A thermoplastic polyurethane elastomer foamed particle and a preparation method thereof

Abstract

The present invention provides thermoplastic polyurethane elastomer foam particles and a preparation method thereof. The preparation method comprises: mixing thermoplastic polyurethane particles with a supercritical fluid, and performing compression molding to foam the particles to obtain the thermoplastic polyurethane elastomer foam particles; the supercritical fluid comprises carbon dioxide and nitrogen. In the present invention, the preparation method utilizes a supercritical fluid process combined with compression molding to prepare the polyurethane foam particles, and the supercritical fluid is a combination of nitrogen and carbon dioxide. This results in the thermoplastic polyurethane elastomer foam particles having good uniformity, regular shape, high expansion ratio, low shrinkage, and excellent performance. Furthermore, the process is simple, energy-efficient, and environmentally friendly, making them suitable for industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane foam materials, and particularly relates to thermoplastic polyurethane elastomer foam particles and a preparation method thereof. Background Art

[0002] Thermoplastic polyurethane (TPU) macromolecules have a block structure consisting of soft and hard segments. Depending on the composition of the soft segment, they can be categorized as polyester or polyether. TPU possesses the excellent elasticity of rubber while also possessing the excellent processability of plastic. It can be molded using thermoplastic processing techniques such as extrusion, injection molding, and blow molding. TPU foam materials, with their porous structure, offer lightweight, low cost, enhanced resilience and cushioning properties, and a wider range of applications.

[0003] Polymer foam materials, which utilize foaming technology to create a large number of bubbles within polymer materials, form a porous structure and are an effective means of achieving lightweight products and conserving materials. The presence of numerous cells also imparts excellent thermal insulation, damping, and noise reduction properties to the material. Generally speaking, a higher expansion ratio of a polymer foam material translates to a lighter product, greater material conservation, and superior insulation and cushioning properties. Compared to non-recyclable and environmentally polluting thermosetting foam materials, recyclable thermoplastic foams offer broader application prospects.

[0004] Traditional foam particles such as expandable polystyrene (EPS), expandable polyethylene (EPE), expandable polyolefin (EPO), etc., can no longer meet the application requirements of high-performance fields due to their low heat resistance. In addition, traditional foaming processes often use organic solvents, chlorofluorocarbons and other foaming agents, which seriously pollute the environment and products.

[0005] Traditional particle foaming often uses the autoclave impregnation method. However, this common autoclave impregnation method also has some problems. For example, due to the poor thermal conductivity of the material, a dispersant (suspending liquid) is usually added to achieve uniform temperature of the material in the autoclave. This results in long heating time, high energy consumption, and an additional post-processing step (separation and drying), which reduces production efficiency. In addition, the polyurethane foam particles in the existing technology are poorly uniform and cannot form regular particles.

[0006] For example, CN112109268A discloses a method for preparing TPU foam beads and the products thereof. The preparation method comprises the following steps: (1) TPU particles and water are measured separately and continuously added to a reactor, and stirred to form a uniform suspension; (2) the suspension and foaming agent are measured separately and pumped to a mixing station to form a mixture; (3) the mixture is conveyed to a heat exchanger and heated to a foaming temperature; (4) the mixture reaching the foaming temperature is conveyed to a multi-stage impregnation vessel via a pipeline, where the foaming agent gradually impregnates the interior of the TPU particles and eventually reaches a dissolution equilibrium; (5) the TPU particles at which the foaming agent has dissolved in equilibrium are continuously discharged through a perforated plate at the end of a pipeline connected to the outlet of the multi-stage impregnation vessel into a receiving tank for foaming to obtain TPU foam beads. The preparation method is complex and energy-intensive.

[0007] Therefore, developing a method for preparing polyurethane foam particles with high foaming ratio, good foaming uniformity, regular shape, good performance, simple process and low energy consumption is an urgent problem to be solved in this field. Summary of the Invention

[0008] In response to the shortcomings of the prior art, the present invention provides thermoplastic polyurethane elastomer foam particles and a method for preparing the same. The method utilizes a supercritical fluid process combined with a compression molding technique to prepare the polyurethane foam particles, wherein the supercritical fluid is a combination of nitrogen and carbon dioxide. This method results in the thermoplastic polyurethane elastomer foam particles having good uniformity, regular shape, high expansion ratio, low shrinkage, and excellent performance, along with a simple process, low energy consumption, and environmental friendliness, making them suitable for industrial production.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a method for preparing thermoplastic polyurethane elastomer foam particles, the preparation method comprising:

[0011] Thermoplastic polyurethane particles are mixed with a supercritical fluid, and then subjected to mold compression and foaming to obtain the thermoplastic polyurethane elastomer foamed particles; the supercritical fluid comprises carbon dioxide and nitrogen.

[0012] In the present invention, a mixed supercritical fluid of nitrogen and carbon dioxide is used for foaming. The nitrogen escape rate inside the bubbles is low and the pressure is high. During the gas exchange process, sufficient air pressure can be maintained inside the bubbles to support the bubble structure. This effectively avoids the problems of large bubble shrinkage and small foaming ratio caused by the low internal bubble pressure in the pure carbon dioxide foaming process. In combination with the use of molding technology, the uniformity of the polyurethane foam particles can be further improved, the foaming ratio is high, the particle shape is regular, the shrinkage rate is small, and the high and low temperature resistance is good. In addition, the process is simple, the cost is low, and it is environmentally friendly.

[0013] Preferably, the total pressure of the supercritical fluid is 5 to 16 MPa, for example, 5 MPa, 5.5 MPa, 6 MPa, 6.5 MPa, 7 MPa, 7.5 MPa, 8 MPa, 8.5 MPa, 9 MPa, 9.5 MPa, 10 MPa, 10.5 MPa, 11 MPa, 11.5 MPa, 12 MPa, 12.5 MPa, 13 MPa, 13.5 MPa, 14 MPa, 14.5 MPa, 15 MPa, 15.5 MPa, 16 MPa, etc.

[0014] Preferably, the pressure ratio of carbon dioxide to nitrogen is (1-6):1, for example, it can be 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4:1, 4.2:1, 4.4:1, 4.6:1, 4.8:1, 5:1, 5.2:1, 5.4:1, 5.6:1, 5.8:1, 6:1, etc.; more preferably, it is (2.5-6):1.

[0015] In the present invention, when the pressure ratio of carbon dioxide to nitrogen is within the above-defined range, the foaming effect is better.

[0016] Preferably, the mixing is performed in a molding device.

[0017] Preferably, the mixing temperature is 130-160°C, for example, it can be 130°C, 132°C, 134°C, 136°C, 138°C, 140°C, 142°C, 143°C, 144°C, 145°C, 146°C, 147°C, 148°C, 149°C, 150°C, 151°C, 152°C, 153°C, 154°C, 155°C, 156°C, 157°C, 158°C, 159°C, 160°C, etc.; more preferably, it is 140-160°C.

[0018] Preferably, the mixing step comprises: placing thermoplastic polyurethane particles into a molding device, closing the film, heating the film to 130-160° C., filling the film with a supercritical fluid, and mixing the film.

[0019] In the present invention, the mixing includes: evenly spreading thermoplastic polyurethane particles in the mold cavity of the molding equipment, starting the hydraulic system to close the mold; then starting the heating system of the molding equipment, setting the temperature value, and heating; when the temperature reaches 130-160°C, filling the mold cavity with supercritical fluid for mixing.

[0020] In the present invention, the heating medium used by the molding equipment is heat-conducting oil.

[0021] Preferably, the compression foaming comprises the steps of pressure-maintaining swelling and pressure-releasing foaming.

[0022] Preferably, the pressure-maintaining swelling time is 15 to 60 min, for example, it can be 15 min, 16 min, 18 min, 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min, 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min, 40 min, 42 min, 44 min, 46 min, 48 min, 50 min, 52 min, 54 min, 56 min, 58 min, 60 min, etc.; more preferably, it is 20 to 45 min.

[0023] In the present invention, the pressure-maintaining swelling allows the supercritical fluid to fully penetrate and swell the thermoplastic polyurethane elastomer particles, and after reaching an equilibrium state, a polymer-supercritical fluid homogeneous system is formed; when the pressure-maintaining swelling time is within the above-defined range, the polyurethane foam particles have better foaming performance.

[0024] Preferably, the pressure is released until the system pressure is 0.

[0025] Preferably, the pressure relief rate is 30 to 90 MPa / s, for example, it can be 30 MPa / s, 32 MPa / s, 35 MPa / s, 38 MPa / s, 40 MPa / s, 42 MPa / s, 45 MPa / s, 48 MPa / s, 50 MPa / s, 52 MPa / s, 55 MPa / s, 58 MPa / s, 60 MPa / s, 62 MPa / s, 65 MPa / s, 68 MPa / s, 70 MPa / s, 72 MPa / s, 75 MPa / s, 78 MPa / s, 80 MPa / s, 82 MPa / s, 85 MPa / s, 88 MPa / s, 90 MPa / s, etc.

[0026] Preferably, the pressure relief time is less than 5s, for example, it can be 0.1s, 0.2s, 0.3s, 0.4s, 0.5s, 1s, 1.5s, 2s, 2.5s, 3s, 3.5s, 4s, 4.5s, etc.

[0027] In the present invention, the pressure relief rate is too slow, the time is too long, the foaming effect is poor, and the obtained polyurethane foam particles have poor performance.

[0028] Preferably, the thermoplastic polyurethane particles include polyester polyurethane particles and / or polyether polyurethane particles.

[0029] Preferably, the diameter of the thermoplastic polyurethane particles is 0.6 to 9 mm, for example, 0.6 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, etc.

[0030] Preferably, the hardness of the thermoplastic polyurethane particles is 70-90A, for example, 70A, 75A, 80A, 85A, 90A, etc.

[0031] As a preferred technical solution of the present invention, the preparation method comprises:

[0032] Thermoplastic polyurethane particles are placed in a molding device, the film is closed, the temperature is raised to 130-160° C., a supercritical fluid is filled therein, mixed, pressure-maintained and swollen for 15-60 minutes, and then the pressure is released at a pressure release rate of 30-90 MPa / s until the system pressure reaches 0, thereby foaming to obtain the thermoplastic polyurethane elastomer foamed particles; the total pressure of the supercritical fluid is 5-16 MPa, and the supercritical fluid includes carbon dioxide and nitrogen with a pressure ratio of (1-6):1.

[0033] In a second aspect, the present invention provides thermoplastic polyurethane elastomer foam particles, which are prepared according to the preparation method described in the first aspect.

[0034] Preferably, the density of the thermoplastic polyurethane elastomer foam particles is 0.1 to 0.2 g / cm 3 , for example, it can be 0.11 g / cm 3 、0.112g / cm 3 , 0.114g / cm 3 、0.115g / cm 3 , 0.116g / cm 3 、0.118g / cm 3 , 0.12g / cm 3 , 0.122g / cm 3 , 0.124g / cm 3 , 0.126g / cm 3 , 0.128g / cm 3 , 0.13g / cm 3 , 0.132g / cm 3 , 0.134g / cm 3 , 0.136g / cm 3 , 0.138g / cm 3 , 0.14g / cm 3 , 0.142g / cm 3 , 0.144g / cm 3 , 0.146g / cm 3, 0.148g / cm 3 , 0.15g / cm 3 、0.154g / cm 3 、0.158g / cm 3 , 0.16g / cm 3 、0.162g / cm 3 , 0.164g / cm 3 、0.168g / cm 3 , 0.17g / cm 3 , 0.174g / cm 3 、0.178g / cm 3 , 0.18g / cm 3 , 0.184g / cm 3 , 0.188g / cm 3 , 0.19g / cm 3 , 0.194g / cm 3 , 0.198g / cm 3 , 0.2g / cm 3 wait.

[0035] Preferably, the foaming pore size of the thermoplastic polyurethane elastomer foam particles is 20 to 90 μm, for example, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, etc.

[0036] The numerical range described in the present invention includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values included in the range.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The preparation method of thermoplastic polyurethane foam particles provided by the present invention uses a supercritical fluid foaming process combined with molding technology, which is clean and environmentally friendly, and avoids the use of various unsafe and environmentally friendly foaming agents that cause problems such as product yellowing and odor. The particles do not need to be cleaned after foaming, the process flow is short, the energy consumption is low, and the particle foaming effect is good.

[0039] 2. The preparation method of thermoplastic polyurethane foam particles provided by the present invention adopts a supercritical fluid mixed with nitrogen and carbon dioxide for foaming, so that the thermoplastic polyurethane elastomer particles have a small shrinkage rate when placed in the air after foaming is completed, have a high foaming ratio, can ensure sufficient infiltration of the foaming precursor, and ensure uniform foaming of the particles.

[0040] 3. The preparation method of the thermoplastic polyurethane foam particles provided by the present invention has high production efficiency and a wide range of product applications; the final foaming ratio of the prepared thermoplastic polyurethane foam particles after aging can reach 4 to 10 times, the foaming pore diameter is 20 to 90 μm, the weight is light, and the performance is excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a scanning electron microscope image of thermoplastic polyurethane elastomer foam particles obtained by the preparation method provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0043] The materials and instruments used in the present invention are as follows:

[0044] Thermoplastic polyurethane particles: 80A polyether thermoplastic polyurethane particles (BASF 1180A, density 1.11g / cm 3 )

[0045] Molding equipment: Jiangsu Shuangma Intelligent Technology Co., Ltd. AMS-250.

[0046] Example 1

[0047] This embodiment provides a method for preparing thermoplastic polyurethane elastomer foam particles, comprising the following steps:

[0048] (1) Evenly spread 80A polyether thermoplastic polyurethane particles in the mold cavity of the molding equipment, and start the hydraulic system to close the mold;

[0049] (2) Start the heating system of the molding equipment, set the temperature to 145°C, and heat it with thermal oil;

[0050] (3) After the temperature reaches the set value, a mixed fluid of supercritical CO2 and supercritical N2 is filled into the mold cavity. The total pressure of the mixed fluid is 10 MPa, and the pressure ratio of the supercritical CO2 and supercritical N2 is 3:1. The mold cavity is subjected to pressure-maintaining infiltration and swelling for 30 minutes. After reaching equilibrium, a polymer-supercritical fluid homogeneous system is formed.

[0051] (4) The pressure in the mold cavity is quickly reduced from 10 MPa to 0 by releasing the pressure through a pneumatic ball valve at a pressure relief rate of 30 MPa / s, thereby obtaining the thermoplastic polyurethane elastomer foamed particles.

[0052] The morphology of the thermoplastic polyurethane elastomer foamed particles obtained in Example 1 was characterized using a scanning electron microscope. Figure 1 As shown, it can be seen that the particles foam evenly.

[0053] Example 2

[0054] This embodiment provides a method for preparing thermoplastic polyurethane elastomer foam particles, comprising the following steps:

[0055] (1) Evenly spread 80A polyether thermoplastic polyurethane particles in the mold cavity of the molding equipment, and start the hydraulic system to close the mold;

[0056] (2) Start the heating system of the molding equipment, set the temperature to 155°C, and heat it with thermal oil;

[0057] (3) After the temperature reaches the set value, a mixed fluid of supercritical CO2 and supercritical N2 is filled into the mold cavity. The total pressure of the mixed fluid is 10 MPa, and the pressure ratio of the supercritical CO2 and supercritical N2 is 3:1. The mold cavity is subjected to pressure-maintaining infiltration and swelling for 25 minutes. After reaching equilibrium, a polymer-supercritical fluid homogeneous system is formed.

[0058] (4) The pressure in the mold cavity is quickly reduced from 10 MPa to 0 by releasing the pressure through a pneumatic ball valve at a pressure relief rate of 35 MPa / s, thereby obtaining the thermoplastic polyurethane elastomer foamed particles.

[0059] Example 3

[0060] This embodiment provides a method for preparing thermoplastic polyurethane elastomer foam particles, comprising the following steps:

[0061] (1) Evenly spread 80A polyether thermoplastic polyurethane particles in the mold cavity of the molding equipment, and start the hydraulic system to close the mold;

[0062] (2) Start the heating system of the molding equipment, set the temperature to 150°C, and heat it with thermal oil;

[0063] (3) After the temperature reaches the set value, a mixed fluid of supercritical CO2 and supercritical N2 is filled into the mold cavity. The total pressure of the mixed fluid is 10 MPa, and the pressure ratio of the supercritical CO2 and supercritical N2 is 3:1. The mold cavity is subjected to pressure-maintaining infiltration and swelling for 20 minutes. After reaching equilibrium, a polymer-supercritical fluid homogeneous system is formed.

[0064] (4) The pressure in the mold cavity is quickly reduced from 10 MPa to 0 by releasing the pressure through a pneumatic ball valve at a pressure relief rate of 45 MPa / s, thereby obtaining the thermoplastic polyurethane elastomer foamed particles.

[0065] Example 4

[0066] This embodiment provides a method for preparing thermoplastic polyurethane elastomer foam particles, comprising the following steps:

[0067] (1) Evenly spread 80A polyether thermoplastic polyurethane particles in the mold cavity of the molding equipment, and start the hydraulic system to close the mold;

[0068] (2) Start the heating system of the molding equipment, set the temperature to 140°C, and heat it with thermal oil;

[0069] (3) After the temperature reaches the set value, a mixed fluid of supercritical CO2 and supercritical N2 is filled into the mold cavity. The total pressure of the mixed fluid is 10 MPa, and the pressure ratio of the supercritical CO2 and supercritical N2 is 3:1. The mold cavity is subjected to pressure-maintaining infiltration and swelling for 35 minutes. After reaching equilibrium, a polymer-supercritical fluid homogeneous system is formed.

[0070] (4) The pressure in the mold cavity is quickly reduced from 10 MPa to 0 by releasing the pressure through a pneumatic ball valve at a pressure relief rate of 40 MPa / s, thereby obtaining the thermoplastic polyurethane elastomer foamed particles.

[0071] Example 5

[0072] This embodiment provides a method for preparing thermoplastic polyurethane elastomer foam particles, comprising the following steps:

[0073] (1) Evenly spread 80A polyether thermoplastic polyurethane particles in the mold cavity of the molding equipment, and start the hydraulic system to close the mold;

[0074] (2) Start the heating system of the molding equipment, set the temperature to 142°C, and heat it with thermal oil;

[0075] (3) After the temperature reaches the set value, a mixed fluid of supercritical CO2 and supercritical N2 is filled into the mold cavity. The total pressure of the mixed fluid is 11 MPa, and the pressure ratio of the supercritical CO2 and supercritical N2 is 3.8:1. The mold cavity is subjected to pressure-maintaining, infiltration, and swelling. The pressure-maintaining time is 38 minutes. After reaching equilibrium, a polymer-supercritical fluid homogeneous system is formed.

[0076] (4) The pressure in the mold cavity is quickly reduced from 11 MPa to 0 by releasing the pressure through a pneumatic ball valve at a pressure relief rate of 45 MPa / s, thereby obtaining the thermoplastic polyurethane elastomer foamed particles.

[0077] Example 6

[0078] This embodiment provides a method for preparing thermoplastic polyurethane elastomer foam particles, comprising the following steps:

[0079] (1) Evenly spread 80A polyether thermoplastic polyurethane particles in the mold cavity of the molding equipment, and start the hydraulic system to close the mold;

[0080] (2) Start the heating system of the molding equipment, set the temperature to 148°C, and heat it with thermal oil;

[0081] (3) After the temperature reaches the set value, a mixed fluid of supercritical CO2 and supercritical N2 is filled into the mold cavity. The total pressure of the mixed fluid is 12 MPa, and the pressure ratio of the supercritical CO2 and supercritical N2 is 4.6:1. The mold cavity is subjected to pressure-maintaining infiltration and swelling for 42 minutes. After reaching equilibrium, a polymer-supercritical fluid homogeneous system is formed.

[0082] (4) The pressure in the mold cavity is quickly reduced from 12 MPa to 0 by releasing the pressure through a pneumatic ball valve at a pressure relief rate of 50 MPa / s, thereby obtaining the thermoplastic polyurethane elastomer foamed particles.

[0083] Example 7

[0084] This embodiment provides a method for preparing thermoplastic polyurethane elastomer foam particles, which differs from Example 1 only in that the pressure ratio of supercritical CO2 to supercritical N2 in step (3) is 2:1, and the other steps and process parameters are the same as those in Example 1.

[0085] Example 8

[0086] This embodiment provides a method for preparing thermoplastic polyurethane elastomer foam particles, which differs from Example 1 only in that the pressure ratio of supercritical CO2 to supercritical N2 in step (3) is 7:1, and the other steps and process parameters are the same as those in Example 1.

[0087] Example 9

[0088] This embodiment provides a method for preparing thermoplastic polyurethane elastomer foam particles, which differs from Example 1 only in that the temperature value set in step (2) is 120°C, and the holding time in step (3) is 10 minutes. The other steps and process parameters are the same as those in Example 1.

[0089] Example 10

[0090] This embodiment provides a method for preparing thermoplastic polyurethane elastomer foam particles, which differs from Example 1 only in that the temperature value set in step (2) is 170°C, and the holding time in step (3) is 80 minutes. The other steps and process parameters are the same as those in Example 1.

[0091] Example 11

[0092] This embodiment provides a method for preparing thermoplastic polyurethane elastomer foam particles, which differs from Example 1 only in that the pressure relief rate in step (4) is 10 MPa / s, and the other steps and process parameters are the same as those in Example 1.

[0093] Comparative Example 1

[0094] This comparative example provides a method for preparing thermoplastic polyurethane elastomer foamed particles, which differs from Example 1 only in that the molding equipment is replaced by a reactor, and the other steps and process parameters are the same as those in Example 1.

[0095] Performance Testing

[0096] (1) Density and expansion ratio

[0097] Density is generally measured using a solid density tester. The measurement method is the Archimedean buoyancy method. The density of the foamed particles is measured by the displacement method. The mass m1 of the foamed particles in the air is weighed using a density balance. The sample is then immersed in water until there are no bubbles on the surface of the sample. The mass m2 of the same volume of water discharged is measured; this is the density ρ of the foamed particles. f =m1 / m2.

[0098] The expansion ratio refers to the multiple by which the volume of the particles after foaming increases compared to the volume of the raw materials before foaming, i.e. the volume expansion ratio. f ρ f and ρ(g / cm 3 ), are the density of foamed sample and the density of unfoamed sample, respectively.

[0099] (2) Number average cell diameter and cell density

[0100] The samples were cut into smooth slices of approximately uniform thickness using a razor blade. The surfaces were then gold-sprayed and the cell structure of the cross-sections was observed and analyzed using a scanning electron microscope. Cell size was calculated using Image Pro Plus software to obtain the number-average cell diameter. The number-average cell diameter d and cell density Nc were calculated using the following formulas:

[0101] d=∑d i n i / ∑n i

[0102]

[0103] Where: d is the number average cell diameter, μm; n i The equivalent diameter is d i The number of cells, Nc is the cell density, cells / cm 3 ρ fand ρ are the density of foamed sample and the density of unfoamed sample (measured by drainage method), g / cm 3 .

[0104] (3) Ripening shrinkage

[0105] Ripening: The resulting foamed beads are washed and allowed to stand at room temperature and pressure for at least 48 hours to obtain aging particles. The expansion ratio of foamed particles is an important indicator of their quality, as it directly affects the expansion ratio of molded products and influences the use of molded products. The expansion ratios of particles produced at different saturation temperatures and pressures include the initial expansion ratio a1 and the final expansion ratio a2. The initial and final expansion ratios can be calculated using the following formulas:

[0106] a1=ρ / ρ f1

[0107] a2=ρ / ρ f2

[0108] Where, ρ is the density of TPU raw material particles; ρ f1 is the density of the particles obtained after pressure relief; ρ f2 is the density of the pellets after aging. (Unit: g / cm 3 )

[0109] Ripening shrinkage = (a1-a2) / a1*100%

[0110] (4) Appearance: The appearance of the foamed particles was visually observed and divided into three grades; if the surface of the foamed particles was white and smooth, and basically maintained the appearance and shape of the raw materials, and the particles were elastic, it was marked as "1"; if the surface of the foamed particles was rough, the pore size was uneven, and some of them collapsed and could not be restored, it was marked as "2"; if the particles had no elasticity and the internal foaming was not complete, it was marked as "3".

[0111] The specific test results are shown in Table 1:

[0112] Table 1

[0113]

[0114] As can be seen from the above table, the method for preparing thermoplastic polyurethane elastomer foamed particles provided by the present invention adopts a supercritical fluid process combined with a molding technology to prepare polyurethane foamed particles. The supercritical fluid is a combination of nitrogen and carbon dioxide, and specific process parameters are coordinated with each other to ensure that the thermoplastic polyurethane elastomer foamed particles have good uniformity, regular shape, high foaming ratio, low shrinkage, and excellent performance. As can be seen from Examples 1 to 6, the density of the thermoplastic polyurethane elastomer foamed particles is 0.118 to 0.155 g / cm 3The expansion ratio after aging is 7.16-9.41, the shrinkage after aging is 11.69-14.35%, and the cell density is (4.57-6.78)×10 6 pieces / cm 3 .

[0115] It can be seen from Examples 1, 7 and 8 that the ratio of carbon dioxide to nitrogen is not optimal, the expansion ratio of the thermoplastic polyurethane elastomer foamed particles is reduced, and the shrinkage after aging is increased.

[0116] It can be seen from Examples 1, 9 and 10 that the foaming temperature and the holding time are not within the specific ranges, and the foaming performance is poor.

[0117] It can be seen from Examples 1 and 11 that the pressure relief rate is too slow, the pressure relief time is long, the expansion ratio of the thermoplastic polyurethane elastomer foam particles is reduced, the shrinkage rate after aging is increased, and the appearance is poor.

[0118] It can be seen from Example 1 and Comparative Example 1 that the preparation method provided by the present application adopts a supercritical fluid process combined with a molding technology, and the performance of the foamed particles obtained is better than that of the foamed particles obtained by using a reactor.

[0119] In summary, the preparation method of thermoplastic polyurethane elastomer foamed particles provided by the present invention selects a specific process, so that the thermoplastic polyurethane elastomer foamed particles have good uniformity, regular shape, high foaming ratio, small shrinkage, excellent performance, simple process, low energy consumption, environmental protection, and are suitable for industrial production.

[0120] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing thermoplastic polyurethane elastomer foam particles, characterized in that: The preparation method comprises: Mixing thermoplastic polyurethane particles with a supercritical fluid, and performing mold compression foaming to obtain the thermoplastic polyurethane elastomer foamed particles; The supercritical fluid includes carbon dioxide and nitrogen; The total pressure of the supercritical fluid is 5-16 MPa; The pressure ratio of carbon dioxide to nitrogen is (2.5-6):1; The mixing temperature is 130-160°C; The molded foaming includes the steps of pressure-maintaining swelling and pressure-releasing foaming; The pressure-maintaining and swelling time is 15 to 60 minutes; The pressure relief rate is 30-90 MPa / s.

2. The preparation method according to claim 1, characterized in that The mixing is carried out in a molding device.

3. The preparation method according to claim 1, characterized in that The mixing temperature is 140-160°C.

4. The preparation method according to claim 2, characterized in that The mixing step comprises: placing thermoplastic polyurethane particles into a molding device, closing the film, heating the film to 130-160° C., filling the film with supercritical fluid, and mixing the film.

5. The preparation method according to claim 1, characterized in that The pressure-maintaining and swelling time is 20 to 45 minutes.

6. The preparation method according to claim 1, characterized in that The pressure is released until the system pressure is 0.

7. The preparation method according to claim 1, characterized in that The pressure relief time is less than 5 s.

8. The preparation method according to claim 1, characterized in that The thermoplastic polyurethane particles include polyester polyurethane particles and / or polyether polyurethane particles.

9. The preparation method according to claim 1, characterized in that The hardness of the thermoplastic polyurethane particles is 70-90A.

10. The preparation method according to claim 1, characterized in that The diameter of the thermoplastic polyurethane particles is 0.6-9 mm.

11. A thermoplastic polyurethane elastomer foamed particle, characterized in that: The thermoplastic polyurethane elastomer foamed particles are prepared according to the preparation method according to any one of claims 1 to 10.

12. The thermoplastic polyurethane elastomer foamed particles according to claim 11, characterized in that The density of the thermoplastic polyurethane elastomer foamed particles is 0.1-0.2 g / cm 3 .

13. The thermoplastic polyurethane elastomer foamed particles according to claim 11, characterized in that The foaming pore diameter of the thermoplastic polyurethane elastomer foam particles is 20-90 μm.

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