METHOD FOR MODIFYING A 3D PRINTED OBJECT

Abstract

The invention relates to a method for modifying an object comprising the step of: I) providing an object which is made at least partially of a construction material comprising a thermoplastic polyurethane. The method also comprises the following steps: II) contacting, at least in part, the construction material, for a first predetermined period of time, with a first liquid comprising ≥80% by weight, based on the total weight of the first liquid, of a polar aprotic solvent; III) contacting, for a second predetermined period of time, the areas of the construction material that were in contact with the liquid in step II) with a second liquid comprising ≥80% by weight, based on the total weight of the second liquid, of a polar protic solvent. Preferably, the first liquid is DMSO or acetone and the second liquid is water.

Claims

1. A process for modifying an article comprising: I) providing an article which is at least partially constructed from a build material comprising a thermoplastic polyurethane; II) at least partially contacting the build material for a first predetermined duration with a first liquid including ≥80% by weight of a polar aprotic solvent based on a total weight of the first liquid; III) contacting for a second predetermined duration regions of the build material contacted with the first liquid in step II) with a second liquid including ≥80% by weight of a polar protic solvent based on a total weight of the second liquid.

2. The process as claimed in claim 1, wherein the polar aprotic solvent in the first liquid comprises acetone, methyl ethyl ketone, dimethyl sulfoxide, or a mixture thereof.

3. The process as claimed in claim 1, wherein the first liquid further includes water, a polyisocyanate, a polyol, or a mixture of at least two of the abovementioned components.

4. The process as claimed in claim 1, wherein the polar protic solvent in the second liquid includes water, methanol, ethanol, n-propanol, isopropanol, or a mixture of at least two of the abovementioned components.

5. The process as claimed in claim 1, wherein in step II) the first predetermined duration is ≥1 second to ≤120 seconds and/or wherein in step III) the second predetermined duration is ≥1 second to ≤120 seconds.

6. The process as claimed in claim 1, further comprising heating the article to a temperature of ≥50° C. for a predetermined duration after step III).

7. The process as claimed in claim 1, wherein the regions of the build material contacted with the solvent in step II) have a porosity Φ of ≥0.01 to ≤0.6 and the porosity Φ is expressed as:
Φ=1−(ρ/ρ.sub.0) wherein ρ represents the density of the volume assigned to the sections of the article that are contacted with the solvent and ρ.sub.0 represents the true density of the build material.

8. The process as claimed in claim 1, wherein the article is at least partially produced by means of an additive manufacturing process using the build material.

9. The process as claimed in claim 8, wherein the additive manufacturing process comprises the steps of: applying a layer of particles comprising the build material to 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 selected portions of adjacent layers become joined to form the article.

10. The process as claimed in claim 9, wherein the energizing comprises: irradiating the selected portion of the layer with an energy beam to join the particles in the selected portion.

11. The process as claimed in claim 9, wherein the energizing comprises: applying a liquid to the selected portion of the layer, wherein the liquid increases absorption of energy in regions of the layer contacted by the liquid relative to regions of the layer not contacted by the liquid; 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.

12. The process as claimed in claim 8, wherein the additive manufacturing process comprises the steps of: applying a filament of the at least partially molten build material to a carrier, such that a layer of the build material is obtained, corresponding to a first selected cross section of the article; applying a filament of the at least partially molten build material onto a previously applied layer of the build material to obtain a further layer of the build 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 build material onto a previously applied layer of the build material until the article has been formed.

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

14. An at least partially modified article obtained by a process as claimed in claim 1.

15. The article as claimed in claim 14, wherein sections of the article having been modified by the process have a higher tensile strength according to DIN 53504 and/or a higher breaking elongation according to DIN 53504 than corresponding sections on an unmodified but otherwise identical article.

Description

EXAMPLES

[0084] The present invention is more particularly elucidated with reference to the following examples without, however, being limited thereto.

[0085] The examples employed the following thermoplastic polyurethane materials:

TABLE-US-00001 Example no. Material 1 Ester-based TPU having a Shore D hardness of 59 (measured on an injection- molded specimen according to DIN ISO 7619-1, 1 second test time) and a glass transition temperature of about −13° C. (measured on an injection-molded specimen based on DIN ISO 671-1, frequency 1 Hz) 2 Luvosint X92 A-2 (Lehmann & Voss). Ester-based TPU. 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. 3 Ether-based TPU having a Shore A hardness of 72 (measured on a laser- sintered specimen according to DIN ISO 7619-1, 3 second test time) and a glass transition temperature of about −37° C. (measured on an injection-molded specimen based on DIN ISO 671-1, frequency 1 Hz) 4 Ether-based TPU having a Shore D hardness of 70-74 (measured on an injection-molded specimen according to DIN ISO 7619-1, 1 second test time) and a glass transition temperature of about 60° C. (measured on an injection- molded specimen based on DIN ISO 671-1, frequency 1 Hz) 5 Ether-based TPU having a Shore D hardness of 65 (measured on a laser- sintered specimen according to DIN ISO 7619-1, 1 second test time) and a glass transition temperature of about 60° C. (measured on an injection-molded specimen based on DIN ISO 671-1, frequency 1 Hz)

[0086] The TPU materials were processed into S2 test specimens. These test specimens were produced on a powder SLS apparatus or in the case of Example 4 on an FDM apparatus.

[0087] In the individual examples test specimens were subjected to visual and haptic assessment in respect of their surface quality. In addition, tensile strengths and breaking elongations were determined in a tensile test according to DIN 53504. After determination of starting values (“zero values”) the test specimens were immersed in acetone or dimethyl sulfoxide for the times indicated, subsequently rinsed with water and then dried at 30° C. over 24 hours in a recirculating air drying cabinet. The thus treated test specimens were again subjected to visual and haptic assessment in respect of their surface quality and tensile strengths and breaking elongations were determined.

[0088] The scale for evaluating the surfaces of the printed test specimens was as follows:

TABLE-US-00002 0 Starting state: rough, powdery, leaves powder particles behind 1 rough, no longer any loose powder 2 no longer as rough as starting state, no longer any loose powder 3 feels slightly smoothed, powder structure still recognizable on surface, no longer any loose powder 4 Surface feels almost smooth, no longer any loose powder 5 Surface feels completely smooth, no structure and no longer any loose powder

TABLE-US-00003 Example Immersion Value according no. Solvent time [s] to scale 1 Acetone 30 1 1 DMSO 30 3 2 Acetone 30 1 2 DMSO 30 3 3 Acetone 30 2 3 DMSO 30 5 5 Acetone 30 1 5 DMSO 30 5

[0089] In all examples the assessment of the test specimen for the zero value was “0”.

Example 1

[0090]

TABLE-US-00004 Change in Change in tensile breaking Tensile strength Breaking elongation Immersion strength from zero elongation from zero Solvent time [s] [N/mm.sup.2] value [%] [%] value [%] Zero value 2.21 14.4 Acetone 30 2.57 16.29 18.89 31.18 60 2.35 6.33 18.49 28.40 DMSO 15 2.53 14.48 24.67 71.32 30 2.44 10.41 20.21 40.35 45 2.6 17.65 24.19 67.99 60 2.82 27.60 28.16 95.56

Example 2

[0091]

TABLE-US-00005 Change in Change in tensile breaking Tensile strength Breaking elongation Immersion strength from zero elongation from zero Solvent time [s] [N/mm.sup.2] value [%] [%] value [%] Zero value 2.81 74.18 Acetone 30 3.06 8.90 98.33 32.56 60 3.44 22.42 98.11 32.26 DMSO 30 3.13 11.39 118.23 59.38 45 3.57 27.05 109.88 48.13 60 3.32 18.15 121.46 63.74

Example 3

[0092]

TABLE-US-00006 Change in Change in tensile breaking Tensile strength Breaking elongation Immersion strength from zero elongation from zero Solvent time [s] [N/mm.sup.2] value [%] [%] value [%] Zero value 3.06 119.32 Acetone 30 3.19 4.25 145.46 21.91 DMSO 15 3.34 9.15 134.25 12.51 30 3.63 18.63 147.47 23.59

Example 4

[0093]

TABLE-US-00007 Change in Change in tensile breaking Tensile strength Breaking elongation Immersion strength from zero elongation from zero Solvent time [s] [N/mm.sup.2] value [%] [%] value [%] Zero value 4.65 4.44 DMSO 15 5.58 20.00 8.6 93.69 30 5.18 11.40 7.36 65.77 45 5.58 20.00 7.4 66.67

Example 5

[0094]

TABLE-US-00008 Change in Change in tensile breaking Tensile strength Breaking elongation Immersion strength from zero elongation from zero Solvent time [s] [N/mm.sup.2] value [%] [%] value [%] Zero value 2.54 3.82 Acetone 30 2.81 10.63 4.41 15.45 DMSO 15 2.55 0.39 18.78 391.62 30 2.62 3.15 13.99 266.23 45 2.8 10.24 17.98 370.68 60 2.41 −5.12 19.38 407.33