Silver powder, silver paste and method for preparing silver powder for photocuring additive manufacturing

Abstract

The present application discloses a silver powder, silver paste and a method for preparing the silver powder for photocuring additive manufacturing, which relates to the technical field of additive manufacturing materials, and can improve the penetration of ultraviolet light, thereby making the silver powder have a better printing effect when performing photocuring additive manufacturing. The silver powder includes: the grain size of the silver powder is greater than 50 nanometers, the crystal morphology of the silver powder is a spherical polyhedron, and the crystal surface of the silver powder is a smooth crystal surface. Since the silver powder has a large particle size and the crystal morphology of the silver powder is a spherical polyhedron, the crystal surface is relatively smooth, so the silver powder can effectively reduce the absorption of ultraviolet light. At the same time, since the silver powder is a spherical polyhedron, a plurality of micro multi-level reflective light-transmitting layers can be formed in the slurry layer, thereby improving the penetration of ultraviolet light in the slurry. The slurry prepared using the silver powder can achieve rapid photocuring. Therefore, the silver powder has a better printing effect when performing photocuring additive manufacturing.

Description

Technical Field

[0001] The present application relates to the technical field of additive manufacturing materials, and in particular to a silver powder, a silver paste and a method for preparing the silver powder for photocuring additive manufacturing. Background Art

[0002] Additive manufacturing is commonly known as 3D printing. The light curing technology (DLP) mainly controls the image curing of photosensitive polymer liquid by layer-by-layer light irradiation, and solidifies the entire printing layer in a relatively short time. Therefore, it has the remarkable characteristics of more efficient and high-precision near-net forming. It is a new manufacturing technology widely used in the fields of ceramics, plastics, biomedicine, etc. Now some metals can also be additively manufactured through DLP technology. Usually, the metal material is made into powder, then mixed with photosensitive resin into slurry, and then the slurry is printed and formed using light curing technology.

[0003] One of the key technologies of light-curing 3D printing technology is the preparation of metal powder materials, which usually requires that the prepared metal powder materials are evenly and stably distributed and have good penetration of ultraviolet light. However, the existing silver powder materials on the market have strong absorption and reflection effects on ultraviolet light, which will cause the silver powder to not cure normally during the 3D printing process, resulting in poor printing effects when printing silver products using DLP technology. Summary of the invention

[0004] The present application provides a silver powder, a silver paste and a method for preparing the silver powder for photocuring additive manufacturing, which can improve the penetration of ultraviolet light, thereby enabling the silver powder to have a better printing effect when performing photocuring additive manufacturing.

[0005] In a first aspect of an embodiment of the present application, a silver powder for photocuring additive manufacturing is provided. The silver powder is used for photocuring additive manufacturing. The silver powder includes: a grain size of the silver powder is greater than 50 nanometers, a crystal morphology of the silver powder is a spherical polyhedron, and a crystal surface of the silver powder is a smooth crystal surface.

[0006] In one embodiment, the particle size of the silver powder is 4.5 microns to 20 microns.

[0007] In one embodiment, the reflectivity of the silver powder to 405 nm light is 35% to 55%.

[0008] In one embodiment, the blue light whiteness of the silver powder is 70-85.

[0009] In one embodiment, the specific surface area of ​​the silver powder is 0.05 m 2 / g~0.2m 2 / g, the specific surface area is measured by BET specific surface area test method.

[0010] In one embodiment, the bulk density of the silver powder is 3 to 5 g / cm3 The tap density of silver powder is 5-6.5g / cm 3 .

[0011] According to a second aspect of the embodiment of the present application, a silver paste for photocuring additive manufacturing is provided, wherein the silver paste comprises: a photosensitive resin, a dispersant, an anti-settling agent and the silver powder according to the first aspect of the embodiment of the present application.

[0012] In one embodiment, the silver paste is in the 405nm band and the light-curing 3D printer power is 20mw / cm 2 ~35mw / cm 2 When light curing is performed under the conditions of

[0013] When the silver powder content is less than 70%wt, the 3-second curing depth of the silver paste is not less than 70μm; when the silver powder content is 80%wt, the 3-second curing depth of the silver paste is not less than 50μm.

[0014] In a third aspect of the embodiment of the present application, a method for preparing silver powder for photocuring additive manufacturing is provided, which is used to prepare the silver powder in the first aspect of the embodiment of the present application, and the method comprises:

[0015] Dissolving silver nitrate crystals in pure water to obtain a silver nitrate solution, and adding nitric acid to the silver nitrate solution to obtain a target silver nitrate solution;

[0016] dissolving ascorbic acid crystals in pure water to obtain an ascorbic acid solution;

[0017] After the target silver nitrate solution and the ascorbic acid solution are kept warm respectively, the target silver nitrate solution is added to the ascorbic acid solution while the ascorbic acid solution is stirred, and the solution is allowed to stand for a preset time to obtain silver powder.

[0018] In one embodiment, the silver nitrate solution is 0.7-2.0 mol / L, and the nitric acid is 0.6-1.5 mol / L.

[0019] The beneficial effects brought by the technical solution provided by the embodiment of the present application include at least:

[0020] The embodiment of the present application provides a silver powder for photocuring additive manufacturing, the particle size of the silver powder is greater than 50 nanometers, the crystal morphology of the silver powder is a spherical polyhedron, and the crystal surface of the silver powder is smooth. Since the particle size of this silver powder is larger than that of the silver powder on the market, and the crystal morphology of the silver powder is a spherical polyhedron, and the crystal surface is smooth, this silver powder can effectively reduce the absorption of ultraviolet light. At the same time, since the silver powder is a spherical polyhedron, a plurality of micro multi-level reflective light-transmitting layers can be formed in the slurry layer, thereby improving the penetration of ultraviolet light in the slurry. The slurry prepared using the silver powder can achieve rapid photocuring. Therefore, the silver powder has a better printing effect when performing photocuring additive manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A flow chart of a method for preparing silver powder for photocuring additive manufacturing provided in an embodiment of the present application;

[0022] Figure 2 The different types of silver powder in each control group in Table 1 of the present application embodiment are at 25mw / cm 2 The morphology of the SEM images during curing under power irradiation, wherein (a) is the control group 1, (b) is the control group 2, (c) is the control group 3, (d) is the control group 4, (e) is the control group 5, and (f) is the control group 6;

[0023] Figure 3 A scanning electron microscope image of a silver powder provided in an embodiment of the present application;

[0024] Figure 4 A method for utilizing the embodiment of the present application Figure 3 Cross-sectional views of the cured layer of the silver paste prepared from silver powder when irradiated for 3S, 6S and 9S respectively during photocuring printing, wherein (a) is for 3S, (b) is for 6S and (c) is for 9S;

[0025] Figure 5 A scanning electron microscope image of another silver powder provided in the embodiment of the present application;

[0026] Figure 6 A method for utilizing the embodiment of the present application Figure 5 Cross-sectional views of the cured layer of the silver paste prepared from silver powder when irradiated 3S, 6S and 9S respectively during photocuring printing, where (a) is 3S, (b) is 6S, and (c) is 9S. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0028] In the following, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present disclosure, unless otherwise specified, "plurality" means two or more.

[0029] Additionally, the use of “based on” or “according to” is meant to be open and inclusive, as a process, step, calculation, or other action “based on” or “according to” one or more conditions or values ​​may, in practice, be based on additional conditions or beyond values.

[0030] Additive manufacturing is commonly known as 3D printing. The light curing technology (DLP) mainly controls the image curing of photosensitive polymer liquid by layer-by-layer light irradiation, and solidifies the entire printing layer in a relatively short time. Therefore, it has the remarkable characteristics of more efficient and high-precision near-net forming. It is a new manufacturing technology widely used in the fields of ceramics, plastics, biomedicine, etc. Now some metals can also be additively manufactured through DLP technology. Usually, the metal material is made into powder, then mixed with photosensitive resin into slurry, and then the slurry is printed and formed using light curing technology.

[0031] One of the key technologies of photocuring 3D printing technology is the preparation of metal powder materials, which usually requires the prepared metal powder materials to be evenly and stably distributed and have good penetration of ultraviolet light. Metal powder materials have strong absorption and reflection of ultraviolet light, which will cause failure to cure normally. Therefore, it is particularly important to obtain suitable light penetration by preparing suitable metal powder materials to achieve fast and efficient photocuring. However, the silver powder on the market is currently used as a filler for conductive pastes, such as silver powder for photovoltaics and silver powder for conductive glue. It is usually an ultrafine spherical, flaky or irregular silver powder with a cumulative 50% particle size (D50) of 0.5 to 10 μm, mostly spherical powder of 1 to 3 μm, and processed into flaky powder after special requirements. The preparation method is mostly liquid phase chemical reduction method, and the slurry is mainly used for thermal curing, which cannot meet the requirements of photocuring 3D printing.

[0032] Due to the high reflectivity of the silver powder material prepared by physical method and the high absorbency of the silver powder prepared by chemical method, the ultraviolet light cannot effectively penetrate the slurry layer during exposure, and the activation energy absorbed by the photocurable resin in the slurry cannot reach the intensity of the cross-linking reaction, resulting in the slurry being unable to solidify or being difficult to finally form due to unsatisfactory thickness of the solidified layer and structural defects of the solidified component after solidification.

[0033] Secondly, when preparing photocuring slurry, small-size agglomerated silver powder particles with rough surface have a rough surface and large porosity. When exposed to ultraviolet light, the holes will absorb light and lose it, which will also easily lead to failure to cure or a thin cured layer, thereby causing structural defects.

[0034] In order to solve the above problems, the embodiment of the present application provides a silver powder for photocuring additive manufacturing. When used as a photocuring 3D printing slurry material, the particle size of the silver powder is greater than 50 nanometers, the crystal morphology of the silver powder is a spherical polyhedron, and the crystal surface of the silver powder is smooth. Since the particle size of this silver powder is larger than that of the silver powder on the market and the crystal morphology of the silver powder is a spherical polyhedron, the crystal surface is relatively smooth, therefore, this silver powder can effectively reduce the absorption of ultraviolet light. At the same time, since the silver powder is a spherical polyhedron, a plurality of micro multi-level reflective light-transmitting layers can be formed in the slurry layer, thereby improving the penetration of ultraviolet light in the slurry. The slurry prepared using the silver powder can achieve rapid photocuring. Therefore, the silver powder has a better printing effect when performing photocuring additive manufacturing.

[0035] The present application embodiment provides a silver powder for photocuring additive manufacturing, the silver powder is used for photocuring additive manufacturing, and the silver powder includes:

[0036] The grain size of the silver powder is greater than 50 nanometers, the crystal morphology of the silver powder is a spherical polyhedron, and the crystal surface of the silver powder is a smooth crystal surface.

[0037] Optionally, the particle size of the silver powder is 4.5 microns to 20 microns.

[0038] The particle size distribution of the silver powder measured by a laser diffraction / scattering particle size distribution measuring device by a wet method was above 4.5 μm and below 20 μm, and the cumulative 50% particle size (D50) in the volume-based particle size distribution was about 10 μm.

[0039] Optionally, the reflectivity of the silver powder to 405nm light is 35% to 55%.

[0040] Optionally, the blue light whiteness of the silver powder is 70 to 85. The blue light whiteness of the silver powder is measured by a whiteness meter.

[0041] Optionally, the specific surface area of ​​the silver powder is 0.05m 2 / g~0.2m 2 / g, the specific surface area is measured by BET specific surface area test method.

[0042] The specific surface area of ​​silver powder is 0.05m 2 / g~0.2m 2 / g indicates that the specific surface area of ​​the silver powder is small.

[0043] Optionally, the bulk density of the silver powder is 3 to 5 g / cm 3 The tap density of silver powder is 5-6.5g / cm 3 .

[0044] Optionally, an embodiment of the present application further provides a silver paste for photocuring additive manufacturing, wherein the silver paste comprises: a photosensitive resin, a dispersant, an anti-settling agent, and the silver powder in the above embodiment.

[0045] Among them, the silver paste is in the 405nm band, and the power of the light-curing 3D printer is 20mw / cm 2 ~35mw / cm 2 When the silver powder content is less than 70%wt, the 3-second curing depth of the silver paste is not less than 70μm; when the silver powder content is 80%wt, the 3-second curing depth of the silver paste is not less than 50μm. This shows that the silver paste obtained by using the silver powder can achieve stable photocuring 3D printing of pure silver products with complex structures.

[0046] like Figure 1 As shown, the embodiment of the present application also provides a method for preparing silver powder for photocuring additive manufacturing, which is used for the silver powder in the above embodiment. The method comprises the following steps:

[0047] Step 101, dissolving silver nitrate crystals in pure water to obtain a silver nitrate solution, and adding nitric acid to the silver nitrate solution to obtain a target silver nitrate solution;

[0048] Step 102, dissolving ascorbic acid crystals in pure water to obtain an ascorbic acid solution;

[0049] Step 103: After the target silver nitrate solution and the ascorbic acid solution are kept warm respectively, the target silver nitrate solution is added to the ascorbic acid solution while the ascorbic acid solution is stirred, and the solution is allowed to stand for a preset time to obtain silver powder.

[0050] Among them, the silver nitrate solution is 0.7-2.0 mol / L, and the nitric acid is 0.6-1.5 mol / L.

[0051] Specifically, the preparation method of the silver powder of the present invention refers to reducing and precipitating the silver powder by using a reducing agent through a chemical reduction method, and increasing the nitric acid concentration in the medium during the reduction process to increase the reverse reaction rate to control the number of nuclei, so that the formed crystal nuclei and the dendrites formed on the crystal surface are reversely dissolved, thereby achieving slow nucleation, crystal growth, and controllable morphology and polycrystalline surface. At the same time, no dispersant is added during the reaction process to ensure growth on an open crystal surface.

[0052] The preparation method mainly comprises the following steps: preparation of silver nitrate solution, preparation of reducing agent solution, mixed reduction, silver powder cleaning, surface modification, silver powder drying, silver powder classification and the like.

[0053] Preparation of silver nitrate solution: As an aqueous reaction system containing silver ions, an aqueous solution containing silver nitrate, a silver complex or a silver intermediate can be used. In order to make the silver powder have an appropriate particle size and good crystallinity, it is preferred to add nitric acid to the silver nitrate aqueous solution to obtain an acidic silver nitrate aqueous solution. The amount of silver nitrate is 0.5 to 2 mol / L, preferably 1 mol / L, and the amount of nitric acid added is controlled to be 0.6 to 1.5 mol / L, preferably 1.0 mol / L.

[0054] Preparation of reducing agent solution: There are many reducing agents that can be used for silver powder reduction, mainly ascorbic acid, hydrazine hydrate, glucose, formaldehyde solution, hydroquinone, hydrogen peroxide, borohydride, etc. In order to facilitate the control of the reaction rate, the present invention selects a reducing agent that generates hydrogen ions by reaction, preferably ascorbic acid, or a mixed reducing agent of ascorbic acid and hydrazine hydrate, glucose, formaldehyde solution, hydroquinone, etc. The reducing agent is dissolved in pure water. In order to control the reaction rate, the reducing agent concentration is preferably equivalent to 1.05 to 1.5 times the stoichiometric concentration of complete silver reduction, preferably 1.2 times. It is not recommended to add too much reducing agent.

[0055] Mixed reduction: quickly add the reducing agent to the silver nitrate solution. During the reduction, the reaction solution must be stirred for 5 to 10 minutes to allow the reduction-nucleus and dendrite dissolution-re-reduction growth process to proceed fully. The solution is basically clear at the beginning of the mixture, and as the reaction proceeds, the solution gradually becomes turbid and grayish white. The entire reaction process lasts for 1 to 2 minutes. The liquid temperature during the reduction reaction is preferably above 5°C and below 40°C, more preferably above 15°C and below 30°C. Due to the limited excess of reducing agent and the existence of reverse dissolution reaction, incomplete reduction of silver ions may occur. After the mixed solution is separated into solid and liquid, the residual silver ions in the liquid are recovered by reduction or ion adsorption. In addition, in order to obtain silver powder with a larger particle size, it is not recommended to add organic dispersants such as PVP during the reduction process.

[0056] Silver powder cleaning: After the above mixed reducing solution is stirred, let it stand for 30 minutes, and pour the supernatant into the waste liquid recovery tank to recover the residual silver ions. The silver powder at the bottom is washed with pure water several times. The end point of the washing can be judged by the pH of the water after washing. It is preferred to carry out the washing until the pH of the washing solution is not less than 6.

[0057] Surface modification: In order to make the silver powder have better wettability with organic resin when preparing silver paste, the surface of the silver powder needs to be hydrophobically modified. Weigh 0.2-2% of the mass of the silver powder, preferably 0.5% of the fatty acid dissolved in an alcohol solution, and the mass of ethanol is 1-1.5 times the mass of the silver powder. Fatty acids are preferably stearic acid, oleic acid, and ricinoleic acid. Add the modifier ethanol solution to the silver powder and stir thoroughly for 30 minutes to coat the hydrophobic surfactant on the surface of the silver powder. Let it stand for 30 minutes and pour out the excess ethanol solution.

[0058] Silver powder drying: Move the modified slurry silver powder into a glass drying tray, flatten it to a thickness of less than 1 cm, and put it into an oven for drying. The drying temperature is preferably below 80°C. If the temperature is too high, the silver powder will sinter and agglomerate with each other during drying, affecting its use.

[0059] Silver powder classification: Dry crushing and classification of dried silver powder. Put the silver powder into an air flow crusher to crush the silver powder under the action of high-speed air flow. Use an air flow classifier for classification, and select silver powder with a particle size of 4.5μm to 20μm, preferably 6 to 15μm. In addition, drying, crushing and classification can also be performed using an integrated device that can perform drying, crushing and classification.

[0060] Preferred reference indicators for silver powder

[0061] The silver powder of the present invention is mixed with trimethylolpropane triacrylate (EO3TMPTA), 1,6-hexanediol diacrylate (HDDA), 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), acrylic block copolymer and polyurea-modified N-methylpyrrolidone solution, stirred in a high-speed dispersant for 8 hours to obtain a photocurable slurry, and printed on a photocurable 3D printer. The printing conditions are: layer thickness of 50 μm / layer, layer-by-layer exposure time of 3 seconds, and photomechanical energy of 25 mw / cm 2 .

[0062] Silver powder particle size distribution

[0063] The cumulative 50% particle size (D50) of the silver powder in the volume-based particle size distribution measured by laser diffraction particle size distribution measurement method is about 10 μm, preferably 8 to 12 μm. If the particle size is too small, the absorption of ultraviolet light increases, which is not conducive to ultraviolet light penetration and affects the photocuring efficiency. If the particle size is too large, the prepared slurry sediments faster, which is not conducive to printing and the printing accuracy deteriorates.

[0064] Color and morphology of silver powder

[0065] The method for measuring the whiteness of the above silver powder is as follows: According to the national standard GB / T 13025.2-2008, the blue light whiteness Wr value is measured by a whiteness meter: WBD-2A digital whiteness meter, and the value is 70-85. The absorbance of the powder in the 405nm band is inversely proportional to the whiteness, that is, the lower the whiteness, the stronger the absorption of the powder to the 405nm band light, which hinders the solidification of the slurry. In this technology, too high whiteness is often accompanied by the agglomeration of the powder, and the agglomeration of the powder material will affect the uniformity of the solid phase dispersion in the slurry, so the preferred whiteness Wr value is 70-75.

[0066] BET specific surface area of ​​silver powder

[0067] (Reference) The BET specific surface area of ​​the silver powder can be measured using a nitrogen adsorption measuring instrument according to a nitrogen adsorption method. In the present invention, the BET specific surface area of ​​the silver powder is 0.05 m 2 / g or more and 0.2m 2 / g or less, preferably 0.1m 2 / g or more and 0.2m 2 / g or less. If the BET specific surface area is less than 0.05m 2 / g, the size of the silver powder is too large and will settle in the slurry; if the above BET specific surface area exceeds 0.2m 2 / g, indicating that the powder particle size is small or the surface is rough, and the crystallinity is low, which affects the curing efficiency.

[0068] To further illustrate the difference in light curing behavior between the silver powder of the present invention and other silver powders, further description is now given.

[0069] Table 1 Different types of silver powder at 25mw / cm 2 Comparison table of curing behavior under power irradiation

[0070]

[0071] Figure 2 The following are the different types of silver powder in the six control groups in Table 1 at 25mw / cm 2 The morphology of the SEM during curing under power irradiation is shown in Table 1. Samples 1 and 2 are the silver powders recommended in the examples, and samples 4 to 6 are the same type of commercially available and homemade silver powders. As shown in Table 1, silver powders 4 to 6 are irradiated at 25 mw / cm 2 No effective solidified layer can be generated under high-power irradiation. Although No. 6 has a shallow solidified layer, it cannot be used in photocuring additive manufacturing.

[0072] Furthermore, the present application also provides a plurality of specific embodiments.

[0073] Example 1

[0074] A method for preparing silver powder for photocuring additive manufacturing comprises the following components: an oxidant component comprises: 0.25 mol of nitric acid dissolved in a 1.5 mol / L silver nitrate solution, with a total volume of 1 L; and a reducing agent component comprises 1.8 L of a 0.5 mol / L ascorbic acid solution.

[0075] In the above formula, the mass fraction of concentrated nitric acid is 65% to 68%, silver nitrate is dry powder crystals, and ascorbic acid is L(-)-C6H8O6 with a relative molecular mass of 176.13.

[0076] The method for preparing the silver powder of the above composition for photocuring additive manufacturing comprises the following steps:

[0077] S1. Preparation of silver nitrate component solution A: Weigh 255 g of silver nitrate crystals and dissolve them in 0.5 L of pure water. Then add 0.6 mol of concentrated nitric acid to the solution, and then adjust the volume of the solution to 1 L to obtain solution A.

[0078] S2. Preparation of ascorbic acid component solution B: Weigh 158.4 g of ascorbic acid and dissolve it in 1 L of pure water. Dissolve it fully and stir it evenly, then make the volume to 1.8 L to obtain solution B.

[0079] S3. Seal the beakers of Solution A and Solution B with film and place them in a 50°C water bath and heat for 30 minutes.

[0080] S4. Take out solution A and solution B, place the stirrer in solution B, set the stirring speed to 350 r / min, and the stirring time to 1 min.

[0081] S5. Turn on the agitator, and after the speed stabilizes at 350 r / min, pour solution A into solution B within 2 to 3 seconds to react.

[0082] S6. After the stirrer stops stirring, let it stand for 10 minutes, then add pure water to clean the silver powder solution 3 to 5 times, and use pH test paper to test the pH value of the solution to about 7.

[0083] S7. Weigh 0.5 g of stearic acid and dissolve it in 95% alcohol solution to modify the surface of the silver powder to make it hydrophobic and lipophilic. Then dry and grind it to obtain a silver powder for photocuring additive manufacturing.

[0084] S8. Mix the silver powder with photosensitive resin and other additives to prepare a photocurable slurry, and print it on a photocurable 3D printer. The printing conditions are: layer thickness of 50 μm / layer, layer-by-layer exposure time of 3 seconds, and photomechanical energy of 25 mw / cm 2 .

[0085] The obtained silver powder particle size ranges from about 10 to 13 μm, the silver powder crystal surface is spherical, the grain size is 36 nm, and the specific surface area is 0.183 m 2 / g, bulk density is 3.75g / cm3, tap density is 5.1g / cm 3 . 405nm band, optical power is 25mw / cm 2 When the solid content is 75%wt, the curing depth is about 75μm in 3 seconds, about 90μm in 6 seconds, and about 110μm in 9 seconds. The sedimentation rate is 1.5% in 48 hours. The curing efficiency is high. It is recommended that the layer-by-layer printing time is 2 to 3 seconds and the layer thickness is 50 to 70μm. It is suitable for rapid manufacturing of small-volume components. Figure 3 , which is a scanning electron microscope image of the silver powder prepared in the example of the present application. Figure 4It is a cross-sectional view of the solidified layer when the silver paste prepared by the silver powder is irradiated for 3S, 6S and 9S respectively during photocuring printing, wherein: Figure 4 Figure (a) is a cross-sectional view of the irradiated 3S cured layer. Figure 4 Figure (b) is a cross-sectional view of the irradiated 6S solidified layer. Figure 4 Figure (c) is a cross-sectional view of the irradiated 9S cured layer.

[0086] Example 2

[0087] A method for preparing silver powder for photocuring additive manufacturing comprises the following components: an oxidant component comprises: 0.6 mol of nitric acid dissolved in a 1 mol / L silver nitrate solution, with a total volume of 1 L; and a reducing agent component comprises 1.2 L of a 0.5 mol / L ascorbic acid solution.

[0088] In the above formula, the mass fraction of concentrated nitric acid is 65% to 68%, silver nitrate is dry powder crystals, and ascorbic acid is L(-)-C6H8O6 with a relative molecular mass of 176.13.

[0089] The method for preparing the silver powder of the above composition for photocuring additive manufacturing comprises the following steps:

[0090] S1. Preparation of silver nitrate component solution A: Weigh 170 g of silver nitrate crystals and dissolve them in 0.5 L of pure water. Then add 0.6 mol of concentrated nitric acid to the solution, and then adjust the volume of the solution to 1 L to obtain solution A.

[0091] S2. Preparation of ascorbic acid component solution B: Weigh 105.6 g of ascorbic acid and dissolve it in 500 ml of pure water. Fully dissolve and stir to obtain solution B.

[0092] S3. Seal the beakers of Solution A and Solution B with film and place them in a 50°C water bath and heat for 30 minutes.

[0093] S4. Take out solution A and solution B, place the stirrer in solution B, set the stirring speed to 350 r / min, and the stirring time to 1 min.

[0094] S5. Turn on the agitator, and after the speed stabilizes at 350 r / min, pour solution A into solution B within 2 to 3 seconds to react.

[0095] S6. After the stirrer stops stirring, let it stand for 10 minutes, add pure water to clean the silver powder solution 3 to 5 times, and use pH test paper to test the pH value of the solution to about 7.

[0096] S7. Weigh 0.5 g of stearic acid and dissolve it in 95% alcohol solution to modify the surface of the silver powder to make it hydrophobic and lipophilic. Then dry and grind it to obtain a silver powder for photocuring additive manufacturing.

[0097] S8. Mix the silver powder with photosensitive resin and other additives to prepare a photocurable slurry, and print it on a photocurable 3D printer. The printing conditions are: layer thickness of 30 μm / layer, layer-by-layer exposure time of 6 seconds, and photomechanical energy of 25 mw / cm 2 .

[0098] The obtained silver powder particle size ranges from 5 to 8 μm, the surface of the silver powder crystal is spherical, the grain size is 51 nm, and the specific surface area is 0.26 m 2 / kg, bulk density is 3.33g / cm 3 , tap density is 4.35g / cm 3 . 405nm band, optical power is 25mw / cm 2 When the solid content is 75%wt, the curing depth is about 55μm in 3 seconds, about 65μm in 6 seconds, about 78μm in 9 seconds, and the sedimentation rate is 0.5% in 48 hours. It is recommended that the layer-by-layer printing time is 5 to 6 seconds. The slurry system is more stable, with a layer thickness of 30 to 40μm, which is suitable for manufacturing large-volume components with a printing time of more than 10 hours; Figure 5 , which is a scanning electron microscope image of the silver powder prepared in the example of the present application. Figure 6 It is a cross-sectional view of the solidified layer when the silver paste prepared by the silver powder is irradiated for 3S, 6S and 9S respectively during photocuring printing, wherein: Figure 6 Figure (a) is a cross-sectional view of the irradiated 3S cured layer. Figure 6 Figure (b) is a cross-sectional view of the irradiated 6S solidified layer. Figure 6 Figure (c) is a cross-sectional view of the irradiated 9S cured layer.

[0099] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0100] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A silver powder for photocuring additive manufacturing, characterized in that: The silver powder is used for photocuring additive manufacturing, and the silver powder comprises: The grain size of the silver powder is greater than 50 nanometers, the crystal morphology of the silver powder is a spherical polyhedron, and the crystal surface of the silver powder is a smooth crystal surface; The particle size of the silver powder is 4.5 microns to 20 microns; The reflectivity of the silver powder to 405 nanometer light is 35% to 55%; The blue light whiteness of the silver powder is 70 to 85; The specific surface area of ​​the silver powder is 0.05 m 2 / g~0.2m 2 / g, the specific surface area is measured using the BET specific surface area test method; The bulk density of the silver powder is 3-5 g / cm 3 The tap density of the silver powder is 5 to 6.5 g / cm 3 .

2. A silver paste for photocuring additive manufacturing, characterized in that: The silver paste comprises: a photosensitive resin, a dispersant, an anti-settling agent and the silver powder according to claim 1; The silver paste is in the 405nm band, and the power of the light-curing 3D printer is 20mw / cm 2 ~35mw / cm 2 When light curing is performed under the conditions of, when the silver powder content is less than 70%wt, the 3-second curing depth of the silver paste is not less than 70μm; when the silver powder content is 80%wt, the 3-second curing depth of the silver paste is not less than 50μm.

3. A method for preparing silver powder for photocuring additive manufacturing, characterized in that: For preparing the silver powder according to claim 1, the method comprises: Dissolving silver nitrate crystals in pure water to obtain a silver nitrate solution, and adding nitric acid to the silver nitrate solution to obtain a target silver nitrate solution; dissolving ascorbic acid crystals in pure water to obtain an ascorbic acid solution; After the target silver nitrate solution and the ascorbic acid solution are kept warm respectively, the target silver nitrate solution is added to the ascorbic acid solution while the ascorbic acid solution is stirred, and the solution is allowed to stand for a preset time to obtain the silver powder; The silver nitrate solution is 0.7-2.0 mol / L, and the nitric acid is 0.6-1.5 mol / L.

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