A nano-binder coated zirconia feedstock and a method of making the same

Abstract

The application relates to the technical field of ceramic injection molding, and discloses a nano-binder-coated zirconia feedstock and a preparation method thereof. The nano-binder-coated zirconia feedstock is composed of zirconia ceramic particles and a nano-binder layer coated on the surface of the zirconia ceramic particles; the nano-binder layer is a composite layer structure, comprising an organic silane molecular layer grafted on the surface of the zirconia ceramic particles and a mixed binder layer attached to the surface of the organic silane molecular layer through covalent bonding. The application realizes molecular-level chemical bonding between the zirconia ceramic particles and the binder, significantly improves the interface bonding strength, avoids micro-cracks and pore defects caused by interface separation during the debinding process, and simultaneously solves the phase segregation problem caused by the flow rate difference between the powder and the binder during injection molding.

Description

Technical Field

[0001] This invention relates to the field of ceramic injection molding technology, and discloses a nano-binder-encapsulated zirconia feedstock and its preparation method. Background Technology

[0002] Nano-binder-encapsulated zirconia feedstock technology is a core raw material system in the field of advanced ceramic injection molding. It involves compounding submicron or nano-sized zirconia powder with a polymer binder system to obtain injection molding feedstocks that combine good flowability with high solids content. Zirconia ceramics, due to their excellent mechanical properties, corrosion resistance, and biocompatibility, are widely used in medical implants, fiber optic ferrules, and structural components. The uniformity of the feedstock and the interfacial bonding state directly determine the yield and microstructure uniformity of subsequent debinding and sintering processes. The design goal of the nano-binder-encapsulated structure is to achieve a strong chemical bond between the organic and inorganic phases, avoiding phase separation caused by ordinary mechanical mixing, thereby improving the stability of the ceramic injection molding process and the quality of the manufactured parts.

[0003] Currently, conventional methods for preparing zirconia feedstock mainly employ high-energy ball milling or intensive mixing processes to physically blend micron-sized zirconia powder with traditional binder systems such as paraffin-based and polyaldehyde-based binders. This approach suffers from the following prominent problems: First, the powder and binder only undergo simple physical coating without chemical bonding, leading to microcracks and pores at the binder-powder interface during debinding. Second, conventional mixing methods struggle to achieve complete and uniform encapsulation of zirconia ceramic particles by the nano-binder, especially when the solid content exceeds 50 vol%, resulting in a sharp increase in feedstock viscosity and a significant decrease in flowability. Third, the binder in feedstocks prepared by existing methods often exhibits a continuous phase distribution rather than an ideal "core-shell" encapsulation structure, causing differences in flow rates between the powder and binder during injection molding, leading to phase segregation and uneven green body density distribution. Fourth, traditional binder systems have a wide debinding temperature window, complex thermal decomposition products, and high residual carbon content, affecting the light transmittance and mechanical properties of sintered zirconia ceramics. In addition, some improved processes use solution methods for surface modification, but these methods have problems such as difficulty in solvent recovery, long process cycles, and poor batch-to-batch consistency, making it difficult to meet the requirements for stable industrial production.

[0004] Therefore, developing a feedstock capable of achieving complete and uniform encapsulation of zirconia ceramic particles by nano-binders and its simple and efficient preparation method has significant engineering and practical value. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a nano-binder-encapsulated zirconia feedstock and its preparation method, so as to solve the problems in the prior art where the zirconia powder and the binder are only physically mixed, the interfacial bonding strength is low, which leads to the easy generation of microcracks during the debinding process, phase segregation during injection molding, and the inability to form a complete and uniform nanoscale encapsulation layer.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A nano-binder-coated zirconia feed consists of zirconia ceramic particles and a nano-binder layer coated on the surface of the zirconia ceramic particles; The nano-binder layer has a composite layer structure, including: An organosilane molecular layer is grafted onto the surface of the zirconium oxide ceramic particles via Si-O-Zr chemical bonds, and the surface of the organosilane molecular layer contains active functional groups. A hybrid adhesive layer is attached to the surface of the organosilane molecular layer by covalent bonds, wherein the covalent bonds are formed by the reaction of reactive functional groups in the hybrid adhesive layer with active functional groups on the surface of the organosilane molecular layer; The organosilane molecular layer is formed from an organosilane compound having the general formula YR-SiX3, wherein Y is an amino, epoxy, mercapto, or methacryloyloxy group constituting the active functional group, R is a C1-C6 alkylene group, and X is a methoxy or ethoxy group. The mixed adhesive layer comprises a thermoplastic resin and a waxy substance, wherein the molecular chain of the thermoplastic resin contains functional groups that can react with the active functional group Y to form covalent bonds.

[0007] Preferably, the organosilane molecular layer is formed by hydrolyzing the organosilane compound to generate silanol groups, which then undergo a condensation reaction with the active hydroxyl groups on the surface of the zirconium oxide ceramic particles to form Si-O-Zr chemical bonds, thereby introducing active functional groups onto the surface of the organosilane molecular layer.

[0008] Preferably, the mixed adhesive layer is formed by mixing a thermoplastic resin containing reactive functional groups on its molecular chain with a wax substance, wherein the reactive functional groups react chemically with the active functional groups introduced on the surface of the organosilane molecular layer to form covalent bonds, thereby covalently bonding the mixed adhesive layer to the surface of the organosilane molecular layer.

[0009] Preferably, the median particle size D50 of the zirconia ceramic particles is 0.1-0.4 μm; The average thickness of the nano-binder layer is 10-50 nm.

[0010] Preferably, the thickness of the nano-binder layer is controlled within the range of 10-50 nm, which ensures that the mixed binder layer completely encapsulates the zirconia particles, while avoiding the problem of excessively thick binder layer leading to excessively high feed viscosity and reduced flowability.

[0011] Preferably, the reactive functional groups contained in the thermoplastic resin molecular chain are epoxy groups, hydroxyl groups, maleic anhydride groups, or carbon-carbon double bonds.

[0012] Preferably, when Y is amino, the reactive functional group on the thermoplastic resin molecular chain is an epoxy group, and the amino group and the epoxy group form a carbon-nitrogen bond through a ring-opening reaction; when Y is epoxy, the reactive functional group on the thermoplastic resin molecular chain is a hydroxyl group, and the epoxy group and the hydroxyl group form an ether bond through a ring-opening reaction; when Y is mercapto, the reactive functional group on the thermoplastic resin molecular chain is a maleic anhydride group, and the mercapto group and the maleic anhydride group form a thioester bond through a ring-opening reaction; when Y is methacryloxy, the reactive functional group on the thermoplastic resin molecular chain is a carbon-carbon double bond, and the methacryloxy group and the carbon-carbon double bond form a carbon-carbon single bond through a free radical copolymerization reaction.

[0013] Preferably, when Y is an epoxy group, the ring-opening reaction between the epoxy group on the surface of the modified zirconia ceramic powder and the hydroxyl group on the thermoplastic resin molecular chain requires the addition of a catalyst to promote the reaction.

[0014] Preferably, when Y is methacryloxy, the free radical copolymerization reaction between the methacryloxy group on the surface of the modified zirconia ceramic powder and the carbon-carbon double bond on the thermoplastic resin molecular chain requires the addition of an initiator to promote the reaction.

[0015] Preferably, the thermoplastic resin includes at least one of ethylene-glycidyl methacrylate copolymer, polyethylene glycol, maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, and maleic anhydride-grafted ethylene-vinyl acetate copolymer. The waxy substances include at least one of paraffin wax, microcrystalline wax, beeswax, and polyethylene wax.

[0016] Preferably, the mass ratio of the thermoplastic resin to the wax is (2-4):(8-6).

[0017] This invention also discloses a method for preparing the above-described nano-binder-encapsulated zirconia feedstock, comprising the following steps: Step 1: Dissolve the organosilane compound in an aqueous ethanol solution, adjust the pH to 4-5, add zirconia ceramic powder, and react to hydrolyze the organosilane compound to generate silanol groups. The silanol groups undergo a condensation reaction with the active hydroxyl groups on the surface of the zirconia ceramic particles, forming an organosilane molecular layer with Si-O-Zr chemical bonds on the surface of the zirconia ceramic particles. Active functional groups are introduced on the surface of the organosilane molecular layer. After the reaction is complete, filter, wash, and dry to obtain modified zirconia ceramic powder. Step 2: Mix the thermoplastic resin containing reactive functional groups on the molecular chain with wax substances and melt them to obtain a homogeneous binder melt; After preheating, the modified zirconia ceramic powder is added to the homogeneous binder melt and reacted. The reactive functional groups on the thermoplastic resin molecular chains in the homogeneous binder melt react chemically with the active functional groups on the organosilane molecular layer on the surface of the modified zirconia ceramic powder to form covalent bonds. A covalently bonded mixed binder layer is formed on the surface of the organosilane molecular layer. After the reaction is completed, the mixture is extruded and granulated to obtain nano-binder-coated zirconia feed.

[0018] Preferably, in step one, the mass ratio of organosilanes, zirconium oxide ceramic powder and ethanol aqueous solution is (0.15-0.8):(0.5-2):10, and the reaction conditions are stirring at 60-80℃ under nitrogen protection for 8-24 hours.

[0019] Preferably, in step two, the mass of the thermoplastic resin and waxy substances accounts for 8%-12% of the mass of the zirconia ceramic powder in step one.

[0020] Preferably, in step two, the melting temperature for preparing the homogeneous binder melt is 140-160℃.

[0021] Preferably, in step two, when preparing the nano-binder-coated zirconia feed, the preheating temperature of the modified zirconia ceramic powder is 120-140℃, and the reaction conditions are 140-160℃ for 30-70 seconds. -1 Mixing reaction at shear rate for 30-60 min.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: In this invention, an organosilane molecular layer with Si-O-Zr chemical bonds is formed on the surface of zirconia ceramic particles through a condensation reaction between organosilane compounds and active hydroxyl groups on the surface of the particles. Active functional groups (amino, epoxy, mercapto, or methacryloyloxy) are introduced onto the surface of the organosilane molecular layer. Through chemical reactions (ring-opening reaction, free radical copolymerization reaction) between these active functional groups and reactive functional groups (epoxy groups, hydroxyl groups, maleic anhydride groups, or carbon-carbon double bonds) on the thermoplastic resin molecular chain, a covalently bonded composite layer structure is formed. Compared to the existing interfacial bonding method where ceramic powder and binder are only physically mixed or physically coated, this invention achieves a strong molecular-level bond between zirconia ceramic particles and the mixed binder layer through a double-layer chemical bonding interface of Si-O-Zr inorganic-organic bonded layer + organic-organic covalent bonded layer. This significantly improves the interfacial bonding strength and avoids microcracks and pore defects caused by interfacial separation during debinding. In this invention, the nano-binder layer adopts a two-layer composite structure of organosilane molecular layer + mixed binder layer, and the average thickness of the nano-binder layer is controlled within the range of 10-50nm. Unlike the feed form of the binder in the prior art, which is a continuous phase distribution or a single-layer physical coating, the mixed binder layer is fixed to the surface of organosilane molecular layer by covalent bonds, rather than being freely dispersed between powder particles. Therefore, during the injection molding process, there is no difference in the relative flow rate between the zirconia ceramic particles and the mixed binder layer, which fundamentally solves the problems of phase segregation and uneven green density distribution caused by the difference in flow rate between powder and binder in the prior art. This invention employs a two-step preparation process. First, the surface of zirconia ceramic particles is chemically modified with organosilane in an organic solvent system to obtain modified zirconia ceramic powder with active functional groups. Then, during melt mixing, the reactive functional groups on the thermoplastic resin molecular chain react in situ with the active functional groups on the surface of the modified zirconia ceramic powder to form a covalently bonded mixed adhesive layer. This avoids the physical mixing step required after surface modification using existing solution methods, eliminating the need for additional compatibilizers or coupling agents. The process has a short cycle time, good batch-to-batch consistency, and due to the presence of chemical bonding, the integrity and uniformity of the mixed adhesive layer's encapsulation of zirconia ceramic particles are significantly better than existing physical mixing methods. Attached Figure Description

[0023] Figure 1 The graph shows the TG-DTA measurement results of unmodified zirconia ceramics and the modified zirconia ceramics prepared in Example 1. Figure 2 Infrared spectra of γ-aminopropyltriethoxysilane and the modified zirconia ceramic prepared in Example 1; Figure 3This is a TEM image of the zirconium oxide feedstock encapsulated with the nano-binder prepared in Example 1. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] Example 1 This embodiment discloses a method for preparing zirconium oxide feedstock encapsulated with nano-binder, comprising the following steps: Step 1: Dissolve the organosilane compound γ-aminopropyltriethoxysilane in a 70wt% ethanol aqueous solution, adjust the pH to 4 by adding acetic acid dropwise, and add zirconia ceramic powder (median particle size D50 is 0.25μm). The mass ratio of γ-aminopropyltriethoxysilane, zirconia ceramic powder and 70wt% ethanol aqueous solution is 0.25:0.5:10. Stir and react at 65℃ under nitrogen protection for 24h to hydrolyze γ-aminopropyltriethoxysilane to generate silanol groups. The silanol groups undergo a condensation reaction with the active hydroxyl groups on the surface of the zirconia ceramic particles to form an organosilane molecular layer with Si-O-Zr chemical bonds on the surface of the zirconia ceramic particles. Active functional groups amino groups are introduced on the surface of the organosilane molecular layer. After the reaction is complete, filter to remove the solvent ethanol aqueous solution, wash twice with ethanol, and dry in a vacuum drying oven at 50℃ to constant weight to obtain modified zirconia ceramic powder. Thermogravimetric-differential thermal analysis (TG-DTA) was used to test both the unmodified zirconia ceramic powder and the prepared modified zirconia ceramic powder. The results are as follows: Figure 1 As shown; Figure 1 In the diagram, curve (a) represents unmodified zirconia ceramic, and curve (b) represents modified zirconia ceramic powder; from Figure 1 It can be seen that the grafting rate of γ-aminopropyltriethoxysilane on the zirconia ceramic surface is 4.1%; Fourier transform infrared spectroscopy (FTIR) was used to test γ-aminopropyltriethoxysilane and the prepared modified zirconia ceramic powder. The results are as follows: Figure 2 As shown; curve (a) represents γ-aminopropyltriethoxysilane, and curve (b) represents modified zirconia ceramic powder; from Figure 2 It can be seen that in curve (a), 1100cm -1 The strong absorption peak at 800 cm⁻¹ is the asymmetric stretching vibration peak of O-Si-O. -1 The absorption peak at 3450 cm⁻¹ is a Si-O symmetric stretching vibration peak. -1The peak at 3000-2900 cm⁻¹ represents the stretching vibration peak of Si-OH; in curve (b), the peak is at 3000-2900 cm⁻¹. -1 The peak at 1630 cm⁻¹ represents the CH stretching vibration of the methylene group in the KH550 molecule. -1 The absorption peak at this location is the scissor vibration of -NH2, indicating the successful introduction of amino groups. Ethylene-glycidyl methacrylate copolymer (DuPont Elvaloy® 4170, GMA content 8%, melt index 10g / 10min (190℃ / 2.16kg)) and 58# fully refined paraffin wax (melting point 58-60℃, oil content ≤0.5%) were mixed at a mass ratio of 2:8. The amount of the mixture of ethylene-glycidyl methacrylate copolymer and paraffin wax accounted for 10% of the mass of zirconia ceramic powder. The mixture was melted at a melting temperature of 140℃ to obtain a homogeneous binder melt. The modified zirconia ceramic powder was preheated to 120℃. After preheating, it was added to a homogeneous binder melt and heated at 140℃ for 30 seconds. -1 The mixture was mixed and reacted at a shear rate for 60 min, so that the epoxy groups on the molecular chain of ethylene-glycidyl methacrylate copolymer in the homogeneous binder melt and the active functional groups of amino groups on the organosilane molecular layer on the surface of the modified zirconia ceramic powder formed carbon-nitrogen bonds through ring-opening reaction, forming a covalently bonded mixed binder layer on the surface of the organosilane molecular layer. After the reaction was completed, the mixture was extruded and granulated to obtain nano-binder-encapsulated zirconia feedstock. The microstructure of the nano-binder-encapsulated zirconium oxide feedstock was observed using transmission electron microscopy (TEM), and the results are as follows: Figure 3 As shown; by Figure 3 It can be seen that the nano-binder-encapsulated zirconia feed exhibits a clear core-shell structure, with the core being zirconia ceramic particles and the shell being a nano-binder layer with an average thickness of 35 nm.

[0026] Example 2 This embodiment discloses a method for preparing zirconium oxide feedstock encapsulated with nano-binder, comprising the following steps: Step 1: Dissolve the organosilane compound γ-glycidoxypropyltrimethoxysilane in a 70wt% ethanol aqueous solution, adjust the pH to 5 by adding acetic acid dropwise, and add zirconia ceramic powder (median particle size D50 is 0.25μm). The mass ratio of γ-glycidoxypropyltrimethoxysilane, zirconia ceramic powder and 70wt% ethanol aqueous solution is 0.25:0.5:10. Stir and react at 65℃ under nitrogen protection for 24h to hydrolyze γ-glycidoxypropyltrimethoxysilane to generate silanol groups. The silanol groups undergo a condensation reaction with the active hydroxyl groups on the surface of the zirconia ceramic particles to form an organosilane molecular layer with Si-O-Zr chemical bonds on the surface of the zirconia ceramic particles. Active functional groups epoxy groups are introduced on the surface of the organosilane molecular layer. After the reaction is completed, filter to remove the solvent ethanol aqueous solution, wash twice with ethanol, and dry in a vacuum drying oven at 50℃ to constant weight to obtain modified zirconia ceramic powder. The grafting rate of γ-glycidoxypropyltrimethoxysilane on the zirconia ceramic surface was determined to be 4.0% using TG-DTA. Step 2: Mix polyethylene glycol (PEG-6000, melting point 60-65℃, molecular weight 5500-7500) and 75# microcrystalline wax (melting point 75-85℃, oil content ≤3%) at a mass ratio of 4:6. The amount of the polyethylene glycol and microcrystalline wax mixture accounts for 10% of the mass of the zirconia ceramic powder. Add 0.2% of the mass of polyethylene glycol tetrabutylammonium bromide (TBAB) as a catalyst, melt, and melt at a melting temperature of 150℃ to obtain a homogeneous binder melt. The modified zirconia ceramic powder was preheated to 130℃. After preheating, it was added to a homogeneous binder melt and heated at 150℃ for 50 seconds. -1 The mixture was mixed and reacted at a shear rate for 45 min, allowing the hydroxyl groups on the polyethylene glycol molecular chains in the homogeneous binder melt to form ether bonds with the active functional groups on the organosilane molecular layer on the surface of the modified zirconia ceramic powder through a ring-opening reaction. This resulted in a covalently bonded mixed binder layer on the surface of the organosilane molecular layer. After the reaction was completed, the mixture was extruded and granulated to obtain zirconia feedstock encapsulated with nano-binder.

[0027] Example 3 This embodiment discloses a method for preparing zirconium oxide feedstock encapsulated with nano-binder, comprising the following steps: Step 1: Dissolve the organosilane compound γ-mercaptopropyltrimethoxysilane in a 70wt% ethanol aqueous solution, adjust the pH to 4.5 by adding acetic acid dropwise, and add zirconia ceramic powder (median particle size D50 is 0.25μm). The mass ratio of γ-mercaptopropyltrimethoxysilane, zirconia ceramic powder and 70wt% ethanol aqueous solution is 0.25:0.5:10. Stir and react at 65℃ under nitrogen protection for 24h to hydrolyze γ-mercaptopropyltrimethoxysilane to generate silanol groups. The silanol groups undergo a condensation reaction with the active hydroxyl groups on the surface of the zirconia ceramic particles to form an organosilane molecular layer with Si-O-Zr chemical bonds on the surface of the zirconia ceramic particles. The active functional group thiol group is introduced into the surface of the organosilane molecular layer. After the reaction is completed, filter to remove the solvent ethanol aqueous solution, wash twice with ethanol, and dry in a vacuum drying oven at 50℃ to constant weight to obtain modified zirconia ceramic powder. The grafting rate of γ-mercaptopropyltrimethoxysilane on the zirconia ceramic surface was determined to be 3.9% using TG-DTA. Step 2: Mix maleic anhydride-grafted ethylene-vinyl acetate copolymer (OREVAC®18211, grafting rate 1%-1.4%, melt index 0.8-1.5g / 10min (190℃ / 2.16kg)) with polyethylene wax (AC 540A, Honeywell, melting point 105℃) at a mass ratio of 3:7. The amount of the mixture of maleic anhydride-grafted ethylene-vinyl acetate copolymer and polyethylene wax accounts for 10% of the mass of zirconia ceramic powder. Melt at a melting temperature of 150℃ to obtain a homogeneous binder melt. The modified zirconia ceramic powder was preheated to 130℃. After preheating, it was added to a homogeneous binder melt and heated at 150℃ for 50 seconds. -1 The mixture was mixed and reacted at a shear rate for 45 min, allowing the maleic anhydride groups on the maleic anhydride-grafted ethylene-vinyl acetate copolymer molecular chain in the homogeneous binder melt to form thioester bonds through a ring-opening reaction with the active functional groups thiol groups on the organosilane molecular layer on the surface of the modified zirconia ceramic powder. This formed a covalently bonded mixed binder layer on the surface of the organosilane molecular layer. After the reaction was completed, the mixture was extruded and granulated to obtain zirconia feedstock encapsulated with nano-binder.

[0028] Example 4 This embodiment discloses a method for preparing zirconium oxide feedstock encapsulated with nano-binder, comprising the following steps: Step 1: Dissolve the organosilane compound γ-methacryloxypropyltrimethoxysilane in a 70wt% ethanol aqueous solution, adjust the pH to 4.5 by adding acetic acid dropwise, and add zirconia ceramic powder (median particle size D50 is 0.25μm). The mass ratio of γ-methacryloxypropyltrimethoxysilane, zirconia ceramic powder and 70wt% ethanol aqueous solution is 0.25:0.5:10. Stir and react at 65℃ under nitrogen protection for 24h to hydrolyze γ-methacryloxypropyltrimethoxysilane to generate silanol groups. The silanol groups undergo a condensation reaction with the active hydroxyl groups on the surface of the zirconia ceramic particles to form an organosilane molecular layer with Si-O-Zr chemical bonds on the surface of the zirconia ceramic particles. Active carbon-carbon double bonds are introduced on the surface of the organosilane molecular layer. After the reaction is complete, filter to remove the solvent ethanol aqueous solution, wash twice with ethanol, and dry in a vacuum drying oven at 50℃ to constant weight to obtain modified zirconia ceramic powder. The grafting rate of γ-methacryloxypropyltrimethoxysilane on the zirconia ceramic surface was determined to be 3.8% using TG-DTA. Step 2: Mix maleic anhydride-grafted polypropylene (EPOLENE® E-43, grafting rate 0.9%-1.1%, melting point 158℃, acid value 45mg KOH / g) and white beeswax (melting point 61-66℃, acid value 17-24mg KOH / g) at a mass ratio of 3:7. The amount of the mixture of maleic anhydride-grafted polypropylene and white beeswax accounts for 10% of the mass of zirconia ceramic powder. Add 0.3% of the mass of maleic anhydride-grafted polypropylene as dicumyl peroxide (DCP) as an initiator, melt, and melt at a melting temperature of 150℃ to obtain a homogeneous binder melt. The modified zirconia ceramic powder was preheated to 130℃. After preheating, it was added to a homogeneous binder melt and heated at 150℃ for 50 seconds. -1 The mixture was mixed and reacted at a shear rate for 45 min, allowing the maleic anhydride groups on the maleic anhydride-grafted polypropylene molecular chains in the homogeneous binder melt to form carbon-carbon single bonds through free radical copolymerization with the active functional group methacryloyloxy on the organosilane molecular layer on the surface of the modified zirconia ceramic powder. This resulted in a covalently bonded mixed binder layer on the surface of the organosilane molecular layer. After the reaction was completed, the mixture was extruded and granulated to obtain nano-binder-encapsulated zirconia feedstock.

[0029] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that the zirconia ceramic powder was not modified by the organosilane compound γ-aminopropyltriethoxysilane, and the operation of step two in Example 1 was performed directly.

[0030] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that the ethylene-glycidyl methacrylate copolymer in step two of Example 1 is replaced with pure polyethylene that does not contain any reactive functional groups.

[0031] Test case The performance of the nano-binder-coated zirconia feed samples prepared in Examples 1-4 and Comparative Examples 1-2 was tested: (1) Melt flow index test: Refer to standard GB / T3682.1-2018, use a melt flow rate meter to test the melt flow index (140℃, 5kg) of the feed sample; (2) Green density test: The feed sample was made into a standard tensile sample in the injection molding machine (mold temperature 40℃, injection pressure 80MPa, holding pressure 60MPa, holding time 3s). Five points were taken at equal intervals along the length of the sample (one point at each end and three points at equal intervals in the middle). The density of each point was measured by Archimedes' displacement method and the average value was calculated. (3) Green bending strength test: The feed sample was injection molded into a long strip green sample of 80mm×10mm×4mm. According to the standard GB / T9341-2008, the three-point bending method was used to conduct the bending test on the universal testing machine with a span of 64mm and a loading rate of 2mm / min. (4) Observation of defects after degreasing: The green sample was placed in a degreasing furnace and degreased in air atmosphere. The heating program was as follows: room temperature → 150℃ (2℃ / min), 150℃ for 1h; 150℃ → 350℃ (1℃ / min), 350℃ for 2h; 350℃ → 500℃ (2℃ / min), 500℃ for 1h; and then cooled naturally to room temperature. The surface and cross-sectional morphology of the degreased sample were observed using an optical microscope and a scanning electron microscope. (5) Sintering density test: The degreased sample was placed in a high-temperature sintering furnace and sintered in air atmosphere. The heating program was: room temperature → 600℃ (5℃ / min), 600℃ for 1h; 600℃ → 1450℃ (3℃ / min), 1450℃ for 2h; and then naturally cooled to room temperature. The density of the sintered body was measured by Archimedes' water displacement method. The performance test results are shown in Table 1: Table 1 As shown in Table 1, the nano-binder-encapsulated zirconia feedstock prepared in this invention has excellent melt flowability, high green density, high green bending strength, no degreasing microcracks, and high sintering density. Regarding melt flow index (MFI), the core-shell structure formed by chemical bonding in this invention provides excellent flowability of the feedstock in the molten state, and the MFI value can be adjusted within a wide range for different thermoplastic resin systems to meet the requirements of different injection molding processes. Regarding green body density, the mixed binder layer is covalently fixed to the surface of the organosilane molecular layer, resulting in no phase segregation during injection molding and a uniform and highly densified green body density distribution. Regarding green body flexural strength, the double-layer chemically bonded interface formed by Si-O-Zr chemical bonding and organic-organic covalent bonding significantly improves the interfacial bonding strength between zirconia ceramic particles and the mixed binder layer. Regarding post-debinding defects, the chemically bonded interface effectively suppresses microcracks and pore defects caused by interfacial separation during debinding. Regarding sintering density, the uniform core-shell encapsulation structure and good interfacial bonding are beneficial for densification during sintering. Compared with Example 1, in Comparative Example 1, the zirconia ceramic powder was not modified with organosilane compounds, and there was no Si-O-Zr chemical bonding on the powder surface. The mixed binder layer was only physically coated and attached to the powder surface, resulting in low interfacial bonding strength. This led to a significant decrease in melt flow index and green bending strength. After degreasing, a large number of microcracks and pores appeared, and the sintering density was significantly reduced. In Comparative Example 2, the ethylene-glycidyl methacrylate copolymer was replaced with pure polyethylene without any reactive functional groups. The thermoplastic resin molecular chain had no epoxy groups and could not undergo ring-opening reaction with the amino groups on the surface of the organosilane molecular layer to form carbon-nitrogen bonds. The mixed binder layer and the organosilane molecular layer were only physically entangled rather than chemically bonded, further reducing the interfacial bonding strength. This resulted in the lowest melt flow index and green bending strength among all samples, the most severe defects after degreasing, and the lowest sintering density.

[0032] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A nano-binder-coated zirconia feedstock, characterized in that, It consists of zirconia ceramic particles and a nano-binder layer encapsulating the surface of the zirconia ceramic particles; The nano-binder layer has a composite layer structure, including: An organosilane molecular layer is grafted onto the surface of the zirconium oxide ceramic particles via Si-O-Zr chemical bonds, and the surface of the organosilane molecular layer contains active functional groups. A hybrid adhesive layer is attached to the surface of the organosilane molecular layer by covalent bonds, wherein the covalent bonds are formed by the reaction of reactive functional groups in the hybrid adhesive layer with active functional groups on the surface of the organosilane molecular layer; The organosilane molecular layer is formed from an organosilane compound having the general formula YR-SiX3, wherein Y is an amino, epoxy, mercapto, or methacryloyloxy group constituting the active functional group, R is a C1-C6 alkylene group, and X is a methoxy or ethoxy group. The mixed adhesive layer comprises a thermoplastic resin and a waxy substance, wherein the molecular chain of the thermoplastic resin contains functional groups that can react with the active functional group Y to form covalent bonds.

2. The nano-binder-coated zirconia feed according to claim 1, characterized in that, The median particle size D50 of the zirconia ceramic particles is 0.1-0.4 μm; The average thickness of the nano-binder layer is 10-50 nm.

3. The nano-binder-coated zirconia feed according to claim 1, characterized in that, The reactive functional groups contained in the thermoplastic resin molecular chain are epoxy groups, hydroxyl groups, maleic anhydride groups, or carbon-carbon double bonds. Furthermore, when Y is an amino group, the reactive functional group on the thermoplastic resin molecular chain is an epoxy group; when Y is an epoxy group, the reactive functional group on the thermoplastic resin molecular chain is a hydroxyl group; when Y is a mercapto group, the reactive functional group on the thermoplastic resin molecular chain is a maleic anhydride group; and when Y is a methacryloyloxy group, the reactive functional group on the thermoplastic resin molecular chain is a carbon-carbon double bond.

4. The nano-binder-coated zirconia feed according to claim 1, characterized in that, The thermoplastic resin includes at least one of ethylene-glycidyl methacrylate copolymer, polyethylene glycol, maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, and maleic anhydride-grafted ethylene-vinyl acetate copolymer. The waxy substances include at least one of paraffin wax, microcrystalline wax, beeswax, and polyethylene wax.

5. The nano-binder-coated zirconia feed according to claim 4, characterized in that, The mass ratio of the thermoplastic resin to the waxy substance is (2-4):(8-6).

6. A method for preparing a nano-binder-encapsulated zirconia feedstock as described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Dissolve the organosilane compound in an aqueous ethanol solution, adjust the pH to 4-5, add zirconium oxide ceramic powder, react, filter, wash, and dry to obtain modified zirconium oxide ceramic powder. Step 2: Mix the thermoplastic resin containing reactive functional groups on the molecular chain with wax substances and melt them to obtain a homogeneous binder melt; After preheating, the modified zirconia ceramic powder is added to the homogeneous binder melt and reacted. After the reaction is completed, it is extruded and granulated to obtain nano-binder-coated zirconia feed.

7. The preparation method according to claim 6, characterized in that, In step one, the mass ratio of organosilanes, zirconium oxide ceramic powder and ethanol aqueous solution is (0.15-0.8):(0.5-2):10, and the reaction conditions are stirring at 60-80℃ under nitrogen protection for 8-24 hours.

8. The preparation method according to claim 6, characterized in that, In step two, the mass of thermoplastic resin and waxy substances accounts for 8%-12% of the mass of zirconia ceramic powder in step one.

9. The preparation method according to claim 6, characterized in that, In step two, the melting temperature for preparing the homogeneous binder melt is 140-160℃.

10. The preparation method according to claim 6, characterized in that, In step two, when preparing the nano-binder-coated zirconia feedstock, the preheating temperature of the modified zirconia ceramic powder is 120-140℃, and the reaction conditions are 140-160℃ for 30-70 seconds. -1 Mixing reaction at shear rate for 30-60 min.

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