Polyolefin insulation pipe and method for manufacturing the same

Abstract

The application discloses a kind of polyolefin heat preservation pipe and preparation method thereof, belong to polyolefin pipe technical field.The application adopts low-density polyethylene A, low-density polyethylene B and metallocene polyethylene as resin system, which helps to limit cell growth, and adds specially-made carbon dioxide nucleating agent, the carbon dioxide nucleating agent treated by modification forms a homogeneous system saturated with supercritical carbon dioxide, under supercritical carbon dioxide foaming process, forms a cell structure with uniform cells, high density and high closed cell rate, which is beneficial to improve the heat preservation performance, and the peeling is not easy to leave glue, which is beneficial to installation and use.In addition, the outer protective layer uses ethylene-vinyl acetate copolymer or polyethylene resin as main material, and the weather-resistant master batch in the weather-resistant master batch interacts with the composite antioxidant and the ultraviolet absorbent, and the crosslinking agent enhances the molecular chain network, which significantly improves the anti-aging performance, so that the pipeline has significant weather resistance.

Description

Technical Field

[0001] This invention relates to the field of polyolefin pipe technology, and more specifically, to a polyolefin insulated pipe and its preparation method. Background Technology

[0002] Polyolefin pipes are widely used in building hot and cold water supply systems due to their excellent overall performance. However, when transporting cold water, condensation easily forms on the outer wall of polyolefin pipes, damaging the decorative layer; when transporting hot water, heat loss is significant, reducing energy efficiency. Therefore, insulation treatment for polyolefin pipes is a common requirement in the industry.

[0003] For example, in the case of PPR pipes, a type of polyolefin pipe, the mainstream PPR pipe insulation solutions on the market mainly fall into two categories: First, after the PPR working pipe is installed, an EPE pearl cotton insulation pipe or a rubber-plastic insulation pipe is then installed, or the manufacturer performs the casing / wrapping prefabrication in a subsequent process. However, this method results in gaps between the insulation layer and the working pipe, leading to a loose bond. Air seepage into these gaps not only causes secondary condensation, reducing insulation efficiency, but also makes construction inconvenient due to pipe slippage during hot-melt socket connections. Second, a foaming agent is used to produce polyolefin insulation pipes through an online synchronous foaming molding process, achieving integration of the insulation layer and the outer protective layer. However, the existing technology still needs to improve the control of foam cell quality and the interlayer bonding strength. After the insulation layer is peeled off from the inner pipe, a large amount of adhesive residue remains on the surface of the inner pipe, affecting the processing and utilization of the pipe material. For example, Chinese patent application number CN201611183366.2 discloses a PPR insulation composite pipe for home decoration and its preparation method, which uses a post-coating foamed polyethylene insulation layer process. Furthermore, this solution involves first cutting the manufactured insulation pipe axially and then wrapping it around the PP-R inner pipe. Then, a hot melt welding gun is used to weld the axially cut opening and extrude the outer protective layer. This is a post-wrapping insulation pipe process, which is relatively complex.

[0004] Supercritical carbon dioxide foaming technology, as a green and safe physical foaming technology, has attracted attention due to the non-flammable, environmentally friendly, and non-toxic nature of its foaming agent. While existing technologies also utilize this technology for plastic foaming, it is primarily used in planar products, and its application in pipelines, especially integrated PPR insulated pipes, remains largely unexplored. For example, Chinese patent application CN202511228418.2 discloses a method for preparing supercritical carbon dioxide thermosetting polyurethane foam, resulting in foam with uniform and stable pore size, while also meeting the requirements of high strength, wear resistance, high temperature resistance, and corrosion resistance. However, there is still room for improvement in the integration of this material with pipes.

[0005] Therefore, it is of great significance to achieve efficient co-extrusion and firm bonding of polyolefin working tube, foamed insulation layer and outer protective layer; and to avoid problems such as cell merging and collapse during foaming, so as to obtain a stable and uniform cell structure to achieve long-term reliable insulation performance. Summary of the Invention

[0006] In view of this, in order to solve one of the above-mentioned technical problems, the present invention provides a polyolefin insulation pipe and its preparation method, the specific technical solution of which is as follows:

[0007] A polyolefin insulation pipe, comprising a polyolefin inner tube, an insulation layer and an outer protective layer, wherein the insulation layer is prepared by a supercritical carbon dioxide foaming process.

[0008] The insulation layer comprises the following raw materials in parts by weight:

[0009] Low-density polyethylene A 60-80 parts, low-density polyethylene B 15-20 parts, metallocene polyethylene 5-20 parts, carbon dioxide nucleating agent 0.1-1 part, foaming agent 0.1-0.3 parts, foaming regulator 0.01-0.05 parts, dispersant 0.2-0.8 parts;

[0010] The outer protective layer comprises the following raw materials in parts by weight:

[0011] 100 parts of ethylene vinyl acetate copolymer and / or polyethylene resin, 1-15 parts of weather-resistant masterbatch, 1-3 parts of brightener and 1-3 parts of color masterbatch;

[0012] The weather-resistant masterbatch is prepared from a carrier resin, a crosslinking agent, a composite antioxidant, a stabilizer, an anti-ultraviolet absorber, and a lubricant in a mass ratio of (45-50):(3-9):(1-3):(0.1-1):(1-7):(0.5-1).

[0013] Furthermore, the preparation method of the carbonyl nucleating agent is as follows:

[0014] Talc powder was dispersed in a dilute alkaline solution and stirred at 50-100 rpm for 20-60 minutes. After washing until neutral, it was dispersed in an ethanol aqueous solution, and nano-silica was added. The mixture was stirred at 100-200 rpm for 30-60 minutes, centrifuged, washed, and then dispersed in a silane coupling agent. Polypropylene glycol and dibutyltin dilaurate were then added, and the mixture was reacted at 70-85℃ for 1-5 hours. After multiple washings, the mixture was dried to obtain the final product.

[0015] Furthermore, under the conditions of 190℃ and 2.16kg, the melt index of the low-density polyethylene A is 4-6 g / 10min, and the melt index of the low-density polyethylene B is 6-8 g / 10min.

[0016] Furthermore, the foaming agent is at least one of azodicarbonamide and sodium bicarbonate;

[0017] The foaming regulator is at least one of dioctyl phthalate and fatty alcohol polyoxyethylene;

[0018] The dispersant is at least one of ethylene bis-stearamide and stearic acid.

[0019] Furthermore, the vinyl acetate content in the ethylene vinyl acetate copolymer is 5%-15% by mass.

[0020] Furthermore, the carrier resin is at least one of polyethylene resin and polypropylene resin;

[0021] The crosslinking agent is at least one of pentaerythritol triacrylate, ethoxylated trimethylolpropane triacrylate, and maleic anhydride.

[0022] Furthermore, the composite antioxidant is obtained by mixing bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite and 5,7-di-tert-butyl-3-(3,4-dimethylphenyl)benzofuran-2(3H)-one in a mass ratio of (3-6):(4-7).

[0023] Further, the stabilizer is at least one of 3,5-di-tert-butyl-4-hydroxybenzoate n-hexadecyl ester and dioctyltin maleate.

[0024] Further, the UV absorber is at least one of 2,4-bis(2,4-dimethylyl)-6-(2-hydroxy-4-n-octyloxophenyl)-1,3,5-triazine, 2,4-bis(4-biphenyl)-6-(2,4-dihydroxy)phenyl-1,3,5-triazine, and 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole.

[0025] In addition, the present invention also provides a method for preparing a polyolefin insulation pipe, the method comprising the following steps:

[0026] S1. Dry the surface of the molded polyolefin inner tube;

[0027] S2. Add the raw materials for the preparation of the insulation layer to the extrusion equipment. After plasticizing and melting at a temperature of 150℃-170℃ in the front section of the extruder, inject CO2 from the middle section of the extruder. After the CO2 and the plasticized and melted material are mixed evenly, the temperature is gradually reduced to 120℃-135℃ to obtain the insulation layer melt material. The insulation layer melt material enters the composite mold.

[0028] The supercritical carbon dioxide foaming process conditions are as follows: the supercritical carbon dioxide injection pressure is 15MPa-25MPa.

[0029] S3. After the raw materials for the preparation of the outer protective layer are mixed evenly, they are added to the outer layer extruder. After plasticizing and melting, the outer protective layer melt material is obtained and enters the composite mold.

[0030] S4. The molten insulation material from step S2 and the molten outer protective layer material from step S3 are combined in a composite mold and then wrapped around the surface-dried polyolefin inner tube described in step S1, which passes through the composite mold. After cooling, the insulation layer forms uniform pores, thus producing a polyolefin insulation pipe.

[0031] Compared with existing technologies, its beneficial effects include:

[0032] 1. This invention uses low-density polyethylene A, low-density polyethylene B, and metallocene polyethylene as the resin system. Uniform swelling can be achieved without the addition of compatibilizers. The addition of an appropriate amount of metallocene polyethylene also helps to form crystal nuclei. The interface between the crystalline and amorphous regions has a lower nucleation energy barrier, thereby inducing heterogeneous nucleation of cells. It also helps to limit the excessive growth of cells, which is beneficial for controlling cell size, increasing cell density, and preventing cell rupture, collapse, and cell coalescence.

[0033] 2. This invention incorporates a specially formulated carbon dioxide nucleating agent. This modified carbon dioxide nucleating agent allows the resin system and the carbon dioxide nucleating agent to diffuse and adsorb more carbon dioxide during the preparation of the insulation layer, forming a supercritical carbon dioxide-saturated homogeneous system. Under supercritical carbon dioxide foaming technology, this results in a uniform, dense, and highly closed-cell structure, which improves insulation performance. It also prevents adhesive residue after peeling, facilitating installation and use. Furthermore, when peeling off the insulation layer from the joint section, the insulation material is less likely to remain on the outer surface of the polyolefin pipe, making the hot-melt socket connection safer. Additionally, the addition of polypropylene glycol during the preparation of the carbon dioxide nucleating agent helps improve the strength of the cell walls, preventing cell collapse and coalescence during growth, thereby promoting a higher closed-cell ratio insulation layer and further ensuring insulation performance.

[0034] 3. The insulation layer prepared by this invention has a better bonding interface with the polyolefin inner tube, making it less likely to leave adhesive residue after peeling, which is beneficial for installation and use.

[0035] 4. The outer protective layer of the present invention uses ethylene vinyl acetate copolymer and / or polyethylene resin and weather-resistant masterbatch as the main materials. The weather-resistant masterbatch is enhanced by the interaction of composite antioxidants and UV absorbers, and the molecular chain network is strengthened by crosslinking agents, which significantly improves the anti-aging performance and makes the pipe have significant weather resistance. Attached Figure Description

[0036] The invention will be further understood from the following description taken in conjunction with the accompanying drawings. The components in the drawings are not necessarily drawn to scale, but rather the emphasis is on illustrating the principles of the embodiments. In different views, the same reference numerals designate corresponding parts.

[0037] Figure 1 This is a schematic diagram of the structure of the insulation layer prepared in Example 1 of this invention. Figure 1 ;

[0038] Figure 2 This is a schematic diagram of the structure of the insulation layer prepared in Embodiment 1 of the present invention. Figure 2 ;

[0039] Figure 3 This is a schematic diagram of the product structure of the polyolefin insulation pipe prepared in Example 1 of the present invention;

[0040] Figure 4 Part a in the diagram is a schematic diagram of the anti-fogging test of the polyolefin insulation pipe prepared in Example 1 of the present invention. Figure 4 Part b in the diagram is a schematic diagram of the anti-fogging test of the polyolefin insulation pipe prepared in Comparative Example 2.

[0041] Figure 5 Part c is a schematic diagram of the peelable insulation layer and outer protective layer of the polyolefin insulation pipe prepared in Example 1 of the present invention. Figure 5 Part d in the diagram is a schematic diagram of the peeled insulation layer and outer protective layer of the polyolefin insulation pipe prepared in Comparative Example 1.

[0042] Explanation of reference numerals in the attached figures:

[0043] 1-Polyolefin inner tube; 2-Insulation layer; 3-Outer protective layer. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to its embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of the invention.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. It should be noted that, unless otherwise specified, all raw materials not described in detail in this invention are commercially available, and any processes not mentioned are considered prior art.

[0046] An embodiment of the present invention provides a polyolefin insulation pipe, which includes a polyolefin inner tube, an insulation layer, and an outer protective layer. The preparation process of the insulation layer includes a supercritical carbon dioxide foaming process.

[0047] The insulation layer comprises the following raw materials in parts by weight:

[0048] Low-density polyethylene A 60-80 parts, low-density polyethylene B 15-20 parts, metallocene polyethylene 5-20 parts, carbon dioxide nucleating agent 0.1-1 part, foaming agent 0.1-0.3 parts, foaming regulator 0.01-0.05 parts, dispersant 0.2-0.8 parts;

[0049] The outer protective layer comprises the following raw materials in parts by weight:

[0050] 100 parts of ethylene vinyl acetate copolymer and / or polyethylene resin, 1-15 parts of weather-resistant masterbatch, 1-3 parts of brightener and 1-3 parts of color masterbatch;

[0051] The weather-resistant masterbatch is prepared from a carrier resin, a crosslinking agent, a composite antioxidant, a stabilizer, an anti-ultraviolet absorber, and a lubricant in a mass ratio of (45-50):(3-9):(1-3):(0.1-1):(1-7):(0.5-1).

[0052] In one embodiment, the method for preparing the carbonyl nucleating agent is as follows:

[0053] Talc powder was dispersed in a dilute alkaline solution and stirred at 50-100 rpm for 20-60 minutes. After washing until neutral, it was dispersed in an ethanol aqueous solution, and nano-silica was added. The mixture was stirred at 100-200 rpm for 30-60 minutes, centrifuged, washed, and then dispersed in a silane coupling agent. Polypropylene glycol and dibutyltin dilaurate were then added, and the mixture was reacted at 70-85℃ for 1-5 hours. After multiple washings, the mixture was dried to obtain the final product.

[0054] In one embodiment, the weight ratio of talc, aqueous ethanol solution, nano silica, silane coupling agent, polypropylene glycol and dibutyltin dilaurate is (9-15):(20-25):(3-7):(15-20):(2-7):(0.1-2).

[0055] In one embodiment, the weight ratio of the talc powder to the dilute alkaline aqueous solution is (9-15):(25-50).

[0056] In one embodiment, the talc powder has a particle size D90 of 10μm-50μm, a whiteness of ≥90%, and a silica content of ≥60%.

[0057] In one embodiment, the dilute alkaline solution is a sodium hydroxide solution, and the sodium hydroxide solution contains 2%-8% sodium hydroxide by mass.

[0058] In one embodiment, the ethanol aqueous solution contains 20%-50% ethanol by mass.

[0059] In one embodiment, the silane coupling agent is at least one of 11-aminoundecyltriethoxysilane and n-octadecyltrimethoxysilane.

[0060] In one embodiment, the particle size of the carbonyl nucleating agent is 10 nm-200 nm.

[0061] In one embodiment, at 190°C and 2.16 kg, the melt index of the low-density polyethylene A is 4-6 g / 10 min, and the melt index of the low-density polyethylene B is 6-8 g / 10 min.

[0062] In one embodiment, the low-density polyethylene A has a number-average molecular weight of 17,000-18,000 and a weight-average molecular weight of 100,000-120,000.

[0063] In one embodiment, the low-density polyethylene B has a number-average molecular weight of 20,000-21,000 and a weight-average molecular weight of 90,000-100,000.

[0064] In one embodiment, the foaming agent is at least one of azodicarbonamide and sodium bicarbonate;

[0065] The foaming regulator is at least one of dioctyl phthalate and fatty alcohol polyoxyethylene;

[0066] The dispersant is at least one of ethylene bis-stearamide and stearic acid.

[0067] In one embodiment, the vinyl acetate copolymer contains 5%-15% by mass of vinyl acetate.

[0068] In one embodiment, the carrier resin is at least one of polyethylene resin and polypropylene resin;

[0069] The crosslinking agent is at least one of pentaerythritol triacrylate, ethoxylated trimethylolpropane triacrylate, and maleic anhydride.

[0070] In one embodiment, the composite antioxidant is obtained by mixing bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite and 5,7-di-tert-butyl-3-(3,4-dimethylphenyl)benzofuran-2(3H)-one in a mass ratio of (3-6):(4-7).

[0071] In one embodiment, the stabilizer is at least one of hexadecyl 3,5-di-tert-butyl-4-hydroxybenzoate and dioctyltin maleate.

[0072] In one embodiment, the UV absorber is at least one of 2,4-bis(2,4-dimethylyl)-6-(2-hydroxy-4-n-octyloxophenyl)-1,3,5-triazine, 2,4-bis(4-biphenyl)-6-(2,4-dihydroxy)phenyl-1,3,5-triazine, and 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole;

[0073] In one embodiment, the lubricant is at least one of oxidized polyethylene wax, calcium stearate, and paraffin wax.

[0074] In one embodiment, the brightener is microcrystalline wax.

[0075] In one embodiment, the weather-resistant masterbatch is prepared by sequentially adding a carrier resin, a crosslinking agent, a composite antioxidant, a stabilizer, an anti-ultraviolet absorber, and a lubricant into an extruder, followed by melt extrusion, cooling, and granulation to obtain the weather-resistant masterbatch.

[0076] In one embodiment, during the preparation of weather-resistant masterbatch, the temperature of the first zone of melt extrusion is 150℃-160℃, the temperature of the second to fourth zones is 170℃-190℃, the temperature of the fifth zone is 175℃-180℃, and the temperature of the die head is 180℃-185℃.

[0077] In one embodiment, the present invention also provides a method for preparing a polyolefin insulation pipe, the method comprising the following steps:

[0078] S1. Dry the surface of the molded polyolefin inner tube;

[0079] S2. Add the raw materials for the preparation of the insulation layer to the extrusion equipment. After plasticizing and melting at a temperature of 150℃-170℃ in the front section of the extruder, inject CO2 from the middle section of the extruder. After the CO2 and the plasticized and melted material are mixed evenly, the temperature is gradually reduced to 120℃-135℃ to obtain the insulation layer melt material. The insulation layer melt material enters the composite mold.

[0080] The supercritical carbon dioxide foaming process conditions are as follows: the supercritical carbon dioxide injection pressure is 15MPa-25MPa.

[0081] S3. After the raw materials for the preparation of the outer protective layer are mixed evenly, they are added to the outer layer extruder. After plasticizing and melting, the outer protective layer melt material is obtained and enters the composite mold.

[0082] S4. The molten insulation material from step S2 and the molten outer protective layer material from step S3 are combined in a composite mold and then wrapped around the surface-dried polyolefin inner tube described in step S1, which passes through the composite mold. After cooling, the insulation layer forms uniform pores, thus producing a polyolefin insulation pipe.

[0083] In one embodiment, the polyolefin inner tube is a polyolefin all-plastic pipe or composite pipe of random copolymer polypropylene (PPR), polypropylene (PP), heat-resistant polyethylene (PE-RT), cross-linked polyethylene (PE-X), PE (polyethylene), or PB (polybutene).

[0084] In one embodiment, in step S3, the temperature of the plasticizing melt is 180°C-220°C.

[0085] In one embodiment, in step S3, the axial shear strength of the insulation layer is ≥20 kPa.

[0086] In one embodiment, the outer diameter of the polyolefin inner tube is 20-30 mm.

[0087] In one embodiment, the thickness of the insulation layer is 3-10 mm.

[0088] In one embodiment, the thickness of the outer protective layer is 0.2-0.5 mm.

[0089] The above-mentioned solution, through the optimization of components and the improvement of processes, works synergistically to obtain polyolefin insulation pipes with excellent overall performance.

[0090] The implementation schemes of the present invention will now be described in detail with reference to specific embodiments.

[0091] It should be noted that the polyolefin inner tubes in the following examples are existing products. For the sake of experimental consistency, the polyolefin inner tubes used in the examples and comparative examples are the same products, namely PPR inner tubes, and their composition and process are not described in detail.

[0092] Example 1:

[0093] A method for preparing a polyolefin thermal insulation pipe includes the following steps:

[0094] S1. Dry the surface of the molded polyolefin inner tube;

[0095] S2. By weight ratio, 75 parts of low-density polyethylene A, 15 parts of low-density polyethylene B, 10 parts of metallocene polyethylene, 0.4 parts of carbon dioxide nucleating agent, 0.2 parts of azodicarbonamide, 0.03 parts of dioctyl phthalate and 0.5 parts of stearic acid are added to the extrusion equipment. After plasticizing and melting at 150℃-170℃ in the front section of the extruder, CO2 is injected from the middle section of the extruder. After the CO2 is mixed evenly with the plasticized and melted material, the temperature is gradually reduced to 120℃-135℃ to obtain the thermal insulation layer melt material. The thermal insulation layer melt material enters the composite mold.

[0096] In this process, 12 parts by weight of talc powder were dispersed in 30 parts by weight of a 3% dilute alkaline solution, stirred at 50 r / min for 30 min, washed until neutral, and then dispersed in 25 parts by weight of a 20% ethanol aqueous solution. 5 parts by weight of nano-silica were added, and the mixture was stirred at 100 r / min for 35 min. After centrifugation and washing, the mixture was dispersed in 15 parts by weight of n-octadecyltrimethoxysilane, and 5 parts by weight of polypropylene glycol and 0.5 parts by weight of dibutyltin dilaurate were added. The mixture was reacted at 75 °C for 3 h. After multiple washings, the mixture was dried to obtain a carbon dioxide-loving nucleating agent.

[0097] The supercritical carbon dioxide foaming process conditions are as follows: the supercritical carbon dioxide injection pressure is 18.9 MPa;

[0098] S3. According to the weight ratio, 100 parts of ethylene vinyl acetate copolymer, 10 parts of weather-resistant masterbatch, 1 part of microcrystalline wax and 1 part of color masterbatch are mixed evenly and added to the extruder. The mixture is plasticized and melted at a temperature of 200°C to obtain the outer protective layer melt material. The outer protective layer melt material enters the composite mold.

[0099] The preparation method of the weather-resistant masterbatch is as follows: 50 parts by weight of polyethylene resin, 7 parts by weight of pentaerythritol triacrylate, 3 parts by weight of composite antioxidant (obtained by mixing bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite and 5,7-di-tert-butyl-3-(3,4-dimethylphenyl)benzofuran-2(3H)-one in a mass ratio of 1.2:1.8), 0.5 parts by weight of 3,5-di-tert-butyl-4-hydroxybenzoic acid n-hexadecyl ester, 3 parts by weight of 2,4-bis(2,4-xylyl)-6-(2-hydroxy-4-n-octyloxophenyl)-1,3,5-triazine and 0.7 parts by weight of calcium stearate are sequentially added to an extruder. The extrusion is performed by melt extrusion, with the temperature of the first zone being 155°C, the temperature of the second to fourth zones being 185°C, the temperature of the fifth zone being 175°C, and the temperature of the die head being 180°C. After cooling, the mixture is granulated to obtain the weather-resistant masterbatch.

[0100] S4. The molten insulation material from step S2 and the molten outer protective layer material from step S3 are combined in a composite mold and then wrapped around the surface-dried polyolefin inner tube described in step S1, which passes through the composite mold. After cooling, the insulation layer forms uniform pores, thus producing a polyolefin insulation pipe.

[0101] Example 2:

[0102] The difference between Example 2 and Example 1 is that the ratio of raw materials for preparing the insulation layer (molten insulation layer) in step S2 of Example 2 is different, while the rest is the same as in Example 1.

[0103] The preparation method of the insulation layer (molten insulation material) in Example 2 is as follows:

[0104] By weight, 78 parts of low-density polyethylene A, 15 parts of low-density polyethylene B, 7 parts of metallocene polyethylene, 0.5 parts of carbon dioxide nucleating agent, 0.2 parts of azodicarbonamide, 0.03 parts of dioctyl phthalate, and 0.5 parts of stearic acid are added to the extrusion equipment. After plasticizing and melting at 150℃-170℃ in the front section of the extruder, CO2 is injected from the middle section of the extruder. After the CO2 is mixed evenly with the plasticized and melted material, the temperature is gradually reduced to 120℃-135℃ to obtain the thermal insulation layer melt material, which then enters the composite mold.

[0105] Example 3:

[0106] The difference between Example 3 and Example 1 is that the supercritical carbon dioxide foaming process conditions are different in Example 3, but otherwise they are the same as in Example 1.

[0107] In Example 3, the supercritical carbon dioxide foaming process conditions were as follows: the supercritical carbon dioxide injection pressure was 19.2 MPa.

[0108] Comparative Example 1:

[0109] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses a single low-density polyethylene A with a weight ratio of 100 parts, that is, without the addition of low-density polyethylene B and metallocene polyethylene, while the rest is the same as Example 1.

[0110] Comparative Example 2:

[0111] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses a single metallocene polyethylene with a weight ratio of 100 parts, that is, without the addition of low-density polyethylene A and low-density polyethylene B, while the rest is the same as Example 1.

[0112] Comparative Example 3:

[0113] The difference between Comparative Example 3 and Example 1 is that conventional talc powder was used to replace the carbonyl nucleating agent of the present invention in Comparative Example 3, while the rest was the same as in Example 1.

[0114] Comparative Example 4:

[0115] The difference between Comparative Example 4 and Example 1 is that the preparation method of the carbonyl nucleating agent in Comparative Example 4 is different, while the rest is the same as in Example 1.

[0116] The preparation method of the carbon dioxide-loving nucleating agent in Comparative Example 4 is as follows: 12 parts by weight of talc powder are dispersed in 20 parts by weight of n-octadecyltrimethoxysilane, stirred at 75°C for 3 hours, washed multiple times, and dried to obtain the nucleating agent.

[0117] Comparative Example 5:

[0118] The difference between Comparative Example 5 and Example 1 is that the supercritical carbon dioxide foaming process conditions in Comparative Example 5 are different from those in Example 1, while the other conditions are the same as those in Example 1.

[0119] The supercritical carbon dioxide foaming process conditions described in Comparative Example 5 are as follows: the input pressure of supercritical carbon dioxide is 12.5 MPa.

[0120] Comparative Example 6:

[0121] The difference between Comparative Example 6 and Example 1 is that the supercritical carbon dioxide foaming process conditions in Comparative Example 6 are different from those in Example 1, while the rest are the same as in Example 1.

[0122] The supercritical carbon dioxide foaming process conditions described in Comparative Example 6 are as follows: the input pressure of supercritical carbon dioxide is 28 MPa.

[0123] Comparative Example 7:

[0124] Compared with Example 1, Comparative Example 7 differs in that the outer sheath in Comparative Example 7 uses polyurethane resin instead of ethylene vinyl acetate copolymer, while the rest is the same as in Example 1.

[0125] Comparative Example 8:

[0126] The difference between Comparative Example 8 and Example 1 is that the weather-resistant masterbatch in Comparative Example 8 did not contain a composite antioxidant, but otherwise it was the same as Example 1.

[0127] Comparative Example 9:

[0128] The difference between Comparative Example 9 and Example 1 is that no weather-resistant masterbatch was added in Comparative Example 9, but otherwise it is the same as Example 1.

[0129] I. The physical dimensions of the polyolefin insulation pipe samples prepared in Examples 1-3 are shown in Table 1 below.

[0130] Table 1: Physical Dimensions (mm)

[0131]

[0132] II. Performance tests were conducted on the insulation layers of the polyolefin insulation pipe samples prepared in Examples 1-3 and the comparative samples prepared in Comparative Examples 1-6. Apparent density was tested according to GB / T6343-2009; thermal conductivity according to GB / T17794-2021; puncture strength according to GB / T21302-2007; and appearance was observed by the naked eye of those skilled in the art, with the aid of a microscope or magnifying glass when necessary. The results are shown in Table 2 below.

[0133] Table 2: Performance Test Results of Thermal Insulation Layer

[0134]

[0135] Analysis of the data in Table 2 shows that the present invention, by optimizing the composition of the insulation layer and the foaming process conditions, can obtain an insulation layer with uniform pores and a density within a suitable range. Compared with Example 1, Comparative Example 1 uses a single low-density polyethylene A, and Comparative Example 2 uses a single metallocene polyethylene, which leads to an imbalance in the resin melt system, high density, and affects the foaming effect, resulting in poor pore structure. Comparative Example 3 uses conventional talc to replace the carbon dioxide nucleating agent of the present invention, resulting in poor nucleation effect and inability to form uniform and fine pores, leading to a decrease in insulation performance. The preparation method of the carbon dioxide nucleating agent in Comparative Example 4 is different. The surface of the talc is not loaded with nano-silica, making its foaming effect worse than that of Example 1. However, the carbon dioxide nucleating agent prepared by the present invention is loaded with nano-silica, which is conducive to the formation of more nucleation sites. Its excellent compatibility makes it easier for CO2 to be adsorbed and enriched on the surface of the nucleating agent, which is beneficial to promoting the foaming effect. In Comparative Example 5, the low pressure resulted in insufficient foaming, leading to poor cell quality. In Comparative Example 6, the excessive pressure caused cell rupture, preventing the formation of more closed pores and affecting the cell structure. Rupture and collapse significantly impact the insulation performance of the insulation layer, indicating that a suitable foaming process helps to obtain an ideal insulation layer.

[0136] III. Since the outer protective layer of Comparative Examples 1 to 6 is the same as that of Example 1, only the insulation layer of the polyolefin insulation pipe samples prepared in Examples 1 to 3 and the comparative polyolefin insulation pipe samples prepared in Comparative Examples 7 to 9 were tested for weather resistance. The method was: accelerated aging with xenon lamp for 3500 hours, gloss retention rate (%). The results are shown in Table 3.

[0137] Table 3: Weather Resistance Test

[0138]

[0139] Analysis of the data in Table 3 shows that the outer protective layer of the present invention exhibits significant weather resistance. After 3500 hours of accelerated aging under a xenon lamp, no powdering phenomenon was observed on the surface. Compared with Example 1, the use of polyurethane resin to replace ethylene vinyl acetate copolymer in Comparative Example 7 did not have a greater impact on weather resistance than Comparative Example 8 and Comparative Example 9, but it was slightly worse than Example 1. This indicates that the optimized resin and weather-resistant masterbatch of the present invention can form a more compatible system, resulting in better weather resistance. The weather-resistant masterbatch in Comparative Example 8 did not contain a composite antioxidant, and the weather-resistant masterbatch in Comparative Example 9 did not contain any weather-resistant masterbatch, resulting in a significant decrease in weather resistance in Comparative Example 8 and Comparative Example 9. This indicates that the present invention, through the compounding of components, forms a better cross-linking system, and the addition of the weather-resistant masterbatch of the present invention can significantly improve the weather resistance of the outer protective layer, giving the polyolefin insulation pipe excellent weather resistance.

[0140] IV. The polyolefin insulation pipe samples of Examples 1-3 and the comparative samples of Comparative Examples 1-9 were subjected to hot and cold water circulation tests and anti-fogging tests. The hot and cold water circulation test was conducted in accordance with GB / T19993-2005. The anti-fogging test method was as follows: an ice-water mixture was injected into the pipe, both ends of the pipe were sealed, and the pipe was placed in a constant temperature and humidity test chamber at 35°C and 70% humidity for 20 minutes. Condensation was then observed on the corresponding polyolefin insulation pipe samples. The results are shown in Table 4.

[0141] Table 4: Results of Hot and Cold Water Circulation Test and Anti-fogging Test

[0142]

[0143] As can be seen from the data analysis in Table 4, changes in the performance of the insulation layer and the outer protective layer will also affect the overall application performance of the polyolefin insulation pipe. The polyolefin insulation pipe obtained by this invention has excellent overall performance and better applicability.

[0144] In addition, combined Figures 1-5 To further explain the technical solution of the present invention, Figure 1 This is a schematic diagram of the structure of the insulation layer prepared in Example 1 of this invention. Figure 1 ; Figure 2 This is a schematic diagram of the structure of the insulation layer prepared in Embodiment 1 of the present invention. Figure 2 ,from Figure 1 as well as Figure 2 As can be seen, the insulation layer prepared by the present invention has uniform closed pores and the overall quality of the foam cells is good. Figure 3 This is a schematic diagram of the product structure of the polyolefin insulation pipe prepared in Example 1 of the present invention, wherein 1 is the polyolefin inner tube, 2 is the insulation layer, and 3 is the outer protective layer. Figure 3 As can be seen from the above, the polyolefin inner tube 1, the insulation layer 2 and the outer protective layer 3 of the polyolefin insulation pipe prepared by the present invention are tightly bonded together, and the foam cells of the insulation layer are uniform, with good foaming quality and no problems of collapse or pore merging are observed. Figure 4 Part a in the diagram is a schematic diagram of the anti-fogging test of the polyolefin insulation pipe prepared in Example 1 of the present invention. Figure 4 Part b in the diagram is a schematic diagram of the anti-fogging test of the polyolefin insulation pipe prepared in Comparative Example 2. Figure 4 As can be seen from the results, the polyolefin insulation pipe of the present invention has excellent insulation performance and no obvious condensation during application, while Comparative Example 2 showed obvious condensation on its surface after testing. Figure 5 Part c is a schematic diagram of the peelable insulation layer and outer protective layer of the polyolefin insulation pipe prepared in Example 1 of the present invention. Figure 5 Part d in the diagram is a schematic diagram of the peeled insulation layer and outer protective layer of the polyolefin insulation pipe prepared in Comparative Example 1. Figure 5As can be seen from the peel test, the insulation layer of the polyolefin insulation pipe prepared in Example 1 did not adhere excessively to the surface of the polyolefin inner tube, and the surface was smooth, making it more convenient to use. The polyolefin insulation pipe prepared in Comparative Example 1 had more residual adhesive, which caused some obstruction during connection and affected the quality of the pipe. This shows that the present invention can balance insulation performance, strength and peelability by optimizing the composition of the insulation layer.

[0145] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0146] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A polyolefin insulation pipe, the polyolefin insulation pipe comprising a polyolefin inner tube, an insulation layer, and an outer protective layer, characterized in that, The preparation process of the insulation layer includes supercritical carbon dioxide foaming process; The insulation layer comprises the following raw materials in parts by weight: Low-density polyethylene A 60-80 parts, low-density polyethylene B 15-20 parts, metallocene polyethylene 5-20 parts, carbon dioxide nucleating agent 0.1-1 part, foaming agent 0.1-0.3 parts, foaming regulator 0.01-0.05 parts, dispersant 0.2-0.8 parts; Under conditions of 190℃ and 2.16 kg, the melt index of the low-density polyethylene A is 4-6 g / 10 min, and the melt index of the low-density polyethylene B is 6-8 g / 10 min; the number-average molecular weight of the low-density polyethylene A is 17,000-18,000, and the weight-average molecular weight is 100,000-120,000; the number-average molecular weight of the low-density polyethylene B is 20,000-21,000, and the weight-average molecular weight is 90,000-100,000. The preparation method of the carbonyl nucleating agent is as follows: Talc powder is dispersed in a sodium hydroxide solution, wherein the sodium hydroxide solution contains 2%-8% by mass. The mixture is stirred at 50-100 rpm for 20-60 minutes, washed until neutral, and then dispersed in an ethanol aqueous solution. Nano-silica is added, and the mixture is stirred at 100-200 rpm for 30-60 minutes. After centrifugation and washing, the mixture is dispersed in a silane coupling agent, and then polypropylene glycol and dibutyltin dilaurate are added. The mixture is reacted at 70-85°C for 1-5 hours. After multiple washings, the mixture is dried to obtain the final product. The outer protective layer comprises the following raw materials in parts by weight: 100 parts of ethylene vinyl acetate copolymer and / or polyethylene resin, 1-15 parts of weather-resistant masterbatch, 1-3 parts of brightener and 1-3 parts of color masterbatch; The weather-resistant masterbatch is prepared from a carrier resin, crosslinking agent, composite antioxidant, stabilizer, UV absorber, and lubricant in a mass ratio of (45-50):(3-9):(1-3):(0.1-1):(1-7):(0.5-1); the composite antioxidant is prepared from bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite and 5,7-di-tert-butyl-3-(3,4-dimethylphenyl)benzofuran-2 in a mass ratio of (3-6):(4-7). The mixture of (3H)-ketones is obtained; the stabilizer is at least one of 3,5-di-tert-butyl-4-hydroxybenzoate n-hexadecyl ester and dioctyltin maleate; the UV absorber is at least one of 2,4-bis(2,4-dimethylyl)-6-(2-hydroxy-4-n-octyloxophenyl)-1,3,5-triazine, 2,4-bis(4-biphenyl)-6-(2,4-dihydroxy)phenyl-1,3,5-triazine, and 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole.

2. The polyolefin insulation pipe according to claim 1, characterized in that, The foaming agent is at least one of azodicarbonamide and sodium bicarbonate; The foaming regulator is at least one of dioctyl phthalate and fatty alcohol polyoxyethylene; The dispersant is at least one of ethylene bis-stearamide and stearic acid.

3. The polyolefin insulation pipe according to claim 1, characterized in that, The vinyl acetate copolymer contains 5%-15% by mass.

4. The polyolefin insulation pipe according to claim 1, characterized in that, The carrier resin is at least one of polyethylene resin and polypropylene resin; The crosslinking agent is at least one of pentaerythritol triacrylate, ethoxylated trimethylolpropane triacrylate, and maleic anhydride.

5. A method for preparing a polyolefin thermal insulation pipe, characterized in that, The preparation method is used to prepare the polyolefin insulation pipe according to any one of claims 1 to 4, and the preparation method includes the following steps: S1. Dry the surface of the molded polyolefin inner tube; S2. Add the raw materials for the preparation of the insulation layer to the extrusion equipment. After plasticizing and melting at a temperature of 150℃-170℃ in the front section of the extruder, inject CO2 from the middle section of the extruder. After the CO2 and the plasticized and melted material are mixed evenly, the temperature is gradually reduced to 120℃-135℃ to obtain the insulation layer melt material. The insulation layer melt material enters the composite mold. The supercritical carbon dioxide foaming process conditions are as follows: the supercritical carbon dioxide injection pressure is 15MPa-25MPa. S3. After the raw materials for the preparation of the outer protective layer are mixed evenly, they are added to the outer layer extruder. After plasticizing and melting, the outer protective layer melt material is obtained and enters the composite mold. S4. The molten insulation material from step S2 and the molten outer protective layer material from step S3 are combined in a composite mold and then wrapped around the surface-dried polyolefin inner tube described in step S1, which passes through the composite mold. After cooling, the insulation layer forms uniform pores, thus producing a polyolefin insulation pipe.

Images