Three-dimensional printing of balls with a predetermined energy return

Abstract

In an example method for making a ball, a polymeric build material is selected. Based at least on the type of ball and the selected polymeric build material, i) a ball mass and ii) a lattice structure with a cell geometry to contribute to a predetermined energy return of the ball are selected. The selected lattice structure is 3D printed in a spherical shape of the ball. During 3D printing, layers of the selected build material are iteratively applied, a fusing agent is selectively applied, according to a 3D object model of the selected lattice structure in the spherical shape, on each of the iteratively applied layers, and each of the iteratively applied layers, having the fusing agent applied thereto, is exposed to electromagnetic radiation.

Description

86325147 1 THREE-DIMENSIONAL PRINTING OF BALLS WITH A PREDETERMINED ENERGY RETURN BACKGROUND

[0001] Balls have a variety of uses, ranging from sports to children’s toys to entertainment (e.g., juggling). Because of the wide variety of uses, the properties that are desirable for one type of ball may be very different from another type of ball. Even within a particular category, e.g., children’s toys, sports, etc., the properties from one ball to another may vary widely. For example, some children’s toys are soft with little to no bounce, while others are flexible and exhibit some bounce. For another example, different sport balls have different sizes, shapes, weight, bounce, rebound, grip, or the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Features of examples of the present disclosure will become apparent by reference to the following detailed description and drawings, in which like reference numerals correspond to similar, though perhaps not identical, components. For the sake of brevity, reference numerals or features having a previously described function may or may not be described in connection with other drawings in which they appear.

[0003] Fig.1A is a schematic and perspective view of one example of a cell geometry for a lattice structure used to form an example of a 3D printed ball;

[0004] Fig.1B is a schematic and perspective view of another example of a cell geometry for a lattice structure used to form another example of a 3D printed ball;

[0005] Fig.1C is a schematic and perspective view of still another example of a cell geometry for a lattice structure used to form still another example of a 3D printed ball;

[0006] Fig.1D is a schematic and perspective view of yet another example of a cell geometry for a lattice structure used to form yet another example of a 3D printed ball;86325147 2

[0007] Fig.2 depicts an example of one hourglass geometric cell superimposed on a geometric framework of a spherical ball;

[0008] Fig.3A is a perspective view of a 3D object model of a ball with the cell geometry of Fig.1A;

[0009] Fig.3B is a perspective view of a 3D object model of a ball with the cell geometry of Fig.1B;

[0010] Fig.3C is a perspective view of a 3D object model of a ball with the cell geometry of Fig.1C;

[0011] Fig.3D is a perspective view of a 3D object model of a ball with the cell geometry of Fig.1D;

[0012] Fig.4 is a schematic illustration of an example of a 3D printing method;

[0013] Fig.5 is a schematic and cross-sectional view of a 3D printed ball including a hollow core and a lattice structure surrounding the outer core;

[0014] Fig.6 illustrates different netting offsets; and

[0015] Fig.7A and Fig.7B are top views of still other views of cell geometries for lattice structures including angled middle beams. DETAILED DESCRIPTION

[0016] In the examples disclosed herein, a three-dimensional (3D) printing process is used to generate a ball having a lattice structure and specific properties for a specific application. During the design portion of the 3D printing process, the type of ball and the polymeric build material that are to be used are identified. Taking into account these two selections, a mass, a diameter, and a particular energy return for the 3D printed ball are identified. The present inventors have found that the particular energy return can be achieved in the 3D printed ball by modulating one or more parameters of a lattice structure. The lattice structure of the 3D printed ball may be selected to match certain bulk properties of the polymeric build material or to reduce the certain bulk properties of the polymeric build material. The parameters of the lattice structure can be modulated as described herein through its geometry and netting offset, as well as through the agents (e.g., fusing agent, detailing agent, coloring agent, etc.) used in the 3D printing process.86325147 3

[0017] Definitions

[0018] It is to be understood that terms used herein will take on their ordinary meaning in the relevant art unless specified otherwise. Several terms used herein and their meanings are set forth below.

[0019] The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0020] The terms comprising, including, containing and various forms of these terms are synonymous with each other and are meant to be equally broad.

[0021] As used herein and unless stated otherwise, the term “absorption” means that at least 80% of radiation having wavelengths within the specified range is absorbed by the material being described. Also used herein and unless stated otherwise, “transparency” means that 25% or less of radiation having wavelengths within the specified range is absorbed by the material being described.

[0022] The phrase “does not substantially absorb” means that the absorptivity of the polymeric build material at a particular wavelength is 25% or less (e.g., 20%, 10%, 5%, etc.).

[0023] The phrase “energy return,” as used herein in terms of a solid ball formed of bulk material or with the lattice structures disclosed herein, is Y / X, where Y is the distance that the ball rebounds / bounces after being dropped from a distance X. With the examples set forth herein, Y / X varies as a function of X because the amount of energy absorbed by the lattice structures described herein is a non-linear function of the drop distance X. Without being held bound by any theory, the following is an explanation of “energy return” as it relates to a bouncing ball. The principle of conservation of energy states that the energy of interacting bodies or particles in a closed system remains constant. Thus, a ball, dropped from a height Y converts potential energy into kinetic energy as the ball falls and gains velocity (kinetic energy of a moving object is proportional to the mass and the square of the velocity). When the ball impacts a surface and reverses direction, the velocity of the ball may be zero for an instant. The kinetic energy is stored in the ball (and the surface) as a form of potential energy, by distorting (e.g., flattening) the ball from its equilibrium shape (e.g., a sphere). The energy may be stored in the ball in various forms, including by86325147 4 stretching or compressing the ball, heat, and by permanently distorting the ball beyond the yield point of the material. The elasticity of the ball will tend toward its equilibrium state (e.g., sphere), and the ball will be propelled by this elasticity toward the location from which the ball was dropped. However, because of losses due to, for example, conversion of kinetic energy (e.g. through friction processes) to heat, the ball will not have enough energy to reach the original drop height. The amount of energy that is “lost” to heat, sound, aerodynamic drag, transfer of energy to the air, and permanent distortion of elements of the ball, reduces the “energy return” of the ball. The energy return for a ball made from a “bulk material”, (i.e., a solid ball) may depend on the material. For example, a superball may have an energy return of about 92%. On the other hand, a ball made of mud or putty may not bounce at all, (i.e., zero energy return).

[0024] The energy return of a solid ball formed of bulk material may be more linear as the energy return may be less dependent upon the drop height. All else being equal, a solid ball may lose less energy to distortion and interaction with the air, even at higher speeds that would be experienced at a higher drop height.

[0025] A suitable energy return for a properly inflated basketball may be about 72% and for a pickleball may be about 41%. The “predetermined energy return of the ball” refers to the energy return that the 3D printed ball should exhibit once it is 3D printed with the parameters selected. The predetermined energy return is based on how a similar ball (e.g., pickleball) performs when used or tested in accordance with its typical application or standard (e.g., during a pickleball match or a drop bounce test).

[0026] In some of the examples disclosed herein, a solid ball formed of the polymeric build material has a bulk energy return; and the 3D printed ball (with the lattice structure) exhibits a maintained or reduced energy return relative to the bulk energy return. As such, “maintained energy return” refers to the predetermined energy return of the 3D printed ball when it is within 10% of the energy return of the solid ball formed of the same bulk material. “Reduced energy return” refers to the predetermined energy return of the 3D printed ball when it is lower than the energy return of a solid ball formed of the same bulk material by more than 10%. “Increased energy return” refers to the predetermined energy return of the 3D printed ball when it86325147 5 is higher than the energy return of a solid ball formed of the same bulk material by more than 10%.

[0027] It is to be understood the term “beam,” when used herein in the context of a truss may also be understood as a “member.” As used herein, the term “beam” does not imply any particular direction of applied load unless specifically written otherwise herein. As used herein, a “member” may include a “beam,” a “strut,” a “column,” or a “post”.

[0028] The outermost lattice beams may have “netting” or “netting offset” applied thereto to generate smooth surfaces at the spherical boundary of the 3D printed ball. “Netting” is nominally applied (i.e., offset = 0) when the netting beam centerline falls on the boundary of the 3D printed ball, and any beam portion falling outside the boundary is removed. It is to be understood that the 3D printed netting beam may be 3D printed in a “net” condition, without a requiring subtractive manufacturing techniques to arrive at the final shape. “Netting offset” refers to when the netting beam centerline is moved from the actual center of the beam.

[0029] A lattice structure includes multiple cells, where each “cell” includes inner and outer beams forming hexagonal or pentagonal perimeters that are connected by multiple middle beams. The cell geometry refers to the overall geometry of the cell, including the positioning of the middle beams.

[0030] The phrase “polymeric build material” refers to a composition that includes solid polymer particles, either alone or in combination with other solid additives.

[0031] Throughout this disclosure, a weight percentage that is referred to as “wt% active” refers to the loading of an active component of a stock formulation that is present, e.g., in the fusing agent, or in the detailing agent, etc. For example, particles of a radiation absorbing substance may be present in a water-based formulation (e.g., a stock solution or dispersion) before being incorporated into the fusing agent. In such examples, the wt% active of the radiation absorbing substance accounts for the loading (as a weight percent) of the radiation absorbing substance solids that are present in the formulation being described and does not account for the weight of the other components (e.g., water, etc.) that are present in the stock solution or dispersion86325147 6 with the radiation absorbing substance. The term “wt%,” without the term “active”, refers to the loading (e.g., in the fusing agent) of a 100% active component that does not include other non-active components therein.

[0032] Polymeric Build Material

[0033] The polymeric build material includes the polymer particles described herein. In some instances, the polymeric build material consists of the polymer particles. In other instances, the polymeric build material includes the polymer particles and one or more of the additives set forth herein.

[0034] The polymeric particles are thermoplastic materials, such as thermoplastic polyamide or thermoplastic polyurethane. Thermoplastic polyamides are block copolymers of polyamide and polyethers or polyesters. One example of a thermoplastic polyamide has a bulk energy return of about 75%. Thermoplastic polyurethanes are block copolymers consisting of hard segments (e.g., an aromatic segment, such as methylene diphenyl diisocyanate) and soft segments (e.g., a polyether segment, such as a polyol) linked by a urethane bond. Examples of suitable thermoplastic polyurethanes are commercially available from BASF Corp. (with a bulk energy return of about 65%) and The Lubrizol Corp (with a bulk energy return of about 45%). These materials are particularly suitable for the 3D printed balls described herein, as they have been found to impart a noise dampening effect in addition to the particular energy return as described herein. A more pliable outer beam structure and the spreading out of impulse forces (over time) contributes, at least in part, to the noise dampening effect.

[0035] Thermoplastic materials have bulk properties, such as energy return. As examples, the energy return of some thermoplastic polyurethanes is about 45%, while the energy return of some thermoplastic polyamides is about 75%.

[0036] In some examples, the polymeric build material may be in the form of a powder. In other examples, the polymeric build material may be in the form of a powder-like material, which includes, for example, short fibers having a length that is greater than its width. In some examples, the powder or powder-like material may be86325147 7 formed from—or may include—short fibers that may, for example, have been cut into short lengths from long strands or threads of material.

[0037] The polymeric build material may be made up of similarly sized particles and / or differently sized particles. In an example, the average particle size of the polymeric build material ranges from about 2 µm to about 225 μm. In another example, the average particle size of the polymeric build material ranges from about 10 µm to about 130 μm. The term “average particle size”, as used herein, may refer to a number-weighted mean diameter or a volume-weighted mean diameter of a particle distribution of the material being referred to.

[0038] The thermoplastic elastomer polymeric build materials set forth herein may have a melting range within the range of from about 130°C to about 250°C. In some examples (e.g., when the thermoplastic elastomer is a polyether block amide), the thermoplastic elastomer may have a melting range of from about 130°C to about 175°C. In some other examples (e.g., when the thermoplastic elastomer is a thermoplastic polyurethane), the thermoplastic elastomer may have a melting range of from about 130°C to about 180°C or a melting range of from about 175°C to about 210°C.

[0039] In some examples, the polymeric build material does not substantially absorb radiation having a wavelength within the range of 300 nm to 1400 nm.

[0040] In some examples, in addition to the polymeric build material, the build material composition may include an antioxidant, a whitener, an antistatic agent, a flow aid (i.e., an anti-caking additive), or a combination thereof. While several examples of these additives are provided, it is to be understood that these additives are selected to be thermally stable (i.e., will not decompose) at the 3D printing temperatures.

[0041] Antioxidant(s) may be added to the polymeric build material to prevent or slow molecular weight decreases of the polymeric build material and / or to prevent or slow discoloration (e.g., yellowing) of the polymeric build material by preventing or slowing oxidation of the polymer particles. In some examples, the polymeric particles may discolor upon reacting with oxygen, and this discoloration may contribute to the discoloration of the polymeric build material. The antioxidant may be selected to minimize discoloration. In some examples, the antioxidant may be a radical86325147 8 scavenger. In these examples, the antioxidant may include IRGANOX® 1098 (benzenepropanamide, N,N'-1,6-hexanediylbis(3,5-bis(1,1-dimethylethyl)-4-hydroxy)), IRGANOX® 254 (a mixture of 40% triethylene glycol bis(3-tert-butyl-4-hydroxy-5- methylphenyl), polyvinyl alcohol and deionized water), and / or other sterically hindered phenols. In other examples, the antioxidant may include a phosphite and / or an organic sulfide (e.g., a thioester). The antioxidant may be in the form of fine particles (e.g., having an average particle size of 5 µm or less) that are dry blended with the polymer particles. In an example, the antioxidant may be included in the polymeric build material in an amount ranging from about 0.01 wt% to about 5 wt%, based on a total weight of the polymeric build material. In other examples, the antioxidant may be included in the polymeric build material in an amount ranging from about 0.01 wt% to about 2 wt% or from about 0.2 wt% to about 1 wt%, based on the total weight of the polymeric build material.

[0042] Whitener(s) may be added to the polymeric build material to improve its visibility. Examples of suitable whiteners include titanium dioxide (TiO2), zinc oxide (ZnO), calcium carbonate (CaCO3), zirconium dioxide (ZrO2), aluminum oxide (Al2O3), silicon dioxide (SiO2), boron nitride (BN), and combinations thereof. In some examples, a stilbene derivative may be used as the whitener and a brightener. In these examples, the temperature(s) of the 3D printing process may be selected so that the stilbene derivative remains stable (i.e., the 3D printing temperature does not thermally decompose the stilbene derivative). In an example, the whitener may be included in the polymeric build material in an amount ranging from greater than 0 wt% to about 10 wt%, based on the total weight of the polymeric build material.

[0043] Antistatic agent(s) may be added to the polymeric build material to suppress tribo-charging. Examples of suitable antistatic agents include aliphatic amines (which may be ethoxylated), aliphatic amides, quaternary ammonium salts (e.g., behentrimonium chloride or cocamidopropyl betaine), esters of phosphoric acid, polyethylene glycolesters, or polyols. Some suitable commercially available antistatic agents include HOSTASTAT® FA 38 (natural based ethoxylated alkylamine), HOSTASTAT® FE2 (fatty acid ester), and HOSTASTAT® HS 1 (alkane sulfonate), each of which is available from Clariant Int. Ltd.). In an example, the antistatic agent is86325147 9 added in an amount ranging from greater than 0 wt% to less than 5 wt%, based on the total weight of the polymeric build material.

[0044] Flow aid(s) or anti-caking agent(s) may be added to improve the coating flowability and reduce agglomeration of the polymeric build material. Flow aids may be particularly beneficial when the polymeric particles have an average particle size less than 25 μm. The flow aid improves the flowability of the polymeric build material by reducing the friction, the lateral drag, and the tribocharge buildup (by increasing the particle conductivity). Examples of suitable flow aids include aluminum oxide (Al2O3), 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), and polydimethylsiloxane (E900). In an example, the flow aid is added in an amount ranging from greater than 0 wt% to less than 5 wt%, based upon the total weight of the polymeric build material.

[0045] The build material composition may be included in a 3D printing kit with one or more of the agents described herein and used in the 3D printing method disclosed herein.

[0046] Agents

[0047] In the examples disclosed herein, energy return is modulated and mass is controlled in order to obtain a ball with playability in a particular sport or other application. As will be described in detail in reference to the method, a fusing agent is used to achieve full coalescence of the polymeric build material patterned with the fusing agent. The components of the fusing agent may be varied to alter the stiffness, flexibility, porosity, ductility, durability, color, radius of gyration (which affects stiffness), interlamellar amorphous thickness (which affects flexibility and malleability), or other desirable properties. Alternatively, additional agents may be used to alter various properties of the 3D printed ball. The various agents will now be described.86325147 10

[0048] Fusing Agent

[0049] The fusing agent generally includes a radiation absorbing substance and a liquid vehicle. In examples, the fusing agent consists of the radiation absorbing substance and the liquid vehicle. In other examples, the fusing agent includes the radiation absorbing substance, the liquid vehicle, and one or more additional components (e.g., additives), where the additional components may be incorporated into the liquid vehicle during formation of the fusing agent. Each of the components of the fusing agent will now be described.

[0050] Radiation Absorbing Substance(s)

[0051] The radiation absorbing substance of the fusing agent is an electromagnetic radiation (EMR) absorbing material that converts absorbed EMR to thermal energy. Different radiation absorbing substances can absorb different wavelengths of light.

[0052] Some examples of the fusing agent include a radiation absorbing substance having absorption at least in the visible light region (e.g., light wavelengths ranging from 400 nm to about 750 nm). Fusing agents that include these types of energy absorbers impart a dark grey or black color to the resulting 3D printed object, and thus are referred to herein as a “high tint fusing agent.” Some examples of the high tint fusing agent include a radiation absorbing substance that also has absorption in at least a portion of the infrared region (e.g., 760 nm to 4000 nm), in addition to the visible light region. When exposed to electromagnetic radiation during 3D printing, the radiation absorbing substance in the high tint fusing agent generates heat that is suitable for coalescing / fusing the polymeric build material in contact therewith, which leads to 3D objects (or 3D objects regions) having mechanical integrity and relatively uniform mechanical properties (e.g., strength, elongation at break, etc.).

[0053] The radiation absorbing substance included in the high tint fusing agent may be an infrared light absorbing colorant or a near-infrared light absorbing colorant. Any infrared or near-infrared colorants, e.g., those produced by Fabricolor Holdings LLC, Eastman Kodak, or BASF, Yamamoto, may be used in the high tint fusing agent. As one example, the high tint fusing agent may be a printing liquid formulation including carbon black as the radiation absorbing substance. Examples of this printing86325147 11 liquid formulation are commercially known as CM997A, 516458, C18928, C93848, C93808, or the like, all of which are available from HP Inc.

[0054] As another example, the high tint fusing agent may be a printing liquid formulation including near-infrared absorbing dyes as the radiation absorbing substances. Examples of this printing liquid formulation are described in U.S. Patent No.9,133,344, which is incorporated herein by reference in its entirety.

[0055] Some examples of the near-infrared absorbing dye are water-soluble near-infrared absorbing dyes selected from the group consisting of: (I)86325147 12 (II)86325147 13 III)86325147 14 IV)and a combination thereof. In the above structures (I) – (IV), M can be a divalent metal atom (e.g., copper, etc.) or can have OSO3Na axial groups filling any unfilled valence shells if the metal is more than divalent (e.g., indium, etc.), R can be hydrogen or any C1-C8alkyl group (including substituted alkyl and unsubstituted alkyl), and Z can be a counterion such that the overall charge of the near-infrared absorbing dye is86325147 15 neutral. For example, the counterion can be a sodium ion (Na+), a lithium ion (Li+), a potassium ion (K+), ammonium (NH4+), etc.

[0056] Some other examples of the near-infrared absorbing dye that may be included in the high tint fusing agent are hydrophobic near-infrared absorbing dyes selected from the group consisting of: (V)86325147 16 (VI)86325147 17 II)and a combination thereof. For the hydrophobic near-infrared absorbing dyes (structures (V) – (VII), M can be a divalent metal atom (e.g., copper, etc.) or can include a metal that has Cl, Br, or OR’ (R’=H, CH3, COCH3, COCH2COOCH3, COCH2COCH3) axial groups filling any unfilled valence shells if the metal is more than divalent, and R can be hydrogen or any C1-C8 alkyl group (including substituted alkyl and unsubstituted alkyl).

[0057] Other near-infrared absorbing dyes or pigments may be used as the radiation absorbing substances in the high tint fusing agent. Some examples include anthraquinone dyes or pigments, metal dithiolene dyes or pigments, cyanine dyes or pigments, perylenediimide dyes or pigments, croconium dyes or pigments, pyrilium or86325147 18 thiopyrilium dyes or pigments, boron-dipyrromethene dyes or pigments, or aza-boron- dipyrromethene dyes or pigments.

[0058] Anthraquinone dyes or pigments and metal (e.g., nickel) dithiolene dyes or pigments may have the following structures, respectively: III)X)86325147 19 where R in the anthraquinone dyes or pigments (structure (VIII)) may be hydrogen or any C1-C8 alkyl group (including substituted alkyl and unsubstituted alkyl), and where R in the nickel dithiolene (structure (IX)) may be hydrogen, COOH, SO3, NH2, any C1- C8 alkyl group (including substituted alkyl and unsubstituted alkyl), or the like.

[0059] Cyanine dyes or pigments and perylenediimide dyes or pigments may have the following structures, respectively: (X)(XI) where R in the perylenediimide dyes or pigments (structure (XI) may be hydrogen or any C1-C8alkyl group (including substituted alkyl and unsubstituted alkyl).86325147 20

[0060] Croconium dyes or pigments and pyrilium or thiopyrilium dyes or pigments may have the following structures, respectively: XII)(XIII)

[0061] Boron-dipyrromethene dyes or pigments and aza-boron-dipyrromethene dyes or pigments may have the following structures, respectively:86325147 21 IV)V) Aza- oo - py o e e e yespg e s

[0062] Other suitable near-infrared absorbing dyes may include aminium dyes, tetraaryldiamine dyes, phthalocyanine dyes, and others.

[0063] Other near-infrared absorbing materials that may be used as radiation absorbing substance in the high tint fusing agent conjugated polymers (i.e., a polymer86325147 22 that has a backbone with alternating double and single bonds), such as poly(3,4- ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), a polythiophene, poly(p-phenylene sulfide), a polyaniline, a poly(pyrrole), a poly(acetylene), poly(p- phenylene vinylene), polyparaphenylene, or combinations thereof.

[0064] The total amount of radiation absorbing substance that is present in the high tint fusing agent ranges from greater than 0 wt% active to about 40 wt% active, based on a total weight of the high tint fusing agent. In other examples, the amount of the radiation absorbing substance that is present in the high tint fusing agent ranges from about 0.3 wt% active to about 30 wt% active, or from about 1 wt% active to about 20 wt% active, from about 1.0 wt% active to about 10.0 wt% active, or from 4.0 wt% active to about 15.0 wt% active, based on the total weight of the high tint fusing agent. It is believed that these example loadings for the radiation absorbing substance provide a balance between the high tint fusing agent having jetting reliability (e.g., through an inkjet applicator) and heat and / or radiation absorbance efficiency.

[0065] The radiation absorbing substance that is included in the high tint fusing agent may have an average particle diameter (e.g., volume-weighted mean diameter) ranging from greater than 0 nm to less than 500 nm. In another example, the radiation absorbing substance in the high tint fusing agent has an average particle diameter ranging from greater than 0 nm to 250 nm. In still another example, the radiation absorbing substance in the high tint fusing agent has an average particle diameter ranging from about 10 nm to about 200 nm.

[0066] Other examples of the fusing agent are referred to herein as the “low tint fusing agent” because they enable the 3D printed ball to be slightly colored (not dark grey or black), or to retain a color of the build material used to form the 3D objects (e.g., white or off-white), or to take on the color of a coloring agent applied with the low tint fusing agent or to the 3D printed ball. In some examples, the low tint fusing agent includes a radiation absorbing substance having absorption at wavelengths ranging from 800 nm to 4000 nm and having transparency at wavelengths ranging from 400 nm to 780 nm. This combination of absorption (at wavelengths ranging from 800 nm to 4000 nm) and transparency (at wavelengths ranging from 400 nm to 780 nm) allows the low tint fusing agent to absorb enough radiation to coalesce / fuse build material86325147 23 particles in contact therewith, while allowing the 3D objects (or 3D objects regions) to be slightly colored, white, off-white, or the color of the coloring agent. In other examples, the low tint fusing agent includes a dye having absorption in the visible light region (e.g., light wavelengths ranging from 400 nm to about 750 nm).

[0067] In some examples, the radiation absorbing substance included in the low tint fusing agent is a plasmonic resonance absorber having absorption at wavelengths ranging from 800 nm to 4000 nm and transparency at wavelengths ranging from 400 nm to 780 nm. As such, the absorption of this type of radiation absorbing substance is the result of plasmonic resonance effects. Electrons associated with the atoms of the energy absorber may be collectively excited by radiation, which results in collective oscillation of the electrons. The wavelengths that can excite and oscillate these electrons collectively are dependent on the number of electrons present in the energy absorber particles, which in turn is dependent on the size of the radiation absorbing substance particles. The amount of energy that can collectively oscillate the particle’s electrons is low enough that very small particles of the radiation absorbing substance (e.g., particles having a size ranging from 1 nm to 100 nm) may absorb radiation with wavelengths several times higher (e.g., from 8 to 800 or more times) the size of the particles of the radiation absorbing substance. The use of these particles allows the low tint fusing agent to be inkjet jettable as well as electromagnetically selective (e.g., having absorption at wavelengths ranging from 800 nm to 4000 nm and transparency at wavelengths ranging from 400 nm to 780 nm).

[0068] In these examples, the radiation absorbing substance included in the low tint fusing agent may be an inorganic pigment. Examples of suitable inorganic pigments include lanthanum hexaboride (LaB6), tungsten bronzes (AxWO3), indium tin oxide (In2O3:SnO2, ITO), antimony tin oxide (Sb2O3:SnO2, ATO), titanium nitride (TiN), cesium tungsten oxide (Cs2WO4), aluminum zinc oxide (AZO), ruthenium oxide (RuO2), silver (Ag), gold (Au), platinum (Pt), iron pyroxenes (AxFeySi2O6 wherein A is Ca or Mg, x = 1.5–1.9, and y = 0.1-0.5), modified iron phosphates (AxFeyPO4), modified copper phosphates (AxCuyPOz), and modified copper pyrophosphates (AxCuyP2O7). Tungsten bronzes may be alkali doped tungsten oxides. Examples of suitable alkali dopants (i.e., A in AxWO3) may be cesium, sodium, potassium, or86325147 24 rubidium. In an example, the alkali doped tungsten oxide may be doped in an amount ranging from greater than 0 mol% to about 0.33 mol% based on the total mol% of the alkali doped tungsten oxide. Suitable modified iron phosphates (AxFeyPO) may include copper iron phosphate (A = Cu, x = 0.1-0.5, and y = 0.5-0.9), magnesium iron phosphate (A = Mg, x = 0.1-0.5, and y = 0.5-0.9), and zinc iron phosphate (A = Zn, x = 0.1-0.5, and y = 0.5-0.9). For the modified iron phosphates, it is to be understood that the number of phosphates may change based on the charge balance with the cations. Suitable modified copper pyrophosphates (AxCuyP2O7) include iron copper pyrophosphate (A = Fe, x = 0-2, and y = 0-2), magnesium copper pyrophosphate (A = Mg, x = 0-2, and y = 0-2), and zinc copper pyrophosphate (A = Zn, x = 0-2, and y = 0- 2). Combinations of the inorganic pigments may also be used.

[0069] The inorganic pigment may have an average particle diameter (e.g., volume-weighted mean diameter) ranging from greater than 0 nm to less than 220 nm. In another example, the radiation absorbing substance in the low tint fusing agent has an average particle diameter ranging from greater than 0 nm to 120 nm.

[0070] The amount of the inorganic pigment that is present in the low tint fusing agent ranges from greater than 0 wt% active to about 40 wt% active, based on a total weight of the low tint fusing agent. In other examples, the amount of the inorganic pigment that is present in the low tint fusing agent ranges from about 0.3 wt% active to 30 wt% active, or from about 1 wt% active to about 20 wt% active, from about 1.0 wt% active to about 10.0 wt% active, or from about 4.0 wt% active to about 15.0 wt% active, based on the total weight of the low tint fusing agent. It is believed that these example loadings for the inorganic pigment provide a balance between the low tint fusing agent having jetting reliability (e.g., through an inkjet applicator) and heat and / or radiation absorbance efficiency.

[0071] In other examples, the low tint fusing agent includes a dye having absorption (e.g., at least 80% absorption) in the visible light region (e.g., light wavelengths ranging from 400 nm to about 750 nm). Examples of suitable dye includes Direct Black (DB) 168, Acid Yellow (AY) 23, AY 17, Acid Red (AR) 52, AR 289, Reactive Red 180 (RR 180), and Direct Blue (DB) 199.86325147 25

[0072] The amount of the dye that is present in the low tint fusing agent ranges from about 0.005 wt% active to about 0.75 wt% active, based on a total weight of the low tint fusing agent. As other examples, the amount of the dye may range from about 0.005 wt% active to any of the following: about 0.60, 0.55, 0.50, 0.45, 0.40, 0.35, 0.30, 0.25, 0.20, 0.15, 0.10, or 0.05 wt% active, based on the total weight of the low tint fusing agent. At these loadings, the dyes impart very little color to the 3D printed ball, but enable sufficient fusing / coalescence.

[0073] Still other examples of the radiation absorbing substance that may be used in either the high tint fusing agent or in the low tint fusing agent absorb at least some of the light wavelengths within the range of 400 nm to 4000 nm. Examples of this type of radiation absorbing substance include glass fibers, titanium dioxide, clay, mica, talc, barium sulfate, calcium carbonate, phosphate pigments, silicate pigments, and / or natural filler materials, such as nano-cellulose. These energy absorbers are often white or lightly colored. Phosphates may have a variety of counterions, such as copper, zinc, iron, magnesium, calcium, strontium, the like, and combinations thereof. 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, such as those listed above or a combination thereof. For example, M2P2O7 can include compounds such as Cu2P2O7, Cu / MgP2O7, Cu / ZnP2O7, or any other suitable combination of counterions. Silicates can have the same or similar counterions as phosphates. Example silicates can include M2SiO4, M2Si2O6, and other silicates where M is a counterion having an oxidation state of +2. For example, the silicate M2Si2O6 can include Mg2Si2O6, Mg / CaSi2O6, MgCuSi2O6, Cu2Si2O6, Cu / ZnSi2O6, or other suitable combination of counterions. It is noted that the phosphates and silicates described herein are not limited to counterions having a +2 oxidation state, and that other counterions can also be used to prepare other suitable near-infrared pigments.

[0074] In addition to the radiation absorbing substance, the fusing agent also includes the liquid vehicle, which will now be described.

[0075] Fusing Agent Liquid Vehicle86325147 26

[0076] Any example of the fusing agent (i.e., the high tint fusing agent or the low tint fusing agent) includes a liquid vehicle. The fusing agent vehicle, or “FA vehicle,” may refer to the liquid in which the radiation absorbing substance(s) is / are dispersed or dissolved to form the fusing agent. In some examples, the FA vehicle may consist of water alone, an aqueous solvent alone, or a non-aqueous solvent alone, and no other components. In other examples, the FA vehicle may include water, and may further include additional components, depending, in part, upon the applicator that is to be used to dispense the fusing agent. As examples, the fusing agent may further include one or more of the following additives: dispersant(s), co-solvent(s), surfactant(s), antimicrobial agent(s), anti-kogation agent(s), chelating agent(s), humectant(s), stabilizer(s), pore forming component(s), and / or pH adjusters. Any of these may be added to the liquid vehicle of the fusing agent.

[0077] The FA vehicle may include a dispersant to aid in the dispersion of the radiation absorbing substance. When used, the dispersant uniformly distributes the radiation absorbing substance throughout the high tint or low tint fusing agent. Examples of suitable dispersants include polymer or small molecule dispersants, charged groups attached to the energy absorber surface, or other suitable dispersants. Some specific examples of suitable dispersants include a water-soluble acrylic acid polymer (e.g., CARBOSPERSE® K7028 available from Lubrizol), water-soluble styrene-acrylic acid copolymers / resins (e.g., JONCRYL® 296, JONCRYL® 671, JONCRYL® 678, JONCRYL® 680, JONCRYL® 683, JONCRYL® 690, etc. available from BASF Corp.), a high molecular weight block copolymer with pigment affinic groups (e.g., DISPERBYK®-190 available BYK Additives and Instruments), or water- soluble styrene-maleic anhydride copolymers / resins.

[0078] Whether a single dispersant is used or a combination of dispersants is used in the high tint or low tint fusing agent, the total amount of dispersant(s) may range from about 10 wt% active to about 200 wt% active based on a weight of the radiation absorbing substance in the high tint or low tint fusing agent.

[0079] The FA vehicle may include a water soluble or water miscible organic solvent and / or co-solvent. Classes of water soluble or water miscible organic co- solvents that may be used include aliphatic alcohols, aromatic alcohols, diols, glycol86325147 27 ethers, polyglycol ethers, lactams, formamides (substituted and unsubstituted), acetamides (substituted and unsubstituted), glycols, and long chain alcohols. Examples of these co-solvents include primary aliphatic alcohols, secondary aliphatic alcohols, 1,2-alcohols, 1,3-alcohols, 1,5-alcohols, 1,6-hexanediol or other diols (e.g., 1,2-propanediol, 1,5-pentanediol, 2-methyl-1,3-propanediol, etc.), ethylene glycol alkyl ethers, propylene glycol, propylene glycol alkyl ethers, higher homologs (C6-C12) of polyethylene glycol alkyl ethers, triethylene glycol, tetraethylene glycol, tripropylene glycol methyl ether, N-alkyl caprolactams, unsubstituted caprolactams, 2-pyrrolidone, 1-methyl-2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, and the like. Other examples of organic co-solvents include dimethyl sulfoxide (DMSO), isopropyl alcohol, ethanol, pentanol, acetone, or the like.

[0080] The co-solvent(s) may be present in the fusing agent in a total amount ranging from greater than 0.01 wt% to about 20 wt%, based on the total weight of the fusing agent. In an example, the fusing agent includes from about 2 wt% to about 15 wt%, or from about 7.5 wt% to about 12.5 wt% of the co-solvent(s), based on the total weight of the fusing agent. In a specific example, the co-solvent(s) is / are present in the fusing agent in an amount of about 10.0 wt%, based on the total weight of the fusing agent.

[0081] In one specific example, the low tint fusing agent vehicle includes a co- solvent mixture that contains from about 0.1 wt% active to about 10 wt% active of benzyl alcohol and from about 10 wt% active to about 40 wt% active of a co-solvent to improve miscibility between the benzyl alcohol and the water, wherein the wt% of the benzyl alcohol and the wt% of the co-solvent are based on the total weight of the low tint fusing agent. In this example, the benzyl alcohol in the co-solvent mixture is a plasticizer that can i) reduce the amount of infrared radiation required to adequately melt and coalesce the polymeric build material by locally reducing the melting temperature in the polymer bed during 3D printing, and ii) increase the flexibility of portions of the 3D printed ball printed with this particular example of the low tint fusing agent. In this particular example, the co-solvent is selected from the group consisting of 1-(2-hydroxyethyl)-2-pyrrolidone, 1,5-pentanediol, 1,2-hexanediol, 2-pyrrolidinone, triethylene glycol, tetraethylene glycol, 2-methyl-1,3-propanediol, 1,6-hexanediol,86325147 28 tripropylene glycol methyl ether, 1,2-propanediol (i.e., propylene glycol), diethylene glycol butyl either, polyethylene glycol having a weight average molecular weight ranging from about 190 Daltons to about 420 Daltons, glycerol, betaine, and combinations thereof.

[0082] Any example of the fusing agent vehicle may further include a surfactant. Suitable surfactant(s) for the fusing agent include non-ionic, anionic, or cationic surfactants. Some example surfactants include alkyl polyethylene oxides, alkyl phenyl polyethylene oxides, polyethylene oxide block copolymers, acetylenic polyethylene oxides, polyethylene oxide (di)esters, polyethylene oxide amines, protonated polyethylene oxide amines, protonated polyethylene oxide amides, dimethicone copolyols, substituted amine oxides, fluorosurfactants, and the like. Some specific examples include a self-emulsifiable, non-ionic wetting agent based on acetylenic diol chemistry (e.g., SURFYNOL® SEF from Evonik Degussa), a non-ionic fluorosurfactant (e.g., CAPSTONE® fluorosurfactants, such as CAPSTONE® FS-35, from Chemours), an ethoxylated low-foam wetting agent (e.g., SURFYNOL® 440 or SURFYNOL® CT- 111 from Evonik Degussa), an ethoxylated wetting agent and molecular defoamer (e.g., SURFYNOL® 420 from Evonik Degussa), non-ionic wetting agents and molecular defoamers (e.g., SURFYNOL® 104E from Evonik Degussa), and / or water- soluble, non-ionic surfactants (e.g., TERGITOL™ TMN-6, TERGITOL™ 15-S-7, or TERGITOL™ 15-S-9 (a secondary alcohol ethoxylate) from The Dow Chemical Company or TEGO® Wet 510 (organic surfactant) available from Evonik Degussa). Yet another suitable (anionic) surfactant includes alkyldiphenyloxide disulfonate (e.g., the DOWFAX™ series, such a 2A1, 3B2, 8390, C6L, C10L, and 30599, from The Dow Chemical Company).

[0083] Whether a single surfactant is used or a combination of surfactants is used, the total amount of surfactant(s) in the fusing agent may range from about 0.01 wt% active to about 3 wt% active, based on the total weight of the fusing agent. In an example, the total amount of surfactant(s) in the fusing agent is about 0.75 wt% active, based on the total weight of the fusing agent.

[0084] The fusing agent vehicle may further include an antimicrobial agent. Antimicrobial agents are also known as biocides and / or fungicides. Examples of86325147 29 suitable antimicrobial agents include the NUOSEPT® (Ashland Inc.), UCARCIDE™ or KORDEK™ or ROCIMA™ (The Dow Chemical Company), PROXEL® (Arch Chemicals) series, ACTICIDE® B20 and ACTICIDE® M20 and ACTICIDE® MBL (blends of 2-methyl-4-isothiazolin-3-one (MIT), 1,2-benzisothiazolin-3-one (BIT) and Bronopol) (Thor Chemicals), AXIDE™ (Planet Chemical), NIPACIDE™ (Clariant), blends of 5-chloro-2-methyl-4-isothiazolin-3-one (CIT or CMIT) and MIT under the tradename KATHON™ (The Dow Chemical Company), and combinations thereof.

[0085] In an example, the total amount of antimicrobial agent(s) in the fusing agent ranges from about 0.01 wt% active to about 0.05 wt% active, based on the total weight of the fusing agent.

[0086] The fusing agent vehicle may further include an anti-kogation agent that is to be jetted using thermal inkjet printing. “Kogation” refers to the deposit of dried printing liquid (e.g., fusing agent) on a heating element of a thermal inkjet printhead. Anti-kogation agent(s) is / are included to assist in preventing the buildup of kogation.

[0087] Examples of suitable anti-kogation agents include oleth-3-phosphate (commercially available as CRODAFOS™ O3A or CRODAFOS™ N-3A) or dextran 500k. Other suitable examples of the anti-kogation agents include CRODAFOS™ HCE (phosphate-ester from Croda Int.), CRODAFOS® O10A (oleth-10-phosphate from Croda Int.), or DISPERSOGEN® LFH (polymeric dispersing agent with aromatic anchoring groups, acid form, anionic, from Clariant), etc. It is to be understood that any combination of the anti-kogation agents listed may be included in the fusing agent.

[0088] The anti-kogation agent may be present in the fusing agent in an amount ranging from about 0.01 wt% active to about 1.5 wt% active, based on the total weight of the fusing agent.

[0089] The fusing agent vehicle may further include chelating agents, e.g., to eliminate the deleterious effects of heavy metal impurities. In an example, the chelating agent is selected from the group consisting of methylglycinediacetic acid, trisodium salt; 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt monohydrate; ethylenediaminetetraacetic acid (EDTA); hexamethylenediamine tetra(methylene phosphonic acid), potassium salt; and a combination thereof. Methylglycinediacetic acid, trisodium salt (Na3MGDA) is commercially available as TRILON® M from BASF86325147 30 Corp. 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt monohydrate is commercially available as TIRON™ monohydrate. Hexamethylenediamine tetra(methylene phosphonic acid), potassium salt is commercially available as DEQUEST® 2054 from Italmatch Chemicals.

[0090] Whether a single chelating agent is used in the fusing agent or a combination of chelating agents is used in the fusing agent, the total amount of chelating agent(s) in the fusing agent may range from 0 wt% active to about 0.5 wt% active based on the total weight of the fusing agent. In an example, the chelating agent is present in the fusing agent in an amount ranging from about 0.01 wt% active to about 0.2 wt% active, based on the total weight of fusing agent.

[0091] The fusing agent vehicle may further include humectant(s). An example of a suitable humectant is ethoxylated glycerin having the following formula: VI)in which the total of a+b+c ranges from about 5 to about 60, or in other examples, from about 20 to about 30. An example of the ethoxylated glycerin is LIPONIC® EG-1 (LEG-1, glycereth-26, a+b+c=26, available from Lipo Chemicals).

[0092] In an example, the total amount of the humectant(s) present in the fusing agent ranges from 0.01 wt% active to about 10 wt% active, based on the total weight of the fusing agent.

[0093] When inorganic pigments are used as the radiation absorbing substance in the fusing agent (e.g., in examples of the low tint fusing agent), the liquid vehicle may also include a stabilizer. The stabilizer aids in extending the shelf life of the fusing agent and in maintaining the printability of the fusing agent, and thus improves the overall stabilization of the fusing agent.86325147 31

[0094] One example of a suitable stabilizer for inorganic pigments is a silane coupling agent. The silane coupling agent helps bond the organic (e.g., dispersant) and inorganic (e.g., pigment) materials. Examples of suitable silane coupling agents include the SILQUEST® A series manufactured by Momentive. Whether a single silane coupling agent is used or a combination of silane coupling agents is used, the total amount of silane coupling agent(s) in the fusing agent may range from about 0.1 wt% active to about 50 wt% active, based on the weight of the radiation absorbing substance in the low tint fusing agent. In an example, the total amount of silane coupling agent(s) in the low tint fusing agent ranges from about 1 wt% to about 30 wt% based on the weight of the radiation absorbing substance in the fusing agent. In another example, the total amount of silane coupling agent(s) in the fusing agent ranges from about 2.5 wt% active to about 25 wt% active, based on the weight of the radiation absorbing substance in the fusing agent.

[0095] Another example of a suitable stabilizer is a zwitterionic stabilizer. This stabilizer may be particularly suitable when cesium tungsten oxide is used as the radiation absorbing substance in the low tint fusing agent. While the zwitterionic stabilizer has an overall neutral charge, at least one area of the molecule has a positive charge (e.g., amino groups) and at least one other area of the molecule has a negative charge. The cesium tungsten oxide nanoparticles may have a slight negative charge. The zwitterionic stabilizer molecules may orient around the slightly negative cesium tungsten oxide nanoparticles with the positive area of the zwitterionic stabilizer molecules closest to the cesium tungsten oxide nanoparticles and the negative area of the zwitterionic stabilizer molecules furthest away from the cesium tungsten oxide nanoparticles. Then, the negative charge of the negative area of the zwitterionic stabilizer molecules may repel cesium tungsten oxide nanoparticles from each other. The zwitterionic stabilizer molecules may form a protective layer around the cesium tungsten oxide nanoparticles, and prevent them from coming into direct contact with each other and / or increase the distance between the particle surfaces (e.g., by a distance of from about 1 nm to about 2 nm). Thus, the zwitterionic stabilizer may prevent the cesium tungsten oxide nanoparticles from agglomerating and / or settling in the low tint fusing agent.86325147 32

[0096] The zwitterionic stabilizer may be selected from the group consisting of C2 to C8 betaines, C2 to C8 aminocarboxylic acids having a solubility of at least 10 g in 100 g of water, taurine, and combinations thereof. Examples of the C2to C8aminocarboxylic acids include beta-alanine, gamma-aminobutyric acid, glycine, and combinations thereof.

[0097] The zwitterionic stabilizer may be present in the low tint fusing agent in an amount of from about 0.2 wt% active to about 35 wt% active, based on the total weight of the low tint fusing agent. When the zwitterionic stabilizer is the C2 to C8 betaine, the C2to C8betaine may be present in an amount of from about 8 wt% to about 35 wt% active of the total weight of the low tint fusing agent. When the zwitterionic stabilizer is the C2 to C8 aminocarboxylic acid, the C2 to C8 aminocarboxylic acid may be present in an amount of from about 0.5 wt% active to about 20 wt% active of the total weight of the low tint fusing agent. When the zwitterionic stabilizer is taurine, taurine may be present in an amount of from about 2 wt% active to about 35 wt% active of the total weight of the low tint fusing agent.

[0098] In one example, the weight ratio of the cesium tungsten oxide nanoparticles to the zwitterionic stabilizer may be from 1:10 to 10:1; or the weight ratio of the cesium tungsten oxide nanoparticles to the zwitterionic stabilizer may be 1:1.

[0099] The liquid vehicle of any example of the fusing agent may also include a pH adjuster. The type and amount of pH adjuster that is added may depend upon the initial pH of the fusing agent and a suitable pH of the fusing agent. If the initial pH is too high (e.g., above 12), an acid may be added to lower the pH, and if the initial pH is too low (below 7.5), a base may be added to increase the pH. Examples of suitable pH adjusters include metal hydroxide bases, such as potassium hydroxide (KOH), sodium hydroxide (NaOH), etc. In an example, the metal hydroxide base may be added to the 3D printing fusing agent in an aqueous solution. In another example, the metal hydroxide base may be added to the 3D printing fusing agent in an aqueous solution including 5 wt% of the metal hydroxide base (e.g., a 5 wt% potassium hydroxide aqueous solution). Examples of suitable acidic pH adjusters that may be used include methane sulfonic acid, nitric acid, and phosphoric acid. The pH adjuster may be a buffer that helps to maintain the suitable pH of the fusing agent. As an86325147 33 example, tris(hydroxymethyl)aminomethane hydrochloride (TRIZMA or TRIS) may be added.

[0100] In an example, the total amount of pH adjuster(s) in the fusing agent ranges from greater than 0 wt% active to about 0.1 wt% active, based on the total weight of the fusing agent.

[0101] It is to be understood that the liquid vehicle of any example of the fusing agent may also include one or more pore forming component(s). The pore forming component(s) may be used in the fusing agent to introduce porosity into the beams of the lattice structure. This can help with reducing the mass of the 3D printed ball. Examples of pore forming component(s) include carbohydrazide, urea, a urea homologue, a carbamide-containing compound, ammonium carbonate, ammonium nitrate, ammonium nitrite, and a combination thereof. When included, the total amount of the pore forming component(s) ranges from about 0.5 wt% to about 8 wt% with respect to a total weight of the fusing agent.

[0102] When any of these additional components / additives are present in the fusing agent vehicle, the balance of the fusing agent vehicle is water (e.g., deionized water, purified water, etc.), which as described herein, may vary depending upon the other components in the fusing agent.

[0103] Detailing Agent

[0104] A detailing agent may be used to pattern negative areas according to the ball’s 3D object model. Any portion of the polymeric build material in a given layer that should not coalesce to become part of the 3D printed ball is considered a negative area. The use of the detailing agent in these areas aids in obtaining the precise geometry of the lattice structure. The detailing agent may also be used with the fusing agent in order to alter the extent of fusing, and in turn the flexibility, of the 3D printed ball.

[0105] The detailing agent includes water (e.g., deionized water, distilled water, etc.) alone or with an additional co-solvent. In an example, the detailing agent consists of water. In another example, the detailing agent includes water with a surfactant and a co-solvent. The detailing agent may consist of water, the surfactant, and the co-solvent, with no other components.86325147 34

[0106] The surfactant(s) that may be used in the detailing agent include any of the surfactants listed herein in reference to the fusing agent, or any other suitable surfactant. The total amount of surfactant(s) in the detailing agent may range from about 0.01 wt% active to about 5 wt% active, based on a total weight of the detailing agent.

[0107] The solvent(s) or co-solvent(s) that may be used in the detailing agent include any of the co-solvents listed herein in reference to the fusing agent, or any other suitable co-solvent. When used in combination with water, the total amount of co-solvent(s) in the detailing agent may range from about 0.01 wt% to about 65 wt%, based on the total weight of the detailing agent.

[0108] In some examples, the detailing agent vehicle does not include a colorant (e.g., pigment or dye). In these examples, the detailing agent is colorless. As used herein, “colorless,” means that the detailing agent is achromatic and does not include a colorant.

[0109] In some other examples, the detailing agent does include a colorant. The detailing agent may consist of the colorant, the surfactant, the co-solvent, and a balance of water, with no other components.

[0110] When the detailing agent vehicle includes the colorant, the colorant may be a dye of any color having substantially no absorbance in a range of 650 nm to 2500 nm. By “substantially no absorbance,” it is meant that the dye absorbs no radiation having wavelengths in a range of 650 nm to 2500 nm, or that the dye absorbs less than 10% of radiation having wavelengths in a range of 650 nm to 2500 nm. The dye may also be capable of absorbing radiation with wavelengths of 650 nm or less. As such, the dye absorbs at least some wavelengths within the visible spectrum, but absorbs little or no wavelengths within the near-infrared spectrum. This is in contrast to the radiation absorbing substance in the fusing agent which absorbs wavelengths within the near-infrared spectrum in at least some examples. As such, the colorant in the detailing agent will not substantially absorb the fusing radiation, and thus will not initiate melting and fusing (coalescence) of the polymeric build material in contact therewith when the build material layer is exposed to the energy during 3D printing.86325147 35

[0111] It may be desirable to add color to the detailing agent when the detailing agent is used in conjunction with the high tint fusing agent, or with the low tint fusing agent and a coloring agent. Color in the detailing agent may be desirable in either of these instances because some of the colorant from the detailing agent may become embedded in the polymeric build material that fuses / coalesces at the edges of the lattice structure. As such, in some examples, the dye in the detailing agent may be selected so that its color matches the color of the radiation absorbing substance in the high tint fusing agent, or the color of the coloring agent used in conjunction with the low tint fusing agent.

[0112] In an example, the dye is a black dye that matches the color of the high tint fusing agent. Some examples of the black dye include azo dyes having sodium or potassium counter ion(s) and diazo (i.e., double azo) dyes having sodium or potassium counter ion(s). Examples of azo and diazo dyes may include tetrasodium (6Z)-4-acetamido-5-oxo-6-[[7-sulfonato-4-(4-sulfonatophenyl)azo-1- naphthyl]hydrazono]naphthalene-1,7-disulfonate with a chemical structure of: (XVII) (commercially available as Foo ac ); eraso um -amno- - y roxy-3-[[7-sulfonato-4-[(4- sulfonatophenyl)azo]-1-naphthyl]azo]naphthalene-2,7-disulfonate with a chemical86325147 36 structure of: III) (commercial oxo-3-[[4-(2-sulfonatooxyethylsulfonyl)phenyl]diazenyl]-6-[[4-(2- sulfonatooxyethylsulfonyl)phenyl]hydrazinylidene]naphthalene-2,7-disulfonate with a chemical structure of: X) (ino-5-oxo-3-[[4- (2-sulfonatooxyethylsulfonyl)phenyl]diazenyl]-6-[[4-(2- sulfonatooxyethylsulfonyl)phenyl]hydrazinylidene]naphthalene-2,7-disulfonate with a86325147 37 chemical structure of X); and combinations the yeused in the detailing agent include multipurpose black azo-dye based liquids, such as PRO-JET® Fast Black 1 (made available by Fujifilm Holdings), and black azo-dye based liquids with enhanced water fastness, such as PRO-JET® Fast Black 2 (made available by Fujifilm Holdings).

[0113] In some instances, another colorant may be included in the detailing agent with or in place of the black dye. In an example, the other dye may be a cyan dye. The other dye may also have substantially no absorbance above 650 nm. The other dye may be any colored dye that contributes to improving the hue and color uniformity of the edges of the lattice structure of the final 3D printed ball.

[0114] Some examples of the other dye include a salt, such as a sodium salt, an ammonium salt, or a potassium salt. Some specific examples include ethyl-[4-[[4- [ethyl-[(3-sulfophenyl) methyl] amino] phenyl]-(2-sulfophenyl) ethylidene]-1-cyclohexa- 2,5-dienylidene]-[(3-sulfophenyl) methyl] azanium with a chemical structure of: I)86325147 38 (commercially available as Acid Blue 9, where the counter ion may alternatively be sodium counter ions or potassium counter ions); sodium 4-[(E)-{4- [benzyl(ethyl)amino]phenyl}{(4E)-4-[benzyl(ethyl)iminio]cyclohexa-2,5-dien-1- ylidene}methyl]benzene-1,3-disulfonate with a chemical structure of: II) (commercially a tructure of:(XXIII) (commerciallyava abe as rect ue 99); and combnatons t ereof.

[0115] In an example of the detailing agent, the dye may be present in an amount ranging from about 1 wt% active to about 3 wt% active, based on the total weight of the detailing agent. In another example of the detailing agent including a combination of dyes, one dye (e.g., the black dye) is present in an amount ranging86325147 39 from about 1.50 wt% active to about 1.75 wt% active based on the total weight of the detailing agent, and the other dye (e.g., the cyan dye) is present in an amount ranging from about 0.25 wt% active to about 0.50 wt% active, based on the total weight of the detailing agent.

[0116] Some examples of the detailing agent include additional components, such as anti-kogation agent(s), antimicrobial agent(s), chelating agent(s), humectant(s), and / or pH adjusters.

[0117] The anti-kogation agent(s) that may be used in the detailing agent include any of the anti-kogation agents listed herein in reference to the fusing agent, or any other suitable anti-kogation agent. The total amount of anti-kogation agent(s) in the detailing agent may range from about 0.01 wt% active to about 1.5 wt% active, based on the total weight of the detailing agent.

[0118] The antimicrobial agent(s) that may be used in the detailing agent include any of the antimicrobial agents listed herein in reference to the fusing agent, or any other suitable antimicrobial agent. The total amount of antimicrobial agent(s) in the detailing agent may range from about 0.01 wt% active to about 0.05 wt% active, based on the total weight of the detailing agent.

[0119] The chelating agent(s) that may be used in the detailing agent include any of the chelating agents listed herein in reference to the fusing agent, or any other suitable chelating agent. The total amount of chelating agent(s) in the detailing agent may range from about 0.01 wt% active to about 0.2 wt% active, based on the total weight of the detailing agent.

[0120] The humectant(s) that may be used in the detailing agent include any of the humectant(s) listed herein in reference to the fusing agent, or any other suitable humectant. The total amount of humectant(s) in the detailing agent may range from about 0.01 wt% active to about 10 wt% humectant, based on the total weight of the detailing agent.

[0121] The pH adjuster(s) that may be used in the detailing agent include any of the pH adjuster(s) listed herein in reference to the fusing agent, or any other suitable humectant. The total amount of pH adjuster(s) in the detailing agent ranges from86325147 40 greater than 0 wt% active to about 0.1 wt% active, based on the total weight of the detailing agent.

[0122] The balance of the detailing agent is water or the solvent. As such, the amount of water or solvent present in the detailing agent may vary depending upon the amounts of the other components that are included.

[0123] Coloring Agent

[0124] The coloring agent may be used in the 3D printing methods to impart color to the 3D printed ball. The coloring agent can be selectively applied in the same manner as the fusing agent (e.g., via inkjet printing), and can be added to the polymer build material during the printing process or can be added to the exterior of the 3D printed ball after it is formed. The color density and shade may be varied by the amount of the coloring agent that is applied.

[0125] The coloring agent may include a colorant (i.e., pigment and / or dye), a co-solvent, and a balance of water. In some examples, the coloring agent consists of these components, and no other components. The colorant may be a black colorant, a cyan colorant, a magenta colorant, a yellow colorant, or a combination of colorants that together achieve a particular color.

[0126] Any of the co-solvents set forth herein for the fusing agent may be used for the coloring agent. In one example, the co-solvent mixture of benzyl alcohol and the solvent of benzyl alcohol may be used in the coloring agent.

[0127] In some other examples, the coloring agent may further include a binder (e.g., an acrylic latex binder, which may be a copolymer of any two or more of styrene, acrylic acid, methacrylic acid, methyl methacrylate, ethyl methacrylate, and butyl methacrylate). In still other examples, the coloring agent may further include additional components, such as dispersant(s), humectant(s), non-ionic or anionic surfactant(s), anti-kogation agent(s), antimicrobial agent(s), chelating agent(s), and / or pH adjuster(s) (each of which are described herein in reference to the fusing agent). Some examples of the coloring agent also include urea, which can improve fusing and overall durability of the 3D printed ball.

[0128] An example of the pigment based coloring agent may include from about 1 wt% to about 10 wt% of pigment(s), from about 10 wt% to about 30 wt% of co-86325147 41 solvent(s), from about 1 wt% to about 10 wt% of dispersant(s), from about 0.1 wt% to about 5 wt% of binder(s), from 0.01 wt% to about 1 wt% of anti-kogation agent(s), from about 0.05 wt% to about 0.1 wt% antimicrobial agent(s), from about 1 wt% to about 2 wt% urea, and a balance of water. An example of the dye based coloring agent may include from about 1 wt% to about 7 wt% of dye(s), from about 10 wt% to about 30 wt% of co-solvent(s), from about 1 wt% to about 7 wt% of dispersant(s), from about 0.05 wt% to about 0.1 wt% antimicrobial agent(s), from 0.05 wt% to about 0.1 wt% of chelating agent(s), from about 0.005 wt% to about 0.2 wt% of pH adjuster(s), and a balance of water.

[0129] Some examples of the coloring agent include a set of cyan, magenta, and yellow agents, such as C1893A (cyan), C1984A (magenta), and C1985A (yellow); or C4801A (cyan), C4802A (magenta), and C4803A (yellow); all of which are available from HP Inc. Other commercially available coloring agents 18 include C9384A (printhead HP 72), C9383A (printhead HP 72), C4901A (printhead HP 940), and C4900A (printhead HP 940).

[0130] Property Altering Agents

[0131] One or more additional agents may be used in conjunction with the fusing agent in order to alter all or a portion of the 3D printed ball. This / these agent(s) is / are separate from the fusing agent and enable the selective application of a particular property altering component to predetermined area(s) during 3D printing. As such, these agents may be used to selectively alter one or more properties of the 3D printed ball at the voxel level.

[0132] In one example, a separate pore forming agent may be used with the fusing agent to impart porosity to at least some of the beams of the lattice structure. The pore forming agent may be any example of the detailing agent described herein combined with any example of the pore forming component described herein. Thus, an example pore forming agent may include water, a co-solvent, a surfactant, a humectant, an antimicrobial agent, a pore forming component, and a pH adjuster. Any of these components may be used in any of the amounts set forth herein, except that the total amount is with respect to the pore forming agent.86325147 42

[0133] In another example, a separate density adjusting agent may be used with the fusing agent to alter the density of some of the beams of the lattice structure. The density adjusting agent may be any example of the detailing agent described herein with a density modifier added thereto. Thus, an example density adjusting agent may include water, a co-solvent, a surfactant, a humectant, an antimicrobial agent, a density modifier, and a pH adjuster. An example of a suitable density modifier includes silver nanoparticles. The density modifier can be included in an amount ranging from about 10 wt% active to about 30 wt% active, based on a total weight of the density adjusting agent. Any of the other components may be used in any of the amounts set forth herein, except that the total amount is with respect to the density adjusting agent.

[0134] In still another example, a separate stiffness adjusting agent may be used with the fusing agent to alter the stiffness of some of the beams of the lattice structure. The stiffness adjusting agent may be any example of the detailing agent described herein with a stiffness modifier added thereto. Thus, an example stiffness adjusting agent may include water, a co-solvent, a surfactant, a humectant, an antimicrobial agent, a stiffness modifier, and a pH adjuster. An example of a suitable stiffness modifier includes carbon nanotubes. The stiffness modifier can be included in an amount ranging from about 10 wt% active to about 30 wt% active, based on a total weight of the stiffness adjusting agent. Any of the other components may be used in any of the amounts set forth herein, except that the total amount is with respect to the stiffness adjusting agent. The stiffness adjusting agent may be used to print a 3D printed ball with an increased energy return.

[0135] It is believed that other agents may be used to adjust the degree of crystallinity in the polymeric build material. By increasing the size of crystalline domains, energy return could be reduced, or vice versa.

[0136] 3D Printing Process

[0137] The method disclosed herein involves selecting a polymeric build material; based at least on the type of 3D printed ball and the selected polymeric build material, selecting i) a ball mass and ii) a lattice structure with a cell geometry to86325147 43 contribute to a predetermined energy return of the 3D printed ball; and 3D printing the selected lattice structure in a spherical shape of the 3D printed ball by: iteratively applying layers of the selected build material; according to a 3D object model of the selected lattice structure in the spherical shape, selectively applying a fusing agent on each of the iteratively applied layers; and exposing each of the iteratively applied layers, having the fusing agent applied thereto, to electromagnetic radiation.

[0138] At the outset of the 3D printing process, the polymer build material is selected. Any of the examples of the polymeric build material described herein may be used.

[0139] Also at the outset of the 3D printing process, the ball that is to be 3D printed, is also selected. Any type of ball may be formed, including a toy ball, a sport ball, an exercise ball, a therapy ball, or the like. Examples of sport balls include pickleballs, tennis balls, racquetballs, basketballs, baseballs, soccer balls, volleyballs, bowling balls, footballs, golf balls, etc. Although soccer can be played with a volleyball, and rugby can be played with a football, it is to be understood that there may be standards that define certain characteristics of at least some types of balls. There may be organizations that have published rules or standards that describe a ball that may be used in a sport that is sanctioned by the particular organization. For example, “USA Pickleball” is the National Governing Body for the sport of pickleball in the U.S. USA Pickleball has published a standard for the ball to be used in the game of pickleball. The USA Pickleball Equipment Standards Manual contains a ball specification that, among other things, provides that an official pickleball has a diameter within a certain diameter range, and a mass within a certain mass range. Thus, an “official pickleball” may be one “type” of ball that may be produced according to the present disclosure.

[0140] Based at least on the type of ball and the selected polymeric build material, selecting i) a ball mass and ii) a lattice structure with a cell geometry contribute to a predetermined energy return of the ball.

[0141] The ball mass that is selected may be within a suitable range for the type of ball that is selected. The mass may depend, in part, upon the particular size of the ball and its intended use. As examples, the mass of a pickleball may range from about86325147 44 22 g to about 27 g; the mass of a basketball may range from about 10 g (e.g., a mini basketball) to about 620 g (full size men’s basketball); and the mass of a football may range from about 10 g (e.g., a mini football) to about 460 g (regulation sized football).

[0142] The lattice structure that is selected has an individual cell geometry that contributes to a predetermined energy return of the ball. Because the energy return for a lattice structure is a function of the input energy, the cell geometry is modulated (by altering truss structure, beam diameter, and netting offset as described herein) so that properties of the resulting 3D printed ball match or reduce certain bulk properties of the selected polymeric build material. For example, if a particular polymeric build material is relatively stiff, a small beam diameter may be selected; if another polymeric build material is not as stiff, a larger beam diameter may be selected. The geometry may be adjusted so that the total mass (density x volume) of the polymeric build material is within specifications. The overall stiffness of the lattice structure may be determined empirically or analytically. Finite element modeling and iterative strategies may be used to reduce the number of iterations to reach a suitable combination of mass, spherical diameter, and performance including energy return, sound, and durability. It is to be understood that a core or other internal structure may be included to adjust mass and moment of inertia. It is to be further understood that 3D printing may make empirical iteration an attractive alternative to iterative building of analytical models.

[0143] The individual cell geometry and the lattice structure formed therefrom may be generated using suitable software, such as Houdini.

[0144] Examples of the individual cell geometries will be described in reference to Fig.1A through Fig.1D. Each individual cell geometry includes an outer perimeter PO, an inner perimeter PI, and a lattice type L. As illustrated in each of Fig.1A through Fig.1D, each perimeter PO, PIis a hexagon. The cell geometry includes outer beams 12 and inner beams 14, which are respectively arranged in the shape of the perimeter PO, PI. The point at which one outer beam 12 is connected to an adjacent outer beam 12 along the perimeter POis an outer node 18A, 18B. Similarly, the point at which one inner beam 14 is connected to an adjacent inner beam 14 along the perimeter PIis an inner node 20A, 20B.86325147 45

[0145] The lattice type L of the individual cell geometry connects the outer and inner beams, 12, 14, and thus introduces depth to the cell geometry. The lattice type L may be selected from the group consisting of a straight beam geometry (Fig.1A), a twisted x geometry (Fig.1B), an hourglass geometry (Fig.1C), and combinations thereof (Fig.1D). Each lattice type L includes middle beams 16, 16’, 16’’, 16O, 16I which forms the truss structure of the cell geometry.

[0146] The straight beam geometry shown in Fig.1A can take two forms. In one form, individual middle beams 16 are radially positioned to respectively connect opposing nodes 18A and 20A, 18B and 20B. In this example, four beams (i.e., one outer beam 12, one inner beam 14, and two middle beams 16) are connected at the nodes 18A, 20A, 18B, 20B, and thus form a square or a rectangular shape with a hole located at its center. This configuration is repeated at all of the beams 12, 14 along the perimeters PO, PI. This particular geometry may be used to avoid incorporating additional mass to the 3D printed ball. In another form, solid walls connect the outer and inner beams 12, 14. The straight beam geometry with solid walls resembles a honeycomb.

[0147] The angle that the middle beam 16 takes as it connects from the outer perimeter PO to the inner perimeter PI may be 0°, as shown in Fig.1A. Alternatively, this angle may be rotated so that the beams 16 do not connect directly adjacent nodes 18A and 20C, 18B and 20B, etc. Two examples are shown in Fig.7A and Fig.7B. In Fig.7A, the angle that the middle beams 16 take as they respectively connect from nodes 18A, 18B of the outer perimeter POto nodes 20A, 20B of the inner perimeter PIis 60°. In Fig.7B, the angle that the middle beams 16 take as they respectively connect from nodes 18A, 18B of the outer perimeter PO to nodes 20A, 20B of the inner perimeter PI is 120°. Another example is shown in Fig.1C, where the angle of the middle beams 16 (shown as 16Oand 16I) are at 180° and thus converge at a center point 22. By altering the rotation, the stiffness and energy return can be adjusted.

[0148] The twisted x geometry is shown in Fig.1B. Like the first form of the straight beam geometry, the twisted x geometry includes individual middle beams 16 that are radially positioned to respectively connect opposing nodes 18A and 20A, 18B and 20B. As shown in Fig.1B, this geometry further includes two additional middle86325147 46 beams 16’, 16’’ that cross each other in the square or a rectangular shaped hole formed by the four beams (i.e., one outer beam 12, one inner beam 14, and two middle beams 16). Each of the additional middle beams 16’, 16’’ connects nodes, e.g., 18A and 20B, 18B and 20A, that are diagonal to one another in a given four beam configuration.

[0149] The hourglass geometry is shown in Fig.1C. In this example, middle beams 16O extend from each node 18A, 18B of the outer perimeter PO and middle beams 16I extend from each node 20A, 20B of the inner perimeter PI. All of the middle beams 16O, 16Iconverge at a central point 22 of the outer and inner perimeters PO, PI. In one example, this central point 22 is equidistant form each node 18A, 18B, 20A, 20B. In another example, the central point 22 is located at a center of both perimeters 16O, 16I, but is closer (in the Z-direction) to one of the perimeters 16O, 16I. In this example, the opposed nodes (e.g., 18A, 20A) or diagonal nodes (e.g., 18A, 20B) are not directly connected to one another. The cell geometry shown in Fig.1C may be referred to as a tetrahedral lattice, in part because the repeated beam structure (e.g., 12 and 2x16Oand 14 and 2x16I) are triangular. The cell geometry of Fig.1C resembles two layers of right hexagonal pyramids, the first layer having base vertices lying on a geodesic sphere and the second layer having the base vertices lying on a concentric geodesic sphere.

[0150] Any of the previously described cell geometries may be combined together in a single cell geometry. An example is depicted in Fig.1D. In this example the first form of the straight beam geometry (Fig.1A) is combined with the hourglass geometry (Fig.1C). In other words, the middle beams 16O, 16Iare incorporated into the cell geometry of Fig.1A.

[0151] The lattice structures disclosed herein can be softened, e.g., stiffness and energy return decreased, by reducing the beam diameter, altering netting offset, changing the cell aspect ratio, or by shallowing the angle of the middle beams 16. As such, reducing the stiffness of the structure may decrease the energy return. In other words, a softer or more elastic ball may not bounce as high as a stiffer, less elastic ball.86325147 47

[0152] Referring now to Fig.6, a schematic illustration of netting and netting offset is depicted. As noted herein, “netting” is nominally applied (i.e., offset = 0) when the netting beam centerline falls on the boundary of the 3D printed ball, and any beam portion falling outside the boundary B is removed from the model. Nominal application of netting results in the outermost beams being semi-circular in cross section. The netting may be offset to give the outermost lattice beams a different thickness or a different appearance. This is achieved by offsetting the netting beam centerline relative to the part boundary B. With a positive offset, less of the beam is removed and more of the original beam shape is retained; and with a negative offset, more of the beam is removed and less of the original beam shape is retained. In Fig.6, the removed beam portions are identified by the striped sections. The netting scale may be quantified using the diameter, where D / 2 = offset 0, more positive values (i.e., 0.1, 0.2, up to 1) indicate that the netting centerline is moved with respect to the boundary B such that more than half of the beam remains after portion removal, and more negative values (i.e., -0.1, -0.2, down to -1) indicate that the netting centerline is moved with respect to the boundary B such that less than half of the beam remains after portion removal. A more negative netting offset may leave less beam material for the outermost beam to absorb impulse energy, leading to a softer ball and a greater reduction in energy return.

[0153] The netting offset is applicable to the outer beams 12 of the cell geometry, and not to the middle beams 16, 16’, 16’’, 16O, 16I (collectively referred to with reference numeral “16”) or inner beams 14. Thus, the middle and inner beams 16, 14 retain their round cross-sectional shape (i.e., their diameter) throughout their length. In contrast, the netting offset may be applied to the outer beams 12 so that the outermost facing surfaces of the cell geometry, and thus the lattice structure, are flat and retain a specific portion of the round cross-sectional shape (either more than half of the beam or less than half of the beam). The outer beams 12 may first be selected with a suitable diameter, and then the netting offset may be applied to flatten and soften the original structure at a suitable position along the original diameter with respect to the boundary B of the ball. In one example, the cell geometry includes outer beams 12 with a netting offset that contributes to the predetermined energy86325147 48 return of the 3D printed ball and middle beams 16 with a truss structure that contribute to stiffness of the 3D printed ball.

[0154] The diameter of each of the inner beams 14 and the middle beams 16 may be adjusted to alter the durability, stiffness, and energy return of the ball. Inner beams 14 and the middle beams 16 that are too thin may affect the durability of the ball or the playability of the ball (e.g., energy return is deleteriously affected due, potentially, to irreversible plastic deformation). Inner beams 14 and the middle beams 16 that are too thick may increase the mass and the stiffness of the ball, which may reduce the chance of plastic deformation and increase storage modulus, thus leading to higher energy return. For any of the balls described herein, the diameter of each of the inner beams 14 and the middle beams 16 may range from about 1 mm to about 3.1 mm.

[0155] The overall thickness of the cell geometry may also be adjusted to achieve the predetermined energy return for the 3D printed ball that is being manufactured. The thickness of the cell geometry is measured as the distance between the outer and inner beams 12, 14. For a pickleball, tennis ball, baseball or the like, the thickness of the cell geometry may range from about 5 mm to about 7 mm. For a basketball, soccer ball, volleyball, or the like, the thickness of the cell geometry may range from about 10 mm to about 20 mm.

[0156] The aspect ratio of the single hexagonal cell is the width (d) to height / thickness (h) (see Fig.1A). The hexagonal cell aspect ratio can be adjusted to alter the buckling behavior and the general stiffness of the 3D printed ball. A cell aspect ratio of d / h > 1 will be softer due to the beam angles, but will promote better energy return because the beams remain in compression. Conversely, a cell aspect ratio of d / h < 1 can lead to buckling, which leads to energy loss.

[0157] Once the individual cell geometry is designed, a 3D rendering of the lattice structure is created by repeating or tiling the individual cell geometries across the 3D shape of the ball. Some cells with pentagonal perimeters may be strategically placed among the cell geometries in order to create the 3D shape. An example of one hourglass geometric cell superimposed on a spherical ball is depicted in Fig.2. The resulting 3D object model of the ball includes a single layer of the lattice structure in86325147 49 the 3D shape (e.g., sphere, etc.) of the ball. Examples of 3D object models corresponding with each of the cell geometries shown in Fig.1A through Fig.1D are respectively shown in Fig.3A through Fig.3D. This 3D object model is then utilized to 3D print the ball.

[0158] An example of the 3D printing process is shown in Fig.4. As shown in Fig.4, a layer 24 of the polymeric build material 26 is applied on a build area platform 28. A printing system may be used to apply the polymeric build material 26. The printing system may include the build area platform 28, a build material supply 30 containing the polymeric build material 26, and a build material distributor 32.

[0159] The build area platform 28 receives the polymeric build material 26 from the build material supply 30. The build area platform 28 may be moved along the x- axis and the y-axis respectively, so that the polymeric build material 26 may be delivered to the build area platform 28 or to a previously formed 3D printed layer 34 of the 3D printed ball. In an example, when the polymeric build material 26 is to be delivered, the build area platform 28 may be programmed to advance enough so that the build material distributor 32 can push the polymeric build material 26 onto the build area platform 28 to form a substantially uniform layer 24 of the polymeric build material 26 thereon. The build area platform 28 may also be returned to its original position, for example, when a new ball is to be 3D printed.

[0160] The build material supply 30 may be a container, bed, or other surface that is to position the polymeric build material 26 between the build material distributor 32 and the build area platform 28. The build material supply 30 may include heaters so that the polymeric build material 26 is heated to a supply temperature ranging from about 25°C to about 150°C (heaters not shown in Fig.4). In these examples, the supply temperature may depend, in part, on the polymeric build material 26 used and / or the 3D printer used. As such, the range provided is one example, and higher or lower temperatures may be used.

[0161] The build material distributor 32 may be moved, e.g., along the x-axis, over the build material supply 30 and across the build area platform 28 to spread the polymeric build material 26 over the build area platform 28 and form the layer 24. The build material distributor 32 may also be returned to a position adjacent to the build86325147 50 material supply 30 following the spreading of the polymeric build material 26. The build material distributor 33 may be a blade (e.g., a doctor blade), a roller, a combination of a roller and a blade, and / or any other device capable of spreading the polymeric build material 26 over the build area platform 28. For instance, the build material distributor 32 may be a counter-rotating roller. In some examples, the build material supply 30 or a portion of the build material supply 30 may translate along with the build material distributor 32 such that polymeric build material 26 is delivered continuously to the build area platform 28 rather than being supplied from a single location at the side of the printing system as depicted in Fig.4.

[0162] The build material supply 30 may supply the polymeric build material 26 into a position so that it is ready to be spread onto the build area platform 28. The build material distributor 32 may spread the supplied polymeric build material 26 onto the build area platform 28. The controller may process data, and in response, control the build material supply 30 to appropriately position the particles of the polymeric build material 26, and may process data, and in response, control the build material distributor 32 to spread the polymeric build material 26 over the build area platform 28 to form the layer 24 of the polymeric build material 26 thereon. In Fig.4, one build material layer 24 has been formed.

[0163] The layer 24 has a substantially uniform thickness across the build area platform 28. In an example, the build material layer 24 has a thickness ranging from about 50 µm to about 120 µm. In another example, the thickness of the build material layer 24 ranges from about 30 μm to about 300 μm. It is to be understood that thinner or thicker layers may also be used. For example, the thickness of the build material layer 24 may range from about 20 μm to about 500 μm. The layer thickness may be about 2x (i.e., 2 times) the average diameter of the build material composition particles at a minimum for finer part definition. In some examples, the layer thickness may be about 1.2x the average diameter of the polymer particles in the polymeric build material 26.

[0164] After the polymeric build material 26 has been applied, and prior to further processing, the build material layer 24 may be exposed to heating. In an example, the heating temperature may be below the melting range of the polymer86325147 51 particles of the polymeric build material 26. As examples, the pre-heating temperature may range from about 5°C to about 50°C below the lowest temperature of the melting range of the polymer particles. In an example, the pre-heating temperature ranges from about 50°C to about 205°C. In still another example, the pre-heating temperature ranges from about 100°C to about 190°C. It is to be understood that the pre-heating temperature may depend, in part, on the polymeric build material 26 used. As such, the ranges provided are some examples, and higher or lower temperatures may be used.

[0165] Pre-heating of the layer 24 may be accomplished by using any suitable heat source that exposes all the polymeric build material 26 in the layer 24 to the heat. Examples of the heat source include a thermal heat source (e.g., a heater (not shown) integrated into the build area platform 28 (which may include sidewalls)) or a radiation source 36.

[0166] As shown in Fig.4, after the layer 24 is formed, and in some instances is pre-heated, the fusing agent 38 is selectively applied on at least some of the polymeric build material 26 in the layer 24 using an applicator 40 to form patterned portion(s) 42.

[0167] The applicator 40 may be a thermal inkjet printhead, a piezoelectric printhead, a continuous inkjet printhead, or any other suitable device that can be used to selectively deposit the fusing agent 38 onto the build material layer 24 at the portion(s) 42. The 3D object model is sliced into layers, and the patterned portions 42 correspond with the lattice structure in the slice that is then-currently being 3D printed.

[0168] When it is desirable to form a white, colored, or slightly tinted, 3D printed layer 34, the low tint fusing agent may be used to pattern the polymeric build material 26 at the portion(s) 42. The low tint fusing agent is clear or slightly tinted, and thus the resulting 3D printed layer 34 may appear white or the color of the polymeric build material 26. When it is desirable to form a darker color or black 3D printed layer 34, the high tint fusing agent may be used. The high tint fusing agent is dark or black, and thus the resulting 3D printed layer 34 may appear grey, black or another dark color. In other instances, both the low tint and high tint fusing agents may be applied to the layer 24 in respective sections of the portion(s) 42. For example, the high tint fusing agent may be applied to form the inner and middle beams 14, 16 of the lattice86325147 52 structure (e.g., for stiffness) and the low tint fusing agent containing the co-solvent mixture disclosed herein may be applied to form the outer beams 12 (e.g., for flexibility).

[0169] The amount of the fusing agent 38 that is applied per unit of the polymeric build material 26 in the patterned portion 42 may be sufficient to absorb and convert enough electromagnetic radiation so that the polymeric build material 26 in the patterned portion 42 will coalesce / fuse. The amount of the fusing agent 38 that is applied per unit of the polymeric build material 26 may depend, at least in part, on the loading of the radiation absorbing substance in the fusing agent 38, and the polymer particles in the polymeric build material 26. In particular, the concentration of the radiation absorbing substance in the fusing agent 38 can be considered. This concentration can be used to determine how much fusing agent 38 to apply to achieve a weight ratio of fusing agent 38 to polymeric build material 26 for acceptable layer-by- layer fusing. Thus, if applying the fusing agent 38 (10 wt%) to the polymeric build material 26 (90 wt%) at about a 1:9 weight ratio, then the radiation absorbing substance to polymeric build material 26 weight ratio (as applied) can be from about 1:9000 to about 1:30. If more (up to 20 wt%) or less (down to 5 wt%) of the fusing agent 38 is applied to the polymeric build material 26, then these ratios can be adjusted accordingly. That stated, the weight ratio of the radiation absorbing substance to the polymeric build material 26 (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. When the fusing agent includes a radiation absorbing substance, such as carbon black, the method may further iniclude adjusting an amount of the fusing agent 38 that is selectively applied on each of the iteratively applied layers to alter stiffness of the 3D printed ball.

[0170] Thermal energy generated during radiation exposure may propagate into the portion(s) 46, that do not have the fusing agent 38 applied thereto. The detailing agent 44 described herein aids in inhibiting the propagation of thermal energy into the portion(s) 46 during radiation exposure, and thus helps to prevent the coalescence of the polymeric build material 26 within the portion(s) 46. As such, the detailing agent 44 may be used to pattern portion(s) 46 of the build material layer 24 that are not86325147 53 supposed to coalesce and form part of the 3D printed layer 34. In the example shown in Fig.4, the detailing agent 44 can be applied to portion(s) 46 that are located along an edge of the 3D object model. While not shown, it is to be understood that the detailing agent 44 can also be applied to portion(s) 46 that are interspersed among the portion(s) 42 that are patterned with the fusing agent 38. For example, the detailing agent 44 can be used to pattern the hollow core of the 3D printed ball and any holes / void areas that are present in the cell geometry and lattice structure, while the beams of the cell geometry and lattice structure are patterned with the fusing agent 38. Thus, one example method involves selectively applying the detailing agent 44 on at least some of the iteratively applied layers to pattern void areas of the lattice structure.

[0171] The detailing agent 44 may also be applied in the same portion(s) 42 with the fusing agent 38 when it is desirable to tailor (reduce) the extent of coalescence / fusing. This may be desirable when a more pliable 3D printed ball is to be formed.

[0172] The applicator 40’ may be any suitable example of the applicator described herein, such a thermal inkjet printhead, a piezoelectric printhead, or a continuous inkjet printhead.

[0173] When additional agent(s), e.g., a separate pore forming agent, coloring agent, etc. is / are to be used in the 3D printing process, the additional agent(s) may also be applied using an applicator 40, 40’ and according to the 3D object model. Thus, example methods include selectively applying, according to the 3D object model, a density adjusting agent (or a pore forming agent, or a coloring agent, or a stiffness adjusting agent) with the fusing agent 38 in predetermined areas of at least some of the iteratively applied layers. In one specific example, the method includes selectively applying a pore forming agent with the fusing agent 38 to introduce porosity within beams of the lattice structure. For example, the separate pore forming agent may be applied to the layer(s) with the fusing agent 38 to pattern the inner beams, which will reduce the mass of the inner beams and improve durability of the 3D printed ball. For another example, a separate density adjusting agent may be applied to the portion(s) 42 at the top of the ball with the fusing agent 38 in order to increase the mass and make a top-heavy ball. The cell geometry may be altered to redistribute a86325147 54 mass of the lattice structure relative to a reference lattice structure, thereby modulating a moment of inertia of the 3D printed ball. As one example, the cell geometry may be altered by applying the density adjusting agent at particular areas so that these areas are denser than areas without the density adjusting agent. In turn, the mass of the ball is redistributed, which modulates the moment of inertia. Since the moment of inertia of an element of mass is proportional to the square of the distance from the center of rotation, relocating mass away from the center of rotation will increase the moment of inertia. Relocating mass closer to the center of rotation will decrease the moment of inertia. For still another example, a separate stiffness adjusting agent may be used to create stiffer middle beams. One example method involves introducing at least one of a plasticizer with the fusing agent 38 to achieve a lower stiffness and energy return. The plasticizer may be introduced in the separate stiffness adjusting agent or as a component of the fusing agent 38.

[0174] After the fusing agent 38, the detailing agent 44, and any additional agent(s) are selectively applied in the specific portion(s) 42, 42 of the layer 24, the entire layer 24 of the polymeric build material 26 is exposed to electromagnetic radiation (shown as EMR in Fig.4).

[0175] The electromagnetic radiation is emitted from the radiation source 36. The length of time the electromagnetic radiation is applied for, or energy exposure time, may be dependent, for example, on one or more of: characteristics of the radiation source 36, characteristics of the polymeric build material 26, and / or characteristics of the fusing agent 38 or the detailing agent 44. In an example, a single point of the build material layer 24 is exposed to electromagnetic radiation for a period of time ranging from 0.01 second to 1 second.

[0176] It is to be understood that the electromagnetic radiation exposure may be accomplished in a single radiation event or in multiple radiation events. In an example, the exposing of the polymeric build material 26 is accomplished in multiple radiation events. In a specific example, the number of radiation events ranges from 3 to 8. In still another specific example, the exposure of the polymeric build material 26 to electromagnetic radiation may be accomplished in 3 radiation events. It may be desirable to expose the build material composition 24 to electromagnetic radiation in86325147 55 multiple radiation events to sufficiently elevate the temperature of the polymeric build material 26 in the patterned portion(s) 42, without overheating the build material composition 24 in the portion(s) 46.

[0177] The fusing agent 38 enhances the absorption of the radiation in the portion(s) 42, converts the absorbed radiation to thermal energy, and promotes the transfer of the thermal heat to the polymeric build material 26 in contact therewith. In an example, the fusing agent 38 sufficiently elevates the temperature of the polymeric build material 26 in the portion(s) 42 to a temperature within the melting range of the polymeric particles in the polymeric build material 26; and thus, coalescing / fusing (e.g., thermal merging, melting, binding, etc.) of the polymeric build material 26 takes place during EMR (electromagnetic radiation) exposure. The application of the electromagnetic radiation forms the 3D printed layer 34 which includes a portion of the lattice structure.

[0178] In some examples, the electromagnetic radiation has a wavelength ranging from 800 nm to 4000 nm, or from 800 nm to 1400 nm, or from 800 nm to 1200 nm. Radiation having wavelengths within the provided ranges may be absorbed (e.g., 80% or more of the applied radiation is absorbed) by the fusing agent 12, 26’ and may heat the polymeric build material 26 in contact therewith, and may not be substantially absorbed (e.g., 25% or less of the applied radiation is absorbed) by the build material composition 24 in portion(s) 36.

[0179] After the 3D printed layer 34 is formed, additional 3D object layer(s) 34 may be formed thereon to create the 3D printed ball with the predetermined energy return. To form the next layer, additional polymeric build material 26 may be applied on the already-formed 3D printed layer 34. The fusing agent 38 and detailing agent 44 are then selectively applied as described herein. After the agents 38, 44 are applied, the entire layer 24 of is exposed to electromagnetic radiation in the manner described herein. The application of additional polymeric build material 34 and the selective application of the agents 38, 44, the electromagnetic radiation exposure may be iteratively repeated for a predetermined number of cycles to form the final 3D printed ball, in accordance with a 3D object model.86325147 56

[0180] The 3D printed ball may be exposed to post processing techniques, such as sand blasting or solvent exposure to smooth the surface and clean the ball.

[0181] A coloring agent may be applied with the fusing agent 30 or to the 3D printed ball after it is formed and post-processed to impart color to the 3D printed ball.

[0182] In some examples of the method, identifying marks may be incorporated into the 3D printed ball. As examples, fluorescent or magnetic agents (e.g., detailing agents with fluorescent materials or magnetic materials may be used during the 3D printing process to add identifiers.

[0183] Balls

[0184] As described in the previous section, the 3D printed balls have a predetermined energy return that is obtained using the method described herein.

[0185] A cross-section of one ball 10 is shown in Fig.5. The 3D printed ball includes a hollow core 48, and a single layered lattice structure 50 surrounding the hollow core 48, wherein the single layered lattice structure 50 is formed of the coalesced polymeric build material and has a predetermined mass, cell geometry, and netting offset that contribute to the predetermined energy return.

[0186] In examples where the 3D printed ball 10 exhibits a reduced energy return relative to the bulk energy return, one of: the polymeric build material is thermoplastic polyamide and the cell geometry of the lattice structure includes a tetrahedral; or the polymeric build material is thermoplastic polyurethane and the cell geometry of the lattice structure includes rotated middle beams. In an example where the 3D printed ball 10 exhibits the maintained energy return, the polymeric build material is thermoplastic polyurethane and the cell geometry of the lattice structure includes a tetrahedral or a twisted X.

[0187] In still other examples, the 3D printed ball is a small ball having a diameter ranging from about 6.5 cm to about 8 cm (e.g., tennis ball, pickleball, or the like) and one of: i) the coalesced polymeric build material is a thermoplastic polyurethane, the predetermined mass 28 g, the predetermined cell geometry has rotated middle beams, and the predetermined netting offset is about -0.7; ii) the coalesced polymeric build material is a thermoplastic polyamide, the predetermined86325147 57 mass is about 25 g, the predetermined cell geometry is a tetrahedral, and the predetermined netting offset is about -0.5; or iii) the coalesced polymeric build material is a thermoplastic polyurethane, the predetermined mass is about 24 g, the predetermined cell geometry has rotated middle beams, and the predetermined netting offset is about 1.

[0188] In other examples, the ball 10 includes the lattice structure throughout the entire volume of the ball. In still other examples, the ball 10 includes a 3D printed solid or porous core surrounded by the lattice structure.

[0189] To further illustrate the present disclosure, an example is given herein. It is to be understood that this example is provided for illustrative purposes and is not to be construed as limiting the scope of the present disclosure. EXAMPLE

[0190] Different polymeric build materials (PBM, see Tables 1 and 2) were used in this example. Two different thermoplastic polyurethanes (one from BASF Corp. (TPU #1) and one from Lubrizol Corp. (TPU #2), which have different hardnesses and melting temperatures) and a thermoplastic polyamide were used in this example. The bulk energy return for solid balls of these materials is, respectively, 75%, 65%, and 45%.

[0191] The materials were used to 3D print pickleballs using a fusing agent (with carbon black as the radiation absorbing substance) and electromagnetic radiation exposure. The predetermined energy return for the pickleballs was 41%. Energy return was determined by dropping the pickleball from a height of 78 inches (X), measuring the height (Y) after the bounce, and calculating (Y / X)*100. A height should be within 30 inches to 34 inches (energy return ranging from 38.5% - 43.6%).

[0192] Table 1 illustrates three different example pickleballs and the materials and characteristics of each that can achieve a desirable energy return.86325147 58 Table 1 - Example 3D Printed Balls PBM Lattice Wall Inner Middle Outer Netting Ball Ball Energy Thick- Beam Beam Beam offset Vol. Mass Return Di t Di t Di t (%) 41.6 43.641.0a e us aes ee ee ea pe pc e as a e ae as and characteristics of each that can achieve the predetermined energy return. Table 2 - Comparative Example 3D Printed Balls PBM Lattice Wall Inner Middle Outer Netting Ball Ball Energy Thick- Beam Beam Beam offset Vol. Mass Return (%) 46 46.8

[0194] The comparative examples illustrate that the predetermined energy return is not obtained with every cell geometry, wall thickness, diameter, netting office, etc. Overall, these results illustrate that adjusting the cell geometry of the lattice86325147 59 structure to match or reduce certain bulk properties of the build material used enables a pickleball with a particular energy return to be generated via 3D printing with a fusing agent.

[0195] Additional Notes

[0196] It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein. It should also be appreciated that terminology explicitly employed herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.

[0197] Reference throughout the specification to “one example”, “another example”, “an example”, and so forth, means that a particular element (e.g., feature, structure, and / or characteristic) described in connection with the example is included in at least one example described herein, and may or may not be present in other examples. In addition, it is to be understood that the described elements for any example may be combined in any suitable manner in the various examples unless the context clearly dictates otherwise.

[0198] It is to be understood that the ranges provided herein include the stated range and any value or sub-range within the stated range, as if such values or sub- ranges were explicitly recited. For example, a range of about 300 nm to 1400 nm, should be interpreted to include not only the explicitly recited limits of about 300 nm to about 1400 nm, but also to include individual values, such as about 708 nm, about 945.5 nm, etc., and sub-ranges, such as from about 425 nm to about 825 nm, from about 550 nm to about 940 nm, etc. Furthermore, when “about” and / or “substantially” are / is utilized to describe a value, they are meant to encompass minor variations (up to + / - 5%) from the stated value.86325147 60

[0199] While several examples have been described in detail, it is to be understood that the disclosed examples may be modified. Therefore, the foregoing description is to be considered non-limiting.

Claims

86325147 61 What is claimed is:

1. A method for making a 3D printed ball, comprising: selecting a polymeric build material; based at least on the type of 3D printed ball and the selected polymeric build 5 material, selecting i) a ball mass and ii) a lattice structure with a cell geometry to contribute to a predetermined energy return of the 3D printed ball; and 3D printing the selected lattice structure in a spherical shape of the 3D printed ball by: iteratively applying layers of the selected build material; 10 according to a 3D object model of the selected lattice structure in the spherical shape, selectively applying a fusing agent on each of the iteratively applied layers; and exposing each of the iteratively applied layers, having the fusing agent applied thereto, to electromagnetic radiation. 15 2. The method as defined in claim 1, wherein: a solid ball formed of the polymeric build material has a bulk energy return; and the 3D printed ball exhibits a maintained or reduced energy return relative to the bulk energy return. 20 3. The method as defined in claim 2, wherein: the 3D printed ball exhibits a reduced energy return relative to the bulk energy return; and one of: i) the polymeric build material is thermoplastic polyamide; and 25 the cell geometry of the lattice structure includes a tetrahedral; or ii) the polymeric build material is thermoplastic polyurethane; and the cell geometry of the lattice structure includes rotated middle beams.

4. The method as defined in claim 2, wherein: 30 the 3D printed ball exhibits the maintained energy return; the polymeric build material is thermoplastic polyurethane; and86325147 62 the cell geometry of the lattice structure includes a tetrahedral or a twisted X.

5. The method as defined in claim 1, wherein the cell geometry includes: outer beams with a netting offset that contributes to the predetermined energy 5 return of the 3D printed ball; and middle beams with a truss structure that contribute to stiffness of the 3D printed ball.

6. The method as defined in claim 1, further comprising selectively applying a 10 pore forming agent with the fusing agent to introduce porosity within beams of the lattice structure.

7. The method as defined in claim 1, wherein the fusing agent includes a radiation absorbing substance, and the method further comprises adjusting an amount 15 of the fusing agent that is selectively applied on each of the iteratively applied layers to alter stiffness of the 3D printed ball.

8. The method as defined in claim 1, further comprising altering the cell geometry to redistribute a mass of the lattice structure relative to a reference lattice 20 structure, thereby modulating a moment of inertia of the 3D printed ball.

9. The method as defined in claim 1, further comprising selectively applying, according to the 3D object model, a density adjusting agent with the fusing agent in predetermined areas of at least some of the iteratively applied layers. 25 10. The method as defined in claim 1, further comprising selectively applying a detailing agent on at least some of the iteratively applied layers to pattern void areas of the lattice structure.86325147 63 11. The method as defined in claim 1, further comprising selectively applying a coloring agent on each of the iteratively applied layers with the fusing agent to impart color to the 3D printed ball. 5 12. The method as defined in claim 1, further comprising introducing at least one of a plasticizer with the fusing agent to achieve a lower predetermined stiffness.

13. A 3D printed ball having a predetermined energy return, comprising: a hollow core; and 10 a single layered lattice structure surrounding the hollow core, wherein the single layered lattice structure: is formed of a coalesced polymeric build material; and has a predetermined mass, cell geometry, and netting offset that contribute to the predetermined energy return. 15

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