High-precision abrasive cloth with gradient particle size abrasive distribution

Abstract

The invention relates to the technical field of abrasive cloth for grinding, polishing or cutter grinding and manufacturing of the abrasive cloth, in particular to high-precision abrasive cloth with gradient particle size abrasive distribution, which comprises a flexible substrate, a pre-coating layer, an abrasive layer and a composite adhesive layer with cross-linking density gradient, the continuous cutting path, efficient heat dissipation and good surface consistency can be achieved, grinding materials are not prone to falling off, the grinding service life is remarkably prolonged, and the machining precision is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of abrasive cloth for grinding, polishing or sharpening and its manufacturing technology, specifically a high-precision abrasive with gradient particle size distribution. Background Technology

[0002] High-precision abrasive cloth, as an important component of coated abrasives, is widely used in the surface processing of metals, composite materials, and precision parts. Its performance depends primarily on the matrix strength, the adhesive system, and the type, size, and distribution of the abrasive particles. Traditional abrasive cloths often use a single-particle-size or randomly mixed-particle-size abrasive, which, while meeting conventional grinding needs to some extent, has significant shortcomings in terms of overall performance such as high precision, high efficiency, and long lifespan. In recent years, to improve the cutting stability, heat dissipation, and surface finish of abrasive cloths, the industry has begun to explore multi-component abrasive composites and structural optimization designs.

[0003] Patent CN112917400B discloses a high-performance composite material precision polishing abrasive cloth and its preparation method. The abrasive cloth body sequentially comprises a matrix, a pre-coating layer, an abrasive layer, and a composite adhesive layer. The abrasive layer contains various abrasive components such as silicon carbide, alumina, and ceramic microcrystalline abrasives, and is bonded with adhesive systems such as phenolic resin, epoxy resin, and polyurethane. This technical solution, through composite abrasives and a multi-layer adhesive structure, enables the abrasive cloth to combine the cutting stability of bonded abrasives with the flexibility of coated abrasives, significantly improving grinding efficiency and service life. However, although the various abrasives in this solution are mixed in weight proportions, the spatial distribution of abrasives of different particle sizes is not directionally controlled, resulting in a random arrangement of abrasives during the abrasive application process. This prevents the formation of cutting layers from coarse to fine or with a gradient transition, thus limiting its surface consistency and processing efficiency in ultra-precision polishing scenarios.

[0004] Patent CN209579263U discloses a waterproof abrasive cloth for precision CNC grinding machines. Its abrasive layer contains three groups of abrasive particles of different sizes, arranged alternately in a matrix on a polyurethane base layer. This structure, through the combination of abrasive particles of different sizes, achieves a multi-stage cutting effect to some extent, improving grinding accuracy and lifespan. However, this solution only involves a simple transverse alternation of abrasive particles of different sizes, lacking a particle size gradient design along the thickness direction of the abrasive cloth or the grinding depth direction, thus failing to construct a continuous cutting path integrating "rough grinding" and "fine grinding." Furthermore, its abrasive arrangement relies on mechanical positioning, making it difficult to maintain high consistency in high-speed continuous production. It also lacks synergistic optimization by incorporating the gradient curing or penetration characteristics of the adhesive, leading to early detachment or clogging of the abrasive particles during use, affecting the overall stability of grinding performance.

[0005] In summary, while existing high-precision abrasive cloth technology has made some progress in abrasive composites and structural design, it still has significant shortcomings in controlling the spatial gradient distribution of abrasive particle size, making it difficult to simultaneously meet the dual requirements of efficient coarse grinding and fine polishing. Therefore, there is an urgent need to develop a high-precision abrasive cloth with a gradient abrasive particle size distribution. By scientifically designing the particle size hierarchy and arrangement of abrasive particles on the surface and in the depth direction of the abrasive cloth, the cutting force can be released step by step and heat can be effectively dissipated, thereby significantly improving the surface quality, grinding efficiency, and product lifespan. Summary of the Invention

[0006] This invention provides a high-precision abrasive cloth with gradient particle size distribution. It aims to solve the problems of discontinuous cutting paths, low heat dissipation efficiency, poor surface consistency, and easy abrasive shedding caused by random abrasive arrangement in the prior art by constructing an abrasive particle size gradient distribution system with a clear hierarchical structure in the thickness direction and surface plane direction of the abrasive cloth, and by combining the synergistic control of adhesive penetration depth and curing rate.

[0007] In a first aspect, the present invention provides a method for preparing high-precision abrasive cloth with gradient particle size distribution, comprising the following steps: S10: Provide a flexible substrate, and coat the surface of the flexible substrate with a pre-coating adhesive, wherein the pre-coating adhesive is a mixture of phenolic resin, epoxy resin and polyurethane resin in a mass ratio of 3:2:1, with a solid content of 40% to 60%, and a coating amount of 80g to 120g per square meter, and then dry at a temperature of 90°C to 110°C for 30 to 60 minutes to form a pre-coating. S20: Three electrostatic sand-planting operations are performed sequentially on the pre-coated surface. Each sand-planting operation uses abrasive particles with different particle sizes. The first sand-planting operation uses first-grade coarse abrasive with a particle size of 100 to 150 micrometers. The second sand-planting operation uses second-grade medium abrasive with a particle size of 60 to 90 micrometers. The third sand-planting operation uses third-grade fine abrasive with a particle size of 20 to 40 micrometers. Before each sand-planting operation, an electrostatic field is applied to the pre-coated surface with a voltage of 6,000 to 12,000 volts. The sand-planting densities are 300 to 400 particles per square centimeter, 200 to 300 particles per square centimeter, and 100 to 200 particles per square centimeter, respectively. S30: After completing three sand plantings, a coating adhesive is sprayed onto the surface of the sand cloth. The coating adhesive is made by mixing modified phenolic resin and nano silica sol in a mass ratio of nine to one. The solid content of the nano silica sol is 10% to 20%, the particle size is 10 to 30 nanometers, and the spraying amount is 40 to 70 grams per square meter. S40: The abrasive after the sprayed adhesive layer is placed in a gradient temperature oven for segmented curing. In the first stage, the temperature is maintained at 80°C to 100°C for 20 to 40 minutes to allow the surface of the adhesive layer to initially cross-link. In the second stage, the temperature is raised to 140°C to 160°C and maintained for 40 to 80 minutes to allow the middle layer of the adhesive layer to fully cure. In the third stage, the temperature is raised to 180°C to 200°C and maintained for 60 to 120 minutes to allow the bottom layer of the adhesive layer to fully cross-link with the pre-coated interface, ultimately forming an abrasive fixing system with a three-dimensional gradient structure.

[0008] According to the present invention, by sequentially applying electrostatic abrasive particles of different sizes to the pre-coated surface three times, and controlling the density and electrostatic field strength of each application, large-diameter abrasive particles preferentially embed into the deeper regions of the pre-coated layer, medium-diameter abrasive particles are located in the middle layer, and small-diameter abrasive particles are mainly distributed on the surface layer, thereby forming a vertical particle size gradient from coarse to fine in the thickness direction of the abrasive cloth. Simultaneously, since the abrasive particles vertically impact the pre-coated surface under the action of the electric field during the electrostatic abrasive application process, their embedding depth is related to the particle kinetic energy, which is determined by both particle size and electric field strength. Therefore, by adjusting the voltage and abrasive particle size combination for each application, the embedding depth ratio of each particle size in the pre-coated layer can be precisely controlled. In addition, the adhesive layer uses modified phenolic resin containing nano-silica and is combined with a three-stage gradient temperature curing process, which makes the adhesive layer exhibit different cross-linking densities and penetration capabilities in different depth areas. The surface adhesive layer rapidly cross-links to fix fine abrasives, the middle adhesive layer penetrates moderately to wrap medium abrasives and provide support, and the bottom adhesive layer penetrates deeply and fuses with the pre-coating layer to anchor coarse abrasives, thereby achieving graded anchoring and stress buffering of abrasives in the depth direction.

[0009] In some embodiments, in step S10, the flexible substrate is a polyester fiber nonwoven fabric or a polyamide woven fabric with a basis weight of 150 to 250 grams per square meter and a breaking strength of not less than 800 Newtons per 5 centimeters.

[0010] In some embodiments, in step S10, the pre-coating adhesive further contains 0.5% to 2% of a silane coupling agent, wherein the silane coupling agent is γ-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane.

[0011] In some embodiments, in step S20, the first-stage coarse abrasive, the second-stage medium abrasive, and the third-stage fine abrasive are all ceramic microcrystalline alumina abrasives with a Mohs hardness of not less than nine, a crystal structure of α-phase alumina, and a particle size distribution standard deviation of not more than ten micrometers for each particle size abrasive.

[0012] In some embodiments, in step S20, the time interval between the three sand-planting operations does not exceed five minutes, and no intermediate drying or curing treatment is performed after each sand-planting, so as to maintain the viscous state of the pre-coated surface and ensure that the subsequent abrasive can be partially embedded in the gaps between the sand-planted layers to form an interlocking structure.

[0013] In some embodiments, in step S20, the electrostatic field voltage used for the second sand planting is reduced by 10% to 20% compared to the first, and the electrostatic field voltage used for the third sand planting is further reduced by 10% to 20% compared to the second, in order to match the settling speed and embedding requirements of abrasives with different particle sizes.

[0014] In some embodiments, in step S30, the modified phenolic resin is a cashew phenol-modified phenolic resin with a free phenol content of less than 1.5 percent and a viscosity of 500 mPa second to 1500 mPa second (25 degrees Celsius).

[0015] In some embodiments, in step S30, the nano-silica sol is prepared by hydrolysis and condensation of tetraethyl orthosilicate under acidic conditions, with a pH value of two to four and a storage stability of not less than thirty days.

[0016] In some embodiments, in step S40, the gradient heating oven is provided with an independent temperature control zone, and a low temperature zone, a medium temperature zone and a high temperature zone are set sequentially along the direction of the sand cloth travel, with the temperature fluctuation range of each zone controlled within ±3 degrees Celsius.

[0017] In some embodiments, step S40 is followed by a surface finishing step: using a rotating brush to lightly sweep the surface of the abrasive cloth at a linear speed of five to ten meters per second to remove loose sand particles that are not firmly bonded, while controlling the exposed height of the top of the fine abrasive on the surface to be within the range of five to fifteen micrometers.

[0018] In some embodiments, at least one of the abrasives used in the three-stage sand planting process undergoes plasma treatment on its surface. The treatment gas is air or oxygen, the power is 200 watts to 500 watts, and the treatment time is 30 seconds to 120 seconds, in order to increase its surface hydroxyl density and enhance its chemical bonding ability with the adhesive.

[0019] In some embodiments, the surface viscosity of the pre-coating before abrasive embedding is monitored in real time by an online viscosity sensor and controlled between 5,000 mPa second and 15,000 mPa second (25 degrees Celsius) to ensure the consistency of abrasive embedding depth.

[0020] In some embodiments, the adhesive layer is subjected to vacuum degassing treatment before spraying, with a vacuum degree of -0.08 MPa to -0.1 MPa and a degassing time of 10 to 20 minutes, in order to eliminate the influence of air bubbles on the uniformity of abrasive coating.

[0021] In some embodiments, the abrasive cloth undergoes a humidity adjustment process after curing, balancing for 24 to 48 hours in an environment with a relative humidity of 50% to 70% and a temperature of 25 to 35 degrees Celsius, to relax the internal stress of the adhesive layer and improve dimensional stability.

[0022] Secondly, the present invention provides a high-precision abrasive cloth with a gradient abrasive particle distribution, the structure of which, from bottom to top, comprises a flexible substrate, a pre-coating layer, a gradient abrasive layer, and a coating layer; the gradient abrasive layer comprises three abrasive distribution regions: the bottom layer is coarse abrasive with a particle size of 100 to 150 micrometers, the bottom of which is embedded in the pre-coating layer to a depth of 30 to 50 micrometers, and the top of which protrudes 50 to 80 micrometers above the pre-coating layer surface; the middle layer is medium abrasive with a particle size of 60 to 90 micrometers, the bottom of which is located between the pre-coating layer surface and a depth of 20 micrometers, and the top of which protrudes 20 to 50 micrometers above the pre-coating layer surface; the top layer is fine abrasive with a particle size of 20 to 40 micrometers, the bottom of which is located between the pre-coating layer surface and a depth of 10 micrometers, and the top of which protrudes 5 to 20 micrometers above the pre-coating layer surface; the three abrasive layers... The abrasive particles are staggered in the horizontal direction, with the spacing between adjacent particles of the same grade being 1.5 to 2.5 times their respective particle diameters. The overlapping area of ​​different grades of abrasive particles on the projection plane does not exceed 30% of the projected area of ​​a single particle. The composite adhesive layer consists of three cross-linked structures from the surface to the inside: the surface layer has a cross-linking density of 0.8 to 1.2 cross-linking points per cubic micrometer and a thickness of 5 to 15 micrometers; the middle layer has a cross-linking density of 0.5 to 0.8 cross-linking points per cubic micrometer and a thickness of 15 to 30 micrometers; and the bottom layer has a cross-linking density of 0.3 to 0.5 cross-linking points per cubic micrometer and a thickness of 30 to 50 micrometers, and contains nano-silica particles with a volume fraction of 3% to 7%. The nano-silica particles are uniformly dispersed in the bottom layer of the composite adhesive layer and form Si-OC covalent bonds with the phenolic resin.

[0023] According to the present invention, this high-precision abrasive cloth, by constructing a clear abrasive particle size gradient and adhesive crosslinking gradient in the thickness direction, allows coarse abrasive to bear the main cutting load in the early stage of grinding, quickly removing material; as the coarse abrasive gradually wears down, medium abrasive begins to participate in cutting, maintaining a stable removal rate; finally, fine abrasive dominates surface finishing, achieving a high surface finish. Simultaneously, the staggered arrangement of the abrasive layers in the horizontal direction avoids localized overheating or scratches caused by the aggregation of abrasive particles of the same size, while the gradient crosslinking structure of the adhesive layer provides differentiated support stiffness: the high crosslinking density of the surface layer prevents premature detachment of fine abrasive, the moderate crosslinking of the middle layer provides elastic buffering, and the low crosslinking of the bottom layer, but containing nano-reinforcing phases, ensures a strong and tough bond with the pre-coating layer. Furthermore, the introduction of nano-silica into the bottom layer of the adhesive layer not only improves the interfacial bonding strength but also forms a microporous channel network, which is beneficial for the lateral conduction of grinding heat and the removal of grinding debris, reducing clogging.

[0024] In some embodiments, the mass ratio of coarse abrasive, medium abrasive, and fine abrasive in the gradient abrasive layer is 4:3:2, and all three abrasives are ceramic microcrystalline alumina of the same system, in order to avoid interface cracking caused by differences in thermal expansion coefficients.

[0025] In some embodiments, the thickness of the pre-coating is 20 to 40 micrometers, and its glass transition temperature is 120 to 140 degrees Celsius, ensuring sufficient viscoelasticity to accommodate the embedding of abrasive particles of different sizes during the sand-planting process.

[0026] In some embodiments, the total thickness of the adhesive layer is fifty to eighty micrometers, and its thermal decomposition temperature is not lower than 350 degrees Celsius, ensuring structural stability under the high-temperature environment generated by high-speed grinding.

[0027] In some embodiments, the static peel strength of the abrasive cloth at 50% relative humidity is not less than 8 Newtons per centimeter, the dynamic grinding life is increased by more than 40% compared with traditional single-particle abrasive cloth, and the surface roughness Ra value can be stably controlled within the range of 0.1 micrometer to 0.4 micrometer.

[0028] In some embodiments, the particle size ratio of any two adjacent abrasive particles in the gradient abrasive layer is between 1.5 and 2.5 to ensure the continuity of the cutting transition and avoid surface ripples or vibration marks caused by excessive particle size jumps.

[0029] In some embodiments, the surface of the nano-silica particles in the bottom layer of the adhesive layer is modified with octadecyltrichlorosilane to improve their compatibility with organic resins, enhance their dispersion stability, and prevent significant agglomeration during storage.

[0030] In some embodiments, after the abrasive cloth is stored in a wound state for six months, its abrasive shedding rate is less than 0.5 percent, indicating that the gradient anchoring structure has excellent long-term stability.

[0031] In some embodiments, the preparation method is suitable for wide-width continuous production lines with a line speed of 30 to 50 meters per minute and a sand planting accuracy deviation controlled within ±5%, meeting the requirements of industrial mass production.

[0032] In some embodiments, the high-precision abrasive cloth with gradient particle size distribution is suitable for precision grinding and polishing of stainless steel, titanium alloys, carbon fiber composites and optical glass, and shows significant advantages, especially in scenarios where high removal rate and low surface damage are required. Detailed Implementation

[0033] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0034] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0035] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0036] As described in the background section above, current high-precision abrasive cloths often employ a single particle size or random mixed particle size arrangement, leading to problems such as discontinuous cutting paths, low heat dissipation efficiency, poor surface uniformity, and easy abrasive detachment. Although existing technologies have attempted to improve performance through composite abrasives or multi-level particle size combinations, they lack a systematic design for the spatial gradient distribution of abrasives in the thickness and horizontal directions, and fail to coordinate the penetration depth and curing rate of the adhesive with the abrasive embedding behavior, making it difficult to achieve the integration of efficient coarse grinding and fine polishing.

[0037] Based on this, this application provides a high-precision abrasive cloth with gradient particle size distribution and its preparation method. The aim is to achieve graded anchoring, stress buffering and heat conduction optimization of the abrasive by constructing a vertical particle size gradient from coarse to fine in the thickness direction of the abrasive cloth, forming an interlocking horizontal arrangement in the surface plane direction, and combining the gradient cross-linking structure of the composite adhesive layer with the nano-reinforcing phase.

[0038] In a first aspect, this application provides a method for preparing high-precision abrasive cloth with gradient particle size distribution, comprising the following steps: S10: Provide a flexible substrate, and coat the surface of the flexible substrate with a pre-coating adhesive, wherein the pre-coating adhesive is a mixture of phenolic resin, epoxy resin and polyurethane resin in a mass ratio of 3:2:1, with a solid content of 40% to 60%, and a coating amount of 80g to 120g per square meter, and then dry at a temperature of 90°C to 110°C for 30 to 60 minutes to form a pre-coating. S20: Three electrostatic sand-planting operations are performed sequentially on the pre-coated surface. Each sand-planting operation uses abrasive particles with different particle sizes. The first sand-planting operation uses first-grade coarse abrasive with a particle size of 100 to 150 micrometers. The second sand-planting operation uses second-grade medium abrasive with a particle size of 60 to 90 micrometers. The third sand-planting operation uses third-grade fine abrasive with a particle size of 20 to 40 micrometers. Before each sand-planting operation, an electrostatic field is applied to the pre-coated surface with a voltage of 6,000 to 12,000 volts. The sand-planting densities are 300 to 400 particles per square centimeter, 200 to 300 particles per square centimeter, and 100 to 200 particles per square centimeter, respectively. S30: After completing three sand plantings, a coating adhesive is sprayed onto the surface of the sand cloth. The coating adhesive is made by mixing modified phenolic resin and nano silica sol in a mass ratio of nine to one. The solid content of the nano silica sol is 10% to 20%, the particle size is 10 to 30 nanometers, and the spraying amount is 40 to 70 grams per square meter. S40: The abrasive after the sprayed adhesive layer is placed in a gradient temperature oven for segmented curing. In the first stage, the temperature is maintained at 80°C to 100°C for 20 to 40 minutes to allow the surface of the adhesive layer to initially cross-link. In the second stage, the temperature is raised to 140°C to 160°C and maintained for 40 to 80 minutes to allow the middle layer of the adhesive layer to fully cure. In the third stage, the temperature is raised to 180°C to 200°C and maintained for 60 to 120 minutes to allow the bottom layer of the adhesive layer to fully cross-link with the pre-coated interface, ultimately forming an abrasive fixing system with a three-dimensional gradient structure.

[0039] According to this application, in step S10, the flexible substrate is preferably a polyester fiber nonwoven fabric or a polyamide woven fabric, with a basis weight controlled between 150 g / m² and 250 g / m², and a breaking strength of not less than 800 Newtons per 5 cm, to ensure that the substrate does not deform or crack during high-speed grinding. The pre-coating adhesive adopts a ternary composite system of phenolic resin, epoxy resin, and polyurethane resin, wherein the phenolic resin provides high-temperature stability and rigidity, the epoxy resin enhances adhesion and water resistance, and the polyurethane resin imparts flexibility and impact resistance. The three are mixed in a mass ratio of 3:2:1 to balance rigidity and flexibility, avoiding uneven abrasive embedding due to excessive brittleness or softness of a single resin system during the abrasive embedding process. In addition, 0.5% to 2% of a silane coupling agent, such as γ-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane, can be added to the pre-coating adhesive to enhance the interfacial bonding force between the inorganic abrasive and the organic adhesive layer. After coating, the film is dried at 90 to 110 degrees Celsius to allow the solvent to evaporate and form a semi-cured film with a certain degree of viscoelasticity. The surface viscosity is monitored in real time by an online viscosity sensor and controlled between 5,000 mPa second and 15,000 mPa second (25 degrees Celsius) to ensure that the abrasive can be stably embedded without rebounding during subsequent sand planting.

[0040] In step S20, the three-stage electrostatic abrasive coating is the core of constructing the gradient structure. The first coating uses coarse abrasive particles with a diameter of 100 to 150 micrometers. Under an electrostatic field of 6,000 to 12,000 volts, the large-diameter abrasive particles gain high kinetic energy, vertically impacting the pre-coated surface and embedding into a deeper region, typically 30 to 50 micrometers deep, with the top protruding 50 to 80 micrometers above the pre-coated surface. The second coating uses medium abrasive particles with a diameter of 60 to 90 micrometers. At this stage, the electrostatic field voltage is reduced by 10% to 20% compared to the first coating (e.g., from 10,000 volts to 8,000 volts) to match the settling characteristics of the smaller particles, controlling the embedding depth between the pre-coated surface and 20 micrometers, with the top protruding 20 to 50 micrometers. The third coating uses fine abrasive particles with a diameter of 20 to 40 micrometers. The electrostatic field voltage is further reduced (e.g., to 6,000 volts), causing the particles to primarily adhere to the surface layer, with an embedding depth not exceeding 10 micrometers and the top protruding 5 to 20 micrometers. The time interval between the three abrasive planting operations shall not exceed five minutes, and no intermediate drying shall be performed to maintain the adhesion of the pre-coated surface, allowing the subsequently planted abrasive to partially embed into the gaps between the previous abrasive layers, forming a horizontally interlocking structure. The spacing between adjacent abrasive particles of the same grade shall be controlled to be 1.5 to 2.5 times their particle size, and the overlap area of ​​different grades of abrasive on the projection plane shall not exceed 30% of the projected area of ​​a single particle to avoid shading effects. All abrasives are preferably ceramic microcrystalline alumina with a Mohs hardness of not less than nine, a crystal structure of α-phase alumina, and a particle size distribution standard deviation of not more than ten micrometers to ensure particle size uniformity. At least one grade of abrasive (usually fine abrasive) shall be plasma treated with air or oxygen as the treatment gas, at a power of 200 to 500 watts, for 30 to 120 seconds, to introduce hydroxyl groups on its surface, enhancing the chemical bonding with the adhesive.

[0041] In step S30, the adhesive layer solution is a 9:1 mixture of cashew nut shell modified phenolic resin and nano-silica sol. The cashew nut shell modified phenolic resin has a free phenol content of less than 1.5%, a viscosity of 500 mPa·s to 1500 mPa·s (25 degrees Celsius), and exhibits excellent toughness and environmental friendliness. The nano-silica sol is prepared by hydrolysis and condensation of tetraethyl orthosilicate under acidic conditions, with a pH value of 2 to 4, a particle size of 10 to 30 nanometers, and a solid content of 10% to 20%. Before spraying, the adhesive layer solution needs to undergo vacuum degassing treatment at a vacuum level of -0.08 MPa to -0.1 MPa for 10 to 20 minutes to eliminate air bubbles and ensure uniform coating of the abrasive. The spraying amount is controlled at 40 to 70 grams per square meter; too little will result in insufficient coating, while too much will clog the gaps between the abrasive particles.

[0042] In step S40, gradient temperature curing is crucial for achieving gradient cross-linking of the adhesive layer. The oven is divided into three independent temperature-controlled zones along the direction of the abrasive cloth's movement, with temperature fluctuations controlled within ±3 degrees Celsius. The first stage involves holding the adhesive layer at 80-100 degrees Celsius for 20-40 minutes to rapidly achieve initial cross-linking of the surface layer and fix the fine abrasive particles. The second stage involves raising the temperature to 140-160 degrees Celsius and holding for 40-80 minutes to fully cure the middle layer of adhesive, providing elastic support. The third stage involves raising the temperature to 180-200 degrees Celsius and holding for 60-120 minutes to allow the bottom layer of adhesive to deeply penetrate and fully cross-link with the pre-coating interface. Simultaneously, nano-silica particles form Si-OC covalent bonds with the phenolic resin, enhancing interfacial strength. After curing, surface finishing is performed: a rotating brush is used to lightly sweep the surface at a linear speed of 5-10 meters per second to remove loose sand, ensuring the exposed height of the fine abrasive particles is controlled between 5 and 15 micrometers. Subsequently, the adhesive layer is equilibrated for 24 to 48 hours in an environment with a relative humidity of 50% to 70% and a temperature of 25 to 35 degrees Celsius to relax the internal stress and improve dimensional stability.

[0043] Secondly, this application provides a high-precision abrasive cloth with a gradient abrasive particle distribution. Its structure, from bottom to top, includes a flexible substrate, a pre-coating layer, a gradient abrasive layer, and a backing layer. In the gradient abrasive layer, the mass ratio of coarse, medium, and fine abrasive particles is 4:3:2, all of which are from the same ceramic microcrystalline alumina system, avoiding differences in thermal expansion coefficients. The pre-coating layer has a thickness of 20 to 40 micrometers and a glass transition temperature of 120 to 140 degrees Celsius. The backing layer has a total thickness of 50 to 80 micrometers and a thermal decomposition temperature of not less than 350 degrees Celsius. The bottom layer of the backing layer contains 3% to 7% by volume nano-silica particles, the surface of which is modified with octadecyltrichlorosilane to improve resin compatibility. This abrasive cloth exhibits a static peel strength of not less than 8 Newtons per centimeter at 50% relative humidity, a dynamic grinding life that is more than 40% higher than that of traditional single-particle abrasive cloth, and a surface roughness Ra value that is stable at 0.1 to 0.4 micrometers. The ratio of the abrasive grain size between any two adjacent levels is between 1.5 and 2.5, ensuring a continuous cutting transition. After six months of storage, the abrasive shedding rate is less than 0.5%, making it suitable for precision machining of stainless steel, titanium alloys, carbon fiber composites, and optical glass.

[0044] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially. Example 1

[0045] S10: A polyester fiber nonwoven fabric with a weight of 200 grams per square meter is selected as the flexible substrate. A pre-coating adhesive solution (50% solid content) is mixed with phenolic resin, epoxy resin and polyurethane resin in a ratio of 3:2:1. The coating amount is 100 grams per square meter. The coating is dried at 100 degrees Celsius for 45 minutes to form a pre-coating layer with a thickness of 30 micrometers and a surface viscosity of 10,000 millipascals (25 degrees Celsius). S20: The first sand application uses coarse abrasive with a particle size of 120 micrometers and a standard deviation of 8 micrometers, with an electrostatic field voltage of 10 kilovolts and a sand application density of 350 particles per square centimeter; five minutes later, the second sand application uses medium abrasive with a particle size of 80 micrometers, a voltage of 8 kilovolts, and a density of 250 particles per square centimeter; five minutes after that, the third sand application uses fine abrasive with a particle size of 30 micrometers, a voltage of 6 kilovolts, and a density of 150 particles per square centimeter; the fine abrasive is then treated with oxygen plasma (power 300 watts, time 60 seconds). S30: Spray a composite adhesive layer made of cashew phenol-modified phenolic resin (viscosity 1000 mPa second) and nano silica sol (solid content 15%, particle size 20 nanometers) in a 9:1 ratio. Spraying amount is 50 grams per square meter. Vacuum degassing (-0.09 MPa, 15 minutes) is performed before spraying. S40: Gradient temperature curing: First stage: 90 degrees Celsius for 30 minutes, second stage: 150 degrees Celsius for 60 minutes, third stage: 190 degrees Celsius for 90 minutes; then, the brush is rotated for trimming (linear speed of 8 meters per second), and the mixture is equilibrated for 36 hours at a relative humidity of 60% and a temperature of 30 degrees Celsius. Example 2

[0046] Except for the following differences, the rest is the same as in Example 1: the voltage for the second sand planting is 9 kV (only reduced by 10%), and the voltage for the third sand planting is 7.2 kV; the solid content of nano-silica sol in the composite layer is 20%; the third stage of gradient heating is 200 degrees Celsius and held for 120 minutes. Example 3

[0047] Except for the following differences, the rest is the same as in Example 1: the flexible substrate is polyamide woven fabric with a weight of 250 grams per square meter; the pre-coating layer contains 1.5% γ-glycidoxypropyltrimethoxysilane; the three sand-planting densities are 400, 300 and 200 grains per square centimeter, respectively; and the amount of adhesive layer sprayed is 70 grams per square meter.

[0048] Comparative Example 1 The traditional single-particle-size abrasive cloth preparation method is adopted: only ceramic microcrystalline alumina abrasive with a particle size of 80 micrometers is used, and electrostatic sanding is carried out in one step (voltage of 10 kilovolts, density of 300 particles per square centimeter). The adhesive layer is ordinary phenolic resin (without nano silica). The curing is carried out by heating to 180 degrees Celsius and holding for 120 minutes in one step.

[0049] Comparative Example 2 Three-stage sand planting was adopted without gradient voltage control: 10 kV voltage was used for each of the three sand plantings, and the rest was the same as in Example 1.

[0050] Comparative Example 3 Three-stage sand planting was used, but the adhesive layer was cured without gradient: after the adhesive layer was sprayed, it was directly kept at 180 degrees Celsius for 120 minutes, and the rest was the same as in Example 1.

[0051] The abrasive cloths prepared in the above embodiments and comparative examples were subjected to performance tests, and the results are shown in the table below: sample Static peel strength (Newtons per centimeter) Dynamic grinding life (relative value, %) Surface roughness Ra (micrometers) Abrasive shedding rate (6 months, %) Cutting continuity score (1-5 points) Example 1 8.5 142 0.25 0.3 4.7 Example 2 8.8 148 0.22 0.2 4.8 Example 3 9.0 150 0.20 0.2 4.9 Comparative Example 1 5.2 100 0.65 1.8 2.5 Comparative Example 2 6.0 115 0.50 1.2 3.2 Comparative Example 3 6.5 120 0.45 1.0 3.5 As shown in the table above, the embodiments of the present invention are significantly superior to the comparative examples in terms of peel strength, grinding life, surface roughness, and abrasive stability. Comparative Example 1 has the worst performance due to its single particle size and lack of gradient structure; Comparative Example 2 suffers from discontinuous cutting due to uncontrolled abrasive embedding depth caused by the lack of voltage gradient adjustment; Comparative Example 3 suffers from easy abrasive detachment because the adhesive layer cannot form graded anchoring due to the lack of curing gradient. Example 3 exhibits the best overall performance, indicating that matrix reinforcement, coupling agent addition, and high abrasive density further improve the overall performance.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing high-precision abrasive cloth with gradient particle size distribution, characterized in that, Includes the following steps: S10: Provide a flexible substrate, and coat the surface of the flexible substrate with a pre-coating adhesive, wherein the pre-coating adhesive is a mixture of phenolic resin, epoxy resin and polyurethane resin in a mass ratio of 3:2:1, with a solid content of 40% to 60%, and a coating amount of 80g to 120g per square meter, and then dry at a temperature of 90°C to 110°C for 30 to 60 minutes to form a pre-coating. S20: Three electrostatic sand-planting operations are performed sequentially on the pre-coated surface. Each sand-planting operation uses abrasive particles with different particle sizes. The first sand-planting operation uses first-grade coarse abrasive with a particle size of 100 to 150 micrometers. The second sand-planting operation uses second-grade medium abrasive with a particle size of 60 to 90 micrometers. The third sand-planting operation uses third-grade fine abrasive with a particle size of 20 to 40 micrometers. Before each sand-planting operation, an electrostatic field is applied to the pre-coated surface with a voltage of 6,000 to 12,000 volts. The sand-planting densities are 300 to 400 particles per square centimeter, 200 to 300 particles per square centimeter, and 100 to 200 particles per square centimeter, respectively. S30: After completing three sand plantings, a coating adhesive is sprayed onto the surface of the sand cloth. The coating adhesive is made by mixing modified phenolic resin and nano silica sol in a mass ratio of nine to one. The solid content of the nano silica sol is 10% to 20%, the particle size is 10 to 30 nanometers, and the spraying amount is 40 to 70 grams per square meter. S40: The abrasive after the sprayed adhesive layer is placed in a gradient temperature oven for segmented curing. In the first stage, the temperature is maintained at 80 to 100 degrees Celsius for 20 to 40 minutes. In the second stage, the temperature is raised to 140 to 160 degrees Celsius and maintained for 40 to 80 minutes. In the third stage, the temperature is raised to 180 to 200 degrees Celsius and maintained for 60 to 120 minutes, finally forming an abrasive fixing system with a three-dimensional gradient structure.

2. The method according to claim 1, characterized in that, In step S10, the flexible substrate is a polyester fiber nonwoven fabric or a polyamide woven fabric with a basis weight of 150 to 250 grams per square meter and a breaking strength of not less than 800 Newtons per 5 centimeters.

3. The method according to claim 1, characterized in that, In step S10, the pre-coating adhesive also contains 0.5% to 2% of a silane coupling agent, wherein the silane coupling agent is γ-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane.

4. The method according to claim 1, characterized in that, In step S20, the first-stage coarse abrasive, the second-stage medium abrasive, and the third-stage fine abrasive are all ceramic microcrystalline alumina abrasives with a Mohs hardness of not less than nine, a crystal structure of α-phase alumina, and a particle size distribution standard deviation of not more than ten micrometers for each particle size abrasive.

5. The method according to claim 1, characterized in that, In step S20, the time interval between the three sand planting operations shall not exceed five minutes, and no intermediate drying or curing treatment shall be performed after each sand planting.

6. The method according to claim 1, characterized in that, In step S20, the electrostatic field voltage used for the second sand planting is reduced by 10% to 20% compared to the first time, and the electrostatic field voltage used for the third sand planting is reduced by another 10% to 20% compared to the second time.

7. The method according to claim 1, characterized in that, In step S30, the modified phenolic resin is cashew phenol modified phenolic resin, with a free phenol content of less than 1.5 percent and a viscosity of 500 mPa second to 1,500 mPa second (25 degrees Celsius).

8. The method according to claim 1, characterized in that, The step S40 is followed by a surface finishing step: using a rotating brush to lightly sweep the surface of the abrasive cloth at a linear speed of five to ten meters per second, so that the exposed height of the top of the fine abrasive on the surface is controlled within the range of five to fifteen micrometers.

9. A high-precision abrasive cloth with gradient particle size distribution, characterized in that, Its structure, from bottom to top, includes a flexible substrate, a pre-coating layer, a gradient abrasive layer, and a coating layer. The gradient abrasive layer comprises three abrasive distribution regions: the bottom layer consists of coarse abrasive particles with a particle size of 100 to 150 micrometers, with the bottom of the particles embedded in the pre-coating layer to a depth of 30 to 50 micrometers and the top protruding 50 to 80 micrometers above the pre-coating surface; the middle layer consists of medium abrasive particles with a particle size of 60 to 90 micrometers, with the bottom of the particles located between the pre-coating surface and a depth of 20 micrometers and the top protruding 20 to 50 micrometers above the pre-coating surface. The surface layer consists of fine abrasive particles with a particle size of 20 to 40 micrometers. The bottom of the particles is located between the pre-coated surface and a depth of 10 micrometers, while the top protrudes 5 to 20 micrometers above the pre-coated surface. The three layers of abrasive particles are staggered in the horizontal direction, with the spacing between adjacent particles of the same grade being 1.5 to 2.5 times their respective particle sizes. The overlap area of ​​different grades of abrasive particles on the projection plane does not exceed 30% of the projected area of ​​a single particle. The adhesive layer consists of three cross-linked structures from the surface to the interior: the surface layer has a cross-linking density of 0.8 to 1.2 cross-linking points per cubic micrometer and a thickness of 5 to 15 micrometers; the middle layer has a cross-linking density of 0.5 to 0.8 cross-linking points per cubic micrometer and a thickness of 15 to 30 micrometers; and the bottom layer has a cross-linking density of 0.3 to 0.5 cross-linking points per cubic micrometer and a thickness of 30 to 50 micrometers. It also contains nano-silica particles with a volume fraction of 3% to 7%. These nano-silica particles are uniformly dispersed in the bottom layer of the adhesive layer and form Si-OC covalent bonds with the phenolic resin.