JP2018015972A - Three-dimensional molding method, molded article and three-dimensional molding apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a shaped article having high density and high strength using excess powder generated in molding.SOLUTION: A three-dimensional molding method includes: a step of forming a layer formed from powder for three-dimensional molding formed from a thermoplastic resin composition, and selectively solidifying the powder by selective irradiation of the layer with electromagnetic irradiation rays, and includes the following (a) to (c) steps: (a) setting loose bulk density of the excess powder which is not solidified in molding to a range of more than 20% with respect to true density; (b) mixing the excess powder and unused powder to obtain mixed powder; and (c) forming the layer from the mixed powder.SELECTED DRAWING: None

Description

  The present invention relates to a three-dimensional modeling method, a three-dimensional object, and a three-dimensional modeling apparatus.

In recent years, the three-dimensional modeling technique is also called a 3D printer and has attracted much attention.
There are several types of modeling methods, and the characteristics of materials and modeling objects that can be used differ depending on the method.
As one of several modeling methods, there is a PBF (powder bed fusion) method capable of high strength and high accuracy modeling.

  PBF (Powder Bed Fusion) methods include SLS (Selective Laser Sintering) method that forms a model by selectively irradiating a laser, or a planar laser using a mask. There is an SMS (Selective Mask Sintering) system that applies the above. The PBF molding method is called a recoater on the layer after selectively melting and bonding the powder by selectively irradiating a laser beam to a thin layer of metal, ceramic or resin. A thin layer is formed by laying another above-mentioned material with a roller (lamination process), and the same operation is repeated to obtain a shaped object. Devices using this PBF method are already commercially available in various countries including Japan. A detailed description of the PBF method can be found in Patent Documents 1 to 4.

  When resin powder is used as a material in the PBF method, modeling is performed by heating the supplied resin powder layer for the purpose of suppressing crystallization of the molten resin. The temperature at the time of modeling needs to be not less than the crystallization temperature of the resin powder material and not more than the melting point. By being kept at that temperature, the resin melted by laser irradiation becomes supercooled and crystallization does not proceed. Therefore, volume shrinkage accompanying crystallization does not proceed rapidly, and the occurrence of warpage during modeling of the modeled object is suppressed.

  In the PBF modeling, a certain amount of surplus powder remaining without being melted and sintered in the laminating step can be generated. Here, the surplus powder is damaged by heat and / or thermal oxidation due to modeling, and has different material properties and manufacturing parameters compared to the unused powder.

  In the known method, the above-mentioned surplus powder is mixed with unused powder at a predetermined mass ratio and reused. The mixing ratio is determined by a difference in the material properties and modeling quality between the surplus powder and the unused powder, and is an index indicating the recyclability of the raw materials. That is, the lower the mixing ratio of the unused powder, the higher the recyclability of the powder material. Moreover, in order to suppress an increase in cost due to the use of unused powder, it is desirable that the mixing ratio of unused powder is low.

In Patent Document 5, as a technique for intentionally changing the characteristics of the surplus powder to improve recyclability, the surplus powder is treated with water or steam to lower the molecular weight of the resin than before the treatment. It describes that the recyclability is improved by reducing the influence of an increase in molecular weight due to post-condensation due to heat during modeling.
In Patent Document 6, as a technique for improving the modeling quality by increasing the bulk density of the powder during the lamination process, surface defects of the modeled object are generated by mechanically compressing the powder during the formation of the layered structure. Is described.

  The powder flowability of the surplus powder is often inferior to that of unused powder due to the change in physical properties of the material. For this reason, a smooth powder layer is not formed in the laminating step, and powder clogging may be uneven depending on the position, and a powder layer containing many voids may be locally formed. These voids lead to the formation of holes in the modeled object when the laser beam is used for modeling. These holes lead to a decrease in the mechanical properties of the shaped object.

  The object of the present invention is to produce a high-density and high-strength shaped article using surplus powder generated during shaping, and to provide a more efficient method for utilizing surplus powder. It is possible to improve the quality of the process and the shaped object and improve the economic efficiency.

The object of the present invention can be achieved by a three-dimensional modeling method having the following configuration.
Three-dimensional modeling having a step of forming a layer made of a three-dimensional modeling powder made of a thermoplastic resin composition and a step of selectively solidifying the powder by selectively irradiating the layer with electromagnetic radiation. It is a method, Comprising: Each three-dimensional modeling method characterized by including each process of following (a)-(c).
(A) The process which makes loose bulk density of the surplus powder which was not solidified at the time of shaping | molding more than 20% with respect to a true density (b) The process which mixes the said surplus powder and unused powder and makes it mixed powder (C) forming the layer with the mixed powder

  According to the present invention, it becomes possible for a modeled object made of surplus powder generated after modeling to maintain quality such as mechanical properties such as density, strength, and accuracy above a certain level. Moreover, since the mixing ratio of the unused powder added to the surplus powder can be reduced according to the present invention, not only the cost can be reduced, but also the discarded powder can be reduced to 0 or an extremely small amount.

It is a figure for demonstrating an example of the manufacturing method of a three-dimensional molded item.

Hereinafter, although embodiment of this invention is described, this invention is not limited to embodiment described below.
The present invention was not formed in a method for forming a high-quality three-dimensional structure using a PBF sintering method, for example, an SLS (selective laser sintering) method or an SMS (selective mask sintering) method. It is characterized by reusing powder.

As a method of reusing powder that has not been shaped (hereinafter also referred to as “surplus powder”) in PBF, a method of mixing surplus powder and unused powder at a predetermined ratio and reusing it as a mixed powder is common. Has been used. Depending on the shape of the modeling model and the modeling temperature, the surplus powder may agglomerate, partially melt / solidify, condense due to heat, and the like, and may change the material characteristics of the unused powder.
However, according to the present invention, it is possible to provide a three-dimensional modeling powder with an increased recycling rate of excess powder (mixing ratio with respect to unused powder), for example, a mass mixing ratio of excess powder and unused powder. It is possible to obtain a high-strength three-dimensional structure by using the three-dimensional structure forming powder in a range of 5: 5 to 10: 0.
The mixing ratio may be determined as appropriate according to the resin type of the powder, the number of reuses, desired strength, production efficiency, cost, and the like.

In order to obtain the powder for three-dimensional modeling as described above, an excess powder recovered without being subjected to modeling is used in which the loose bulk density (loose density) is improved. The loose bulk density of the excess powder is preferably in the range of more than 20% with respect to the true density, more preferably 25% or more, and particularly preferably 35% to 70%.
Specific treatments include a method of re-adding external additives and mixing, a treatment for dehydrating the powder surface using a dryer or desiccant to improve fluidity, and removing the charge on the powder surface. In this way, the loose bulk density of the powder containing the surplus powder can be improved by performing the treatment for removing the influence of the electrostatic force.
Further, the above-mentioned surplus powder treatment method is an environment-friendly treatment method because a special chemical substance is not used.

  The loose bulk density is the degree of powder clogging due to its own weight, and is one of the apparent density (bulk density) of the powder. When no pressure is applied to the powder surface when supplied by the recoater, the degree of powder clogging during the laminating process is close to a loose bulk density. As a well-known bulk density, there is a hard bulk density (tap density), which is different from the situation where powder is clogged during lamination. When the loose bulk density of the powder used for modeling is high, the powder is spread densely and uniformly during the lamination process. When a densely packed powder surface is irradiated with a laser, it is easier to form a densely shaped object than a coarsely packed powder surface. In addition, variations in the density of the modeled object are also reduced. By increasing the density of the modeled object, mechanical properties such as strength are improved. In addition, since the loose bulk density is high, the powder in the laser irradiation part is melted and sintered with high accuracy, so that the modeling accuracy is improved.

  As a method for improving the loose bulk density of the surplus powder, there is a process for improving the fluidity by dehydrating moisture on the surface of the powder using a drier or a desiccant (J. Jpn. Soc. Color Mater., 78 (7 ), 315-329 (2005)). When the above treatment is performed, the water content is preferably 2.0% by mass or less, more preferably 1.3% by mass or less, and particularly preferably 0.9% by mass or less.

Examples of the thermoplastic resin constituting the three-dimensional modeling powder (hereinafter also referred to as “powder composition”) made of the thermoplastic resin composition used in the present invention include polyolefin, polyamide, polyester, polyaryl ketone, polyphenylene sulfide, Any suitable polymer or combination of polymers such as liquid crystal polymer (LCP), polyacetal, polyimide, fluororesin, etc. can be mentioned, and the powder composition can contain one or more of these resins in an appropriate amount. .
In addition to the polymer, the powder composition may contain one or more additional materials (additives such as flame retardants, plasticizers, heat-stable additives, crystal nucleating agents, etc.). These additional materials can be included in the powder composition by blending the material with the polymer particles or by adhering or absorbing to the surface of the polymer particles.

  Polyolefin includes polyethylene (PE) and polypropylene (PP). Polyamide includes PA410, PA6, PA66, PA610, PA612, PA11, PA12, and semi-aromatic PA4T, PAMXD6, PA6T, PA9T, PA10T, etc. Also included are so-called aramids made from terephthalic acid monomers.

  Examples of the polyester include PET (polyethylene terephthalate) and PBT (polybutadiene terephthalate). Examples of the polyaryl ketone include PEEK (polyether ether ketone), PEK (polyether ketone), and PEKK (polyether ketone ketone). In addition, any crystalline polymer may be used, and polyacetal (POM), polyimide, polyether sulfone, or the like may be used. There may be two melting point peaks such as PA9T (in order to melt completely, it is necessary to raise the resin temperature above the second melting point peak).

  In a preferred embodiment, the powder composition in the present invention may contain any fluidizing agent. The amount added may be sufficient to cover the particle surface, and the total amount is preferably in the range of about 0.1% by mass to 10% by mass. The fluidizing agent is preferably a particulate inorganic material having a volume average particle size of less than about 10 μm. Examples of suitable granulating agents include alumina, titania, talc, glass-like silica, hydrated silica, those modified on the silica surface with a silane coupling agent, and one or more kinds of magnesium silicate.

The three-dimensional structure formed by laser sintering using the powder provided for the present invention is preferably warped or distorted due to a phase change that occurs during sintering and during cooling after sintering, smoke generation, etc. Does not exhibit inappropriate process characteristics.
In some embodiments, glass fillers, glass beads, carbon fibers, aluminum balls, and the like may be included as reinforcing agents for improving strength (see International Publication No. 2008/057844).

  Another aspect of the present invention is a method of forming a three-dimensional structure from a powder composition by performing a sintering process each time a new layer is drawn by a roller or the like, and the powder layer portion is selectively (partially selected) in the sintering process. ). A new powder layer is applied to the previously formed layer, selectively melted again, and this process is repeated until the desired three-dimensional object is manufactured. Melting of the powder composition is typically performed by electromagnetic irradiation, although the selectivity of melting is selective, for example, by inhibitors, absorbers, or electromagnetic irradiation (eg, masked or by direct laser beam). Achieved by application. Any suitable electromagnetic radiation source can be used, and examples thereof include a laser light source, an infrared radiation source, a microwave generator, a radiation heater, and an LED lamp. Or these may be combined.

  In some embodiments, selective mask sintering (SMS) technology can be used to produce the three-dimensional object of the present invention. The SMS process is described in, for example, US Pat. No. 6,531,086. The SMS process uses a shielding mask to selectively block infrared radiation, resulting in selective irradiation of a portion of the powder layer. When the SMS process is used for the method for producing an article from the powder composition of the present invention, it is preferable that the powder composition contains one or more substances that enhance the infrared absorption characteristics of the powder composition. Examples of the substance that enhances the infrared absorption characteristics of the powder composition include a heat absorbent and / or a dark substance (carbon fiber, carbon black, carbon nanotube, or carbon fiber, cellulose nanofiber).

  Although it is a suitable method for producing a three-dimensional structure by the PBF method using the powder composition of the present invention, a three-dimensional structure using this method is preferably a plurality of laminated layers containing a polymer matrix. And includes a bonded sintered layer. The sintered layer can have a thickness suitable for the shaping process. Each of the plurality of sintered layers is preferably, on average, preferably at least about 10 μm thick, more preferably at least about 50 μm thick, and even more preferably at least about 100 μm thick.

  The particle size distribution of the resin powder used in the present invention is attributable to the PBF system, but is generally 100 μm per layer. Therefore, a powder composed of a crystalline thermoplastic resin composition whose crystal is controlled to have a 50% volume average particle diameter of 5 to 100 μm is desirable, but in order to achieve more dimensional stability, the 50% volume average particle diameter is 5 -50 μm is more preferable.

  The powder composition preferably contains one or more crystalline thermoplastic resins. As the thermoplastic resin, a crystalline thermoplastic resin whose crystal is controlled is preferable. The crystalline thermoplastic resin in the present invention means a crystalline resin having thermoplasticity, and means a resin having a melting peak when measured according to JISL7121 (plastic transition temperature measurement method: ISO 3146). The above crystal-controlled crystalline thermoplastic resin means that the crystal size and crystal orientation are controlled by a method such as heat treatment, stretching, external stimulation, and the like. An annealing process to increase the crystallinity by heating at a temperature above the glass transition point of each resin, a method to increase crystallinity by applying ultrasonic waves, a method to increase crystallinity by dissolving in a solvent and volatilizing slowly, an external electric field A highly crystalline resin powder can be obtained by passing through steps such as crystal growth by application treatment, or by pulverizing a highly oriented and highly crystallized material by stretching.

  Using the powder composition of the present invention to form articles for use in applications such as prototypes of electronic equipment parts, prototypes for strength tests, small-volume products used in aerospace and automotive industry dress-up tools, etc. it can. The PBF and other systems are expected to be superior in strength compared to the FDM and inkjet systems, so that they can be used as practical products. The production speed is not suitable for a mass production method such as injection molding. For example, a necessary production amount can be achieved by making a large number of small parts in a flat shape. Further, since a mold such as injection molding is not required, overwhelming cost reduction and delivery time reduction can be achieved in trial production and prototype production.

FIG. 1 is a schematic view showing an example of an apparatus for carrying out the three-dimensional modeling method of the present invention.
As shown in FIG. 1, the powder is stored in a powder supply tank 5 and supplied to the laser scanning space 6 using a roller 4 according to the amount of use. The temperature of the supply tank 5 is preferably adjusted by the heater 3. The laser output from the electromagnetic irradiation source 1 is irradiated to the laser scanning space 6 using the reflecting mirror 2. The three-dimensional structure can be obtained by sintering the powder by the heat of the laser.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated further more concretely, this invention is not limited at all by these Examples.

In the examples and comparative examples, the following materials were used.
Regarding PA12 powder, commercially available SLS grade powder was used.
For powders other than PA12, powders obtained by freeze-pulverizing thermoplastic resin pellets sold by standard grade companies for extrusion molding at −200 ° C. were used. The pulverized powder was made to have a width of 5 to 100 μm. The 50% volume average particle size was 20 μm to 90 μm.
In order to improve the fluidity of the powder, 1% by mass of fumed silica (RA200H manufactured by Aerosol) and 0.5% by mass of zinc stearate (Kawamura Kasei Kogyo Co., Ltd.) were blended with the above powder to obtain a homogeneous compound powder. . The powder was an unused powder.
Table 1 describes the thermoplastic trees used as raw materials.

  Moreover, it modeled once on the conditions mentioned later with respect to the said powder, and the powder which was not modeled was collect | recovered as an excess powder. The surplus powder was subjected to shaking with VSS-P300S manufactured by Tsutsui Rikaki Machine Co., Ltd., and the solidified resin powder was removed. Thereafter, as in each of the following examples, the unused powder was added at a predetermined ratio to the surplus powder subjected to the loose bulk density improvement treatment, and dry mixed for 3 hours. This was mixed powder and used for modeling.

(Measurement of moisture content of excess powder and measurement of loose bulk density)
The moisture content of the surplus powder was measured using MD50 manufactured by A & D. The temperature was measured at a temperature 10 ° C. lower than the melting point of the material to be measured. The measurement was terminated when the time when moisture was not detected at a rate of 0.05% / min or more continued for 30 seconds.
The loose bulk density of the excess powder was measured using a multifunctional powder physical property measuring instrument (MT-02) manufactured by Seishin Enterprise Co., Ltd. The same powder was measured three times, and the average value was taken as the measured value.

(Manufacture of 3D objects by SLS method)
Using a SLS manufacturing apparatus [AM S5500P manufactured by RICOH], a three-dimensional model was manufactured. The setting conditions are as follows: the layer thickness is 0.1 mm, the laser output is about 10 to 150 watts, the laser scanning interval is 0.48 mm, and the modeling temperature (powder surface temperature of the modeling tank) is 3 to 20 from the melting point of the resin powder. The temperature was set at a lower temperature. Since these conditions are affected by the thermal properties of the resin powder and the installation environment (temperature and humidity) of the apparatus, it is necessary to appropriately adjust each parameter for each SLS apparatus. During the laser irradiation, there was no particular smoke generation and good resolution was exhibited, and no warping was observed. Therefore, the above conditions were determined as appropriate modeling conditions in each of the examples and comparative examples. Furthermore, it can be said that each powder is suitable as a powder for SLS modeling because it can be modeled under these appropriate laser modeling conditions.

(Measurement of density and bending strength of shaped objects)
The density of the shaped object was measured by the Archimedes method. Density measurement by the Archimedes method was carried out using a specific gravity measurement kit AD-1653 manufactured by A & D. The liquid that sinks the model was pure water.
The bending strength of the modeled object was evaluated by using an AGS-5kN manufactured by Shimadzu Corporation in a bending test according to ISO 527. The test speed was constant at 5 mm / min. The maximum stress was the bending strength. Three measurements were taken and the average value was taken as the measured value.
In Table 2, the evaluation result about the molded object of an Example and a comparative example is shown.

[Example 1]
The surplus powder of the PA12 powder was dried under vacuum. The apparatus used for the vacuum drying was a vacuum dryer LCV-233P with a vacuum pump manufactured by Espec Corporation. Vacuum drying was performed at 30 ° C. for 5 hours. It was 0.9 mass% when the moisture content of the powder was measured. When the loose bulk density of the excess powder was measured, it was 36% of the true density of PA12 of 1.02 g / cm ³ . The surplus powder and the unused powder were dry-mixed at a mass ratio of 5: 5 for 3 h, and modeling was performed under the conditions described above. When the density of the modeled object was measured by the Archimedes method, the density was 91%. When the bending strength of such a shaped article was measured, it was 60 MPa.

[Example 2]
In Example 2, the moisture content and loose bulk density were measured in the same manner as in Example 1 except that the time for vacuum drying in Example 1 was changed to 10 h. The moisture content was 0.7% by mass, and the loose bulk density was 48% with respect to the true density. After performing the above-mentioned shaking, modeling was performed without mixing with unused powder. In the same manner as in Example 1, the density measurement of the modeled object and the strength evaluation of the modeled object were performed.
Table 2 shows the moisture content of the excess powder, the loose bulk density, the mixing rate, and the evaluation result of the shaped article.

[Example 3]
In Example 3, the measurement of the moisture content of the surplus powder, the measurement of the loose bulk density, and the production of the molded product are performed in the same manner as in Example 1 except that the time for performing vacuum drying in Example 1 is changed to 50 h. And the modeled object was evaluated.
Table 2 shows the moisture content of the excess powder, the loose bulk density, the mixing rate, and the evaluation result of the shaped article.

[Example 4]
Example 4 is the same as Example 1 except that in Example 1, instead of vacuum drying, a method of storing for one week in an aluminum lamb zip containing silica gel in a temperature and humidity environment of 23 ° C. and 50% was used. Then, measurement of the moisture content of the surplus powder, measurement of loose bulk density, production of the modeled article and evaluation of the modeled article were performed. Table 2 shows the moisture content of the excess powder, the loose bulk density, the mixing rate, and the evaluation result of the shaped article.

[Example 5]
In Example 5, in the same manner as in Example 4 except that PBT was used as a raw material in place of PA12 in Example 4, measurement of the moisture content of excess powder, measurement of loose bulk density, The model was evaluated.
Table 2 shows the moisture content of the excess powder, the loose bulk density, the mixing rate, and the evaluation result of the shaped article.

[Example 6]
In Example 6, in the same manner as in Example 4 except that PA9T was used as a raw material instead of PA12 in Example 4, the measurement of the moisture content of the excess powder, the measurement of the loose bulk density, the production of the shaped article, and The model was evaluated.
Table 2 shows the moisture content of the excess powder, the loose bulk density, the mixing rate, and the evaluation result of the shaped article.

[Example 7]
In Example 7, in the same manner as in Example 4 except that POM was used as a raw material instead of PA12 in Example 4, the measurement of the moisture content of the surplus powder, the measurement of the loose bulk density, The model was evaluated.
Table 2 shows the moisture content of the excess powder, the loose bulk density, the mixing rate, and the evaluation result of the shaped article.

[Example 8]
In Example 8, in the same manner as in Example 4 except that PP was used as a raw material in place of PA 12, the measurement of the moisture content of the surplus powder, the measurement of the loose bulk density, the production of the shaped article, and The model was evaluated.
Table 2 shows the moisture content of the excess powder, the loose bulk density, the mixing rate, and the evaluation result of the shaped article.

[Example 9]
In Example 9, in Example 4, except that the storage period in the aluminum laminated zip was changed to 50 h, in the same manner as in Example 4, the measurement of the moisture content of the surplus powder, the measurement of the loose bulk density, Manufacturing and modeling were evaluated.
Table 2 shows the moisture content of the excess powder, the loose bulk density, the mixing rate, and the evaluation result of the shaped article.

[Example 10]
In Example 10, in the same manner as in Example 4 except that the storage period in the aluminum laminated zip was changed to 10h in Example 4, the measurement of the moisture content of the surplus powder, the measurement of the loose bulk density, Manufacturing and modeling were evaluated.
Table 2 shows the moisture content of the excess powder, the loose bulk density, the mixing rate, and the evaluation result of the shaped article.

[Example 11]
In Example 11, in Example 4, the storage period in the aluminum laminated zip was changed to 1h. The mixing ratio of unused powder was 60%. Except for these, storage, measurement of moisture content, and powder mixing were performed in the same manner as in Example 4.
Table 2 shows the moisture content of the excess powder, the loose bulk density, the mixing rate, and the evaluation result of the shaped article.

[Comparative Example 1]
In Comparative Example 1, in the same manner as in Example 4 except that the storage method was left for 50 hours in an environment exposed to 23 ° C. and 50% temperature and humidity, the storage and moisture content was the same as in Example 4. Measurement and powder mixing were performed. The moisture content of the surplus powder, loose density, mixing rate, and the evaluation results of the shaped product are shown in Table 2.

[Comparative Example 2]
In Comparative Example 2, in Example 4, the storage method was left for 50 hours in an environment exposed to 23 ° C. and 50% temperature and humidity, and the mixing ratio of unused powder was changed to 50%. Other than that was carried out similarly to Example 4, and measured the moisture content of the surplus powder, the measurement of loose bulk density, manufacture of a molded article, and evaluation of the molded article.
Table 2 shows the moisture content of the excess powder, the loose bulk density, the mixing rate, and the evaluation result of the shaped article.

[Comparative Example 3]
In Comparative Example 3, in the same manner as in Example 4 except that PP was used as a raw material instead of PA12 in Example 4, the measurement of the moisture content of the surplus powder, the measurement of the loose bulk density, and the production of the molded article And the modeled object was evaluated.
Table 2 shows the moisture content of the excess powder, the loose bulk density, the mixing rate, and the evaluation result of the shaped article.
It was.

DESCRIPTION OF SYMBOLS 1 Electromagnetic irradiation source 2 Reflector 3 Heater 4 Roller 5 Supply tank 6 Laser scanning space

US Pat. No. 4,247,508 US Pat. No. 4,863,538 US Pat. No. 5,017,753 US Pat. No. 6,110,411 Japanese Patent No. 4,964,990 German Patent Application No. 102006023484

Claims (9)

Three-dimensional modeling having a step of forming a layer made of a three-dimensional modeling powder made of a thermoplastic resin composition and a step of selectively solidifying the powder by selectively irradiating the layer with electromagnetic radiation. It is a method, Comprising: Each three-dimensional modeling method characterized by including each process of following (a)-(c).
(A) The process which makes loose bulk density of the surplus powder which was not solidified at the time of shaping | molding more than 20% with respect to a true density (b) The process which mixes the said surplus powder and unused powder and makes it mixed powder (C) forming the layer with the mixed powder   The three-dimensional modeling method according to claim 1, wherein in the step (b), a mass mixing ratio of surplus powder and unused powder in the mixed powder is set in a range of 5: 5 to 10: 0.   The three-dimensional modeling method according to any one of claims 1 to 3, wherein in the step (a), a loose bulk density of the surplus powder is set to a density in a range of 35% to 70% with respect to a true density.   The three-dimensional modeling method according to any one of claims 1 to 3, wherein a crystalline thermoplastic resin composition powder is used as the surplus powder and the unused powder.   The three-dimensional modeling method according to any one of claims 1 to 4, wherein a crystalline thermoplastic resin composition powder containing polyamide is used as the surplus powder and the unused powder.   The three-dimensional modeling method according to any one of claims 1 to 5, wherein a 50% volume average particle size of the three-dimensional modeling powder is 5 to 100 µm.   The three-dimensional modeling method according to any one of claims 1 to 6, wherein the step (a) is a step of setting the moisture content of the surplus powder to 2% by mass or less.   The three-dimensional molded item formed by the three-dimensional modeling method of any one of Claims 1-7. Means for forming a layer made of a three-dimensional modeling powder made of a thermoplastic resin composition;
Means for selectively solidifying the powder by selectively irradiating the layer with electromagnetic radiation;
Means for adjusting the loose bulk density of the surplus powder that was not solidified at the time of modeling;
Means for mixing the surplus powder and unused powder to form a mixed powder.