High-pressure-resistant heat-resistant PVC insulating electrical sleeve and preparation method thereof

Abstract

The application discloses a high-pressure-resistant and heat-resistant PVC insulating electrician sleeve and a preparation method thereof, and belongs to the technical field of PVC pipes for buildings. The high-pressure-resistant and heat-resistant PVC electrician sleeve comprises the following raw materials in parts by weight: 75-85 parts of PVC resin, 15-25 parts of maleic anhydride grafted CPVC, 2.5-3.5 parts of calcium-zinc stabilizer, 0.2-0.5 parts of internal lubricant, 0.4-1.2 parts of external lubricant, 25-40 parts of a mixture of EVA and furan-based semi-aromatic polyamide cross-linked modified calcium carbonate-mica powder, 0-3 parts of talc, 0.5-1.5 parts of impact-resistant ACR resin, 0.5-1.5 parts of silicone toughening agent, 2-4 parts of CPE, 0.1-0.3 parts of antioxidant, and 1-2 parts of rutile titanium white powder. The PVC insulating electrician sleeve has improved toughness, heat deformation resistance and impact resistance through optimized formula design.

Description

Technical Field

[0001] This invention belongs to the technical field of PVC pipes for building materials, specifically relating to a high-pressure-resistant and heat-resistant PVC insulating electrical conduit and its preparation method. Background Technology

[0002] PVC electrical conduit is an important type of conduit for electrical wiring inside buildings. It boasts advantages such as corrosion resistance, lightweight, and flexibility, and is widely used in concrete structures, between floors, and within walls. However, existing PVC electrical conduits still have some problems. First, due to the low toughness and poor impact resistance of PVC material, it is prone to brittle fracture during storage, transportation, installation, and use, especially at low temperatures. Second, traditional PVC electrical conduit formulations often use precipitated calcium carbonate as a filler, but this filler has poor compatibility with organic materials and insufficient rigidity, resulting in weak compressive strength. Furthermore, to increase production capacity, some manufacturers have tried adding PE wax as a lubricant, but this leads to limited compatibility of PE wax in PVC systems containing calcium-zinc stabilizers, causing it to easily precipitate and affecting the product's mechanical properties.

[0003] To address these issues, researchers have been exploring new material formulations and preparation methods. Currently, a common approach is to add elastomer-based toughening modifiers such as CPE, ACR, and MBS to improve toughness and flexibility. However, these improvements often bring side effects, such as increased production costs and reduced heat resistance or flame retardancy, requiring further optimization.

[0004] Therefore, developing a novel formulation that improves the compressive strength and toughness of PVC electrical conduits while maintaining good heat resistance and flame retardancy has become a key research focus. Simultaneously, it is also necessary to consider how to reduce production costs and improve production efficiency while ensuring product quality. This requires innovation in formulation design, rationally selecting and optimizing the proportions and types of components to achieve a balance of performance and maximize application value. Summary of the Invention

[0005] This invention provides a high-compression-strength and heat-resistant PVC insulating electrical conduit and its preparation method, which can solve the problems of poor compression resistance and insufficient heat resistance in the modification of PVC electrical conduits in the prior art.

[0006] The objective of this invention can be achieved through the following technical solutions: A high-pressure-resistant and heat-resistant PVC electrical conduit, by weight, comprises the following raw materials: 75-85 parts PVC resin, 15-25 parts maleic anhydride-grafted CPVC, 2.5-3.5 parts calcium-zinc stabilizer, 0.2-0.5 parts internal lubricant, 0.4-1.2 parts external lubricant, 25-40 parts EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture, 0-3 parts talc, 0.5-1.5 parts impact-resistant ACR resin, 0.5-1.5 parts organosilicon toughening agent, 2-4 parts CPE, 0.1-0.3 parts antioxidant, and 1-2 parts rutile titanium dioxide.

[0007] Furthermore, the PVC resin is a general-purpose SG-5 type resin with a viscosity of 108 to 120.

[0008] Furthermore, the preparation steps of the maleic anhydride-grafted CPVC are as follows: Maleic anhydride was dissolved in acetone to obtain a maleic anhydride solution with a concentration of 0.5-1.5 g / mL. PVC powder was added to the maleic anhydride solution, with a mass ratio of PVC to maleic anhydride of 12-16:1. After stirring and mixing, the mixture was transferred to a reaction vessel and allowed to stand for 12-24 hours. The temperature was raised to 50-60℃ and stirred for 1-3 hours. After cooling to room temperature, chlorine gas was introduced to purge the air from the reaction vessel. Chlorine gas was continued to be introduced at a rate of 100-150 g / min per cubic meter of reaction system. The chlorination reaction was carried out at a constant temperature of 120-140℃, controlling the chlorine content to be 66%-69%. The chlorine gas introduction was stopped, and the mixture was cooled to below 100℃. After the chlorine gas was extracted, air was added to purge the residual chlorine. The crude product was dissolved in tetrahydrofuran, and methanol was added to precipitate the product. After removing impurities, the product was filtered and dried to obtain maleic anhydride-grafted CPVC.

[0009] Furthermore, the calcium-zinc stabilizer is an environmentally friendly calcium-zinc stabilizer, and its components include zinc stearate and calcium stearate.

[0010] Furthermore, the internal lubricant is at least one of monoglyceride, OPE, and stearic acid.

[0011] Furthermore, the external lubricant is at least one of polyethylene wax, Fischer-Tropsch wax, and paraffin wax.

[0012] Furthermore, the preparation steps of the EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture are as follows: EVA, calcium carbonate, and mica powder were mixed at a mass ratio of 1:(4-6):(2.5-4). Furan-based semi-aromatic polyamide was added at 40-60% of the mass of EVA, and dicumyl peroxide was added simultaneously as an initiator. After stirring and mixing evenly, the mixture was melt-extruded and granulated in a twin-screw extruder at 190-220℃ to obtain a mixture of EVA and furan-based semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder.

[0013] EVA and furanyl semi-aromatic polyamide form a cross-linked network under the action of an initiator, coating inorganic materials (calcium carbonate and mica powder) to prepare modified materials. Furanyl semi-aromatic polyamide exhibits high thermal stability, and the introduced rigid furanyl groups improve the compressive strength of PVC conduits. Simultaneously, the presence of aliphatic chains enhances the material's toughness. Both EVA and furanyl semi-aromatic polyamide contain polar and non-polar groups, resulting in better compatibility with PVC resin and a smaller polarity difference, leading to better dispersion of the modified material. The introduced furanyl groups can react with maleic anhydride-grafted CPVC at high temperatures to form cross-links. Cross-linking enhances the interfacial bonding between different materials, reduces brittleness, improves stress concentration, and enhances impact resistance. The resulting modified material exhibits better compatibility with other raw materials in PVC electrical conduits, improving compressive strength and heat resistance.

[0014] Furthermore, the EVA has a VA content of 20-25% and a melt flow index of 4-8 g / min.

[0015] Furthermore, the mica powder has a particle size of 5~20μm and an aspect ratio >50; The calcium carbonate has a particle size distribution D50 of 1–5 μm, a purity ≥99.5%, and a specific surface area ≥30 m². 2 / g, pore volume 0.5~1.5cm³ 3 / g.

[0016] Furthermore, the furanyl semi-aromatic polyamide is prepared by polymerization reaction of 2,5-furandicarboxyl chloride and 1,6-hexanediamine.

[0017] Furthermore, the dicumyl peroxide is 1-10% of the mass of EVA.

[0018] Furthermore, the molecular weight of the impact-resistant ACR resin is 300,000 to 1,000,000.

[0019] Furthermore, the antioxidant is a hindered phenolic antioxidant.

[0020] Furthermore, the rutile titanium dioxide has a particle size of 0.5–1 μm.

[0021] The present invention also provides a method for preparing the high-compression and heat-resistant PVC electrical conduit as described above, characterized by comprising the following steps: Step 1: Weigh the raw materials according to the above formula and set aside; Step 2: Add PVC resin, maleic anhydride-grafted CPVC, impact-resistant ACR resin, CPE, and silicone toughening agent to a high-speed mixer. Set the speed to 1000-1500 rpm and start mixing. Once the materials are evenly mixed, add EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture. Continue mixing and stirring until evenly mixed. Then add calcium zinc stabilizer, internal lubricant, external lubricant, talc, antioxidant, and rutile titanium dioxide. Stir until evenly mixed and then transfer to a cooling mixer. Set the speed to 50-100 rpm and start low-speed stirring. Cool to 45℃~55℃ and discharge to obtain a cold mix. Step 3: Pass the cold mixture through a vibrating screen to remove lumps, then transfer it to a storage tank and let it stand for more than 3 hours to obtain PVC dry mixture. Step 4: The PVC dry mix is ​​fed to a twin-screw extruder for extrusion molding to obtain a high-compression-strength and heat-resistant PVC insulating electrical conduit.

[0022] Furthermore, the barrel processing temperature of the twin-screw extruder is 170℃~190℃, the die temperature is 195~205℃, the die temperature is 180℃~190℃, the main screw speed is 50~70r / min, and the melt pressure is 21MPa~23.5MPa.

[0023] The beneficial effects of this invention are: (1) The PVC insulated electrical conduit of the present invention, through optimized formula design, uses a combination of PVC and maleic anhydride grafted CPVC, which significantly improves the material’s resistance to heat deformation. The scientific combination of various materials such as impact-resistant ACR resin, CPE, and organosilicon toughening agent improves the toughness and impact resistance of the conduit, effectively solving the problem of brittle fracture that is prone to occur during storage, transportation, installation and use of traditional PVC electrical conduit, and extending the service life and safety of the product.

[0024] (2) The present invention uses a mixture of EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder as filler material, which replaces the traditional precipitated calcium carbonate filler system, improves the compatibility of filler material with organic matter, enhances the rigidity and compressive strength of the material, significantly improves the compressive performance of PVC electrical conduit, and meets the high compressive strength requirements.

[0025] (3) In this invention, the cross-linked modified calcium carbonate-mica powder mixture of EVA and furanyl semi-aromatic polyamide and maleic anhydride grafted CPVC form a cross-linked structure by reacting furanyl and maleic anhydride groups during the melt processing. The introduction of the rigid furan ring group enhances the compressive strength and improves the heat resistance. The cross-linked structure enhances the interfacial bonding force, improves stress concentration, and improves the impact resistance.

[0026] (4) The PVC electrical conduit of the present invention has good performance and service life, and can meet the use requirements of electrical conduit inside buildings. It has the advantages of corrosion resistance, light weight and easy bending, and is suitable for various complex building environments. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1 A high-pressure-resistant and heat-resistant PVC electrical conduit, by weight, comprises the following raw materials: 80 parts of PVC resin (SG-5 type), 20 parts of maleic anhydride-grafted CPVC, 3 parts of environmentally friendly calcium-zinc stabilizer, 0.35 parts of OPE, 0.9 parts of polyethylene wax, 30 parts of EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture, 1 part of talc, 1 part of impact-resistant ACR resin (molecular weight 300,000-1,000,000), 1 part of organosilicon toughening agent, 3 parts of CPE, 0.2 parts of antioxidant 1010, and 1.3 parts of rutile titanium dioxide (particle size 0.5-1μm).

[0029] Preparation of maleic anhydride-grafted CPVC: Maleic anhydride was dissolved in acetone to obtain a maleic anhydride solution with a concentration of 1.0 g / mL. PVC powder was added to the maleic anhydride solution at a mass ratio of 15:1. After stirring and mixing, the mixture was transferred to a reaction vessel and allowed to stand for 24 h. The temperature was raised to 60 °C and stirred for 2 h. After cooling to room temperature, chlorine gas was introduced to purge the air from the reaction vessel. Chlorine gas was continued to be introduced at a rate of 120 g / min per cubic meter of reaction system. The chlorination reaction was carried out at a constant temperature of 130 °C. After the chlorination reaction started, the amount of chlorine introduced accounted for 66% to 69% of the mass of PVC. The chlorine content was controlled at 66% to 69%. When the chlorine content was reached, the chlorine gas introduction was stopped. The mixture was cooled to below 100 °C. After the chlorine gas was extracted, air was added to purge the residual chlorine. The crude product was dissolved in tetrahydrofuran, and methanol was added to precipitate the precipitate. After removing impurities, the product was filtered and dried to obtain maleic anhydride-grafted CPVC.

[0030] Preparation of furanyl semi-aromatic polyamide: 5 mol of 2,5-furandicarboxylic acid chloride was dissolved in 150 mL of dichloromethane to obtain an oil phase reaction solution. 0.5 mol of tetrabutylammonium bromide and 5 mol of 1,6-hexanediamine were dissolved in 150 mL of 1 mol / L KOH aqueous solution to obtain an aqueous phase reaction solution. The aqueous phase reaction solution was added dropwise to the oil phase reaction solution, and the mixture was stirred for 40 min. After filtration, the mixture was washed successively with deionized water, anhydrous methanol, and dichloromethane. The mixture was then placed in a vacuum drying oven at 80 °C for 24 h and dried to obtain furanyl semi-aromatic polyamide.

[0031] Preparation of EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture: EVA (VA content 20-25%, melt index 4-8 g / min) was mixed with calcium carbonate and mica powder at a mass ratio of 1:5:3. Furanyl semi-aromatic polyamide was added at 50% of the EVA mass, and dicumyl peroxide was added simultaneously as an initiator at 5% of the EVA mass. After thorough mixing, the mixture was melt-extruded and granulated at 200°C in a twin-screw extruder to obtain a crosslinked calcium carbonate-mica powder mixture modified with EVA and furanyl semi-aromatic polyamide. The calcium carbonate had a particle size distribution D50 of 1-5 μm, a purity ≥99.5%, and a specific surface area ≥30 m². 2 / g, pore volume 0.5~1.5cm³ 3 / g, the particle size of mica powder is 5~20μm, and the aspect ratio is >50.

[0032] Preparation of PVC electrical conduit: Step 1: Weigh the raw materials according to the above formula and set aside.

[0033] Step 2: Add PVC resin, maleic anhydride-grafted CPVC, impact-resistant ACR resin, CPE, and silicone toughening agent to a high-speed mixer. Set the speed to 1200 rpm and start mixing. Once the materials are evenly mixed, add EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture. Continue mixing and stirring until evenly mixed. Then add calcium zinc stabilizer, internal lubricant, external lubricant, talc, antioxidant, and rutile titanium dioxide. Stir until evenly mixed and then transfer to a cooling mixer. Set the speed to 80 rpm and start low-speed stirring. Cool to 45°C and discharge to obtain a cold mix.

[0034] Step 3: Pass the cold mixture through a vibrating screen to remove lumps, then transfer it to a storage tank and let it stand for more than 3 hours to obtain PVC dry mixture.

[0035] Step 4: The PVC dry mix is ​​fed into a twin-screw extruder for extrusion molding. After the billet exits through a sizing sleeve, vacuum chamber, and water tank for cooling and shaping, it is printed and cut to length to obtain high-pressure and heat-resistant PVC insulating electrical conduit. The twin-screw extruder barrel processing temperature is set as follows: Zone 1: 170℃, Zone 2: 190℃, Zone 3: 185℃, Zone 4: 180℃; the die temperature is set as follows: Zones 1-2: 185℃, Zones 3-6: 190℃; the die head temperature is set as 200℃; the main screw speed is 60 r / min; the main current is 85-90A; and the melt pressure is 22.5MPa-23.0MPa.

[0036] Example 2-3 The only difference from Example 1 is the raw material ratio of the PVC electrical conduit. The preparation steps are the same as in Example 1, and the specific ratio is shown in Table 1: Table 1

[0037] Example 4 The only difference from Example 1 is that the weight of the EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture is adjusted to 25 parts, and the other preparation steps are the same as in Example 1.

[0038] Example 5 The only difference from Example 1 is that the weight of the EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture is adjusted to 40 parts, and the other preparation steps are the same as in Example 1.

[0039] Example 6 The only difference from Example 1 is that when preparing the EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture, the mass ratio of EVA to calcium carbonate and mica powder is adjusted to 1:4:2.5, and the other preparation steps are the same as in Example 1.

[0040] Example 7 The only difference from Example 1 is that when preparing the EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture, the mass ratio of EVA to calcium carbonate and mica powder is adjusted to 1:6:4, and the other preparation steps are the same as in Example 1.

[0041] Example 8 The only difference from Example 1 is that when preparing the EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture, the amount of dicumyl peroxide added is 1% of the mass of EVA, and the other preparation steps are the same as in Example 1.

[0042] Example 9 The only difference from Example 1 is that when preparing the EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture, the amount of dicumyl peroxide added is 10% of the mass of EVA, and the other preparation steps are the same as in Example 1.

[0043] Comparative Example 1 The only difference from Example 1 is that CPVC is used instead of maleic anhydride grafted CPVC.

[0044] A PVC electrical conduit, by weight, comprises the following raw materials: 80 parts of PVC resin (SG-5 type), 20 parts of CPVC (chlorine content 66%~69%), 3 parts of environmentally friendly calcium-zinc stabilizer, 0.35 parts of OPE, 0.9 parts of polyethylene wax, 30 parts of EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture, 1 part of talc, 1 part of impact-resistant ACR resin (molecular weight 300,000~1,000,000), 1 part of organosilicon toughening agent, 3 parts of CPE, 0.2 parts of antioxidant 1010, and 1.3 parts of rutile titanium dioxide (particle size 0.5~1μm).

[0045] The preparation steps for furanyl semi-aromatic polyamide are the same as in Example 1.

[0046] The steps for preparing the EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture are the same as in Example 1.

[0047] Preparation of PVC electrical conduit: Step 1: Weigh the raw materials according to the above formula and set aside.

[0048] Step 2: Add PVC resin, CPVC, impact-resistant ACR resin, CPE, and silicone toughening agent to a high-speed mixer. Set the speed to 1200 rpm and start mixing. Once the materials are evenly mixed, add EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture. Continue mixing and stirring until evenly mixed. Then add calcium zinc stabilizer, internal lubricant, external lubricant, talc, antioxidant, and rutile titanium dioxide. Stir until evenly mixed and then transfer to a cooling mixer. Set the speed to 80 rpm and start low-speed stirring. Cool to 45°C and discharge to obtain a cold mix.

[0049] Step 3: Pass the cold mixture through a vibrating screen to remove lumps, then transfer it to a storage tank and let it stand for more than 3 hours to obtain PVC dry mixture.

[0050] Step 4: The PVC dry mix is ​​fed into a twin-screw extruder for extrusion molding. After the billet exits through a sizing sleeve, vacuum chamber, and water tank for cooling and shaping, it is printed and cut to length to obtain PVC insulated electrical conduit. The twin-screw extruder barrel processing temperature is set as follows: Zone 1: 170℃, Zone 2: 190℃, Zone 3: 185℃, Zone 4: 180℃; the die temperature is set as follows: Zones 1-2: 185℃, Zones 3-6: 190℃; the die head temperature is set as 200℃; the main screw speed is 60 r / min; the main current is 85-90A; and the melt pressure is 22.5MPa-23.0MPa.

[0051] Comparative Example 2 The only difference from Example 1 is that a calcium carbonate-mica powder mixture is used instead of EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture.

[0052] A PVC electrical conduit, by weight, comprises the following raw materials: 80 parts PVC resin (SG-5 type), 20 parts maleic anhydride-grafted CPVC, 3 parts environmentally friendly calcium-zinc stabilizer, 0.35 parts OPE, 0.9 parts polyethylene wax, 30 parts calcium carbonate-mica powder mixture, 1 part talc, 1 part impact-resistant ACR resin (molecular weight 300,000-1,000,000), 1 part silicone toughening agent, 3 parts CPE, 0.2 parts antioxidant 1010, and 1.3 parts rutile titanium dioxide (particle size 0.5-1 μm).

[0053] The steps for preparing maleic anhydride-grafted CPVC are the same as in Example 1.

[0054] Preparation of a mixture of calcium carbonate and mica powder: Calcium carbonate and mica powder were mixed at a mass ratio of 5:3 to obtain a calcium carbonate-mica powder mixture. The calcium carbonate had a particle size distribution (D50) of 1–5 μm, a purity ≥99.5%, and a specific surface area ≥30 m². 2 / g, pore volume 0.5~1.5cm³ 3 / g, the particle size of mica powder is 5~20μm, and the aspect ratio is >50.

[0055] Preparation of PVC electrical conduit: Step 1: Weigh the raw materials according to the above formula and set aside.

[0056] Step 2: Add PVC resin, maleic anhydride-grafted CPVC, impact-resistant ACR resin, CPE, and silicone toughening agent to a high-speed mixer. Set the speed to 1200 rpm and start mixing. Once the materials are evenly mixed, add the calcium carbonate-mica powder mixture and continue mixing. After even mixing, add calcium-zinc stabilizer, internal lubricant, external lubricant, talc, antioxidant, and rutile titanium dioxide. Mix evenly and then transfer to a cooling mixer. Set the speed to 80 rpm and start low-speed mixing. Cool to 45°C and discharge to obtain a cold mix.

[0057] Step 3: Pass the cold mixture through a vibrating screen to remove lumps, then transfer it to a storage tank and let it stand for more than 3 hours to obtain PVC dry mixture.

[0058] Step 4: The PVC dry mix is ​​fed into a twin-screw extruder for extrusion molding. After the billet exits through a sizing sleeve, vacuum chamber, and water tank for cooling and shaping, it is printed and cut to length to obtain PVC insulated electrical conduit. The twin-screw extruder barrel processing temperature is set as follows: Zone 1: 170℃, Zone 2: 190℃, Zone 3: 185℃, Zone 4: 180℃; the die temperature is set as follows: Zones 1-2: 185℃, Zones 3-6: 190℃; the die head temperature is set as 200℃; the main screw speed is 60 r / min; the main current is 85-90A; and the melt pressure is 22.5MPa-23.0MPa.

[0059] Comparative Example 3 The only difference from Example 1 is that only EVA was used to modify calcium carbonate and mica powder.

[0060] A PVC electrical conduit, by weight, comprises the following raw materials: 80 parts of PVC resin (SG-5 type), 20 parts of maleic anhydride-grafted CPVC, 3 parts of environmentally friendly calcium-zinc stabilizer, 0.35 parts of OPE, 0.9 parts of polyethylene wax, 30 parts of EVA-modified calcium carbonate-mica powder mixture, 1 part of talc, 1 part of impact-resistant ACR resin (molecular weight 300,000-1,000,000), 1 part of organosilicon toughening agent, 3 parts of CPE, 0.2 parts of antioxidant 1010, and 1.3 parts of rutile titanium dioxide (particle size 0.5-1 μm).

[0061] The steps for preparing maleic anhydride-grafted CPVC are the same as in Example 1.

[0062] Preparation of EVA-modified calcium carbonate-mica powder mixture: EVA (VA content 20-25%, melt index 4-8 g / min) was mixed with calcium carbonate and mica powder at a mass ratio of 1:5:3. Dicumyl peroxide (5% of the EVA mass) was added as an initiator. After thorough mixing, the mixture was melt-extruded and granulated at 200°C in a twin-screw extruder to obtain an EVA-modified calcium carbonate-mica powder mixture. The calcium carbonate had a particle size distribution (D50) of 1-5 μm, a purity ≥99.5%, and a specific surface area ≥30 m². 2 / g, pore volume 0.5~1.5cm³ 3 / g, the particle size of mica powder is 5~20μm, and the aspect ratio is >50.

[0063] Preparation of PVC electrical conduit: Step 1: Weigh the raw materials according to the above formula and set aside.

[0064] Step 2: Add PVC resin, maleic anhydride-grafted CPVC, impact-resistant ACR resin, CPE, and silicone toughening agent to a high-speed mixer. Set the speed to 1200 rpm and start mixing. Once the materials are evenly mixed, add the EVA-modified calcium carbonate-mica powder mixture and continue mixing. After even mixing, add calcium-zinc stabilizer, internal lubricant, external lubricant, talc, antioxidant, and rutile titanium dioxide. Mix evenly and then transfer to a cooling mixer. Set the speed to 80 rpm and start low-speed mixing. Cool to 45°C and discharge to obtain a cold mix.

[0065] Step 3: Pass the cold mixture through a vibrating screen to remove lumps, then transfer it to a storage tank and let it stand for more than 3 hours to obtain PVC dry mixture.

[0066] Step 4: The PVC dry mix is ​​fed into a twin-screw extruder for extrusion molding. After the billet exits through a sizing sleeve, vacuum chamber, and water tank for cooling and shaping, it is printed and cut to length to obtain PVC insulated electrical conduit. The twin-screw extruder barrel processing temperature is set as follows: Zone 1: 170℃, Zone 2: 190℃, Zone 3: 185℃, Zone 4: 180℃; the die temperature is set as follows: Zones 1-2: 185℃, Zones 3-6: 190℃; the die head temperature is set as 200℃; the main screw speed is 60 r / min; the main current is 85-90A; and the melt pressure is 22.5MPa-23.0MPa.

[0067] Comparative Example 4 The only difference from Example 1 is that EVA and furanyl polyamide are directly blended to modify calcium carbonate and mica powder.

[0068] A PVC electrical conduit, by weight, comprises the following raw materials: 80 parts of PVC resin (SG-5 type), 20 parts of maleic anhydride-grafted CPVC, 3 parts of environmentally friendly calcium-zinc stabilizer, 0.35 parts of OPE, 0.9 parts of polyethylene wax, 30 parts of EVA and furanyl semi-aromatic polyamide blend modified calcium carbonate-mica powder mixture, 1 part of talc, 1 part of impact-resistant ACR resin (molecular weight 300,000-1,000,000), 1 part of organosilicon toughening agent, 3 parts of CPE, 0.2 parts of antioxidant 1010, and 1.3 parts of rutile titanium dioxide (particle size 0.5-1 μm).

[0069] The steps for preparing maleic anhydride-grafted CPVC are the same as in Example 1.

[0070] The preparation steps for furanyl semi-aromatic polyamide are the same as in Example 1.

[0071] Preparation of EVA and furanyl semi-aromatic polyamide blend modified calcium carbonate-mica powder mixture: EVA (VA content 20-25%, melt index 4-8 g / min) was mixed with calcium carbonate and mica powder at a mass ratio of 1:5:3. Furanyl semi-aromatic polyamide was added at 50% of the EVA mass. After thorough mixing, the mixture was melt-extruded and granulated at 200°C in a twin-screw extruder to obtain a calcium carbonate-mica powder mixture modified with EVA and furanyl semi-aromatic polyamide. The calcium carbonate had a particle size distribution D50 of 1-5 μm, a purity ≥99.5%, and a specific surface area ≥30 m². 2 / g, pore volume 0.5~1.5cm³ 3 / g, the particle size of mica powder is 5~20μm, and the aspect ratio is >50.

[0072] Preparation of PVC electrical conduit: Step 1: Weigh the raw materials according to the above formula and set aside.

[0073] Step 2: Add PVC resin, maleic anhydride-grafted CPVC, impact-resistant ACR resin, CPE, and silicone toughening agent to a high-speed mixer. Set the speed to 1200 rpm and start mixing. Once the materials are evenly mixed, add EVA and furanyl semi-aromatic polyamide-modified calcium carbonate-mica powder mixture. Continue mixing and stirring until evenly mixed. Then add calcium-zinc stabilizer, internal lubricant, external lubricant, talc, antioxidant, and rutile titanium dioxide. Stir until evenly mixed and then transfer to a cooling mixer. Set the speed to 80 rpm and start low-speed stirring. Cool to 45°C and discharge to obtain a cold mix.

[0074] Step 3: Pass the cold mixture through a vibrating screen to remove lumps, then transfer it to a storage tank and let it stand for more than 3 hours to obtain PVC dry mixture.

[0075] Step 4: The PVC dry mix is ​​fed into a twin-screw extruder for extrusion molding. After the billet exits through a sizing sleeve, vacuum chamber, and water tank for cooling and shaping, it is printed and cut to length to obtain PVC insulated electrical conduit. The twin-screw extruder barrel processing temperature is set as follows: Zone 1: 170℃, Zone 2: 190℃, Zone 3: 185℃, Zone 4: 180℃; the die temperature is set as follows: Zones 1-2: 185℃, Zones 3-6: 190℃; the die head temperature is set as 200℃; the main screw speed is 60 r / min; the main current is 85-90A; and the melt pressure is 22.5MPa-23.0MPa.

[0076] Comparative Example 5 The only difference from Example 1 is that EVA, furanyl polyamide, calcium carbonate and mica powder are directly added to the raw materials.

[0077] A PVC electrical conduit, by weight, comprises the following raw materials: 80 parts PVC resin (SG-5 type), 20 parts maleic anhydride-grafted CPVC, 3 parts environmentally friendly calcium-zinc stabilizer, 0.35 parts OPE, 0.9 parts polyethylene wax, 3.2 parts EVA, 1.6 parts furanyl semi-aromatic polyamide, 15.8 parts calcium carbonate, 9.4 parts mica powder, 1 part talc powder, 1 part impact-resistant ACR resin (molecular weight 300,000-1,000,000), 1 part silicone toughening agent, 3 parts CPE, 0.2 parts antioxidant 1010, and 1.3 parts rutile titanium dioxide (particle size 0.5-1 μm). The EVA content is 20-25%, the melt flow index is 4-8 g / min, the calcium carbonate particle size distribution (D50) is 1-5 μm, the purity is ≥99.5%, and the specific surface area is ≥30 m². 2 / g, pore volume 0.5~1.5cm³ 3 / g, the particle size of mica powder is 5~20μm, and the aspect ratio is >50.

[0078] The steps for preparing maleic anhydride-grafted CPVC are the same as in Example 1.

[0079] The preparation steps for furanyl semi-aromatic polyamide are the same as in Example 1.

[0080] Preparation of PVC electrical conduit: Step 1: Weigh the raw materials according to the above formula and set aside.

[0081] Step 2: Add PVC resin, maleic anhydride-grafted CPVC, impact-resistant ACR resin, CPE, and silicone toughening agent to a high-speed mixer. Set the speed to 1200 rpm and start mixing. Once the materials are evenly mixed, add EVA, furanyl semi-aromatic polyamide, calcium carbonate, and mica powder. Continue mixing and stirring until evenly mixed. Then add calcium-zinc stabilizer, internal lubricant, external lubricant, talc, antioxidant, and rutile titanium dioxide. Stir until evenly mixed and then transfer to a cooling mixer. Set the speed to 80 rpm and start low-speed stirring. Cool to 45°C and discharge to obtain a cold mix.

[0082] Step 3: Pass the cold mixture through a vibrating screen to remove lumps, then transfer it to a storage tank and let it stand for more than 3 hours to obtain PVC dry mixture.

[0083] Step 4: The PVC dry mix is ​​fed into a twin-screw extruder for extrusion molding. After the billet exits through a sizing sleeve, vacuum chamber, and water tank for cooling and shaping, it is printed and cut to length to obtain PVC insulated electrical conduit. The twin-screw extruder barrel processing temperature is set as follows: Zone 1: 170℃, Zone 2: 190℃, Zone 3: 185℃, Zone 4: 180℃; the die temperature is set as follows: Zones 1-2: 185℃, Zones 3-6: 190℃; the die head temperature is set as 200℃; the main screw speed is 60 r / min; the main current is 85-90A; and the melt pressure is 22.5MPa-23.0MPa.

[0084] Comparative Example 6 The only difference from Example 1 is that maleic anhydride-grafted CPVC resin is replaced with PVC resin.

[0085] A PVC electrical conduit, by weight, comprises the following raw materials: 100 parts PVC resin (SG-5 type), 3 parts environmentally friendly calcium-zinc stabilizer, 0.35 parts OPE, 0.9 parts polyethylene wax, 30 parts EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture, 1 part talc, 1 part impact-resistant ACR resin (molecular weight 300,000-1,000,000), 1 part silicone toughening agent, 3 parts CPE, 0.2 parts antioxidant 1010, and 1.3 parts rutile titanium dioxide (particle size 0.5-1 μm).

[0086] The preparation steps for furanyl semi-aromatic polyamide are the same as in Example 1.

[0087] The steps for preparing the EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture are the same as in Example 1.

[0088] Preparation of PVC electrical conduit: Step 1: Weigh the raw materials according to the above formula and set aside.

[0089] Step 2: Add PVC resin, impact-resistant ACR resin, CPE, and silicone toughening agent to a high-speed mixer. Set the speed to 1200 rpm and start mixing. Once the materials are evenly mixed, add EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture. Continue mixing and stirring until evenly mixed. Then add calcium zinc stabilizer, internal lubricant, external lubricant, talc, antioxidant, and rutile titanium dioxide. Stir until evenly mixed and then transfer to a cooling mixer. Set the speed to 80 rpm and start low-speed stirring. Cool to 45°C and discharge to obtain a cold mix.

[0090] Step 3: Pass the cold mixture through a vibrating screen to remove lumps, then transfer it to a storage tank and let it stand for more than 3 hours to obtain PVC dry mixture.

[0091] Step 4: The PVC dry mix is ​​fed into a twin-screw extruder for extrusion molding. After the billet exits through a sizing sleeve, vacuum chamber, and water tank for cooling and shaping, it is printed and cut to length to obtain PVC insulated electrical conduit. The twin-screw extruder barrel processing temperature is set as follows: Zone 1: 170℃, Zone 2: 190℃, Zone 3: 185℃, Zone 4: 180℃; the die temperature is set as follows: Zones 1-2: 185℃, Zones 3-6: 190℃; the die head temperature is set as 200℃; the main screw speed is 60 r / min; the main current is 85-90A; and the melt pressure is 22.5MPa-23.0MPa.

[0092] The PVC electrical conduits (specification 305-20) prepared in Examples 1-9 and Comparative Examples 1-6 were tested for performance according to GB / T 43815-2024 "Rigid Polyvinyl Chloride (PVC-U) Insulating Electrical Conduits and Fittings for Building". The test results are shown in Table 2.

[0093] Table 2

[0094] As shown in Table 1, among Examples 1-3, Example 2 exhibits the best performance indicators through optimized raw material ratios. However, from a cost-effectiveness perspective, Example 2 uses a relatively large amount of maleic anhydride-grafted CPVC, which increases costs. Based on the formulation of Example 1, Examples 4 and 5 further optimize the formulations. In Example 5, the amount of modified calcium carbonate-mica powder mixture added is too high. As a filler, excessive addition can disrupt the stylistically continuous phase of the organic material, resulting in reduced mechanical properties of the prepared PVC sleeve. In Examples 1, 6, and 7, the low amount of EVA during modification has limited effect on improving compatibility. A high amount of EVA leads to excessive coating, reducing the proportion of inorganic materials in an equal mass of modified mixture, which in turn reduces the compressive strength and heat resistance of the PVC sleeve. In Examples 8 and 9, the amount of initiator affected the degree of crosslinking between EVA and furanyl semi-aromatic polyamide. A low degree of crosslinking also reduces the degree of crosslinking with maleic anhydride-grafted CPVC in the raw materials, weakening the interfacial bonding and reducing overall performance. Excessive initiator induces more self-crosslinking of EVA, preventing the formation of an interwoven crosslinked structure between EVA and furanyl semi-aromatic polyamide, thus reducing the improvement effect on compressive strength and heat resistance. The PVC insulating electrical conduit prepared in these examples showed significantly higher compressive strength and heat deformation resistance compared to the comparative example, achieving the objective of this invention in terms of high compressive strength and heat resistance.

[0095] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0096] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high pressure and heat resistant PVC insulated electrical conduit, characterized in that, By weight, it includes the following ingredients: 75-85 parts PVC resin, 15-25 parts maleic anhydride-grafted CPVC, 2.5-3.5 parts calcium-zinc stabilizer, 0.2-0.5 parts internal lubricant, 0.4-1.2 parts external lubricant, 25-40 parts EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture, 0-3 parts talc, 0.5-1.5 parts impact-resistant ACR resin, 0.5-1.5 parts organosilicon toughening agent, 2-4 parts CPE, 0.1-0.3 parts antioxidant, 1-2 parts rutile titanium dioxide; The preparation steps of the EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture are as follows: EVA, calcium carbonate, and mica powder were mixed at a mass ratio of 1:(4-6):(2.5-4). Furanyl semi-aromatic polyamide was added at 40-60% of the mass of EVA, and dicumyl peroxide was added as an initiator. After stirring and mixing evenly, the mixture was melt-extruded and granulated in a twin-screw extruder at 190-220℃ to obtain a mixture of EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder. The furanyl semi-aromatic polyamide was prepared by polymerization of 2,5-furandicarboxylic acid chloride and 1,6-hexanediamine.

2. A high pressure and heat resistant PVC insulated electrical conduit as claimed in claim 1, wherein, The PVC resin is a general-purpose SG-5 type resin with a viscosity of 108 to 120.

3. A high pressure and heat resistant PVC electrical conduit as claimed in claim 1, wherein, The preparation steps of the maleic anhydride-grafted CPVC are as follows: Maleic anhydride was dissolved in acetone to obtain a maleic anhydride solution with a concentration of 0.5-1.5 g / mL. PVC powder was added to the maleic anhydride solution, with a mass ratio of PVC to maleic anhydride of 12-16:

1. After stirring and mixing, the mixture was transferred to a reaction vessel and allowed to stand for 12-24 hours. The temperature was raised to 50-60℃ and stirred for 1-3 hours. After cooling to room temperature, chlorine gas was introduced to purge the air from the reaction vessel. Chlorine gas was continued to be introduced at a rate of 100-150 g / min per cubic meter of reaction system. The chlorination reaction was carried out at a constant temperature of 120-140℃, controlling the chlorine content to be 66%-69%. The chlorine gas introduction was stopped, and the mixture was cooled to below 100℃. After the chlorine gas was extracted, air was added to purge the residual chlorine. The crude product was dissolved in tetrahydrofuran, and methanol was added to precipitate the product. After removing impurities, the product was filtered and dried to obtain maleic anhydride-grafted CPVC.

4. A high pressure and heat resistant PVC electrical conduit as claimed in claim 1, wherein, The calcium-zinc stabilizer is an environmentally friendly calcium-zinc stabilizer, and its components include zinc stearate and calcium stearate.

5. A high pressure and heat resistant PVC electrical conduit as claimed in claim 1, wherein, The internal lubricant is at least one of monoglyceride, OPE, and stearic acid; The external lubricant is at least one of polyethylene wax, Fischer-Tropsch wax, and paraffin wax.

6. The high-pressure-resistant and heat-resistant PVC insulating electrical conduit according to claim 1, characterized in that, The EVA has a VA content of 20-25% and a melt flow index of 4-8 g / min; The mica powder has a particle size of 5~20μm and an aspect ratio >50; The particle size distribution D50 of the calcium carbonate is 1-5 μm, the purity is ≥ 99.5%, the specific surface area is ≥ 30 m 2 / g, and the pore volume is 0.5-1.5 cm 3 / g.

7. The high-pressure-resistant and heat-resistant PVC insulating electrical conduit according to claim 1, characterized in that, The dicumyl peroxide is 1-10% of the mass of EVA.

8. The high-pressure-resistant and heat-resistant PVC insulating electrical conduit according to claim 1, characterized in that, The molecular weight of the impact-resistant ACR resin is 300,000 to 1,000,000; The antioxidant is a hindered phenolic antioxidant; The rutile titanium dioxide has a particle size of 0.5–1 μm.

9. A method for preparing a high-compression-strength and heat-resistant PVC insulating electrical conduit as described in any one of claims 1-8, characterized in that, Includes the following steps: Step 1: Weigh the raw materials according to the formula and set aside; Step 2: Add PVC resin, maleic anhydride-grafted CPVC, impact-resistant ACR resin, CPE, and silicone toughening agent to a high-speed mixer. Set the speed to 1000-1500 rpm and start mixing. Once the materials are evenly mixed, add EVA and furanyl semi-aromatic polyamide crosslinked modified calcium carbonate-mica powder mixture. Continue mixing and stirring until evenly mixed. Then add calcium zinc stabilizer, internal lubricant, external lubricant, talc, antioxidant, and rutile titanium dioxide. Stir until evenly mixed and then transfer to a cooling mixer. Set the speed to 50-100 rpm and start low-speed stirring. Cool to 45℃~55℃ and discharge to obtain a cold mix. Step 3: Pass the cold mixture through a vibrating screen to remove lumps, then transfer it to a storage tank and let it stand for more than 3 hours to obtain PVC dry mixture. Step 4: The PVC dry mix is ​​fed to a twin-screw extruder for extrusion molding to obtain a high-compression-strength and heat-resistant PVC insulating electrical conduit.

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