MATERIALS FOR 3D MULTI-STAGE METHOD

Abstract

The present invention relates to materials for a multi-stage method for producing one or multiple molded bodies. The materials may be used in a method including constructing one or multiple molded bodies in layers by repeatedly applying particulate material by the 3D printing method; pre-solidifying the molded body; unpacking the pre-solidified molded body and removing unsolidified particulate material, and final solidification of the molded body for achieving a final strength due to the action of thermal energy. The invention also relates to a device which may be used for this method.

Claims

1. A material system for producing one or more molded bodies, comprising: i) a particulate material having a casing or a coating including a soluble polymer: ii) a printable liquid capable of being selectively printed with an ink jet print head and including a solvent capable of liquefying the soluble polymer for forming bridges between adjacent particles; wherein the particulate material and/or the printable liquid includes a reactive component that reacts at an elevated temperature for achieving a final strength of the molded body.

2. The material system of claim 1, wherein the casing or coating comprises or includes thermoplastic polymers, soluble polymers, waxes, synthetic and natural resins, sugars, salts, inorganic network formers or water glasses.

3. The material system of claim 1, wherein the reactive component chemically reacts at temperature of 110 C. to 200 C. to achieve a final strength of the molded body.

4. The material system of claim 1, wherein the solvent includes water, a hydrocarbon, an alcohol, an ester, an ether, a ketone, an aldehyde, an acetate, a succinate, a monomer, a formaldehyde, a phenol, or any combination thereof.

5. The material system of claim 1, wherein the casing or coating includes a binder.

6. The material system of claim 5, wherein the binder includes some or all the reactive component including a polymerizable monomer.

7. The material system of claim 6, wherein the coating or casing includes an activator for starting a polymerization reaction.

8. The material system of claim 1, wherein the particulate material includes a core component containing natural silica sand, kephalite, cera beads, zircon sand, chromite sand, olivine sand, chamotte, corundum, or glass spheres.

9. The material system of claim 8, wherein the core component has a grain size of about 140 m.

10. The material system of claim 1, wherein the material system includes an inert material for supporting the molded bodies during a reaction at an elevated temperature occurring after formation of bridges between adjacent particles.

11. The material system of claim 1, wherein the solvent reacts and solidifies with the polymer of the casing or coating.

12. The material system of claim 6, wherein the particulate material includes a base containing natural silica sand, kephalite, cera beads, zircon sand, chromite sand, olivine sand, chamotte, corundum, or glass spheres; the solvent includes water, a hydrocarbon, an alcohol, an ester, an ether, a ketone, an aldehyde, an acetate, a succinate, a monomer, a formaldehyde, a phenol, or any combination thereof; and the casing or coating comprises or includes thermoplastic polymers, soluble polymers, waxes, synthetic and natural resins, sugars, salts, inorganic network formers or water glasses.

13. The material system of claim 12, wherein the binder includes a phenol resin, a furan, urea or amino resin, a novolak or resol, a urea formaldehyde resin, a furfuryl alcohol urea formaldehyde resin, a phenol modified furan resin, a phenol formaldehyde resin, a furfuryl alcohol phenol formaldehyde resin, or an epoxy.

14. The material system of claim 12, wherein a viscosity of the polymer of the casing or coating in the melt state is about is about 10 to about 1,000 Pas, and the viscosity of the polymer in the solvent is 0.002 to 0.1 Pas.

15. The material system of claim 1, wherein the particulate material has a core of silica sand having a grain size of about 140 m; the casing or coating includes a resol resin; and the solvent includes isopropyle alcohol, ethanol, or a mixture of ethanol and isopropyl alcohol.

16. The material system of claim 15, wherein the printable liquid includes a dioxolane additive.

17. The material system of claim 1, wherein all of the components of the material system are in the particulate material or the printable liquid.

18. The material system of claim 1, wherein the concentration of the printable liquid is about 10 weight percent, based on the total weight of the particulate material and the printable liquid in the regions printed by the liquid.

19. The material system of claim 1, wherein the printable liquid includes a dye for identifying the locations that have been printed.

20. The material system of claim 1, wherein the polymer of the casing or coating includes a polyamide, a polyethylene, an amorphous poly alpha-olefin, an ethylene vinyl acetate copolymer, a polyester elastomer, a polyurethane elastomer, a copolyamide elastomer, or a vinyl pyrrolidone/vinyl acetate copolymer.

21. The material system of claim 1, wherein the casing or coating includes Corrodur, dioxolane, or both.

22. The material system of claim 1, wherein the coating or casing contains materials for starting a polymerization with the binder

23. The material system of claim 1, wherein the coating or casing contains a color indicator which is activated by a binder.

24. The material system of claim 1, wherein the material system includes a nucleating agent.

Description

DESCRIPTION OF THE FIGURES

[0052] FIG. 1 shows particulate material (100), a sand grain (101) being encased with binder (102).

[0053] FIG. 2 shows the process of evaporating particulate material (200), to which solvent was added, whereby the particles (200, comprising 201 and 202) are bound and the material is presolidified. The evaporation of the solvent may also be accelerated by the application of heat (203).

[0054] FIG. 3 shows the structure of a presolidified molded body (300).

[0055] FIG. 4 shows the operation after printing; in this case the solvent begins to penetrate binder coating (402) of particle core (401).

[0056] FIGS. 5a through 5d show the evaporation process of the solvent, the mixture concentrating in the contact point (503) between the particles (500) (FIG. 5d).

[0057] As described above, the molded body is formed by binding individual particles (FIG. 3).

[0058] The particulate material-based process is based on a particulate material (100) which is encased by a binder (102) (FIG. 1). Casing (102) characteristically has different properties than base material (101). The sand known from the Croning process may be mentioned as an example. In this case, a grain of sand (101) is coated with a novolak resin (102). This resin is melted on and mixed with the sand during the manufacturing process. The sand continues to be mixed until the resin has cooled. The individual grains are separated thereby and a pourable material (100) results.

[0059] Base materials having an average grain diameter between 10 and 2,000 m may be considered as suitable sands for processing in the method according to the invention. Different base materials, such as natural silica sand, kerphalite, cera beads, zircon sand, chromite sand, olivine sand, chamotte, corundum and glass spheres are suitable for subsequent use in casting processes.

[0060] Binders may be applied in a wide range of materials. Important representatives are phenol resins (resol resins and novolaks), acrylic resins and polyurethanes. All thermoplastics may furthermore be thermally applied to the grains. Examples of materials that may be used according to the invention are polyethylene, polypropylene, polyoxymethylene, polyamides, acrylonitrile, acrylonitrile styrene butadiene, polystyrene, polymethyl methacrylate, polyethyl methacrylate and polycarbonate.

[0061] Additionally or entirely without the supply of heat, solvents may be used to coat grains coated according to the invention with a bindable material. Other casings may also be implemented by means of solvents. For example, water glass may be dissolved in water and mixed with sand. The material is subsequently dried and broken. Excessively coarse particles are removed by sieving. Since the dissolution process is reversible, the material thus obtained may be used in the process according to the invention by printing it with water as the printing fluid.

[0062] In one preferred embodiment of the invention materials may be provided in casing (102) which demonstrate a reaction with the fluid binder during the dissolution process. For example, starters may be provided for a polymerization. In this manner, the evaporation process of the solvent in the particulate material may be accelerated, since less printing solution needs to escape from the particulate material cake by evaporation. As a result, the molded parts may reach their green strength faster and thus be unpacked from the particulate material earlier.

[0063] Since the printed parts do not differ much from the surrounding loose particulate material in a solvent process, it may be sensible to dye the molded parts by introducing a pigment into the print medium. In this case, it is possible to use a color reaction based on the combination of two materials. For example, litmus may be used in the solvent. The base material is mixed with the salt of an acid prior to coating with the binder. As a result, not only is a dyeing possible but also a control of the intensity of the dissolution reaction. If the reactive substance, for example, is in direct contact with the grain of the base material, and if it is protected by the casing, the color indicator shows that the casing was completely dissolved.

[0064] The process of evaporating the solvent may also be accelerated by supplying heat (FIG. 2). This may take place by means of convection or heat radiators. The combination of an air draft and heating is particularly effective. It should be noted that if the drying process is too fast, the binder may only be partially dissolved. Optimum values with regard to strength development and unpacking time may be ascertained through tests and variations of the solvent.

[0065] A printing fluid is applied to the coated grain in the printing process. In its main function, the printing fluid dissolves the binder casing. In the case of Croning sand, approximately 10 wt % of printing fluid is printed for this purpose. Isopropyl alcohol, for example, is suitable as the solvent. After printing, the solvent begins to penetrate the binder casing (FIG. 4). The concentration of the casing material in the solvent increases. When solvent evaporates, the mixture concentrates in the contact point between the particles (FIG. 5). Additional evaporation causes the casing material in the contact point to solidify. Due to the comparatively low viscosities, a favorable process window results, in contrast to melting processes. With the aid of commercial Croning sand of the HttenesAlbertus RFS 5000 type, for example, an unpacking flexural strength of more than 100 N/cm.sup.2, preferably more than 120 N/cm.sup.2, is reached. This is sufficient to unpack even large-format, delicate parts safely and distortion-free.

[0066] After the removal method stepalso referred to as unpackingthe molded parts are supplied to the final solidification step. The molded parts are subsequently supplied to additional follow-up processes. This method step of the invention is preferably carried out in the form of a heat treatment step. Parts made of Croning sand, which are manufactured according to the process according to the invention, may be used as an example. After unpacking, these parts are preferably re-embedded in another particulate material. However, this material does not have a binder casing and preferably has good thermal conductivity. The parts are subsequently heat-treated above the melting temperature of the binder in an oven. In one of the preferred embodiments, the special phenol resin of the casing is cross-linked, and the strength increases significantly. Melting adhesives are generally preferred for this method step of final solidification. The following may preferably be used as base polymers: PA (polyamides), PE (polyethylenes), APAO (amorphous poly alpha olefines), EVAC (ethylene vinyl acetate copolymers), TPE-E (polyester elastomers), TPE-U (polyurethane elastomers), TPE-A (copolyamide elastomers) and vinylpyrrolidone/vinyl acetate copolymers. Other common additives known to those skilled in the art, such as nucleating agents, may be added.

[0067] Using the method according to the invention, molded parts having flexural strengths of more than 1,000 N/cm.sup.2 are produced with the aid of commercial sands

EXAMPLE 1

[0068] A Croning sand of the Httenes-Albertus RFS 5000 type is used in a layering process. For this purpose, the sand is deposited onto a build plane in a 0.2-mm layer. With the aid of a drop-on-demand print head, the sand is subsequently printed with a solution of isopropyl alcohol according to the cross-sectional surface of the desired object in such a way that approximately 10 wt % is introduced into the printed areas. The build plane is then shifted relative to the layering mechanism by the thickness of the layer, and the operation comprising the layer application and printing starts again. This cycle is repeated until the desired component is printed. The entire operation is carried out under normal conditions. The temperature in the process room should be between 18 C. and 28 C., preferably between 20 C. and 24 C.

[0069] Approximately 24 hours must pass before the final layers of sand have developed an adequate strength. The component may then be unpacked, i.e., removed from the surrounding sand and freed of all powder deposits. When printed test bodies are dried in the circulating air oven for 30 minutes at a temperature of 40 C., they demonstrate a flexural strength of 120 N/cm.sup.2.

[0070] The parts are then prepared for the subsequent heat treatment step. For this purpose, they are introduced, for example, into uncoated sand, which is situated in a temperature-resistant container. To ensure a good contact between the part and the supporting sand, vibrations are applied to the container during placement and filling with sand.

[0071] Any deformation may be avoided in the manner during the hardening reaction, i.e., the final solidification step, at high temperatures. The component is thus heated in the oven for 10 hours at a temperature of 150 C. After removal from the oven, approximately 30 minutes must again pass until the component has cooled enough to allow it to be handled and removed from the powder bed. Following this process step, the deposits may be removed by sand blasting. Treated bending test bodies demonstrate a flexural strength of 800 to 1,000 N/cm.sup.2 following this final solidification step.

EXAMPLE 2

[0072] A layering process is carried out in a manner similar to the first example. A Croning sand of the Httenes-Albertus CLS-55 type is used in this case. For this purpose, the sand is again deposited onto a build plane in a 0.2-mm layer. A solution of 15% Corrodur from Httenes-Albertus, 42.5% ethanol and 42.5% isopropyl alcohol is used as the printing fluid.

[0073] Approximately 10 wt % of fluid is printed onto the sand.

[0074] The flexural strength after unpacking the molded body and completing this first method step, which is also referred to as the presolidification step, is 140 N/cm.sup.2 in this case. The final flexural strength after the second method step, which is also referred to as the final solidification step, is again 800 N/cm.sup.2.

EXAMPLE 3

[0075] The process for this preferred manufacturing method is carried out in a manner similar to the previous examples. In this case, strengths of 800 N/cm.sup.2 are achieved using untreated sand as the base. A mixture of 50% Corrodur and 50% dioxolane is used as the binder fluid. 10 wt % are printed. The process takes place at room temperature. The component does not have to be unpacked from the particulate material after printing, since the unencased material cannot be bound by means of thermal energy. Either the entire box or, for example, one printed box may be introduced into the oven to carry out the final solidification step. A sand volume of 8820 cm, which contains a bending test body, is heat-treated in the oven for 24 hours at a temperature of 150. The strength upon conclusion of the final solidification step is approximately 800 N/cm.sup.2. A determination of the organic proportion by means of ignition loss determination demonstrates 5 wt %. The material in this case corresponds to the RFS-5000 and CLS-55 products from Httenes-Albertus. After the oven process, the parts may be cleaned by sand blasting.