A method for manufacturing a stone paper inner container

Abstract

The application belongs to the technical field of stone paper packaging manufacturing, and particularly relates to a stone paper inner holder preparation method. The stone paper material sheet is heated to a high elastic state and has thermoplasticity, and then is moved to the top of a female die of a preheated and constant-temperature hot-pressing die and is placed on the female die. Then, compressed air is sent through the air charging and discharging holes at the bottom of the female die to complete the tensile pre-deformation of the stone paper material sheet. After the lower pressing of the male die and the die closing and plastic shaping, the inner holder blank is obtained after cooling and setting. Finally, the edges are trimmed to obtain the inner holder finished product. The forming speed is fast, the processing efficiency is high, the integrated three-dimensional modeling with complex curved surfaces and continuous cavities can be simply manufactured, the stone paper material sheet is environmentally friendly and recyclable, the resin required for the raw material can be prepared from old plastic, and the stone paper has the advantages of low cost and environmental protection.

Description

Technical Field

[0001] This invention belongs to the field of stone paper packaging manufacturing technology, specifically relating to a method for preparing a stone paper inner tray. Background Technology

[0002] Inner trays are primarily used to secure and cushion contents, providing protective space. They are widely used in electronics, cosmetics, food, gifts, and precision instruments. Currently, most inner trays are manufactured using traditional plant fiber paper, an environmentally friendly material. Mainstream molding processes include pulp molding, die-cutting and folding of sheets or boards, and thermoforming.

[0003] However, the aforementioned traditional processes based on plant fiber paper all have certain limitations. Specifically, pulp molding requires a secondary processing step of wet pressing and subsequent drying and shaping, resulting in a long production cycle and high energy consumption; die-cutting and folding box making relies on the bending and splicing of materials, making it difficult to form integrated structures with complex curved surfaces and continuous cavities, thus limiting design freedom; and plant fiber paper has limited plastic deformation capacity during thermoforming, with a typically low elongation ratio, making it difficult to achieve deep stretching and intricate three-dimensional shapes. This limits its application in high-end, compact packaging. Therefore, seeking an alternative material and suitable process that combines excellent processing performance and environmental friendliness has become an inherent requirement for the industry's development.

[0004] With increasing global emphasis on ecological protection and sustainable resource utilization, stone paper, made primarily from inorganic mineral powders such as calcium carbonate and resin, is gradually being promoted as a new type of environmentally friendly material. In its production, the resin raw materials are often derived from recycled plastics, and finished stone paper products can also be directly recycled and reused, offering advantages such as being green, environmentally friendly, and cost-effective. Furthermore, stone paper products possess characteristics such as waterproofing, moisture resistance, high mechanical strength, and low energy consumption in production, and are currently being gradually applied in industries such as packaging and printing. Given that its matrix is ​​a thermoplastic polymer, the molecular chains can rearrange and reposition under heating conditions, theoretically possessing the potential to achieve complex plastic molding through hot pressing. Moreover, it allows for the reuse of recycled plastic and stone paper products, making the use of stone paper to prepare inner trays a promising option.

[0005] Therefore, it is necessary to provide a corresponding molding process for stone paper that combines environmental protection characteristics with excellent processing performance in order to prepare finished inner trays for various fields. Summary of the Invention

[0006] In view of the requirements for environmental protection, material processing performance and cost in the manufacture of finished inner trays in the existing technology, the present invention provides a method for preparing stone paper inner trays.

[0007] A method for preparing a stone paper inner tray includes: Step S1: conveying a stone paper sheet to a preset position and simultaneously heating the top and bottom surfaces of the stone paper sheet to make the stone paper sheet exhibit a highly elastic state; Step S2: moving the stone paper sheet above a female mold of a hot press mold and placing it on the female mold, then clamping and fixing the edges of the stone paper sheet; Step S3: introducing compressed air through the air inlet and outlet holes at the bottom of the female mold to make the highly elastic stone paper sheet bulge upward in an arc shape, completing the stretching pre-deformation of the stone paper sheet; Step S4: Heat the male and female molds of the hot press mold to the same temperature as the stone paper sheet and keep it warm. Then, control the male mold of the hot press mold to press down and fit it against the stretched and pre-deformed stone paper sheet. At this time, stop the supply of compressed air. Then, the male mold drives the stone paper sheet to move downward together and discharges the gas between the stone paper sheet and the female mold until it is completely closed with the female mold. When the pressing pressure reaches the preset value and the male mold and the female mold are closed, stop the pressing action and enter the pressure holding stage. Step S5: Stop the heat holding of the hot press mold and let it cool for a predetermined time. After that, the stone paper sheet is shaped into an inner support blank. Release the pressure of the hot press mold and control the male mold to rise so that it separates from the female mold and completes the mold opening. Step S6: Release the clamps on the inner support blank and send compressed air through the air inlet and outlet holes to separate the inner support blank from the female mold. Then, take out the inner support blank and send it to the edge trimming machine for edge trimming to obtain the finished inner support.

[0008] Further, in step S1, the manufacturing steps of the stone paper sheet are as follows: Step S11: Prepare the following raw materials in parts by weight: 0.3-0.5 parts compatibilizer, 78-88 parts modified calcium carbonate, 10-15 parts resin, 4-6 parts flame retardant, 0.8-1.2 parts lubricant, and 0.2-0.4 parts anti-aging agent; Step S12: Mix the raw materials in step S11 to obtain a mixed powder; Step S13: Humidify and granulate the mixed powder, and dry it to obtain dried particles; Step S14: Extrude the dried particles through a twin-screw extruder to obtain an extruded sheet; Step S15: Stretch the extruded sheet to obtain a sheet; Step S16: Calender and shape the sheet, and cool it to obtain the stone paper sheet.

[0009] Further, in step S11, the preparation method of the modified calcium carbonate includes the following steps: S111, weighing 1.5-2.0% of the mass of calcium carbonate with methacryloyloxysilane coupling agent; weighing 0.5-1.0% of the mass of calcium carbonate with aminosilane coupling agent, and mixing the methacryloyloxysilane coupling agent and aminosilane coupling agent with an ethanol aqueous solution accounting for 3-6 times their total mass to obtain a composite coupling agent solution; wherein, the calcium carbonate includes calcium carbonate I, calcium carbonate II and calcium carbonate III in a mass ratio of (1.4-1.7):1:(0.3-0.5), and the average particle size of calcium carbonate I is smaller than the average particle size of calcium carbonate II. The average particle size of calcium carbonate II is smaller than that of calcium carbonate III; S112, calcium carbonate is placed in a high-speed mixer, and 0.3-0.5% of a dispersant by mass of calcium carbonate is weighed and added. The mixture is stirred to obtain fully dispersed calcium carbonate. The calcium carbonate is then dried and cooled for later use; S113, calcium carbonate and composite coupling agent solution are placed in a high-speed mixer and mixed, reacted, filtered, and dried at 50℃-55℃ to obtain coupling agent modified calcium carbonate; S114, the temperature of the high-speed mixer is raised to 80-90℃, PP-g-MAH powder is added, and the mixture is stirred under heat preservation conditions and cooled to room temperature to obtain modified calcium carbonate.

[0010] Further, the resin comprises polypropylene, thermoplastic polyurethane and polyamide in a mass ratio of (1.8-2):(0.4-0.6):(0.8-1).

[0011] Further, in step S16, the sheet material is calendered and shaped using a calendering device; specifically, the calendering device includes a frame and a calendering roll group and an embossing roll group mounted on the frame for calendering and producing stone paper sheets. A working channel is provided on the frame, and the calendering roll group and the embossing roll group are sequentially distributed and rotatably arranged within the working channel. The embossing roll group includes a composite rubber roll and a mirror roll; the mirror roll is located directly above the composite rubber roll and forms a shaped channel with it; the composite rubber roll includes an outer roll body and a heat-resistant rubber layer covering the outer surface of the outer roll body, and a first cavity is formed within the outer roll body; a first tubular connector and a second pipe are respectively provided at both ends of the outer roll body. The outer roller body is rotatably connected to both sides of the working channel through the first tubular joint and the second tubular joint, and extends through to the outside; both the first tubular joint and the second tubular joint are in communication with the first cavity; a closed inner roller body is provided in the first cavity, and a spiral protrusion is distributed on the outer surface of the inner roller body. The end of the spiral protrusion is connected to the inner sidewall of the first cavity and forms a spiral flow channel in communication with the first cavity; the spiral flow channel is used to supply coolant to the first tubular joint and flow to the second tubular joint; a first drive mechanism is provided on one side of the frame, which is used to drive the mirror roller and the composite rubber roller to rotate synchronously and to compact and shape the stone paper sheet passing through the shaping channel.

[0012] Further, in step S1, the heating temperature T is 90℃-150℃; the heating duration t≥30d, where t is in seconds and d is the thickness of the stone paper sheet in mm; in step S4, the preset value of the downward pressure is 0.12MPa-1MPa.

[0013] Further, in step S1, the top and bottom surfaces of the stone paper sheet are simultaneously heated by a double-sided heating device. The double-sided heating device includes a heating chamber, a feeding channel, and a discharging channel. The left and right sides of the heating chamber have symmetrically arranged feeding and discharging ports. The feeding channel is connected to the feeding port, and the discharging channel is connected to the discharging port. Both the feeding and discharging channels include a conveyor frame and several conveying rollers rotatably mounted on the conveyor frame, with the conveying rollers arranged horizontally side-by-side. Several guide rollers, parallel to the conveying rollers, are rotatably mounted inside the heating chamber, with the upper surfaces of the guide rollers and the upper surfaces of the conveying rollers on the same horizontal plane. Both the conveying rollers and guide rollers include a stainless steel roller body and a Teflon coating on the surface of the stainless steel roller body. Several sets of infrared heating tubes and several sets of infrared heating elements are also fixedly installed inside the heating chamber. The heating element consists of a second heat pipe, an upper mounting bracket, and a lower mounting bracket. The first infrared heating pipe is located above the guide roller, and several groups of first infrared heating pipes are arranged in an equidistant array along the direction from the inlet to the outlet. The upper mounting bracket is located above the first infrared heating pipe. The second infrared heating pipe and the lower mounting bracket are both located below the guide roller and are symmetrically arranged with the first infrared heating pipe and the lower mounting bracket, respectively. At least one turbine fan is installed on both the upper and lower mounting brackets. An upper vent hood communicating with the heating chamber is provided at the upper end of the heating chamber, and a lower vent hood communicating with the heating chamber is provided at the lower end of the heating chamber. A support base is also provided at the lower end of the heating chamber. The stone paper sheet enters the heating chamber through the conveyor roller of the inlet channel for heating and is then discharged through the conveyor roller of the outlet channel. At least one infrared temperature probe for detecting the stone paper sheet is installed on the conveyor frame of the outlet channel.

[0014] Furthermore, both the male mold and the female mold include a mold body; the mold body of the female mold is recessed inward to form a molding cavity; the inflation and deflation port is located at the bottom of the molding cavity and is connected to an air inlet pipe; the bottom of the mold body of the male mold extends into the molding cavity to cooperate with the female mold; both the mold bodies of the female mold and the male mold have a built-in heating mechanism and at least one temperature sensor for detecting the temperature of the mold body; the heating mechanism includes several mounting holes arranged side by side in the mold body; a heating rod is built into each mounting hole, a limiting ring is fixedly provided on the surface of the heating rod, a threaded cap is movably sleeved on the surface of the limiting ring, and the heating rod is fixed to the mounting hole by the threaded cap. At the opening; a connector is fixedly installed on the surface of the heating rod away from the mounting hole, and the connector is connected to an external power supply through a current regulator; the current regulator and the temperature sensor are respectively electrically connected to a controller; a cooling sleeve is fitted on the outer periphery of the mold body of both the female mold and the male mold, and the connector passes through the cooling sleeve and extends to the outside; the cooling sleeve includes a sleeve body fitted on the outer periphery of the mold body, an annular groove is opened on the upper part of the sleeve body, and a spiral cooling pipe is provided in the annular groove. One end of the cooling pipe is connected to a coolant inlet pipe, and the other end is connected to a coolant outlet pipe. A solenoid valve electrically connected to the controller is respectively provided on the coolant inlet pipe and the coolant outlet pipe.

[0015] Further, step S3 specifically includes: injecting compressed air into the female mold at a constant pressurization rate through the inflation and deflation holes at the bottom of the female mold until the injected air pressure reaches a preset air pressure value, and then maintaining the preset air pressure value output, causing the highly elastic stone paper sheet to bulge upward in an arc shape, completing the stretching pre-deformation of the stone paper sheet; wherein, the preset air pressure value H is the pre-stretch height; E is the elastic modulus of the stone paper sheet in a highly elastic state; d is the thickness of the stone paper sheet; K is the preset shape coefficient; and D is the length of the pre-deformed stone paper sheet.

[0016] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: This invention belongs to the field of stone paper packaging manufacturing technology, specifically relating to a method for preparing stone paper inner trays. The method involves heating a stone paper sheet to a highly elastic state, making it thermoplastic, then moving it above a preheated and temperature-controlled hot press mold's female mold and placing it on the female mold. Compressed air is then introduced through the air inlet and outlet holes at the bottom of the female mold to complete the stretching and pre-deformation of the stone paper sheet. The male mold then presses down and closes the mold to shape the sheet. After cooling and solidification, an inner tray preform is obtained. Finally, the edges are trimmed to obtain the finished inner tray. This method offers fast molding speed and high processing efficiency, enabling the easy manufacture of integrated three-dimensional shapes with complex curved surfaces and continuous cavities. Furthermore, the stone paper sheet is environmentally friendly and recyclable, and the resin required for its production can be recycled from old plastics, offering advantages such as low cost and environmental friendliness. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the steps of a method for preparing a stone paper inner tray provided by the present invention; Figure 2 This is a schematic diagram of a method for preparing a stone paper inner tray provided by the present invention; Figure 3 This is a three-dimensional structural diagram of the calendering equipment provided by the present invention; Figure 4 This is a schematic diagram of the internal structure of the calendering equipment provided by the present invention; Figure 5 This is a schematic diagram of the structure of the composite rubber roller provided by the present invention; Figure 6 This is a schematic diagram of the internal structure of the heating box provided by the present invention; Figure 7 A simplified structural schematic diagram of the hot pressing mold provided by the present invention; Figure 8 A simplified schematic diagram of the cross-sectional structure of the female mold provided by the present invention; Figure 9 This is a schematic diagram of the structure of the heating rod provided by the present invention; Attached Figure

[0018] 1. Stone paper sheet; 2. Frame; 201. Working channel; 3. Calendering roll assembly; 31. Roller A; 32. Roller B; 33. Roller C; 34. Roller D; 4. Embossing roll assembly; 41. Composite rubber roller; 411. Outer roller body; 412. Heat-resistant rubber layer; 413. First cavity; 414. First tubular joint; 415. Second tubular joint; 416. Inner roller body; 417. Spiral protrusion; 418. Spiral flow channel; 418; 42. Mirror roller; 43. Shaping channel; 5. Heating box; 6. Feed channel; 7. Discharge channel; 51. Feed inlet; 52. Discharge outlet; 61. Conveyor frame; 62. Conveyor roller; 54. 55. Infrared heating tube 1; 56. Infrared heating tube 2; 57. Upper mounting bracket; 58. Lower mounting bracket; 59. Turbine fan; 10. Upper vent hood; 11. Lower vent hood; 12. Support base; 13. Infrared temperature probe; 14. Hot press mold; 151. Female mold; 16. Male mold; 17. Inflation and exhaust port; 18. Inner tray finished product; 19. Mold body; 10. Molding cavity; 11. Temperature sensor; 12. Heating rod; 13. Restriction ring; 14. Threaded cap; 15. Connector; 16. Coolant inlet pipe; 17. Coolant outlet pipe; 18. Cooling jacket; 19. Sleeve body; 10. Cooling pipe. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0020] refer to Figure 1 and Figure 2 As shown, the present invention provides a method for preparing a stone paper inner tray, including steps S1 to S6.

[0021] Specifically, step S1: The stone paper sheet 1 is conveyed to a preset position, and the top and bottom surfaces of the stone paper sheet 1 are simultaneously heated, causing the stone paper sheet 1 to exhibit a highly elastic state. In this embodiment, the stone paper sheet 1 is a single-structure sheet or multi-layer composite material made of stone paper; the multi-layer composite material includes, but is not limited to, hollow extruded plates, multi-layer co-extruded sheets / films, corrugated plates, and honeycomb panels. The stone paper sheet 1 can be manufactured using recycled materials, possessing the characteristics of being green and environmentally friendly, and having low cost.

[0022] In practical use, when the heating temperature of the stone paper sheet 1 is controlled between its viscous flow temperature and melting temperature, the stone paper sheet 1 exhibits a highly elastic state. In the highly elastic state, the molecular chains of the stone paper sheet 1 are still entangled and fixed, but the chain segments can move freely, extend and curl. That is, the stone paper sheet 1 can maintain its original shape and is soft and deformable.

[0023] Wherein, the heating temperature T is 90℃-150℃; the heating duration t≥30d, where t is in seconds and d is the thickness of the stone paper sheet 1 in mm.

[0024] In step S1, the manufacturing steps of the stone paper sheet 1 are as follows: Step S11: Prepare the following raw materials in parts by weight: 0.3-0.5 parts compatibilizer, 78-88 parts modified calcium carbonate, 10-15 parts resin, 4-6 parts flame retardant, 0.8-1.2 parts lubricant, and 0.2-0.4 parts anti-aging agent. In this embodiment, the resin is manufactured using recycled plastics, thereby achieving resource reuse, reducing costs, and possessing environmentally friendly characteristics.

[0025] Step S12: Mix the raw materials from step S11 to obtain a mixed powder.

[0026] Step S13: Moisten and granulate the mixed powder, then dry it to obtain dried particles.

[0027] Step S14: The dried particles are extruded through a twin-screw extruder to obtain extruded sheets.

[0028] Step S15: Stretch the extruded sheet to obtain a sheet.

[0029] Step S16: The sheet is calendered and shaped, and then cooled to obtain the stone paper sheet 1.

[0030] The stone paper sheet 1 prepared by this invention possesses excellent comprehensive mechanical properties and outstanding flame retardant characteristics. By using modified calcium carbonate and resin, the mechanical properties of the material are significantly improved. Simultaneously, the synergistic addition of an environmentally friendly halogen-free flame retardant significantly increases the oxygen index of the stone paper, making it suitable for packaging applications with high safety requirements. This ensures the prepared stone paper exhibits excellent mechanical properties, no powdering, and good processing flowability, enhancing the dispersion effect of the flame retardant and improving flame retardancy.

[0031] In addition, the addition of lubricant reduces internal friction and die resistance of the twin-screw extruder during the extrusion, calendering, and compression molding of the particle melt, resulting in a smooth and flat extruded sheet surface free of crystal points and cracks. It also improves the fluidity of the particle melt, helping to shorten the molding cycle. The addition of anti-aging agent effectively inhibits resin degradation and interface aging of the modified calcium carbonate powder under light, high temperature, and oxidative conditions, delaying yellowing, brittleness, and mechanical degradation of the stone paper sheet 1. This improves the weather resistance, high and low temperature resistance, and long-term storage stability of the stone paper sheet 1, extending its service life.

[0032] In step S11, the method for preparing the modified calcium carbonate includes steps S111 to S116.

[0033] Specifically, the steps are as follows: S111, weigh 1.5-2.0% of the mass of calcium carbonate in methacryloyloxysilane coupling agent; weigh 0.5-1.0% of the mass of calcium carbonate in aminosilane coupling agent, and mix the methacryloyloxysilane coupling agent and aminosilane coupling agent with an ethanol aqueous solution that accounts for 3-6 times their total mass to obtain a composite coupling agent solution.

[0034] By modifying calcium carbonate with methacryloyloxysilane coupling agent, aminosilane coupling agent and PP-g-MAH powder, the prepared modified calcium carbonate and resin have higher compatibility, and improved mechanical properties and anti-floating powder effect.

[0035] Specifically, the two silane coupling agents react chemically with the hydroxyl groups on the surface of calcium carbonate through their silane ends, forming a strong Si-O-Ca covalent bond. Aminosilanes have a strong affinity for polyamides; the amino group can form strong hydrogen bonds with the carboxyl groups at the ends of the PA molecular chain or the amide bonds in the chain, and may even undergo amidation to form covalent bonds; the amino group can also form hydrogen bonds with the urethane bonds in polyamides. The methacryloyloxy group of methacryloylsilane has good compatibility with both soft and hard segments in thermoplastic polyurethanes, and can be tightly entangled through intermolecular forces and van der Waals forces. One end of PP-g-MAH firmly grasps the surface of the already coupled filler through covalent bonds. The main chain of PP-g-MAH is polypropylene, which can be integrated into the resin matrix through interdiffusion, entanglement, and even co-crystallization of the molecular chains. Through the synergistic effect of these three, the mechanical properties and anti-floating powder effect are improved.

[0036] The calcium carbonate comprises calcium carbonate I, calcium carbonate II, and calcium carbonate III in a mass ratio of (1.4-1.7):1:(0.3-0.5), wherein the average particle size of calcium carbonate I is smaller than that of calcium carbonate II, and the average particle size of calcium carbonate II is smaller than that of calcium carbonate III.

[0037] This invention achieves graded filling through multi-scale particle blending of calcium carbonate, thereby improving mechanical properties and anti-floating powder effects. The mixing of particles of different sizes allows smaller particles to fill the gaps between larger particles, and even smaller particles to fill even smaller gaps. This enables the calcium carbonate to achieve the densest packing, improving flowability and processability, enhancing mechanical properties, and resulting in a more uniform stress distribution, avoiding stress concentration caused by localized defects.

[0038] S112. Place calcium carbonate in a high-speed mixer, weigh and add 0.3-0.5% of the dispersant by weight of calcium carbonate, stir and mix to obtain fully dispersed calcium carbonate; then dry and cool the calcium carbonate for later use. S113. Place calcium carbonate and composite coupling agent solution into a high-speed mixer, mix and react at 50℃-55℃, filter and dry to obtain coupling agent modified calcium carbonate. S114. Raise the temperature of the high-speed mixer to 80-90℃, add PP-g-MAH powder, stir under heat preservation conditions, and cool to room temperature to obtain modified calcium carbonate.

[0039] Preferably, in step S11, the resin comprises polypropylene, thermoplastic polyurethane and polyamide in a mass ratio of (1.8-2):(0.4-0.6):(0.8-1).

[0040] By compounding PP, PA, and UF resins, the interfacial bonding strength between modified calcium carbonate and these resins can be greatly improved, enabling highly uniform and stable dispersion of modified calcium carbonate in the compounded resins. This not only gives the resulting stone paper excellent mechanical properties and no surface powder precipitation, but also improves the melt processing fluidity of the system and promotes the uniform dispersion of flame retardants in the substrate, further enhancing the overall flame retardant performance.

[0041] Preferably, in step S16, the sheet is calendered and shaped by a calendering device; specifically, the calendering device includes a frame 2 and a calendering roller group 3 and an embossing roller group 4 arranged on the frame 2 for calendering to produce stone paper sheet 1. The frame 2 is provided with a working channel 201, and the calendering roller group 3 and the embossing roller group 4 are sequentially distributed and rotatably arranged in the working channel 201.

[0042] The calendering roll group 3 includes rollers A31, B32, C33, and D34 rotatably mounted in the working channel 201. Rollers A31, B32, C33, and D34 are all the same size. Roller B32 is located on the side of roller A31 closer to the embossing roll group 4 and is in a calendering fit. Roller C33 is located directly below roller B32 and is in a calendering fit. Roller D34 is located directly below roller C33 and is in a calendering fit.

[0043] The embossing roller assembly 4 includes a composite rubber roller 41 and a mirror roller 42; the mirror roller 42 is located directly above the composite rubber roller 41, and forms a shaped channel 43 between them. The composite rubber roller 41 has a surface hardness of 30°A to 90°A, and its surface is ground and polished.

[0044] The composite rubber roller 41 includes an outer roller body 411 and a heat-resistant rubber layer 412 covering the outer surface of the outer roller body 411. A first cavity 413 is formed inside the outer roller body 411. A first tubular connector 414 and a second tubular connector 415 are respectively provided at both ends of the outer roller body 411. The outer roller body 411 is rotatably connected to both sides of the working channel 201 through the first tubular connector 414 and the second tubular connector 415, and extends through to the outside. The first tubular connector 414 and the second tubular connector 415 are both in communication with the first cavity 413. Inside the first cavity 413... A closed inner roller body 416 is provided, and a spiral protrusion 417 is distributed on the outer surface of the inner roller body 416. The end of the spiral protrusion 417 is connected to the inner sidewall of the first cavity 413 and forms a spiral flow channel 418 communicating with the first cavity 413. The spiral flow channel 418 is used to supply coolant from the first tubular connector 414 to the second tubular connector 415. A first drive mechanism is provided on one side of the frame 2. The first drive mechanism is used to drive the mirror roller 41 and the composite rubber roller 42 to rotate synchronously and to compact and shape the stone paper sheet 1 passing through the shaping channel 43.

[0045] The stone paper sheet 1 produced by the calendering roll group 3 is conveyed into the shaping channel 43, thereby driving the mirror roll 41 and the composite rubber roll 42 to rotate synchronously, so that the stone paper sheet 1 in the shaping channel 43 is pressed and compacted, completing the shaping of the stone paper sheet 1. At the same time, during the pressing and compaction process, coolant is continuously introduced into the first cavity 413 through the first tubular joint 414, then flows through the spiral flow channel 418 in the outer roll body 411, and finally flows out through the second tubular joint 415. The circulation of coolant continuously absorbs the heat on the composite rubber roll 41, effectively avoiding the phenomenon of coolant adhering to the finished stone paper and uneven heating and flaking damage to the rubber roll caused by using a water tank to cool the rubber roll, thereby improving the yield of stone paper production. In addition, the spiral flow channel 418 effectively extends the flow path and residence time of the coolant in the outer roll body 411, thereby effectively improving the efficiency of heat exchange.

[0046] Preferably, refer to Figure 3 As shown, in step S1, the top and bottom surfaces of the stone paper sheet 1 are heated simultaneously by a double-sided heating device.

[0047] The double-sided heating device includes a heating chamber 5, a feeding channel 6, and a discharging channel 7; the left and right sides of the heating chamber 5 are symmetrically provided with a feeding port 51 and a discharging port 52; the feeding channel 6 is connected to the feeding port 51, and the discharging channel 7 is connected to the discharging port 52.

[0048] Both the feeding channel 6 and the discharging channel 7 include a conveying frame 61 and several conveying rollers 62 rotatably mounted on the conveying frame 61, and the conveying rollers 62 are arranged horizontally side by side; several guide rollers 53 are rotatably mounted inside the heating box 5 and arranged parallel to the conveying rollers 62, and the upper surface of the guide rollers 53 and the upper surface of the conveying rollers 62 are located on the same horizontal plane.

[0049] The conveying roller 62 and the guide roller 53 each include a stainless steel roller body and a Teflon coating on the surface of the stainless steel roller body.

[0050] The heating chamber 5 is also equipped with several sets of infrared heating tubes 54, several sets of infrared heating tubes 55, an upper mounting bracket 56, and a lower mounting bracket 57. The infrared heating tubes 54 are located above the guide roller 53, and the several sets of infrared heating tubes 54 are arranged in an equidistant array along the direction from the feed inlet 51 to the discharge outlet 52. The upper mounting bracket 56 is located above the infrared heating tubes 54. The infrared heating tubes 55 and the lower mounting bracket 57 are both located below the guide roller 53 and are symmetrically arranged with respect to the infrared heating tubes 54 and the lower mounting bracket 57, respectively. At least one turbine fan 58 is installed on both the upper mounting bracket 56 and the lower mounting bracket 57; an upper vent 8 communicating with the upper end of the heating chamber 5 is provided, and a lower vent 9 communicating with the lower end of the heating chamber 5 is provided, and a support base 10 is also provided at the lower end of the heating chamber 5. The stone paper sheet 1 enters the heating chamber 5 through the conveyor roller 62 of the feeding channel for heating, and is then sent out through the conveyor roller 62 of the discharge channel 7; at least one infrared temperature probe 11 for detecting the stone paper sheet 1 is installed on the conveyor frame 61 of the discharge channel 7.

[0051] Stone paper sheet 1 enters the feeding channel 7. At this time, the conveying roller 62 rotates synchronously under the drive, feeding the stone paper sheet 1 from the feeding port 51 into the heating chamber 5. After entering the heating chamber 5, the stone paper sheet 1 is transported towards the discharge port 52 by the guide roller 53. In the heating chamber 5, multiple sets of infrared heating tubes 1-54 continuously radiate infrared rays downwards to heat the top surface of the stone paper sheet 1 conveyed by the guide roller 53, while multiple sets of infrared heating tubes 2-55 continuously radiate infrared rays upwards to synchronously heat the bottom surface of the stone paper sheet 1. During the heating process, the turbine fan 58 installed on the upper mounting frame 56 and the lower mounting frame 57 starts, agitating the gas in the heating chamber 5 and forcing the hot air to circulate, thereby breaking the temperature stratification caused by the natural rise of hot air, making the temperature distribution in the heating chamber 5 more uniform, effectively avoiding the problem of local overheating or uneven heating of the stone paper sheet 1, and improving the heating efficiency of the stone paper sheet 1.

[0052] Meanwhile, the water vapor or volatile substances evaporated during the heating of the stone paper sheet 1 are drawn upwards and downwards by the hot airflow. The upward portion is discharged through the upper vent 8, and the downward portion is discharged through the lower vent 9. The heated stone paper sheet 1 is then moved out from the discharge port 52 on the other side of the heating chamber 5 and enters the discharge channel 7 for output.

[0053] In addition, by setting the infrared temperature probe 11, the surface temperature of the completed stone paper sheet 1 can be obtained, thereby determining whether the stone paper sheet 1 has reached the high elastic state. At the same time, the overall conveying speed of the guide roller and the conveying roller can be controlled according to the temperature.

[0054] Step S2: Move the stone paper sheet 1 above the female mold 121 of a hot press mold 12 and place it on the female mold 121, and then clamp and fix the edge of the stone paper sheet 1.

[0055] Step S3: Compressed air is introduced through the air inlet / outlet 1211 at the bottom of the female mold 121, causing the highly elastic stone paper sheet 1 to bulge upwards in an arc shape, completing the pre-stretching deformation of the stone paper sheet 1. By pre-stretching the stone paper sheet 1, it is possible to achieve uniform stretching before stamping, significantly improving its forming performance and reducing the risk of defects such as cracking, wrinkling, and excessive springback due to local stress concentration during subsequent stamping. At the same time, the pre-stretching deformation can make the internal stress distribution of the stone paper sheet 1 more uniform, effectively improving the yield of the stamped inner tray finished product.

[0056] Specifically, step S3 is as follows: compressed air is supplied into the female mold 121 at a constant pressurization rate through the air inlet and outlet 1211 at the bottom of the female mold 121 until the supplied air pressure reaches the preset air pressure value, and then the preset air pressure value is maintained to output, so that the highly elastic stone paper sheet 1 bulges upward in an arc shape, thus completing the stretching pre-deformation of the stone paper sheet 1.

[0057] Among them, the preset air pressure value H is the pre-stretch height; E is the elastic modulus of the stone paper sheet 1 in a highly elastic state; d is the thickness of the stone paper sheet 1; K is the preset shape coefficient; and D is the length of the pre-deformed stone paper sheet 1.

[0058] The principle of this formula is as follows: By sending in compressed air, a uniformly distributed air pressure load is applied to the stone paper sheet 1, causing the stone paper sheet 1 to deform upward in an arc shape; when the external load generated by the air pressure reaches a deformation equilibrium state with the bending stiffness determined by the thickness and elastic modulus of the stone paper sheet itself, the air pressure value required for the corresponding pre-stretching height can be quantitatively determined by this formula, thereby achieving precise control of the pre-stretching deformation process of the stone paper sheet.

[0059] Step S4: Heat the male mold 122 and female mold 121 of the hot pressing mold 12 to the same temperature as the stone paper sheet 1 and keep it warm. Then control the male mold 122 of the hot pressing mold 12 to press down and fit with the stretched and pre-deformed stone paper sheet 1. At this time, stop the supply of compressed air. Then the male mold 122 drives the stone paper sheet 1 to move down together and discharges the gas between the stone paper sheet 1 and the female mold 121 until it is completely closed with the female mold 121. When the pressing pressure reaches the preset value and the male mold 122 and the female mold 121 are closed, stop the pressing action and enter the pressure holding stage.

[0060] When the male mold 122 moves downward together with the stone paper sheet 1, the gas between the stone paper sheet 1 and the female mold 121 will be quickly discharged from the gaps on both sides, and at the same time, the gas will be pumped out through the air filling and exhaust holes 1211 to assist in the discharge.

[0061] In this embodiment, the preset value of the pressing pressure is 0.12MPa-1MPa. The preset value of the pressing pressure is determined according to the heating temperature of the stone paper sheet 1 and the thickness of the stone paper sheet 1. The appropriate pressing pressure can be selected according to the actual situation to ensure the stamping speed while ensuring the stamping quality.

[0062] Step S5: Stop the heat preservation of the hot press mold 12 and allow it to cool for a predetermined time. After the stone paper sheet 1 is shaped into an inner support body, the pressure of the hot press mold 12 is released and the male mold 122 is controlled to rise so that it separates from the female mold 121, thus completing the mold opening.

[0063] Step S6: Release the clamp on the inner support blank and send compressed air through the inflation and deflation hole 1211 to separate the inner support blank from the female mold 121; then take out the inner support blank and send it to the edge trimming machine to obtain the inner support finished product 13.

[0064] Compressed air is introduced through the inflation and deflation port 1211, and the air pressure impact of the compressed air causes the inner mold plate to separate from the female mold 121, thus achieving a non-contact demolding operation.

[0065] After heating the stone paper sheet 1 to a highly elastic state, it is moved above the female mold 121 of the preheated and constant-temperature hot press mold 12 and placed on the female mold 121. Compressed air is then introduced through the air inlet and outlet 1211 at the bottom of the female mold 121 to complete the stretching and pre-deformation of the stone paper sheet 1. After being pressed and closed by the male mold 122, it is cooled and shaped to obtain the inner support blank. After trimming, the inner support finished product 13 is obtained. The molding speed is fast and the processing efficiency is high. It can easily manufacture an integrated three-dimensional shape with complex curved surfaces and continuous cavities. At the same time, the stone paper sheet is environmentally friendly and recyclable. The resin required for its raw materials can also be recycled from old plastics, which has the advantages of low cost and environmental protection characteristics.

[0066] For reference, the core performance of the stone paper inner tray and the plant fiber inner tray was tested under the conditions of 2.0 mm thickness, 23℃ temperature, and 50%RH humidity. The structure is shown in Table 1 below: Table 1 Performance Test Results

[0067] Based on the comparison of core performance parameters in Table 1, stone paper inner trays are significantly superior to plant fiber inner trays in key mechanical indicators such as surface hardness, stiffness, compressive strength, and tensile strength. At the same time, the molding cycle is shortened by 94%, and the single machine capacity is increased by about 18 times. This indicates that stone paper inner trays have excellent rigid support, cushioning protection, and efficient manufacturing characteristics, and are suitable for precision packaging scenarios with high strength, moisture resistance, and complex shapes.

[0068] refer to Figure 7 , Figure 8 and Figure 9 As shown, in this embodiment, both the male mold 122 and the female mold 121 include a mold body 14; the mold body 14 of the female mold 121 is recessed inward to form a molding cavity 141; the air inlet / outlet 1211 is opened at the bottom of the molding cavity 141 and connected to an air inlet pipe; the bottom of the mold body 14 of the male mold 122 extends into the molding cavity 141 and cooperates with the female mold 121.

[0069] The male mold 122 can move downward under the external power provided by the pressurizing equipment, and the bottom of its mold body 14 enters the forming cavity 141 of the female mold 121 to complete the mold closing, thereby causing the stone paper material 1 located in the female mold 121 to be deformed by pressure, and finally shaped into the inner tray finished product 13.

[0070] Both the female mold 121 and the male mold 122 have a built-in heating mechanism and at least one temperature sensor 142 for detecting the temperature of the mold body 14. The heating mechanism includes several mounting holes arranged side by side in the mold body 14. A heating rod 143 is built into each mounting hole. A limiting ring 144 is fixedly provided on the surface of the heating rod 143. A threaded cap 145 is movably sleeved on the surface of the limiting ring 144. The heating rod 143 is fixed to the opening of the mounting hole by the threaded cap 145. A connector 146 is fixedly provided on the surface of the heating rod 143 away from the mounting hole. The connector 146 is connected to an external power supply through a current regulator. The current regulator and the temperature sensor 142 are respectively electrically connected to a controller.

[0071] In practical use, the controller can send commands to the current regulator according to the preset molding temperature curve, adjusting the current input to each heating rod 143 to begin heating the mold body 14 of the female mold 121 and male mold 122 until it reaches the target temperature. Simultaneously, the temperature of the mold body 14 is monitored in real time by the temperature sensor 142, and the data is fed back to the controller. The controller compares the measured temperature with the set value and dynamically adjusts the power of the heating rods 143 using algorithms such as PID control, achieving precise control of the heating rate and constant temperature maintenance, thus achieving heating and heat preservation of the mold body 14.

[0072] A cooling sleeve 15 is fitted on the outer periphery of the mold body 14 of both the female mold 121 and the male mold 122. The connector 146 passes through the cooling sleeve 15 and extends to the outside. The cooling sleeve 15 includes a sleeve body 151 fitted on the outer periphery of the mold body 14. An annular groove is opened in the sleeve body 151. A spiral cooling pipe 152 is provided in the annular groove. One end of the cooling pipe 152 is connected to a coolant inlet pipe 147, and the other end is connected to a coolant outlet pipe 148. A solenoid valve electrically connected to the controller is provided on both the coolant inlet pipe 147 and the coolant outlet pipe 148.

[0073] After the inner mold blank is initially shaped in the molding cavity 141, the controller sends a command to open the solenoid valves on the coolant inlet pipe 147 and coolant outlet pipe 148. A pump can be used to pump coolant from the storage tank, which then flows through the coolant inlet pipe 147 into the spiral cooling pipe 152 embedded in the annular groove of the cooling jacket 15. This allows the coolant to flow around the mold body 14 along a spiral path, fully and evenly absorbing the heat inside the mold body 14, and finally flowing out from the coolant outlet pipe 148, thus cooling the mold body 14. Based on feedback from the temperature sensor 142, the controller can stop the cooling cycle after the mold temperature has cooled to a safe mold opening temperature, and command the male mold 122 to rise and open the mold, removing the cooled and shaped inner mold blank.

[0074] By setting up heating rod 143 and cooling jacket 15, combined with temperature sensor 142 and controller, rapid and precise programmed control of the entire process of mold heating, heat preservation and cooling can be achieved, which significantly improves the process stability of stone paper stamping. Example

[0075] The distinguishing feature of Example 2 compared to Example 1 is as follows: In the manufacturing steps of the stone paper sheet 1, the following is also included between steps S11 and S12: Step S011: The recycled stone paper products are sorted, impurities are removed, and then washed and dried in sequence to obtain recycled stone paper material. In this embodiment, the drying is carried out by air drying at room temperature or low temperature drying. The temperature of low temperature drying is controlled at 60-80℃ to avoid the resin in the recycled stone paper material from aging due to high temperature, and to ensure that the moisture content of the recycled stone paper material is less than 5%.

[0076] Step S011: The recycled stone paper is fed into a crusher and crushed into particles with a diameter of 5-10 mm; then the crushed particles are fed into a grinder and ground into powder. In this embodiment, the particle size of the powder is 100-200 mesh.

[0077] Step S12 involves mixing the raw materials from step S11 with the powdered particles from step S111 to obtain a mixed powder. In this embodiment, the mass ratio of the raw materials to the powdered particles in the mixed powder is 3:7.

[0078] By recycling waste stone paper, turning it into powder granules, and mixing it with new raw materials to produce new stone paper, and by using resin made from recycled plastics in the raw materials, the consumption of virgin resin and mineral powder can be greatly reduced, and the energy consumption generated in the production process of virgin raw materials can be reduced. This forms a closed-loop system of "waste-regeneration-reuse", continuously reducing resource waste and achieving the goals of sustainable resource utilization and ecological environmental protection.

[0079] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a stone paper inner tray, characterized in that, include: Step S1: The stone paper sheet is conveyed to a preset position, and the top and bottom surfaces of the stone paper sheet are heated simultaneously to make the stone paper sheet exhibit a highly elastic state; Step S2: Move the stone paper sheet above the female mold of a hot press mold and place it on the female mold, then clamp and fix the edge of the stone paper sheet; Step S3: Compressed air is introduced through the air inlet and outlet holes at the bottom of the female mold, causing the highly elastic stone paper sheet to bulge upward in an arc shape, thus completing the stretching and pre-deformation of the stone paper sheet. Step S4: Heat the male and female molds of the hot press mold to the same temperature as the stone paper sheet and keep them at that temperature. Then, control the male mold of the hot press mold to press down and fit it against the stretched and pre-deformed stone paper sheet. At this time, stop the supply of compressed air. Then, the male mold moves the stone paper sheet downward together and discharges the gas between the stone paper sheet and the female mold until it is completely closed with the female mold. When the pressing pressure reaches the preset value and the male mold and the female mold are closed, stop the pressing action and enter the pressure holding stage. Step S5: Stop the heat preservation of the hot press mold and allow it to cool for a predetermined time. After the stone paper sheet is shaped into an inner support blank, release the pressure of the hot press mold and control the male mold to rise so that it separates from the female mold, thus completing the mold opening. Step S6: Release the clamps on the inner support blank and introduce compressed air through the inflation and deflation holes to separate the inner support blank from the female mold; then take out the inner support blank and send it to the edge trimming machine to obtain the finished inner support blank.

2. The method for preparing a stone paper inner tray according to claim 1, characterized in that, In step S1, the manufacturing steps of the stone paper sheet are as follows: Step S11: Prepare the following raw materials in parts by weight: 0.3-0.5 parts compatibilizer, 78-88 parts modified calcium carbonate, 10-15 parts resin, 4-6 parts flame retardant, 0.8-1.2 parts lubricant, and 0.2-0.4 parts anti-aging agent; Step S12: Mix the raw materials from step S11 to obtain a mixed powder; Step S13: Moisten and granulate the mixed powder, then dry it to obtain dried particles; Step S14: The dried particles are extruded through a twin-screw extruder to obtain extruded sheets; Step S15: Stretch the extruded sheet to obtain a sheet; Step S16: The sheet is calendered and shaped, and then cooled to obtain the stone paper sheet.

3. The method for preparing a stone paper inner tray according to claim 2, characterized in that, In step S11, the method for preparing the modified calcium carbonate includes the following steps: S111. Weigh 1.5-2.0% of the mass of calcium carbonate in methacryloyloxysilane coupling agent; weigh 0.5-1.0% of the mass of calcium carbonate in aminosilane coupling agent, and mix the methacryloyloxysilane coupling agent and aminosilane coupling agent with an aqueous ethanol solution that accounts for 3-6 times their total mass to obtain a composite coupling agent solution. The calcium carbonate comprises calcium carbonate I, calcium carbonate II, and calcium carbonate III in a mass ratio of (1.4-1.7):1:(0.3-0.5), wherein the average particle size of calcium carbonate I is smaller than that of calcium carbonate II, and the average particle size of calcium carbonate II is smaller than that of calcium carbonate III. S112. Place calcium carbonate in a high-speed mixer, weigh and add 0.3-0.5% of the dispersant by weight of calcium carbonate, stir and mix to obtain fully dispersed calcium carbonate; then dry and cool the calcium carbonate for later use. S113. Place calcium carbonate and composite coupling agent solution into a high-speed mixer, mix and react at 50℃-55℃, filter and dry to obtain coupling agent modified calcium carbonate. S114. Raise the temperature of the high-speed mixer to 80-90℃, add PP-g-MAH powder, stir under heat preservation conditions, and cool to room temperature to obtain modified calcium carbonate.

4. The method for preparing a stone paper inner tray according to claim 2, characterized in that, The resin comprises polypropylene, thermoplastic polyurethane and polyamide in a mass ratio of (1.8-2):(0.4-0.6):(0.8-1).

5. The method for preparing a stone paper inner tray according to claim 2, characterized in that, In step S16, the sheet is calendered and shaped by a calendering device; specifically, the calendering device includes a frame and a calendering roller group and an embossing roller group arranged on the frame for calendering to produce stone paper sheet. The frame is provided with a working channel, and the calendering roller group and the embossing roller group are sequentially distributed and rotatably arranged in the working channel. The embossing roller assembly includes a composite rubber roller and a mirror roller; the mirror roller is located directly above the composite rubber roller and forms a shaped channel with the composite rubber roller; The composite rubber roller includes an outer roller body and a heat-resistant rubber layer covering the outer surface of the outer roller body. A first cavity is formed inside the outer roller body. A first tubular connector and a second tubular connector are respectively provided at both ends of the outer roller body. The outer roller body is rotatably connected to both sides of the working channel through the first tubular connector and the second tubular connector, and extends through to the outside. Both the first tubular connector and the second tubular connector are in communication with the first cavity. A closed inner roller body is provided inside the first cavity. A spiral protrusion is distributed on the outer surface of the inner roller body. The end of the spiral protrusion is connected to the inner wall of the first cavity and forms a spiral flow channel in communication with the first cavity. The spiral flow channel is used to supply coolant to the first tubular connector and allow it to flow to the second tubular connector. A first driving mechanism is provided on one side of the frame. The first driving mechanism is used to drive the mirror roller and the composite rubber roller to rotate synchronously and to compact and shape the stone paper sheet passing through the shaping channel.

6. The method for preparing a stone paper inner tray according to claim 1, characterized in that, In step S1, the heating temperature T is 90℃-150℃; the heating duration t≥30d, where t is in seconds and d is the thickness of the stone paper sheet in mm; in step S4, the preset value of the downward pressure is 0.12MPa-1MPa.

7. The method for preparing a stone paper inner tray according to claim 1, characterized in that, In step S1, the top and bottom surfaces of the stone paper sheet are heated simultaneously using a double-sided heating device. The double-sided heating device includes a heating chamber, a feeding channel, and a discharging channel; the left and right sides of the heating chamber are symmetrically provided with a feeding port and a discharging port; the feeding channel is connected to the feeding port, and the discharging channel is connected to the discharging port. Both the feeding channel and the discharging channel include a conveyor frame and several conveyor rollers rotatably mounted on the conveyor frame, with the conveyor rollers arranged horizontally side by side; several guide rollers are rotatably mounted inside the heating box and arranged parallel to the conveyor rollers, with the upper surface of the guide rollers and the upper surface of the conveyor rollers located on the same horizontal plane; both the conveyor rollers and the guide rollers include a stainless steel roller body and a Teflon coating on the surface of the stainless steel roller body. The heating chamber is also fixedly equipped with several sets of infrared heating tubes I, several sets of infrared heating tubes II, an upper mounting frame, and a lower mounting frame; The first infrared heating tube is located above the guide roller, and several groups of the first infrared heating tubes are arranged in an equidistant array along the direction from the feed inlet to the discharge outlet; the upper mounting frame is located above the first infrared heating tube; the second infrared heating tube and the lower mounting frame are both located below the guide roller, and are arranged symmetrically with the first infrared heating tube and the lower mounting frame, respectively. At least one turbine fan is installed on both the upper and lower mounting brackets; an upper vent hood communicating with the heating box is provided at the upper end of the heating box, a lower vent hood communicating with the heating box is provided at the lower end of the heating box, and a support base is also provided at the lower end of the heating box. The stone paper sheet enters the heating chamber through the conveyor roller of the feeding channel for heating, and is then sent out through the conveyor roller of the discharge channel; at least one infrared temperature probe for detecting the stone paper sheet is installed on the conveyor frame of the discharge channel.

8. The method for preparing a stone paper inner tray according to claim 1, characterized in that, Both the male mold and the female mold include a mold body; the mold body of the female mold is recessed inward to form a molding cavity; the inflation and deflation holes are located at the bottom of the molding cavity and are connected to an air inlet pipe. The bottom of the male mold body extends into the molding cavity and mates with the female mold; both the female mold and the male mold body have a built-in heating mechanism and at least one temperature sensor for detecting the temperature of the mold body. The heating mechanism includes several mounting holes arranged side-by-side within the mold body; each mounting hole contains a heating rod, a limiting ring is fixedly disposed on the surface of the heating rod, and a threaded cap is movably fitted onto the surface of the limiting ring, the heating rod being fixed to the opening of the mounting hole by the threaded cap; a connector is fixedly disposed on the surface of the heating rod away from the mounting hole, the connector being connected to an external power source through a current regulator; the current regulator and the temperature sensor are respectively electrically connected to a controller; A cooling sleeve is fitted around the outer periphery of both the female and male mold bodies. The connector passes through the cooling sleeve and extends to the outside. The cooling sleeve includes a sleeve body fitted around the outer periphery of the mold body. An annular groove is formed on the upper part of the sleeve body. A spiral cooling pipe is provided in the annular groove. One end of the cooling pipe is connected to a coolant inlet pipe, and the other end is connected to a coolant outlet pipe. A solenoid valve electrically connected to the controller is provided on both the coolant inlet pipe and the coolant outlet pipe.

9. The method for preparing a stone paper inner tray according to claim 1, characterized in that, Step S3 specifically includes: Compressed air is supplied into the female mold at a constant pressurization rate through the air inlet and outlet at the bottom of the female mold until the supplied air pressure reaches the preset air pressure value. Then, the preset air pressure value is maintained and output, so that the highly elastic stone paper sheet bulges upward in an arc shape, completing the stretching pre-deformation of the stone paper sheet. Among them, the preset air pressure value H is the pre-stretch height; E is the elastic modulus of the stone paper sheet in a highly elastic state; d is the thickness of the stone paper sheet; K is the preset shape coefficient; and D is the length of the pre-deformed stone paper sheet.

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