Process for producing 3D structures from powdered rubber material and its products

Abstract

A process is described for producing a three dimensional structure, the process including the following steps a) applying of at least a first material M.sub.1 onto a substrate to build a first layer L.sub.1 on the substrate; b) layering of at least one further layer L.sub.y of the first material M.sub.1 or of a further material M.sub.x onto the first layer L.sub.1, wherein the at least one further layer Ly covers the first layer L.sub.1 and/or previous layer L.sub.y−1 at least partially to build a precursor of the three dimensional structure; c) curing the precursor to achieve the three dimensional structure; wherein at least one of the materials M.sub.1 or M.sub.x provides a Mooney viscosity of >10 ME at 60° C. and of <200 ME at 100° C. before curing and wherein at least one of the first material Mi or of the further material M.sub.x is a powder. Also, a three dimensional structure is described which is available according to the process according to the invention.

Claims

1. A process for producing a three dimensional structure, the process including at least the following steps a) applying of at least a first material M.sub.1 onto a substrate to build a first layer L.sub.1 on the substrate; b) layering of at least one further layer L.sub.y of the first material M.sub.1 or of a further material M.sub.x onto the first layer L.sub.1, wherein the at least one further layer L.sub.y covers the first layer L.sub.1 and/or previous layer L.sub.y−1 at least partially to build a precursor of the three dimensional structure; c) curing the precursor to achieve the three dimensional structure; wherein at least one of the materials M.sub.1 or M.sub.x provides a Mooney viscosity of >10 ME at 60° C. and of <200 ME at 100° C. before curing, wherein at least one of the materials, the first material M.sub.1 or the further material M.sub.x is a powder, wherein the powder comprises a plurality of powder components compounded together to form a compounded powder material that is compounded before step c).

2. The process according to claim 1, wherein the powder provides an average particle size in a range of from 10 to 5000 μm.

3. The process according to claim 1, wherein the powder is produced by grinding at least one component of the first material M.sub.1 or at least one component of the further material M.sub.x at a temperature of below 30° C.

4. The process according to claim 1, wherein the process provides at least one of the following features: I) the curing step c) is started independently for each layer L.sub.1 to L.sub.y before, during or after one of the steps a) or b); II) step a) comprises a selective attachment step a″); III) step b) comprises a selective attachment step b″).

5. The process according to claim 1, wherein at least one of the used materials provides at least one of the following features: (1) at least one of the materials M.sub.1 or M.sub.x has a Tg below 25° C. before and/or after curing step c); (2) at least one of the materials M.sub.1 or M.sub.x has a molecular weight of 5 to 5000 kg/mol; (3) at least one of the materials M.sub.1 or M.sub.x or the three dimensional structure has an elongation at break of >30% after curing step c); (4) at least one of the materials M.sub.1 or M.sub.x experiences no phase transition (Tg or Tm) above 50° C. before and/or after curing step c); (5) at least one of the materials M.sub.1 or M.sub.x has a Mooney viscosity of >10 ME at 60° C. and <200 ME at 100° C.

6. The process according to claim 1, wherein the hardness of the cured material M.sub.1c or M.sub.xc after step c) has increased by at least 5 Shore A points compared to the applied material M.sub.1 in step a) or M.sub.x in step b) before curing.

7. The process according to claim 1, wherein at least one of the following steps is executed according to digital data related to the shape of the three dimensional structure which are established and provided by a computer aided process: the applying of material M.sub.1 in step a); the selective attachment of at least a part of material M.sub.1 in a step a″); the layering of material M.sub.x in step b); the selective attachment of at least a part of material M.sub.x in a step b″).

8. The process according to claim 1, wherein the compounded powder material comprises 100 parts of an ultra-high viscosity polymer, 0 to 300 parts of an organic or inorganic filler, 0 to 150 parts of a plasticizer, 0 to 40 parts of a metal oxide, 0 to 20 parts of an anti-degradent, 0 to 10 parts of process aids, 0 to 20 parts of coagent and 0.1 to 20 parts of a curative.

9. The process according to claim 1, wherein the three dimensional structure is cured in step c) at a temperature≥the temperature of the building volume where at least step a) or step b) are performed.

10. A three dimensional structure resulting from the process of claim 1.

11. The three dimensional structure according to claim 10, wherein the three dimensional structure provides a ratio of chemical crosslinking density to entanglement crosslinking density of <2.

12. The three dimensional structure according to claim 10, wherein the three dimensional structure has a dimension in a range of 1 mm*1 mm*1 mm to 2 m*2 m*10000 m.

13. The three dimensional structure according to claim 10 or produced according to a process according to claim 1, wherein the three dimensional structure is at least a part of one of the following objects selected from the group consisting of a mattress, a seat, a shoe, a sole, an insole, a shoe sole, a helmet, a protector, a handle, a garment, a tire, a damper, a timing belt, a drive belt, a hose, an air spring, a wristlet, a sieve, a membrane, a sealing, an O-ring, a gasket, a tube, a net, a rope, a protective suit or a combination of at least two thereof.

14. The process according to claim 1, wherein the compounded powder material is compounded before step a) or b).

15. The process according to claim 1, wherein the compounded powder material is ground to achieve an average particle size in a range of from 10 to 5000 μm.

16. The process according to claim 15, wherein the compounded powder material is ground via cryogenic grinding.

17. The process according to claim 1, wherein the plurality of powder components comprises powder components having different average powder particle diameters.

18. The process according to claim 1, wherein the powder comprises less than 1 wt % water, based on a total weight of the material forming the powder.

Description

METHODS

(1) 1. Mooney viscosity: the Mooney viscosity is measured according to DIN 53523. The Mooney viscosity is measured according to DIN 53523, with the large rotor, 1 min preheating and 4 min measurement interval, known in the prior art as ML 1+4. 2. Shear viscosity: the shear viscosity is measured in a Wells/Brookfield cone-plate-viscosimeter at a shear rate of 1/s at 25° C. 3. Hardness: The Shore A hardness is measured according to DIN 53505. 4. Bending modulus: the bending modulus is measured according to DIN EN ISO 178. 5. Tensile testing: The tensile strength, tensile modulus and elongation at break are measured according to DIN 53504. 6. Compression set: The compression set is measured according to DIN 53517. 7. Glass transition temperature T.sub.g: The T.sub.g is measured according to DIN 53765. 8. Chemical crosslinking density/entanglement crosslinking density: The chemical crosslinking density and ratio of entanglement crosslinks compared to chemical crosslinking density can be conveniently assessed by using Flory-Rhener theory for equilibrium swelling of crosslinked networks in ideal solvents in combination with mechanical stress-strain testing. This method is described in detail in: Polymer, Volume 30, Issue 11, November 1989, Pages 2060-2062 9. Temperature dependent modulus E′: is measured between 25° C. and 200° C. in a DMA (dynamic mechanical analysis) https://en.wikipedia.org/wiki/Dynamic_mechanical_analysis, at shear rates of 1/s e.g. with a METTLER TOLEDO DMA 1. 10. Torque: The measurement of the t.sub.80 and t.sub.100 time and corresponding torque is preferably performed on a vulcanising rheometer which is preferably based on a moving die rheometer according to a Vulkameter curing test at 200° C. according to DIN 53529 using a Visco-Elastograph from Göttfert.

Expected Results

(2) In Table 1 together with the explanatory passage below, the general expected behavior of inventive compositions and non-inventive compositions has been listed.

(3) TABLE-US-00001 TABLE 1 Examples of inventive compositions* to form material M.sub.1 or M.sub.x and non-inventive compositions Ethylen Ethylen- Thermo- Nitril Polychloroprene propylen vinylacetate plastic Engineering Engineering Ingredients rubber (CR)* (EPDM)* (EVA)* urethane Thermo- Thermo- phr (NBR)* rubber rubber rubber (TPU) plast (ABS) plast PA12 Polymer 100 100 100 100 100 100 100 Filler Filler 200 100 200 150 Plasticizer 5 5 10 5 Metal 2 2 2 2 Oxide Anti- 1 1 1 1 degradents Process 0.5 0.5 0.5 0.5 Aids Coagent 1 1 5 5 Curative 2 2 8 8 *inventive examples

(4) The non-inventive samples could not be processed like the inventive samples because they resulted uniformly in non-sintered powders after being treated in the SLS printer which had been used for the inventive samples as described before. Comparative samples produced according to suitable 3D printing technologies showed significantly different properties compared to the inventive samples especially with regards to change of properties in a DMA test of the materials between 25° C. and 200° C. as disclosed under Methods, since all comparative materials melted (TPU, ABS, PA12) and/or changed dramatically in their E′modulus whereas the inventive materials kept their shape and experienced only a limited reduction of their modulus.

EXPERIMENTAL PART

(5) All necessary materials to compose the first material M.sub.1 or any of the further materials M.sub.2 to M.sub.x were mixed in a two-step process, first in a 1.51 internal mixer at 40° C. mixer temperature and secondly on a standard lab scale 2 roll mixer of company Vogt Labormaschinen GmbH at 20° C. roll temperature. First the ultra-high viscosity liquid listed in table 2 was plasticized in the internal mixer. After that, the further ingredients listed in table 2 were added starting with filler, then plasticizer, then Metal Oxide, then process aid, then coagent and finally curative. The overall 2 step process took up to 30 minutes. The addition of the ingredients was performed in such a way that optimal distribution of the ingredients was ensured as known in the art. The temperature of the material did not exceed 100° C. during the mixing process.

(6) The inventive compositions according to table 2 were further processed on the roll to achieve 2 mm thin sheets of rubber formulations which were then processed and tested according to standard rubber methods, e.g. Mooney viscosity, vulcanization testing, pressure vulcanization of S2 test specimen, tensile testing, Shore A measurements. Further the material was used for providing feedstock for the process for producing a three dimensional structure, also called 3D printing process, as described below.

(7) All inventive formulations have been purchased from Lanxess AG, Germany as ready mixed compounds.

(8) All comparative materials where purchased as Polyamide particles from Hunan Farsoon High-tech Co., Ltd named Polyamide FS 3300 PA, and used without further treatment.

(9) TABLE-US-00002 TABLE 2 Examples of inventive compositions/compounds (*) to build material 1* corresponding to M.sub.1, 2* corresponding to M.sub.2 to 5* corresponding to M.sub.5 Example 1* M.sub.1 2* M.sub.2 3* M.sub.3 4*M.sub.4 5* M.sub.5 Ingredients phr [parts per hundred rubber] THERBAN AT 3404 100 PERBUNAN 2831 F 100 LEVAPREN 600 100 BAYPREN 210 100 KELTAN 2470L 100 CORAX N 550/30 30 30 30 30 30 SUNPAR 2280 5 UNIPLEX 546 5 5 5 5 RHENOFIT DDA-70 1.4 1.4 1.4 1.4 1.4 VULKANOX ZMB2/C5 0.4 0.4 0.4 0.4 0.4 MAGLITE DE 2 2 2 2 2 ZINKOXYD AKTIV 2 2 2 2 2 PERKADOX 14-40 B-PD 7 2 7 1.5 7 KETTLITZ-TAIC 1.5 1.5 1.5 The ingredients were compounded to achieve compounds 1* (M.sub.1) to 5* (M.sub.5). This was achieved by the following steps: Compounding 1* 2* 3* 4* 5* Mixing calculated density g/cmm 1.182 1.177 1.252 1.388 1.107 Mixing steps Internal mixer 1.5 liter volume Mixing Step 1 1 1 1 1 Parameters RPM: 1/min 40 Stamp pressure: bar 8 Temperature [° C.]: 40 Roll mixer as mentioned above Mixing Step 2 2 2 2 2 Parameters RPM 1/min 20 Temperature [° C.] 30 Vulcanisation 1* 2* 3* 4* 5* Moving-Die-Rheometer (MDR2000E) Nr 1 2 3 4 5 Parameter Test temperature ° C. 180 for all samples Test time min 30 for all samples Torque minimum [Nm] 0.54 0.67 0.21 1.29 0.62 Torque maximum [Nm] 17.77 19.23 16.9 23.22 28.81 Torque end [Nm] 17.62 19.21 16.83 23.21 28.78 T 10% [sec] 47.33 41.28 36.85 36.02 47.75 T 25% [sec] 76.53 65.3 49.04 58.29 75.53 T 30% [sec] 86.63 73.98 53.39 67.28 85.51 T 50% [sec] 134.33 116.55 78.45 112.35 134.95 T 70% [sec] 205.83 183.36 129.99 181.83 215.3 T 80% [sec] 263.82 238.68 178.86 255.24 282.96 T 90% [sec] 365.82 337.92 268.86 439.62 403.53 T 95% [sec] 467.31 446.52 361.53 725.01 528.63 tan D end [rad] 0.04 0.02 0.02 0.02 0.01 Example 1* 2* 3* 4* 5* Mooney (viscosity) ML1 + 4 Rotor L Preheating min 1 Time to measure min 4 Temperature ° C. 60 ML 1 + 4 ME 142 96 74 11376 Example 1* 2* 3* 4* 5* Mooney (viscosity) ML1 + 4 Rotor L Preheating min 1 Time to measure min 4 Temperature ° C. 100 ML 1 + 4 ME 52 40 27 60 36 DSC −100 to 200° C., 20° C./min Tg before cure ° C. −31.5 −40.4 −32.9 −43.0 −45.1 Tm before cure ° C. — — — 39.8*.sup.1 44.3*.sup.1 Start of vulcanisation ° C. 140 150 145 140 140 Tg after cure ° C. −30.2 −37.4 −29.5 −41.3 −42.1 Tm after cure ° C. — — — — — 1 2 3 4 5 cure temperature ° C. 180 180 180 180 180 press actual time min 12 12 12 12 12 hardness and tensile strength @ RT (test combbination) Density g/ccm 1.2 1.2 1.2 1.4 1.1 M10 MPa 0.5 0.5 0.4 0.6 0.6 M25 MPa 0.8 1 0.9 1.1 1.1 M50 MPa 1.2 1.6 1.6 1.8 1.7 M100 MPa 2.4 3.5 4.3 3.9 3.8 M300 MPa 16.3 — — — — elongation at break % 371 187 215 230 199 tensile strength MPa 22.2 9.9 15.7 16.3 13.7 hardness ShA vulcanized 57 61 58 66 66 hardness ShA unvulcanized 11 5 9 36 21 *.sup.1only small peaks indicating crystalline content ≤10%/weight of formulation. Peaks disappear after curing. curing - rubber -- test sheets comparative results of standard rubber manufacture, pressure vulcanized sheets used to cut out tensile test pieces.

(10) For 3D printing via selective laser sintering the materials processed as described above where grinded using liquid nitrogen using a cryogrinding equipment GSM 250 from ACU-Pharma. Processing of formulated inventive compounds yielded ca. 20% of powdered rubber compounds (by weight) with medium particle sizes <0.5 mm as filtered through a 0.5 mm sieve. The thus received particles where dusted in ca. 2% of talcum and slowly brought to 23° C. temperature to prevent agglomeration.

(11) To form articles by laser sintering of the inventive materials M.sub.1 to M.sub.5 (also referred to as 1* to 5*) each 12 g of the formulations where gathered in an aluminum vessel of 60 mm diameter and 8 mm depth, the powder was casted and subsequently pressed into a smooth surface and sintered at 23° C. in a SLS printer of Sharebot S.r.l., Italy of the type Snow White. Round shapes of 20 mm diameter and one layer where printed at room temperature. The laser energy of the used CO.sub.2 laser was 6.3 W Scanning speed was 1.8 m/s and hatch distance was 0.1 mm. This is equivalent to an energy amount per run of 0.035 J/mm.sup.2. To achieve stable shapes of 20 mm diameter 5 laser runs for the inventive sample was needed at a building room temperature of 23° C. The sintered one layer test pieces where gathered with a pincer and cleaned carefully by a medium hard brush from non sintered particles. Afterwards the test pieces where put into a hot air oven and vulcanized for 10 min at 200° C. to achieve a vulcanized test piece of ca. 2 mm thickness and 20 mm diameter. On the sintered particles density and hardness measurements where performed. Results are shown in table 2 and table 3. Inventive samples are marked by *. Inventive and comparative samples where tested under the same conditions.

(12) TABLE-US-00003 TABLE 3 Samples: Inventive compound 5* (M.sub.5) Comparative sample FS 3300 PA Test specimen 20 mm diameter sintered yes yes Hardness (Shore A/D) A: 20 D: 72 Density kg/l 0.3 0.9 Vulcanisation 10 min at 200° C. Shape survived yes no Hardness (Shore A/D) A: 59 D: 72

(13) Surprisingly, the inventive sample forms a stable shape after sintering and keeps this shape after vulcanizing while at the same time curing to a mechanically typical rubber material. Also, it could be shown that the sub sequential post curing is a vital process step to achieve the desired properties. On the other hand the inventive process applied to non inventive materials does not yield satisfying results even using the most well known standard laser sintering material PA 12 (FS3300 PA).

(14) Further the comparative example shows distinctly different processing behaviors compared to the inventive examples and printing procedures and significantly inferior product behavior after 3D printing especially regarding change of E-modulus with temperature between 25° C. and 150° C. (no rubber plateau, and a phase transition).