Thermoplastic elastomer foamed material and preparation method and application thereof

Abstract

The present application relates to a kind of thermoplastic elastomer foamed material and its preparation method and application, belong to the technical field of foamed material manufacturing.The preparation method of the present application uses the combination screw structure of twin-screw extruder and single screw extruder to control the uniform mixing of polymer melt and supercritical fluid, the gas-melt mixture obtained is injected into low-temperature mold, and the transient back pressure of mold is higher than the pressure of the gas-melt mixture when injecting the mold, the higher transient back pressure controls the gas-melt mixture not to be foamed due to the instantaneous pressure drop of injection mold, so as to effectively reduce the opening rate of product, then the mass of material in mold is controlled by reducing back pressure, finally, the thermoplastic elastomer foamed material with low density, low opening rate, high resilience and excellent surface quality is prepared by instantaneous back pressure release.

Description

Technical Field

[0001] This invention belongs to the field of foam material manufacturing technology, specifically relating to a thermoplastic elastomer foam material, its preparation method, and its application. Background Technology

[0002] Footwear foam materials have the performance requirements of being lightweight, highly elastic, and having low compression set. Processing methods for footwear foam materials include PU foam casting, IP injection cross-linking foaming EVA molding, and ETPU bead steam molding. All of these methods can achieve dimensional accuracy control of foamed footwear materials through mold structure, and performance control of footwear foam products can be achieved through formula design and foaming process.

[0003] Supercritical fluid injection molding foaming of thermoplastic elastomers has been widely reported in academia. It involves using supercritical fluid as a foaming agent, injecting it into the screw of an injection molding machine to form a homogeneous polymer / fluid melt, and then injecting the temperature-controlled polymer / fluid melt into a mold. After foaming, injection-molded foamed products of a specific shape are obtained. A typical polymer supercritical fluid injection molding foaming technology is called MuCell technology, which involves the design of a dedicated injection screw structure and the matching of the gas injection system. However, traditional MuCell foaming technology has a very short screw structure and can only inject a small amount of supercritical fluid, thus achieving a maximum weight reduction of only 30%. Due to the temperature of the foamed melt, severe cell coalescence occurs, resulting in large cell structures. Flow marks are formed due to the rapid flow of the foamed melt in the mold, leading to poor surface quality of the product. When injecting high fluid content, the injection-molded foamed products exhibit significantly uneven cell distribution. To address the challenges of the MuCell foaming process, academic literature reports methods such as core extraction using a mold to inject a high-content supercritical fluid into the mold to form a polymer / fluid melt. This melt is then cooled and rapidly depressurized to induce foaming, achieving densities of 0.15-0.2 g / cm³. 3 Injection-molded foamed elastomer products. However, in practical applications, it has been found that for products with complex structures, such as shoe midsoles, the design of the core-pulling structure is difficult, and the core-pulling thickness in different areas is not easy to control, which can easily lead to uneven weight reduction in different areas. At the same time, the mold core-pulling technology can impose stringent requirements on the processing precision and mold material of the mold, which can easily lead to melt leakage and poor surface quality of the product, significantly affecting the stability and practicality of the mold core-pulling process.

[0004] Therefore, it is of great significance to develop a foamed shoe material with excellent surface quality and performance. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems existing in the prior art and to provide a thermoplastic elastomer foam material, its preparation method, and its application.

[0006] This invention is achieved through the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a thermoplastic elastomer foam material, comprising the following steps:

[0008] (1) The raw materials are melt-blended in a twin-screw extruder to obtain a polymer melt;

[0009] (2) The polymer melt obtained in step (1) and the supercritical fluid are mixed in a single screw extruder at 200℃-220℃ and cooled to 140℃-180℃ to obtain an air-melt mixture;

[0010] (3) The gas-melt mixture obtained in step (2) is injected into a mold at a temperature of 0℃-40℃. When the gas-melt mixture is injected into the mold, the transient back pressure of the mold is higher than the pressure of the gas-melt mixture. After reducing the back pressure, the pressure is maintained and released to obtain the thermoplastic elastomer foam material.

[0011] In step (1), the raw materials, by mass, include the following components: 80-100 parts of thermoplastic elastomer, 0.1-3 parts of chain extender, and 1-10 parts of lubricant.

[0012] This invention employs a combination of twin-screw and single-screw extruders to control the uniform mixing of polymer melt and supercritical fluid. The temperature of the mixture is reduced to 140℃-180℃ to ensure fluidity and melt strength. When the resulting gas-melt mixture is injected into the mold, the transient back pressure of the mold is higher than the pressure of the gas-melt mixture itself. This higher transient back pressure prevents the gas-melt mixture from foaming due to the instantaneous pressure drop during injection, effectively reducing the open-cell ratio of the product. Subsequently, the material quality within the mold is controlled by reducing the back pressure. Finally, a thermoplastic elastomer foam material with low density, low open-cell ratio, high resilience, and excellent surface quality is prepared through instantaneous back pressure release. Furthermore, this invention controls the mold temperature at a relatively low range of 0℃-40℃. This allows for rapid cooling of the polymer / fluid gas-melt mixture, increasing melt strength and stabilizing the cell structure during rapid back pressure release foaming, thus reducing the density of the foam material. It also rapidly cools the gas-melt mixture within the mold, reducing the material's residence time and improving processing efficiency.

[0013] In step (3), the temperature of the mold is 0℃-40℃, for example, including but not limited to 0℃, 1℃, 2℃, 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, or any value between two of them.

[0014] Preferably, the thermoplastic elastomer includes at least one of thermoplastic polyurethane elastomer (TPU), thermoplastic polyester elastomer (TPEE), polyether block amide (PEBA), and hydrogenated styrene-butadiene block copolymer (SEBS).

[0015] More preferably, the thermoplastic elastomer includes at least one of aliphatic thermoplastic polyurethane elastomer (aliphatic TPU), aliphatic thermoplastic polyester elastomer (aliphatic TPEE), and aliphatic polyether block amide (aliphatic PEBA).

[0016] When aliphatic thermoplastic elastomers are selected, the resulting foamed materials have better resilience and lower open-cell ratios due to the better chain flexibility of aliphatic elastomers.

[0017] Preferably, the chain extender comprises at least one of a difunctional acid derivative, an isocyanate, an acid anhydride, and an epoxide.

[0018] Preferably, the lubricant includes at least one of polyethylene wax, stearic acid, lead stearate, zinc stearate, and paraffin wax.

[0019] Optionally, the raw materials may also include 0-10 parts of nucleating agent and 0-1 parts of antioxidant by mass.

[0020] Preferably, the nucleating agent includes at least one of calcium carbonate, talc, mica, montmorillonite, nano-silica, carbon black, and carbon nanotubes; the antioxidant includes at least one of amine antioxidants and phosphorus antioxidants.

[0021] Preferably, in step (2), the supercritical fluid includes at least one of CO2 fluid and N2 fluid.

[0022] Preferably, in step (1), the temperature of the twin-screw extruder is 130℃-210℃.

[0023] The twin-screw extruder used in this invention is a commonly used screw structure in the field. Specifically, the twin-screw extruder includes a feeding section and a mixing section, and the single-screw extruder includes a feeding section, an air injection section, a mixing section, a cooling section, a compression section, an injection molding machine nozzle, and a sealing ejector pin.

[0024] Preferably, the cooling section of the single-screw extruder accounts for 1 / 3 of the total length, and the cooling method of the cooling section is water cooling or forced air cooling.

[0025] Preferably, the temperatures of the feeding section, the air injection section, and the mixing section are each independently 200℃-220℃, the temperature of the cooling section is 150℃-180℃, and the temperature of the compression section is 140℃-180℃.

[0026] Preferably, in step (2), the content of the supercritical fluid in the gas-melt mixture is 1wt%-5wt%.

[0027] Preferably, in step (3), the pressure of the gas-molten mixture is 15 MPa-25 MPa. The pressure of the gas-molten mixture can be any selection from 15 MPa, 16 MPa, 18 MPa, 20 MPa, 21 MPa, 22 MPa, 23 MPa, 25 MPa, or a range of any two values.

[0028] In this invention, the pressure of the gas-molten mixture can be adjusted by regulating the pressure during the injection of the supercritical fluid.

[0029] Preferably, in step (3), the transient back pressure is 16 MPa-30 MPa. The transient back pressure can be any selection from 16 MPa, 18 MPa, 20 MPa, 21 MPa, 22 MPa, 23 MPa, 25 MPa, 28 MPa, and 30 MPa, or a range of any two values.

[0030] Preferably, in step (3), the back pressure of the mold before the gas-melt mixture is injected into the mold is lower than the pressure of the gas-melt mixture; the back pressure during the pressure holding is 5MPa-15MPa, and the pressure holding time is 3s-30s.

[0031] The back pressure of the mold during the pressure holding period can be any selection from 5 MPa, 6 MPa, 8 MPa, 10 MPa, 11 MPa, 12 MPa, 13 MPa, and 15 MPa, or a range of any two values. The pressure holding time can be any selection from 3s, 5s, 10s, 15s, 20s, 25s, and 30s, or a range of any two values.

[0032] Preferably, in step (3), the back pressure of the mold before the gas-melt mixture is injected into the mold is 1MPa-15MPa.

[0033] Before the gas-melt mixture is injected into the mold, the back pressure of the mold is lower than the pressure of the gas-melt mixture; otherwise, the material cannot be injected into the mold. At the moment the gas-melt mixture is injected into the mold, the dynamic back pressure is higher than the pressure of the gas-melt mixture; otherwise, foaming will occur, resulting in a high porosity of the product.

[0034] More preferably, in step (3), the temperature of the mold is 10℃-30℃.

[0035] In step (3) of this invention, the gas-melt mixture is injected into a mold with a low temperature, so that the temperature of the gas-melt mixture drops rapidly, thereby meeting the need for rapid growth of the bubble and the need for the bubble not to rupture significantly.

[0036] Preferably, in step (3), the gas that generates the back pressure includes at least one of air, CO2, and N2.

[0037] In this invention, the back pressure of the mold can be controlled by injecting high-pressure gas into the outside of the mold. If a stepped back pressure is required, high-pressure gas is first injected into the outside of the mold to provide instantaneous back pressure. Then, the gas-melt system is injected into the mold. When the pressure of the gas-melt mixture system injected into the mold reaches the specified pressure, the system pressure is reduced to the specified value and maintained by moving the mold and injecting the gas-melt mixture fluid. After a specified time, the mold is quickly opened to release pressure and foam to obtain the product. If no stepped back pressure is set, the mold is fixed, the gas-melt mixture system is injected to the specified pressure and maintained. After a specified time, the mold is quickly opened to release pressure and foam to obtain the product.

[0038] Secondly, the present invention provides a thermoplastic elastomer foam material prepared by the method for preparing the aforementioned thermoplastic elastomer foam material.

[0039] Thirdly, the present invention provides the application of the thermoplastic elastomer foam material in footwear materials and protective materials.

[0040] The thermoplastic elastomer foam material prepared by the method of the present invention has low density, low porosity and high resilience, as well as excellent surface quality, and can be applied to footwear materials, protective materials and other fields.

[0041] The present invention has the following beneficial effects:

[0042] The method for preparing thermoplastic elastomer foamed materials provided by this invention adopts a twin-screw-single-screw combined structure. By controlling the content of chain extender and lubricant, as well as the mold back pressure and temperature, the resulting parts have low density, which is conducive to achieving lightweighting. The open porosity does not exceed 50%, the resilience can reach 70%, and the compression set does not exceed 30%, with a maximum of 15%. At the same time, the surface is smooth and without obvious defects, which has broad application prospects in many fields such as sports shoe midsoles and protective materials. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the mold back pressure in step (3) of the preparation method of thermoplastic elastomer foam material in an embodiment of the present invention. Detailed Implementation

[0044] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0045] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0046] In each embodiment and comparative example component,

[0047] The aliphatic TPU: Yantai Wanhua WHT-A885;

[0048] The TPEE mentioned is: DuPont BexloyGPV63B5 NC010;

[0049] The PEBA mentioned is Arkema 7233;

[0050] The aromatic TPU is Lubrizol 168K.

[0051] The SEBS mentioned is Celanese 270NZ7658;

[0052] The chain extender is an epoxide chain extender, ADR4468, from BASF.

[0053] The lubricant is: polyethylene wax, commercially available;

[0054] Unless otherwise specified, all components and raw materials used in the embodiments and comparative examples of this invention are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0055] Example 1

[0056] A method for preparing a thermoplastic elastomer foam material includes the following steps:

[0057] (1) After physical blending of the raw materials, they are added to a twin-screw extruder for melt blending to obtain polymer melt; the composition and mass fraction of the raw materials are shown in Table 1; the twin-screw extruder includes a feeding section and a mixing section, the temperature of the feeding section is 130°C, and the temperature of the mixing section is 210°C.

[0058] (2) The polymer melt obtained in step (1) is injected into a single-screw extruder, and supercritical fluid is injected into the single-screw extruder at the same time. The supercritical fluid is a carbon dioxide / nitrogen mixture, wherein the mass ratio of carbon dioxide fluid to nitrogen fluid is 3:1, and the inlet pressure is 18MPa. The polymer melt and supercritical fluid are mixed at 210°C by the shearing action of the screw to form a homogeneous gas-melt system, and then enter the cooling section for cooling. The cooling temperature is shown in Table 1 to obtain a gas-melt mixture. The content of the supercritical fluid in the gas-melt mixture is 3wt%.

[0059] (3) The gas-melt mixture obtained in step (2) is injected into the mold. The temperature of the mold and the mold back pressure holding time before and after injection are shown in Table 1 to obtain the thermoplastic elastomer foam material.

[0060] Examples 2-6 and Comparative Examples 1-6

[0061] The differences between the preparation methods of the thermoplastic elastomer foamed materials in Examples 2-6 and Comparative Examples 1-6 and Example 1 lie in the different components or preparation parameters, as shown in Tables 1 and 2.

[0062] Table 1 Parameters of Examples 1-6

[0063]

[0064] Table 2 Parameters of Comparative Examples 1-6

[0065]

[0066] The thermoplastic elastomer foam materials prepared in each embodiment and comparative example were subjected to the following tests and characterizations, as detailed below:

[0067] 1. Density: Tested using a density balance;

[0068] 2. Open area ratio: Tested using an open area ratio tester;

[0069] 3. Rebound rate: Measured using a ball rebound tester, rebound rate % = (ball rebound height / initial height) × 100%;

[0070] 4. Compression permanent deformation: Take a cube sample with a side length of 20mm, compress the sample to 50% using a compression mold, and then place the whole sample in a 50℃ environment. After 3 hours, take out the sample and place it at room temperature for 30 minutes before measuring the final thickness h of the sample. Calculate the result using the formula: Compression permanent deformation = h / 20mm × 100%.

[0071] 5. Surface quality: Obtained through visual inspection.

[0072] The test results are shown in Tables 3 and 4.

[0073] Table 3 Test results of the thermoplastic elastomer foam materials in the examples.

[0074]

[0075] Table 4 shows the test results of the comparative thermoplastic elastomer foam materials.

[0076]

[0077] As can be seen from the test results in Tables 3 and 4, the thermoplastic elastomer foam material prepared by the method of controlling the back pressure of the mold in a stepped release manner according to the present invention has low density, low porosity, low compression deformation and high resilience, and excellent surface quality. It can be applied to various protective material technology fields such as sports protective footwear materials.

[0078] In Comparative Example 1, no chain extender was added; in Comparative Example 2, no lubricant was added. These omissions affected foaming, resulting in a significant decrease in the resilience of the foamed material, an increase in open porosity, increased compression deformation, and a decrease in surface quality. In Comparative Example 3, the temperature of the gas-melt mixture was too high, causing slight foaming and cell coalescence upon entry into the mold, leading to an increase in open porosity, increased compression deformation, and decreased resilience. In Comparative Example 4, the mold temperature was too high, causing unstable foaming and a decrease in the performance of the foamed material. In Comparative Example 5, no back pressure was set in the mold; the pressure during holding was formed after the gas-melt mixture system was injected, which differed from the stepped back pressure of the embodiments. Because no back pressure was set in the mold, foaming occurred immediately upon injection of the gas-melt mixture into the mold, resulting in a significant increase in the open porosity of the foamed material, a poorer compression deformation effect, and a significant decrease in resilience. In Comparative Example 6, after the gas-molten mixture was injected into the mold, the back pressure was not reduced to maintain the pressure, and the back pressure was released directly, which resulted in an increase in the porosity of the material and a significant deterioration in all aspects of its performance.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a thermoplastic elastomer foam material, characterized in that, Includes the following steps: (1) The raw materials are melt-blended in a twin-screw extruder to obtain a polymer melt; (2) The polymer melt obtained in step (1) and the supercritical fluid are mixed in a single screw extruder at 200℃-220℃ and cooled to 140℃-180℃ to obtain an air-melt mixture; (3) The gas-melt mixture obtained in step (2) is injected into a mold at a temperature of 0℃-40℃. When the gas-melt mixture is injected into the mold, the transient back pressure of the mold is higher than the pressure of the gas-melt mixture. After reducing the back pressure, the pressure is maintained and released to obtain the thermoplastic elastomer foam material. In step (1), the raw materials, by mass, include the following components: 80-100 parts of thermoplastic elastomer, 0.1-3 parts of chain extender, and 1-10 parts of lubricant; In step (3), the back pressure during pressure holding is 5MPa-15MPa.

2. The method for preparing the thermoplastic elastomer foam material according to claim 1, characterized in that, The thermoplastic elastomer includes at least one of thermoplastic polyurethane elastomer, thermoplastic polyester elastomer, polyether block amide, and hydrogenated styrene-butadiene block copolymer; and / or, the chain extender includes at least one of bifunctional acid derivatives, isocyanates, acid anhydrides, and epoxides; and / or, the lubricant includes at least one of polyethylene wax, stearic acid, lead stearate, zinc stearate, and paraffin wax; and / or, the supercritical fluid includes at least one of CO2 fluid and N2 fluid.

3. The method for preparing the thermoplastic elastomer foam material according to claim 1 or 2, characterized in that, The thermoplastic elastomer includes at least one of aliphatic thermoplastic polyurethane elastomer, aliphatic thermoplastic polyester elastomer, and aliphatic polyether block amide.

4. The method for preparing the thermoplastic elastomer foam material according to claim 1, characterized in that, In step (1), the temperature of the twin-screw extruder is 130℃-210℃.

5. The method for preparing the thermoplastic elastomer foam material according to claim 1, characterized in that, In step (2), the content of the supercritical fluid in the gas-melt mixture is 1wt%-5wt%.

6. The method for preparing the thermoplastic elastomer foam material according to claim 1, characterized in that, In step (3), the pressure of the gas-molten mixture is 15 MPa-25 MPa; and / or, in step (3), the transient back pressure is 16 MPa-30 MPa.

7. The method for preparing the thermoplastic elastomer foam material according to claim 1, characterized in that, In step (3), the back pressure of the mold before the gas-melt mixture is injected into the mold is lower than the pressure of the gas-melt mixture; and / or, the holding time is 3s-30s.

8. The method for preparing the thermoplastic elastomer foam material according to claim 1, characterized in that, In step (3), the temperature of the mold is 10℃-30℃.

9. The thermoplastic elastomer foam material prepared by the method for preparing thermoplastic elastomer foam material according to any one of claims 1-8.

10. The application of the thermoplastic elastomer foam material according to claim 9 in footwear materials and protective materials.

Images