Method for producing an at least partially coated object

Abstract

The invention relates to a method for producing an at least partially coated object, comprising the step of producing the object from a construction material by means of an additive manufacturing method, the construction material comprising a thermoplastic polyurethane material. Following the production of the object, the method comprises the step of at least partially bringing a preparation into contact with the object, the preparation being selected from: an aqueous polyurethane dispersion; an aqueous dispersion of a polymer comprising OH groups, this dispersion also containing a compound comprising NCO groups; an aqueous preparation of a compound containing NCO groups, but not containing any polymers comprising OH groups; or a combination of at least two thereof. The invention also relates to an at least partially coated object that was obtained by a method according to the invention.

Claims

1. A process for producing an at least partially coated article comprising: producing the article using an additive manufacturing process from a construction material comprising a thermoplastic polyurethane material; and at least partially contacting the article with a preparation selected from: aqueous polyurethane dispersion, aqueous dispersion of an OH-containing polymer, wherein this dispersion further contains an NCO-containing compound, aqueous preparation of an NCO-containing compound, wherein this preparation contains no OH-containing polymers, or a combination of at least two of these, wherein the residual content of organic solvents in the preparation is less than 2% by weight relative to the total preparation; and wherein regions of the article contacted by the preparation have an elastic modulus at 50% elongation determined according to DIN 53504 that is 5% greater than an elastic modulus at 50% elongation of regions of the article not contacted by the preparation.

2. The process as claimed in claim 1, wherein the aqueous polyurethane dispersion is obtained when A) isocyanate-functional prepolymers are produced from A1) organic polyisocyanates, A2) polymeric polyols having number-average molecular weights of 400 to 8000 g/mol and OH functionalities of 1.5 to 6 and A3) optionally hydroxyl-functional compounds having molecular weights of 62 to 399 g/mol and optionally containing olefinically unsaturated compounds and A4) optionally isocyanate-reactive, anionic or potentially anionic and/or optionally nonionic hydrophilization agents, and B) the free NCO groups thereof are then wholly or partially reacted B1) optionally with amino-functional compounds having molecular weights of 32 to 400 g/mol and B2) with amino-functional, anionic or potentially anionic hydrophilization agents by chain extension and the prepolymers are dispersed in water before, during or after step B).

3. The process as claimed in claim 1, wherein the aqueous dispersion of an OH-containing polymer which further contains an NCO-containing compound comprises the components: A) one or more compounds comprising uncrosslinked polymer-bonded (meth)acrylates having an OH number of 20 to 300 mg KOH/g of substance and/or B) optionally compounds distinct from A) having at least one isocyanate-reactive group and at least one radiation-curable double bond, C) optionally one or more compounds having at least one isocyanate-reactive group but no radiation-curable double bonds, D) one or more compounds having at least one isocyanate-reactive group and additionally groups which are nonionic, anionic or capable of forming anionic groups and have a dispersing effect for the polyurethane acrylates or D) one or more compounds having at least one isocyanate-reactive group and additionally groups which are cationic or capable of forming cationic groups and have a dispersing effect for the polyurethane acrylates, E) one or more organic compounds having 2 or more isocyanate groups, F) optionally neutralizing amines in combination with compounds D) or F) neutralization acids F) in combination with compounds D), G) optionally urethanization catalysts and optionally further assistant and additive substances.

4. The process as claimed in claim 1, wherein the NCO-containing compound in the aqueous preparation of the NCO-containing compound without OH-containing polymers in the preparation is a compound based on aliphatic, cycloaliphatic, araliphatic and/or aromatic diisocyanates having: a) an average isocyanate functionality of at least 2.0 b) a content of isocyanate groups (calculated as NCO; molecular weight=42) of 5.0% to 25.0% by weight and c) an anionically and/or nonionically hydrophilizing component.

5. The process as claimed in claim 1, sections of the article that are contacted with the preparation have a porosity ? of ?0.01 to ?0.6 and the porosity ? is expressed as:
?=1?(?/?.sub.0) wherein ? represents the density of the volume assigned to the sections of the article that are contacted with the preparation and ?.sub.0 represents the true density of the construction material.

6. The process as claimed in claim 1, wherein the additive manufacturing process comprises: applying a layer of particles comprising the construction material onto a target surface; energizing a selected portion of the layer corresponding to a cross section of the article to join the particles in the selected portion; repeating the steps of applying and energizing for a plurality of layers so that the joined portions of the adjacent layers become joined to form the article.

7. The process as claimed in claim 6, wherein the energizing of a selected portion of the layer comprises: irradiating a selected portion of the layer corresponding to a cross section of the article with an energy beam to join the particles in the selected portion.

8. The process as claimed in claim 6, wherein the energizing of a selected portion of the layer comprises: applying a liquid to a selected portion of the layer corresponding to a cross section of the article, wherein the liquid increases the absorption of energy in the regions of the layer contacted by it relative to the regions not contacted by it; irradiating the layer so that the particles in regions of the layer contacted by the liquid are joined to one another and the particles in regions of the layer not contacted by the liquid are not joined to one another.

9. The process as claimed in claim 1, wherein the additive manufacturing process comprises: applying a filament of an at least partially molten construction material onto a carrier to obtain a layer of the construction material corresponding to a first selected cross section of the article; applying a filament of the at least partially molten construction material onto a previously applied layer of the construction material to obtain a further layer of the construction material which corresponds to a further selected cross section of the article and which is joined to the previously applied layer; repeating the step of applying a filament of the at least partially molten construction material onto a previously applied layer of the construction material until the article has been formed.

10. The process as claimed in claim 1, wherein the construction material comprises a thermoplastic polyurethane elastomer having a melting range (DSC, differential scanning calorimetry; second heating at a heating rate of 5 K/min) of ?20? C. to ?240? C., a Shore hardness according to DIN ISO 7619-1 of ?40 A to ?85 D.

11. The process as claimed in claim 1, wherein the construction material comprises a thermoplastic polyurethane elastomer having a melting range (DSC, differential scanning calorimetry; second heating at a heating rate of 5 K/min) of ?20? C. to ?240? C., a Shore A hardness according to DIN ISO 7619-1 of ?40 A to ?85 D, and a melt volume rate (MVR) according to ISO 1133 (10 kg) at a temperature T of 5 to 15 cm.sup.3/10 min and exhibiting a change in the melt volume rate (10 kg) at an increase of temperature T by 20? C. of ?90 cm.sup.3/10 min.

12. The process as claimed in claim 1, wherein the construction material comprises a thermoplastic polyurethane elastomer obtained from the reaction of the following components: a) at least one organic diisocyanate b) at least one compound having isocyanate-reactive groups and having a number-average molecular weight (M.sub.n) of ?500 g/mol to ?6000 g/mol and a number-average functionality of the sum total of the components b) of ?1.8 to ?2.5 c) at least one chain extender having a molecular weight (Mn) of 60-450 g/mol and a number-average functionality of the sum total of the chain extenders c) of 1.8 to 2.5.

13. The process as claimed in claim 1, wherein the construction material comprises a thermoplastic polyurethane elastomer having a melting range (DSC, differential scanning calorimetry; 2.sup.nd heating at a heating rate of 5 K/min) of ?20? C. to ?100? C. and a magnitude of complex viscosity |?*| (determined by viscometry measurement in the melt with a plate/plate oscillation shear viscometer at 100? C. and an angular frequency of 1/s) of ?10 Pas to ?1 000 000 Pas.

14. The process as claimed in claim 1, wherein the construction material comprises a thermoplastic polyurethane elastomer obtained from the reaction of a polyisocyanate component and a polyol component, wherein the polyol component comprises a polyester polyol having a no-flow point (ASTM D5985) of ?25? C.

15. The process as claimed in claim 1, wherein the residual content of organic solvents in the preparation is less than 1% by weight relative to the total preparation.

Description

EXAMPLES 1 to 4: PRODUCTION OF POLYURETHANE DISPERSIONS

(1) The production of polyurethane dispersions employable according to the invention is described hereinbelow without, however, being limited thereto. Unless otherwise stated all percentages are based on weight. Unless otherwise stated all analytical measurements relate to temperatures of 23? C. The solids contents were determined according to DIN-EN ISO 3251. Unless explicitly otherwise stated NCO contents were determined by volumetric means according to DIN-EN ISO 11909. The check for free NCO groups was conducted by means of IR spectroscopy (band at 2260 cm.sup.?1). The viscosities reported were determined by means of rotary viscometry to DIN 53019 at 23? C. with a rotary viscometer from Anton Paar Germany GmbH, Ostfildern, DE. Determination of the average particle sizes (number-average is reported) of the polyurethane dispersions was carried out by laser correlation spectroscopy (instrument: Malvern Zetasizer 1000, Malver Inst. Limited).

(2) Substances and abbreviations used: Diaminosulfonate: NH.sub.2CH.sub.2CH.sub.2NHCH.sub.2CH.sub.2SO.sub.3Na (45% in water) Desmophen 2020/C2200: Polycarbonate polyol, OH number 56 mg KOH/g, number-average molecular weight 2000 g/mol (Covestro AG, Leverkusen, DE) PolyTHF 2000: polytetramethylene glycol polyol, OH number 56 mg KOH/g, number-average molecular weight 2000 g/mol (BASF AG, Ludwigshafen, DE) PolyTHF 1000: polytetramethylene glycol polyol, OH number 112 mg KOH/g, number-average molecular weight 1000 g/mol (BASF AG, Ludwigshafen, DE) Polyether LB 25: monofunctional ethylene oxide-/propylene oxide-based polyether, number-average molecular weight 2250 g/mol, OH number 25 mg KOH/g (Covestro AG, Leverkusen, DE)

Example 1

(3) 987.0 g of PolyTHF 2000, 375.4 g of PolyTHF 1000, 761.3 g of Desmophen C2200 and 44.3 g of polyether LB 25 were heated to 70? C. in a standard stirring apparatus. Subsequently, at 70? C., a mixture of 237.0 g of hexamethylene diisocyanate and 313.2 g of isophorone diisocyanate was added over 5 min and the mixture was stirred at 120? C. until the theoretical NCO value had been achieved. The finished prepolymer was dissolved with 4830 g of acetone and cooled to 50? C. before a solution of 25.1 g of ethylenediamine, 116.5 g of isophoronediamine, 61.7 g of diaminosulfonate and 1030 g of water was added over 10 min. The after stirring time was 10 min. The mixture was then dispersed by addition of 1250 g of water. This was followed by removal of the solvent by distillation under vacuum. The residual content of acetone was below 1% by weight based on the finished dispersion.

(4) The obtained white dispersion had the following properties: Solids content: 61% Particle size (LCS): 312 nm Viscosity (viscometer, 23? C.): 241 mPas pH (23? C.): 6.02

Example 2

(5) 450 g of PolyTHF 1000 and 2100 g of PolyTHF 2000 were heated to 70? C. Subsequently, at 70? C., a mixture of 225.8 g of hexamethylene diisocyanate and 298.4 g of isophorone diisocyanate was added over 5 min and the mixture was stirred at 100-115? C. until the NCO content had fallen below the theoretical value. The finished prepolymer was dissolved with 5460 g of acetone at 50? C. before a solution of 29.5 g of ethylenediamine, 143.2 g of diaminosulfonate and 610 g of water was added over 10 min. The after stirring time was 15 min. The mixture was then dispersed over 10 min by addition of 1880 g of water. This was followed by removal of the solvent by distillation under reduced pressure to obtain a storage-stable dispersion. The residual content of acetone was below 1% by weight based on the finished dispersion.

(6) Solids content: 56%

(7) Particle size (LCS): 276 nm

(8) Viscosity: 1000 mPas

(9) pH (23? C.): 7.15

Example 3

(10) 1649.0 g of a polyester composed of adipic acid, hexanediol and neopentyl glycol having an average molecular weight of 1700 g/mol were heated to 65? C. Subsequently, at 70? C., 291.7 g of hexamethylene diisocyanate were added over 5 min and the mixture was stirred at 100-115? C. until the NCO content had fallen below the theoretical value. The finished prepolymer was dissolved with 3450 g of acetone at 50? C. and then a solution of 16.8 g of ethylenediamine, 109.7 g of diaminosulfonate and 425 g of water was metered in within 3 min. The after stirring time was 15 min. The mixture was then dispersed over 10 min by addition of 1880 g of water. This was followed by removal of the solvent by distillation under reduced pressure to obtain a storage-stable dispersion.

(11) Solids content: 42%

(12) Particle size (LCS): 168 nm

(13) Viscosity: 425 mPas

(14) pH: 7.07

Example 4

(15) 82.5 g of PolyTHF 1000, 308 g of PolyTHF 2000 and 10.0 g of 2-ethylhexanol were heated to 70? C. Subsequently, at 70? C., a mixture of 41.4 g of hexamethylene diisocyanate and 54.7 g of isophorone diisocyanate was added over 5 min and the mixture was stirred at 110-125? C. until the NCO content had fallen below the theoretical value. The finished prepolymer was dissolved with 880 g of acetone at 50? C. before a solution of 3.8 g of ethylenediamine, 4.6 g of isophoronediamine, 26.3 g of diaminosulfonate and 138 g of water was added over 10 min. The after stirring time was 15 min. The mixture was then dispersed over 10 min by addition of 364 g of water. This was followed by removal of the solvent by distillation under reduced pressure to obtain a storage-stable dispersion.

(16) Solids content: 49%

(17) Particle size (LCS): 181 nm

(18) Viscosity: 1300 mPas

(19) pH: 7.22

Example 5: Coatings with Dispersions

(20) Employed as the construction material was a pulverulent, ester-based thermoplastic polyurethane such as was described in example 1 of WO 2015/197515 A1. This was synthesized 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 1,4-butanediol and about 1.45 mol of 1,4-butanediol, about 0.22 mol of 1,6-hexanediol, about 2.67 mol of technical 4,4-diphenylmethane diisocyanate (MDI) comprising >98% by weight of 4,4-MDI, 0.05% by weight of Irganox 1010 (pentaerythritoltetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) from BASF SE), 1.1% by weight of Licowax E (montanic ester from Clariant) and 250 ppm of tin dioctooate by the known static mixer-extruder process. The obtained TPU had the following properties: melting range (DSC, differential scanning calorimetry; second heating at a heating rate of 5 K/min) of ?20? C. to ?200? C., Shore A hardness according to DIN ISO 7619-1 of ?40 A to ?85 D, a melt volume rate (MVR) according to ISO 1133 at a temperature T of 5 to 15 cm.sup.3/10 min and a change in the melt volume rate (10 kg) for an increase in this temperature T by 20? C. of ?90 cm.sup.3/10 min.

(21) This construction material was used to produce an S2 test specimen by means of a powder laser sintering process (SLS).

(22) The obtained S2 test specimen was immersed in an aqueous polyurethane dispersion known as Impranil DLN W50 (Covestro AG, Leverkusen, DE), of an anionic aliphatic polyester polyurethane dispersion, for 10 min and subsequently dried to constant weight at room temperature.

(23) Before and after coating with the polyurethane dispersion the test specimen was evaluated in respect of its haptic properties on a scale of 1 to 5 points, wherein a score of 1 point denotes very unpleasant haptic properties and a value of 5 points denotes very pleasant haptic properties. The test specimen was given an evaluation of 2 points before coating and 4 points after coating.

(24) The production of further test specimens was carried out with a Snowwhite SLS powder SLS apparatus from Sharebot using the following apparatus parameters: Temperature of powder surface: 80? C., scan rate: 300 mm/s, laser output: 60%, Hatch Distance: 0.2 mm, layer height: 0.15 mm. The powder employed was the ester-based thermoplastic polyurethane powder Luvosint X92A-1 WT from Lehmann & Voss. According to the data in the datasheet this material had a glass transition temperature (ISO 6721-1) of ?13.6? C., a melt volume rate MVR 190? C./2.16 kg (ISO 1133) of 18 cm.sup.3/min and a Shore A hardness (ISO 868) of a laser-sintered component of 88.

(25) The thus-obtained test specimens having a porosity ? of about 0.3 were immersed in various aqueous dispersions at room temperature for 10 minutes, allowed to drip-dry for 15 minutes, and then heat treated at 70? C. for 15 minutes and at 100? C. for a further 3 minutes in a circulating air drying cabinet before, after a further three days of storage at room temperature, being tested in the tensile test according to DIN 53504. This comprised testing the elastic modulus at 50% elongation, the breaking elongation and the breaking stress.

(26) It is very readily apparent from the results described hereinbelow that under comparable conditions the inventive combination of polyurethane-based sintered products with polyurethane-containing and/or isocyanate-containing infiltrants achieves markedly higher moduli and tensile strengths compared to untreated specimens. It is thought that this evidences the particularly good interaction between the polyurethane construction material and polyurethane and/or isocyanate-based infiltrants.

(27) The inventive examples are marked * while the comparative examples are marked (V). 3 hours before infiltration all dispersions were admixed with stirring with 0.3 parts of BYK 331 (a silicone-containing surface additive for solventless and solvent-containing industrial and automotive lacquers and printing inks obtainable from Altana Group).

(28) TABLE-US-00001 Sample no. Description 1 (V) sintered bar as starting product, heat-treated as described 2 (V) as per sample no. 1, additionally infiltrated with water 3 (V) as per sample no. 1, additionally infiltrated with Acronal A 310 S (acrylate copolymer dispersion, 50% solids; BASF SE) 4* as per sample no. 1, additionally infiltrated with Dispercoll U54 (polyurethane dispersion, 50% solids; Covestro AG) 5* as per sample no. 1, additionally infiltrated with Bayhydur 3100, 50% in water (hydrophilized isocyanate; Covestro AG) 6* as per sample no. 1, additionally infiltrated with a mixture of Baydrol UH 2557 (polyurethane dispersion, 30% solids; Covestro AG) and 10% by weight of Bayhydur 3100

(29) The mass increases of the samples after infiltrations were:

(30) TABLE-US-00002 Sample no. Initial weight [g] Increase [g] Increase [%] 1 (V) 1.018 0 0 2 (V) 1.028 0 0 3 (V) 1.030 0.049 4.72 4* 1.061 0.054 5.09 5* 1.084 0.087 8.03 6* 1.046 0.053 5.07

(31) The results of the mechanical tests were as follows:

(32) TABLE-US-00003 Elastic modulus Breaking Breaking Sample at 50% elongation stress elongation no. [N/mm.sup.2] [N/mm.sup.2] [%] 1 (V) 2.829 3.876 132 2 (V) 2.927 4.242 147 3 (V) 2.780 4.138 160 4* 3.460 6.290 221 5* 3.334 6.386 236 6* 3.450 5.013 183

(33) Further tests were performed on printed S2 test specimens in the form of tensile bars. These were printed in the FDM process with an ABS material (100180, ABS plastic 2, 1 kg 1.75 mmnatural) from German Reprap.

(34) The printer employed was a Prusa i3 MK2 with a 0.4 mm die and a temperature of 255? C. The printing parameters were: extrusion die diameter 0.4 mm, layer height 0.2 mm, printing rate 40 mm/s, infill 100%, extrusion temperature 255? C., printing bed temperature 100? C.

(35) The thus-obtained ABS test specimens in S2 rod form were immersed in various aqueous dispersions at room temperature for 10 minutes, allowed to drip-dry for 15 minutes, and then heat treated at 70? C. for 15 minutes and at 100? C. for a further 3 minutes in a circulating air drying cabinet before, after a further three days of storage at room temperature, being tested in the tensile test according to DIN 53504. This comprised testing the elastic modulus at 50% elongation, the breaking elongation and the breaking stress.

(36) Before and after coating with the polyurethane dispersion the test specimen was evaluated in respect of its haptic properties on a scale of 1 to 5 points, wherein a score of 1 point denotes very unpleasant haptic properties and a value of 5 points denotes very pleasant haptic properties. The test specimen was given an evaluation of 3 points before coating and 4 points after coating.

(37) TABLE-US-00004 Sample no. Description 7 (V) printed bar as starting product, heat-treated as described 8 (V) as per sample no. 7 (V), additionally infiltrated with Dispercoll U54 (polyurethane dispersion, 50% solids; Covestro AG) 9 (V) as per sample 7 (V), additionally infiltrated with Acronal A 310 S (acrylate copolymer dispersion, 50% solids: BASF SE) 10 (V) as per sample 7(V), additionally Infiltrated with Bayhydur 3100, 50% in water (hydrophilized isocyanate; Covestro AG)

(38) The mass increases of the samples after infiltrations were:

(39) TABLE-US-00005 Sample no. Initial weight [g] Weight after increase [g] Increase [%] 7 (V) 1.19 0 0 8 (V) 1.199 1.2185 1.62 9 (V) 1.19047 1.2135 1.93 10 (V) 1.1995 1.2235 2.00

(40) The results of the mechanical tests were as follows:

(41) TABLE-US-00006 Sample Elastic modulus Breaking stress Elongation no. [N/mm.sup.2] [N/mm.sup.2] at break [%] 7 (V) 1580 33 4.4 8 (V) 1600 34 2.7 9 (V) 1580 36 4.8 10 (V) 1550 36 3.7

(42) It is clearly apparent that the coating with inventive coatings of noninventive materials such as ABS plastic in the form of S2 test bars produced by the additive manufacturing process FDM as described above does as expected generate a noticeable improvement in haptic surface properties but has no significant influence on the mechanical properties of the components and thus exhibits no improvement of mechanical properties.