An integrated gradient polyurethane foam and a method of making the same

Abstract

The application discloses an integrated gradient polyurethane foam material and a preparation method thereof, and belongs to the technical field of foam materials. The polyether polyol, a foaming agent, a chain extender, a crosslinking agent, a cell stabilizer and a catalyst are uniformly mixed to obtain a preformed material; the preformed material and isocyanate are mixed and uniformly mixed to obtain a foaming material; the foaming material is poured into a mold, a surface in the lifting direction of the foaming material is taken as an acting surface, and a load is applied; after the load is applied, free foaming is carried out; after foaming is completed, a foam sample is taken out, and aging is carried out to obtain the integrated gradient polyurethane foam. The technical method adopted by the application is simple and easy to reproduce, and the purposes of reducing energy consumption, reducing cost or improving efficiency can be achieved. The gradient foam material prepared by the application realizes the continuous transition of density and cell size, avoids internal damage caused by interface problems, and has the characteristics of light weight, high strength, compression resistance, energy absorption and shock absorption.

Description

Technical Field

[0001] The invention relates to an integrated gradient polyurethane foam material and a preparation method thereof, belonging to the technical field of foam materials. Background Art

[0002] Polyurethane foam (PUF) is a microporous foam material. Its uniform and fine pore structure gives it high strength, good toughness, and smooth stress transmission, making it widely used in footwear, cushioning, and explosion-proof materials. PUF can dissipate energy through the resilient deformation of the matrix and pore structure, especially in shock absorption. Numerous studies have shown that the mechanical properties of foam are closely related to its relative density and pore morphology. However, homogeneous foams have flattened overall properties, and improving energy absorption performance often requires increasing foam density and material costs. Therefore, gradient foams with a hierarchical pore structure have gradually become a research focus.

[0003] Gradient foam material is a new type of porous composite material whose composition and structure show continuous gradient changes. It can meet the design requirements of its overall function and performance by optimizing the structure. The existing preparation methods of polymer gradient foam materials are:

[0004] (1) The bonding method (CN110696440A, document “Preparation and Performance Study of Gradient Density Polyurethane Foam Plastics”) bonds single-layer materials of different properties together to construct gradient foam. The above method is simple, but there are interface problems that cannot be ignored. It does not belong to integrated preparation. In addition, due to the presence of a bonding layer with a sudden change in density, stress is difficult to continue to transmit across the strong interface, resulting in stress first cohesion at the interface and generating transverse shear tearing at this location, leading to crush failure.

[0005] (2) The supercritical foaming method (CN110204778A, CN108795052A, CN108164831A, CN106336522A) requires the completion of gas saturation adsorption of thermoplastic materials under high temperature and high pressure conditions, and then forms gradient bubbles through two-stage adsorption or two-stage pressure release processes. This method has high energy consumption and strict requirements on equipment.

[0006] (3) The 3D printing method (CN109376497A, CN107200583A) prepares gradient foam by printing molten wire along a predetermined path. This method has complex path control, low variability of the foam cells, and low production capacity due to the limitation of printing speed.

[0007] (4) Freezing method (CN109180992A) uses a directional freezing method to prepare gradient aerogel materials. This method requires hot and cold treatment, has high energy consumption and low production capacity.

[0008] (5) Melt coextrusion method (CN108164814A) After the base material and the nucleating agent in different proportions are blended and extruded into sheets, the sheets are melted and overlapped. Since the nucleating agent is conducive to the formation of bubbles, the bubble distribution is positively correlated with the concentration of the nucleating agent. This characteristic is used to obtain a gradient porous material after foaming. This method is cumbersome and has high energy consumption.

[0009] (6) The microwave method (CN117820714A) is similar to melt coextrusion. It uses substrate sheets containing different concentrations of microwave absorbents to melt and overlap, and then obtains gradient foam materials after pre-foaming and microwave secondary foaming. Due to the difference in microwave absorbent concentration, a gradient temperature field can be formed, which affects the foaming degree and forms gradient foam. This method is more complicated, requires more stringent equipment conditions, and has high energy consumption.

[0010] Although the above methods can all construct gradient foam materials, they all have some limitations, resulting in insufficient development of gradient foam materials.

[0011] Therefore, developing an integrated method for preparing gradient polyurethane foam materials to reduce dependence on equipment and further reduce production costs has extremely high practical and economic value. Summary of the Invention

[0012] To address these issues, the present invention utilizes pressure-assisted foaming technology to produce integrated gradient foams through a one-step chemical foaming process. The method employed in the present invention is simple and easily reproducible, achieving goals such as reducing energy consumption, lowering costs, and improving efficiency. The resulting gradient foam material achieves a continuous transition between density and pore size, avoiding internal damage caused by interfacial issues.

[0013] A first object of the present invention is to provide a method for preparing an integrated gradient polyurethane foam, the method comprising:

[0014] (1) mixing a polyether polyol, a blowing agent, a chain extender, a crosslinking agent, a foaming agent, and a catalyst to obtain a prefabricated material; and mixing the prefabricated material and an isocyanate to obtain a foamed material;

[0015] (2) pouring the foaming material into a mold, applying a load to the surface of the foaming material in the lifting direction as the working surface; after the load is applied, free foaming is carried out; after the foaming is completed, the foam sample is taken out and matured to obtain an integrated gradient polyurethane foam;

[0016] Among them, the load intensity during the load action is 8 to 12 bar, the constant load is 2 to 10 seconds, and the free foaming is 0 to 8 seconds (constant load method);

[0017] or,

[0018] The load intensity starts from 0 bar, and the load intensity changes at a rate of 0.8-4.0 bar / s, the gradient load is 2-10 s, and the free foaming is 0-8 s (step load method).

[0019] In an embodiment, the foaming agent is water; preferably, the foaming agent is industrial grade deionized water.

[0020] In an embodiment, the chain extender is one or both of ethylene glycol and 1,4-butanediol.

[0021] In an embodiment, the crosslinking agent is diethanolamine.

[0022] In an embodiment, the foam stabilizer is silicone oil.

[0023] In an embodiment, the catalyst is one or more of triethylenediamine, Tegoamin DMEA, and A33.

[0024] In an embodiment, the time from the start of pouring the foaming material into the mold to the gelation of the foaming material is referred to as the processing window; the length of the processing window is closely related to the properties of the substrate (foaming material) and is affected by the feeding ratio; in the present application, the processing window is the sum of the length of the load time and the length of the free foaming time, i.e., the operation time, and the length is 5-20 s.

[0025] Preferably, the processing window is 10 s.

[0026] In an embodiment, in step (1), the mass fraction ratio of the polyether polyol, the foaming agent, the chain extender, the crosslinking agent, the foam stabilizer, and the catalyst is 90-110:0.65-0.85:4-6:2-4:0.3-0.7:1.5-2.

[0027] In an embodiment, characterized in that, in step (1), the mass fraction ratio of the preformed material and the isocyanate is 98.45-123.55:75:86.5.

[0028] In an embodiment, in step (2), the maturation is placing the foam sample at 40-70℃ for 48-72 h.

[0029] A second object of the present application is to provide an integrated gradient polyurethane foam prepared by any of the above-mentioned methods.

[0030] A third object of the present application is to provide the use of any of the above-mentioned methods or the above-mentioned integrated gradient polyurethane foam in the field of materials.

[0031] In an embodiment, the use in the field of materials includes: preparing building materials, furniture, packaging materials, protective equipment, medical devices, sports equipment.

[0032] A fourth object of the present invention is to provide a pad for impact protection, the pad containing the above-mentioned integrated gradient polyurethane foam.

[0033] A fifth object of the present invention is to provide a building material comprising the above-mentioned integrated gradient polyurethane foam.

[0034] A sixth object of the present invention is a method for improving the compressive strength, specific energy absorption performance and impact resistance of a polyurethane foam material, the method comprising:

[0035] (1) mixing a polyether polyol, a blowing agent, a chain extender, a crosslinking agent, a foaming agent, and a catalyst to obtain a prefabricated material; and mixing the prefabricated material and an isocyanate to obtain a foamed material;

[0036] (2) pouring the foaming material into a mold, applying a load to the surface of the foaming material in the lifting direction as the working surface; after the load is applied, free foaming is carried out; after the foaming is completed, the foam sample is taken out and matured to obtain an integrated gradient polyurethane foam;

[0037] Among them, the load intensity during load action is 8 to 12 bar, the constant load is 2 to 10 seconds, and the free foaming is 0 to 8 seconds;

[0038] or,

[0039] During the load action, the load intensity starts from 0 bar, and the load intensity change rate is 0.8 to 4.0 bar / s. The gradient loading time is 2 to 10 seconds, and the free foaming time is 0 to 8 seconds.

[0040] In one embodiment, in step (1), the mass ratio of polyether polyol, foaming agent, chain extender, crosslinking agent, foam leveling agent and catalyst is 90-110:0.65-0.85:4-6:2-4:0.3-0.7:1.5-2.

[0041] In one embodiment, it is characterized in that, in step (1), the mass ratio of the prefabricated material to the isocyanate is 98.45-123.55:75-86.5.

[0042] In one embodiment, in step (2), the aging is performed by placing the foam sample at 40-70° C. for 48-72 hours.

[0043] Beneficial effects of the present invention:

[0044] The present invention utilizes pressure-assisted foaming technology to prepare integrated gradient foam through one-step chemical foaming. The preparation method of the present invention is simple, environmentally friendly, low-cost and highly efficient. The prepared integrated gradient foam has good performance and high strength.

[0045] Specifically:

[0046] (1) The integrated gradient foam prepared by the present invention under constant load has a compressive strength of more than 524kPa; the specific energy absorption reaches 25KJ / m 3 g and above, up to 124KJ / m 3 g; energy absorption efficiency reaches over 97.77%;

[0047] (2) The integrated gradient foam prepared by the present invention through gradient loading has a compressive strength of more than 227kPa; the specific energy absorption reaches 12KJ / m 3 g and above, up to 103KJ / m 3 ·g; Energy absorption efficiency reaches over 98.13%. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is the scanning electron microscope image result of sample JT-1 prepared in Example 1.

[0049] Figure 2 This is the scanning electron microscope image result of sample JT-2 prepared in Example 2.

[0050] Figure 3 This is the scanning electron microscope image result of sample JT-3 prepared in Example 3.

[0051] Figure 4 This is the scanning electron microscope image result of sample LX-1 prepared in Example 4.

[0052] Figure 5 This is the scanning electron microscope image result of sample LX-2 prepared in Example 5.

[0053] Figure 6 This is the scanning electron microscope image result of sample LX-3 prepared in Example 6.

[0054] Figure 7 This is the scanning electron microscope image result of the sample JZ-PUF prepared in Comparative Example 1. DETAILED DESCRIPTION

[0055] The following describes preferred embodiments of the present invention. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0056] The present invention uses mechanical pressure-assisted foaming technology, whereby the gas generated by the chemical reaction forms cells during the agglomeration process. The key to the invention is that the externally applied pressure restricts the expansion of the cells, thereby causing significant changes in the cell structure.

[0057] During the critical processing window, the molecular network structure has not yet fully solidified. The increased viscosity imparts a certain strength to the cell walls, albeit a relatively fragile and easily deformed state. The external load applied to the matrix forces the gas within the cells to resist the deformation and contraction caused by the external pressure from the inside out, until a dynamic equilibrium is reached. This equilibrium results in cell bending, forming an oblate structure. Furthermore, due to the continuous nature of stress transmission, the degree of cell bending gradually decreases from the outside inward, forming a natural gradient structure. As stress transmission increases, the thickness of the denser region gradually increases under the same pressure for the same duration.

[0058] This integrated gradient foam exhibits a continuously increasing cell size distribution. In the dense zone, the cells are oval, smaller, and more dense; in the conventional zone, the cells are nearly round, larger, and less dense. These two distinct morphological characteristics give the elastomer its unique physical properties. In the dense zone, due to its thicker cell walls, energy dissipated during compression primarily occurs through bending deformation; in the conventional zone, with its thinner cell walls, energy dissipated often involves tearing. This thicker dense zone design effectively reduces the risk of matrix tearing during impact. Furthermore, the presence of the conventional zone significantly improves the material's overall specific energy absorption capacity.

[0059] This invention utilizes two unique methods to efficiently manufacture integrated gradient foam. The first, the constant load method, stands out for its powerful load-assisted foaming effect. It can significantly increase the gradient difference of the foam, thereby creating a foam structure with significant gradient characteristics. This improves the material's specific energy absorption performance while also enhancing the material's resistance to impact and tearing. The second, the step load method, excels in regulating the material's pore density. It can effectively reduce the reverse propagation of stress waves, thereby significantly reducing the recoil effect during impact. These two methods, each with its own advantages, provide strong technical support for the manufacture of high-performance gradient foams.

[0060] The integrated gradient foam described in the present invention has the characteristics of light weight, high strength, compression resistance, energy absorption and shock absorption. The preparation method is greatly simplified and does not require high temperature and high pressure to reduce energy consumption.

[0061] Test method:

[0062] 1. Micromorphology characterization

[0063] The cross-sectional cell structure was characterized using a scanning electron microscope (SEM) as follows:

[0064] (1) Cell size statistics: The cell size was counted using Image J software, and the average value was recorded. The cell size of the gradient foam was the weighted average value of different regions, in μm.

[0065] (2) Cell density statistics: The number of cells was counted using Image J software, and the average value was recorded. Cell density (N) is defined as the total number of cells per cubic centimeter of foam sample. The cell density of gradient foam is the weighted average of different regions, with a unit of 10 5 × cells / cm 3 .

[0066] (3) Open and closed porosity test: The gas replacement method is used to analyze the cell type using a fully automatic open and closed porosity analyzer to test the actual volume of the sample and then give the open and closed porosity of the sample in %.

[0067] 2. Compression and impact protection performance

[0068] (1) Compression resistance test:

[0069] According to GBT 6669-2008 "Determination of compression set of flexible foam polymeric materials", the compression performance of the foam was tested using a microcomputer-controlled universal testing machine. Two test speeds were used for single-cycle quasi-static compression tests, with loading and unloading rates of 1 mm / min and 10 mm / min respectively. The test obtained a loading-unloading curve with a maximum compressive strain of 80%, and the compressive strength (σmax) at 80% strain was obtained in kPa. The specific energy absorption (SEA) in kJ / m 3 ·g.

[0070] (2) Impact resistance test:

[0071] Using a drop-weight impact test, low-velocity impact tests were performed on various foam samples using a floor-standing drop-weight tester. This study employed a hemispherical punch with a diameter of 16 mm, internally fitted with a 30 kN force transducer. The impact energy was 20 J, and the energy absorption efficiency (EAR) of each sample was calculated in %.

[0072] The raw materials used in the embodiment are:

[0073] Polyether polyols were purchased from Zhejiang Huafeng New Materials Co., Ltd.

[0074] The isocyanate model is PM200;

[0075] The chain extender was ethylene glycol, which is commercially available;

[0076] The cross-linking agent was diethanolamine, which is commercially available;

[0077] The uniform foaming agent is silicone oil, commercially available;

[0078] The catalyst is A33 (a gel type polyurethane catalyst, with a composition of 33% triethylene diamine and 67% dipropylene glycol (DPG) solution), commercially available from Yichen Innovative Materials (Shanghai) Co., Ltd.

[0079] The mold size is 10 cm x 10 cm x 5 cm.

[0080] Example 1: Preparation of integrated gradient polyurethane foam under constant load

[0081] The integrated gradient polyurethane foam is prepared under constant load, and the steps are as follows:

[0082] (1) The polyether polyol, foaming agent (water), chain extender, crosslinking agent, uniform foaming agent and catalyst are mixed in a mass ratio of 100:0.75:5:3:0.5:1.75 to obtain a preform; then the preform and isocyanate are mixed in a mass ratio of 111:80.75 to obtain a foaming material (191.75 g);

[0083] (2) The foaming material is placed in a mold, and during the processing window period, the surface in the lifting direction of the foaming material is used as the action surface, and a mechanical load block with a length and width equal to the mold and a fine control stroke is used to apply a stepped load to the foaming material; the load strength is 10 bar, the total constant load time is 3 s, then no load is applied for free foaming for 7 s, so that the overall operation time matches the homogeneous foam gelation time (operation time = load time + free foaming; the gelation time is closely related to the properties of the substrate and is affected by the feed ratio, and the gelation time in this example is 10 s); after 1 min of foaming, the foam sample is taken out and placed in a 50°C oven for 48 h of curing to prepare an integrated gradient foam, sample No. JT-1.

[0084] The scanning electron microscope image results of sample JT-1 are shown in Figure 1 .

[0085] Example 2: Preparation of integrated gradient polyurethane foam under constant load

[0086] On the basis of Example 1, the constant load time in step (2) is changed to 6 s, and the free foaming time is 4 s, and the remaining conditions are consistent with Example 1, to prepare an integrated gradient foam, sample No. JT-2.

[0087] The scanning electron microscope image results of sample JT-2 are shown in Figure 2 .

[0088] Example 3: Preparation of integrated gradient polyurethane foam under constant load

[0089] On the basis of Example 1, the constant load time in step (2) was changed to 9 s and the free foaming time was changed to 1 s. The other conditions were the same as those in Example 1, and an integrated gradient foam was prepared, sample number JT-3.

[0090] The scanning electron microscope image of sample JT-3 is as follows Figure 3 shown.

[0091] Example 4: Preparation of integrated gradient polyurethane foam material with gradient loading

[0092] The steps for preparing an integrated gradient polyurethane foam material with gradient loading are as follows:

[0093] (1) mixing polyether polyol, (foaming agent) water, chain extender, crosslinking agent, foam leveling agent and catalyst in a mass ratio of 100:0.75:5:3:0.5:1.75 to obtain a prefabricated material; then mixing the prefabricated material and isocyanate in a mass ratio of 111:80.75 to obtain a foamed material;

[0094] (2) The foaming material is placed in the mold. During the processing window, a continuous load is applied to the foaming material with the surface in the lifting direction of the foaming material as the action surface; the load intensity starts from 0 bar and increases evenly to 10 bar, and the total time of the gradient load is 3 s (that is, the load intensity change rate is 3.33 bar / s). For another period of time, no load is applied at all for free foaming, so that the overall operation time matches the gelation time of the homogeneous foam; 1 minute after the foaming is completed, the foam sample is taken out and placed in a 50°C oven for curing for 48 hours to prepare an integrated gradient foam, sample number LX-1.

[0095] The scanning electron microscope image of sample LX-1 is as follows Figure 4 shown.

[0096] Example 5: Preparation of integrated gradient polyurethane foam material with gradient loading

[0097] On the basis of Example 4, the gradient loading time in step (2) was changed to 6s, the free foaming time was changed to 4s, and the other conditions were consistent with Example 4 to prepare an integrated gradient foam, sample number LX-2.

[0098] The scanning electron microscope image of sample LX-2 is as follows Figure 5 shown.

[0099] Example 6: Preparation of integrated gradient polyurethane foam material with gradient loading

[0100] On the basis of Example 4, the gradient loading time in step (2) was changed to 9s, the free foaming time was changed to 1s, and the other conditions were consistent with Example 4 to prepare an integrated gradient foam, sample number LX-3.

[0101] The scanning electron microscope image of sample LX-3 is as follows Figure 6 shown.

[0102] Comparative Example 1: No load applied

[0103] The polyurethane foam material was prepared without applying a load as follows:

[0104] (1) mixing polyether polyol, (foaming agent) water, chain extender, crosslinking agent, foam leveling agent and catalyst in a mass ratio of 100:0.75:5:3:0.5:1.75 to obtain a prefabricated material; then mixing the prefabricated material and isocyanate in a mass ratio of 111:80.75 to obtain a foamed material;

[0105] (2) Place the foaming material in a mold and allow it to foam freely. After 1 minute of foaming, take out the foam sample and place it in a 50°C oven for aging for 48 hours. A homogeneous foam is obtained, sample number JZ-PUF.

[0106] The scanning electron microscope image of the sample JZ-PUF is shown in the following figure: Figure 7 shown.

[0107] Example 7: Testing the performance of integrated gradient foam

[0108] The integrated gradient foams prepared in Examples 1 to 6 and Comparative Example 1 were tested for various properties.

[0109] (1) Microstructure parameters

[0110] Table 1 shows the results for cell size, cell density, and open / closed porosity. The results indicate that Example 3 produced the smallest cell size, highest cell density, and lowest open / closed porosity, significantly outperforming the other examples and comparative examples. While all samples had similar mass, the varying volumes resulted in significant differences in average density.

[0111] The density of integrated gradient foam is higher than that of homogeneous foam. This is due to the introduction of dense areas. The higher the content of dense areas, the greater the average density and the more obvious the gradient structure.

[0112] Therefore, integrated gradient foam can achieve or even exceed the performance of homogeneous foam with a smaller mass, thus saving material costs. Cell size, openness, and cell density interact with each other and together determine the basic properties of the material. Openness reflects the openness of the cells, which potentially affects the material's stress transmission and absorption. A high openness due to cell merging also increases the corresponding cell size. Conversely, as the cell diameter increases, the cell density decreases. Smaller cell size, higher cell density, and lower openness contribute to the foam's ability to achieve both compression and impact resistance.

[0113] Table 1 Microstructure parameters

[0114]

[0115] (2) Protection performance test

[0116] The compressive strength and specific energy absorption results are shown in Table 2. The results show that the integrated gradient foam prepared in Example 3 has the highest compressive strength and specific energy absorption, which are significantly higher than those of other examples and comparative examples.

[0117] In terms of impact resistance, all samples demonstrated a high energy absorption efficiency exceeding 97%. Although JT-3's EAR is weaker than that of homogeneous foam due to the structural characteristics of the material, the presence of dense regions makes the dense structure more conducive to tear resistance. The tear depth of the integrated gradient foam is much smaller than that of the homogeneous foam (Comparative Example 1). In other words, JZ-PUF and step-loaded foams can dissipate energy through tearing, but this energy absorption method shortens the service life of the material.

[0118] Table 2 Protection performance

[0119]

[0120]

[0121] It can be seen from the above data that the integrated gradient foam materials prepared in Examples 1 to 6 have greatly improved compression and impact protection performance compared with ordinary foam materials; and as the load effect increases, the pore size gradually decreases, the gradient difference increases, and the performance improvement is more significant.

[0122] Comparative Example 2: Changing the load intensity

[0123] (1) Based on Example 1, the load intensity was changed to 20 bar, and the other conditions were the same as those in Example 1.

[0124] The results showed that it was impossible to prepare integrated gradient foam.

[0125] During the processing window, the molecular chains of the matrix are not fully networked, and their strength is insufficient to support excessive load strength. At the same time, the viscosity of the foam is still increasing, which will cause the bubbles to stick together and foaming to fail.

[0126] (2) Based on Example 1, the load intensity was changed to 1 bar, and the other conditions were the same as those in Example 1.

[0127] The results showed that it was impossible to prepare integrated gradient foam.

[0128] Because the hole wall is polymer macromolecular material, has certain rigidity, lower load is in semi-formed cell's bearing strength range, the cell will not be deformed, the foam prepared is homogeneous foam.

[0129] Comparative Example 3: Change the rate of load intensity change

[0130] (1) On the basis of Example 4, change the rate of load intensity change to 5 bar / s, and the rest of the conditions are consistent with Example 1.

[0131] It is found that integrated gradient foam cannot be prepared.

[0132] When the rate of load intensity change is higher than the rising speed of the foam, the contact time with the substrate is insufficient, which is equivalent to no pressure-assisted foaming, and a common homogeneous foam is prepared.

[0133] (1) On the basis of Example 4, change the rate of load intensity change to 0.1 bar / s, and the rest of the conditions are consistent with Example 1.

[0134] It is found that integrated gradient foam cannot be prepared.

[0135] When the rate of load intensity change is very slow, the load intensity hardly changes within the processing window, and its effect is similar to that of the mold cover of conventional homogeneous foam, which finally leads to the preparation of homogeneous foam.

[0136] Comparative Example 4: Free foaming first and then applying load

[0137] (1) On the basis of Example 1, change the load mode in step (2) to: free foaming for 7 s, and then applying constant load for 3 s (load intensity is 10 bar), and the rest of the conditions are consistent with Example 1.

[0138] It is found that integrated gradient foam cannot be prepared.

[0139] (2) On the basis of Example 4, change the load mode in step (2) to: free foaming for 7 s, and then applying gradient load for 3 s (load intensity starts from 0 bar and uniformly increases to 10 bar, i.e. the rate of load intensity change is 3.33 bar / s), and the rest of the conditions are consistent with Example 1.

[0140] It is found that integrated gradient foam cannot be prepared.

[0141] The reasons why integrated gradient foam cannot be produced using processes (1) and (2) are similar: regardless of how the subsequent auxiliary load changes, as long as free rise is performed first, the substrate will reach a semi-gel state before the load acts, and the structural strength of the pores will increase, making it difficult for the substrate to maintain its deformed shape. The deformation at this time is elastic deformation, and the deformed pores will return to their original shape after the load is removed. Therefore, the foam produced is still a homogeneous foam.

[0142] Although the present invention has been disclosed above in terms of preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for preparing an integrated gradient polyurethane foam, characterized in that: The method comprises: (1) mixing a polyether polyol, a blowing agent, a chain extender, a crosslinking agent, a foaming agent, and a catalyst to obtain a prefabricated material; and mixing the prefabricated material and an isocyanate to obtain a foamed material; (2) pouring the foaming material into a mold, applying a load to the surface of the foaming material in the lifting direction as the working surface; after the load is applied, free foaming is carried out; after the foaming is completed, the foam sample is taken out and matured to obtain an integrated gradient polyurethane foam; Among them, the load intensity during load action is 8 to 12 bar, the constant load is 2 to 10 seconds, and the free foaming is 0 to 8 seconds; or, During the load action, the load intensity starts from 0 bar, and the load intensity changes at a rate of 0.8 to 4.0 bar / s, with gradient loading for 2 to 10 seconds and free foaming for 0 to 8 seconds.

2. The method according to claim 1, characterized in that In step (1), the mass ratio of polyether polyol, foaming agent, chain extender, crosslinking agent, foam leveling agent and catalyst is 90-110:0.65-0.85:4-6:2-4:0.3-0.7:1.5-2.

3. The method according to claim 1, characterized in that In step (1), the mass ratio of the prefabricated material to the isocyanate is 98.45-123.55:75-86.

5.

4. The method according to claim 1, wherein In step (2), the aging is to place the foam sample at 40 to 70° C. and mature it for 48 to 72 hours.

5. The integrated gradient polyurethane foam prepared by the method according to any one of claims 1 to 4.

6. Use of the method according to any one of claims 1 to 4 or the integrated gradient polyurethane foam according to claim 5 in the field of materials.

7. The use according to claim 6, characterized in that Applications of the material in the field include: preparing building materials, furniture, packaging materials, protective equipment, medical equipment or sports equipment.

8. A pad for impact protection, characterized in that: The pad contains the integrated gradient polyurethane foam of claim 5.

9. A building material, characterized in that The building material contains the integrated gradient polyurethane foam according to claim 5.

10. A method for improving the compressive strength, specific energy absorption and impact resistance of polyurethane foam materials, characterized in that: The method comprises: (1) mixing a polyether polyol, a blowing agent, a chain extender, a crosslinking agent, a foaming agent, and a catalyst to obtain a prefabricated material; and mixing the prefabricated material and an isocyanate to obtain a foamed material; (2) pouring the foaming material into a mold, applying a load to the surface of the foaming material in the lifting direction as the working surface; after the load is applied, free foaming is carried out; after the foaming is completed, the foam sample is taken out and matured to obtain an integrated gradient polyurethane foam; Among them, the load intensity during load action is 8 to 12 bar, the constant load is 2 to 10 seconds, and the free foaming is 0 to 8 seconds; or, During the load action, the load intensity starts from 0 bar, and the load intensity changes at a rate of 0.8 to 4.0 bar / s, with gradient loading for 2 to 10 seconds and free foaming for 0 to 8 seconds.

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