WO2025033483A1 - Powder material for 3d printer, three-dimensional modeled article, and method for producing three-dimensional modeled article - Google Patents

Abstract

Provided is a powder material for a 3D printer, the powder material exhibiting excellent fluidity and being capable of suppressing the occurrence of flying of the powder material during modeling. Also provided are a three-dimensional modeled article obtained using the powder material for a 3D printer, the three-dimensional modeled article exhibiting excellent appearance and excelling in mechanical characteristics and heat resistance, and a method for producing the three-dimensional modeled article.　A powder material (X) for a 3D printer comprises a polyacetal copolymer resin powder (I) and metal oxide particles (II). The content of the particles (II) is 0.01-0.5 mass% with respect to the total mass of the powder material (X).

Description

Powder material for 3D printers, 3D objects, and method for manufacturing 3D objects

This disclosure relates to powder materials for 3D printers, three-dimensional objects, and methods for manufacturing three-dimensional objects.

3D printers have become increasingly popular in recent years because they can create three-dimensional objects without using molds or large-scale melting equipment. Known modeling methods using 3D printers include fused deposition modeling (FDM), stereolithography (STL), and selective laser sintering (SLS). The selective laser sintering method is a method in which thin layers are formed using powdered material, and then the thin layers are irradiated with a high-power laser beam or electron beam to sinter them, and the sintered layers are stacked one after the other to create a model. This method is more suitable for precision modeling than other modeling methods.

Polyamide 11, polyamide 12, polypropylene, etc. are widely known as powder materials that can be used in powder sintering 3D printers. Patent documents 1 and 2 describe polyacetal powder that can be used as a powder material for selective laser sintering 3D printers. Patent document 3 describes a powder for 3D printers that can create three-dimensional objects with excellent appearance, high density, and high strength.

JP 2020-002247 A JP 2013-508199 A International Publication No. 2023/090195

The objective of the present disclosure is to provide a powder material for 3D printers that has excellent fluidity and can suppress the powder material from flying up during modeling, as well as a three-dimensional object that uses the powder material and has excellent appearance, mechanical properties, and heat resistance, and a method for manufacturing the three-dimensional object.

The present disclosure encompasses the following aspects.
[1] A powder material (X) for 3D printers,
A polyacetal copolymer resin powder (I) and metal oxide particles (II),
The content of the particles (II) is 0.01 to 0.5% by mass relative to the total mass of the powder material (X).

The present disclosure provides a powder material for 3D printers that has excellent fluidity and can suppress the occurrence of powder flying up during modeling, as well as a three-dimensional object using the powder material that has excellent appearance, mechanical properties, and heat resistance, and a method for manufacturing the three-dimensional object.

Hereinafter, one embodiment of the present disclosure will be described in detail, but the scope of the present disclosure is not limited to the embodiment described here, and various modifications can be made within the scope of the present disclosure. Each aspect disclosed in this specification can be combined with any other feature disclosed in this specification. In addition, when multiple upper and lower limit values are described for a specific parameter, any upper and lower limit values among these upper and lower limit values can be combined to form a suitable numerical range. In addition, the lower and/or upper limit values of the numerical range described in this disclosure are numerical values within the numerical range and may be replaced with numerical values shown in the examples. The expression "X to Y" indicating a numerical range means "X or more and Y or less". When a specific description described for one embodiment is also applicable to other embodiments, the description may be omitted in other embodiments.
The configurations and combinations thereof in each embodiment are merely examples, and addition, omission, substitution, and other modifications of the configurations are possible as appropriate without departing from the spirit of the present disclosure. The present disclosure is not limited to the embodiments.
Each feature disclosed herein may be combined with any other feature disclosed herein.

[Powder material for 3D printers (X)]
The powder material (X) for 3D printers according to this embodiment (hereinafter also referred to as "powder material (X)") contains a polyacetal copolymer resin powder (I) and metal oxide particles (II), and is characterized in that the content of the particles (II) is 0.01 to 0.5% by mass with respect to the total mass of the powder material (X). The powder material (X) for 3D printers has excellent fluidity and can suppress the occurrence of the powder material flying up during modeling. In addition, a three-dimensional object having excellent appearance, mechanical properties, and heat resistance can be obtained.

<Polyacetal Copolymer Resin Powder (I)>
The powder material (X) contains a polyacetal copolymer resin powder (I) (hereinafter, also referred to as "powder (I)"). The powder (I) is composed of a polyacetal copolymer resin.

A polyacetal copolymer resin is a copolymer resin that contains an oxymethylene unit (-CH ₂ O-) as a main constituent unit and further contains a comonomer unit other than the oxymethylene unit. In this specification, the term "main constituent unit" refers to a monomer unit that accounts for 50% by mass or more, preferably 70% by mass or more, of all constituent units (100% by mass) that constitute the polyacetal copolymer resin.

(comonomer unit)
The comonomer unit is preferably an oxyalkylene unit having 2 or more carbon atoms. When the comonomer unit is an oxyalkylene unit having 2 or more carbon atoms, the thermal stability is likely to be good. In addition, the comonomer unit is more preferably at least one oxyalkylene unit selected from an oxyethylene group, an oxypropylene group, and an oxytetramethylene group, and particularly preferably contains an oxyethylene group.
When oxyethylene units are contained as comonomer units, the proportion of the oxyethylene units in all comonomer units (100% by mass) is preferably 90% by mass or more and 100% by mass or less, and more preferably 95% by mass or more and 100% by mass or less.
The comonomer units contained in the polyacetal copolymer resin may be of one type or of two or more types.

From the viewpoint of retarding crystallization, the proportion of the comonomer units in the polyacetal copolymer resin is preferably 1.0 mass% or more and 6.0 mass% or less, more preferably 1.5 mass% or more and 5.5 mass% or less, even more preferably 2.0 mass% or more and 5.0 mass% or less, and particularly preferably 2.5 mass% or more and 4.5 mass% or less, relative to the total constituent units (100 mass%) of the polyacetal copolymer resin.
In one embodiment, the proportion of the comonomer units in the polyacetal copolymer resin may be 3.5 mass% relative to the total structural units (100 mass%) of the polyacetal copolymer resin, and may be within the range in which this is the upper or lower limit of the above-mentioned numerical range.

The ratio of the comonomer unit in the polyacetal copolymer resin can be calculated by ¹ H-NMR. For example, powder (I) is dissolved in deuterated hexafluoroisopropanol to a concentration of 5 mass % to prepare a sample. The sample is analyzed by ¹ H-NMR to calculate the ratio of the integral ratio of the comonomer unit (e.g., an oxyalkylene unit having 2 or more carbon atoms, as described later) to the integral ratio of the peak of all monomers in the polyacetal copolymer resin.

The polyacetal copolymer resin may be any of a random copolymer, a block copolymer, and a graft copolymer. From the viewpoint of thermal stability, a random copolymer is preferred.
The degree of polymerization, the degree of branching, and the degree of crosslinking of the polyacetal copolymer resin can be appropriately adjusted within a range that satisfies the above-mentioned melt flow rate (MFR).

In one embodiment, it is preferable that the powder (I) has an average particle size (D50) of 40 μm or more and 60 μm or less, a particle size (D10) at which the volume-based cumulative frequency of the powder (I) is 10% is 15 μm or more, and a particle size (D90) at which the volume-based cumulative frequency of the powder (I) is 90% is 100 μm or less. When the average particle size (D50), particle size (D10), and particle size (D90) are within the above ranges, the powder flowability is poor, recoatability during molding is deteriorated, and it is difficult to obtain a good powder surface.

The terms "average particle size (D50)", "particle size (D10) with a volume-based cumulative frequency of 10%" (hereinafter simply referred to as particle size (D10)), and "particle size (D90) with a volume-based cumulative frequency of 90%" (hereinafter simply referred to as particle size (D90)) refer to the particle size (D50), particle size (D10), and particle size (D90) with a cumulative frequency of 50%, 10%, and 90%, respectively, in the volume-based arithmetic average particle size measured by a laser diffraction/scattering particle size distribution measurement method. The average particle size (D50), D10 particle size, and D90 particle size can be measured, for example, using a laser diffraction/scattering particle size distribution measurement device (for example, product name: LA-960, manufactured by Horiba, Ltd.).

In one embodiment, the average particle size (D50) of the powder (I) is more preferably 45 μm or more and 60 μm or less, and even more preferably 45 μm or more and 55 μm or less. In one embodiment, the particle size (D10) at which the volume-based cumulative frequency of the powder (I) is 10% is more preferably 15 μm or more and 30 μm or less, and even more preferably 15 μm or more and 25 μm or less. In one embodiment, the particle size (D90) at which the volume-based cumulative frequency of the powder (I) is 90% is more preferably 80 μm or more and 100 μm or less, and even more preferably 90 μm or more and 100 μm or less. The combination of the above numerical ranges of the average particle size (D50), particle size (D10), and particle size (D90) is not limited, and various combinations can be adopted.
In one embodiment, the powder (I) may have an average particle size (D50) of 50 μm, a particle size (D10) at which the volume-based cumulative frequency is 10% of the total particle size (D10) of 20 μm, and a particle size (D90) at which the volume-based cumulative frequency is 90% of the total particle size (D90) of 94 μm, or one or two of these may be within the upper or lower limit of the above-mentioned numerical range.

In one embodiment, the ratio (D90/D10) of the particle size at which the volume-based cumulative frequency of powder (I) is 90% (D90) to the particle size at which the volume-based cumulative frequency is 10% (D10) is preferably 10 or less, more preferably 1 to 8, and even more preferably 2 to 6. If D90/D10 is 10 or less, the powder has better fluidity and is more likely to be prevented from flying up during molding.

(Melt Flow Rate (MFR))
The MFR of the powder (I) measured at a temperature of 190° C. and a load of 2.16 kgf is 1.0 g/10 min or more and 8.0 g/10 min or less, preferably 1.2 g/10 min or more and 7.0 g/10 min or less, and more preferably 1.4 g/10 min or more and 6.0 g/10 min or less. When the MFR is within the above range, the strength of the molded object becomes good. The MFR of the powder (I) can be measured in accordance with ISO 1133 (condition D) under conditions of a temperature of 190° C. and a load of 2.16 kgf.

The weight average molecular weight (Mw) of the polyacetal copolymer resin according to this embodiment is not particularly limited as long as it has the effect of the present invention, and can be appropriately adjusted within a range in which the MFR is 1.0 to 8.0 g/10 min. In one aspect, the Mw of the polyacetal copolymer resin may be 10,000 or more and 400,000 or less. If the Mw is within the above range, the strength of the molded object is likely to be good. The Mw can be measured (polystyrene equivalent) by size exclusion chromatography (SEC).

The shape of the powder (I) is not particularly limited as long as it has the effects of the present invention, and may be any of spherical (including nearly spherical), spindle-shaped, irregular particulate, fibril, fibrous, etc. From the viewpoints of packing property and powder flowability, spherical (including nearly spherical) and irregular particulate are preferred.
The powder (I) may be used alone or in combination of two or more. When two or more types of powder (I) are used in combination, it is preferable to adjust the blending ratio so that the mixture of powder (I) satisfies the above-mentioned comonomer amount, average particle size, and MFR values, and/or satisfies the above-mentioned average particle size (D50), particle size (D10), and particle size (D90).

The proportion of powder (I) in powder material (X) is preferably 50% by mass or more, more preferably 70% by mass or more, based on the total mass of powder material (X). The upper limit is 99.99% by mass or less, and may be 99.98% by mass or less, 99.97% by mass or less, 99.96% by mass or less, or 99.95% by mass or less. In other words, the proportion of powder (I) in powder material (X) may be 50 to 99.99% by mass, 60 to 99.98% by mass, 70 to 99.97% by mass, 80 to 99.96% by mass, 90 to 99.95% by mass, 95 to 99.95% by mass, or 99.85 to 99.95% by mass, based on the total mass of powder material (X).

In one embodiment, the content of polyacetal copolymer resin in the thermoplastic resin component contained in powder material (X) is preferably 80% by mass or more, preferably 90% by mass or more, preferably 98% by mass or more, and may be 100% by mass.

<Method for producing polyacetal copolymer resin powder (I)>
The powder (I) can be produced by obtaining a polyacetal copolymer resin by a known polymerization method, and then pulverizing the copolymer resin by a known method. One embodiment of the method for producing the powder (I) will be described below.

(Method of producing polyacetal copolymer resin)
The polyacetal copolymer resin can be produced by polymerizing a monomer mixture containing a cyclic trimer or tetramer of formaldehyde as a main monomer and a comonomer in the presence of a polymerization catalyst and a chain transfer agent. In this specification, the term "main monomer" refers to a monomer that is contained in an amount of 50% by mass or more relative to the total monomers (100% by mass) constituting the polyacetal copolymer resin. In this specification, the term "comonomer" refers to a monomer that is copolymerizable with the main monomer and can constitute the above-mentioned comonomer unit.
The main monomer preferably contains trioxane. Trioxane is generally obtained by reacting an aqueous formaldehyde solution in the presence of an acid catalyst, and the trioxane may be purified by a method such as distillation. It is preferable to use trioxane containing a small amount of impurities such as water and methanol.

Examples of the comonomer include alkylene oxides having two or more carbon atoms and cyclic acetal compounds.
Examples of alkylene oxides having 2 or more carbon atoms include ethylene oxide, propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, etc. These alkylene oxides may be used alone or in combination of two or more.
Examples of the cyclic acetal compound include 1,3-dioxolane, propylene glycol formal, diethylene glycol formal, triethylene glycol formal, 1,4-butanediol formal, 1,5-pentanediol formal, 1,6-hexanediol formal, etc. These cyclic acetal compounds may be used alone or in combination of two or more kinds.
Of the above, the comonomer preferably contains a cyclic acetal compound, and more preferably contains 1,3-dioxolane.

The proportion of the comonomer units in the polyacetal copolymer resin may be 1.0% by mass or more and 6.0% by mass or less, 1.5% by mass or more and 5.5% by mass or less, 2.0% by mass or more and 5.0% by mass or less, or 2.5% by mass or more and 4.5% by mass or less, relative to the total monomers (100% by mass). In one embodiment, the proportion of the comonomers in the polyacetal copolymer resin may be 3.5% by mass relative to the total monomers (100% by mass), and this may be the upper or lower limit of the numerical range described above.

In this embodiment, the polyacetal copolymer resin can be produced by a method such as bulk polymerization of a monomer mixture containing trioxane and a comonomer, optionally with the addition of an appropriate amount of a molecular weight regulator, using a cationic polymerization catalyst.

The polymerization apparatus is not particularly limited, and known apparatus can be used. In addition, any method such as batch type or continuous type can be used. The polymerization temperature is preferably kept at 65 to 135°C. The polymerization catalyst after polymerization can be deactivated by adding a basic compound or an aqueous solution thereof to the reaction product recovered from the polymerization apparatus or to the reaction product in the polymerization apparatus.

The cationic polymerization catalysts used in this embodiment include lead tetrachloride; tin tetrachloride; titanium tetrachloride; aluminum trichloride; zinc chloride; vanadium trichloride; antimony trichloride; phosphorus pentafluoride; antimony pentafluoride; boron trifluoride, boron trifluoride diethyl etherate, boron trifluoride dibutyl etherate, boron trifluoride dioxanate, boron trifluoride acetic anhydrate, boron trifluoride triethylamine complex compounds and other boron trifluoride coordination compounds; perchloric acid, acetyl perchlorate. Examples of suitable catalysts include inorganic and organic acids such as t-butyl perchlorate, hydroxyacetic acid, trichloroacetic acid, trifluoroacetic acid, and p-toluenesulfonic acid; complex salt compounds such as triethyloxonium tetrafluoroborate, triphenylmethylhexafluoroantimonate, allyldiazonium hexafluorophosphate, and allyldiazonium tetrafluoroborate; alkyl metal salts such as diethylzinc, triethylaluminum, and diethylaluminum chloride; heteropolyacids; and isopolyacids. Among these, boron trifluoride coordination compounds such as boron trifluoride, boron trifluoride diethyl etherate, boron trifluoride dibutyl etherate, boron trifluoride dioxanate, boron trifluoride acetic anhydrate, and boron trifluoride triethylamine complex compounds are particularly preferred. These catalysts can also be used by diluting them in advance with an organic solvent or the like.

The molecular weight regulator used in this embodiment includes linear formal compounds. Examples of linear formal compounds include methylal, ethylal, dibutoxymethane, bis(methoxymethyl) ether, bis(ethoxymethyl) ether, bis(butoxymethyl) ether, and the like. Among these, it is preferable to use at least one selected from the group consisting of methylal, ethylal, and dibutoxymethane.

In addition, examples of basic compounds that can be used to neutralize and deactivate the polymerization catalyst include ammonia; amines such as triethylamine, tributylamine, triethanolamine, and tributanolamine; hydroxide salts of alkali metals and alkaline earth metals; and other known catalyst deactivators. After the polymerization reaction is completed, it is preferable to quickly add an aqueous solution of such a compound to the reaction product to deactivate it. After the polymerization and deactivation methods, washing, separation and recovery of unreacted monomers, drying, and the like can be carried out as necessary by conventionally known methods to obtain a polyacetal copolymer resin.

If necessary, various stabilizers can be added to carry out stabilization treatment such as decomposition and removal or sealing of unstable terminals of the polyacetal copolymer resin. As the stabilizer, conventionally known antioxidants, heat stabilizers, etc. can be used. For example, hindered phenol compounds, nitrogen-containing compounds, hydroxides of alkali or alkaline earth metals, inorganic salts, carboxylates, etc. can be used alone or in combination of two or more.

Furthermore, as necessary, one or more of general additives for polyacetal copolymer resins, such as colorants such as dyes and pigments, lubricants, crystal nucleating agents, release agents, antistatic agents, surfactants, or organic polymer materials, may be added to the extent that the effects of the polyacetal copolymer resin of this embodiment are not impaired.

The polyacetal copolymer resin obtained by the above manufacturing method is molded into pellets, fibers, films, etc., and then pulverized by dry pulverization, wet pulverization, or freeze pulverization using a jet mill, a bead mill, a hammer mill, a ball mill, a cutter mill, a pin mill, a stone mill, or the like to obtain a powder (I) having an average particle size of 40 μm to 60 μm. A method of dissolving the polyacetal copolymer resin in a solvent and then spray drying, a poor solvent precipitation method of forming an emulsion in a solvent and then contacting it with a poor solvent, and a submerged drying method of forming an emulsion in a solvent and then drying and removing the organic solvent can also be used. When blending the polyacetal copolymer resin with other thermoplastic resins (organic polymer materials), a method of mixing the polyacetal copolymer resin with the other thermoplastic resin, and then dissolving and removing the other thermoplastic resin with a solvent to obtain a powder (I) having the above average particle size can also be used. A method of pulverizing an oligomer of the polyacetal copolymer resin and then solid-phase polymerizing it to obtain a powder (I) having the above average particle size can also be used.

<Metal oxide particles (II)>
The powder material (X) contains metal oxide particles (II) (hereinafter also referred to as "powder (II)"), and the content of the particles (II) is 0.01 to 0.5 mass% with respect to the total mass of the powder material (X). By containing the powder (II) in the above range, the powder material (X) has excellent fluidity and can suppress the powder material from flying up during molding. In addition, a three-dimensional object having excellent appearance, mechanical properties, and heat resistance can be obtained.
The content of the particles (II) is preferably 0.02 to 0.4 mass% relative to the total mass of the powder material (X), more preferably 0.03 to 0.3 mass%, even more preferably 0.04 to 0.2 mass%, and particularly preferably 0.05 to 0.15 mass%. In one embodiment, the content of the particles (II) may be 0.05 mass% or 0.15 mass% relative to the total mass of the powder material (X), or may be within the range of the upper or lower limit of any of the above numerical ranges.

In this specification, "metal oxide particles" refers to particles of a compound of a metal element and oxygen. Nonmetals and metalloids (boron, silicon, germanium, arsenic, antimony, tellurium, selenium, polonium, astatine, etc., which are generally defined as metalloids) are not metal elements, so the term "metal oxide particles" does not include particles of these oxides. For example, particles of silicon (Si) oxide, such as silica (SiO ₂ ) particles, which have been used conventionally as a flow agent or filler, are not included in the term "metal oxide particles" defined in this specification.

The mechanism by which blending a predetermined amount of metal oxide particles into polyacetal copolymer resin powder (I) improves the fluidity of powder material (X), suppresses the powder material from flying up during modeling, and allows a three-dimensional object with excellent mechanical properties and heat resistance to be obtained is not clear at this stage. Non-limiting mechanisms are thought to be that the metal oxide particles adhere to the polyacetal copolymer resin powder (I), and powder (II) acts as a bearing between the particles of powder (I), improving fluidity and making it difficult for the powder material to fly up during modeling, and that the metal oxide particles improve the crystallinity of the molten polyacetal copolymer resin powder (I) at the sintering temperature during modeling with a 3D printer.

Examples of metal oxides include alumina, magnesium oxide, zirconia, titania, ceria, zinc oxide, tin oxide, copper oxide, etc., and it is preferable to include at least one selected from these, more preferably at least one selected from alumina and titania, and even more preferably to include alumina. The metal oxide may be one type or a mixture of two or more types.

In one embodiment, the powder (II) preferably contains fumed metal oxide particles, and more preferably consists of fumed metal oxide particles. The fumed metal oxide particles tend to have a smaller particle size. By containing the fumed metal oxide particles in the powder (II), the flowability of the powder material (X) is improved and the occurrence of the powder material flying up during molding can be further suppressed.
As used herein, "fumed metal oxide particles" refers to metal oxide particles produced by a process involving hydrolysis in a flame generated by the reaction of metal compounds of a feed stream (such as, for example, aluminum chloride for fumed alumina) with hydrogen and oxygen. "Fumed metal oxide particles" are also referred to as "pyrogenic metal oxides." The reaction first forms highly dispersed primary particles, which coalesce to form aggregates during the further course of the reaction. The aggregate size of these powders is generally in the range of 0.2-1 μm. These powders can be partially broken down by appropriate grinding and converted to particles in the nanometer (nm) range that are advantageous for the present disclosure.

In one embodiment, the average particle size (D50) of the particles (II) is preferably 5 nm or more and 20 nm or less, more preferably 10 nm or more and 15 nm or less. In one embodiment, the average particle size (D50) of the particles (II) may be 13 nm or 18 nm, or may be within the range of the upper or lower limit of the above numerical range.
By setting the average particle size (D50) of the particles (II) within the above range, it is possible to easily obtain the effect of suppressing the powder material from flying up during molding, which is excellent in fluidity. In addition, it is possible to easily obtain a three-dimensional object having excellent appearance, mechanical properties, and heat resistance. The method for measuring the average particle size (D50) is as described above.

In one embodiment, powder (II) preferably comprises, and more preferably consists of, fumed metal oxide particles having a hydrophobic surface treatment. Metal oxide particles prepared by a flame hydrolysis process are inherently hydrophilic unless specifically treated. To form hydrophobic metal oxide particles, the hydrophilic metal oxide particles are subjected to a chemical post-treatment with a hydrophobic agent. Suitable hydrophobic agents include, but are not limited to, organosilane compounds such as alkoxysilanes, silazanes, and siloxanes.

In one embodiment, the fumed metal oxide particles may be selected from fumed alumina, fumed magnesium oxide, fumed zirconia, fumed titania, fumed ceria, fumed zinc oxide, fumed tin oxide, and any mixtures thereof with each other.
In one embodiment, powder (II) preferably comprises fumed alumina, and more preferably powder (II) consists of fumed alumina.

In one embodiment, the BET specific surface area of the particles (II) is preferably 50 m ² /g to 150 m ² /g, more preferably 60 m ² /g to 140 m ² /g, or even more preferably 70 m ² /g to 130 m ² /g.
The particles (II) having a BET specific surface area in the above range further improve the fluidity of the powder material (X). The BET specific surface area refers to the surface area per unit weight of the powder calculated by applying the BET adsorption isotherm to the adsorption isotherm of an inert gas to calculate the monolayer adsorption amount, and using this value and the molecular cross-sectional area of the adsorbed molecule. In this specification, the BET specific surface area is the BET specific surface area measured in accordance with JIS Z 8830:2013.

In one embodiment, the total content of powder (I) and powder (II) in powder material (X) is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and can be 100% by mass.

Powder material (X) may contain fillers other than powder (I) and powder (II). Examples of fillers other than powder (I) (hereinafter referred to as "other fillers") include various fibrous, granular, and plate-like inorganic and organic fillers, and powders of thermoplastic resins other than polyacetal resins (other thermoplastic resins).

(Other fillers)
Examples of inorganic fillers include granular fillers having an average particle size of 500 nm or less, preferably 400 nm or less, plate-like fillers, and fibrous fillers having an average fiber length of 100 μm or less. By including such inorganic fillers, the powder (I) is more likely to have improved powder flowability and dispersibility. In addition, the strength of the resulting three-dimensional object is more likely to be improved.
However, as shown in the comparative example described later, when silica particles, which are semimetal oxide particles, are blended with the polyacetal copolymer resin powder (I), it becomes difficult to prevent the powder material from flying up during modeling using a 3D printer, and the appearance, mechanical properties, and heat resistance of the resulting model are inferior. Therefore, when the powder material (X) contains silica particles, it is preferable that the content is small, for example, preferably less than 0.001% by mass, more preferably less than 0.0001% by mass, relative to the total mass of the powder material (X), and even more preferably does not contain silica particles.

If the powder material (X) contains other fillers, the content thereof may be 0.01 to 70 parts by mass per 100 parts by mass of the powder (I).

(Other thermoplastic resins)
The powder material (X) may contain a powder of a thermoplastic resin other than the powder (I). Examples of the other thermoplastic resin include polyethylene resin, polypropylene resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyamide resin, etc. These may be used alone or in combination of two or more.
The other thermoplastic resin is preferably blended into the powder material (X) as a powder having an average particle size (D50) of 40 μm to 60 μm. When the powder material (X) contains a powder of the other thermoplastic resin, the blending amount thereof can be 0.01 to 30 parts by mass with respect to 100 parts by mass of the powder (I).

[Method for producing powder material (X) for 3D printers]
The powder material (X) can be produced by mixing the powder (I) and the powder (II) with other additives as necessary by a conventionally known method, such as a mixing method by shaking, a mixing method involving pulverization such as a ball mill, or a mixing method using an agitating blade such as a Henschel mixer (FM mixer).
Since there is a difference in specific gravity between powder (I) and powder (II), a mixing method using a mixer having a mechanism for inverting the powder upside down is more preferable.

[Three-dimensional objects]
The three-dimensional object according to this embodiment is formed using the above-mentioned powder material (X). That is, the three-dimensional object according to this embodiment includes a sintered body of the powder material (X). Such a three-dimensional object has a good appearance and is excellent in mechanical strength and heat resistance.
In one embodiment, the three-dimensional object has a flexural modulus of preferably 1900 MPa or more, more preferably 2000 MPa or more, even more preferably 2050 MPa or more, and even more preferably 2100 MPa or more, measured in accordance with ISO 178. Since the three-dimensional object has the flexural modulus measured in accordance with ISO 178, the three-dimensional object according to one embodiment has excellent mechanical strength.
In one embodiment, the three-dimensional object has a deflection temperature under load measured in accordance with ISO 75-1 and 75-2 of preferably 98° C. or more, and more preferably 100° C. or more. Since the three-dimensional object has the deflection temperature under load measured in accordance with ISO 75-1 and 75-2, the three-dimensional object according to one embodiment has excellent heat resistance.

[Method of manufacturing a three-dimensional object]
The method for producing a three-dimensional object according to this embodiment includes a step of supplying the above-mentioned powder material (X) to a powder sintering 3D printer. Then, the supplied powder material (X) is used to produce a three-dimensional object (production step).

<Modeling process>
In the modeling process using a powder sintering 3D printer, a thin layer is formed with the supplied powder material (X), and the thin layer is irradiated with laser light in a shape corresponding to the cross-sectional shape of the object to be modeled, thereby sintering the powder material (X). By sequentially repeating this process, the sintered thin layers are stacked to produce a three-dimensional model. The conditions for forming a thin layer with the powder material (X), the conditions of the laser light, etc. are not particularly limited, and can be appropriately adjusted according to the settings of the powder sintering 3D printer used. The powder material (X) according to this embodiment includes a powder (I) that is easily melted by irradiation with laser light and has the characteristic that the powder after melting is not sintered immediately (i.e., the balance between melting and sintering is good), and a powder (II) that improves fluidity. Therefore, it is possible to obtain a three-dimensional model that is less likely to have voids or gaps, has excellent appearance, and is excellent in mechanical properties and heat resistance. Since the powder material (X) includes powder (I) and powder (II), there is less chance of the powder material flying up during modeling. As a result, workability is improved.
The powder sintering 3D printer may be a conventionally known printer, such as the product name "Raphael (registered trademark) II 300-HT" manufactured by Aspect Corporation.

Another embodiment of the present disclosure is the use of powder material (X) as a resin raw material for a three-dimensional object produced using a 3D printer, or a method of using the same.

A non-limiting list of exemplary embodiments and combinations of exemplary embodiments of the present disclosure are disclosed below.
[1] A powder material (X) for 3D printers,
A polyacetal copolymer resin powder (I) and metal oxide particles (II),
The content of the particles (II) is 0.01 to 0.5% by mass relative to the total mass of the powder material (X).
[2]
The powder (I) has an average particle size (D50) of 40 μm or more and 60 μm or less,
The particle size (D10) at which the volume-based cumulative frequency of the powder (I) is 10% is 15 μm or more;
The powder material (X) according to [1], wherein the powder (I) has a particle size (D90) at which the volume-based cumulative frequency is 90% of the powder (I) is 100 μm or less.
[3] The powder material (X) according to [1] or [2], wherein the particles (II) comprise fumed metal oxide particles.
[4] The proportion of comonomer units in the total constitutional units (100 mass%) of the polyacetal copolymer resin is 1.0 mass% or more and 6.0 mass% or less,
The powder material (X) according to any one of [1] to [3], wherein the melt flow rate of the powder (I) measured at a temperature of 190 ° C. and a load of 2.16 kgf is 1.0 g / 10 min or more and 8.0 g / 10 min or less.
[5] The powder material (X) according to any one of [1] to [4], wherein the average particle size (D50) of the particles (II) is 5 nm or more and 20 nm or less.
[6] The powder material (X) according to any one of [1] to [5], wherein the particles (II) comprise fumed metal oxide particles having a hydrophobic surface.
[7] The powder material (X) according to any one of [1] to [6], wherein the particles (II) contain fumed alumina.
[8] A three-dimensional object comprising the powder material (X) according to any one of [1] to [7].
[9] A method for producing a three-dimensional object, comprising carrying out modeling using the powder material (X) according to any one of [1] to [7].

The present invention will be explained in more detail below with reference to examples, but the interpretation of this disclosure is not limited to these examples.

[Example 1]
(Preparation of polyacetal copolymer resin powder (I))
Polymerization was carried out using a continuous mixer reactor equipped with an outer jacket through which a heat transfer medium (or coolant) passes and a paddle-equipped rotating shaft having a cross section in the shape of two partially overlapping circles. Specifically, trioxane and a comonomer (1,3-dioxolane) were added to the reactor in the ratios shown in Table 1 while rotating the two paddle-equipped rotating shafts at 150 rpm. Furthermore, methylal was added as a molecular weight regulator in the ratios shown in Table 1.
Next, a catalyst mixture in which boron trifluoride gas as a catalyst was mixed with trioxane so that the boron trifluoride content was 0.005 mass% was continuously added and fed to carry out bulk polymerization. After the polymerization was completed, the reaction product discharged from the reactor was quickly passed through a crusher while being added to an aqueous solution containing 0.1 mass% triethylamine at 80°C to deactivate the catalyst. After separation, washing, and drying, a crude polyacetal copolymer was obtained.

Next, 4 parts by mass of a 5% by mass aqueous solution of triethylamine and 0.03 parts by mass of pentaerythrityl-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant) were added to 100 parts by mass of this crude polyacetal copolymer, and the mixture was melt-kneaded at 210° C. in a twin-screw extruder to remove unstable portions of the crude polyacetal copolymer. 0.3 parts by mass of pentaerythrityl-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 0.15 parts by mass of melamine were further added as stabilizers to 100 parts by mass of the polyacetal copolymer obtained by the above method, and the mixture was melt-kneaded at 210° C. in a twin-screw extruder to obtain a pellet-shaped polyacetal copolymer resin.
The amount of comonomer relative to all monomers (100% by mass) in this polyacetal copolymer resin was 5.9% by mass. The ratio of comonomer units (calculated as oxyethylene units) to all structural units (100% by mass) in the polyacetal copolymer resin, calculated by ¹ H-NMR as described below, was 3.5% by mass.
Next, the obtained polyacetal copolymer resin was pulverized using a jet mill to obtain a polyacetal copolymer resin powder (I).
The average particle size (D50), D90 particle size, D10 particle size, D90/D10, and melt flow rate (MFR) of the obtained powder (I) were measured by the following methods. The results are shown in Table 1.

<Comonomer unit ratio>
The obtained powder (I) was dissolved in deuterated hexafluoroisopropanol to a concentration of 5% by mass to prepare a sample. The sample was analyzed by ¹ H-NMR (Bruker Corporation, product name: AvanceIII 400, magnetic field strength: 400 MHz, reference material: tetramethylsilane, temperature: 27° C., number of integrations: 128) to determine the ratio of the integral ratio of the comonomer unit (oxyethylene group) to the integral ratio of the peaks of all monomers in the polyacetal copolymer resin.

<Average particle size (D50), D90 particle size and D10 particle size>
The average particle size (D50), D90 particle size, and D10 particle size of the powder (I) were measured using a laser diffraction/scattering particle size distribution analyzer (manufactured by Horiba, Ltd., product name: LA-960) and acetone as a dispersion solvent. Each particle size was calculated as an arithmetic average particle size based on volume.

<Melt flow rate (MFR)>
The MFR of the powder (I) was measured using a Melt Indexer L220 manufactured by Tateyama Kagaku High-Technologies Corporation at a temperature of 190° C. and a load of 2.16 kgf in accordance with ISO 1133.

(Preparation of Powder Material (X))
The powder (I) prepared above was mixed with the following particles as shown in Table 1, and mixed in a Henschel mixer (manufactured by Nippon Coke & Engineering Co., Ltd., product name: FM75) at 885 rpm for 1 minute and at 1770 rpm for 3 minutes to prepare powder materials (X) according to the examples and comparative examples. The repose angle of each powder material (X) was evaluated as follows. The results are shown in Table 1.

(Particles mixed into powder (I))
Examples 1 and 2 (metal oxide particles (II)): hydrophobic fumed alumina (manufactured by Nippon Aerosil Co., Ltd., product name: AEROXIDE (registered trademark) Alu C RK, surface-treated with alkylsilane, average particle size 13 nm, BET specific surface area 100 m ² /g)
Comparative Examples 2 and 3 (non-metal oxide particles): hydrophilic fumed silica (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) 200, surface untreated, average particle size 12 nm, BET specific surface area 200 m ² /g)
Comparative Example 4 (non-metal oxide particles): hydrophobic fumed silica (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R974, surface treated with dimethyldichlorosilane, average particle size 12 nm, BET specific surface area 200 m ² /g)

<Angle of repose>
The angle of repose of each of the prepared powder materials (X) was measured as follows. The results are shown in Table 1.
For each powder material (X), 200 ml of powder material was poured into a funnel with an opening diameter of 56 mm and a hole diameter of 12 mm from a height of 1 cm to the upper edge of the funnel under conditions of 25 ° C. and 60% humidity, and was dropped onto a circular platform with a diameter of 12.2 cm located 7.5 cm from the lower mouth of the funnel without vibration. The height of the fallen cone-shaped deposit was measured, and the angle between the horizontal plane and the generatrix was calculated to be the angle of repose (unit: degree). In the case of a powder sintering method 3D printer, the recoater usually operates on the powder surface while continuing to supply the powder material, so if the fluidity of the powder material is low, it will cause the molding property to deteriorate. The smaller the angle of repose, the better the powder fluidity.

(Sculpture)
Each powder material (X) was supplied to a powder sintering 3D printer (manufactured by Aspect Corporation, product name: Raphael II 300-HT, laser type: _CO2 laser (10.6 μm), output: 12 W) to create a test piece of 80 mm × 10 mm × 4 mm as a three-dimensional object. The dispersibility during modeling, the rise of the powder material (X) during modeling, the appearance of the obtained three-dimensional object, the flexural modulus, and the deflection temperature under load were evaluated and measured as follows. The results are shown in Table 1.

<Dispersibility>
The occurrence of agglomerates of metal oxide particles (II) or non-metal oxide particles on the powder surface during molding was observed, and the dispersibility of the powder material (X) was evaluated according to the following evaluation criteria.
A: No agglomerates of metal oxide particles (II) or non-metal oxide particles were visually observed on the powder surface during shaping.
B: Aggregates of metal oxide particles (II) or non-metal oxide particles were visually observed on the powder surface during shaping.
-: Not rated.

<Powder material (X) flying up during molding>
The powder material (X) flying up from the powder surface during molding was visually observed and evaluated according to the following evaluation criteria.
A: No powder material (X) was visually observed rising from the powder surface.
B: Powder material (X) was visually observed floating up from the powder surface.
In the case of powder sintering 3D printers, the recoater usually operates constantly on the powder surface to continuously supply powder material, which causes the powder material to fly up, which can have a negative impact on the working environment and personnel.
The less the powder material (X) is lifted from the powder surface during shaping, the safer the working environment and the human body.

<Appearance of 3D model>
The appearance of the obtained three-dimensionally shaped product was visually evaluated in terms of the presence or absence of warping and voids in the test pieces of the three-dimensionally shaped product.
(Evaluation Criteria)
A: The surface of the molded object was smooth and free of warping and voids.
B: The surface of the molded object was rough, but the molded object had little warping and voids.
C: A molded object was obtained, but it had many warps and voids.
The less warping and voids there are, the more formable the powder material is.

<Flexural modulus>
Using the test pieces of the obtained three-dimensionally molded objects, the flexural modulus was measured in accordance with ISO 178. A three-dimensionally molded object having a higher flexural modulus has better mechanical properties.

<Deflection temperature under load>
The deflection temperature under load of the obtained test pieces of the three-dimensional object was measured in accordance with ISO 75-1 and 75-2. The bending stress was 1.8 MPa. A three-dimensional object having a higher deflection temperature under load has better heat resistance.

As shown in Table 1, the powder material (X) of Examples 1 and 2, which meets the configuration of this embodiment, has the characteristics of an angle of repose of 40° or less (i.e., good fluidity) and good dispersibility, and there is little powder material flying around during molding. The appearance, flexural modulus, and deflection temperature under load of the molded object were also good.
On the other hand, the powder material according to Comparative Example 1-3, which does not satisfy the constitution of including the polyacetal copolymer resin powder (I) and the metal oxide particles (II), did not have the characteristic of good dispersibility. In addition, compared with the powder material of the Example, the powder material flew up a lot during molding, and the appearance, flexural modulus, and deflection temperature under load of the molded object were also inferior. The powder material according to Comparative Example 4 had an angle of repose of 40° or less and had the characteristic of good dispersibility, but compared with the powder material of the Example, the powder material flew up a lot during molding, and the appearance, flexural modulus, and deflection temperature under load of the molded object were also inferior.
From the above results, it was confirmed that the powder material (X) of this embodiment has excellent fluidity and can suppress the powder material from flying up during modeling. It was also confirmed that the use of the powder material (X) of this embodiment can provide a three-dimensional model that has excellent appearance, mechanical properties, and heat resistance.

The powder material of this embodiment has excellent fluidity and can suppress the occurrence of powder flying during modeling, so it can be suitably used as a powder material for various 3D printers, and has industrial applicability.
The three-dimensional structure of the present embodiment has excellent appearance, mechanical properties, and heat resistance, and can therefore be suitably used as various components and the like, and has industrial applicability.
The method for producing a three-dimensional object of the present embodiment enables the production of a three-dimensional object that has excellent appearance, mechanical properties, and heat resistance, and can therefore be suitably used for the production of various three-dimensional objects, etc., and has industrial applicability.

Claims (9)

A powder material (X) for 3D printers,
A polyacetal copolymer resin powder (I) and metal oxide particles (II),
The content of the particles (II) is 0.01 to 0.5% by mass relative to the total mass of the powder material (X). The powder (I) has an average particle size (D50) of 40 μm or more and 60 μm or less,
The particle size (D10) at which the volume-based cumulative frequency of the powder (I) is 10% is 15 μm or more;
The powder material (X) according to claim 1, wherein the powder (I) has a particle size (D90) at which the volume-based cumulative frequency is 90% is 100 μm or less. The powder material (X) of claim 1 or 2, wherein the particles (II) comprise fumed metal oxide particles. The proportion of comonomer units in the total structural units (100% by mass) of the polyacetal copolymer resin is 1.0% by mass or more and 6.0% by mass or less,
The powder material (X) according to claim 1 or 2, wherein the melt flow rate of the powder (I) measured at a temperature of 190°C and a load of 2.16 kgf is 1.0 g/10 min or more and 8.0 g/10 min or less. The powder material (X) according to claim 1 or 2, wherein the average particle size (D50) of the particles (II) is 5 nm or more and 20 nm or less. The powder material (X) of claim 1 or 2, wherein the particles (II) comprise fumed metal oxide particles whose surfaces have been treated to be hydrophobic. The powder material (X) according to claim 1 or 2, wherein the particles (II) comprise fumed alumina. A three-dimensional object comprising the powder material (X) according to claim 1 or 2. A method for manufacturing a three-dimensional object, comprising carrying out modeling using the powder material (X) according to claim 1 or 2.