A method for producing ultrafine grit sandpaper for precision polishing

Abstract

This invention relates to the field of sandpaper production technology, and in particular to a method for producing ultrafine-grained sandpaper for precision grinding, overcoming the shortcomings of existing technologies. The method includes the following steps: S1, suspension preparation; S2, microfluidic cutting; S3, ultrasonic atomization spraying; S5, directional sedimentation and solidification. Compared with existing technologies, this invention, through a system-level methodology, organically combines microfluidics, ultrasonic physics, electrostatics, and rheological control, filling the technological gap in the precise control of particle micro-arrangement in the field of ultrafine-grained sandpaper manufacturing, and has significant industrial application value.

Description

Technical Field

[0001] This invention relates to the field of sandpaper production technology, and in particular to a method for producing ultrafine-grained sandpaper for precision polishing. Background Technology

[0002] With the rapid development of semiconductor manufacturing and precision optical processing technologies, ultra-precision grinding has become a crucial step in ensuring workpiece surface quality. As a core consumable in the grinding process, ultra-fine grit sandpaper plays an irreplaceable role in high-precision processing scenarios such as wafer polishing and lens grinding. These applications place extremely high demands on the abrasive particle size distribution, uniformity of arrangement, and consistency of cutting performance on the sandpaper surface, directly affecting the yield and surface roughness of the final product.

[0003] The production of ultrafine abrasive paper primarily relies on the coating and fixation technology of abrasive particles onto the substrate surface. Existing production processes typically involve the preparation of abrasive slurry, the application of a substrate binder, and the implantation of the abrasive particles onto the substrate surface via electrostatic abrasive coating or roller coating. This process aims to achieve stable adhesion of abrasive particles to the substrate and attempts to control the abrasive distribution density through adjustments to process parameters, thereby meeting the fundamental requirement of uniform cutting force in precision grinding.

[0004] However, traditional abrasive coating processes face significant challenges when processing nano- or submicron-sized ultrafine abrasives. Due to the extremely small particle size, the van der Waals forces and electrostatic attraction between particles are significantly enhanced, leading to a high likelihood of micro-agglomeration of the abrasive during slurry preparation or coating. These agglomerated large particle clusters generate random deep scratches during grinding, severely compromising the microscopic uniformity of the workpiece surface. Simultaneously, existing processes lack precise control over individual abrasive particles, making it difficult to achieve uniform, single-particle distribution of abrasive on the substrate surface, easily resulting in localized abrasive buildup. This not only reduces the effective cutting area of ​​the sandpaper but also causes localized overheating due to uneven cutting force distribution, thereby affecting the physical properties of precision parts.

[0005] Therefore, we propose a method for producing ultrafine grit sandpaper for precision polishing to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a method for producing ultrafine-grained sandpaper for precision polishing, so as to solve the problems mentioned in the background art.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for producing ultrafine grit sandpaper for precision polishing includes the following steps: S1. Preparation of suspension: The ultrafine abrasive, dispersant and solvent are mixed. The primary agglomerates of the ultrafine abrasive are broken up by the high shear stress field generated by the high shear emulsifier. The dispersant molecules build a steric hindrance effect or electrostatic repulsion effect on the surface of the ultrafine abrasive to form a suspension with a first preset mass fraction. S2. Microfluidic cutting: The suspension is injected into the central channel of the microfluidic chip as the dispersed phase fluid, while the continuous phase fluid is injected into the lateral channels of the microfluidic chip. The continuous phase fluid and the dispersed phase fluid are immiscible. At the intersection of the channels, the continuous phase fluid is used to squeeze and shear the dispersed phase fluid to periodically cut the dispersed phase fluid, forming microdroplets with abrasive particles and high monodispersity. S3, Ultrasonic Atomization Spray: After the microdroplets are discharged from the outlet of the microfluidic chip, they enter the ultrasonic atomization area. The high-frequency vibration generated by the piezoelectric ceramic transducer causes the capillary waves on the surface of the microdroplets to become unstable and split into secondary droplets. During the movement of the secondary droplets toward the substrate, they are loaded with the same charge through high-voltage corona discharge. S4. Substrate pretreatment: Apply an adhesive selected from UV-curable resin, epoxy resin or polyurethane resin to the surface of the corona-treated polyethylene terephthalate substrate and pre-dry it. By controlling the amount of solvent residue, the adhesive is in a semi-dry state when it reaches the sand planting area. S5. Directional Settling and Curing: Under the guidance of electrostatic force and airflow, charged secondary droplets move directionally to the surface of polyethylene terephthalate substrate. The Coulomb repulsion between the secondary droplets automatically adjusts the distribution spacing in space, so that the secondary droplets are uniformly deposited on the surface of the semi-dry adhesive layer. Then, ultraviolet light irradiation is used to trigger the cross-linking polymerization reaction of the adhesive, locking the ultrafine abrasive in the preset position to form uniformly distributed ultrafine sandpaper.

[0008] Compared with the prior art, the beneficial effects achieved by the present invention are: 1. This invention utilizes microfluidic technology to cut abrasive suspensions into micron-sized droplets, achieving individualized isolation of abrasive particles in physical space. Because each microdroplet is encapsulated by a continuous phase fluid during its formation, and statistical probability control ensures that the vast majority of droplets contain only a single abrasive particle, the agglomeration of ultrafine abrasives caused by van der Waals forces and electrostatic attraction is eliminated at the source. Combined with subsequent ultrasonic atomization and charge loading technologies, the abrasive remains in a monolithic state until it is deposited onto the substrate, eliminating the risk of random deep scratches caused by abrasive clusters and significantly improving the surface roughness consistency of the workpiece after precision grinding.

[0009] 2. This invention utilizes the Coulomb repulsion effect between charged droplets to construct a self-organized arrangement mechanism during the abrasive deposition process. As the like-charged abrasive droplets move towards the substrate, the repulsive force between them ensures their equidistant spatial distribution, avoiding abrasive accumulation or blank areas common in traditional electrostatic abrasive deposition processes. By precisely adjusting the microfluidic flow rate ratio, ultrasonic frequency, and substrate travel speed, quantitative control of the abrasive distribution density can be achieved. This uniform distribution at the monomer level results in extremely uniform cutting force distribution during sanding, effectively preventing localized overheating, extending the lifespan of the sandpaper, and ensuring the processing quality of high-value workpieces.

[0010] 3. This invention organically combines microfluidics, ultrasonic atomization, and high-voltage electrostatic sand deposition to construct a continuous production process. By controlling the binder at a preset viscosity, the technical challenge of stable positioning of ultrafine abrasive particles in a wet coating is solved. The introduction of ultraviolet light rapid curing technology ensures that individual abrasive particles are instantly locked upon contact with the substrate, maintaining the stability of their microscopic arrangement. The entire process parameters are highly controllable and repeatable, resulting in sandpaper with extremely low surface quality deviations, meeting the stringent requirements of the precision optics and semiconductor industries for high-quality abrasive consumables.

[0011] 4. For nanoscale abrasives with a preset mesh size of high or higher, traditional processes often cannot achieve precise abrasive deposition due to limitations in fluid dynamics. This invention further refines the droplets through ultrasonic atomization and utilizes electric field force to overcome the interference of gravity and air resistance, achieving directional and quantitative sedimentation of nanoparticles. This microscopic manipulation capability of extremely fine particles fills the gap in existing ultrafine abrasive paper production technology and provides reliable technical support for achieving higher levels of surface roughness.

[0012] In summary, this invention, through a system-level methodology, organically combines microfluidics, ultrasonic physics, electrostatics, and rheological control, filling the technological gap in the precise control of particle micro-arrangement in the field of ultrafine sandpaper manufacturing, and has significant industrial application value. Attached Figure Description

[0013] The technical solution and other beneficial effects of this application will become apparent from the following detailed description of specific embodiments in conjunction with the accompanying drawings.

[0014] In the attached diagram: Figure 1 This is a schematic diagram of the overall technical solution architecture of a method for producing ultrafine-grained sandpaper for precision polishing proposed in this invention. Figure 2 This is a schematic diagram of the core principle framework of individualized isolation and Coulomb repulsion self-organized arrangement of abrasive particles in this invention; Figure 3This is a flowchart illustrating the logical flow framework of the present invention, from microfluidic cutting of suspension to directional deposition of abrasive. Detailed Implementation

[0015] The following disclosure provides many different embodiments or examples for implementing different structures of this application. To simplify the disclosure, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the scope of this application. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, various specific examples of processes and materials are provided in this application, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0016] See attached document Figure 1-3 To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments.

[0017] Example 1: A method for producing ultrafine-grained sandpaper for precision grinding, the specific implementation process of which involves precise control of the entire process from micro-particle manipulation to macro-coating and curing. This method achieves monomer-level uniform distribution of abrasive particles on the substrate surface through the deep coupling of microfluidic technology, ultrasonic atomization technology and high-voltage electrostatic sanding technology.

[0018] Step 1, Suspension preparation: First, ultrafine abrasives are selected as the cutting material. The abrasive material is chosen from one or more combinations of diamond powder, cubic boron nitride, silicon carbide, and alumina, depending on the hardness and surface characteristics of the workpiece. The average particle size of the abrasive is controlled between 0.1 μm and 5 μm, corresponding to a mesh size between 3000 and 15000 mesh. To ensure the independence of the abrasive in subsequent processes, the raw abrasive is pretreated, including 3-5 ultrasonic cleanings with deionized water to remove adsorbed impurity ions from the surface, followed by drying in a vacuum oven at 120°C for 24 hours.

[0019] Subsequently, the pretreated abrasive, dispersant, and solvent are mixed according to a preset ratio. The dispersant is selected based on the isoelectric point of the abrasive surface and the polarity of the solvent, and is chosen from anionic surfactants (such as sodium dodecylbenzenesulfonate), cationic surfactants (such as hexadecyltrimethylammonium bromide), or nonionic surfactants (such as polyvinylpyrrolidone). The amount of dispersant added is adapted to the mass of the ultrafine abrasive, usually controlled at 1%-3% of the abrasive mass, to reduce the surface energy of the abrasive particles through steric hindrance or electrostatic repulsion effects, thus inhibiting initial agglomeration. The solvent is one or a mixture of deionized water, anhydrous ethanol, and isopropanol, and its viscosity and surface tension must meet the hydrodynamic requirements of the subsequent microfluidic chip.

[0020] The above components are added to a high-shear emulsifier and continuously stirred at 3000-8000 rpm for 30-60 minutes. During this process, the high-speed rotor of the emulsifier generates strong radial and axial flows, forming an extremely high shear stress field, which completely breaks down any potential primary abrasive agglomerates. The prepared suspension has a mass fraction of 5%-15% and does not exhibit significant sedimentation or stratification within 24 hours, with its dynamic viscosity remaining between 2-10 mPa·s.

[0021] Step 2, microfluidic cutting: The prepared suspension is used as the dispersed phase, while a continuous phase fluid is prepared simultaneously. The continuous phase fluid is selected from transparent fluids that are immiscible with the suspension (such as dimethyl silicone oil, perfluoropolyether oil, or liquid paraffin). To enhance the stability of the two-phase interface, the viscosity of the continuous phase fluid is set to be greater than that of the dispersed phase suspension, typically between 20 and 100 mPa·s.

[0022] The microfluidic chip employs a cross-shaped focusing channel structure, with its internal channels fabricated from polydimethylsiloxane or glass using micro- and nano-fabrication techniques. The characteristic width of the channels is set between 50 μm and 200 μm. The suspension is injected at a constant flow rate from the central channel via a precision injection pump, while the continuous phase fluid is injected at a higher flow rate from the two symmetrical channels on either side. At the central region where the channels converge, the continuous phase fluid exerts strong compression and shearing forces on the dispersed phase fluid. By adjusting the two-phase flow rate ratio, the dispersed phase fluid is periodically "cut off" under shear force, forming a series of highly monodisperse microdroplets.

[0023] The diameter of the microdroplets is precisely controlled by adjusting the flow rate ratio. According to the fluid dynamics model, the formation diameter of the microdroplets follows the following rules:

[0024] in, Indicates the diameter of the generated microdroplets. Indicates the characteristic width of the flow channel. This indicates the flow rate of the dispersed phase suspension. This represents the total flow rate of the continuous phase fluid. (The text then abruptly shifts to a different topic:) and The ratio was controlled between 5:1 and 20:1, and the diameter of the generated microdroplets was locked between 10 and 100 μm.

[0025] The generation frequency of microdroplets is controlled within the range of 500-5000 Hz. Based on the statistical relationship between the volume fraction of abrasive particles in the suspension and the volume of microdroplets, precise calculations ensure that more than 90% of the microdroplets contain only a single abrasive particle. If the abrasive concentration is too high, the suspension is diluted to reduce the probability of two or more particles appearing in a single droplet; if the concentration is too low, the generation frequency is increased to ensure production efficiency.

[0026] Step 3, ultrasonic atomization spray: Microdroplets encapsulating individual abrasive particles are continuously discharged from the outlet of the microfluidic chip and directly enter the working area of ​​the ultrasonic atomizing transducer. The core components of the ultrasonic atomizer include a piezoelectric ceramic transducer and an atomizing head made of titanium alloy. The transducer's operating frequency is set within a preset range of 100kHz-2.4MHz.

[0027] When microdroplets come into contact with the surface of the high-speed vibrating atomizing head, a violent ultrasonic cavitation effect is generated inside the droplet, and the capillary waves on the droplet surface become unstable because the amplitude exceeds a critical value. This instability causes the original microdroplet to rapidly split into even smaller secondary droplets, with a particle size distribution between 1 and 10 μm. During atomization, the dry airflow in the atomization chamber accelerates the evaporation of solvent on the droplet surface, resulting in a significant reduction in the thickness of the solvent layer coating the abrasive particles.

[0028] A high-voltage corona discharge ring is installed at the outlet of the atomizing nozzle. A negative voltage of 5-20KV is applied to the discharge ring by a high-voltage DC power supply, causing each secondary droplet passing through this area to acquire a negative charge of the same polarity through ion collision. The amount of charge is controlled by adjusting the voltage value to ensure that the droplet charge reaches 30% to 60% of the Rayleigh limit, thereby ensuring sufficient electrostatic stability of the droplets during flight. Guided by the airflow, the charged droplets are sprayed downwards in a cone-shaped mist.

[0029] Step 4, Substrate Pretreatment: Polyethylene terephthalate (PET) substrate, used as the carrier for the abrasive, has a thickness selected from 50-125 μm. Before entering the coating stage, the PET substrate first undergoes an online corona treatment machine, where high-voltage corona discharge breaks down the molecular chains on the substrate surface, introducing polar groups such as hydroxyl and carboxyl groups, increasing its surface energy to over 45 dyn / cm to enhance the wettability of the binder.

[0030] Subsequently, a uniform layer of binder is continuously coated onto the surface of the PET substrate using a slot extrusion coater. The binder comprises UV-curable acrylate resin, photoinitiator, leveling agent, and coupling agent. The dry film thickness of the coating is controlled between 40% and 60% of the average abrasive particle size.

[0031] The coated substrate enters the pre-drying zone. The pre-drying zone uses infrared radiation heating combined with hot air circulation, with the temperature controlled between 60℃ and 90℃. By adjusting the length of the drying tunnel and the substrate's running speed, the residual solvent in the binder is controlled, ensuring the binder is in a specific semi-dry state when it reaches the sand-planting zone. At this point, the surface viscosity of the binder is precisely controlled between 10-50 Pa·s. This viscosity range ensures that the settled abrasive particles are effectively captured upon contact, while preventing them from being completely submerged in the binder due to gravity or impact, ensuring the cutting edge of the abrasive is effectively exposed.

[0032] Step 5, Directional Settlement and Solidification: The sedimentation chamber contains a controlled physical field environment. Negatively charged abrasive droplets enter the chamber and are attracted by the electrostatic force generated by the grounding plate at the bottom, moving directionally towards the substrate surface. The airflow velocity within the chamber is controlled at 0.2-0.5 m / s, aligned with the electric field lines, serving as an auxiliary guide.

[0033] Because each droplet carries the same negative charge, there is a significant Coulomb repulsion between them. This repulsion plays a role in automatically adjusting the spatial distance between droplets during flight. According to Coulomb's law, the repulsive force between two charged droplets follows this rule:

[0034] in, Coulomb repulsion, The vacuum permittivity, For the charge of a single droplet, This represents the center-to-center distance between droplets. When two droplets approach each other, the repulsive force increases dramatically, forcing the droplets to tend towards an evenly spaced distribution in space.

[0035] When charged droplets are deposited on the surface of a semi-dry binder layer with a viscosity of 10-50 Pa·s, the kinetic energy of the droplets is rapidly absorbed due to the damping effect of the binder, and the abrasive particles and their residual solvent are locked at the deposition site. Due to the continuous presence of Coulomb repulsion, the abrasive particles deposited on the substrate surface exhibit a highly regular and equidistant arrangement, effectively avoiding secondary contact and agglomeration of the abrasive particles.

[0036] Finally, the sand-coated substrate enters the UV curing tunnel. The curing tunnel is equipped with a high-power high-pressure mercury lamp or a light-emitting diode (LED-UV) UV light source, with the main peak of the output wavelength located at 365 nm. The irradiation energy density is set at 800-1500 mJ / cm². Under strong UV irradiation, the photoinitiator inside the adhesive rapidly decomposes to generate free radicals, initiating a highly cross-linked polymerization reaction of the acrylate monomers. Within 1-3 seconds, the adhesive transforms from a semi-dry state into a fully cured hard film, firmly locking the individual abrasive particles onto the surface of the PET substrate, forming ultra-fine-grained sandpaper with a uniform monomer distribution.

[0037] Specific application example 1: Preparation of 5000-grit diamond precision sandpaper In this application example, diamond micropowder with an average particle size of 2.5 μm was selected. During the suspension preparation stage, deionized water was used as the solvent, and 2% by mass of polyvinylpyrrolidone was added as a dispersant. The mass fraction of diamond micropowder was set to 10%. The mixture was treated at a shear speed of 5000 rpm for 45 minutes.

[0038] In the microfluidic cutting stage, a cross-channel chip with a feature width of 100 μm was selected. The continuous phase used was dimethyl silicone oil at 50 mPa·s. The flow rate of the dispersed phase was set at 0.05 mL / min, and the flow rate of the continuous phase was set at 0.8 mL / min. Online microscopy observation showed that the diameter of the microdroplets stabilized at 45 ± 2 μm, and the droplet generation frequency was approximately 1200 Hz.

[0039] During the ultrasonic atomization stage, the transducer operating frequency was set to 1.7 MHz. The atomized secondary droplets were charged under a negative high-voltage electric field of 15 kV. A 75 μm thick PET film was used as the substrate, and the adhesive coating thickness was 1.2 μm. After pre-drying, the adhesive viscosity was adjusted to 30 Pa·s.

[0040] The final sandpaper was characterized by scanning electron microscopy (SEM). The surface distribution density of abrasive particles was 12,000-13,000 per square millimeter, with single particles accounting for more than 95%, and no obvious agglomerations of more than three particles. When grinding a single-crystal silicon wafer, the surface roughness Ra after processing reached 8 nanometers, and there were no random deep scratches visible to the naked eye.

[0041] Specific Application Example 2: Preparation of 10000-mesh silicon carbide ultrafine polishing belt In this application example, green silicon carbide abrasive with an average particle size of 1 μm was selected. The suspension mass fraction was set to 8%, a mixture of isopropanol and deionized water was used as the solvent, and sodium dodecylbenzenesulfonate was selected as the dispersant.

[0042] The flow rate ratio of the microfluidic chip was adjusted to 20:1 to further reduce the probability of dual particles in the microdroplets. The ultrasonic atomization frequency was increased to 2.4MHz to generate finer droplets to accommodate abrasive particles with a diameter of 1μm. The voltage of the high-voltage electrostatic field was increased to 18KV to enhance the Coulomb repulsion between particles.

[0043] The adhesive used on the substrate surface employs a low-shrinkage UV-curing system, with the coating thickness controlled at 0.5 μm. The curing energy density is increased to 1200 mJ / cm² to ensure a strong bond at the bottom of the ultrafine particles. The produced polishing tape exhibits extremely high consistency in the end-face polishing of ceramic ferrules for fiber optic connectors, increasing the geometric parameter pass rate of the ferrule end face from 85% in conventional processes to over 98%.

[0044] Example 2: Based on Example 1, this example provides an alternative for non-aqueous suspension systems to produce water-sensitive precision grinding consumables.

[0045] In step 1, the solvent is replaced with a mixture of anhydrous ethanol and ethylene glycol methyl ether. Because organic solvents evaporate rapidly, during the ultrasonic atomization process in step 3, the solvent can be rapidly partially evaporated by adjusting the temperature of the atomization chamber to 40°C. This ensures that before the secondary droplets contact the substrate, the abrasive particles inside are surrounded by only a very thin solvent film, further reducing the droplet mass and improving its response sensitivity in an electric field.

[0046] In step 2, the continuous phase fluid is replaced with a highly fluorinated perfluoropolyether oil. Perfluoropolyether oil possesses extremely low surface energy and extremely high chemical stability, enabling it to form clear interfaces with most organic solvents, thereby maintaining the monodispersity of microdroplets at higher shear rates. Experimental data show that when using fluorinated oil as the continuous phase, the microdroplet size distribution coefficient (CV value) can be reduced to below 3%.

[0047] In step 4, the binder system is adjusted to a hybrid system of epoxy acrylate and polyurethane acrylate. This system exhibits a wider viscosity window during the pre-drying stage, allowing for viscosity control of 10-50 Pa·s within the temperature range of 60℃-100℃ by controlling the time. Furthermore, the hybrid system exhibits better toughness after curing, effectively supporting the lateral impact force of abrasive particles during high-speed grinding.

[0048] In step 5, to further improve the accuracy of abrasive arrangement, the grounding plate at the bottom of the settling chamber is replaced with an electrode array with a micro-grid structure. By applying a spatially modulated electric field to the electrode array, charged droplets can be induced to deposit according to a preset geometric pattern (such as hexagonal close packing), thereby achieving digital customization of sandpaper cutting performance.

[0049] Example 3: This example focuses on describing an optimized production process for nanoscale abrasives (above 15,000 mesh), mainly targeting the final polishing requirements of semiconductor wafers.

[0050] In step 1, nanodiamonds with a particle size of 200-500 nanometers were selected as the abrasive. Due to the strong tendency of nanoparticles to aggregate, a planetary ball milling process was introduced when preparing the suspension. The abrasive, solvent, and dispersant were placed in a zirconia ball mill jar and ball-milled at 400 rpm for 12 hours. The strong impact and friction during the ball milling process ensured that the surface of the nanoparticles was completely covered by dispersant molecules, forming a stable colloidal system.

[0051] In step 2, the flow channel surface of the microfluidic chip is treated with a nano-coating to give it superoleophobic properties. This treatment effectively prevents the adsorption and retention of nano-abrasives on the flow channel walls, ensuring the long-term stability of the production process. The mass fraction of the dispersed phase suspension is reduced to 5% to match the volumetric statistical distribution of the nanoscale particles.

[0052] In step 3, a dual-fluid ultrasonic atomizing nozzle is employed. A high-speed auxiliary airflow is introduced simultaneously with ultrasonic vibration. This auxiliary airflow not only helps to further refine the droplets but also provides additional momentum after the droplets are charged, overcoming the disadvantage that nano-sized droplets are highly susceptible to surrounding air disturbances. The electrostatic voltage is set at 12KV, and the uniformity of corona discharge is improved by optimizing the geometry of the discharge needle.

[0053] In step 4, a 200-nanometer-thick primer is pre-coated onto the surface of the PET substrate to enhance the chemical bonding between the main adhesive and the substrate. The main adhesive is a low-viscosity, high-hardness nanocomposite resin containing 5% by mass of nano-silica reinforcing phase.

[0054] In step 5, high-purity nitrogen is filled into the settling chamber as a protective gas, and the ambient humidity is controlled below 30%. A dry environment helps maintain the stability of the droplet charge and prevents charge loss due to excessive air humidity. The curing process uses a stepped irradiation method. First, low-power ultraviolet light is used for pre-fixation to initially lock the abrasive particles in place, and then high-power ultraviolet light is used for deep curing. This effectively reduces the volume shrinkage stress during the curing process and ensures the microscopic smoothness of the nano-abrasive particle distribution.

[0055] Testing showed that the spacing deviation of the abrasive particles on the surface of the nanoscale sandpaper produced in this embodiment was controlled within 15%. When polishing silicon carbide wafers, the surface roughness RMS value can reach below 0.2 nanometers, fully meeting the stringent requirements of third-generation semiconductor substrate processing.

[0056] The above provides a detailed description of a method for producing ultrafine sandpaper for precision grinding, as provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for producing ultrafine-grained sandpaper for precision polishing, characterized in that, Includes the following steps: S1. Preparation of suspension: The ultrafine abrasive, dispersant and solvent are mixed. The primary agglomerates of the ultrafine abrasive are broken up by the high shear stress field generated by the high shear emulsifier. The dispersant molecules build a steric hindrance effect or electrostatic repulsion effect on the surface of the ultrafine abrasive to form a suspension with a first preset mass fraction. S2. Microfluidic cutting: The suspension is injected into the central channel of the microfluidic chip as the dispersed phase fluid, while the continuous phase fluid is injected into the lateral channels of the microfluidic chip. The continuous phase fluid and the dispersed phase fluid are immiscible. At the intersection of the channels, the continuous phase fluid is used to squeeze and shear the dispersed phase fluid to periodically cut the dispersed phase fluid, forming microdroplets with abrasive particles and high monodispersity. S3, Ultrasonic Atomization Spray: After the microdroplets are discharged from the outlet of the microfluidic chip, they enter the ultrasonic atomization area. The high-frequency vibration generated by the piezoelectric ceramic transducer causes the capillary waves on the surface of the microdroplets to become unstable and split into secondary droplets. During the movement of the secondary droplets toward the substrate, they are loaded with the same charge through high-voltage corona discharge. S4. Substrate pretreatment: Apply an adhesive selected from UV-curable resin, epoxy resin or polyurethane resin to the surface of the corona-treated polyethylene terephthalate substrate and pre-dry it. By controlling the amount of solvent residue, the adhesive is in a semi-dry state when it reaches the sand planting area. S5. Directional Settling and Curing: Under the guidance of electrostatic force and airflow, charged secondary droplets move directionally to the surface of polyethylene terephthalate substrate. The Coulomb repulsion between the secondary droplets automatically adjusts the distribution spacing in space, so that the secondary droplets are uniformly deposited on the surface of the semi-dry adhesive layer. Then, ultraviolet light irradiation is used to trigger the cross-linking polymerization reaction of the adhesive, locking the ultrafine abrasive in the preset position to form uniformly distributed ultrafine sandpaper.

2. The method for producing ultrafine-grained sandpaper for precision polishing according to claim 1, characterized in that, In step S1, the ultrafine abrasive is selected from one or more combinations of diamond powder, cubic boron nitride, silicon carbide or alumina. The ultrafine abrasive needs to be pretreated before mixing. The pretreatment includes multiple ultrasonic cleanings with deionized water to remove adsorbed impurity ions on the surface of the ultrafine abrasive, followed by drying in a vacuum environment at 120°C. The dispersant is selected from one or more combinations of anionic surfactants, cationic surfactants, or nonionic surfactants, and the solvent is one or more mixtures of deionized water, anhydrous ethanol, and isopropanol. The amount of dispersant added is adapted to the surface isoelectric point of the ultrafine abrasive and the polarity of the solvent. The surface energy of the ultrafine abrasive particles is reduced by the physical adsorption or chemical bonding of the dispersant molecular chains on the surface of the ultrafine abrasive particles. The high-shear emulsifier generates radial and axial flow under the action of a high-speed rotor, creating a shear stress field inside the suspension. The force of the shear stress field is greater than the van der Waals force between ultrafine abrasive particles.

3. The method for producing ultrafine-grained sandpaper for precision polishing according to claim 1, characterized in that, In step S2, the microfluidic chip adopts a cross-focusing flow channel structure. Its internal flow channel is made of polydimethylsiloxane or glass material through micro-nano processing technology. The internal flow channel has a preset characteristic width between 50-200μm. The continuous phase fluid is selected from one of silicone oil, perfluoropolyether oil or liquid paraffin. The viscosity of the continuous phase fluid is set to be greater than the viscosity of the dispersed phase fluid. By adjusting the flow rate ratio of the continuous phase fluid to the dispersed phase fluid, the diameter of the generated microdroplets is controlled by the functional relationship between the characteristic width and the flow rate ratio. Based on the statistical correspondence between the volume fraction of abrasive in the suspension and the volume of microdroplets, the generation frequency of microdroplets is adjusted to ensure that more than 90% of the microdroplets contain only a single abrasive particle, thus achieving individualized isolation of abrasive particles in physical space.

4. The method for producing ultrafine-grained sandpaper for precision polishing according to claim 1, characterized in that, In step S3, the piezoelectric ceramic transducer is coupled to the atomizing head made of titanium alloy. Its working frequency is set between 100KHz and 2.4MHz. It is transmitted to the microdroplets through mechanical vibration, which induces the ultrasonic cavitation effect inside the microdroplets. The secondary droplets fly in the dry air flow in the atomizing chamber. The solvent on the surface of the secondary droplets evaporates, resulting in a reduction in the thickness of the solvent layer wrapped on the surface of the abrasive particles. A high-voltage corona discharge ring is installed at the outlet of the atomizing head. A negative high voltage is applied to the discharge ring by a high-voltage DC power supply, so that each secondary droplet passing through the area carries a charge of the same polarity through ion collision. The charge of the secondary droplets is controlled by adjusting the value of the negative high voltage to ensure that the secondary droplets have electrostatic stability during flight.

5. The method for producing ultrafine-grained sandpaper for precision polishing according to claim 1, characterized in that, In step S4, before entering the coating section, the polyethylene terephthalate substrate is subjected to corona discharge generated by an online corona treatment machine to destroy the molecular chains on the surface of the substrate and introduce hydroxyl or carboxyl polar groups, so that the surface energy of the substrate can be increased to a preset energy threshold of 45dyn / cm or more, thereby enhancing the wetting performance of the adhesive on the surface of the substrate. The binder forms a uniform coating on the substrate surface through a slot extrusion coating process, and the thickness of the coating is set according to the average particle size of the ultrafine abrasive. The pre-drying process is carried out in a constant temperature oven, using infrared radiation heating combined with hot air circulation mode. By adjusting the drying time and temperature, the binder is brought to a specific viscosity range. The damping effect generated by the viscosity range captures secondary droplets while preventing ultrafine abrasive particles from being completely submerged in the binder due to gravity or impact.

6. The method for producing ultrafine-grained sandpaper for precision polishing according to claim 1, characterized in that, In step S5, directional sedimentation is carried out in a sand-planting sedimentation chamber equipped with a bottom grounding electrode plate. The charged secondary mist droplets are attracted by the electrostatic field force generated by the grounding electrode plate and move towards the substrate in a cone-shaped mist band. The airflow velocity in the sand-planting settling chamber is controlled, and the airflow direction is consistent with the direction of the electric field lines; Due to the continuous presence of Coulomb repulsion, the abrasive particles deposited on the substrate surface are arranged at equal intervals, eliminating the risk of random deep scratches caused by abrasive accumulation. Ultraviolet light irradiation is achieved through a high-pressure mercury lamp or a light-emitting diode ultraviolet light source. The output wavelength of the light source matches the photoinitiator in the binder, initiating highly cross-linked polymerization of the monomers and transforming the binder from a semi-dry state into a fully cured hard film, thereby locking the position of individual abrasive particles.

7. The method for producing ultrafine-grained sandpaper for precision polishing according to claim 1, characterized in that, For abrasives with particle sizes in the nanometer range, a planetary ball milling process is introduced in step S1 to ensure that the dispersant molecules completely cover the surface of the nano abrasive through impact and friction inside the ball mill jar. In step S2, the flow channel surface of the microfluidic chip is treated with a nano-coating to give the flow channel surface super oleophobic properties, preventing the nano abrasives from adsorbing and remaining on the flow channel wall. In step S3, a dual-fluid ultrasonic atomizing nozzle is used to introduce a high-speed auxiliary airflow to further refine the secondary droplets and provide additional momentum to the charged secondary droplets to overcome air turbulence. In step S5, high-purity nitrogen is introduced into the sand settling chamber as a protective gas, and the ambient humidity is controlled below the preset humidity threshold of 30% to maintain the stability of the charge of the secondary droplets. The secondary droplets are cured by step-by-step irradiation. The curing shrinkage stress is reduced by first pre-fixing with low power and then deep curing with high power.

8. The method for producing ultrafine-grained sandpaper for precision polishing according to claim 1, characterized in that, When a non-aqueous solvent is used to prepare a suspension, the continuous phase fluid in step S2 is selected as perfluoropolyether oil, which utilizes the low surface energy characteristics of perfluoropolyether oil to form a physical interface between the dispersed phase fluid and the continuous phase fluid. In step S4, the binder system is adjusted to a hybrid system of epoxy acrylate and polyurethane acrylate. By adjusting the component ratio of the hybrid system, the viscosity control window after pre-drying is expanded, and the toughness of the cured film is improved to support the lateral impact force on the abrasive particles. In step S5, the grounding plate is replaced with an electrode array with a micro-grid structure. By applying a spatially modulated electric field to the electrode array, selective deposition of charged secondary droplets is induced, thereby achieving digital customization of the abrasive arrangement structure on the sandpaper surface.

Images