Polyurethane foam preparation process and device based on liquid carbon dioxide foaming

Abstract

The invention discloses a polyurethane foam preparation process and device based on liquid carbon dioxide foaming, and belongs to the field of polyurethane production. The preparation process comprises the following steps: S1, conveying polyether polyol, polymer polyol and a liquid carbon dioxide foaming agent into a front static mixer, uniformly mixing under a certain pressure state, and conveying into a main mixer; s2, inputting isocyanate into a main mixer in a high-pressure state, and uniformly mixing and stirring the isocyanate and other uniformly mixed raw materials in the main mixer; s3, conveying the water, the silicone oil surfactant, the foaming catalyst and the gel catalyst into a main mixer, stirring and mixing with the raw materials, and conveying into an emulsifier; s4, the mixed raw materials and auxiliary materials are subjected to step-by-step pressure release through a multi-layer screen structure of the emulsifier, so that the liquid carbon dioxide is gradually converted into a gas state from a liquid state in the emulsification and pressure release process and is gradually gasified and foamed, and finally the soft polyurethane foam is prepared through pouring.

Description

Technical Field

[0001] The invention relates to the field of polyurethane production, and in particular to a polyurethane foam preparation process and device based on liquid carbon dioxide foaming. Background Art

[0002] Carbon dioxide foaming technology uses supercritical carbon dioxide as a foaming agent and injects it into molten plastic raw materials through a specific process. Under appropriate temperature and pressure conditions, carbon dioxide expands rapidly and forms tiny bubbles that fill the inside of the plastic, eventually forming a foamed product with a microporous structure.

[0003] For example, the patent document with patent number 202221251790.7 discloses a liquid carbon dioxide sponge foaming equipment, including a first mixer, a second mixer, a liquid carbon dioxide storage tank, a cyanate storage tank, a first raw material storage tank group, a second raw material storage tank group, an injection device and a conveying device; the first raw material storage tank group is connected to the first mixer pipeline; the second raw material storage tank group and the cyanate storage tank are both connected to the second mixer pipeline; the liquid carbon dioxide storage tank is connected to the first mixer pipeline; the discharge port at the bottom of the first mixer is connected to the feed port pipeline of the second mixer; the injection device is connected to the discharge port pipeline set at the bottom of the second mixer; the conveying device is located at the bottom of the injection device, and the injection port of the injection device is set toward the conveying surface of the conveying device.

[0004] The above technical solution can reduce the temperature during the sponge foaming process and avoid spontaneous combustion during the sponge foaming process. The sponge produced by the liquid carbon dioxide sponge foaming equipment has a softer feel, a high degree of open-cell planning and excellent resilience.

[0005] However, in the above technical solution, functional raw materials such as catalysts, foam stabilizers and additives need to be first introduced into the first mixer, and then introduced into the second mixer to react and generate polyurethane foam elastomer after pre-stirring in the first mixer. During the transfer process of the catalyst, foam stabilizer and additives, some raw materials may remain in the first mixer, resulting in deviations in the ratio of raw materials and affecting the reaction quality.

[0006] In addition, after the raw materials and auxiliary materials are mixed, they are directly sprayed out through the injection device. The pressure difference between the mixing chamber and the outside is too large, which will cause the nucleation and foaming inside the raw materials to be too rapid, causing some bubbles to burst due to excessive growth, affecting the internal structure of the polyurethane sponge.

[0007] Therefore, it is necessary for us to improve such a structure to overcome the above-mentioned defects. Summary of the invention

[0008] The purpose of the present invention is to provide a polyurethane foam preparation process and device based on liquid carbon dioxide foaming to solve the deficiencies in the prior art.

[0009] The above technical objectives of the present invention are achieved through the following technical solutions: A polyurethane foam preparation process based on liquid carbon dioxide foaming comprises the following steps: S1. The polyether polyol, polymer polyol and liquid carbon dioxide blowing agent are transported to the front static mixer and mixed evenly under a pressure of 0-50 bar and then transported to the main mixer; S2. The isocyanate is input into the main mixer under high pressure of 30-100 bar, and the isocyanate is mixed with the polyether polyol, polymer polyol and liquid carbon dioxide blowing agent after mixing in the main mixer; S3. The water, silicone surfactant, foaming catalyst and gel catalyst are transported into the main mixer, stirred and mixed with the isocyanate, polyether polyol, polymer polyol and liquid carbon dioxide blowing agent, and then transported into the emulsifier; S4. The mixed raw materials and auxiliary materials are gradually released from pressure through the multi-layer screen structure of the emulsifier, so that the liquid carbon dioxide gradually changes from liquid to gas during the emulsification and pressure release process, gradually vaporizes and foams, and is finally poured into the foaming line mold for foaming to make soft polyurethane foam.

[0010] Furthermore, the specific process of step S4 is as follows: A1: Foam a fixed amount of mixture and obtain the gas pressure value after foaming; A2: Calculate the pressure release value of the mixture per unit volume based on the obtained gas pressure value; A3: continuously input the mixture into the emulsifier for foaming. During this process, steps A1 and A2 are repeated to calculate the real-time pressure release value P2 of the mixture; A4: Compare the standard pressure release value P1 with the real-time pressure release value P2 to obtain the pressure deviation value ΔP; A5: Execute the corresponding control strategy according to the calculation result of the pressure deviation value ΔP in step A1.

[0011] Furthermore, step A1 specifically includes the following steps: A11: Set the opening of the flow control valve, input a fixed amount of mixture into the emulsifier, and the mixture expands and foams after the pressure is released step by step through the filtration unit, and record the gas pressure count value at this time; Step A11 is the basis for the subsequent calculation of the standard pressure release value and the real-time pressure release value, providing data support for pressure reduction control; Step A2 specifically includes the following steps: A21: Based on the input mixture volume and the gas pressure counter value after the mixture is fully expanded and foamed, calculate the mixture pressure release value P1 per unit volume, and use P1 as the standard pressure release value; Step A5 specifically includes the following steps: A51: If the standard pressure release value P1 is the same as the real-time pressure release value P2, that is, ΔP=0, the foaming effect of the mixture reaches the maximum processing expectation of the equipment, the opening of the flow control valve is kept unchanged, and a stable foaming process is maintained; If the standard pressure release value P1 exceeds the real-time pressure release value P2, that is, ΔP>0, it means that the amount of mixture introduced into the emulsifier is too large and cannot be fully foamed. Reduce the opening of the flow control valve until ΔP=0, and stop reducing the opening of the flow control valve; Specifically, when ΔP>0, it means that the amount of mixture introduced into the emulsifier is too large, exceeding the upper limit of the processing capacity of the equipment, and cannot be fully foamed. In this case, the opening of the flow control valve is gradually reduced to reduce the input speed of the mixture; at the same time, the change of the real-time pressure release value P2 is monitored. After each adjustment, the pressure deviation value ΔP is recalculated. When ΔP=0, stop reducing the opening of the flow control valve.

[0012] A device for preparing soft polyurethane foam based on liquid carbon dioxide foaming, comprising A material storage unit, which is used to store raw materials for preparing soft polyurethane foam; A feeding pipeline unit, which is used to transport the raw materials stored in the storage unit into the mixing area; A mixing zone, which is used to mix the input raw materials for preparing the flexible polyurethane foam under high pressure conditions to maintain the phase state of the raw materials; The emulsifier is used to emulsify the various component raw materials fully mixed in the mixing area through a multi-layer screen structure and then pour them into the foaming line mold for foaming to make soft polyurethane foam.

[0013] Further, the material storage unit includes a first material storage tank, a second material storage tank and a third material storage tank for storing the main material, and a fourth material storage tank, a fifth material storage tank, a sixth material storage tank, a seventh material storage tank and an eighth material storage tank for storing the auxiliary material; The main ingredients include polyether polyol, polymer polyol and isocyanate; the auxiliary materials include liquid carbon dioxide foaming agent, water foaming agent, silicone oil surfactant, foaming catalyst and gel catalyst.

[0014] Furthermore, the feeding pipeline unit includes a plurality of main material conveying pipelines respectively connected to a main material tank, and a plurality of auxiliary material conveying pipelines respectively connected to an auxiliary material tank; The main material conveying pipeline is respectively provided with a feeding pump, a high-pressure metering pump, a flow meter, a filter and a three-way pneumatic valve, one outlet of the three-way pneumatic valve is connected to the mixing area, and the other outlet of the three-way pneumatic valve is connected to the return port of the main material tank through a loop pipeline; The fourth storage tank is used to store liquid carbon dioxide foaming agent. A feeding pump, a high-pressure metering pump, a flow meter, a pressure control valve, a pneumatic three-way valve and a liquid carbon dioxide cooling system are provided on the auxiliary material conveying pipeline connected to the fourth storage tank; one outlet of the three-way pneumatic valve is connected to the mixing area, and the other outlet of the three-way pneumatic valve is connected to the return port of the fourth storage tank through a loop pipeline; the liquid carbon dioxide cooling system is used to maintain the liquid carbon dioxide in the auxiliary material conveying pipeline in a temperature range of -°C to -°C to ensure the temperature required for the liquid carbon dioxide to foam; The fifth material storage tank, the sixth material storage tank, the seventh material storage tank and the eighth material storage tank are respectively connected to an auxiliary material conveying pipeline, on which a high-pressure metering pump, a flow meter, a filter and a pneumatic three-way valve are respectively provided, one outlet of the pneumatic three-way valve is connected to the mixing area, and the other outlet of the three-way pneumatic valve is connected to the return port of the auxiliary material tank through a loop pipeline.

[0015] Furthermore, the mixing zone includes a main mixer and a static mixer arranged at the front end of the main mixer; One outlet of the three-way pneumatic valve of the first storage tank, the second storage tank and the fourth storage tank is connected to the static mixer; one outlet of the three-way pneumatic valve of the third storage tank, the fifth storage tank, the sixth storage tank, the seventh storage tank and the eighth storage tank is connected to the top of the main mixer; A mechanical stirring device and a pressure control valve are provided in the main mixer, which are used to stir and mix the main material and auxiliary material under set high pressure conditions and maintain the phase state of the main material and the auxiliary material.

[0016] Furthermore, the emulsifier is arranged at the terminal outlet of the main mixer, an emulsifying chamber is arranged inside the emulsifier, the top of the emulsifying chamber is communicated with the terminal outlet of the main mixer, a plurality of layers of screen structures are arranged inside the emulsifying chamber, the main material and the auxiliary material stirred and mixed in the main mixer enter the emulsifying chamber, are emulsified through the plurality of layers of screen structures, and then are poured into the foaming line mold through the outlet at the bottom of the emulsifying chamber for foaming to make soft polyurethane foam.

[0017] Furthermore, the emulsifier releases pressure step by step through a multi-layer screen structure, the multi-layer screen structure includes 1-5 layers of screen combinations with different apertures, the aperture of the screen is 50-400 microns, the aperture of the screen is adjusted according to the viscosity and particle size of the foaming raw material and the content of liquid carbon dioxide, and the liquid carbon dioxide is gradually gasified and foamed in the emulsifier by gradually releasing the pressure.

[0018] In summary, the present invention has the following beneficial effects: By distinguishing between main materials and auxiliary materials, polyether polyols, polymer polyols and liquid carbon dioxide foaming agents that need to be mixed multiple times are transported to the front static mixer to be evenly mixed under a certain pressure state (0-50bar), and then transported to the main mixer for stirring and mixing; other raw materials and main materials are directly transported to the main mixer through pipelines to be stirred and mixed together with the mixed polyether polyols, polymer polyols and liquid carbon dioxide foaming agents, thereby reducing the deviation of the raw material ratio caused by the residual raw material transfer and affecting the reaction quality.

[0019] The mixed raw materials and auxiliary materials are gradually released from the multi-layer screen structure of the emulsifier to release pressure, so that the liquid carbon dioxide is gradually gasified and foamed in the emulsifier, thereby ensuring that the internal bubbles of the polyurethane sponge can fully nucleate and foam, and finally poured from the outlet at the bottom of the emulsification chamber into the foaming line mold for foaming to make soft polyurethane foam. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a flow chart of a polyurethane foam preparation process based on liquid carbon dioxide foaming.

[0021] Figure 2 It is a structural block diagram of the device for preparing soft polyurethane foam based on liquid carbon dioxide foaming according to the present invention.

[0022] Figure 3 Schematic diagram of the mechanical stirring device of the present invention.

[0023] Figure 4 It is a schematic diagram of the internal structure of the emulsifier described in the present invention. DETAILED DESCRIPTION

[0024] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below in conjunction with illustrations and specific embodiments.

[0025] like Figures 1 to 4 As shown, the present invention proposes a polyurethane foam preparation process based on liquid carbon dioxide foaming, comprising the following steps: S1. The polyether polyol, polymer polyol and liquid carbon dioxide blowing agent are transported to the front static mixer and mixed evenly under a pressure of 0-50 bar and then transported to the main mixer; S2. The isocyanate is input into the main mixer under high pressure of 30-100 bar, and the isocyanate is mixed with the polyether polyol, polymer polyol and liquid carbon dioxide blowing agent after mixing in the main mixer; S3. The water, silicone surfactant, foaming catalyst and gel catalyst are transported into the main mixer, stirred and mixed with the isocyanate, polyether polyol, polymer polyol and liquid carbon dioxide blowing agent, and then transported into the emulsifier; S4. The mixed raw materials and auxiliary materials are gradually released from pressure through the multi-layer screen structure of the emulsifier, so that the liquid carbon dioxide gradually changes from liquid to gas during the emulsification and pressure release process, gradually vaporizes and foams, and is finally poured into the foaming line mold for foaming to make soft polyurethane foam.

[0026] The specific process of step S4 is as follows: The following steps are involved: A1: Foam a fixed amount of mixture and obtain the gas pressure value after foaming; A2: Calculate the pressure release value of the mixture per unit volume based on the obtained gas pressure value; A3: continuously input the mixture into the emulsifier for foaming. During this process, steps A1 and A2 are repeated to calculate the real-time pressure release value P2 of the mixture; A4: Compare the standard pressure release value P1 with the real-time pressure release value P2 to obtain the pressure deviation value ΔP; A5: Execute the corresponding control strategy according to the calculation result of the pressure deviation value ΔP in step A1.

[0027] Step A1 specifically includes the following steps: A11: Set the opening of the flow control valve, input a fixed amount of mixture into the emulsifier, and the mixture expands and foams after the pressure is released step by step through the filtration unit, and record the gas pressure count value at this time; Step A11 is the basis for the subsequent calculation of the standard pressure release value and the real-time pressure release value, providing data support for pressure reduction control; Step A2 specifically includes the following steps: A21: Based on the input mixture volume and the gas pressure counter value after the mixture is fully expanded and foamed, calculate the mixture pressure release value P1 per unit volume, and use P1 as the standard pressure release value; Step A5 specifically includes the following steps: A51: If the standard pressure release value P1 is the same as the real-time pressure release value P2, that is, ΔP=0, the foaming effect of the mixture reaches the maximum processing expectation of the equipment, the opening of the flow control valve is kept unchanged, and a stable foaming process is maintained; If the standard pressure release value P1 exceeds the real-time pressure release value P2, that is, ΔP>0, it means that the amount of mixture introduced into the emulsifier is too large and cannot be fully foamed. Reduce the opening of the flow control valve until ΔP=0, and stop reducing the opening of the flow control valve; Specifically, when ΔP>0, it means that the amount of mixture introduced into the emulsifier is too large, exceeding the upper limit of the processing capacity of the equipment, and cannot be fully foamed. In this case, the opening of the flow control valve is gradually reduced to reduce the input speed of the mixture; at the same time, the change of the real-time pressure release value P2 is monitored. After each adjustment, the pressure deviation value ΔP is recalculated. When ΔP=0, stop reducing the opening of the flow control valve.

[0028] A device for preparing soft polyurethane foam based on liquid carbon dioxide foaming, comprising A material storage unit, which is used to store raw materials for preparing soft polyurethane foam; A feeding pipeline unit, which is used to transport the raw materials stored in the storage unit into the mixing area; A mixing zone, which is used to mix the input raw materials for preparing the flexible polyurethane foam under high pressure conditions to maintain the phase state of the raw materials; The emulsifier is used to emulsify the various component raw materials fully mixed in the mixing area through a multi-layer screen structure and then pour them into the foaming line mold for foaming to make soft polyurethane foam.

[0029] The material storage unit includes a first material storage tank 1, a second material storage tank 2 and a third material storage tank 3 for storing the main material, and a fourth material storage tank 4, a fifth material storage tank 5, a sixth material storage tank 6, a seventh material storage tank 7 and an eighth material storage tank 8 for storing the auxiliary material; The main ingredients include polyether polyol, polymer polyol and isocyanate; the auxiliary materials include liquid carbon dioxide foaming agent, water foaming agent, silicone oil surfactant, foaming catalyst and gel catalyst.

[0030] The feeding pipeline unit includes a plurality of main material conveying pipelines respectively connected to a main material tank, and a plurality of auxiliary material conveying pipelines respectively connected to an auxiliary material tank; The main material conveying pipeline is respectively provided with a feeding pump, a high-pressure metering pump, a flow meter, a filter and a three-way pneumatic valve, one outlet of the three-way pneumatic valve is connected to the mixing area, and the other outlet of the three-way pneumatic valve is connected to the return port of the main material tank through a loop pipeline; The fourth storage tank 4 is used to store liquid carbon dioxide foaming agent. A feeding pump, a high-pressure metering pump, a flow meter, a pressure control valve, a pneumatic three-way valve and a liquid carbon dioxide cooling system are provided on the auxiliary material conveying pipeline connected to the fourth storage tank 4; one outlet of the three-way pneumatic valve is connected to the mixing area, and the other outlet of the three-way pneumatic valve is connected to the return port of the fourth storage tank 4 through a loop pipeline; the liquid carbon dioxide cooling system is used to maintain the liquid carbon dioxide in the auxiliary material conveying pipeline at a temperature range of -15°C to -25°C to ensure the temperature required for the liquid carbon dioxide to foam; The fifth storage tank 5, the sixth storage tank 6, the seventh storage tank 7 and the eighth storage tank 8 are respectively connected to an auxiliary material conveying pipeline, on which a high-pressure metering pump, a flow meter, a filter and a pneumatic three-way valve are respectively provided, one outlet of the pneumatic three-way valve is connected to the mixing area, and the other outlet of the three-way pneumatic valve is connected to the return port of the auxiliary material tank through a loop pipeline.

[0031] The mixing zone includes a main mixer 9 and a static mixer 10 arranged at the front end of the main mixer; One outlet of the three-way pneumatic valve of the first storage tank 1, the second storage tank 2 and the fourth storage tank 4 is connected to the static mixer 10; one outlet of the three-way pneumatic valve of the third storage tank 3, the fifth storage tank 5, the sixth storage tank 6, the seventh storage tank 7 and the eighth storage tank 8 is connected to the top of the main mixer 9; A mechanical stirring device 11 and a pressure control valve are provided in the main mixer 9, which are used to stir and mix the main material and the auxiliary material under a set high pressure condition and to maintain the phase state of the main material and the auxiliary material.

[0032] The emulsifier is arranged at the terminal outlet of the main mixer 9, an emulsifying chamber 12 is arranged inside the emulsifier, the top of the emulsifying chamber 12 is communicated with the terminal outlet of the main mixer 9, a plurality of layers of screen structures are arranged inside the emulsifying chamber 12, the main material and the auxiliary material stirred and mixed in the main mixer 9 enter the emulsifying chamber 12, are emulsified through the plurality of layers of screen structures, and then are poured into the foaming line mold through the outlet at the bottom of the emulsifying chamber 12 for foaming to make soft polyurethane foam.

[0033] The emulsifier releases pressure step by step through a multi-layer screen structure, which includes 1-5 layers of screen combinations with different apertures. The aperture of the screen is 50-400 microns. The aperture of the screen is adjusted according to the viscosity, particle size and content of liquid carbon dioxide of the foaming raw material. The aperture of the screen decreases from top to bottom, and it is necessary to ensure that the main material and auxiliary material after stirring and mixing in the main mixer 9 can flow through the screens of all apertures in sequence, so that the liquid carbon dioxide is gradually gasified and foamed in the emulsifier by gradually releasing the pressure.

[0034] See also Figure 4 The emulsifier is provided with The first filter layer 13 and the second filter layer 14 are arranged on the top of the emulsification chamber 12 and are used to perform primary filtration and secondary filtration on the raw materials transported into the emulsification chamber 12; Nucleation layer 15, when the filtered raw material passes through the nucleation layer 15, the pressure will be released, and the carbon dioxide dissolved in the raw material will be supersaturated due to the decrease of solubility and form bubble nuclei; Bubble growth layer 16, after the bubble nuclei grow and stabilize, the raw material further releases pressure through the bubble growth layer 16, so that the bubble nuclei continue to expand; The pressure is completely released in the layer 17 . The raw material with a number of bubbles generated inside passes through the pressure completely released layer 17 , so that the pressure is completely released, and finally a porous structure is formed inside.

[0035] The following is a comparative analysis of the technical indicators before and after the implementation of the polyurethane foam preparation process of this application, which is quantitatively verified based on international standard test methods such as ISO and ASTM and combined with actual production data: 1. Raw material utilization rate Using the weight loss method to test, the raw material utilization rate of the traditional process is 92.5±2.0%, while the raw material utilization rate of the step-by-step mixing process of the present application is 96.5±0.5%; 2. Main mixer stirring time and stirring power Using the visual method to measure, the stirring time of the traditional process is 180±10s, while the stirring time of the step-by-step mixing process of the present application is 140±5s. The stirring power required to achieve the same shear rate (1000s⁻¹) is reduced by about 10%.

[0036] The working principle of the present invention is as follows: By distinguishing between main materials and auxiliary materials, polyether polyols, polymer polyols and liquid carbon dioxide foaming agents that need to be mixed multiple times are transported to the front static mixer to be evenly mixed under a certain pressure state (0-50bar), and then transported to the main mixer for stirring and mixing; other raw materials and main materials are directly transported to the main mixer through pipelines to be stirred and mixed together with the mixed polyether polyols, polymer polyols and liquid carbon dioxide foaming agents, thereby reducing the deviation of the raw material ratio caused by the residual raw material transfer and affecting the reaction quality.

[0037] The mixed raw materials and auxiliary materials are gradually released from the multi-layer screen structure of the emulsifier to release pressure, so that the liquid carbon dioxide is gradually gasified and foamed in the emulsifier, and finally poured into the foaming line mold from the outlet at the bottom of the emulsification chamber to foam and make soft polyurethane foam.

[0038] In this document, the directions or positional relationships indicated by terms such as "up", "down", "front", "back", "left", "right", "top", "bottom", "inside", "outside", "vertical", and "horizontal" are based on the directions or positional relationships shown in the accompanying drawings and are only for the clarity of expressing the technical solutions and the convenience of description, and therefore should not be understood as limitations of the present invention.

[0039] In this document, the terms "comprises," "comprising," or any other variations thereof, are intended to cover a non-exclusive inclusion of elements other than those listed and may also include additional elements not expressly listed.

[0040] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. The present invention may be subject to various changes and improvements without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A polyurethane foam preparation process based on liquid carbon dioxide foaming, characterized in that: The steps include: S1. The polyether polyol, polymer polyol and liquid carbon dioxide blowing agent are transported to the front static mixer and mixed evenly under a pressure of 0-50 bar and then transported to the main mixer; S2. The isocyanate is input into the main mixer under high pressure of 30-100 bar, and the isocyanate is mixed with the polyether polyol, polymer polyol and liquid carbon dioxide blowing agent after mixing in the main mixer; S3. The water, silicone surfactant, foaming catalyst and gel catalyst are transported into the main mixer, stirred and mixed with the isocyanate, polyether polyol, polymer polyol and liquid carbon dioxide blowing agent, and then transported into the emulsifier; S4. The mixed raw materials and auxiliary materials are gradually released from pressure through the multi-layer screen structure of the emulsifier, so that the liquid carbon dioxide gradually changes from liquid to gas during the emulsification and pressure release process, gradually vaporizes and foams, and is finally poured into the foaming line mold for foaming to make soft polyurethane foam.

2. The polyurethane foam preparation process based on liquid carbon dioxide foaming according to claim 1, characterized in that: The specific process of step S4 is as follows: The following steps are involved: A1: Foam a fixed amount of mixture and obtain the gas pressure value after foaming; A2: Calculate the pressure release value of the mixture per unit volume based on the obtained gas pressure value; A3: continuously input the mixture into the emulsifier for foaming. During this process, steps A1 and A2 are repeated to calculate the real-time pressure release value P2 of the mixture; A4: Compare the standard pressure release value P1 with the real-time pressure release value P2 to obtain the pressure deviation value ΔP; A5: Execute the corresponding control strategy according to the calculation result of the pressure deviation value ΔP in step A1.

3. The process for preparing polyurethane foam based on liquid carbon dioxide foaming according to claim 2, characterized in that: Step A1 specifically includes the following steps: A11: Set the opening of the flow control valve, input a fixed amount of mixture into the emulsifier, and the mixture expands and foams after the pressure is released step by step through the filtration unit, and record the gas pressure count value at this time; Step A11 is the basis for the subsequent calculation of the standard pressure release value and the real-time pressure release value, providing data support for pressure reduction control; Step A2 specifically includes the following steps: A21: Based on the input mixture volume and the gas pressure counter value after the mixture is fully expanded and foamed, calculate the mixture pressure release value P1 per unit volume, and use P1 as the standard pressure release value; Step A5 specifically includes the following steps: A51: If the standard pressure release value P1 is the same as the real-time pressure release value P2, that is, ΔP=0, the foaming effect of the mixture reaches the maximum processing expectation of the equipment, the opening of the flow control valve is kept unchanged, and a stable foaming process is maintained; If the standard pressure release value P1 exceeds the real-time pressure release value P2, that is, ΔP>0, it means that the amount of mixture introduced into the emulsifier is too large and cannot be fully foamed. Reduce the opening of the flow control valve until ΔP=0, and stop reducing the opening of the flow control valve; Specifically, when ΔP>0, it means that the amount of mixture introduced into the emulsifier is too large, exceeding the upper limit of the processing capacity of the equipment, and cannot be fully foamed. In this case, the opening of the flow control valve is gradually reduced to reduce the input speed of the mixture; at the same time, the change of the real-time pressure release value P2 is monitored. After each adjustment, the pressure deviation value ΔP is recalculated. When ΔP=0, stop reducing the opening of the flow control valve.

4. A device for implementing the polyurethane foam preparation process based on liquid carbon dioxide foaming as claimed in claim 1, characterized in that: include A material storage unit, which is used to store raw materials for preparing soft polyurethane foam; A feeding pipeline unit, which is used to transport the raw materials stored in the storage unit into the mixing area; A mixing zone, which is used to mix the input raw materials for preparing the flexible polyurethane foam under high pressure conditions to maintain the phase state of the raw materials; The emulsifier is used to emulsify the various component raw materials fully mixed in the mixing area through a multi-layer screen structure and then pour them into the foaming line mold for foaming to make soft polyurethane foam.

5. The polyurethane foam preparation device based on liquid carbon dioxide foaming according to claim 4, characterized in that: The material storage unit comprises a first material storage tank (1), a second material storage tank (2) and a third material storage tank (3) for storing the main material, and a fourth material storage tank (4), a fifth material storage tank (5), a sixth material storage tank (6), a seventh material storage tank (7) and an eighth material storage tank (8) for storing the auxiliary material; The main ingredients include polyether polyol, polymer polyol and isocyanate; the auxiliary materials include liquid carbon dioxide foaming agent, water foaming agent, silicone oil surfactant, foaming catalyst and gel catalyst.

6. The polyurethane foam preparation device based on liquid carbon dioxide foaming according to claim 5, characterized in that: The feeding pipeline unit includes a plurality of main material conveying pipelines respectively connected to a main material tank, and a plurality of auxiliary material conveying pipelines respectively connected to an auxiliary material tank; The main material conveying pipeline is respectively provided with a feeding pump, a high-pressure metering pump, a flow meter, a filter and a three-way pneumatic valve, one outlet of the three-way pneumatic valve is connected to the mixing area, and the other outlet of the three-way pneumatic valve is connected to the return port of the main material tank through a loop pipeline; The fourth storage tank (4) is used to store liquid carbon dioxide foaming agent. A feeding pump, a high-pressure metering pump, a flow meter, a pressure control valve, a pneumatic three-way valve and a liquid carbon dioxide cooling system are provided on the auxiliary material conveying pipeline connected to the fourth storage tank (4); one outlet of the three-way pneumatic valve is connected to the mixing area, and the other outlet of the three-way pneumatic valve is connected to the return port of the fourth storage tank (4) through a loop pipeline; the liquid carbon dioxide cooling system is used to maintain the liquid carbon dioxide in the auxiliary material conveying pipeline at a temperature range of -15°C to -25°C, so as to ensure the temperature required for the liquid carbon dioxide to foam; The fifth material storage tank (5), the sixth material storage tank (6), the seventh material storage tank (7) and the eighth material storage tank (8) are respectively connected to an auxiliary material delivery pipeline, on which a high-pressure metering pump, a flow meter, a filter and a pneumatic three-way valve are respectively provided, one outlet of the pneumatic three-way valve is connected to the mixing area, and the other outlet of the three-way pneumatic valve is connected to the return port of the auxiliary material tank through a loop pipeline.

7. The polyurethane foam preparation device based on liquid carbon dioxide foaming according to claim 6, characterized in that: The mixing zone comprises a main mixer (9) and a static mixer (10) arranged at the front end of the main mixer; One outlet of the three-way pneumatic valve of the first storage tank (1), the second storage tank (2) and the fourth storage tank (4) is connected to the static mixer (10); one outlet of the three-way pneumatic valve of the third storage tank (3), the fifth storage tank (5), the sixth storage tank (6), the seventh storage tank (7) and the eighth storage tank (8) is connected to the top of the main mixer (9); A mechanical stirring device (11) and a pressure control valve are provided in the main mixer (9), which are used to stir and mix the main material and the auxiliary material under set high pressure conditions and to maintain the phase state of the main material and the auxiliary material.

8. The polyurethane foam preparation device based on liquid carbon dioxide foaming according to claim 7, characterized in that: The emulsifier is arranged at the terminal outlet of the main mixer (9), an emulsifying chamber (12) is arranged inside the emulsifier, the top of the emulsifying chamber (12) is communicated with the terminal outlet of the main mixer (9), a multi-layer screen structure is arranged inside the emulsifying chamber (12), the main material and the auxiliary material stirred and mixed in the main mixer (9) enter the emulsifying chamber (12), are emulsified by the multi-layer screen structure, and then poured into a foaming line mold through the outlet at the bottom of the emulsifying chamber (12) for foaming, thereby forming a soft polyurethane foam.

9. The polyurethane foam preparation device based on liquid carbon dioxide foaming according to claim 8, characterized in that: The emulsifier releases pressure step by step through a multi-layer screen structure, which includes a combination of 1 to 5 layers of screens with different apertures, the aperture of the screen is 50 to 400 microns, and the aperture of the screen is adjusted according to the viscosity and particle size of the foaming raw material and the content of liquid carbon dioxide. By gradually releasing the pressure, the liquid carbon dioxide is gradually gasified and foamed in the emulsifier.

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