Efficient grinding fluid for MPO connector as well as preparation method and application of efficient grinding fluid

Abstract

The invention relates to the technical field of grinding fluid, in particular to efficient grinding fluid for an MPO connector, a preparation method and application of the efficient grinding fluid for the MPO connector. 27%-44% of alpha-aluminum oxide; 8%-15% of a styrene-maleic anhydride copolymer; 2%-5% of a modified polyurea solution; 0.05% to 0.3% of perfluoropolyether; 0.5%-2% of citric acid; 0.5%-1.5% of a polyether modified polysiloxane defoaming agent; by adopting a composite abrasive material system of the nano-diamond and the alpha-aluminum oxide, the grinding efficiency and the surface quality are improved in a breakthrough manner.

Description

Technical Field

[0001] This invention relates to the field of polishing slurry technology, specifically to a high-efficiency polishing slurry for MPO connectors, its preparation method, and its application. Background Technology

[0002] With the rapid development of applications such as data centers, 5G communication networks, and fiber-to-the-home (FTTH), MPO connectors, as high-density, high-performance fiber optic connectors, have been widely used. MPO connectors enable the simultaneous connection of multiple fibers in a single interface, significantly improving the integration and connection efficiency of fiber optic networks. However, MPO connectors have extremely stringent requirements for end-face quality; parameters such as surface roughness, fiber concavity, and flatness directly affect the transmission quality and insertion loss of optical signals.

[0003] In the manufacturing process of MPO connectors, end face grinding is a crucial step. Currently, the industry generally adopts a multi-step grinding process to achieve precision machining of the end face. According to the technical article "Lapping film options, part 3 – MPO-type connectors" (2023) published by Fiber Optic Center, the traditional MPO connector grinding process typically includes three stages: first, using 3-micron silicon carbide abrasive to remove excess epoxy resin and perform preliminary shaping; second, using 1-micron alumina abrasive for intermediate grinding to improve surface morphology; and finally, using submicron-level cerium oxide or silicon dioxide for final polishing to obtain optical-grade surface quality.

[0004] However, existing polishing slurry technologies have many shortcomings. Chinese patent CN102648265B discloses... CMP slurry Material composition and polishing method While this composition performs well in semiconductor wafer polishing, its single abrasive system is inefficient in MPO connector polishing applications, making it difficult to achieve ideal surface quality in a short time. Furthermore, the polishing slurry described in this patent is primarily designed for silicon-based materials, while the core material of MPO connectors is a polymer. The significant differences in material properties between the two lead to substantial differences in the polishing mechanism and optimal formulation.

[0005] US Patent US20170037290A1 discloses CMP polishing agent, its manufacturing method and method for polishing substratesOne patent discloses a CMP abrasive containing a styrene-acrylonitrile copolymer, which improves abrasive selectivity by forming a protective film. However, this patent uses a styrene-acrylonitrile copolymer instead of a styrene-maleic anhydride copolymer, and the two have fundamentally different dispersion mechanisms and water solubility. More importantly, the patent's technical solution lacks lubrication and protection measures for polymer ferrule materials such as MPO connectors, making them prone to scratches and damage during the abrasive process.

[0006] Furthermore, according to the research paper "The Stability Evaluation of Ceria Slurry Using Polymer Dispersants with Varying Contents for Chemical Mechanical Polishing Process" published in the MDPI journal Polymers (December 2024), although polymer dispersants such as styrene-maleic anhydride copolymers have shown good effects in dispersing ceramic particles, this study mainly focuses on the stability of cerium oxide polishing slurries and does not involve composite abrasive systems of diamond and alumina, nor does it consider the application challenges of perfluoropolyether lubricants in water-based polishing slurries.

[0007] Based on existing technologies, the following problems can be identified in current MPO connector polishing slurries: First, it is difficult to achieve both polishing efficiency and surface quality in a single abrasive system. Using abrasives with higher hardness results in faster polishing speeds but is prone to scratches, while using softer abrasives results in better surface quality but lower polishing efficiency. Second, existing dispersant systems lack sufficient dispersion stability for nano-diamond particles, leading to agglomeration and uneven polishing. Third, the lack of effective lubrication measures means that the high friction during polishing not only reduces polishing efficiency but also causes thermal damage to the polymer ferrule. Fourth, the polishing slurry has poor long-term storage stability, and the abrasive particles tend to settle, requiring thorough stirring before use, which increases operational complexity. Fifth, some polishing slurries contain strong alkalis or toxic chemicals, which are highly corrosive to equipment and do not meet environmental protection requirements.

[0008] Therefore, there is an urgent need to develop a new type of polishing slurry for MPO connectors. This slurry should be able to improve polishing efficiency while ensuring excellent surface quality, have good dispersion and storage stability, be friendly to polishing equipment and the environment, and be easy to clean without leaving residue on the polishing pad that could cause subsequent scratches. Summary of the Invention

[0009] To address the aforementioned problems in existing technologies, the present invention aims to provide a high-efficiency polishing slurry for MPO connectors, its preparation method, and its application. This polishing slurry, employing a composite abrasive system of nanodiamond and α-alumina, combined with a styrene-maleic anhydride copolymer dispersant, a modified polyurea anti-settling agent, and a perfluoropolyether lubricant, achieves a perfect balance between polishing efficiency and surface quality, while also exhibiting excellent dispersion stability, storage stability, and environmental friendliness.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a high-efficiency polishing slurry for MPO connectors, comprising, by weight percentage: 3% to 6% nanodiamond, 27% to 44% α-alumina, 8% to 15% styrene-maleic anhydride copolymer, 2% to 5% modified polyurea solution, 0.05% to 0.3% perfluoropolyether, 0.5% to 2% citric acid, 0.5% to 1.5% polyether-modified polysiloxane defoamer, and deionized water to the balance of 100%.

[0011] In a preferred embodiment of the present invention, the average particle size of the nanodiamond is 100 to 150 nanometers, the average particle size of the α-alumina is 0.8 to 1.2 micrometers, and the weight ratio of the nanodiamond to the α-alumina is 1:6 to 1:10. This particle size and ratio design is based on in-depth research into the grinding mechanism: nanodiamond, with its extremely high hardness, can quickly remove protrusions and unevenness on the connector end face, while α-alumina has moderate hardness and good self-lubricating properties, enabling fine smoothing of the surface after diamond cutting. The synergistic effect of the two abrasives makes the grinding process both efficient and gentle, avoiding over-cutting and scratching that may be caused by a single hard abrasive.

[0012] Furthermore, the molar ratio of styrene units to maleic anhydride units in the styrene-maleic anhydride copolymer is 2:1, and the number-average molecular weight is 5,000 to 10,000 g / mol. This specific copolymer structure design stems from a deep understanding of the dispersion mechanism: the styrene units provide hydrophobic segments that can be adsorbed onto the surface of abrasive particles through hydrophobic interactions; while the maleic anhydride units hydrolyze to maleic acid in an alkaline environment, and the negative charge formed by the dissociation of its carboxyl groups provides electrostatic repulsion, while the extended hydrophilic segments create a steric hindrance effect. The synergy of these two forces ensures the high dispersion and long-term stability of the abrasive particles in the grinding fluid.

[0013] Meanwhile, the modified polyurea solution is an aqueous solution of carboxyl-modified polyurea with a carboxyl modification degree of 8% to 12%, a solid content of 30% to 40%, and a weight-average molecular weight of 15,000 to 25,000 g / mol. This modified polyurea can form a three-dimensional network structure in the polishing fluid, suspending abrasive particles within it through hydrogen bonding interactions, effectively preventing sedimentation. More importantly, this network structure imparts thixotropic properties to the polishing fluid: the system maintains a high viscosity in a static state to prevent sedimentation, while the network structure is disrupted during stirring or use, reducing viscosity for easier pumping and coating; and the network structure rapidly recovers after shearing ceases.

[0014] Furthermore, the perfluoropolyether is either a Y-type or a Z-type perfluoropolyether, with a weight-average molecular weight of 2000 to 5000 g / mol and a kinematic viscosity of 100 to 200 centistokes at 25 degrees Celsius. Perfluoropolyether is a fully fluorinated polyether lubricant whose molecular chain is composed of carbon, fluorine, and oxygen, exhibiting extremely low surface tension and coefficient of friction. During the polishing process, perfluoropolyether can form an extremely thin lubricating film between the connector end face and the polishing pad, significantly reducing friction, heat generation, and surface damage. Although perfluoropolyether itself is highly hydrophobic, stable dispersion in water-based polishing fluids can be achieved through precise control of its addition amount and optimization of the emulsification process.

[0015] The pH value of the grinding slurry of this invention is controlled between 9.5 and 10.0. This pH range has been carefully optimized: at this pH, the carboxyl groups of the styrene-maleic anhydride copolymer are fully dissociated, resulting in the best dispersion effect; at the same time, citric acid, as a buffer, can maintain pH stability and avoid equipment corrosion and environmental hazards that may be caused by strong alkali; in addition, a moderately alkaline environment is conducive to the slight activation of the polymer core surface, thereby improving grinding efficiency.

[0016] This invention also provides a method for preparing the above-mentioned grinding slurry, which includes seven key steps, each with carefully optimized process parameters to ensure the quality of the final product. First, deionized water is added to a mixing tank, the stirring device is started, the stirring speed is controlled at 2000 rpm, and the temperature is maintained between 20°C and 25°C. Then, styrene-maleic anhydride copolymer is slowly added to the mixing tank, and stirring is continued for 30 minutes until completely dissolved, obtaining a dispersant solution. Next, nanodiamonds and α-alumina are premixed for 5 minutes, and then the mixed abrasive is slowly added to the dispersant solution. The stirring speed is increased to 2500 rpm, and high-shear dispersion is performed for 60 minutes to obtain an abrasive dispersion. Subsequently, the abrasive is... A modified polyurea solution is slowly added to the dispersion, and the stirring speed is reduced to 2000 rpm. The stirring is continued for 120 minutes to form a three-dimensional network structure, resulting in an anti-settling system. Then, perfluoropolyether and polyether-modified polysiloxane defoamer are added sequentially to the anti-settling system, and the mixture is stirred for 30 minutes to ensure uniform dispersion of the components, resulting in a mixed grinding slurry. The pH of the mixed grinding slurry is then adjusted to 9.5 to 10.0 using a citric acid aqueous solution to obtain the finished grinding slurry. Finally, the finished grinding slurry is filtered through a filter bag with a 5-micron pore size to remove impurities before packaging.

[0017] In a preferred embodiment, the shear rate of the high-shear dispersion process is greater than 10,000 per second. This high shear force can effectively break up abrasive agglomerates and fully disperse nanodiamonds and α-alumina. The mass concentration of the citric acid aqueous solution is 10%, which provides sufficient pH adjustment capability without affecting the stability of the grinding fluid due to excessive acid.

[0018] The polishing slurry of this invention exhibits excellent performance in polishing the end faces of MPO fiber optic connectors. During polishing, the polishing pressure is controlled between 0.2 and 0.4 MPa, a range that ensures sufficient abrasive action without causing excessive pressure on the polymer ferrule. The polishing speed is 100 to 200 rpm, achieving an optimal balance between polishing efficiency and surface quality. The polishing slurry flow rate is 30 to 50 ml per minute, ensuring a constant supply of polishing slurry to the polishing area. After polishing with the polishing slurry of this invention, the surface roughness Ra value of the connector end face can reach an ultra-smooth surface of less than 1 nanometer, and the fiber indentation is controlled within the ideal range of -50 nanometers to -400 nanometers, fully meeting the technical requirements of high-performance MPO connectors.

[0019] Compared with the prior art, the present invention has the following beneficial effects: First, this invention achieves a breakthrough improvement in grinding efficiency and surface quality by employing a composite abrasive system of nanodiamond and α-alumina. Nanodiamond, as the hardest material in nature, has a Mohs hardness of 10, enabling rapid cutting of connector end-face materials. α-alumina, with a Mohs hardness of 9, is slightly lower than diamond but still sufficiently hard. Its near-spherical particle morphology and self-lubricating properties allow it to gently smooth the surface without creating new scratches during the fine grinding stage. In the initial grinding stage, diamond particles play a major role, quickly removing surface protrusions. As the surface gradually becomes smoother, the role of α-alumina becomes more prominent, finely correcting microscopic unevenness. This composite abrasive design, combining coarse and fine particles and rigidity and flexibility, reduces grinding time by 3% to 8% compared to existing technologies, while reducing surface roughness by 20% to 30%, achieving a dual improvement in efficiency and quality.

[0020] Secondly, this invention uses a styrene-maleic anhydride copolymer as a dispersant. The amphiphilic structure of this copolymer makes it an ideal dispersant for composite abrasive systems. Specifically, the hydrophobicity of the styrene units allows them to firmly adsorb onto the surfaces of diamond and alumina particles through hydrophobic interactions, forming a first protective layer. Meanwhile, the maleic anhydride units hydrolyze to maleic acid in an alkaline environment, and its two carboxyl groups fully dissociate into carboxylate anions at pH 9.5 to 10.0, giving the abrasive particle surface a strong negative charge. According to the DLVO theory, the electrostatic repulsion between charged particles is proportional to the square of the charge density; therefore, a high density of negative charge generates a strong electrostatic repulsion, effectively preventing particles from approaching each other and agglomerating. Simultaneously, the maleic acid segments extending in the aqueous phase also create a steric hindrance effect; even if particles accidentally approach each other during Brownian motion, the steric hindrance will prevent them from getting closer. The dual protection mechanism of electrostatic repulsion and steric hindrance ensures that the abrasive particles can be stably dispersed in the grinding fluid for a long time. Tests have shown that the grinding fluid using the dispersant of this invention does not show significant sedimentation after standing at room temperature for 30 days, and the Zeta potential remains above -40 millivolts, indicating that the system is in a highly stable state.

[0021] Third, this invention introduces modified polyurea as an anti-settling agent, which is an innovative solution. The urea groups in the modified polyurea molecules can form hydrogen bonds, and multiple polyurea molecules cross-link through hydrogen bonds to construct a three-dimensional network structure. This network suspends the abrasive particles within it, acting as a skeletal support. Even more remarkably, the carboxyl modification gives the polyurea molecules a negative charge, enabling them to generate electrostatic interactions with the similarly negatively charged abrasive particles, further enhancing the network's ability to constrain the particles. This three-dimensional network structure endows the grinding fluid with excellent thixotropic properties: when stationary, the intact network structure maintains a high viscosity, firmly fixing the abrasive particles and preventing sedimentation; when shear forces such as stirring or pumping are applied, the hydrogen bonds are broken, the network structure disintegrates, and the system viscosity rapidly decreases, making the grinding fluid easier to flow and use; after the shearing stops, the hydrogen bonds quickly reform, the network structure recovers, and the system viscosity rebounds. This characteristic of being solid when stationary and flowing when in motion not only solves the problem of long-term storage stability but also gives the grinding fluid excellent operability during use.

[0022] Fourth, this invention creatively applies perfluoropolyether lubricant to water-based polishing fluids, representing a significant technological breakthrough. The molecular chain of perfluoropolyether is entirely composed of carbon, fluorine, and oxygen. The high electronegativity and large atomic radius of fluorine atoms make the CF bond extremely stable, resulting in an overall molecule with extremely low surface energy and a low coefficient of friction. During polishing, perfluoropolyether molecules can rapidly adsorb onto the connector end face and polishing pad surface, forming an ultra-thin lubricating film only a few molecules thick. This lubricating film acts like a molecular-level shock absorber, transforming the original direct solid-solid contact into an indirect solid-liquid-solid contact, drastically reducing the coefficient of friction from 0.35-0.50 to 0.08-0.12, a reduction of 70%-80%. This significant reduction in friction brings multiple benefits: First, the heat generated during polishing is greatly reduced, avoiding thermal damage to the polymer ferrule; second, lower friction means that the abrasive can roll more smoothly rather than scratch under the same pressure, reducing scratches; third, reduced friction also reduces wear on the polishing pad and polishing machine, extending equipment lifespan. More importantly, perfluoropolyethers are extremely chemically inert, will not react with abrasives, dispersants, or other components, nor will they be corroded by acids or alkalis, thus ensuring long-lasting and stable lubrication performance. Although perfluoropolyethers are hydrophobic, by precisely controlling the addition amount within a low range of 0.05% to 0.3%, combined with a high-shear emulsification process, stable dispersion in water-based systems can be achieved, which is a key technical skill of this invention.

[0023] Fifth, this invention uses citric acid as a pH adjuster instead of traditional strong bases such as sodium hydroxide, reflecting the design philosophy of environmental protection and equipment protection. Citric acid is a natural organic acid with three carboxyl groups, exhibiting excellent buffering capacity in aqueous solutions. When the pH value fluctuates, the multi-level dissociation equilibrium of citric acid can respond rapidly, maintaining pH stability by absorbing or releasing protons. This buffering effect ensures that the pH value of the grinding fluid remains within the optimal range during storage and use, guaranteeing the dispersion effect of the dispersant and the overall performance of the grinding fluid. Compared to strong bases, the weak acidity of citric acid makes it extremely less corrosive to the metal parts of grinding equipment, greatly extending the service life of the equipment and reducing maintenance costs. At the same time, citric acid is biodegradable, environmentally friendly, and meets the requirements of green manufacturing. In addition, the chelating properties of citric acid can also bind any metal impurity ions that may be present, preventing these ions from catalyzing the degradation of other components or causing abrasive agglomeration, further improving the stability of the grinding fluid.

[0024] Sixth, the polishing slurry of this invention possesses excellent cleaning performance, an advantage that is often overlooked but is actually very important. Many existing polishing slurries are difficult to clean thoroughly after use, and the abrasive and additives remaining on the surface of the polishing pad can cause scratches and contamination during subsequent polishing. This invention optimizes the structure and dosage of each component in the formulation, enabling the polishing slurry to be easily rinsed clean with deionized water after the polishing task is completed. The specific mechanism is as follows: the styrene-maleic anhydride copolymer has good water solubility under alkaline conditions, and can quickly dissolve and remove adsorbed abrasive during cleaning; the three-dimensional network of modified polyurea rapidly disintegrates during dilution and rinsing, releasing suspended particles; and although perfluoropolyether is hydrophobic, it can be effectively removed even with a large amount of water rinsing due to its extremely small dosage and thorough emulsification. Practical applications show that polishing pads using the polishing slurry of this invention can be restored to cleanliness with a simple water wash, greatly shortening cleaning time, improving production efficiency, and reducing the risk of cross-contamination due to residue.

[0025] Seventh, this invention achieves a comprehensive balance and improvement in grinding efficiency, surface quality, equipment wear, and environmental performance. Experimental data shows that using the grinding slurry of this invention, the grinding time of MPO connectors is reduced by more than 30% compared to traditional silicon carbide-based grinding slurries and by about 20% compared to single alumina grinding slurries; the surface roughness Ra value can be stably achieved to 0.8 to 1.0 nanometers, which is superior to the 1.5 to 2.5 nanometers of existing technologies; the fiber concavity is controlled within the ideal window of -100 to -300 nanometers, ensuring low insertion loss of the connector; the number of scratches on the grinding end face is reduced from 8 to 15 per end face in traditional processes to 2 to 5 per end face, a reduction of 60% to 80%; the wear rate of the grinding equipment is reduced by 30% to 40%, extending the service life of the equipment; moreover, the entire formula does not contain toxic or harmful substances, and the waste liquid can be discharged after simple neutralization, fully complying with environmental protection regulations. These comprehensive performance improvements are not simply additive, but stem from the carefully designed synergistic effect between the components, reflecting the depth and breadth of technological innovation in this invention.

[0026] In summary, this invention solves a series of problems existing in MPO connector polishing fluids, such as low efficiency, poor quality, insufficient stability, and environmental unfriendliness, by organically combining a composite abrasive system, a high-efficiency dispersion system, a thixotropic anti-settling system, and an ultra-low friction lubrication system. It provides a new type of polishing fluid that is technologically advanced, high-performance, and economical for the high-quality manufacturing of MPO connectors, and has significant technical value and broad application prospects. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily obscuring the concept of the invention.

[0028] Unless otherwise specified, all raw materials used in the following examples are commercially available products that can be purchased through conventional commercial channels. Specifically, the nanodiamonds used are HF-ND-125 type synthetic nanodiamonds produced by Huifeng Diamond Technology Co., Ltd. This product is synthesized via an explosive method, has an average particle size of 125 nanometers, a purity greater than 98%, and is a grayish-black powder. α-alumina is produced by Alfa Aesar, Inc. The grinding powder, product number 43820, has an average particle size of 1.0 micrometer, a purity of over 99.5%, and a corundum crystal structure, appearing as a white powder. The styrene-maleic anhydride copolymer uses SMA EF40 type copolymer produced by Sartamer (France). This product has a styrene to maleic anhydride molar ratio of 2:1, a number-average molecular weight of approximately 8000 g / mol, an acid value of 280 to 320 mg / g potassium hydroxide, and appears as pale yellow solid granules. The modified polyurea uses a carboxyl-modified polyurea solution similar to BYK-410 from BYK (Germany), with a solid content of 35%. The polyurea has a weight-average molecular weight of approximately 20000 g / mol, a carboxyl modification degree of approximately 10%, and is dissolved in deionized water, appearing as a colorless to slightly yellow viscous liquid. The perfluoropolyether used is Krytox GPL106 type Y perfluoropolyether from DuPont, USA, with a weight-average molecular weight of approximately 3000 g / mol, a kinematic viscosity of 150 centipoise at 25°C, and a density of 1.87 g / cm³, appearing as a colorless, transparent, oily liquid. The citric acid used is food-grade citric acid monohydrate, purchased from Henan Wanbang Chemical Co., Ltd., with a purity greater than 99.5%, appearing as a colorless or white crystalline powder. The polyether-modified polysiloxane defoamer used is SILFOAMSE393 defoamer from Wacker Chemie, Germany, which is a polyether-modified polydimethylsiloxane with a solid content of 100%, a surface tension of approximately 23 millinewtons per meter, and appears as a colorless, transparent liquid. The deionized water was prepared in the laboratory, with a conductivity of less than 5 microsiemens per centimeter, a pH value of 6.5 to 7.5, and a total organic carbon content of less than 1 part per 50 billion.

[0029] The detection methods involved in the following embodiments are as follows: Surface roughness was measured using a Bruker Dimension Icon atomic force microscope with a scanning range of 5 μm × 5 μm, a tapping mode, and a silicon probe. The Ra value was obtained through Nanoscope Analysis software. Fiber optic indentation was measured using a Canadian... The measurement was performed using a Norland Products IFM-200 fiber optic end-face interferometer at a wavelength of 632.8 nm, with five repeated measurements taken and the average value calculated. The pH of the grinding slurry was measured using a Mettler Toledo FiveEasy Plus pH meter, calibrated with standard buffer solutions of pH 4.01, 6.86, and 9.18 before use. Viscosity was measured using a Brookfield DV2T rotational viscometer with a No. 4 rotor, at a temperature controlled at 25°C and a rotation speed of 100 rpm. Zeta potential was measured using a Malvern Zetasizer Nano ZS dynamic light scattering instrument, diluted 100 times, at a temperature of 25°C, using a DTS1070 folded capillary cell. Particle size distribution was measured using a Malvern Mastersizer 3000 laser particle size analyzer, with deionized water as the dispersion medium, a dispersion pressure of 2 bar, and the measurement model based on Mie scattering theory. Insertion loss was measured using a CertiFiber Pro optical power meter from Fluke Corporation, USA, at wavelengths of 1310 nm and 1550 nm. The light source was a stable laser source. After cleaning the connector, the measurement was performed in a standard test fixture, and the test was repeated 3 times and the average value was taken.

[0030] Example 1 This embodiment presents a high-efficiency polishing slurry for MPO connectors, designed according to a preferred formulation. The polishing slurry comprises, by weight percentage: 4.2% nanodiamond, 33.8% α-alumina, 12% styrene-maleic anhydride copolymer, 3% modified polyurea solution, 0.1% perfluoropolyether, 1% citric acid, 0.9% polyether-modified polysiloxane defoamer, and 45% deionized water. This formulation is the optimal solution obtained through extensive experimental optimization, wherein the weight ratio of nanodiamond to α-alumina is 1:8, which is within the middle value of the claims and effectively balances polishing efficiency and surface quality.

[0031] The preparation process includes the following steps: First, add 45 kg of deionized water to the mixing tank, start the mechanical stirring device, and adjust the stirring speed to 2000 rpm. Maintain the temperature at 23 degrees Celsius using jacketed circulating cooling water. While continuously stirring, slowly add 12 kg of styrene-maleic anhydride copolymer solid particles through the hopper, controlling the addition time to approximately 10 minutes to avoid excessively high local concentrations. After addition, continue stirring for 30 minutes. During the stirring process, the copolymer particles gradually swell and dissolve, and the solution changes from slightly turbid to a transparent pale yellow, with the pH value rising to approximately 8.5. This indicates that maleic anhydride has partially hydrolyzed to maleic acid, and the copolymer has fully dissolved to form a homogeneous dispersant solution.

[0032] Next, the abrasives were premixed in a separate mixer. 4.2 kg of nanodiamond and 33.8 kg of α-alumina powder were added to the mixer, and dry mixing was performed for 5 minutes. The purpose of dry premixing is to ensure a preliminary uniform distribution of the two abrasives, preventing stratification due to density differences when the liquid phase is added later. During the mixing process, the black nanodiamond powder gradually mixed with the white α-alumina powder to form a uniform grayish-white powder.

[0033] Then, the premixed abrasive was slowly and continuously added to the dispersant solution via a screw feeder over a period of approximately 20 minutes. Simultaneously, the stirring speed was increased to 2500 rpm, and a high-shear disperser was activated to assist dispersion. The high-shear disperser used was an IKA T50 digital homogenizer, set to 10000 rpm with a gear head diameter of 50 mm, achieving a shear rate of approximately 12000 Hz. Under this high shear force, the abrasive agglomerates were rapidly broken up, and the nanodiamond and α-alumina particles were fully dispersed in the dispersant solution. High-shear dispersion continued for 60 minutes, during which samples were taken every 15 minutes from three locations: the bottom of the tank, the middle of the tank, and the liquid surface. Particle size distribution was measured using a laser particle size analyzer. When the D50 particle size difference at the three locations was less than 0.1 μm, and the D50 value difference between the 60-minute and 45-minute samples was less than 0.05 μm, the dispersion had reached a steady state, and high-shear dispersion was stopped. The resulting abrasive dispersion is uniformly grayish-white, with no obvious particle feel, and has good fluidity when poured.

[0034] Next, 3 kg of modified polyurea solution was slowly added to the abrasive dispersion. Due to the high viscosity of the modified polyurea solution, it was first diluted to twice its original volume with a small amount of deionized water for easier addition and dispersion, and then added dropwise to the abrasive dispersion over 15 minutes. Simultaneously, the stirring speed was reduced to 2000 rpm to ensure thorough mixing without excessively damaging the polyurea molecular chain structure. After adding the modified polyurea, the viscosity of the system gradually increased because the polyurea molecules began to form a network structure through hydrogen bonding. Stirring was continued for 120 minutes to allow the system to fully equilibrium. At this point, the static viscosity was measured to be approximately 200 mPa·s, while at a shear rate of 100 rpm, the viscosity decreased to approximately 90 mPa·s. This significant shear thinning phenomenon demonstrates the formation of the thixotropic network structure. The resulting anti-settling system remained a uniform grayish-white color under visual observation, and while slightly viscous, it flowed smoothly when poured.

[0035] Subsequently, functional additives were added to the anti-settling system sequentially. First, 0.1 kg of perfluoropolyether was added. Due to its high density and strong hydrophobicity, perfluoropolyether requires special emulsification technology. Specifically, the perfluoropolyether was pre-emulsified with 0.5 kg of modified polyurea solution in a high-speed stirrer for 10 minutes to form a preliminary emulsion. This pre-emulsion was then slowly added to the anti-settling system. Pre-emulsification disperses the perfluoropolyether into tiny droplets, while the modified polyurea acts as an emulsifier to stabilize these droplets, allowing the perfluoropolyether to remain stable in the water-based system. Next, 0.9 kg of polyether-modified polysiloxane defoamer was added. The defoamer was added very slowly, drop by drop, at the center of the stirring vortex to avoid generating excessive foam. After adding both functional additives, the stirring speed was maintained at 2000 rpm for 30 minutes to ensure thorough and uniform dispersion of all components. During stirring, pay attention to the liquid level. If a small amount of foam appears, it is normal and the defoamer will eliminate it during the subsequent settling process.

[0036] Next, pH adjustment is performed, a crucial step in ensuring the performance of the grinding slurry. First, a 10% citric acid aqueous solution is prepared by dissolving 1 kg of citric acid monohydrate in 9 kg of deionized water. A pH electrode is inserted into the grinding slurry, and the citric acid solution is slowly added dropwise using a dropping funnel while continuously stirring, with real-time monitoring of the pH change. Since the initial pH of the grinding slurry is approximately 8.5, citric acid needs to be added to raise it to the target range. The addition of citric acid must be very slow, especially when the pH approaches 9.5, as this region has a strong buffering capacity and the pH change is slow. Through precise control, the pH is finally adjusted to 9.8, with a total citric acid dosage of approximately 1 kg, consistent with the formulation design. After adjustment, stirring continues for 10 minutes to ensure a uniform pH throughout the system. Multiple samples are taken, and the pH values ​​are consistently between 9.7 and 9.9, indicating successful pH adjustment. The resulting grinding slurry is a uniform grayish-white color, slightly viscous, flows smoothly when poured, and exhibits no significant foaming after the surface calms.

[0037] Finally, the finished grinding slurry was filtered through a filtration device. A stainless steel filter cartridge containing a polypropylene filter bag with a pore size of 5 micrometers was used to remove any small amounts of large particles and insufficiently dispersed abrasive agglomerates. Due to the thixotropic nature of the grinding slurry, it could pass smoothly through the filter bag under certain pressure. The filtration pressure was controlled at 0.2 MPa, and the flow rate was approximately 50 liters per hour. The filtered grinding slurry exhibited a more uniform appearance. Laser particle size analyzer measurements showed a D50 particle size of 0.72 micrometers, a D90 particle size of 1.85 micrometers, and a D10 particle size of 0.15 micrometers. The narrow and concentrated particle size distribution indicated good abrasive dispersion and the absence of large particles. The filtered grinding slurry was then packaged into 20 kg high-density polyethylene drums, sealed, and stored in a cool, dark place.

[0038] The grinding slurry prepared in this embodiment exhibits excellent performance indicators: pH value of 9.8, solid content of 54.0%, viscosity of 88 mPa·s at 25°C and 100 rpm, static viscosity of 195 mPa·s, thixotropic index of 2.2, density of 1.50 g / cm³, and Zeta potential of -46 mV, indicating a highly stable system. After storage at 25°C for 30 days, no significant stratification or sedimentation was observed, and the Zeta potential only decreased to -44 mV, maintaining stable performance indicators. The successful preparation of this grinding slurry demonstrates that a product with stable performance and excellent quality can be obtained by following the formulation and process of this invention.

[0039] Example 2 This embodiment prepared a polishing slurry for MPO connectors with a relatively low amount of nanodiamond to verify the application effect of the lower limit value of nanodiamond. The polishing slurry comprises, by weight percentage: 3% nanodiamond, 27% α-alumina, 8% styrene-maleic anhydride copolymer, 2% modified polyurea solution, 0.05% perfluoropolyether, 0.5% citric acid, 0.5% polyether-modified polysiloxane defoamer, and 58.95% deionized water. In this formulation, the amounts of nanodiamond and α-alumina are both at the lower limit of the claims, and the weight ratio of nanodiamond to α-alumina is 1:9, which is at the upper limit of the claims. Correspondingly, the amounts of various additives are also at the lower limit, while the amount of deionized water reaches the upper limit, making the total of the formulation exactly 100%.

[0040] The preparation method is basically the same as in Example 1, but the specific parameters were adjusted accordingly. In step one, 58.95 kg of deionized water was added to the mixing tank, the stirring speed was 2000 rpm, and the temperature was 23 degrees Celsius. Then, 8 kg of styrene-maleic anhydride copolymer was added, and the mixture was stirred for 30 minutes until completely dissolved. In step two, 3 kg of nanodiamond and 27 kg of α-alumina were dry-premixed for 5 minutes. In step three, the premixed abrasive was added to the dispersant solution, the stirring speed was increased to 2500 rpm, and high-shear dispersion was performed for 60 minutes. In step four, 2 kg of modified polyurea solution was added, the stirring speed was reduced to 2000 rpm, and the mixture was stirred for 120 minutes. In step five, 0.05 kg of perfluoropolyether and 0.5 kg of defoamer were added sequentially, and the mixture was stirred for 30 minutes. In step six, the pH value was adjusted to 9.5 with citric acid solution, approximately 0.5 kg of citric acid was used. In step seven, the product is packaged after being filtered through a 5-micron filter bag.

[0041] The polishing slurry prepared in this embodiment has a smaller total abrasive content, resulting in a solid content of 30.5% and a corresponding decrease in viscosity to approximately 60 mPascals per second. Although the amount of nanodiamond is small, the slurry still maintains a certain polishing capacity due to the increased proportion of α-alumina. Subsequent tests show that this polishing slurry is suitable for applications where polishing efficiency is not critical but surface quality is important, and it can achieve extremely low surface roughness.

[0042] Example 3 This embodiment prepared a polishing slurry with a high content of nanodiamond and α-alumina to verify the polishing performance under high abrasive content. The polishing slurry, by weight percentage, comprises 6% nanodiamond, 44% α-alumina, 15% styrene-maleic anhydride copolymer, 5% modified polyurea solution, 0.3% perfluoropolyether, 2% citric acid, 1.5% polyether-modified polysiloxane defoamer, and 26.2% deionized water. In this formulation, the amounts of nanodiamond and α-alumina are both taken at the upper limit of the claims, and the weight ratio of nanodiamond to α-alumina is 1:7.3, close to the lower limit. Correspondingly, the amounts of various additives are also taken at the upper limit to ensure good dispersion and stability under high abrasive content, while the amount of deionized water is reduced to the lower limit.

[0043] The preparation method is the same as in Example 1, but the amounts of each component are adjusted according to the above formula. In step one, 26.2 kg of deionized water and 15 kg of styrene-maleic anhydride copolymer are added; in step two, 6 kg of nanodiamond and 44 kg of α-alumina are premixed; in step three, high-shear dispersion is performed, and due to the high abrasive content, the dispersion time is extended to 75 minutes to ensure sufficient dispersion; in step four, 5 kg of modified polyurea solution is added, and the stirring time is extended to 150 minutes to fully form a network structure; in step five, 0.3 kg of perfluoropolyether and 1.5 kg of defoamer are added; in step six, the pH is adjusted to 10.0 with citric acid, approximately 2 kg of which is used; in step seven, the mixture is filtered and packaged.

[0044] The grinding slurry prepared in this embodiment has a high solid content of 73.3% and a significantly increased viscosity of approximately 150 mPascals per second. This high abrasive content endows the slurry with extremely strong grinding capabilities, making it particularly suitable for coarse grinding stages where high grinding efficiency is required. However, it is important to note that grinding pressure and time should be appropriately controlled during use to avoid over-grinding.

[0045] Example 4 This embodiment prepared a polishing slurry with nanodiamond particles of 100 nanometers to verify the polishing effect of smaller-sized diamond particles. The polishing slurry comprises, by weight percentage: 5% nanodiamond, 35% α-alumina, 10% styrene-maleic anhydride copolymer, 3.5% modified polyurea solution, 0.15% perfluoropolyether, 1.5% citric acid, 1% polyether-modified polysiloxane defoamer, and 43.85% deionized water. The average particle size of the nanodiamonds used is 100 nanometers, which is the lower limit of the scope of the claims; the particles are finer and have a larger specific surface area.

[0046] The preparation method is basically the same as in Example 1, and the preparation is carried out according to the above-mentioned formulation and dosage. Since 100-nanometer diamond particles are more difficult to disperse than 125-nanometer particles, in the high-shear dispersion stage of step three, the shear rate is increased to 15,000 per second, and the dispersion time is extended to 90 minutes to ensure that the nanodiamonds are fully dispersed and do not agglomerate. The process parameters for other steps are the same as in Example 1.

[0047] In the polishing slurry prepared in this embodiment, the smaller particle size of the nanodiamonds and the greater size difference between them and α-alumina facilitate the formation of a well-graded composite abrasive system. Smaller diamond particles can penetrate finer surface irregularities for cutting, resulting in lower surface roughness. However, smaller particles are also more prone to agglomeration, thus requiring stronger dispersion measures.

[0048] Example 5 This embodiment prepared a polishing slurry with nanodiamond particles of 150 nm and α-alumina particles of 1.2 μm to verify the application effect of a larger particle size combination. The polishing slurry comprises, by weight percentage: 4.5% nanodiamond, 40% α-alumina, 12% styrene-maleic anhydride copolymer, 4% modified polyurea solution, 0.2% perfluoropolyether, 1.2% citric acid, 1.2% polyether-modified polysiloxane defoamer, and 36.9% deionized water. The average particle size of the nanodiamond used is 150 nm, and the average particle size of the α-alumina is 1.2 μm, which are the upper limits of the claims.

[0049] The preparation method is basically the same as in Example 1, but in the high-shear dispersion stage of step three, since the particles are relatively large and dispersion is relatively easy, the dispersion time can be appropriately shortened to 50 minutes. Other steps are carried out according to the above-mentioned formulation dosage and process parameters of Example 1.

[0050] In the polishing slurry prepared in this embodiment, the larger-diameter abrasive particles exhibit stronger cutting ability and higher material removal rate, making it suitable for applications requiring high polishing efficiency. However, correspondingly, the surface roughness may be slightly higher than that of polishing slurries with smaller-diameter abrasive particles. By adjusting the particle size combination of nanodiamond and α-alumina, the polishing performance can be optimized for different application requirements.

[0051] Example 6 This embodiment prepared a grinding slurry with a styrene-maleic anhydride copolymer molecular weight of 5000 g / mol to verify the dispersion effect of a lower molecular weight dispersant. The grinding slurry, by weight percentage, comprises 4% nanodiamond, 30% α-alumina, 13% styrene-maleic anhydride copolymer, 3% modified polyurea solution, 0.1% perfluoropolyether, 1% citric acid, 0.8% polyether-modified polysiloxane defoamer, and 48.1% deionized water. The styrene-maleic anhydride copolymer used is Sartomer's SMA EF30 product, with a number average molecular weight of approximately 5000 g / mol, which is the lower limit of the scope of the claims.

[0052] The preparation method is the same as in Example 1, following the dosage and formulation described above. It is worth noting that the lower molecular weight copolymer dissolves in water more quickly, reducing the dissolution time in step one to 20 minutes. Due to its lower molecular weight, the copolymer contains more molecules per unit mass, providing higher surface adsorption density, but with a relatively weaker steric hindrance effect. Therefore, the copolymer dosage was appropriately increased to 13% in the formulation design to compensate for the insufficient steric hindrance.

[0053] The grinding slurry prepared in this embodiment exhibits good dispersion stability, with a Zeta potential reaching -48 mV, indicating strong electrostatic repulsion. Lower molecular weight dispersants more easily penetrate the narrow spaces between abrasive particles, which is beneficial for breaking up agglomerates; therefore, the initial dispersion effect of this grinding slurry is excellent.

[0054] Example 7 This embodiment prepared a grinding slurry with a styrene-maleic anhydride copolymer having a molecular weight of 10,000 g / mol to verify the application effect of a higher molecular weight dispersant. The grinding slurry, by weight percentage, comprises 4.5% nanodiamond, 35% α-alumina, 9% styrene-maleic anhydride copolymer, 3.5% modified polyurea solution, 0.15% perfluoropolyether, 1% citric acid, 0.9% polyether-modified polysiloxane defoamer, and 45.95% deionized water. The styrene-maleic anhydride copolymer used is a product with a number average molecular weight of approximately 10,000 g / mol, which is the upper limit of the scope of the claims.

[0055] The preparation method is basically the same as in Example 1. Higher molecular weight copolymers dissolve more slowly, requiring an extension of the stirring time to 40 minutes in step one to ensure complete dissolution. The advantage of high molecular weight copolymers lies in their stronger steric hindrance effect; each polymer molecule adsorbed on the particle surface has a longer hydrophilic segment extending into the aqueous phase, forming a thicker protective layer. Therefore, the amount of copolymer in the formulation can be appropriately reduced to 9%, saving costs while maintaining good dispersion.

[0056] The grinding slurry prepared in this embodiment exhibits outstanding long-term storage stability. Tests showed that accelerated storage at 40 degrees Celsius for 15 days is equivalent to approximately 6 months of storage at room temperature. During this period, the Zeta potential only decreased from -44 mV to -41 mV, and the particle size distribution remained essentially unchanged. This indicates that the steric hindrance effect provided by the high molecular weight dispersant makes a significant contribution to long-term stability.

[0057] Example 8 This embodiment prepared a polishing slurry with a modified polyurea carboxyl modification degree of 8% to verify the anti-settling effect of polyurea with a lower degree of modification. The polishing slurry, by weight percentage, comprises 4.2% nanodiamond, 33.8% α-alumina, 12% styrene-maleic anhydride copolymer, 4% modified polyurea solution, 0.1% perfluoropolyether, 1% citric acid, 0.9% polyether-modified polysiloxane defoamer, and 44% deionized water. The modified polyurea used has a carboxyl modification degree of 8%, which is the lower limit of the claims, a solid content of 30%, and a weight-average molecular weight of approximately 15,000 g / mol.

[0058] The preparation method is the same as in Example 1. Lower carboxyl modification means fewer carboxyl groups on the polyurea molecular chain, lower charge density, and weaker electrostatic interaction with abrasive particles; however, hydrogen bonding between polyurea molecules can still form a three-dimensional network structure. Due to the lower modification degree, to obtain sufficient anti-settling effect, the amount of modified polyurea solution in the formulation was appropriately increased to 4%.

[0059] The thixotropic properties of the polishing slurry prepared in this embodiment are slightly weaker than those of the embodiment with a higher degree of modification, with a thixotropic index of approximately 1.8, but it can still effectively prevent abrasive sedimentation. The advantage of this polishing slurry is that the polyurea modification degree is relatively low, resulting in relatively low cost, making it suitable for applications where anti-settling performance requirements are not extremely high.

[0060] Example 9 This embodiment prepared a polishing slurry with a modified polyurea carboxyl modification degree of 12% and a weight-average molecular weight of 25,000 g / mol to verify the anti-settling performance of highly modified, high-molecular-weight polyurea. The polishing slurry, by weight percentage, comprises 4.2% nanodiamond, 33.8% α-alumina, 12% styrene-maleic anhydride copolymer, 2.5% modified polyurea solution, 0.1% perfluoropolyether, 1% citric acid, 0.9% polyether-modified polysiloxane defoamer, and 45.5% deionized water. The modified polyurea used has a carboxyl modification degree of 12% and a weight-average molecular weight of 25,000 g / mol, both of which are the upper limit of the claims, and a solid content of 40%.

[0061] The preparation method is the same as in Example 1, but because the modified polyurea solution has a high viscosity, it needs to be diluted with more water in step four, diluted to three times the original volume, and then added slowly. Highly modified, high molecular weight polyurea has the strongest anti-settling ability, and a unit mass of polyurea can form a more stable three-dimensional network, so the amount used in the formulation can be reduced to 2.5%.

[0062] The grinding slurry prepared in this embodiment exhibits the strongest thixotropic properties, with a thixotropic index of 2.8, a static viscosity as high as 250 mPa·s, and a shear viscosity of only 85 mPa·s. During storage, even under temperature fluctuations and vibrations, the abrasive particles do not settle. This grinding slurry is particularly suitable for applications requiring long-term storage or transportation under harsh conditions.

[0063] Example 10 This embodiment prepared a polishing slurry with a perfluoropolyether weight-average molecular weight of 2000 g / mol and a kinematic viscosity of 100 centistokes to verify the lubrication effect of a low molecular weight, low viscosity lubricant. The polishing slurry, by weight percentage, comprises 4.2% nanodiamond, 33.8% α-alumina, 12% styrene-maleic anhydride copolymer, 3% modified polyurea solution, 0.25% perfluoropolyether, 1% citric acid, 0.9% polyether-modified polysiloxane defoamer, and 44.85% deionized water. The perfluoropolyether used is DuPont Krytox GPL102, with a weight-average molecular weight of approximately 2000 g / mol and a kinematic viscosity of approximately 100 centistokes at 25 degrees Celsius, both of which are the lower limit of the claims.

[0064] The preparation method is basically the same as in Example 1. Lower viscosity perfluoropolyethers have better flowability and are easier to emulsify and disperse in the grinding slurry. In step five, due to its low viscosity, the pre-emulsification time can be shortened to 5 minutes. However, due to its lower molecular weight, the lubricating effect provided by a single molecule is relatively weak; therefore, the amount of perfluoropolyether in the formulation was appropriately increased to 0.25%.

[0065] In the polishing slurry prepared in this embodiment, the low-viscosity perfluoropolyether can spread more quickly on the friction interface to form a lubricating film, resulting in a fast response speed. It provides lubrication protection the instant polishing begins, reducing friction and wear during the start-up phase. This polishing slurry is suitable for applications involving high-speed polishing or frequent start-stop cycles.

[0066] Example 11 This embodiment prepared a polishing slurry with a perfluoropolyether weight-average molecular weight of 5000 g / mol and a kinematic viscosity of 200 centipoise to verify the performance of a high molecular weight, high viscosity lubricant. The polishing slurry, by weight percentage, comprises 4.2% nanodiamond, 33.8% α-alumina, 12% styrene-maleic anhydride copolymer, 3% modified polyurea solution, 0.08% perfluoropolyether, 1% citric acid, 0.9% polyether-modified polysiloxane defoamer, and 45.02% deionized water. The perfluoropolyether used is DuPont Krytox GPL107, with a weight-average molecular weight of approximately 5000 g / mol and a kinematic viscosity of approximately 200 centipoise at 25°C, both of which are the upper limit of the claims.

[0067] The preparation method is basically the same as in Example 1, but in the pre-emulsification stage of step five, due to the high viscosity of perfluoropolyether, the pre-emulsification time needs to be extended to 15 minutes, and the stirring speed needs to be appropriately increased to a higher value to ensure sufficient emulsification. High molecular weight, high viscosity perfluoropolyether monomolecules provide stronger lubrication effect and better durability of lubricating film, so the amount used in the formulation can be reduced to 0.08%.

[0068] The polishing slurry prepared in this embodiment exhibits outstanding performance during prolonged continuous polishing. The high-viscosity perfluoropolyether lubricating film is not easily sheared and can provide stable lubrication protection throughout the polishing process. This polishing slurry is particularly suitable for applications requiring high-volume continuous production.

[0069] Example 12 This embodiment prepared a polishing slurry using a Z-type perfluoropolyether to verify the application effects of perfluoropolyethers with different structures. The polishing slurry, by weight percentage, comprises 4.2% nanodiamond, 33.8% α-alumina, 12% styrene-maleic anhydride copolymer, 3% modified polyurea solution, 0.1% perfluoropolyether, 1% citric acid, 0.9% polyether-modified polysiloxane defoamer, and 45% deionized water. The perfluoropolyether used has a Z-type structure and the molecular formula CF3O-(CF2O). m -(CF2CF2O) n -CF3, with a weight-average molecular weight of approximately 3000 g / mol and a kinematic viscosity of approximately 150 centistokes.

[0070] The preparation method is exactly the same as in Example 1. The Z-type perfluoropolyether has a linear molecular chain structure, and compared to the branched structure of the Y-type, it exhibits lower surface tension and better spreadability. At the friction interface, the Z-type perfluoropolyether can form a more uniform lubricating film. However, the thermal stability of the Z-type is slightly lower than that of the Y-type, requiring caution when used in high-temperature environments.

[0071] The grinding slurry prepared in this embodiment performs excellently in room temperature grinding applications, with a friction coefficient slightly lower than that of Example 1 using Y-type perfluoropolyether. Both perfluoropolyether structures have their own advantages and disadvantages, and the choice can be made based on specific application requirements.

[0072] Comparative Example 1 This comparative example prepared an abrasive slurry containing only α-alumina abrasive and no nanodiamonds to compare the advantages of composite abrasives. The comparative slurry, by weight percentage, comprised 38% α-alumina, 12% styrene-maleic anhydride copolymer, 3% modified polyurea solution, 0.1% perfluoropolyether, 1% citric acid, 0.9% polyether-modified polysiloxane defoamer, and 45% deionized water. Compared to Example 1, this comparative example replaced 4.2% of the nanodiamonds with the same mass of α-alumina, keeping the total abrasive amount unchanged.

[0073] The preparation method is the same as in Example 1, except that only 38 kg of α-alumina is added in the premixing stage of step two, without mixing with nanodiamonds. The process parameters and operating methods for the other steps are exactly the same.

[0074] The polishing slurry prepared in this comparative example is white in appearance, slightly lighter than that of the example containing black nanodiamonds. Subsequent polishing tests showed that, due to the lack of high-hardness nanodiamonds, the polishing efficiency of this comparative slurry was significantly lower than that of Example 1, and the polishing time needed to be extended by approximately 25% to achieve the same smoothness. Although α-alumina can achieve a certain polishing effect, a single abrasive cannot achieve an organic combination of rapid cutting and fine smoothing, demonstrating the necessity of a composite abrasive system.

[0075] Comparative Example 2 This comparative example prepared an abrasive slurry containing only nanodiamond abrasive without α-alumina, further verifying the synergistic effect of composite abrasives. The comparative slurry, by weight percentage, comprised 38% nanodiamond, 12% styrene-maleic anhydride copolymer, 3% modified polyurea solution, 0.1% perfluoropolyether, 1% citric acid, 0.9% polyether-modified polysiloxane defoamer, and 45% deionized water. Compared to Example 1, this comparative example replaced 33.8% of the α-alumina with the same mass of nanodiamond, keeping the total abrasive amount unchanged.

[0076] The preparation method was the same as in Example 1, but only 38 kg of nanodiamond was added in the premixing stage of step two. Due to the significant increase in the amount of nanodiamond, the dispersion time in the high-shear dispersion stage of step three needed to be extended to 100 minutes to ensure that such a high concentration of nanoparticles could be fully dispersed.

[0077] The grinding slurry prepared in this comparative example was dark gray-black and had high viscosity. Grinding tests showed that although this comparative slurry possessed extremely strong cutting power and a fast grinding speed, the surface quality after grinding was poor, with a surface roughness Ra value as high as 1.8 nanometers, and a significantly increased number of scratches, reaching 10 to 15 per end face. This is because although nanodiamonds have extremely high hardness, their high hardness also means that the cutting action on the substrate is too harsh, lacking the flexible smoothing effect of α-alumina, easily leaving micro-scratches on the surface. This comparative example strongly demonstrates that simply increasing the hardness of the abrasive does not achieve the best grinding effect; the synergistic effect of composite abrasives is necessary to balance efficiency and quality.

[0078] Comparative Example 3 This comparative example prepared a grinding slurry without styrene-maleic anhydride copolymer dispersant, relying solely on modified polyurea as the dispersant, to verify the importance of a dedicated dispersant. The comparative slurry, by weight percentage, comprised 4.2% nanodiamond, 33.8% α-alumina, 15% modified polyurea solution, 0.1% perfluoropolyether, 1% citric acid, 0.9% polyether-modified polysiloxane defoamer, and 45% deionized water. Compared to Example 1, this comparative example removed 12% of the styrene-maleic anhydride copolymer and increased the amount of modified polyurea solution from 3% to 15% in an attempt to simultaneously achieve dispersion and anti-settling functions.

[0079] The preparation method was adjusted accordingly: in step one, only deionized water and citric acid were added to adjust the pH to about 9.5; in step two, the abrasive was directly mixed with deionized water without going through the dispersant dissolution step; in step three, high shear dispersion was carried out, but due to the lack of a special dispersant, the dispersion effect was not good; in step four, a large amount of modified polyurea solution was added in an attempt to improve the dispersion; steps five and six were the same as in Example 1; and step seven was filtered and packaged.

[0080] The grinding slurry prepared in this comparative example exhibited poor dispersion stability. Although the modified polyurea also possesses some dispersing ability, its primary function is to form a three-dimensional network structure to prevent sedimentation, rather than to form an effective dispersion protective layer on the particle surface. Actual testing revealed that the zeta potential of this comparative slurry was only -25 mV, far lower than the -46 mV of Example 1, indicating insufficient surface charge density and weak electrostatic repulsion. Laser particle size analysis showed the presence of significant large particle agglomerates, with D90 particle sizes exceeding 5 micrometers. In grinding applications, these agglomerates can lead to surface scratches and uneven grinding. This comparative example demonstrates the irreplaceable nature of the dedicated dispersant, styrene-maleic anhydride copolymer; while the modified polyurea can prevent sedimentation, it cannot effectively disperse nanoscale abrasive particles.

[0081] Comparative Example 4 This comparative example prepared a polishing slurry without perfluoropolyether lubricant to verify the key role of lubricant in reducing scratches and friction. The comparative slurry, by weight percentage, comprised 4.2% nanodiamond, 33.8% α-alumina, 12% styrene-maleic anhydride copolymer, 3% modified polyurea solution, 1% citric acid, 0.9% polyether-modified polysiloxane defoamer, and 45.1% deionized water. Compared to Example 1, this comparative example removed 0.1% of the perfluoropolyether and replaced it with an equal amount of deionized water.

[0082] The preparation method is basically the same as in Example 1, except that in step five, perfluoropolyether is not added, but only defoamer is added and stirred for 30 minutes. The process parameters and operating methods of other steps are exactly the same.

[0083] The polishing slurry prepared in this comparative example showed no significant difference from that of Example 1 in terms of appearance, viscosity, zeta potential, and other physicochemical properties, indicating that removing 0.1% of the perfluoropolyether had little impact on the macroscopic properties of the polishing slurry. However, in practical polishing applications, the differences were significant. Due to the lack of lubricant, the coefficient of friction during the polishing process was high, measured to be approximately 0.38, more than three times that of Example 1. The high friction resulted in the generation of more heat during polishing, which could cause thermal damage to the polymer ferrule. More seriously, the connector end face lacking lubrication protection developed numerous scratches after polishing, with an average of 12 to 18 obvious scratches per end face, which was 5 to 6 times that of Example 1. Although these scratches were minor, they would seriously affect optical signal transmission and increase insertion loss. This comparative example fully demonstrates that although the amount of perfluoropolyether lubricant used is extremely small, it has a crucial impact on polishing quality and is an indispensable component for achieving high-quality polishing.

[0084] Comparative Example 5 This comparative example prepared a grinding slurry without modified polyurea anti-settling agent to verify the importance of anti-settling agent for long-term storage stability. The comparative slurry, by weight percentage, comprised 4.2% nanodiamond, 33.8% α-alumina, 12% styrene-maleic anhydride copolymer, 0.1% perfluoropolyether, 1% citric acid, 0.9% polyether-modified polysiloxane defoamer, and 48% deionized water. Compared to Example 1, this comparative example removed 3% of the modified polyurea solution and replaced it with an equal amount of deionized water.

[0085] The preparation method was simplified: steps one through three were the same as in Example 1; step four was skipped, and the modified polyurea solution was not added; steps five through seven were the same as in Example 1. Since a three-dimensional network structure was not required, the entire preparation process was shortened by approximately 2 hours.

[0086] The grinding slurry prepared in this comparative example exhibited good performance initially, with a Zeta potential of -45 mV, uniform particle size distribution, a viscosity of approximately 75 mPa·s, and no significant thixotropy. Upon initial preparation, this control slurry was usable and achieved good grinding results. However, storage stability tests revealed significant problems: after standing at room temperature for 7 days, slight stratification began to appear, with a small amount of sediment visible at the bottom of the container; after 15 days, stratification became obvious, requiring vigorous shaking or stirring to redisperse; after 30 days, a hard sediment layer formed at the bottom, making redispersible with simple stirring, and the Zeta potential dropped to -32 mV. This comparative example demonstrates that while styrene-maleic anhydride copolymers provide short-term dispersion stability, long-term storage stability requires a three-dimensional network structure formed by modified polyurea to suspend the abrasive particles. This is crucial for commercially available grinding slurries, as the time from production to end-user use often takes weeks or even months.

[0087] Grinding performance test To comprehensively evaluate the performance of each embodiment and comparative example, systematic grinding tests were conducted under uniform grinding conditions. The grinding equipment used was a Seiko MPO-12 multi-core connector grinding machine from Nippon Seiko, and the grinding pads were SUBA-X polyester grinding pads from Universal Photonics, USA. These pads have a microporous surface structure, which is beneficial for the retention and distribution of the grinding slurry. The MPO connectors used in the tests were standard 12-core MPO male connectors, with ferrules made of polyphenylene sulfide and single-mode fiber with a core diameter of 9 micrometers. Before grinding, the connector end faces had already undergone rough grinding, with a surface flatness within 10 micrometers.

[0088] The grinding process parameters are uniformly set as follows: grinding pressure is 0.3 MPa, which is precisely applied to the connector end face through a pneumatic control system, with pressure fluctuations controlled within ±0.02 MPa; grinding speed is 150 rpm, with the grinding pad and connector fixture rotating in the same direction; the grinding slurry flow rate is 40 ml / min, continuously supplied to the grinding area via a peristaltic pump to ensure sufficient slurry throughout the grinding process; the grinding time is adjusted according to the grinding efficiency of different samples to achieve a smooth end face. During the grinding process, the grinding pressure and speed are recorded every 10 seconds to ensure stable process parameters. After grinding, the connector end face and grinding pad are thoroughly rinsed with deionized water, and then gently wiped dry with a lint-free cloth to avoid leaving water stains and particles.

[0089] After cleaning, the connectors were placed in a constant temperature and humidity laboratory for 2 hours to reach thermal equilibrium before surface quality testing. Surface roughness testing was performed using an atomic force microscope (AFM). Five test points were randomly selected on different optical fibers on the connector end face. Each test point had a scanning range of 5 μm × 5 μm, a scanning speed of 1 Hz, and each scan line contained 512 data points. The AFM probe used was a BRUKER RTESPA silicon probe with a tip radius of less than 10 nm, capable of accurately detecting nanoscale surface morphology. The measured surface morphology data were processed using Nanoscope Analysis software. First, a first-order plane fitting was performed to remove overall tilt, and then the arithmetic mean roughness Ra value was calculated. The Ra values ​​of the five test points were averaged, and the standard deviation was calculated.

[0090] Fiber optic concavity testing employs a fiber optic end-face interferometer, which utilizes the principle of optical interference to precisely measure the height difference between the fiber end-face and the ferrule end-face. During testing, a clean connector end-face is placed close to the interferometer's reference plane, and the interference fringes are observed. If the fiber end-face is lower than the ferrule end-face, indicating fiber concavity, the interference fringes will appear circular and bend inwards. The concavity degree is calculated from the fringe spacing. Measurements are repeated five times for each fiber, and the average value is recorded.

[0091] The number of scratches was counted using an optical microscope at 1000x magnification. A full scan was performed on each fiber end face to record all visible scratches. A scratch was defined as a linear or arc-shaped defect with a length greater than 1 micrometer and a width greater than 50 nanometers. The total number of scratches on the 12 fibers was divided by 12 to obtain the average number of scratches on each end face.

[0092] Insertion loss testing was performed using an optical power meter, with 1310 nm and 1550 nm being two commonly used communication wavelengths. First, a reference optical power was established using a reference jumper. Then, the test connector was inserted into the optical path, and the optical power after insertion was measured. The ratio of the measured power to the measured power is the insertion loss. The insertion and removal test was repeated three times, and the average value was taken.

[0093] In addition to the aforementioned quality indicators, grinding efficiency was also tested. Grinding efficiency is characterized by the time required to achieve the target surface quality. The target was set as a surface roughness Ra of less than 1.2 nm and an fiber indentation in the range of -50 to -400 nm. The net grinding time required for each sample to reach this target was recorded; the shorter the time, the higher the efficiency.

[0094] The cleaning performance of the polishing slurry was evaluated by cleaning time and residual amount. After polishing, the slurry supply was stopped, and the polishing pads and connectors were rinsed with deionized water at a flow rate of 100 ml per minute for 30 seconds. The polishing pad surface was then visually inspected for any obvious residue. If residue was present, rinsing was continued until clean, and the total cleaning time was recorded. Simultaneously, the turbidity of the rinsing waste liquid was tested; lower turbidity indicated less residue and more thorough cleaning.

[0095] Wear assessment of the polishing equipment was conducted through long-term testing. One hundred connectors were continuously polished using the same polishing slurry, with the wear of the polishing pads checked after every 10 connectors polished. The height change of the polishing pad surface was measured using a profilometer; the amount of height reduction was the wear amount. Simultaneously, the polishing pad surface was inspected for damage, peeling, or other defects. The wear amounts caused by different polishing slurries were compared to assess their impact on the equipment.

[0096] All test data are detailed in Tables 1 and 2.

[0097] Table 1. Formulation composition and physicochemical properties of each embodiment and comparative example. Sample number Nano diamond α-alumina SMA copolymer Modified polyurea PFPE Citric acid Defoamer Deionized water pH value Viscosity Zeta potential (%) (%) (%) (%) (%) (%) (%) (%) (mPa·s) (mV) Example 1 4.2 33.8 12 3 0.1 1 0.9 45 9.8 88 -46 Example 2 3 27 8 2 0.05 0.5 0.5 58.95 9.5 60 -42 Example 3 6 44 15 5 0.3 2 1.5 26.2 10 150 -48 Example 4 5 35 10 3.5 0.15 1.5 1 43.85 9.7 95 -44 Example 5 4.5 40 12 4 0.2 1.2 1.2 36.9 9.9 110 -45 Example 6 4 30 13 3 0.1 1 0.8 48.1 9.6 82 -48 Example 7 4.5 35 9 3.5 0.15 1 0.9 45.95 9.8 92 -44 Example 8 4.2 33.8 12 4 0.1 1 0.9 44 9.8 85 -43 Example 9 4.2 33.8 12 2.5 0.1 1 0.9 45.5 9.8 90 -47 Example 10 4.2 33.8 12 3 0.25 1 0.9 44.85 9.8 88 -46 Example 11 4.2 33.8 12 3 0.08 1 0.9 45.02 9.8 88 -46 Example 12 4.2 33.8 12 3 0.1 1 0.9 45 9.8 88 -46 Comparative Example 1 0 38 12 3 0.1 1 0.9 45 9.8 85 -45 Comparative Example 2 38 0 12 3 0.1 1 0.9 45 9.8 105 -47 Comparative Example 3 4.2 33.8 0 15 0.1 1 0.9 45 9.5 120 -25 Comparative Example 4 4.2 33.8 12 3 0 1 0.9 45.1 9.8 88 -46 Comparative Example 5 4.2 33.8 12 0 0.1 1 0.9 48 9.8 75 -45 Note: SMA copolymer refers to styrene-maleic anhydride copolymer; modified polyurea refers to carboxyl-modified polyurea solution; PFPE refers to perfluoropolyether; defoamer refers to polyether-modified polysiloxane defoamer. Viscosity test conditions are 25 degrees Celsius and 100 rpm.

[0098] Table 2 Grinding performance of each embodiment and comparative example Sample number Grinding time Surface roughness Ra Fiber concavity Number of scratches Insertion loss coefficient of friction Cleaning time relative efficiency (Second) (nm) (nm) (each end face) (dB) (Second) (%) Example 1 28 0.85 -220 2.5 0.18 0.11 35 100 Example 2 32 0.75 -180 2 0.16 0.1 30 88 Example 3 24 0.95 -280 3 0.2 0.12 45 117 Example 4 29 0.8 -200 2.3 0.17 0.11 33 97 Example 5 27 0.9 -250 2.8 0.19 0.11 38 104 Example 6 30 0.88 -210 2.6 0.18 0.11 36 93 Example 7 29 0.87 -225 2.4 0.18 0.11 35 97 Example 8 30 0.9 -230 2.7 0.19 0.11 37 93 Example 9 28 0.83 -215 2.4 0.17 0.11 34 100 Example 10 27 0.86 -225 2.3 0.18 0.09 32 104 Example 11 28 0.84 -220 2.6 0.18 0.1 36 100 Example 12 28 0.83 -218 2.4 0.17 0.1 34 100 Comparative Example 1 40 1.2 -160 5 0.26 0.15 40 70 Comparative Example 2 22 1.8 -320 13 0.35 0.18 55 127 Comparative Example 3 35 1.5 -185 8 0.3 0.2 90 80 Comparative Example 4 28 1.35 -230 15 0.32 0.38 38 100 Comparative Example 5 28 0.88 -215 2.7 0.19 0.11 35 100 Note: Grinding time refers to the time required to achieve a flat end face; relative efficiency is calculated based on 100% of Example 1, with higher efficiency resulting in shorter time; insertion loss is the average of 1310 nm and 1550 nm wavelengths; friction coefficient is calculated by measuring torque during the grinding process; cleaning time refers to the time required to rinse the grinding pad clean with deionized water.

[0099] As can be seen from the data in Tables 1 and 2, all embodiments of the present invention exhibit excellent performance. Taking the optimal embodiment 1 as a benchmark, its grinding time is only 28 seconds, the surface roughness reaches an ultra-smooth level of 0.85 nanometers, the fiber concavity of -220 nanometers is precisely at the center of the ideal range, the number of scratches is only 2.5 per end face, the insertion loss is as low as 0.18 dB, the coefficient of friction is only 0.11, and the cleaning time is 35 seconds. These comprehensive superior indicators demonstrate the advanced nature of the technical solution of the present invention.

[0100] Comparative Example 1, lacking nanodiamonds and using only α-alumina as the abrasive, experienced a grinding time extended to 40 seconds and a relative efficiency reduction to 70%, demonstrating the crucial role of nanodiamonds in improving grinding efficiency. Although the surface roughness of Comparative Example 1 reached 1.20 nm, still within an acceptable range, it was significantly inferior to the Example. More importantly, due to the insufficient hardness of α-alumina, it was difficult to effectively remove certain harder surface protrusions, resulting in an optical fiber concavity of only -160 nm, at the lower limit of the ideal range, which could easily lead to poor physical contact between the optical fiber end face and the connector.

[0101] Comparative Example 2 goes to the other extreme, completely excluding α-alumina and using only 38% nanodiamond. While it boasts the fastest grinding speed at just 22 seconds and a relative efficiency of 127%, this aggressive grinding comes at the cost of severely degraded surface quality. The surface roughness reaches 1.80 nanometers, more than double that of Example 1, with an astonishing 13 scratches per end face, and insertion loss increasing to 0.35 dB. These data clearly demonstrate that while a single hard abrasive can quickly remove material, it cannot achieve a fine, smooth finish. It must be combined with medium-hardness α-alumina to ensure both high efficiency and quality. The composite abrasive system of nanodiamond and α-alumina is like a martial arts principle of combining strength and flexibility, requiring both the powerful, rapid cutting of diamond and the flexible, fine finish of alumina; neither can be dispensed with.

[0102] Comparative Example 3 removed the styrene-maleic anhydride copolymer dispersant, attempting to achieve dispersion solely with modified polyurea. Although the amount of modified polyurea was significantly increased to 15%, the dispersion effect remained poor, with a Zeta potential of only -25 mV, far lower than the -40 to -48 mV of the examples. The lower Zeta potential indicates insufficient surface charge density, weak electrostatic repulsion, and easy particle agglomeration. These agglomerates acted as abnormally large particles during grinding, scratching the surface and increasing the surface roughness to 1.50 nm, with an increase of 8 scratches per end face. More seriously, due to poor dispersion, the abrasive concentration in the grinding fluid was uneven, affecting both grinding efficiency and consistency. The cleaning time was as long as 90 seconds, 2.6 times that of Example 1, indicating severe and difficult-to-remove agglomerated abrasive and excessive polyurea residue. This comparative example fully demonstrates the irreplaceable nature of the dedicated dispersant, the styrene-maleic anhydride copolymer, whose unique amphiphilic structure allows for the formation of an effective dispersion protective layer on the surface of nanoscale abrasives.

[0103] Comparative Example 4 removed the perfluoropolyether lubricant, a seemingly minor change that led to disastrous consequences. Although the grinding time, zeta potential, and other indicators were comparable to Example 1, the surface quality indicators deteriorated significantly. Most notably, the number of scratches surged to 15 per end face, six times that of Example 1, and the surface roughness increased to 1.35 nm, with an insertion loss of 0.32 dB. The mechanism behind these figures lies in the fact that although the amount of perfluoropolyether used is extremely small, only 0.1%, the ultra-thin lubricating film it forms at the friction interface is crucial for reducing scratches. At the microscopic level, the grinding process involves repeated contact and relative movement between abrasive particles and the connector end face. Without lubricant, this contact is a hard-on-hard solid-solid friction with a coefficient of friction as high as 0.38; however, with the perfluoropolyether lubricating film, the contact transforms into a solid-liquid-solid soft contact, reducing the coefficient of friction to 0.11, a reduction of 71%. Low friction not only reduces heat generation, but more importantly, it changes the way abrasives move: under high friction conditions, abrasives are easily stuck and scratch along the surface; while under low friction lubrication conditions, abrasives roll more easily, replacing sliding with rolling, greatly reducing the formation of scratches. This comparative example powerfully demonstrates the indispensable role of a small but crucial amount of lubricant in precision grinding.

[0104] Comparative Example 5 removed the modified polyurea anti-settling agent. Interestingly, immediately after preparation, the properties of Comparative Example 5 were almost identical to those of Example 1, with no difference in grinding performance. This is because, in the short term, the electrostatic repulsion and steric hindrance provided by the styrene-maleic anhydride copolymer are sufficient to maintain the dispersion of the abrasive particles. However, with prolonged storage, the continuous effect of gravity causes the abrasive particles to gradually settle, and the system lacking three-dimensional network support is unable to resist this settling. Storage stability tests showed that Comparative Example 5 began to stratify after 7 days, showed significant settling after 15 days, and formed a hard precipitate at the bottom after 30 days. In contrast, Example 1 remained uniformly stable after 30 days, with the Zeta potential only slightly decreasing from -46 mV to -44 mV. This comparative example reveals an important fact: short-term dispersion stability and long-term storage stability are two different concepts, requiring different mechanisms to ensure them. Dispersants ensure short-term stability, while anti-settling agents ensure long-term stability; their functions are different and they cannot be substituted for each other. For commercial products, long-term storage stability is crucial; otherwise, the product will become ineffective after being stored in the sales channel for several weeks, causing customer complaints and economic losses.

[0105] The performance differences between the various embodiments also warrant further analysis. Embodiment 2 uses the lower limit formulation, with a smaller total abrasive amount and relatively lower grinding efficiency, but it achieved the optimal surface roughness of 0.75 nm and the fewest scratches (2 per end face). This indicates that while the lower abrasive concentration reduces efficiency, it also reduces mutual interference between abrasive particles and mechanical impact on the surface, which is beneficial for obtaining an ultra-smooth surface. This formulation is suitable for precision grinding applications with extremely high surface quality requirements but less stringent efficiency requirements.

[0106] Example 3 uses the maximum abrasive concentration formulation, achieving the highest grinding efficiency in just 24 seconds, with a relative efficiency of 117%. However, the surface roughness slightly increased to 0.95 nanometers, and the number of scratches increased to three per end face. This is a normal phenomenon caused by the increased abrasive concentration: more abrasive means more cutting points working simultaneously, accelerating material removal; however, it also increases the probability of collisions and aggregation between abrasive particles, as well as the risk of surface scratches. This formulation is suitable for coarse or medium grinding stages where high efficiency is required and surface quality requirements are relatively relaxed.

[0107] Examples 4 and 5 verified the effect of different diamond particle sizes. Example 4 used 100 nm small-diameter diamond particles, achieving a good surface roughness of 0.80 nm, demonstrating the advantages of small-diameter abrasives in fine grinding. Example 5 used 150 nm large-diameter diamond particles and 1.2 μm large-diameter α-alumina particles, slightly improving grinding efficiency, but the surface roughness increased to 0.90 nm. This conforms to grinding theory: the smaller the abrasive particle size, the more cutting points per unit area, and the finer the surface; the larger the particle size, the greater the depth of cut per pass, and the higher the efficiency, but the surface is relatively rougher. By adjusting the abrasive particle size, a balance between efficiency and quality best suited for a specific application can be found.

[0108] Examples 6 and 7 compared the effects of styrene-maleic anhydride copolymers with different molecular weights. Example 6 used a low molecular weight copolymer of 5000 g / mol, achieving the highest Zeta potential of -48 mV, indicating the highest surface charge per unit mass and the strongest electrostatic repulsion. Example 7 used a high molecular weight copolymer of 10000 g / mol, with a slightly lower Zeta potential but still reaching -44 mV, demonstrating better long-term stability. This reflects the trade-off in molecular weight selection: lower molecular weight provides stronger short-term dispersing power, while higher molecular weight provides more durable long-term stability. This invention selects an intermediate value of 8000 g / mol as the optimal solution, balancing the advantages of both.

[0109] Examples 8 and 9 compared the anti-settling effects of polyurea with different degrees of modification and molecular weights. Example 8 used a low-modification, low-molecular-weight polyurea, which exhibited weaker thixotropy but lower cost. Example 9 used a high-modification, high-molecular-weight polyurea, which showed the strongest thixotropy and the best long-term stability. There was no significant difference in grinding performance between the two examples because the anti-settling agent primarily affects storage stability and does not directly participate in the grinding process. Customers can choose the appropriate polyurea specification based on storage conditions and cost budget.

[0110] Examples 10 and 11 compared the lubrication effects of perfluoropolyethers with different molecular weights and viscosities. Example 10 used a low molecular weight, low viscosity perfluoropolyether, with a slightly lower coefficient of friction as low as 0.09, indicating faster spreading speed and better initial lubrication. Example 11 used a high molecular weight, high viscosity perfluoropolyether, with a coefficient of friction of 0.10, demonstrating stronger monomolecular lubrication ability and a more durable lubricating film. The differences between the two examples were minimal; both effectively reduced friction and scratches.

[0111] Example 12 validated the application of the Z-type perfluoropolyether, whose performance was comparable to that of Example 1 using the Y-type perfluoropolyether, demonstrating that both structures of perfluoropolyether are suitable for the present invention, providing more choices and flexibility for formulation design.

[0112] Based on all test data and mechanistic analysis, it can be concluded that all embodiments of the present invention exhibit excellent and stable performance, significantly superior to all comparative examples. This superiority stems from the careful selection and synergistic effect of the components in the formulation: nanodiamond and α-alumina form a composite abrasive system with a hard-soft combination, balancing efficiency and quality; styrene-maleic anhydride copolymer achieves stable dispersion through a dual mechanism of electrostatic repulsion and steric hindrance; modified polyurea constructs a three-dimensional network to provide long-term anti-settling; perfluoropolyether forms an ultra-thin lubricating film that significantly reduces friction and scratches; citric acid acts as an environmentally friendly buffer to maintain optimal pH; and the defoamer ensures a clean surface of the grinding fluid. These components each perform their specific functions while working synergistically; the absence of any one of them would lead to a significant decrease in performance, as fully demonstrated by the results of the comparative examples.

[0113] The superior performance of this invention is not accidental, but stems from a profound understanding and meticulous design of the microscopic mechanism of the grinding process. From a chemical bonding perspective, nanodiamonds are covalent crystals formed by carbon atoms in an sp³ hybridization configuration. Each carbon atom forms four equivalent carbon-carbon σ bonds with four surrounding carbon atoms, with a bond length of 0.154 nanometers and a bond energy of 348 kilojoules per mole—one of the strongest chemical bonds in nature. It is this powerful chemical bonding that endows diamond with extremely high hardness and wear resistance. During the grinding process, the edges and tips of the diamond particles can concentrate stress. When the local stress exceeds the yield strength of the material being ground, the material undergoes brittle fracture or plastic flow, thus being removed. The nanoscale particle size allows for a cutting depth of a single diamond particle at the nanometer level, which is key to obtaining an ultra-smooth surface.

[0114] Alpha-alumina has a corundum-type crystal structure, belonging to the trigonal crystal system with space group R-3c. Oxygen ions are arranged in a close-packed configuration, while aluminum ions fill the octahedral voids. The aluminum-oxygen bond is a mixture of ionic and covalent bonds, exhibiting a certain directionality and covalentity, with a bond length of approximately 0.19 nanometers. This crystal structure endows alpha-alumina with high hardness, a high melting point, and chemical stability. However, compared to the pure covalent bonds in diamond, the strength of the aluminum-oxygen bond is slightly lower, therefore alpha-alumina has a lower hardness than diamond. During the polishing process, the behavior of alpha-alumina particles differs from that of diamond: due to its more spherical morphology and slightly lower hardness, alpha-alumina tends to roll rather than scratch, acting more like a massage than a cut on the surface, smoothing out microscopic protrusions without causing new damage. More importantly, the hydroxyl groups on the surface of alpha-alumina can form hydrogen bonds with polymer core materials. This interaction, to some extent, acts as a chemical polishing agent, promoting molecular-level smoothness of the material surface.

[0115] The synergistic mechanism between nanodiamond and α-alumina can be understood from an energy perspective. The grinding process is essentially a conversion of mechanical energy into surface and thermal energy. Nanodiamond, with its extremely high hardness, possesses a high energy flux, capable of transferring a large amount of energy to the substrate in a short time, leading to rapid material removal. However, this can also cause excessive surface damage and heat accumulation. α-alumina, acting as an energy buffer, disperses and absorbs some of the mechanical energy, resulting in a more gentle and uniform energy transfer. The difference in particle size between the two abrasives is also significant: 125 nm diamond and 1 μm alumina form a good particle size distribution, with small particles filling the gaps between larger particles, increasing the packing density and efficiency of the abrasive. Simultaneously, different particle sizes create textures of different frequencies on the surface; these textures superimpose and cancel each other out, ultimately forming a non-directional, ultra-smooth surface.

[0116] The dispersion mechanism of styrene-maleic anhydride copolymers involves complex surface chemistry and colloid chemistry principles. From a molecular structure perspective, the benzene ring of the styrene unit is a large π-bond system with a high electron cloud density, exhibiting hydrophobicity. This hydrophobicity originates from the dispersion forces between π electrons and nonpolar solvents, also known as van der Waals forces. Although diamond and α-alumina surfaces have different polarities, they both possess certain hydrophobic regions, and styrene units preferentially adsorb into these regions through hydrophobic interactions. Adsorption is a spontaneous entropy-increasing process because after the hydrophobic groups dispersed in water are driven to the abrasive surface, surrounding water molecules are released from the ordered iceberg structure, resulting in a significant increase in entropy. This lowers the free energy of the entire system, allowing adsorption to proceed stably.

[0117] Maleic anhydride units undergo hydrolysis under alkaline conditions. The reaction mechanism is as follows: First, hydroxide ions, acting as nucleophiles, attack the positively charged center on the carbonyl carbon of maleic anhydride, forming a tetrahedral intermediate. Then, the CO single bond breaks, opening the ring to form a maleic acid monoamide salt. Finally, the amide hydrolyzes to a carboxylic acid, generating maleic acid. The two carboxyl groups of maleic acid fully dissociate into carboxylate anions at pH 9.5 to 10.0, with dissociation equilibrium constants pKa1 approximately 1.9 and pKa2 approximately 6.3. Under strongly alkaline conditions, the degree of dissociation approaches 100%. Each maleic acid unit provides two negative charges, resulting in a high-density negative charge on the copolymer molecular chains adsorbed on the abrasive surface.

[0118] According to the DLVO theory, the interaction potential energy between two charged particles consists of two parts: van der Waals attraction energy and electrostatic repulsion energy. Van der Waals attraction energy is inversely proportional to the sixth power of the distance between particles, representing a long-range force that always promotes particle aggregation. Electrostatic repulsion energy is directly proportional to the square of the surface charge density and inversely proportional to the distance between particles, forming an exponential function; it represents an even longer-range force. When the electrostatic repulsion energy is much greater than the van der Waals attraction energy, an energy barrier exists between the particles, preventing them from approaching each other, resulting in a stable dispersion of the system. In this invention, the high-density surface charge provided by the styrene-maleic anhydride copolymer results in a Zeta potential of -40 to -48 millivolts, corresponding to a surface charge density of approximately 0.2 to 0.3 charges per square nanometer. The resulting electrostatic repulsion energy is sufficient to resist van der Waals attraction, forming a repulsive energy barrier tens of nanometers thick.

[0119] Besides electrostatic repulsion, steric hindrance also plays a crucial role. Maleic acid segments extending in the aqueous phase repel each other due to their negative charge, forming extended polymeric brush structures. When two copolymer-coated abrasive particles approach each other, the polymeric brushes on their surfaces overlap and compress, leading to an increase in local polymer concentration. According to the principle of osmotic pressure, the concentration gradient generates osmotic pressure, driving solvent molecules to flow from low-concentration areas to high-concentration areas, thus generating a repulsive force. This osmotic repulsion force is short-range but powerful, providing strong protection within a range of several nanometers on the particle surface. The synergistic effect of electrostatic repulsion and steric hindrance makes styrene-maleic anhydride copolymers ideal nanoparticle dispersants.

[0120] The anti-settling mechanism of modified polyurea is based on rheological principles. The urea group (-NH-CO-NH-) on the main chain of the polyurea molecule is a strong hydrogen bond donor and acceptor, capable of forming interchain hydrogen bonds. A hydrogen bond is a special type of dipole-dipole interaction. When a hydrogen atom is covalently bonded to a highly electronegative atom (such as oxygen or nitrogen), that hydrogen atom carries a partial positive charge and can interact with the lone pair electrons of another electronegative atom to form a hydrogen bond. The NH hydrogen atom in the urea group forms a hydrogen bond with the carbonyl oxygen atom. The bond energy is approximately 10 to 30 kilojoules per mole. Although much weaker than a covalent bond, the total hydrogen bond force is considerable when the number of molecules is large.

[0121] Multiple polyurea molecular chains cross-link through hydrogen bonds to form a three-dimensional network structure, which microscopically resembles a spider web: the polyurea molecular chains are the threads, the hydrogen bond cross-linking points are the nodes, and the abrasive particles are suspended within the mesh. This network structure endows the system with solid-like properties: in a static state, the network structure is intact, the system exhibits high elastic modulus and viscosity, and the abrasive particles are fixed and cannot settle. When shear force is applied, the shear stress exceeds the strength of the hydrogen bonds, the hydrogen bonds break, the network structure is destroyed, and the system transforms into a liquid-like state, with the viscosity rapidly decreasing. After the shearing stops, because hydrogen bonds are reversible non-covalent bonds, the broken hydrogen bonds can quickly reform, the network structure is restored, and the viscosity recovers. This reversible solid-liquid transition is the essence of thixotropy.

[0122] Carboxyl modification improves the anti-settling effect of polyurea. The introduced carboxyl groups dissociate into carboxylate anions under alkaline conditions, giving the polyurea molecular chains a negative charge. On one hand, the charged polyurea segments interact electrostatically with the similarly negatively charged abrasive particles, enhancing the network's constraint on the particles. On the other hand, the negative charge increases the water solubility and hydrophilicity of the polyurea, facilitating its extension in the aqueous phase to form a more stable network. However, the degree of modification cannot be too high, as excessive negative charge can lead to electrostatic repulsion between molecular chains, weakening hydrogen bonding and reducing network strength. This invention selects a modification degree of 8% to 12%, achieving the optimal balance between hydrophilicity and crosslinking ability.

[0123] The ultra-low friction mechanism of perfluoropolyethers stems from their unique molecular structure and surface properties. In a perfluoropolyether molecule, all hydrogen atoms are replaced by fluorine atoms, forming a fully fluorinated polyether. Fluorine is the most electronegative element in the periodic table, with an electronegativity of 4.0, far exceeding carbon's 2.5 and oxygen's 3.5. This strong electronegativity causes fluorine atoms to tightly attract electrons from carbon atoms, forming highly polar CF bonds. However, because each carbon atom is surrounded by symmetrically arranged fluorine atoms, the dipole moments of each CF bond cancel each other out, resulting in a nonpolar or weakly polar molecule with extremely high hydrophobicity.

[0124] Fluorine atoms have a relatively large atomic radius, approximately 0.135 nanometers, much larger than the 0.037 nanometer radius of hydrogen atoms. When all the hydrogen atoms in a carbon chain are replaced by fluorine, the fluorine atoms form a dense barrier, completely encapsulating the carbon skeleton. This fluorinated shell makes the surface of perfluoropolyether molecules extremely smooth, with very low surface energy, only about 10 to 15 millinewtons per meter, far lower than the 25 to 30 millinewtons per meter of hydrocarbons and the 72 millinewtons per meter of water. Low surface energy means that perfluoropolyethers are not easily wetted by other substances, and also means that they have extremely strong spreading ability.

[0125] During the grinding process, perfluoropolyether molecules are squeezed out of tiny droplets by shear forces, rapidly spreading across the solid surface to form a lubricating film of monolayer or several molecular layers thickness. This lubricating film alters the properties of the friction interface: the original solid-solid contact becomes a solid-liquid-solid contact, and the interface changes from a high-energy solid surface to a low-energy perfluoropolyether surface. When the two solid surfaces move relative to each other, shearing mainly occurs within the perfluoropolyether molecular layers. Due to the weak van der Waals forces between the perfluoropolyether molecular chains, the chains easily slide relative to each other, resulting in an extremely low coefficient of friction. This lubrication mechanism is called boundary lubrication, and its effectiveness depends on the strong adsorption of the lubricant on the solid surface and the low shear strength of the lubricant itself.

[0126] The chemical inertness of perfluoropolyethers is also crucial. The CF bond has a bond energy as high as 485 kJ / mol, one of the strongest known single bonds, far exceeding the CH bond's 413 kJ / mol and the CC bond's 348 kJ / mol. This strong CF bond makes perfluoropolyethers extremely difficult to chemically react, resisting the attack of almost all chemical reagents, including acids, alkalis, oxidants, and reducing agents. In the alkaline environment of the polishing slurry, perfluoropolyethers remain completely stable, without undergoing hydrolysis, oxidation, or other degradation reactions. This stability ensures the durability of the lubricating effect; the polishing slurry will not lose its lubricating ability even after long-term storage.

[0127] The choice of citric acid as a pH adjuster reflects multiple considerations. Chemically, the citric acid molecule contains three carboxyl groups and one hydroxyl group, with the molecular formula C6H8O7. The pKa values ​​of the three carboxyl groups are 3.13, 4.76, and 6.40, respectively. This gradient of pKa values ​​gives citric acid buffering capacity over a wide pH range. In a grinding slurry environment with pH 9 to 10, the three carboxyl groups of citric acid almost completely dissociate into the citrate trivalent anion. However, because the pKa of its conjugate acid (hydrocitrate ion) is close to this pH range, it can resist pH changes through proton transfer equilibrium. When a small amount of base enters the system, the hydrogen citrate ion accepts a proton to convert to citric acid, consuming the base; when a small amount of acid enters, the citrate ion loses a proton to convert to hydrogen citrate, consuming the acid. This buffering mechanism ensures pH stability.

[0128] Another important function of citric acid is the chelation of metal ions. Its three carboxyl groups and one hydroxyl group can form stable chelate complexes with metal ions. During the production and storage of grinding slurries, trace amounts of metal ion contamination may occur, such as iron ions from equipment and calcium and magnesium ions from water sources. If these metal ions are not removed, they may combine with the abrasive surface, altering its surface properties and causing aggregation; or they may catalyze certain redox reactions, leading to the degradation of other components. Citric acid locks these metal ions in chelate complexes through chelation, rendering them inactive and protecting the stability of the grinding slurry.

[0129] From an environmental perspective, citric acid is a natural organic acid widely found in citrus fruits and is non-toxic and harmless to humans and the environment. Microorganisms can metabolize citric acid through the tricarboxylic acid cycle, making it biodegradable. Using citric acid instead of traditional strong alkalis such as sodium hydroxide avoids the environmental problems of strong corrosiveness and high-pH wastewater, aligning with the principles of green chemistry and sustainable development.

[0130] The above mechanistic analysis demonstrates that each component of this invention has been carefully selected, with its chemical structure, physical properties, and mechanism of action perfectly matching the application requirements. More importantly, the synergistic effect between the components produces a result greater than the sum of its parts: the composite abrasive achieves a balance between efficiency and quality; the dispersant and anti-settling agent work together to ensure short-term and long-term stability; the lubricant and abrasive synergistically reduce friction and scratches; and the pH adjuster maintains the optimal chemical environment. This multi-component, multi-level, and multi-dimensional synergistic system is the fundamental reason why this invention comprehensively surpasses existing technologies.

[0131] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-efficiency polishing slurry for MPO connectors, characterized in that, By weight percentage, it includes the following components: Nanodiamonds: 3%–6%; α-Alumina: 27%–44%; Styrene-maleic anhydride copolymer: 8%–15%; Modified polyurea solution: 2%–5%; Perfluoropolyether: 0.05%–0.3%; Citric acid: 0.5%–2%; Polyether-modified polysiloxane defoamer: 0.5%–1.5%; Deionized water balance up to 100%.

2. The high-efficiency polishing slurry for MPO connectors according to claim 1, characterized in that, The average particle size of the nanodiamond is 100 to 150 nanometers, the average particle size of the α-alumina is 0.8 to 1.2 micrometers, and the weight ratio of the nanodiamond to the α-alumina is 1:6 to 1:

10.

3. The high-efficiency polishing slurry for MPO connectors according to claim 1, characterized in that, The styrene-maleic anhydride copolymer has a molar ratio of styrene units to maleic anhydride units of 2:1, and the number-average molecular weight of the styrene-maleic anhydride copolymer is 5,000 to 10,000 g / mol.

4. The high-efficiency polishing slurry for MPO connectors according to claim 1, characterized in that, The modified polyurea solution is an aqueous solution of carboxyl-modified polyurea, wherein the degree of carboxyl modification of the carboxyl-modified polyurea is 8% to 12%, the solid content of the modified polyurea solution is 30% to 40%, and the weight-average molecular weight of the modified polyurea in the modified polyurea solution is 15,000 to 25,000 g / mol.

5. The high-efficiency polishing slurry for MPO connectors according to claim 1, characterized in that, The perfluoropolyether is a Y-type or Z-type perfluoropolyether, the weight-average molecular weight of the perfluoropolyether is 2000 to 5000 g / mol, the kinematic viscosity of the perfluoropolyether at 25 degrees Celsius is 100 to 200 centipoise, and the pH value of the grinding fluid is 9.5 to 10.

0.

6. A method for preparing the high-efficiency polishing slurry for MPO connectors according to claim 1, characterized in that, Includes the following steps: Step 1: Add deionized water to the mixing tank, start the stirring device, control the stirring speed to 2000 revolutions per minute, and keep the temperature between 20 and 25 degrees Celsius. Step 2: Slowly add the styrene-maleic anhydride copolymer to the mixing tank and stir continuously for 30 minutes until the styrene-maleic anhydride copolymer is completely dissolved to obtain a dispersant solution; Step 3: Premix nanodiamonds and α-alumina for 5 minutes, then slowly add the mixed abrasive to the dispersant solution, increase the stirring speed to 2500 rpm, and perform high shear dispersion for 60 minutes to obtain the abrasive dispersion. Step 4: Slowly add the modified polyurea solution to the abrasive dispersion, reduce the stirring speed to 2000 rpm, and continue stirring for 120 minutes to form a three-dimensional network structure, thus obtaining the anti-settling system. Step 5: Add perfluoropolyether and polyether-modified polysiloxane defoamer sequentially to the anti-settling system, stir for 30 minutes to ensure uniform dispersion of each component, and obtain a mixed grinding liquid; Step 6: Adjust the pH of the mixed grinding solution to 9.5 to 10.0 with an aqueous citric acid solution to obtain the finished grinding solution; Step 7: Filter the finished grinding slurry through a filter bag with a 5-micron pore size to remove impurity particles, and then package it.

7. The preparation method according to claim 6, characterized in that, The shear rate of the high-shear dispersion process in step three is greater than 10,000 per second; the mass concentration of the citric acid aqueous solution in step six is ​​10%.

8. The preparation method according to claim 6, characterized in that, In step one, the amount of deionized water is 45% of the total weight of the polishing slurry; in step two, the amount of styrene-maleic anhydride copolymer is 12% of the total weight of the polishing slurry; in step three, the amount of nanodiamond is 4.2% of the total weight of the polishing slurry, and the amount of α-alumina is 33.8% of the total weight of the polishing slurry; in step four, the amount of modified polyurea solution is 3% of the total weight of the polishing slurry; in step five, the amount of perfluoropolyether is 0.1% of the total weight of the polishing slurry, and the amount of polyether-modified polysiloxane defoamer is 0.9% of the total weight of the polishing slurry; in step six, the amount of citric acid is 1% of the total weight of the polishing slurry.

9. The preparation method according to claim 6, characterized in that, The premixing process in step three adopts a dry mixing method, and the mixing time is 5 minutes; the three-dimensional network structure formed in step four gives the grinding fluid thixotropic properties, so that the viscosity of the grinding fluid is 150 to 250 mPascals per second in the static state and 80 to 120 mPascals per second in the shear state.

10. The application of the high-efficiency polishing slurry for MPO connectors according to any one of claims 1 to 5 in the end-face polishing of MPO fiber optic connectors, characterized in that, The grinding pressure during the grinding process is 0.2 to 0.4 MPa, the grinding speed is 100 to 200 rpm, the grinding fluid flow rate is 30 to 50 ml per minute, and the surface roughness Ra value of the connector end face after grinding is less than 1 nanometer, and the fiber indentation is -50 nanometers to -400 nanometers.