A high-performance PVC low-foaming board and its manufacturing method

Abstract

This invention discloses a high-performance PVC low-foaming board and its preparation method. The low-foaming board is composed of rigid PVC resin powder, an interface-anchored nanocomposite crosslinking agent, a calcium-zinc stabilizer, a foaming regulator, a lubricant, an AC foaming agent, color powder, and calcium carbonate. The interface-anchored nanocomposite crosslinking agent has a coating structure of "organic nano-montmorillonite + EVA-g-TAIC graft copolymer". The preparation method includes dry premixing, two-stage temperature-controlled extrusion foaming, water-cooling shaping, and 80-120 kGy electron beam radiation crosslinking. This invention solves the problem of premature crosslinking interfering with foaming in traditional TAIC during high-temperature extrusion by pre-constructing a latent crosslinking precursor. The synergistic effect of the chemical crosslinking network and physical bonding formed at the three-phase interface by the nanosheets and EVA coating layer under radiation activation increases the notched impact strength of the material by more than 140% and the heat distortion temperature by 25-35℃, while maintaining low density and high closed-cell rate. This technology is suitable for the industrial production of high-end building decorative panels.

Description

Technical Field

[0001] This invention relates to the field of polymer foam material modification technology, and more specifically, to a high-strength and tough PVC low-foaming board based on an interface-anchored nanocomposite crosslinking agent and its preparation method. Background Technology

[0002] Polyvinyl chloride (PVC) low-foaming boards are widely used in building decoration, advertising boards, and packaging liners due to their advantages such as light weight, heat insulation, and ease of processing. However, traditional PVC low-foaming boards face significant technical bottlenecks in practical applications: First, the rigidity of PVC molecular chains leads to increased brittleness as the cell walls thin during foaming, resulting in generally low notched impact strength (typically <3kJ / m²). Second, the addition of large amounts of inorganic fillers (such as calcium carbonate) to compensate for mechanical properties further deteriorates toughness, while the introduction of elastomers (such as EVA and CPE), although toughening, significantly reduces tensile strength and heat distortion temperature, creating a "rigidity-toughness imbalance." Third, traditional chemical crosslinking agents are prone to premature crosslinking during the high-temperature plasticizing stage of extrusion, leading to a sharp increase in melt viscosity, difficulty in foaming, and even surface roughness or collapse of the board.

[0003] In the prior art, CN106633520B discloses a high-strength, impact-resistant, and weather-resistant PVC building board, which, by weight, is mainly prepared from the following raw materials: polyvinyl chloride (PVC): 100 parts, chlorinated PVC: 5-80 parts, straw fiber powder: 5-60 parts, toughening agent: 2-15 parts, functional filler: 5-100 parts, stabilizer: 3-6 parts, foaming agent: 0.2-3.0 parts, foaming regulator: 3-12 parts, internal lubricant: 0.3-2.0 parts, and external lubricant: 0.3-2.0 parts. This invention incorporates functional fillers, which stabilizes the PVC foaming system and significantly improves the heat resistance and aging resistance of the board; the corrosion resistance of the foamed material is significantly increased, broadening the application range of the product; the strength and impact performance of the product are superior to those of currently available PVC foamed boards; and the use of crop straw powder to replace traditional wood powder saves forest resources and solves the problem of straw burning. This method of improving the weather resistance of PVC sheets by modifying montmorillonite with quaternary ammonium salts and compounding it with straw fiber does not solve the compatibility problem between radiation crosslinking and foaming processes.

[0004] CN113337054B discloses a high-strength heat-resistant PVC foam board and its preparation method. The high-strength heat-resistant PVC foam board, by weight, comprises the following raw materials: 90-100 parts PVC resin, 0.5-0.8 parts foaming agent, 3-7 parts foaming regulator, 4-6 parts heat stabilizer, 3-5 parts chlorinated polyethylene, 20-30 parts kaolin, 0.5-1 part stearic acid, 0.5-1 part oxidized polyethylene wax, and 0-3 parts titanium dioxide. The heat stabilizer is a porous polymer with thiourea grafted on its surface and calcium carbonate loaded internally. This heat stabilizer, with its special structure, can replace unstable chlorine atoms in PVC and remove hydrogen chloride, thereby reducing the strength loss of PVC due to degradation during processing and use. Simultaneously, it can form covalent crosslinks between PVC molecular chains, further improving the strength of the PVC foam board. This porous polymer heat stabilizer with thiourea grafted on its surface mainly focuses on improving thermal stability, lacking targeted design for controlling the foam pore structure and radiation crosslinking efficiency. This conventional component blending has a ceiling on the improvement of product mechanical properties and cannot achieve a synergistic unity of high strength, high toughness, and high heat resistance.

[0005] Therefore, there is an urgent need in this field for a technology that can achieve deep synergy between formulation component design and processing technology, and can break through the limitations of traditional PVC low-foaming board preparation technology. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing PVC low-foaming boards, such as difficulty in achieving both rigidity and toughness, low radiation crosslinking efficiency, and easy interference with the foaming process. This invention provides a high-strength and tough PVC low-foaming board based on an interface-anchored nanocomposite crosslinking agent and its preparation method. By constructing a composite agent with a latent crosslinking structure and matching it with a two-stage temperature-controlled extrusion and precise electron beam irradiation process, a microscopic spatial synergy of nano-reinforcement, elastic toughening, and radiation crosslinking is achieved.

[0007] To achieve the above objectives, the present invention provides a high-performance PVC low-foaming board, comprising the following components by weight: 100 parts of rigid PVC resin powder; 8-15 parts of nanocomposite crosslinking aid; 3-5 parts calcium-zinc stabilizer; Foaming regulator 2-4 parts; Oxidized polyethylene wax 0.5-1.0 parts; G60 internal lubricant 0.8-1.5 parts; PE wax 0.3-0.8 parts; AC foaming agent 1.5-3.0 parts; Color powder 0.5-1.0 parts; 5-15 parts of light calcium carbonate; The nanocomposite crosslinking aid consists of organic nano-montmorillonite as the core and a graft copolymer coating layer of ethylene-vinyl acetate copolymer grafted with triallyl isocyanurate (EVA-g-TAIC) as the shell, forming a coated composite microparticle structure. After pre-constructing an organic MMT core and then coating it with EVA-g-TAIC to form an interface-anchored nanocomposite aid, the TAIC double bonds in the coating layer are spatially encapsulated by the long chains of EVA, remaining in a latent state at extrusion temperatures (<185℃), effectively avoiding premature crosslinking of traditional TAIC during the high-temperature plasticizing stage. Furthermore, during subsequent irradiation, TAIC can be precisely positioned at the three-phase interface of PVC / EVA / nanofiller, improving crosslinking efficiency by over 60%.

[0008] Preferably, the preparation method of the interface-anchored nanocomposite crosslinking aid includes the following steps: (1) Disperse sodium-based nano-montmorillonite in anhydrous ethanol, add silane coupling agent KH-570, stir and react at 60-80℃ for 3-5h, centrifuge, wash and dry to obtain organic nano-montmorillonite; (2) The organic nano-montmorillonite, ethylene-vinyl acetate copolymer (EVA), triallyl isocyanurate (TAIC) and initiator dicumyl peroxide (DCP) are put into a mixer and subjected to a melt grafting reaction at 110-130°C and 40-60 r / min for 15-25 min. (3) Dissolve the grafted product in toluene, add n-hexane to precipitate, filter, vacuum dry to constant weight, and pulverize through a 200-mesh sieve to obtain the interface anchoring nanocomposite crosslinking aid.

[0009] Furthermore, the VA content in the EVA is 18% to 28%, the TAIC dosage is 5% to 12% of the EVA mass, and the DCP dosage is 0.3% to 0.8% of the EVA mass.

[0010] Preferably, the foaming regulator is an acrylate copolymer ACR-401 or ACR-K400; the K value of the rigid PVC resin powder is 58-62.

[0011] Preferably, the high-performance PVC low-foaming board needs to be irradiated by an electron accelerator with an irradiation dose of 80-120 kGy and an electron beam energy of 1.5-2.5 MeV.

[0012] This invention also provides a method for preparing the above-mentioned high-performance PVC low-foaming board, comprising the following steps: S1. Dry premixing: Add rigid PVC resin powder, calcium-zinc stabilizer, foaming regulator, oxidized polyethylene wax, G60 internal lubricant, PE wax, AC foaming agent, color powder, light calcium carbonate and interface anchoring nanocomposite crosslinking agent into a high-speed mixer according to the formula ratio, stir at high speed at 80-95℃ for 4-6 minutes, and after discharge, cool to below 40℃ in a cold mixer to obtain mixed powder. S2. Extrusion and Foaming: The mixed powder is fed into a parallel twin-screw extruder, plasticized and foamed, and then extruded through a flat die head; the barrel temperature is controlled in sections: Zone 1 135~145℃, Zone 2 155~165℃, Zone 3 168~178℃, Zone 4 172~182℃, and the die head temperature is 165~175℃; the melt pressure is controlled at 8~12MPa; S3, Cooling and Shaping: The extruded foamed board immediately enters the three-roll calender and water-cooling shaping device, and the roller temperature is controlled at 50-65℃ to quickly freeze and shape the cell structure. S4. Radiation crosslinking: The shaped low-foaming board is irradiated by an electron accelerator with an irradiation dose of 80-120 kGy, an electron beam energy of 1.5-2.5 MeV, and a transmission speed of 5-10 m / min to obtain the finished product.

[0013] Preferably, in step S2, the screw length-to-diameter ratio of the twin-screw extruder is 36-40:1, the rotation speed is 18-25 r / min, and the feeding frequency is matched with the main machine speed to ensure that the material residence time in the barrel is controlled within 2.5-3.5 min.

[0014] Preferably, before the irradiation treatment in step S4, the temperature of the foamed board blank has been reduced to room temperature (20-25°C), the irradiation environment is an inert gas protection environment or an atmospheric pressure air environment, and the irradiation is left to stand and age for 24-48 hours.

[0015] Preferably, the interface-anchored nanocomposite crosslinking aid does not undergo significant crosslinking reaction within the extrusion temperature range of step S2, and the TAIC double bonds in its graft copolymer coating layer only initiate three-dimensional network crosslinking of the PVC / EVA matrix under electron beam irradiation in step S4.

[0016] Preferably, the crosslinking gel content of the PVC low-foaming board obtained by radiation crosslinking in step S4 is greater than 58%.

[0017] The beneficial effects of this invention are as follows: The high-performance PVC low-foaming board and its manufacturing method provided by this invention abandon the simple superposition approach of traditional "EVA+MMT+TAIC" physical blending. Instead, it forms an interface-anchored nanocomposite additive by pre-constructing an "organic MMT core + EVA-g-TAIC coating layer." The TAIC double bonds in the coating layer are spatially encapsulated by the long chains of EVA, remaining in a latent state at extrusion temperatures (<185℃), effectively preventing premature crosslinking of traditional TAIC during the high-temperature plasticizing stage. Furthermore, during subsequent irradiation, TAIC is precisely positioned at the three-phase interface of PVC / EVA / nanofiller, increasing the crosslinking rate of TAIC by more than 30%.

[0018] Overcoming the technical bias of "rigidity-toughness imbalance": Nano-montmorillonite sheets are exfoliated in situ under shear force, acting as a highly efficient heterogeneous nucleating agent to refine the pore size to 50–120 μm with a closed-cell rate >92%; the EVA coating layer absorbs impact energy, while the radiation cross-linking network forms a dual locking mechanism of physical anchors and chemical cross-linking at the interface. The synergistic effect of these three elements increases notched impact strength by 140%–180%, tensile strength by 35%–50%, and heat distortion temperature by 25–35℃, while maintaining a density of 0.45–0.55 g / cm³.

[0019] The process is highly compatible and can be scaled up industrially: the two-stage temperature-controlled extrusion and low-dose electron beam irradiation processes are completely independent, and foaming and crosslinking are decoupled. Irradiation, as a post-molding treatment, does not change the main structure of the existing extrusion production line; only an irradiation unit needs to be added online, demonstrating strong potential for industrialization. Detailed Implementation

[0020] The embodiments described below are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the technical concepts and practical guidance described in the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0021] First, 50 g of sodium-based nano-montmorillonite (MMT, interlayer spacing 1.1 nm) was weighed and dispersed in 500 mL of anhydrous ethanol, and sonicated for 30 min. Then, 5 g of silane coupling agent KH-570 was added, and the mixture was stirred at 80 °C for 4 h. After centrifugation and washing three times with ethanol, the mixture was vacuum dried at 60 °C to obtain organo-modified nano-montmorillonite (o-MMT).

[0022] Take 30g of o-MMT, 100g of EVA (VA content 28%), 8g of TAIC, and 0.5g of DCP and add them to the mixing chamber of a torque rheometer. The parameters of the torque rheometer are: 120℃, 50r / min, and melt grafting for 20min. Dissolve the product in 200mL of toluene, slowly pour it into n-hexane to precipitate, filter, vacuum dry, and pass through a 200-mesh sieve to obtain a light yellow powdery interface-anchored nanocomposite crosslinking aid (denoted as IMNA).

[0023] Specific examples of PVC low-foaming board preparation are as follows: Example 1

[0024] Formula (parts by weight): 100 parts PVC resin powder (K=60); 10 parts IMNA additive; 4 parts calcium-zinc stabilizer; 3 parts foaming regulator ACR-401; 0.8 parts oxidized polyethylene wax; 1.2 parts G60; 0.5 parts PE wax; 2.5 parts AC foaming agent; 0.8 parts color powder; 10 parts light calcium carbonate.

[0025] The specific preparation process steps are as follows: S1. Dry premixing: Add rigid PVC resin powder, calcium-zinc stabilizer, foaming regulator, oxidized polyethylene wax, G60 internal lubricant, PE wax, AC foaming agent, color powder, light calcium carbonate and interface anchoring nanocomposite crosslinking agent into a high-speed mixer according to the formula ratio, stir at high speed at 80-95℃ for 4-6 minutes, and after discharge, cool to below 40℃ in a cold mixer to obtain mixed powder. S2. Extrusion and Foaming: The mixed powder is fed into a parallel twin-screw extruder, plasticized and foamed, and then extruded through a flat die head; the barrel temperature is controlled in sections: Zone 1 135~145℃, Zone 2 155~165℃, Zone 3 168~178℃, Zone 4 172~182℃, and the die head temperature is 165~175℃; the twin-screw extruder speed is 22r / min, and the melt pressure is 10MPa; S3, Cooling and Shaping: The extruded foamed board immediately enters the three-roll calender and water-cooling shaping device, and the roller temperature is controlled at 50-65℃ to quickly freeze and shape the cell structure. S4. Radiation crosslinking: The shaped low-foaming board is irradiated by an electron accelerator with an irradiation dose of 100 kGy, an electron beam energy of 1.5 to 2.5 MeV, and a transmission speed of 5 to 10 m / min to obtain the finished product. Example 2

[0026] Formula: 100 parts PVC; 8 parts IMNA additive; 3.5 parts calcium-zinc stabilizer; 2.5 parts ACR-401; 0.6 parts oxidized wax; 1.0 part G60; 0.4 parts PE wax; 2.0 parts AC foaming agent; 0.6 parts color powder; 12 parts calcium carbonate.

[0027] The specific preparation process is the same as in Example 1, except that the irradiation dose is 80 kGy. Example 3

[0028] Formula: 100 parts PVC; 15 parts IMNA additive; 5 parts calcium-zinc stabilizer; 4 parts ACR-401; 1.0 part oxidized wax; 1.5 parts G60; 0.8 parts PE wax; 3.0 parts AC foaming agent; 1.0 part color powder; 5 parts calcium carbonate.

[0029] The specific preparation process is the same as in Example 1, except that the irradiation dose is 120 kGy.

[0030] Comparative sample preparation: Comparative Example 1 (conventional physical blending): 100 parts PVC; 8 parts EVA (VA 28%); 2 parts nano MMT; 1 part TAIC; the remaining components were the same as in Example 1. All components were directly mixed at high speed, then extruded, cooled, and irradiated with the same dose.

[0031] Comparative Example 2 (without nano-reinforcement): 100 parts PVC; 10 parts EVA-g-TAIC graft (without MMT); the remaining components are the same as in Example 1.

[0032] Comparative Example 3 (non-radiation crosslinking): 100 parts PVC; 10 parts IMNA additive; the remaining components were the same as in Example 1. Extrusion cooling only, without irradiation.

[0033] Comparative Example 4 (Common Market Formula): 100 parts PVC; 4 parts calcium-zinc stabilizer; 3 parts acrylate (ACR); 0.8 parts oxidized wax; 1.2 parts G60; 0.5 parts PE wax; 2.5 parts AC foaming agent; 0.8 parts colorant; 25 parts calcium carbonate.

[0034] Performance Testing and Results Analysis Test standards: tensile strength / elongation at break (GB / T 1040.2), notched impact strength of cantilever beam (GB / T1843), heat distortion temperature (GB / T 1634, 1.82MPa), Vicat softening point (GB / T 1633), density (GB / T 6343). Test results are shown in Table 1. Table 1: Performance Comparison Data of Examples and Comparative Examples

[0035] The test results above show that Comparative Example 1, which uses direct physical blending of EVA, MMT, and TAIC, although the components are the same as those in this invention, lacks the innovative structure of "organic nano-montmorillonite core and EVA-g-TAIC interface anchoring." This results in MMT agglomeration in the PVC matrix and premature local crosslinking of TAIC at high extrusion temperatures, leading to uneven melt flow, cell merging, and rupture. Its impact strength is only 8.6 kJ / m², and its HDT is only 78°C, far lower than that of Example 1. This demonstrates that simply replacing components or physical blending cannot achieve the synergistic effect of this invention.

[0036] Comparative Example 3, without irradiation, showed a sharp drop in impact strength to 6.8 kJ / m² and HDT to 72°C, demonstrating that TAIC in IMNA must be activated by irradiation to construct a three-dimensional network. Comparative Example 2, with the MMT core removed and only EVA-g-TAIC used, exhibited acceptable toughness, but its tensile strength and HDT were significantly lower than those of the examples, proving that the nanosheets act as a "skeleton" for stress transfer and thermal barrier in the cross-linked network.

[0037] Crosslinking gel content is a core indicator for measuring the degree of polymer crosslinking. Uncrosslinked polymer chains are soluble in suitable solvents, while crosslinked network structures are insoluble. The crosslinking density can be characterized by calculating the mass fraction of the insoluble portion using solvent extraction.

[0038] The testing methods used in this paper are as follows: (1) Sample preparation: Cut the PVC low foaming board prepared in the examples and comparative examples into small pieces of about 2mm×2mm×2mm and weigh them accurately (m0, accurate to 0.1mg). (2) Solvent extraction: The sample was placed in a Soxhlet extractor and extracted with acetone as solvent at 56±2℃ for 24h. (3) Drying and weighing: Take out the sample and dry it in a vacuum drying oven at 60℃ until constant weight, and weigh the mass of insoluble matter (m1). (4) Calculation of gel content: Gel content (%) = (m1 / m0) × 100% Table 2: Comparison of Irradiation Dose and Gel Content

[0039] Note: Comparative Example*: Irradiation dose 250 kGy, other conditions the same as in Example 1. The examples utilize an "interface anchoring-irradiation activation" mechanism to significantly increase the crosslinked gel content. Example 1 showed a crosslinked gel content of 68.3% (compared to only 45.2% in Comparative Example 1). With increasing irradiation dose, the gel content initially increased and then slightly decreased, reaching an optimal value of 68.3% at 150 kGy. Compared to Comparative Example 1 (45.2%), the crosslinked gel content increased by 51.1%, demonstrating that the radiation crosslinking process effectively constructed a three-dimensional network structure. The gel content decreased slightly at an irradiation dose of 250 kGy, indicating that excessive irradiation may induce molecular chain breakage (radiative degradation), verifying the existence of an optimal irradiation window. Compared to Comparative Example 4 (commercially available conventional high-calcium powder formulation), Example 1 showed a 290% increase in notched impact strength, a 44% increase in HDT, and a lower density (0.48 vs 0.52). This performance leap is not due to a single component but rather an innovative result of the combined effects of "latent crosslinking precursor design + two-stage decoupling process."

[0040] Furthermore, experimental verification showed that when the irradiation dose was <50kGy, the crosslinking density was insufficient, and the HDT increase was <15℃; when it was >150kGy, the PVC main chain underwent radiation degradation (yellowing index ΔE > 5), and the mechanical properties declined. This invention limits the optimal window to 80-120kGy. If the temperature in the fourth zone of the extruder is >185℃, the AC foaming agent decomposes prematurely, causing material to overflow from the die head; if it is <165℃, plasticization is poor, and the cell wall thickness is uneven. This invention achieves process robustness through strict temperature control and matching with the thermal stability of the IMNA additive.

[0041] The present invention has been described in detail above with reference to the embodiments. It should also be noted that the specific technical features described in the above embodiments can be combined and modified in any suitable manner without contradiction. The present invention will not further describe all possible combinations. Furthermore, other variations and combinations based on the various technical features of the present invention should also be considered as part of the content disclosed in this invention and fall within the protection scope of this invention.

Claims

1. A high-performance PVC low-foaming board, characterized in that, By weight, it includes the following components: 100 parts of rigid PVC resin powder; 8-15 parts of nanocomposite crosslinking aid; 3-5 parts calcium-zinc stabilizer; Foaming regulator 2-4 parts; Oxidized polyethylene wax 0.5-1.0 parts; G60 internal lubricant 0.8-1.5 parts; PE wax 0.3-0.8 parts; AC foaming agent 1.5-3.0 parts; Pigment powder 0.5–1.0 parts; 5-15 parts of light calcium carbonate; The nanocomposite crosslinking aid is a composite microparticle formed by organic nano-montmorillonite as the core and "ethylene-vinyl acetate copolymer grafted with triallyl isocyanurate" as the coating layer.

2. The high-performance PVC low-foaming board according to claim 1, characterized in that, The preparation method of the nanocomposite crosslinking aid includes the following steps: (1) Disperse sodium-based nano-montmorillonite in anhydrous ethanol, add silane coupling agent KH-570, stir and react at 60-80℃ for 3-5h, centrifuge, wash and dry to obtain organic nano-montmorillonite; (2) The organic nano-montmorillonite, ethylene-vinyl acetate copolymer EVA, triallyl isocyanurate TAIC and initiator dicumyl peroxide DCP are put into a mixer and subjected to melt grafting reaction at 110-130℃ and 40-60r / min for 15-25min. (3) Dissolve the grafted product in toluene, add n-hexane to precipitate, filter, vacuum dry to constant weight, and pulverize through a 200-mesh sieve to obtain the nanocomposite crosslinking aid.

3. The high-strength and tough PVC low-foaming board according to claim 1 or 2, characterized in that, The EVA contains 18% to 28% VA, TAIC is used at 5% to 12% of the EVA mass, and DCP is used at 0.3% to 0.8% of the EVA mass.

4. The high-performance PVC low-foaming board according to claim 1, characterized in that, The foaming regulator is an acrylate copolymer ACR-401 or ACR-K400; the K value of the rigid PVC resin powder is 58-62.

5. The high-performance PVC low-foaming board according to claim 1, characterized in that, The high-performance PVC low-foaming board needs to be irradiated by an electron accelerator with an irradiation dose of 80-120 kGy and an electron beam energy of 1.5-2.5 MeV.

6. A method for preparing a high-performance PVC low-foaming board as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Dry premixing: Add rigid PVC resin powder, calcium-zinc stabilizer, foaming regulator, oxidized polyethylene wax, G60 internal lubricant, PE wax, AC foaming agent, color powder, light calcium carbonate and nano-composite crosslinking agent into a high-speed mixer according to the formula ratio, stir at high speed at 80-95℃ for 4-6 minutes, and after discharge, cool to below 40℃ in a cold mixer to obtain mixed powder. S2. Extrusion and Foaming: The mixed powder is fed into a parallel twin-screw extruder, plasticized and foamed, and then extruded through a flat die head; the barrel temperature is controlled in sections: Zone 1 135~145℃, Zone 2 155~165℃, Zone 3 168~178℃, Zone 4 172~182℃, and the die head temperature is 165~175℃; the melt pressure is controlled at 8~12MPa; S3, Cooling and Shaping: The extruded foamed board immediately enters the three-roll calender and water-cooling shaping device, and the roller temperature is controlled at 50-65℃ to quickly freeze and shape the cell structure. S4. Radiation crosslinking: The shaped low-foaming board is irradiated by an electron accelerator with an irradiation dose of 80-120 kGy, an electron beam energy of 1.5-2.5 MeV, and a transmission speed of 5-10 m / min to obtain the finished product.

7. The preparation method according to claim 6, characterized in that, In step S2, the screw length-to-diameter ratio of the twin-screw extruder is 36-40:1, the rotation speed is 18-25 r / min, and the feeding frequency is matched with the main machine speed to ensure that the material residence time in the barrel is controlled within 2.5-3.5 min.

8. The preparation method according to claim 6, characterized in that, Before the irradiation treatment in step S4, the temperature of the foamed board blank has been reduced to room temperature of 20-25°C. The irradiation environment is an inert gas protection environment or an atmospheric pressure air environment. After irradiation, it is left to stand and age for 24-48 hours.

9. The preparation method according to claim 6, characterized in that, The nanocomposite crosslinking aid does not undergo significant crosslinking reaction within the extrusion temperature range of step S2, and the TAIC double bonds in its graft copolymer coating layer only initiate three-dimensional network crosslinking of the PVC / EVA matrix under electron beam irradiation in step S4.

10. The preparation method according to claim 6, characterized in that, The crosslinking gel content of the PVC low-foaming board obtained by radiation crosslinking in step S4 is greater than 58%.

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