Source: https://patents.google.com/patent/US9523934B2/en
Timestamp: 2017-08-19 18:46:31
Document Index: 41189647

Matched Legal Cases: ['Application No. 61', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80', 'art 80']

US9523934B2 - Engineering-grade consumable materials for electrophotography-based additive manufacturing - Google Patents /g;Ia=/"/g;Ja=/'/g;Ka=/\x00/g;Da=/[\x00&<>"']/; _.Na=function(a,c){var d=0;a=(0,_.Aa)(String(a)).split(".");c=(0,_.Aa)(String(c)).split(".");for(var e=Math.max(a.length,c.length),f=0;0==d&&fc?1:0}; var Va;_.Oa=Array.prototype.indexOf?function(a,c,d){return Array.prototype.indexOf.call(a,c,d)}:function(a,c,d){d=null==d?0:0>d?Math.max(0,a.length+d):d;if(_.p(a))return _.p(c)&&1==c.length?a.indexOf(c,d):-1;for(;dc?null:_.p(a)?a.charAt(c):a[c]};_.Wa=function(a,c){return 0<=(0,_.Oa)(a,c)};_.Xa=function(a,c){c=(0,_.Oa)(a,c);var d;(d=0<=c)&&Array.prototype.splice.call(a,c,1);return d};_.Ya=function(a){var c=a.length;if(0=arguments.length?Array.prototype.slice.call(a,c):Array.prototype.slice.call(a,c,d)}; var ab,cb,db,eb;_.$a=function(a,c,d){for(var e in a)c.call(d,a[e],e,a)};ab=function(a,c){for(var d in a)if(c.call(void 0,a[d],d,a))return!0;return!1};_.bb=function(a){var c=[],d=0,e;for(e in a)c[d++]=a[e];return c};cb=function(a){var c=[],d=0,e;for(e in a)c[d++]=e;return c};db=function(a,c){return null!==a&&c in a};eb="constructor hasOwnProperty isPrototypeOf propertyIsEnumerable toLocaleString toString valueOf".split(" "); _.fb=function(a,c){for(var d,e,f=1;f",0);_.Ib=_.Hb("",0);_.Jb=_.Hb("
Engineering-grade consumable materials for electrophotography-based additive manufacturing
US9523934B2
US14332566
US20150024316A1 (en )
James E. Orrock
B29C67/0074—Rapid manufacturing and prototyping of 3D objects by additive depositing, agglomerating or laminating of plastics material, e.g. by stereolithography or selective laser sintering using only solid materials, e.g. laminating sheet material precut to local cross sections of the 3D object
B29C67/0077—Rapid manufacturing and prototyping of 3D objects by additive depositing, agglomerating or laminating of plastics material, e.g. by stereolithography or selective laser sintering using only solid materials, e.g. laminating sheet material precut to local cross sections of the 3D object using layers of powder being selectively joined, e.g. by selective laser sintering or melting
G03G9/08766—Polyamides, e.g. polyesteramides
B29K2105/002—Agents changing electric characteristics
B29K2105/0023—Agents changing electric characteristics improving electric conduction
A part material for printing three-dimensional parts with an electrophotography-based additive manufacturing system, the part material including a composition having an engineering-grade thermoplastic material and a charge control agent. The part material is provided in a powder form having a controlled particle size, and is configured for use in the electrophotography-based additive manufacturing system having a layer transfusion assembly for printing the three-dimensional parts in a layer-by-layer manner.
This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/847,343, filed on Jul. 17, 2013, and entitled “Engineering-Grade Consumable Materials For Electrophotography-Based Additive Manufacturing System”.
An aspect of the present disclosure is directed to a part material for printing 3D parts with an electrophotography-based additive manufacturing system. The part material has a composition that includes an engineering-grade thermoplastic material (e.g., having a heat deflection temperature ranging from about 100° C. to about 150° C.) and a charge control agent. The part material is provided in a powder form having a controlled particle size (e.g., a D50 particle size ranging from about 5 micrometers to about 30 micrometers), and is configured for use in the electrophotography-based additive manufacturing system having a layer transfusion assembly for printing the 3D parts in a layer-by-layer manner. In some embodiments, the part material may be provided in an interchangeable cartridge or other similar device, along with carrier particles, for use with the electrophotography-based additive manufacturing system.
Another aspect of the present disclosure is directed to a method for printing a 3D part with an electrophotography-based additive manufacturing system having an electrophotography engine, a transfer medium, and a layer transfusion assembly. The method includes providing a part material to the electrophotography-based additive manufacturing system, where the part material compositionally includes a charge control agent and an engineering-grade thermoplastic material (e.g., having a heat deflection temperature ranging from about 100° C. to about 150° C.), and has a powder form. In some embodiments, the part material may be provided in an interchangeable cartridge or other similar device, along with carrier particles, for use with the electrophotography-based additive manufacturing system.
FIG. 1 is a front view of an example electrophotography-based additive manufacturing system for printing 3D parts from part materials of the present disclosure, along with associated support structures from support materials.
The present disclosure is directed to amorphous and/or semi-crystalline, engineering-grade consumable materials, which are engineered for use in an electrophotography-based additive manufacturing system to print 3D parts with high resolutions and fast printing rates. During a printing operation, an electrophotography (EP) engine may develop or otherwise image each layer of the part (and any associated support material) using the electrophotography process. The developed layers are then transferred to a layer transfusion assembly where they are transfused (e.g., using heat and/or pressure) to print one or more 3D parts and support structures in a layer-by-layer manner.
As discussed below, the consumable material is a powder-based part material derived from one or more engineering-grade thermoplastic materials, a charge control agent, preferably a heat absorbent (e.g., an infrared absorber) if required, and optionally one or more additional materials, such as a flow control agent, which may also function as an external surface-treatment triboelectric charge control agent and/or a triboelectric modification additive. The part material is engineered for use with electrophotography-based additive manufacturing systems to print 3D parts having high part resolutions and good physical properties (e.g., good part strength, density, chemical resistance, usable temperature ranges, and the like). This allows the resulting 3D parts to function as end-use parts, if desired.
The part material of the present disclosure is preferably printed along with a powder-based support material that is engineered to complement the part materials. For example, each layer of the support material is preferably transfused along with an associated layer of the part material. As such, the support material preferably has a melt rheology that is similar to, or more preferably substantially the same as, the melt rheology of its associated part material.
FIGS. 1-4 illustrate system 10, which is an example electrophotography-based additive manufacturing system for printing 3D parts and associated support structures with the part of the present disclosure, and associated support materials. As shown in FIG. 1, system 10 includes a pair of EP engines 12 p and 12 s, belt transfer assembly 14, biasing mechanisms 16 and 18, and layer transfusion assembly 20. Examples of suitable components and functional operations for system 10 include those disclosed in Hanson et al., U.S. Publication Nos. 2013/0077996 and 2013/0077997, and in Comb et al., U.S. patent application Ser. Nos. 13/790,382 and 13/790,406.
Photoconductive surface 46 is a thin film extending around the circumferential surface of conductive drum body 44, and is preferably derived from one or more photoconductive materials, such as amorphous silicon, selenium, zinc oxide, organic materials, and the like. As discussed below, surface 46 is configured to receive latent-charged images of the sliced layers of a 3D part or support structure (or negative images), and to attract charged particles of the part or support material to the charged or discharged image areas, thereby creating the layers of the 3D part or support structure.
In the shown example, the image-forming assembly for surface 46 of EP engine 12 s is used to form layers 64 s of the support material of the present disclosure (referred to as support material 66 s), where a supply of support material 66 s may be retained by development station 58 (of EP engine 12 s) along with carrier particles. Similarly, the image-forming assembly for surface 46 of EP engine 12 p is used to form layers 64 p of the part material of the present disclosure (referred to as part material 66 p), where a supply of part material 66 p may be retained by development station 58 (of EP engine 12 p) along with carrier particles.
Each development station 58 may also include one or more devices for transferring the charged part or support material 66 p or 66 s to surface 46, such as conveyors, fur brushes, paddle wheels, rollers, and/or magnetic brushes. For instance, as surface 46 (containing the latent charged image) rotates from imager 56 to development station 58 in the direction of arrow 52, the charged part material 66 p or support material 66 s is attracted to the appropriately charged regions of the latent image on surface 46, utilizing either charged area development or discharged area development (depending on the electrophotography mode being utilized). This creates successive layers 64 p or 64 s as photoconductor drum 12 continues to rotate in the direction of arrow 52, where the successive layers 64 p or 64 s correspond to the successive sliced layers of the digital representation of the 3D part or support structure.
Transfer belt 22 is a transfer medium for transferring the developed successive layers 64 p and 64 s from photoconductor drum 42 (or an intermediary transfer drum or belt) to layer transfusion assembly 16. Examples of suitable transfer belts for belt 22 include those disclosed in Comb et al., U.S. patent application Ser. Nos. 13/790,382 and 13/790,406. Belt 22 includes front surface 22 a and rear surface 22 b, where front surface 22 a faces surface 46 of photoconductor drum 42 and rear surface 22 b is in contact with biasing mechanisms 16 and 18.
Controller 36 preferably rotates photoconductor drums 36 of EP engines 12 p and 12 s at the same rotational rates that are synchronized with the line speed of belt 22 and/or with any intermediary transfer drums or belts. This allows system 10 to develop and transfer layers 64 p and 66 s in coordination with each other from separate developer images. In particular, as shown, each part layer 64 p may be transferred to belt 22 with proper registration with each support layer 64 s to produce a combined part and support material layer 64. As can be appreciated, some layers transferred to layer transfusion assembly 20 may only include support material 66 s or may only include part material 66 p, depending on the particular support structure and 3D part geometries and layer slicing.
In a further alternative embodiment, one or both of EP engines 12 p and 12 s may also include one or more intermediary transfer drums and/or belts between photoconductor drum 42 and belt 22. For example, as shown in FIG. 3, EP engine 12 p may also include intermediary drum 42 a that rotates an opposing rotational direction from arrow 52, as illustrated by arrow 52 a, under the rotational power of motor 50 a. Intermediary drum 42 a engages with photoconductor drum 42 to receive the developed layers 64 p from photoconductor drum 42, and then carries the received developed layers 64 p and transfers them to belt 22.
FIG. 4 illustrates an example embodiment for layer transfusion assembly 20. As shown, layer transfusion assembly 20 includes build platform 68, nip roller 70, heaters 72 and 74, post-fuse heater 76, and air jets 78 (or other cooling units). Build platform 68 is a platform assembly or platen of system 10 that is configured to receive the heated combined layers 64 (or separate layers 64 p and 64 s) for printing a 3D part and support structure, referred to as 3D part 80 and support structure 82, in a layer-by-layer manner. In some embodiments, build platform 68 may include removable film substrates (not shown) for receiving the printed layers 64, where the removable film substrates may be restrained against build platform using any suitable technique (e.g., vacuum drawing).
Build platform 68 is supported by z-axis gantry 84, which is a guide mechanism configured to move build platform 68 along the z-axis and the x-axis to produce a reciprocating rectangular pattern, where the primary motion is back-and-forth along the x-axis (illustrated by broken lines 86. Gantry 84 may be operated by motor 88 based on commands from controller 36, where motor 88 may be an electrical motor, a hydraulic system, a pneumatic system, or the like.
Heater 72 is one or more heating devices (e.g., an infrared heater and/or a heated air jet) configured to heat layers 64 to a temperature near an intended transfer temperature of the thermoplastic-based powder, such as at least a fusion temperature of the thermoplastic-based powder, prior to reaching nip roller 70. Each layer 64 desirably passes by (or through) heater 72 for a sufficient residence time to heat the layer 64 to the intended transfer temperature. Heater 74 may function in the same manner as heater 72, and heats the top surfaces of 3D part 80 and support structure 82 to an elevated temperature, such as at the same transfer temperature as the heated layers 64 (or other suitable elevated temperature).
As mentioned above, the support material of the present disclosure used to print support structure 82 preferably has a melt rheology that is similar to or substantially the same as the melt rheology part material of the present disclosure used to print 3D part 80. This allows part and support materials of layers 64 p and 64 s to be heated together with heater 74 to substantially the same transfer temperature, and also allows the part and support materials at the top surfaces of 3D part 80 and support structure 82 to be heated together with heater 74 to substantially the same temperature. Thus, the part layers 64 p and the support layers 64 s may be transfused together to the top surfaces of 3D part 80 and support structure 82 in a single transfusion step as combined layer 64.
Post-fuse heater 76 is located downstream from nip roller 70 and upstream from air jets 78, and is configured to heat the transfused layers to an elevated temperature in the post-fuse or heat-setting step. Again, the close melt rheologies of the part and support materials allow post-fuse heater 76 to post-heat the top surfaces of 3D part 80 and support structure 82 together in a single post-fuse step.
Prior to printing 3D part 80 and support structure 82, build platform 68 and nip roller 70 may be heated to their desired temperatures. For example, build platform 68 may be heated to the average part temperature of 3D part 80 and support structure 82 (due to the close melt rheologies of the part and support materials). In comparison, nip roller 70 may be heated to a desired transfer temperature for layers 64 (also due to the close melt rheologies of the part and support materials).
During the printing operation, belt 22 carries a layer 64 past heater 72, which may heat the layer 64 and the associated region of belt 22 to the transfer temperature. Suitable transfer temperatures for the part and support materials of the present disclosure include temperatures that exceed the glass transition temperature of the part and support materials, where the layer material is softened but not melted.
As further shown in FIG. 4, during operation, gantry 84 may move build platform 68 (with 3D part 80 and support structure 82) in a reciprocating rectangular pattern 86. In particular, gantry 84 may move build platform 68 along the x-axis below, along, or through heater 74. Heater 74 heats the top surfaces of 3D part 80 and support structure 82 to an elevated temperature, such as the transfer temperatures of the part and support materials. As discussed in Comb et al., U.S. Patent Publication Nos. 2013/0186549 and 2013/0186558, heaters 72 and 74 may heat layers 64 and the top surfaces of 3D part 80 and support structure 82 to about the same temperatures to provide a consistent transfusion interface temperature. Alternatively, heaters 72 and 74 may heat layers 64 and the top surfaces of 3D part 80 and support structure 82 to different temperatures to attain a desired transfusion interface temperature.
As the transfused layer 64 passes the nip of nip roller 70, belt 22 wraps around nip roller 70 to separate and disengage from build platform 68. This assists in releasing the transfused layer 64 from belt 22, allowing the transfused layer 64 to remain adhered to 3D part 80 and support structure 82. Maintaining the transfusion interface temperature at a transfer temperature that is higher than its glass transition temperature, but lower than its fusion temperature, allows the heated layer 64 to be hot enough to adhere to 3D part 80 and support structure 82, while also being cool enough to readily release from belt 22. Additionally, as discussed above, the close melt rheologies of the part and support materials allow them to be transfused in the same step.
After release, gantry 84 continues to move build platform 68 along the x-axis to post-fuse heater 76. At post-fuse heater 76, the top-most layers of 3D part 80 and support structure 82 (including the transfused layer 64) may then be heated to at least the fusion temperature of the thermoplastic-based powder in a post-fuse or heat-setting step. This melts the material of the transfused layer 64 to a highly fusable state such that polymer molecules of the transfused layer 64 quickly interdiffuse to achieve a high level of interfacial entanglement with 3D part 80 and support structure 82.
After the printing operation is completed, the resulting 3D part 80 and support structure 82 may be removed from system 10 and undergo one or more post-printing operations. For example, support structure 82 may be sacrificially removed from 3D part 80 using an aqueous-based solution, such as an aqueous alkali solution. Under this technique, support structure 82 may at least partially dissolve in the solution, separating it from 3D part 80 in a hands-free manner.
In comparison, part materials are chemically resistant to aqueous alkali solutions. This allows the use of an aqueous alkali solution to be employed for removing the sacrificial support structure 82 without degrading the shape or quality of 3D part 80. Examples of suitable systems and techniques for removing support structure 82 in this manner include those disclosed in Swanson et al., U.S. Pat. No. 8,459,280; Hopkins et al., U.S. Pat. No. 8,246,888; and Dunn et al., U.S. Publication No. 2011/0186081; each of which are incorporated by reference to the extent that they do not conflict with the present disclosure.
As briefly discussed above, the part material of the present disclosure compositionally includes one or more amorphous and/or semi-crystalline, engineering-grade thermoplastic materials, such as one or more polyamides, polyoxymethylenes, polycarbonates, polysulfones, thermoplastic polyurethanes, copolymers thereof, and mixtures thereof. These thermoplastics typically have heat deflection temperatures ranging from about 100° C. to about 150° C. Examples of suitable engineering-grade thermoplastic materials are discussed further below in conjunction with associated techniques for producing powders of the part materials.
As used herein, semi-crystalline thermoplastic materials have measureable melting points (5 calories/gram or more) using differential scanning calorimetry (DSC) pursuant to ASTM D3418-08. Furthermore, the semi-crystalline thermoplastic materials are preferably polymeric materials (e.g., polymers) capable of exhibiting an average percent crystallinity in a solid state of at least about 10% by weight, and include polymeric materials having crystallinities up to 100% (i.e., fully-crystalline polymeric materials). In comparison, amorphous thermoplastic materials have substantially no measurable melting points (less than 5 calories/gram) using DSC pursuant to ASTM D3418-08.
As mentioned above, the part material is engineered for use in an EP-based additive manufacturing system (e.g., system 10) to print 3D parts (e.g., 3D part 80). As such, the part material may also include one or more materials to assist in developing layers with EP engine 12 p, to assist in transferring the developed layers from EP engine 12 p to layer transfusion assembly 20, and to assist in transfusing the developed layers with layer transfusion assembly 20.
For example, in the electrophotographic process with system 10, the part material is preferably charged triboelectrically through the mechanism of frictional contact charging with carrier particles at development station 58. This charging of the part material may be referred to by its triboelectric charge-to-mass (Q/M) ratio, which may be a positive or negative charge and has a desired magnitude. The Q/M ratio is inversely proportional to the powder density of the part material, which can be referred to by its mass per unit area (M/A) value. For a given applied development field, as the value of Q/M ratio of the part material is increased from a given value, the M/A value of the part material decreases, and vice versa. Thus, the powder density for each developed layer of the part material is a function of the Q/M ratio of the part material.
It has been found that, in order to provide successful and reliable development of the part material onto development drum 44 and transfer to layer transfusion assembly 20 (e.g., via belt 22), and to print 3D part 80 with a good material density, the part material preferably has a suitable Q/M ratio for the particular architecture of EP engine 12 p and belt 22. Examples of preferred Q/M ratios for the part material range from about −5 micro-Coulombs/gram (μC/g) to about −50 μC/g, more preferably from about −10 μC/g to about −40 μC/g, and even more preferably from about −15 μC/g to about −35 μC/g, and even more preferably from about −25 μC/g to about −30 μC/g.
In this embodiment, the Q/M ratio is based on a negative triboelectric charge. However, in an alternative embodiment, system 10 may operate such that the Q/M ratio of the part material has a positive triboelectric charge with the above-discussed magnitudes. In either embodiment, these magnitudes of Q/M ratio prevent the electrostatic forces constraining the part material to the carrier surfaces from being too excessive, and that any level of “wrong sign” powder is minimized. This reduces inefficiencies in the development of the part material at EP engine 12 p, and facilitates the development and transfer of each layer 64 p with the desired M/A value.
Furthermore, if a consistent material density of 3D part 80 is desired, the desired Q/M ratio (and corresponding M/A value) is preferably maintained at a stable level during an entire printing operation with system 10. However, over extended printing operations with system 10, development station 58 may need to be replenished with additional amounts of the part material. This can present an issue because, when introducing additional amounts of the part material to development station 58 for replenishment purposes, the part material is initially in an uncharged state until mixing with the carrier particles. As such, the part material also preferably charges to the desired Q/M ratio at a rapid rate to maintain a continuous printing operation with system 10.
Accordingly, controlling and maintaining the Q/M ratio during initiation of the printing operation, and throughout the duration of the printing operation, will control the resultant rate and consistency of the M/A value of the part material. In order to reproducibly and stably achieve the desired Q/M ratio, and hence the desired M/A value, over extended printing operations, the part material preferably includes one or more charge control agents, which may be added to the copolymer during the manufacturing process of the part material.
In embodiments in which the Q/M ratio of the part material has a negative charge, suitable charge control agents for use in the part material include acid metal complexes (e.g., oxy carboxylic acid complexes of chromium, zinc, and aluminum), azo metal complexes (e.g., chromium azo complexes and iron azo complexes), mixtures thereof, and the like.
Alternatively, in embodiments in which the Q/M ratio of the part material has a positive charge, suitable charge control agents for use in the part material include azine-based compounds, and quaternary ammonium salts, mixtures thereof, and the like. These agents are effective at positively charging the copolymer when frictionally contact charged against appropriate carrier particles.
The charge control agents preferably constitute from about 0.1% by weight to about 5% by weight of the part material, more preferably from about 0.5% by weight to about 2% by weight, and even more preferably from about 0.75% by weight to about 1.5% by weight, based on the entire weight of the part material. As discussed above, these charge control agents preferably increase the charging rate of the copolymer against the carrier, and stabilize the Q/M ratio over extended continuous periods of printing operations with system 10.
In many situations, system 10 prints layers 64 p with a substantially consistent material density over the duration of the printing operations. Having a part material with a controlled and consistent the Q/M ratio allows this to be achieved. However, in some situations, it may be desirable to adjust the material density between the various layers 64 p in the same printing operation. For example, system 10 may be operated to run in a grayscale manner with reduced material density, if desired, for one or more portions of 3D part 80.
In addition to incorporating the charge control agents, for efficient operation EP engine 12 p, and to ensure fast and efficient triboelectric charging during replenishment of the part material, the mixture of the part material preferably exhibits good powder flow properties. This is preferred because the part material is fed into a development sump (e.g., a hopper) of development station 58 by auger, gravity, or other similar mechanism, where the part material undergoes mixing and frictional contact charging with the carrier particles.
As can be appreciated, blockage or flow restrictions of the part material during the replenishment feeding can inhibit the supply of the part material to the carrier particles. Similarly, portions of the part material should not become stuck in hidden cavities in development station 58. Each of these situations can alter the ratio of the part material to the carrier particles, which, as discussed above, is preferably maintained at a constant level to provide the desired Q/M ratio for the charged part material.
For example, the part material may constitute from about 1% by weight to about 30% by weight, based on a combined weight of the part material and the carrier particles, more preferably from about 5% to about 20%, and even more preferably from about 5% to about 10%. The carrier particles accordingly constitute the remainder of the combined weight.
The powder flow properties of the part material can be improved or otherwise modified with the use of one or more flow control agents, such as inorganic oxides. Examples of suitable inorganic oxides include hydrophobic fumed inorganic oxides, such as fumed silica, fumed titania, fumed alumina, mixtures thereof, and the like, where the fumed oxides may be rendered hydrophobic by silane and/or siloxane-treatment processes. Examples of commercially available inorganic oxides for use in the part material include those under the tradename “AEROSIL” from Evonik Industries AG, Essen, Germany.
The flow control agents (e.g., inorganic oxides) preferably constitute from about 0.1% by weight to about 10% by weight of the part material, more preferably from about 0.2% by weight to about 5% by weight, and even more preferably from about 0.3% by weight to about 1.5% by weight, based on the entire weight of the part material.
As discussed above, the one or more charge control agents are suitable for charging the part material to a desired Q/M ratio for developing layers of the part material at EP engine 12 p, and for transferring the developed layers (e.g., layers 64) to layer transfusion assembly 20 (e.g., via belt 22). However, the multiple printed layers in a 3D environment effectively prevents the electrostatic transfer of part material after a given number of layers are printed. Instead, layer transfusion assembly 20 utilizes heat and pressure to transfuse the developed layers together in the transfusion steps.
In particular, heaters 72 and/or 74 may heat layers 64 and the top surfaces of 3D part 80 and support structure 82 to a temperature near an intended transfer temperature of the part material, such as at least a fusion temperature of the part material, prior to reaching nip roller 70. Similarly, post-fuse heater 76 is located downstream from nip roller 70 and upstream from air jets 78, and is configured to heat the transfused layers to an elevated temperature in the post-fuse or heat-setting step.
Accordingly, the part material may also include one or more heat absorbers configured to increase the rate at which the part material is heated when exposed to heater 72, heater 74, and/or post-heater 76. For example, in embodiments in which heaters 72, 74, and 76 are infrared heaters, the heat absorber(s) used in the part material may be one or more infrared (including near-infrared) wavelength absorbing materials. As discussed below, these heat absorbers may be incorporated into the particles of the copolymer during the manufacturing of the part material. Absorption of infrared light causes radiationless decay of energy to occur within the particles, which generates heat in the part material.
The heat absorber is preferably soluble or dispersible in the solvated copolymers used for the preparation of the part material with a limited coalescence process, as discussed below. Additionally, the heat absorber also preferably does not interfere with the formation of the copolymer particles, or stabilization of these particles during the manufacturing process. Furthermore, the heat absorber preferably does not interfere with the control of the particle size and particle size distribution of the copolymer particles, or the yield of the copolymer particles during the manufacturing process.
Suitable infrared absorbing materials for use in the part material may vary depending on the desired color of the part material. Examples of suitable infrared absorbing materials include carbon black (which may also function as a black pigment for the part material), as well as various classes of infrared absorbing pigments and dyes, such as those that exhibit absorption in the wavelengths ranging from about 650 nanometers (nm) to about 900 nm, those that exhibit absorption in the wavelengths ranging from about 700 nm to about 1,050 nm, and those that exhibit absorption in the wavelengths ranging from about 800 nm to about 1,200 nm. Examples of these pigments and dyes classes include anthraquinone dyes, polycyanine dyes metal dithiolene dyes and pigments, tris aminium dyes, tetrakis aminium dyes, mixtures thereof, and the like.
The infrared absorbing materials also preferably do not significantly reinforce or otherwise alter the melt rheological properties of the engineering-grade thermoplastic material, such as the zero shear viscosity versus temperature profile of the engineering-grade thermoplastic material. For example, this can be achieved using a non-reinforcing type of carbon black, or a “low structure” type of carbon black, at low concentrations relative to the engineering-grade thermoplastic material.
Accordingly, in embodiments that incorporate heat absorbers, the heat absorbers (e.g., infrared absorbers) preferably constitute from about 0.5% by weight to about 10% by weight of the part material, more preferably from about 1% by weight to about 5% by weight, and in some more preferred embodiments, from about 2% by weight to about 3% by weight, based on the entire weight of the part material.
The part material may also include one or more additional additives that preferably do not interfere with the formation of the thermoplastic particles, or stabilization of these particles during the manufacturing process, and that preferably do not interfere with the control of the particle size and particle size distribution of the thermoplastic particles, or the yield of the thermoplastic particles during the manufacturing process.
Examples of suitable additional additives include colorants (e.g., pigments and dyes in addition to, or alternatively to, the heat absorbers), polymer stabilizers (e.g., antioxidants, light stabilizers, ultraviolet absorbers, and antiozonants), biodegradable additives, and combinations thereof. In embodiments that incorporate additional additives, the additional additives may collectively constitute from about 0.1% by weight to about 10% by weight of the part material, more preferably from about 0.2% by weight to about 5% by weight, and even more preferably from about 0.5% by weight to about 2% by weight, based on the entire weight of the part material.
For use in electrophotography-based additive manufacturing systems (e.g., system 10), the part material preferably has a controlled average particle size and a narrow particle size distribution, as described below in the Particle Sizes and Particle Size Distributions standard. For example, preferred D50 particles sizes include those up to about 100 micrometers if desired, more preferably from about 10 micrometers to about 30 micrometers, more preferably from about 10 micrometers to about 20 micrometers, and even more preferably from about 10 micrometers to about 15 micrometers.
σ ⁢ ⁢ g ~ D ⁢ ⁢ 90 D ⁢ ⁢ 50 ~ D ⁢ ⁢ 50 D ⁢ ⁢ 10
The part material is preferably manufactured by polymerizing or otherwise providing the engineering-grade thermoplastic material(s), and then formulating the part material from the engineering-grade thermoplastic material(s) (and other components) with the above-discussed particle sizes and particle size distributions. The particular formulation technique, however, is dependent on the engineering-grade thermoplastic material utilized in the part material.
For instance, when the engineering-grade thermoplastic material is a polyamide material, the part material may be produced with a milling process, a spray-drying process, or a limited coalescence process. Following the milling or spray-drying process, the resulting powder may undergo one or more additional classification processes to attain the desired particle sizes and particle size distribution, if required. Examples of suitable milling systems for the milling process include those commercially available under the tradename “IMD GRAN-U-LIZERS” from Modern Process Equipment Corporation, Chicago, Ill.
In some embodiments, the milling process may be performed as a cryomilling process. For example, a feedstock of the polyamide(s), the charge control agent, any heat absorber, and/or any additional additive may be suspended as a cryogen slurry (e.g., in liquid nitrogen or liquid argon), and then undergo a cryomilling process at cryogenic temperatures.
Alternatively, in a spray-drying process, a feedstock of the polyamide(s), the charge control agent, any heat absorber, and/or any additional additives may be dissolved or otherwise suspended in a carrier liquid (e.g., solvent). The resulting solution or slurry is then sprayed from an atomizer or spray nozzle along with a heated drying gas (e.g., heated dry air or nitrogen). The heated drying gas can be passed as a co-current or counter-current flow to the spray direction, as desired.
The sprayed droplets of the solution or slurry rapidly dry to produce the powder form of the part material, preferably with controlled particle sizes and a narrow particle size distribution. The powder may then be collected and undergo one or more additional classification processes to attain the desired particle sizes and particle size distribution, if required. The flow control agent may also optionally be blended with the powder at this point in the process, if desired.
In a further alternative embodiment, the part material may be formulated from the polyamide(s) with a limited coalescence process, such as the process disclosed in Bennett et al., U.S. Pat. No. 5,354,799. For example, the constituents of the part material (e.g., the polyamide(s), charge control agent, heat absorber, and/or additional additives) may be dissolved or otherwise suspended in an organic solvent to a suitable concentration range such as from about 10% to about 20% by weight of the poylamide(s) in the organic solvent. Examples of suitable organic solvents include ethyl acetate, propyl acetate, butyl acetate, dichloromethane, methyl ethyl ketone, cyclohexane, toluene, mixtures thereof, and the like.
The stabilized solvated droplet suspension may then be passed to a flash evaporator, where the organic solvent may be removed to a condensate tank using applied vacuum. The solid particles of the resulting part material, which remain dispersed in the aqueous phase, may then be transferred to a stirred holding vessel, and the colloidal silica may be removed, such as with the use of an aqueous sodium hydroxide solution, filtration, and water.
The part material may then be dried to produce its powder form. If necessary, following particle size analysis, the dry powder of the part material may be subjected to further sieving to remove oversize particles, and/or classification to remove any level of fines that are considered detrimental to subsequent performance in system 10. This process typically produces the part material in a yield ranging from about 90% by weight to about 99% by weight, based on the original amount of the polyamide(s) employed.
Examples of suitable polyamide materials for use in the part material may include polyamide homopolymers and copolymers derived from monomers that include caprolactam, diamines in combination with monomers that include dicarboxylic acids, and mixtures thereof. The diamine monomers and the dicarboxylic acid monomers are each preferably aliphatic monomers, and more preferably are each acyclic aliphatic monomers. However, in other embodiments, the diamine monomers and/or the dicarboxylic acid monomers may include aromatic or cycloaliphatic groups while maintaining crystalline domains. Furthermore, in some embodiments, the semi-crystalline polyamide(s) may include cyclic groups in grafted pendant chains (e.g., maleated groups), as discussed below. Preferred polyamide homopolymers and copolymers for the semi-crystalline polyamide(s) may be represented by the following structural formulas:
where R1, R2, and R3 may each be a hydrocarbon chain having 3-12 carbon atoms. The hydrocarbon chains for R1, R2, and R3 may be branched (e.g., having small alkyl groups, such as methyl groups) or unbranched, and which are preferably aliphatic, acyclic, saturated hydrocarbon chains.
As used herein, reference to a repeating unit identifier “n” in a polymer structural formula means that the bracketed formula repeats for n units, where n is a whole number that may vary depending on the molecular weight of the given polymer. Furthermore, the particular structures of the bracketed formulas may be the same between the repeating units (i.e., a homopolymer) or may be vary between the repeating units (i.e., copolymer). For example, in the above-shown Formula 1, R1 may be the same structure for each repeating unit to provide a homopolymer, or may be two or more different structures that repeat in an alternating copolymer manner, a random copolymer manner, a block copolymer manner, a graft copolymer manner (as discussed below), or combinations thereof.
Preferred polyamides include nylon-type materials such as polycarpolactum (PA6), polyhexamethyleneaidpamide (PA6,6), polyhexamethylenenonamide (PA6,9), polyhexamethylenesebacamide (PA6,10), polyamide 6/12 (PA6,12), polyenantholactum (PA7), polyundecanolactum (PA11), polylaurolactam (PA12), and mixtures thereof. More preferably, the polyamides for the semi-crystalline polyamide(s) include PA6; PA6,6; PA 6,12; PA11; polylaurolactam (PA12), and mixtures thereof.
In embodiments in which the engineering-grade thermoplastic material is a polyoxymethylene material, a polycarbonate material, or a thermoplastic polyurethane material, the part material may be produced with either of the above-discussed milling process or the above-discussed spray-drying process. Additionally, for polycarbonate materials and thermoplastic polyurethane materials, the part material may be produced with above-discussed limited coalescence process. With any of these techniques technique, the resulting powder may also undergo one or more additional classification processes to attain the desired particle sizes and particle size distribution, if required.
Examples of suitable polyoxymethylene materials for use in the part material include acetal copolymers, acetal homopolymers, and mixtures thereof, more preferably acetal homopolymers, such as those commercially available under the tradename “DELRIN” from E.I. du Pont de Nemours and Company, Wilmington, Del.
After being formulated, the part material preferably has particle sizes and particle size distributions as discussed above. In some embodiments, the resulting part material may be surface treated with one or more external flow control agents, as discussed above, to increase the powder flow properties of the part material. For example, the part material may be dry blended under high speed and sheer, preferably at 25° C., with one or more external flow control agents. This uniformly distributes, coats, and partially embeds the flow control agent(s) into the individual particles of the part material, without significantly altering the particle size or particle size distribution.
The formulated part material may then be filled into a cartridge or other suitable container for use with EP engine 12 p in system 10. For example, the formulated part material may be supplied in a cartridge, which may be interchangeably connected to a hopper of development station 58. In this embodiment, the formulated part material may be filled into development station 58 for mixing with the carrier particles, which may be retained in development station 58. Development station 58 may also include standard toner development cartridge components, such as a housing, delivery mechanism, communication circuit, and the like.
The carrier particles in development station 58 may be any suitable magnetized carrier particles for charging the part material, such as carrier particles having strontium ferrite cores with polymer coatings. The cores are typically larger in size than the particles of the part material, such as averaging from about 20 micrometers to about 40 micrometers in diameter. The polymer coatings may vary depending on the Q/M ratios desired for the part material. Examples of suitable polymer coatings include poly(methyl methacrylate) (PMMA) for negative charging, or poly(vinylidene fluoride) (PVDF) for positive charging. Suitable weight ratios of the part material to the carrier particles in development station or cartridge 58 include those discussed above.
Alternatively, development station 58 itself may be an interchangeable cartridge device that retains the supply of the part material. In further alternative embodiments, EP engine 12 p itself may be an interchangeable device that retains the supply of the part material.
When the part material is loaded to system 10, system 10 may then perform printing operations with the part material to print 3D parts (e.g., 3D part 80), preferably with a suitable support structure (e.g., support structure 82). The layers of each 3D part are developed from the part material with EP engine 12 p and transferred to layer transfusion assembly 20, where they are heated and transfused to each other to print the 3D parts in a layer-by-layer manner using an additive manufacturing technique.
In some preferred embodiments, a resulting 3D part is encased laterally (i.e., horizontally to the build plane) in the support structure, as shown in FIG. 4. This is believed to provide good dimensional integrity and surface quality for the 3D part while using a reciprocating build platen 68 and a nip roller 70. The resulting 3D part may exhibit visually observable layers with layer thicknesses depending on the thicknesses of the layers developed by EP engine 12 p and the nip pressure at layer transfusion assembly 20. Compositionally, the resulting 3D part includes the part material, such as the copolymer, charge control agent, heat absorber, flow control agent, and/or any additional additives.
1. Glass Transition Temperature and Heat Deflection Temperature
The glass transition temperature is determined using the classical ASTM method employing Differential Scanning calorimetry (DSC) ASTM D3418-12e1 and is reported in degrees Celsius. The test is performed with a DSC analyzer commercially available under the tradename “SEIKO EXSTAR 6000” from Seiko Instruments, Inc., Tokyo, Japan, with a 10-milligram sample of the support material copolymer. The data is analyzed using software commercially available under the tradenames “DSC Measurement V 5.7” and “DSC Analysis V5.5”, also from Seiko Instruments, Inc., Tokyo, Japan. The temperature profile for the test includes (i) 25° C. to 160° C. heating rate 10 Kelvin/minute (first heating period), (ii) 160° C. to 20° C. cooling rate 10 Kelvin/minute, and (iii) 20° C. to 260° C. heating rate 10 Kelvin/minute (second heating period). The glass transition temperature is determined using only the heat flow characteristics of the second heating period.
The heat deflection temperature is determined pursuant to ASTM D648-07.
A 0.7-gram sample of the mixture (sample powder and carrier particles) is placed onto a clean stainless steel disc, which serves as the bottom electrode in a gap plate under an applied field. This bottom plate is mounted and positioned above the rotating multi-pole magnet, and a clean top plate disc electrode is mounted securely above the bottom plate, and parallel to it, so as to provide a controlled gap of 5 millimeters between the top and bottom electrode plates, using insulating polytetrafluoroethylene (PTFE under tradename “TEFLON”) spacers at the electrodes' periphery.
The temperature is then increased from 50° C. at a rate of 5° C. per minute, allowing the sample to first soften and then flow. The rheometer measures the sample viscosity using the flow resistance of the melt to flow through a small die orifice, as a piston of the rheometer is driven through a cylinder. The rheometer records the softening point, the temperature at which flow begins, and the rate at which flow increases as a result of the temperature increase, until the cylinder is exhausted of sample melt. The rheometer also calculates the apparent viscosity in Pascal-seconds at each temperature point in the ramp. From this data, the apparent viscosity versus temperature profile can be determined.
1. A part material for printing three-dimensional parts with an electrophotography-based additive manufacturing system, the part material comprising:
a thermoplastic material having a heat deflection temperature ranging from about 100° C. to about 150° C. wherein the thermoplastic material comprises polycarpolactum (PA6), polyhexamethyleneadipamide (PA6,6), polyhexamethylenenonamide (PA6.9), polyhexamethylenesebacamide (PA6,10), polyamide 6/12 (PA6,12), polyenantholactum (PA7), polyundecanolactum (PA11), polylaurolactam (PA12), or mixtures thereof; and
a charge control agent;
wherein the part material is provided in a powder form having a D50 particle size ranging from about 5 micrometers to about 30 micrometers and having a particle size distribution with a D10 value, a D50 value and a D90 value wherein a D90/D50 particle size distribution and a D50/D10 particle size distribution are in a range of between about 1.0 and 1.4 and wherein the D90/D50 particle size distribution and the D50/D10 particle size distribution are within about 10% of each other; and
wherein the part material is configured for use in the electrophotography-based additive manufacturing system having a layer transfusion assembly for printing the three-dimensional parts in a layer-by-layer manner using heat and/or pressure.
2. The part material of claim 1, wherein the composition further comprises a heat absorber, wherein the heat absorber constitutes from about 0.5% by weight to about 10% by weight of the part material.
3. The part material of claim 1, wherein the D50 particle size ranges from about 10 micrometers to about 20 micrometers.
4. The part material of claim 1, wherein the charge control agent is selected from the group consisting of chromium oxy carboxylic acid complexes, zinc oxy carboxylic acid complexes, aluminum oxy carboxylic acid complexes, and mixtures thereof.
5. The part material of claim 1, wherein the charge control agent constitutes from about 0.1% by weight to about 5% by weight of the part material.
6. The part material of claim 1, wherein the composition further comprises a flow control agent constituting from about 0.1% by weight to about 10% by weight of the part material.
7. The part material of claim 1, wherein the polyamide comprises PA6; PA6,6; PA6,12; PA11; polylaurolactam (PA12), or mixtures thereof.
8. The part material of claim 1, wherein the part material is triboelectrically charged to a Q/M ratio having a negative charge or a positive charge.
9. The part material of claim 8, wherein the magnitude of the Q/M ratio ranges from about 5 micro-Coulombs/gram to about 50 micro-Coulombs/gram.
10. The part material of claim 1, wherein the part material is in an uncharged state until mixing with carrier particles.
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