Molding powder

Abstract

Provided is a molding material for a powder bed fusion method, said molding material containing a powder of a fluororesin.

Description

[0001] This application is a divisional application of PCT / JP2018 / 032995 filed on September 6, 2018, with the application number 201880077767.0, and the title of "Powder for molding". TECHNICAL FIELD

[0002] The present application relates to a powder for molding, particularly a powder for molding used in a powder bed fusion method. BACKGROUND

[0003] In recent years, as a technique for molding a three-dimensional stereoscopic structure, attention is being paid to a stereoscopic molding apparatus, so-called 3D printer. As a method relating to three-dimensional stereoscopic molding, for example, a vat photopolymerization method in which a monomer of a light-curable resin in a vat is irradiated with light to perform molding, a material extrusion method in which a flowable material is extruded from a nozzle and stacked to perform molding, a binder jetting method in which a powder material is bonded by jetting a binder thereon to perform molding, an inkjet method in which a liquid resin is jetted and solidified to perform molding, a powder bed fusion method in which a powder material is selectively fused and solidified or sintered by irradiating an energy beam thereon to perform molding, and the like are known. Among them, in recent years, attention is being paid to the powder bed fusion method.

[0004] Molding using the above-described powder bed fusion method is generally performed as follows: a powder material housed in a powder material housing container is pushed by a recoater, and a thin layer of the powder material is formed on a molding table while being moved thereon, and an energy beam is irradiated on the thin layer to perform fusion bonding. By repeating this operation, a three-dimensional stereoscopic structure can be molded. A manufacturing method and a manufacturing apparatus using such a powder bed fusion method are described, for example, in Patent Literature 1.

[0005] PRIOR ART DOCUMENT PATENT LITERATURE Patent Literature 1: Japanese Patent Application Publication No. 2017-007221 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION In the above-described powder bed fusion method, various materials such as general-purpose plastics and metals can be used as a molding material, but a fluororesin has not been used as a molding material. However, a fluororesin is lightweight and excellent in heat resistance and chemical resistance, and a stereoscopic structure obtained by molding a fluororesin is very useful in various fields, particularly in the fields of automobiles, aircraft, rockets, and the like.

[0007] Therefore, an object of the present application is to provide a molding material for a powder bed fusion method for molding a stereoscopic structure of a fluororesin.

[0008] TECHNICAL SOLUTION FOR SOLVING THE PROBLEMS The present application includes the following.

[0009] 1. A molding material for a powder bed fusion method, comprising a powder of a fluororesin.

[0010] 2. The molding material according to claim 1, wherein the powder of the fluororesin has a tap density of 0.3 g / ml or more and 1.5 g / ml or less.

[0011] 3. The molding material according to claim 1 or 2, wherein the powder of the fluororesin has a particle size of 10 μm or more and 300 μm or less in terms of D50.

[0012] 4. The molding material according to any one of claims 1 to 3, wherein the powder of the fluororesin has a Hausner ratio of 1.10 or more and 1.30 or less.

[0013] 5. The molding material according to any one of claims 1 to 4, wherein the powder of the fluororesin has a sphericity of 0.60 or more.

[0014] 6. The molding material according to any one of claims 1 to 5, wherein the powder of the fluororesin has a sphericity of 0.70 or more and 0.95 or less.

[0015] 7. The molding material according to any one of claims 1 to 6, wherein the fluororesin is a tetrafluoroethylene-perfluoroalkoxyethylene copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, or an ethylene-tetrafluoroethylene copolymer.

[0016] 8. The molding material according to any one of claims 1 to 7, further comprising silica particles.

[0017] Effects of the Invention According to the present application, by using a molding material containing a powder of a fluororesin, a three-dimensional structure of a fluororesin can be formed by a powder bed fusion method. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a perspective view of a molded body produced in an example. DETAILED DESCRIPTION

[0019] Hereinafter, a molding material of the present application will be described.

[0020] The fluororesin contained in the molding material of the present application is not particularly limited as long as it is a fluororesin that can be used in a powder bed fusion method, that is, a fluororesin that can be fused. The fluororesin can be preferably a thermoplastic fluororesin that can be fused by an energy ray such as various kinds of laser light, for example, a CO2 laser, a fiber laser, a YAG laser, preferably a CO2 laser.

[0021] As the above-mentioned fluororesin, for example, as a fluorine-containing olefin unit, one or two or more kinds of tetrafluoroethylene (TFE) unit, chlorotrifluoroethylene (CTFE) unit, fluoroethylene (VF) unit, vinylidene fluoride (VDF) unit, hexafluoropropylene (HFP) unit, trifluoroethylene (TrFE) unit, perfluoro (alkyl vinyl ether) (PAVE) unit, fluorine-containing dioxole, and the like can be exemplified. In one embodiment, as the PAVE unit, perfluoromethyl vinyl ether unit, perfluoropropyl vinyl ether unit, and the like can be exemplified. In addition, as a non-fluorine-containing olefin unit, a hydrocarbon-based monomer reactive with the above-mentioned fluoroolefin, and the like can be exemplified. As the above-mentioned hydrocarbon-based monomer, for example, at least one non-fluorine-containing olefin unit selected from the group consisting of olefins, alkyl vinyl ethers, vinyl esters, alkyl allyl ethers, and alkyl allyl esters is preferred.

[0022] In one embodiment, as the above-mentioned fluororesin, tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), Neoflon EFEP (trademark) tetrafluoroethylene-hexafluoropropylene-perfluoro (alkyl vinyl ether) copolymer (PAVE), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, tetrafluoroethylene-vinylidene fluoride copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and the like can be exemplified. These fluororesins can be used alone or in a mixture of two or more kinds.

[0023] In a preferred embodiment, the above-mentioned fluororesin can be, for example, tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), or ethylene-tetrafluoroethylene copolymer (ETFE). These fluororesins can be used alone or in a mixture of two or more kinds. These fluororesins are preferably used alone.

[0024] In one embodiment, the number average molecular weight of the above-mentioned fluororesin is not particularly limited, and can be, for example, 100,000 or more and 100 million or less, and is preferably 500,000 or more and 5 million or less. In a preferred embodiment, the modeling material of the present application can be used in a powder bed fusion method, and thus the fluororesin can be of a relatively low molecular weight, for example, 3 million or less, 2 million or less, or 1 million or less. By using a fluororesin of a low molecular weight, the mechanical strength of a three-dimensional structure obtained by modeling is improved.

[0025] In the present application, the above-mentioned fluororesin is contained in the modeling material in the form of a powder.

[0026] The inventors of the present application have studied a molding material containing the above-described fluororesin, and as a result, have found that, in order to further improve moldability, it is effective to make the thin layer formed using a recoater more uniform and to improve the recoatability of the fluororesin powder on a molding table. The recoatability of the molding material can be changed by changing the properties of the fluororesin powder, such as the fluidity. For example, by increasing the fluidity of the fluororesin powder, the recoatability of the molding material can be improved.

[0027] In one embodiment, the particle diameter of the above-described fluororesin powder is preferably 10 μm or more and 300 μm or less, more preferably 20 μm or more and 250 μm or less, further preferably 30 μm or more and 250 μm or less, and more further preferably 40 μm or more and 150 μm or less, in terms of D50. By making the particle diameter (D50) of the fluororesin 10 μm or more, the fluidity of the molding material is improved, and a uniform thin layer is easily formed. By further increasing the particle diameter (D50) of the fluororesin, the fluidity of the molding material can be further improved. In addition, by making the particle diameter (D50) of the fluororesin 300 μm or less, a smooth surface is easily obtained in the three-dimensional structure obtained by molding. By further reducing the particle diameter (D50) of the fluororesin, a smoother surface can be obtained in the three-dimensional structure.

[0028] In one embodiment, the particle diameter of the above-described fluororesin powder is preferably 3 μm or more and 100 μm or less, more preferably 10 μm or more and 50 μm or less, and further preferably 20 μm or more and 50 μm or less, in terms of D10. By making the particle diameter (D10) of the fluororesin 3 μm or more, the fluidity of the molding material is improved, and a uniform thin layer is easily formed. By further increasing the particle diameter (D10) of the fluororesin, the fluidity of the molding material can be further improved. In addition, by making the particle diameter (D10) of the fluororesin 100 μm or less, a smooth surface is easily obtained in the three-dimensional structure obtained by molding. By further reducing the particle diameter (D10) of the fluororesin, a smoother surface can be obtained in the three-dimensional structure.

[0029] In one embodiment, the particle diameter of the above-described fluororesin powder is preferably 30 μm or more and 800 μm or less, more preferably 50 μm or more and 600 μm or less, and further preferably 80 μm or more and 500 μm or less, for example, 80 μm or more and 300 μm or less or 80 μm or more and 200 μm or less, in terms of D90. By making the particle diameter (D90) of the fluororesin 30 μm or more, the fluidity of the molding material is improved, and a uniform thin layer is easily formed. By further increasing the particle diameter (D90) of the fluororesin, the fluidity of the molding material can be further improved. In addition, by making the particle diameter (D90) of the fluororesin 800 μm or less, a smooth surface is easily obtained in the three-dimensional structure obtained by molding. By further reducing the particle diameter (D90) of the fluororesin, a smoother surface can be obtained in the three-dimensional structure.

[0030] In a preferred embodiment, the particle size of the fluororesin powder described above is preferably 10 μm or more and 300 μm or less, more preferably 20 μm or more and 250 μm or less, further preferably 30 μm or more and 250 μm or less, and still further preferably 40 μm or more and 150 μm or less, in terms of D50. In terms of D10, it is preferably 3 μm or more and 100 μm or less, more preferably 10 μm or more and 50 μm or less, and further preferably 20 μm or more and 50 μm or less. In terms of D90, it is preferably 30 μm or more and 800 μm or less, more preferably 50 μm or more and 600 μm or less, and further preferably 80 μm or more and 500 μm or less, for example, 80 μm or more and 300 μm or less or 80 μm or more and 200 μm or less.

[0031] In the present invention, the particle size described above can be measured by a laser diffraction method.

[0032] In one embodiment, the tap density of the fluororesin powder described above is preferably 0.3 g / ml or more and 1.5 g / ml or less, and more preferably 0.5 g / ml or more and 1.0 g / ml or less. By making the tap density of the fluororesin powder 0.3 g / ml or more, the volume change at the time of melting and molding the fluororesin can be reduced. By further increasing the tap density of the fluororesin, the volume change can be further reduced. In addition, by making the tap density of the fluororesin powder 1.0 g / ml or less, the flowability of the molding material is improved, and a uniform thin layer is easily formed. By further reducing the tap density of the fluororesin, the flowability of the molding material can be further improved. In the present invention, the tap density described above can be measured by the method described in JIS K 6891.

[0033] In one embodiment, the Hausner ratio of the fluororesin powder described above is preferably 1.10 or more and 1.30 or less, and more preferably 1.20 or more and 1.25 or less. By making the Hausner ratio of the fluororesin powder within such a range, the flowability of the molding material is improved, and a uniform thin layer is easily formed. The "Hausner ratio" refers to the ratio expressed by the tap density / static tap density. In the present invention, the Hausner ratio described above can be measured using a powder comprehensive property tester (manufactured by Sekika Mikrolab Co., Ltd.).

[0034] In one embodiment, the sphericity of the fluororesin powder described above is preferably 0.60 or more, more preferably 0.60 or more and 0.98 or less, further preferably 0.70 or more and 0.95 or less, and still further preferably 0.80 or more and 0.95 or less. By setting the sphericity of the fluororesin powder within such a range, the flowability of the molding material is improved, and a uniform thin layer is easily formed. The "sphericity" refers to the deviation from a perfect sphere of the powder, and is the average of the ratio (maximum diameter / short diameter) of the maximum diameter and the short diameter orthogonal thereto of each of 50 particles in a photograph projection obtained by taking a photograph using a transmission electron microscope. The closer the sphericity is to 1, the closer the powder is to a perfect sphere.

[0035] The fluororesin powder used in the present application is not particularly limited, and can be produced, for example, by a method including the following steps.

[0036] a step of obtaining a polymerized powder of a fluoropolymer by polymerizing a fluorine-containing olefinic monomer by suspension polymerization; a step of densifying the polymerized powder to a specific gravity of 90% or more of the true specific gravity using a roll, and obtaining a crushed powder, as desired; a step of feeding the polymerized powder or the crushed powder into a friction mill; a step of processing the polymerized powder or the crushed powder into a desired shape; and a step of recovering the fluoropolymer powder from the friction mill.

[0037] The fluoropolymer powder obtained by the production method described above is a powder processed into a desired shape using a friction mill, and is therefore spherical and has a high static loose density. The production method described above is superior in productivity to conventional methods, and can efficiently obtain powder particles having a high static loose density.

[0038] Friction mill A device in which a plurality of fins are arranged on the outer peripheral portion of a rotating shaft inside a rotary drum, and powder is made to flow in the rotary drum by rotating the fins to cause centrifugal diffusion and vortex action. The powder is given mechanical stress by being pressed against the inner wall of the device. A stirring member having a function of discharging and recovering the powder toward the rotating shaft can also be operated. The processing is preferably performed at a fluoropolymer powder temperature of 50 to 200°C.

[0039] Further, the friction-type grinder is preferably designed so as to have a rotating body having a plurality of blades on an outer periphery, and a housing having a cylindrical inner peripheral surface close to radial front end portions of the blades, the blades adjacent to each other in an axial direction of the rotating body extend in different directions from the axis, and at least one set of the blades adjacent to each other in the axis are inclined in opposite directions with respect to the axis. As such a device, for example, a device described in Japanese Patent Application Publication No. 2010-180099 can be used.

[0040] In the device of this design, a large compressive force and a shear force are applied to the powder between the radial front end portions of the plurality of blades and the inner peripheral surface of the housing, and the powder having a high static tap density can be efficiently produced.

[0041] As such a device, for example, NOBILTA manufactured by Hikari Kikai K.K. can be used.

[0042] The molding material of the present application can contain other materials than the powder of the fluororesin described above.

[0043] As the other materials, for example, a molding aid such as silica (Si02) glass fiber, carbon fiber, graphite, carbon nanotube, carbon nanohorn, fullerene, alumina, clay, montmorillonite, talc, and the like can be used. By adding the molding aid, particularly silica, to the molding material of the present application, the flowability and moldability of the molding material are improved.

[0044] The content of the silica described above with respect to the entire molding material is preferably 0.1% by weight or more and 1.0% by weight or less, more preferably 0.1% by weight or more and 0.5% by weight or less, and further preferably 0.1% by weight or more and 0.3% by weight or less. By making the content of the silica 0.1% by weight or more, the flowability and moldability of the molding material are improved. By further increasing the content of the silica, the flowability and moldability of the molding material are further improved. Further, by making the content of the silica 1.0% by weight or less, the content of the fluororesin can be sufficiently ensured, and the characteristics of the fluororesin can be sufficiently exhibited in the three-dimensional structure.

[0045] The silica described above preferably has a particle size equivalent to that of the fluororesin described above.

[0046] As the other material, a laser-absorbing coloring material can be exemplified. The laser-absorbing coloring material is not particularly limited as long as it is a material capable of absorbing laser light having a wavelength of about 1 μm, and carbon, metal, pigment, dye, or the like can be used. It is preferable to use carbon as a main component. The average particle diameter of the laser-absorbing coloring material is preferably about 10 μm, and the particle diameter is preferably in a range of 2 μm or more and 40 μm or less. The content of the laser-absorbing coloring material in the modeling material is, for example, preferably in a range of 0.05% by weight or more and 0.20% by weight or less.

[0047] In one embodiment, the particle diameter of the above-described silica is preferably 10 μm or more and 300 μm or less, more preferably 20 μm or more and 250 μm or less, further preferably 30 μm or more and 250 μm or less, and still further preferably 40 μm or more and 150 μm or less, in terms of D50.

[0048] In a preferable embodiment, the modeling material of the present application can be a mixture of PFA and silica.

[0049] Next, a modeling method using the modeling material of the present application according to the powder bed fusion method will be described.

[0050] A modeling device using the powder bed fusion method generally has a powder storage container that stores a modeling material on both sides of a modeling table on which modeling is performed. In addition, a recoater that supplies the modeling material in the powder storage container to the modeling table and forms a thin layer, and a laser portion that irradiates laser light to the thin layer are included.

[0051] First, a required amount of modeling material is stored in the powder storage container. Next, the height of the modeling table is lowered by an amount corresponding to the thickness of the thin layer. On the other hand, the bottom surface of the powder storage container is raised, and an appropriate amount of modeling material is carried upward from the powder storage container. The modeling material is carried onto the modeling table by the recoater, and the recoater is moved in a manner to flatten the surface, whereby a thin layer is formed on the modeling table. Next, laser scanning is performed in accordance with slice data of a three-dimensional structure to be modeled, and the thin layer is fused and bonded, and the powder is solidified. By repeating this operation, layers corresponding to the slice data are sequentially formed, and a three-dimensional structure is modeled.

[0052] When modeling is performed, the temperature of the powder in the powder storage container as a supply area, and the temperature of the powder on the modeling table as a modeling area are preferably appropriately controlled in accordance with the modeling material used. By controlling these temperatures, a more uniform thin layer can be formed, and more precise modeling can be performed.

[0053] Example As the fluororesin, powders of PFA, FEP, ETFE, and EFEP were prepared. The characteristics of each powder are shown in Table 1 below.

[0054] [Table 1] Examples 1 to 6 As shown in the following table, the above-mentioned powder of fluororesin, and a mixture of the powder of fluororesin and the powder of silica were used to make a test piece in which a hollow cube of 30 mm on a side was contained in a hollow cube of 60 mm on a side (the minimum thickness of the wall was 0.8 mm) using a 3D printer of the powder bed fusion type. Figure 1 The fluororesin used, and the content of silica when contained, are shown in Table 2 below. In addition, the temperature of the supply zone and the molding zone at the time of molding are shown together in Table 2.

[0055] [Table 2] The above-mentioned test results confirmed that molding was possible in all cases. In Example 1, a number of warps were observed; in Examples 2 and 4, roughness was observed on the surface. In particular, in Example 5, a perfect test piece was obtained.

[0056] Industrial applicability The molding material of the present application can be suitably used for molding of a wide variety of products, in particular molding using the powder bed fusion method.

Claims

1. A molding material for powder bed fusion method, characterized in that: contain: Fluororesin powder, The fluororesin powder has a static bulk density of not less than 0.3 g / ml and not more than 1.5 g / ml. The particle size of the fluororesin powder is 3 μm to 100 μm in terms of D10, 10 μm to 300 μm in terms of D50, and 30 μm to 800 μm in terms of D90.

2. The modeling material according to claim 1, wherein: The Hausner ratio of the fluororesin powder is 1.10 or more and 1.30 or less.

3. The modeling material according to claim 1 or 2, characterized in that: The fluororesin powder has a sphericity of 0.60 or greater.

4. The modeling material according to claim 1 or 2, characterized in that: The sphericity of the fluororesin powder is 0.70 or more and 0.95 or less.

5. The modeling material according to claim 1 or 2, characterized in that: The fluororesin is a tetrafluoroethylene-perfluoroalkoxyethylene copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer or an ethylene-tetrafluoroethylene copolymer.

6. The modeling material according to claim 1 or 2, characterized in that: Also contains: Silica particles.

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