chloride; Powder d includes 33-37 parts of polyester plasticizer, 5-7 parts of rutile nano-titanium dioxide, 0.4-0.6 parts of ultraviolet absorber and 0.2-0.4 parts of hindered amine light stabilizer, wherein the average particle size of rutile nano-titanium dioxide is 0.2-0.3 μm.

4. The method for preparing the UV-resistant photovoltaic PVC pipe according to claim 1, characterized in that, Step S2 specifically includes the following steps: Step S21: Dry mix a and dry mix b are respectively fed into the extruder to melt, to obtain melt a and melt b. Then melt a and melt b are introduced into the corresponding four-layer co-extrusion die to obtain the base material tube a. Step S22: First, load the hot melt adhesive into the coating machine and raise the temperature of the coating machine head to 110-120℃; then, pull the cooled and shaped substrate tube a through the coating machine head, so that the molten hot melt adhesive is coated on the surface of the substrate tube a, and after cooling, a substrate tube b with a thin layer is obtained.

5. The method for preparing the UV-resistant photovoltaic PVC pipe according to claim 4, characterized in that, In step S21, the double-layered substrate tube a includes an inner tube blank and an outer tube blank; wherein, melt a forms the inner tube blank and melt b forms the outer tube blank. In step S22, the hot melt adhesive is a polyurethane hot melt adhesive with a softening point ≥120℃ and a melt viscosity of 5000-10000mPa·s; the thickness of the thin layer is 20-30μm.

6. The method for preparing the UV-resistant photovoltaic PVC pipe according to claim 1, characterized in that, Step S3 specifically includes the following steps: Step S31: Mix glycidyl methacrylate and polymerization inhibitor evenly to obtain a mixture; Step S32: The dry mixture c is fed into the extruder to melt, and the mixture is injected into the melt corresponding to the dry mixture c at the end of the metering section of the extruder. Then the melt containing the mixture is passed into a static mixer to mix and obtain melt c. Step S33: The dry mixture d is put into the extruder to melt and obtain melt d. Then the substrate tube b is moved into the corresponding four-layer co-extrusion die, and melt c and melt d are introduced into the corresponding four-layer co-extrusion die at the same time, so that melt c and melt d successively cover the surface of the substrate tube b to obtain composite tube blank a.

7. The method for preparing the UV-resistant photovoltaic PVC pipe according to claim 6, characterized in that, In step S31, the amount of glycidyl methacrylate is 95 parts by weight and the amount of polymerization inhibitor is 4-6 parts by weight; the polymerization inhibitor is hydroquinone polymerization inhibitor. In step S32, the injection amount of the mixture is 2.0-2.5% of the mass of the dry mixture c; the temperature of the static mixer is 165-175℃, and the residence time of the melt containing the mixture in the static mixer is 40-60s; In step S33, the composite tube blank a includes an inner layer and an outer layer formed sequentially on the surface of the base tube b, wherein the inner layer is formed by melt c and the outer layer is formed by melt d, the wall thickness of the inner layer accounts for 20-25% of the total wall thickness of the composite tube blank a, and the wall thickness of the outer layer accounts for 30-35% of the total wall thickness of the composite tube blank a.

8. The method for preparing the UV-resistant photovoltaic PVC pipe according to claim 1, characterized in that, Step S4 specifically includes the following steps: Step S41: Pass the composite tube blank a through a 3-4m high temperature maintenance zone within 22-48s to maintain the surface temperature of the composite tube blank a at the first temperature, thereby obtaining the composite tube blank b. Step S42: Pass the composite tube blank b through the vacuum shaping water tank and the spray cooling water tank in sequence to obtain the composite tube blank c; Step S43: The composite tube blank c is pulled, marked and wound to obtain a semi-finished tube; the semi-finished tube is then stored at room temperature and humidity 40-70%RH for more than 72 hours to obtain a UV-resistant photovoltaic PVC pipe.

9. The method for preparing the UV-resistant photovoltaic PVC pipe according to claim 8, characterized in that, In step S41, the first temperature is 160-165℃; In step S42, the temperature of the vacuum shaping water tank is 50-60℃, and the temperature of the spray cooling water tank is 15-21℃.

10. A UV-resistant photovoltaic PVC pipe, characterized in that, The UV-resistant photovoltaic PVC pipe is obtained by the preparation method as described in any one of claims 1-9.

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