Fusing fluid and materials kit for the print and fuse manufacture of three-dimensional objects

Abstract

Provided is a fusing fluid for the print and fuse manufacture of three-dimensional objects from particulate build material, wherein the fusing fluid comprises or consists of a non-aqueous carrier liquid; a radiation absorber; and optionally a dispersant and / or one or more further additives; wherein the fusing fluid has a boiling range lying within a temperature window of 150 to 350 °C at normal pressure of 101.3 kPa with a boiling range width of less than or equal to 70 °C, wherein the boiling range is defined by a boiling onset temperature Tb_onset and a boiling endset temperature Tb_endset determined according to the method described in the specification, and wherein the boiling range width is Tb_endset minus Tb_onset. Further provided are: a materials kit comprising the fusing fluid and a particulate build material, optionally wherein the particulate build material comprises a flame retardant component; a method and apparatus for the print and fuse manufacture of a three-dimensional object utilizing the materials kit; use of the fusing fluid or of the materials kit in a print and fuse method; and a resulting object having improved flame retardancy.

Description

[0001] FUSING FLUID AND MATERIALS KIT FOR THE PRINT AND FUSE MANUFACTURE OF THREE-DIMENSIONAL OBJECTS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a fusing fluid for the print and fuse manufacture of three- dimensional objects from particulate build material, wherein the fusing fluid comprises or consists of a non-aqueous carrier liquid, a radiation absorber, optionally a dispersant and optionally a one or more further additives as well as a materials kit for the print and fuse manufacture of three-dimensional objects from particulate build material. Furthermore, the present invention relates to a method for the print and fuse manufacture of a three-dimensional object from a particulate build material, wherein the fusing fluid or the materials kit according to the present invention is utilized, as well as a three-dimensional object obtained or obtainable by said method. The present invention further relates to the use of said fusing fluid or said materials kit in print and fuse methods for improving the flame retardancy of the obtained three- dimensional objects. Finally, the present invention relates to an apparatus for the print and fuse manufacture of three-dimensional objects from a particulate build material, whereby the fusing fluid or the materials kit according to the invention is applied.

[0004] BACKGROUND AND PRIOR ART

[0005] Additive manufacturing is reaching industrial capabilities and the volume of parts that can be manufactured in a single build is increasing. The areas of application for additive manufacturing have already reached major industrial sectors such as the automotive and aerospace industries. This in turn places additional requirements on the parts such as strict compliance with flammability standards.

[0006] In order to sufficiently reduce flammability I improve flame retardancy, an approach that is widely used in selective laser sintering is that flame retardant components are added to the polymeric build material from which the part is formed. For instance, DE 10 2004 001 324 A1 describes the use of a powdery composition for selective laser sintering, wherein the powder inter alia comprises at least one polymer and at least one ammonium polyphosphate flame retardant. US 2013 / 0041061 A1 discloses fireproofing polyamide powders and their use in sintering processes, wherein the polyamide powder comprises at least one flame retardant, the flame retardant being a blend of at least one organic phosphinate of a metal, of at least one ammonium polyphosphate, and of a zinc borate synergist. Selective laser sintering, or SLS, is a powder bed fusion process in which a laser is used to trace the cross section of the object in each layer to selectively heat, melt and fuse the build material in each layer. Over recent years, a faster powder bed fusion technique has been developed, sometimes referred to as “print and fuse”, in which selectivity is instead provided by the selective deposition of an infrared absorber to define the cross section within each layer and a non-selective heat source is applied to melt the particulate build material within the defined cross section. Typically, the absorber is deposited in form of a fluid by printheads in a single pass over the entire layer, resulting in much shorter layer processing times compared to SLS, and rendering the process cost effective for the industrial manufacture of parts. Examples of “print and fuse” processes are broadly based on the so-called “high speed sintering” technology developed at Loughborough University, derivatives of which are industrially applied for example by Hewlett Packard’s HP Multi Jet Fusion® machines and Stratasys’ H350® SAF® technology printers. With regard to the fusion fluids used, a distinction is usually made between those that use either an aqueous or a non-aqueous - usually oil based - carrier liquid. However, aqueous based fusion fluids have the disadvantage that they typically require a second fluid to be deposited to achieve sufficiently selective energy absorption between areas of build material that received absorber and those void of absorber. Such a second fluid is typically infrared-absorption inhibiting and / or has cooling properties. The need to use a second fluid however increases the cost of the parts due to duplication in the fluid deposition system, and due to additional maintenance and additional material costs. Meanwhile print and fuse methods that use non-aqueous based fusing fluids do not require a second fluid.

[0007] Print and fuse applications have reached a throughput and quality that make them especially interesting to the automotive and aerospace sectors. However, the flame retardancy of three- dimensional objects obtained by print and fuse applications, especially fuse applications using non-aqueous based fusing fluids, is still in its infancy and requires further development and improvement to be suitable for this application. In particular, print and fuse methods which use non-aqueous based fusing fluids often display insufficient flame retardancy properties, even when flame retardants are added to the particulate build material, rendering the use of conventional non-aqueous based absorber fluids in print and fuse processes unsuitable for such applications.

[0008] Therefore, there remains a need for solutions that improve the flame retardancy properties of three-dimensional objects obtained by print and fuse methods that use non-aqueous fusing fluids, preferably without decreasing the throughput and quality of the method and the obtained objects.

[0009] PROBLEM

[0010] Accordingly, the object of the present invention is to reduce the flammability, or rather improve the flame retardancy, of three-dimensional objects obtained by print and fuse manufacturing processes which use non-aqueous based fusing fluids.

[0011] SUMMARY

[0012] The invention is set out in the appended independent claims, while particular embodiments of the invention are set out in the appended dependent claims.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Reference is now directed to the drawings, in which:

[0015] Figure 1 : shows a TGA thermal curve (A) and the first derivative of said TGA thermal curve of Inventive Fusing Fluid F1 ;

[0016] Figure 2: shows the first derivative curves of the TGA thermal curves of Inventive Fusing Fluids F1 , F2 and F3 as well as Comparative Fusing Fluid F4;

[0017] Figure 3: shows a simplified cross-sectional view of an exemplary apparatus 1 for the print and fuse manufacture of three-dimensional objects from a materials kit according to the invention; and

[0018] Figure 4: shows pictures of the modified FAR 25.853 test taken at 40s of the flame application for samples of (A) Inventive Fusing Fluid F1 and (B) Comparative Fusing Fluid F4.

[0019] In the drawings, like elements are indicated by reference signs throughout. It should be noted that the drawings may not be to scale and that certain features may be exaggerated in size to be more clearly visible.

[0020] SOLUTION OF THE PROBLEM AND DETAILED DESCRIPTION

[0021] The problem is solved by providing a fusing fluid for the print and fuse manufacture of three- dimensional objects from particulate build material, wherein the fusing fluid comprises or consists of a) a non-aqueous carrier liquid; b) a radiation absorber; c) optionally a dispersant; and d) optionally one or more further additives; wherein the fusing fluid has a boiling range lying within a temperature window of 150 to 350 °C at normal pressure of 101.3 kPa with a boiling range width of less than or equal to 70 °C, wherein the boiling range is defined by a boiling onset temperature Tb_onset and a boiling endset temperature Tb_endset determined according to the method described below, wherein the boiling range width is Tb_endset minus Tb_onset.

[0022] Furthermore, the problem is solved by providing a materials kit for the print and fuse manufacture of three-dimensional objects from particulate build material comprising or consisting of:

[0023] • a particulate build material; and

[0024] • a fusing fluid according to the invention.

[0025] In the course of the development work that led to the present invention, it was discovered that, surprisingly, the fusing fluid itself negatively influences the flame retardancy of the produced three-dimensional objects. Even when particulate build materials with flame retardants were used, the formed parts did not lead to consistent passing of the FAR25.853 burn test. In comparison, these failing rates did not occur when the same particulate build materials were used in SLS methods, which resulted in objects that typically passed the before-mentioned test.

[0026] Furthermore, it was found that three-dimensional objects produced by SLS and subsequently treated with conventional fusing fluid also do not consistently pass the FAR 25.853 burn test. “Treated” in the context herein means that the laser-formed three-dimensional samples were soaked in fusing fluid for a duration of 30 min and subsequently placed in a vacuum of 10 to 20 mbar at 150 °C for 16 hours. A 30 min duration was chosen to ensure that, from monitoring the mass gain of the samples, all soaked samples had absorbed fusing fluid to such a degree that no significant further increase in mass gain could be determined. In this way, the amount of fluid absorbed was assumed to be consistent between samples. In this way, fusing fluid is introduced at least in part to the sample and is then at least partially removed to simulate a print and fuse sample. This treatment of SLS printed samples with fusing fluid allowed for fast screening of fusing fluids while still capturing the pertinent material properties of samples generated using a print and fuse process. The treatment of SLS-formed three-dimensional samples with the fusing fluid thus additionally shows that conventional non-aqueous based fusing fluids have a negative effect on the flame retardancy properties of the objects. Moreover, said treatment of SLS-formed three-dimensional samples was found to be a sufficiently suitable method for simulating the degree of flame retardancy of objects formed by print and fuse methods.

[0027] Without being bound to any theory, it has been discovered that by using a fusing fluid in which the fusing fluid has boiling range lying within a temperature window of 150 to 350 °C at normal pressure of 101.3 kPa with a boiling range width of less than or equal to 70 °C (determined according to method described below), leads to three-dimensional objects with improved flame retardancy when formed by a print and fuse method. In comparison, conventional non-aqueous based fusing fluids have a boiling range width of above 70 °C. For instance, HAF® fusing fluid (X3D-01011 ) by Stratasys - a conventional fusing fluid - has a boiling range width of 81 °C (determined according to method described below). The fusing fluids according to the invention were found to improve the flame retardancy of three-dimensional objects formed by a print and fuse process.

[0028] The present invention will now be explained in detail below.

[0029] In the present disclosure, flammability I flame retardancy of three-dimensional objects is determined via a modified FAR 25.853 Part 1 (a)(1 )(i) protocol, i.e. the 60s vertical burn test (hereafter referred to also simply as modified FAR 25.853). For the burn tests performed herein, samples with modified dimensions of 70x200x1.5 mm compared to the standard dimensions (76 x 305 x thickness) were made. A sample thickness of 1 .5 mm was chosen as a suitable thickness to evaluate materials on, since such a sample thickness was found to be suitably sensitive to failure and non failure of the modified FAR 25.853 burn test. Samples that pass the FAR 25.853 test consistently at this thickness all showed self-extinguishing of the sample during the 60s application of the flame. This self-extinguishing of the sample within the 60s application of the flame was therefore used as an additional criterion for samples to robustly pass the test.

[0030] The definition and determination of the boiling range, which extends from a boiling onset temperature Tb_onset to a boiling endset temperature Tb_endset, the boiling range width, which is Tb_endset minus Tb_onset, and the peak boiling point (Tb_peak) of the fusing fluid will now be described. The boiling onset temperature Tb_onset and the boiling endset temperature Tb_endset and the peak boiling point of the fusing fluids are determined by thermogravimetric analysis (“TGA”) on a simultaneous thermogravimetric analysis and differential scanning calorimetry (“DSC”) apparatus. Experiments were conducted in duplicate on a simultaneous TGA-DSC 1 from Mettler Toledo. Samples of 7-9 mg ef fusing fluid were weighed with a precision balance and crimped in 100 microliter aluminum pans of known mass and with a 50 pm laser perforated lid for allowing vaporization of the material on heating. An identical empty pan was used as reference. The hole in the pan allowed the measurements to be performed at normal pressure of 101.3 kPa (= 1 atm; “atmospheric pressure”). After a balance stabilization time of 5 minutes at 30°C, a heating ramp at 20°C / min in the range 30°C to 500°C and using nitrogen at 10ml / min as purge gas was applied for determining the parameters that numerically characterize the thermal stability of the investigated fusing fluid samples. Prior to starting each experiment, a conventional procedure for buoyancy effect corrections and bias-free data was carried out by measuring a baseline (under identical conditions to those of the fusing fluids but with and empty crucible) that was afterwards automatically subtracted from the sample measurement. The following Table 1 offers a description of the types of baselines engaged in current data evaluation for which the “horizontal left” is used for TGA’s first derivative, in comparison with the industry default baseline type “line” (according to Mettler Toledo STARe Software version 18.00a, Help Topics).

[0031] 1Mettler Toledo STARe Software version 18.00a, Help Topics

[0032] From the first derivative of the TGA curve (TGA’ curve), which plots rate of weight loss, d(weight) / dT), a peak boiling point (Tb_peak) according to the invention is determined from the global extreme point of the first derivative curve TGA’ (i.e. the maximum weight loss rate). Said global extreme point lies between Tb_onset and Tb_endset of the TGA’ curve, which is obtained during the above described 30 to 500 °C measurement window. Any extreme points which may occur at temperatures outside the 30 to 500 °C measurement window are not included here. The boiling onset temperature (Tb_onset) is defined herein as the temperature at which the baseline tangent (tan_base) intersects with an onset tangent (tan_onset) drawn along the steepest slope of the curve to the lower temperature side of the peak boiling point. Similarly, the boiling endset temperature (Tb_endset) is calculated as the temperature where an endset tangent (tan_endset) drawn along the slope of the curve to the higher temperature side of the peak boiling point of the event intersects with the baseline tangent (tan_base). The tangent lines herein are automatically fitted by the onset and endset tangent functions in the Mettler Toledo STARe software. Herein, the boiling onset temperature is also simply referred to as onset, or Tb_onset, and the boiling endset temperature is simply referred to as endset, or Tb_endset.

[0033] The ’’boiling range” as defined according to the invention herein extends from Tb_onset to Tb_endset, i.e. the boiling range starts at the absolute value of Tb_onset and ends at the absolute value of Tb_endset as determined from the TGA derivative curve.

[0034] The “boiling range width” according to the invention, herein also referred to as Tb_width, is defined herein as the temperature difference or ATb between Tb_onset and Tb_endset. In other words, the boiling range width (Tb_width or ATb) is Tb_endset minus Tb_onset.

[0035] The “temperature window” or “boiling range temperature window” as referred to herein of 150 to 350 °C represents the temperature window within which the boiling range of an inventive fusing fluid falls. This means that Tb_onset is > 150 °C and Tb_endset < 350 °C.

[0036] Reported values herein are the average of 2 measurements that were taken for each fluid. The terms boiling range, boiling range width and peak boiling point as defined above may herein also be referred to synonymously as ‘weight loss temperature range’, ‘weight loss temperature range width’ and ‘peak weight loss temperature’, respectively.

[0037] The determination of the boiling onset temperature Tb_onset, the boiling endset temperature Tb_endset and the peak boiling point as described above and as defined herein is illustrated in more detail with reference to Figure 1 and Figure 2 (just one measurement of the 2 measurements taken for each fluid is shown). Fig. 1 shows (A) the TGA thermal curve and (B) the first derivative curve of said TGA thermal curve, TGA’, of an inventive fusing fluid F1 described in detail in the examples below. The boiling range (and thus the boiling range width) can be determined from the first derivative curve TGA (see Fig. 1 (B)) using the intersections with the baseline tangent of each of the two tangents tan_onset and tan_endset to the inflection points of the falling and rising sides of the boiling peak. The two tangents tan_onset and tan_endset are shown by the dashed / dotted lines and their intersections with the baseline are marked. The peak boiling point is the global extreme point recorded in the derivative curve during the 30 to 500 °C measurement window. Thus, the inventive fusing fluid F1 has a boiling onset temperature (Tb_onset) of 217 °C and a boiling endset temperature (Tb_endset) of 250 °C, which results in a boiling range of 217 to 250 °C and which therefore lies in the required temperature window of 150 to 350 °C. Consequently, the boiling range width of the inventive fusing fluid F1 is 33 °C (Tb_width = Tb_endset - Tb_onset = 250 °C - 217 °C = 33 °C), and falls within the requirement of being less than or equal to 70 °C. In addition, the inventive fusing fluid F1 has a peak boiling point of 239 °C.

[0038] Fig. 2 displays the first derivative curves TGA’ of the inventive fusing fluids F1 , F2 and F3 compared to a comparative fusing fluid F4, which is a conventional fusing fluid in print and fuse methods. The inventive fusing fluids F1 , F2, F3 and comparative fluid F4 are described in detail in the examples below. As can be seen from Fig. 2, the inventive fusing fluids have much narrower boiling range widths compared to the comparative fusing fluid F4.

[0039] Fusing Fluid:

[0040] The inventive fusing fluid for the print and fuse manufacture of three-dimensional objects from particulate build material comprises or consists of a) a non-aqueous carrier liquid; b) a radiation absorber; c) optionally a dispersant; and d) optionally one or more further additives; wherein the fusing fluid has a boiling range lying within a temperature window of 150 to 350 °C at normal pressure of 101.3 kPa with a boiling range width of less than or equal to 70 °C, wherein the boiling range is defined by a boiling onset temperature Tb_onset and a boiling endset temperature Tb_endset determined according to the method described above, wherein the boiling range width is Tb_endset minus Tb_onset.

[0041] In other words, the fusing fluid has a boiling range width ATb (or Tb_width) defined by the difference between Tb_onset and Tb_endset, wherein the absolute values of Tb_onset and Tb_endset fall within a temperature window (or “boiling range temperature window”) of 150 to 350 °C at normal pressure of 101.3 kPa, and wherein the boiling range width is less than or equal to 70 °C.

[0042] Said boiling range of the fusing fluid preferably lies within a temperature window of 170 to 320 °C, preferably within a temperature window of 190 to 290 °C, and more preferably within a temperature window of 210 to 260 °C at a normal pressure of 101.3 kPa. Furthermore, it is preferred that the boiling range width of the boiling range of the fusing fluid is from 0.5 °C to 70 °C, preferably from 1 °C to 60 °C, more preferably from 5 °C to 50 °C, even more preferably from 5 °C to 40 °C, and most preferably from 10 °C to 40 °C. Additionally, it is preferred that the fusing fluid has a peak boiling point, as determined according to the method described above, in a peak temperature range of 170 to 280 °C, preferably in a peak temperature range of 190 to 270 °C, more preferably in a peak temperature range of 200 to 260 °C, even more preferably in a peak temperature range of 210 to 250 °C. The term “peak temperature range” means the temperature range in which the peak boiling point lies.

[0043] Furthermore, the fusing fluid preferably has suitable rheological properties such that optimum jetting parameters for the operation of the printhead (fluid deposition module) may be achieved, such as droplet formation including droplet size, shape, and length of the drop tail from the orifice plate of the printhead before break off, and the meniscus shape of the fluid formed at the nozzle orifice. Typically, the viscosity and the surface tension of the fusing fluid determine its rheology and are dependent on the requirement of the printhead used, a suitable example of which may for example be a Xaar 1003 printhead by the company Xaar pic. Hence, it is preferred that the fusing fluid has a viscosity in the range which is acceptable by the specific print head used to deposit the fusing fluid. In particular the fusing fluid has a viscosity in a range from 5 to 100 cP, preferably from 6 to 20 cP at a jetting temperature, which may be 35 °C to 80°C, preferably 35 °C to 40°C. This can be achieved by adding a viscosity modifier to the fusing fluid. Suitable viscosity modifiers are mentioned below. The modification of the surface tension of the fusing fluid may be achieved by adding further additives such as surfactants. Suitable surfactants are further described below.

[0044] The components of the inventive fusing fluid will now be described in more detail below.

[0045] Non-aqueous carrier liquid:

[0046] The non-aqueous carrier liquid of the fusing fluid preferably comprises or consists of hydrocarbons, alkyl benzoates, benzyl alcohols, benzyl esters, benzaldehydes, carboxylic acid esters, alkanols, alkanones, diols, methoxytoluenes, methylnaphthalenes, cyclic carbonate esters, terpenes or a combination thereof. When a combination of the before-mentioned compounds is used (“a combination thereof’), it is preferred that these are miscible, thus forming a homogeneous mixture.

[0047] When hydrocarbons are used as the non-aqueous carrier liquid, the carrier liquid comprises or consists preferably of a mixture of hydrocarbons with at least 9 up to a maximum of 20 carbon atoms, more preferably a mixture of hydrocarbons with at least 11 up to a maximum of 16 carbon atoms, even more preferably a mixture of hydrocarbons having 11 to 16 carbon atoms. An example of such mixture of hydrocarbons is the commercially available “Isoparaffin MC 80”, which is a mixture of isoparaffinic hydrocarbons C11-C16 from the company JBL Solutions B.V. (Netherland). Alternatively, when hydrocarbons are used the carrier liquid may also comprise or consists of a single hydrocarbon such as a pure alkane, preferably nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, icosane, or isomers of the before mentioned, more preferably dodecane.

[0048] With regard to the alkyl benzoates, in particular alkyl benzoates, wherein the “alkyl moiety” ranges from 1 to 8 carbon atoms, are used. Examples for such alkyl benzoates are methyl benzoate, ethyl benzoate, propyl benzoate, isopropyl benzoate, butyl benzoate, isobutyl benzoate, pentyl benzoate, hexyl benzoate and octyl benzoate.

[0049] Examples for benzyl alcohols, benzyl esters, benzaldehydes, carboxylic acid ester, alkanols, alkanones, diols, methoxytoluenes, methylnaphthalenes, cyclic carbonate esters and terpenes are: benzyl alcohol, 4-Methoxybenzyl alcohol, benzyl acetate, benzyl propionate, benzyl butyrate, benzyl pentanoate, benzyl hexanoate, benzaldehyde, 4-methoxybenzaldehyde, methyl hexanoate, ethyl hexanoate, methyl octanoate, ethyl octanoate, methyl decanoate, ethyl decanoate, methyl dodecanoate, ethyl dodecanoate, methyl tetradecanoate, ethyl tetradecanoate, methyl hexadecanoate, ethyl hexadecanoate, methyl palmitoleate, ethyl palmitoleate, methyl myristoleate, ethyl myristoleate, methyl undecenoate, ethyl undecenoate, methyl pentadecanoate, ethyl pentadecanoate, methyl heptadecanoate, 2-ethylhexanol, (Oxolan-2-yl)methanol, phenylacetone, ethylene glycol, propylene glycol, butane-1 ,4-diol, pentane-1 ,5-diol, hexane-1 ,6-diol, 4-methoxytoluene, 1 -methylnaphthalene, propylene carbonate and 1-methyl-4-(prop-1-en-2-yl)cyclohex-1-ene.

[0050] It is particularly preferable that the non-aqueous carrier liquid comprises or consists of an alkyl benzoate or a mixture of hydrocarbons, wherein

[0051] • the alkyl benzoate is more preferably ethyl benzoate, propyl benzoate, isopropyl benzoate, butyl benzoate or isobutyl benzoate; and

[0052] • the mixture of hydrocarbons is more preferably a mixture of hydrocarbons with at least 9 up to a maximum of 20 carbon atoms, even more preferably a mixture of hydrocarbons with at least 11 up to a maximum of 16 carbon atoms, still even more preferably a mixture of hydrocarbons having 11 to 16 carbon atoms. The term "liquid" in non-aqueous carrier liquid a) here is typically to be understood in such a way that it is in the liquid state at a temperature of at least 40 °C, preferably of at least 30 °C, more preferably of at least 20 °C.

[0053] Furthermore, it is preferred that the non-aqueous carrier liquid has a dielectric constant of < 10, more preferred of < 9, even more preferred of < 7, measured at 20 °C and a frequency of 100 kHz.

[0054] The non-aqueous carrier liquid can also comprise or consist of fatty acids. In particular, the non-aqueous carrier liquid may comprise or consist of lauric acid, myristic acid, linoleic acid, ricinoleic acid, arachidic acid, behenic acid, caprylic acid, capric acid and combinations thereof. The fatty acids can also be combined with the aforementioned compounds (hydrocarbons, alkyl benzoates, benzyl alcohols, benzyl esters, benzaldehydes, carboxylic acid esters, alkanols, alkanones, diols, methoxytoluenes, methylnaphthalenes, cyclic carbonate esters and terpenes), especially if they are miscible and form a homogeneous mixture.

[0055] Radiation absorber:

[0056] The fusing fluid also comprises a radiation absorber. The radiation absorber is arranged to absorb fusing radiation sufficiently so as to cause fusion by at least partial melting of a particulate build material in contact with the radiation absorber when exposing said material to fusing radiation in the course of a print and fusing method. In other words, the radiation absorber is capable of absorbing fusing radiation to produce heat. Preferably, the radiation absorber at least absorbs fusing radiation that is infrared fusing radiation, preferably in a range of 780 nm to about 3000 nm, more preferably near infrared radiation in a range of 780 nm to 2500 nm. The wavelength of the fusing energy thus preferably has a peak in the range of 780 nm to about 3000 nm, for example around 1000nm.

[0057] The radiation absorber is preferably selected from the group comprising or consisting of carbon black, carbon nanotubes, graphenes, graphites, antimony tin oxide, indium tin oxide, tungsten oxide, nigrosins, or a combination thereof, more preferably carbon black. The nigrosins are preferably oil soluble (e.g. Solvent Black 7) or alcohol soluble (e.g. Solvent Black 5). In particular, it is preferred that the radiation absorber is carbon black.

[0058] Dispersant:

[0059] Furthermore, a dispersant can optionally be included in the fusing fluid. In particular, dispersants can help disperse the radiation absorber described above, for example where the radiation absorber is an immiscible solid like for instance carbon black. The selection of the dispersant will depend on the substance to be dispersed and the dispersion medium - in this case the non-aqueous carrier liquid.

[0060] Preferably the dispersant is selected from the group comprising or consisting of modified polyurethanes, polyester-modified polyalkylene imines, structured acrylate copolymers with pigment-affinic groups, polyether-containing block copolymers, polyolefine containing block copolymers, or a combination thereof.

[0061] Further additives:

[0062] Optionally, the fusing fluid may comprise one or more further additives. In particular, the further additive is a viscosity modifier to tailor the viscosity of the fusing fluid to the range acceptable by the specific print head used to deposit the fusing fluid. For example, the viscosity may be in a range from 6 to 20 cP. For example, the viscosity modifier may be added to achieve a viscosity of for example around 5-100cP at jetting temperature, which may be around for example 35 to 80°C, preferably for example around 5-20cP around 35 °C to 40°C. The viscosity of the fluid and the surface tension are dependent on the requirement of the print head used, a suitable example of which may for example be a Xaar 1003 printhead by the company Xaar pic. The viscosity modifier is preferably selected from the group comprising or consisting of olefin copolymers, polyalkyl methacrylate homopolymers, polyalkyl methacrylate (co)polymers, amorphous polyamides, polyureas, or a combination thereof, preferably ethylene propylene diene copolymers, ethyl propylene copolymers, poly(methyl methacrylate), poly(ethyl methacrylate), poly(propyl methacrylate), poly(butyl methacrylate), poly(dodecyl methacrylate-co-methyl methacrylate, poly(butyl methacrylate-co-methyl methacrylate), or a combination thereof.

[0063] Further additives may also be surfactants to modify the surface tension of the fusing fluid. The surfactant used is preferably an oil-soluble steric stabilizer. The oil-soluble surfactant is preferably selected from the group comprising, but not limited to, carboxylates, sulfates, sulfonates, phosphate esters, or a combination / variation of.

[0064] The viscosity and the surface tension of the fluid determine the rheology of the fluid and whether optimum jetting parameters for the operation of the printhead may be achieved, such as droplet formation including droplet size, shape, and length of the drop tail from the orifice plate of the printhead before break off, and the meniscus shape of the fluid formed at the nozzle orifice. Amounts:

[0065] The fusing fluid preferably comprises or consists of a) 70 to 98 wt.-% of the non-aqueous carrier liquid, preferably 80 to 95 wt.-%; b) 2 to 15 wt.-% of the radiation absorber, preferably 3 to 8 wt.-%, more preferably 4 to 6 wt.-%; c) 0 to 15 wt.-% of the dispersant, preferably 2 to 7 wt.-%; and I or d) 0 to 10 wt.-% of the one or more further additives, preferably 0.5 to 5 wt.-% based on the total weight of the fusing fluid.

[0066] Materials Kit:

[0067] The invention also relates to a materials kit for the print and fuse manufacture of three- dimensional objects from particulate build material. The materials kit comprises or consists of a particulate build material; and a fusing fluid according to the invention.

[0068] It is preferred that the particulate build material is a polymeric particulate build material comprising or consisting of at least 50 wt% polymer, based on the total amount of the particulate build material, preferably of 60 to 100 wt.-%, more preferably of 70 to 95 wt.-%, even more preferably of 80 to 90 wt.-%. The particulate build material is preferably selected from the group comprising or consisting of thermoplastic polymeric powder build materials, more preferably polyamides, polyurethanes, or combination thereof, even more preferably polyamide 11 , polyamide 12, polyamide 10.10, polyamide 10.12, polyamide 12.12, polyamide 6.66, polyamide 6.12, polyamide 6.10, polyamide 6.13, polyamide 4.10, or a combination thereof. The term “thermoplastic” in “thermoplastic polymeric powder build materials” also includes thermoplastic elastomers.

[0069] Furthermore, the particulate build material preferably also comprises one or more flame retardant components, for example selected from one or more of: brominated polyacrylates, brominated polystyrenes, ammonium polyphosphates, melamine polyphosphate, aluminum diethyl-phosphinate, 3,9-Dimethyl-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane-3,9- dioxide (also known as Afflamit® PCO900 (by the company Thor)) and 9,10-Dihydro-9-oxa- 10-phosphaphenanthrene-10-oxide (DOPO), wherein the particulate build material especially comprises brominated polyacrylates. Moreover, it is preferred that the one or more flame retardant components are present in an amount of less than or equal to 30 wt.-% in the particulate build material, based on the total amount of the particulate build material, more preferably 2 to 30 wt.-%, still more preferably 4 to 22 wt.-%, even more preferably 6 to 15 wt.- % The particulate build material may comprise further, for example non-polymeric, components, for example one or more of glass beads, glass fibers, metal particles, carbon particles such as carbon fibers, ceramic particles or ceramic fibers, or (nano)clays. Said components may be coated with a polymeric material like the before-mentioned polymeric to form a composite of a polymer shell around a non-polymeric core.

[0070] The particulate build material of the materials kit herein may have a median particle size D50 of 5 pm to 250 pm, preferably of 15 pm to 150 pm, more preferably 25 pm to 90 pm. Furthermore, the width and / or degree of symmetry of the particle size distribution of the particulate build material may be further defined by its D10 and D90 values, which may range from 1 pm (D10) to 300 pm (D90), preferably from 5 pm (D10) to 250 pm (D90), more preferably from 10 pm (D10) to 200 pm (D90), wherein the D10, D50 and D90 values are determined according to the following method. Particle size distribution ("PSD”) as referred to herein was measured with a QICPIC / L QP0610 & RODOS / L M instrument with a 85 Hz frame rate and PAQXOS 6.0.1 feret_mean, ellipsoid(FERET), non-ISO software. A pressure of 1 bar, 70mbar vacuum, 20% feed rate with a VIBRI feeder and a gap width of 3mm was used as a dispersing method. The PSD was measured by adding 0.5 mg to 1.0 g of sample to the instrument feeder to allow it to be distributed to the high speed image analyzer. The high speed image analyzer comprises a pulsed light source with nanosecond range illumination times and a high-resolution, high-speed camera. The particles are optically frozen while the high-speed camera captures the razor-sharp particle projections with a frequency of up to 500 frames per second. The result is given as a particle size distribution range between 1 .8-4000 pm. Particle size is typically shown as D10, D50, D90, which gives the relative size of particles at 10%, 50%, and 90% of the cumulative distribution of particles (by volume).

[0071] With regard to the materials kit, it is further preferred that the fusing fluid has a peak boiling point and the particulate material has a peak melting point, the peak boiling point is determined according to the method specified above and the peak melting point is determined according to the methods specified below, wherein the peak boiling point of the fusing fluid is not more than 75 °C above the peak melting point of the particulate build material, and is more preferably from 5 to 75°C, even more preferably from 7 to 62 °C, still even more preferably 10 to 50 °C above the peak melting point of the particulate build material.

[0072] The peak melting point, or the peak melting temperature Tm_peak, of the particulate build material is determined via differential scanning calorimetry (“DSC”)). Thus, experiments were conducted in duplicate on a conventional heat-flux DSC 2 from Mettler Toledo. After a signal equilibration time of 5 minutes at 30°C, a heating ramp at 10°C / min in the range from 30°C to 250°C using nitrogen at 10ml / min as purge gas was applied for determining the thermal parameters of the investigated particulate materials. The peak melting temperature Tm_peak is determined from the first heating curve using standard analysis by a person skilled in the art (using Mettler Toledo STARe Software version 18.00a).

[0073] In addition, it preferred that the particulate build material has a peak melting point as determined according to the method described in the specification, wherein the boiling endset temperature Tb_endset of the boiling range of the fusing fluid is not more than 100 °C above the peak melting point of the particulate build material, preferably is from 10 to 100 °C above the peak melting point of the particulate build material, more preferably is from 15 to 90 °C, even more preferably is from 20 to 80 °C above the peak melting point of the particulate build material.

[0074] The fusing fluid of the materials kit preferably has suitable rheological properties such that optimum jetting parameters for the operation of the printhead (fluid deposition module) may be achieved, such as droplet formation including droplet size, shape, and length of the drop tail from the orifice plate of the printhead before break off, and the meniscus shape of the fluid formed at the nozzle orifice. Typically, the viscosity and the surface tension of the fusing fluid determine its rheology and are dependent on the requirement of the printhead used, a suitable example of which may for example be a Xaar 1003 printhead by the company Xaar pic. Hence it is preferred that the fusing fluid of the materials kit has a viscosity in the range which is acceptable by the specific print head used to deposit the fusing fluid. In particular the fusing fluid has a viscosity in a range from 5 to 100 cP, preferably from 6 to 20 cP at a jetting temperature, which may be 35 to 80°C, preferably 35 °C to 40°C. This can be achieved by adding a viscosity modifier to the fusing fluid of the materials kit. Suitable viscosity modifiers are mentioned above. The modification of the surface tension ef fusing fluid may be achieved by adding further additives like in particular surfactants. Suitable surfactants are also described above.

[0075] Method and three-dimensional object:

[0076] The invention further relates to a method for the print and fuse manufacture of a three- dimensional object from a particulate build material. Said method comprises or consists of the following steps:

[0077] A) forming a particulate build material layer from the particulate build material; B) according to printing data based on a three-dimensional object model of the three- dimensional object, selectively dispensing a fusing fluid onto the particulate build material layer to define within the particulate build material layer a cross section of the three- dimensional object to be formed;

[0078] C) exposing the particulate build material layer with the fusing fluid dispensed thereto with fusing radiation to selectively fuse the particulate build material within the cross section; and

[0079] D) repeating steps A) to C) until the three-dimensional object is formed, wherein the fusing fluid is a fusing fluid according to the invention, or the fusing fluid and the particulate build material are those as defined above or are from a materials kit according to the invention.

[0080] In print and fuse applications, the printing data for operating the print heads is provided in form of “slice” data, where each slice corresponds to a layer of the object to be formed. Slices are generated by placing a model of the object to be formed in a virtual build volume that corresponds to the actual build volume in the additive manufacturing apparatus. Usually, geometrical transformations are applied to the object model and / or the virtual build volume to compensate for shrinkage of the build volume as it cools down, and to correct for process dependent object distortions. After that, the transformed virtual build volume containing the object model is divided into a stack of sequential slices that corresponds to the stack of all layers that will be distributed in the apparatus to form the object. Each slice is a two- dimensional bitmap of data in terms of pixels. Each pixel defines a location on the layer, and importantly which locations are to receive fusing fluid to define a cross section of the object. The amount of absorber that is to be deposited may not be a constant amount per pixel. The slice data may further define a variable amount of fusing fluid that is to be provided to each pixel, similar to “greyscale” or “halftone” printing in the 2D printing industry, in which the volume of the fusing fluid is varied per unit area on the print medium to achieve different optical densities of pigment on the printed media. In the case of fusing fluid in print and fuse processes, varying the amount of fusing fluid from one pixel to another achieves a varying amount of infrared absorber between corresponding locations on the layer, and thus the energy that will be absorbed at those locations. This allows controlling at or close to pixel resolution the temperature distribution over the cross section of the object while infrared radiation is applied. Typically, the perimeter region of the cross section receives a higher amount of absorber than the inner region of the cross section to achieve a good surface finish on the one hand and to avoid overheating towards the center of the cross section (and the underlying, or subsequent overlying, cross sections) on the other. It may therefore be desirable to provide a fusing fluid that does not comprise flame retardant components, since applying a variable fusing fluid amount will inevitably lead to applying a variable amount of flame retardant, and thus variable flame retardancy within the formed part and between parts. The determination of the amount of fusing fluid for each pixel is typically a result of a thermal model applied to each slice, and depends on the shape, size and feature resolution of each object.

[0081] Step (B) of the method for the print and fuse manufacture may comprise, for one or more of the layers, depositing different amounts ef fusing fluid over different “voxels” of the object cross section, wherein each voxel is a unit volume of the layer defined by a two-dimensional unit area corresponding to a pixel in the slice data, and by the layer thickness.

[0082] The use of the inventive fusing fluid or of the inventive materials kit in said method leads to improved flame retardancy properties in the formed three-dimensional objects. The invention therefore also relates to a three-dimensional object obtained or obtainable by the inventive method as described above. Said three-dimensional object preferably self-extinguishes within 60 seconds during flame application, measured according to the modified FAR 25.853 Part 1 (a)(1 )(i) test method described above, preferably within 50 seconds.

[0083] Use of the fusing fluid and of the materials kit:

[0084] The fusing fluid or the materials kit according to the invention can be used, and may be particularly suitable when used, in print and fuse methods to improve the flame retardancy of the obtained three-dimensional objects, preferably in the method according to the invention. The flame retardancy is preferably defined as described above. Especially, it is preferred that the use of the inventive fluid or of the material kit leads to a three-dimensional object that selfextinguishes within 60 seconds during flame application, measured according to the modified FAR 25.853 Part 1 (a)(1 )(i) test method described above, preferably within 50 seconds.

[0085] Apparatus:

[0086] The invention further relates to an apparatus for the print and fuse manufacture of three- dimensional objects from a particulate build material, preferably for the method according to the invention. The apparatus comprises a build container comprising a build platform for supporting particulate build material layers; a particulate build material supply system configured to supply to and distribute particulate build material over the build platform to form each particulate build material layer; a fluid deposition system containing a fusing fluid and configured to selectively dispense the fusing fluid onto the top particulate build material layer according to printing data based on a three-dimensional object model so as to define a cross section of the object to be formed; a fusing device for providing fusing radiation to the particulate build material layer so as to cause melting of the build material within the defined cross section; wherein the fusing fluid is a fusing fluid according to the invention, or the fusing fluid and the particulate build material are those as defined above or are from a materials kit according to the invention.

[0087] The particulate build material supply system may comprise a particulate build material supply tank for, or comprising, the particulate build material, and a distribution device configured to distribute the particulate material over the build platform so as to form each particulate build material layer. The fluid deposition system may comprise a fluid reservoir, which contains or is configured to contain the fusing fluid according to the invention, and a fluid deposition module connected to the fluid reservoir and configured to selectively dispense the fusing fluid onto the top particulate build material layer according to printing data based on a three- dimensional object model so as to define a cross section of the object to be formed. The fluid deposition module may comprise one or more droplet deposition devices such as inkjet printheads.

[0088] The apparatus may further comprise, or be connectable to, a control unit configured to control the systems and / or modules throughout a build process in order to form the three-dimensional objects. For instance, the control unit may be configured to communicate the printing data based on a three-dimensional object model to the fluid deposition system, or rather the fluid deposition module, which for example comprises one or more droplet deposition devices such as inkjet printheads. The one or more droplet deposition devices in turn are configured to selectively dispense the fusing fluid supplied to the fluid deposition module from the fluid reservoir onto the particulate build material layer according to the printing data. The control unit may further be configured to control the particulate build material supply system to form each new layer and to control the fusing device (and optionally one or more warming devices and temperature sensors) in a synchronized manner. Such operation and control of a print and fuse process is generally known to the skilled person and will not be described in more detail here. Figure 3 shows a simplified cross-sectional view of an exemplary apparatus 1 for the print and fuse manufacture of three-dimensional objects from a materials kit according to the invention. The apparatus 1 comprises a build container 10, a particulate build material supply system 20, a fluid deposition system 30 containing the fusing fluid according to the invention, a fusing device 40, a warming device 50 and a control unit 70.

[0089] The build container 10 comprises a build platform 12, which is vertically movable via a platform lifting device 14, and opposing build container walls 16 which seal against the vertically movable build platform 12, thus forming an enclosure with an opening at the top to hold a build bed I powder cake 60 of vertically stacked particulate build material layers. The top particulate build material layer 62 is indicated by a dotted line. Before each layer is distributed by the distribution device 26, the build platform 12 is lowered by the platform lifting device 14, such as a motor driven piston, configured to move the build platform 12 during the print and fuse process down and to eject the finished build volume upwards, out of the build container 10, after completion of the build process. The vertical motion (along z) is indicated by a bold up down arrow. When the platform 12 is lowered by a layer thickness, it forms a recess with the top plate 28.

[0090] The particulate build material supply system 20 is located adjacent to the build container 10, and both are connected by a top plate 28. The particulate build material supply system 20 comprises a particulate build material supply tank 22 connected to and configured to supply fresh build material to a dosing module 24. The dosing module 24 in this example apparatus is located below the top plate 28 and adjacent to the build container 10 with respect to the direction of layer distribution and is configured to dose a consistent amount of dosed particulate build material P to the level of the top plate 28. The particulate build material supply system 20 further comprises a distribution device 26, shown in Fig. 3 in the form of a counter rotating roller, which is configured to traverse along the direction indicated as x, from left to right, to distribute the dosed particulate build material P over the build platform 12 to fill the recess and form a new top particulate build material layer 62.

[0091] Furthermore, the fluid deposition system 30 comprises a fluid reservoir 32 for containing a supply of fusing fluid according to the invention and a fluid deposition module 30. The fluid reservoir 32 is connected to the fluid deposition module 34 for example via flexible hoses to supply the fluid deposition module with fusing fluid. The fluid deposition module 34 of the fluid deposition system 30 is arranged to traverse over the build container 10 to selectively dispense the fusing fluid onto the top particulate build material layer 62. In Fig. 3 the traverse may be applied ahead of, and synchronized with, the distribution device, as indicated by the bold arrows pointing from left to right. The fluid reservoir 32 is configured to receive and contain a supply ef fusing fluid according to the invention.

[0092] The fluid deposition system 30 may be coupled to the fusing device 40, which may be in the form of an elongate infrared fusing lamp spanning the width of the build material layer (along the y-direction, not indicated) and which traverses the build platform 12 to follow behind the fluid deposition module to immediately apply fusing radiation to and cause melting of the build material within the defined object cross section 64.

[0093] In addition, the apparatus 1 may comprise one of more warming devices 50 for achieving a predefined bed temperature of the top particulate build material layer 62 and that is chosen to lie between the melting point and the solidification temperature of the particulate material. The predefined bed temperature may be selected to lie within for example around 5 to 30 °C below the melting point of the particulate build material and is selected to avoid temperature differentials high enough to cause curling of the fused object cross section 64 on the one hand, and accidental fusing and / or sticking of the particulate build material surrounding the object cross section 64 on the other hand. In Fig. 3, the warming device 50 may be coupled to the distribution device 26 to immediately preheat the layer as it is formed. Furthermore, not shown, an overhead heating device and temperature sensor may be mounted above the build container 10 in a fixed position in the ceiling of the apparatus, and may be configured to be operated in response to measurements of the sensor to maintain the top layer at the predefined bed temperature. The fusing device 40 coupled to the fluid deposition module 34, and the distribution device 26 optionally coupled to the warming device 50, may be mounted on individual sleds (not shown) that are movable back and forth over the top plate 28. The control unit 70 is configured to control the systems and modules throughout a build process in order to form the three-dimensional object 2.

[0094] During a build process, the fluid deposition module 34 is operated to selectively dispense the fusing fluid supplied by the fluid reservoir 32 onto a newly formed top particulate build material layer 62 according to printing data based on a three-dimensional object model so as to define an object cross section 64 of the object 2 to be formed within the top particulate build material layer 62 of the build bed 60. Next, the fusing lamp 40 is operated to provide fusing radiation to the top particulate build material layer 62, causing melting of the build material within the defined object cross section 64 and thus forming of the object 2 iteratively. This process is repeated until the three-dimensional object 2 is produced. The control unit 70 may be configured to control the motion of the build platform 12, the operation of the particulate build material supply system 20, the fluid deposition system 30, the fusing device 40 and optionally the warming device 50 in a synchronized manner. Once the build process is complete, the finished object 2 can be removed from the build volume / powder cake 60.

[0095] Embodiments:

[0096] The invention relates in particular to the following embodiments:

[0097] According to a first embodiment, the invention relates to a fusing fluid for the print and fuse manufacture of three-dimensional objects from particulate build material, wherein the fusing fluid comprises or consists of a) a non-aqueous carrier liquid; b) a radiation absorber; c) optionally a dispersant; and d) optionally one or more further additives; wherein the fusing fluid has a boiling range lying within a temperature window of 150 to 350 °C at normal pressure of 101.3 kPa with a boiling range width of less than or equal to 70 °C, wherein the boiling range is defined by a boiling onset temperature Tb_onset and a boiling endset temperature Tb_endset determined according to the method described in the specification, wherein the boiling range width is Tb_endset minus Tb_onset.

[0098] According to a second embodiment, the invention relates to the fusing fluid according to the first embodiment, wherein the boiling range of the fusing fluid lies within the temperature window of 170 to 320 °C at a normal pressure of 101.3 kPa, preferably within the temperature window of 190 to 290 °C, more preferably within the temperature window of 210 to 260 °C.

[0099] According to a third embodiment, the invention relates to the fusing fluid according to the first or second embodiment, wherein the boiling range width of the boiling range of the fusing fluid is from 0.5 °C to 70 °C, preferably from 1 °C to 60 °C, more preferably from 5 °C to 50 °C, even more preferably from 5 °C to 40 °C, and most preferably from 10 °C to 40 °C.

[0100] According to a fourth embodiment, the invention relates to the fusing fluid according to any of the preceding embodiments, wherein the fusing fluid has a peak boiling point in a peak temperature range of 170 to 280 °C, determined according the method described in the specification, preferably in a peak temperature range of 190 to 270 °C, more preferably in a peak temperature range of 200 to 260 °C, even more preferably in a peak temperature range of 21 O to 250 °C. According to a fifth embodiment, the invention relates to the fusing fluid according to any of the preceding embodiments, wherein the non-aqueous carrier liquid comprises or consists of hydrocarbons, alkyl benzoates, benzyl alcohols, benzyl esters, benzaldehydes, carboxylic acid esters, alkanols, alkanones, diols, methoxytoluenes, methylnaphthalenes, cyclic carbonate esters, terpene or a combination thereof, preferably nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, icosane, isomers of the before mentioned, methyl benzoate, ethyl benzoate, propyl benzoate, isopropyl benzoate, butyl benzoate, isobutyl benzoate, pentyl benzoate, hexyl benzoate and octyl benzoate, benzyl alcohol, 4-Methoxybenzyl alcohol, benzyl acetate, benzyl propionate, benzyl butyrate, benzyl pentanoate, benzyl hexanoate, benzaldehyde, 4- methoxybenzaldehyde, methyl hexanoate, ethyl hexanoate, methyl octanoate, ethyl octanoate, methyl decanoate, ethyl decanoate, methyl dodecanoate, ethyl dodecanoate, methyl tetradecanoate, ethyl tetradecanoate, methyl hexadecanoate, ethyl hexadecanoate, methyl palmitoleate, ethyl palmitoleate, methyl myristoleate, ethyl myristoleate, methyl undecenoate, ethyl undecenoate, methyl pentadecanoate, ethyl pentadecanoate, methyl heptadecanoate, 2-ethylhexanol, (Oxolan-2-yl)methanol, phenylacetone, ethylene glycol, propylene glycol, butane-1 ,4-diol, pentane-1 ,5-diol, hexane-1 ,6-diol, 4-methoxytoluene, 1- methylnaphthalene, propylene carbonate and 1-methyl-4-(prop-1-en-2-yl)cyclohex-1-ene or a combination thereof, more preferably dodecane, a mixture of hydrocarbons with at least 9 up to a maximum of 20 carbon atoms, ethyl benzoate, propyl benzoate, isopropyl benzoate, butyl benzoate or isobutyl benzoate.

[0101] According to a sixth embodiment, the invention relates to the fusing fluid according to any of the preceding embodiments, wherein the non-aqueous carrier liquid comprises or consists of an alkyl benzoate or a mixture of hydrocarbons, wherein

[0102] • the alky benzoate is preferably ethyl benzoate, propyl benzoate, isopropyl benzoate, butyl benzoate or isobutyl benzoate; and

[0103] • the mixture of hydrocarbons is preferably a mixture of hydrocarbons with at least 9 up to a maximum of 20 carbon atoms, more preferable a mixture of hydrocarbons with at least 11 up to a maximum of 16 carbon atoms, even more preferably a mixture of hydrocarbons having 11 to 16 carbon atoms.

[0104] According to a seventh embodiment, the invention relates to the fusing fluid according to any of the preceding embodiments, wherein the radiation absorber is selected from the group comprising or consisting of carbon black, carbon nanotubes, graphenes, graphites, antimony tin oxide, indium tin oxide, tungsten oxide, nigrosins, or a combination thereof, preferably carbon black. According to an eighth embodiment, the invention relates to the fusing fluid according to any of the preceding embodiments, wherein the dispersant is selected from the group comprising or consisting of modified polyurethanes, polyester-modified polyalkylene imines, structured acrylate copolymers with pigment-affinic groups, polyether-containing block copolymers, polyolefine containing block copolymers, or a combination thereof.

[0105] According to a ninth embodiment, the invention relates to the fusing fluid according to any of the preceding embodiments, wherein the one or more further additives is a viscosity modifier, which is preferably selected from the group comprising or consisting of olefin copolymers, polyalkyl methacrylate homopolymers, polyalkyl methacrylate (co)polymers, amorphous polyamides, polyureas, or a combination thereof, preferably ethylene propylene diene copolymers, ethyl propylene copolymers, poly(methyl methacrylate), poly(ethyl methacrylate), poly(propyl methacrylate), poly(butyl methacrylate), poly(dodecyl methacrylate-co-methyl methacrylate, poly(butyl methacrylate-co-methyl methacrylate), or a combination thereof.

[0106] According to a tenth embodiment, the invention relates to the fusing fluid according to any of the preceding embodiments, wherein the fusing fluid comprises or consists of a) 70 to 98 wt.-% of the non-aqueous carrier liquid, preferably 80 to 95 wt.-%; b) 2 to 15 wt.-% of the radiation absorber, preferably 3 to 8 wt.-%, more preferably 4 to 6 wt.-%; c) 0 to 15 wt.-% of the dispersant, preferably 2 to 7 wt.-%; and I or d) 0 to 10 wt.-% of the one or more further additives, preferably 0.5 to 5 wt.-% based on the total weight of the fusing fluid.

[0107] According to an eleventh embodiment, the invention relates to a materials kit for the print and fuse manufacture of three-dimensional objects from particulate build material comprising or consisting of: a particulate build material; and a fusing fluid according to any one of embodiments 1 to 10.

[0108] According to a twelfth embodiment, the invention relates to the materials kit according to embodiments eleven, wherein the particulate build material is a polymeric particulate build material comprising or consisting of at least 50 wt% polymer, based on the total amount of the particulate build material, preferably of 60 to 100 wt.-%, more preferably of 70 to 95 wt.-%, even more preferably of 80 to 90 wt.-%.

[0109] According to a thirteenth embodiment, the invention relates to the materials kit according to embodiment eleven or twelve, wherein the particulate build material is selected from the group comprising or consisting of thermoplastic polymeric powder build materials, preferably polyamides, polyurethanes, or combination thereof, more preferably polyamide 11 , polyamide 12, polyamide 10.10, polyamide 10.12, polyamide 12.12, polyamide 6.66, polyamide 6.12, polyamide 6.10, polyamide 6.13, polyamide 4.10, or a combination thereof.

[0110] According to a fourteenth embodiment, the invention relates to the materials kit according to any one of embodiments eleven to thirteen, wherein the particulate build material comprises one or more flame retardant components, preferably one or more of: brominated polyacrylates, brominated polystyrenes, ammonium polyphosphates, melamine polyphosphate, aluminum diethyl-phosphinate, 3,9-Dimethyl-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane-3,9- dioxide and 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, more preferably wherein the particulate build material comprises brominated polyacrylates.

[0111] According to a fifteenth embodiment, the invention relates to the materials kit according to embodiment fourteen, wherein the one or more flame retardant components are present in an amount of less than or equal to 30 wt.-% in the particulate build material, based on the total amount of the particulate build material, preferably 2 to 30 wt.-%, more preferably 4 to 22 wt.- %, even more preferably 6 to 15 wt.-%.

[0112] According to a sixteenth embodiment, the invention relates to the materials kit according to any one of embodiments eleven to fifteen, wherein the particulate build material has a median particle size D50 of 5 to 250 pm, preferably of 15 to 150 pm, more preferably of 25 to 90 pm, determined according to the method described in the specification.

[0113] According to a seventeenth embodiment, the invention relates to the materials kit according to any one of embodiments eleven to sixteen, wherein the fusing fluid has a peak boiling point and the particulate material has a peak melting point, both determined according to the methods described in the specification, wherein the peak boiling point of the fusing fluid is not more than 75 °C above the peak melting point of the particulate build material, preferably is from 5 to 75°C above the peak melting point of the particulate build material, more preferably from 7 to 62 °C, even more preferably from 10 to 50 °C.

[0114] According to an eighteenth embodiment, the invention relates to the materials kit according to any one of embodiments eleven to seventeen, wherein the particulate build material has a peak melting point as determined according to the method described in the specification, wherein the boiling endset temperature Tb_endset of the boiling range of the fusing fluid is not more than 100 °C above the peak melting point of the particulate build material, preferably is from 10 to 100 °C above the peak melting point of the particulate build material, more preferably is from 15 to 90 °C, even more preferably is from 20 to 80 °C above the peak melting point of the particulate build material. According to a nineteenth embodiment, the invention relates to a method for the print and fuse manufacture of a three-dimensional object from a particulate build material, the method comprising the steps of:

[0115] A) forming a particulate build material layer from the particulate build material;

[0116] B) according to printing data based on a three-dimensional object model of the three-dimensional object, selectively dispensing a fusing fluid onto the particulate build material layer to define within the particulate build material layer a cross section of the three-dimensional object to be formed;

[0117] C) exposing the particulate build material layer with the fusing fluid dispensed thereto with fusing radiation to selectively fuse the particulate build material within the cross section; and

[0118] D) repeating steps A) to C) until the three-dimensional object is formed, wherein the fusing fluid is a fusing fluid according to any one of embodiments 1 to 10, or the fusing fluid and the particulate build material are those as defined in any one of embodiments 11 to 18 or are from a materials kit according to any one of embodiments 11 to 18.

[0119] According to a twentieth embodiment, the invention relates to a three-dimensional object obtained or obtainable by a method according to embodiment nineteen.

[0120] According to a twenty-first embodiment, the invention relates to the three-dimensional object according to embodiment twenty, wherein the three-dimensional object self-extinguishes within 60 seconds during flame application, measured according to the modified FAR 25.853 Part 1 (a)(1 )(i) test method described in the specification, preferably within 50 seconds.

[0121] According to a twenty-second embodiment, the invention relates to the use of a fusing fluid according to any one of embodiments 1 to 10 or of a materials kit according to any one of embodiments 11 to 18 in print and fuse methods for improving the flame retardancy of the obtained three-dimensional objects, preferably in a method according to embodiment 19.

[0122] According to a twenty-third embodiment, the invention relates to an apparatus (1 ) for the print and fuse manufacture of three-dimensional objects (2) from a particulate build material, preferably for the method according to embodiment 19, the apparatus (1 ) comprising a build container (10) comprising a build platform (12) for supporting particulate build material layers; a particulate build material supply system (20) configured to supply to and distribute particulate build material over the build platform (12) to form each particulate build material layer; a fluid deposition system (30) containing a fusing fluid and configured to selectively dispense the fusing fluid onto the top particulate build material layer (62) according to printing data based on a three-dimensional object model so as to define a cross section of the object (64) to be formed; - a fusing device (40) for providing fusing radiation to the particulate build material layer so as to cause melting of the build material within the defined cross section; wherein the fusing fluid is a fusing fluid according to any one of embodiments 1 to 10, or the fusing fluid and the particulate build material are those as defined in any one of embodiments 11 to 18 or are from a materials kit according to any one of embodiments 11 to 18.

[0123] The present invention is explained in more detail with reference to the following examples.

[0124] Measurement methods: The flame retardancy of three-dimensional samples was determined via the modified FAR 25.853 Part 1 (a)(1 )(i) protocol (as described above). Thus, in the burning tests performed, samples with dimensions of 70x200x1.5 mm were used. Samples were considered to have passed the modified FAR 25.853 test if the sample self-extinguished during the 60s application of the flame. If samples passed the FAR 25.853 test consistently at the thickness of 1.5 mm, all showed self-extinguishing of the sample during the 60s application of the flame. This self-extinguishing of the sample within the 60s application was used as a criterion for samples to robustly pass the test. measurements The boiling range, the boiling range width Tb_onset, Tb_endset, the peak boiling point and the peak melting point / peak melting temperature were determined as described above.

[0125] Materials:

[0126] The following materials were used to form samples for burn testing:

[0127] Particulate Build Material:

[0128] • FR-106 (fire retardant Nylon 11 , a dry blend of PA11 and poly brominated polyacrylate from the company ALM; peak melting point (Tm.peak) = 191 °C determined as described above; D10 = 56 pm, D50 = 118 pm, D90 = 173 pm, determined as described above);

[0129] • PA806 FR (fire retardant Nylon 11 , a dry blend of Rilsan Invent PA11 and poly brominated polyacrylate); from the company ALM; peak melting point (Tm.peak) = 203 °C determined as described above; D10 = 22 pm, D50 = 55 pm, D90 = 99 pm, determined as described above);

[0130] • PA814 FR (fire retardant Nylon 11 ; similar to PA806 FR but with a high concentration of poly brominated polyacrylate from the company ALM; peak melting point (Tm.peak) = 203 °C determined as described above; D10 = 17 pm, D50 = 44 pm, D90 = 82 pm, determined as described above). Non-aqueous carrier liquids:

[0131] • Isoparaffin MC 80 (a mixture of isoparaffinic hydrocarbons C11 -C16; from the company

[0132] JBL Solutions B.V. (Netherlands))

[0133] • Butyl benzoate (purity 99%; from the company Sigma-Aldrich)

[0134] Radiation absorbers:

[0135] • Carbon Black TPK 1099R (from the company Cabot Corporation)

[0136] • Disperbyk®-2157 (polyester-modified polyalkylene imine from the company BYK Chemie GmbH);

[0137] • Byk-Max-D 4220 (combination of anionic and amphoteric surfactants from the company BYK Chemie GmbH)

[0138] • Disperbyk®-2200 (high molecular weight copolymer with pigment affinic groups from the company BYK Chemie GmbH).

[0139] The inventive Fusing Fluid F1 was prepared by adding the following components to a 200 ml vial: 38.75 g Isoparaffin MC 80, 3.75 g Disperbyk®-2157, 7.5 g carbon black TPK1099 and 100 g zirconia ball. The vial was shaken overnight after which a good dispersion was obtained. Subsequently the fluid was decanted and diluted further with Isoparaffin MC 80 (2:1 ratio) in order to achieve a final carbon black concentration of 5 wt.-%.

[0140] The resulting inventive Fusing Fluid F1 had the following composition and properties:

[0141] • Properties: Boiling range = 217 - 250 °C (Tb_onset = 217 °C; Tb_endset = 250 °C), boiling range width ATb = 33 °C, peak boiling point = 239 °C (all values were determined as described above);

[0142] • Composition: 92.5 wt.-% Isoparaffin MC 80; 5 wt.-% Carbon Black TPK 1099R; 2.5 wt.- % Disperbyk®-2157.

[0143] The Inventive Fusing Fluid F2 was prepared by adding the following components to a 200 ml vial: 38.75 g Isoparaffin MC 80, 3.75 g Byk-Max-D 4220, 7.5 g carbon black TPK1099 and 100 g zirconia ball. The vial was shaken overnight after which a good dispersion was obtained. Subsequently the fluid was decanted and diluted further with Isoparaffin MC 80 (2:1 ratio) in order to achieve a final carbon black concentration of 5 wt.-%. The resulting inventive Fusing Fluid F2 had the following composition and properties:

[0144] • Properties: Boiling range = 216 - 253 °C (Tb_onset = 216 °C; Tb_endset = 253 °C), boiling range width ATb = 37 °C, peak boiling point = 240 °C (all values were determined as described above);

[0145] • Composition: 92.5 wt.-% Isoparaffin MC 80; 5 wt.-% Carbon Black TPK 1099R; 2.5 wt.-% Max-D-4220.

[0146] The Inventive Fusing Fluid F3 was prepared by adding the following components to a 200 ml vial: 38.75 g Butyl benzoate, 3.75 g Disperbyk-2200, 7.5 g carbon black TPK1099 and 100 g zirconia ball. The vial was shaken overnight after which a good dispersion was obtained. Subsequently the fluid was decanted and diluted further with butyl benzoate (2:1 ratio) in order to achieve a final carbon black concentration of 5 wt.-%.

[0147] The resulting inventive Fusing Fluid F3 had the following composition and properties:

[0148] • Properties: Boiling range = 244 - 256 °C (Tb_onset = 244 °C; Tb_endset = 256 °C), boiling range width ATb = 12 °C, peak boiling point = 249 °C (all values were determined as described above);

[0149] • Composition: 92.5 wt.-% butyl benzoate; 5 wt.-% Carbon Black TPK 1099R; 2.5 wt.- % Disperbyk®-2200.

[0150] HAF™ conventional fusing fluid (X3D-01011 ) from the company Stratasys was used as Comparative Fusing Fluid F4. Said fusing fluid has the following composition and properties:

[0151] • Properties: Boiling range = 232 - 313 °C (Tb_onset = 232 °C; Tb_endset = 313 °C), boiling range width ATb = 81 °C, peak boiling point = 288 °C (all values were determined as described above);

[0152] • Composition comprises at least: non-aqueous carrier liquid (Petroleum Distillates, hydrotreated middle and light; Hydrocarbons C14-C18 (n-alkanes, isoalkanes, cyclics, aromatics 2-30%)); Radiation Absorber: carbon black.

[0153] Experiments:

[0154] Reference Example 1

[0155] • PA806 FR was SLS printed on a Prodways P2000ST Promaker using typical print settings, most notably bed temperature Tbed = 182°C, Laser Power = 50 W, Hatching distance = 0.2 mm, Laser speed = 12700 mm / s (single scan). Modified FAR 25.853 samples with dimensions of 70 x 200 x 1.5 mm were printed slightly smaller than standard in view of the limited size of the build volume.

[0156] The samples were burned using a setup complying with the above-mentioned modified FAR 25.853 protocol. Samples were subjected to the flame for 60s after which the flame was removed.

[0157] The PA806 FR samples self-extinguished within at most 45 s during application of the flame;

[0158] • PA814 FR samples were generated and tested as described for PA806 FR above. The samples self-extinguished within at most 45 s during application of the flame;

[0159] • FR-106 samples were generated in a similar manner as described above, with the difference of using a bed temperature Tbed = 175°C. The samples self-extinguished within a burn time of at most 45 s during application of the flame and thus passed the burn test criteria defined herein.

[0160] Reference Example 2 (Reference Print and Fuse samples):

[0161] PA814 FR samples were manufactured on a Stratasys H350 print and fuse printer at a bed temperature of 182°C with greyscales varying from 20% to 100%, which correlate to from 1.7 volume% to 8.4 volume% fusing fluid in the final sample.

[0162] Comparative Fusing Fluid F4 as described above (HAF™ fusing fluid (X3D-01011 from Stratasys) was used here as a conventional fusing fluid. Samples were printed with dimensions of 70 x 200 x 1 .5 mm and tested with the above-mentioned modified FAR 25.853 protocol.

[0163] A clear difference in flame retardancy of the samples could be noted (even at low greyscales, such as 20% greyscale or 1.7 volume% ef fusing fluid in the final sample) could be observed compared to samples from Reference Example 1. Samples from Reference Example 2 led to bigger burn length, occasionally non-extinguishing dripping (within 3s), and continuing to burn after flame removal (for >15s). It was furthermore identified that these samples did not consistently self-extinguish within the 60s of flame application, which is the additional criteria defined herein for a robust pass. Therefore, Reference samples 2 failed the tests.

[0164] Inventive Example 3 (Testing of Inventive Fusing Fluids F1 , F2, F3 in comparison to Comparative Fusing Fluid F4):

[0165] In order to evaluate the influence of the fusing fluids on flame retardancy, a protocol was developed (also described above) in which SLS-printed samples of 1.5 mm (+ / - 0.1 mm) thickness were treated as described above, by soaking them in a fusing fluid for 30 min, after which they were removed from the fluid and put in a vacuum oven (10-20 mbar) at 150°C for 16 hours (“treated samples”). In this way, fusing fluid was introduced to and removed from at least the “skin” of the sample to simulate the surface properties of samples resulting from a print and fuse process. This method allowed for fast screening of fluids without fabrication on a print and fuse machine while still capturing the essential material properties of print and fuse samples. These treated samples were tested using the above-mentioned modified FAR 25.853 test protocol, specifically aiming at identifying if samples would pass in a robust way.

[0166] In this way, SLS-printed samples were treated with Inventive Fusing Fluids F1 , F2, F3 and Comparative Fusing Fluid F4 (each in duplicates) described above. The results are shown in the following Table 2:

[0167] Table 2

[0168] (‘>Sample did not extinguish during flame application; Sample did not bum after removal of flame .

[0169] The treatment with Inventive Fusing Fluid F1 , Inventive Fusing Fluid F2 or Inventive Fusing Fluid F3 clearly leads to an improvement of the flame retardancy of the printed samples, resulting in self-extinguishing of the sample while the flame was still being applied.

[0170] A far superior burn behavior of samples treated with inventive fusing fluids is further demonstrated in Figure 4, showing pictures taken at 40 s during the 60s application of the flame during the modified FAR 25.853 test of PA814 FR samples treated with Inventive Fusing Fluid F1 (see Fig. 4 (A)) and Comparative Fusing Fluid F4 (see Fig. 4 (B)). As can be seen in Fig. 4 (A), the sample treated with Inventive Fusing Fluid F1 self-extinguishes (stops burning) during the 60s flame application. In comparison, Comparative Fusing Fluid F4 burns heavily during the whole 60s of flame application (see Fig. 4 (B)). Hence, the inventive fluid F1 drastically improves the flame retardancy of the sample. Reference signs of Fig. 3:

[0171] 1 apparatus

[0172] 2 object

[0173] 10 build container

[0174] 12 build platform

[0175] 14 platform lifting device

[0176] 16 build container walls

[0177] 20 particulate build material supply system

[0178] 22 particulate build material supply tank

[0179] 24 dosing module

[0180] 26 distribution device

[0181] 28 top plate

[0182] 30 fluid deposition system

[0183] 32 fluid reservoir

[0184] 34 fluid deposition module

[0185] 40 fusing device (fusing lamp)

[0186] 50 warming device

[0187] 60 build bed I powder cake

[0188] 62 top particulate build material layer

[0189] 64 object cross section

[0190] 70 control unit

[0191] P dosed particulate build material

Claims

33Claims1. A fusing fluid for the print and fuse manufacture of three-dimensional objects from particulate build material, wherein the fusing fluid comprises or consists of a) a non-aqueous carrier liquid; b) a radiation absorber; c) optionally a dispersant; and d) optionally one or more further additives; w h e r e i n the fusing fluid has a boiling range lying within a temperature window of 150 to 350 °C at normal pressure of 101.3 kPa with a boiling range width of less than or equal to 70 °C, wherein the boiling range is defined by a boiling onset temperature Tb_onset and a boiling endset temperature Tb_endset determined according to the method described in the specification, wherein the boiling range width is Tb_endset minus Tb_onset.

2. Fusing fluid according to claim 1 , wherein the boiling range of the fusing fluid lies within the temperature window of 170 to 320 °C at a normal pressure of 101.3 kPa, preferably within the temperature window of 190 to 290 °C, more preferably within the temperature window of 21 O to 260 °C.

3. Fusing fluid according to claim 1 or claim 2, wherein the boiling range width of the boiling range of the fusing fluid is from 0.5 °C to 70 °C, preferably from 1 °C to 60 °C, more preferably from 5 °C to 50 °C, even more preferably from 5 °C to 40 °C, and most preferably from 10 to 40 °C.

4. Fusing fluid according to any preceding claim, wherein the fusing fluid has a peak boiling point in a peak temperature range of 170 to 280 °C, determined according the method described in the specification, preferably in a peak temperature range of 190 to 270 °C, more preferably in a peak temperature range of 200 to 260 °C, even more preferably in a peak temperature range of 210 to 250 °C.

5. Fusing fluid according to any preceding claim, wherein the non-aqueous carrier liquid comprises or consists of hydrocarbons, alkyl benzoates, benzyl alcohols, benzyl esters, benzaldehydes, carboxylic acid esters, alkanols, alkanones, diols, methoxytoluenes, methylnaphthalenes, cyclic carbonate esters, terpene or a combination thereof, preferably dodecane, a mixture of hydrocarbons with at least 9 up to a maximum of 20 carbon atoms, ethyl benzoate, propyl benzoate, isopropyl benzoate, butyl benzoate or isobutyl benzoate.

346. Fusing fluid according to any preceding claim, wherein the non-aqueous carrier liquid comprises or consists of an alkyl benzoate or a mixture of hydrocarbons, wherein• the alky benzoate is preferably ethyl benzoate, propyl benzoate, isopropyl benzoate, butyl benzoate or isobutyl benzoate; and• the mixture of hydrocarbons is preferably a mixture of hydrocarbons with at least 9 up to a maximum of 20 carbon atoms, more preferable a mixture of hydrocarbons with at least 11 up to a maximum of 16 carbon atoms, even more preferably a mixture of hydrocarbons having 11 to 16 carbon atoms.

7. Fusing fluid according to any preceding claim, wherein the radiation absorber is selected from the group comprising or consisting of carbon black, carbon nanotubes, graphenes, graphites, antimony tin oxide, indium tin oxide, tungsten oxide, nigrosins, or a combination thereof, preferably carbon black.

8. Fusing fluid according to any preceding claim, wherein the dispersant is selected from the group comprising or consisting of modified polyurethanes, polyester-modified polyalkylene imines, structured acrylate copolymers with pigment-affinic groups, polyether-containing block copolymers, polyolefine containing block copolymers, or a combination thereof.

9. Fusing fluid according to any preceding claim, wherein the one or more further additives is a viscosity modifier, which is preferably selected from the group comprising or consisting of olefin copolymers, polyalkyl methacrylate homopolymers, polyalkyl methacrylate (co)polymers, amorphous polyamides, polyureas, or a combination thereof, preferably ethylene propylene diene copolymers, ethyl propylene copolymers, poly(methyl methacrylate), poly(ethyl methacrylate), poly(propyl methacrylate), poly(butyl methacrylate), poly(dodecyl methacrylate-co-methyl methacrylate, poly(butyl methacrylate-co-methyl methacrylate), or a combination thereof.

10. Fusing fluid according to any preceding claim, wherein the fusing fluid comprises or consists of a) 70 to 98 wt.-% of the non-aqueous carrier liquid, preferably 80 to 95 wt.-%; b) 2 to 15 wt.-% of the radiation absorber, preferably 3 to 8 wt.-%, more preferably 4 to 6 wt.-%; c) 0 to 15 wt.-% of the dispersant, preferably 2 to 7 wt.-%; and I or d) 0 to 10 wt.-% of the one or more further additives, preferably 0.5 to 5 wt.-% based on the total weight of the fusing fluid.

11. A materials kit for the print and fuse manufacture of three-dimensional objects from particulate build material comprising or consisting of:• a particulate build material; and• a fusing fluid according to any one of claims 1 to 10.

12. The materials kit according to claim 11 , wherein the particulate build material is a polymeric particulate build material comprising or consisting of at least 50 wt% polymer, based on the total amount of the particulate build material, preferably of 60 to 100 wt.-%, more preferably of 70 to 95 wt.-%, even more preferably of 80 to 90 wt.-%.

13. The materials kit according to claim 11 or claim 12, wherein the particulate build material is selected from the group comprising or consisting of thermoplastic polymeric powder build materials, preferably polyamides, polyurethanes, or combination thereof, more preferably polyamide 11 , polyamide 12, polyamide 10.10, polyamide 10.12, polyamide 12.12, polyamide 6.66, polyamide 6.12, polyamide 6.10, polyamide 6.13, polyamide 4.10, or a combination thereof.

14. The materials kit according to any one of claims 11 to 13, wherein the particulate build material comprises one or more flame retardant components, preferably selected from one or more of: brominated polyacrylates, brominated polystyrenes, ammonium polyphosphates, melamine polyphosphate, aluminum diethyl-phosphinate, 3,9-Dimethyl- 2,4,8, 10-tetraoxa-3,9-diphosphaspiro[5.5]undecane-3,9-dioxide and 9,10-Dihydro-9-oxa- 10-phosphaphenanthrene-10-oxide, more preferably wherein the particulate build material comprises brominated polyacrylates.

15. The materials kit according to claim 14, wherein the one or more flame retardant components are present in an amount of less than or equal to 30 wt.-% in the particulate build material, based on the total amount of the particulate build material, preferably 2 to 30 wt.-%, more preferably 4 to 22 wt.-%, even more preferably 6 to 15 wt.-%.

16. The materials kit according to any one of claims 11 to 15, wherein the particulate build material has a median particle size D50 of 5 to 250 pm, preferably of 15 to 150 pm, more preferably of 25 to 90 pm, determined according to the method described in the specification.

17. The materials kit according to any one of claims 11 to 16, wherein the fusing fluid has a peak boiling point and the particulate material has a peak melting point, both determinedaccording to the methods described in the specification, wherein the peak boiling point of the fusing fluid is not more than 75 °C above the peak melting point of the particulate build material, preferably is from 5 to 75°C above the peak melting point of the particulate build material, more preferably from 7 to 62 °C, even more preferably from 10 to 50 °C.

18. The materials kit according to any one of claims 11 to 17, wherein the particulate build material has a peak melting point as determined according to the method described in the specification, wherein the boiling endset temperature Tb_endset of the boiling range of the fusing fluid is not more than 100 °C above the peak melting point of the particulate build material, preferably is from 10 to 100 °C above the peak melting point of the particulate build material, more preferably is from 15 to 90 °C, even more preferably is from 20 to 80 °C above the peak melting point of the particulate build material.

19. A method for the print and fuse manufacture of a three-dimensional object from a particulate build material, the method comprising the steps of:A) forming a particulate build material layer from the particulate build material;B) according to printing data based on a three-dimensional object model of the three- dimensional object, selectively dispensing a fusing fluid onto the particulate build material layer to define within the particulate build material layer a cross section of the three- dimensional object to be formed;C) exposing the particulate build material layer with the fusing fluid dispensed thereto with fusing radiation to selectively fuse the particulate build material within the cross section; andD) repeating steps A) to C) until the three-dimensional object is formed, wherein the fusing fluid is a fusing fluid according to any one of claims 1 to 10, or the fusing fluid and the particulate build material are those as defined in any one of claims 11 to 18 or are from a materials kit according to any one of claims 11 to 18.

20. A three-dimensional object obtained or obtainable by a method according to claim 19.21 . Three-dimensional object according to claim 20, wherein the three-dimensional object selfextinguishes within 60 seconds during flame application, measured according to the modified FAR 25.853 Part 1 (a)(1 )(i) test method described in the specification, preferably within 50 seconds.3722. Use of a fusing fluid according to any one of claims 1 to 10 or of a materials kit according to any one of claims 11 to 18 in print and fuse methods for improving the flame retardancy of the obtained three-dimensional objects, preferably in a method according to claim 19.

23. An apparatus for the print and fuse manufacture of three-dimensional objects from a particulate build material, preferably configured to carry out the method according to claim 19, the apparatus comprising: a build container comprising a build platform for supporting particulate build material layers; a particulate build material supply system configured to supply to and distribute particulate build material over the build platform to form each particulate build material layer; a fluid deposition system containing a fusing fluid and configured to selectively dispense the fusing fluid onto the top particulate build material layer according to printing data based on a three-dimensional object model so as to define a cross section of the object to be formed; and a fusing device for providing fusing radiation to the particulate build material layer so as to cause melting of the build material within the defined cross section; wherein the fusing fluid is a fusing fluid according to any one of claims 1 to 10, or the fusing fluid and the particulate build material are those as defined in any one of claims 11 to 18 or are from a materials kit according to any one of claims 11 to 18.

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