Impact-resistant cover plate filled with PU foam and preparation process of impact-resistant cover plate

Abstract

The invention discloses an impact-resistant cover plate filled with PU foam and a preparation process of the impact-resistant cover plate, and relates to the technical field of impact-resistant cover plates. The anti-impact cover plate is composed of a composite laminated board, PU foam and composite filler. The double-sided laminated board is prepared from polypropylene short fibers and Kevlar short fibers, the PU foam is prepared from polyether polyol and polyisocyanate, and the composite filler is prepared from a nano aluminum oxide base material and a PU foam base material; the preparation method comprises the following steps: placing the laminated board in a mold, placing the composite filler on the surface of the laminated board according to a set distance, fixing the opposite side angles of the composite filler, uniformly stirring the polyether polyol, the triethylene diamine, the dibutyltin dilaurate, the dimethyl silicone oil, the triethanolamine, the diethylene glycol and the deionized water, adding the composite filler, and uniformly stirring. And adding polymethylene polyphenyl polyisocyanate, uniformly stirring, adding into a mold, covering with a laminated board, and sealing and curing to obtain the impact-resistant cover plate filled with the PU foam.

Description

Technical Field

[0001] The present invention relates to the technical field of impact-resistant covers, and specifically to an impact-resistant cover filled with PU foam and its preparation process. Background Art

[0002] In the fields of mechanical equipment and transportation tools, etc., as an important protective component, the cover plate often needs to withstand low-speed impacts to prevent internal components from being damaged due to collisions or vibrations. Currently, the impact-resistant cover plate materials are mainly filled with PU foam. Due to its excellent shock absorption and buffering performance, it has been widely used in occasions with high requirements for impact resistance. PU foam materials have the advantages of light weight, good energy absorption effect, and aging resistance, and can effectively disperse the impact force and reduce structural damage. However, a single PU foam filling is prone to fatigue under long-term and high-frequency impacts, resulting in performance degradation, and is easily affected by process factors such as filling uniformity and density control during the preparation process, resulting in unstable impact resistance effects.

[0003] To overcome the above deficiencies, some studies have begun to explore composite filling structures, that is, on the basis of PU foam filling, other composite fillers are introduced, and a high-strength laminate is used as the surface support. This composite structure cover plate can further improve the impact resistance, durability, and fatigue resistance, and especially shows excellent impact absorption and dispersion effects in low-speed impact tests. However, there is still room for optimization in the preparation process of the current composite filling cover plate, especially in achieving the goals of structural lightweight and production efficiency improvement while ensuring the uniform distribution and adhesion of PU foam and composite fillers.

[0004] Therefore, how to further optimize the process design and material ratio of the composite filling impact-resistant cover plate to achieve a more efficient and durable impact resistance effect has become an important research direction at present. Summary of the Invention

[0005] The purpose of the present invention is to provide an impact-resistant cover filled with PU foam and its preparation process to solve the problems raised in the prior art.

[0006] To achieve the above purpose, the present invention provides the following technical solutions: An impact-resistant cover filled with PU foam, the impact-resistant cover is composed of a composite laminate, PU foam, and a composite filler; the double-sided laminate is made of polypropylene short fibers and Kevlar short fibers, the PU foam is made of polyether polyol and polyisocyanate, and the composite filler is made of nano-aluminum oxide substrate 4 and PU foam substrate 3.

[0007] Further, the preparation method of the composite laminate includes the following steps: Mix polypropylene short fibers and Kevlar short fibers evenly according to a set ratio, and place them under a hot press for hot pressing to obtain a composite laminate; Further, during the preparation of the composite laminate, the mass ratio of polypropylene short fibers to Kevlar short fibers is (7 - 3):(3 - 7); the hot pressing temperature of the hot press is 180 - 185 °C, and the time is 5 - 6 min.

[0008] Further, the preparation method of the PU foam includes the following steps: Stir polyether polyol, triethylenediamine, dibutyltin dilaurate, dimethyl silicone oil, triethanolamine, diethylene glycol, and deionized water evenly, add polymethylene polyphenyl polyisocyanate and stir evenly, heat to 70 - 72 °C and react for 12 - 14 h to obtain PU foam; Further, the proportion of each component in the preparation process of the PU foam, by mass fraction, includes: 25 - 35 parts of polyether polyol, 0.25 - 0.3 parts of triethylenediamine, 0.125 - 0.15 parts of dibutyltin dilaurate, 0.5 - 0.75 parts of dimethyl silicone oil, 0.75 - 1 part of triethanolamine, 0.2 - 0.3 parts of diethylene glycol, 0.5 - 1 part of deionized water, and 37.5 - 50 parts of polymethylene polyphenyl polyisocyanate.

[0009] Further, the preparation method of the nano - alumina substrate 4 includes the following steps: Add nano - alumina particles to the mixed solvent, ultrasonically disperse, add chitosan, stir evenly, and let stand for 8 - 10 h to obtain a mixed slurry; before using the mixed slurry, stir it evenly, spin - coat it in an "S" - shaped mold, and heat to 50 - 55 °C for 2 - 3 h to obtain the nano - alumina substrate 4; Further, during the preparation of the nano - alumina substrate 4, the mass ratio of nano - alumina particles to chitosan is (10.8 - 12.5):(1 - 1.2); Further, the mixed solvent is composed of 1M acetic acid and absolute ethanol in a volume ratio of 1:1.

[0010] Further, the preparation method of the PU foam substrate 3 includes the following steps: Add thermoplastic PU particles into an injection molding machine, injection - mold, cut to obtain a thermoplastic PU plate; place the thermoplastic PU plate in a high - pressure container with a layer of melamine foam on both the top and bottom, inject CO2 into the container, perform two - step adsorption, gas - release foaming, and cut to obtain the PU foam substrate 3; Further, during the preparation of the thermoplastic PU plate, the injection rate is 80 cm 3 / s, and the injection volume is 65 cm 3, the injection holding pressure is 60 MPa, the injection holding time is 5 s, and the injection mold temperature is 50 °C; the injection barrel temperatures are 50 °C, 180 °C, 210 °C, 220 °C, 220 °C, and 210 °C respectively; the size of the thermoplastic PU board includes a diameter of 15 cm and a thickness of 3 mm; Further, in the preparation process of the PU foam substrate 3, the two-step adsorption includes low-pressure CO2 adsorption and high-pressure CO2 adsorption. The adsorption process temperature is 130 - 135 °C. The adsorption pressure during the low-pressure CO2 adsorption process is 5 - 6 MPa, and the time is 30 min. The adsorption pressure during the high-pressure CO2 adsorption process is 15 MPa, and the time is 8 - 10 min.

[0011] Further, the preparation method of the PU foam substrate 3 includes the following steps: Coat the upper and lower surfaces of the PU foam substrate 3 with the composite sol, and heat it to 40 - 45 °C for curing for 12 h; Further, the preparation method of the composite sol includes the following steps: Add tetraethyl orthosilicate and absolute ethanol to deionized water, heat to 50 - 55 °C and stir for 1 - 1.5 h, adjust the pH to 3 - 4, stir evenly, and keep it at 50 °C for aging for 48 h to obtain silica sol; add KH550 to phytic acid, react at room temperature for 1 h, add the silica sol, and stir evenly to obtain the composite sol; During the preparation process of the silica sol, the molar ratio of tetraethyl orthosilicate: absolute ethanol: deionized water is 4:1:2; During the preparation process of the composite sol, the mass ratio of KH550: phytic acid: silica sol is 1:5:1.

[0012] Further, the preparation method of the composite filler includes the following steps: Coat 40 wt% aqueous polyurethane on the surface of the PU foam substrate 3, place the center of the nano-alumina substrate 4 overlapping and aligned with the PU foam substrate 3 on the surface of the PU foam substrate 3 to obtain a single-layer filler; stack each single-layer filler in a clockwise direction at 15° for 10 - 11 layers, coat 40 wt% aqueous polyurethane on the surface of the topmost single-layer filler, place the PU foam substrate 3 on its surface, and heat to 80 - 85 °C for curing for 5 - 6 min to obtain the composite filler; Further, the coating thickness of 40 wt% aqueous polyurethane for the single-layer filler is 20 μm.

[0013] Furthermore, in the composite filler, 40 wt% aqueous polyurethane is coated between each layer of single filler, with a thickness of 20 μm; in the nano-alumina substrate 4, the outer angle 1 is 90°, the inner angle 2 is 45°, the width is 0.5 mm, and the thickness is 100 μm; in the PU foam substrate, the diameter is 20 - 30 mm and the thickness is 1 mm.

[0014] Furthermore, in the impact-resistant cover plate, the thickness of the composite laminate is 3 mm, the thickness of the PU foam is 20 mm, the thickness of the impact-resistant cover plate is 26 mm, and the edge interval of the composite filler is 50 - 60 mm; A preparation method of an impact-resistant cover plate filled with PU foam includes the following steps: placing a laminate in a mold, placing the composite filler on the surface of the laminate according to a set distance, fixing the opposite angles of the composite filler, stirring polyether polyol, triethylenediamine, dibutyltin dilaurate, dimethyl silicone oil, triethanolamine, diethylene glycol, and deionized water evenly, adding polymethylene polyphenyl polyisocyanate, stirring evenly, adding it into the mold, covering the laminate, and sealing and heating to 70 - 72 °C for curing for 12 - 14 h to obtain the impact-resistant cover plate filled with PU foam.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention selects a nano-alumina substrate as the substrate and uses a gyroid chiral structure to enhance the absorption of impact incident force; on this basis, it is combined with the PU foam substrate with a transverse gradient cell morphology prepared by two-step adsorption microcellular foaming in the present invention. Utilizing the microcellular - macroporous gradient hierarchical foam structure with the pore size range of 30 μm to 400 μm in the PU foam substrate, the gradient structure of large pores in the middle region and small pores in the edge region further enhances the elasticity and resilience of the composite filler. The gyroid chiral structure and the PU foam substrate provide excellent resilience and cushioning performance for the impact-resistant cover plate.

[0016] 2. The present invention uses the nano-alumina substrate as the hard layer and the PU foam substrate as the soft layer, and the prepared composite filler shows an alternating arrangement of hard and soft layers; when impacted, the nano-alumina particles in the nano-alumina substrate are forced to move and accumulate at the edge of the depression, and the interlayer extrusion causes the hard nano-alumina substrate layer to densify. Interface sliding and interlayer fiber bridging occur during the impact process. The soft layer of the PU foam substrate deforms during the impact process, generating a series of diagonal shear bands. Macroscopically, the weak interface between the hard layer and the soft layer causes crack deflection and the growth of multiple microcracks, absorbing a large amount of impact energy. Microscopically, the relative movement between adjacent particles during the impact process leads to the formation of fiber bridges between nanoparticles. The multi-scale energy absorption mechanism from macro to micro synergistically enhances the impact resistance of the composite filler.

[0017] 3. By further adjusting the size of the composite filler and the edge spacing of the composite filler, the prepared impact-resistant cover plate achieves the best buffering and impact-resistant performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a top view structural schematic diagram of the single-layer filler of the present invention; Among them, the outer corner 1, the inner corner 2, the PU foam substrate 3, and the nano-alumina substrate 4; Figure 2 It is a side view structural schematic diagram of the impact-resistant cover plate of the present invention. SPECIFIC EMBODIMENTS

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0020] In the following embodiments, the specifications of the polypropylene staple fiber are: length 70 mm, fineness 3 D, purchased from Taiwan Chemical Fiber Co., Ltd.; the specifications of the Kevlar staple fiber are: length 50 mm, fineness, 2820 D, 1000 D, 2160 D multifilament, purchased from Formosa Industries Co., Ltd.; the specifications of the polyether polyol are: OH content 430 mgKOH / g, viscosity at 25 °C 2500 mPa·S; the specifications of the polymethylene polyphenyl polyisocyanate are: NCO content 30%, viscosity at 25 °C 200 mPa·S; the specifications of the nano-alumina particles are: particle size 150 nm; the waterborne polyurethane is purchased from Shanghai Macklin Biochemical Co., Ltd.; the rest of the raw materials are all commercially available.

[0021] In the following embodiments, the preparation method of the composite laminate includes the following steps: Mix 5 parts of polypropylene staple fiber and 5 parts of Kevlar staple fiber evenly according to the set ratio, and place them under a hot press at 180 °C for hot pressing for 5 minutes to obtain a composite laminate; In the following embodiments, the preparation method of the nano-alumina substrate 4 includes the following steps: Add 10.8 g of nano-alumina particles to 40 mL of a mixed solvent, ultrasonically disperse, add 1 g of chitosan, stir evenly, and let stand for 8 h to obtain a mixed slurry; before using the mixed slurry, stir it evenly, spin-coat it in an "S"-shaped mold at 500 rpm, and heat it to 50 °C and maintain it for 2 h to obtain the nano-alumina substrate 4; In the following embodiments, the preparation method of the composite sol includes the following steps: Add 4 mol of tetraethyl orthosilicate and 1 mol of absolute ethanol to 2 mol of deionized water. Heat to 50 °C and stir for 1 h. Adjust the pH to 3, stir evenly, and age at 50 °C for 48 h to obtain silica sol. Add 1 g of KH550 to 5 g of phytic acid, react at room temperature for 1 h, add 1 g of silica sol, and stir evenly to obtain a composite sol.

[0022] Example 1: A preparation method of an impact-resistant cover plate filled with PU foam: S1: Add thermoplastic PU particles into an injection molding machine, perform injection molding and cutting to obtain a thermoplastic PU plate. Place the thermoplastic PU plate in a high-pressure container with a layer of melamine foam on each of the top and bottom. Inject CO2 into the container, adsorb at 130 °C and 5 MPa of low-pressure CO2 for 30 min and at 135 °C and 15 MPa of high-pressure CO2 for 8 min, release the gas for foaming, cut, coat the upper and lower surfaces of the PU foam substrate 3 with the composite sol, and heat to 40 °C for curing for 12 h to obtain the PU foam substrate 3; S2: Coat 40 wt% of waterborne polyurethane on the surface of the PU foam substrate 3. Overlap and align the center of the nano-alumina substrate 4 with the PU foam substrate 3 and place it on the surface of the PU foam substrate 3 to obtain a single-layer filler. Stack 10 layers of each single-layer filler in a clockwise rotation at 15°. Coat 40 wt% of waterborne polyurethane on the surface of the topmost single-layer filler, place the PU foam substrate 3 on its surface, and heat to 80 °C for curing for 5 min to obtain a composite filler; S3: Place the laminate in a mold. Place the composite filler on the surface of the laminate according to the set distance. Fix the opposite corners of the composite filler. Stir 25 parts of polyether polyol, 0.25 part of triethylenediamine, 0.125 part of dibutyltin dilaurate, 0.5 part of dimethyl silicone oil, 0.75 part of triethanolamine, 0.2 part of diethylene glycol, and 0.5 part of deionized water evenly, add 37.5 parts of polymethylene polyphenyl polyisocyanate and stir evenly, add it to the mold, cover the laminate, and seal and heat to 70 - 72 °C for curing for 12 - 14 h to obtain an impact-resistant cover plate filled with PU foam; In the PU foam substrate, the diameter is 20 mm and the thickness is 1 mm. In the impact-resistant cover plate, the thickness of the composite laminate is 3 mm, the thickness of the PU foam is 20 mm, the thickness of the impact-resistant cover plate is 26 mm, and the edge interval of the composite filler is 50 mm.

[0023] Example 2: A preparation method of an impact-resistant cover plate filled with PU foam: S1: Add thermoplastic PU particles into an injection molding machine, perform injection molding and cutting to obtain a thermoplastic PU plate; Place the thermoplastic PU plate in a high-pressure container with a layer of melamine foam on each of the top and bottom, inject CO2 into the container, adsorb with low-pressure CO2 at 130 °C and 6 MPa for 30 min and adsorb with high-pressure CO2 at 135 °C and 15 MPa for 10 min, release the gas for foaming, cut, coat the upper and lower surfaces of the PU foam substrate 3 with a composite sol, and heat to 40 °C for curing for 12 h to obtain the PU foam substrate 3; The remaining steps are the same as those in Example 1.

[0024] Example 3: A preparation method of an impact-resistant cover plate filled with PU foam: S2: Coat 40 wt% waterborne polyurethane on the surface of the PU foam substrate 3, place the center of the nano-alumina substrate 4 overlapping and aligned with the PU foam substrate 3 on the surface of the PU foam substrate 3 to obtain a single-layer filler; Stack 11 layers of each single-layer filler in a clockwise rotation at 15 °, coat 40 wt% waterborne polyurethane on the surface of the topmost single-layer filler, place the PU foam substrate 3 on its surface, and heat to 80 °C for curing for 5 min to obtain a composite filler; The remaining steps are the same as those in Example 1.

[0025] Example 4: A preparation method of an impact-resistant cover plate filled with PU foam: In the PU foam substrate, the diameter is 30 mm and the thickness is 1 mm. In the impact-resistant cover plate, the thickness of the composite laminate is 3 mm, the thickness of the PU foam is 20 mm, the thickness of the impact-resistant cover plate is 26 mm, and the edge interval of the composite filler is 50 mm.

[0026] The remaining steps are the same as those in Example 1.

[0027] Example 5: A preparation method of an impact-resistant cover plate filled with PU foam: In the PU foam substrate, the diameter is 20 mm and the thickness is 1 mm. In the impact-resistant cover plate, the thickness of the composite laminate is 3 mm, the thickness of the PU foam is 20 mm, the thickness of the impact-resistant cover plate is 26 mm, and the edge interval of the composite filler is 60 mm.

[0028] The remaining steps are the same as those in Example 1.

[0029] Example 6: A preparation method of an impact-resistant cover plate filled with PU foam: In the PU foam substrate, the diameter is 30 mm and the thickness is 1 mm. In the impact-resistant cover plate, the thickness of the composite laminate is 3 mm, the thickness of the PU foam is 20 mm, the thickness of the impact-resistant cover plate is 26 mm, and the edge interval of the composite filler is 60 mm.

[0030] The remaining steps are the same as those in Example 1.

[0031] Comparative Example 1: A preparation method of an impact-resistant cover plate filled with PU foam: S1: Add thermoplastic PU particles into an injection molding machine, perform injection molding, and cut to obtain a thermoplastic PU plate; place the thermoplastic PU plate in a high-pressure container with a layer of melamine foam on each of the top and bottom, inject CO2 into the container, adsorb low-pressure CO2 at 130°C and 5 MPa for 30 min, release the gas for foaming, cut, coat the upper and lower surfaces of the PU foam substrate 3 with a composite sol, and heat to 40°C for curing for 12 h to obtain the PU foam substrate 3; The remaining steps are the same as those in Example 1.

[0032] Comparative Example 2: A preparation method of an impact-resistant cover plate filled with PU foam: S1: Add thermoplastic PU particles into an injection molding machine, perform injection molding, and cut to obtain a thermoplastic PU plate; place the thermoplastic PU plate in a high-pressure container with a layer of melamine foam on each of the top and bottom, inject CO2 into the container, adsorb low-pressure CO2 at 130°C and 5 MPa for 30 min and adsorb high-pressure CO2 at 135°C and 15 MPa for 5 min, release the gas for foaming, cut, coat the upper and lower surfaces of the PU foam substrate 3 with a composite sol, and heat to 40°C for curing for 12 h to obtain the PU foam substrate 3; The remaining steps are the same as those in Example 1.

[0033] Comparative Example 3: A preparation method of an impact-resistant cover plate filled with PU foam: S1: Add thermoplastic PU particles into an injection molding machine, perform injection molding, and cut to obtain a thermoplastic PU plate; place the thermoplastic PU plate in a high-pressure container with a layer of melamine foam on each of the top and bottom, inject CO2 into the container, adsorb low-pressure CO2 at 130°C and 5 MPa for 30 min and adsorb high-pressure CO2 at 135°C and 15 MPa for 12 min, release the gas for foaming, cut, coat the upper and lower surfaces of the PU foam substrate 3 with a composite sol, and heat to 40°C for curing for 12 h to obtain the PU foam substrate 3; The remaining steps are the same as those in Example 1.

[0034] Comparative Example 4: A preparation method of an impact-resistant cover plate filled with PU foam: S2: Coat 40 wt% aqueous polyurethane on the surface of the PU foam substrate 3, place the center of the nano-aluminum oxide substrate 4 overlapping and aligned with the PU foam substrate 3 on the surface of the PU foam substrate 3 to obtain a single-layer filler; stack 9 layers of each single-layer filler in a clockwise direction at 15°, coat 40 wt% aqueous polyurethane on the surface of the topmost single-layer filler, place the PU foam substrate 3 on its surface, and heat to 80°C for curing for 5 min to obtain a composite filler; The remaining steps are the same as those in Example 1.

[0035] Comparative Example 5: A preparation method of an impact-resistant cover plate filled with PU foam: S2: Coat 40 wt% of waterborne polyurethane on the surface of the PU foam substrate 3, place the center of the nano-alumina substrate 4 overlapping and aligned with the PU foam substrate 3 on the surface of the PU foam substrate 3 to obtain a single-layer filler; Stack 12 layers of each single-layer filler in a clockwise rotation at 15°, coat 40 wt% of waterborne polyurethane on the surface of the topmost single-layer filler, place the PU foam substrate 3 on its surface, and heat to 80 °C for curing for 5 min to obtain a composite filler; The remaining steps are the same as those in Example 1.

[0036] Comparative Example 6: A preparation method of an impact-resistant cover plate filled with PU foam: In the PU foam substrate, the diameter is 50 mm and the thickness is 1 mm. In the impact-resistant cover plate, the thickness of the composite laminate is 3 mm, the thickness of the PU foam is 20 mm, the thickness of the impact-resistant cover plate is 26 mm, and the edge interval of the composite filler is 50 mm; The remaining steps are the same as those in Example 1.

[0037] Comparative Example 7: A preparation method of an impact-resistant cover plate filled with PU foam: In the PU foam substrate, the diameter is 20 mm and the thickness is 1 mm. In the impact-resistant cover plate, the thickness of the composite laminate is 3 mm, the thickness of the PU foam is 20 mm, the thickness of the impact-resistant cover plate is 26 mm, and the edge interval of the composite filler is 20 mm; The remaining steps are the same as those in Example 1.

[0038] Experiment: Low-speed impact test: Measured by a drop hammer impact tester. The drop hammer freely falls from a fixed height to ensure that the incident load each time is 9.0 kN. The drop hammer impacts the sample located in the middle of the load cell to detect the residual load. The lower the residual force, the better the buffering ability of the impact-resistant cover plate.

[0039] The sample size is based on the actual implementation examples and the actual preparation situation of the comparative examples. The impact-resistant cover plate is composed of 3 composite fillers horizontally and has two rows in total. During the test, the impacted surface is the laminate on the side away from the composite filler.

[0040] The experimental results are shown in Table 1 below.

[0041] Table 1 Data table for performance test of impact-resistant cover plates

[0042] Conclusion: The impact-resistant cover plate filled with PU foam prepared by the present invention has excellent impact resistance.

[0043] In Comparative Example 1, since only one low-pressure adsorption foaming was used, the prepared PU foam substrate lacked a gradient foam structure, resulting in a decrease in impact resistance; in Comparative Example 2, due to the too short high-pressure adsorption time, there were too many macroporous structures, resulting in a decrease in impact resistance; in Comparative Example 3, due to the too long high-pressure adsorption time, there were too few macroporous structures, and the foam pore structure was too dense, resulting in a decrease in impact resistance; in Comparative Example 4, due to the small number of stacked layers, the impact resistance decreased; in Comparative Example 5, due to the large number of stacked layers, the impact resistance decreased; in Comparative Example 6, the diameter of the composite filler was too large, resulting in a decrease in impact resistance; in Comparative Example 7, the edge spacing of the composite filler was too small, resulting in a decrease in impact resistance.

[0044] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be construed as limiting the claimed invention.

Claims

1. An impact-resistant cover plate filled with PU foam, characterized in that: The impact-resistant cover plate is composed of a composite laminate, PU foam and a composite filler; the double-sided laminate is made of polypropylene staple fibers and Kevlar staple fibers, the PU foam is made of polyether polyol and polyisocyanate, and the composite filler is made of a nano-alumina substrate (4) and a PU foam substrate (3).

2. The impact-resistant cover plate filled with PU foam according to claim 1, characterized in that: The method for preparing the composite laminate comprises the following steps: The polypropylene short fibers and the Kevlar short fibers are mixed evenly according to a set ratio, and are placed under a hot press for hot pressing to obtain a composite laminate; In the preparation process of the composite laminate, the mass ratio of polypropylene short fiber to Kevlar short fiber is (7-3) to (3-7); the hot pressing temperature of the hot press is 180-185° C., and the time is 5-6 minutes.

3. The impact-resistant cover plate filled with PU foam according to claim 1, wherein: The preparation method of the PU foam comprises the following steps: The polyether polyol, triethylenediamine, dibutyltin dilaurate, dimethyl silicone oil, triethanolamine, diethylene glycol and deionized water are stirred evenly, polymethylene polyphenyl polyisocyanate is added and stirred evenly, and the mixture is heated to 70-72°C and reacted for 12-14 hours to obtain PU foam; The proportions of each component in the preparation process of PU foam, by mass, include: 25-35 parts of polyether polyol, 0.25-0.3 parts of triethylenediamine, 0.125-0.15 parts of dibutyltin dilaurate, 0.5-0.75 parts of dimethyl silicone oil, 0.75-1 parts of triethanolamine, 0.2-0.3 parts of diethylene glycol, 0.5-1 parts of deionized water, and 37.5-50 parts of polymethylene polyphenyl polyisocyanate.

4. The impact-resistant cover plate filled with PU foam according to claim 1, wherein: The preparation method of the nano-alumina substrate (4) comprises the following steps: Add nano-alumina particles to a mixed solvent, disperse by ultrasonication, add chitosan, stir evenly, and let stand for 8-10 hours to obtain a mixed slurry; before using the mixed slurry, stir it evenly, spin-coat it in an "S"-shaped mold, heat it to 50-55° C. and maintain it for 2-3 hours to obtain a nano-alumina substrate (4); During the preparation of the nano-alumina substrate (4), the mass ratio of nano-alumina particles to chitosan is (10.8-12.5): (1-1.2).

5. The impact-resistant cover plate filled with PU foam according to claim 1, wherein: The preparation method of the PU foam substrate (3) comprises the following steps: Thermoplastic PU particles are added to an injection molding machine, injection molded, and cut to obtain a thermoplastic PU board; the thermoplastic PU board is placed in a high-pressure container containing a layer of melamine foam on the top and bottom, CO2 is injected into the container, two-step adsorption, gas release and foaming, and cut to obtain a PU foam substrate (3); During the preparation of the PU foam substrate (3), the two-step adsorption includes low-pressure CO2 adsorption and high-pressure CO2 adsorption. The adsorption process temperature is 130-135°C, the adsorption pressure during the low-pressure CO2 adsorption process is 5-6MPa, and the time is 30min. During the high-pressure CO2 adsorption process, the adsorption pressure is 15MPa, and the time is 8-10min.

6. The impact-resistant cover plate filled with PU foam according to claim 5, characterized in that: The preparation method of the PU foam substrate (3) comprises the following steps: The composite sol is coated on the upper and lower surfaces of the PU foam substrate (3), and heated to 40-45°C for curing for 12 hours; The preparation method of the composite sol comprises the following steps: Add tetraethyl orthosilicate and absolute ethanol to deionized water, heat to 50 - 55 °C and stir for 1 - 1.5 h, adjust the pH to 3 - 4, stir evenly, keep it aging at 50 °C for 48 h to obtain silica sol; add KH550 to phytic acid, react at room temperature for 1 h, add the silica sol, and stir evenly to obtain the composite sol; During the preparation process of the silica sol, the molar ratio of tetraethyl orthosilicate∶absolute ethanol∶deionized water is 4∶1∶2; During the preparation process of the composite sol, the mass ratio of KH550∶phytic acid∶silica sol is 1∶5∶1.

7. The impact-resistant cover plate filled with PU foam according to claim 1, wherein: The preparation method of the composite filler includes the following steps: Coat 40 wt% waterborne polyurethane on the surface of the PU foam substrate (3), place the center of the nano-alumina substrate (4) overlapping and aligned with the PU foam substrate (3) on the surface of the PU foam substrate (3) to obtain a single-layer filler; stack 10 - 11 layers of each single-layer filler in a clockwise rotation at 15°, coat 40 wt% waterborne polyurethane on the surface of the topmost single-layer filler, place the PU foam substrate (3) on its surface, heat to 80 - 85 °C and cure for 5 - 6 min to obtain the composite filler; The coating thickness of 40 wt% waterborne polyurethane on the single-layer filler is 20 μm.

8. The impact-resistant cover plate filled with PU foam according to claim 7, wherein: In the composite filler, 40 wt% waterborne polyurethane is coated between each single-layer filler with a thickness of 20 μm; in the nano-alumina substrate (4), the outer angle (1) is 90°, the inner angle (2) is 45°, the width is 0.5 mm, and the thickness is 100 μm; in the PU foam substrate, the diameter is 20 - 30 mm and the thickness is 1 mm.

9. The impact-resistant cover plate filled with PU foam according to claim 1, wherein: In the impact-resistant cover plate, the thickness of the composite laminate is 3 mm, the thickness of the PU foam is 20 mm, the thickness of the impact-resistant cover plate is 26 mm, and the edge interval of the composite filler is 50 - 60 mm.

10. A method for preparing an impact-resistant cover plate filled with PU foam, characterized in that: Including the following steps: Place the laminate in the mold, place the composite filler on the surface of the laminate according to the set distance, fix the opposite angles of the composite filler, stir polyether polyol, triethylenediamine, dibutyltin dilaurate, dimethyl silicone oil, triethanolamine, diethylene glycol and deionized water evenly, add polymethylene polyphenyl polyisocyanate, stir evenly, add it to the mold, cover the laminate, seal and heat to 70 - 72 °C and cure for 12 - 14 h to obtain the impact-resistant cover plate filled with PU foam.

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