JP7613153B2 - Thermoplastic resin particles and method for manufacturing three-dimensional objects by powder bed fusion using the same - Google Patents

Description

The present invention relates to thermoplastic resin particles and a method for using them to manufacture three-dimensional objects by powder bed fusion bonding.

Powder bed fusion is known as a 3D printing technology for producing three-dimensional objects (hereinafter, sometimes referred to as "modeled objects"). In this method, after providing a layer of thermoplastic resin particles, a laser is selectively irradiated at a position corresponding to the cross section of the object to melt the thermoplastic resin particles and bond and laminate the layers of thermoplastic resin particles together. In addition, an electromagnetic radiation absorber or suppressor is printed at a position corresponding to the cross section, and selectively absorbs thermal energy such as infrared rays to melt the thermoplastic resin particles and bond and laminate the layers of thermoplastic resin particles together to form a three-dimensional object (hereinafter, sometimes referred to as "modeling"). Compared to other methods for creating three-dimensional objects, this method has the advantage of being able to model high-strength resin, and in recent years, there has been an increasing trend to use models obtained by this method as final products.

In light of this, there is an increasing demand for high-strength objects, and in order to obtain such objects, it is important to prevent the formation of voids inside the object that can cause defects. In other words, when laying down layers of thermoplastic resin particles, it is necessary to prepare particles that are layered at a high density so that as little gas as possible remaining in the gaps between the raw thermoplastic resin particles remains inside the object.

In response to the above problem, Patent Document 1 discloses bimodal particles made of amorphous resin having a first D50 (particle size at which the cumulative curve from the small particle size side is 50%) of less than 1 mm and a D50 that is 0.414 times the first D50, and claims that undesired voids can be prevented by highly packed particles. Patent Document 2 discloses resin powder of 30 μm to 100 μm, including resin particles with a primary particle size of 1.50 μm or less, and claims that the generation of internal voids during lamination can be prevented.

Patent No. 6552727 JP 2020-189965 A

However, although Patent Document 1 describes two particle size ratios that theoretically result in high packing, it does not take into account interactions such as interparticle adhesion. In other words, generally, the more the particles are packed, the lower the fluidity tends to be, and although the particle packing rate is high, there are problems with fluidity.

In addition, in Patent Document 2, fine resin particles are used as a lubricant to prevent static electricity and achieve excellent fluidity. However, sufficient consideration has not been given to the density of the stacked particles, and the particle packing rate has not been sufficiently increased.

Therefore, the objective of the present invention is to provide thermoplastic resin particles with a high particle packing rate and excellent fluidity in order to obtain a highly packed object in three-dimensional modeling using the powder bed fusion method.

In order to solve the above problems, the thermoplastic resin particles used in the powder bed fusion method of the present invention are as follows:
Thermoplastic resin particles, characterized in that the thermoplastic resin particles are spherical and have a D50 particle size of 10 μm or more and 100 μm or less, the volumetric particle size distribution is bimodal, and when the mode diameter of the larger peak in the volumetric particle size distribution is S1 and the mode diameter of the smaller peak is S2, S2/S1 is 0.10 or more and 0.45 or less, and the value obtained by dividing the tap density of the thermoplastic resin particles by the true density of the resin constituting the thermoplastic resin particles is 0.72 or more and 0.9 or less.

The method for producing a three-dimensional object of the present invention is a method for producing a three-dimensional object by powder bed fusion bonding using the thermoplastic resin particles.

The present invention aims to provide thermoplastic resin particles with a high particle packing rate and excellent fluidity in order to obtain highly packed objects in three-dimensional modeling using the powder bed fusion method.

The present invention is explained in detail below.

In the powder bed fusion molding method, a layer of thermoplastic resin particles, which is the raw material, is formed, and then the particles at the position corresponding to the cross section of the desired object are melted and welded by a heat source. When forming a layer of thermoplastic resin particles, gas is always present in the gaps between the particles, so in order to obtain a high-density object without voids, the gas needs to be discharged from the system when melting and welding. However, in conventional thermoplastic resin particles, the density is low when filled, and a relatively large amount of gas is present when a layer of thermoplastic resin particles is formed, so the gas cannot be completely discharged when melting and welding, and voids exist in the obtained object, and the density is lower than the true density of the thermoplastic resin raw material. In response to this, a method is known in which the above-mentioned thermoplastic resin particles, that is, bimodal particles made of a particle having a first D50 of less than 1 mm and an amorphous resin having a D50 of 0.414 times the first D50, are used for close packing to minimize voids in the particle state. It is also said that the particles are highly packed, preventing unwanted voids in the molded object.

However, in a randomly mixed particle system, the ideal close-packed structure does not form. Furthermore, generally, the higher the packing rate, the lower the powder's fluidity, making it difficult to form a uniform layer of thermoplastic resin particles. For this reason, it has not been possible to achieve both good thermoplastic resin particle layer forming properties (powder spreading properties) and high-density molded objects.

As a result of thorough research into this issue, the inventors discovered that thermoplastic resin particles with a bimodal peak at a specific particle size ratio and high tap density have both good fluidity (spreadability) and high packing properties, and that the use of these particles allows the production of high-density molded objects.

In other words, the thermoplastic resin particles used in the powder bed fusion method of the present invention are thermoplastic resin particles for producing a three-dimensional object by the powder bed fusion method, characterized in that the volumetric particle size distribution is bimodal, and when the mode diameter of the larger peak in the volumetric particle size distribution is S1 and the mode diameter of the smaller peak is S2, S2/S1 is 0.1 to 0.45, and the tap density of the thermoplastic resin particles divided by the true density of the resin that constitutes the thermoplastic resin is 0.6 to 0.9.

The powder bed fusion method in the present invention is a 3D printing method in which a layer of thermoplastic resin particles, which is the raw material, is formed, and the position corresponding to the cross section of the desired object is melted and welded by a heat source, and a layer of thermoplastic resin particles is further formed on top of the layer, and this operation is repeated to obtain a three-dimensional object. In this case, electromagnetic radiation is preferably used as the heat source, and more preferably coherent electromagnetic radiation (so-called laser light). When non-coherent light such as a halogen lamp is used as the electromagnetic radiation, a light energy absorber or a light energy absorption inhibitor may be printed at a position corresponding to the cross section of the desired object to efficiently utilize the energy of the electromagnetic radiation. The light energy absorber is a substance that absorbs electromagnetic radiation. Examples of such substances include carbon black, carbon fiber, copper hydroxyphosphate, near infrared absorbing dyes, near infrared absorbing pigments, metal nanoparticles, polythiophene, poly(p-phenylene sulfide), polyaniline, poly(pyrrole), polyacetylene, poly(p-phenylene vinylene), polyparaphenylene, poly(styrene sulfonate), poly(3,4-ethylenedioxythiophene)-poly(styrene phosphonate) p-diethylaminobenzaldehyde diphenylhydrazone, or conjugated polymers consisting of combinations thereof, which may be used alone or in combination. The light energy absorption inhibitor is a substance that does not easily absorb electromagnetic radiation. Examples of such substances include substances that reflect electromagnetic radiation such as titanium, heat insulating powders such as mica powder and ceramic powder, and water, which may be used alone or in combination. These light energy absorbers or light energy absorption inhibitors may be used alone or in combination. In the process of printing the light energy absorbent or light energy inhibitor into a shape corresponding to the cross-sectional shape of the desired object, a known method such as inkjet printing can be used. In this case, the light energy absorbent or light energy absorption inhibitor may be used as is, or may be dispersed or dissolved in a solvent.

The thermoplastic resin particles in the present invention are spherical or nearly spherical particles made of a thermoplastic resin. Here, known thermoplastic resins can be used as needed. Specific examples include polycarbonate, polyacetal, polyester, polysulfone, polyarylate, polyurethane, polyamide, polyarylene sulfide, polyphenylene sulfide, polyamideimide, polyetheretherketone, polyetherimide, polyethersulfone, and other polyethers, polyethylene, polypropylene, vinyl polymers such as polymethyl methacrylate, and alloys and copolymers thereof. Among them, in the powder bed fusion bonding method, crystalline thermoplastic resin particles are preferred because precise objects can be obtained by shaping at a temperature above the crystallization temperature and below the melting point of the thermoplastic resin used, and polyacetal, polyester, polyetheretherketone, polyamide, polyurethane, polyphenylene sulfide, polyethylene, and polypropylene are preferred. Polyether, polyester, polyamide, polyphenylene sulfide, and polyamideimide are more preferred because they have excellent solvent resistance, polyester, polyamide, polyphenylene sulfide, and polyether ether ketone are even more preferred because they have excellent heat resistance and can be molded with a general-purpose 3D printer, and polyamide is the most preferred because it has excellent toughness. These may be used alone or in combination. For example, different types of thermoplastic resins may be copolymerized, may be alloyed in the particles, or particles of different thermoplastic resins may be mixed.

The polyester in this invention is a polymer containing ester bonds in the repeating structure, and is obtained by polycondensation of a polybasic acid or a polybasic acid dialkyl ester and a polyhydric alcohol as the main raw materials. Specific examples of polyesters include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polycyclohexane dimethylene terephthalate, polyhexylene terephthalate, polyethylene naphthalate, polypropylene naphthalate, polybutylene naphthalate, polyethylene isophthalate/terephthalate, polypropylene isophthalate/terephthalate, polybutylene isophthalate/terephthalate, polyethylene terephthalate/naphthalate, polypropylene terephthalate/naphthalate, polybutylene terephthalate/naphthalate, polybutylene terephthalate/decane dicarboxylate, polyethylene terephthalate/cyclohexane dimethylene terephthalate, polyethylene terephthalate/polyethylene glycol, polypropylene terephthalate/polyethylene glycol, polybutylene terephthalate/polyethylene glycol, polyethylene terephthalate/polytetramethylene glycol, polypropylene terephthalate/polytetramethylene glycol, polybutylene terephthalate/polytetramethylene glycol, polyethylene Polyethylene terephthalate/isophthalate/polytetramethylene glycol, polypropylene terephthalate/isophthalate/polytetramethylene glycol, polybutylene terephthalate/isophthalate/polytetramethylene glycol, polyethylene terephthalate/succinate, polypropylene terephthalate/succinate, polybutylene terephthalate/succinate, polyethylene terephthalate/adipate, polypropylene terephthalate/adipate, polybutylene terephthalate/adipate, polyethylene terephthalate/sebac polypropylene terephthalate/sebacate, polybutylene terephthalate/sebacate, polyethylene terephthalate/isophthalate/adipate, polypropylene terephthalate/isophthalate/adipate, polybutylene terephthalate/isophthalate/succinate, polybutylene terephthalate/isophthalate/adipate, polybutylene terephthalate/isophthalate/sebacate, bisphenol A/terephthalic acid, bisphenol A/isophthalic acid, bisphenol A/terephthalic acid/isophthalic acid, etc.

Among these polyester resins, polybutylene terephthalate resin (PBT resin) is preferably used. PBT resin is composed of 80% by weight or more, preferably 85% by weight or more of polybutylene terephthalate, and may be copolymerized or mixed with other resins other than PBT resin.

In the present invention, the polyamide is a polymer containing an amide bond in the repeating structure. Such polyamides are produced by known methods such as polycondensation reaction of amino acids, anionic ring-opening polymerization of lactams and an initiator, cationic ring-opening polymerization or ring-opening polymerization after hydrolysis with water, polycondensation reaction of dicarboxylic acids and diamines or their salts, or a combination of these. Specific examples of such polyamides include polyamide 4, polyamide 5, polyamide 6, polyamide 8, polyamide 11, polyamide 12, polyamide 44, polyamide 46, polyamide 410, polyamide 411, polyamide 412, polyamide 56, polyamide 510, polyamide 511, polyamide 512, polyamide 64, polyamide 65, polyamide 66, polyamide 610, polyamide 611, polyamide 612, polyamide 104, polyamide 106, polyamide 1010, polyamide 1011, polyamide 1012, polyamide 124, polyamide 125, polyamide 126, polyamide 1210, polyamide 1212, polyamide 6T, polyamide 10T, polyamide 12T, polyamide 6I, polyamide 10I, polyamide 12I, and further copolymers of these polyamides, such as polyamide 6/polyamide 66 copolymer. Since they can be manufactured relatively inexpensively, polyamide 6, polyamide 11, polyamide 12, polyamide 46, polyamide 66, polyamide 610, polyamide 612, polyamide 106, polyamide 1010, polyamide 1011, polyamide 1012, polyamide 1212, polyamide 6T, polyamide 6I, or a copolymer consisting of a combination selected from these are preferred. From the viewpoint of having a melting point and crystallization temperature suitable as a material for 3D printers, polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 1010, polyamide 1012, polyamide 1212, polyamide 6T, polyamide 6I, or a copolymer consisting of a combination selected from these are more preferred. From the viewpoint of excellent balance between elastic modulus and toughness, polyamide 6, polyamide 12, polyamide 66, polyamide 1010, polyamide 1012, polyamide 6T, polyamide 6I, or a copolymer consisting of a combination selected from these are more preferable, and from the viewpoint of excellent solvent resistance, polyamide 6, polyamide 12, polyamide 66, polyamide 6T, polyamide 6I, or a copolymer consisting of a combination selected from these are significantly more preferable, and polyamide 6 is the most preferable.

The polyamide may contain other copolymerizable components as long as the invention is not impaired. The copolymerizable components may be appropriately selected from elastomer components such as polyolefins and polyalkylene glycols that impart flexibility, and rigid aromatic components that improve heat resistance and strength. In addition, the polyamide may be end-capped with a substance such as benzoic acid, hexanoic acid, terephthalic acid, isophthalic acid, benzylamine, aniline, hexylamine, p-diaminobenzene, or m-diaminobenzene.

The thermoplastic resin particles of the present invention may contain antioxidants, heat stabilizers, weather resistance agents, lubricants, pigments, dyes, plasticizers, antistatic agents, flame retardants, flow modifiers, etc. for the purpose of improving moldability, improving the heat resistance of the particles, and improving the heat resistance, flame retardancy, and weather resistance of the molded object. Two or more of these may be used in combination.

Examples of such antioxidants include organic antioxidants such as phenols, amines, sulfurs, lactones, and phosphites; and inorganic salt-based antioxidants such as copper salts such as copper chloride, copper bromide, copper iodide, copper acetate, copper acetylacetonate, copper carbonate, copper borofluoride, copper citrate, copper hydroxide, copper nitrate, copper sulfate, and copper oxalate; and manganese salts. Commercially available antioxidants containing these as the main component may also be used as appropriate.

Such flame retardants include nitrogen-based flame retardants such as melamine cyanurate, metal hydroxide flame retardants such as magnesium hydroxide and aluminum hydroxide, phosphorus-based flame retardants such as ammonium polyphosphate, melamine polyphosphate, metal phosphinates and red phosphorus, and halogen-based flame retardants such as brominated polystyrene, brominated polyphenylene oxide, brominated polycarbonate and brominated epoxy resin. Commercially available flame retardants containing these as the main components may also be used as appropriate.

As such flow modifiers, fatty acid metal salts are preferably used, and examples thereof include capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, and melissic acid.

Furthermore, the thermoplastic resin particles in the present invention may contain a lubricant to improve fluidity. Examples of such lubricants include silica (silicon dioxide) such as fused silica, crystalline silica, and amorphous silica, alumina (aluminum oxide), alumina colloid (alumina sol), and alumina white, calcium carbonate such as light calcium carbonate, heavy calcium carbonate, finely powdered calcium carbonate, and special calcium carbonate-based fillers, nepheline syenite fine powder, calcined clay such as montmorillonite and bentonite, clay (aluminum silicate powder) such as silane-modified clay, silicic acid-containing compounds such as talc, diatomaceous earth, and silica sand, crushed natural minerals such as pumice powder, pumice balloon, slate powder, and mica powder, barium sulfate, litho Examples of suitable fillers include minerals such as porcelain, calcium sulfate, molybdenum disulfide, and graphite; glass fillers such as glass fibers, glass beads, glass flakes, and foamed glass beads; fly ash spheres, volcanic glass hollow bodies, synthetic inorganic hollow bodies, single crystal potassium titanate, carbon nanotubes, carbon hollow spheres, fullerenes, anthracite powder, artificial cryolite, titanium oxide, magnesium oxide, basic magnesium carbonate, dolomite, potassium titanate, calcium sulfite, mica, asbestos, calcium silicate, molybdenum sulfide, and fine particles of thermosetting resins such as melamine resin and benzoguanamine resin. More preferred are silica, alumina, calcium carbonate powder, and titanium oxide. Particularly preferred are silica and alumina, which are hard and contribute to improving strength.

Commercially available products of this type of silica include the fumed silica "AEROSIL" (registered trademark) series manufactured by Nippon Aerosil Co., Ltd., the dry silica "Reolosil" (registered trademark) series manufactured by Tokuyama Corporation, and the sol-gel silica powder X-24 series manufactured by Shin-Etsu Chemical Co., Ltd.

The average particle size of the lubricant is preferably 20 nm or more and 1 μm or less. The upper limit of the average particle size of the lubricant is preferably 1 μm, more preferably 500 nm, more preferably 400 nm, particularly preferably 300 nm, and most preferably 200 nm. The lower limit is preferably 20 nm, more preferably 30 nm, more preferably 50 nm, and particularly preferably 100 nm. If the average particle size of the lubricant is within the above range, the fluidity of the thermoplastic resin particles is improved and the lubricant can be uniformly dispersed in the thermoplastic resin particles.

The average particle size of the lubricant in this invention is the particle size (D50 particle size) at which the cumulative curve from the small particle side becomes 50% when the cumulative curve is calculated with the total volume of the microparticles obtained by analyzing the scattered light of a laser by dynamic light scattering method as 100%.

The amount of the lubricant is preferably more than 0.01 parts by mass and less than 5 parts by mass with respect to 100 parts by mass of the thermoplastic resin particles. The upper limit of the amount is preferably 3 parts by mass or less, more preferably 1 part by mass or less, even more preferably 0.5 parts by mass or less, particularly preferably 0.3 parts by mass or less, and extremely preferably 0.1 parts by mass or less. The lower limit of the amount is preferably more than 0.02 parts by mass, more preferably more than 0.03 parts by mass, and even more preferably more than 0.04 parts by mass. If the amount of the lubricant is more than 0.01 parts by mass, the flowability of the thermoplastic resin particles is further improved, and the filling property when molded is increased, so that voids that cause defects in mechanical properties are less likely to occur, and the obtained molded product exhibits high strength. If the amount of the lubricant is less than 5 parts by mass, the lubricant does not cover the surface of the thermoplastic resin particles, which prevents sintering, and a molded product with high strength can be obtained.

The weight-average molecular weight of the resin constituting the thermoplastic resin particles in the present invention is preferably in the range of 8,000 or more and 300,000 or less. If the weight-average molecular weight is less than 8,000, the physical properties of the manufactured object may be inferior, so 8,000 or more is preferable, 10,000 or more is more preferable, 30,000 or more is even more preferable, and 40,000 or more is extremely preferable. Also, if the weight-average molecular weight exceeds 300,000, the viscosity is too high when melting and welding the particles, and the particles do not weld together well, so 300,000 or less is preferable, 200,000 or less is more preferable, and 150,000 or less is even more preferable.

The range of the molecular weight distribution of the thermoplastic resin in the present invention is preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less, from the viewpoint of suppressing the formation of undesired voids during molding. By definition, the lower limit is 1.

In the present invention, the weight average molecular weight refers to the weight average molecular weight measured by gel permeation chromatography using hexafluoroisopropanol as a solvent and converted into polymethyl methacrylate. If the thermoplastic resin is not soluble in hexafluoroisopropanol, the value measured after dissolving it in pentafluorophenol is used. The molecular weight distribution refers to the weight average molecular weight measured by gel permeation chromatography and converted into polymethyl methacrylate, divided by the number average molecular weight.

The thermoplastic resin particles in the present invention are characterized by a bimodal volumetric particle size distribution. The volumetric particle size distribution is a distribution of particle sizes weighted by volume, and the bimodal volumetric particle size distribution means that when the particle size distribution is plotted on a coordinate system with particle size on the horizontal axis and volumetric frequency on the vertical axis, the graph has two maximum values. The particle size distribution of the thermoplastic resin particles can be measured with a laser diffraction particle size distribution meter. In the present invention, when the particle size of the larger peak in the volumetric particle size distribution graph is S1 and the particle size of the smaller peak is S2, S2/S1 is 0.10 or more and 0.45 or less. If S2/S1 exceeds 0.45, the thermoplastic resin particles are not sufficiently packed, and the purpose of obtaining a high-density molded object cannot be achieved. In order to improve the packing rate, S2/S1 is preferably 0.4 or less, more preferably 0.35 or less, and even more preferably 0.30 or less. If S2/S1 is less than 0.10, the thermoplastic resin particles will not be sufficiently packed, and a high-density molded object will not be obtained. To improve the packing rate, S2/S1 is preferably 0.15 or more, and more preferably 0.20 or more.

In the present invention, the particle diameter S1 of the larger peak of the thermoplastic resin particles is preferably 30 μm or more and 120 μm or less. If S1 exceeds 120 μm, when forming a layer of thermoplastic resin particles by the powder bed fusion method, the thickness of the layer cannot be made thin, and a highly detailed molded object tends not to be obtained. From the viewpoint of obtaining a more detailed molded object, S1 is preferably 100 μm or less, more preferably 80 μm or less. Also, if S1 is less than 30 μm, the number of fine particles increases in the entire thermoplastic resin particles, which makes it easy for aggregation to occur and reduces fluidity, and therefore the layer of thermoplastic resin particles may not be formed well. From the viewpoint of suppressing the occurrence of aggregation, S1 is preferably 40 μm or more, more preferably 50 μm or more.

In the present invention, the particle size S2 of the smaller peak of the thermoplastic resin particles is preferably 5 μm or more and 40 μm or less. If S2 is larger than 40 μm, the amount of coarse particles increases in the entire thermoplastic resin particles, and when a layer of thermoplastic resin particles is formed by the powder bed fusion method, the layer thickness cannot be thinned and a highly detailed object cannot be obtained. From the viewpoint of obtaining a highly detailed object, 30 μm or less is preferable. If S2 is smaller than 5 μm, the thermoplastic resin particles are likely to aggregate and the fluidity is reduced, so that a layer of thermoplastic resin particles cannot be formed well. From the viewpoint of suppressing the occurrence of aggregation, S2 is preferably 10 μm or more, and more preferably 15 μm or more.

The thermoplastic resin particles in the present invention preferably have a D50 particle size of 10 μm or more and 100 μm or less. If the D50 particle size is 10 μm or less, fine particles increase in the entire thermoplastic resin particles, which makes it easy for aggregation to occur and reduces fluidity, and therefore the layer of thermoplastic resin particles may not be formed well. From the viewpoint of suppressing the occurrence of aggregation, the D50 particle size is preferably 20 μm or more, and more preferably 30 μm or more. If the D50 particle size is larger than 100 μm, when forming a layer of thermoplastic resin particles by the powder bed fusion method, the layer thickness cannot be thinned, and a highly detailed molded object may not be obtained. From the viewpoint of obtaining a highly detailed molded object, the D50 particle size is preferably 70 μm or less, and more preferably 60 μm or less.

In addition, in the present invention, the D10 particle size is preferably 1 μm or more and 30 μm or less. When the D10 particle size is less than 1 μm, the thermoplastic resin particles are likely to aggregate and the fluidity is reduced, so that the layer of the thermoplastic resin particles may not be formed well. From the viewpoint of suppressing the occurrence of aggregation, the D10 particle size is preferably 3 μm or more, and more preferably 5 μm or more. When the D10 particle size is 30 μm or more, the number of coarse particles increases in the entire plastic resin particles, so that when a layer of the thermoplastic resin particles is formed by the powder bed fusion method, the layer thickness cannot be thinned, and a highly fine molded object cannot be obtained. From the viewpoint of obtaining a highly fine molded object, the D10 particle size is preferably 25 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less. When the D10 particle size is less than 1 μm, the thermoplastic resin particles are likely to aggregate and the fluidity is reduced, so that the layer of the thermoplastic resin particles may not be formed well. From the viewpoint of suppressing the occurrence of aggregation, the D10 particle size is preferably 3 μm or more, and more preferably 5 μm or more.

In addition, in the present invention, it is preferable that the D90 particle size is 50 μm or more and 120 μm or less. If the D90 particle size is 120 μm or more, the number of coarse particles increases, so when forming a layer of thermoplastic resin particles by the powder bed fusion method, the layer thickness cannot be thinned, and a highly detailed molded object may not be obtained. From the viewpoint of obtaining a highly detailed molded object, the D90 particle size is preferably 100 μm or less, and more preferably 90 μm or less. If the D90 particle size is less than 50 μm, the number of fine particles increases in the entire thermoplastic resin particles, which makes it easy for aggregation to occur and reduces fluidity, so that a layer of thermoplastic resin particles may not be formed well. From the viewpoint of suppressing the occurrence of aggregation, the D90 particle size is preferably 55 μm or more, and more preferably 60 μm or more.

The D10, D50, and D90 particle sizes of thermoplastic resin particles are the particle sizes at which the cumulative frequency from the small particle size side of the particle size distribution measured by a laser diffraction particle size distribution meter is 10%, 50%, and 90%, respectively.

In the volume-based particle size distribution of the thermoplastic resin particles of the present invention, when the frequency of particle size S1 is F1 and the frequency of particle size S2 is F2, it is preferable that F2/F1 is 0.15 or more and 2 or less. When it is in this range, it becomes easier to achieve both the packing property and the fluidity of the particles. It is more preferable that the lower limit of F2/F1 is 0.2 or more, and the upper limit is more preferably 1 or less, and even more preferably 0.75 or less.

The thermoplastic resin particles of the present invention are characterized in that the tap density of the thermoplastic resin particles divided by the true density of the resin constituting the thermoplastic resin particles is 0.6 or more and 0.9 or less. When forming a layer of thermoplastic resin particles in the powder bed fusion method, the particles are compressed and close to a tapped state. Therefore, in order to obtain a high-density molded object, the filling rate in the tapped state, that is, the value divided by the true density of the resin constituting the thermoplastic resin particles (tap filling rate) is important. Thermoplastic resin particles having a value divided by the true density of the resin constituting the thermoplastic resin particles of 0.6 or more and 0.9 or less are packed at a sufficiently high density to reduce the porosity of the molded object, and good fluidity (powder spreadability) is also ensured. If the value obtained by dividing the tap density of the thermoplastic resin particles by the true density of the resin constituting the thermoplastic resin particles is less than 0.6, the particle filling rate of the layer of thermoplastic resin particles formed during molding in the powder bed fusion method is insufficient, and the voids in the desired molded object cannot be sufficiently reduced. On the other hand, if the value obtained by dividing the tap density of the thermoplastic resin particles by the true density of the resin constituting the thermoplastic resin particles is greater than 0.9, the filling property is too high and sufficient fluidity cannot be ensured to form a layer of the thermoplastic resin particles. From the viewpoint of reducing voids in the molded product, the value obtained by dividing the tap density of the thermoplastic resin particles by the true density of the resin constituting the thermoplastic resin particles is preferably 0.65 or more, more preferably 0.7 or more, and even more preferably 0.75 or more, and from the viewpoint of increasing the fluidity of the thermoplastic resin particles, it is preferably less than 0.85.

The tap density of the thermoplastic resin particles refers to the mass per unit volume when the powder is gently filled into a container and then densely packed by tapping, and is measured in accordance with the Japanese Industrial Standards (JIS) JIS K 7370 (2000) "Determination of Packed Apparent Bulk Density". The true density of the resin that constitutes the thermoplastic resin particles is measured in accordance with the Japanese Industrial Standards (JIS) JIS Z 8807 (2012) "Method of measurement of density and specific gravity of solids".

The present invention is also characterized in that the Hausner ratio, which is the value obtained by dividing the tap bulk density of the thermoplastic resin particles by the apparent bulk density, is 1 or more and 1.5 or less. Here, the apparent bulk density refers to the mass per unit volume when the thermoplastic resin particles are filled in a container. Here, the apparent bulk density is measured in accordance with the Japanese Industrial Standards (JIS) K 7365 (1999) "Method of determining the apparent density of a material that can be poured from a specified funnel". In general, the value obtained by dividing the tap bulk density by the apparent bulk density is called the Hausner ratio, which is an index of the fluidity of a powder, and the smaller the value, the higher the fluidity. In principle, the tap bulk density cannot be smaller than the apparent bulk density, so the lower limit of the value obtained by dividing the tap bulk density of the thermoplastic resin particles by the apparent bulk density is 1. If the tap bulk density of the thermoplastic resin particles divided by the apparent bulk density exceeds 1.5, the fluidity is low and a layer of the thermoplastic resin particles cannot be formed neatly. From the viewpoint of making the surface of the obtained molded object more refined, it is preferably 1.3 or less, more preferably 1.25 or less, and even more preferably 1.2 or less.

The sphericity of the thermoplastic resin particles in the present invention is preferably 80 or more. The sphericity is a value expressed by 100 x minor axis/major axis, where the major axis is the longest diameter of a particle and the minor axis is the largest diameter perpendicular to the major axis, when the particle is observed by an electron microscope or the like. In other words, the closer this value is to 100, the more spherical the shape is, and the maximum value is 100 according to the calculation method. From the viewpoint that the closer the shape is to a perfect sphere, the better the fluidity, the more preferably the sphericity of the thermoplastic resin particles is 85 or more, more preferably 90 or more, and particularly preferably 95 or more.

The thermoplastic resin particles in the present invention are preferably ones with a smooth surface, since this improves the fluidity. Surface smoothness can be evaluated by the linseed oil absorption of the particles per unit weight. That is, the smoother the surface, the less uneven the particles are, and the smaller the linseed oil absorption, which indicates the amount of linseed oil absorbed. The linseed oil absorption of the polyamide microparticles of the present invention is preferably 100 mL/100 g or less, more preferably 80 mL/100 g or less, even more preferably 70 mL/100 g or less, and particularly preferably 60 mL/100 g or less. The lower limit of the linseed oil absorption is 0 mL/100 g from the definition. The linseed oil absorption is measured in accordance with the Japanese Industrial Standards (JIS) JIS K 5101 "Pigment Test Method - Refined Linseed Oil Method". Surface smoothness can also be expressed by the BET specific surface area by gas adsorption, and the smoother the surface, the smaller the BET specific surface area. Specifically, it is preferably 10 ^m2 /g or less, more preferably 5 ^m2 /g or less, even more preferably 3 ^m2 /g or less, particularly preferably 1 ^m2 /g or less, and most preferably 0.5 ^m2 /g or less. The lower limit of the BET specific surface area is 0 ^m2 /g by definition. The BET specific surface area is measured in accordance with the Japanese Industrial Standards (JIS) JIS R1626 (1996) "Method of measuring specific surface area by gas adsorption BET method".

The thermoplastic resin particles in the present invention can be prepared by mixing thermoplastic resin particles having two different particle size distributions. The respective thermoplastic resin particles before mixing may be produced by any method, and any existing method can be used. Examples of such methods include a method of physically grinding a thermoplastic resin prepared in advance, a chemical grinding method in which a solution in which a thermoplastic resin prepared in advance is dissolved in a good solvent is cooled or added to a poor solvent to precipitate as a powder, a kneading method in which a thermoplastic resin constituting the thermoplastic resin particles and a resin that is incompatible with it are melt-kneaded to form a sea-island structure, and then the sea phase is dissolved, an emulsion method in which an emulsion in which a solution in which a thermoplastic resin constituting the thermoplastic resin particles is dissolved in a good solvent is used as the dispersed phase, and then particles are precipitated, a method in which a thermoplastic resin dissolved in a good solvent is melted and kneaded to form an island-sea structure, and then the sea phase is dissolved, an emulsion method in which particles are precipitated after forming an emulsion in which a solution in which a thermoplastic resin constituting the thermoplastic resin particles is dissolved in a good solvent is used as the dispersed phase, and a method in which a thermoplastic resin dissolved in a good solvent is melted and kneaded to form an island-sea structure, and then the sea phase is dissolved, and then the particles are precipitated. Examples of such methods include the atomization method, in which a plastic resin is atomized by spraying to produce particles; suspension polymerization, in which a water-insoluble monomer or a solution of a monomer is dispersed in an aqueous medium and polymerized; emulsion polymerization, in which micelles are formed in an aqueous medium using a surfactant or the like, and polymerized and granulated inside the micelles; precipitation polymerization, in which a monomer is soluble in a solvent but a polymer is insoluble in the solvent, is polymerized in a medium in which the monomer is soluble, but the polymer is insoluble; seed polymerization, in which a seed particle is absorbed by a monomer and then polymerized to increase the particle size; and a method in which polymerization is performed in a polymer medium that is compatible with the monomer but not with the polymer, and polymer particles are precipitated after the polymerization is completed. Since spherical particles with a particle size of about 1 to 300 μm can be obtained simultaneously with the polymerization, a method in which polymerization is performed in a polymer medium that is compatible with the monomer but not with the polymer, and polymer particles are precipitated after the polymerization is completed is preferable. After producing thermoplastic resin particles by these methods, the particle size distribution may be appropriately adjusted using a particle separator such as a sieve. In addition, commercially available particles may be purchased and mixed before mixing, and further crushing, classification, etc. may be performed as appropriate before mixing.

When the thermoplastic resin particles of the present invention are produced by mixing thermoplastic resin particles having two different particle size distributions, each of the thermoplastic resin particles may have any chemical composition as long as the desired chemical composition is obtained after mixing.

When the thermoplastic resin particles of the present invention are produced by mixing thermoplastic resin particles having two different particle size distributions, the D50 particle size of the thermoplastic resin particles before mixing is 5 μm or more and 120 μm or less. If it is outside this range, the particle size distribution of the thermoplastic resin particles after mixing will not fall within the desired range. It is preferably 10 μm or more and 100 μm or less.

When the thermoplastic resin particles of the present invention are produced by mixing thermoplastic resin particles having two different particle size distributions, it is preferable that the volumetric particle size distribution of the thermoplastic resin particles before mixing is monodisperse, from the viewpoint of easily controlling the particle size distribution of the thermoplastic resin particles after mixing. A monodisperse volumetric particle size distribution means that when the particle size distribution is plotted on a coordinate system with particle size on the horizontal axis and volumetric frequency on the vertical axis, the graph has one maximum value.

When the thermoplastic resin particles of the present invention are produced by mixing thermoplastic resin particles having two different particle size distributions, the particle size distribution index of the thermoplastic resin particles before mixing is preferably 3.0 or less, and more preferably 2.5 or less, from the viewpoint of increasing the tap bulk density of the thermoplastic resin particles after mixing. Theoretically, the lower limit is 1. Here, the particle size distribution index is the value obtained by dividing the volume average particle size measured by a laser diffraction particle size distribution meter by the number average particle size.

When the thermoplastic resin particles of the present invention are produced by mixing thermoplastic resin particles having two different particle size distributions, the sphericity is preferably 80 or more, more preferably 85 or more, even more preferably 90 or more, and most preferably 95 or more, from the viewpoint of improving the fluidity of the thermoplastic resin particles after mixing. The upper limit of the sphericity is 100 by definition.

When the thermoplastic resin particles of the present invention are produced by mixing thermoplastic resin particles having two different particle size distributions, it is preferable that the surface is smooth in order to improve the fluidity of the thermoplastic resin particles after mixing.

In the present invention, when the thermoplastic resin particles are prepared by mixing two different types of thermoplastic resin particles having different particle size distributions, any existing method such as dry blending or wet blending can be selected as the method for mixing the particles. Examples of dry blending methods include a container rotation type and a container fixed for stirring. As a container rotation type mixer, any shape such as a horizontal cylinder type, an inclined cylinder type, a V-shape, a double cone type, a regular cube type, an S-shape, or a continuous V-shape can be selected according to the particle properties. As a mixer for stirring with a fixed container, a ribbon type, a screw type, a rod type, or a combination of these with stirring blades can be selected, and a horizontal or vertical rotation axis can be selected as desired. In addition, mixers such as a vibration mill and a vibration sieve can be used, and a combination of these mixing methods can be used. Furthermore, wet mixing may be used, and a method in which a slurry is prepared with a medium such as water in which the thermoplastic resin particles do not dissolve, and the whole is homogenized using a mixing device such as a screw, and then dried can be used.

Furthermore, within the scope of the present invention, when mixing or after mixing thermoplastic resin particles having two different particle size distributions, lubricants for improving flowability, antioxidants, heat stabilizers, weather resistance agents, lubricants, pigments, dyes, plasticizers, antistatic agents, flame retardants, flow modifiers, etc. may be added.

The present invention will be described below based on examples, but the present invention is not limited to these.

[Measurement method]
In the examples, the measurements used are as follows:

(1) Apparent bulk density, tapped bulk density, and Hausner ratio of thermoplastic resin particles The apparent density of the thermoplastic resin particles was determined by dropping 50 g of thermoplastic resin particles from a funnel into a 100 ^cm3 graduated cylinder, reading the volume, and dividing the weight of the polymer powder by the volume, according to Japanese Industrial Standards (JIS) JIS Z 7365 (1999). The tapped density of the thermoplastic resin particles was determined by dropping 50 g of thermoplastic resin particles from a funnel into a 100 ^cm3 graduated cylinder, reading the volume after tapping, and dividing the weight of the thermoplastic resin particles by the volume, according to Japanese Industrial Standards (JIS) JIS Z 7370 (2000). Furthermore, the value obtained by dividing the tapped bulk density by the apparent bulk density was determined as the Hausner ratio.

(2) True Density of Thermoplastic Resin Particles The true density of the thermoplastic resin particles was calculated according to the Japanese Industrial Standards (JIS) JIS Z 8807 (2012) by introducing about 10 g of polymer powder and a solvent having a smaller specific gravity than the polymer powder into a Gay-Lussac-type pycnometer, and measuring the weights of the pycnometer alone, the pycnometer powder, the pycnometer + powder + solvent, and the pycnometer + solvent, and then calculating according to the following formula.

Note that d: true powder density, d0: solvent density, Wa: weight of pycnometer, Wb: weight of pycnometer + powder, Wc: weight of pycnometer + powder + solvent, Wd: weight of pycnometer + solvent.

(3) Tapped filling rate The tapped bulk density obtained by the method (1) was calculated from the true density of the resin obtained by the method (2) according to Equation 2, and this was taken as the tapped filling rate.

Pr: tap filling rate, Dtap: tap bulk density, Dpolym: true density of the resin.

(4) D10, D50, D90 particle size, mode diameter of thermoplastic resin particles Add a dispersion liquid in which about 100 mg of thermoplastic resin particles are dispersed in about 5 mL of deionized water to a laser diffraction particle size distribution meter (Microtrac MT3300EXII) manufactured by Nikkiso Co., Ltd. until the concentration becomes measurable, and perform ultrasonic dispersion for 60 seconds at 30 W in the measuring device, and then measure the particle size distribution measured in 10 seconds at a cumulative frequency of 10%, 50%, and 90% from the small particle size side, which are the particle sizes D10, D50, and D90 particle sizes, respectively. In addition, the particle size showing the most frequent value is the mode diameter. The refractive index during measurement is 1.52, and the refractive index of the medium (deionized water) is 1.333.

(5) Sphericity of Thermoplastic Resin Particles The sphericity of the thermoplastic resin particles was calculated from the minor axis and major axis of 30 particles randomly selected from a photograph taken with a scanning electron microscope (JSM-6301NF, manufactured by JEOL Ltd.) according to the following mathematical formula 3.

S: sphericity, a: major axis, b: minor axis, n: 30 (number of measurements).

(6) Linseed oil absorption of thermoplastic resin particles In accordance with Japanese Industrial Standards (JIS) JIS K 5101 "Pigment test method, refined linseed oil method," about 100 mg of thermoplastic resin particles was precisely weighed on a watch glass, refined linseed oil (manufactured by Kanto Chemical Co., Ltd.) was gradually added drop by drop using a burette, and the mixture was kneaded with a palette knife. The dropping and kneading were repeated until a sample mass was formed, and the end point was the point at which the paste became smooth and hard. The oil absorption (mL/100 g) was calculated from the amount of refined linseed oil used for dropping.

(7) Crystallization temperature and melting point of thermoplastic resin particles Using a differential scanning calorimeter (DSCQ20) manufactured by TA Instruments, the temperature was raised once in a nitrogen atmosphere from 30° C. to a temperature 30° C. higher than the endothermic peak indicating the melting point of the polymer at a heating rate of 20° C./min, and then held for 1 minute, and then cooled to 30° C. at a heating rate of 20° C./min and held for 1 minute. The crystallization temperature and melting point of thermoplastic resin particles refer to the apex of the endothermic peak associated with melting and the exothermic peak associated with crystallization. Approximately 8 mg of polymer powder was required for the measurement.

(8) Molecular weight of thermoplastic resin constituting thermoplastic resin particles The weight average molecular weight of polyamide was calculated by gel permeation chromatography in comparison with a calibration curve of polymethyl methacrylate. The measurement sample was prepared by dissolving about 3 mg of polyamide fine particles in about 3 g of hexafluoroisopropanol.
Apparatus: Waters e-Alliance GPC system
Column: HFIP-806M x 2 manufactured by Showa Denko K.K.
Mobile phase: 5 mmol/L sodium trifluoroacetate/hexafluoroisopropanol Flow rate: 1.0 mL/min
Temperature: 30°C
Detection: Differential refractometer.

(9) Porosity of the molded object The porosity was calculated using a precision balance (CP225D) manufactured by Sartorius and a specific gravity/density measurement kit (YDK01) according to Equation 4. The densities of water and air were corrected according to temperature in accordance with the Chemical Handbook.

Note that Ds is the density of the object, Wa is the weight of the object in air, Ww is the weight of the object in water, Pw is the density of water, and Pa is the density of air.

[Preparation of Particle 1]
In a 3L autoclave, 360 g of ε-caprolactam (special grade reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 240 g of polyethylene glycol (1st grade polyethylene glycol 6,000 manufactured by Wako Pure Chemical Industries, Ltd.), 2.5 g of IRGANOX1098 (manufactured by BASF Japan Co., Ltd.) as an antioxidant, and 50 g of deionized water were added and sealed, and the process of pressurizing with nitrogen to 1 MPa and releasing the pressure to 0.1 MPa was repeated three times, and the inside of the container was replaced with nitrogen, and then the pressure was adjusted to 0.1 MPa and the container was sealed. Thereafter, the stirring speed was set to 62 rpm and the temperature was raised to 230°C. At this time, the pressure in the system was 1.4 MPa, and stirring was continued at 62 rpm for 3 hours while maintaining the pressure and temperature. Next, pressure was released at a rate of 0.2 MPa·min, and the internal pressure was set to 0 MPa. Thereafter, the polymerization temperature was set to 210°C, and nitrogen was flowed at a rate of 5 L/min to perform polymerization for 1 hour. Finally, the slurry was discharged into a 2000g water bath to obtain a slurry. After the slurry was thoroughly homogenized by stirring, it was filtered, and 2000g of water was added to the filtered product, and it was washed at 80°C. The slurry liquid was then filtered again to remove the aggregates that had been passed through a 100μm sieve, and the isolated filtered product was dried at 80°C for 12 hours to obtain polyamide 6 particles. The melting point of the obtained polyamide 6 particles was 217°C, the crystallization temperature was 173°C, and the weight average molecular weight was 35,000. The mode diameter was 54μm, the D90/D10 was 2.5, the sphericity was 96, and the linseed oil absorption was 35mL/100g. The true density of the resin was measured to be 1.13.

[Preparation of Particle 2]
Except for changing the stirring speed to 32 rpm, the same granulation process as for particle 1 was carried out to obtain polyamide 6 particles. The melting point of the obtained polyamide 6 particles was 218°C, the crystallization temperature was 174°C, and the weight average molecular weight was 32,000. The mode diameter was 70 μm, the D90/D10 was 2.7, the sphericity was 93, and the linseed oil absorption was 26 mL/100 g. The true density of the resin was measured and found to be 1.13.

[Preparation of Particle 3]
Except for changing the stirring speed to 85 rpm, the same granulation process as for particle 1 was carried out to obtain polyamide 6 particles. The melting point of the obtained polyamide 6 particles was 215°C, the crystallization temperature was 172°C, and the weight average molecular weight was 39,000. The mode diameter was 23 μm, the D90/D10 was 2.6, the sphericity was 93, and the linseed oil absorption was 55 mL/100 g. The true density of the resin was measured and found to be 1.13.

[Preparation of Particle 4]
Except for changing the stirring speed to 90 rpm, the same granulation process as for particle 1 was carried out to obtain polyamide 6 particles. The melting point of the obtained polyamide 6 particles was 216°C, the crystallization temperature was 170°C, and the weight average molecular weight was 46,000. The mode diameter was 23 μm, the D90/D10 was 2.5, the sphericity was 98, and the linseed oil absorption was 60 mL/100 g. The true density of the resin was measured and found to be 1.13.

[Preparation of Particle 5]
Polyamide 6 particles were obtained by granulation in the same manner as in Particles 1, except that the stirring speed was set to 100 rpm. The mode diameter of the obtained polyamide 6 particles was 10 μm, and the sphericity was 95. The true density of the resin was measured and found to be 1.13.

[Preparation of Particle 6]
Polyamide 6 particles were obtained by granulation in the same manner as in Particles 1, except that the stirring speed was set to 73 rpm. The mode diameter of the obtained polyamide 6 particles was 35 μm, and the sphericity was 93. The true density of the resin was measured and found to be 1.13.

[Preparation of Particle 7]
Polyamide 6 particles were obtained by granulation in the same manner as in Particles 1, except that the stirring speed was set to 25 rpm. The mode diameter of the obtained polyamide 6 particles was 92 μm, and the sphericity was 90. The true density of the resin was measured and found to be 1.13.

[Example 1]
1500 g of the prepared particles 1 and 250 g of particles 4 were thoroughly mixed in a mortar, and then the mixture was passed through a sieve with 300 μm openings three times to make the whole uniform. Furthermore, 5.3 g of trimethylsilylated amorphous silica (X-24-9500 manufactured by Shin-Etsu Chemical Co., Ltd.) having an average particle size of 170 nm was added as a lubricant, and the whole was further mixed and passed through a sieve with 300 μm openings three times to make the whole uniform. The particle size distribution on a volume basis of the mixed particles thus obtained was measured to be bimodal, with the particle sizes of the respective peaks being 70 μm and 15 μm. The sphericity of the mixed particles was also 95. The bulk density of the mixed particles was measured to find that the apparent bulk density was 0.70 and the tapped bulk density was 0.86, and the Hausner ratio calculated from these was 1.23, and the tapped filling rate was calculated to be 0.76.

A three-dimensional object was manufactured using 1,500 g of this mixed particle in a powder bed fusion bonding device (RaFaEl ΙΙ 150C-HT) manufactured by Aspect Corporation. The powder spread during the modeling was good, and no roughness of the powder surface was observed. The density of the obtained model was 1.125, and the porosity of the model was 0.5%. The characteristics are shown in Table 1.

[Example 2]
Mixed particles were prepared in the same manner as in Example 1, using 1200 g of the prepared particles 1, 400 g of particles 4, and 4.8 g of trimethylsilylated amorphous silica (X-24-9500 manufactured by Shin-Etsu Chemical Co., Ltd.) having an average particle size of 170 nm as a lubricant. The volume-based particle size distribution of the obtained mixed particles was measured and found to be bimodal, with the particle sizes of the respective peaks being 70 μm and 15 μm. The sphericity of the mixed particles was also 97. The bulk density of the mixed particles was measured and found to have an apparent bulk density of 0.74 and a tapped bulk density of 0.91. The Hausner ratio calculated from these was 1.23, and the tapped filling rate was calculated to be 0.81.

A three-dimensional object was manufactured using 1,500 g of this mixed particle in a powder bed fusion bonding device (RaFaEl ΙΙ 150C-HT) manufactured by Aspect Corporation. The powder spread during the modeling was good, and no roughness of the powder surface was observed. The density of the obtained model was 1.127, and the porosity of the model was 0.3%. The characteristics are shown in Table 1.

[Example 3]
Mixed particles were prepared in the same manner as in Example 1, using 1000 g of the prepared particles 1, 500 g of particles 4, and 4.5 g of trimethylsilylated amorphous silica (X-24-9500 manufactured by Shin-Etsu Chemical Co., Ltd.) having an average particle size of 170 nm as a lubricant. The volume-based particle size distribution of the obtained mixed particles was measured and found to be bimodal, with the particle sizes of the respective peaks being 70 μm and 15 μm. The sphericity of the mixed particles was also 97. The bulk density of the mixed particles was measured and found to have an apparent bulk density of 0.65 and a tapped bulk density of 0.81. The Hausner ratio calculated from these was 1.25, and the tapped filling rate was calculated to be 0.72.

A three-dimensional object was manufactured using 1,500 g of this mixed particle in a powder bed fusion bonding device (RaFaEl ΙΙ 150C-HT) manufactured by Aspect Corporation. The powder spread during the modeling was good, and no roughness of the powder surface was observed. The density of the obtained model was 1.122, and the porosity of the model was 0.7%. The characteristics are shown in Table 1.

[Example 4]
Mixed particles were prepared in the same manner as in Example 1, using 1500 g of the prepared particles 1, 250 g of particles 3, and 5.3 g of trimethylsilylated amorphous silica (X-24-9500 manufactured by Shin-Etsu Chemical Co., Ltd.) having an average particle size of 170 nm as a lubricant. The volume-based particle size distribution of the obtained mixed particles was measured and found to be bimodal, with the particle sizes of the respective peaks being 70 μm and 23 μm. The sphericity of the mixed particles was also 94. The bulk density of the mixed particles was measured and found to have an apparent bulk density of 0.68 and a tapped bulk density of 0.81. The Hausner ratio calculated from these was 1.19, and the tapped filling rate was calculated to be 0.72.

A three-dimensional object was manufactured using 1,500 g of this mixed particle in a powder bed fusion bonding device (RaFaEl ΙΙ 150C-HT) manufactured by Aspect Corporation. The powder spread during the modeling was good, and no roughness of the powder surface was observed. The density of the obtained model was 1.120, and the porosity of the model was 0.9%. The characteristics are shown in Table 1.

[Example 5]
Mixed particles were prepared in the same manner as in Example 1, using 1200 g of the prepared particles 1, 400 g of particles 3, and 4.8 g of trimethylsilylated amorphous silica (X-24-9500 manufactured by Shin-Etsu Chemical Co., Ltd.) having an average particle size of 170 nm as a lubricant. The volume-based particle size distribution of the obtained mixed particles was measured and found to be bimodal, with the particle sizes of the respective peaks being 70 μm and 23 μm. The sphericity of the mixed particles was also 94. The bulk density of the mixed particles was measured and found to have an apparent bulk density of 0.69 and a tapped bulk density of 0.83. The Hausner ratio calculated from these was 1.20, and the tapped filling rate was calculated to be 0.73.

A three-dimensional object was manufactured using 1,500 g of this mixed particle in a powder bed fusion bonding device (RaFaEl ΙΙ 150C-HT) manufactured by Aspect Corporation. The powder spread during the modeling was good, and no roughness of the powder surface was observed. The density of the obtained model was 1.121, and the porosity of the model was 0.8%. The characteristics are shown in Table 1.

[Example 6]
Mixed particles were prepared in the same manner as in Example 1, using 1500 g of the prepared particles 2, 250 g of particles 4, and 5.3 g of trimethylsilylated amorphous silica (X-24-9500 manufactured by Shin-Etsu Chemical Co., Ltd.) having an average particle size of 170 nm as a lubricant. The volume-based particle size distribution of the obtained mixed particles was measured and found to be bimodal, with the particle sizes of the respective peaks being 54 μm and 15 μm. The sphericity of the mixed particles was also 95. The bulk density of the mixed particles was measured and found to have an apparent bulk density of 0.63 and a tapped bulk density of 0.84, with the Hausner ratio calculated from these being 1.33 and the tapped filling rate being calculated to be 0.74.

A three-dimensional object was manufactured using 1,500 g of this mixed particle in a powder bed fusion bonding device (RaFaEl ΙΙ 150C-HT) manufactured by Aspect Corporation. The powder spread during the modeling was good, and no roughness of the powder surface was observed. The density of the obtained model was 1.123, and the porosity of the model was 0.6%. The characteristics are shown in Table 1.

[Example 7]
Mixed particles were prepared in the same manner as in Example 1, using 1200 g of the prepared particles 2, 400 g of particles 4, and 4.8 g of trimethylsilylated amorphous silica (X-24-9500 manufactured by Shin-Etsu Chemical Co., Ltd.) having an average particle size of 170 nm as a lubricant. The volume-based particle size distribution of the obtained mixed particles was measured and found to be bimodal, with the particle sizes of the respective peaks being 54 μm and 15 μm. The sphericity of the mixed particles was also 96. The bulk density of the mixed particles was measured and found to have an apparent bulk density of 0.70 and a tapped bulk density of 0.85, with the Hausner ratio calculated from these being 1.21 and the tapped filling rate being calculated to be 0.75.

A three-dimensional object was manufactured using 1,500 g of this mixed particle in a powder bed fusion bonding device (RaFaEl ΙΙ 150C-HT) manufactured by Aspect Corporation. The powder spread during the modeling was good, and no roughness of the powder surface was observed. The density of the obtained model was 1.124, and the porosity of the model was 0.5%. The characteristics are shown in Table 1.

[ Comparative Example 4 ]
Mixed particles were prepared in the same manner as in Example 1, using 1500 g of the prepared particles 2, 250 g of particles 3, and 5.3 g of trimethylsilylated amorphous silica (X-24-9500 manufactured by Shin-Etsu Chemical Co., Ltd.) having an average particle size of 170 nm as a lubricant. The volume-based particle size distribution of the obtained mixed particles was measured and found to be bimodal, with the particle sizes of the respective peaks being 54 μm and 23 μm. The sphericity of the mixed particles was also 93. The bulk density of the mixed particles was measured and found to have an apparent bulk density of 0.65 and a tapped bulk density of 0.79, with the Hausner ratio calculated from these being 1.22 and the tapped filling rate being calculated to be 0.70.

A three-dimensional object was manufactured using 1,500 g of this mixed particle in a powder bed fusion bonding device (RaFaEl ΙΙ 150C-HT) manufactured by Aspect Corporation. The powder spread during the modeling was good, and no roughness of the powder surface was observed. The density of the obtained model was 1.118, and the porosity of the model was 1.1%. The characteristics are shown in Table 1.

[ Comparative Example 5 ]
Mixed particles were prepared in the same manner as in Example 1, using 1200 g of the prepared particles 7, 400 g of particles 6, and 4.8 g of trimethylsilylated amorphous silica (X-24-9500 manufactured by Shin-Etsu Chemical Co., Ltd.) having an average particle size of 170 nm as a lubricant. The volume-based particle size distribution of the obtained mixed particles was measured and found to be bimodal, with the particle sizes of the respective peaks being 92 μm and 35 μm. The sphericity of the mixed particles was also 92. The bulk density of the mixed particles was measured and found to have an apparent bulk density of 0.60 and a tapped bulk density of 0.74, with the Hausner ratio calculated from these being 1.23 and the tapped filling rate being calculated to be 0.65.

A three-dimensional object was manufactured using 1,500 g of this mixed particle in a powder bed fusion bonding device (RaFaEl ΙΙ 150C-HT) manufactured by Aspect Corporation. The powder spread during the modeling was good, and no roughness of the powder surface was observed. The density of the obtained model was 1.115, and the porosity of the model was 1.3%. The characteristics are shown in Table 1.

[ Comparative Example 6 ]
Mixed particles were prepared in the same manner as in Example 1, using 1200 g of the prepared particles 6, 400 g of particles 5, and 4.8 g of trimethylsilylated amorphous silica (X-24-9500 manufactured by Shin-Etsu Chemical Co., Ltd.) having an average particle size of 170 nm as a lubricant. The volume-based particle size distribution of the obtained mixed particles was measured and found to be bimodal, with the particle sizes of the respective peaks being 35 μm and 10 μm. The sphericity of the mixed particles was also 94. The bulk density of the mixed particles was measured and found to have an apparent bulk density of 0.55 and a tapped bulk density of 0.73. The Hausner ratio calculated from these was 1.33, and the tapped filling rate was calculated to be 0.65.

A three-dimensional object was produced using 1,500 g of this mixed particle in a powder bed fusion bonding device (RaFaEl ΙΙ 150C-HT) manufactured by Aspect Corporation. Slight roughness of the powder surface was observed during the modeling process, but this was not enough to impede the modeling. The density of the model obtained was 1.115, and the porosity of the model was 1.3%. The properties are shown in Table 1.

[Comparative Example 1]
Mixed particles were prepared in the same manner as in Example 1, using 1200 g of the prepared particles 1, 400 g of particles 6, and 4.8 g of trimethylsilylated amorphous silica (X-24-9500 manufactured by Shin-Etsu Chemical Co., Ltd.) having an average particle size of 170 nm as a lubricant. The volume-based particle size distribution of the obtained mixed particles was measured and found to be bimodal, with the particle sizes of the respective peaks being 70 μm and 35 μm. The sphericity of the mixed particles was also 94. The bulk density of the mixed particles was measured and found to have an apparent bulk density of 0.54 and a tapped bulk density of 0.67, with the Hausner ratio calculated from these being 1.24 and the tapped filling rate being calculated to be 0.59.

A three-dimensional object was manufactured using 1,500 g of this mixed particle in a powder bed fusion bonding device (RaFaEl ΙΙ 150C-HT) manufactured by Aspect Corporation. The powder spread during the modeling was good, and no roughness of the powder surface was observed. The density of the obtained model was 1.110, and the porosity of the model was 1.8%. The characteristics are shown in Table 1.

[Comparative Example 2]
Mixed particles were prepared in the same manner as in Example 1, using 1000 g of the prepared particles 2 and 1000 g of the particles 4, and 6.0 g of trimethylsilylated amorphous silica (X-24-9500 manufactured by Shin-Etsu Chemical Co., Ltd.) having an average particle size of 170 nm as a lubricant. The volume-based particle size distribution of the obtained mixed particles was measured and found to be bimodal, with the particle sizes of the respective peaks being 54 μm and 15 μm. The sphericity of the mixed particles was also 93. The bulk density of the mixed particles was measured and found to have an apparent bulk density of 0.44 and a tapped bulk density of 0.72, with the Hausner ratio calculated from these being 1.64 and the tapped filling rate being calculated to be 0.64.

Using 1,500 g of this mixed particle, a three-dimensional object was manufactured using a powder bed fusion device (RaFaEl ΙΙ 150C-HT) manufactured by Aspect Corporation. However, the powder did not disperse well, and the powder surface became rough during the modeling process, so the modeling had to be stopped midway.

[Comparative Example 3]
Two types of particles with mode diameters of 97 μm and 40 μm were prepared by freeze-pulverization of nylon 6 (CM1010) manufactured by Toray Industries, Inc. The mixed particles were prepared in the same manner as in Example 1, using 1200 g and 400 g of nylon 6, respectively, and 9.6 g of trimethylsilylated amorphous silica (X-24-9500 manufactured by Shin-Etsu Chemical Co., Ltd.) with an average particle size of 170 nm as a lubricant. The volume-based particle size distribution of the obtained mixed particles was measured and found to be bimodal, with the particle sizes of the respective peaks being 95 μm and 43 μm. The sphericity of the mixed particles was also 68. The bulk density of the mixed particles was measured and found to have an apparent bulk density of 0.54 and a tap bulk density of 0.67, with the Hausner ratio calculated from these being 1.47, and the tap filling rate calculated to be 0.50.

A three-dimensional object was manufactured using 1,500 g of this mixed particle in a powder bed fusion bonding device (RaFaEl ΙΙ 150C-HT) manufactured by Aspect Corporation. Powder surface roughness was confirmed during the manufacturing process. The density of the resulting object was 1.093, and the porosity of the object was 3.3%. The properties are shown in Table 1.

Claims (10)

Thermoplastic resin particles, characterized in that the thermoplastic resin particles are spherical and have a D50 particle size of 10 μm or more and 100 μm or less, have a bimodal volumetric particle size distribution, and when the mode diameter of the larger peak in the volumetric particle size distribution is S1 and the mode diameter of the smaller peak is S2, S2/S1 is 0.10 or more and 0.45 or less, and have a tap filling factor, which is a value obtained by dividing the tap density of the thermoplastic resin particles by the true density of the resin constituting the thermoplastic resin particles, of 0.72 or more and 0.9 or less. 2. The thermoplastic resin particles according to claim 1, characterized in that the mode diameter S1 of the larger peak of the particle diameter distribution on a volume basis is 40 μm or more and 120 μm or less, and the mode diameter S2 of the smaller peak of the particle diameter distribution on a volume basis is 5 μm or more and 40 μm or less. Thermoplastic resin particles according to claim 1 or 2, characterized in that the Hausner ratio, which is the tap bulk density divided by the apparent bulk density, is 1 or more and 1.5 or less. Thermoplastic resin particles according to any one of claims 1 to 3, characterized in that the D10 particle size is 1 μm or more and 30 μm or less. Thermoplastic resin particles according to any one of claims 1 to 4, characterized in that the D90 particle size is 50 μm or more and 120 μm or less. Thermoplastic resin particles according to any one of claims 1 to 5, characterized in that the resin constituting the thermoplastic resin particles is polyamide. 6. The thermoplastic resin particles according to claim 1, having a sphericity of 94 or more. Thermoplastic resin particles according to any one of claims 1 to 7, characterized in that the resin constituting the thermoplastic resin particles is at least one selected from polyamide 6, polyamide 12, polyamide 66, polyamide 1010, polyamide 1012, polyamide 1212, polyamide 46, polyamide 6T, and polyamide 6I, or a copolymer thereof. 9. The thermoplastic resin particles according to claim 1, which are used for producing a three-dimensional object by powder bed fusion. A method for producing a three-dimensional object by powder bed fusion bonding using the thermoplastic resin particles according to any one of claims 1 to 9 .