Thermoplastic elastomer foam material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of functional high-molecular polymer foaming materials, and particularly relates to a thermoplastic elastomer foaming material as well as a preparation method and application thereof. The method comprises the following steps: coating the surfaces of thermoplastic elastomer particles with a film, and carrying out hot pressing to obtain a thermoplastic elastomer sheet; after the thermoplastic elastomer sheet is saturated in supercritical fluid, pressure relief foaming is conducted, the film is automatically separated, and the thermoplastic elastomer foaming material without the skin layer is obtained. According to the invention, a non-toxic and environment-friendly physical foaming agent (supercritical fluid) is used for preparing the thermoplastic elastomer foaming material which is controllable in foam hole size, uniform in structure and completely free of residual solvent, and the thermoplastic elastomer foaming material has excellent wear resistance in a CMP oxidation environment.

Description

Technical Field

[0001] The invention belongs to the technical field of functional high molecular polymer foaming materials, and particularly relates to a thermoplastic elastomer foaming material and a preparation method and application thereof. Background Art

[0002] Silicon carbide (SiC), the most representative third-generation wide-bandgap semiconductor material, possesses a wide bandgap, high critical breakdown potential, and high-temperature resistance, offering enormous potential for application in high-performance power semiconductor technology. Chemical mechanical polishing (CMP) is currently considered one of the most effective methods for achieving global planarization and ultra-smooth, damage-free nanoscale surfaces on SiC. Due to its high hardness, brittleness, and chemical stability, SiC is difficult to process. Therefore, during the CMP process, potassium permanganate (KMnO4), a strong oxidant, is often added to the polishing slurry to increase material removal rates and, consequently, polishing quality. During the SiC CMP process, the mechanical grinding action between the wafer and the abrasive, as well as the chemical corrosion of the oxidant in the polishing slurry, causes wear on the polishing pad, resulting in performance degradation and shortening the pad's lifespan. These demanding polishing conditions place even stricter demands on the polishing pad's wear resistance.

[0003] Currently, polishing pads are mostly made of non-woven fabrics and damping fabrics. Although existing technologies have designed and optimized the raw material formulas and molding processes for wear-resistant and oxidation-resistant polishing pads, polishing pads based on non-woven fabrics and damping fabrics all use wet processes, which have many process variables and poor controllability. Wet processes use water as a dispersion medium, which can easily cause fiber collapse and uneven accumulation during dehydration and drying. The pore size distribution of non-woven fabrics and damping fabrics is uneven, affecting the flow of polishing fluid and the distribution of abrasive particles. Chemicals retained during the molding process can easily cause localized over-corrosion, resulting in cumbersome processes and complex operations. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a thermoplastic elastomer foam material and a preparation method and application thereof, wherein the thermoplastic elastomer foam material prepared by the method has excellent wear resistance in a CMP oxidative environment.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a thermoplastic elastomer foam material, comprising the following steps:

[0007] After coating the surface of the thermoplastic elastomer particles with a film, hot pressing is performed to obtain a thermoplastic elastomer sheet;

[0008] After the thermoplastic elastomer sheet is saturated in a supercritical fluid, the pressure is released for foaming, and the film is automatically separated to obtain a thermoplastic elastomer foam material without a skin layer.

[0009] Preferably, the supercritical fluid comprises supercritical CO2 and / or supercritical N2.

[0010] Preferably, the saturation pressure is 8 to 15 MPa; and the saturation time is 30 to 120 min.

[0011] Preferably, the pressure relief rate of the pressure relief foaming is 100 to 600 MPa / s.

[0012] Preferably, the temperature during the saturation and pressure relief foaming process is Tg+(120-190° C.), where Tg is the glass transition temperature of the thermoplastic elastomer particles.

[0013] Preferably, the thermoplastic elastomer particles include thermoplastic polyurethane elastomer, thermoplastic polyester elastomer or thermoplastic polyamide elastomer.

[0014] Preferably, the film material used for the coating includes polyimide, polyethylene terephthalate or polyetheretherketone.

[0015] Preferably, the hot pressing temperature is 180-220° C.; the hot pressing pressure is 5-20 MPa; and the hot pressing time is 5-15 min.

[0016] The present invention also provides a thermoplastic elastomer foam material prepared by the preparation method of the above technical solution, wherein the thermoplastic elastomer foam material has a foaming ratio of 1.27 to 1.79, a cell size of 25 to 70 μm, and a cell density of (1.96 to 12.2) E+06 cells / cm 3 The wear amount is 0.15~4.19mg / 100r, and the wear amount after soaking in 5wt.% KMnO4 solution is 4.63~15.43mg / 100r.

[0017] The present invention also provides the use of the thermoplastic elastomer foam material described in the above technical solution as a polishing pad in chemical mechanical polishing.

[0018] The invention provides a method for preparing a thermoplastic elastomer foam material, comprising the following steps: coating the surface of thermoplastic elastomer particles with a film, and then performing hot pressing to obtain a thermoplastic elastomer sheet; saturating the thermoplastic elastomer sheet in a supercritical fluid, and then releasing the pressure to foam the sheet, and allowing the film to automatically separate to obtain a thermoplastic elastomer foam material without a skin layer.

[0019] The present invention uses a non-toxic, environmentally friendly physical foaming agent (supercritical fluid) to prepare a foam material with controllable pore size, uniform structure, and no residual solvent. The pore structure of the thermoplastic elastomer foam material prepared by the present invention not only plays a stress buffering role in the oxidizing environment of SiCCMP, but also shows important value in chemical protection. On the one hand, the pores have good deformation and recovery capabilities under load, which can significantly reduce shear stress concentration and delay fatigue and damage of the thermoplastic elastomer foam material; on the other hand, the pore wall acts as a physical barrier for the diffusion of oxidants, effectively hindering the diffusion of KMnO4 inside the thermoplastic elastomer foam material and reducing chemical corrosion. This "mechanical buffering + chemical shielding" synergistic mechanism significantly improves the wear resistance of the thermoplastic elastomer foam material in the CMP oxidizing environment, and shows great potential in the application of SiCCMP polishing pads. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a scanning electron microscope image of the thermoplastic elastomer foam material prepared in Example 1;

[0021] Figure 2 This is a scanning electron microscope image of the thermoplastic elastomer foam material prepared in Example 2;

[0022] Figure 3 This is a scanning electron microscope image of the thermoplastic elastomer foam material prepared in Example 3;

[0023] Figure 4 This is a scanning electron microscope image of the thermoplastic elastomer foam material prepared in Example 4;

[0024] Figure 5 This is a scanning electron microscope image of the thermoplastic elastomer foam material prepared in Example 5;

[0025] Figure 6 This is a scanning electron microscope image of the thermoplastic elastomer foam material prepared in Example 6;

[0026] Figure 7 This is a scanning electron microscope image of the thermoplastic elastomer foam material prepared in Comparative Example 4;

[0027] Figure 8 This is a scanning electron microscope image of the thermoplastic elastomer foam material prepared in Comparative Example 5;

[0028] Figure 9 This is a scanning electron microscope image of the thermoplastic elastomer foam material prepared in Comparative Example 6;

[0029] Figure 10 This is a scanning electron microscope image of the thermoplastic elastomer foam material prepared in Comparative Example 7. DETAILED DESCRIPTION

[0030] The present invention provides a method for preparing a thermoplastic elastomer foam material, comprising the following steps:

[0031] After coating the surface of the thermoplastic elastomer particles with a film, hot pressing is performed to obtain a thermoplastic elastomer sheet;

[0032] After the thermoplastic elastomer sheet is saturated in a supercritical fluid, the pressure is released for foaming, and the film is automatically separated to obtain a thermoplastic elastomer foam material without a skin layer.

[0033] Unless otherwise specified, the present invention has no special requirements on the sources of the raw materials used, and commercially available products known to those skilled in the art can be used.

[0034] The invention coats the surface of thermoplastic elastomer particles with a film and then performs hot pressing to obtain a thermoplastic elastomer sheet.

[0035] As an embodiment, the thermoplastic elastomer particles include thermoplastic polyurethane elastomer (TPU), thermoplastic polyester elastomer (TPEE) or thermoplastic polyamide elastomer (PEBA), and in a specific embodiment, it is a thermoplastic polyester elastomer; the Shore hardness of the thermoplastic elastomer particles is 40 to 75D, and in a specific embodiment, it is 40D; the thermoplastic polyurethane elastomer includes a polyether thermoplastic polyurethane elastomer and / or a polyester thermoplastic polyurethane elastomer, and in a specific embodiment, it is a polyether thermoplastic polyurethane elastomer.

[0036] In one embodiment, the coating material includes polyimide (PI), polyethylene terephthalate (PET), or polyetheretherketone (PEEK), specifically polyethylene terephthalate in the specific embodiment; the coating is performed using a flat-plate vulcanizer. The film of the present invention can act as a gas barrier, and a skin-free foamed material is produced through a diffusion-limited physical foaming process, eliminating the traditional skin removal process through polishing or scraping. The microporous structure of the foamed material surface can roughen the polishing pad surface, facilitating the collection of processing waste, transporting polishing fluid, and ensuring chemical corrosion, thereby improving polishing uniformity and efficiency.

[0037] As an embodiment, the hot pressing temperature is 180-220°C, specifically 180-200°C in a specific embodiment; the hot pressing pressure is 5-20 MPa, specifically 10-15 MPa in a specific embodiment; the hot pressing time is 5-15 min, specifically 10 min in a specific embodiment.

[0038] As an embodiment, the thermoplastic elastomer sheet has a diameter of 10 to 30 cm, specifically 10 cm, and a thickness of 1.2 to 3 mm, specifically 2 mm.

[0039] After obtaining the thermoplastic elastomer sheet, the present invention saturates the thermoplastic elastomer sheet in a supercritical fluid, releases the pressure for foaming, and the membrane automatically separates to obtain a thermoplastic elastomer foam material without a skin layer.

[0040] As an embodiment, the supercritical fluid includes supercritical CO2 and / or supercritical N2, and in specific embodiments, it is supercritical CO2; the saturation pressure is 8 to 15 MPa, and in specific embodiments, it is 8.5, 10, 11, 12, or 14 MPa; the saturation time is 30 to 120 minutes, and in specific embodiments, it is 45 to 90 minutes. The present invention uses a physical foaming agent (supercritical fluid) to replace water and organic solvents, avoiding the generation of harmful residues in the foaming material, eliminating subsequent dehydration and solvent recovery steps, significantly shortening the process flow, and improving production efficiency.

[0041] The present invention limits the saturation pressure to the above range, which enables the thermoplastic elastomer to absorb sufficient foaming agent (supercritical fluid), thereby enabling the nucleation and growth of foam cells in the subsequent foaming (pressure relief) process. The present invention adopts a saturation pressure within the above range to avoid the low foaming ratio, small pore size, excessively thick foam wall, increased brittleness, increased plastic deformation, and reduced wear resistance caused by low saturation pressure and less foaming agent absorbed by the thermoplastic elastomer. It also avoids the high foaming ratio and low tensile strength of the prepared foam material caused by high foaming agent pressure. Since the material mainly undergoes tensile deformation during the wear process, when the applied tensile stress exceeds its tensile strength, it will lead to the removal of the foam material, causing wear, which manifests as a reduction in wear resistance.

[0042] The present invention adopts a saturation time within the above range, which can not only avoid the reduction of processing efficiency due to too long saturation time, but also avoid the incomplete dissolution of the foaming agent (supercritical fluid) in the thermoplastic elastomer due to too short saturation time, which is insufficient to support the nucleation and growth of the foam cells, resulting in low foaming ratio, small pore size, excessively thick foam wall, increased brittleness, increased plastic deformation, and reduced wear resistance.

[0043] As an embodiment, the pressure relief foaming process has a pressure relief rate of 100 to 600 MPa / s, and in specific embodiments, 200 to 400 MPa / s. The present invention utilizes a pressure relief foaming rate within this range to promote uniform cell formation and wall thickness growth, forming a structurally stable cell structure, effectively improving the stability and durability of the thermoplastic elastomer foam during wear, and exhibiting excellent wear resistance. Conversely, an excessively fast or slow pressure relief foaming rate can lead to a disordered cell structure, rupture or collapse of the cell walls, and reduced wear resistance.

[0044] As an embodiment, the temperature during the saturation and pressure relief foaming process is Tg+(120-190°C), where Tg is the glass transition temperature of the thermoplastic elastomer particles. In a specific embodiment, the Tg of TPU is -42°C, TPEE is -38°C, and PEBA is -60°C. In a specific embodiment, the temperature during the saturation and pressure relief foaming process is 93, 105, 115, 125, 130 or 135°C.

[0045] The present invention adopts the temperature within the above range during the saturation and pressure relief foaming process, which can avoid the foam cells from coalescing and bursting due to the melt strength being insufficient to support the foam cell growth due to excessively high temperature, thereby reducing the mechanical buffering and chemical shielding effects and lowering the wear resistance; and can also avoid the foaming temperature being too low and the excessive melt strength making it difficult for bubbles to grow, thereby causing low foaming ratio, small pore size, excessively thick foam cell walls, increased brittleness, increased plastic deformation and reduced wear resistance.

[0046] The present invention uses supercritical CO2 as a foaming agent, and the foaming process mainly includes the following three stages: gas dissolution: under high temperature and high pressure, CO2 can dissolve in large quantities into thermoplastic elastomer particles to form a gas-polymer solution; nucleation: after depressurization, CO2 precipitates, inducing the formation of a large number of bubble nuclei; cell growth and stabilization: the bubbles expand and fix the structure, and finally form foam. The present invention can accurately adjust these three stages by controlling the foaming conditions (such as temperature, saturation pressure, holding time, and pressure relief rate), thereby achieving structural regulation. The saturation pressure determines the solubility of CO2 and affects the nucleation density. The foaming temperature changes the melting state of the thermoplastic elastomer and the diffusion rate of CO2. The holding time ensures that CO2 is fully dissolved and evenly distributed, reduces the deviation of the pore structure, and promotes stable nucleation. The pressure relief rate determines the gas evolution rate and expansion rate. A moderate rate can avoid bubble rupture and collapse, and improve the morphological stability of the thermoplastic elastomer foam material. By controlling the foaming conditions, the present invention can achieve precise regulation of the pore size and the foaming ratio, obtain a microporous foam material with uniform structure and stable morphology, and improve the overall consistency and functional stability of the thermoplastic elastomer foam material.

[0047] The present invention also provides a thermoplastic elastomer foam material prepared by the preparation method of the above technical solution, wherein the thermoplastic elastomer foam material has a foaming ratio of 1.27 to 1.79, a cell size of 25 to 70 μm, and a cell density of (1.96 to 12.2) E+06 cells / cm 3 The wear amount is 0.15~4.19mg / 100r, and the wear amount after soaking in 5wt.% KMnO4 solution is 4.63~15.43mg / 100r.

[0048] As an embodiment, the plastic elastomer foam material has a foaming ratio of 1.27, 1.35, 1.43, 1.44, 1.45 or 1.79, a cell size of 25.05, 40.46, 51.01, 52.62, 52.84 or 69.20 μm, and a cell density of (1.96, 2.79, 3.11, 3.17, 3.24 or 12.2) E+06 cells / cm 3 The wear amount is 0.15, 0.18, 0.25, 0.28, 3.31 or 4.19 mg / 100r, and the wear amount after immersion in 5wt.% KMnO4 solution is 4.63, 5.01, 5.11, 5.42, 12.58 or 15.43 mg / 100r.

[0049] The present invention also provides the use of the thermoplastic elastomer foam material described in the above technical solution as a polishing pad in chemical mechanical polishing.

[0050] The present invention has no special limitation on the application of the thermoplastic elastomer foam material as a polishing pad in chemical mechanical polishing, and any application method well known in the art can be used.

[0051] The thermoplastic elastomer foam material prepared by the present invention exhibits wear resistance superior to that of the substrate in an oxidizing environment. The pore structure can effectively disperse stress concentration during wear, while limiting the diffusion of oxidants within the material and inhibiting chemical degradation. It shows great potential in the application of SiC CMP polishing pads.

[0052] The technical solutions of the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention, but they should not be understood as limiting the scope of protection of the present invention.

[0053] Example 1

[0054] (1) Thermoplastic polyamide elastomer (PEBA) (E40S3, density 1.01 g / cm) was vulcanized using a flat plate vulcanizer. 3 , hardness 40D, purchased from Evonik) the surface of the particles was coated with PET and then hot pressed at 180°C and 15 MPa for 10 min to form a PEBA sheet with a diameter of 10 cm and a thickness of 2 mm;

[0055] (2) The PEBA sheet was heated to 105°C in the mold cavity, and supercritical CO2 was injected into the mold cavity to 11 MPa. After saturation for 1 hour, the mold cavity was pressure-released and foamed at 400 MPa / s to obtain a thermoplastic elastomer foam material without a skin layer for subsequent experiments.

[0056] Examples 2 to 6

[0057] The differences from Example 1 are shown in Table 1, and are mainly due to the different elastomer types or foaming conditions.

[0058] The chemical oxidation resistance test method after immersion in a 5wt.% KMnO4 solution refers to patent CN118930802A, "A Chemical Oxidation-Resistant Polishing Pad, Its Preparation Method, and Use." The prepared thermoplastic elastomer foam material is immersed in a 5wt.% KMnO4 solution at 50±1°C in a sealed container for 24 hours. After cleaning and drying, the thickness of the chemical oxidation layer formed on the side section is observed under an optical microscope. A smaller chemical oxidation layer thickness indicates better chemical oxidation resistance.

[0059] Table 1 Preparation conditions and wear properties of Examples 1 to 6

[0060]

[0061]

[0062] Comparative Example 1

[0063] A flat vulcanizing press was used to vulcanize polyether thermoplastic polyurethane elastomer (TPU, 58219NAT055, density 1.14 kg / cm 3 The surface of the particles was coated with PET and then hot-pressed at 200°C into a sheet with a diameter of 10 cm and a thickness of 2 mm.

[0064] Comparative Example 2

[0065] The difference from Comparative Example 1 is that PEBA particles are used and the hot pressing temperature is 180°C.

[0066] Comparative Example 3

[0067] The difference from Comparative Example 2 is that TPEE (4056, density 1.16 g / cm 3 , hardness 40D, purchased from DuPont) particles.

[0068] Comparative Examples 4 to 7

[0069] The differences from Example 1 are shown in Table 2, and are mainly due to the different elastomer types or foaming conditions.

[0070] Table 2 Preparation conditions and wear properties of comparative examples 1 to 7

[0071]

[0072]

[0073] Performance Testing

[0074] For the thermoplastic elastomer foam materials of Examples 1 to 6 and Comparative Examples 4 to 7, an analytical balance with an attached density component was used to determine the apparent density of the sample and calculate the foaming ratio. The obtained thermoplastic elastomer foam material was quenched by liquid nitrogen, gold was sprayed on the cross section, and the pore structure was measured and analyzed using a scanning electron microscope. The samples of Examples 1 to 6 and Comparative Examples 1 to 7 were immersed in a 5wt.% KMnO4 solution and soaked in a sealed container at 50±1°C for 24 hours. After cleaning and drying, the thickness of the chemical oxidation layer formed by oxidation on the side section was observed under an optical microscope. The smaller the thickness of the chemical oxidation layer, the better the resistance to chemical oxidation. The wear resistance test was performed using a Taber wear tester (H18 grinding wheel). The sample was cut into the required measuring size: a diameter of 10 cm, and a small hole with a diameter of 6.35 mm was drilled in the center. According to GB / T30314-2021, a high-precision balance was used to measure the mass loss before and after wear with an accuracy of 10 -4 g. The wear loss (I) is then calculated using the following equation:

[0075] I=(AB)×1000 / C

[0076] Where A is the initial mass of the sample before wear, g; B is the final mass of the sample after wear, g; and C is the number of revolutions recorded by the counter.

[0077] The test results are shown in Table 1, Table 2 and Figures 1 to 10 shown.

[0078] From Table 1, Table 2 and Figures 1 to 10 It can be seen that the thermoplastic elastomer foams prepared by Examples 1 to 6 and Comparative Examples 4 to 7 have controllable foaming ratios and uniform cell structures.

[0079] In comparative examples 1 to 3, at the same hardness, the wear resistance of the TPU matrix in non-oxidizing and oxidizing environments is the best.

[0080] Depend on Figure 1 、 Figure 2 and Figure 5 It can be seen that in Examples 1, 2 and 5, when the matrix hardness, foaming ratio and cell size are the same, the wear resistance of the TPU thermoplastic elastomer foam material in non-oxidizing and oxidizing environments is still optimal.

[0081] In Example 1 and Comparative Example 2, Example 2 and Comparative Example 3, and Examples 3-6 and Comparative Example 1, after the thermoplastic elastomer was foamed, the wear resistance of the samples in a non-oxidizing environment was lower than that of the substrate, but the wear resistance was higher than that of the substrate in an oxidizing environment. During the wear process, the material primarily undergoes tensile deformation. When the applied tensile stress exceeds its tensile strength, the foamed material is removed, causing wear. The tensile strength of the material determines its wear resistance. Since the tensile strength of the foamed material is lower than that of the substrate after foaming, the wear resistance decreases. Since the material is oxidized when immersed in potassium permanganate solution, an easily removable oxide layer is formed on the surface of the material. The wear resistance after immersion is related not only to its tensile strength but also to the thickness of the chemical oxidation layer. Compared with the substrate, the pore walls of the foamed material act as a physical barrier to the diffusion of oxidants, effectively hindering the diffusion of KMnO4 within the thermoplastic elastomer foam, reducing the thickness of the easily removable oxide layer, reducing wear, and improving wear resistance.

[0082] Comparative Examples 4 to 7 (see Figures 7-10 ) and Examples 3 to 6 (see Figures 3 to 6 ), TPU foam materials with a foaming ratio of 1.27 to 1.79 and a cell size of 25 to 70 μm have better wear resistance in an oxidizing environment than unfoamed TPU. TPU foam materials outside this range have lower wear resistance in an oxidizing environment than unfoamed TPU.

[0083] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention rather than all the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a thermoplastic elastomer foam material, characterized in that: The following steps are involved: After coating the surface of the thermoplastic elastomer particles with a film, hot pressing is performed to obtain a thermoplastic elastomer sheet; After the thermoplastic elastomer sheet is saturated in a supercritical fluid, the pressure is released for foaming, and the film is automatically separated to obtain a thermoplastic elastomer foam material without a skin layer.

2. The preparation method according to claim 1, characterized in that The supercritical fluid includes supercritical CO2 and / or supercritical N2.

3. The preparation method according to claim 1 or 2, characterized in that The saturation pressure is 8 to 15 MPa; and the saturation time is 30 to 120 minutes.

4. The preparation method according to claim 1, characterized in that The pressure relief rate of the pressure relief foaming is 100-600 MPa / s.

5. The preparation method according to claim 1, characterized in that The temperature during the saturation and pressure relief foaming process is Tg+(120-190° C.), where Tg is the glass transition temperature of the thermoplastic elastomer particles.

6. The preparation method according to claim 1 or 5, characterized in that The thermoplastic elastomer particles include thermoplastic polyurethane elastomer, thermoplastic polyester elastomer or thermoplastic polyamide elastomer.

7. The preparation method according to claim 1, characterized in that The film material used for the coating includes polyimide, polyethylene terephthalate or polyetheretherketone.

8. The preparation method according to claim 1, characterized in that The temperature of the hot pressing is 180-220° C.; the pressure of the hot pressing is 5-20 MPa; and the time of the hot pressing is 5-15 minutes.

9. The thermoplastic elastomer foam material prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The thermoplastic elastomer foam material has a foaming ratio of 1.27 to 1.79, a cell size of 25 to 70 μm, and a cell density of (1.96 to 12.2) E+06 cells / cm 3 The wear amount is 0.15~4.19mg / 100r, and the wear amount after soaking in 5wt.% KMnO4 solution is 4.63~15.43mg / 100r.

10. Use of the thermoplastic elastomer foam material according to claim 9 as a polishing pad in chemical mechanical polishing.

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