POWDER-BASED ADDITIVE MANUFACTURING PROCESS

Abstract

The invention relates to an additive manufacturing process (3D printing) using particles having a meltable polymer. The meltable polymer comprises a thermoplastic polyurethane polymer which has a flowing temperature (intersection of E and E in the DMA) of 80 C. to <180 C. and a Shore A hardness according to DIN ISO 7619-1 of 50 Shore A and <85 Shore A and which, at a temperature T, has a melt volume rate (melt volume rate (MVR)) according to ISO 1133 of 5 to <15 cm.sup.3/10 min. The invention also relates to an item which can be obtained by means of the method.

Claims

1. A method of producing an article, comprising: applying a layer of particles to a target surface, wherein at least some of the particles include a fusible polymer; introducing energy into a selected portion of the layer corresponding to a cross section of the article in a chamber to bond the particles in the selected portion to form a bonded portion; and repeating the steps of applying and introducing energy for a multitude of layers to bond the bonded portions of adjacent layers in order to form the article; wherein the fusible polymer comprises a thermoplastic polyurethane polymer having a flow temperature of 80 C. to 180 C. and a Shore A hardness of 50 Shore A and 85 Shore A based on DIN ISO 7619-1 and a melt volume flow rate at a temperature T of 5 to 15 cm.sup.3/10 min based on ISO 1133 and a change in the melt volume flow rate of 90 cm.sup.3/10 min in the event of an increase of temperature T by 20 C.

2. The method as claimed in claim 1, wherein introducing energy comprises: irradiating the selected portion of the layer corresponding to a cross section of the article with an energy beam to bond the particles in the selected portion.

3. The method as claimed in claim 1, wherein introducing comprises: applying a liquid to the selected portion of the layer corresponding to a cross section of the article, wherein said liquid increases absorption of energy in regions of the layer with which it comes into contact relative to regions with which it does not come into contact; irradiating the layer so that the particles in regions of the layer contacted with the liquid are bonded to one another and the particles in regions of the layer not contacted by the liquid are not bonded to one another.

4. The method as claimed in claim 1, wherein the particles applied are at least intermittently heated or cooled.

5. The method as claimed in claim 1, wherein the thermoplastic polyurethane polymer has a glass transition temperature of 0 C.

6. The method as claimed in claim 1, wherein the thermoplastic polyurethane polymer has a storage modulus E at 80 C. that is 30% of the storage modulus E at 0 C. based on dynamic-mechanical analysis in a tensile test at 1 Hz and 2 C./min.

7. The method as claimed in claim 1, wherein the thermoplastic polyurethane polymer has the following properties: a glass transition temperature of 0 C.; at a temperature T.sub.E, max the polymer has a maximum of the loss modulus E; at a temperature T.sub.1=T.sub.E, max10 C. the polymer has a first storage modulus E.sub.1; at a temperature T.sub.2=T.sub.1+50 C. the polymer has a second storage modulus E2; E.sub.2 is 0.3% to 2% of E.sub.1.

8. The method as claimed in claim 1, wherein at least some of the particles include the fusible polymer and a further polymer and/or an inorganic particle.

9. The method as claimed in claim 1, further comprising subjecting the article to an aftertreatment comprising: mechanical smoothing of the surface, controlled local heating, heating of the entire article, controlled local cooling, cooling of the entire article, contacting of the article with steam, contacting of the article with the vapor of an organic solvent, irradiating the article with electromagnetic radiation, immersing the article into a liquid bath, or a combination of at least two of these.

10. The method as claimed in claim 1, wherein the particles are at least partly suspended in a liquid phase after applying a layer of particles to the target surface.

11. An article produced by a method as claimed in claim 1.

12. The article as claimed in claim 11, wherein the article comprises sintered thermoplastic polyurethane having a phase separation into hard phases and soft phases, and a proportion of the soft phases, as determined by scanning force microscopy, accounts for 40% of a sum total of hard phases and soft phases.

13. The article as claimed in claim 12, wherein the sintered thermoplastic polyurethane has a tan delta value that varies by 0.2 in the temperature range between 0 C. and 100 C. based on a dynamic-mechanical analysis according to ISO 6721-4.

14. A particulate composition for production of articles in powder-based additive manufacturing methods, comprising thermoplastic polyurethane obtained from a reaction of the following components: a) at least one organic diisocyanate, b) at least one compound having groups reactive toward isocyanate groups and having a number-average molecular weight of 500 g/mol to 6000 g/mol and a number-average functionality of a sum total of components b) of 1.8 to 2.5, c) at least one chain extender having a number-average molecular weight of 60 to 450 g/mol and a number-average functionality of a sum total of chain extenders c) of 1.8 to 2.5, in the presence of d) optionally catalysts, e) optionally auxiliaries and/or additives, f) optionally one or more chain terminators, wherein the thermoplastic polyurethane has a flow temperature of 80 C. to 180 C., Shore A hardness of 50 Shore A and 85 Shore A based on DIN ISO 7619-1, a melt volume flow rate at a temperature T of 5 to 15 cm.sup.3/10 min based on ISO 1133, and a change in melt volume flow rate of 90 cm.sup.3/10 min in the event of an increase in temperature T by 20 C.

15. The particulate composition as claimed in claim 14, wherein at least 90% by weight of the particles has a particle diameter of less than 0.25 mm and the composition contains 0.02% to 0.5% by weight of flow agent, based on the total weight of the composition.

Description

EXAMPLES

[0083] The present invention is elucidated in detail by the examples which follow, but without being limited thereto. Percentages by weight are based on the total amount of reactive organic constituents used (alcohols, amines, water, isocyanates).

[0084] TPUs usable in accordance with the invention and TPUs for comparative examples have been produced by two standard processing methods: the prepolymer method and the one-shot/static mixer method.

[0085] In the prepolymer method, the polyol or polyol mixture is preheated to 180 to 210 C., initially charged with a portion of the isocyanate, and converted at temperatures of 200 to 240 C. The speed of the twin-screw extruder used here is about 270 to 290 rpm. This preceding partial reaction affords a linear, slightly pre-extended polymer that reacts to completion with residual isocyanate and chain extender further down the extruder. This method is described by way of example in EP-A 747 409.

[0086] In the one-shot/static mixer method, all comonomers are homogenized by means of a static mixer or another suitable mixing device at high temperatures (above 250 C.) within a short time (below 20 s) and then reacted to completion and discharged by means of a twin-screw extruder at temperatures of 90 to 180 C. and a speed of 260-280 rpm. This method is described by way of example in application DE 19924089.

[0087] The thermal-mechanical characteristics of the TPUs obtained were ascertained on injection-molded specimen plaques having dimensions 50 mm*10 mm*1 mm. The measurement parameters for the DMA measurements were frequency of 1 Hz and a heating rate of 2 C./min over a temperature interval of 150 C. to 250 C., in accordance with DIN-EN-ISO 6721-4.

Example 1

[0088] The TPU (thermoplastic polyurethane) was prepared by the prepolymer method from 1 mol of a polyester diol mixture consisting of a polyester diol having a number-average molecular weight of about 2000 g/mol, based on adipic acid, hexanediol and neopentyl glycol, and a polyester diol having a number-average molecular weight of about 2250 g/mol, based on adipic acid and butanediol (in the ratio of 2:1), and 1.30 mol of 2,2-(1,4-phenylenedioxy)diethanol, 2.30 mol of technical grade diphenylmethane 4,4-diisocyanate (MDI) with >98% by weight of 4,4-MDI, 0.07% by weight of Irganox 1010 (pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) from BASF SE) and 78 ppm of tin dioctoate and 1.1% by weight of Loxamid 3324 (N,N-ethylenebisstearylamide).

[0089] A polyurethane having a glass transition temperature (maximum E in the DMA) of 38 C., a Shore A hardness (ISO 868) measured on an injection-molded specimen of 81 Shore A and a flow temperature (crossover point of E and E in the DMA) of 169 C. was obtained.

Example 2

[0090] The TPU (thermoplastic polyurethane) was prepared by the prepolymer method from 1 mol of polyether diol having a number-average molecular weight of about 2000 g/mol, based on propylene oxide, and about 2.81 mol of butane-1,4-diol, about 0.28 mol of hexane-1,6-diol, about 4.09 mol of technical grade diphenylmethane 4,4-diisocyanate (MDI) with >98% by weight of 4,4-MDI, 0.3% by weight of Irganox 1010 (pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) from BASF SE), 1.0% by weight of Loxamid 3324 (N,N-ethylenebisstearylamide) and 30 ppm of Ti(IV) catalyst.

[0091] A polyurethane having a glass transition temperature (maximum E in the DMA) of 38 C., a Shore A hardness (ISO 868) measured on an injection-molded specimen of 80 Shore A and a flow temperature (crossover point of E and E in the DMA) of 153 C. was obtained.

Example 3

[0092] The TPU (thermoplastic polyurethane) was prepared by the prepolymer method from 1 mol of polyether diol having a number-average molecular weight of about 2000 g/mol, based on propylene oxide, and about 1.74 mol of butane-1,4-diol, about 0.14 mol of hexane-1,6-diol, about 2.88 mol of technical grade diphenylmethane 4,4-diisocyanate (MDI) with >98% by weight of 4,4-MDI, 0.4% by weight of Irganox 1010 (pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) from BASF SE), 1.0% by weight of Loxamid 3324 (N,N-ethylenebisstearylamide) and 20 ppm of Ti(IV) catalyst.

[0093] A polyurethane having a glass transition temperature (maximum E in the DMA) of 39 C., a Shore A hardness (ISO 868) measured on an injection-molded specimen of 65 Shore A and a flow temperature (crossover point of E and E in the DMA) of 129 C. was obtained.

Comparative Example V1

[0094] The TPU (thermoplastic polyurethane) was prepared by the static mixer-extruder method from 1 mol of polyester diol having a number-average molecular weight of about 900 g/mol, based on about 56.7% by weight of adipic acid and about 43.3% by weight of butane-1,4-diol, and about 1.45 mol of butane-1,4-diol, about 0.22 mol of hexane-1,6-diol, about 2.67 mol of technical grade diphenylmethane 4,4-diisocyanate (MDI) with >98% by weight of 4,4-MDI, 0.05% by weight of Irganox 1010 (pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) from BASF SE), 1.1% by weight of Licowax E (montanic esters from Clariant) and 250 ppm of tin dioctoate.

[0095] A polyurethane having a glass transition temperature (maximum E in the DMA) of 24 C., a Shore A hardness (ISO 868) measured on an injection-molded specimen of 92 Shore A and a flow temperature (crossover point of E and E in the DMA) of 142 C. was obtained.

Comparative Example V2

[0096] The TPU (thermoplastic polyurethane) was prepared by the known prepolymer method from 1 mol of polyester diol mixture consisting of a polyester diol having a number-average molecular weight of about 900 g/mol, based on adipic acid and butane-1,4-diol, and a polyester diol having a number average molecular weight of about 2250 g/mol, based on adipic acid and butane-1,4-diol (ratio of 5:95), and about 2.53 mol of butane-1,4-diol, about 3.53 mol of technical grade diphenylmethane 4,4-diisocyanate (MDI) with >98% by weight of 4,4-MDI, 0.07% by weight of Irganox 1010 (pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) from BASF SE), 0.25% by weight of Loxamid 3324 (N,N-ethylenebisstearylamide) and 106 ppm of tin dioctoate.

[0097] A polyurethane having a glass transition temperature (maximum E in the DMA) of 40 C., a Shore A hardness (ISO 868) measured on an injection-molded specimen of 86 Shore A and a flow temperature (crossover point of E and E in the DMA) of 160 C. was obtained.

Comparative Example V3

[0098] The TPU (thermoplastic polyurethane) was prepared by the prepolymer method from 1 mol of polyester diol having a number-average molecular weight of about 2055 g/mol and 4.85 mol of 2,2-(1,4-phenylenedioxy)diethanol, 5.85 mol of technical grade diphenylmethane 4,4-diisocyanate (MDI) with >98% by weight of 4,4-MDI, 0.03% by weight of Irganox 1010 (pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) from BASF SE) and 100 ppm of tin dioctoate, and 0.5% by weight of Loxamid 3324 (N,N-ethylenebisstearylamide).

[0099] A polyurethane having a glass transition temperature (maximum E in the DMA) of 13 C., a Shore A hardness (ISO 868) measured on an injection-molded specimen of 97 Shore A and a flow temperature (crossover point of E and E in the DMA) of 205 C. was obtained.

[0100] The following table lists further analysis data:

TABLE-US-00001 Tan Exam- T.sub.MVR [ C.] MVR.sub.T+20 C. variation E ple 5-15 cm.sup.3/ [cm.sup.3/ (0 C. to (80 C.)/E no. 10 min 10 min] 100 C.) E.sub.2/E.sub.1 (0 C.) 1 200 >100 0.0947 1.4% 61% 2 195 >100 0.1996 1.6% 30% 3 180 >100 0.1732 0.5% 42% V1 160 about 69 0.1088 .sup.8% 14% V2 185 about 54 0.1119 2.4% 28% V3 237 >100 0.074 25% 11%

[0101] The figures E.sub.1 and E.sub.2 are defined as follows: [0102] at a temperature T.sub.E, max the polymer has a maximum of the loss modulus E (dynamic-mechanical analysis); [0103] at a temperature T.sub.1=T.sub.E, max10 C. the polymer has a first storage modulus E.sub.1 (dynamic-mechanical analysis); [0104] at a temperature T.sub.2=T.sub.1+50 C. the polymer has a second storage modulus E.sub.2 (dynamic-mechanical analysis).

[0105] 0.5-2.0% by weight, based on TPU, of hydrophobized fumed silica was added as flow agent (Aerosil R972 from Evonik) to the TPUs prepared according to examples 1, 2 and 3 and comparative examples V1, V2 and V3, the mixture was processed mechanically under cryogenic conditions (cryogenic comminution) in a pinned-disk mill to give powder and then classified by means of a sieving machine. 90% by weight of the particles obtained had a particle diameter of less than 140 m (measured by means of laser diffraction (HELOS particle size analysis)).

[0106] Subsequently, S2 test specimens were produced by a powder sintering method having the following parameters:

TABLE-US-00002 Number of Exam- Construction Laser Layer sintering ple space temp. power thickness operations no. [ C.] [W] [mm] per layer Component 2 110 60 0.15 2 Corresponds 3 110 60 0.15 2 Corresponds