Injection molding powder, method for manufacturing injection molding powder, and method for manufacturing metal sintered body

Abstract

To provide: an injection molding powder capable of reducing the used amount of a binder to be added to a compound while securing fluidity of the compound; an injection molding powder production method; and a metal sintered compact production method capable of producing a metal sintered compact having high dimensional accuracy.SOLUTION: An injection molding powder includes a metal powder, and a film with which a particle surface of the metal powder is coated and which contains a fluorine compound, wherein a contact angle of hexadecane measured at 25°C by a θ / 2 method is 60° or more and 110° or less in a state in which the injection molding powder is laid in layers.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to injection molding powder, a method for producing injection molding powder, and a method for producing a metal sintered body. [Background technology]

[0002] In recent years, additive manufacturing using metal powder has become increasingly popular as a technique for creating three-dimensional objects. This technique involves a process of calculating the cross-sectional shape when the object is thinly sliced ​​from a plane perpendicular to the layering direction, a process of forming a powder layer by leveling the metal powder, and a process of solidifying a portion of the powder layer based on the calculated shape. By repeating the process of forming a powder layer and solidifying a portion of it, the three-dimensional object is created.

[0003] Methods for creating three-dimensional objects include Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS), and Binder Jet, depending on the principle of solidification.

[0004] Patent Document 1 discloses a method for manufacturing EB-sintered 3D printer-formed products, which uses an electron beam (EB) instead of a laser as a modification of powder bed sintering additive manufacturing. This method involves layering surface-treated metal powder for EB-sintered 3D printers, optionally performing preheating, and then sintering by EB irradiation to produce a metal molded product. Surface-treated metal powder for EB-sintered 3D printers is a powder in which the surface of a metal powder manufactured by a known method is surface-treated with a coupling agent. By using such surface-treated metal powder, conductivity during layering is improved. Therefore, it can be suitably sintered by EB. In addition, partial sintering can be suppressed by preheating.

[0005] However, the surface-treated metal powder described in Patent Document 1 has the problem that its fluidity tends to decrease at high temperatures and when it absorbs moisture.

[0006] On the other hand, in fused deposition modeling (FDM), a three-dimensional object is obtained by mixing metal powder and a binder and injecting this mixture. This method has the advantage that the fluidity of the mixture is easily ensured by the binder. Furthermore, a sintered metal body can be obtained by degreasing and sintering the manufactured three-dimensional object. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2017-25392 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, depending on the shape and molding conditions of the three-dimensional object being manufactured, it may be necessary to sufficiently increase the fluidity of the compound. For this reason, a large amount of binder must be mixed into the compound. This binder is removed after the three-dimensional object is manufactured through a degreasing or sintering process, but this process causes shrinkage of the object. Such shrinkage can lead to a decrease in the dimensional accuracy of the sintered body when the three-dimensional object is sintered.

[0009] Since the amount of binder used increases with the amount of shrinkage, the challenge is to reduce the amount of binder used while maintaining the fluidity of the compound. [Means for solving the problem]

[0010] The injection molding powder according to the application example of the present invention is Metal powder and The particle surface of the aforementioned metal powder is coated with a film containing a fluorine compound, Equipped with, In the injection molding powder, the coating is formed on the outermost surface. The hexadecane, when laid in layers, is characterized by having a contact angle of 60° to 110° measured at 25°C using the θ / 2 method.

[0011] The method for producing injection molding powder according to an application example of the present invention is: A process for producing injection molding powder, comprising mixing the metal powder and a fluorine compound powder composed of a fluorine compound, and mechanically adhering the fluorine compound powder to the particle surface of the metal powder to form the coating, It is characterized by having the following features.

[0012] The method for producing injection molding powder according to an application example of the present invention is: A process to produce the injection molding powder by mixing the metal powder and monomer gas, causing a polymerization reaction to occur in the monomer gas on the particle surface of the metal powder to generate the fluorine compound, thereby forming the coating, It is characterized by having the following features.

[0013] The method for producing injection molding powder according to an application example of the present invention is: A process to produce the injection molding powder by mixing the metal powder and a fluorine compound precursor, polymerizing the fluorine compound precursor on the particle surface of the metal powder to produce the fluorine compound, thereby forming the coating, It is characterized by having the following features.

[0014] The method for manufacturing a metal sintered body according to an application example of the present invention is as follows: The process involves mixing an injection molding powder and an organic binder according to an application example of the present invention to prepare an injection molding composition, The process involves injection molding the aforementioned injection molding composition to obtain an injection-molded body, The process of subjecting the injection-molded body to a sintering treatment, It is characterized by having the following features. [Brief explanation of the drawing]

[0015] [Figure 1]It is a cross-sectional view schematically showing one particle of the powder for injection molding according to the embodiment. [Figure 2] It is a process diagram for explaining a method for manufacturing the powder for injection molding according to the embodiment. [Figure 3] It is a process diagram for explaining a method for manufacturing a metal sintered body according to the embodiment. [Figure 4] It is a flow curve showing the change in viscosity with respect to the change in shear rate when a shear rate is applied to a mixture of the powder for injection molding of Example 1 and the powder for injection molding of Comparative Example 1 and polystyrene.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, the powder for injection molding of the present invention, the method for manufacturing the powder for injection molding, and the method for manufacturing a metal sintered body will be described in detail based on the accompanying drawings.

[0017] 1. Powder for Injection Molding First, the powder for injection molding according to the embodiment will be described. The powder for injection molding refers to, for example, metal powder used in the metal powder injection molding method (MIM method), the thermal melting lamination method using metal powder (metal FDM method), and the like. Note that since both the MIM method and the metal FDM method are common in that a compound containing a metal powder and an organic binder is injected to obtain a molded body, in this specification, these methods are also collectively referred to as the "injection molding method".

[0018] FIG. 1 is a cross-sectional view schematically showing one particle of the powder for injection molding 1 according to the embodiment. In the following description, one particle of the powder for injection molding 1 is also referred to as an "injection molding particle 4".

[0019] The injection molding particle 4 shown in FIG. 1 has metal particles 2 and a coating 3 provided on the surface of the metal particles 2. The coating 3 is provided so as to cover the surface of the metal particles 2 and contains a fluorine compound. Note that the coating in this specification is a concept that includes not only the state of covering the entire surface of the metal particles 2 but also the state of covering a part of the surface. Also, in the following description, an aggregate of metal particles 2 is also referred to as a "metal powder".

[0020] In this type of injection molding powder 1, it is possible to suppress excessive affinity for organic binders, thereby ensuring the fluidity of the compound even when the amount of organic binder used is reduced. As a result, when the compound is molded by injection molding, the density of the injection molding powder 1 in the molded body can be increased. Consequently, a molded body with less shrinkage due to degreasing can be obtained, and the decrease in dimensional accuracy of the final metal sintered body can be suppressed.

[0021] 1.1. Metal particles The constituent material of the metal particles 2 is not particularly limited and may be any metallic material that is sinterable. Examples include elemental materials such as Fe, Ni, Co, and Ti, or alloys and intermetallic compounds mainly composed of these elements.

[0022] Examples of Fe-based alloys include stainless steels such as austenitic stainless steel, martensitic stainless steel, and precipitation-hardening stainless steel, as well as low-carbon steel, carbon steel, heat-resistant steel, die steel, high-speed tool steel, Fe-Ni alloy, and Fe-Ni-Co alloy.

[0023] Examples of Ni-based alloys include Ni-Cr-Fe alloys, Ni-Cr-Mo alloys, and Ni-Fe alloys.

[0024] Examples of Co-based alloys include Co-Cr alloys, Co-Cr-Mo alloys, and Co-Al-W alloys.

[0025] Examples of Ti-based alloys include alloys of Ti with metallic elements such as Al, V, Nb, Zr, Ta, and Mo, specifically Ti-6Al-4V and Ti-6Al-7Nb.

[0026] The average particle size of the metal powder is preferably 3.0 μm to 30.0 μm, and more preferably 5.0 μm to 15.0 μm. This allows for particularly high filling of the metal powder during injection molding, resulting in a molded body with minimal shrinkage. As a result, a metal sintered body with high dimensional accuracy can be obtained.

[0027] The average particle size of the metal powder is defined as the particle size at which the cumulative frequency from the smallest diameter side accounts for 50% of the cumulative particle size distribution on a volume basis obtained by laser diffraction.

[0028] 1.2.Coating The coating 3 covers the surface of the metal particles 2. The coating 3 contains a fluorine compound. Because the fluorine compound has a low surface free energy, it exhibits not only water repellency but also oil repellency. For this reason, the coating 3 containing the fluorine compound has low affinity for organic binders. As a result, when the injection molding particles 4 are kneaded with an organic binder, the viscosity does not increase easily. Therefore, the injection molding particles 4 exhibit good fluidity even when kneaded with a small amount of organic binder.

[0029] Furthermore, because fluorine compounds are highly water-repellent, the injection molding powder 1 has excellent moisture resistance. This suppresses rusting of metal particles 2 due to moisture absorption. As a result, it is possible to suppress the deterioration of the properties of the metal sintered body caused by rusting.

[0030] Fluorine compounds are not particularly limited as long as they are compounds containing fluorine atoms. Examples of fluorine compounds include fully fluorinated resins such as PTFE (polytetrafluoroethylene resin), partially fluorinated resins such as PVF (polyvinylidene fluoride) and PCTFE (polychlorotrifluoroethylene), and various fluororesins such as PFA (tetrafluoroethylene perfluoroalkyl vinyl ether resin), FEP (fluorinated ethylene propylene resin), PFEP (hexafluoroethylene propylene resin), and E / TFE (ethylene / tetrafluoroethylene copolymer). One or more of these can be used.

[0031] Furthermore, the fluorine compound may be a coupling agent containing a fluorine atom or a compound derived from a metal alkoxide containing a fluorine atom. Examples of coupling agents containing a fluorine atom include fluoroalkylsilanes and fluoroarylsilanes.

[0032] Furthermore, fluorine compounds have the advantage of easily increasing the coverage rate on the surface of metal particles 2 due to their low Young's modulus. Therefore, a coating 3 containing a fluorine compound makes it possible to achieve both a thinner film thickness and a higher coverage rate. This also makes it possible to create a compound with a reduced ratio of not only organic binder but also coating 3.

[0033] The Young's modulus of the fluorine compound is preferably 3.0 GPa or less, more preferably 0.05 GPa to 2.0 GPa, and even more preferably 0.1 GPa to 1.0 GPa. By using a fluorine compound with such a Young's modulus, the coverage rate of the coating 3 on the surface of the metal particles 2 can be particularly increased, and the film thickness of the coating 3 can be made thinner and more uniform. This makes it possible to increase the occupancy rate of metal powder in the compound without impairing the fluidity of the compound. However, if the Young's modulus exceeds the upper limit, the rigidity of the coating 3 will increase, which may cause the coating 3 to peel off easily. On the other hand, the Young's modulus may fall below the lower limit, but the rigidity of the coating 3 will become too low, which may also cause the coating 3 to peel off easily.

[0034] The coating 3 may also contain components other than fluorine compounds. Examples of components other than fluorine compounds include organic materials other than fluorine compounds, glass materials, ceramic materials and other inorganic materials. The content of components other than fluorine compounds in the coating 3 is preferably 30% by mass or less, and more preferably 10% by mass or less.

[0035] Furthermore, the coating 3 may be composed of multiple layers, provided that each layer contains a fluorine compound. However, from the viewpoint of preventing delamination between layers and making it difficult to reduce the film thickness, it is preferable to make the coating 3 a single layer.

[0036] The average thickness of the coating 3 is preferably 3 nm to 100 nm, more preferably 5 nm to 30 nm, and even more preferably 5 nm to 10 nm. This ensures sufficient coverage of the coating 3 while suppressing the drawbacks of the coating 3 being too thick. If the average thickness of the coating 3 falls below the lower limit, the coverage of the coating 3 may be insufficient depending on the constituent materials of the coating 3. On the other hand, if the average thickness of the coating 3 exceeds the upper limit, the coating 3 may become more prone to peeling, or the occupancy rate of metal particles 2 in the compound may decrease, depending on the constituent materials of the coating 3.

[0037] The average thickness of the coating 3 is measured, for example, by magnifying and observing the cross-section of the injection-molded particle 4. Specifically, the injection-molded particle 4 is cut with a focused ion beam to prepare a cross-sectional thin section sample. Next, the obtained cross-sectional thin section sample is observed with a scanning transmission electron microscope, and the thickness of the coating 3 is measured at five or more locations for each particle. The measured values ​​are then averaged, and the calculated result is taken as the average thickness of the coating 3. The extent of the coating 3 can be confirmed, for example, by EDX analysis (energy-dispersive X-ray analysis), Auger electron spectroscopy, etc.

[0038] Furthermore, the oil-repellent properties of the coating 3 may be adjusted by applying a hydrophilic treatment to its surface. It is thought that hydroxyl groups are introduced on the surface of the coating 3 after the hydrophilic treatment has been applied, replacing the fluorine atoms contained in the fluorine compound. These hydroxyl groups are then thought to produce hydrophilicity. Therefore, if the fluidity of the compound becomes too high, the fluidity can be adjusted by applying a hydrophilic treatment to the surface of the coating 3.

[0039] Examples of hydrophilization treatments include plasma treatment, ozone treatment, corona treatment, and ultraviolet irradiation treatment. Plasma treatment or ozone treatment is particularly preferred. This allows for efficient and high-density hydrophilization. Examples of treatment gases for plasma treatment include water vapor, oxygen, argon, and nitrogen.

[0040] The coating 3 preferably has a coverage rate of 40% or more on the surface of the metal particles 2, and more preferably 60% to 95%. This reduces the area in direct contact between the metal particles 2 and the organic binder when the injection molding powder 1 is kneaded with the organic binder. As a result, the viscosity generated between the metal particles 2 and the organic binder is suppressed, and the fluidity of the compound can be further improved. The coverage rate may exceed the upper limit, but it is preferable that it be below the upper limit from the viewpoint of easily producing injection molding powder 1 with a stable coverage rate.

[0041] The coverage of coating 3 can be determined by surface-sensitive elemental analysis techniques, such as elemental analysis by X-ray photoelectron spectroscopy (XPS). Specifically, the ratio of elements unique to metal particles 2 is measured by elemental analysis of the surface of injection-molded particles 4 using XPS. Next, coating 3 is removed by a removal process. Examples of this process include liquid-phase treatment using a liquid that dissolves coating 3, and gas-phase treatment that decomposes and removes coating 3. Removal of coating 3 exposes the surface of metal particles 2. Next, elemental analysis is performed again on the surface using XPS to calculate the ratio of elements unique to metal particles 2. Here, as an example, the ratio of Si is measured from the peak area ratio of the Si2p peak obtained by elemental analysis using XPS. Then, when the ratio of Si after treatment is set to 100, the relative value X of the ratio of Si before treatment is calculated. The value of 100-X corresponds to the amount of Si in metal particles 2 that is covered by coating 3. Therefore, 100-X can be taken as the coverage of coating 3.

[0042] The oil-repellent properties of coating 3 are primarily determined by the concentration of fluorine atoms in the fluorine compound. The concentration of fluorine atoms is calculated by performing elemental analysis of coating 3 using XPS and basing it on the area ratio of the F1s peak to other peaks. The area ratio of the F1s peak calculated by this method is preferably between 10% and 75% of the total peak area, more preferably between 30% and 60%, and even more preferably between 35% and 55%. This ensures that coating 3 contains fluorine atoms at a sufficient concentration. As a result, the amount of organic binder required to ensure the fluidity of the compound can be further reduced.

[0043] The injection molding powder 1 with the coating 3 is kneaded together with an organic binder to form a compound. The resulting compound is injection molded, and the resulting molded body is degreased and sintered to obtain a sintered metal body. At this time, the fluorine compound contained in the coating 3 diffuses into the deeper parts of the metal particles 2 due to heating during injection molding and degreasing, thereby increasing the adhesion between the metal particles 2 and the coating 3. In addition, the presence of the coating 3 between adjacent metal particles 2 increases the bonding strength between the metal particles 2. As a result, the shape retention of the molded body and the degreased body can be further improved.

[0044] 1.3.Contact angle The oil repellency of injection molding powder 1 can be evaluated based on the contact angle of a liquid measured while the powder is laid in layers. The contact angle can be measured using the following procedure.

[0045] First, double-sided tape is attached to a flat surface. Next, injection molding powder 1 is spread over the double-sided tape. Then, the spread injection molding powder 1 is lightly pressed down with a plate-shaped member. Next, any excess injection molding powder 1 is blown away with an air blower. This yields a test specimen for contact angle measurement.

[0046] Next, the contact angle of hexadecane on the test specimen is measured using the θ / 2 method with a DropMaster 500 contact angle measuring device manufactured by Kyowa Interface Science Co., Ltd. The measurement conditions are a temperature of 25°C and a relative humidity of 50% ± 5%. A metal powder with an average particle size of 7 μm is used, and 3 μL of hexadecane is dropped onto the sample. The measurement is taken 5 seconds after the drop is applied.

[0047] The contact angle of hexadecane measured for injection molding powder 1, which is laid out in layers, is said to be between 60° and 110°. By exhibiting such a contact angle with hexadecane, injection molding powder 1 can suppress an increase in viscosity even when mixed with an organic binder. In other words, injection molding powder 1 exhibits appropriate viscosity even when mixed with an organic binder, achieving both the shape retention required for the molded article and the fluidity required for the compound.

[0048] Furthermore, if the contact angle of hexadecane falls below the lower limit, the oil repellency decreases, increasing the viscosity of the injection molding powder 1 with respect to the organic binder and reducing the fluidity of the compound. On the other hand, if the contact angle of hexadecane exceeds the upper limit, the oil repellency becomes too high, making it difficult for the injection molding powder 1 to disperse in the organic binder. This reduces the homogeneity of the compound.

[0049] The contact angle is preferably 70° to 105°, more preferably 80° to 100°, and even more preferably 85° to 100°.

[0050] 1.4. Viscosity of the mixture of injection molding powder and organic binder When injection molding powder 1 is kneaded with an organic binder to prepare a compound, the fluidity of the compound can be increased. This fluidity can be evaluated, for example, based on the viscosity of the mixture of injection molding powder 1 and polystyrene. The viscosity of the mixture can be measured by the following procedure.

[0051] First, a mixture is prepared by adding polystyrene equivalent to 7 volume percent of injection molding powder. Next, the mixture is stirred until homogeneous. Then, the viscosity of the stirred mixture is measured using a rheometer while varying the shear rate applied to the mixture. For example, a dynamic viscoelasticity measuring instrument such as the ARES-G2 manufactured by T.A. Instrument Japan is used as the rheometer. The sample temperature during measurement is 20°C, the measurement mode is rotation mode, and a parallel plate geometry is used. Next, a curve (flow curve) showing the change in viscosity with respect to the change in shear rate is obtained.

[0052] When the viscosity at a shear rate of 0.5 [1 / s] is defined as the "viscosity at low shear rates," the viscosity of the mixture containing injection molding powder 1 at low shear rates is preferably 20 [Pa·s] or higher, more preferably 50 [Pa·s] or higher and 2000 [Pa·s] or lower, and even more preferably 100 [Pa·s] or higher and 1000 [Pa·s] or lower. As a result, the compound containing injection molding powder 1 becomes less fluid during storage and after molding, when little shear rate is applied. Consequently, leakage and sagging during storage are suppressed, and the shape retention of the injection molded article can be improved.

[0053] When the viscosity at a shear rate of 500 [1 / s] is defined as the viscosity at high shear rates, the viscosity of the mixture containing injection molding powder 1 at high shear rates is preferably 0.5 [Pa·s] or less, more preferably 0.001 [Pa·s] or more and 0.3 [Pa·s] or less, and even more preferably 0.01 [Pa·s] or more and 0.1 [Pa·s] or less. As a result, the compound containing injection molding powder 1 exhibits high fluidity during injection molding when a shear rate is applied.

[0054] Furthermore, the rate of change in viscosity [Pa·s] (the ratio of the change in viscosity to the change in shear rate) is calculated when the shear rate is increased from 0.5 [1 / s] to 500 [1 / s]. The mixture containing injection molding powder 1 preferably has a rate of change in viscosity with respect to the change in shear rate of 0.05 to 10.0, more preferably 0.3 to 5.0, and even more preferably 0.5 to 2.0. If the rate of change in viscosity with respect to the change in shear rate is within the above range, the slope of the flow curve becomes sufficiently large, so that the viscosity of the mixture can satisfy the above range at both low and high shear rates. In other words, the compound containing injection molding powder 1 has high viscosity at low shear rates, such as during storage or after molding, which helps to suppress leakage, sagging, and deformation of the injection molded product during storage. It also exhibits high fluidity at high shear rates, such as during injection molding. Therefore, by using injection molding powder 1, it is possible to improve the handling properties of the compound, enhance its moldability, and improve the shape retention of the injection-molded body. As a result, it ultimately contributes to the production of metal sintered bodies with high dimensional accuracy.

[0055] 1.5. Effects of this embodiment As described above, the injection molding powder 1 according to this embodiment comprises a metal powder and a coating 3 containing a fluorine compound that covers the surface of the metal powder particles (the surface of the metal particles 2). Furthermore, when this injection molding powder 1 is laid out in layers, the contact angle of hexadecane measured at 25°C by the θ / 2 method is 60° to 110°.

[0056] With this configuration, even when the injection molding powder 1 is kneaded with the organic binder, the increase in viscosity is suppressed. As a result, when preparing a compound by kneading the injection molding powder 1 and the organic binder, the fluidity of the compound can be ensured even if the amount of organic binder used is reduced. Consequently, when the compound is molded by injection molding, the density of the injection molding powder 1 in the molded body can be increased, and a molded body with less shrinkage due to degreasing can be obtained. Ultimately, this makes it possible to manufacture a metal sintered body with high dimensional accuracy.

[0057] Furthermore, in the injection molding powder 1 according to this embodiment, it is preferable that the average particle size of the metal powder is 3.0 μm or more and 30.0 μm or less.

[0058] This allows for particularly high filling of metal powder during compound injection molding, resulting in a molded body with minimal shrinkage. Consequently, a metal sintered body with high dimensional accuracy can be obtained.

[0059] Furthermore, in the injection molding powder 1 according to this embodiment, it is preferable that the area ratio of the F1s peak detected by X-ray photoelectron spectroscopy (XPS) is 10% or more and 75% or less of the total peak area.

[0060] As a result, coating 3 contains fluorine atoms at a sufficient concentration. Consequently, the amount of organic binder required to ensure the fluidity of the compound can be further reduced.

[0061] Furthermore, in the injection molding powder 1 according to this embodiment, when the mixture is mixed with polystyrene and the viscosity of the resulting mixture is measured using a rheometer while changing the shear rate, it is preferable that the rate of change of viscosity with respect to the change in shear rate is 0.05 or more and 10.0 or less.

[0062] This increases the slope of the flow curve, which shows the change in viscosity with respect to changes in shear rate. As a result, leakage and sagging of the compound during storage are suppressed, and the shape retention of the molded product is improved, while also increasing the fluidity of the compound during injection molding. Consequently, a metal sintered body with high dimensional accuracy can be obtained.

[0063] 2. Method for producing powder for injection molding Next, a method for producing injection molding powder according to an embodiment will be described.

[0064] Figure 2 is a process diagram illustrating a method for manufacturing injection molding powder according to an embodiment. The method for producing injection molding powder shown in Figure 2 comprises a preparation step S102 and a coating formation step S104.

[0065] 2.1. Preparation process In preparation step S102, metal powder is prepared. The metal powder may be produced by any method. Examples of production methods include various atomization methods such as water atomization, gas atomization, and rotary water flow atomization, as well as reduction, carbonylation, and pulverization methods. Of these, atomization is preferred. In other words, the metal powder is preferably atomized powder. Atomized powder is fine, highly spherical, and has high production efficiency. In particular, water atomized powder or rotary water flow atomized powder has a thin oxide film on its surface because it is produced by contact between molten metal and water. This oxide film can serve as a base for the coating 3. Therefore, the adhesion between the metal particles 2 and the coating 3 can be improved.

[0066] If commercially available metal powders are procured, this step can be omitted.

[0067] 2.2. Film formation process In the coating formation step S104, a coating 3 is formed that covers the surface of the metal particles 2. This yields the injection molding powder 1.

[0068] The method for forming the coating 3 is not particularly limited, but examples include dry formation methods such as mechanochemical methods, plasma polymerization, ALD (Atomic Layer Deposition), CVD (Chemical Vapor Deposition), and ion plating, and wet formation methods such as sol-gel methods and electrolytic reduction methods.

[0069] The following will explain, in order, the mechanochemical method, the plasma polymerization method, and the sol-gel method as representative examples.

[0070] 2.2.1. Mechanochemical Method The mechanochemical method is a method of changing the physicochemical properties of particles by applying mechanical stress to them. For example, by using a mechanochemical reactor having a cylindrical chamber equipped with a compression tool and blades and rotating at high speed, a mechanical interaction (mechanochemical reaction) can be generated between metal particles 2 and the raw materials for the coating 3, thereby forming a coating 3 on the surface of the metal particles 2. Therefore, the mechanochemical method is used as a coating formation method. Specifically, first, metal particles 2 and the raw materials for the coating 3 are placed in the chamber. Examples of raw materials for the coating 3 include fluorine compound powder and other additives. When the chamber is rotated, these inputs collide with each other and are pressed against the inner wall of the chamber. As a result, the raw materials for the coating 3 are pressed against the surface of the metal particles 2 and form a coating. In this way, injection molding particles 4 are obtained. Furthermore, by using this mechanical coating method, the coating 3 can be properly adhered even when contaminants are attached to the surface of the metal particles 2, when the adhesion strength is low, or when the surface roughness is small. In addition, since the coating 3 is not formed in a high-temperature state, thermal deformation of the metal particles 2, such as unintended crystal coarsening, can be suppressed. This prevents a decrease in the mechanical properties of the metal particles 2.

[0071] Furthermore, as mentioned above, fluorine compounds have a lower Young's modulus compared to other resin materials and inorganic materials. Therefore, by using a mechanochemical method, a thin coating 3 with high coverage can be efficiently formed.

[0072] Examples of mechanochemical reactors include the "Nobilta" (registered trademark) pulverizer and the "Mechanofusion" (registered trademark) pulverizer manufactured by Hosokawa Micron Corporation, and the "Hybridicer" (registered trademark) pulverizer manufactured by Nara Machinery Works Co., Ltd.

[0073] Examples of fluorine compound powders include the various fluororesin powders mentioned above, and one or more of these powders or mixtures thereof are used. The fluororesin constituting the fluorine compound powder is preferably PTFE or PFA. These fluororesins exhibit high oil repellency, particularly due to their low surface free energy. Therefore, using these fluororesin powders as the fluorine compound powder further reduces the amount of organic binder used when preparing the compound.

[0074] The average particle size of the fluorine compound powder is not particularly limited, but is preferably 0.2 to 5.0 times the average particle size of the metal powder, more preferably 0.5 to 2.0 times, and even more preferably 0.7 to 1.5 times. This allows the metal powder and the fluorine compound powder to be mixed more uniformly, and the thickness of the coating 3 can be made more uniform.

[0075] Furthermore, the average particle size of the fluorine compound powder is preferably 0.1 μm or more and 100 μm or less, more preferably 3 μm or more and 50 μm or less, and even more preferably 5 μm or more and 10 μm or less.

[0076] The average particle size of the fluorine compound powder is defined as the particle size at which the cumulative frequency of particles originating from the smaller diameter side accounts for 50% of the volume-based particle size distribution obtained by laser diffraction.

[0077] The amount of raw materials for the coating 3 added is adjusted as appropriate according to the desired thickness of the coating 3 to be formed. For example, the amount of raw materials for the coating 3 added is preferably 0.1% by mass or more of the metal powder, and more preferably 0.4% by mass or more. However, even if there is a large amount of raw materials for the coating 3, only a limited amount of the raw materials will adhere to the surface of the metal particles 2, so there is no particular upper limit that needs to be set. However, considering that the mixing energy is reliably transferred to the surface of the metal particles 2, the amount of raw materials for the coating 3 added is preferably 3.0% by mass or less of the metal powder, and more preferably 1.0% by mass or less.

[0078] As described above, the method for producing injection molding powder according to this embodiment includes a coating formation step S104 utilizing a mechanochemical reaction. In the coating formation step S104 of this embodiment, metal powder and fluorine compound powder composed of a fluorine compound are mixed, and the fluorine compound powder is mechanically attached to the particle surface of the metal powder (the surface of the metal particle 2). This forms a coating 3 that covers the surface of the metal particle 2, thereby producing injection molding powder 1.

[0079] This manufacturing method utilizes a mechanochemical reaction, allowing the coating 3 to adhere well even when contaminants are present on the surface of the metal particles 2, when adhesion is low, or when the surface roughness is small. Therefore, this manufacturing method allows for the efficient production of injection molding powder 1.

[0080] Furthermore, in the method for producing injection molding powder according to this embodiment, the fluorine compound powder is PTFE powder or PFA powder. The fluororesins that make up these fluororesin powders have particularly low surface free energy and therefore exhibit high oil repellency. For this reason, by using these fluororesin powders as the fluorine compound powder, the amount of organic binder used when preparing the compound can be further reduced.

[0081] 2.2.2. Plasma polymerization method Plasma polymerization is a method of forming a coating by generating a plasma discharge while introducing a monomer gas, thereby depositing polymers onto the surface of the object to be treated.

[0082] A fluorine-containing gas is used as the monomer gas. Examples of fluorine-containing gases include CHF3 gas, C4F8 gas, and C4F 10 Examples include gas, Fluorinert (registered trademark), etc. For example, C5F Fluorinert is an example. 12 , C6F 14 , C7F 16 These are some examples. Note that if Fluorinert is in liquid form, it should be used in gaseous form.

[0083] Furthermore, an additive gas (crosslinking gas) that acts as a crosslinking agent may be used. The crosslinking gas crosslinks monomers during the plasma polymerization process. Therefore, the crosslinking gas is preferably added when the molecular weight of the monomer gas is high. By adding the crosslinking gas, even when the movement of the monomer gas is slow and the probability of reaction occurring at the active site is low, this can be compensated for, and plasma polymerization can be promoted. Examples of crosslinking gases include fluoroalkane gases with three or fewer carbon atoms. Specifically, examples include CF4 gas, C2F5 gas, C3F8 gas, etc.

[0084] Furthermore, if a monomer gas containing a double bond in its molecule, such as C4F8 gas, is used, or if the monomer gas has high reactivity, the addition of the bridging gas may be omitted. Furthermore, examples of discharge gases include noble gases such as He and Ar, and nitrogen gas.

[0085] In addition, examples of additive gases used in polymerization reactions include hydrocarbon gases such as methane, ethane, propane, and butane, as well as halogens, oxygen, hydrogen, NF3, SF6, and CF4.

[0086] Other components besides the monomer gas may be added as needed, or they may be omitted.

[0087] When these gases are introduced into the chamber of the plasma polymerization apparatus and a plasma discharge is generated, the monomer gas reaches the surface of the metal particles 2, which are the material to be treated. Then, due to the active species contained in the plasma, a polymerization reaction occurs in the monomer gas, and a coating 3 is formed.

[0088] The driving force for inducing the polymerization reaction in the monomer gas is not limited to plasma discharge; for example, ultraviolet irradiation may also be used. However, plasma discharge is preferred from the viewpoint of being able to form a dense coating 3. Because the dense coating 3 is hard, it is less likely to break even when thin. Therefore, the proportion of metal powder in the compound can be increased.

[0089] As described above, the method for producing injection molding powder according to this embodiment includes a coating formation step S104 by polymerizing a monomer gas. In the coating formation step S104 of this embodiment, metal powder and monomer gas are mixed, and a polymerization reaction occurs in the monomer gas on the particle surface of the metal powder (the surface of the metal particle 2) to produce a fluorine compound. This forms a coating 3 that covers the surface of the metal particle 2, and the injection molding powder 1 is produced.

[0090] According to this manufacturing method, a film 3 with a uniform thickness and high coverage can be formed by the circulation of monomer gas. Therefore, according to this manufacturing method, injection molding powder 1 that can increase the metal powder occupancy rate in the compound can be efficiently produced.

[0091] Furthermore, in the method for producing injection molding powder according to this embodiment, the monomer gas is a reactive gas containing fluorine-containing groups, and a fluorine compound is produced by plasma polymerization. Plasma polymerization allows for the direct formation of a dense coating 3 on the surface of the metal particles 2 from the monomer gas. This results in a thin coating 3 that is difficult to break. Plasma polymerization is also useful because of its high efficiency in forming the coating 3.

[0092] 2.2.3. Sol-gel method The sol-gel method is a method for forming a coating by polymerization of a fluorine compound precursor.

[0093] Examples of fluorine compound precursors include coupling agents containing fluorine atoms and metal alkoxides containing fluorine atoms. Note that metal alkoxides include silicon alkoxides. Of these, coupling agents containing fluorine atoms are preferred because they enable stable reactions.

[0094] A coupling agent containing a fluorine atom is a compound having a fluorine-containing group and 1 to 3 hydrolyzable groups.

[0095] Examples of the fluorine-containing group include a fluoroalkyl group, a perfluoroalkyl group, a fluoroaryl group, a perfluoroaryl group, etc. Specific examples include the organic groups listed below.

[0096] F(CF2) u - (CF3)2CF(CF2) v - CF3(CF2)2O(CF(CF3)CF2O)​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Examples of metal alkoxides containing a fluorine atom include trifluoropropyltrimethoxysilane, nonafluorohexyltrimethoxysilane, and heptadecafluorodecatrimethoxysilane.

[0102] The metal alkoxide is preferably monofunctional, difunctional, or trifunctional, and more preferably difunctional or trifunctional. Here, for example, difunctional means that the number of alkoxide groups is 2 moles per mole of metal alkoxide.

[0103] A dispersion is prepared by dispersing such a fluorine compound precursor and metal powder in a dispersion medium. Examples of dispersion mediums include lower alcohols such as ethanol and methanol, and fluorine-based liquids such as Fluorinert®. However, fluorine-based liquids are preferably used to ensure uniform dispersion of the fluorine compound precursor. The amount of dispersion medium used per 1 part by mass of fluorine compound precursor is, for example, about 10 to 50 parts by mass. The amount of fluorine compound precursor added per 1 part by mass of metal powder is, for example, about 0.01 to 0.1 parts by mass.

[0104] Alternatively, instead of preparing a dispersion, a method may be used in which a mixture of a fluorine compound precursor and a dispersion medium is brought into contact with soft magnetic powder.

[0105] Next, the dispersion is stirred after adjusting its pH. The pH is adjusted to, for example, 9-13. Alkaline solutions such as aqueous ammonia or aqueous sodium hydroxide solution can be used as pH adjusters. Stirring causes hydrolysis of the hydrolyzable groups of the fluorine compound precursor, changing them to, for example, silanol. The changed silanols react with each other, causing dehydration condensation, which forms film 3.

[0106] Furthermore, ultrasonic irradiation may be applied before or after mixing the alkaline solution. Such ultrasonic irradiation promotes the uniform dispersion of the metal powder and allows for a more uniform formation of the coating 3 on the particle surface. Also, the order in which the alkaline solution is added is not limited to the order described above, and different timings may be used.

[0107] Furthermore, after the formation of the coating 3, the resulting injection molding powder may be heat-treated as needed. The heat treatment conditions are, for example, a temperature of 60°C to 120°C and a time of 10 minutes to 300 minutes. This can remove hydrates remaining on the coating 3 and improve the adhesion of the coating 3.

[0108] As described above, the method for producing injection molding powder according to this embodiment includes a coating formation step S104 utilizing the sol-gel method. In the coating formation step S104 of this embodiment, metal powder and a fluorine compound precursor are mixed, and the fluorine compound precursor is polymerized on the particle surface of the metal powder (the surface of the metal particle 2) to produce a fluorine compound. This forms a coating 3 and produces injection molding powder 1.

[0109] This manufacturing method utilizes the sol-gel process, allowing for the self-assembly of fluorine compound precursors to form a high-density coating 3 with high coverage. As a result, a thin yet durable coating 3 can be obtained.

[0110] Furthermore, the fluorine compound precursor is, for example, a coupling agent containing a fluorine-containing group. With such a coupling agent, a bond is formed between the hydrolyzable group and the hydroxyl group present on the surface of the metal particles 2, allowing a high-density coating 3 to be formed with a uniform thickness. In addition, by using a fluorine-containing group as a functional group, it becomes easier to control the oil repellency. As a result, it is possible to obtain an injection molding powder 1 that can more effectively balance the shape retention required for molded articles and the fluidity required for compounds.

[0111] Furthermore, the fluorine compound precursor is, for example, a metal alkoxide containing a fluorine-containing group. With such a metal alkoxide, the hydrolyzed metal alkoxide undergoes a dehydration condensation reaction with the surface of the metal particles 2, allowing for the formation of a high-density coating 3 with a uniform thickness. Moreover, this sol-gel method is simple in that it does not require special equipment or chemicals.

[0112] 3. Method for manufacturing a metal sintered body Next, a method for manufacturing a metal sintered body according to an embodiment will be described.

[0113] Figure 3 is a process diagram illustrating the manufacturing method of a metal sintered body according to the embodiment. The method for manufacturing a metal sintered body shown in Figure 3 comprises a composition preparation step S202, an injection molding step S204, and a sintering step S206.

[0114] 3.1. Composition preparation process In the composition preparation step S202, the injection molding powder 1 and the organic binder are mixed to prepare the injection molding composition.

[0115] Examples of organic binders include various thermoplastic resins such as general-purpose plastics, engineering plastics, and super engineering plastics. Examples of general-purpose plastics include polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polystyrene (PS), polyvinyl acetate (PVAc), polytetrafluoroethylene (PTFE), acrylonitrile butadiene styrene resin (ABS resin), styrene acrylonitrile copolymer (AS resin), and acrylic resin (PMMA). Examples of engineering plastics include polyamide (PA), polyacetal (POM), polycarbonate (PC), modified polyphenylene ether (m-PPE, modified PPE, PPO), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), syndiotactic polystyrene (SPS), and cyclic polyolefin (COP). Examples of super engineering plastics include polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), polysulfone (PSF), polyethersulfone (PES), amorphous polyarylate (PAR), polyetheretherketone (PEEK), thermoplastic polyimide (PI), polyamideimide (PAI), and thermoplastic polyurethane (TPU). Organic binders are typically made from one or more of these resins.

[0116] For mixing, for example, various mixers can be used. Afterward, if necessary, the injection molding composition may be kneaded and compounded. Depending on the type of injection molding method, the compound may be molded into pellets or filaments.

[0117] 3.2. Injection molding process In injection molding step S204, the injection molding composition is injection molded to obtain an injection molded body. Injection molding includes, as mentioned above, metal powder injection molding (MIM), fused deposition modeling (FDM) using metal powder, etc.

[0118] 3.3. Sintering Process In the sintering process S206, the injection-molded body is subjected to a sintering treatment. This results in a sintered metal body.

[0119] Sintering is a process in which metal powder particles are sintered together by heating an injection-molded body. An example of heating conditions is 980°C to 1600°C for 0.2 hours to 24 hours. Examples of heating atmospheres include air, inert gas, and reduced pressure.

[0120] Furthermore, prior to the sintering process, the injection-molded body may be subjected to a degreasing treatment. Degreasing is a process that removes at least a portion of the organic binder by heating the injection-molded body.

[0121] The resulting sintered metal body can be used, for example, as part of or as part of transportation equipment components such as automobile parts, bicycle parts, railway vehicle parts, ship parts, aircraft parts, and space transport vehicle parts; electronic equipment components such as personal computer parts, mobile phone terminal parts, tablet terminal parts, and wearable device parts; electrical equipment components such as refrigerators, washing machines, and air conditioners; machine parts such as machine tools and semiconductor manufacturing equipment; plant components such as nuclear power plants, thermal power plants, hydroelectric power plants, oil refineries, and chemical complexes; and decorative items such as watch parts, metal tableware, jewelry, and eyeglass frames.

[0122] As described above, the method for manufacturing a metal sintered body according to this embodiment comprises a composition preparation step S202, an injection molding step S204, and a sintering step S206.

[0123] In the composition preparation step S202, the injection molding powder 1 and the organic binder are mixed to prepare a compound (injection molding composition). In the injection molding step S204, the compound is injection molded to obtain an injection molded body. In the sintering step S206, the injection molded body is subjected to a sintering treatment.

[0124] With this configuration, the compound has high fluidity and the amount of organic binder used is reduced, which suppresses shrinkage associated with degreasing in injection-molded articles. As a result, a metal sintered body with high dimensional accuracy can be obtained.

[0125] The injection molding powder, the method for manufacturing the injection molding powder, and the method for manufacturing a metal sintered body of the present invention have been described above based on preferred embodiments, but the present invention is not limited thereto. For example, the method for manufacturing the injection molding powder and the method for manufacturing a metal sintered body of the present invention may be modified by adding any desired steps to the above embodiments. [Examples]

[0126] Next, specific embodiments of the present invention will be described. 4. Preparation of powder for injection molding 4.1. Example 1 First, stainless steel SUS316L powder was prepared using the water atomization method. The volume-based particle size distribution of the obtained metal powder was acquired using a laser diffraction scattering particle size distribution analyzer. Then, the average particle size was calculated based on the acquired particle size distribution. The calculation results are shown in Table 1.

[0127] Next, the obtained metal powder was subjected to ozone treatment. Next, 50 mg of trifluoropropyltrimethoxysilane, a fluorine compound precursor, was diluted 10 times by mass with Fluorinert® to prepare a treatment solution. The resulting treatment solution was then sprayed onto 50 g of metal powder and brought into contact with it.

[0128] Next, the metal powder to which the treatment solution had been sprayed was heated to 100°C while being stirred and dried, and then slowly cooled to room temperature by natural cooling. In this way, a coating was formed on the particle surface of the metal powder by the sol-gel method, and powder for injection molding was obtained.

[0129] 4.2. Example 2 Injection molding powder was obtained in the same manner as in Example 1, except that the obtained injection molding powder was subjected to a hydrophilic treatment. The time of the hydrophilic treatment was adjusted so that the contact angles shown in Table 1 were obtained. The hydrophilic treatment was performed using atmospheric pressure plasma treatment with water vapor as the treatment gas.

[0130] 4.3. Examples 3 and 4 Injection molding powder was obtained in the same manner as in Example 2, except that the time for the hydrophilization treatment was changed.

[0131] 4.4. Example 5 Injection molding powder was obtained in the same manner as in Example 1, except that the manufacturing conditions for the injection molding powder were changed as shown in Table 1.

[0132] 4.5. Example 6 Injection molding powder was obtained in the same manner as in Example 2, except that the time for the hydrophilization treatment was changed.

[0133] 4.6. Example 7 Injection molding powder was obtained in the same manner as in Example 5, except that the manufacturing conditions for the injection molding powder were changed as shown in Table 1.

[0134] 4.7. Example 8 Injection molding powder was obtained in the same manner as in Example 1, except that the manufacturing conditions for the injection molding powder were changed as shown in Table 1.

[0135] 4.8. Comparative Example 1 Injection molding powder was obtained in the same manner as in Example 1, except that the formation of a coating was omitted.

[0136] 4.9. Comparative Examples 2-4 Injection molding powder was obtained in the same manner as in Example 1, except that the obtained injection molding powder was subjected to a hydrophilic treatment. The time of the hydrophilic treatment was adjusted so that the contact angles shown in Table 1 were obtained. The hydrophilic treatment was performed using atmospheric pressure plasma treatment with water vapor as the treatment gas.

[0137] The symbols for the fluorine compound precursors shown in Table 1 correspond to the following substance names. A-1: Trifluoropropyltrimethoxysilane A-2: Nonafluorohexyltrimethoxysilane A-3: Heptadecafluorodecatrimethoxysilane

[0138] 4.10. Example 9 Injection molding powder was obtained in the same manner as in Example 1, except that a coating was formed on the particle surface of the metal powder by plasma polymerization. The monomer gas used as the raw material was the gas shown in Table 2. Argon gas was used as the discharge gas.

[0139] 4.11. Examples 10 and 11 Injection molding powder was obtained in the same manner as in Example 9, except that the obtained injection molding powder was subjected to a hydrophilic treatment. The time of the hydrophilic treatment was adjusted so that the contact angles shown in Table 2 were obtained. The hydrophilic treatment was performed using atmospheric pressure plasma treatment with water vapor as the treatment gas.

[0140] 4.12. Examples 12 and 13 Injection molding powder was obtained in the same manner as in Example 1, except that a coating was formed on the particle surface of the metal particles by a mechanochemical method. The fluororesin powder shown in Table 2 was used as the raw material fluorine compound powder. The average particle size of the fluororesin powder was 6 μm.

[0141] 4.13. Comparative Example 5 Injection molding powder was obtained in the same manner as in Example 1, except that a coating was formed on the particle surface of the metal particles by a mechanochemical method. Polypropylene powder, a resin powder that does not contain fluorine, was used as the raw material. The average particle size of the PP powder was 5 μm.

[0142] 5. Evaluation of powders for injection molding 5.1.Contact angle The injection molding powders for each example and comparative example were layered on double-sided tape. Next, the contact angle of hexadecane for the injection molding powder was measured using a contact angle measuring device with the θ / 2 method. The measurement results are shown in Tables 1 and 2.

[0143] 5.2. Average thickness of the coating The cross-sections of the injection molding powders for each example and comparative example were observed using an electron microscope. The average thickness of the coating was then calculated from the observation results. The calculation results are shown in Tables 1 and 2.

[0144] 5.3. Coverage The coating rate of the injection molding powders for each example and comparative example was calculated using the method described above. The calculation results are shown in Tables 1 and 2.

[0145] 5.4. Area ratio of fluorine-derived peaks detected by XPS method Elemental analysis was performed on the injection molding powders of each example and comparative example using the XPS method. The area ratio of the F1s peak to the total peak area was then calculated from the analysis results. The calculation results are shown in Tables 1 and 2.

[0146] 5.5. Percentage change of viscosity with respect to change in shear rate The injection molding powders for each example and comparative example were mixed with polystyrene. Next, the viscosity of the resulting mixture was measured using a rheometer while varying the shear rate applied to the mixture. Then, a flow curve showing the change in viscosity with respect to the change in shear rate was obtained. The rate of change in viscosity [Pa·s] when the shear rate was increased from 0.5 [1 / s] to 500 [1 / s] was calculated. The calculation results are shown in Tables 1 and 2.

[0147] 5.6. Viscosity at high shear rates For each example and comparative example, the viscosity at a high shear rate (500 [1 / s]) obtained in the evaluation performed in 5.5 was compared for the injection molding powders. Next, the viscosity at a high shear rate obtained for the injection molding powder of Comparative Example 1 was set to 1, and the relative values ​​of the viscosity at a high shear rate obtained for the injection molding powders of each example and comparative example were calculated. Then, the calculated relative values ​​were evaluated according to the following evaluation criteria.

[0148] A: The relative value is less than 0.1. B: The relative value is between 0.1 and 0.4. C: The relative value is between 0.4 and 0.7. D: The relative value is between 0.7 and 1.0. E: The relative value is 1.0 or greater. The evaluation results are shown in Tables 1 and 2.

[0149] [Table 1]

[0150] [Table 2]

[0151] As shown in Tables 1 and 2, the injection molding powders of each example exhibited lower viscosity when a high shear rate was applied to a mixture with polystyrene compared to the injection molding powders of each comparative example. In other words, it was confirmed that the injection molding powders of each example can realize compounds that exhibit high fluidity during injection molding. Furthermore, from these results, it is considered that the amount of organic binder used can be reduced in order to achieve the same fluidity. Therefore, it was found that the injection molding powder of the present invention makes it possible to reduce the amount of binder added to the compound while ensuring the fluidity of the compound.

[0152] Furthermore, the injection molding powders of each example showed a greater rate of change in viscosity when mixed with polystyrene compared to the injection molding powders of each comparative example.

[0153] Figure 4 shows the flow curves illustrating the change in viscosity with respect to the change in shear rate when a shear rate is applied to the injection molding powder of Example 1 and the mixture of injection molding powder and polystyrene of Comparative Example 1.

[0154] As shown in Figure 4, the flow curve obtained for the injection molding powder of Comparative Example 1 had a gentle slope. In contrast, the flow curve obtained for the injection molding powder of Example 1 had a steep slope. In other words, the latter showed a larger rate of change in viscosity with respect to changes in shear rate compared to the former. Therefore, it was found that compounds containing the latter powder can improve shape retention during molding while increasing fluidity during injection molding.

[0155] Furthermore, the flow curve shown in Figure 4 also revealed that the viscosity at low shear rates obtained for the injection molding powder of Example 1 was higher than the viscosity at low shear rates obtained for the injection molding powder of Comparative Example 1. From this result, it is considered that the compound containing the injection molding powder of Example 1 behaves solid-like at low shear rates and exhibits high viscosity. On the other hand, it is considered that at high shear rates, the compound containing the injection molding powder of Example 1 exhibits high responsiveness to external forces due to the action of the fluorine compound-containing film, resulting in a decrease in viscosity.

[0156] In contrast, the compound containing the injection molding powder in Comparative Example 1 behaves like a liquid even at low shear rates and exhibits low viscosity. Furthermore, it is thought that the liquid-like behavior does not change significantly even when the shear rate is increased thereafter. For these reasons, the viscosity decrease is considered to be limited in the flow curve of Comparative Example 1 shown in Figure 4. [Explanation of symbols]

[0157] 1... Powder for injection molding, 2... Metal particles, 3... Coating, 4... Particles for injection molding, S102... Preparation process, S104... Film forming process, S202... Composition preparation process, S204... Injection molding process, S206... Sintering process

Claims

1. Powder for injection molding, Metal powder and The particle surface of the aforementioned metal powder is coated with a film containing a fluorine compound, Equipped with, In the injection molding powder, the coating is formed on the outermost surface. A powder for injection molding characterized in that, when laid in layers, the contact angle of hexadecane measured at 25°C by the θ / 2 method is between 60° and 110°.

2. The injection molding powder according to claim 1, wherein the average particle size of the metal powder is 3.0 μm or more and 30.0 μm or less.

3. The injection molding powder according to claim 1 or 2, wherein the area ratio of the F1s peak detected by X-ray photoelectron spectroscopy (XPS) is 10% or more and 75% or less of the total peak area.

4. When polystyrene is mixed with the resulting mixture, and the viscosity of the mixture is measured using a rheometer while varying the shear rate, The injection molding powder according to any one of claims 1 to 3, wherein the rate of change of viscosity with respect to the change in shear rate is 0.05 or more and 10.0 or less.

5. The injection molding powder according to any one of claims 1 to 4, wherein the coating is a single layer.

6. A method for producing injection molding powder according to any one of claims 1 to 5, A process for producing injection molding powder, comprising mixing the metal powder and a fluorine compound powder composed of the fluorine compound, and mechanically adhering the fluorine compound powder to the particle surface of the metal powder to form the coating, A method for producing powder for injection molding, characterized by having [a certain characteristic].

7. The method for producing injection molding powder according to claim 6, wherein the fluorine compound powder is PTFE powder or PFA powder.

8. A method for producing injection molding powder according to any one of claims 1 to 5, A process for producing injection molding powder by mixing the metal powder and monomer gas, causing a polymerization reaction to occur in the monomer gas on the particle surface of the metal powder to generate the fluorine compound, thereby forming the coating, A method for producing powder for injection molding, characterized by having [a certain characteristic].

9. The method for producing injection molding powder according to claim 8, wherein the monomer gas is a reactive gas containing a fluorine-containing group, and the fluorine compound is produced by plasma polymerization.

10. A method for producing injection molding powder according to any one of claims 1 to 5, A process to produce injection molding powder by mixing the metal powder and a fluorine compound precursor, polymerizing the fluorine compound precursor on the particle surface of the metal powder to produce the fluorine compound, thereby forming the coating, A method for producing powder for injection molding, characterized by having [a certain characteristic].

11. The method for producing injection molding powder according to claim 10, wherein the fluorine compound precursor is a coupling agent containing a fluorine-containing group.

12. The method for producing injection molding powder according to claim 10, wherein the fluorine compound precursor is a metal alkoxide containing a fluorine group.

13. A step of preparing an injection molding composition by mixing the injection molding powder and organic binder according to any one of claims 1 to 5, The process involves injection molding the aforementioned injection molding composition to obtain an injection-molded body, The process of subjecting the injection-molded body to a sintering treatment, A method for manufacturing a metal sintered body, characterized by having the following features.

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