WO2023086080A1

WO2023086080A1 - Ultraviolet printed objects with opaque regions

Info

Publication number: WO2023086080A1
Application number: PCT/US2021/058743
Authority: WO
Inventors: Aja HARTMAN; Ingeborg Tastl; Krzysztof Nauka
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2021-11-10
Filing date: 2021-11-10
Publication date: 2023-05-19

Abstract

In one example in accordance with the present disclosure, an additive manufacturing system is described. The additive manufacturing system includes a build material distribution device to deposit a layer of a powder build material and an agent distribution system. The agent distribution system is to deposit on top of the layer of powder build material 1) a light-transmissive ultraviolet (UV) fusing agent in a pattern of a slice of a three-dimensional (3D) object to be formed and 2) an opacifying agent to selectively opacify regions of the 3D object to be formed. The additive manufacturing system also includes a UV energy source to, in combination with the light-transmissive UV fusing agent deposited, selectively melt portions of the layer of powder build material. A controller of the additive manufacturing system determines values of the parameters for the opacifying agent deposition to achieve a target opacity.

Description

ULTRAVIOLET PRINTED OBJECTS WITH OPAQUE REGIONS

BACKGROUND

[0001] Additive manufacturing devices produce three-dimensional (3D) objects by building up layers of material. Some additive manufacturing devices may be referred to as "3D printing devices" because they use inkjet or other printing technology to apply some of the manufacturing materials. 3D printing devices and other additive manufacturing devices make it possible to convert a computer-aided design (CAD) model or other digital representation of an object directly into the physical object.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] The accompanying drawings illustrate various examples of the principles described herein and are part of the specification. The illustrated examples are given merely for illustration, and do not limit the scope of the claims.

[0003] Fig. 1 is a block diagram of an additive manufacturing system for generating an ultraviolet (UV) printed object with opaque regions, according to an example of the principles described herein.

[0004] Fig. 2 is an isometric view of an additive manufacturing system for generating a UV-printed object with opaque regions, according to an example of the principles described herein.

[0005] Fig. 3 is a flow chart of a method for generating a UV-printed object with opaque regions, according to an example of the principles described herein. [0006] Figs. 4A - 4D depict various parameters that alter the opacity of regions of a UV-printed object, according to an example of the principles described herein.

[0007] Fig. 5 is a flow chart of a method for generating a UV-printed object with opaque regions, according to an example of the principles described herein.

[0008] Fig. 6 depicts a non-transitory machine-readable storage medium for generating a UV-printed object with opaque regions, according to an example of the principles described herein.

[0009] Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. The figures are not necessarily to scale, and the size of some parts may be exaggerated to more clearly illustrate the example shown. Moreover, the drawings provide examples and/or implementations consistent with the description; however, the description is not limited to the examples and/or implementations provided in the drawings.

DETAILED DESCRIPTION

[0010] Additive manufacturing devices form a three-dimensional (3D) object through the solidification of layers of a build material. Additive manufacturing devices make objects based on data in a 3D model of the object generated, for example, with a computer-aided drafting (CAD) computer program product. The model data is transformed into slices, each slice defining portions of a layer of build material that is to be solidified.

[0011] In one example, to form the 3D printed object, a build material, which may be powder, is deposited on a bed. A fusing agent is then deposited onto portions of the layer of build material that are to be fused to form a layer of the 3D printed object. The system that carries out this type of additive manufacturing may be referred to as a powder and fusing agent-based system. The fusing agent increases the energy absorption of the layer of build material on which the agent is deposited. The build material is then exposed to energy such as electromagnetic radiation. The electromagnetic radiation may include infrared light, laser light, or other suitable electromagnetic radiation. Due to the increased energy absorption properties imparted by the fusing agent, those portions of the build material that have the fusing agent deposited thereon heat to a temperature greater than the fusing temperature of the build material. By comparison, the applied energy is not high enough to increase the heat of the portions of the build material that are free of the fusing agent. This process is repeated in a layer-wise fashion to generate a 3D object. The unfused portions of material can then be separated from the fused portions, and the unfused portions may be recycled for subsequent 3D formation operations.

[0012] Additive manufacturing has become a respected manufacturing technology for its simplicity, efficacy, and the quality of printed products. In particular, a fusing-agent based system may be able to print a product ten times faster than other additive manufacturing technologies. While such additive manufacturing operations have greatly expanded manufacturing and development possibilities, further developments may make 3D printing a part of even more industries.

[0013] For example, fusing-agent based additive manufacturing systems melt plastic particles to form the object. In some cases, the fusing agent imparts a color to the object. However, a translucent object may be formed by, for example, using a light-transmissive ultraviolet (UV) fusing agent. That is, objects formed with a light-transmissive UV fusing agent are inherently translucent when printing with base powder materials that are clear or translucent such as polyamide (PA) 11 , PA 12, polypropylene, or a thermoplastic polyamide (TPA).

[0014] However, it may be desirable that portions of a translucent object are opaque. For example, a backlit keyboard button may be mainly translucent, but may have an opaque region that pertains to a label of the key such that the label of the key is legible while being backlit. Other examples of objects that may be mainly translucent with opaque regions include full color figurines, backlit buttons, indicators, signage, and medical models to name a few. In another example, the systems and methods described herein may facilitate printing different objects that have varying spatial translucency such as objects that imitate skin or marble. In yet another example, the methods and systems facilitate printing an object with covert markings. While particular reference is made to a few examples of translucent additively manufactured objects that have opaque regions, the methods and systems described herein may be implemented to form any of a variety of translucent objects with opaque regions. [0015] Accordingly, the present specification describes systems and methods of varying the opacity of areas of translucent UV-printed plastic objects by modulating an opacifying agent, where the opacifying agent may include an inorganic active ingredient. Specifically, the method includes applying a light- transmissive UV fusing agent across a layer of build material, the pattern of the light-transmissive UV fusing agent defining a slice of a layer of the object to be printed. An opacifying agent may then be applied across the layer in a different pattern. The pattern of the opacifying agent defines those regions of the layer that are to have a different opacity as compared to those regions that do not have the opacifying agent deposited thereon.

[0016] Following deposition of the agents, the layer is exposed to UV light to cause the portions of the build material with the light-transmissive UV fusing agent deposited thereon to fuse to form a solid layer. This process may be repeated per layer until a 3D object is formed.

[0017] Specifically, the present specification describes an additive manufacturing system. The additive manufacturing system includes a build material distribution device to deposit a layer of a powder build material and an agent distribution system. The agent distribution system deposits on top of the layer of powder build material 1) a light-transmissive UV fusing agent in a pattern of a slice of a 3D object to be formed and 2) an opacifying agent to selectively opacify regions of the 3D object to be formed. A UV energy source of the additive manufacturing system, in combination with the light-transmissive UV fusing agent deposited, selectively melts portions of the layer of powder build material. A controller of the additive manufacturing system determines parameters for opacifying agent deposition to achieve a target opacity.

[0018] The present specification also describes a method. According to the method, a layer of powder build material is deposited. A light-transmissive UV fusing agent is deposited on the layer in a first pattern. The first pattern defines a slice of a three-dimensional (3D) object to be formed. An opacifying agent is deposited on top of the layer of powder build material in a second pattern. UV light is applied to selectively fuse portions of the layer of powder build material with the light-transmissive UV fusing agent deposited thereon. [0019] The present specification also describes a non-transitory machine- readable storage medium encoded with instructions executable by a processor of a computing device. The machine-readable storage medium includes instructions to, when executed by the processor, cause the processor to determine, based on an object file for a 3D object to be formed, a quantity of light-transmissive UV fusing agent to deposit to generate a translucent 3D object and determine, based on the object file, parameters for opacifying agent deposition on top of the layer of powder build material to achieve a target opacity in opaque regions of the 3D object to be formed. The machine-readable storage medium also includes instructions to, when executed by the processor, cause the processor to generate an additive manufacturing file used to form the translucent 3D object with associated opaque regions.

[0020] Such systems and methods 1) allow the additive manufacturing of an object with both opaque and translucent regions; 2) allow customization of a degree of opacity in each of the different opaque regions; and 3) are used in conjunction with a UV fusing agent based additive manufacturing system. However, it is contemplated that the systems and methods disclosed herein may address other matters and deficiencies in a number of technical areas. [0021] As used in the present specification and in the appended claims, the term “controller” may refer to an electronic component which may include a processor and memory. The processor may include the hardware architecture to retrieve executable code from the memory and execute the executable code. As specific examples, the controller as described herein may include computer readable storage medium, and a processor, an application specific integrated circuit (ASIC), a semiconductor-based microprocessor, a central processing unit (CPU), and a field-programmable gate array (FPGA), and/or other hardware device. [0022] The memory may include a computer-readable storage medium, which computer-readable storage medium may contain, or store computer usable program code for use by or in connection with an instruction execution system, apparatus, or device. The memory may take many types of memory including volatile and non-volatile memory. For example, the memory may include Random Access Memory (RAM), Read Only Memory (ROM), optical memory disks, and magnetic disks, among others. The executable code may, when executed by the controller cause the controller to implement at least the functionality of additively manufacturing a translucent 3D polymer object with opaque regions as described below.

[0023] Further, as used in the present specification and in the appended claims, the term “light-transmissive” refers to a UV fusing agent that is clear or translucent. That is, a clear UV fusing agent is light-transmissive and a translucent UV fusing agent is also light-transmissive.

[0024] Turning now to the figures, Fig. 1 is a block diagram of an additive manufacturing system (100) for generating a UV-printed object with opaque regions, according to an example of the principles described herein. As described above, the additive manufacturing system (100) may generate 3D objects that have a translucent base, but which object has regions that are more opaque. The level of opacity may be varying across the object. That is, the object may have multiple opaque regions with the opacity in each region being customizable and different than the opacity in other regions.

[0025] The additive manufacturing system (100) may include a build material distribution device (102) to deposit layers of powder build material on a bed. This powder build material may be the raw material from which a 3D object is formed. That is, portions of the powder build material are joined together to form a solid structure. The powder build material may be of a variety of types. In some examples, the build material may comprise a polymer material. For example, the polymer material may be a polyamide material. While specific reference is made to a polyamide material, the polymer material may be of other types which are inherently translucent such as polyamide (PA) 11 , PA 12, nylons, polypropylene, thermoplastic polyamide (TPA), thermoplastic materials, resin, and the like.

[0026] The additive manufacturing system (100) also includes an agent distribution system (104) to deposit agents on the layer of powder build material in various patterns. Specifically, the agent distribution system (104) deposits a light-transmissive UV fusing agent (106) in a pattern to form a slice of a three- dimensional object to be formed. For example, if a 3D object to be formed is a cube, the agent distribution system (104) may deposit the light-transmissive UV fusing agent (106) in a square pattern to form a square slice of the 3D cube.

[0027] Use of a light-transmissive (i.e., clear or translucent) UV fusing agent (106) enables the generation of transparent (clear) and translucent objects that do not have color tints. The light-transmissive UV fusing agent (106) may be of a variety of types. For example, the light-transmissive UV fusing agent (106) may be a triazine, benzotriazole, benzophenone, or ecamsule. Other examples of light-transmissive UV fusing agents (106) that may be implemented include those listed below by their International Union of Pure and Applied Chemistry (IUPAC) designations:

• 2-(benzotriazol-2-yl)-6-[[3-(benzotriazol-2-yl)-2-hydroxy-5-(2,4,4- trimethylpentan-2-yl)phenyl]methyl]-4-(2,4,4-trimethylpentan-2- yl)phenol (or methylene bis-benzotriazolyl tetramethylbutylphenol)

• 5-(2-ethylhexoxy)-2-[4-[4-(2-ethylhexoxy)-2-hydroxyphenyl]-6-(4- methoxyphenyl)-1 ,3,5-triazin-2-yl]phenol

• 2-(benzotriazol-2-yl)-4-(2,4,4-trimethylpentan-2-yl)phenol

• 1 -(4-tert-butylphenyl)-3-(4-methoxyphenyl)propane-1 ,3-dione

• [3-[[4-[[7,7-dimethyl-3-oxo-4-(sulfomethyl)-2- bicyclo[2.2.1]heptanylidene]methyl]phenyl]methylidene]-7,7-dimethyl- 2-oxo-1-bicyclo[2.2.1]heptanyl]methanesulfonic acid

[0028] While particular reference is made to specific light-transmissive UV fusing agents (106), other UV fusing agents (106) that are clear or translucent and that result in transparent and translucent 3D printed objects may be implemented in accordance with the principles described herein.

[0029] In any case, any of the above-mentioned or other light- transmissive UV fusing agents (106) ae used to form the 3D objects and provide the initial translucency which is the basis for variable opacity within the 3D object.

[0030] The agent distribution system (104) also deposits an opacifying agent (108) on top of the layer of powder build material to selectively opacify regions of the 3D object to be formed. The opacifying agent (108) may include particles that do not transmit light. That is, these particles reflect or scatter light. Accordingly, by adding the opacifying agent (108) into particular regions that are to form the 3D object, these particular regions become more opaque than those regions that do not have the opacifying agent (108) deposited thereon. In an example, the opacifying agent (108) may be visually indistinguishable from the powder build material. For example, the opacifying agent (108) may be white. [0031] In general, to spatially vary opacity in a 3D object, the opacifying agent (108) is printed in parallel with the light-transmissive UV fusing agent (106). Modulating the concentration of the opacifying agent (108) within a particular region may alter the opacity in that region. That is, as the amount of opacifying agent (108) is increased, the associated region of the 3D object will become more opaque.

[0032] The opacifying agent (108) may be formulated into jettable inks that include a stable suspension of nanoparticles. The opacifying agent (108) may take a variety of forms. Examples of opacifying agents (108) include, but are not limited to, zinc oxide, titanium dioxide, lanthanum oxide, barium oxide, calcium oxide, magnesium oxide, stannic oxide, barium titanate, antimony trioxide, barium sulfate, and zinc sulfide.

[0033] While particular reference is made to particular opacifying agents (108), other opacifying agents (108) may be implemented in accordance with the principles described herein. Some of these opacifying agents (108) may exhibit absorption at wavelengths emitted by the UV energy source (110). Thus, the opacifying agent (108) may contribute to some degree to powder fusing in addition to its opacifying function. Accordingly, the operation of the UV energy source (110) may account for any heating contribution of the opacifying agent (108) by adjusting the volume of both agents deposited in the printed layer.

[0034] Structurally, the agent distribution system (104) may include at least one liquid ejection device to distribute the agents onto the layers of build material. In some examples, one liquid ejection device may be used to eject both the light-transmissive UV fusing agent (106) and the opacifying agent (108), while in another example different liquid ejection devices may be used to separately eject the light-transmissive UV fusing agent (106) and the opacifying agent (108).

[0035] A liquid ejection device may include at least one printhead (e.g., a thermal ejection based printhead, a piezoelectric ejection based printhead, etc.). In some examples, the agent distribution system (104) is coupled to a scanning carriage, and the scanning carriage moves along a scanning axis over the bed. In one example, printheads that are used in inkjet printing devices may be used in the agent distribution devices. In other examples, the agent distribution system (104) may include other types of liquid ejection devices that selectively eject small volumes of liquid.

[0036] The additive manufacturing system (100) also includes a UV energy source (110) to, in combination with the light-transmissive UV fusing agent (106) deposited, selectively melt portions of the layer of powder build material. As described above, the light-transmissive UV fusing agent (106) increases the UV energy absorption of the layer of build material on which the agent is deposited. Due to the increased UV energy absorption properties imparted by the light-transmissive UV fusing agent (106), those portions of the build material that have the light-transmissive UV fusing agent (106) deposited thereon heat to a temperature greater than the fusing temperature of the build material.

[0037] The additive manufacturing system (100) also includes a controller (112) to determine parameters for opacifying agent deposition to achieve a target opacity. That is, the opacifying agent (108) may be deposited in different ways to achieve different target opacities. In one particular example, the concentration, or amount, of opacifying agent (108) deposited in a particular region may impact the opacity in that region. Other examples of parameters that may be adjusted include a depth below the surface to deposit the opacifying agent and a number of layers that are to define the opaque region. Examples of the effect that each of these parameters has on overall opacity in a region of the 3D object is provided below in connection with Figs. 4A - 4D. Accordingly, the controller may adjust values for each or multiple of these parameters to customize the opacity in a given region. As such, the present additive manufacturing system (100) provides for the customizable and variable opacity across an initially translucent 3D object that is additively manufactured using a light-transmissive UV fusing agent (106).

[0038] Fig. 2 is an isometric view of an additive manufacturing system

(100) for generating a UV-printed object with opaque regions, according to an example of the principles described herein. Components of the additive manufacturing system (100) depicted in Fig. 2 may not be drawn to scale and thus, the additive manufacturing system (100) may have a different size and/or configuration other than as shown therein.

[0039] In an example of an additive manufacturing process, a layer of build material may be deposited onto a bed (214). That is, a build material distribution device (102) may drop powder build material onto the bed (214). In some examples, the bed (214) may be moved up and down, e.g., along the z- axis, so that powder build material may be delivered to the bed (214) or to a previously formed layer of powder build material. For each subsequent layer of powder build material to be delivered, the bed (214) may be lowered so that the build material distribution device (102) and re-distributor (216) can operate to place additional powder build material particles onto the bed (214).

[0040] The build material distribution device (102) is arranged to dispense a build material layer-by-layer onto the bed (214) to additively form the 3D object. In some examples, the build material distribution device (102) has a length at least as long as a length of the bed (214), such that the build material distribution device (102) can coat the entire bed (214) with a layer of build material in a single pass. While Fig. 2 depicts a particular build material distribution device (102), the build material distribution device (102) may include a variety of devices such as, a supply bed or reservoir, a sieve or rotating slotted rod to provide build material to be spread into a new layer by a redistributor (216).

[0041] A re-distributor (216) or other mechanism may precisely redistribute (or recoat) the deposited powder build material into a layer of a desired thickness. While Fig. 2 depicts a particular re-distributor (216), the build material re-distributor (216) may be implemented via a variety of electromechanical or mechanical mechanisms, such as doctor blades, rollers, slot dies, extruders, and/or other structures suitable to spread, deposit, and/or otherwise form a coating of the build material in a generally uniform layer relative to the bed (214) or relative to a previously deposited layer of build material.

[0042] Fig. 2 also clearly depicts an agent distribution system (104) to deposit an agent, such as a light-transmissive UV fusing agent (106) and an opacifying agent (108). In the example depicted in Fig. 2, the agent distribution system (104) includes a first liquid ejection device (218-1) to deposit the light- transmissive UV fusing agent (106) and a second liquid ejection device (218-2) to deposit the opacifying agent (108).

[0043] In some examples, these components, i.e. , the build material distribution device (102), re-distributor (216), and liquid ejection devices (218-1 , 218-2), may be coupled to scanning carriages. During additive manufacturing, these components operate as the scanning carriages to which they are coupled move over the bed (214) along the scanning axis.

[0044] Each of the previously described physical elements may be operatively connected to a controller (112) which controls the additive manufacturing. Specifically, the controller (112) may direct a build material distribution device (102) and any associated scanning carriages to move to add a layer of powder build material. Further, the controller (112) may send instructions to direct the liquid ejection devices (218-1 , 218-2) and any associated scanning carriages to move to selectively deposit the agent(s) onto the surface of a layer of the build material at specific locations to form a translucent 3D printed object slice and any associated opaque regions.

[0045] The controller (112) may send instructions to direct the UV energy source (110) and any associated scanning carriages to move to expose the build material to UV light to selectively melt portions of the build material with light-transmissive UV fusing agent (106) deposited thereon.

[0046] Fig. 3 is a flow chart of a method (300) for generating a UV-printed object with opaque regions, according to an example of the principles described herein. As described above, additive manufacturing involves the layer-wise deposition of build material and fusing certain portions of a layer to form a slice of a 3D object. Accordingly, in this example, the method (300) includes sequentially forming slices of a 3D object. That is, the steps in the method (300) may be repeated for each layer of a 3D object. In some examples, this includes sequentially depositing (block 301) layers of a powder build material and depositing (block 302) a light-transmissive UV fusing agent (106) across the layer of build material in a first pattern. The first pattern defines a layer of a slice of a 3D object. Moreover, as described above, the use of the light-transmissive UV fusing agent (106) allows for the 3D object to be initially translucent.

[0047] The method (300) also includes depositing (block 303) an opacifying agent (108) on the layer of build material in a second pattern. This second pattern defines those portions of the object that are to be opaque, or that are to block more light than other portions of the object. The second pattern may be different than the first pattern. That is, certain portions of the object may be translucent while other portions may be opaque. Those portions that are to form part of the 3D object but that are to remain translucent receive the light-transmissive UV fusing agent (106). Other portions of the layer are to form part of the 3D object but are to be opaque. These portions 1) receive the light-transmissive UV fusing agent (106) such that they fuse to form the 3D object and 2) receive the opacifying agent (108) such that they are opaque and not translucent. That is, the opacifying agent (108) converts regions of the 3D object on which it is deposited from translucent to opaque. [0048] In a particular example, a zinc oxide opacifying agent (108) may be used which may prevent discoloration of the 3D object when exposed to UV energy. That is, in some applications it may be desirable for the 3D object to be achromatic. Discoloration may cause an object to not reach the desired color tolerances for certain applications. For example, titanium dioxide may brown when exposed to the UV energy source (110). Accordingly, titanium dioxide and other opacifying agents (108) may be used when discoloration is permissible.

[0049] The method (300) also includes applying (block 304) UV light to selectively fuse portions of the layer of powder build material with the light- transmissive UV fusing agent (106) deposited thereon. As described above, due to the increased heat absorption properties imparted by the light- transmissive UV fusing agent (106), those portions of the build material that have the light-transmissive UV fusing agent (106) deposited thereon melt together to form the 3D object. By comparison, those portions that are free of the light-transmissive UV fusing agent (106) may not melt and remain unfused. This unfused build material may be separated from the 3D object and re-used in subsequent additive manufacturing operations.

[0050] These operations (blocks 301 , 302, 303, 304) may be repeated to iteratively to build up multiple patterned layers and to form the 3D object. For example, the controller (112) may execute instructions to cause the bed (214) to be lowered to enable the next layer of powder build material to be spread. In addition, following the lowering of the bed (214), the controller (112) may 1) control the build material distribution device (102) to deposit a layer of powder build material on top of the previously formed layer and 2) control the agent distribution system (104) to deposit the light-transmissive UV fusing agent (106) and opacifying agent (108) to form another slice of the 3D object.

[0051 ] Following the deposition of the agents, the controller (112) may control the UV energy source (110) and any scanning carriages associated therewith to expose the layer to UV energy to selectively fuse portions of the build material that are to form a hardened slice of the 3D object. This control may include the sequential activation, per slice, of the scanning carriages to which these components may be coupled.

[0052] Note that while Fig. 3 depicts certain operations performed in a particular order, the order of the operations may be altered. Specifically, in one example the light-transmissive UV fusing agent (106) may be deposited before the opacifying agent (108). In another example, the opacifying agent (108) may be deposited before the light-transmissive UV fusing agent (106).

[0053] A test was performed to validate the use of the opacifying agent (108) to alter the opacity of an otherwise translucent 3D object. Specifically, several different objects were printed with different translucency properties. [0054] In this test, polyamide 12 was used as the powder build material, a bemotrizinole-based ink was used as the light-transmissive UV fusing agent (106), and a zinc oxide jettable suspension was used as the opacifying agent (108). T able (1 ) below correlates the amount of a zinc oxide opacifying agent (in this case measured as a weight percent of the total 3D object) to the total transmission value. Table (1 ) below indicates the total transmission values were measured with a spectrophotometer using an integrating sphere (aperture diameter = 6 millimeters (mm)). The numbers in Table (1) are luminance factors quantifying the percentage of light being transmitted through a material of a specific thickness. In Table (1), high values indicate high transmission whereas low values indicate opacity.

Table (1)

[0055] In Table (1 ), the luminance factor of 10% indicates that the material is not clear, but the incoming light is being scattered inside the object resulting in a translucent appearance perceivable both in a front and back-lit viewing environment. The luminance factor of 1 % indicates that the majority of the light is blocked, that is the object is opaque. In the case of an object with the high amount of opacifying agent (108), most of the light is reflected back resulting in a bright white appearance.

[0056] The amount of the reflected light, as opposite to transmitted light, can also be measured and will be different for the different objects with different amount of opacifying agent (108) deposited thereon. Table (2) below contains the luminance factor of the reflected light of the same two objects.

Table (2)

[0057] In Table (2), the value is a measure of the amount of light that is reflected. Accordingly, an object that is more opaque, such as the test object with more opacifying agent (108) deposited thereon, has a higher luminance factor (i.e. , 81) as compared to a translucent object that reflects a lesser amount of light, i.e., the translucent object with no opacifying agent (108) that has the lesser value of 30.

[0058] Figs. 4A - 4D depict various parameters that alter the opacity of regions of a translucent printed object (420), according to an example of the principles described herein. That is, Figs. 4A - 4D depict a translucent printed object (420) with different opaque regions (422). Each of Figs. 4A - 4D depict the effect of different values of different parameters affects the opacity of the different opaque regions (422).

[0059] Specifically, Fig. 4A depicts the different opacity that may be achieved by controlling the amount of opacifying agent (108) deposited. As described above, the opacifying agent (108) includes particles that scatter light. That is, the light hits these particles and then bounces back. The more particles there are, the greater the scattering effect and less translucency. In Fig. 4A, a greater amount of opacifying agent (108) is indicated with a more densely-filled box. [0060] The controller (112), when determining parameters for opacifying agent (108) deposition, may determine an amount of opacifying agent (108) to deposit, with a greater amount of opacifying agent (108) resulting in greater opacity as depicted in Fig. 4A.

[0061] Fig. 4B depicts the different opacity that may be achieved by controlling the number of layers that define the opaque region (422). That is, increasing the number of layers that define the opaque region (422) also increases the number of light-scattering particles that reflect light. As such, a thicker opaque region (422), increases the opacity in this region.

[0062] In this example, the controller (112), when determining parameters for opacifying agent (108) deposition, may determine a number of layers that define the opaque regions (422), with a greater number of layers resulting in greater opacity as depicted in Fig. 4B.

[0063] Fig. 4C depicts the different opacity that may be achieved by controlling the depth below the surface where the opacifying agent (108) is deposited. As described above, the opacifying agent (108) includes particles that scatter light. The farther away that the particles are from a light source, the less impact they have on opacity.

[0064] In this example, the controller (112), when determining parameters for opacifying agent (108) deposition, may determine a depth below the surface to deposit the opacifying agent (108), with a greater depth resulting in less opacity as depicted in Fig. 4C.

[0065] As demonstrated, any number of parameters may be adjustable so as to achieve a target and customized opacity. In some examples, multiple of these parameters may be adjusted in combination. For example, as depicted in Fig. 4D, different opaque regions (422) may have different depths below the surface and may have different numbers of layers that define the opaque regions (422). As such, the above-described parameters provide a variety of settings that may be selected such that a tailored opacity may be defined.

[0066] As depicted in Figs. 4A - 4D, the controller (112) may determine different values of the parameters for opacifying agent (108) deposition for different regions (422) of the layer. That is, throughout a 3D object, it may be desirable that different regions (422) have different opacities. Accordingly, the controller (112) may select certain parameter values for a first region (422-1 ) which may result in a first opacity in that region. The controller (112) may select other parameter values for a second region (422-2). These different parameter values may result in a second opacity, which is different than the first opacity, at the second region (422-2).

[0067] In addition to these parameters, other parameters may also be selected to achieve a target opacity. For example, the controller (112) may select an opacifying agent (108) based on the size of the particles within the opacifying agent (108). For example, when deploying a narrow-band UV energy source (110) centered at 365 nanometers (nm) together with the corresponding UV fusing agent (106), the opacifying agent (108) containing zinc oxide particles larger than 100 nm may contribute to UV absorption more than when zinc oxide particles less than 50 nm are used. Accordingly, the degree of opacity may be established by selecting an opacifying agent based on its particle sizes or by including particles of a particular size in the opacifying agent.

[0068] Fig. 5 is a flow chart of a method (500) for generating a UV-printed object (420) with opaque regions (422), according to an example of the principles described herein. According to the method (500), regions (422) of the 3D object (420) that are to be opaque are identified (block 501 ). In some examples, this may include extracting such information from an object file. That is, the object file for a 3D object (420) may include geometric properties such as which regions are desired to be translucent, which are desired to be opaque, and a target opacity for each opaque region (422). Accordingly, the controller (112) may extract from the object file, the identification of the opaque regions (422).

[0069] The controller (112) may also determine (block 502) a target opacity for each opaque region (422). Again, in an example, the target opacity may be determined (block 502) by extracting data and/or metadata from the object file. In another example, both the opaque regions (422) and the target opacity for each opaque region (422) may be identified via user input. [0070] Based on the determined target opacity, parameters for opacifying agent (108) deposition may be determined (block 503). Specifically, parameters such as depth from the surface, amount of opacifying agent (108) to deposit, and a number of layers that define the opaque region (422) may be determined such that the target opacity is achieved. As described above, any number of the aforementioned parameters may be adjusted to achieve this target opacity. [0071] The controller (112) may then control additive manufacturing based on the identified regions (422), target opacity, and determined parameters. That is, the controller (112) may control the build material distribution device (102) to deposit (block 504) a layer of powder build material and may control the agent distribution system (104) to deposit (block 505) a light-transmissive UV fusing agent (106) in a first pattern and to deposit (block 506) an opacifying agent (108), such as zinc oxide or others, in a second pattern. Following these depositions, the controller (112) activates the UV energy source (110) to apply (block 507) UV light to selectively fuse portions of the layer of powder build material. These operations may be performed as described above in connection with Fig. 3.

[0072] Fig. 6 depicts a non-transitory machine-readable storage medium (624) for generating a translucent printed object (420) with opaque regions (422), according to an example of the principles described herein. To achieve its desired functionality, the additive manufacturing system (100) includes various hardware components. Specifically, the additive manufacturing system (100) includes a processor and a machine-readable storage medium (624). The machine-readable storage medium (624) is communicatively coupled to the processor. The machine-readable storage medium (624) includes a number of instructions (626, 628, 630) for performing a designated function. The machine- readable storage medium (624) causes the processor to execute the designated function of the instructions (626, 628, 630).

[0073] Referring to Fig. 6, determine UV agent quantity instructions (626), when executed by the processor, cause the processor to determine, based on an object file for a 3D object (420) to be formed, a quantity of light-transmissive UV fusing agent (106) to deposit to generate a translucent 3D object (420). Determine opacifying parameters instructions (628), when executed by the processor, may cause the processor to, determine, based on the object file, parameters for opacifying agent (108) deposition on top of the layer of powder build material to achieve a target opacity in the opaque regions (422) of the 3D object (420) to be formed. Generate additive manufacturing (AM) file instructions (630), when executed by the processor, may cause the processor to generate additive manufacturing instructions to form the translucent 3D object (420) with associated opaque regions (422).

[0074] Such systems and methods 1) allow the additive manufacturing of an object with both opaque and translucent regions; 2) allow customization of a degree of opacity in each of the different opaque regions; and 3) are used in conjunction with a UV fusing agent based additive manufacturing system. However, it is contemplated that the systems and methods disclosed herein may address other matters and deficiencies in a number of technical areas.

Claims

CLAIMS What is claimed is:

1 . An additive manufacturing system, comprising: a build material distribution device to deposit a layer of a powder build material; an agent distribution system to deposit on top of the layer of powder build material: a light-transmissive ultraviolet (UV) fusing agent in a pattern of a slice of a three-dimensional (3D) object to be formed; and an opacifying agent to selectively opacify regions of the 3D object to be formed; a UV energy source to, in combination with the light-transmissive UV fusing agent deposited, selectively melt portions of the layer of powder build material; and a controller to determine values of parameters for opacifying agent deposition to achieve a target opacity.

2. The additive manufacturing system of claim 1 , wherein determining values of the parameters for opacifying agent deposition comprises determining an amount of opacifying agent to deposit.

3. The additive manufacturing system of claim 1 , wherein determining values of the parameters for opacifying agent deposition comprises determining a depth below a surface to deposit the opacifying agent.

4. The additive manufacturing system of claim 1 , wherein determining values of the parameters for opacifying agent deposition comprises determining a number of layers that define an opaque region.

5. The additive manufacturing system of claim 1 , wherein determining values of the parameters for opacifying agent deposition comprises selecting an opacifying agent based on a size of opacifying agent particles.

6. The additive manufacturing system of claim 1 , wherein the controller is to determine different values of the parameters for opacifying agent deposition for different regions of the layer.

7. The additive manufacturing system of claim 1 , wherein the opacifying agent is visually indistinguishable from the powder build material.

8. The additive manufacturing system of claim 1 , wherein the opacifying agent is zinc oxide.

9. The additive manufacturing system of claim 1 , wherein the opacifying agent is selected from the group consisting of: titanium dioxide; lanthanum oxide; barium oxide; calcium oxide; magnesium oxide; stannic oxide; barium titanate; antimony trioxide; barium sulfate; and zinc sulfide.

10. A method, comprising: in a layer-wise fashion: depositing a layer of powder build material; depositing a light-transmissive ultraviolet (UV) fusing agent in a first pattern on the layer of powder build material, the first pattern defining a slice of a three-dimensional (3D) object to be formed; depositing a zinc oxide opacifying agent on top of the layer of powder build material in a second pattern; and applying UV light to selectively fuse portions of the layer of powder build material with the light-transmissive UV fusing agent deposited thereon.

11 . The method of claim 10, wherein the second pattern is different than the first pattern.

12. The method of claim 10, further comprising selecting, per region of the slice to receive the zinc oxide opacifying agent: an amount of zinc oxide opacifying agent to deposit; a depth below a surface to deposit the zinc oxide opacifying agent; and a number of layers that define an opaque region.

13. A non-transitory machine-readable storage medium encoded with instructions executable by a processor of an electronic device, the machine- readable storage medium comprising instructions to, when executed by the processor, cause the processor to: determine, based on an object file for a three-dimensional (3D) object to be formed, a quantity of light-transmissive ultraviolet (UV) fusing agent to deposit to generate the 3D object; determine, based on the object file, values for parameters for opacifying agent deposition on top of a layer of powder build material to achieve a target opacity in opaque regions of the 3D object to be formed; and generate an additive manufacturing file to form the 3D object with associated opaque regions.

14. The non-transitory machine-readable storage medium of claim 13, further comprising instructions to, when executed by the processor, cause the processor to: control a build material distribution device to deposit a layer of powder build material; and control an agent distribution system to deposit the light-transmissive UV fusing agent and opacifying agent.

15. The non-transitory machine-readable storage medium of claim 13, further comprising instructions to, when executed by the processor, cause the processor to: identify opaque regions of the 3D object to be formed; determine a target opacity for different opaque regions; and determine values for the parameters for opacifying agent deposition for each different opaque region to achieve the target opacity for that region.