Resin pellet for three-dimensional fabrication, three-dimensional fabricated article, and method for producing three-dimensional fabricated article

Abstract

A resin pellet according to the present disclosure is for direct pellet-type three-dimensional fabrication, and contains a polyolefin. A loss tangent tan δ obtained by subjecting the resin pellet to dynamic viscoelasticity measurement at a measurement temperature of 220°C satisfies the following conditions: tan δ < 1.00 at a frequency ω = 0.01 Hz, and tan δ ≥ 1.10 at a frequency ω = 1.0 Hz.

Description

Resin pellets for three-dimensional molding, three-dimensional molded objects, and methods for manufacturing three-dimensional molded objects.

[0001] This disclosure relates to resin pellets for three-dimensional molding, three-dimensional molded objects, and methods for manufacturing three-dimensional molded objects.

[0002] In recent years, three-dimensional modeling technology, also known as 3D printing technology, has attracted attention, and among them, fused deposition modeling (FDM) is one of the representative modeling methods. FDM is a method of creating three-dimensional objects by melting resin filament or resin pellets at high temperatures, extruding them through a nozzle, and layering the resin while moving the nozzle along the cross-section of the object. Among FDM methods, the method that uses resin pellets is also called the direct pellet method. The direct pellet method does not require processing the resin into a filament, and modeling can be done directly from resin pellets, so it is low cost and offers a high degree of freedom in material selection, and its use is progressing in industrial applications.

[0003] For example, Patent Document 1 describes a granular material for a thermal melt-type three-dimensional printer made of a thermoplastic elastomer. When measured with a rotary rheometer using a parallel plate of 20 mmφ, a measurement gap of 1.3 mm, and a frequency of 0.1 Hz, the thermoplastic elastomer has a loss tangent tanδ of 0.40 or more and a loss modulus of elasticity G'' of 11000 Pa or less at at least one measurement temperature between 120 and 270°C.

[0004] Patent Document 2 describes a filament suitable for use in addition manufacturing by extrusion. The filament is formed from a composite material comprising semicrystalline polylactic acid and chemical pulp of woody cellulose fibers, wherein the amount of chemical pulp of woody cellulose fibers is such that the composite material of the filament has a complex viscosity (η*) of 10,000 Pa·s or more when measured at a frequency of 0.1 Hz and 180°C, and when manufactured by addition manufacturing by extrusion, the composite molten material formed from the filament reaches a temperature of 133°C or higher (T ｓｕｂ In this case, the ratio of the shear storage modulus to the shear loss modulus (G' / G'') is selected to be 1.0 or greater.

[0005] Patent Document 3 describes a filament for material extrusion type 3D printer molding. The filament is made of a thermoplastic elastomer containing at least a specific component (A), and the ratio of the storage modulus (G'[200°C, 100Hz]) to the loss modulus (G''[200°C, 100Hz]) (tanδ = G''[200°C, 100Hz] / G'[200°C, 100Hz]) measured at 200°C, 100Hz by dynamic viscoelasticity measurement is 0.50 to 2.50. The specific component (A) is at least one block copolymer from the group consisting of a block copolymer containing at least one polymer block derived from a vinyl aromatic compound and a polymer block derived from a conjugated diene and isobutylene, and a block copolymer obtained by hydrogenating the block copolymer.

[0006] Patent Document 4 describes a powder containing thermoplastic particles, wherein the thermoplastic particles comprise a water-soluble organic material and a water-insoluble organic material. When the temperature dependence of the storage modulus and loss modulus in the shear direction of a molded body obtained by pressure molding the powder into a cylindrical shape with a diameter of 10 mm and a thickness of 1 mm is measured by raising the temperature at a rate of 2°C / min using a rotary rheometer with an angular frequency of 1 Hz, if the temperature at which the storage modulus becomes 1 MPa is T°C, then in the temperature range of T°C to (T+10)°C, the storage modulus is always greater than the loss modulus.

[0007] International Publication No. 2021 / 060451, Japanese Patent Publication No. 2017-222169; International Publication No. 2016 / 171191, Japanese Patent Publication No. 2016-210958

[0008] The present disclosure aims to provide resin pellets for direct pellet type three-dimensional molding that can produce molded objects with excellent formability and appearance, three-dimensional molded objects made therefrom, and a method for manufacturing three-dimensional molded objects.

[0009] Examples of embodiments of the present disclosure are listed in the following items [1] to

[14] . [1] A resin pellet for direct pellet type three-dimensional molding, wherein the resin pellet contains polyolefin, and the loss loss tangent tanδ obtained by dynamic viscoelastic measurement of the resin pellet at a measurement temperature of 220°C satisfies the following conditions: tanδ < 1.00 at frequency ω = 0.01 Hz, and tanδ ≥ 1.10 at frequency ω = 1.0 Hz. [2] The resin pellet according to item 1, wherein tanδ ≤ 0.40 at frequency ω = 0.01 Hz. [3] A resin pellet according to item 1 or 2, wherein when tanδ at frequency ω = 0.01 Hz is tanδ(ω = 0.01 Hz) and tanδ at frequency ω = 1.0 Hz is tanδ(ω = 1.0 Hz), the following condition is satisfied: tanδ(ω = 1.0 Hz) / tanδ(ω = 0.01 Hz) ≥ 3.00. [4] A resin pellet according to any one of items 1 to 3, wherein the polyolefin comprises polypropylene. [5] A resin pellet according to any one of items 1 to 4, wherein the polyolefin comprises block copolymerized polypropylene. [6] A resin pellet according to any one of items 1 to 5, further comprising an elastomer. [7] A resin pellet according to item 6, wherein the elastomer comprises an α-olefin copolymer. [8] A resin pellet according to item 7, wherein the α-olefin copolymer comprises at least one selected from the group consisting of propylene-1-butene copolymer, ethylene-1-butene copolymer, and ethylene-propylene copolymer. [9] The resin pellet is the resin pellet according to any one of items 1 to 8, further containing carbon fibers.

[10] The resin pellet is the resin pellet according to any one of items 1 to 9, containing 10% by weight or more and 90% by weight or less of the polyolefin based on the total weight of the resin pellet.

[11] The resin pellet is the resin pellet according to any one of items 1 to 9, containing 10% by weight or more and 90% by weight or less of the polyolefin and 5% by weight or more and 50% by weight or less of the elastomer based on the total weight of the resin pellet.

[12] A three-dimensional object formed using the resin pellet according to any one of items 1 to 11.

[13] A three-dimensional object having a hollow structure, as described in item 12.

[14] A method for manufacturing a three-dimensional object, comprising a lamination step of laminating strands formed by melting resin pellets described in any one of items 1 to 11 in a screw extruder and extruding them from a nozzle.

[0010] According to this disclosure, it is possible to provide resin pellets for direct pellet type three-dimensional molding that can produce molded objects with excellent formability and appearance, three-dimensional molded objects made therefrom, and a method for manufacturing three-dimensional molded objects.

[0011] Figure 1 is a schematic diagram of a three-dimensional object having a hollow structure used for evaluating the formability and appearance of the object in this disclosure.

[0012] One embodiment of this disclosure will be described in detail below, but the scope of this disclosure is not limited to the embodiment described herein, and various modifications can be made without departing from the spirit of this disclosure. Furthermore, if multiple upper and lower limits are given for a particular parameter, any combination of these upper and lower limits can be used to create a suitable numerical range.

[0013] 《Resin Pellets》 The resin pellets according to this disclosure are resin pellets for direct pellet type three-dimensional molding, and the resin pellets contain polyolefin, and the loss tangent tanδ obtained by dynamic viscoelasticity measurement of the resin pellets at a measurement temperature of 220°C satisfies the following conditions: tanδ < 1.00 at a frequency ω = 0.01 Hz, and tanδ ≥ 1.10 at a frequency ω = 1.0 Hz. The resin pellets of this disclosure, having the above configuration, can produce moldable objects with excellent formability and appearance. The reason for this is not limited to theory, but is presumed to be as follows: That is, because tanδ < 1.00 at ω = 0.01 Hz, the molten resin exhibits elastic behavior in the low shear region, resulting in excellent shape retention. Therefore, it is thought that the strands maintain their independence immediately after molding, sagging and distortion are suppressed, and formability is improved. When a 3D printer (three-dimensional printing device) has a large nozzle diameter and a large diameter of extruded strands, the strands remain at a high temperature for a relatively long time immediately after printing because it takes time to cool them down. The resin pellets of this disclosure exhibit elastic behavior in the low-shear region even when molten, making them particularly suitable for 3D printers (three-dimensional printing devices) with large nozzle diameters, where the strands remain at a high temperature for a relatively long time immediately after printing, as described above. In other words, the resin pellets of this disclosure make it possible to achieve both high printing speed and high printability. Furthermore, because tanδ≧1.10 at ω=1.0 Hz, the resin pellets exhibit sufficiently viscous behavior in the high-shear region and are extruded smoothly. In direct-pellet type 3D printers (three-dimensional printing devices), printing is performed by heating and melting resin pellets with a small extruder and extruding them from the nozzle, but at this time, high shear stress is applied to the resin pellets. The resin pellets of this disclosure exhibit viscous behavior in the high-shear region, which is thought to suppress melt fracture during extrusion from the nozzle and improve the appearance quality of the molded object. Thus, by controlling tanδ within a specific range in a direct pellet-type three-dimensional molding resin pellet containing polyolefin, it is possible to balance static and dynamic behavior, thereby providing a resin pellet that can produce molded objects with excellent formability and appearance.

[0014] <Loss tangent tanδ in dynamic viscoelasticity measurement> The resin pellets of this disclosure have a loss tangent tanδ at a frequency ω = 0.01 Hz (hereinafter also simply referred to as "low shear"), obtained by dynamic viscoelasticity measurement at a measurement temperature of 220°C, which is less than 1.00, more preferably less than 0.90, less than 0.80, less than 0.70, less than 0.60, less than 0.50, or less than 0.40. The lower limit of tanδ at low shear, which can be arbitrarily combined with these upper limits, is not particularly limited, but from the viewpoint of easily balancing it with tanδ at high shear, which will be described later, it may be, for example, 0.10 or higher. When tanδ at low shear is within the above range, moldability is further improved.

[0015] The resin pellet has a loss tangent tanδ at a frequency ω = 1.0 Hz (hereinafter also simply referred to as "high shear"), obtained by dynamic viscoelasticity measurement at a measurement temperature of 220°C, which is 1.10 or higher, more preferably greater than 1.10, 1.15 or higher, 1.20 or higher, 1.25 or higher, or 1.30 or higher. The upper limit of tanδ at high shear, which can be arbitrarily combined with these lower limits, is not particularly limited, but from the viewpoint of easily balancing it with the tanδ at low shear as described above, it may be, for example, 2.50 or lower, 2.00 or lower, 1.70 or lower, or 1.50 or lower. The appearance of the molded object is further improved when the tanδ at low shear is within the above range.

[0016] The ratio of tanδ at frequency ω = 1.0 Hz (high shear) (hereinafter also referred to as "tanδ(ω = 1.0 Hz)") to tanδ at frequency ω = 0.01 Hz (low shear) (hereinafter referred to as "tanδ(ω = 0.01 Hz)") (tanδ(ω = 1.0 Hz) / tanδ(ω = 0.01 Hz)) is preferably 3.00 or higher, 3.50 or higher, or 4.00 or higher. The upper limit of the tanδ ratio (tanδ(ω = 1.0 Hz) / tanδ(ω = 0.01 Hz)) that can be arbitrarily combined with these lower limits is not particularly limited, but for example, it is 5.00 or lower, or 4.50 or lower. A tanδ ratio (tanδ(ω=1.0Hz) / tanδ(ω=0.01Hz)) of 3.50 or higher, particularly preferably 4.00 or higher, allows the resin pellet to exhibit more viscous behavior when extruded from the nozzle and more elastic behavior immediately after molding, making it easier to provide resin pellets with excellent moldability and appearance of molded objects. Furthermore, by satisfying the above-mentioned preferred upper limit of the tanδ ratio (tanδ(ω=1.0Hz) / tanδ(ω=0.01Hz)), it becomes easier to provide resin pellets with an excellent balance between static and dynamic behavior, and with excellent moldability and appearance of molded objects.

[0017] To adjust the tanδ(ω=1.0Hz), tanδ(ω=0.01Hz), and their ratio (tanδ(ω=1.0Hz) / tanδ(ω=0.01Hz)) of the resin pellets to within the above-mentioned range, for example, a combination of several different polyolefin resins, such as several types of polypropylene (homopolymer, random copolymer, block copolymer), can be used as the polyolefin; other thermoplastic resins and / or elastomers can be included in addition to the polyolefin; and fillers, such as carbon fibers, can be included. Preferably, by further including an elastomer in addition to the polyolefin, it is easier to adjust the tanδ(ω=1.0Hz), tanδ(ω=0.01Hz), and their ratio (tanδ(ω=1.0Hz) / tanδ(ω=0.01Hz)) to within the above-mentioned range.

[0018] <Composition> (Polyolefin) The resin pellets of this disclosure contain polyolefin. The polyolefin is preferably a polymer having α-olefin as a constituent unit. The number of carbon atoms in the α-olefin is preferably 2 or more, or 3 or more, and preferably 10 or less, 8 or less, or 5 or less. The α-olefin may be a homopolymer using one type alone, or a copolymer combining two or more types. More specifically, examples of polyolefins include polyethylene, polypropylene, and polybutene, and preferably polypropylene. By containing polypropylene as the polyolefin in the resin pellets, it is easier to control tanδ within a specific range.

[0019] Examples of polypropylene include polypropylene homopolymer, random copolymer polypropylene (also referred to as "rPP" in this disclosure), and block copolymer polypropylene (also referred to as block polypropylene; also referred to as "bPP" in this disclosure). rPP is typically a random copolymer of propylene, the main component, and a small amount of comonomer such as ethylene. bPP is typically a block copolymer of propylene, the main component, and a small amount of comonomer such as ethylene, and more specifically, may consist of a polypropylene homopolymer phase and an ethylene-propylene copolymer phase or polyethylene phase. Block copolymer polypropylene may have a sea-island structure in which island phases of ethylene-propylene copolymer phase or polyethylene phase are dispersed in a sea phase of polypropylene homopolymer phase, and ethylene-propylene copolymer (EPR) may be present around the ethylene-propylene copolymer phase or polyethylene phase. Here, "main component" of polypropylene means that it constitutes the largest amount in the copolymer in terms of molar ratio. The ethylene content in rPP and bPP is not limited, but may be, for example, 1 to 20 mol%, or 1 to 10 mol%.

[0020] From the viewpoint of moldability and the appearance of the molded object, it is preferable that the polypropylene contains bPP. By including bPP as polypropylene in the resin pellets, it becomes easier to control tanδ within a specific range, resulting in superior moldability and the appearance of the molded object.

[0021] The melt flow rate (MFR) of polyolefins is preferably 0.5 to 100 g / 10 min at 230°C and a 2.16 kg load, and may be, for example, 3 to 50 g / 10 min. When the MFR is 0.5 g / 10 min or higher, the fluidity of the resin is high, melt fracture during nozzle extrusion is suppressed, and the appearance quality of the molded object is improved. On the other hand, when the MFR is 100 g / 10 min or lower, the melt viscosity is not too high, which more effectively prevents strand sagging immediately after molding, and further improves moldability. By appropriately combining polyolefin resins having different MFRs, such as multiple types of polypropylene (homopolymer, random copolymer, block copolymer), the melt viscosity can be adjusted according to the purpose.

[0022] The polyolefin content is preferably 10% to 90% by weight, based on the total weight of the resin pellets. The lower limit of the polyolefin content may be, for example, 15% or more by weight, 20% or more by weight, or 30% or more by weight. The upper limit of the polyolefin content, which can be optionally combined with these lower limits, may be, for example, 80% or less by weight, 70% or less by weight, or 60% or less by weight. When the polyolefin content is within these ranges, it is easier to control tanδ to a specific range.

[0023] (Other Thermoplastic Resins) The resin pellets of this disclosure may contain other thermoplastic resins in addition to polyolefins. Examples of other thermoplastic resins include, but are not limited to, general-purpose plastics, engineering plastics, and super engineering plastics.

[0024] Examples of general-purpose plastics include polyvinyl chloride (PVC), polyvinylidene chloride, polystyrene (PS), polyvinyl acetate (PVAc), polytetrafluoroethylene (PTFE), acrylonitrile butadiene styrene resin (ABS resin), styrene acrylonitrile copolymer (AS resin), and acrylic resin.

[0025] Examples of engineering plastics include polyamide (PA), polyacetal (POM), polycarbonate (PC), modified polyphenylene ether (m-PPE, modified PPE, PPO), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), syndiotactic polystyrene (SPS), and cyclic polyolefin (COP).

[0026] Examples of super engineering plastics include polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), polysulfone (PSF), polyethersulfone (PES), amorphous polyarylate (PAR), polyetheretherketone (PEEK), thermoplastic polyimide (PI), and polyamideimide (PAI).

[0027] The content of other thermoplastic resins may be, for example, 1% to 20% by weight, 1% to 10% by weight, or 1% to 5% by weight, based on the total weight of the resin pellets. When the content of other thermoplastic resins is within these ranges, it is easier to control tanδ to a specific range.

[0028] (Elastomer) The resin pellets of this disclosure preferably further contain an elastomer in addition to polyolefin. The elastomer is a material having rubber elasticity. Rubber elasticity refers to the property that when a load is applied to a resin, the shape of the resin deforms, and when the load applied to the resin is removed, the shape of the resin tries to return to its original shape. By further containing an elastomer in the resin pellets, it is easier to control tanδ within a specific range.

[0029] An elastomer refers to a thermoplastic resin with rubber elasticity, preferably having a tensile modulus of 6.0 × 10⁻⁶ at 25°C.８ This is a thermoplastic resin with a tensile modulus of less than Pa. The tensile modulus was measured in accordance with JIS K7161-2:2014, with a test speed of 1 mm / min and a 1A type test specimen. The total length of the injection-molded product was 170 mm, and the thickness of the injection-molded product was 2.5 mm.

[0030] From the viewpoint of controlling tanδ to a specific range, the elastomer preferably comprises an α-olefin copolymer. More preferably, the α-olefin copolymer is a copolymer comprising structural units derived from an α-olefin and structural units derived from another olefin different from the α-olefin.

[0031] From the viewpoint of controlling tanδ to a specific range, the number of carbon atoms in the α-olefin copolymer is preferably 3 or more, and preferably 10 or less, 8 or less, or 5 or less. Examples of α-olefins include 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 3,3-dimethyl-1-butene, 4-methyl-1-pentene, and 1-octene. The α-olefin may be used alone or in combination of two or more. 1-butene is preferred as the α-olefin.

[0032] From the viewpoint of controlling tanδ to a specific range, the number of carbon atoms in the other olefin in the α-olefin copolymer may preferably be 2 or more, or 3 or more, and preferably 10 or less, 8 or less, or 5 or less. Examples include ethylene, propylene, and butene.

[0033] From the viewpoint of controlling tanδ to a specific range, preferred α-olefin copolymers include ethylene-α-olefin copolymer (E-αOR), propylene-α-olefin copolymer (P-αOR), and butene-α-olefin copolymer. More specifically, α-olefin copolymers include at least one selected from the group consisting of propylene-1-butene copolymer (PBR), ethylene-1-butene copolymer (EBR), and ethylene-propylene copolymer. More preferably, α-olefin copolymers include a combination of propylene-α-olefin copolymer and ethylene-α-olefin copolymer, and even more preferably, a combination of PBR and EBR. Since both PBR and EBR have butene as a constituent unit, they have high compatibility, making it easier to control tanδ to a specific range, and resulting in superior moldability and appearance of molded products.

[0034] When the resin pellets contain polypropylene as the polyolefin, it is preferable that the elastomer contains an α-olefin copolymer that includes propylene as a constituent component. This improves the compatibility between polypropylene and the α-olefin copolymer, making it easier to control tanδ within a specific range.

[0035] The melt flow rate (MFR) of the elastomer may preferably be 0.5 to 20 g / 10 min or 0.8 to 10 g / 10 min at 230°C and a 2.16 kg load. Within these ranges, the viscoelastic balance when mixed with polyolefin resin is good, and it is easier to control tanδ within a specific range. Specifically, if the MFR of the elastomer is 0.5 g / 10 min or higher, the overall fluidity of the resin when mixed with polyolefin is increased, melt fracture during nozzle extrusion is suppressed, and the appearance quality of the molded product is improved. On the other hand, if the MFR is 20 g / 10 min or lower, the overall melt viscosity of the resin when mixed with polyolefin is not too high, which more effectively prevents strand sagging immediately after molding and further improves moldability.

[0036] The content of the elastomer is preferably 5 wt% to 50 wt% based on the total weight of the resin pellets. The lower limit of the content of the elastomer is preferably 10 wt% or more, 15 wt% or more, or 20 wt% or more. The upper limit of the content of the elastomer that can be arbitrarily combined with these lower limits may preferably be 45 wt% or less, 40 wt% or less, or 35 wt% or less. When the content of the elastomer falls within these ranges, it is easier to control tanδ within a specific range.

[0037] When the elastomer comprises a combination of a propylene-α-olefin copolymer (P-αOR) and an ethylene-α-olefin copolymer (E-αOR), the lower limits of their contents are each independently, based on the total weight of the resin pellets, preferably 1 wt% or more, 5 wt% or more, 10 wt% or more, or 15 wt% or more. The upper limits of the content of P-αOR and the content of E-αOR that can be arbitrarily combined with these lower limits may preferably be 40 wt% or less, 35 wt% or less, 30 wt% or less, or 25 wt% or less. When the content of P-αOR and the content of E-αOR each fall within these ranges, it is easier to control tanδ within a specific range.

[0038] The weight percent of the polyolefin (PO) contained in the resin composition of the present disclosure is defined as W ＰＯ , and the weight percent of the elastomer (EL) is defined as W ＥＬ , it is preferred that W ＰＯ >W ＥＬ . That is, the lower limit of the weight ratio of PO to EL (W ＰＯ / W ＥＬ ) may preferably be more than 1.0, for example 1.1 or more, 1.2 or more, 1.5 or more, 2.0 or more, or 2.5 or more. The upper limit of the weight ratio (W ＰＯ / W ＥＬ ) that can be arbitrarily combined with these lower limits may preferably be 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, 2.5 or less, 2.0 or less, or 1.5 or less. The weight ratio of PO to EL (W ＰＯ / W ＥＬ) is within these ranges, it is easier to control tanδ within a specific range.

[0039] (Filler) The resin pellets of the present disclosure may further contain a filler. Examples of the filler include inorganic or organic fillers, such as carbon fibers, carbon black, graphite, glass fibers, glass flakes, talc, mica, clay, silica, calcium carbonate, alumina, and magnesia. By adding these fillers, the rigidity, dimensional stability, surface properties, thermal conductivity, designability, electrical conductivity, cost, and the like of the shaped article can be appropriately adjusted.

[0040] For example, the resin pellets may further contain carbon fibers. Examples of the carbon fibers include polyacrylonitrile (PAN)-based carbon fibers, pitch-based carbon fibers, and mixtures thereof. When the resin pellets contain carbon fibers, improvements in the mechanical strength, dimensional stability, thermal conductivity, changes in surface texture, and the like of the shaped article can be expected. The carbon fibers may be in the form of short fibers, long fibers, or continuous fibers. These carbon fibers may be subjected to a sizing treatment for the purpose of improving adhesion to the resin, and the sizing agent is preferably a sizing agent having compatibility with the resin constituting the resin pellets such as polyolefin, and examples thereof include epoxy-based and olefin-based sizing agents.

[0041] The content of the carbon fibers may be, for example, 5 wt% to 50 wt%, 10 wt% to 40 wt%, or 10 wt% to 30 wt%, based on the total weight of the resin pellets.

[0042] (Other Components) The resin pellets of the present disclosure may contain other components in addition to the above-described polyolefin, other thermoplastic resins, elastomers, and fillers. Examples of the other components include ultraviolet absorbers, stabilizers, antioxidants, plasticizers, colorants, color regulators, flame retardants, antistatic agents, fluorescent brighteners, matting agents, impact strength modifiers, and the like.

[0043] The content of the other components may be, for example, 0.01 wt% to 10 wt%, 0.1 wt% to 5 wt%, or 0.1 wt% to 3 wt%, based on the total weight of the resin pellets.

[0044] <Shape> The shape of the resin pellets in this disclosure is not particularly limited, and for example, spherical, cylindrical, or irregularly shaped pellets can be used. In general, in direct pellet type 3D printers, stable molding is possible regardless of shape as long as the pellets have good transportability and heating / melting properties. Therefore, the resin pellets in this disclosure can adopt any shape depending on the manufacturing method and material properties.

[0045] 《Method for Manufacturing Resin Pellets》 The resin pellets of this disclosure can be obtained by mixing a desired polyolefin, and, if necessary, various materials such as elastomers and carbon fibers, in predetermined proportions, melt-kneading, and granulating. For melt-kneading and granulation, for example, a single-screw extruder or a twin-screw extruder can be used, making it possible to stably produce pellets with a uniform composition that has excellent kneadability and dispersibility. The kneading conditions (screw configuration, temperature, and rotation speed, etc.) can be appropriately adjusted according to the MFR of the raw resin and the type and content of fillers.

[0046] <Three-Dimensional Printed Objects> The three-dimensional printed objects of this disclosure can be fabricated using the three-dimensional printing resin pellets of this disclosure. The fabrication method may be a direct pellet method. By fabricating the three-dimensional printed objects of this disclosure using the three-dimensional printing resin pellets of this disclosure, resin sagging and distortion during fabrication are suppressed, and the appearance is excellent.

[0047] The three-dimensional molded object of this disclosure preferably has a hollow structure. In this disclosure, a hollow structure refers to a structure that has a space inside the three-dimensional molded object that is not filled with material. The hollow structure is not limited to a structure that has a completely sealed space, and includes, for example, tubular or cylindrical structures as shown in Figure 1. Having a hollow structure in a three-dimensional molded object reduces warping due to molding shrinkage and allows for weight reduction. The method for forming the hollow structure is not particularly limited, but for example, a hollow structure can be formed by continuously laminating strands formed by extruding molten resin from a nozzle during three-dimensional molding. Specifically, the strands extruded from the nozzle are laminated in a closed-loop shape (a shape that is continuous and revolves around without breaks) in a plane or three-dimensional space, thereby forming a space inside the laminated strands and obtaining a three-dimensional molded object with a hollow structure (see, for example, Figure 1). Furthermore, it is preferable that the hollow structure is formed by a so-called single-stroke molding path in which the strands are formed continuously without interruption. The resin pellets of this disclosure exhibit elastic behavior in the low-shear region and thus exhibit excellent shape retention. As a result, even without support when forming the hollow structure, sagging and collapse of the strands can be effectively suppressed, which is extremely advantageous in that three-dimensional molded objects with hollow structures can be fabricated with high precision and excellent appearance.

[0048] <Method for Manufacturing Three-Dimensional Molded Objects> The method for manufacturing three-dimensional molded objects according to the present disclosure can be manufactured by a method that includes a lamination step of laminating strands formed by melting the resin pellets for three-dimensional molding according to the present disclosure in a screw-type extruder and extruding them from a nozzle. The method for manufacturing three-dimensional molded objects according to the present disclosure can provide three-dimensional molded objects with superior appearance, as resin sagging and distortion during molding are suppressed by molding the resin pellets for three-dimensional molding according to the present disclosure in a direct pellet method.

[0049] In manufacturing a three-dimensional object using the resin pellets for three-dimensional molding of this disclosure, a direct pellet type 3D printer (three-dimensional molding device) can be used. The direct pellet type 3D printer has a stage on which the three-dimensional object is formed, a screw extruder, and a moving mechanism for moving the screw extruder relative to the stage. The screw extruder has a cylinder, a heater, a screw disposed inside the cylinder, and a nozzle. The screw extruder is configured to melt and knead the resin pellets for three-dimensional molding supplied into the cylinder by heating with the heater and rotating the screw, and to transport them to the tip of the cylinder and extrude them through the nozzle. An opening is provided at the tip of the nozzle, and the diameter of the opening (nozzle diameter) is not particularly limited, but is preferably 1.0 mm or more, more preferably 2.5 mm or more, even more preferably 5.0 mm, and particularly preferably 7.5 mm or more. By setting the nozzle diameter to 1.0 mm or more, the molding speed of the three-dimensional object can be increased. As described above, the resin pellets for three-dimensional molding disclosed herein have a tanδ (ω = 0.01 Hz) of less than 1.0, making it easier to maintain the shape immediately after molding, even when the nozzle diameter is large and the diameter of the strands extruded from the nozzle during molding is large. Therefore, it is possible to achieve both high molding speed and high moldability.

[0050] Examples of embodiments of this disclosure will be described below with reference to examples and comparative examples, but this disclosure is not limited to the following examples and comparative examples.

[0051] Materials: Details of the various materials used in the examples and comparative examples are as follows.

[0052] <Random Polypropylene Resin (rPP)> rPP1: Prime Polypro (registered trademark) F730NV (manufactured by Prime Polymer Co., Ltd., MFR (230℃, 2.16 kg load): 6.2 g / 10 min) rPP2: Prime Polypro (registered trademark) J13B (manufactured by Prime Polymer Co., Ltd., MFR (230℃, 2.16 kg load): 220 g / 10 min) rPP3: Prime Polypro (registered trademark) F113G (manufactured by Prime Polymer Co., Ltd., MFR (230℃, 2.16 kg load): 3.0 g / 10 min)

[0053] <Blocked Polypropylene Resin (bPP)> bPP2: Propylene polymer A (MFR: 50 g / 10 min) composed of polymers A-1 and A-2 below. Propylene polymer (A-1): 76.5 parts by weight relative to parts by weight of polymer A. MFR: 213 g / 10 min. Content of constituent units derived from propylene: 99.9 mol% (relative to A-1). Propylene-ethylene copolymer (A-2): 23.5 parts by weight relative to parts by weight of polymer A. Intrinsic viscosity [η]: 2.5 dl / g, Content of constituent units derived from ethylene: 39 mol% (relative to A-2).

[0054] <Carbon Fiber-Containing Polypropylene Resin> CFPP1: Plastron (registered trademark) PP-CF40-11 (manufactured by Polyplastics Co., Ltd., carbon fiber content 40% by weight, long-fiber carbon-reinforced PP)

[0055] <Carbon Fiber> CF1: PYROFIL (registered trademark) TR066A (manufactured by Mitsubishi Chemical Corporation, carbon fiber type: PAN 24t, sizing material: epoxy-based)

[0056] <Olefin-based elastomers> EBR1: Tuffmer® DF610 (manufactured by Mitsui Chemicals, ethylene-1-butene copolymer, MFR (230℃, 2.16 kg load): 2.2 g / 10 min) EBR2: Tuffmer® DF605 (manufactured by Mitsui Chemicals, ethylene-1-butene copolymer, MFR (230℃, 2.16 kg load): 0.9 g / 10 min) PBR1: Tuffmer® XM7090 (manufactured by Mitsui Chemicals, propylene-1-butene copolymer, MFR (230℃, 2.16 kg load): 7.0 g / 10 min)

[0057] <Modified Polyolefin Resin> MAH-PP: Maleic acid-modified polypropylene resin (modified PP) obtained by the following synthesis method. 100 parts by weight of polypropylene (manufactured by Prime Polymer Co., Ltd., trade name J106G, MFR (230℃, 2.16 kg): 15 g / 10 min) was pre-mixed with 1 part by weight of dialkyl peroxide (manufactured by NOF Corporation, Perhexa 25B ("Perhexa" is a registered trademark of the company)) and 3 parts by weight of powdered maleic anhydride (manufactured by NOF Corporation, CRYSTAL MAN ("CRYSTAL MAN" is a registered trademark of the company)). This mixture was supplied to a 30 mmφ twin-screw extruder heated to 190℃ and melt-kneaded at 200 rpm. The resulting strand was cooled in a water bath to obtain maleic acid-modified polypropylene. To remove unmodified residual maleic anhydride, this maleic acid-modified polypropylene was vacuum-dried at 40℃ for 2 hours. The maleic acid content of the obtained maleic anhydride-modified polypropylene was 2.5% by weight, and the MFR (230°C, 2.16 kg) was 800 g / 10 min.

[0058] <Polypropylene Resin Composition> PPC1: Polypropylene resin composition (a commercially available polypropylene resin composition containing polypropylene, talc, and PP; MFR (230°C, 2.16 kg load): 31.4 g / 10 min; Density: 1.035 g / cm³) ３ )

[0059] <Example of Resin Pellet Production> <Production of Compounds and Pellet> The above materials were melt-kneaded and granulated using the following compound granulation apparatus and under the following conditions, with the compositions shown in Table 1 (units are in weight %), to obtain each pellet. However, PPC1 in Comparative Example 1 was used as is because it was already in pellet form.

[0060] <Compound Granulation Equipment and Conditions> Equipment: Co-rotating twin-screw extruder HK-25D (manufactured by Parker Corporation) Barrel diameter: 30 mm Screw process length (L / D): 63 Cylinder set temperature: 200°C Screw rotation speed: 150 rpm Pellet length: 3 mm

[0061] 《Measurement and Evaluation Method》 〈Dynamic Viscoelasticity Measurement〉 The loss tangent tanδ of the dynamic viscoelasticity measurement was measured in accordance with JIS K 7244-10. Specifically, a sheet of approximately 60 mm × 60 mm × 1 mm (length × width × thickness) was prepared by compression molding (equipment: Toyo Seiki Mini Test Press MP-WCH) and used as the test specimen. The gauge pressure during compression molding was 20 MPa, and the press temperature was 200°C. The measurement conditions were as follows: Geometry: Parallel plate 20 mmφ Temperature: 220°C Frequency ω: 0.01 to 100 Hz Gap: Near 0.97 mm Set strain: 0.50 Number of measurements: n = 1 Measurement device: ARES-G2 (manufactured by T.A. Instruments Co., Ltd.)

[0062] <Evaluation of Formability and Appearance of Printed Objects> The following direct pellet 3D printer was used. Using the screw extruder equipped with the direct pellet 3D printer, pellets were melted and extruded to produce a three-dimensional object with a hollow structure as shown in Figure 1. The angle of the obliquely printed parts was 45°. Formability and extrusion performance were evaluated according to the following criteria.

[0063] (Direct pellet 3D printer and printing conditions) Equipment: Direct pellet large 3D printer EXF-12 (manufactured by ExtraBold Co., Ltd.) Nozzle diameter: 8 mm Nozzle temperature: 220°C Printing speed: 394 mm / min Layer thickness: 4 mm

[0064] (Evaluation Criteria for Formability) The obtained printed objects were visually inspected and evaluated for formability according to the following criteria: A: No deformation of the form was observed. B: Slight deformation of the form was observed (e.g., peeling of corners or distortion of straight lines). C: Strand tearing or failure of strands to adhere to the build bed occurred, or significant deformation of the form was observed.

[0065] (Evaluation Criteria for the Appearance of the Printed Object) The printed object was visually inspected and its appearance was evaluated according to the following criteria: A: No melt fracture was observed on the surface of the printed object. B: Melt fracture was observed on the surface of the printed object. -: Significant deformation was observed, making it impossible to evaluate the appearance of the printed object.

[0066]

Claims

1. A resin pellet for direct pellet type three-dimensional molding, wherein the resin pellet contains polyolefin, and the loss tangent tanδ obtained by dynamic viscoelasticity measurement of the resin pellet at a measurement temperature of 220°C satisfies the following conditions: tanδ < 1.00 at frequency ω = 0.01 Hz, and tanδ ≥ 1.10 at frequency ω = 1.0 Hz.

2. The resin pellet according to claim 1, wherein tanδ < 0.40 at a frequency ω = 0.01 Hz.

3. When tanδ at frequency ω = 0.01 Hz is defined as tanδ(ω = 0.01 Hz) and tanδ at frequency ω = 1.0 Hz is defined as tanδ(ω = 1.0 Hz), the following condition is satisfied: tanδ(ω = 1.0 Hz) / tanδ(ω = 0.01 Hz) ≥ 3.00, the resin pellet according to claim 1 or 2.

4. The resin pellet according to claim 1 or 2, wherein the polyolefin comprises polypropylene.

5. The resin pellet according to claim 1 or 2, wherein the polyolefin comprises block copolymerized polypropylene.

6. The resin pellet according to claim 1 or 2, wherein the resin pellet further contains an elastomer.

7. The resin pellet according to claim 5, wherein the elastomer comprises an α-olefin copolymer.

8. The resin pellet according to claim 6, wherein the α-olefin copolymer comprises at least one selected from the group consisting of propylene-1-butene copolymer, ethylene-1-butene copolymer, and ethylene-propylene copolymer.

9. The resin pellet according to claim 1 or 2, wherein the resin pellet further contains carbon fibers.

10. The resin pellet according to claim 1 or 2, wherein the resin pellet contains 10% by weight or more and 90% by weight or less of the polyolefin, based on the total weight of the resin pellet.

11. The resin pellet according to claim 5, wherein, based on the total weight of the resin pellet, it contains 10% by weight or more and 90% by weight or less of the polyolefin, and 5% by weight or more and 50% by weight or less of the elastomer.

12. A three-dimensional object formed using the resin pellets described in claim 1 or 2.

13. The three-dimensional object according to claim 12, having a hollow structure.

14. A method for manufacturing a three-dimensional object, comprising a lamination step of laminating strands formed by melting resin pellets according to claim 1 or 2 in a screw-type extruder and extruding them from a nozzle.

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