WO2023055348A1

WO2023055348A1 - Three-dimensional printing with rigid thermoplastic particles

Info

Publication number: WO2023055348A1
Application number: PCT/US2021/052528
Authority: WO
Inventors: Jake H. Thomas; Emre Hiro DISCEKICI; Shannon Reuben Woodruff
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2021-09-29
Filing date: 2021-09-29
Publication date: 2023-04-06

Abstract

A three-dimensional printing kit can include a polymeric build material including from about 80 wt% to 100 wt% rigid thermoplastic particles, and a fusing agent. The fusing agent can include water, from about 5 wt% to about 40 wt% alkyldiol organic cosolvent including a straight-chained C4-C7 saturated carbon chain with two terminal hydroxyl groups, and a radiation absorber to generate heat from absorbed electromagnetic radiation.

Description

THREE-DIMENSIONAL PRINTING

WITH RIGID THERMOPLASTIC PARTICLES

BACKGROUND

[0001 ] Three-dimensional (3D) printing may be an additive printing process used to make three-dimensional solid parts from a digital model. Three-dimensional printing is often used in rapid product prototyping, mold generation, mold master generation, and short run manufacturing. Some three-dimensional printing techniques can be considered additive processes because they involve the application of successive layers of material. This can be unlike other machining processes, which often rely upon the removal of material to create the final part.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] FIG. 1 is a schematic illustration of an example three-dimensional printing kit in accordance with the present disclosure;

[0003] FIG. 2 is a schematic illustration of an example three-dimensional printing system in accordance with the present disclosure;

[0004] FIG. 3 is a flow diagram illustrating an example method of printing a three- dimensional object in accordance with the present disclosure;

[0005] FIG. 4 is a graph comparing the standard deviation of tensile strength for three-dimensional printed objects as measured in the XY-direction and the Z-direction for two different fusing agents in accordance with the present disclosure; and [0006] FIG. 5 is a graph comparing various mechanical properties for three- dimensional printed objects as measured in the XY-direction and the Z-direction for two different fusing agents in accordance with the present disclosure.

DETAILED DESCRIPTION

[0007] Three-dimensional printing can be an additive process involving the application of successive layers of a polymeric build material with a fusing agent printed thereon to cause successive layers of the polymeric build material to become bound together. For example, the fusing agent can be selectively applied to a layer of a polymeric build material on a support bed, e.g., a build platform supporting polymeric build material, to pattern a selected region of a layer of the polymeric build material. The layer of the polymeric build material (which includes the rigid thermoplastic particles) can be exposed to electromagnetic radiation, and due to the presence of the radiation absorber on the printed portions, absorbed light energy at those portions of the layer having the fusing agent printed thereon can be converted to thermal energy, causing that portion to melt or coalesce, while other portions of the polymeric build material do not reach temperatures suitable to melt or coalesce. This can then be repeated on a layer-by-layer basis until the three-dimensional object is formed. More specifically, a polymeric build material including rigid thermoplastic particles can be paired with a fusing agent that includes a straight-chained C4-C7 saturated alkyldiol organic cosolvent to provide more consistent mechanical properties, particularly in the Z- direction or orientation, compared to other fusing agents that do not include the alkyldiol organic solvent. This organic cosolvent is considered to be environmentally friendly and in some examples, can be used instead of other organic cosolvents that may be less environmentally friendly, e.g., pyrrolidones.

[0008] In accordance with this, three-dimensional printing kits, three-dimensional printing systems, and/or methods of printing three-dimensional objects are included in the context of the present disclosure. When discussing these kits, systems, and/or methods herein, these discussions can be considered applicable to one another whether or not they are explicitly discussed in the context of that example. Thus, for example, when discussing a polymeric build material related to three-dimensional printing kits, such disclosure is also relevant to and directly supported in the context of the systems and/or methods, and vice versa. Furthermore, it is noted that terms used herein will have the ordinary meaning in their technical field unless specified otherwise. In some instances, there are terms defined more specifically throughout the specification or included at the end of the present specification, and thus, these terms can have a meaning as described herein.

Three-dimensional Printing Kits

[0009] In accordance with this, a three-dimensional printing kit 100 is shown in FIG. 1 and includes a polymeric build material 110 with from about 80 wt% to 100 wt% rigid thermoplastic particles 112; and a fusing agent 120. The fusing agent includes water 122, from about 5 wt% to about 40 wt% alkyldiol organic cosolvent 124 including a straight-chained C4-C7 saturated carbon chain with two terminal hydroxyl groups, and a radiation absorber 126 to generate heat from absorbed electromagnetic radiation.

[0010] In further detail regarding the fusing agent, in some examples, the alkyldiol organic cosolvent can be a mixture of 1,5-pentandiol and a second straight-chained C4- C7 saturated carbon chain with two terminal hydroxyl groups, or the alkyldiol organic cosolvent can consistent essentially of 1,5-pentanediol. Other example compounds that can be used alone or in combination with 1,5-pentanediol and/or with one another include 1,4-butanediol, 1,6,hexanediol, and/or 1,7-heptanediol. In addition to the water, the alkyldiol organic solvent, and the radiation absorber, there may in some examples be other liquids or dispersed materials present in the fusing agent, such as other organic cosolvent, surfactant, dispersant, biocide, viscosity modifier, pH adjuster, chelator or sequestering compound, preservative, etc. In the specific example shown in FIG. 1 , the lower alkyldiol is shown as a 1,5-pentanediol. In some other examples, the fusing agent can be devoid of lactam organic cosolvents, such as pyrrolidones.

[0011] The radiation absorber can be present in the fusing agent at from about 0.1 wt% to about 10 wt%, In some examples, the radiation absorber can be present at from about 0.5 wt% to about 7.5 wt%, from about 1 wt% to about 10 wt%, or from about 0.5 wt% to about 5 wt%. The radiation absorber can include, for example, carbon black, metal dithiolene complex, a near-infrared absorbing dye, a near-infrared absorbing pigment, metal nanoparticles, a conjugated polymer, or a combination thereof. In some examples, the radiation absorber can be carbon black. In other examples, the radiation absorber can be colored or colorless. Examples of near-infrared absorbing dyes can include aminium dyes, tetraaryldiamine dyes, cyanine dyes, pthalocyanine dyes, dithiolene dyes, and others. A variety of near-infrared absorbing pigments can also be used. Non-limiting examples can include phosphates having a variety of counterions such as copper, zinc, iron, magnesium, calcium, strontium, the like, and combinations thereof. Non-limiting specific examples of phosphates can include M₂P₂O₇, M₄P₂O₉, M₅P₂O₁₀, M₃(PO₄)₂ , M(PO₃)₂, M₂P₄O₁₂, and combinations thereof, where M represents a counterion having an oxidation state of +2. For example, M₂P₂O₇ can include compounds such as CU₂P₂O₇, Cu/MgP₂O₇, Cu/ZnP₂O₇, or any other suitable combination of counterions. The phosphates described herein are not limited to counterions having a +2 oxidation state. Other phosphate counterions can also be used to prepare other suitable near-infrared pigments. Additional near-infrared absorbing pigments can include silicates. Silicates can have the same or similar counterions as phosphates. One non-limiting example can include M₂SiO₄, M₂Si₂O₆, and other silicates where M is a counterion having an oxidation state of +2. For example, the silicate M₂Si₂0₆ can include Mg₂Si₂O₆, Mg/CaSi₂O₆, MgCuSi₂O₆, Cu₂Si₂0₆, Cu/ZnSi₂O₆, or other suitable combination of counterions. The silicates described herein are not limited to counterions having a +2 oxidation state. Other silicate counterions can also be used to prepare other suitable near-infrared pigments.

[0012] The rigid thermoplastic particles (and other particles if present) of the polymeric build material can have a D50 particle size that can range from about 10 μm to about 150 μm. Polymeric particles can alternatively have a D50 particle size that can range from about 10 μm to about 100 μm, from about 20 μm to about 80 μm, from about 30 μm to about 50 μm, from about 25 μm to about 75 μm, from about 40 μm to about 80 μm, from about 50 μm to about 75 μm, from about 75 μm to about 150 μm, from about 60 μm to about 90 μm, or from about 100 μm to about 150 μm, for example.

[0013] The “D50” particle sizes herein are based on the equivalent spherical volume of the particles described, e.g., polyamide particles, thermally conductive particles, radiation absorber particles (in the fusing agent), etc, D50 particle sizes can be measured by laser diffraction, scanning electron microscope (SEM) imaging, or other suitable methodology, but in some examples, the particle size (or particle size distribution) can be measured and/or characterized using a Malvern™ Mastersizer™ 3000 available from Malvern Panalytical (United Kingdom). The particle size analyzer measures particle size using laser diffraction as a laser beam passes through a sample of particles. The angular variation in intensity of light scattered by the particles can be then be measured. Larger particles scatter light at smaller angles, while small particles scatter light at larger angles. The particle analyzer can then analyze the angular scattering data to calculate the size of the particles using the Mie theory of light scattering. The particle size can be reported as a volume equivalent spherical diameter when the particles are not spherical, e.g., having about a 1 :1 aspect ratio.

[0014] Example rigid thermoplastic particles that can be used include polyacetal, polybutylene terephthalate, polycarbonate, polyester, polyether ketone, polyethylene terephthalate, polyethylene, polypropylene, polystyrene, polyamide, a copolymer thereof, or a mixture thereof. In some examples, the polymeric particles can include a polyamide, such as polyamide-6, polyamide-9, polyamide-11 , polyamide-12, polyamide- 66, polyamide-612, or a combination thereof. In other examples, the polymeric particles can include, polybutylene terephthalate, polycarbonate, polyester, polyethylene, polystyrene, copolymers thereof, blends of any of the multiple polymers listed herein, as well as mixtures thereof. Core shell polymer particles of these materials may also be used. In some examples, the build material can exclude amorphous materials.

[0015] Rigid thermoplastic materials as described herein can typically be molded as often as is desired by cooling and reheating them, as long as the material is not overheated. Overheating causes the material to decompose. Another interesting property of thermoplastics that is unique to this category is that some thermoplastics can actually be welded. Conversely, elastomers or elastomeric polymers are materials that are held together by weak intermolecular forces, generally exhibiting low Young’s modulus and high yield strength or high failure strain. Elastomers tend to be viscous as well as elastic, a property known as viscoelasticity. These types of polymers can have unique properties that allow them to deform or stretch under extreme tensile and compressive loads then return to their original shape. Examples of thermoplastic elastomers include thermoplastic polyamide elastomer (TPa), polyolefin elastomer (POE), natural rubber, styrene-butadiene rubber (SBR), ethylene-propylene (diene) monomer (EPM), polyurethane, polybutadiene (butadiene rubber, BR), silicone rubber (SR), fluorosilicone, polyacrylate, neoprene, isoprene (natural rubber), nitrile, or the like. Elastomers have a low Young’s modulus, a high yield strain (or strain at break), and a high tensile strength compared with other materials. The monomers which link elastomers together are usually carbon, hydrogen, oxygen, and/or silicon, and they can be amorphous above their glass transition temperature, providing considerable segmental motion. Conversely, fibers, such as fiberglass, carbon fiber, glass fiber- reinforced composite (GFRC), carbon fiber-reinforced composite (CFRC) tend to have a very high Young’s modulus, providing a space between elastomers and fibers where thermoplastics or plastic materials reside. For example, plastics tend to have moduli somewhere in between fibers and elastomers.

[0016] The present disclosure relates to the use of thermoplastic materials or plastic materials that can be defined as being more rigid or brittle than elastomers and typically less rigid than fibers. Sometimes, these materials are referred to generically as “plastics,” which do not have the stretchability or high elastic elongation properties of elastomers. The ability to resist deformation can be quantified by Young’s modulus, which is a measurement of strength and ultimate elongation. This can be determined by slowly increasing the stress on a material, and then the elongation of the sample is measured, e.g., at various stress levels, until the sample breaks. Stress versus elongation is used to provide Young's modulus values. More specifically, Young’s modulus is a measurement of the strain response of the material to the stress, which can vary depending on how the stress is applied. Materials with higher Young's modulus values tend to have more stiffness, impact strength, chemical resistance, and geometrical tolerance than elastomeric polymers.

[0017] Tensile strength, on the other hand, is a measurement of how much stress the material can withstand, and in further detail, strain at break provides more mechanical property information that relates to the percent of elongation that can occur prior to an object breaking. Tensile strength is a fixed value for a specific material, though it can vary within a class of materials, e.g., chain length differences, etc. For example, polyamide-12 may have a tensile strength of about 60 MPa or less, e.g., about 48 MPa, and a Young's modulus of less than about 2000 MPa, e.g., about 1800 MPa; and polyamide-11 may have a tensile strength of about 60 MPa or less, e.g., about 48 MPa, and a Young’s modulus of about 1700 MPa or less, e.g., about 1600 MPa. These values can vary depending to some degree on the variability of the polymer properties. On the other hand, thermoplastic elastomers (TPE) may have a tensile strength from about 100 MPa or more and a Young’s modulus less than about 100 MPa, for example. These values can vary within a relatively narrow range depending to some degree on the variability of the polymer properties.

[0018] In accordance with these mechanical properties, the term “rigid thermoplastic” is defined herein as thermoplastic materials that are plastic, but are not elastomeric. For example, the rigid thermoplastic materials described herein can have a Young’s modulus from about 500 MPa to about 3000 MPa, or from about 800 MPA to about 2,500 MPa. Furthermore, the tensile strength of the rigid thermoplastics of the present disclosure can be, for example, up to about 80 MPa, or up to about 60 MPa, e.g., from about 20 MPa to about 80 MPa or from about 30 MPa to about 60 MPa. Elastomeric polymer, on the other hand, have one or both values outside of these ranges as defined herein. Though any shape of object can be formed using the materials and printing process described herein, specifically sized and shaped “dog bones” (or barbell-shaped objects) can be prepared to test the mechanical properties. Dog bones formed for testing mechanical properties have an overall length of about 165 mm, a gauge length of about 50 mm, a width of about 13 mm, and a thickness of about 3.2 mm, with about 80 μm layer thickness (with layers parallel with the length of the dog bones for testing mechanical properties in the XY-direction and layers perpendicular with the length of the dog bones when testing mechanical properties in the Z-direction). The pulling stress in the direction of the length of the dog bones is applied at about 50 mm/minute.

[0019] The shape of the particles of the build material can be spherical, irregular spherical, rounded, semi-rounded, discoidal, angular, subangular, cubic, cylindrical, or any combination thereof. In one example, the particles can include spherical particles, Irregular spherical particles, or rounded particles. In some examples, the shape of the particles can be uniform or substantially uniform, which can allow for relatively uniform melting of the particles.

[0020] The polymeric particles in the build material can have a melting point that can range from about 100 °C to about 350 °C, from about 100 °C to about 300 °C, or from about 150 °C to about 250 °C. As examples, the build material can be a polyamide having a melting point of about 160 °C to about 190 °C. A variety of polyamides with melting points or softening points in these ranges can be used. In a specific example, the build material can include polyamide particles, such as polyamide-12, which can have a melting point from about 175 °C to about 200 °C.

[0021 ] Though the polymeric build material can include from about 80 wt% to 100 wt% of rigid thermoplastic particles, in some examples, the polymeric build material can include from about 85 wt% to about 95 wt%, from about 90 wt% to 100 wt%, or 100 wt% rigid thermoplastic particles. The build material may include, in addition to the rigid thermoplastic particles, other polymer particles and/or filler particles, for example. Example filler particles may include charging particles, flow aid particles, or a combination thereof. If included, the other particles can be present at from about 0.01 wt% to about 20 wt%, from about 0.1 wt% to about 10 wt%, or from about 0.2 wt% to about 5 wt%, based upon the total wt% of the build material.

[0022] Charging particles, for example, may be added to suppress tribo-charging. Examples of suitable charging particles include aliphatic amines (which may be ethoxylated), aliphatic amides, quaternary ammonium salts (e.g., behentrimonium chloride or cocamidopropyl betaine), esters of phosphoric acid, polyethylene glycol esters, or polyols. Some suitable commercially available charging particles include HOSTASTAT® FA 38 (natural based ethoxylated alkylamine), HOSTASTAT® FE2 (fatty acid ester), and HOSTASTAT® HS 1 (alkane sulfonate), both from Clariant Int. Ltd. (North America).

[0023] The polymeric build material can, in some examples, further include flow additives, antioxidants, inorganic filler, or any combination thereof. Flow aid particles may be added to increase the coating flowability of the build material, particularly when the particles are on the smaller end of the particle size range. The flow aid particles can increase the flowability of the build material by reducing friction, lateral drag, and tribocharge buildup (by increasing the particle conductivity). Typically, an amount of any of these or other similar components can be at about 5 wt% or less. Example flow additives can include fumed silica, tricalcium phosphate (E341 ), powdered cellulose (E460(ii)), magnesium stearate (E470b), sodium bicarbonate (E500), sodium ferrocyanide (E535), potassium ferrocyanide (E536), calcium ferrocyanide (E538), bone phosphate (E542), sodium silicate (E550), silicon dioxide (E551 ), calcium silicate (E552), magnesium trisilicate (E553a), talcum powder (E553b), sodium aluminosilicate (E554), potassium aluminum silicate (E555), calcium aluminosilicate (E556), bentonite (E558), aluminum silicate (E559), stearic acid (E570), or polydimethylsiloxane (E900), and/or the like. Example antioxidants can include hindered phenols, phosphites, thioethers, hindered amines, and/or the like. Example inorganic fillers can include particles such as alumina, silica, glass beads, glass fibers, carbon nanotubes, cellulose, and/or the like. Some additives may be found in multiple categories of additives, e.g., fumed silica can be a flow additive as well as a filler. In some examples, the filler or other type of additive can become embedded or composited with the rigid thermoplastic particles.

[0024] In some examples, the three-dimensional printing kits 100 can include additional or secondary fluid agent(s) (not shown), such as a detailing agent, a coloring agent, other fluid agents, or any combination of secondary fluid agents. The detailing agent, on the other hand, can include a detailing compound. The detailing compound can reduce a temperature of the build material onto which the detailing agent is applied. In some examples, the detailing agent can be printed around the edges of the portion of the powder that is printed with the fusing agent. The detailing agent can increase selectivity between the fused and unfused portions of the powder bed by reducing the temperature of the powder around the edges of the portion to be fused.

[0025] The detailing compound can be water and/or an organic cosolvent that can evaporate at the temperature of the powder bed. In some cases, the powder bed can be preheated to a preheat temperature within about 10 °C to about 70 °C of the fusing temperature of the polymeric particles. Depending on the type of polymeric particles used, the preheat temperature can be in the range of about 90 °C to about 200 °C or higher. The detailing compound can be a solvent that can evaporate when it comes into contact with the powder bed at the preheat temperature, thereby cooling the printed portion of the powder bed through evaporative cooling.

[0026] In certain examples, the detailing agent can include water, cosolvents, or a combination thereof. In some examples, the detailing agent can be water, or can be mostly water. For example, the detailing agent can be from about 85 wt% to 100 wt%, or from about 85 wt% to about 99 wt% water. In other examples, the detailing agent can be from about 95 wt% to 100 wt%, or from about 95 wt% to about 99 wt% water.

[0027] In some examples, the detailing agent can include an organic cosolvent. The cosolvent can be as identified above in the description of the fusing agent. In another example, cosolvents for use in the detailing agent can include xylene, methyl isobutyl ketone, 3-methoxy-3-methyl-1-butyl acetate, ethyl acetate, butyl acetate, propylene glycol monomethyl ether, ethylene glycol mono tert-butyl ether, dipropylene glycol methyl ether, diethylene glycol butyl ether, ethylene glycol monobutyl ether, 3- methoxy-3-methyl-1 -butanol, isobutyl alcohol, 1 ,4-butanediol, N,N-dimethyl acetamide, and a combination thereof. The cosolvent may be present in the detailing agent at from about 1 wt% to about 15 wt%, at from about 5 wt% to about 10 wt%, at from about 1 wt% to about 10 wt%, or from about 5 wt% to about 15 wt%.

[0028] In still further examples, the detailing agent can be substantially devoid of radiation absorbers. That is, in some examples, the detailing agent can be substantially devoid of ingredients that absorb enough radiation energy to cause particles of the build material to fuse or adhere to one another. In some examples, the detailing agent can include colorants such as dyes or pigments, but in small enough amounts that the colorants do not cause the powder printed with the detailing agent to fuse when exposed to the radiation energy.

[0029] The detailing agent can also include ingredients to allow the detailing agent to be jetted by a fluid applicator, e.g., a fluid ejector, piezo- or thermal-printhead, etc. In some examples, the detailing agent can include jettability imparting ingredients such as those in the fusing agent described above. These ingredients can include water, surfactant, dispersant, cosolvent, biocides, viscosity modifiers, materials for pH adjustment, sequestering compound, preservatives, and so on. These ingredients can be included in any of the amounts described above.

[0030] The coloring agent, if present, can include a liquid vehicle and a colorant, such as a pigment and/or a dye. The liquid vehicle may be similar to liquid vehicles used for formulating ink compositions, the fusing agent described above, or the detailing agent described above.

[0031] The build material may be packaged or co-packaged with the fusing agent, or can be packaged separately to be brought together by the user. Other fluid agents, e.g., coloring agent, detailing agent, or the like, can likewise be co-packaged with the fusing agent and/or build material in separate containers, and/or can be combined with the fusing agent at the time of printing, e.g., loaded together in a three- dimensional printing system.

Three-dimensional Printing Systems

[0032] The three-dimensional printing kits can be used with three-dimensional printing systems 200 as shown in FIG. 2. The system can include the three-dimensional printing kits shown and described in FIG. 1. Thus, the three-dimensional printing system can include a build material 120, a fluid applicator 115, and a radiant energy source 130 to emit electromagnetic energy (e). The fusing agent can include water (in some instances with additional liquid vehicle components, such as organic co-solvent(s), surfactants, etc.) and a radiation absorber. The build material can include from about 80 wt% to 100 wt% rigid thermoplastic particles, and can be applied from a build material supply 140 in layers on a build platform 105 (which in one specific example may be lowered about the distance of a thickness of material to correspond to an applied layer of build material, for example), or a previously applied layer of build material. The fluid applicator can be fluidly coupled to or fluidly coupleable to the fusing agent to selectively and iteratively eject the fusing agent onto successively placed individual layers of the build material. The radiant energy source can be positioned to expose the individual layers of the build material to radiation energy to selectively fuse the rigid thermoplastic particles in contact with the radiation absorber to iteratively form a three-dimensional object, showed in an initial stage where fused build material layers 125 are being formed. Upon building the three-dimensional object using the build material, the fusing agent, and the electromagnetic energy, the object can be removed from the unused build material (sometimes referred to as the powder bed), leaving the three-dimensional object 125A. Notably, if the three-dimensional object were printed in an upright orientation, e.g., from end to end, the resultant three-dimensional object would have the orientation and relative layering as shown at 125B. A “dog bone" printed in this orientation is particularly useful for evaluating the mechanical properties in the Z- direction or orientation.

[0033] Following the selective application of a fusing agent 110 to the polymeric build material 120, the build material can be exposed to energy (e) from the radiation source 130. The radiation source can be an infrared (IR) or near-infrared light source, such as IR or near-IR curing lamps, IR or near-IR light emitting diodes (LED), or lasers with the desirable IR or near-IR electromagnetic wavelengths, and can emit electromagnetic radiation having a wavelength ranging from about 400 nm to about 1 mm. In one example, the emitted electromagnetic radiation can have a wavelength that can range from about 400 nm to about 2 μm. As a note, the radiation source shown is a fixed source, but could be supported and moved along a carriage track with a motor and can be operable to move back and forth.

[0034] In further detail, the fluid applicator 115 can be a printhead or other digital fluid ejector, e.g., thermal or piezo jetting architecture. The fluid applicator, in an example, can be a fusing agent applicator that can be fluidly coupled or coupleable to the fusing agent to iteratively apply the fusing agent to the build material to form individually patterned object layers. The fluid applicator can be any type of apparatus capable of selectively dispensing the fusing agent. For example, the fluid applicator can be a fluid ejector or digital fluid ejector, such as an inkjet printhead, e.g., a piezo-electric printhead, a thermal printhead, a continuous printhead, etc. The fluid applicator could likewise be a sprayer, a dropper, or other similar structure for dispensing the fusing agent to the build material. In an example, the fluid applicator can be located on a carriage track, but could be supported by any of a number of structures. In yet another example, the fluid applicator can include a motor and can be operable to move back and forth over the build material along a carriage when positioned over or adjacent to a powder bed of a build platform.

[0035] In an example, the three-dimensional printing system can further include a build platform 105 to support the build material. The build platform can support the build material 120 to form a powder bed, and can be positioned to permit application of the fusing agent from the fluid applicator 115 onto a layer of the build material. The build platform can be configured to drop in height, thus allowing for successive layers of build material to be applied by a supply and/or spreader. The build material can be layered in the build platform at a thickness that can range from about 5 μm to about 1 mm. In some examples, individual layers can have a relatively uniform thickness. In one example, a thickness of a layer of the build material can range from about 10 μm to about 500 μm, or from about 30 μm to about 200 μm.

[0036] As shown, the three-dimensional object is printed in a layer-by-layer manner in the powder bed. “Layer-by-layer” printing results show material build up in the Z-direction with adjacent layers sequentially becoming fused together, as shown in FIG. 2. For explanatory purposes, two different three-dimensional objects are shown. A first three-dimensional object 125A is shown where the dog bone shape is printed in a horizontal orientation (similar to that shown being printed in the powder bed). A second three-dimensional object 125B is also shown by way of example illustrating that the orientation of the build can be in any direction that the three-dimensional printing system can accommodate. In this example, however, the dog bone-shaped three-dimensional objects are shown in this second orientation to illustrate an object prepared for Z- direction mechanical property testing. In other words, XY-direction mechanical properties can be tested using the first three-dimensional object, and Z-direction mechanical properties can be tested using the identically shaped three-dimensional object, but which is printed in a manner more useful in evaluating Z-direction three- dimensional object mechanical properties.

[0037] As a note, the term “XY-direction” can be interpreted as meaning the X- direction and/or the Y-direction. When conducting mechanical properties testing, such as pulling for strain at break, the direction of testing will be along the XY-plane, but is tested in a single direction, e.g., X-direction or Y-direction, depending on the axis in which the dog bone shape is aligned. Thus, the XY-direction simply refers to the mechanical properties in a direction that is perpendicular to the Z-direction.

Methods of Printing Three-dimensional Objects

[0038] A flow diagram of an example method 300 of three-dimensional (3D) printing is shown in FIG. 3. The method can include iteratively applying 310 individual polymeric build material layers including from about 80 wt% to 100 wt% rigid thermoplastic particles, and based on a three-dimensional object model, iteratively and selectively dispensing 320 a fusing agent onto individual polymeric build material layers. The fusing agent in this example includes water, from about 5 wt% to about 40 wt% alkyldiol organic cosolvent including a straight-chained C4-C7 saturated carbon chain with two terminal hydroxyl groups, and a radiation absorber to generate heat from absorbed electromagnetic radiation. The method further includes iteratively exposing 330 the individual polymeric build material layers with the fusing agent dispensed therewith to electromagnetic radiation to selectively fuse rigid thermoplastic particles of the polymeric build material layers in contact with the radiation absorber and to form a fused three-dimensional object. The compositional components used in this method can be similar to those described herein with respect to the three-dimensional printing kits and three-dimensional printing systems described herein. In some examples, the alkyldiol organic cosolvent can be 1 ,5-pentanediol, or can include a mixture of 1 ,5- pentanediol and a second straight-chained C4-C7 saturated carbon chain with two terminal hydroxyl groups. Any of the other alkyldiol organic cosolvents can likewise be used alone or in combination. In other examples, the rigid thermoplastic particles are selected from polyamide-6, polyamide-9, polyamide-11 , polyamide-12, polyamide-66, polyamide-612, or a combination thereof. In still other examples, the rigid thermoplastic particles can have a Young’s modulus from about 500 MPa to about 3000 MPa. In accordance with the present method, the alkyldiol organic cosolvent can be applied to individual build material layers at an alkyldiol organic cosolvent to polymeric build material weight ratio from about 1 :180 to about 2:45, from about 1 :100 to about 2:45, or from about 1 :180 to about 1 :100.

[0039] When applying the fusing agent to the polymeric build material, the concentration of the alkyldiol organic cosolvent in the fusing agent can be considered in conjunction with the concentration of the radiation absorber. These concentrations can be used to determine how much fusing agent to apply to achieve a weight ratio of fusing agent to polymeric build material and a weight ratio of alkyldiol organic cosolvent to polymeric build material to provide for acceptable layer-by-layer fusing and softening, respectively. For example, the fusing agent, as mentioned, can include from about 0.1 wt% to about 10 wt% radiation absorber in some examples, and can also include from about 5 wt% to about 40 wt% alkyldiol organic cosolvent. Thus, if applying the fusing agent (10 wt%) to the polymeric build material (90 wt%) at about a 1 :9 weight ratio, then the radiation absorber to polymeric build material weight ratio (as applied) can be from about 1 :10000 to about 1 :100, and the alkyldiol organic cosolvent to polymeric build material weight ratio (as applied) can be from about 1 :180 to about 2:45, for example. If more (up to 20 wt%) or less (down to 5 wt%) fusing agent is applied to the polymeric build material, then these ratios can be expanded accordingly. That stated, the weight ratio of the radiation absorber to the polymeric build material (as applied) in some more specific examples can be from about 1 :1000 to about 1 :80, from about 1 :800 to about 1 :100, or from about 1 :500 to about 1 :150, for example. The weight ratio of the alkyldiol organic cosolvent to polymeric build material (as applied) can, in some more specific examples, be from about 1 :150 to about 1 :25, about 1 :125 to about 1 :30, or about 1 :100 to about 1 :40, for example.

[0040] In some examples, in addition to the radiation absorber and the alkyldiol organic cosolvent, there may be other components or dispersed additives therein. Thus, a “liquid vehicle” may include the water, the alkyldiol organic cosolvent, and/or other liquid components, e.g., other organic cosolvents, surfactant, etc. For example, the liquid vehicle can further include from about 0.01 wt% to about 2 wt% or from about 0.01 wt% to about 0.5 wt% surfactant. In other examples, the fusing agent can further include a dispersant. Dispersants can help disperse the radiation absorber or other particulate additives. In some examples, the dispersant itself can also absorb radiation. Non-limiting examples of dispersants that can be included as a radiation absorber, either alone or together with a pigment, can include polyoxyethylene glycol octylphenol ethers, ethoxylated aliphatic alcohols, carboxylic esters, polyethylene glycol ester, anhydrosorbitol ester, carboxylic amide, polyoxyethylene fatty acid amide, poly (ethylene glycol) p-isooctyl-phenyl ether, sodium polyacrylate, and combinations thereof. Other additives may be present as part of the liquid vehicle, as described more fully below.

[0041] In printing in a layer-by-layer manner, the polymeric build material can be spread, the fusing agent applied, the layer of the polymeric build material can be exposed to energy, and then a build platform between the polymeric bed material and the fusing agent application can be adjusted to accommodate the printing of another layer, e.g., about 5 μm to about 1 mm, which can correspond to the thickness of a printed layer of the three-dimensional object. Thus, another layer of the polymeric build material can be added again thereon to receive another application of fusing agent, and so forth. During the build, the radiation absorber in the fusing agent can act to convert the energy to thermal energy and promote the transfer of thermal heat to rigid thermoplastic particles of the polymeric build material in contact with the fusing agent including the radiation absorber. In an example, the fusing agent can elevate the temperature of the rigid thermoplastic particles of the polymeric build material above the melting or softening point of the rigid thermoplastic particles, thereby allowing fusing (e.g., sintering, binding, curing, etc.) of the polymeric build material (or rigid thermoplastic particles thereof) and the formation of an individual layer of the three- dimensional object. The method can be repeated until all the individual polymeric build material layers have been created and a three-dimensional object is formed. In some examples, the method can further include heating the polymeric build material prior to dispensing.

[0042] In one example, the method can further Include iteratively and selectively dispensing a detailing agent onto individual polymeric build material layers laterally at a border between a first area where the individual polymeric build material layer was contacted by the fusing agent and a second area where the individual polymeric build material layer was not contacted by the fusing agent. As mentioned, a detailing agent can include a detailing compound to reduce a temperature of the polymeric build material onto which the detailing agent is applied. In one example, this can be used to prevent caking around the edges due to heat from the area where the fusing agent was applied. The detailing agent can also be applied in the same area where the fusing agent was applied in order to control the temperature and prevent excessively high temperatures when the polymeric build material is fused.

[0043] In another example, the three-dimensional object formed from the method can be softened or otherwise adjusted to some degree with respect to tensile strength, for example, based on the amount of alkyldiol organic cosolvent used compared to other components that may be added to the fusing agent. Specifically, three- dimensional objects can be subject to tensile strength and elongation at break issues which can result in failure due to brittleness. The use of the fusing agents described herein can provide a way of modifying the mechanical properties, or in some cases, increase the consistency of the mechanical properties, of the three-dimensional object.

[0044] The polymeric build material can be capable of being printed into three- dimensional objects with a resolution of about 10 μm to about 150 μm, about 20 μm to about 100 μm, or about 25 μm to about 80 μm. As used herein, “resolution” refers to the size of the smallest feature that can be formed on a three-dimensional object. The polymeric build material can form layers from about 10 μm to about 150 μm thick, depending on the size of rigid thermoplastic particles present in the polymeric build material, thus allowing the fused layers of the printed object to have about the same thickness or a few too many times (e.g., 2 to 20 times) thicker than the D50 particle size of the rigid thermoplastic particles, for example. This can provide a resolution in the z- axis direction (e.g., the direction of the buildup of layers) of about 10 μm to about 150 pm. In some examples, however, the polymeric build material can also have a sufficiently small particle size and sufficiently uniform particle shape to provide an x- and y-axis resolution about the size of the polymer particle size, e.g., about 2 μm to about 150 μm (e.g., the axes parallel to the support surface of the build platform).

Liquid Vehicles for Fusing Agents or Other Fluid Agents

[0045] The liquid used in the fusing agent, the detailing agent, and/or other fluid agents that may be present can be referred to as a “liquid vehicle.” The liquid vehicle(s), for example, may include water, which would be an aqueous liquid vehicle when water is present as a solvent. The liquid vehicle may include water alone or in combination with a variety of additional components. With respect to the fusing agent, the liquid vehicle includes water and organic cosolvent (including the alkyldiol organic cosolvent), but with respect to the detailing agent, the liquid vehicle may be water, or may include water and organic cosolvent, for example. Either or both may or may not include surfactant, for example. Furthermore, in some three-dimensional printing kits, methods, and systems, the detailing agent (or any other fluid agent) may or may not be included altogether. Examples of components that may be included in the liquid vehicle, in addition to water, may include organic cosolvent, surfactant, buffer, antimicrobial agent, anti-kogation agent, chelator, buffer, etc. In an example, the liquid vehicle can include water and organic cosolvent. In another example, the liquid vehicle can include water, organic cosolvent, and a surfactant. In yet another example, the liquid vehicle can include water, organic cosolvent, surfactant, and buffer (or buffer and a chelator).

[0046] The liquid vehicle(s) for the fusing agent, the detailing agent, or any other fluid agent included in the kits, methods, and/or systems herein, in some examples, can include from about 25 wt% to about 90 wt% or from about 40 wt% to about 85 wt% water, and can also include from about 5 wt% to about 60 wt% or from about 10 wt% to about 50 wt% organic cosolvent, with examples including from about 5 wt% to about 40 wt% being the alkyldiol organic cosolvent. These weight percentages are based on the fluid agent as a whole, and not just the liquid vehicle component. Thus, the liquid vehicle can include water that may be deionized, for example. In an example, the liquid vehicle can include organic-solvent to water at a ratio from about 2:1 to about 1 :2, from about 1 :1 to about 1 :2, from about 1 : 1 to about 1 :1 .5 or from about 1 :1 to about 1 :1 .25. In some examples, such as with respect to the detailing agent, the liquid vehicle may carry no solids, may be simply water, or may include as major components a combination of water and organic cosolvent.

[0047] The liquid vehicle(s) in any of these fluid agents may include organic cosolvent(s). Some examples of cosolvent that may be added to the vehicle include 1 - (2-hydroxyethyl)-2-pyrollidinone, 2-pyrrolidinone, 2-methyl-1 ,3-propanediol, triethylene glycol, tetraethylene glycol, tripropylene glycol methyl ether, ethoxylated glycerol-1 (LEG-1 ), or a combination thereof. In one example, the cosolvent in the fusing agent can exclude lacatams, such as pyrrolidones. In either case, the organic cosolvent content in the fusing agent includes the alkyldiol organic cosolvent content described herein.

[0048] The liquid vehicle(s) may also include surfactant. The surfactant can include non-ionic surfactant, cationic surfactant, and/or anionic surfactant. In one example, the fusing agent includes an anionic surfactant. In another example, the fusing agent includes a non-ionic surfactant. In still another example, the fusing agent includes a blend of both anionic and non-ionic surfactant. Example non-ionic surfactant that can be used include a self-emulsifiable, nonionic wetting agent based on acetylenic diol chemistry (e.g., SURFYNOL® SEF from Air Products and Chemicals, Inc., USA), a fluorosurfactant (e.g., CAPSTONE'® fluorosurfactants from DuPont, USA), or a combination thereof. In other examples, the surfactant can be an ethoxylated low-foam wetting agent (e.g., SURFYNOL® 440, SURFYNOL® 465, or SURFYNOL® CT-111 from Air Products and Chemical Inc., USA) or an ethoxylated wetting agent and molecular defoamer (e.g., SURFYNOL® 420 from Air Products and Chemical Inc., USA). Still other surfactants can include wetting agents and molecular defoamers (e.g., SURFYNOL® 104E from Air Products and Chemical Inc., USA), alkylphenylethoxylates, solvent-free surfactant blends (e.g., SURFYNOL® CT-211 from Air Products and Chemicals, Inc., USA), water-soluble surfactant (e.g., TERGITOL® TMN-6, TERGITOL® 15S7, and TERGITOL® 15S9 from The Dow Chemical Company, USA), or a combination thereof. In other examples, the surfactant can include a non-ionic organic surfactant (e.g., TEGO® Wet 510 from Evonik Industries AG, Germany), a non-ionic a secondary alcohol ethoxylate (e.g., TERGITOL® 15-S-5, TERGITOL® 15-S-7, TERGITOL® 15-S- 9, and TERGITOL® 15-S-30 all from Dow Chemical Company, USA), or a combination thereof. Example anionic surfactant can include alkyldiphenyloxide disulfonate (e.g., DOWFAX® 8390 and DOWFAX® 2A1 from The Dow Chemical Company, USA), and oleth-3 phosphate surfactant (e g., CRODAFOS™ N3 Acid from Croda, UK). Example cationic surfactant that can be used include dodecyltrimethylammonium chloride, hexadecyldimethylammonium chloride, or a combination thereof. In some examples, the surfactant (which may be a blend of multiple surfactants) may be present in the fusing agent, the detailing agent, or other fluid agent at an amount ranging from about 0.01 wt% to about 2 wt%, from about 0.05 wt% to about 1.5 wt%, or from about 0.01 wt% to about 1 wt%.

[0049] In some examples, the liquid vehicle(s) may also include a chelator sequestering compound, an antimicrobial agent, a buffer, or a combination thereof. While the amount of these may vary, if present, these can be present in the fusing agent, the detailing agent, or other fluid agent at an amount ranging from about 0.001 wt% to about 20 wt%, from about 0.05 wt% to about 10 wt%, or from about 0.1 wt% to about 5 wt%.

[0050] The liquid vehicle(s) may include a chelator or sequestering compound. Chelators can be used to minimize or to eliminate the deleterious effects of heavy metal impurities. Examples of suitable chelators can include disodium ethylenediaminetetraacetic acid (EDTA-Na), ethylene diamine tetra acetic acid (EDTA), and methyl-glycinediacetic acid (e.g., TRILON® M from BASF Corp., Germany). If included, whether a single chelator is used or a combination of chelators is used, the total amount of chelator in the fusing agent, the detailing agent, or other fluid agent may range from about 0.01 wt% to about 2 wt% or from about 0.01 wt% to about 0.5 wt%.

[0051 ] The liquid vehicle may also include antimicrobial agents. Antimicrobial agents can include biocides and fungicides. Example antimicrobial agents can include the NUOSEPT®, Ashland Inc. (USA), VANCIDE® (R.T. Vanderbilt Co., USA), ACTICIDE® B20 and ACTICIDE® M20 (Thor Chemicals, U.K.), PROXEL® GXL (Arch Chemicals, Inc.. USA), BARDAC® 2250, 2280, BARQUAT® 50-65B, and CARBOQUAT® 250-T, (Lonza Ltd. Corp., Switzerland), KORDEK® MLX (The Dow Chemical Co., USA), and combinations thereof. In an example, if included, the total amount of antimicrobial agents in the fusing agent, the detailing agent, or other fluid agent can range from about 0.01 wt% to about 1 wt%.

[0052] In some examples, the liquid vehicle may further include buffer solution(s). In some examples, the buffer solution(s) can withstand small changes (e.g., less than 1 ) in pH when small quantities of a water-soluble acid or a water-soluble base are added to a composition containing the buffer solution(s). The buffer solution(s) can have pH ranges from about 5 to about 9.5, or from about 7 to about 9, or from about 7.5 to about 8.5. In some examples, the buffer solution(s) can include a poly-hydroxy functional amine. In other examples, the buffer solution(s) can include potassium hydroxide, 2-[4- (2-hydroxyethyl) piperazin-1-yl] ethane sulfonic acid, 2-amino-2-(hydroxymethyl)-1 ,3- propanediol (TRIZMA® sold by Sigma-Aldrich, USA), 3-morpholinopropanesulfonic acid, triethanolamine, 2-[bis-(2-hydroxyethyl)-amino]-2-hydroxymethyl propane-1 ,3-diol (bis tris methane), N-methyl-D-glucamine, N,N,N’N’-tetrakis-(2-hydroxyethyl)- ethylenediamine and N,N,N’N’-tetrakis-(2-hydroxypropyl)-ethylenediamine, beta- alanine, betaine, or mixtures thereof. In yet other examples, the buffer solution(s) can include 2-amino-2-(hydroxymethyl)-1,3-propanediol (TRIZMA® sold by Sigma-Aldrich, USA), beta-alanine, betaine, or mixtures thereof. The buffer solution, if included, can be added in the fusing agent, the detailing agent, or other fluid agent at an amount ranging from about 0.01 wt% to about 10 wt%, from about 0.1 wt% to about 7.5 wt%, or from about 0.05 wt% to about 5 wt%.

Definitions

[0053] It is noted that, as used in this specification and the appended claims, the singular terms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise.

[0054] The term "about" as used herein, when referring to a numerical value or range, allows for a degree of variability in the value or range, for example, within 10%, or, in one aspect within 5%, of a stated value or of a stated limit of a range. The term “about” when modifying a numerical range is also understood to include as one numerical subrange a range defined by the exact numerical value indicated, e.g., the range of about 1 wt% to about 5 wt% includes 1 wt% to 5 wt% as an explicitly supported sub-range.

[0055] As used herein, “kit” can be synonymous with and understood to include a plurality of multiple components where the different components can be separately contained (though in some instances co-packaged in separate containers) prior to use, but these components can be combined together during use, such as during the three- dimensional object build processes described herein. The containers can be any type of a vessel, box, or receptacle made of any material.

[0056] As used herein, “dispensing” when referring to fusing agents that may be used, for example, refers to any technology that can be used to put or place the fluid, e.g., fusing agent, on the polymeric build material or into a layer of polymeric build material for forming a green body object. For example, “dispensing” may refer to “jetting, ” “ejecting,” “dropping,” “spraying,” “applying,” or the like.

[0057] As used herein, “jetting” or “ejecting” refers to fluid agents or other compositions that are expelled from ejection or jetting architecture, such as ink-jet architecture. Ink-jet architecture can include thermal or piezoelectric architecture. Additionally, such architecture can be configured to print varying drop sizes such as up to about 20 picoliters (pL), up to about 30 pL, or up to about 50 pL, etc. Example ranges may include from about 2 pL to about 50 pL, or from about 3 pL to about 12 pL.

[0058] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though the individual member of the list is identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list based on presentation in a common group without indications to the contrary.

[0059] Concentrations, dimensions, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include the numerical values explicitly recited as the limits of the range, as well as to include all the individual numerical values or sub-ranges encompassed within that range as the individual numerical value and/or sub-range is explicitly recited. For example, a weight ratio range of about 1 wt% to about 20 wt% should be interpreted to include the explicitly recited limits of 1 wt% and 20 wt% and to include individual weights such as about 2 wt%, about 11 wt%, about 14 wt%, and sub-ranges such as about 10 wt% to about 20 wt%, about 5 wt% to about 15 wt%, etc.

EXAMPLES

[0060] The following illustrates examples of the present disclosure. Numerous modifications and alternative compositions, methods, and systems may be devised without departing from the present disclosure. The appended claims are intended to cover such modifications and arrangements.

Example 1 - Preparation of a Fusing Agents

[0061] An example fusing agent containing an alkyldiol cosolvent (FA-1 ) and a control fusing agent (FA-C) were prepared by admixing the components set forth in Table 1 together. As a note, the example fusing agent (FA-1) included 1 ,5-pentanediol as the C4-C7 saturated alkyl organic cosolvent with terminal hydroxyl groups. Instead of the alkyldiol organic cosolvent used in FA-1 , the control fusing agent (FA-C) included 2- pyrrolidone and triethylene glycol as the organic cosolvent component.

Table 1 : Example Fusing Agent and Control Fusing Agent

| Example 2 - Preparation of Three-Dimensional Objects for Comparison

[0062] Several three-dimensional printed objects were prepared in the shape of dog bones using the two fusing agents of Table 1 (FA-1 and FA-C) printed layer-by- layer into a polyamide-12 (PA12) powder as the polymeric build material having a D50 particle size of about 50 μm to about 80 μm. The various three-dimensional printed objects were prepared in the shape of Type 5 dog bones in accordance with ASTM D638 using the fusing agents prepared in accordance with Example 1 applied to the particulate build material samples using a Multi-jet Fusion (MJF) layer-by-layer printing process under common printing conditions, including printing bed temperature, layer thickness, fusing agent contone, and infrared energy parameters. More specifically, the print job included four (4) sets of 42 dog bones, for a total of 168 total dog bones. 42 XY dog bones were printed using fusing agent FA-1 in the XY direction or orientation and 42 XY dog bones were printed using fusing agent FA-C in the XY direction or orientation (See 125A at FIG. 2 showing example XY dog bones, not to scale). Furthermore, 42 Z dog bones were printed using fusing agent FA-1 in the Z-direction or orientation and 42 Z dog bones were printed using fusing agent FA-C in the Z-direction or orientation (See 125B at FIG. 2 showing example Z dog bones, not to scale). In other words, some dog bone objects were formed with layers parallel with the length of the dog bones (for testing mechanical properties in the XY-direction) and some dog bone objects were formed with layers perpendicular with the length of the dog bones (for testing mechanical properties in the Z-direction). These four different types of dog bones are labeled as follows:

Table 2: Example Dog Bones

Example 3 - Evaluation of Mechanical Properties

[0063] The dog bones prepared in accordance with Example 2 were evaluated for mechanical properties and averaged over the multiple dog bones for each category prepared, e.g., XY dog bone, XY dog bone-C, Z dog bone, and Z dog bone-C. Tensile strength (MPa), Strain at Break (%), and Young's Modulus (MPa) were measured using a tensile test. Specifically, the dog bones (or barbell-shaped objects) prepared for evaluation had an overall length of about 165 mm, a gauge length of about 50 mm, a width of about 13 mm, and a thickness of about 3.2 mm, with about 80 μm layer thickness. The pulling stress in the direction of the length of the dog bones is applied at about 50 mm/minute. Before carrying out the tensile testing protocol, all samples were pre-conditioned at 23°C and 50% relative humidity for at least 24 hours after being built. An extensometer was used to gauge the true strain of samples within the gauge length. The data collected for the four types of dog bones was plotted on a graph, as shown at FIG. 4.

[0064] As can be seen in FIG. 4, in some categories, the dog bone mechanical property values are relatively comparable. The fusing agent that included the alkyldiol organic cosolvent (1 ,5-pentanediol) relative to the control fusing agent resulted in very similar results in all three categories, in both the XY-direction and the Z-direction testing. However, the consistency of the mechanical properties printed with the dog bones using fusing agent FA-1 was more consistent with fewer outliers. This enhanced object consistency was noted in both the XY-direction and the Z-direction testing, but was particularly pronounced in the Z-direction tensile stress testing and the strain at break testing.

[0065] The tensile strength data shown In FIG. 4 is shown in additional detail in FIG. 5, where the standard deviation of the tensile strength is plotted. As can be seen here, a reduction in object-to-object variability is notable in both the XY-direction and In the Z-direction, with a greater enhancement in consistency shown in the Z-direction in particular. With respect to object consistency, in the Z-direction or orientation, the standard deviation related to printed object consistency is reduced by a factor of about 2, for example.

Claims

27 CLAIMS What is Claimed Is:

1. A three-dimensional printing kit, comprising: a polymeric build material including from about 80 wt% to 100 wt% rigid thermoplastic particles; and a fusing agent including: water, from about 5 wt% to about 40 wt% alkyldiol organic cosolvent including a straight-chained C4-C7 saturated carbon chain with two terminal hydroxyl groups, and a radiation absorber to generate heat from absorbed electromagnetic radiation.

2. The three-dimensional printing kit of claim 1 , wherein the alkyldiol organic cosolvent includes a mixture of 1 ,5-pentanediol and a second straight-chained C4-C7 saturated carbon chain with two terminal hydroxyl groups.

3. The three-dimensional printing kit of claim 1 , wherein the alkyldiol organic cosolvent consists essentially of 1 ,5-pentanediol.

4. The three-dimensional printing kit of claim 1 , wherein the rigid thermoplastic particles have a D50 particle size from about 10 μm to about 150 μm, and are selected from polyacetals, polybutylene terephthalates, polycarbonates, polyesters, polyether ketones, polyethylene terephthalates, polyethylenes, polypropylenes, polystyrenes, polyamides, a copolymer thereof, or a mixture thereof.

5. The three-dimensional printing kit of claim 1 , wherein the rigid thermoplastic particles are selected from polyamide-6, polyamide-9, polyamide-11 , polyamide-12, polyamide-66, polyamide-612, or a combination thereof.

6. The three-dimensional printing kit of claim 1 , wherein the rigid thermoplastic particles have a Young's modulus from about 500 MPa to about 3000 MPa and a tensile strength from about 20 MPa to about 80 MPa.

7. The three-dimensional printing kit of claim 1 , wherein the radiation absorber is present In the fusing agent at from about 0.1 wt% to about 10 wt% and includes carbon black, a metal dithiolene complex, a near-infrared absorbing dye, a near-infrared absorbing pigment, metal nanoparticles, a conjugated polymer, or a combination thereof.

8. The three-dimensional printing kit of claim 1 , further comprising a detailing agent, wherein the detailing agent includes a detailing compound to reduce a temperature of the polymeric build material onto which the detailing agent is applied.

9. A three-dimensional printing system, comprising: a polymeric build material including from about 80 wt% to 100 wt% rigid thermoplastic particles; and a fluid applicator fluidly coupled or coupleable to a fusing agent, wherein the fluid applicator is directable to iteratively apply the fusing agent to layers of the polymeric build material, the fusing agent comprising water, an alkyldiol organic cosolvent including a straight-chained C4-C7 saturated carbon chain with two terminal hydroxyl groups, and a radiation absorber to generate heat from absorbed electromagnetic radiation.

10. The three-dimensional printing system of claim 9, further comprising an electromagnetic radiation source positioned to provide electromagnetic radiation to the layers of the polymeric build material having the fusing agent applied thereto.

11. The three-dimensional printing system of claim 9, wherein the alkyldiol organic cosolvent is 1 ,5-pentanediol, or includes a mixture of 1 ,5-pentanediol and a second straight-chained C4-C7 saturated carbon chain with two terminal hydroxyl groups.

12. A method of printing three-dimensional object, comprising: iteratively applying individual polymeric build material layers including from about 80 wt% to 100 wt% rigid thermoplastic particles; based on a three-dimensional object model, iteratively and selectively dispensing a fusing agent onto individual polymeric build material layers, wherein the fusing agent comprises water, from about 5 wt% to about 40 wt% alkyldiol organic cosolvent including a straight-chained C4-C7 saturated carbon chain with two terminal hydroxyl groups, and a radiation absorber to generate heat from absorbed electromagnetic radiation; and iteratively exposing the individual polymeric build material layers with the fusing agent dispensed therewith to electromagnetic radiation to selectively fuse rigid thermoplastic particles of the polymeric build material layers in contact with the radiation absorber and to form a fused three-dimensional object.

13. The method of claim 12, wherein the alkyldiol organic cosolvent is 1 ,5- pentanediol, or includes a mixture of 1 ,5-pentanediol and a second straight-chained C4- C7 saturated carbon chain with two terminal hydroxyl groups.

14. The method of claim 12, wherein the rigid thermoplastic particles have a Young's modulus from about 500 MPa to about 3000 MPa and a tensile strength from about 20 MPa to about 80 MPa.

15. The method of claim 12, wherein the alkyldiol organic cosolvent is applied to individual build material layers at an alkyldiol organic cosolvent to polymeric build material weight ratio from about 1 :180 to about 2:45.