阅读说明：本技术 三维打印 (Three-dimensional printing ) 是由 K·J·埃里克森 P·奥卢班莫 A·哈特曼 L·赵 于 2018-03-15 设计创作，主要内容包括：一种三维打印系统可包括聚合物构建材料和一种或多种可喷射流体。聚合物构建材料可具有20μm至150μm的平均粒度、第一熔体粘度和75℃至350℃的熔融温度。在一个实例中,可喷射流体可包含水、0.1重量％至10重量％的电磁辐射吸收剂和10重量％至35重量％的有机溶剂增塑剂。使聚合物构建材料层的第一部分与可喷射流体接触可提供基于聚合物构建材料含量计2重量％至10重量％的有机溶剂增塑剂载量。可降低位于第一部分的聚合物构建材料的第一熔体粘度,并可将位于第一部分的聚合物构建材料的熔融温度降低3℃至15℃。(A three-dimensional printing system may include a polymeric build material and one or more ejectable fluids. The polymer build material can have an average particle size of 20 μm to 150 μm, a first melt viscosity, and a melting temperature of 75 ℃ to 350 ℃. In one example, the jettable fluid may include water, 0.1 wt% to 10 wt% of an electromagnetic radiation absorber, and 10 wt% to 35 wt% of an organic solvent plasticizer. Contacting the first portion of the layer of polymeric build material with the jettable fluid can provide an organic solvent plasticizer loading of 2 wt% to 10 wt% based on the polymeric build material content. The first melt viscosity of the polymer build material located in the first portion can be reduced, and the melting temperature of the polymer build material located in the first portion can be reduced by 3 ℃ to 15 ℃.)

1. A three-dimensional printing system, comprising:

a polymeric build material having an average particle size of 20 μ ι η to 150 μ ι η, a first melt viscosity, and a melting temperature of 75 ℃ to 350 ℃; and

a jettable fluid comprising water, 0.1 wt% to 10 wt% of an electromagnetic radiation absorber, and 10 wt% to 35 wt% of an organic solvent plasticizer, wherein after contacting a first portion of a layer of a polymer build material with the jettable fluid to provide a loading of the organic solvent plasticizer in the polymer build material of 2 wt% to 10 wt%, a first melt viscosity of the polymer build material located in the first portion is reduced to a second melt viscosity, and a melting temperature of the polymer build material located in the first portion is reduced by 3 ℃ to 15 ℃.

2. The three-dimensional printing system of claim 1, wherein the electromagnetic radiation absorber is an infrared absorbing colorant, a near-infrared absorbing colorant, or a colorant in the visible spectrum.

3. The three-dimensional printing system of claim 1, further comprising an electromagnetic radiation source to direct electromagnetic radiation toward the top layer of the polymeric build material, wherein the electromagnetic radiation source emits energy at a wavelength to generate heat with the electromagnetic radiation absorber.

4. The three-dimensional printing system of claim 1, wherein the organic solvent plasticizer is p-toluene sulfonamide, m-toluene sulfonamide, o-toluene sulfonamide, urea, ethylene carbonate, propylene carbonate, diethylene glycol, triethylene glycol, tetraethylene glycol, methyl 4-hydroxybenzoate, dimethyl sulfoxide, dioctyl phthalate, gamma-butyrolactone, or mixtures thereof; and wherein the polymeric build material is nylon 6, nylon 8, nylon 9, nylon 11, nylon 12, nylon 66, nylon 612, nylon 812, polyethylene terephthalate (PET), polystyrene, polyacrylate, polyacetal, polypropylene, polycarbonate, polyester, acrylonitrile butadiene styrene, thermoplastic polyurethane, engineering plastic, Polyetheretherketone (PEEK), polymer blends thereof, amorphous polymers thereof, core shell polymers thereof, and copolymers thereof.

5. The three-dimensional printing system of claim 1, wherein the polymeric build material located in the first portion of the layer establishes T when also loaded with 0.05 wt% to 2 wt% of the electromagnetic radiation absorber based on the polymeric build material content_maxAn overbonding temperature and a temperature process window, wherein the temperature process window is from T_maxThe excessive sintering temperature is extended to a ratio T_maxThe excessive sintering temperature is 5 ℃ to 20 ℃ lower.

6. A three-dimensional printing system, comprising:

a polymeric build material having an average particle size of 20 μ ι η to 150 μ ι η, a first melt viscosity, and a melting temperature of 75 ℃ to 350 ℃;

a sprayable fritting fluid comprising water and 0.1 wt% to 10 wt% of an electromagnetic radiation absorber; and

a sprayable plasticizing fluid including water and 10 wt% to 35 wt% of an organic solvent plasticizer,

wherein after contacting the first portion of the layer of polymer build material with the ejectable sintering fluid and the ejectable plasticizing fluid to provide an organic solvent plasticizer loading of 2 wt% to 10 wt% based on the polymer build material content, the first melt viscosity of the polymer build material located in the first portion is reduced to a second, lower melt viscosity, and the melting temperature of the polymer build material located in the first portion is reduced by 3 ℃ to 15 ℃.

7. The three-dimensional printing system of claim 6, wherein the electromagnetic radiation absorber is an infrared absorbing colorant, a near-infrared absorbing colorant, or an energy absorbing colorant in the visible spectrum.

8. The three-dimensional printing system of claim 6, further comprising an electromagnetic radiation source to direct electromagnetic radiation toward the top layer of the polymeric build material, wherein the electromagnetic radiation source emits energy at a wavelength to generate heat with the electromagnetic radiation absorber.

9. The three-dimensional printing system of claim 6, wherein the organic solvent plasticizer is p-toluene sulfonamide, m-toluene sulfonamide, o-toluene sulfonamide, urea, ethylene carbonate, propylene carbonate, diethylene glycol, triethylene glycol, tetraethylene glycol, methyl 4-hydroxybenzoate, dimethyl sulfoxide, dioctyl phthalate, gamma-butyrolactone, or mixtures thereof; and wherein the polymeric build material is nylon 6, nylon 8, nylon 9, nylon 11, nylon 12, nylon 66, nylon 612, nylon 812, polyethylene terephthalate (PET), polystyrene, polyacrylate, polyacetal, polypropylene, polycarbonate, polyester, acrylonitrile butadiene styrene, thermoplastic polyurethane, engineering plastic, Polyetheretherketone (PEEK), polymer blends thereof, amorphous polymers thereof, core shell polymers thereof, and copolymers thereof.

10. The three-dimensional printing system of claim 6, wherein the polymeric build material located in the first portion of the layer establishes T when also loaded with 0.05 wt% to 2 wt% of the electromagnetic radiation absorber based on the polymeric build material content_maxAn overbonding temperature and a temperature process window, wherein the temperature process window is from T_maxThe excessive sintering temperature is extended to a ratio T_maxThe excessive sintering temperature is 5 ℃ to 20 ℃ lower.

11. A three-dimensional printing method, comprising:

forming a layer of 40 μ ι η to 300 μ ι η of a polymeric build material on a build substrate, wherein the polymeric build material has an average particle size of 20 μ ι η to 150 μ ι η, a melting temperature of 75 ℃ to 350 ℃, and a melt viscosity;

selectively spraying an electromagnetic radiation absorber and an organic solvent plasticizer onto a first portion of a layer of polymeric build material such that the electromagnetic radiation absorber and the organic solvent plasticizer contact the first portion at an organic solvent plasticizer loading of 2 wt% to 10 wt% based on the polymeric build material content; and

electromagnetic radiation of a wavelength is directed at the layer of polymeric build material such that a radiation absorber located at the first portion increases a temperature of the polymeric build material to a temperature higher than a region of the layer of polymeric build material outside the first portion, wherein the first portion of the layer has a lower melting temperature and a lower melt viscosity that varies relative to the region of the layer of polymeric build material outside the first portion due to the presence of the organic solvent plasticizer.

12. The method of claim 11, further comprising preheating the polymeric build material to within 4 ℃ to 30 ℃ below the altered lower melting temperature prior to exposing the layer of polymeric build material to electromagnetic radiation.

13. The method of claim 11, further comprising:

adding a second layer of polymeric build material onto the layer after the layer of polymeric build material is melted;

selectively applying an electromagnetic radiation absorber and an organic solvent plasticizer onto a second portion of a second layer of polymeric build material; and

electromagnetic radiation is directed to the second layer of the polymeric build material.

14. The method of claim 11 wherein the organic solvent plasticizer has a vapor pressure of 0mmHg to 25mmHg at 170 ℃.

15. The method of claim 11, wherein the electromagnetic radiation absorber and the organic solvent plasticizer added to the layer of polymeric build material are each selectively jettable by separate jettable fluids.

Brief Description of Drawings

FIG. 1 illustrates an exemplary three-dimensional printing system according to the present disclosure;

FIG. 2 schematically illustrates a viscoelastic coalescence model according to the present disclosure;

fig. 3 provides an exemplary graph illustrating the effect of an organic solvent plasticizer on viscosity vs temperature according to the present disclosure;

FIG. 4 provides one example illustrating the melting temperature of polyamide-12 relative to an increased loading of organic solvent plasticizer according to the present disclosure;

fig. 5 depicts an exemplary density scan calorimetry map in accordance with the present disclosure;

FIG. 6 is a flow chart of an exemplary method of the present disclosure;

figure 7 schematically illustrates, by an exemplary graph, the improved selectivity over voxels processed with organic solvent plasticizers compared to voxels (voxels) without plasticizer applied according to the present disclosure;

FIG. 8 schematically illustrates a thermographic area of a build material bed or substrate with and without an organic solvent plasticizer according to the present disclosure, including a fusion deficient site, a high density fusion site, and an overbusion site; and

fig. 9 provides a black and white thermal image of a bed or substrate of build material including under-sintered sites (black) and high density sintered sites (white) according to the present disclosure.

Detailed description of the invention

The present disclosure relates to three-dimensional (3D) printing systems and methods. More particularly, the system and method can be used for Light Area Processing (LAP) or multi-jet fusion (MJF), where the polymeric build material (granules or powder) is spread layer-by-layer on a powder bed support. The various layers are contacted with one or more jetting fluids comprising an electromagnetic radiation absorber and an organic solvent plasticizer. The two components may be formulated, for example, in a common aqueous liquid vehicle (aqueous liquid vehicle), or may be formulated in separate aqueous liquid vehicles. In either case, the electromagnetic radiation absorber and the organic solvent plasticizer may be applied together onto a first portion of the layer of polymeric build material (leaving another portion of the layer untouched by the electromagnetic radiation absorber and the organic solvent plasticizer). One or more jetting fluids may be ejected from a printhead, such as a fluid ejector similar to, for example, an inkjet printhead, and then the layer (first portion and other portions) may be exposed to electromagnetic radiation to heat the layer of build material, particularly at the first portion. This can be repeated layer by layer until a three-dimensional object is formed. Thus, the layer of polymeric build material, including the first portion and the other portions, may be substantially indiscriminately exposed to electromagnetic radiation, but due to the presence of the electromagnetic radiation absorber, light energy absorbed at the first portion of the layer is converted to thermal energy to melt or coalesce the first portion, while the other portions do not. Further, in accordance with examples of the present disclosure, the first part exhibits a reduced melt viscosity and melting temperature as compared to the pure or virgin polymer build material outside of the first part due to the presence of the organic solvent plasticizer.

Accordingly, the present disclosure is directed to a three-dimensional printing system that can include a polymeric build material having an average particle size of 20 μ ι η to 150 μ ι η, a first melt viscosity, and a melting temperature of 75 ℃ to 350 ℃. The system may also include a sprayable fluid comprising water, 0.1 wt% to 10 wt% of an electromagnetic radiation absorber, and 10 wt% to 35 wt% of an organic solvent plasticizer. Thus, the jettable fluid is both a sintering fluid and a plasticizing fluid. After contacting the first portion of the layer of polymeric build material with the ejectable fluid to provide an organic solvent plasticizer loading of 2 wt% to 10 wt% based on the polymeric build material content, the first melt viscosity of the polymeric build material located in the first portion can be lowered to a second, lower melt viscosity, and the melting temperature of the polymeric build material located in the first portion can also be lowered by 3 ℃ to 15 ℃.

In another example, a three-dimensional printing system can include a polymeric build material having an average particle size of 20 μ ι η to 150 μ ι η, a first melt viscosity, and a melting temperature of 75 ℃ to 350 ℃. The system may further include a sprayable fritted fluid comprising water and 0.1 wt% to 10 wt% of an electromagnetic radiation absorber and a (separate) sprayable plasticizing fluid comprising water and 10 wt% to 35 wt% of an organic solvent plasticizer. After contacting the first portion of the layer of polymeric build material with the ejectable sintering fluid and the ejectable plasticizing fluid (providing an organic solvent plasticizer loading of 2 wt% to 10 wt% based on the polymeric build material content), the first melt viscosity of the polymeric build material located in the first portion can be reduced to a second, lower melt viscosity and the melting temperature of the polymeric build material located in the first portion can be reduced by 3 ℃ to 15 ℃.

In any of these three-dimensional printing systems, whether the electromagnetic radiation absorber and organic solvent plasticizer are in the same jetting fluid or in two separate jetting fluids, there can be several other features available for either system. For example, the electromagnetic radiation absorber can be an infrared absorbing colorant, a near infrared absorbing colorant, or an energy absorbing colorant in the visible spectrum, such as a carbon black pigment. In another example, the three-dimensional printing system can further include an electromagnetic radiation source that can direct electromagnetic radiation toward the polymer buildA top layer of material. The electromagnetic radiation source may emit energy at a wavelength to generate increased heat with, for example, an electromagnetic radiation absorber, which may cause the area it prints to generate more heat than the area outside the printed area (of the electromagnetic radiation absorber and organic solvent plasticizer). In more detail, the organic solvent plasticizer may be p-toluenesulfonamide, m-toluenesulfonamide, o-toluenesulfonamide, urea, ethylene carbonate, propylene carbonate, diethylene glycol, triethylene glycol, tetraethylene glycol, methyl 4-hydroxybenzoate, dimethyl sulfoxide, dioctyl phthalate, γ -butyrolactone, or a mixture thereof. The polymer build material may be nylon 6, nylon 8, nylon 9, nylon 11, nylon 12, nylon 66, nylon 612, nylon 812, polyethylene terephthalate (PET), polystyrene, polyacrylate, polyacetal, polypropylene, polycarbonate, polyester, acrylonitrile butadiene styrene, thermoplastic polyurethane, engineering plastic, Polyetheretherketone (PEEK), polymer blends thereof, amorphous polymers thereof, core shell polymers thereof, and copolymers thereof. In some examples, a polymeric build material located in a first portion of the layer can exhibit a T when loaded with 0.05 wt% to 2 wt% of an electromagnetic radiation absorber (and 2 wt% to 10 wt% of an organic solvent plasticizer), based on the polymeric build material content_maxOver-sintering temperature (over-sintering temperature) and from T_maxThe excessive sintering temperature is extended to a ratio T_maxThe excessive sintering temperature is lower than the processing window of the temperature of 5 ℃ to 20 ℃.

In another example, a three-dimensional printing method can include forming a 40 μm to 300 μm layer of a polymeric build material on a build substrate and selectively jetting an electromagnetic radiation absorber and an organic solvent plasticizer onto a first portion of the layer of polymeric build material such that the electromagnetic radiation absorber and the organic solvent plasticizer contact the first portion at an organic solvent plasticizer loading of 2 wt% to 10 wt% based on the polymeric build material content. The polymer build material can have an average particle size of 20 μm to 150 μm, a melting temperature of 75 ℃ to 350 ℃, and a melt viscosity. The method may further include directing electromagnetic radiation at a wavelength to the layer of polymeric build material such that a radiation absorber located at the first portion increases a temperature of the polymeric build material to a temperature higher than a region of the layer of polymeric build material outside the first portion, wherein the first portion of the layer has a modified lower melting temperature and a modified lower melt viscosity as compared to the region of the layer of polymeric build material outside the first portion due to the presence of the organic solvent plasticizer. In one example, the melt viscosity of the polymer build material located in the first portion (where the electromagnetic radiation absorber and organic solvent plasticizer are printed) can be reduced to a lower melt viscosity, and the melting temperature of the polymer build material located in the first portion (where printed) can be reduced by 3 ℃ to 15 ℃.

The method may further include preheating the polymeric build material to within 4 ℃ to 30 ℃ below the altered lower melting temperature prior to exposing the layer of polymeric build material to electromagnetic radiation. In more detail, the method may further include adding a second layer of polymeric build material onto the layer of polymeric build material after the layer melts, selectively applying an electromagnetic radiation absorber and an organic solvent plasticizer onto a second portion of the second layer of polymeric build material, and directing electromagnetic radiation toward the second layer of polymeric build material, similar to that described for the previously applied layer therebelow. In one example, the organic solvent plasticizer may have a vapor pressure of 0mmHg to 25mmHg at 170 ℃. In another example, the electromagnetic radiation absorber and the organic solvent plasticizer may be selectively applied to the layer of polymeric build material by separate jettable fluids, such as by separate fluid-jet pens. The method may also use some of the same electromagnetic radiation absorbers, organic solvent plasticizers, and polymeric build materials described herein.

It is noted that when discussing the three-dimensional printing system and method of the present disclosure, each of these discussions can be considered applicable to other examples, whether or not they are explicitly discussed in the context of that example. Thus, for example, while polymer build materials are discussed with respect to three-dimensional printing systems, such disclosure is also relevant to and directly supported in the context of other systems and methods, and vice versa.

In more detail, an exemplary three-dimensional printing system is shown at 100 in fig. 1 and may include, for example, a polymer build material 106 (sometimes referred to as a powder bed), a powder bed support 108 or platform (typically having sidewalls to retain the powder build material therein), a fluid ejector 110, an electromagnetic radiation source 112 (shown as two lamps that are movable laterally with the fluid ejector via a carriage), and a powder material source 118. Also shown is a second fluid ejector 110B (which may carry a second ejectable fluid) and a second electromagnetic radiation source 112B (which in this example may be a stationary lamp that does not move laterally). For reference, a printed article 114 is shown in fig. 1, which may be printed using a layer-by-layer printing method. For example, a new "layer" of build material is shown at 116. The jetting fluid 120 is also shown as being ejected from the fluid ejector 110, and in some cases, a second jetting fluid 122 may also be ejected separately, for example, from the fluid ejector 110B. The jetting fluid may comprise an electromagnetic radiation absorber and an organic solvent plasticizer, or the jetting fluid may comprise an electromagnetic radiation absorber and the second jetting fluid may comprise an organic solvent plasticizer, or vice versa. If the jetting fluid contains an electromagnetic radiation absorber without an organic solvent plasticizer, it may be more specifically referred to as a "jet sinterable fluid". Likewise, if the jetting fluid contains an organic solvent plasticizer and does not contain an electromagnetic radiation absorber, it may be more specifically referred to as a "jettable plasticizing fluid". Either may be more generally referred to as "jetting fluid", and a fluid containing both may also be referred to as "jetting fluid".

As shown, the powder bed support 108 and the stacked layer of polymeric build material 106 can support the various layers of the article during the build process. For example, the powder source may lay down a thin layer 116 of, for example, 20 μm to 150 μm of polymeric build material on a powder bed support or a previously applied layer of polymeric build material. The one or more fluid ejectors may then eject one or more ejectable fluids on selected surface areas of the powder bed material. The electromagnetic radiation source may provide pulsed or non-pulsed optical energy of sufficient intensity and wavelength coordinated to generate heat at the polymer build material and the jettable fluid. For example, a scanning lamp energy source may be provided by one or more high wattage bulbs. Non-limiting examples of bulbs can be 400 watts to 2000 watts, such as a pair of 750 watt IR bulbs. The jettable fluid may be a single fluid or may be a plurality of fluids. In either case, however, one or more ejectable fluids transport both the electromagnetic radiation absorber (or binder) and the organic solvent plasticizer to the polymeric build material. Thus, a portion of the polymer build material may be fused and the regions other than where the one or more ejectable fluids are applied may remain free-flowing or substantially free-flowing (e.g., they do not become part of the three-dimensional object or part being fabricated). The powder bed support may thus receive the polymeric build material, which is then flattened by rollers or other mechanical devices, and then, after printing, may be printed and sintered thereon to allow for superposition to form subsequent layers of the article to be built. The fluid ejectors are operable to selectively deposit one or more ejectable fluids onto a polymeric build material contained in or on a substrate. The fluid ejectors are operable to selectively apply one or more patterns of ejectable fluid onto the polymeric build material. As mentioned, a three-dimensional printing system may include multiple fluid ejectors, such as when multiple fluids are to be applied to a polymer build material. The one or more fluid ejectors may be any type of printing device capable of selectively applying one or more ejectable fluids. For example, the one or more fluid ejectors may be inkjet applicators (thermal, piezoelectric, etc.), sprayers, and the like.

In more detail, the electromagnetic radiation source (or light source) can generate a pulse energy that can be sufficient to melt or fuse a portion of a large (large) polymeric build material, but not so high as to fuse regions that do not first contact the one or more jettable fluids. The pulse energy may cause heat to be generated within a wider temperature processing window than a system that does not include the organic solvent plasticizer at the concentrations and weight ratios relative to the polymer build material described herein. In more detail, LAP or MJF three-dimensional printing can typically be performed using a tightly controlled thermal process with a relatively small window of thermal machining tolerances to produce consistent high density quality parts. Outside of these narrow tolerance windows, which can be introduced by thermal non-uniformities on the polymeric build material layer, part non-uniformities can occur. Some causes of thermal non-uniformity may include cooler edges of the build bed base, non-uniformity of lamp irradiance on the build bed base, non-uniformity of powder height and packing in the build bed base, print related effects such as part size and separation distance, etc. These inconsistencies may affect part fusion, density, mechanical properties, etc. According to examples herein, an organic solvent plasticizer may be included in the jettable fluid (either with the electromagnetic radiation absorber or in a separate jettable fluid) to reduce the viscosity of the polymer melt and to reduce the target polymer, such as the melting point of the polymer build material used.

Sintering of small polymer particles, for example, averaging 20 to 150 μm, can be performed by bringing the polymer particles to a melting point and consolidating the powder into a part via a viscosity reduction that allows the molten polymer to flow. In the present disclosure, the addition of an organic solvent plasticizer at an appropriate concentration or weight ratio relative to the polymer build material, e.g., 2 to 10 weight percent or 2.7 to 8 weight percent based on the polymer build material content, can improve powder sintering by increasing the selectivity of the polymer build material with the plasticizer present, as compared to the polymer build material in the absence of the plasticizer. Thus, the temperature range for processing the printed part may have an effectively larger temperature processing window (or sintering window) because the melt flow and melting temperature is reduced compared to the unprinted powder bed material. The term "temperature process window" or "sintering window" refers to the size of the temperature range achieved during the hottest portion of the printing process within which a component can be successfully printed. These terms may be further defined as: i) without excessive sintering, which can be expressed as having a dimensional inaccuracy of > 3% (swelling) relative to the original intended part geometry (no thermal sheet); and ii) more than 95% dense (0.95 density fraction). For larger process windows, more parts with < 3% dimensional inaccuracy and > 95% density can be successfully printed when the "thermal uniformity window" of the polymer build material is equal to or less than the "temperature process window". "thermal uniformity window" can be defined as the T within the powder bed area within the 1/2 inch boundary from the powder bed support wall_maxAnd T_minThe difference in temperature. There tends to be less uniform heating near the wall, so the Tmax to Tmin range near the wall is a good point to test whether there is reasonable uniformity across substantially the entire powder bed. Thus, if lower thermal uniformity of the polymer build material results in a larger "thermal uniformity window," establishing a larger "temperature processing window" using the methods outlined herein can successfully print a larger number of parts as specified by having < 3% dimensional inaccuracy and > 95% density.

In more detail, the sintering window is set at T_maxExtending about 2 ℃ to about 8 ℃ below the (overbelting) temperature provides several practical advantages that can be achieved as described in more detail below. Thus, processing temperatures below the melting temperature of the pure (or virgin) polymer build material to temperatures still above the melting temperature of the polymer build material can be used (due to the presence of the organic solvent plasticizer) to produce higher density parts over a wider temperature range. In other words, it may still be desirable to perform temperature processing above the melting temperature of the pure polymer build material. Therefore, it is to be avoided that T_max(maximum) temperature, which is not the melting temperature but a temperature at which excessive sintering occurs, which is generally above the melting temperature. When the finished part swells in size by at least 3% due to excessive heating, it can be defined as "overbelting". It is beneficial to reach a temperature above the melting temperature of the neat polymer build material because melt viscosity is greatly correlated with temperature, and thus with exceeding the melting temperature, but still remaining (to as great an extent as possible) below T_maxMethods that involve excessive sintering temperatures may provide poorer consolidation or material or part densities than methods that involve heating to temperatures below the original polymer melt temperature.

For clarity, it is true that high density parts can be made without organic solvent plasticizers, but the temperature processing window and processing error tolerance are typically narrow; while by adding an organic solvent plasticizer, lower temperatures can be used to provide below T_maxA larger temperature window for the excessive sintering temperature. Furthermore, even when processed above the typical melting temperature of a pure polymeric build material, the more spatial the processing temperature error or temperature variability introduced by the presence of natural inhomogeneitiesLarger, it is also easier to produce higher density parts. In addition, due to this larger process temperature range and reduced effects of non-uniformity, high density features can generally be formed over a larger area of the build bed base (see examples 2 and 3). In more detail, the use of organic solvent plasticizers as described herein may, in some cases, allow for better processing of small features (features) within the component. The benefits of reduced melting point and lower viscosity allow for higher density parts that can produce small features even with good resolution, since higher temperatures (within a small temperature processing window) are more difficult to achieve for small features during the build process without "overburning" the large features.

As schematically illustrated, coalescence of a polymer build material (or powder bed material) can be understood by a viscoelastic coalescence model, where the driving force for coalescence is a reduction in surface energy. This is illustrated in FIG. 2 and is further illustrated by equation I as follows:

x²/α＝1.5(γ/η)·t

(formula I)

In formula I, γ is the surface energy; η is the viscosity; and t is time. x and a are illustrated in fig. 2 by way of example. The dotted line represents the original size of the particles and the solid line represents the particle size after coalescence or sintering (or upon sintering).

In more detail, coalescence as shown in fig. 2 may be limited by the viscosity of the polymer particles prior to melting. However, when the melting point of the polymer is reached or exceeded, the viscosity tends to decrease dramatically, so that further sintering/coalescence occurs. Thus, according to examples of the present disclosure, an organic solvent plasticizer may reduce the viscosity of polymer particles of a build material in a melt as schematically illustrated in fig. 2, and may also actually reduce the melting point of the polymer as illustrated in fig. 3. In more detail, the graph in FIG. 3 can be further described in equation II as follows:

organic solvent plasticizer loading promotion η ↓↑

Improved coalescence → density ↓ ≈ particle

(formula II)

Wherein η is the viscosity of the oil,is the partial derivative operator and x is the dimension as shown in fig. 2.

Both mechanisms are effective in improving the selectivity of voxels (pixels in three-dimensional space with a z-axis defined by the build material layer depth) to which the organic solvent plasticizer is applied, thereby increasing the fusion and density of the part even at lower temperatures and/or wider temperature processing windows than would otherwise be available. Figures 3 and 4 further illustrate these improved processing properties. The values provided therein are merely examples to illustrate the concept of reduced melt viscosity and melting temperature and thus providing a larger temperature processing window and/or lower temperature processing, as desired. FIG. 4 specifically provides an example of polyamide-12 (PA-12 or nylon-12), and by increasing the concentration of organic solvent plasticizer, the melting temperature of the build material (as a composite of build material + plasticizer) is decreased, and the recrystallization temperature is also decreased relatively linearly. These weight percentages in fig. 4 represent the amount of plasticizer in the finished part. By way of further note, the plasticizer used in this example was toluene sulfonamide, but also included an additional co-solvent, 2-pyrrolidone. 2-pyrrolidone (or other derivatives of 2-pyrrolidone, such as N-2-hydroxyethyl-2-pyrrolidone or N-methyl-2-pyrrolidone) can be added as a co-solvent, but is not generally used as a plasticizer according to examples of the present disclosure due to its relatively high vapor pressure.

A schematic illustration of these principles is shown in more detail in fig. 5. The selectivity, for example the melting temperature (T), is improved here in voxels treated with organic solvent plasticizers compared with voxels without plasticizer application_m) Recrystallization temperature (T)_c) And (4) descending. As illustrated, for more significant effects, organic solvent extenders in the weight percent and weight ratio ranges described herein, e.g., 10 to 35 weight percent organic solvent plasticizer in the jettable fluid and/or 2 to 10 weight percent organic solvent extender (based on polymer build material content) in the polymer build material can be usedHigher loading of plasticizer loading.

In more detail, fig. 5 shows a density scanning calorimetry plot with two peaks, one melting peak at higher temperatures and one recrystallization peak at lower temperatures. In this figure, T₀Refers to the temperature at which the layer can begin to be processed (or printed) immediately after spreading. T is_jf(jetting fluid) refers to the lower temperature of the fluid jet patterned portion of the layer of polymeric build material after the jetting fluid is applied. T is_SinteringRefers to the temperature after the passage of the sintered lamp, which may be or may be the maximum temperature during the build process. Followed by the occurrence of T_{Layer finishing}And represents the temperature before the next powder layer is spread thereon. Furthermore, T_{Component finishing}Refers to the temperature of the part before it is removed from the powder bed (or allowed to cool slowly uniformly). As an annotation, the higher of the two peaks shown in this scanning calorimetry trace represents the melting peak.

In more detail, it has been found that adding too much plasticizer in the finished part results in some mechanical property degradation, so lower loadings are unexpectedly suitable for extending the temperature processing window without degrading the mechanical properties of the finished part. In other words, not too much organic solvent plasticizer loading in the polymer build material can lead to large processing window improvements (while not sacrificing other mechanical properties). For example, the organic solvent plasticizer loading in the polymeric build material can be from about 2 wt% to about 10 wt%, from about 2.7 wt% to about 8 wt%, and these low amounts can provide the benefits described herein. Furthermore, applying too much jetting fluid to the polymer build material will reduce the part temperature too much (creating too much evaporative cooling), so it is reasonable to use as much organic solvent plasticizer in the jetting fluid as feasible, and then apply a lower volume of jetting fluid to the polymer build material. The minimum fluid volume suitable for sufficiently wetting the powder build material to function can be established experimentally. As one example, a range of organic solvent plasticizers in the jetting fluid can be printed at levels of 64 to 196Contone (CL). For example (For permanent), a contone level of 255 is used For full black printing (full black-out printing), which is associated with 9pL drops (along the x and y axes) per 1200dpi space. These values assume that a 21 wt% loading of organic solvent plasticizer (e.g., a mixture of ortho and para-toluene sulfonamide) in the fluid is used in the jetting fluid.

In still more detail, if too much organic solvent plasticizer is loaded into the jetting fluid, the plasticizer may not be soluble enough to remain dissolved and may precipitate out. Thus, according to examples of the present disclosure, the plasticizer content in the jettable (plasticizer) fluid may be 10 wt% to 35 wt%, 15 wt% to 30 wt%, or 20 wt% to 30 wt%. In other examples, if an organic solvent plasticizer having a low boiling point/high vapor pressure, e.g., 0mmHg to 25mmHg at 170 ℃, is used, the organic solvent plasticizer cannot remain in the part during the build process. The tosylamide (plasticizer) has a vapor pressure vs. 2-pyrrolidone (co-solvent) of 317mmHg at 170 ℃ of 0.75mmHg, meaning that a significant amount of 2-pyrrolidone is volatilized during printing, while the tosylamide is not volatilized. Thus, in some cases, 2-pyrrolidone, although it has a plasticizing effect, is not considered a plasticizer in the relatively high to high melting temperature range used herein, e.g., 75 ℃ to 350 ℃. That is, for simplicity, the vapor pressure value may be specified herein as being measured at 170 ℃. As also noted, the melting temperature of the polymer build material with organic solvent can be lowered by 3 ℃ to 15 ℃, 3.5 ℃ to 12 ℃, or 3.5 ℃ to 11.3 ℃, which is also discussed above as being effective to enhance the temperature processing window. For example, at a 2.7 wt.% to 8 wt.% toluene sulfonamide (mixture of ortho and para toluene sulfonamides) loading in the polymeric build material, the melt temperature can be reduced by 3.5 ℃ to 11.3 ℃ for a nylon 12(PA 12) polymeric build material and a carbon black pigment electromagnetic radiation absorber applied to the same area at about 0.5 wt.%.

Turning now to more details regarding materials that may be used in the three-dimensional printing systems and methods described herein, the polymeric build material may be, for example, a particulate material or a powder. As mentioned, the average particle size may be from 20 μm to 150 μm, but may also be from 50 μm to 125 μm, or from 60 μm to 100 μm. Examples of polymeric build materials include semi-crystalline thermoplastic materials having a relatively wide temperature difference between the melting point and recrystallization, e.g., greater than 5 ℃. Some specific examples of polymeric build materials in powder or granular form may include polyamides (PA or nylon), such as nylon 6(PA 6), nylon 8(PA 8), nylon 9(PA 9), nylon 11(PA11), nylon 12(PA 12), nylon 66(PA 66), nylon 612(PA 612), nylon 812(PA 812), and other polyamides. Other specific examples of particulate or powder polymer build materials include polyethylene, polyethylene terephthalate (PET), polystyrene, polyacrylates, polyacetals, polypropylene, polycarbonates, polyesters, acrylonitrile butadiene styrene, thermoplastic polyurethanes, other engineering plastics, other high performance plastics such as Polyetheretherketone (PEEK), and blends of any two or more of the polymers listed herein, and, if available, amorphous forms of these polymers. Core shell polymer particles of these materials may also be used.

The polymer build material can have a melting point of about 75 ℃ to about 350 ℃, 100 ℃ to 300 ℃, or 150 ℃ to 250 ℃. As an example, the polymeric build material may be a polyamide having a melting point of about 170 ℃ to 190 ℃, or a thermoplastic polyurethane having a melting point of about 100 ℃ to about 165 ℃. Various thermoplastic polymers having melting or softening points within these ranges may be used. For example, the particulate polymer may be selected from nylon 6, nylon 8, nylon 9, nylon 11, nylon 12, nylon 66, nylon 612, nylon 812, polyethylene terephthalate (PET), polystyrene, polyacrylate, polyacetal, polypropylene, polycarbonate, polyester, acrylonitrile butadiene styrene, thermoplastic polyurethane, engineering plastics, Polyetheretherketone (PEEK), polymer blends thereof, amorphous polymers thereof, core shell polymers thereof, and copolymers thereof. In one particular example, the particulate polymer may be nylon 12, which may have a melting point of about 175 ℃ to about 200 ℃.

The polymer build material may be composed of particles of similar size or particles of different sizes. The term "size" or "average particle size" is used herein to describe the diameter or average diameter, which may vary with the morphology of the individual particles. In one example, each particle may have a substantially spherical morphology. Substantially spherical particles (e.g., spherical or nearly spherical) have a sphericity > 0.84. Thus, any single particle with a sphericity of < 0.84 is considered to be non-spherical (irregular shape). The size of the substantially spherical particles may be provided by their diameter, and the size of the non-spherical particles may be provided by their average diameter (i.e. the average of a plurality of sizes across the particle) or effective diameter (which is the diameter of a sphere having the same mass and density as the non-spherical particles).

It is to be understood that the polymer build material may comprise a charging agent, a glidant, or a combination thereof, in addition to the polymer particles. One or more charging agents may be added to inhibit triboelectric charging. Examples of suitable one or more charging agents include aliphatic amines (which may be ethoxylated), aliphatic amides, quaternary ammonium salts (e.g., behenyltrimethylammonium chloride or cocamidopropyl betaine), esters of phosphoric acid, polyethylene glycol esters, or polyols. Some suitable commercially available charging agents includeFA 38 (natural based ethoxylated alkylamine),FE2 (fatty acid ester) andHS 1 (alkane sulfonate), each from Clariant int.ltd. In one example, the charging agent can be added in an amount of greater than 0 wt% to 5 wt% based on the total wt% of the polymeric build material. One or more glidants may be added to improve the coating flow of the polymer build material. One or more glidants may be particularly desirable when the particles of the polymer build material are at the smaller end of the particle size range. Glidants can improve the flowability of a polymer build material by reducing friction, lateral drag (by increasing particle conductivity), and triboelectric charge buildup. Examples of suitable glidants include tricalcium phosphate (E341), powdered cellulose (E460(ii)), magnesium stearate (E470b), sodium bicarbonate(E500) Sodium ferrocyanide (E535), potassium ferrocyanide (E536), calcium ferrocyanide (E538), bone phosphate (E542), sodium silicate (E550), silica (E551), calcium silicate (E552), magnesium trisilicate (E553a), talc (E553b), sodium aluminosilicate (E554), potassium aluminum silicate (E555), calcium aluminosilicate (E556), bentonite (E558), aluminum silicate (E559), stearic acid (E570), or polydimethylsiloxane (E900). In one example, the glidant may be added in an amount greater than 0 wt% to less than 5 wt% based on the total wt% of the polymeric build material.

To reduce the melt viscosity and melting temperature of the polymer build material and thus expand the temperature processing window of printable high density components (typically with higher density uniformity), as mentioned, organic solvent plasticizers can be printed in areas that generally coincide with the locations of electromagnetic radiation absorbers. The organic solvent plasticizer may be, for example, p-toluenesulfonamide, m-toluenesulfonamide, o-toluenesulfonamide, urea, ethylene carbonate, propylene carbonate, diethylene glycol, triethylene glycol, tetraethylene glycol, methyl 4-hydroxybenzoate, dimethyl sulfoxide, dioctyl phthalate, γ -butyrolactone, or a mixture thereof. The organic solvent plasticizer may be present in the jettable fluid (with or without the electromagnetic radiation absorber) at 10 wt% to 35 wt%, 15 wt% to 30 wt%, or 20 wt% to 30 wt%; and may be delivered to the layer of polymeric build material at a loading of 2 wt% to 10 wt%, 2.7 wt% to 8.8 wt%, or 3 wt% to 8 wt% based on the polymeric build material content.

The organic solvent plasticizers described herein can have a vapor pressure of less than 25mmHg and in one example less than about 1mmHg at 170 ℃, for example. Other organic cosolvents may also be present that might otherwise provide some plasticization but if the vapor pressure is much higher than 25mmHg, the solvent is too volatile to remain in the polymer build material. For example, 2-pyrrolidone, N-2-hydroxyethyl-2-pyrrolidone, N-methyl-2-pyrrolidone, or other more volatile co-solvent can be present in one or more jetting fluids, such as in a jetting fluid having an electromagnetic radiation absorber and an organic solvent plasticizer, or in one or both of the jetting fluids when the electromagnetic radiation absorber and the organic solvent plasticizer are in two separate jetting fluids. 2-pyrrolidone, for example, can be added to act as a humectant (for jettability) rather than as a plasticizer.

The melting point of the organic solvent plasticizer may also be considered when paired with the polymeric build material. For example, if the melting point is too low relative to the melting point of the polymer build material, the organic solvent plasticizer does not mix well with the molten polymer build material. Thus, for example, the melting point of the organic solvent plasticizer may be selected to have a melting temperature (build material T) that is below the melting temperature of the polymeric build material_m) A melting point (plasticizer T) within 35 ℃ or, in another example, within 15 ℃ below the melting temperature of the polymeric build material_m). For example, p-toluenesulfonamide and m-toluenesulfonamide have a melting temperature (plasticizer T) of slightly below 140 ℃_m136 ℃ to 138 ℃) and the o-toluenesulfonamide has a melting temperature (plasticizer T) of slightly less than 160 ℃_mFrom 156 ℃ to 158 ℃). Thus, based on the melting temperature of the organic solvent plasticizer, a good choice of polymer build material may be to have a melting temperature (build material T) of less than about 173 ℃ to 193 ℃_m) Depending on the choice of toluene sulfonamide or mixtures thereof; or with tighter tolerances, e.g., having a melting point less than 15 ℃ lower than the build material melting temperature, a good choice of polymer build material may be to have a melting temperature (build material T) of less than about 153 ℃ to 173 ℃_m) Again depending on the choice of toluene sulfonamide or mixtures thereof.

To absorb light energy and convert the light energy into heat energy, as mentioned, the electromagnetic radiation absorber can be, for example, an infrared absorbing colorant, such as a near-infrared absorbing colorant, or can be an energy absorbing colorant in the visible spectrum, such as a carbon black pigment. The infrared absorbing colorant may extend from the nominal red boundary of the visible spectrum of 700nm to 1mm, but more particularly, infrared absorbing colorants, such as dyes, in the range of about 800nm to 1400nm may be used in the jettable fluid to convert absorbed light energy into thermal energy. Similar characteristics can be achieved using near infrared colorants in the range of, for example, 950nm to 1150 nm. When used with a light source emitting wavelengths in this range and a polymer build material having low absorbance in this range, the near-infrared dye can cause the printed portion of the polymer powder to melt and coalesce without melting the remaining polymer powder. Thus, near-infrared dyes can be as effective or even more effective at generating heat and coalescing polymer powders as carbon black (which also effectively absorbs light energy and heats the printed portion of the polymer build material, but has the characteristic of always providing a black or gray part).

Infrared colorants, such as near-infrared colorants, used as electromagnetic radiation absorbers may have substantially no effect on the apparent color of the jettable fluid carrying them. This allows for the formulation of colorless jettable fluids that can be used to coalesce a polymeric build material without imparting any visible color to the part. Alternatively, the jettable fluid may include additional pigments and/or dyes to impart a color to the jettable fluid, such as cyan, magenta, yellow, black, red, orange, green, violet, blue, pink, and the like. The colorant may be added to a single jettable fluid having an electromagnetic radiation absorber and an organic solvent plasticizer, to one or both jettable fluids containing one of the electromagnetic radiation absorber or the organic solvent plasticizer, or to a separate ink printed with the electromagnetic radiation absorber and the organic solvent plasticizer. Such ejectable fluid can be used to print colored three-dimensional parts with good optical density.

Exemplary near infrared dyes that may be used include the aminium based near infrared dyes manufactured by HW Sand Corporation: SDA 1906 (lambda)_maxAbsorption 993nm), SDA 3755 (lambda)_maxAbsorption 1049nm) and SDA 7630 (. lamda.)_maxAbsorption 1070nm), and Ni-dithiolene (Ni-dithiolene) based dyes with very low absorbance in the visible range, e.g. in the range of 400 to 700 nm. However, each of these near infrared dyes has a high absorbance in the range of 800nm to 1400 nm. On the other hand, black jettable fluids containing carbon black pigments for use as electromagnetic radiation absorbers have a high degree of absorption in the visible spectrum (generally considered to have a broad absorption spectrum), and thus depending on the desired result (e.g., black or colorless, optional addition of colorants), can be usedThe appropriate absorbent is selected accordingly. Other electromagnetic infrared absorbers having a broader absorption spectrum in the visible range but not black may be used. Examples include aminium-based water-soluble dyes, tetraphenyldiamine-based water-soluble near-infrared dyes, cyanine-based water-soluble near-infrared dyes, and dithiolene-based water-soluble near-infrared dyes.

In some examples, the electromagnetic radiation absorber can be present in the jettable fluid at 0.1 wt% to 10 wt%, 0.5 wt% to 8 wt%, 1 wt% to 6 wt%, etc., whether or not an organic solvent plasticizer is included. At these concentrations, the jettable fluid may be applied to the layer of polymeric build material, typically at 32CL to 196CL, to provide sufficient absorber of electromagnetic radiation for effective sintering.

As mentioned, the electromagnetic radiation absorber may provide an enhanced ability to sufficiently raise the temperature of the polymeric build material above the melting or softening point of the polymeric powder. As used herein, "temperature enhancement capability" refers to the ability of an absorber to convert near infrared light energy into thermal energy to increase the temperature of a printed polymer powder above the temperature of an unprinted portion of the polymer powder. Typically, the polymer build material or powder can be sintered together when the temperature is raised to or above the melting or softening temperature of the polymer, although sintering can also occur below the melting point in some cases. As used herein, "melting point" refers to the temperature at which a polymer transitions from a crystalline phase to a soft, amorphous phase. Some polymers do not have a melting point but rather have a range of polymer softening temperatures. This range can be divided into a lower softening range, an intermediate softening range and an upper softening range. In the lower and intermediate softening ranges, the particles may coalesce to form a part while the remaining polymer powder remains loose. If the upper softening range is used, the entire powder bed becomes cake-like. As used herein, "softening point" means that at this temperature, the polymer particles coalesce while the remaining powder remains separated and loose.

Although the melting and softening points are generally described herein as temperatures for agglomerating the polymer powder, as mentioned, in some cases the polymer particles may be slightly largerBelow the melting or softening point. Thus, "melting point" and "softening point" as used herein may include slightly lower temperatures, such as up to about 5 ℃ lower than the actual melting or softening point. In any case, it is possible to avoid falling below T as much as possible_maxThe temperature of the excessive sintering temperature. For example, even with the extended temperature processing window provided by the systems and methods of the present disclosure, there may be situations where excessive sintering at certain locations is acceptable to achieve high densities, such as 90% or more or 95% or more, along a larger area of the part, thus on average, improving part density compared to parts made without organic solvent plasticizers.

In one example, the electromagnetic radiation absorber can have a temperature build-up capability of about 5 ℃ to about 30 ℃ for a polymer having a melting or softening point of about 75 ℃ to about 350 ℃. If the temperature of the polymeric build material is within about 5 ℃ to about 30 ℃ of the melting or softening point, the electromagnetic radiation absorber can increase the temperature of the printing powder to or above the melting or softening point of the polymeric build material, while the unprinted build material remains at a lower temperature. In some examples, the polymer build material may be preheated to a temperature 4 ℃ to 30 ℃, 10 ℃ to 30 ℃, or 10 ℃ to 20 ℃ below the melting or softening point of the polymer. One or more jettable fluids may then be printed onto the polymeric build material and irradiated with electromagnetic radiation sufficient to coalesce the printed portions of the polymeric build material. Thus, the electromagnetic radiation absorber provides a temperature boost to the polymeric build material compared to unprinted areas of the polymeric build material, and further, the organic solvent plasticizer provides a reduced melting temperature and a reduced melt viscosity sufficient to expand the temperature processing window by greater than 2 times, 3 times, 4 times, or 5 times compared to a polymeric build material printed with the same amount of electromagnetic radiation absorber but without the organic solvent plasticizer.

The one or more jettable fluids may comprise additional components in addition to the electromagnetic radiation absorber and the organic solvent plasticizer. As mentioned, the jettable fluid comprises water, and in some examples as mentioned, colorants, such as dyes and/or pigments, may be included to impart a ready-to-makeThe color of the part. Liquid vehicle formulations can be prepared that contain other ingredients, such as other organic co-solvents that are not plasticizers for the polymeric build material but are added for different purposes, such as jettability, jetting reliability, decap (decap) performance, viscosity modification, and the like. Classes of useful co-solvents can include organic co-solvents including aliphatic alcohols, aromatic alcohols, glycols, glycol ethers, polyglycol ethers, caprolactams, formamides, acetamides, and long chain alcohols. Examples of such compounds include primary aliphatic alcohols, secondary aliphatic alcohols, 1, 2-alcohols, 1, 3-alcohols, 1, 5-alcohols, ethylene glycol alkyl ethers, propylene glycol alkyl ethers, higher homologs of polyethylene glycol alkyl ethers (C)₆-C₁₂) N-alkyl caprolactams, unsubstituted caprolactams, substituted and unsubstituted formamides, substituted and unsubstituted acetamides, and the like. Where these co-solvents serve as temperature reducing plasticizers for particular polymeric build materials, some of these other co-solvents may be considered suitable in such circumstances.

Furthermore, one or more nonionic, cationic and/or anionic surfactants may be present, if present, from 0.01% to 20% by weight. Examples include alkyl polyethylene oxides, alkyl phenyl polyethylene oxides, polyethylene oxide block copolymers, acetylenic polyethylene oxides, polyethylene oxide (di) esters, polyethylene oxide amines, protonated polyethylene oxide amides, dimethicone copolyols, substituted amine oxides, and the like. The amount of surfactant added to the formulations of the present disclosure may be from 0.01 wt% to 20 wt%. Suitable surfactants may include, but are not limited to liponic esters, such as Tergitol available from the Dow Chemical Company^TM15-S-12、Tergitol^TM15-S-7, LEG-1 and LEG-7; triton available from Dow Chemical Company^TMX-100；Triton^TMX-405; and sodium lauryl sulfate.

Consistent with the formulations of the present disclosure, various other additives may be used to enhance the properties of the jettable fluid for particular applications. Examples of such additives are those added to inhibit the growth of harmful microorganisms. These additives may beAre biocides, fungicides and other biocides that are conventionally used in ink formulations. Examples of suitable antimicrobial agents include, but are not limited to(Nudex，Inc.)、UCARCIDE^TM(Union carbide Corp.)、(R.T.Vanderbilt Co.)、(ICI America) and combinations thereof. Chelating agents such as EDTA (ethylenediaminetetraacetic acid) may be included to eliminate the deleterious effects of heavy metal impurities, and buffers may be used to control the pH of the ink. For example, 0.01 to 2 wt% may be used. Viscosity modifiers and buffers may also be present, as well as other additives to modify the properties of the ink as desired. These additives may be present from 0.01 wt% to 20 wt%. If solids are present that should be dispersed in the jettable fluid, such as pigments, the liquid vehicle may also contain dispersants to maintain the solids in suspension, jettability, and the like. In one example, the liquid vehicle can be primarily water.

The portion of the polymeric build material printed with the electromagnetic radiation absorber and the organic solvent plasticizer may be irradiated with a frit lamp configured to emit a wavelength, for example, within the visible spectrum, the near infrared spectrum, or the infrared spectrum. Suitable fusion lamps may include, for example, commercially available infrared and halogen lamps. The fusion lamp may be a fixed lamp or a moving lamp (both shown by way of example in fig. 1). For example, the lights may be mounted on rails to move horizontally across the powder bed support. Such a fritted lamp or lamps may pass multiple times over the bed depending on the exposure required to coalesce the printed layers. One or more fusion lamps may be configured to irradiate the entire powder bed with substantially uniform energy, but as described herein, it may still be difficult to avoid non-uniformities across the powder bed support. In one example, the fritted lamp may be matched with an electromagnetic radiation absorber such that the fritted lamp emits a wavelength of light that matches the highest absorption wavelength of the absorber. An absorber having a narrow peak at a particular wavelength, such as a narrow band in the near infrared range, may be used with a fritted lamp emitting in a narrow wavelength range at about its peak wavelength. Similarly, an electromagnetic radiation absorber that absorbs a wide range of radiation may be used with fusion lamps that emit a wide range of overlapping wavelengths. Matching the electromagnetic radiation absorber and the fritted lamp thereby increases the efficiency of coalescing the polymeric build material with the absorber and plasticizer printed thereon, while the unprinted polymer particles do not absorb so much light and remain at a lower temperature. For example, depending on the amount of electromagnetic radiation absorber and organic solvent plasticizer applied to the polymeric build material, the absorption band of the absorber, the preheat temperature, and the melting or softening point of the build material, an appropriate amount of radiation can be supplied by the fusion lamp. In some examples, the fusion lamp may irradiate the layers using, for example, 2 750 watt bulbs or other similar electromagnetic radiation sources for about 0.5 to about 10 seconds.

In another example, as shown in fig. 6, a three-dimensional printing method 200 can include forming a 40 μm to 300 μm layer of polymeric build material 210 on a build substrate, and selectively jetting an electromagnetic radiation absorber and an organic solvent plasticizer onto a first portion of the layer of polymeric build material such that the electromagnetic radiation absorber and the organic solvent plasticizer contact the first portion 220 at an organic solvent plasticizer loading of 2 wt% to 10 wt% based on the polymeric build material content. The electromagnetic radiation absorber loading in the polymeric build material can be 0.05 wt% to 2 wt% in some examples. The polymer build material can have an average particle size of 20 μm to 150 μm, a melting temperature of 75 ℃ to 350 ℃, and a melt viscosity. The method may also include directing electromagnetic radiation at a wavelength to the layer of polymeric build material such that a radiation absorber located at the first portion increases the temperature of the polymeric build material to a temperature greater than a temperature 230 of a region of the layer of polymeric build material outside of the first portion. The first portion of the layer may also have a modified lower melting temperature and a modified lower melt viscosity as compared to regions of the polymeric build material layer outside of the first portion due to the presence of the organic solvent plasticizer. In one example, the melt viscosity of the polymer build material located in the first portion (where the electromagnetic radiation absorber and organic solvent plasticizer are printed) can be reduced to a lower melt viscosity, and the melting temperature of the polymer build material located in the first portion (where printed) can be reduced by 3 ℃ to 15 ℃.

The method may further include preheating the polymeric build material to within 4 ℃ to 30 ℃ below the altered lower melting temperature prior to exposing the layer of polymeric build material to electromagnetic radiation. In more detail, the method may further include adding a second layer of polymeric build material onto the layer of polymeric build material after the layer melts, selectively applying an electromagnetic radiation absorber and an organic solvent plasticizer onto a second portion of the second layer of polymeric build material, and directing electromagnetic radiation toward the second layer of polymeric build material, similar to that described for the previously applied layer therebelow. The method may also use some of the same electromagnetic radiation absorbers, organic solvent plasticizers, and polymeric build materials described herein. For example, the electromagnetic radiation absorber can be an infrared absorbing colorant, a near infrared colorant, or an energy absorbing colorant in the visible spectrum, such as a carbon black pigment. The organic solvent plasticizer may be p-toluenesulfonamide, m-toluenesulfonamide, o-toluenesulfonamide, urea, ethylene carbonate, propylene carbonate, diethylene glycol, triethylene glycol, tetraethylene glycol, methyl 4-hydroxybenzoate, dimethyl sulfoxide, dioctyl phthalate, γ -butyrolactone, or a mixture thereof. The polymer build material may be nylon 6, nylon 8, nylon 9, nylon 11, nylon 12, nylon 66, nylon 612, nylon 812, polyethylene terephthalate (PET), polystyrene, polyacrylate, polyacetal, polypropylene, polycarbonate, polyester, acrylonitrile butadiene styrene, thermoplastic polyurethane, engineering plastic, Polyetheretherketone (PEEK), polymer blends thereof, amorphous polymers thereof, core shell polymers thereof, and copolymers thereof. In one example, the electromagnetic radiation absorber and the organic solvent plasticizer may be selectively applied to the layer of polymeric build material by separate jettable fluids, such as by separate fluid-jet pens.

It is to be understood that this disclosure is not limited to the particular process steps and materials disclosed herein as such process steps and materials may vary. It is also to be understood that the terminology used herein is used for the purpose of describing particular examples only. These terms are not intended to be limiting, as the scope of the present disclosure is intended to be limited only by the appended claims and equivalents thereof.

It is noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

As used herein, "liquid vehicle" refers to a liquid fluid colorant, an electromagnetic radiation absorber, and/or an organic solvent plasticizer carried with water and, in some instances, other components. A wide variety of liquid vehicles may be used with the systems and methods of the present disclosure, including surfactants, solvents, co-solvents, anti-kogation agents, buffers, biocides, sequestering agents, viscosity modifiers, surfactants, water, and the like.

As used herein, "jetting" or "jettable" refers to a composition that is jettable from a jetting construct, such as an ink-jet construct. The ink-jet configuration can include a thermal or piezo-electric pen having a printing orifice or port adapted to eject small droplets of fluid. In several examples, the fluid drop size can be less than 10 picoliters, less than 20 picoliters, less than 30 picoliters, less than 40 picoliters, less than 50 picoliters, etc.

The term "about" is used herein to provide flexibility to a numerical range endpoint where a given value may be "slightly above" or "slightly below" the endpoint. The degree of flexibility of this term can depend on the particular variable and is determined based on experience and the associated description herein.

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

Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a numerical range of "about 1 wt% to about 5 wt%" should be interpreted to include not only the explicitly recited values of about 1 wt% to about 5 wt%, but also include individual values and sub-ranges within the indicated range. Accordingly, included in this numerical range are individual values, e.g., 2, 3.5, and 4, and sub-ranges, e.g., 1-3, 2-4, and 3-5, etc. This principle applies equally to ranges reciting only one numerical value. Moreover, such an interpretation applies regardless of the breadth of the range or the characteristics being described.

Examples

Several embodiments of the present disclosure are illustrated below. It is to be understood, however, that the following is only illustrative of the application of the principles of the present disclosure. Numerous modifications and alternative compositions, methods, and systems may be devised without departing from the spirit and scope of the present disclosure. It is intended that the appended claims cover such modifications and arrangements.