MATERIALS FOR SELECTIVE LASER SINTERING AND LASER SINTERING USING SUCH MATERIALS

Abstract

Method for the preparation of moldings in a layer-by-layer process in which selectively areas of a powdered layer are melted, sintered, fused, or otherwise solidified, characterized in that as a powder for the powdered layer a thermoplastic, ground polyamide powder is used, in which the polyamide comprises laurolactam and caprolactam, preferably exclusively, and wherein the proportion of caprolactam is in the range of 40-60 mol % of the lactams used.

Claims

1. A powder for the production of moldings in a layer-by-layer process in which areas of a powdered layer are selectively melted, sintered, fused, or solidified, wherein the powder is a thermoplastic, ground polyamide powder in which the polyamide consists of laurolactam and caprolactam, and wherein the proportion of caprolactam is 40-60 mol % of the lactams used.

2. The powder according to claim 1, wherein in the thermoplastic, ground polyamide powder the proportion of caprolactam is at least 50 mol % of the lactams used.

3. The powder according to claim 1, wherein the thermoplastic, ground polyamide powder has a relative viscosity, measured in m-cresol at a temperature of 20° C. and a concentration of 0.5 wt.-% according to ISO 307, in the range of 1.4-1.8, or in the range of 1.5-1.75, and/or wherein the thermoplastic, ground polyamide powder has a melting point in the range of 110-190° C., or in the range of 120-180° C. and/or wherein the thermoplastic, ground polyamide powder has a crystallization temperature in the range of 80-170° C., or in the range of 90-160° C.

4. The powder according to claim 1 for the production of moldings in a layer-by-layer process in which areas of a powdered layer are selectively melted using focused or non-focused input of electromagnetic energy.

5. The powder according to claim 1, wherein in the thermoplastic, ground polyamide powder the proportion of caprolactam is in the range of 40-60 mol %, or 50-60 mol %, of the lactams used, the melting point is in the range of 120-170° C., or in the range of 125-170° C., and the crystallization temperature in the range of 100-140° C., or in the range of 90-160° C., and wherein the polyamide powder is prepared without chain control.

6. The powder according to claim 1, wherein the proportion of caprolactam is in the range of 40-60 mol %, or 50-60 mol %, of the lactams used, the melting point in the range of 150-200° C., or in the range of 155-195° C., and the crystallization temperature in the range of 110-170° C., or in the range of 120-165° C., and wherein the polyamide powder is prepared without chain control.

7. The powder according to claim 1, wherein the powder has neither a recrystallization temperature nor a cold crystallization temperature.

8. The powder according to any one of the preceding claim 1, wherein the thermoplastic, ground polyamide powder is prepared by a cryogrinding process.

9. The powder according to any one of the claim 1, wherein the powder has a diameter D50 measured according to ISO 13322-2 of 50-75 μm, preferably or 50-65 μm, or 50-60 μm, and/or wherein the thermoplastic, ground polyamide powder has an MFR value, measured according to ISO 1133, in the range of 7-12 g/10 min.

10. A copolyamide composed of laurolactam and caprolactam, wherein the proportion of caprolactam is 40-60 mol % of the lactams used, for preparing a powder according to one of the preceding claim 1.

11. A method of using a thermoplastic, ground polyamide powder in which the polyamide comprises laurolactam and caprolactam, and wherein the proportion of caprolactam is 40-60 mol % of the lactams used, for the preparation of moldings in a layer-by-layer process in which selective areas of a powdered layer are fused, sintered, melted, or solidified, including using focused or non-focused input of electromagnetic energy.

12. A method for preparing a thermoplastic polyamide powder for use in a layer-by-layer process in which selective areas of a powdered layer are sintered, melted, or solidified, including by focused or non-focused input of electromagnetic energy, wherein the powder is a thermoplastic, ground polyamide powder in which the polyamide comprises or consists of laurolactam and caprolactam, and wherein the proportion of caprolactam is in the range of 40-60 mol % of the lactams used.

13. A method of printing a three-dimensional article comprising: providing a composition comprising a powder according to claim 1; and selectively solidifying layers of the composition to form the article, including using focused or non-focused input of electromagnetic energy.

14. Moulded A moulded body prepared using a method as defined in claim 13.

15. The method according to claim 11, for the preparation of moldings in a layer-by-layer process in which selective areas of a powdered layer are fused, sintered, melted, or solidified, using focused or non-focused input of electromagnetic energy.

16. The method according to claim 12, wherein the powder is a thermoplastic, ground polyamide powder in which the polyamide consists exclusively of laurolactam and caprolactam.

17. The method according to claim 12, wherein the thermoplastic, ground polyamide powder is prepared by cryo grinding process.

18. The method according to claim 13, wherein the composition is provided in a layer-by-layer process.

Description

DESCRIPTION OF THE INVENTION

[0014] It is an object of the present invention to propose a powder for use in a powder bed fusion method, such as, for example, an SLS method of the type described above. The powder bed fusion method can comprise the use of a focused or non-focused input of electromagnetic energy, thermal energy, or other energy to selectively fuse, melt, sinter, or solidify a powder material in an additive manufacturing process. Preferably, the powder is for the production of articles/moldings in a layer-by-layer process in which areas of a powdered layer are selectively melted using focused or non-focused input of electromagnetic energy. Possible are uses in SLS processes but also multi jet fusion (MJF), selected absorption fusion (SAF) or high speed sintering (HSS) processes.

[0015] Specifically, a powder is to be provided that has at least one of the following advantageous properties: [0016] wide range of mechanical and physical properties that are close to those of conventional PP and PA11 systems; [0017] lower operating temperatures with increased amount of laurolactam, with reduced cooling time and increased recyclability of the product without significantly changing the impact strength of the material. (increased process speed) [0018] Polyamide with material properties without/with reduced shrinkage and with excellent properties in the Z direction, in contrast to the current market standard; [0019] Reduction of production costs compared to PA11 materials; [0020] Possibility of dry mixing of colors within the material to print fully colored parts where the colors do not bleed out.

[0021] A powder in accordance with the present invention is defined as a (at room temperature) solid substance reduced to a state of fine, loose particles for example by crushing, grinding, disintegration, precipitation or a combination thereof.

[0022] According to a first aspect of the present invention, this relates to a powder of a copolyamide for the preparation of moldings in a layered process in which selectively areas of a powdered layer are [0023] (1) melted by input of electromagnetic energy (typically by a controlled laser), [0024] (2) melted by input of thermal energy from a source other than electromagnetic energy, or [0025] (3) otherwise melted, fused, sintered, or solidified to form an article or object.

[0026] Such a powder is characterized according to claim 1, i.e. in that as a powder for the powdery layer a thermoplastic, preferably ground polyamide powder is used, in which the polyamide is composed of, so consists of laurolactam (Lc12) and caprolactam (Lc6), wherein the proportion of laurolactam is 40-60 mol % of the lactam used.

[0027] The powder thus comprises or consists of a thermoplastic, ground polyamide powder in which the polyamide comprises or consists of laurolactam and caprolactam, and wherein the proportion of caprolactam is 40-60 mol % of the lactams used.

[0028] In fact it was shown that if the thermoplastic polyamide powder being the basis of the powder consists of laurolactam (Lc12) and caprolactam (Lc6), the above-mentioned advantages surprisingly can be reached.

[0029] The powder for the layer-by-layer process in which areas of a powdered layer are selectively melted, sintered, fused, or solidified, preferably by focused or non-focused input of electromagnetic energy, either exclusively consists of the thermoplastic polyamide powder or it may comprise the thermoplastic polyamide powder in a mixture with different powder material. The proportion of the thermoplastic polyamide powder in such a mixture powder is typically at least 50% by weight relative to the total of the powder, preferably it is at least 60% by weight or in a proportion as also detailed further below. The powder material different from the thermoplastic polyamide can for example comprise or consist of powder particles of filler materials (organic or inorganic), flow aid materials, stabiliser materials (including heat stabilisation, optical stabilisation), colourants including pigments or dyes, or a combination thereof either in the form of individual particles or particles of a mixture of such materials. Preferably the particle sizes of such different powder particles are selected in the same or essentially the same range as defined further below for the powder particles of the thermoplastic polyamide powder.

[0030] Preferably the powder material different from the thermoplastic polyamide powder as defined above does not include glass fibers or ground glass fibers.

[0031] The thermoplastic polyamide powder in that powder in itself may consist of a single thermoplastic polyamide or a mixture of different thermoplastic polyamides, or that thermoplastic polyamide powder may consist of particles made from a mixture of one or a plurality of thermoplastic polyamide types with further additives. Typically, the thermoplastic polyamide powder comprises at least 70% by weight of the thermoplastic polyamide powder comprising laurolactam (Lc12) and caprolactam (Lc6), relative to 100% of the total weight of the thermoplastic polyamide powder. Preferably the additives make up at most 20% by weight or at most 10% or at most 5% by weight relative to 100% of the total thermoplastic polyamide powder. According to one preferred embodiment, the thermoplastic polyamide powder consists exclusively of one or several thermoplastic polyamide systems made exclusively from laurolactam (Lc12) and caprolactam (Lc6) without any additives. Additives can be selected as detailed further below.

[0032] Alternatively or additionally, the thermoplastic polyamide powder of the powder is free from flame retardant additives.

[0033] According to yet another preferred embodiment, the thermoplastic polyamide powder consists of the polyamide and further additives in an amount of not more than 20 weight % or 15 weight %, preferably in the range of 1-12 weight % or 5-10 weight %, relative to the total weight of the powder.

[0034] Preferably the additive is one or a combination of the following; fillers, preferably selected from the group of talc, aluminium oxide-based fillers, glass fillers, metal carbonates including calcium carbonate; flow agents, preferably selected from the group of fumed or precipitated silica, metal salts of long-chain fatty acids, including metal stearates, titanium dioxide, group 1 salts, fumed aluminium oxide; flame retardants, preferably selected from the group of organic or inorganic mono- or diphosphinates, preferably metal alkyl phosphinate, in particular aluminium diethyl phosphinate, alone or in combination with synergist compounds, preferably containing nitrogen and/or phosphorous, including melem, melam, melon or other melamine or derivatives thereof. Preferably the additives do not include glass fibres, or ground glass fibres.

[0035] Preferably the powder is free from glass fibres or ground glass fibres.

[0036] Preferably the thermoplastic ground polyamide powder is made from starting polyamide material free from glass fibres, which is then ground.

[0037] According to the invention, the thermoplastic ground polyamide consists of polyamide made exclusively from laurolactam (Lc12) and caprolactam (Lc6), wherein the proportion of laurolactam is 40-60 mol % of the lactam used, so there are no further lactams different from laurolactam (Lc12) and caprolactam (Lc6), and also no further diacids or diamines. According to a further aspect of the present invention, this relates to a method for producing a thermoplastic polyamide powder for use in a process as described above. In one example, the method is characterized in particular in that by means of a suitable filtering or screening technology (tumble air jet screener, ultrasound tumbler or winnower) a grain size distribution suitable for the printing process is achieved. In other examples, the method may not use a screening technology.

[0038] Furthermore, in some examples, the method includes forming a thermoplastic polyamide powder using solvent precipitation, solvent pulverization, melt emulsification, melt pulverization, or another micronization technique. In addition, in some embodiments, it is possible to prepare a composition for use in additive manufacturing by blending the polyamide powder with one or more additional components or additives, such as an additive or filler. Such a composition can be prepared, in some examples, by dry blending or wet blending.

[0039] According to a further aspect, the present invention describes powders or compositions for use in additive manufacturing, such as SLS or another additive manufacturing method in which a granular or particulate material is melted, fused, sintered, or otherwise solidified in a selective manner. In some embodiments, such a composition comprises as a component a polyamide powder described herein. The polyamide powder may form all or part of a sinterable powder. In some cases, the polyamide powder is the primary or majority component of a sinterable powder composition. For instance, in some embodiments, a composition for additive manufacturing described herein comprises up to 100 wt. %, up to 99 wt. %, up to 95 wt. %, or up to 90 wt. % copolyamide powder, based on the total weight of the sinterable powder. In some instances, the sinterable powder comprises 50-100 wt. %, 50-99 wt. %, 50-90 wt. %, 50-80 wt. %, 50-70 wt. %, 60-100 wt. %, 60-99 wt. %, 60-90 wt. %, 70-100 wt. %, 70-99 wt. %, 70-90 wt. %, 80-100 wt. %, 80-99 wt. %, 80-95 wt. %, 85-100 wt. %, 85-99 wt. %, 85-95 wt. %, 90-100 wt. %, or 90-99 wt. % copolyamide powder, based on the total weight of the sinterable powder. In some cases, the sinterable powder further comprises another granular, particulate, or powder component, in addition to the copolyamide powder component. Again, preferably the other granular, particulate, or powder component from the thermoplastic polyamide powder as defined above does not include glass fibers or ground glass fibers.

[0040] According to a preferred embodiment, in the thermoplastic, ground polyamide powder, the proportion of caprolactam is at least 50 mol % of the lactams used, preferably in the range of 50-60 mol % of the lactams used.

[0041] The thermoplastic, ground polyamide powder preferably has a relative viscosity (measured in m-cresol at a temperature of 20° C. and a concentration of 0.5 wt.-% according to ISO 307) in the range of 1.4-1.8, preferably in the range of 1.5-1.75.

[0042] The thermoplastic, ground polyamide powder further preferably has a melting point in the range of 110-190° C., preferably in the range of 120-180° C.

[0043] The thermoplastic, ground polyamide powder may have neither a recrystallization temperature nor a cold crystallization temperature. For the cold crystallization temperature (T.sub.cc) the peak value during a second heating cycle is taken; for the recrystallization temperature (T.sub.rc) the value taken during the cool-down phase of the first heating cycle is recorded, all measured in accordance with ISO 11357-3 (2013).

[0044] Typically, the powder is suitable and adapted for the production of moldings in a layer-by-layer process in which areas of a powdered layer are selectively melted using focused or non-focused input of electromagnetic energy.

[0045] According to a preferred embodiment, in the thermoplastic, ground polyamide powder the proportion of caprolactam is in the range of 40-60 mol %, preferably 50-60 mol %, of the lactams used, the melting point is in the range of 120-170° C., preferably in the range of 125-170° C., and the crystallization temperature in the range of 100-140° C., preferably in the range of 90-160° C., and wherein the polyamide powder is prepared without chain control. According to yet another preferred embodiment, the proportion of caprolactam is in the range of 40-60 mol %, preferably 50-60 mol %, of the lactams used, the melting point in the range of 150-200° C., preferably in the range of 155-195° C., and the crystallization temperature in the range of 110-170° C., preferably in the range of 120-165° C., and wherein the polyamide powder is prepared without chain control.

[0046] The powder preferably has neither a recrystallization temperature (T.sub.rc) nor a cold crystallization temperature (T.sub.cc) resulting in a wide possible temperature range for the part bed temperature. If neither T.sub.rc nor T.sub.cc can be measured by DSC, this indicates a very slow crystallization of the powder in a wide temperature range, which also tolerates a wide temperature range during printing. This allows for more robust printing parameters. The thermoplastic, ground polyamide powder can be prepared by a grinding process, preferably by using a cryo grinding process. The grinding is preferably followed by a sieving or filtering process for generating a desired particle size distribution.

[0047] If needed for the preparation of the final powder the thermoplastic polyamide powder may be mixed with different powder particles as detailed further above. The above-mentioned particle size filtering may take place before mixing with the different powder particles or after or both.

[0048] Preferably the particle size distribution is such that 80%, preferably 90%, of the particles are located within a range of sizes of 20-100 μm, preferably in the range of 40-90 μm.

[0049] Preferably, the value of D10 measured according to ISO 13322-2 is in the range of 15-40 μm, preferably in the range of 20-30 μm, and/or the value of D95 measured according to ISO 13322-2 is in the range of 80-99 μm, preferably in the range of 85-98 μm.

[0050] Typically, the powder has a diameter D50 measured according to ISO 13322-2 of 50-75 μm, preferably 50-65 μm, more preferably 50-60 μm.

[0051] The particles preferably have an essentially spherical or potato shape.

[0052] The thermoplastic, ground polyamide powder may preferably have an MFR value, measured according to ISO 1133, in the range of 7-12 g/10 min.

[0053] Furthermore, the present invention relates to a copolyamide composed of laurolactam and caprolactam, wherein the proportion of caprolactam is 40-60 mol % of the lactams used, for preparing a powder as detailed above.

[0054] Further the present invention relates to a use of a thermoplastic, ground polyamide powder in which the polyamide is composed of or comprises laurolactam and caprolactam, preferably exclusively, and wherein the proportion of caprolactam is 40-60 mol % of the lactams used, for the preparation of moldings in a layer-by-layer process in which selective areas of a powdered layer are fused, sintered, melted, or solidified, preferably using focused or non-focused input of electromagnetic energy.

[0055] Also the present invention relates to a method for preparing a thermoplastic polyamide powder for use in a layer-by-layer process in which selective areas of a powdered layer are sintered, melted, or solidified, preferably melted by focused or non-focused input of electromagnetic energy, wherein the powder is a thermoplastic, ground polyamide powder in which the polyamide of comprises or consists of laurolactam and caprolactam, preferably exclusively, and wherein the proportion of caprolactam is in the range of 40-60 mol % of the lactams used, wherein preferably the thermoplastic, ground polyamide powder is prepared by cryo grinding process.

[0056] Further the invention relates to a method of printing a three-dimensional article comprising: providing a composition comprising a powder as detailed above; and selectively solidifying layers of the composition to form the article, preferably using focused or non-focused input of electromagnetic energy. Preferably the composition is provided in a layer-by-layer process.

[0057] In some embodiments, for example, a composition for additive manufacturing described herein comprises a flow aid component.

[0058] Last but not least, the present invention relates to a molded body prepared using a method as described above, or a molded body prepared from or formed from a composition or powder described above.

[0059] Further embodiments are given in the dependent claims.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0060] Preferred embodiments of the invention are described below on the basis of the embodiments, which serve only as an explanation and are not to be interpreted restrictively. According to the invention, the condensation reaction as well as the grinding process and the use are explained.

[0061] Step A—Copolyamide:

[0062] Caprolactam (40.2 kg, 56 mol %) and laurolactam (53.7 kg, 44 mol %) were transferred with water (3.95 wt. %) to an autoclave where the mixture was stirred at 190-200° C. for 120 minutes. The mixture was then heated to 270° C. and 20 bar, and stirred under constant pressure of 20 bar for 5 hours at 290° C. Over 4 hours, the polymer was cooled to 270° C. and the pressure was reduced to 0.3 bar. The temperature was subsequently reduced to 260° C. The polycondensate was then granulated and dried in a standard procedure. Analytics of the granulate: Melting point T, of 130° C. and glass transition temperature T.sub.g of 30° C.

[0063] Step B—Powder:

[0064] The granules obtained from step A were ground with the addition of liquid nitrogen in the counter run with a pin mill of the type Hosokawa 160 C at −50° C., to the raw ground material. Subsequently, the raw ground material was separated with an ultrasonic sieve to the grain size distribution of approximately 40-90 μm, using, screen fabrics of according mesh size are used.

[0065] Measured grain size distribution (μm): D10: 24.4 D50: 52.9 D95: 95.3, as determined on Camsizer XT according to ISO 13322-2. Further properties of the powder are given in the table below.

[0066] Step C: SLS Moldings

[0067] The powder obtained from step C was printed for the production of test bodies (ISO 527) using an SLS printer SPro60 from 3D Systems (equipped with a CO2 Laser).

[0068] The printer was set with the parameters given in the table below:

TABLE-US-00001 PA11 PA12 PP (Duraform EMS- Exam- (Prodways PA CHEMIE ple 1 PM 1200) EX-Nat) AG Lc6/Lc12 Ratio 56/44 — — 0/100 T.sub.m/° C. (ISO 11357) 120-135 130-140 180-205 170-180 T.sub.g/° C. (ISO 11357) 34 — 37 40 T.sub.cc/° C. (ISO 11357) — — — 101 T.sub.rc/° C. (ISO 11357) — 70-90 135-160 144 Warm up duration 8 mm (45 10 mm (1 17 mm (2 10 mm (1 minutes) hour) hours) hour) Part bed temperature 122.fwdarw.120 135.fwdarw.132 187 173.5.fwdarw.172 Left/Right 90 115 135 142 Temperature Laser Parameter: Fill Laser Power (W) 60 35 40 40 Outline Laser Power 25 7 8 8 (W) Slicer Fill Scan 0.20 0.15 0.15 0.15 Spacing (mm) Flowability Excellent Good Excellent Excellent Cracks/Warpage/ None At the Visible None Curling edges Cool down mm (time) 2.54 (16 2.54 (16 2.54 (16 2.54 (16 hours) hours) hours) hours) Viscosity after print: 1.752 n.d. 2.135 n.d Viscosity after 4 1.766 n.d n.d n.d prints(0% refresh) n.d: not determined; —: not indicated because no signal or signal too weak;

[0069] Relative viscosity of the residual powder was measured in m-cresol at a temperature of 20° C. and a concentration of 0.5 wt.-% according to ISO 307.

[0070] Tensile modulus was measured according to ISO 527 with a pulling speed of 1 mm/min ISO tension rod, standard: ISO/CD 3167, type A1, 170×20/10×4 mm at a temperature of 23° C.

[0071] Tensile strength and elongation at break were measured according to ISO 527 with a tensile speed of 5 mm/min ISO tension rod, standard: ISO/CD 3167, type A1, 170×20/10. ×4 mm, temperature 23° C.

[0072] Impact strength was measured according to ISO 179/*eA on ISO test bars according to standard: ISO/CD 3167, type B1, 80×10×4 mm at 23° C.

[0073] Glass transition temperature (T.sub.g), melting point (T.sub.m) measured on pellets/granulate: ISO standard 11357-1, 11357-2, 11357-3 (2013); pelletized material; the differential scanning calorimetry (DSC) was carried out using a DSC 2920 instrument from TA Instruments with a heating rate of 20 K/min and a cooling rate of 5 K/min. The thermogram was analysed using the Universal Analysis 2000 program from TA Instruments. The sample was quenched in dry ice after the first heating run for the purpose of determining the glass transition temperature. The glass transition temperature (T.sub.g) was determined on the second heating run. The midpoint of the glass transition range, which was reported as the glass transition temperature (T.sub.g), was ascertained by the “half-height” method.

[0074] Glass transition temperature (T.sub.g), melting point (T.sub.m), cold crystallization temperature (T.sub.cc), recrystallization temperature (T.sub.rc) measured on powdered material: ISO standard 11357-1, 11357-2, 11357-3 (2013); Powdered material; the differential scanning calorimetry (DSC) was carried out using a DSC 2920 instrument from TA Instruments with a heating rate of 20 K/min and a cooling rate of 5 K/min. The thermogram was analysed using the Universal Analysis 2000 program from TA Instruments.

[0075] The sample was quenched in dry ice after the first heating run for the purpose of determining the glass transition temperature. The glass transition temperature (T.sub.g) was determined on the second heating run. The midpoint of the glass transition range, which was reported as the glass transition temperature (T.sub.g), was ascertained by the “half-height” method. For the cold crystallization temperature (T.sub.cc) the peak value during a second heating cycle is taken; for the recrystallization temperature (T.sub.rc) the value taken during the cool-down phase of the first heating cycle is recorded.

TABLE-US-00002 Mechanical properties Polymer according to: Example 1 PP PA11 PA12 Tensile modulus (MPa) 1312 1273 1355 1879 Tensile strength (MPa) 39.3 28 42.8 50.3 Elongation at break (%) 30.9 15.3 18.6 9.4 Charpy impact strength 72.4 30.1 111 13.4 (kJ/m.sup.2) Charpy notched impact 20.1 n.d 50.3 n.d strength (kJ/m.sup.2) Part colour White/ White Natural White/ Natural Natural Surface finish Smooth Rough Rough Smooth n.d: not determined

[0076] The powder according to the invention is a material that can be printed at relatively low, energy-efficient temperatures while providing very good mechanical properties, in particular with regard to impact strength and elongation at break when compared with other commonly-printed SLS powders PP and PA11 as well as the PA12. Good surface appearance is also achieved in prints involving the inventive powder.

[0077] For the powder according to the invention no T.sub.cc and T.sub.rc can be measured, which provides for a large sintering window/temperature range for 3D printing. The two comparative examples PP and PA11 have a peak in the DSC measurement to read a range of 20 and 25° C., respectively, for the sinter window, which is defined as the window (T.sub.m-T.sub.rc) between the melting temperature T.sub.m and the recrystallization temperature T.sub.rc. In example 1 according to the invention, on the other hand, the crystallization is so slow that this peak is no longer detected, so there is a wide range of the crystallization temperature. The comparative system PA12 with the sintering window according to the above definition of about 30° C. has only an effectively usable temperature window of 5° C. of the powder bed during printing. The powder according to the invention according to example 1 has an effectively usable temperature range twice as wide (about 10° C.) but no measurable sintering window.