Preparation method of shrinkage-resistant supercritical TPU (thermoplastic polyurethane) foaming material
By introducing inorganic fillers with amino or hydroxyl groups into TPU and performing biaxial stretching and supercritical foaming, the shrinkage problem of TPU foam materials was solved, and the dimensional stability and mechanical strength of the material were improved.
Patent Information
- Application Number
- CN202511461246.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-14
- Publication Date
- 2025-12-19
AI Technical Summary
After foaming, TPU supercritical foaming material shrinks rapidly due to the rapid expansion of molecular chains and the destruction of hydrogen bonds, which affects production efficiency. Existing technologies are unable to effectively suppress this phenomenon.
By employing intermolecular forces and chain segment orientation, inorganic fillers with amino or hydroxyl groups are introduced into TPU, and hydrogen bonds and molecular chain segment orientation are formed through pre-dispersion, biaxial stretching, and supercritical foaming processes, thereby inhibiting material shrinkage.
It improves the dimensional stability and mechanical strength of TPU foam materials, reduces the shrinkage rate, and increases production efficiency.
Smart Images
Figure CN121159926A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of foaming materials technology, and in particular to a method for preparing a shrinkage-resistant supercritical TPU foaming material. Background Technology
[0002] Thermoplastic polyurethane elastomer (TPU) is a block linear polymer produced by reacting polyether polyols and isocyanates. TPU possesses excellent comprehensive properties such as high strength, high toughness, and wear resistance, and has good processing performance. It is currently widely used in industries such as defense, medical, and food. Supercritical thermal polymer (TPU) foam material refers to TPU that has a uniform microporous structure formed inside it using supercritical fluids (CO2 or N2), resulting in a material density as low as 0.06 g / cm³. 3 The microporous structure can inhibit the propagation of internal cracks, giving the material good tear resistance and high strength and wear resistance. The production process is green and pollution-free, and the material is a thermoplastic material that can be recycled. After TPU undergoes supercritical foaming, on the one hand, the rapid expansion of the molecular chains breaks the stable hydrogen bonds inside the material, and on the other hand, the diffusion rate of the supercritical foaming gas is higher than that of air, resulting in a pressure difference between the inside and outside of the cell. Therefore, the foamed material shrinks rapidly. To address the shrinkage problem, TPU needs to be cured for a long time to obtain good foamed boards, which reduces production efficiency. Therefore, this invention proposes a method for preparing shrinkage-resistant supercritical TPU foam material to solve the problems existing in the prior art. Summary of the Invention
[0003] To address the above problems, this invention proposes a method for preparing a shrinkage-resistant supercritical TPU foam material. This method uses intermolecular forces and chain segment orientation to inhibit the shrinkage of the TPU foam material.
[0004] To achieve the objectives of this invention, the following technical solution is provided: a method for preparing a shrinkage-resistant supercritical TPU foam material, comprising the following steps: S1: Select an unactivated inorganic filler and activate it using a coupling agent containing amino or hydroxyl groups; S2: The activated powder is uniformly dispersed into the TPU substrate through a pre-dispersion-dispersion process, and then extruded into a sheet using an extruder; S3: Place the extruded TPU sheet in a biaxial stretching apparatus, set the temperature above the TPU Vicat softening point of 50℃ and below the melting point of 160℃, and through biaxial stretching, cause the material to deform in both the transverse and longitudinal directions, and maintain the high temperature and deformation time to make the molecular chain segments oriented along the deformation direction. S4: Place the oriented board in a supercritical reactor, set the temperature between (Tm-30℃) and Tm, introduce supercritical gas, and after saturation, quickly depressurize to obtain supercritical foamed TPU board.
[0005] A further improvement is that, in S1, the inorganic filler is one or more of talc, calcium carbonate, wollastonite, and kaolin.
[0006] A further improvement is that, in S1, the coupling agent is one or more of a silane coupling agent and a titanate coupling agent.
[0007] A further improvement is that, in step S1, the activation process of the inorganic filler is carried out in a high-speed mixer with a stirring speed of 500-2000 r / min and a stirring time of 5-30 min.
[0008] A further improvement is that in the S2 process, the pre-dispersion-dispersion process refers to the process of first pre-dispersing the powder and TPU particles into the TPU particles through internal mixing, open milling and crushing, and then further dispersing them through screw extrusion, which is carried out in a single screw extruder for further mixing.
[0009] A further improvement is made in S2, where the extrusion temperature of the extruder is controlled at 180-230℃ during extrusion.
[0010] Further improvements are made in the following: In S3, during the biaxial stretching process, the stretching speed is 10 mm / min-1000 mm / min, the deformation multiple of the material in the transverse and longitudinal directions is between 10% and 200%, and the high temperature and deformation time are maintained at 10s-600s.
[0011] A further improvement is that, in step S3, the temperature during the biaxial stretching and orientation steps is specifically determined according to the specific model of TPU, ensuring that it is above the Vicat softening point and below the melting point.
[0012] A further improvement is made in S4, where the supercritical gas is either CO2 or N2. When the supercritical gas is CO2, the pressure is between 10-15 MPa, and when the supercritical gas is N2, the pressure is between 20-30 MPa, and the saturation time is 1-10 h.
[0013] A further improvement is that, in S4, during the supercritical foaming process, the rate of rapid depressurization is controlled to be 0.1-10 MPa / s.
[0014] The beneficial effects of this invention are as follows: 1. This invention introduces fillers with amino or hydroxyl groups, which can form hydrogen bonds with TPU, thereby improving the dimensional stability of the material.
[0015] 2. The present invention uses inorganic fillers to act as heterogeneous nucleation points in the supercritical foaming process, thereby increasing the cell density and refining the cell size.
[0016] 3. This invention uses biaxial stretching to orient molecular chain segments along the length and width directions, thereby improving the mechanical strength of the oriented structure and further enhancing the dimensional stability after foaming. Attached Figure Description
[0017] Figure 1 This is a bubble diagram of Embodiment 1 of the present invention; Figure 2 This is a bubble diagram of Embodiment 2 of the present invention; Figure 3 This is a bubble diagram of Embodiment 3 of the present invention; Figure 4 This is a bubble diagram of Embodiment 4 of the present invention; Figure 5 This is a physical performance test diagram of an embodiment of the present invention; Figure 6 This is a schematic diagram illustrating density changes according to an embodiment of the present invention. Detailed Implementation
[0018] To enhance understanding of the present invention, the present invention will be further described in detail below with reference to embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.
[0019] Example 1 according to Figure 1 , 5 As shown in Figure 6, this embodiment proposes a method for preparing a shrinkage-resistant supercritical TPU foam material, including the following steps: An amino-containing silane coupling agent (KH-550) was selected and diluted with 20% silane coupling agent (KH-550) + 72% ethanol + 8% water to obtain an aqueous solution of the coupling agent. Calcium carbonate was pre-dried at 100°C for 4 hours to remove excess moisture. The calcium carbonate was then placed in a high-speed disperser with a mass ratio of KH-550 to calcium carbonate of 1.5:100. After high-speed mixing, it was dried between 90-105°C to ensure that the moisture content of the modified powder was below 250 ppm. The modified powder and 85A TPU were pre-dispersed and granulated through internal mixing-open milling-mechanical crushing. The granulated powder was labeled as M-TPU-CaCO3 with a powder content of 15%. 30% M-TPU-CaCO3 and 70% pure TPU particles are dried and then extruded. To avoid material degradation, the melt temperature is controlled below 200℃. The extruded material is a sheet with dimensions of 300*200*10mm. The sheet is placed in a biaxial stretching apparatus, and the temperature is set to 85℃ for 30 minutes to fully soften the material. It is then biaxially stretched to 390*260mm at a stretching speed of 50mm / min, and the high temperature and deformation are maintained for 55 seconds. After cooling, the thickness becomes 6mm. The material is then placed in a foaming kettle, and the foaming temperature and pressure are set to 136℃ and 15MPa for 3 hours. After saturation, the internal pressure is completely released at a depressurization rate of 10MPa / s for foaming. The material is then left to mature at room temperature.
[0020] The coupling agent contains water, but the calcium carbonate still needs to be dehydrated for the following reasons: Moist calcium carbonate is prone to agglomeration under electrostatic or hydrogen bonding, leading to uneven coating of the calcium carbonate by the coupling agent and uneven dispersion. Since the coupling agent reaction requires moisture, if the powder is not dried, inconsistent local moisture content will occur, causing excessive hydrolysis and self-agglomeration of the coupling agent, resulting in gel formation. Therefore, the drying process is fundamental for better blending of the coupling agent with the powder and for efficient reaction between the coupling agent and the filler. The reaction mechanism of silane coupling agent (KH-550) is as follows: the ethoxy group (-OC2H5) in the molecule undergoes a substitution reaction in the presence of water to produce silanol groups (-Si-OH) and ethanol. This reaction is autocatalytic in the presence of water, and alkalinity and high temperature catalyze the reaction process. The hydrolysis of silane coupling agent (KH-550) at room temperature takes 40-60 minutes to complete. Therefore, the coupling agent is always prepared and used immediately, and ethanol is added to the aqueous solution to inhibit excessive condensation and improve dispersibility. It needs to be prepared as an aqueous solution during use.
[0021] Example 2 according to Figure 2 , 5 As shown in Figure 6, this embodiment proposes a method for preparing a shrinkage-resistant supercritical TPU foam material, including the following steps: An amino-containing silane coupling agent (KH-550) was selected and diluted with 20% silane coupling agent (KH-550) + 72% ethanol + 8% water to obtain an aqueous solution of the coupling agent. Calcium carbonate was pre-dried at 100°C for 4 hours to remove excess moisture. The calcium carbonate was then placed in a high-speed disperser with a mass ratio of coupling agent KH-550 to calcium carbonate of 1.5:100. After high-speed mixing, the mixture was dried between 90-105°C to ensure that the moisture content of the modified powder was below 250 ppm. The modified powder and 85A TPU were pre-dispersed and granulated through internal mixing, open milling, and mechanical crushing. The granulated material is labeled as M-TPU-CaCO3 with a powder content of 15%. 30% M-TPU-CaCO3 and 70% pure TPU particles are dried and then extruded. To avoid material degradation, the melt temperature is controlled below 200℃. The material is extruded into a sheet with dimensions of 300*200*10mm. The material is placed in a foaming kettle, and the foaming temperature and pressure are set to 136℃ and 15MPa, with a saturation time of 6h. After saturation, the internal pressure is completely released at a depressurization rate of 10MPa / s for foaming. The material is then left to mature at room temperature.
[0022] Example 3 according to Figure 3 , 5 As shown in Figure 6, this embodiment proposes a method for preparing a shrinkage-resistant supercritical TPU foam material, including the following steps: After drying, pure TPU particles are extruded. To avoid material degradation, the melt temperature is controlled below 200℃. The extruded material is a sheet with dimensions of 300*200*10mm. The sheet is placed in a biaxial stretching apparatus, and the temperature is set to 85℃ for 30 minutes to fully soften the material. It is then biaxially stretched to 390*260mm at a stretching speed of 50mm / min, and the high temperature and deformation are maintained for 55 seconds. After cooling, the thickness becomes 6mm. The material is then placed in a foaming kettle, and the foaming temperature and pressure are set to 136℃ and 15MPa for 3 hours. After saturation, the internal pressure is completely released at a depressurization rate of 10MPa / s for foaming. The material is then left to mature at room temperature.
[0023] Example 4 according to Figure 4 , 5 As shown in Figure 6, this embodiment proposes a method for preparing a shrinkage-resistant supercritical TPU foam material, including the following steps: After drying, pure TPU particles are extruded. To avoid material degradation, the melt temperature is controlled below 200℃. The extruded material is a sheet with dimensions of 300*200*10mm. The material is placed in a foaming kettle, and the foaming temperature and pressure are set to 136℃ and 15MPa, with a saturation time of 6h. After saturation, the internal pressure is completely released at a depressurization rate of 10MPa / s to allow for foaming. The material is then left to mature at room temperature.
[0024] The density changes show that Example 1, which has both internal hydrogen bond reinforcement and orientation, has higher strength during foaming, resulting in higher foam density and faster curing speed at room temperature. After curing, the shrinkage rate is only 12%, and it only takes 3 days to recover to its original position. Example 2 only has internal hydrogen bond reinforcement, with a shrinkage rate of 19%. Example 3 only has orientation, with a shrinkage rate of 25%. Example 4 has neither hydrogen bonds nor orientation, with a shrinkage rate of 36%.
[0025] The physical performance tests show that the thermal stability and physical and mechanical properties of Example 1 are superior to those of materials with only hydrogen bonds or orientation, and far superior to those of materials without orientation and hydrogen bonds.
[0026] As can be seen from the cell diagram, in Example 1, after the addition of filler and biaxial stretching, the filler played a role in heterogeneous nucleation during the supercritical foaming process, and biaxial stretching balanced the stress in both directions, refining the cell structure. In Example 2, only the filler played a role in heterogeneous nucleation, and the cell structure was larger than that in Example 1. In Example 3, no inorganic filler played a role in heterogeneous nucleation, and only biaxial stretching balanced the stress, so the cell structure was relatively coarse. In Example 4, there was neither filler nor biaxial stretching, so the cell structure was unevenly dispersed, with both large and small cells present.
[0027] Example 5 This embodiment proposes a method for preparing a shrinkage-resistant supercritical TPU foam material, including the following steps: Unactivated inorganic fillers are selected and activated by coupling agents; the inorganic fillers are one or more of talc, calcium carbonate, wollastonite, and kaolin; the coupling agents are one or more of silane coupling agents and titanate coupling agents; in the activation step of the inorganic fillers, the activation process is carried out in a high-speed mixer with a stirring speed of 500-2000 r / min and a stirring time of 5-30 min. The activated powder is uniformly dispersed into the TPU substrate through a pre-dispersion-dispersion process, and then extruded into sheets through an extruder. In the pre-dispersion-dispersion process, the activated powder and the TPU substrate are initially mixed in a high-speed mixer, and the dispersion is further mixed in a twin-screw extruder. During extrusion, the extrusion temperature of the extruder is controlled at 180-230℃. The extruded TPU sheet is placed in a biaxial stretching apparatus. The temperature is set above the Vicat softening point of TPU (50°C) and below the melting point (160°C). Through biaxial stretching, the material deforms in both the transverse and longitudinal directions. Maintaining the high temperature and deformation time causes the molecular chain segments to align along the deformation direction. During biaxial stretching, the stretching speed is 10 mm / min-1000 mm / min, the deformation ratio in both the transverse and longitudinal directions is between 10% and 200%, and the high temperature and deformation time are maintained for 10s-600s. The specific temperature in the biaxial stretching and orientation steps is determined according to the specific TPU type, ensuring it is above the Vicat softening point and below the melting point. The oriented boards are placed in a supercritical reactor, and the temperature is set between (Tm-30℃) and Tm. Supercritical gas is introduced, and after saturation, the pressure is rapidly released to obtain supercritical foamed TPU boards. The supercritical gas is either CO2 or N2. When the supercritical gas is CO2, the pressure is between 10-15 MPa; when the supercritical gas is N2, the pressure is between 20-30 MPa, and the saturation time is 1-10 hours. During the supercritical foaming process, the rate of rapid pressure release is controlled at 0.1-10 MPa / s.
[0028] The preparation method of this shrinkage-resistant supercritical TPU foam material introduces fillers with amino or hydroxyl groups, which can form hydrogen bonds with TPU, improving the dimensional stability of the material. Furthermore, the addition of inorganic fillers in this invention acts as heterogeneous nucleation sites during the supercritical foaming process, increasing the cell density and refining the cell size. At the same time, this invention uses biaxial stretching to orient the molecular chain segments along the length and width directions, improving the mechanical strength of the oriented structure and further enhancing the dimensional stability after foaming.
[0029] The foregoing has shown and described 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 embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.
Claims
1. A method for preparing a shrinkage-resistant supercritical TPU foam material, characterized in that, Includes the following steps: S1: Select an unactivated inorganic filler and activate it using a coupling agent containing amino or hydroxyl groups; S2: The activated powder is uniformly dispersed into the TPU substrate through a pre-dispersion-dispersion process, and then extruded into a sheet using an extruder; S3: Place the extruded TPU sheet in a biaxial stretching apparatus, set the temperature above the TPU Vicat softening point of 50℃ and below the melting point of 160℃, and through biaxial stretching, cause the material to deform in both the transverse and longitudinal directions, and maintain the high temperature and deformation time to make the molecular chain segments oriented along the deformation direction. S4: Place the oriented board in a supercritical reactor, set the temperature between (Tm-30℃) and Tm, introduce supercritical gas, and after saturation, quickly depressurize to obtain supercritical foamed TPU board.
2. The method for preparing a shrinkage-resistant supercritical TPU foam material according to claim 1, characterized in that: In S1, the inorganic filler is one or more of talc, calcium carbonate, wollastonite, and kaolin.
3. The method for preparing a shrinkage-resistant supercritical TPU foam material according to claim 2, characterized in that: In S1, the coupling agent is one or more of silane coupling agents and titanate coupling agents.
4. The method for preparing a shrinkage-resistant supercritical TPU foam material according to claim 3, characterized in that: In step S1, the activation process of the inorganic filler is carried out in a high-speed mixer with a stirring speed of 500-2000 r / min and a stirring time of 5-30 min.
5. The method for preparing a shrinkage-resistant supercritical TPU foam material according to claim 1, characterized in that: In S2, the pre-dispersion-dispersion process involves pre-dispersing the powder and TPU particles into the TPU particles through mixing, open milling, and pulverizing. The dispersion process involves further dispersion through screw extrusion, where the dispersion is further mixed in a single-screw extruder.
6. The method for preparing a shrinkage-resistant supercritical TPU foam material according to claim 5, characterized in that: In S2, during extrusion, the extrusion temperature of the extruder is controlled at 180-230℃.
7. The method for preparing a shrinkage-resistant supercritical TPU foam material according to claim 1, characterized in that: In S3, during the biaxial stretching process, the stretching speed is 10 mm / min-1000 mm / min, the deformation multiple of the material in the transverse and longitudinal directions is between 10% and 200%, and the high temperature and deformation time are maintained at 10s-600s.
8. The method for preparing a shrinkage-resistant supercritical TPU foam material according to claim 7, characterized in that: In step S3, the temperature during the biaxial stretching and orientation steps is specifically determined according to the specific type of TPU, ensuring that it is above the Vicat softening point and below the melting point.
9. The method for preparing a shrinkage-resistant supercritical TPU foam material according to claim 1, characterized in that: In S4, the supercritical gas is either CO2 or N2. When the supercritical gas is CO2, the pressure is between 10-15 MPa. When the supercritical gas is N2, the pressure is between 20-30 MPa. The saturation time is 1-10 h.
10. The method for preparing a shrinkage-resistant supercritical TPU foam material according to claim 9, characterized in that: In step S4, during the supercritical foaming process, the rate of rapid pressure release is controlled to be 0.1-10 MPa / s.