Modified material of shared plastic tray and preparation method of modified material

Abstract

The invention relates to the field of plastic trays, and discloses a modified material of a shared plastic tray and a preparation method of the modified material. The modified material comprises the following raw materials in parts by weight: 60-80 parts of high-density polyethylene, 10-20 parts of polypropylene, 5-15 parts of reinforced fibers, 0.5-1.5 parts of an antioxidant, 0.3-1.0 part of an ultraviolet light absorber, 0.5-1.0 part of a coupling agent, 2-5 parts of an inorganic filler, 0.5-1.0 part of a lubricant and 1-2 parts of a heat stabilizer, and the reinforced fibers are composed of chopped glass fibers and chopped carbon fibers. By adding the antioxidant and the ultraviolet light absorber, oxidation free radicals are effectively captured, ultraviolet energy is absorbed, material degradation is inhibited, meanwhile, an aluminum oxide-silicon dioxide composite nano ceramic coating formed through surface strengthening treatment further blocks erosion of ultraviolet rays and the external environment to the material, and the aging resistance of the tray is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of plastic pallets, and in particular to a modified material for a shared plastic pallet and a preparation method thereof. Background Art

[0002] Plastic pallets, as an important logistics packaging material, play a key role in the logistics and warehousing industries. They are not only lightweight, durable, and easy to clean, but also effectively reduce contamination and moisture exposure during transportation, ensuring the quality of goods. However, over time, plastic pallets are prone to aging, deformation, and cracking, which affect their service life and safety. Therefore, the search for a new modified material that can extend the service life of plastic shared pallets is particularly important.

[0003] Current plastic pallets generally have the problems of short service life and easy damage. To address this problem, there are currently two methods used. One is to optimize the structure of the pallet through physical structural design to increase the carrying capacity. The second method is to mix a certain proportion of glass fiber filler into the base material to improve the material and function of the pallet. However, the surface roughness of this material is relatively high, which is not conducive to cleaning and maintenance. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention provides a modified material for a shared plastic pallet and a preparation method thereof, which solves the common problems of plastic pallets in the existing technology, such as short service life and easy damage. By mixing a certain proportion of glass fiber filler into the base material, the surface roughness is relatively high, which is not conducive to cleaning and maintenance.

[0005] To achieve the above objectives, the present invention is implemented through the following technical scheme: a modified material for a shared plastic pallet, comprising the following raw materials in parts by weight: 60-80 parts of high-density polyethylene, 10-20 parts of polypropylene, 5-15 parts of reinforcing fiber, 0.5-1.5 parts of antioxidant, 0.3-1.0 parts of ultraviolet absorber, 0.5-1.0 parts of coupling agent, 2-5 parts of inorganic filler, 0.5-1.0 parts of lubricant, and 1-2 parts of thermal stabilizer.

[0006] By adopting the above technical solution, the various raw materials work synergistically, effectively improving the overall performance of shared plastic pallets. High-density polyethylene and polypropylene serve as the base materials, giving the pallets basic strength and good molding and processing properties. Reinforced fibers significantly enhance the pallets' mechanical properties, enabling them to withstand greater loads. Antioxidants and UV absorbers inhibit oxidation reactions and absorb UV rays, respectively, extending the pallets' service life. Coupling agents strengthen the bonding between the various raw materials, improving the material's overall performance. Inorganic fillers enhance the pallets' hardness, dimensional stability, and wear resistance, while also reducing costs. Lubricants improve the material's processing fluidity, ensuring smooth molding. Thermal stabilizers inhibit thermal degradation of the material, ensuring the pallets' thermal stability during processing and use.

[0007] Preferably, the reinforcing fibers consist of chopped glass fibers and chopped carbon fibers.

[0008] Preferably, the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], the ultraviolet absorber is 2-hydroxy-4-n-octyloxybenzophenone, the heat stabilizer is a calcium-zinc composite stabilizer, the coupling agent is a silane coupling agent, the inorganic filler is nano-calcium carbonate with a particle size of 20-50 nm, and the surface is modified with stearic acid, and the lubricant is silicone oil or stearate.

[0009] On the other hand, the present application also provides a method for preparing a modified material of a shared plastic pallet, comprising the following steps: S1. Raw material pretreatment: temperature-controlled vacuum drying of high-density polyethylene and polypropylene resin base materials, gradient drying of reinforcing fibers, and coupling agent activation treatment of inorganic fillers; S2, premixing and modification: premix the dried resin base with antioxidant, UV absorber, and heat stabilizer at a low speed, and then introduce the coupling agent and lubricant through high-speed shear mixing; S3. Melt blending: Using a twin-screw extruder, the modified resin matrix is ​​fully melt-blended with the reinforcing fibers and inorganic fillers by controlling the temperature gradient and screw speed in sections; S4, extrusion granulation: control the particle size by constant temperature water granulation, and reduce the moisture content by combining fluidized bed drying; S5, Molding process: adopt segmented temperature-controlled injection molding, multi-level pressure maintenance and real-time monitoring inside the mold; S6. Surface strengthening treatment: Perform wear-resistant strengthening treatment on the bearing surface and edges of the semi-finished plastic pallet.

[0010] Preferably, in the step S1, the high-density polyethylene and polypropylene resin base materials are placed in a vacuum drying oven and dried at 90°C and an absolute pressure of 0.01 MPa for 3 hours, the reinforcing fibers are dried in a 135°C blast drying oven at a gradient temperature of 4.5 hours, and the inorganic filler and the silane coupling agent accounting for 2% of its mass are stirred and activated at 90°C and 400 r / min for 45 minutes.

[0011] Preferably, in step S2, the mixing temperature is 70° C., the stirring speed is 700 r / min, and the mixing time is 12 minutes. After the coupling agent and lubricant are added, the stirring speed is increased to 900 r / min and the mixing is continued for 17 minutes.

[0012] Preferably, in the S3 step, a twin-screw extruder with a length-to-diameter ratio ≥35:1 is used, the temperature of zone 1 of the twin-screw extruder is 190°C, the temperature of zone 2 is 210°C, the temperature of zone 3 is 230°C, the temperature of zone 4 is 250°C, the temperature of zone 5 is 250°C, the head temperature is 240°C, the screw speed is 250r / min, and the residence time of the material in the extruder is 5 minutes.

[0013] Preferably, in step S4, the water temperature of the underwater pelletizing is controlled at 25° C., the particle size is maintained at 4 mm, the drying temperature of the particles in the boiling drying bed is 70° C., the drying time is 6 hours, and the moisture content is reduced to ≤0.1%.

[0014] Preferably, in the step S5, the temperature of the rear section of the injection molding machine barrel is 190°C, the temperature of the middle section is 210°C, the temperature of the front section is 230°C, the nozzle temperature is 230°C, the injection pressure is 100MPa, the holding pressure is 70MPa, the holding time is 15 seconds, the cooling time is 25 seconds, and the parameters are adjusted in real time by the in-mold pressure sensor.

[0015] Preferably, in the step S6, a 0.1-0.3 mm thick alumina-silicon dioxide composite nano-ceramic coating is applied to the bearing surface of the tray, the coating liquid-solid content is 20-30%, and the electrostatic spraying voltage is 80-100 kV, the spray gun distance is 15-20 cm, and the coating is cured at 150-180° C. for 20 to 30 minutes.

[0016] The present invention provides a modified material for a shared plastic pallet and a preparation method thereof. It has the following beneficial effects: 1. The present invention effectively captures oxidative free radicals, absorbs ultraviolet energy, and inhibits material degradation by adding antioxidants and ultraviolet absorbers. At the same time, the aluminum oxide-silicon dioxide composite nano-ceramic coating formed by surface strengthening treatment further blocks the erosion of ultraviolet rays and the external environment on the material, significantly improving the aging resistance of the pallet.

[0017] 2. The present invention composites reinforcing fibers composed of chopped glass fibers and chopped carbon fibers with high-density polyethylene and polypropylene matrix materials, utilizing the synergistic reinforcement effect of the two fibers to significantly improve the pallet's impact resistance, deformation resistance, and load-bearing capacity. At the same time, the addition of surface-modified nano-calcium carbonate inorganic fillers further enhances the material's hardness and dimensional stability, making the pallet less prone to cracking or deformation during frequent handling and stacking, thereby greatly improving the pallet's overall durability.

[0018] 3. During the preparation process, the present invention effectively reduces the surface roughness of the tray through surface modification treatment of inorganic fillers, addition of lubricants and surface strengthening process, making it smoother and easier to clean, solving the problem of rough surface that is not conducive to maintenance in the prior art. At the same time, the segmented temperature-controlled injection molding and gradient drying process optimize the material processing performance, ensuring that the material is uniform and stable in the melt blending, extrusion granulation and other links, improving the controllability of the production process and the consistency of product quality, and taking into account both processing efficiency and tray performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a flow chart of a method for preparing a modified material of a shared plastic pallet. DETAILED DESCRIPTION

[0020] The following will clearly and completely describe the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0021] Please see the attached Figure 1 An embodiment of the present invention provides a modified material for a shared plastic pallet, comprising the following raw materials in parts by weight: 60-80 parts of high-density polyethylene, 10-20 parts of polypropylene, 5-15 parts of reinforcing fiber, 0.5-1.5 parts of an antioxidant, 0.3-1.0 parts of an ultraviolet absorber, 0.5-1.0 parts of a coupling agent, 2-5 parts of an inorganic filler, 0.5-1.0 parts of a lubricant, and 1-2 parts of a thermal stabilizer; the reinforcing fiber comprises chopped glass fiber and chopped carbon fiber; the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], the ultraviolet absorber is 2-hydroxy-4-n-octyloxybenzophenone, the thermal stabilizer is a calcium-zinc composite stabilizer, the coupling agent is a silane coupling agent, the inorganic filler is nano-calcium carbonate with a particle size of 20-50 nm, and the surface is modified with stearic acid, and the lubricant is silicone oil or stearate.

[0022] Specifically, high-density polyethylene: molecular weight range 40,000 to 300,000, as the main matrix of the modified material, gives the shared plastic pallet basic strength and rigidity, ensuring good molding and processing performance. Polypropylene: Works synergistically with high-density polyethylene to further optimize material processing performance while improving the toughness of the pallet. Reinforcement fiber (composite of chopped glass fiber and chopped carbon fiber): compounded with the matrix material, significantly improves the mechanical properties of shared plastic pallets, such as tensile strength, flexural strength and impact strength. Antioxidant (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate]): can effectively capture free radicals generated by oxidation during the use of materials, inhibit oxidation reactions, and extend the service life of shared plastic pallets. Ultraviolet absorber (2-hydroxy-4-n-octyloxybenzophenone): specially used to absorb ultraviolet rays, prevent shared plastic pallets from degradation and aging due to ultraviolet radiation, and maintain the physical properties of the material. Coupling agent (silane coupling agent): forms chemical bonds between different raw materials, strengthens the interfacial bonding between fiber and matrix material, inorganic filler and matrix material, etc., and improves the overall performance of the material. Inorganic fillers (nano-calcium carbonate with a particle size of 20-50nm and surface modified with stearic acid): After addition, they can improve the hardness, dimensional stability and wear resistance of shared plastic pallets, while helping to reduce costs. Lubricant (silicone oil or stearate): Reduces the friction between the material and the equipment during processing, improves the fluidity of the material, and makes the molding of shared plastic pallets smoother. Thermal stabilizer (calcium zinc composite stabilizer): During the processing and use of shared plastic pallets, it inhibits the degradation of the material due to heat, stabilizes the chemical structure of the material, and improves thermal stability.

[0023] A method for preparing a modified material for a shared plastic pallet comprises the following steps: S1. Raw material pretreatment: temperature-controlled vacuum drying of high-density polyethylene and polypropylene resin base materials, gradient drying of reinforcing fibers, and coupling agent activation treatment of inorganic fillers; S2, premixing and modification: premix the dried resin base with antioxidant, UV absorber, and heat stabilizer at a low speed, and then introduce the coupling agent and lubricant through high-speed shear mixing; S3. Melt blending: Using a twin-screw extruder, the modified resin matrix is ​​fully melt-blended with the reinforcing fibers and inorganic fillers by controlling the temperature gradient and screw speed in sections; S4, extrusion granulation: control the particle size by constant temperature water granulation, and reduce the moisture content by combining fluidized bed drying; S5, Molding process: adopt segmented temperature-controlled injection molding, multi-level pressure maintenance and real-time monitoring inside the mold; S6. Surface strengthening treatment: Perform wear-resistant strengthening treatment on the bearing surface and edges of the semi-finished plastic pallet.

[0024] In step S1, the high-density polyethylene and polypropylene resin base materials are placed in a vacuum drying oven and dried at 90°C and an absolute pressure of 0.01 MPa for 3 hours. The reinforcing fibers are dried in a 135°C forced air drying oven at a gradient temperature of 4.5 hours. The inorganic filler and a silane coupling agent accounting for 2% of its mass are stirred and activated at 90°C and 400 r / min for 45 minutes.

[0025] Specifically, temperature-controlled vacuum drying of high-density polyethylene and polypropylene resin base materials removes volatile impurities such as moisture from the raw materials, preventing defects such as bubbles and holes caused by moisture vaporization during subsequent processing, which can affect pallet quality. Gradient drying of the reinforcing fibers allows the moisture within the fibers to evaporate slowly and evenly, preventing embrittlement due to rapid water loss and ensuring the reinforcing effect. Activating the inorganic fillers with a coupling agent forms an active film on the surface of the inorganic filler, strengthening the bond between the filler and the base material and improving material performance. For example, this treatment can increase the pallet's tensile strength by 10-15%.

[0026] In step S2, the mixing temperature is 70° C., the stirring speed is 700 r / min, and the mixing time is 12 minutes. After the coupling agent and lubricant are added, the stirring speed is increased to 900 r / min and the mixing is continued for 17 minutes.

[0027] Specifically, the dried resin base is premixed with antioxidants, UV absorbers, and thermal stabilizers at a low speed to achieve a preliminary, even dispersion of these additives within the resin base. The coupling agent and lubricant are then introduced through high-speed shear mixing. The high-speed shear force further promotes the reaction of the coupling agent with the raw materials and evenly distributes the lubricant throughout the material, optimizing its performance.

[0028] In step S3, a twin-screw extruder with a length-to-diameter ratio ≥35:1 is used, the temperature of zone 1 of the twin-screw extruder is 190°C, the temperature of zone 2 is 210°C, the temperature of zone 3 is 230°C, the temperature of zone 4 is 250°C, the temperature of zone 5 is 250°C, the head temperature is 240°C, the screw speed is 250 r / min, and the residence time of the material in the extruder is 5 minutes.

[0029] Specifically, a twin-screw extruder with an aspect ratio of 35:1 or greater is used. Through a specific segmented temperature gradient (zone 1: 190°C, zone 2: 210°C, zone 3: 230°C, zone 4: 250°C, zone 5: 250°C, and die head temperature: 240°C) and screw speed regulation (250 r / min), the modified resin matrix, reinforcing fibers, and inorganic fillers are gradually melted and thoroughly mixed in different temperature zones. The appropriate temperature gradient ensures optimal melting and mixing of the materials at different stages, while the screw speed controls the material residence time in the extruder (5 minutes), ensuring full fusion of the raw materials and forming a uniform and stable composite material.

[0030] In step S4, the water temperature of the underwater pelletizing is controlled at 25°C, the particle size is maintained at 4 mm, the drying temperature of the particles in the boiling drying bed is 70°C, the drying time is 6 hours, and the moisture content is reduced to ≤0.1%.

[0031] Specifically, the water temperature for underwater pelletizing is controlled at 25°C, ensuring stable material temperature during the pelletizing process. This prevents deformation and sticking of pellets due to excessively high or low temperatures, and maintains the pellet size at the standard 4mm specification. The pellets are dried in the fluidized bed at 70°C for 6 hours, effectively reducing the moisture content to ≤0.1%. This removes moisture from the pellets, preventing it from adversely affecting subsequent molding processes, such as causing defects like bubbles and cracks, and improving product quality.

[0032] In step S5, the temperature of the rear section of the injection molding machine barrel is 190°C, the temperature of the middle section is 210°C, the temperature of the front section is 230°C, the nozzle temperature is 230°C, the injection pressure is 100MPa, the holding pressure is 70MPa, the holding time is 15 seconds, and the cooling time is 25 seconds. The parameters are adjusted in real time through the in-mold pressure sensor.

[0033] Specifically, the injection molding machine barrel temperature is set at 190°C at the rear section, 210°C at the middle section, 230°C at the front section, and 230°C at the nozzle. This temperature setting ensures good material fluidity during the injection molding process, allowing the material to smoothly fill the mold cavity. The injection pressure is 100 MPa, the holding pressure is 70 MPa, the holding time is 15 seconds, and the cooling time is 25 seconds. In-mold pressure sensors adjust these parameters in real time to ensure product dimensional accuracy and surface quality.

[0034] In step S6, a 0.1-0.3 mm thick alumina-silicon dioxide composite nano-ceramic coating is applied to the bearing surface of the pallet, with a liquid-solid content of 20-30%. The coating is electrostatically sprayed at a voltage of 80-100 kV and a spray gun distance of 15-20 cm. The coating is cured at 150-180°C for 20-30 minutes.

[0035] Specifically, a 0.1-0.3mm thick alumina-silicon dioxide composite nano-ceramic coating with a liquid-to-solids content of 20-30% is applied to the pallet's load-bearing surface using electrostatic spraying at a voltage of 80-100kV, sprayed at a distance of 15-20cm, and cured at 150-180°C for 20-30 minutes. This coating significantly improves the wear resistance of the pallet's load-bearing surface, preventing it from wearing out during frequent cargo loading and extending its service life.

[0036] The following is an introduction with reference to specific embodiments: Example

[0037] Raw material ratio: 65 parts of high-density polyethylene, 15 parts of polypropylene, 12 parts of reinforcing fiber (mass ratio of chopped glass fiber and chopped carbon fiber 3:1), 1.0 part of antioxidant (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 0.6 part of UV absorber (2-hydroxy-4-n-octyloxybenzophenone), 0.7 part of coupling agent (silane coupling agent), 3 parts of inorganic filler (nano-calcium carbonate with a particle size of 20-50nm, surface modified with stearic acid), 0.8 part of lubricant (zinc stearate), and 1.5 parts of heat stabilizer (calcium zinc composite stabilizer).

[0038] Preparation steps: S1 Raw material pretreatment: Place the high-density polyethylene and polypropylene resin base materials in a vacuum drying oven and dry them at 90°C and an absolute pressure of 0.01 MPa for 3 hours; dry the reinforcing fibers in a 135°C forced air drying oven at a gradient temperature of 4.5 hours; stir and activate the inorganic filler and 2% of its mass silane coupling agent at 90°C and 400 r / min for 45 minutes.

[0039] S2 premixing and modification: the mixing temperature was 70°C, the stirring speed was 700 r / min, and the mixing time was 12 minutes. After the coupling agent and lubricant were added, the stirring speed was increased to 900 r / min and the mixing was continued for 17 minutes.

[0040] S3 melt blending: A twin-screw extruder with a length-to-diameter ratio of 35:1 was used. The temperature of zone 1, zone 2, zone 3, zone 4, zone 5, and die head were 240°C, the screw speed was 250 r / min, and the residence time of the material in the extruder was 5 minutes.

[0041] S4 extrusion granulation: The water temperature of underwater granulation is controlled at 25℃, the particle size is maintained at 4mm, the drying temperature of the particles in the boiling drying bed is 70℃, the drying time is 6 hours, and the moisture content is reduced to ≤0.08%.

[0042] S5 molding process: The temperature of the rear section of the injection molding machine barrel is 190°C, the temperature of the middle section is 210°C, the temperature of the front section is 230°C, the nozzle temperature is 230°C, the injection pressure is 100MPa, the holding pressure is 70MPa, the holding time is 15 seconds, and the cooling time is 25 seconds. The parameters are adjusted in real time through the in-mold pressure sensor.

[0043] S6 surface strengthening treatment: Coat the pallet bearing surface with a 0.2mm thick aluminum oxide-silicon dioxide composite nano-ceramic coating with a liquid-solid content of 25%. Use electrostatic spraying voltage of 90kV, spray gun distance of 18cm, and cure at 160℃ for 25 minutes.

[0044] Example 2: Raw material ratio: 70 parts of high-density polyethylene, 12 parts of polypropylene, 10 parts of reinforcing fiber (mass ratio of chopped glass fiber and chopped carbon fiber 2:1), 1.2 parts of antioxidant (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 0.8 parts of UV absorber (2-hydroxy-4-n-octyloxybenzophenone), 0.9 parts of coupling agent (silane coupling agent), 4 parts of inorganic filler (nano-calcium carbonate with a particle size of 20-50nm, surface modified with stearic acid), 1.0 part of lubricant (silicone oil), 2.0 parts of heat stabilizer (calcium zinc composite stabilizer).

[0045] Preparation steps: S1 raw material pretreatment: Place the high-density polyethylene and polypropylene resin base materials in a vacuum drying oven and dry them at 90°C and an absolute pressure of 0.01 MPa for 3 hours; dry the reinforcing fibers in a 140°C forced air drying oven at a gradient temperature of 5 hours; and stir and activate the inorganic filler and 2% of its mass silane coupling agent at 90°C and 400 r / min for 45 minutes.

[0046] S2 premixing and modification: the mixing temperature was 70°C, the stirring speed was 700 r / min, and the mixing time was 12 minutes. After the coupling agent and lubricant were added, the stirring speed was increased to 900 r / min and the mixing was continued for 17 minutes.

[0047] S3 melt blending: A twin-screw extruder with a length-to-diameter ratio of 35:1 was used. The temperature of zone 1, zone 2, zone 3, zone 4, zone 5, and die head were 245°C, the screw speed was 280 r / min, and the residence time of the material in the extruder was 5 minutes.

[0048] S4 extrusion granulation: The water temperature of underwater granulation is controlled at 25℃, the particle size is maintained at 4mm, the drying temperature of the particles in the boiling drying bed is 70℃, the drying time is 6 hours, and the moisture content is reduced to ≤0.10%.

[0049] S5 molding process: The temperature of the rear section of the injection molding machine barrel is 190°C, the temperature of the middle section is 210°C, the temperature of the front section is 230°C, the nozzle temperature is 230°C, the injection pressure is 100MPa, the holding pressure is 70MPa, the holding time is 15 seconds, and the cooling time is 25 seconds. The parameters are adjusted in real time through the in-mold pressure sensor.

[0050] S6 surface strengthening treatment: Coat the pallet bearing surface with a 0.3mm thick aluminum oxide-silicon dioxide composite nano-ceramic coating with a liquid-solid content of 30%. Use electrostatic spraying with a voltage of 100kV and a spray gun distance of 20cm, and cure at 180℃ for 30 minutes.

[0051] Comparative Example: Comparative Example 1 (lack of antioxidant): Raw material ratio: 65 parts of high-density polyethylene, 15 parts of polypropylene, 12 parts of reinforcing fiber (mass ratio of chopped glass fiber and chopped carbon fiber 3:1), 0.6 parts of UV absorber (2-hydroxy-4-n-octyloxybenzophenone), 0.7 parts of coupling agent (silane coupling agent), 3 parts of inorganic filler (nano-calcium carbonate with a particle size of 20-50nm, surface modified with stearic acid), 0.8 parts of lubricant (zinc stearate), and 1.5 parts of heat stabilizer (calcium zinc composite stabilizer).

[0052] Preparation steps: The same as in Example 1, except that no antioxidant is added in the S2 premixing and modification step.

[0053] Comparative Example 2 (lack of UV absorber): Raw material ratio: 65 parts of high-density polyethylene, 15 parts of polypropylene, 12 parts of reinforcing fiber (mass ratio of chopped glass fiber and chopped carbon fiber 3:1), 1.0 part of antioxidant (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 0.7 part of coupling agent (silane coupling agent), 3 parts of inorganic filler (nano-calcium carbonate with a particle size of 20-50nm, surface modified with stearic acid), 0.8 part of lubricant (zinc stearate), and 1.5 parts of heat stabilizer (calcium zinc composite stabilizer).

[0054] Preparation steps: The same as in Example 1, but no ultraviolet absorber is added in the S2 premixing and modification step.

[0055] Comparative Example 3 (no surface strengthening treatment): The raw material ratio is the same as that of Example 1.

[0056] Preparation steps: The same as in Example 1, but omitting the S6 surface strengthening treatment step.

[0057] Table 1: Performance comparison of shared plastic pallet modified material examples and comparative examples Comparison items Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Tensile strength before aging (MPa) 38.0 40.5 37.5 37.8 37.9 Tensile strength after aging (MPa) 30.4 34.4 22.5 26.5 28.0 Tensile strength retention rate 80% 85% 60% 70% 74% Flexural strength before aging (MPa) 42.0 45.0 41.5 42.0 42.2 Flexural strength after aging (MPa) 33.6 38.3 24.9 29.4 31.2 Bending strength retention rate 80% 85% 60% 70% 74% Impact strength before aging (kJ / m²) 12.0 13.0 11.8 11.9 12.0 Impact strength after aging (kJ / m²) 9.6 11.0 7.1 8.3 8.9 Impact strength retention rate 80% 85% 60% 70% 74% Color change after aging (grayscale value) 10 8 25 20 15 Surface roughness before aging Ra (μm) 0.5 0.5 0.5 0.5 0.5 Surface roughness after aging Ra (μm) 0.6 0.6 0.9 0.8 0.7 Surface wear after 1000 simulated frictions Minor wear Minor wear Moderate wear Moderate wear Severe wear and tear Whether cracks appear after aging none none have have have Comparison project explanation: Tensile Strength Before Aging (MPa): This indicator measures the shared plastic pallet's ability to resist fracture under tensile loads before aging. A higher value indicates a greater tensile strength the material can withstand during initial normal use. This makes the pallet less likely to deform or break due to tensile forces while carrying cargo, making it a crucial parameter for evaluating the pallet's initial mechanical properties.

[0058] Tensile Strength After Aging (MPa): This indicator reflects the change in the tensile strength of shared plastic pallets after aging. Aging simulates the state of pallets subjected to various environmental factors in actual use, such as oxidation and UV exposure. A higher tensile strength after aging indicates that the material retains good tensile properties after aging. This indicates that the pallet maintains a certain load-bearing capacity and is less susceptible to damage due to stretching even in long-term use or harsh environments.

[0059] Tensile Strength Retention Rate: This is the ratio of the tensile strength after aging to the tensile strength before aging, expressed as a percentage. This indicator intuitively demonstrates the degree to which the material maintains its tensile strength during the aging process. The higher the retention rate, the better the material's aging resistance.

[0060] Flexural Strength Before Aging (MPa): This indicator assesses a shared plastic pallet's ability to resist bending deformation in its unaged state. When a pallet is subjected to bending forces in actual use, materials with higher flexural strength are less likely to deform. For example, during stacking or handling, this indicator reflects the pallet's ability to withstand bending stresses. Higher values ​​indicate greater structural stability under these conditions.

[0061] Post-Aging Flexural Strength (MPa): This value represents the flexural strength of the shared plastic pallet after aging. It reflects the pallet's resistance to bending deformation after aging. The higher the post-aging flexural strength, the better the material's resistance to bending after aging, and the less likely the pallet will bend and break when subjected to bending forces in actual use.

[0062] Flexural Strength Retention: This is the percentage of flexural strength after aging compared to flexural strength before aging, reflecting the material's flexural strength retention during the aging process. A higher retention rate indicates less degradation in the material's flexural properties after aging, and thus better aging resistance. For example, the flexural strength retention rate in Example 2 is 85%, indicating that the material's flexural properties remain high after aging, better meeting the actual bending resistance requirements of pallets.

[0063] Impact Strength Before Aging (kJ / m²): This parameter measures the ability of shared plastic pallets to resist impact loads in their original state. In actual use, pallets may be subject to impacts such as dropped goods and collisions. A higher impact strength before aging indicates a stronger resistance to impact in the material's initial state, making the pallet less likely to break or damage in the event of an unexpected impact. This is a key indicator of pallet safety and durability.

[0064] Impact Strength After Aging (kJ / m²): This value reflects the impact strength changes of shared plastic pallets after aging. A higher impact strength indicates a material's improved resistance to impact. This allows the pallet to maintain its superior impact resistance even in long-term use or harsh environments, effectively reducing damage caused by impact and ensuring its continued use.

[0065] Impact Strength Retention Rate: Calculated as the ratio of the impact strength after aging to the impact strength before aging, expressed as a percentage. This indicator intuitively reflects the degree to which a material retains its impact strength during the aging process. A higher retention rate indicates a smaller decline in the material's impact resistance after aging, and thus better aging resistance. For example, a pallet with a high impact strength retention rate indicates that it can still effectively withstand impacts after aging, making it more reliable in actual use.

[0066] Color Change After Aging (Grayscale): This metric quantifies the degree of color change after aging of shared plastic pallets. The grayscale value measures the depth of color; a larger change indicates a more pronounced color change after aging. Color change is typically due to chemical changes in the material during aging, such as oxidation and UV-induced degradation. Therefore, color change after aging (grayscale) can be used as a reference indicator for assessing the degree of material degradation; higher grayscale values ​​indicate more severe material degradation.

[0067] Surface roughness Ra (μm) before aging: Surface roughness Ra is a parameter used to describe the microscopic geometric characteristics of the shared plastic pallet surface. It indicates the smoothness of the pallet's surface before aging. A lower value indicates a smoother pallet surface. In actual use, a smooth surface facilitates cargo handling and cleaning, while also reducing friction between the cargo and the pallet, preventing damage.

[0068] Aging Surface Roughness Ra (μm): This indicator reflects the change in surface smoothness of a shared plastic pallet after aging. If the aging Ra value increases, it indicates that the pallet's surface has become rougher, which may affect the stability of cargo placement, increase cleaning difficulties, and even cause scratches. Therefore, this indicator can intuitively reflect the impact of aging on the pallet's surface quality. A larger change in the value indicates more severe damage to the surface quality.

[0069] Surface wear after 1000 simulated friction cycles: This comparison evaluates the extent of surface wear on a pallet by simulating the friction experienced when carrying cargo. After 1000 simulated friction cycles, the wear condition of the pallet's surface is observed, including the presence of visible scratches and the depth of the wear marks. The less wear, the better the pallet's surface resistance, indicating its ability to maintain a good surface condition over long-term use, extending the pallet's lifespan.

[0070] Cracks after Aging: This test directly observes whether cracks appear on the surface of shared plastic pallets after aging. The presence of cracks can seriously affect the pallet's strength and load-bearing capacity, reducing its service life and even rendering it inoperable. The absence of cracks after aging indicates that the material has maintained good structural integrity and excellent aging resistance. Conversely, the presence of cracks indicates that the material has aged significantly, significantly impacting its structural performance.

[0071] Analysis and discussion of the differences in test parameters between the examples and the comparative examples: The key role of antioxidants: According to the comparative data in Table 1, Examples 1 and 2, in which antioxidants were added, had tensile strength retention rates of 80% and 85% after aging, respectively. Comparative Example 1, which lacked an antioxidant, had a tensile strength retention rate of only 60%. The antioxidant (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) can effectively capture free radicals generated by oxidation during material use and inhibit oxidation reactions. During material aging, oxidation reactions destroy the molecular chain structure, leading to a decrease in material performance. The presence of the antioxidant in the examples slows the rate of molecular chain destruction, thereby maintaining a high strength retention rate, demonstrating its key role in improving the material's aging resistance.

[0072] The importance of UV absorbers: Example 1 contains a UV absorber (2-hydroxy-4-n-octyloxybenzophenone), while Comparative Example 2 lacks this ingredient. The grayscale values ​​of the color changes after aging in Example 1 and Example 2 are 10 and 8, respectively, while that in Comparative Example 2 is 20. The strength retention rate of Example 1 is also higher than that of Comparative Example 2. This is because UV absorbers are specifically designed to absorb ultraviolet light, preventing material degradation and aging due to UV exposure. Comparative Example 2 lacks this substance, and under the influence of ultraviolet light, the internal structure of the material is damaged, the color changes are obvious, and the mechanical properties deteriorate even more significantly, demonstrating the importance of UV absorbers in maintaining the material's physical properties and aging resistance.

[0073] Effects of Surface Strengthening Treatment: Example 1 underwent surface strengthening treatment, including coating with an alumina-silicon dioxide composite nano-ceramic coating, while Comparative Example 3 remained untreated. After 1000 simulated friction cycles, Examples 1 and 2 showed minimal surface wear, minimal change in surface roughness after aging, and no cracks. Comparative Example 3, on the other hand, showed severe surface wear, a significant increase in surface roughness, and cracks after aging. This demonstrates that the coating formed by surface strengthening treatment significantly improves the wear resistance of the pallet's load-bearing surface, blocks UV rays and environmental damage, and protects the material's internal structure, thereby enhancing the pallet's aging resistance.

[0074] The creative and beneficial effects of added substances: A comprehensive comparison of the examples and comparative examples shows that the added antioxidants, UV absorbers, and surface hardening treatments work together to enhance the pallet's aging resistance at various levels. The antioxidants and UV absorbers inhibit oxidation and UV degradation reactions within the material, while the surface hardening treatment forms a protective barrier on the surface. The synergistic effect of these substances and processes addresses the aging issues of existing plastic pallets, significantly extending their service life and improving their overall performance compared to traditional pallets.

[0075] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A modified material for a shared plastic pallet, characterized in that: The invention comprises the following raw materials in parts by weight: 60-80 parts of high-density polyethylene, 10-20 parts of polypropylene, 5-15 parts of reinforcing fiber, 0.5-1.5 parts of antioxidant, 0.3-1.0 parts of ultraviolet absorber, 0.5-1.0 parts of coupling agent, 2-5 parts of inorganic filler, 0.5-1.0 parts of lubricant and 1-2 parts of heat stabilizer.

2. The modified material of a shared plastic pallet according to claim 1, characterized in that: The reinforcing fibers consist of chopped glass fibers and chopped carbon fibers.

3. The modified material of a shared plastic pallet according to claim 1, characterized in that: The antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], the ultraviolet absorber is 2-hydroxy-4-n-octyloxybenzophenone, the heat stabilizer is a calcium-zinc composite stabilizer, the coupling agent is a silane coupling agent, the inorganic filler is nano-calcium carbonate with a particle size of 20-50 nm, and the surface is modified with stearic acid, and the lubricant is silicone oil or stearate.

4. A method for preparing a modified material for a shared plastic pallet, characterized in that: The modified material for a shared plastic pallet according to any one of claims 1 to 3 comprises the following steps: S1. Raw material pretreatment: temperature-controlled vacuum drying of high-density polyethylene and polypropylene resin base materials, gradient drying of reinforcing fibers, and coupling agent activation treatment of inorganic fillers; S2, premixing and modification: premix the dried resin base with antioxidant, UV absorber, and heat stabilizer at a low speed, and then introduce the coupling agent and lubricant through high-speed shear mixing; S3. Melt blending: Using a twin-screw extruder, the modified resin matrix is ​​fully melt-blended with the reinforcing fibers and inorganic fillers by controlling the temperature gradient and screw speed in sections; S4, extrusion granulation: control the particle size by constant temperature water granulation, and reduce the moisture content by combining fluidized bed drying; S5, Molding process: adopt segmented temperature-controlled injection molding, multi-level pressure maintenance and real-time monitoring inside the mold; S6. Surface strengthening treatment: Perform wear-resistant strengthening treatment on the bearing surface and edges of the semi-finished plastic pallet.

5. The method for preparing a modified material for a shared plastic pallet according to claim 4, characterized in that: In the step S1, the high-density polyethylene and polypropylene resin base materials are placed in a vacuum drying oven and dried at 90°C and an absolute pressure of 0.01 MPa for 3 hours. The reinforcing fibers are dried in a 135°C forced air drying oven at a gradient temperature of 4.5 hours. The inorganic filler and a silane coupling agent accounting for 2% by weight are stirred and activated at 90°C and 400 r / min for 45 minutes.

6. The method for preparing a modified material for a shared plastic pallet according to claim 4, characterized in that: In the step S2, the mixing temperature is 70° C., the stirring speed is 700 r / min, and the mixing time is 12 minutes. After the coupling agent and lubricant are added, the stirring speed is increased to 900 r / min and the mixing is continued for 17 minutes.

7. The method for preparing a modified material for a shared plastic pallet according to claim 4, characterized in that: In the S3 step, a twin-screw extruder with a length-to-diameter ratio ≥35:1 is used, the temperature of zone 1 of the twin-screw extruder is 190°C, the temperature of zone 2 is 210°C, the temperature of zone 3 is 230°C, the temperature of zone 4 is 250°C, the temperature of zone 5 is 250°C, the head temperature is 240°C, the screw speed is 250 r / min, and the residence time of the material in the extruder is 5 minutes.

8. The method for preparing a modified material for a shared plastic pallet according to claim 4, characterized in that: In step S4, the water temperature of the underwater pelletizing is controlled at 25° C., the particle size is maintained at 4 mm, the drying temperature of the particles in the boiling drying bed is 70° C., the drying time is 6 hours, and the moisture content is reduced to ≤0.1%.

9. The method for preparing a modified material for a shared plastic pallet according to claim 4, characterized in that: In the step S5, the temperature of the rear section of the injection molding machine barrel is 190°C, the temperature of the middle section is 210°C, the temperature of the front section is 230°C, the nozzle temperature is 230°C, the injection pressure is 100 MPa, the holding pressure is 70 MPa, the holding time is 15 seconds, and the cooling time is 25 seconds. The parameters are adjusted in real time by the in-mold pressure sensor.

10. The method for preparing a modified material for a shared plastic pallet according to claim 4, characterized in that: In the step S6, a 0.1-0.3 mm thick alumina-silicon dioxide composite nano-ceramic coating is applied to the bearing surface of the tray, with a liquid-solid content of 20-30%. The coating is electrostatically sprayed at a voltage of 80-100 kV and a spray gun distance of 15-20 cm, and cured at 150-180° C. for 20-30 minutes.

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