Raw material powder for layered structures

Abstract

To obtain a highly fluid raw material powder for laminated structures. [Solution] A raw material powder for laminated structures used in the manufacture of a laminated structure having a multilayer structure of raw material powder layers, comprising a base powder with an average particle size of 2 μm to 30 μm and silica powder with an average particle size of 3 nm to 200 nm, wherein the base powder is a metal powder and / or ceramic powder, and the silica powder has been subjected to a hydrophobic treatment on its surface.

Description

[Technical Field]

[0001] This invention relates to a raw material powder for laminated structures. [Background technology]

[0002] There is a technology for manufacturing metal molded parts using a 3D printer. In this technology, a layer of raw material powder containing metal powder is first formed. Then, a binder print pattern is formed on this layer.

[0003] Next, the binder is cured to form a cured pattern of the printed pattern within that layer. This process is repeated many times to form a three-dimensional cured pattern composed of a laminate of cured patterns from each layer. Then, the three-dimensional cured pattern is sintered by heat treatment. This yields a laminated structure. This laminated structure becomes a molded metal product.

[0004] This technology allows for the production of metal products with complex three-dimensional shapes. This technology requires high fluidity in the raw material powder. Patent Document 1 describes a technique for improving the fluidity of the raw material powder by adding a fluidizing agent. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 7204793 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to obtain a raw material powder for laminated structures with high fluidity. [Means for solving the problem]

[0007] The present invention relates to a raw material powder for a laminated structure used in the production of a laminated structure having a structure in which raw material powder layers are laminated in multiple layers. The raw material powder for the laminated structure includes a base material powder having an average particle size of 2 μm to 30 μm and silica powder having an average particle size of 3 nm to 200 nm. The base material powder is a metal powder and / or a ceramic powder, and the silica powder is a raw material powder for a laminated structure whose surface has been subjected to a hydrophobization treatment.

[0008] In the present invention, an embodiment in which the silica powder is wet silica powder can be mentioned. In the present invention, an embodiment in which the content ratio of the silica powder is 5 ppm to 70 ppm can be mentioned. In the present invention, an embodiment in which the particle size of the silica powder with respect to the particle size of the base material powder is 0.15% or less can be mentioned. In the present invention, an embodiment in which the particle size of the silica powder with respect to the particle size of the base material powder is 0.15% or less and the content ratio of the silica powder is 70 ppm or less can be mentioned.

[0009] In the present invention, the silica powder is a wet silica powder modified with a functional group represented by the formula (1): -OSiX 1 X 2 X 3 and a functional group represented by the formula (2): -OSiY 1 Y 2 Y 3 An embodiment can be mentioned. Here, in the above formulas (1) and (2); X 1 is a phenyl group, vinyl group, epoxy group, methacryl group, amino group, ureido group, mercapto group, isocyanate group, or acrylic group; X 2 , X 3 are each independently selected from -OSiR3 and -OSiY 4 Y 5 Y 6 ; Y 1 is R; Y 2 , Y 3 are each independently selected from R and -OSiY 4 Y 5 Y 6 ; Y 4 is R; Y 5 and Y 6R and -OSiR3 are independently selected; R is independently selected from alkyl groups having 1 to 3 carbon atoms. Note that X 2 , X 3 , Y 2 , Y 3 , Y 5 , and Y 6 Either of these is the X of the adjacent functional group 2 , X 3 , Y 2 , Y 3 , Y 5 , and Y 6 It may be joined with any of the following using -O-. [Effects of the Invention]

[0010] According to the present invention, a raw material powder for laminated structures with high fluidity can be obtained. [Brief explanation of the drawing]

[0011] [Figure 1] This is a conceptual diagram of a binder jet 3D printer. [Figure 2] This diagram shows the manufacturing process of a laminated structure. [Figure 3] This diagram shows the manufacturing process of a laminated structure. [Figure 4] These are photographs (A) and (B) that serve as substitutes for drawings, showing images of the raw material powder obtained by scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX). [Modes for carrying out the invention]

[0012] (Overview of 3D printers) Figure 1 is a conceptual diagram of a 3D printer 100 that manufactures a metal layered structure (three-dimensional structure) using raw material powder containing metal powder. The 3D printer 100 comprises a stage 10, a hopper 12 that forms a raw material powder layer PL on the stage 10, and an inkjet dispenser 14 that supplies liquid binder B to the raw material powder layer PL.

[0013] The 3D printer 100 is equipped with a stage 10 that can be moved up and down electrically. The stage 10 is equipped with a printing stage 11 that functions as a surface on which a layered structure made of powder is formed. In the space above the printing stage 11, a hopper 12 and an inkjet dispenser 14 are arranged that can move horizontally relative to the printing stage 11. The hopper 12 is a means for supplying the raw material powder P. As the hopper 12 is moved horizontally relative to the printing stage 11, the raw material powder P is scattered onto the printing stage 11 by gravity from the hopper 12.

[0014] The layer of raw material powder scattered on the printing stage 11 is spread out on the printing stage 11 by the horizontally moving roller 13 to a predetermined thickness. This forms a raw material powder layer PL of a specific thickness.

[0015] Liquid binder B is sprayed onto the raw material powder layer PL from the inkjet dispenser 14 in a predetermined specific printing pattern. This state is shown in Figure 1(B). Binder B is an aqueous solution containing an organic binder and corresponds to the ink of a printer. The inkjet dispenser 14 corresponds to the ink supply head of a printer and has an XY stage movement mechanism in the horizontal direction, and can be moved electrically in the left-right direction and the depth direction of the figure.

[0016] As the inkjet dispenser 14 is moved in the left-right direction in the diagram, binder B is sprayed from the inkjet dispenser 14 onto the raw material powder layer PL in a specific spray pattern (see Figure 1(B)). This forms a specific printed pattern of binder B on linear regions of the raw material powder layer PL. By repeating the above process while shifting the inkjet dispenser 14 in the depth direction in the diagram, a specific printed pattern PLa of binder B is formed on the raw material powder layer PL. The printed pattern PLa has a two-dimensional pattern shape with the thickness of the raw material powder layer PL.

[0017] The 3D printer 100 is equipped with a heater 15, which is a heating means. By moving the heater 15 horizontally above the raw material powder layer PL, which is selectively sprayed with binder B, the printed pattern PLa is heated, and the printed pattern PLa hardens due to the function of binder B.

[0018] (An example of a manufacturing process) Figures 2 and 3 illustrate the manufacturing process of a layered structure using a 3D printer 100. First, raw material powder is supplied onto the printing stage 11 to form a raw material powder layer PL (Figure 2(A)). Next, a roller 13 is used to flatten the raw material powder layer PL and set it to a specified thickness (Figure 2(B)). Here, the thickness of the raw material powder layer PL after flattening is set to 100 μm. The thickness of the raw material powder layer PL after flattening can be selected from a range of, for example, 50 μm to 200 μm.

[0019] Next, the binder B is printed onto the raw material powder layer PL using a predetermined printing pattern (Figure 2(C)). Figure 2(C) shows the state where binder B has been sprayed onto the area labeled PLa. Next, the binder is cured (Figure 2(D)). In this process, the heater 15 is passed over the raw material powder layer PL, and the binder is cured by heating. By curing the binder, a cured layer 30 is formed from the hardened raw material powder.

[0020] By repeating the processes shown in Figures 2(A) to 2(D), a laminate of raw material powder layers PL with a hardened layer 30 is obtained. Figure 2(F) shows a state in which two layers of raw material powder layers PL are laminated, with hardened layers 31 and 32 of raw material powder slightly offset from each other. Figure 3(A) shows a laminate 33 in which multiple layers of raw material powder layers with hardened layers (shaded areas) are formed. The number of layers to be laminated is determined by the thickness of the final product. For example, if the thickness of one layer is 100 μm, and the thickness of the final product is 10 mm or more, then 100 or more layers will be laminated.

[0021] After the binder curing process, the uncured portion of the raw material powder layer PL is removed by suction using a suction nozzle (not shown in the figure). The portion of the raw material powder layer PL where binder B is not printed (introduced) remains uncured and in the form of fluid powder, and is removed by the suction described above. By removing the uncured raw material powder, a laminate 34 of the cured raw material powder layer, as illustrated in Figure 3(B), is obtained.

[0022] Once a laminated body 34 of hardened raw material powders is obtained, it is removed from the 3D printer 100 and heated to, for example, 1300°C to 1400°C for sintering. This process integrates the laminated body 34, yielding a laminated structure 35 which is a sintered body with a three-dimensional structure (Figure 3(C)). The sintering temperature is appropriately selected depending on the material of the raw material powders.

[0023] HIP (Hot Isostatic Pressing) treatment may be performed after the sintering process. HIP treatment is performed, for example, at 1150°C × 100 MPa × 3 hours.

[0024] In the process shown in Figure 2, the fluidity of the raw material powder is crucial. Insufficient fluidity of the raw material powder leads to insufficient and non-uniform packing density of the raw material powder in the raw material powder layer PL, resulting in a decrease in the quality of the raw material powder layer PL after planarization. This decrease in the quality of the raw material powder layer PL affects the quality of the final laminated structure 35. Specifically, it can lead to defects and insufficient strength within the laminated structure 35 after sintering.

[0025] (Raw material powder) The raw material powder consists of a base powder and a fluidizing agent, which is an additive powder that enhances fluidity. The base powder is the main raw material that makes up the laminated structure.

[0026] (base material powder) The base powder will depend on the target product, which will consist of a sintered body. Examples of base powders include steel powder. For example, if the product is a mold, alloy powders of alloy steels used for hot molds, such as SKD61, can be used. If the product is a cast steel product, high-tensile carbon steel cast iron, such as SCC material, can be used. In addition, at least one of the following can be used: stainless steel, Inconel (registered trademark), metal powders and alloy powders that have a proven track record of use in MIM (metal powder injection molding), carbonyl iron powder, carbonyl nickel powder, nickel-based alloy powder, cobalt-based alloy powder, copper and copper alloy powder, aluminum and aluminum alloy powder, titanium and titanium alloy powder, magnesium and magnesium alloy powder, and ceramic powder. An example of a raw material powder is water atomized powder. The average particle size of the raw material powder is, for example, 3 to 50 μm. The base powder content in the raw material powder should be 99.9% by weight or more.

[0027] (Smoothing agent) The fluidizer is a hydrophobic surface-treated wet silica (SiO2) powder. The average particle size of the wet silica powder is 3 to 200 nm. The wet silica powder has the function of increasing the fluidity of the base particles by adhering to their surface and coating it as a fine powder. Therefore, it is important to cover the surface of the base particles uniformly with high adhesion. Hydrophobic surface-treated wet silica (SiO2) powder is suitable for achieving this objective. Furthermore, to achieve the objective of coating the surface of the base particles, the average particle size of the wet silica powder is preferably about 0.5 / 1000 to 1.5 / 1000 of the base particle size. The appropriate content of the fluidizer in the raw material powder is about 0.0005% to 0.007% by weight (5 ppm to 70 ppm by weight).

[0028] Wet silica powder is synthesized from water glass (sodium silicate) in water. Examples of wet silica sols that can be used in this invention include the Snowtex series from Nissan Chemical Industries, Ltd., the Cataloid series from JGC Catalysts & Chemicals Inc., and the Silica Doll series from Nippon Chemical Industrial Co., Ltd.

[0029] The method for producing wet silica powder is not particularly limited. Examples include the water glass method, the alkoxide method, and the VMC method, with the water glass method being preferable. The water glass method is a method for precipitating wet silica powder by performing ion exchange, introduction and removal of substitution groups by chemical reaction, and control of pH and temperature on water glass. For example, by ion exchange with an ion exchange resin, an aqueous slurry in which silica powder on the order of nanometers is dispersed can be prepared. The particle size of the secondary powder constituting the wet silica powder is not particularly limited, but the volume average particle size may be 10 μm or more, or 100 μm or more. Furthermore, wet silica powder can be produced by dissolving metallic silicon in an alkaline solution and then precipitating it (a method similar to the water glass method).

[0030] A pretreatment step is applied to the preparation of wet silica powder. The pretreatment step consists of a surface treatment step and a step to remove the liquid medium (solidification step). The surface treatment step involves surface treatment with a silane coupling agent and organosilazane in a liquid medium containing water (water, or water plus alcohol, etc.). The silane coupling agent has three alkoxy groups and one of the following: a phenyl group, a vinyl group, an epoxy group, a methacrylic group, an amino group, a ureido group, a mercapto group, an isocyanate group, or an acrylic group. The molar ratio of the silane coupling agent to the organosilazane is (silane coupling agent):(organosilazane) = 1:2 to 1:10.

[0031] The hydrophobic surface treatment process comprises a first treatment step of treating with the aforementioned silane coupling agent, and a second treatment step of treating with organosilazane.

[0032] The hydrophobic surface treatment step involves applying formula (1):-OSiX to the silica powder obtained by the above method. 1 X 2 X 3 A functional group represented by formula (2):-OSiY 1 Y 2 Y 3This is a process to obtain wet silica powder on which a functional group represented by formula (1) is bonded to the surface. Hereinafter, the functional group represented by formula (1) will be called the first functional group, and the functional group represented by formula (2) will be called the second functional group.

[0033] X in the first functional group 1 X is a phenyl group, vinyl group, epoxy group, methacrylic group, amino group, ureido group, mercapto group, isocyanate group, or acrylic group. 2 , X 3 These correspond to -OSiR3 or -OSiY, respectively. 4 Y 5 Y 6 Y 4 is R. Y 5 , Y 6 These are R or -OSiR3, respectively.

[0034] Y in the second functional group 1 is R. Y 2 , Y 3 These are -OSiR3 or OSiY, respectively. 4 Y 5 Y 6 That is the case.

[0035] The more -OSiR3 groups present in the first and second functional groups, the more R groups the wet silica powder will have on its surface. The more R groups (alkyl groups with 1 to 3 carbon atoms) present in the first and second functional groups, the less likely the wet silica powder is to aggregate.

[0036] Regarding the first functional group, X 2 , X 3 The number of R's is minimized when each of them is -OSiR3. Also, X 2 and X 3 Each of these is -OSiY 4 Y 5 Y 6 And Y 5 , Y 6 The number of R's is maximized when each of them is -OSiR3.

[0037] Regarding the second functional group, Y2 and Y 3 When each of Y 2 and Y 3 is -OSiR3, the number of R is minimized. Also, when each of Y 4 and Y 5 and Y 6 is -OSiY 5 Y 6 Y

[0038] The number of X 1 contained in the first functional group, the number of R contained in the first functional group, and the number of R contained in the second functional group may be appropriately set according to the abundance ratio of R and X 1 to each other, the particle size of the wet silica powder, and the use.

[0039] In addition, any one of X 2 and X 3 and Y 2 and Y 3 and Y 5 and Y 6 may be bonded to -O- with any one of X 2 and X 3 and Y 2 and Y 3 and Y 5 and Y 6 in an adjacent functional group. For example, any one of X 2 and X 3 and Y 5 and Y 6 in the first functional group may be bonded to -O- with any one of X 2 and X 3 and Y 5 and Y 6 in the first functional group adjacent to this first functional group. Similarly, any one of Y 2 and Y 3 and Y 5 and Y 6 in the second functional group may be bonded to -O- with any one of Y 2 and Y 3 and Y 5 and Y 6 in the second functional group adjacent to this second functional group. Furthermore, X 2 and X3 , Y 5 , and Y 6 Either of these is the second functional group adjacent to this first functional group Y 2 , Y 3 , Y 5 , and Y 6 It may be joined to any of the following with -O-.

[0040] In wet silica powder, if the abundance ratio of the first functional group to the second functional group is 1:12 to 1:60, X will form on the surface of the wet silica powder. 1 R and are present in a well-balanced manner. For this reason, wet silica powder in which the abundance ratio of the first functional group to the second functional group is 1:12 to 1:60 exhibits particularly excellent affinity to the base powder and aggregation suppression effect. Also, X 1 The unit surface area (nm) of wet silica powder 2 If there are 0.5 to 2.5 groups per unit, a sufficient number of first functional groups will be bonded to the surface of the wet silica powder, and a sufficient number of R groups will also be present, derived from the first and second functional groups. Therefore, in this case as well, the affinity to the base powder and the aggregation suppression effect of the wet silica powder will be fully exhibited.

[0041] In either case, the unit surface area (nm) of the wet silica powder 2 The number of R particles per particle is preferably 1 to 10. In this case, X particles present on the surface of the wet silica powder. 1 The balance between the number of Rs and the number of Rs is improved, resulting in a good balance between affinity to the base powder and the effect of suppressing aggregation of wet silica powder.

[0042] In wet silica powder, it is preferable that all hydroxyl groups present on the surface of the silica powder are replaced by a first functional group or a second functional group. The sum of the first and second functional groups is the unit surface area (nm) of the wet silica powder. 2 If there are 2.0 or more hydroxyl groups per unit area, it can be said that in wet-processed silica powder, almost all of the hydroxyl groups present on the surface of the silica powder are replaced by either the first or second functional group.

[0043] Wet silica powder has a radius (R) on its surface. This can be confirmed by infrared absorption spectroscopy. Specifically, when the infrared absorption spectrum of wet silica powder is measured by solid-state diffuse reflectance, it is 2962±2 cm⁻¹. -1 There is a maximum absorption of CH stretching vibrations.

[0044] Furthermore, as mentioned above, wet silica powder is less prone to agglomeration. Even if wet silica powder does agglomerate slightly, it can be redispersed by ultrasonic treatment. For example, by irradiating a mixture of wet silica powder dispersed in methyl ethyl ketone with ultrasonic waves at an oscillation frequency of 10-50 kHz and an output of 200-800 W, the wet silica powder can be dispersed to virtually primary powder. The ultrasonic irradiation time in this case is only about 5-15 minutes. Whether or not the wet silica powder has dispersed to primary powder can be confirmed by measuring the particle size distribution. Specifically, the methyl ethyl ketone dispersed material of this wet silica powder is measured using a particle size distribution measuring device such as a Microtrac device. If a particle size distribution of the wet silica powder is present, it can be said that the wet silica powder has dispersed to primary powder.

[0045] Because wet silica powder is less prone to agglomeration, it can be provided as wet silica powder that is not dispersed in a liquid medium such as water or alcohol. Furthermore, because wet silica powder is less prone to agglomeration, it can be easily washed with water. The wet silica powder is treated in a surface treatment step (surface treatment step) in a liquid medium containing water, using a silane coupling agent and organosilazane. The silane coupling agent consists of three alkoxy groups and a phenyl group, vinyl group, epoxy group, methacrylate group, amino group, ureido group, mercapto group, isocyanate group, or acrylic group (i.e., the above X 1 ) has.

[0046] Surface treatment with a silane coupling agent replaces the hydroxyl groups present on the surface of the silica powder with functional groups derived from the silane coupling agent. The functional group derived from the silane coupling agent is given by formula (3); -OSiX 1 X 4 X 5It is represented by formula (3). The functional group represented by formula (3) is called the third functional group. X in the third functional group 1 X in the functional group represented by formula (1) is 1 It is the same as X 4 , X 5 These are each alkylocoxy groups. By surface treatment with organosilazane, the third functional group X 4 , X 5 -OSiY is derived from organosilazan. 1 Y 2 Y 3 The hydroxyl groups are replaced by the functional group represented by formula (2), the second functional group. If not all of the hydroxyl groups on the surface of the silica powder are replaced by the third functional group, the hydroxyl groups remaining on the surface of the silica powder are replaced by the second functional group. Therefore, the surface of the surface-treated wet silica powder contains the functional group represented by formula (1):-OSiX 1 X 2 X 3 The functional group represented by (i.e., the first functional group) and formula (2):-OSiY 1 Y 2 Y 3 The functional group represented by (i.e., the second functional group) is bonded to it. Since the molar ratio of the silane coupling agent to the organosilazane is silane coupling agent:organosilazane = 1:2 to 1:10, the ratio of the number of first functional groups to the second functional group in the resulting wet silica powder is theoretically 1:12 to 1:60.

[0047] In the surface treatment process, the silica powder may be surface-treated simultaneously with a silane coupling agent and an organosilazane. Alternatively, the silica powder may be surface-treated first with a silane coupling agent, and then with an organosilazane. Alternatively, the silica powder may be surface-treated first with an organosilazane, then with a silane coupling agent, and then again with an organosilazane. In any case, the amount of organosilazane should be adjusted so that not all hydroxyl groups on the surface of the silica powder are replaced by the second functional group. Note that all hydroxyl groups on the surface of the silica powder may be replaced by the third functional group, or only some may be replaced by the third functional group and the rest by the second functional group. X included in the third functional group 4 , X 5 It is preferable that all of these be substituted with a second functional group.

[0048] Furthermore, a portion of the organosilazane may be replaced with a second silane coupling agent. The second silane coupling agent may have three alkoxy groups and one alkyl group. In this case, the X contained in the third functional group 4 , X 5 However, it is substituted with a fourth functional group derived from the second silane coupling agent. The fourth functional group is given by formula (4); -OSiY 1 X 6 X 7 It is represented by Y. 1 Y in the second functional group 1 It is the same R as X 6 , X 7 These are either an alkoxy group or a hydroxyl group. The fourth functional group is X 6 , X 7 The X group is either substituted with a second functional group derived from organosilazane or with another fourth functional group. In this case, the amount of R present on the surface of the wet silica powder can be further increased. Note that when replacing part of the organosilazane with the second silane coupling agent, it is necessary to surface treat with the second silane coupling agent and then surface treat with the organosilazane again. The X group contained in the fourth functional group 6 , X7 This is because it will ultimately be replaced with a second functional group derived from organosilazane.

[0049] When a portion of the organosilazane is replaced with a second silane coupling agent, the X contained in the first functional group described above 4 , X 5 It is substituted with a second functional group derived from an organosilazane, or with a fourth functional group derived from a second silane coupling agent. 4 , X 5 If it is substituted with a fourth functional group, then the X contained in the fourth functional group 6 , X 7 X is either substituted with a second functional group or substituted with another fourth functional group. 6 , X 7 If it is substituted by another fourth functional group, then the X contained in the fourth functional group 6 , X 7 The first functional group is substituted with a second functional group. Therefore, the second silane coupling agent can replace up to 5 a / 3 mol of the amount (a) mol of organosilazane that would be used when surface treatment is performed with only the first coupling agent and organosilazane (when the organosilazane is not replaced with the second silane coupling agent). In this case, the amount of organosilazane required is 8 a / 3 mol.

[0050] The alkoxy groups of the silane coupling agent and the second silane coupling agent are not particularly limited, but those with a relatively small number of carbon atoms are preferred, preferably having 1 to 12 carbon atoms. Considering the hydrolysis properties of the alkoxy group, it is more preferable that the alkoxy group is one of a methoxy group, an ethoxy group, a propoxy group, or a butoxy group.

[0051] Examples of silane coupling agents include phenyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane.

[0052] Any organosilazane that can replace the hydroxyl groups and alkoxy groups derived from the silane coupling agent on the surface of the silica powder with the second functional group described above is acceptable, but it is preferable to use one with a small molecular weight. Specifically, examples include tetramethyldisilazane, hexamethyldisilazane, and pentamethyldisilazane.

[0053] Examples of second silane coupling agents include methyltrimethoxysilane, methyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, hexyltrimethoxysilane, and hexyltriethoxysilane.

[0054] Furthermore, during the surface treatment process, a polymerization inhibitor may be added to suppress the polymerization of the silane coupling agent and the second silane coupling agent. Common polymerization inhibitors such as 3,5-dibutyl-4-hydroxytoluene (BHT) and p-methoxyphenol (methoquinone) can be used.

[0055] The wet silica powder may include a solidification step after the surface treatment step. The solidification step involves precipitating the wet silica powder after surface treatment with a mineral acid, washing and drying the precipitate with water to obtain a solid wet silica powder. As mentioned above, general silica powder is very prone to aggregation, making it very difficult to redisperse silica powder once it has been solidified. However, wet silica powder is less prone to aggregation, so it is less likely to aggregate even after solidification, and even if it does aggregate, it is easy to redisperse. In the washing step, it is preferable to repeat the washing until the electrical conductivity of the water used to extract the wet silica powder (specifically, water in which the silica powder has been immersed at 121°C for 24 hours) is 50 μS / cm or less.

[0056] Examples of mineral acids used in the solidification process include hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid, with hydrochloric acid being particularly preferred. While the mineral acid may be used as is, it is preferable to use it as an aqueous solution. The concentration of mineral acid in the aqueous solution is preferably 0.1% by mass or higher, and more preferably 0.5% by mass or higher. The amount of the aqueous mineral solution can be approximately 6 to 12 times the mass of the wet silica powder to be washed.

[0057] Washing with a mineral acid solution can be performed multiple times. For washing with a mineral acid solution, it is preferable to immerse the wet silica powder in the mineral acid solution and then stir it. Furthermore, it can be left immersed for 1 to 24 hours, or even up to 72 hours. During this period, stirring can be continued or stopped. When washing in the mineral acid solution, the temperature can be heated above room temperature.

[0058] Afterward, the washed and suspended wet silica powder is filtered and then washed with water. It is desirable that the water used does not contain alkali metal ions (for example, less than 1 ppm by mass). Examples include deionized water, distilled water, or pure water. Washing with water can be done by dispersing and suspending the wet silica powder and then filtering, similar to washing with a mineral acid solution, or by continuously passing water through the filtered wet silica powder. The end of washing with water can be determined by the electrical conductivity of the extracted water as described above, or when the alkali metal concentration in the wastewater after washing the wet silica powder falls below 1 ppm, or when the alkali metal concentration in the extracted water falls below 5 ppm. Note that the water may be heated above room temperature during washing.

[0059] Wet silica powder can be dried by conventional methods, such as heating or leaving it under reduced pressure (vacuum).

[0060] (Coating of the base powder with a fluidizing agent) The method for attaching the fluidizing agent to the surface of the base powder is not particularly limited and can be done by simply mixing or by applying vibration after mixing.

[0061] (Example 1) A mixed powder was prepared by adding SUS316L with an average particle size of 10 μm as the base powder (main raw material powder) and 10 ppm of wet silica powder with a primary particle size of 10 nm and a surface modified with phenyl groups as a fluidizing agent. This mixed powder is the raw material powder described in the process explanation in Figures 2 and 3. The fluidity FF value of the obtained mixed powder was 7.4. The amount added is the weight percentage in the mixed powder. In this case, the content of wet silica powder in the mixed powder is 0.001% by weight.

[0062] The flow function (FF) value is an indicator of the flowability of a powder. A higher FF value indicates higher flowability. The flow function (FF) value is obtained by a shear test of the powder. In the shear test, a constant pressure is applied to the powder layer using a shear test cell, and the shear stress σ is measured when the powder layer is sheared under a normal stress τ. The flow function (FF) value is then calculated from the measured normal stress τ and shear stress σ. In this example, the flow function (FF) value was measured using a powder rheometer (FT4, manufactured by Freeman Technology). The flow function (FF) value is described, for example, in (J. Soc. Powder Technol., Japan, 54, 90-96 (2017)).

[0063] (Example 2) The mixed powder was prepared in the same manner as in Example 1, except that the amount of fluidizing agent added was changed to 50 ppm. The fluidity FF value of the powder was 7.0.

[0064] (Example 3) The mixed powder was prepared in the same manner as in Example 2, except that the surface treatment of the fluidizer was changed to a carbon film. The fluidity FF value of the powder was 7.0.

[0065] (Comparative Example 1) A mixed powder was prepared in the same manner as in Example 1, except that a fluidizing agent was not added. The fluidity FF value of the powder was 4.4.

[0066] (Comparative Example 2) A mixed powder was prepared in the same manner as in Example 1, except that the fluidizing agent was changed to dry silica with primary particles of 30 nm in size, whose surface is modified with hydrophilic groups. The fluidity FF value of the powder was 5.4.

[0067] (Comparative Example 3) A mixed powder was prepared in the same manner as in Example 1, except that the fluidizing agent was changed to dry silica with primary particles of 30 nm in size and modified with methyl groups on the surface. The fluidity FF value of the powder was 6.3.

[0068] (Comparative Example 4) The mixed powder was prepared in the same manner as in Example 1, except that the amount of fluidizing agent added was changed to 100 ppm. The fluidity FF value of the powder was 4.5.

[0069] (Comparative Example 5) A mixed powder was prepared in the same manner as in Example 2, except that the fluidizing agent was changed to wet silica with primary particles of 25 nm in size and modified with phenyl groups on the surface. The fluidity FF value of the powder was 5.0.

[0070] (Comparative Example 6) A mixed powder was prepared in the same manner as in Example 2, except that the fluidizing agent was changed to wet silica with primary particles of 50 nm in size and modified with phenyl groups on the surface. The fluidity FF value of the powder was 4.0.

[0071] (Evaluation and Analysis) Table 1 summarizes Examples 1-3 and Comparative Examples 1-6.

[0072] [Table 1]

[0073] The following can be considered from Table 1. First, the target liquidity FF value is set to 6.0 or higher, preferably 6.5 or higher, and more preferably 7.0 or higher.

[0074] First, the surface condition of the fluidizers in Examples 1-3 and Comparative Examples 3-6 is hydrophobic. From Examples 1-3 and Comparative Example 3, it can be seen that making the surface condition of the fluidizer hydrophobic can increase the fluidity of the mixed powder (raw material powder).

[0075] Table 1 shows that by setting the particle size of the fluidizer to approximately 0.1% of the particle size of the main raw material (base powder), and further setting the amount added to 10 ppm to 50 ppm, a fluidity FF value of 7.0 or higher can be achieved. The lower limit for the amount of fluidizer to be added is considered to be around 5 ppm. Even a small amount of fluidizer present on the surface of the main raw material will exhibit the effect of improving the flow properties, but below 5 ppm, the desired fluidity will not be improved.

[0076] A comparison of Example 2, Comparative Example 5, and Comparative Example 6 suggests that reducing the particle size of the fluidizer improves the fluidity FF value.

[0077] A comparison of Example 2, Comparative Example 5, and Comparative Example 6 shows that the fluidity improvement effect is significant when the particle size of the fluidizer is 0.1% of the particle size of the base powder, whereas when the particle size of the fluidizer is 0.25% of the particle size of the base powder (25 nm for 10 μm), the fluidity FF value is 5.0, indicating "no effect on fluidity improvement."

[0078] Looking at Example 2 and Comparative Example 5, it is estimated that the (particle size of the fluidizer / particle size of the base powder) (%) for which the fluidity FF value is 6.0 is between 0.1% and 0.25%. Therefore, assuming that there is a linear correlation between the ratio of the fluidizer particle size to the particle size of the base powder and the fluidity FF when this ratio is between 0.1% and 0.25%, the value of (particle size of the fluidizer / particle size of the base powder) for which the fluidity FF value is 6.0 was estimated by interpolation. According to the inventors' estimation, the value of (particle size of the fluidizer / particle size of the base powder) for which the fluidity FF value = 6 is approximately 0.18% (particle size is approximately 18 nm under the conditions in Table 1). Furthermore, under the above assumption, the value of (particle size of the fluidizer / particle size of the base powder) for which the fluidity FF value = 6.5 is approximately 0.14% (approximately 14 nm under the conditions in Table 1). Therefore, in order to achieve a fluidity FF value of 6.0 or higher, preferably 6.5 or higher, it is concluded that the particle size of the fluidizer relative to the particle size of the base powder should be 0.18% or less, preferably 0.14% or less.

[0079] The basis for obtaining the above results regarding particle size is explained below. First, consider a graph with the fluidity FF value on the horizontal axis (X axis) and the particle size ratio of the fluidizer to the base powder (%) on the vertical axis (Y axis). On this graph, plot points using the values ​​obtained from Example 2 and Comparative Example 5 as coordinates. Then, set a straight line passing through these plotted points (2 points). The equation of this straight line is Y = -(3 / 40)X + (5 / 8). Here, X is the fluidity FF value and Y is (particle size of the fluidizer / particle size of the base particles) (%). Substituting X = 6.0 into the above formula, we get Y = 0.175. Also, substituting X = 6.5 into the above formula, we get Y = 0.1375.

[0080] The minimum particle size of the fluidizing agent is approximately 5 nm. Below this value, it becomes difficult to obtain the powder with good controllability in terms of manufacturing and measurement technology.

[0081] Furthermore, as can be seen from the comparison between Example 2 and Comparative Example 4, when the amount of fluidizer added (silica added) increases from 50 ppm to 100 ppm, the fluidity FF value of the mixed powder (raw material powder) decreases significantly from 7.0 to 4.5. In the cases of Example 2 and Comparative Example 4, assuming that the relationship between the amount of fluidizer added (silica added) and the fluidity FF value of the mixed powder (raw material powder) is linear, the fluidity FF value of the mixed powder is 6.0 when the amount of fluidizer added is 70 ppm, and the fluidity FF value of the mixed powder is 6.5 when the amount of fluidizer added is 60 ppm. Therefore, in this case, the upper limit of the amount of fluidizer added to the mixed powder (raw material powder) is estimated to be around 70 ppm, preferably around 60 ppm.

[0082] The following explains the basis for obtaining the above results regarding the amount of fluidizer added. First, consider a graph with the fluidity FF value on the horizontal axis (X axis) and the amount of fluidizer added on the vertical axis (Y axis). On this graph, plot points using the values ​​obtained from Example 2 and Comparative Example 4 as coordinates. Then, set a straight line passing through these plotted points (2 points). The equation of this straight line is Y = -20X + 190. Here, X is the fluidity FF value and Y is the amount of fluidizer added (in ppm). Substituting X = 6.0 into the above formula gives Y = 70. Also, substituting X = 6.5 into the above formula gives Y = 60.

[0083] The lower limit for the amount of fluidizer added to a mixed powder is approximately 5 ppm. Below this value, the effect of improving fluidity decreases.

[0084] As mentioned above, more is not always better when it comes to adding fluidizing agents; there is an upper limit. Our findings on this point are explained below. Figure 4 is a photographic representation of an image obtained by scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX) of the mixed powder. Figure 4(A) is for Example 1, and Figure 4(B) is for Comparative Example 4. Both are focused on detecting silicon elements. The only difference between Figure 4(A) (Example 1) and Figure 4(B) (Comparative Example 4) is the amount of fluidizing agent added.

[0085] Figure 4 shows the distribution of the fluidizer (surface-treated silica powder) on the surface of the mixed powder. Comparing Figure 4(A) (Example 1) and Figure 4(B) (Comparative Example 4), it can be seen that the fluidizer is more uniformly distributed in Figure 4(A) (Example 1). The areas with high brightness in Figure 4(B) (Comparative Example 4) indicate the presence of a large amount of silica component (component of the fluidizer). In other words, Figure 4(B) shows that the fluidizer is partially solidified.

[0086] Comparative Example 3 is the case where dry silica is used. Considering the improvement in fluidity by reducing the particle size of the fluidizer and by reducing the amount of fluidizer added, it is suggested that even when using dry silica, the fluidity FF value may improve by reducing the particle size and the amount added. However, dry silica is generally called fumed silica and forms a strong secondary aggregate in its dry state. Therefore, the possibility of improving the fluidity FF value is lower than that of wet silica with a well-dispersible surface treatment. [Industrial applicability]

[0087] This invention can be used in 3D printing technology using the binder jet method. [Explanation of Symbols]

[0088] 100...3D printer, 10...stage, 11...printing stage, 12...hopper, 13...roller, 14...inkjet dispenser, 15...heater, 16...camera, 17...light-emitting unit, 20...control system, 21...control unit, 22...image analysis unit, PL...raw material powder layer, B...binder, PLa...part of the raw material powder layer PL where the binder is introduced (printing pattern of the binder).

Claims

1. A raw material powder for laminated structures used in the manufacture of laminated structures having a multilayer structure in which raw material powder layers are stacked in multiple layers, A base powder having an average particle size of 2 μm to 30 μm, Silica powder with an average particle size of 3 nm to 200 nm and Includes, The base powder is a metal powder and / or ceramic powder. The silica powder is a raw material powder for laminated structures, having been subjected to a hydrophobic treatment on its surface.

2. The raw material powder for a laminated structure according to claim 1, wherein the silica powder is a wet silica powder.

3. The raw material powder for laminated structures according to claim 1, wherein the content ratio of the silica powder is 5 ppm to 70 ppm.

4. The raw material powder for a laminated structure according to claim 1, wherein the particle size of the silica powder relative to the particle size of the base material powder is 0.18% or less.

5. The particle size of the silica powder relative to the particle size of the base powder is 0.18% or less. The raw material powder for laminated structures according to claim 1, wherein the content ratio of the silica powder is 70 ppm or less.

6. The silica powder is a wet silica powder modified with a functional group represented by the formula (1): -OSiX ５ X ２ X ３ and a functional group represented by the formula (2): -OSiY １ Y ２ Y ３ The raw material powder for the laminated structure according to claim 1, which is a wet silica powder modified with a functional group represented by the formula (1) and (2) above. (In the above formulas (1) and (2); X １ is a phenyl group, vinyl group, epoxy group, methacryl group, amino group, ureido group, mercapto group, isocyanate group, or acrylic group; X ２ and X ３ are each independently selected from -OSiR ３ and -OSiY ４ Y ５ Y ６ respectively; Y １ is R; Y ２ and Y ３ are each independently selected from R and -OSiY ４ Y ５ Y ６ respectively. Y ４ is R; Y ５ and Y ６ are each independently selected from R and -OSiR ３ respectively; R is independently selected from alkyl groups having 1 to 3 carbon atoms. Incidentally, any of X ２ , X ３ , Y ２ , Y ３ , Y ５ , and Y ６ may be bonded to -O- with any of the adjacent functional groups X ２ , X ３ , Y ２ , Y ３ , Y ５ , and Y ６ .)

7. A raw material powder for a laminated structure according to any one of claims 1 to 6, wherein the fluidity FF value is 6.0 or higher.

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