Material for additive manufacture of three-dimensional components with a printing process

Abstract

The material for the additive manufacture of components with a printing process is formed using at least 55% by volume of particles of a metal, 40% by volume of a ceramic or 40% by volume of metal and ceramic, 15% by volume to 30% by volume of a microcrystalline wax, at least 0.3% by volume to at most 3% by volume of ultrahigh molecular-weight polyethylene, 1% by volume to 2.5% by volume of an esterified beeswax and at least one further organic additive.

Description

[0001] Material for additive manufacturing of three-dimensional components using a printing process

[0002] The invention relates to a material for the additive manufacturing of components using a printing process. The material can be processed using a wide variety of printing devices and can be fed to the respective printing device, for example, in strand form, as a paste, suspension, rod, or in the form of individual pellets. It can be processed, in particular, using a heated dispenser, heated pellet printer, heated screen printer, FFF filament printer, or by injection molding.

[0003] Such materials are known in principle and are also used. The components are essentially constructed from the material from which the solid particles are made, which are then embedded in an organic matrix for printing. To increase efficiency and productivity, the highest possible proportion of solid particles is desired. However, the higher this proportion, the more difficult such a material is to produce and, typically, to process during printing. A homogeneous distribution of the solid particles without agglomeration within the organic matrix must be maintained during printing and thereafter.This places correspondingly high demands on the organic components with which the particles are to be bound before the organic components are released, by a solvent treatment or expelled, by thermal treatment, by decomposition or evaporation in a furnace, in order to then obtain a component that has been manufactured entirely from the material of the particles, by sintering the particles, in a furnace.

[0004] During the printing process, the particles must be embedded in the organic matrix and move within it as much as possible. This ensures that even when mechanical forces are applied, there is no significant shearing effect on the particles. This would lead to an inhomogeneous distribution of the particles within the material, which is present as a pasty mass during the printing process at elevated temperatures, usually in the range of 100°C to approximately 150°C. Any opening or tearing of the organic matrix during printing should also be avoided, as this could lead to defects and possibly voids in a component. The organic components should therefore be sufficiently bonded to one another, and the viscosity and flow behavior should be adjusted so that deposited material strands retain their shape and contour sharpness as much as possible during the printing process.However, the consistency must allow printing without clogging, for example, a nozzle of the printer.

[0005] In addition, the starting material, which can be a filament for an FFF printer, for example, should also have sufficient hardness, flexibility and stability so that a geometric shape can be retained after completion of the actual printing or manufacturing process, but before the final sintering or solidification, and in particular no running or cracking can occur when removing the organic material, using a solvent such as ethyl acetate and during thermal debinding, which would undesirably change the specified geometric shape of the printed or manufactured semi-finished product or green body.Another important requirement that must be met is the longest possible processability of such a material after its production, i.e., ensuring that the manufactured material does not change its flexibility and mechanical properties, especially that the properties related to printability are not altered or only slightly altered, thereby deteriorating them. Esterified beeswaxes can prove advantageous for this purpose.

[0006] It is therefore an object of the invention to provide possibilities by which a material can be made available which has improved printing properties even over a longer period of time after its production and which has a very high solids content with homogeneous distribution of the respective particles during and after the printing process.

[0007] According to the invention, this object is achieved with a material having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized with features defined in the dependent claims.

[0008] The material according to the invention is provided with a solids content of either at least 55 vol.% metallic particles, preferably at least 60 vol.% metallic particles, or ceramic particles (at least 40 vol.% ceramic particles, preferably at least 50 vol.% ceramic particles) or metallic and ceramic particles of at least 40 vol.%, preferably at least 50 vol.%,

[0009] 15 vol.% to 30 vol.% of a microcrystalline wax, at least 0.3 vol.% to a maximum of 3 vol.% ultra-high molecular-weight polyethylene (UHMWPE), 1 vol.% to 2.5 vol.% of an esterified beeswax (stearyl / behenyl beeswax) and at least one further organic additive.

[0010] As a further additive, 0.1 vol.% to 10 vol.% of amide waxes, 0.5 vol.% to 3 vol.% of low-density polyethylene waxes (LDPE waxes) or ethylene-vinyl acetate copolymer waxes (EVAC waxes) (particularly suitable are LDPE and EVAC waxes whose molecular weights are less than 13,000, preferably in the range 600 - 9000 and have a viscosity of 1000 mPas - 10,000 mPas at temperatures of approximately 140 °C, preferably 2000 - 8000 mPas), 3 vol.% to 8 vol.% of a paraffin wax, preferably with a melting temperature in the range of 45 °C - 65 °C, 0.5 vol.% to 3.5 vol.% of low-density polyethylene (LDPE polymer) with a melt flow index preferably of 15-24 g / 10 min at temperatures of approximately 190 °C / 2.16 kg, and a density of 0.91-0.96 g / ml. Amide waxes can be used, among other things, to prevent nozzle clogging during printing.

[0011] It is advantageous to contain a maximum of 1 vol.% ultra-high molecular-weight polyethylene (UHMWPE). The UHMWPE should preferably have a density in the range of 0.92 g / cm 3 up to 0.97 g / cm 3 have.

[0012] Amide waxes that may be present are octadecanamide, distearylethylenediamide, erucamide / cis-13-docosenamide, oleamide / cis-9,10-octadecenamide and / or docosanamide / behenamide.

[0013] It should be a microcrystalline wax or a mixture of microcrystalline waxes with a melting temperature in the range 75 °C to 85 °C, a kinematic (dynamic) viscosity at a temperature of 100 °C in the range 8 mm 2 / s up to 25 mm 2 / s, preferably 10 mm 2 / s up to 20 mm 2 / s measured according to ASTM D 445 and a molecular mass of at least 300, preferably at least 400 and particularly preferably at least 450, a needle penetration depth of 25-35 according to ASTM 1321 (Standard Test Method for Needle Penetration of Petroleum Waxes).

[0014] Stearyl beeswax and / or behenyl beeswax should also be included as esterified beeswax. A mixture with a ratio of 50% stearyl beeswax to 50% behenyl beeswax is preferred (acid value < 3 mg KOH / g, preferably 1.1 mg KOH / g, congealing point 64 °C - 69 °C, saponification value 78 mg KOH / g - 90 mg KOH / g, preferably 82.1 mg KOH).

[0015] For the respective solid metal and / or ceramic, particles with an average particle size d50 in the range of 100 nm to 50 pm should be present. The particles should preferably be semi-spherical or nearly spherical, and particularly preferably spherical. For metallic particles, a diameter d50 in the range of 2 pm - 20 pm is preferred, and particularly preferably a diameter d50 in the range of 4 pm - 14 pm. For ceramic particles, a diameter d50 in the range of 0.5 pm - 10 pm is preferred, and particularly preferably a diameter d50 in the range of 1 pm - 4 pm.

[0016] The components of the mass UHMWPE and microcrystalline wax represent the most important components of the organic matrix in which the particles are incorporated to achieve a flexible state, which enables, for example, the production of a flexible filament for an FFF filament printer.

[0017] UHMWPE is a linear semi-crystalline polyethylene and exhibits very high viscosity and tensile strength, making it difficult or even impossible to process on its own. However, once the UHMWPE melts at approximately 132°C, the microcrystalline wax and the UHMWPE suddenly begin to form a gel-like or rubber-like mass when stirred. The viscosity decreases with increasing temperature, allowing the UHMWPE to be processed. The microcrystalline wax acts similarly to a plasticizer. The long-chain UHMWPE molecules form a framework / backbone into which shorter-chain organic molecules, as well as solid particles, can be embedded.

[0018] The UHMWPE melt itself has poor flowability, even at temperatures significantly higher than its melting point. Even at 250°C and loads up to 21.6 kg, the melt flow rate of UHMWPE is almost zero. This behavior makes UHMWPE particularly suitable for forming a backbone in FFF printing of sinterable materials. The viscosity of UHMWPE, with a molecular weight of 3,000,000 g / mol, is about 2500 times higher than that of other polyethylenes such as HDPE or LDPE with a molecular weight of 300,000 g / mol. According to references, the melt viscosity of UHMWPE could be up to 10 8Pa-s. With a rise in temperature, a pure UHMWPE melt does not enter a viscous flow state, but rather maintains a transparent, rubbery state. In fact, the UHMWPE melt does not have a viscous flow state like HDPE or LDPE because its theoretical viscous flow temperature is higher than its decomposition temperature, as can be seen from the literature.

[0019] Substituting microcrystalline wax with paraffin wax or other waxes results in a material that is significantly less flexible and suitable for FFF printing. However, paraffin wax can potentially be used for other processes, such as injection molding or screen printing.

[0020] The ultra-long-chain UHMWPE contained in the system significantly reduces the vol. % content of organic polymer material, which is referred to as the backbone in such a system. Additional optional LDPE polymers and / or LDPE waxes advantageously help prevent agglomeration of the long UHMWPE chains by attaching themselves between the UHMWPE chains. However, they are not a relevant component in forming the so-called backbone, but they do support processability.

[0021] Generally, a polymer with a relatively high volume fraction of 15–25 vol% and a molecular weight of 250,000 g / mol is used in a feedstock to form a backbone, as the chains are generally significantly shorter than those of UHMWPE. These polymers, as a solvent-insoluble component of the binder, can only be removed thermally in the furnace.

[0022] Also advantageous is that the initial decomposition temperature of UHMWPE is 450°C, probably due to the strong intermolecular interactions and the extremely high molecular weight, which is relatively high compared to other polyethylenes, and can therefore fulfill a supporting function for longer.

[0023] The organic components and polymers that generally belong to the backbone (in our case this concerns: UHMWPE (1,000,000-3,000,000 g / mol), LDPE, LDPE wax and EVAC wax) should be contained in the material according to the invention in a low proportion of only < 4.9 vol% in total.

[0024] The extremely long-chain UHMWPE molecules perform an improved binder function compared to other polymers / polyolefins. Due to their much longer chain structure (UHMWPE molecular weight 1,000,000–3,000,000 g / mol), they can form stabilizing percolation networks early and more effectively. They are virtually non-flowable and possess exceptional sliding and mechanical properties, thus avoiding the disadvantages otherwise associated with conventional polymer blends with high polymer content (15–25 vol%).

[0025] The low backbone content of UHMWPE reduces, for example, the critical crack formation during thermal removal of the polymer in an oven and enables rapid solvent debinding of the short-chain wax components through larger diffusion paths, for example during ethyl acetate solvent debinding, in a pre-debinding step before the manufactured or printed green part is transferred to an oven for thermal debinding.

[0026] Its advantageous properties are evident even in very small amounts compared to the other organic components contained in the matrix. UHMWPE therefore forms an essential component of the so-called backbone. The backbone can also include the LDPE polymer and / or LDPE wax and / or EVAC wax. However, these are not particularly relevant and tend to interfere with solvent debinding. Rather, they serve to additionally stabilize the long UHMWPE chains and disperse the solid particles.

[0027] Polymeric LDPE can insert itself between chains of the UHMWPE and prevent its agglomeration, especially in the microcrystalline wax, and additionally helpfully block it, so that the UHMWPE is present in a more homogeneous distribution in the organic matrix and this can also be maintained permanently until the organic components are removed during the additive manufacturing of components in a furnace.

[0028] An ethylene-vinyl acetate copolymer wax (EVAC wax) can also be a component of the binder in the matrix. Unlike the other insoluble components of the binder, it is a copolymer of polar and non-polar components and is insoluble, or only very difficult to dissolve, in a solvent. These copolymers decompose only thermally. In conjunction with similarly polar particles, particularly ceramic particles, they have a beneficial effect on the achievable print quality. EVACs can be included in the composition at a maximum of 3 vol.% to improve the miscibility and printability of the particle-containing material heated for printing. The ethylene-vinyl acetate copolymer wax should have a kinematic (dynamic) viscosity at a temperature of 140°C in the range of 4000 mPas to 6000 mPas, measured using a viscometer according to EN ISO 3219, with a molecular weight preferably less than 10.000, particularly preferably in the range 3000 to 5000.

[0029] Amide waxes diffuse to the surface of the material, creating smooth surfaces. They reduce nozzle clogging during the printing process and improve the sliding properties of the pasty mass during printing, which can also have a beneficial effect on surface quality. Amide wax can also prevent sticking to a print bed. This is particularly important because microcrystalline wax or other waxes can be highly adhesive. Amide waxes also act as dispersing agents for the solid particles contained in the organic matrix, allowing the particles to be more homogeneously distributed.

[0030] It may also contain 0.1 vol.% - 10 vol.% amide wax or a mixture consisting of stearamide / octadecanamide, distearylethylenediamide / ethylene bis(stearamide) - EBS, erucamide / cis-13-docosenamide, oleamide / cis-9,10-octadecenamide and / or docosanamide / behenamide.

[0031] Esterified beeswax combinations of stearyl beeswax and behenyl beeswax have a positive effect on the mechanical properties of the material, preventing it from becoming brittle over time and allowing filaments to retain the advantageous properties of a flexible filament for a longer period after production. In particular, filaments manufactured with small amounts of stearyl beeswax and behenyl beeswax remain flexible longer and are easier and safer to use.

[0032] Paraffin wax can be included, but is not mandatory. It reduces costs as a filler material and is easily removed after printing. It can be helpful for accelerating solvent debinding and for mixing materials.

[0033] During preparation of the compound, the respective components should be mixed homogeneously at a temperature greater than the melting temperature of the UHMWPE. Temperatures > 135 °C, especially > 150 °C, should be maintained.

[0034] In principle, almost any metal or ceramic material can be used to produce filaments or pellets. The only limiting factor is whether the respective metal or ceramic material can be bonded together with sufficient strength to form a component through a sintering process or by bonding after removal of the organic components, usually through solvent debinding and thermal treatment / evaporation or decomposition.

[0035] In most cases, the particles are bonded together by sintering. The organic components primarily serve to shape the green body during printing, as the powdered materials used cannot easily be formed into a specific shape and held in this shape before the individual particles are finally bonded together.

[0036] Due to the small volume fraction of organic long-chain polymer components in relation to the solids content, which are only present after solvent debinding, the effort required to remove these components is lower and less critical.

[0037] In particular, any short-chain components remaining after solvent treatment (e.g., waxes) can quickly migrate to the surface by capillary action, where they evaporate without being blocked by a dense polymer network. This accelerates and simplifies the thermal debinding process.

[0038] The following are examples of possible compositions of starting materials according to the invention, which are suitable, for example, for FFF printing. Extrusion into FFF filaments for the fused filament fabrication (FFF) process takes place at approximately 30 °C to 45 °C. Cu powder 61.94 vol%

[0039] (particle size max. 63 pm]

[0040] Microcrystalline wax 25.79 vol.%

[0041] (Multiwax W-445 - Sonneborn LLC) (Ts 76 °C - 83 °C)

[0042] UHMWPE 0.8 Vol%

[0043] LDPE wax 1.03 Vol-%

[0044] LDPE polymer 2.9 Vol-%

[0045] Octadecanamide 1.52 vol.-%

[0046] (Ts 89 °C - 102 °C)

[0047] Stearyl and behenyl beeswax 1.83 vol.% (50:50)

[0048] Paraffin wax 4.19 vol.%

[0049] Example 2

[0050] Stainless steel powder 316L 60.99 vol.%

[0051] (particle size max. 63 pm]

[0052] Microcrystalline wax 23.96 vol.%

[0053] (Multiwax W-445 - Sonneborn LLC)

[0054] (Ts 76.7 °C - 82.2 °C)

[0055] UHMWPE 0.85 vol.% LDPE wax 0.96 vol.%

[0056] LDPE polymer 1.52 vol.%

[0057] Octadecanamide

[0058] (Ts 89 °C-102 ?C) 2.84 vol.-%

[0059] Ethylene bis(stearamide) - EBS) 1.76 vol.%

[0060] (Ts 140 °C)

[0061] Docosenoamide 1.47 vol%

[0062] (Ts 84 °C)

[0063] Stearyl and behenyl beeswax 1.72 vol.%

[0064] (50 : 50)

[0065] Paraffin wax 3.92 vol.%

[0066] Example 3

[0067] AbOs powder spherical 61.88 vol% (particle size max. 10 pm]

[0068] Microcrystalline wax 22.71 vol.%

[0069] (Multiwax W-445 - Sonneborn LLC)

[0070] (Ts 76 °C - 83 °C)

[0071] UHMWPE 0.71 vol%

[0072] LDPE wax 0.91 vol.%

[0073] LDPE polymer 2.7 vol.%

[0074] Octadecanamide

[0075] (Ts 89 °C-102 ?C) 2.7 vol.% Ethylene bis(stearamide) - EBS) 1.67 vol.%

[0076] (Ts 140 °C)

[0077] Docosenoamide 1.38 Vol-%

[0078] (Ts 84 °C)

[0079] Stearyl and behenyl beeswax 1.62 vol.%

[0080] (50 : 50)

[0081] Paraffin wax 3.72 vol.%

[0082] Example 4

[0083] 440C tool steel 61.01 vol.% (particle size max. 63 pm]

[0084] Microcrystalline wax 24.21 vol.%

[0085] (Multiwax W-445 - Sonneborn LLC)

[0086] (Ts 76 °C - 83 °C)

[0087] UHMWPE 1.06 vol%

[0088] LDPE wax 0.91 vol.%

[0089] LDPE polymer 1.17 vol.%

[0090] Octadecanamide

[0091] (Ts 89 °C-102 °C) 2.7 vol%

[0092] Ethylene bis(stearamide) - EBS) 1.77 vol.%

[0093] (Ts 140 °C)

[0094] Docosenoamide 1.38 vol.%

[0095] (Ts 84 °C) Stearyl and behenyl beeswax 1.84 vol.% (50 : 50)

[0096] Paraffin wax 3.91 Vol.-%

[0097] 17-4PH stainless steel 62.04 vol%

[0098] (Particle size max. 63 um]

[0099] Microcrystalline wax 25.91 vol.%

[0100] (Multiwax W-445 - Sonneborn LLC) (Ts 76 °C - 83 °C)

[0101] UHMWPE 0.94 vol%

[0102] LDPE wax 1.05 vol.%

[0103] LDPE polymer 2.04 vol.%

[0104] EVAC waxes 0.47 vol.%

[0105] Octadecanamide

[0106] (Ts 89 °C-102 ?C) 0.95 vol.-%

[0107] Stearyl and behenyl beeswax 1.72 vol.% (50:50)

[0108] Paraffin wax 4.89 vol.%

Claims

Patent claims 1. Material for the additive manufacturing of components using a printing process, wherein the material contains at least 55 vol.% particles of a metal, 40 vol.% of a ceramic or 40 vol.% metal and ceramic, 15 vol% to 30 vol% of a microcrystalline wax, at least 0.3 vol% to a maximum of 3 vol% ultra-high molecular-weight polyethylene, 1 vol.% to 2.5 vol.% of an esterified beeswax and at least one other organic additive.

2. Material according to claim 1, characterized in that 0.5 vol.% to 10 vol.% of an amide wax is contained in the material as an additive.

3. Material according to one of the preceding claims, characterized in that a mixture of stearyl beeswax and behenyl beeswax is contained as esterified beeswax.

4. Material according to one of the preceding claims, characterized in that backbone-forming polymers are contained in a proportion of < 4.9 vol.%.

5. Material according to one of the preceding claims, characterized in that a maximum of 1 vol.% of ultra-high molecular weight polyethylene is contained, preferably ultra-high molecular weight polyethylene with a density of 0.92 g / cm 3 up to 0.97 g / cm 3 is included.

6. Material according to one of the preceding claims, characterized in that 3 vol.% to 8 vol.% paraffin wax is contained as an additive.

7. Material according to one of the preceding claims, characterized in that as an additive 0.5 vol.% to 3 vol.% Low Density Polyethylenes are contained in the form of a wax, wherein the molecular mass is preferably less than 13,000. Material according to one of the preceding claims, characterized in that a microcrystalline wax or a mixture of microcrystalline waxes with a melting temperature in the range of 75 °C to 85 °C, a kinematic viscosity at a temperature of 100 °C in the range of 8 mm 2 / s up to 25 mm 2 / s, preferably 10 mm 2 / s up to 20 mm 2 / s measured according to ASTM D445, a molecular weight of at least 300, preferably at least 400 and particularly preferably at least 450 according to ASTM D6352 and a needle penetration depth of 25-35 according to ASTM D1321. Material according to one of the preceding claims, characterized in that 0.1 vol.% - 10 vol.% amide wax or a mixture consisting of stearamide / octadecanamide, distearylethylenediamide / ethylene bis(stearamide) - EBS, erucamide / cis-13-docosenamide, oleamide / cis-9,10-octadecenamide and / or docosanamide / behenamide is contained as an additive.Material according to one of the preceding claims, characterized in that an ethylene-vinyl acetate copolymer wax with a dynamic viscosity at a temperature of 140°C in the range of 4000 mPas to 6000 mPas, measured with a viscometer according to EN ISO 3219, is included as an additive, wherein the molecular mass is preferably less than 10,000. Material according to one of the preceding claims, characterized in that particles with an average particle size d50 in the range of 0.5 pm - 30 pm are included, which are preferably semispherical and particularly preferably spherical particles.

13. Material according to one of the preceding claims, characterized in that the material is in the form of a filament, rod or pellets.