A polyurethane polishing pad with gradient pore size and its preparation method

Abstract

This invention discloses a polyurethane polishing pad with gradient pore size and its preparation method. The invention utilizes a microwave-assisted foaming process, taking advantage of the selective heating characteristics of microwaves, to form a gradient structure with continuously varying pore sizes along the thickness direction of the polyurethane foam. The polishing pad has a density of 0.20–0.50 g / cm³, a hardness of 45–100, and a foam pore size of 2–150 μm. This invention solves the problems of uneven foam pores, poor water permeability, and easy delamination of multilayer adhesives in traditional polishing pads. It features uniform foaming, efficient processing, controllable gradient, and excellent overall performance, making it suitable for chemical mechanical polishing applications in semiconductors, 3C products, and precision optical glass.

Description

Technical Field

[0001] This invention belongs to the field of polyurethane preparation technology, specifically relating to a polyurethane polishing pad with gradient pore size and its preparation method, which is particularly applicable to the manufacturing of core consumables for chemical mechanical polishing (CMP). Background Technology

[0002] With the rapid development of the semiconductor industry, the requirements for the surface flatness of semiconductor raw material wafers are becoming increasingly stringent. Chemical mechanical polishing (CMP) is the only technology that can achieve global planarization, and polishing pads are one of the essential core materials for the CMP process. The most widely used polishing pads in industrial applications are made of polymer materials, with polyurethane foam as their main component. Factors affecting polishing pads include pad hardness, compression ratio, filler content, roughness, and density. Currently, polyurethane polishing pads are required when polishing materials such as precision optical glass, quartz glass, and semiconductors.

[0003] The permeability (also known as porosity) of polyurethane polishing pads is an important performance indicator. Increased permeability improves heat dissipation efficiency during polishing, facilitates waste removal, and allows for timely supply of fresh polishing slurry. Conversely, lower permeability makes it difficult for the large amount of grinding heat to dissipate during polishing, and the polishing pad is prone to glazing, resulting in a shorter service life and poorer polishing effect. The higher the porosity of the polishing pad, the stronger its ability to transport polishing slurry, and the more uniform the polishing slurry distribution within the working area, which is beneficial for improving processing efficiency. However, if the porosity is too high, the polishing pad is prone to deformation, affecting the planarization effect. Therefore, controlling the pore size can balance planarity with the storage of polishing slurry without it penetrating into the interior of the polishing pad, thus stabilizing the polishing effect and extending the service life.

[0004] Existing polyurethane polishing pads have poor water resistance and heat resistance, necessitating the development of a novel polyurethane polishing pad. Gradient pore size is a structure with asymmetric pores, meaning the pore size changes continuously along a certain direction. Modifying the structure of the polyurethane polishing pad to possess a gradient pore size structure can better address these issues.

[0005] Chinese patent application CN2022105658303 describes a high-efficiency permeable filter brick with gradient pore size, its preparation method, and its application. The invention involves preparing ceramsite green balls of different particle sizes and layering them according to their particle size. After pressing, molding, and firing, the permeable brick exhibits a gradient pore size distribution. This facilitates the use of high-pressure water backwashing to flush out blockages generated during long-term filtration, thereby extending the service life of the permeable brick.

[0006] Chinese patent application CN2020103462489 discloses a method for preparing a gas diffusion layer with gradient pore size for an SPE electrolyzer. The method employs a casting process to manufacture the microporous diffusion layer, which is simple and allows for wide-area production. A vacuum plasma spraying method is used to create a macroporous layer on the surface of the microporous layer, ensuring interlayer bonding strength while forming a gradient pore size within the diffusion layer. The microporous structure helps suppress the aggregation and growth of bubbles on the membrane electrode surface, while the macroporous structure facilitates liquid transport from the bipolar plate side to the electrode surface. The combination of these two pore structures promotes gas-liquid mass transfer and reduces energy consumption for hydrogen production via water electrolysis.

[0007] The aforementioned two technical solutions, with their proposed pore size gradient structures, demonstrate excellent performance applications in ceramic composite membranes and renewable energy, but have not yet been applied to polyurethane foam. Due to the poor water and heat resistance of polyurethane polishing pads, their performance during polishing is generally mediocre, presenting certain drawbacks. These issues can be addressed by employing a gradient pore size method. Furthermore, traditional polishing pads often feature a single pore size structure, making it difficult to simultaneously meet the different requirements of coarse polishing (requiring large pores to accommodate large abrasive grains and high-flow-rate polishing fluid) and fine polishing (requiring small pores to improve flatness and fine removal). Some existing technologies use the physical bonding of multiple layers of sheets with different pore sizes to achieve the gradient, but this suffers from weak interlayer bonding, cumbersome processes, and a tendency to delamination and failure. Summary of the Invention

[0008] This invention addresses the shortcomings of existing technologies by providing a polyurethane polishing pad with gradient pore sizes and its preparation method. Through microwave-assisted foaming heating, a continuous gradient pore size structure along the thickness direction is formed in a single step, solving problems such as uneven pore size, poor water permeability, multi-layer adhesion and delamination, and low process efficiency, thus meeting the needs of high-end precision polishing. Specifically, through a single foaming process, a continuous gradient structure with pore sizes decreasing (or vice versa) is directly formed along the thickness direction of the polyurethane foam. This is not a physical superposition but a gradual change in the material's internal structure, fundamentally solving the performance defects of multi-layer adhesion. Furthermore, traditional polyurethane foaming often uses heat conduction heating (such as ovens or oil baths), which transfers heat from the outside in, easily leading to uneven temperatures between the mold edge and center, and between the surface and interior, resulting in inconsistent pore sizes and distribution, as well as long heating times and high energy consumption. This invention introduces a microwave generator, utilizing the selective heating characteristics of microwaves—directly acting on polar molecules (such as water, foaming agents, polar polyols, etc.)—to simultaneously heat the interior of the material. This invention fundamentally changes the heat transfer mechanism, achieving precise temperature control, rapid curing, and uniform foaming. Existing methods for controlling cell size typically rely on chemical formulations (foaming agent dosage, catalyst activity) or ambient temperature, resulting in indirect and delayed adjustments that are difficult to dynamically intervene in during the foaming process. This invention establishes a direct controllable relationship between microwave power (500-1500W), frequency (25-125KHz), time (5-20s), and cell size. Utilizing the strong interaction between microwaves and water molecules (foaming agent), it precisely controls the bubble nucleation rate, growth time, and system viscosity changes by adjusting microwave parameters, thereby achieving "online active control" of the final pore size and optimizing the cell structure of the polishing pad.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a polyurethane polishing pad with gradient pore size, comprising the following steps:

[0010] Step (1) Preparation of polyurethane prepolymer: Stir and vacuum dehydrate polyether polyol in an oil bath at 100-140℃ for 1-2 hours, preferably at 120℃ for 1-2 hours. After cooling to 60-80℃, add isocyanate, heat to 80-100℃ and add catalyst. React under nitrogen protection for 1.5-3.0 hours. After monitoring the NCO content to the preset value, vacuum degassing is performed.

[0011] Step (2) Mixing preparation: The isocyanate, catalyst and curing agent are dried and dehydrated, and the first mixture is prepared by polyester polyol, catalyst and foaming agent respectively. The second mixture is prepared by polyurethane prepolymer, curing agent, filler and isocyanate.

[0012] Step (3) Microwave foaming: The first mixture and the second mixture are quickly mixed and poured into a mold with a microwave coil layer within 10 to 20 seconds. The microwave parameters are adjusted to assist in foaming and form a gradient pore size foam material along the thickness direction.

[0013] Step (4) Post-processing: The foamed material is cut and trimmed to obtain a gradient pore size polyurethane polishing pad.

[0014] Further, in step (1), the polyether polyol has a molecular weight of 400-4000 and a functionality of 2, preferably 1000-3000; the isocyanate is polymeric MDI, with a preset NCO content of 10-20%; the catalyst is dibutyltin dilaurate (DBTDL), and the amount used is 0.03-0.05 wt% of the total mass of the prepolymer; by mass, the polyether polyol is 50-100 parts and the isocyanate is 40-80 parts.

[0015] Further, the foaming agent in step (2) is water, with a mass fraction of 0.1 to 0.7; the curing agent is dimethylthiotoluene diamine (DMTDA); the filler is one of cerium oxide, alumina, zirconium oxide, and silicon carbide; and the amount of catalyst is 3.0 to 5.0 wt% of the total mass of the reaction system.

[0016] Furthermore, in step (2), the first mixture is made by high-speed stirring of dehydrated polyester polyol, catalyst, and foaming agent at a speed of 1000-2000 rpm for 20-45 s; the second mixture is made by high-speed stirring of polyurethane prepolymer, curing agent, filler, and isocyanate at a speed of 1000-2000 rpm.

[0017] Furthermore, in step (2), the mass ratio of the first mixture to the second mixture is 1:0.5~1.

[0018] Furthermore, the microwave foaming parameters in step (3) are: power 500W~1500W, frequency 25KHz~125KHz, time 5~15s; microwaves are applied through a coil generator, and the aperture gradient in the thickness direction is controlled by energy attenuation.

[0019] Furthermore, in step (3), after the first mixture and the second mixture are mixed, the stirring speed is 1000-2000 rpm, and after stirring, the mixture is quickly injected into the mold to complete the foaming.

[0020] The present invention also provides a polyurethane polishing pad, wherein the polyurethane polishing pad is an integrally molded structure of polyurethane foam material, with a density of 0.20 to 0.50 g / cm³, a Shore C hardness of 45 to 100, and the foam pores are continuously gradient distributed along the thickness direction with a pore size range of 2 to 150 μm.

[0021] Furthermore, the gradient pore size is formed by microwave-assisted foaming in one step, and is not a multi-layer sheet physical bonding structure. The pore size changes continuously and gradually along the thickness direction without interlayer interfaces.

[0022] Furthermore, the polyurethane polishing pad is used for chemical mechanical polishing of semiconductor wafers, precision optical glass, and 3C products. It can simultaneously meet the needs of rough polishing and fine polishing, and has high water permeability, good heat resistance, is not easily glazed, and has a long service life.

[0023] The beneficial effects of this invention are:

[0024] Excellent cell structure: One-piece molded continuous gradient pore size, 2~150μm precisely controllable, uniformly distributed, high sphericity, adjustable open and closed pore ratio, significantly improving water permeability.

[0025] Highly efficient and energy-saving process: Microwave foaming takes only 5-15 seconds, while traditional thermosetting requires more than 30 minutes, reducing energy consumption by more than 70% and significantly shortening the process cycle, making it suitable for industrial mass production.

[0026] Product performance has been comprehensively improved: hardness is adjustable from 45 to 100, density is controllable from 0.20 to 0.50 g / cm³, heat resistance, water resistance, and wear resistance are enhanced, it is less prone to glazing, and its service life is extended by more than 50%. It simultaneously meets the needs of both rough and fine polishing, eliminating the need to replace polishing pads; there is no risk of delamination or peeling, and polishing stability is high; suitable for high-end precision polishing of semiconductor wafers, optical glass, 3C casings, etc. Flexible adjustment allows for online dynamic control of the aperture gradient through microwave power, frequency, and time, adapting to different polishing scenarios and offering strong versatility. Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope (SEM) image of the cross-section of the polyurethane polishing pad in Embodiment 3 of the present invention;

[0028] Figure 2 This is a scanning electron microscope (SEM) image of the cross-section of the polyurethane polishing pad in Embodiment 4 of the present invention;

[0029] Figure 3 This is a scanning electron microscope (SEM) image of a cross-section of the polyurethane polishing pad according to Embodiment 6 of the present invention.

[0030] Figure 4 This is a scanning electron microscope (SEM) image of the cross-section of the polyurethane polishing pad in Embodiment 9 of the present invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Reference Figures 1-4 As shown, the present invention provides a polyurethane polishing pad with gradient pore size. The polyurethane polishing pad with gradient pore size has a density of 0.20-0.50 g / cm3, a hardness of 45-100 (Shore C hardness), and the foam pore size of the polyurethane polishing pad is 2-150 μm.

[0033] This invention also provides a method for preparing a polyurethane polishing pad with gradient pore sizes. First, polyether polyol and isocyanate are added to a reaction vessel in a specific ratio to synthesize a polyurethane prepolymer. Then, polyester polyol, isocyanate, filler, catalyst, foaming agent, curing agent, and prepolymer are mixed and stirred at high speed before being directly poured into a foaming mold. Finally, a coil-type microwave generator is used to assist foaming on the outer layer of the foaming mold. By controlling different microwave power, temperature, and time, the cell size is controlled to form a polyurethane foam structure with different gradient pore sizes. The specific steps include:

[0034] (1) Preparation of polyurethane prepolymer: Polyether polyol was added to a three-necked flask and stirred under vacuum at 120°C in an oil bath for 1-2 hours to remove water and other small molecules. The mixture was then allowed to cool naturally to about 60-80°C. A measured amount of isocyanate was then added to the vacuum-dehydrated polyether polyol and stirred until homogeneous at 60-80°C. The mixture was then gradually heated to 80-100°C, and 0.03-0.05 wt% of catalyst was added simultaneously. The mixture was stirred at 80-100°C for 1.5-3.0 hours, with N2 protection throughout the reaction. During the reaction, the NCO content in the polyurethane prepolymer was determined using the dibutylamine-toluene method. When the NCO content reached the theoretical preset value, the reaction was stopped, and the polyurethane prepolymer was evacuated to remove air bubbles. Pre-removal of free water and small molecule impurities from polyether polyols prevents defects such as cross-pores and collapse during subsequent foaming; nitrogen protection prevents isocyanate oxidation and hydrolysis, ensuring stable and controllable prepolymer reaction; precise monitoring of NCO content ensures uniform prepolymer structure and stable mechanical properties.

[0035] (2) Preparation of mixture: Before mixing, isocyanate and catalyst need to be dried in an oven and fully dehydrated.

[0036] First, the dehydrated polyester polyol is added to the dried reaction vessel. The measured amount of catalyst and foaming agent is accurately weighed. Then, the catalyst and foaming agent are added to the reaction vessel in sequence and stirred using a mechanical stirring device to obtain the first mixture, which is then set aside for later use.

[0037] Weigh out a fixed amount of curing agent and filler, add the prepared polyurethane prepolymer, curing agent, and filler to a container and stir to mix. After mixing evenly, add the weighed isocyanate and stir to obtain a second mixture, which is then set aside for later use. Drying and dehydrating the isocyanate, catalyst, and curing agent can prevent premature reaction with water and subsequent gelation. Preparing the two mixtures separately can delay the reaction start-up time, ensuring uniform mixing before rapid foaming, and improving cell consistency and gradient controllability.

[0038] (3) Preparation of foamed samples: The prepared second mixture is quickly poured into the first mixture and stirred rapidly. Within 10-20 seconds, it is quickly poured into a foaming mold with a microwave coil layer for microwave foaming. By adjusting the pore size in the thickness direction through microwave foaming, the polyurethane foam material with gradient pore size of the present invention is obtained. Rapid mixing and rapid pouring into the mold can prevent premature reaction and resulting in decreased fluidity; the microwave coil layer achieves uniform heating, avoiding the problem of large internal and external temperature differences in traditional heat conduction; a continuous gradient pore size is naturally formed along the thickness direction, and one-time molding without layering takes into account both water permeability and polishing flatness.

[0039] (4) The polyurethane foam material in step (3) is cut and trimmed to prepare a polyurethane polishing pad with gradient pore size. The target size and surface flatness are obtained by conventional cutting and trimming. The process is simple, low-cost, suitable for mass production, and ensures the accuracy of the polishing pad.

[0040] This invention involves synthesizing a polyurethane prepolymer by mixing polyether polyol and isocyanate in a reactor, then mixing and stirring polyester polyol, isocyanate, filler, catalyst, foaming agent, curing agent, and the polyurethane prepolymer at high speed before pouring the mixture into a foaming mold. A coil-type microwave generator is used to assist foaming on the outer layer of the mold. By controlling different microwave power and temperature, the size and structure of the foam cells are controlled, resulting in a polyurethane foam structure with varying pore sizes. The polyurethane polishing pad prepared by this invention exhibits excellent performance and, compared to existing polishing pads, possesses the advantage of controllable pore size. It has broad market application potential in polishing fields where high permeability and heat resistance are required.

[0041] The core advantage of microwave foaming technology lies in its "selective bulk heating" mechanism, which fundamentally changes the heat transfer method of traditional heat conduction foaming. Traditional heating relies on a heat flow gradient from the outside to the inside, which easily leads to uneven temperatures between the mold edge and center, and between the surface and the interior, resulting in problems such as inconsistent cell size and high closed-cell ratio. Microwave energy, on the other hand, can be selectively absorbed directly by polar molecules in the polyurethane system (especially water as a foaming agent), causing the entire material to heat up simultaneously, and the foaming reaction to proceed synchronously. This results in a uniform cell structure with narrower size distribution, better sphericity, and a controllable ratio of open and closed cells. More importantly, microwaves undergo natural energy attenuation when penetrating the foaming mold and material—high energy absorption and vigorous foaming occur near the microwave source, resulting in larger pore sizes; while low energy absorption and gentle foaming occur far from the source, resulting in smaller pore sizes. By adjusting the power (500-1500W), frequency (25-125KHz), and duration (5-20s) of the coil microwave generator, this attenuation gradient can be precisely controlled, achieving a gradient pore size structure that continuously varies along the thickness direction during a single foaming process. Compared to traditional heating and curing methods that take tens of minutes or even hours, microwave foaming only requires 5-15 seconds, significantly shortening the process cycle, reducing energy consumption and the risk of thermal side reactions, while providing a highly repeatable and online adjustable advanced control method for industrial mass production.

[0042] In a preferred embodiment of the present invention, the molecular weight of the polyether polyol in step (1) is 400-4000, the functionality is 2, and the preferred molecular weight is 1000-3000; the isocyanate is polymeric MDI, and the preset NCO content is 10-20%; the catalyst is dibutyltin dilaurate (DBTDL); by mass, the polyether polyol is 50-100 parts and the isocyanate is 40-80 parts; the polyether polyol with specific molecular weight and functionality can balance the foaming fluidity and foam mechanical strength; the polymeric MDI has moderate reactivity and good heat resistance; the NCO content of 10-20% ensures moderate crosslinking density; the trace catalyst can stably control the reaction rate and avoid explosive polymerization or insufficient reaction.

[0043] In step (2), the foaming agent is water, the curing agent is dimethylthiotoluene diamine (DMTDA), and the filler is one of cerium oxide, alumina, zirconium oxide, and silicon carbide. Water is a green and environmentally friendly foaming agent with low cost. It reacts with isocyanate to generate CO2 and form uniform cells. DMTDA can improve the curing rate and heat resistance. Inorganic fillers significantly improve wear resistance, hardness, and polishing removal rate. The amount of catalyst is precisely controlled to synchronize foaming and gelation, ensuring the stability of the cell structure.

[0044] In step (2), the stirring speed is 1000-2000 rpm and the stirring time is 20-45 s; the amount of catalyst is 3.0-5.0 wt% of the whole system and the mass fraction of foaming agent is 0.1-0.7; the mass ratio of the first mixture to the second mixture is 1:0.5-1; this ratio can balance the foaming capacity, crosslinking strength and filler dispersibility, ensure the stability of the foaming process, and avoid the problem of excessively large or small cells or structural collapse due to imbalance of proportion.

[0045] In step (3), the stirring speed is 1000-2000 rpm. High-speed stirring can make the components disperse evenly, without agglomeration or stratification; specific speed and time can avoid introducing too many air bubbles, while ensuring sufficient mixing, so that the subsequent foaming pore size is uniform and the gradient is continuous.

[0046] In a preferred embodiment of the present invention, the microwave power of microwave foaming in step (3) is 500W to 1500W, the microwave foaming frequency is 25KHz to 125KHz, and the microwave foaming time is 5 to 15s; the microwave parameters can be precisely controlled online to adjust the size of the foam cells and the gradient slope; the short-time efficient heating greatly shortens the process cycle; the energy naturally decays along the thickness direction, realizing a continuous gradient of large holes near the source side and small holes far from the source side, without the need for multi-layer bonding.

[0047] In a preferred embodiment of the present invention, the polyurethane foam material cutting and trimming process in step (4) is a conventional process.

[0048] This invention utilizes microwave heating and refinement of water vapor molecules to foam a mixture of semi-prepolymer and isocyanate. Microwave-assisted foaming is then employed on the outer layer of the foaming mold, controlling the pore size by varying microwave power to create a polyurethane foam structure with different pore sizes. Traditional polyurethane polishing pads suffer from uneven pore size distribution and difficulty in controlling the pore structure during foaming. Microwave-assisted foaming, however, allows for precise control of the pore structure, significantly improving water permeability. The gradient pore size polyurethane polishing pad exhibits superior performance and holds great promise for applications in 3C and semiconductor processing.

[0049] The polyurethane polishing pad of this invention has an adjustable pore diameter that can be adjusted according to actual needs. Compared with traditional polishing pads, which have the limitation of applicability due to the same pore size, the gradient pore structure can effectively combine with abrasive particles during the polishing process, satisfying different processes from coarse polishing to fine polishing. Depending on the pore size, it can accommodate polishing liquid to participate in the removal of materials, enhancing the chemical action and improving the removal efficiency, resulting in a stable and efficient polishing process.

[0050] This invention provides a method that combines microwave-assisted foaming and curing processes to obtain a polyurethane foam with uniform and controllable pore size, gradient pore size, and excellent heat resistance. Existing technologies use a layer-by-layer bonding method to achieve gradient pore size in polishing pads, which struggles to simultaneously achieve wafer planarization and high polishing efficiency. Compared to existing methods, this invention overcomes the difficulties of cumbersome processes and poor performance, achieving advantages such as rapid energy saving, stable process, uniform and controllable foam quality, and good overall foam performance. Compared to traditional heat curing methods, microwave-assisted foaming and curing is a process of internal frictional heat generation and outward diffusion, exhibiting strong selectivity, short heating time, minimal heat loss, uniform material heating, easy control of input power, and no pollution during the heating process. This provides an effective method for polyurethane foaming processes and has broad application prospects.

[0051] The sources of the chemicals mentioned in the embodiments of this invention are as follows:

[0052] Polyether polyol: Manufacturer: Beijing Huawi Ruike Chemical Technology Co., Ltd., Product No.: S24146-500g; Molecular weight: 2000; Functionality: 2; Hydroxyl value: 56 ± 2 mgKOH / g.

[0053] Polymer MDI: Manufacturer: Wanhua Chemical, Product No. PM-200; -NCO content: 30.5%~32.0%; Functionality: 2.7~2.9.

[0054] Dibutyltin dilaurate: Manufacturer: Thermo Fisher Scientific (ACROS), Distributor: Sinopharm Chemical Reagent Co., Ltd., Product No.: C382690050; Purity: ≥98%.

[0055] Dimethylthiotoluene diamine: Manufacturer: RHAWN, Distributor: Shanghai Ximi Biotechnology Co., Ltd., Product No.: R117958-500g; Purity: ≥99.5%; Amine value: 536 ± 5 mgKOH / g.

[0056] Alumina: Manufacturer: Macklin, Product No.: Alumina; Density: 3.97 g / cm3; Purity: 99.99% metals basis, α crystal form approximately 95%, γ crystal form approximately 5%.

[0057] Polyester polyol: Manufacturer: Huafeng Chemical Co., Ltd., Product No.: PE204, Key parameters: Molecular weight 400; Hydroxyl value 280±10 mgKOH / g.

[0058] The polyester polyol mentioned in this invention is preferably polycaprolactone polyol.

[0059] Example 1: A method for preparing a polyurethane polishing pad with gradient pore size, the specific steps of which are as follows:

[0060] Preparation of polyurethane prepolymer: 80 parts of polyether polyol with a molecular weight of 2000 and a functionality of 2 were added to a three-necked flask and stirred at 120°C under oil bath conditions for 1.5 h under vacuum to remove moisture and small molecule impurities. The mixture was then allowed to cool naturally to 70°C. 60 parts of polymeric MDI were added and stirred until homogeneous. The temperature was gradually increased to 90°C. Dibutyltin dilaurate (DBTDL) catalyst, accounting for 0.04 wt% of the total mass of the prepolymer, was added and stirred under N2 protection for 2 h. The NCO content was determined by dibutylamine-toluene titration. The reaction was stopped when the NCO content reached 15%. The mixture was then degassed under vacuum for 30 min to obtain the polyurethane prepolymer.

[0061] Preparation of the mixture: Polymerized MDI, DBTDL, and dimethyl thiotoluene diamine (DMTDA) were placed in an oven at 110℃ and dried for 2 hours. 70 parts of the dehydrated polyester polyol were added to the dried reaction vessel, along with 4.0 wt% DBTDL and 0.3 parts deionized water. The mixture was stirred at 1500 rpm for 30 seconds until homogeneous to obtain the first mixture. The above polyurethane prepolymer, 10 parts DMTDA, and 15 parts alumina filler were mixed evenly, and 50 parts of polymerized MDI were added. The mixture was stirred at 1500 rpm for 30 seconds to obtain the second mixture. The mass ratio of the first mixture to the second mixture was controlled to be 1:0.8.

[0062] Microwave foaming: The second mixture is quickly poured into the first mixture and stirred at a high speed of 1500 rpm for 15 seconds. The mixture is then quickly poured into a custom foaming mold equipped with a coil microwave generator. Microwave-assisted foaming is carried out under the conditions of microwave power of 500W, frequency of 25kHz, and foaming time of 5s to obtain a gradient pore size polyurethane foam material.

[0063] Post-processing: The foamed polyurethane material was cured at room temperature for 24 hours, and then subjected to conventional cutting, grinding, and trimming to obtain a polyurethane polishing pad with gradient pore size. The resulting polishing pad had a hardness (ShoreC) of 45, an average pore size of 150μm, and a gradient pore distribution with a complete structure.

[0064] Example 2: A method for preparing a polyurethane polishing pad with gradient pore size, the specific steps of which are as follows:

[0065] Preparation of polyurethane prepolymer: 80 parts of polyether polyol with a molecular weight of 2000 and a functionality of 2 were added to a three-necked flask and stirred at 120°C under oil bath conditions for 1.5 h under vacuum to remove moisture and small molecule impurities. The mixture was then allowed to cool naturally to 70°C. 60 parts of polymeric MDI were added and stirred until homogeneous. The temperature was gradually increased to 90°C. Dibutyltin dilaurate (DBTDL) catalyst, accounting for 0.04 wt% of the total mass of the prepolymer, was added and stirred under N2 protection for 2 h. The NCO content was determined by dibutylamine-toluene titration. The reaction was stopped when the NCO content reached 15%. The mixture was then degassed under vacuum for 30 min to obtain the polyurethane prepolymer.

[0066] Preparation of the mixture: Polymerized MDI, DBTDL, and dimethyl thiotoluene diamine (DMTDA) were placed in an oven at 110℃ and dried for 2 hours. 70 parts of the dehydrated polyester polyol were added to the dried reaction vessel, along with 4.0 wt% DBTDL and 0.3 parts deionized water. The mixture was stirred at 1500 rpm for 30 seconds until homogeneous to obtain the first mixture. The above polyurethane prepolymer, 10 parts DMTDA, and 15 parts alumina filler were mixed evenly, and 50 parts of polymerized MDI were added. The mixture was stirred at 1500 rpm for 30 seconds to obtain the second mixture. The mass ratio of the first mixture to the second mixture was controlled to be 1:0.8.

[0067] Microwave foaming: The second mixture is quickly poured into the first mixture and stirred at a high speed of 1500 rpm for 15 seconds. The mixture is then quickly poured into a custom foaming mold equipped with a coil microwave generator. Microwave-assisted foaming is carried out under the conditions of microwave power of 500W, frequency of 50kHz, and foaming time of 5s to obtain a gradient pore size polyurethane foam material.

[0068] Post-processing: The foamed polyurethane material was cured at room temperature for 24 hours, and then cut, polished, and trimmed to obtain a polyurethane polishing pad with a gradient pore size. The resulting polishing pad had a hardness (ShoreC) of 62, an average pore size of 125μm, and moderate pore size with a continuous gradient.

[0069] Example 3: A method for preparing a polyurethane polishing pad with gradient pore size, the specific steps of which are as follows:

[0070] Preparation of polyurethane prepolymer: 80 parts of polyether polyol with a molecular weight of 2000 and a functionality of 2 were added to a three-necked flask and stirred at 120°C under oil bath conditions for 1.5 h under vacuum to remove moisture and small molecule impurities. The mixture was then allowed to cool naturally to 70°C. 60 parts of polymeric MDI were added and stirred until homogeneous. The temperature was gradually increased to 90°C. Dibutyltin dilaurate (DBTDL) catalyst, accounting for 0.04 wt% of the total mass of the prepolymer, was added and stirred under N2 protection for 2 h. The NCO content was determined by dibutylamine-toluene titration. The reaction was stopped when the NCO content reached 15%. The mixture was then degassed under vacuum for 30 min to obtain the polyurethane prepolymer.

[0071] Preparation of the mixture: Polymerized MDI, DBTDL, and dimethyl thiotoluene diamine (DMTDA) were placed in an oven at 110℃ and dried for 2 hours. 70 parts of the dehydrated polyester polyol were added to the dried reaction vessel, along with 4.0 wt% DBTDL and 0.3 parts deionized water. The mixture was stirred at 1500 rpm for 30 seconds until homogeneous to obtain the first mixture. The above polyurethane prepolymer, 10 parts DMTDA, and 15 parts alumina filler were mixed evenly, and 50 parts of polymerized MDI were added. The mixture was stirred at 1500 rpm for 30 seconds to obtain the second mixture. The mass ratio of the first mixture to the second mixture was controlled to be 1:0.8.

[0072] Microwave foaming: The second mixture is quickly poured into the first mixture and stirred at a high speed of 1500 rpm for 15 seconds. The mixture is then quickly poured into a custom foaming mold equipped with a coil microwave generator. Microwave-assisted foaming is carried out under the conditions of microwave power of 500W, frequency of 75kHz, and foaming time of 5s to obtain a gradient pore size polyurethane foam material.

[0073] Post-processing: The foamed polyurethane material was cured at room temperature for 24 hours, and then cut, polished, and trimmed to obtain a polyurethane polishing pad with a gradient pore size. The resulting polishing pad had a hardness (ShoreC) of 73, an average pore size of 92μm, and dense and uniform pores with no obvious defects.

[0074] Example 4: A method for preparing a polyurethane polishing pad with gradient pore size, the specific steps of which are as follows:

[0075] Preparation of polyurethane prepolymer: 80 parts of polyether polyol with a molecular weight of 2000 and a functionality of 2 were added to a three-necked flask and stirred at 120°C under oil bath conditions for 1.5 h under vacuum to remove moisture and small molecule impurities. The mixture was then allowed to cool naturally to 70°C. 60 parts of polymeric MDI were added and stirred until homogeneous. The temperature was gradually increased to 90°C. Dibutyltin dilaurate (DBTDL) catalyst, accounting for 0.04 wt% of the total mass of the prepolymer, was added and stirred under N2 protection for 2 h. The NCO content was determined by dibutylamine-toluene titration. The reaction was stopped when the NCO content reached 15%. The mixture was then degassed under vacuum for 30 min to obtain the polyurethane prepolymer.

[0076] Preparation of the mixture: Polymerized MDI, DBTDL, and dimethyl thiotoluene diamine (DMTDA) were placed in an oven at 110℃ and dried for 2 hours. 70 parts of the dehydrated polyester polyol were added to the dried reaction vessel, along with 4.0 wt% DBTDL and 0.3 parts deionized water. The mixture was stirred at 1500 rpm for 30 seconds until homogeneous to obtain the first mixture. The above polyurethane prepolymer, 10 parts DMTDA, and 15 parts alumina filler were mixed evenly, and 50 parts of polymerized MDI were added. The mixture was stirred at 1500 rpm for 30 seconds to obtain the second mixture. The mass ratio of the first mixture to the second mixture was controlled to be 1:0.8.

[0077] Microwave foaming: The second mixture is quickly poured into the first mixture and stirred at a high speed of 1500 rpm for 15 seconds. The mixture is then quickly poured into a custom foaming mold equipped with a coil microwave generator. Microwave-assisted foaming is carried out under the conditions of microwave power of 500W, frequency of 100kHz, and foaming time of 5s to obtain a gradient pore size polyurethane foam material.

[0078] Post-processing: The foamed polyurethane material was cured at room temperature for 24 hours, followed by routine cutting, grinding, and finishing to obtain a polyurethane polishing pad with gradient pore sizes. The resulting polishing pad had a hardness (ShoreC) of 92 and an average pore size of 55 μm (see...). Figure 1 The cells are evenly distributed and the gradient structure is stable.

[0079] Example 5: A method for preparing a polyurethane polishing pad with gradient pore size, the specific steps of which are as follows:

[0080] Preparation of polyurethane prepolymer: 80 parts of polyether polyol with a molecular weight of 2000 and a functionality of 2 were added to a three-necked flask and stirred at 120°C under oil bath conditions for 1.5 h under vacuum to remove moisture and small molecule impurities. The mixture was then allowed to cool naturally to 70°C. 60 parts of polymeric MDI were added and stirred until homogeneous. The temperature was gradually increased to 90°C. Dibutyltin dilaurate (DBTDL) catalyst, accounting for 0.04 wt% of the total mass of the prepolymer, was added and stirred under N2 protection for 2 h. The NCO content was determined by dibutylamine-toluene titration. The reaction was stopped when the NCO content reached 15%. The mixture was then degassed under vacuum for 30 min to obtain the polyurethane prepolymer.

[0081] Preparation of the mixture: Polymerized MDI, DBTDL, and dimethyl thiotoluene diamine (DMTDA) were placed in an oven at 110℃ and dried for 2 hours. 70 parts of the dehydrated polyester polyol were added to the dried reaction vessel, along with 4.0 wt% DBTDL and 0.3 parts deionized water. The mixture was stirred at 1500 rpm for 30 seconds until homogeneous to obtain the first mixture. The above polyurethane prepolymer, 10 parts DMTDA, and 15 parts alumina filler were mixed evenly, and 50 parts of polymerized MDI were added. The mixture was stirred at 1500 rpm for 30 seconds to obtain the second mixture. The mass ratio of the first mixture to the second mixture was controlled to be 1:0.8.

[0082] Microwave foaming: The second mixture is quickly poured into the first mixture and stirred at a high speed of 1500 rpm for 15 seconds. The mixture is then quickly poured into a custom foaming mold equipped with a coil microwave generator. Microwave-assisted foaming is carried out under the conditions of microwave power of 500W, frequency of 125kHz, and foaming time of 5s to obtain a gradient pore size polyurethane foam material.

[0083] Post-processing: The foamed polyurethane material was cured at room temperature for 24 hours, followed by routine cutting, grinding, and finishing to obtain a polyurethane polishing pad with gradient pore sizes. The resulting polishing pad had a hardness (Shore C) of 104 and an average pore size of 25 μm (see...). Figure 2 The bubbles are dense and regular, making them suitable for fine polishing applications.

[0084] Example 6: A method for preparing a polyurethane polishing pad with gradient pore size, the specific steps of which are as follows:

[0085] Preparation of polyurethane prepolymer: 80 parts of polyether polyol with a molecular weight of 2000 and a functionality of 2 were added to a three-necked flask and stirred at 120°C under oil bath conditions for 1.5 h under vacuum to remove moisture and small molecule impurities. The mixture was then allowed to cool naturally to 70°C. 60 parts of polymeric MDI were added and stirred until homogeneous. The temperature was gradually increased to 90°C. Dibutyltin dilaurate (DBTDL) catalyst, accounting for 0.04 wt% of the total mass of the prepolymer, was added and stirred under N2 protection for 2 h. The NCO content was determined by dibutylamine-toluene titration. The reaction was stopped when the NCO content reached 15%. The mixture was then degassed under vacuum for 30 min to obtain the polyurethane prepolymer.

[0086] Preparation of the mixture: Polymerized MDI, DBTDL, and dimethyl thiotoluene diamine (DMTDA) were placed in an oven at 110℃ and dried for 2 hours. 70 parts of the dehydrated polyester polyol were added to the dried reaction vessel, along with 4.0 wt% DBTDL and 0.3 parts deionized water. The mixture was stirred at 1500 rpm for 30 seconds until homogeneous to obtain the first mixture. The above polyurethane prepolymer, 10 parts DMTDA, and 15 parts alumina filler were mixed evenly, and 50 parts of polymerized MDI were added. The mixture was stirred at 1500 rpm for 30 seconds to obtain the second mixture. The mass ratio of the first mixture to the second mixture was controlled to be 1:0.8.

[0087] Microwave foaming: The second mixture is quickly poured into the first mixture and stirred at a high speed of 1500 rpm for 15 seconds. The mixture is then quickly poured into a custom foaming mold equipped with a coil microwave generator. Microwave-assisted foaming is carried out under the conditions of microwave power of 500W, frequency of 75kHz, and foaming time of 10s to obtain a gradient pore size polyurethane foam material.

[0088] Post-processing: The foamed polyurethane material was cured at room temperature for 24 hours, followed by routine cutting, grinding, and finishing to obtain a polyurethane polishing pad with gradient pore sizes. The resulting polishing pad had a hardness (ShoreC) of 89 and an average pore size of 55 μm (see...). Figure 3 The bubble size is moderate and the gradient is clear.

[0089] Example 7: A method for preparing a polyurethane polishing pad with gradient pore size, the specific steps of which are as follows:

[0090] Preparation of polyurethane prepolymer: 80 parts of polyether polyol with a molecular weight of 2000 and a functionality of 2 were added to a three-necked flask and stirred at 120°C under oil bath conditions for 1.5 h under vacuum to remove moisture and small molecule impurities. The mixture was then allowed to cool naturally to 70°C. 60 parts of polymeric MDI were added and stirred until homogeneous. The temperature was gradually increased to 90°C. Dibutyltin dilaurate (DBTDL) catalyst, accounting for 0.04 wt% of the total mass of the prepolymer, was added and stirred under N2 protection for 2 h. The NCO content was determined by dibutylamine-toluene titration. The reaction was stopped when the NCO content reached 15%. The mixture was then degassed under vacuum for 30 min to obtain the polyurethane prepolymer.

[0091] Preparation of the mixture: Polymerized MDI, DBTDL, and dimethyl thiotoluene diamine (DMTDA) were placed in an oven at 110℃ and dried for 2 hours. 70 parts of the dehydrated polyester polyol were added to the dried reaction vessel, along with 4.0 wt% DBTDL and 0.3 parts deionized water. The mixture was stirred at 1500 rpm for 30 seconds until homogeneous to obtain the first mixture. The above polyurethane prepolymer, 10 parts DMTDA, and 15 parts alumina filler were mixed evenly, and 50 parts of polymerized MDI were added. The mixture was stirred at 1500 rpm for 30 seconds to obtain the second mixture. The mass ratio of the first mixture to the second mixture was controlled to be 1:0.8.

[0092] Microwave foaming: The second mixture is quickly poured into the first mixture and stirred at a high speed of 1500 rpm for 15 seconds. The mixture is then quickly poured into a custom foaming mold equipped with a coil microwave generator. Microwave-assisted foaming is carried out under the conditions of microwave power of 500W, frequency of 75kHz, and foaming time of 15 seconds to obtain a gradient pore size polyurethane foam material.

[0093] Post-processing: The foamed polyurethane material was cured at room temperature for 24 hours, and then subjected to conventional cutting, grinding, and trimming to obtain a polyurethane polishing pad with a gradient pore size. The resulting polishing pad had a hardness (ShoreC) of 60, an average pore size of 90μm, a clear pore gradient, and no collapse defects.

[0094] Example 8: A method for preparing a polyurethane polishing pad with gradient pore size, the specific steps of which are as follows:

[0095] Preparation of polyurethane prepolymer: 80 parts of polyether polyol with a molecular weight of 2000 and a functionality of 2 were added to a three-necked flask and stirred at 120°C under oil bath conditions for 1.5 h under vacuum to remove moisture and small molecule impurities. The mixture was then allowed to cool naturally to 70°C. 60 parts of polymeric MDI were added and stirred until homogeneous. The temperature was gradually increased to 90°C. Dibutyltin dilaurate (DBTDL) catalyst, accounting for 0.04 wt% of the total mass of the prepolymer, was added and stirred under N2 protection for 2 h. The NCO content was determined by dibutylamine-toluene titration. The reaction was stopped when the NCO content reached 15%. The mixture was then degassed under vacuum for 30 min to obtain the polyurethane prepolymer.

[0096] Preparation of the mixture: Polymerized MDI, DBTDL, and dimethyl thiotoluene diamine (DMTDA) were placed in an oven at 110℃ and dried for 2 hours. 70 parts of the dehydrated polyester polyol were added to the dried reaction vessel, along with 4.0 wt% DBTDL and 0.3 parts deionized water. The mixture was stirred at 1500 rpm for 30 seconds until homogeneous to obtain the first mixture. The above polyurethane prepolymer, 10 parts DMTDA, and 15 parts alumina filler were mixed evenly, and 50 parts of polymerized MDI were added. The mixture was stirred at 1500 rpm for 30 seconds to obtain the second mixture. The mass ratio of the first mixture to the second mixture was controlled to be 1:0.8.

[0097] Microwave foaming: The second mixture is quickly poured into the first mixture and stirred at a high speed of 1500 rpm for 15 seconds. The mixture is then quickly poured into a custom foaming mold equipped with a coil microwave generator. Microwave-assisted foaming is carried out under the conditions of microwave power of 500W, frequency of 75kHz, and foaming time of 20s to obtain a gradient pore size polyurethane foam material.

[0098] Post-processing: The foamed polyurethane material was cured at room temperature for 24 hours, and then cut, polished, and trimmed in a conventional manner to obtain a polyurethane polishing pad with a gradient pore size. The resulting polishing pad had a hardness (ShoreC) of 47, an average pore size of 150μm, and the cells were mainly large pores with a complete structure.

[0099] Example 9: A method for preparing a polyurethane polishing pad with gradient pore size, the specific steps of which are as follows:

[0100] Preparation of polyurethane prepolymer: 80 parts of polyether polyol with a molecular weight of 2000 and a functionality of 2 were added to a three-necked flask and stirred at 120°C under oil bath conditions for 1.5 h under vacuum to remove moisture and small molecule impurities. The mixture was then allowed to cool naturally to 70°C. 60 parts of polymeric MDI were added and stirred until homogeneous. The temperature was gradually increased to 90°C. Dibutyltin dilaurate (DBTDL) catalyst, accounting for 0.04 wt% of the total mass of the prepolymer, was added and stirred under N2 protection for 2 h. The NCO content was determined by dibutylamine-toluene titration. The reaction was stopped when the NCO content reached 15%. The mixture was then degassed under vacuum for 30 min to obtain the polyurethane prepolymer.

[0101] Preparation of the mixture: Polymerized MDI, DBTDL, and dimethyl thiotoluene diamine (DMTDA) were placed in an oven at 110℃ and dried for 2 hours. 70 parts of the dehydrated polyester polyol were added to the dried reaction vessel, along with 4.0 wt% DBTDL and 0.3 parts deionized water. The mixture was stirred at 1500 rpm for 30 seconds until homogeneous to obtain the first mixture. The above polyurethane prepolymer, 10 parts DMTDA, and 15 parts alumina filler were mixed evenly, and 50 parts of polymerized MDI were added. The mixture was stirred at 1500 rpm for 30 seconds to obtain the second mixture. The mass ratio of the first mixture to the second mixture was controlled to be 1:0.8.

[0102] Microwave foaming: The second mixture is quickly poured into the first mixture and stirred at a high speed of 1500 rpm for 15 seconds. The mixture is then quickly poured into a custom foaming mold equipped with a coil microwave generator. Microwave-assisted foaming is carried out under the conditions of microwave power of 750W, frequency of 75kHz, and foaming time of 5s to obtain a gradient pore size polyurethane foam material.

[0103] Post-processing: The foamed polyurethane material was cured at room temperature for 24 hours, followed by routine cutting, grinding, and finishing to obtain a polyurethane polishing pad with gradient pore sizes. The resulting polishing pad had a hardness (ShoreC) of 93 and an average pore size of 70 μm (see...). Figure 4 The bubbles are evenly distributed and have a regular gradient structure.

[0104] Example 10: A method for preparing a polyurethane polishing pad with gradient pore size, the specific steps of which are as follows:

[0105] Preparation of polyurethane prepolymer: 80 parts of polyether polyol with a molecular weight of 2000 and a functionality of 2 were added to a three-necked flask and stirred at 120°C under oil bath conditions for 1.5 h under vacuum to remove moisture and small molecule impurities. The mixture was then allowed to cool naturally to 70°C. 60 parts of polymeric MDI were added and stirred until homogeneous. The temperature was gradually increased to 90°C. Dibutyltin dilaurate (DBTDL) catalyst, accounting for 0.04 wt% of the total mass of the prepolymer, was added and stirred under N2 protection for 2 h. The NCO content was determined by dibutylamine-toluene titration. The reaction was stopped when the NCO content reached 15%. The mixture was then degassed under vacuum for 30 min to obtain the polyurethane prepolymer.

[0106] Preparation of the mixture: Polymerized MDI, DBTDL, and dimethyl thiotoluene diamine (DMTDA) were placed in an oven at 110℃ and dried for 2 hours. 70 parts of the dehydrated polyester polyol were added to the dried reaction vessel, along with 4.0 wt% DBTDL and 0.3 parts deionized water. The mixture was stirred at 1500 rpm for 30 seconds until homogeneous to obtain the first mixture. The above polyurethane prepolymer, 10 parts DMTDA, and 15 parts alumina filler were mixed evenly, and 50 parts of polymerized MDI were added. The mixture was stirred at 1500 rpm for 30 seconds to obtain the second mixture. The mass ratio of the first mixture to the second mixture was controlled to be 1:0.8.

[0107] Microwave foaming: The second mixture is quickly poured into the first mixture and stirred at a high speed of 1500 rpm for 15 seconds. The mixture is then quickly poured into a custom foaming mold equipped with a coil microwave generator. Microwave-assisted foaming is carried out under the conditions of microwave power of 1000W, frequency of 75kHz, and foaming time of 5 seconds to obtain a gradient pore size polyurethane foam material.

[0108] Post-processing: The foamed polyurethane material was cured at room temperature for 24 hours, and then cut, polished, and trimmed in a conventional manner to obtain a polyurethane polishing pad with a gradient pore size. The resulting polishing pad had a hardness (ShoreC) of 64, an average pore size of 110 μm, a continuous pore gradient, and good permeability.

[0109] Example 11: A method for preparing a polyurethane polishing pad with gradient pore size, the specific steps of which are as follows:

[0110] Preparation of polyurethane prepolymer: 80 parts of polyether polyol with a molecular weight of 2000 and a functionality of 2 were added to a three-necked flask and stirred at 120°C under oil bath conditions for 1.5 h under vacuum to remove moisture and small molecule impurities. The mixture was then allowed to cool naturally to 70°C. 60 parts of polymeric MDI were added and stirred until homogeneous. The temperature was gradually increased to 90°C. Dibutyltin dilaurate (DBTDL) catalyst, accounting for 0.04 wt% of the total mass of the prepolymer, was added and stirred under N2 protection for 2 h. The NCO content was determined by dibutylamine-toluene titration. The reaction was stopped when the NCO content reached 15%. The mixture was then degassed under vacuum for 30 min to obtain the polyurethane prepolymer.

[0111] Preparation of the mixture: Polymerized MDI, DBTDL, and dimethyl thiotoluene diamine (DMTDA) were placed in an oven at 110℃ and dried for 2 hours. 70 parts of the dehydrated polyester polyol were added to the dried reaction vessel, along with 4.0 wt% DBTDL and 0.3 parts deionized water. The mixture was stirred at 1500 rpm for 30 seconds until homogeneous to obtain the first mixture. The above polyurethane prepolymer, 10 parts DMTDA, and 15 parts alumina filler were mixed evenly, and 50 parts of polymerized MDI were added. The mixture was stirred at 1500 rpm for 30 seconds to obtain the second mixture. The mass ratio of the first mixture to the second mixture was controlled to be 1:0.8.

[0112] Microwave foaming: The second mixture is quickly poured into the first mixture and stirred at a high speed of 1500 rpm for 15 seconds. The mixture is then quickly poured into a custom foaming mold equipped with a coil microwave generator. Microwave-assisted foaming is carried out under the conditions of microwave power of 1500W, frequency of 75kHz, and foaming time of 5 seconds to obtain a gradient pore size polyurethane foam material.

[0113] Post-processing: The foamed polyurethane material was cured at room temperature for 24 hours, followed by conventional cutting, grinding, and finishing to obtain a polyurethane polishing pad with a gradient pore size. The resulting polishing pad had a hardness (ShoreC) of 46, an average pore size of 150 μm, large and uniform pores, and a significant gradient structure. The properties are shown in Table 1.

[0114] Table 1

[0115] Example Frequency / KHz Time / s Power / W hardness Pore ​​size / μm 1 25 5 500 45 150 2 50 5 500 62 125 3 75 5 500 73 92 4 100 5 500 92 55 5 125 5 500 104 25 6 75 10 500 89 55 7 75 15 500 60 90 8 75 20 500 47 150 9 75 5 750 93 70 10 75 5 1000 64 110 11 75 5 1500 46 150

[0116] Comparative Example 1: A method for preparing a polyurethane polishing pad, the specific steps of which are as follows:

[0117] Preparation of polyurethane prepolymer: 80 parts of polyether polyol with a molecular weight of 2000 and a functionality of 2 were added to a three-necked flask and stirred at 120°C under oil bath conditions for 1.5 h under vacuum to remove moisture and small molecule impurities. The mixture was then allowed to cool naturally to 70°C. 60 parts of polymeric MDI were added and stirred until homogeneous. The temperature was gradually increased to 90°C. Dibutyltin dilaurate (DBTDL) catalyst, accounting for 0.04 wt% of the total mass of the prepolymer, was added and stirred under N2 protection for 2 h. The NCO content was determined by dibutylamine-toluene titration. The reaction was stopped when the NCO content reached 15%. The mixture was then degassed under vacuum for 30 min to obtain the polyurethane prepolymer.

[0118] Preparation of the mixture: Polymerized MDI, DBTDL, and dimethyl thiotoluene diamine (DMTDA) were placed in an oven at 110℃ and dried for 2 hours. 70 parts of the dehydrated polyester polyol were added to the dried reaction vessel, along with 4.0 wt% DBTDL and 0.3 parts deionized water. The mixture was stirred at 1500 rpm for 30 seconds until homogeneous to obtain the first mixture. The above polyurethane prepolymer, 10 parts DMTDA, and 15 parts alumina filler were mixed evenly, and 50 parts of polymerized MDI were added. The mixture was stirred at 1500 rpm for 30 seconds to obtain the second mixture. The mass ratio of the first mixture to the second mixture was controlled to be 1:0.8.

[0119] (3) Conventional heating and foaming: The second mixture is quickly poured into the first mixture, stirred at 1500 rpm for 15 seconds, poured into a regular foaming mold, and placed in a 100°C oven for 30 minutes to cure, thus obtaining polyurethane foam material.

[0120] (4) Post-processing: The foamed polyurethane material is placed at room temperature for 24 hours to mature, and then cut, polished and trimmed in a conventional manner to obtain a polyurethane polishing pad. The resulting polishing pad has uneven distribution of cell size, no gradient pore structure, poor water permeability, and is prone to glazing during the polishing process.

[0121] Comparative Example 2: A method for preparing a polyurethane polishing pad, the specific steps of which are as follows:

[0122] Preparation of polyurethane prepolymer: 80 parts of polyether polyol with a molecular weight of 2000 and a functionality of 2 were added to a three-necked flask and stirred at 120°C under oil bath conditions for 1.5 h under vacuum to remove moisture and small molecule impurities. The mixture was then allowed to cool naturally to 70°C. 60 parts of polymeric MDI were added and stirred until homogeneous. The temperature was gradually increased to 90°C. Dibutyltin dilaurate (DBTDL) catalyst, accounting for 0.04 wt% of the total mass of the prepolymer, was added and stirred under N2 protection for 2 h. The NCO content was determined by dibutylamine-toluene titration. The reaction was stopped when the NCO content reached 15%. The mixture was then degassed under vacuum for 30 min to obtain the polyurethane prepolymer.

[0123] Preparation of the mixture: Polymerized MDI, DBTDL, and dimethyl thiotoluene diamine (DMTDA) were placed in an oven at 110℃ and dried for 2 hours. 70 parts of the dehydrated polyester polyol were added to the dried reaction vessel, along with 4.0 wt% DBTDL and 0.3 parts deionized water. The mixture was stirred at 1500 rpm for 30 seconds until homogeneous to obtain the first mixture. The above polyurethane prepolymer, 10 parts DMTDA, and 15 parts alumina filler were mixed evenly, and 50 parts of polymerized MDI were added. The mixture was stirred at 1500 rpm for 30 seconds to obtain the second mixture. The mass ratio of the first mixture to the second mixture was controlled at 1:0.8. Three types of polyurethane foam sheets with large pore size, medium pore size, and small pore size were prepared using conventional foaming processes.

[0124] (3) Layered hot pressing molding: Three types of sheets are hot-pressed and bonded at 120℃ and 0.5MPa using polyurethane adhesive to form a gradient pore structure.

[0125] (4) Post-processing: The hot-pressed material is left to mature at room temperature for 24 hours, and then cut, polished and trimmed in a conventional manner to obtain a polyurethane polishing pad. The resulting polishing pad has weak interlayer bonding, is prone to delamination during use, has poor cell continuity, and an incomplete gradient structure.

[0126] Comparative Example 3: A method for preparing a polyurethane polishing pad, the specific steps of which are as follows:

[0127] Preparation of polyurethane prepolymer: 80 parts of polyether polyol with a molecular weight of 2000 and a functionality of 2 were added to a three-necked flask and stirred at 120°C under oil bath conditions for 1.5 h under vacuum to remove moisture and small molecule impurities. The mixture was then allowed to cool naturally to 70°C. 60 parts of polymeric MDI were added and stirred until homogeneous. The temperature was gradually increased to 90°C. Dibutyltin dilaurate (DBTDL) catalyst, accounting for 0.04 wt% of the total mass of the prepolymer, was added and stirred under N2 protection for 2 h. The NCO content was determined by dibutylamine-toluene titration. The reaction was stopped when the NCO content reached 15%. The mixture was then degassed under vacuum for 30 min to obtain the polyurethane prepolymer.

[0128] Preparation of the mixture: Polymerized MDI, DBTDL, and dimethyl thiotoluene diamine (DMTDA) were placed in an oven at 110℃ and dried for 2 hours. 70 parts of the dehydrated polyester polyol were added to the dried reaction vessel, along with 4.0 wt% DBTDL and 0.3 parts deionized water. The mixture was stirred at 1500 rpm for 30 seconds until homogeneous to obtain the first mixture. The above polyurethane prepolymer, 10 parts DMTDA, and 15 parts alumina filler were mixed evenly, and 50 parts of polymerized MDI were added. The mixture was stirred at 1500 rpm for 30 seconds to obtain the second mixture. The mass ratio of the first mixture to the second mixture was controlled to be 1:0.8.

[0129] (3) Room temperature natural foaming: The second mixture is quickly poured into the first mixture and stirred at 1500 rpm for 15 seconds. It is then quickly poured into a normal foaming mold and allowed to foam and solidify naturally at room temperature for 2 hours without microwave assistance or external heating to obtain polyurethane foam material.

[0130] (4) Post-processing: The foamed polyurethane material is placed at room temperature for 24 hours to mature, and then cut, polished and trimmed in a conventional manner to obtain a polyurethane polishing pad. The resulting polishing pad has an extremely uneven pore size distribution, with a large number of cross-holes and cell collapse defects, no effective gradient structure, poor mechanical properties, and cannot meet the requirements for precision polishing.

[0131] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a polyurethane polishing pad with gradient pore size, characterized in that, Includes the following steps: The polyether polyol was stirred and dehydrated under vacuum in an oil bath at 100-140℃ for 1-2 hours. After cooling to 60-80℃, isocyanate was added, the temperature was raised to 80-100℃ and a catalyst was added. The reaction was carried out under nitrogen protection for 1.5-3.0 hours to obtain the polyurethane prepolymer. Isocyanate, catalyst, and curing agent are dried and dehydrated, and then mixed with polyester polyol, catalyst, and foaming agent to prepare a first mixture. A second mixture is prepared by mixing polyurethane prepolymer, curing agent, filler, and isocyanate. The first mixture and the second mixture are mixed and stirred for 10-20 seconds and then poured into a mold with a microwave coil layer. The microwave parameters are adjusted to assist foaming, forming a gradient pore size foam material along the thickness direction. The foamed material is cut and trimmed to obtain a polyurethane polishing pad with gradient pore size.

2. The preparation method according to claim 1, characterized in that, The polyether polyol has a molecular weight of 400-4000 and a functionality of 2; the isocyanate is polymeric MDI; and the catalyst is dibutyltin dilaurate.

3. The preparation method according to claim 2, characterized in that, The foaming agent is water; the curing agent is dimethylthiotoluene diamine; and the filler is one of cerium oxide, aluminum oxide, zirconium oxide, and silicon carbide.

4. The preparation method according to claim 3, characterized in that, The first mixture is prepared by stirring polyester polyol, catalyst, and foaming agent at a stirring speed of 1000-2000 rpm for 20-45 seconds; the second mixture is prepared by stirring polyurethane prepolymer, curing agent, filler, and isocyanate at a stirring speed of 1000-2000 rpm.

5. The preparation method according to claim 4, characterized in that, The mass ratio of the first mixture to the second mixture is 1:0.5 to 1.

6. The preparation method according to claim 5, characterized in that, The microwave foaming parameters are: power 500W~1500W, frequency 25KHz~125KHz, time 5~15s; microwaves are applied through a coil generator, and the aperture gradient in the thickness direction is controlled by energy attenuation.

7. The preparation method according to claim 6, characterized in that, After mixing the first and second mixtures, the stirring speed is 1000-2000 rpm. After stirring, the mixture is poured into a mold to complete the foaming process.

8. A polyurethane polishing pad obtained by the preparation method according to any one of claims 1-7, characterized in that, The polyurethane polishing pad is an integrally molded structure of polyurethane foam material with a density of 0.20 to 0.50 g / cm³, a Shore C hardness of 45 to 100, and foam pores distributed in a continuous gradient along the thickness direction with a pore size range of 2 to 150 μm.

9. The polyurethane polishing pad according to claim 8, characterized in that, The gradient pore size is formed by microwave-assisted foaming in one step, and the pore size is continuously and gradually changed along the thickness direction without interlayer interfaces.

10. The polyurethane polishing pad according to claim 9, characterized in that, The polyurethane polishing pad is used for chemical mechanical polishing of semiconductor wafers, precision optical glass, and 3C products.

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