Modified copper powder for additive manufacturing and composite slurry and application thereof

Abstract

The invention relates to the technical field of electronic packaging and thermal management materials, in particular to modified copper powder for additive manufacturing and composite slurry and application of the modified copper powder. The surface of the copper powder is treated through silane hydrolysate to form a compact siloxane network temporary coating layer, and the coating layer can effectively inhibit oxidation of the copper powder in storage and slurry environments and remarkably improve the dispersity of the copper powder in a resin system. Therefore, the ceramic-metal composite slurry containing the modified copper powder can guarantee the comprehensive performance of the slurry, and is suitable for a manufacturing process of a high-performance heat-conducting and electric-conducting composite material based on photopolymerization.

Description

Technical Field

[0001] This application relates to the field of electronic packaging and thermal management materials technology, and more specifically, it relates to a modified copper powder for additive manufacturing, its composite slurry, and its applications. Background Technology

[0002] As electronic devices rapidly develop towards high power density, miniaturization, and multifunctional integration, electronic packaging materials not only need to dissipate heat efficiently, but also must have excellent electrical connection or electromagnetic shielding capabilities, while taking into account both lightweight and structural reliability.

[0003] Against this backdrop, composite materials that combine the excellent thermal / electrical conductivity of metals with the good mechanical properties and low density of ceramics, such as the copper-alumina system, have become ideal candidate materials. However, traditional preparation methods still face bottlenecks in forming complex structures and precisely controlling the two-phase distribution.

[0004] Among related technologies, photopolymerization additive manufacturing technology based on digital light processing has brought a revolutionary breakthrough to the precision and free molding of such composite materials compared with traditional technologies. It can directly manufacture heat dissipation or conductive structures with complex internal cavities and fine meshes, and has high material utilization and good surface quality. However, the preparation of its core technology – high-performance photosensitive suspension slurry – faces severe challenges, and many problems remain unsolved at present, as follows: 1) Pure copper powder is extremely prone to oxidation: During the preparation, storage, and even printing of the paste, an oxide layer will form on the surface of the copper powder, which will affect the photocuring process and impair the electrical and thermal conductivity of the product. 2) Significant density difference: Copper powder has a much higher density than alumina ceramic powder. The two are very likely to settle differently in low-viscosity resin slurry, resulting in uneven slurry composition and fluctuations in the density of the printed layer, which ultimately affects the uniformity and performance of the sintered body.

[0005] Related reports suggest that copper powder can be modified with metal plating or polymer coatings to address these challenges. However, these modification methods each have significant limitations and often fail to achieve comprehensive performance at the slurry stage. Therefore, this paper presents a modified copper powder for additive manufacturing, its composite slurry, and its applications. Summary of the Invention

[0006] To address the aforementioned technical problems, this application provides a modified copper powder and its composite slurry for additive manufacturing, along with its applications. This technology is highly suitable for manufacturing processes of high-performance thermally and electrically conductive composite materials based on photopolymerization, and can simultaneously ensure the comprehensive performance of the slurry stage.

[0007] In a first aspect, this application provides a modified copper powder for additive manufacturing, wherein the surface of the copper powder is coated with a siloxane network layer formed by the hydrolysis and condensation of aminohydrosilanes.

[0008] The above technical solution abandons the traditional approach of physical mixing or permanent coating, and instead utilizes aminohydrosilane to construct a covalently bonded siloxane (Si-O-Si) network coating layer in situ on the surface of copper powder. This structure fundamentally changes the surface properties of copper powder, as detailed below: Firstly, the dense Si-O-Si network provides excellent insulation performance, which can effectively prevent moisture and oxygen in the environment from contacting the copper substrate for a long time, thus achieving intrinsic oxidation resistance. Secondly, the exposed organic functional groups (such as -NH2) in the network transform the originally high surface energy and easily aggregated metal surface into a modified interface with good affinity and reactivity with organic resins. Therefore, the product itself constitutes a versatile functional raw material that can be stably stored, transported and used in a variety of downstream processes.

[0009] Preferably, the aminohydrosilane is selected from 3-aminopropyltriethoxysilane.

[0010] Preferably, the thickness of the siloxane network layer is 2-10 nm.

[0011] Through the above technical solutions, the specific selection of aminohydrosilanes and control of coating thickness further realize the synergistic modification of the copper powder surface from "chemical properties" to "physical structure," providing an ideal functional filler for obtaining high-performance slurries, as detailed below: Specific selection of aminohydroxysilanes: The strong polarity and reactivity of their terminal amino functional groups ensure that the coating layer can form a strong interfacial bond with the resin matrix, fundamentally improving compatibility; Precise control of the coating thickness enables the formation of a continuous and complete barrier to isolate water and oxygen while minimizing the negative impact on the intrinsic physical properties of copper powder and avoiding residual problems caused by excessive coating thickness during subsequent sintering.

[0012] Secondly, this application provides a method for preparing modified copper powder for additive manufacturing, using the following technical solution: A method for preparing modified copper powder for additive manufacturing, comprising the following steps: S1. Hydrolyze the aminohydrosilane coupling agent in an acidic water-alcohol solution to obtain a silane hydrolysate; S2. Copper powder surface pretreatment; S3. Under an inert atmosphere, the pretreated copper powder from S2 is added to the silane hydrolysate to react and form a coating layer on the surface of the copper powder. S4. The reaction product is washed and dried to obtain the surface-modified copper powder.

[0013] Preferably, the reaction temperature in S3 is 40-70℃.

[0014] The above technical solution enables the stable and repeatable production of modified copper powder with uniform coating and consistent performance, providing a process guarantee for the industrialization of the product. A detailed analysis follows: The core three-step process of hydrolysis-reaction-post-treatment ensures that silane can be directionally adsorbed and condensed on the surface of copper powder in an active form, forming a chemically bonded coating layer.

[0015] Thirdly, this application provides a ceramic-metal composite slurry for photocurable additive manufacturing, comprising 5-25 wt% modified copper powder or the product obtained by the above preparation method.

[0016] Preferably, it also includes Al2O3 ceramic powder, sintering aid, photocurable resin, reactive diluent, photoinitiator, dispersant and leveling agent.

[0017] Through the above technical solution, the slurry product directly solves the fundamental material problem faced in the preparation of ceramic-metal composite materials in the field of photocurable additive manufacturing, namely, how to introduce a sufficient amount of stable metal phase into the system without sacrificing the printing processability. The synergy between the components ensures the balance between multiple mutually restrictive objectives such as high solids content, good rheological properties, sufficient photocuring and debinding sintering compatibility.

[0018] Fourthly, this application provides an application of a composite slurry, wherein the electronic packaging material or thermal management material is obtained by sintering the composite slurry after it has been cured using DLP 3D printing technology.

[0019] In summary, this application has the following beneficial effects: 1. This application provides a strategy for coating copper powder with silane hydrolysate, and based on this, a composite slurry for photocurable additive manufacturing is developed. This solution synergistically solves three major technical problems: easy oxidation of copper powder in the slurry environment, sedimentation and agglomeration due to density differences, and poor compatibility with resin system. It provides a stable and reliable basic material for the preparation of high-performance ceramic-metal composite materials. 2. This application constructs a dense and controllable thickness siloxane network temporary coating layer on the surface of copper powder by controlling the hydrolysis-condensation process of silane under weakly acidic conditions. The coating layer is chemically anchored to the surface of copper powder by Si-O-Cu covalent bonds, forming a strong core-shell structure. The exposed amino (-NH2) and other organic functional groups significantly enhance the compatibility between copper powder and photosensitive resin-polyurethane acrylate, achieving multiple protections and functionalizations from "physical isolation" to "chemical bonding and interface optimization", thereby further ensuring the application of copper powder in slurry. 3. The silane temporary coating layer in this application plays a dual key role, as follows: During the slurry preparation and storage stages, it acts as a physical barrier and interface modification layer, effectively isolating water and oxygen and inhibiting Cu. 0 To Cu 2+ The oxidation of the slurry and the significant improvement of particle dispersion stability through steric hindrance and electrostatic repulsion can achieve no sedimentation after 7 days of standing. In the subsequent high-temperature sintering stage, the silane temporary coating layer can also be decomposed and transformed, avoiding the problems of residual carbon impurities in the polymer coating layer or the introduction of heterogeneous interfaces by the metal coating layer in the existing methods, thereby ensuring the purity and comprehensive performance of the final composite material. 5. Compared with traditional copper powder modification technologies such as metal coating or polymer coating, the silane temporary coating scheme provided in this application has the advantages of high efficiency, economy and environmental friendliness. It not only solves the bottleneck of stability in the slurry stage, but its "temporary" nature also meets the requirements of the sintering process for interface purity. It lays an indispensable material foundation for the preparation of high thermal conductivity, high electrical conductivity and high density ceramic matrix composites through photopolymer additive manufacturing technology, and has broad application prospects. Attached image description: Figure 1 Infrared image of the silane hydrolysate after hydrolysis and ripening in Preparation Example 1; Figure 2 SEM images of the control group and the modified copper powder in Preparation Example 1 after 0 days and 14 days of storage; Figure 3 To prepare the XRD image of the modified copper powder in Example 1 after 14 days of storage; Figure 4 XPS full spectrum and quantitative analysis chromatogram of the modified copper powder in Example 1; Figure 5 To prepare detailed elemental spectra of the modified copper powder in Example 1; Figure 6 To prepare a low-magnification STEM-HAADF image of the modified copper powder in Example 1; Figure 7 To prepare a low-magnification STEM-HAADF image of the modified copper powder in Example 1; Figure 8 To prepare a low-magnification STEM-HAADF image of the modified copper powder in Example 1 from another perspective; Figure 9 HRTEM image of the modified copper powder in Example 1; Figure 10 To obtain another HRTEM image of the modified copper powder in Example 1; Figure 11 High-magnification STEM-HAADF images and qualitative analysis diagrams of each element are shown for the modified copper powder prepared in Example 1. Figure 12STEM-EDS mapping images of each element and superimposed mapping images of each element were prepared for the modified copper powder in Example 1. Figure 13 The test graphs show the sedimentation products of control group 1-A and example 1-B in a 7-day sedimentation experiment. Figure 14 The viscosity change curves of the slurry in control group 1-A and example 1-B are shown. Figure 15 The curves show the variation of slurry viscosity of composite materials with different Cu contents in Examples 1-4; Figure 16 The thixotropic curves of composite slurries with different Cu contents in Examples 1-4 are shown. Figure 17 The figures show the viscoelasticity variation curves of composite slurries with different Cu contents in Examples 1-4. Figure 18 The UV curing curves of composite slurries with different Cu contents in Examples 1-4 are shown. Figure 19 The curves show the curing depth changes of composite slurries with different Cu contents in Examples 1-4 at 1s, 3s, 6s and 9s after photocuring. Detailed Implementation

[0020] The following is in conjunction with the embodiments and appendices Figure 1-19 To provide further details regarding this application, all raw materials used in this application, except where otherwise specified in the table below, are commercially available common materials.

[0021] Table: List of Raw Materials and Their Sources Preparation Example 1 A modified copper powder for additive manufacturing is prepared by the following steps: S1. First, add 160 mL of anhydrous ethanol and 18 mL of deionized water to a beaker, stir magnetically (300 rpm) for 5 minutes at room temperature (25°C), and adjust the pH of the solution to 5 using glacial acetic acid. Then, 22 mL of aminohydrosilane coupling agent-KH-550 was added to the separatory funnel at a rate of 1 drop / s. The temperature of the solution in the beaker was controlled at 25±2℃ by cooling with an ice-water bath, and the magnetic stirring speed was maintained at 500 rpm. During this process, the pH value of the solution was checked every few minutes. The pH value was maintained at ≤4.5 by adding glacial acetic acid. After the addition was completed, the solution was transferred to a round bottom flask, sealed, and then magnetically stirred at 400 rpm for 30 minutes in a constant temperature oil bath at 40℃. After the stirring was completed, the solution was removed from the oil bath and allowed to stand at 25℃ for 60 minutes for aging treatment, and then set aside for later use. The equations for the above-mentioned siloxane hydrolysis reaction are as follows:

[0022] S2. Immerse 40g of high-purity micron-sized copper powder in acetone solution, sonicate for 10 minutes to remove surface stains, and then pour out the waste liquid. Then, prepare the micro-etching solution by adding 10g of citric acid and 2mL of H2O2 to 200mL of deionized water and stirring until homogeneous. Then, add copper powder and magnetically stir (200rpm) for 10 minutes at room temperature to etch and activate the solution. After completion, wash the copper powder with water multiple times until the pH value is close to 7. Then, immerse the copper powder in anhydrous ethanol, sonicate for 5 minutes to remove excess water, filter, and dry in an oven at 60℃ for 30 minutes for later use.

[0023] S3. Add the pretreated copper powder from S2 to the silane hydrolysate that has been matured in S1 in batches. The reaction is carried out under a nitrogen atmosphere. Stir at 300 rpm for 5 minutes at room temperature until there are no floating powder agglomerates. Then, place the three-necked round-bottom flask in an oil bath and heat it to 60°C at a rate of 2°C / min. React at 60°C for 60 minutes, using a high speed of 400 rpm for the first 30 minutes and a low speed of 200 rpm for the last 30 minutes. S4. After the reaction is complete, wash the precipitate repeatedly with clean water, centrifuge at 1000 rpm to separate the precipitate, pour off the supernatant, and place the precipitate in an oven at 60°C for 10 minutes. -1 Dry at 60°C for 60 minutes, then raise the temperature to 80°C and continue drying at 10°C. -2 The mixture is kept at Pa for 60 minutes to obtain copper powder completely coated with silane hydrolysate, which is the modified copper powder used for additive manufacturing.

[0024] To further verify the material characterization and coating results of the modified copper powder, the silane hydrolysate and modified copper powder from the preparation example were selected as the test objects, and the following comparative samples were set up: Control group (unmodified copper powder sample): Take the high-purity micron-sized copper powder (i.e., copper powder that has not undergone silane coating treatment) that was cleaned with acetone, etched and activated with citric acid and dried in step S2 of Preparation Example 1, and divide it into two equal portions.

[0025] Experimental group (modified copper powder sample): The surface-modified copper powder finally obtained in Preparation Example 1 was divided into two equal portions.

[0026] Place the two samples from each group into identical wide-mouth glass sample bottles, leaving the bottle openings unsealed, and store them in an open environment in a laboratory setting (temperature 25±2℃, relative humidity 50±10%).

[0027] One sample was immediately subjected to characterization tests after preparation (referred to as day 0), while the other sample was stored continuously in the above environment for 14 days (referred to as day 14) before undergoing the same series of characterization tests. The specific test methods and standards are as follows:

[0028] Using an infrared spectrometer (Thermo Fisher Scientific NICOLET IS 5, USA) at 400-4000 cm⁻¹ -1 Infrared spectral data of silane hydrolysate were obtained within the specified range.

[0029] The crystal structure of the modified copper powder was characterized using an X-ray diffractometer (Rigaku SmartLab 600, Japan) at a scanning rate of 5° / min and a scanning range of 2θ of 5-80°.

[0030] The microstructure of the unmodified powder and the modified powder was analyzed using a scanning electron microscope (Hitachi SU8010, Japan). To enhance electronic conductivity, all samples were sputter-coated with gold before observation. In addition, the fine structure and elemental composition of the modified copper powder were analyzed in depth using a transmission electron microscope (FEI Talos F200X G2, USA) and its equipped energy dispersive spectrometer (EDS). After being ultrasonically dispersed in ethanol, the powder was drop-coated onto an ultrathin molybdenum mesh carrier. Its microstructure, crystal features and elemental distribution could be characterized by high-resolution imaging, bright-dark field imaging and EDS elemental mapping.

[0031] The elemental composition and chemical state of the modified copper powder surface were characterized using an X-ray photoelectron spectroscopy (Thermo Scientific K-Alpha, USA), including full spectrum and fine spectrum scanning of each element. Charge correction was performed using the C1s peak position of adsorbed carbon on the sample surface (standard binding energy of 284.8 eV). Avantage software was used for data acquisition and spectrum peak fitting.

[0032] The results of the above tests can be referred to Figure 1-12 The specific analysis is as follows: Depend on Figure 1 Infrared images of the silane hydrolysate after hydrolysis and ripening show that at 968 cm⁻¹... -1 Near the silane molecule, no obvious stretching vibration absorption peaks attributable to the Si-O-C2H5 bond were observed, indicating that the ethoxy group (-OC2H5) at the end of the silane molecule has been fully involved in the hydrolysis reaction. At 880cm -1 The absorption peaks that appear nearby can be attributed to the stretching vibrations of the newly formed Si-OH bonds, which indicates the presence of the hydrolysis product silanol (-SiOH); At 1090cm -1 The absorption peak appearing at this point is a typical characteristic of the asymmetric stretching vibration of the Si-O-Si bond. The absorption peak here means that the silanol molecules generated by hydrolysis have undergone a preliminary condensation reaction, generating an oligomeric siloxane structure, which is conducive to the formation of a stable coating layer on the surface of copper powder.

[0033] At 2930cm -1 The nearby absorption peak belongs to the asymmetric stretching vibration of -CH2-, indicating that the propyl segment of the silane (-CH2-CH2-CH2-) remained intact throughout the hydrolysis process without breakage, and the peak at 3370 cm⁻¹... -1 The presence of the characteristic peak of NH asymmetric stretching vibration in the vicinity indicates the presence of amino groups (-NH2), which is beneficial to the compatibility of modified copper powder with organic resin matrix.

[0034] Depend on Figure 2 SEM images of the control group and modified copper powder after 0 and 14 days of storage show that, compared with the uncoated Cu powder control group, the surface of the silane-coated Cu powder is smoother and flatter, and the adhesion between Cu powder particles is significantly reduced, and the dispersibility is improved. After being stored at room temperature for 14 days, the control group without coated Cu powder particles showed obvious flocculent protrusions on its surface, and the contact points between particles became blurred, with aggravated agglomeration. This was because the uncoated Cu powder particles had oxidized.

[0035] However, when the coated Cu powder was stored under the same conditions, it still maintained a smooth surface morphology and good dispersibility, and no obvious oxidation corrosion products were observed. This indicates that the silane coating layer can effectively prevent Cu powder from being oxidized and provide Cu powder with good dispersibility.

[0036] In addition, by Figure 3 The XRD images of the modified copper powder after 14 days of storage show that only the sharp diffraction peaks of pure Cu are visible, and almost no characteristic peaks of any oxides are observed, further proving that the silane coating layer effectively prevents the oxidation of pure Cu.

[0037] Depend on Figure 4 The XPS full spectrum and fine spectrum of each element of the modified copper powder show the characteristic photoelectron peaks of C, O, Cu, Si and N. Quantitative analysis revealed that the relative content of Cu on the outermost surface of the sample was only 7.52%, while the other elements dominated the surface composition of the sample, indicating that the silane coating layer achieved a relatively complete coating of the copper substrate. And through further observation Figure 5The fine spectra of each element, in the O 1s peak fitting, are attributed to the Si-O-Cu interface bond at a binding energy of 530.8 eV, confirming the existence of a small amount of chemical bonding between silane and the copper substrate. At a binding energy of 532.2 eV, it is a Si-O-Si network, which occupies the main component and forms the framework of the outer coating layer. At a binding energy of 533.5 eV, it is a small amount of residual hydroxyl groups on the surface, which may be related to the hydrolysis residue of silane.

[0038] The single peak of N 1s (binding energy of 399.2 eV) is clearly assigned to the primary amino group (-NH2), confirming that the amino functional group of the silane coupling agent did not undergo protonation or decomposition during the coating process. The spectrum of Si 2p shows a symmetrical single peak at 102 eV, which belongs to the Si-O-Si network. The symmetry of the single peak indicates that the silane hydrolysis and condensation are sufficient, forming a uniform and dense coating layer.

[0039] The Cu 2p spectrum shows only two main peaks with no obvious satellite peaks, confirming that copper exists on the surface in the form of Cu0 / Cu. + The presence of the silane coating, combined with the absence of the CuO characteristic peak at 529.5 eV in O 1s, indicates that the silane coating significantly inhibits the oxidation of the copper substrate. The XPS results show that the silane coating can effectively inhibit the oxidation of Cu and achieve relatively good coating integrity (≥93%).

[0040] Depend on Figure 6 The low-magnification STEM-HAADF image of the modified copper powder shows that, since the copper powder is a three-dimensional, thick micron-sized particle, when the electron beam passes through the sample, it appears gray in the middle of the thicker particles and bright white at the thinner edges. Therefore, we need to focus our attention on the outer edge line of the particles.

[0041] exist Figure 7 and Figure 8 In high-magnification HAADF images, an extremely fine and slightly brighter gray transition layer—the red dashed line—can be seen outside the bright edge. This fine gray transition layer is the coating layer outside the Cu powder, and its signal intensity is between the black background and the bright Cu edge.

[0042] At the same time, by Figure 9 and Figure 10 The presence of the coating layer can also be clearly observed in the HRTEM image. It forms a uniform and continuous coating layer on the Cu powder with a thickness of about 2-3 nm.

[0043] exist Figure 11In Area 1, the presence of Si and O signals indicates that the coating layer is composed of Si and O, confirming the presence of silane hydrolysis products. The C signal in the figure mainly comes from the support film (ultra-thin carbon film) used in sample preparation. At the same time, the organic part in silane may also generate a small amount of C signal.

[0044] Figure 12 The image shows a STEM-EDS mapping image of Cu powder. In the image, we can see that the Si and O element signals are wrapped around the Cu element signals, forming a core-shell structure. The coating layer is uniform and continuous with no obvious exposed areas. This is consistent with the previous high-magnification HAADF image, which together confirms the rationality of the coating process.

[0045] Examples 1-4 A ceramic-metal composite slurry for photocurable additive manufacturing, the components of which and their corresponding masses (g) are shown in the table below, wherein the modified copper powder was prepared by Preparation Example 1: Table: Components and their mass (g) in Examples 1-4 and the control group Note: The unit of each component value in the table is grams (g), and the total amount of each example and control group formula is 100g.

[0046] To further verify the performance of the composite slurry, the slurry prepared in Example 1 was selected as the experimental group for testing. Simultaneously, a control slurry was prepared, whose formulation was identical to that of Example 1, except that the modified copper powder was replaced with an equal mass of unmodified copper powder. This control slurry was designated as control group 1-A, and the following tests were performed:

[0047] The rheological properties of the slurry, including slurry viscosity, viscoelasticity, and thixotropic properties, were characterized at room temperature using a rheometer (TA Instruments DHR-2, USA).

[0048] Viscosity testing was performed using a 25mm diameter steel conical plate with a gap size of 200μm and a shear rate of 0.01-100s. -1 .

[0049] The viscoelasticity test used a steel conical plate with a diameter of 25 mm, a gap size of 200 μm, and an oscillation strain of 0.01-1000%.

[0050] The two-stage thixotropic property test used a steel conical plate with a diameter of 25 mm and a gap size of 200 μm, with a shear rate range of 0.01 to 10 s⁻¹. -1 and 10s -1 The two segments are up to 0.01.

[0051] A rheometer (TA Instruments DHR-2, USA) with UV-LED accessories was used to study the photocuring kinetics. A 20mm diameter steel parallel plate and a transparent acrylic plate clamp were used, with a gap of 200μm. The UV light intensity was 100mW / cm². 2 The duration is 200 seconds, including 60 seconds of ultraviolet light exposure and 30 seconds of curing time.

[0052] The curing performance of the slurry was tested using a ceramic 3D printing machine with adjustable UV light power (China Adventech ADT-3D-ZP-Printer). The maximum face power (45mW / cm²) was used. 2 The light was used for curing, and a series of exposure times were set (1s, 3s, 6s, 9s), with a spot area of ​​54cm². 2 After curing, clean the uncured slurry from the sample surface, and use a micrometer to measure the thickness of the cured layer at different locations on the sample and take the average value. This thickness is the curing depth under that light intensity power.

[0053] The results of the above tests can be referred to Figure 13-19 The specific analysis is as follows: like Figure 13 As shown, after the two slurries were left to stand for 7 days, it was found that the control group 1-A experienced more severe sedimentation and the supernatant was light blue-green. In contrast, the slurry of Example 1-B did not show stratification and showed no obvious sedimentation compared to the control group 1-A. To investigate the composition of the supernatant of control group 1-A slurry, a sodium hydroxide precipitation test was performed. With the addition of NaOH, a distinct sky-blue flocculent precipitate (Cu(OH)2) appeared in the supernatant of control group 1-A, confirming the presence of Cu. 2+ The existence of.

[0054] The above results indicate that the silane hydrolysate effectively isolates the copper powder from contact with moisture and oxygen by forming a dense organosilicon film on the surface of the copper powder, thereby effectively inhibiting the occurrence of oxidation and corrosion reactions, enhancing the oxidation resistance and chemical stability of the copper powder in the slurry environment, and reducing the agglomeration between copper powder particles, thus improving its dispersion stability in the slurry system. Therefore, the sedimentation phenomenon is also significantly improved.

[0055] Meanwhile, the leveling agent promotes uniform spreading of the slurry by reducing surface tension, while the dispersant further inhibits particle agglomeration and sedimentation through the synergistic effect of steric hindrance and electrostatic repulsion. This synergistic effect enables the slurry of Example 1-B to achieve longer-term stability.

[0056] like Figure 14As shown, both groups of slurries exhibit typical shear-thinning behavior. However, the slurry of Example 1-B shows a lower viscosity value at the same shear rate compared to the control group 1-A slurry. This is because the silane coating layer eliminates the defects of easy oxidation and high surface energy of the uncoated Cu powder surface.

[0057] It is well known in the art that CuO has a higher surface energy and is more likely to undergo uncontrolled adsorption with polar components in resin systems, thus forming flocculation. At the same time, the high surface energy causes particles to tend to aggregate to reduce the total surface energy. However, silane coatings can solve these problems, as follows: The presence of a dense and continuous Si-O-Si network framework prevents the aggregation of Cu particles. Furthermore, after hydrolysis, the amino (-NH2) functional groups at the silane ends face outwards, making them highly compatible with the polyurethane methacrylate and hydroxyethyl methacrylate resin systems. The strongly polar ester groups (-COOR) and hydroxyl groups (-OH) contained within the resin form strong hydrogen bonds with -NH2, thereby enabling the resin to easily wet and coat each Cu particle, improving internal compatibility.

[0058] For silane-coated Cu powder, its surface is a uniform organic layer rich in -NH2. The anchoring groups of BYK-111 can be more evenly and firmly adsorbed onto this layer, while simultaneously providing a steric hindrance layer and a silane layer superimposed effect. In a well-dispersed silane-coated slurry, BYK-333 can effectively spread across the entire liquid-gas interface, reducing liquid surface tension and promoting rapid and smooth spread of the slurry on the printing platform, thus eliminating scratches.

[0059] Therefore, coating Cu powder with silane hydrolysate and supplementing it with leveling agents and dispersants can significantly improve the oxidation resistance, dispersion stability and rheological properties of Al2O3-Cu composite slurry, providing an effective method for successfully realizing DLP 3D printing of ceramic-metal composite materials.

[0060] like Figure 15 As shown, all five groups of slurries exhibited shear thinning behavior. It is worth noting that as the Cu content increased, the slurry viscosity generally increased first and then decreased. The slurry viscosity reached its maximum when the Cu content was 10wt%, indicating that the slurry viscosity is mainly determined by the interaction between solid particles.

[0061] When the Cu content is low (≤10wt%), finer Cu particles will fill the gaps between Al2O3 particles, thereby disrupting the optimal packing state between the original pure Al2O3 particles. Meanwhile, the finer Cu particles have a larger specific surface area than Al2O3 particles, thus adsorbing more resin and dispersant molecules, reducing the amount of liquid acting on the Al2O3 particles. This leads to increased resistance to particle flow, causing the slurry viscosity to rise continuously, peaking at 10%.

[0062] However, when the Cu content exceeds 10 wt%, a large number of Cu particles fill the gaps between Al2O3 particles, acting as a lubricant between the larger Al2O3 particles and reducing friction between them. As the lubricating effect of the Cu particles gradually outweighs the resistance caused by the increased surface area and their interactions, the viscosity of the slurry will begin to decrease macroscopically.

[0063] like Figure 16 As shown, the area of ​​the thixotropic ring only increases slightly with the increase of Cu content, but the position of the thixotropic ring in slurries with different Cu contents changes significantly: when the Cu content is 5wt%, the entire thixotropic ring moves towards the direction of higher stress, and the filling of finer Cu particles makes the three-dimensional network structure inside the slurry more robust. Therefore, the slurry needs to be subjected to greater external force to make it flow. However, when the Cu content increases to 10wt% and above, the thixotropic ring begins to move towards the direction of lower stress.

[0064] The above results indicate that the internal structure of the slurry becomes more easily disrupted, and the yield stress of the slurry decreases accordingly. This further confirms that in slurries with higher Cu content, the lubricating effect of Cu powder on large Al2O3 particles is dominant, thus reducing the overall strength of the three-dimensional network structure. The variation in the position of the thixotropic rings fully reveals the influence of Cu content changes on the strength of the slurry's internal structure. This rheological property is crucial for controlling the coating performance of DLP 3D printing slurries.

[0065] like Figure 17 As shown, all five slurries exhibited significant viscoelastic responses across the entire oscillatory strain range. In the low strain region, G' was significantly higher than G'', indicating that a stable three-dimensional network structure was formed within the slurry through interparticle interactions, resulting in solid-like behavior. This ensures sufficient shape retention of the slurry in a static state, thus ensuring strong and stable interlayer bonding during DLP printing.

[0066] As the oscillating strain gradually increases, G'' begins to dominate, and the slurry exhibits fluid-like behavior. When the applied mechanical energy is sufficient to disrupt the three-dimensional structure within the slurry, G'' will exceed G', and the slurry will macroscopically exhibit shear thinning. Reflected in the DLP 3D printing process, under the high shear force of the coating blade, the slurry viscosity decreases, and its fluidity increases, thus achieving rapid and uniform application. However, when the shear force is removed, the slurry quickly returns to a near-solid state, maintaining the printed shape and preventing collapse.

[0067] like Figure 18 As shown, all five slurries exhibited good UV curing performance, but the curing rate did not simply increase or decrease monotonically with increasing Cu content. Compared to the pure Al₂O₃ slurry, the slurry with 5 wt% Cu content showed a significantly improved curing rate, but the curing rate decreased when the Cu content increased to 10 wt%. Further increasing the Cu content to 15 wt% and 20 wt% resulted in a renewed acceleration of the curing rate, exceeding that of the slurry with 5 wt% Cu content. This non-linear change reflects a competitive mechanism within the multiphase photocuring system.

[0068] In the low content range of 5wt% Cu, the accelerated curing is attributed to the photothermal effect of the metal particles. The Cu powder absorbs UV radiation and converts it into heat energy. The local heating promotes the initiation of free radicals in the acrylic resin and the chain growth reaction kinetics.

[0069] When the Cu content reaches 10wt%, the scattering and diffuse reflection of ultraviolet light by Cu particles reach their peak. The light shielding effect severely reduces the penetration efficiency of ultraviolet light. When the negative effect exceeds the photothermal effect of the metal, the curing rate begins to decrease compared to before.

[0070] However, when the Cu content reaches 15wt% and 20wt%, the light propagation path within the slurry is optimized with further increases in Cu content, reducing ineffective scattering due to reflection between Cu particles. Simultaneously, the higher Cu content promotes uniform heat diffusion within the slurry, and the photothermal effect of the metal achieves overall heating of the slurry. The photothermal effect of the metal and the optimization of the light propagation path work synergistically, thereby increasing the photocuring rate at high Cu content.

[0071] like Figure 19 As shown, the curing depth does not exhibit a monotonically linear relationship with the Cu content. With further increases in Cu content, the curing depth initially decreases and then increases. This is because when the Cu content is 5 wt%, the photothermal effect and light-shielding effect of Cu interact. The photothermal effect influences the photocuring kinetics, while the light-shielding effect limits the curing depth.

[0072] When the Cu content reaches 10wt%, the shielding effect reaches its peak, severely hindering the effective penetration of ultraviolet light and resulting in the lowest curing depth.

[0073] However, when the Cu content reaches 15wt% and 20wt%, the curing depth gradually recovers. This is because when the Cu content is high, the interconnected Cu particles increase the propagation rate of the photothermal effect, thereby overcoming some of the light scattering disadvantages of high Cu content.

[0074] It is worth noting that the Cu-containing slurry reached curing depth saturation at a curing time of 3 seconds, and subsequent increases in curing time had a slow effect on curing depth. The study of photocuring kinetics and the changes in curing time and depth provides a valid basis for the formulation of composite material slurries and the design of subsequent DLP 3D printing processes.

[0075] In summary, surface modification of copper powder using silane hydrolysate is a key technology for preparing high-performance Cu-Al2O3 composite slurry for DLP printing. This technology solves the problems of copper powder oxidation, agglomeration, and poor compatibility with resin from the source by constructing a chemically bonded organosilicon coating layer, thereby synergistically optimizing the slurry's storage stability, rheological properties, and photocuring characteristics.

[0076] This application, through in-depth research on the influence of copper content, further reveals the intrinsic regulation law of slurry viscosity, thixotropy and photocuring behavior, providing a solid theoretical basis for slurry formulation design and printing process optimization for different application needs, and significantly promoting the industrial application of this material system in high-end electronic packaging, customized heat dissipation devices and other fields.

[0077] The above are all modifications that can be made to this embodiment without contributing any inventive step, or solutions that clearly constitute technical teaching, after reading this specification. However, as long as they are within the scope of the claims of this application, they should be protected by patent law.

Claims

1. A modified copper powder for additive manufacturing, characterized in that, The surface of the copper powder is coated with a siloxane network layer formed by the hydrolysis and condensation of aminohydrosilane.

2. The modified copper powder for additive manufacturing according to claim 1, characterized in that, The aminohydrosilane is selected from 3-aminopropyltriethoxysilane.

3. The modified copper powder for additive manufacturing according to claim 1, characterized in that, The thickness of the siloxane network layer is 2-10 nm.

4. The method for preparing the modified copper powder for additive manufacturing according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Hydrolyze the aminohydrosilane coupling agent in an acidic water-alcohol solution to obtain a silane hydrolysate; S2. Copper powder surface pretreatment; S3. Under an inert atmosphere, the pretreated copper powder from S2 is added to the silane hydrolysate to react and form a coating layer on the surface of the copper powder. S4. The reaction product is washed and dried to obtain the surface-modified copper powder.

5. The method for preparing modified copper powder for additive manufacturing according to claim 4, characterized in that, The reaction temperature in S3 is 40-70℃.

6. A ceramic-metal composite slurry for photocurable additive manufacturing, characterized in that, It includes 5-25 wt% of the modified copper powder of claims 1-3 or the product prepared in claims 4-5.

7. The ceramic-metal composite slurry for photocurable additive manufacturing according to claim 6, characterized in that, It also includes Al2O3 ceramic powder, sintering aids, photocurable resins, reactive diluents, photoinitiators, dispersants, and leveling agents.

8. The application of the composite paste according to any one of claims 6-7 in the preparation of electronic packaging materials or thermal management materials.

9. The application according to claim 8, characterized in that, Electronic packaging materials or thermal management materials are obtained by sintering the composite slurry described in any one of claims 6-7 after curing it using DLP 3D printing technology.

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