Combination of a Material and a Bath Fluid for Use in Rapid Prototyping Methods

(19) United States US 20050215744A1 (12) Patent Application Publication (10) Pub. No.: US 2005/0215744 A1 Wiese et al. (43) Pub. Date: Sep. 29, 2005 (54) COMBINATION OF A MATERIAL AND A BATH FLUID FOR USE IN RAPID PROTOTYPING METHODS (75) Inventors: Hinrich Wiese, Kaufbeuren (DE); Gerhard Maier, Munchen (DE) Correspondence Address: EDWARDS & ANGELL, LLP P.O. BOX 55874 BOSTON, MA 02205 (US) (73) Assignee: PolyMaterials AG, Kauibeuren (DE) (21) Appl. No.: 10/519,894 (22) PCT Filed: Jun. 27, 2003 (86) PCT No.: PCT/EP03/06858 (30) Foreign Application Priority Data Jun. 28, 2002 (DE) ................................... .. 102 29 124.1 Publication Classification (51) Int. Cl.7 ................................................. .. C08F 118/02 (52) U.s. Cl. ............................................................ .. 526/319 (57) ABSTRACT The present invention relates to combinations of a building material and a bath fluid for methods for directly printing visual-aid models or elements, in particular, for the use in the office or at home. Furthermore, the present invention relates to the polymers obtained by the reaction of the building material and the bath fluid and to elements or models produced from the combinations according to the present invention. The use of the combinations according to the present invention in rapid prototyping methods enables the production of elements having varying mechanical proper- ties. Coloured elements can be obtained by adding colou- rants. The elements made from the building materials according to the present invention exhibit mechanical prop- erties, a thermostability and accuracy in every detail, thus rendering them suitable as visual-aid models and discussion models for design, architectural, constructional and other blueprints. The surface quality, the rigidity and the hardness of the elements can be improved by post-treatment. US 2005/0215744 A1 COMBINATION OF A MATERIAL AND A BATH FLUID FOR USE IN RAPID PROTOTYPING METHODS [0001] The present invention relates to combinations of a building material and a bath fluid for methods for directly printing visual-aid models or elements, in particular, for the use in the office or at home. The invention further relates to polymers obtained from the reaction of the building material and the bath fluid and to the elements and models produced from the combinations according to the present invention. The use of the combinations according to the present inven- tion in rapid prototyping methods enables the production of elements having varying mechanical properties. Coloured elements can be obtained by adding colourants. The ele- ments made of the building materials according to the present invention exhibit mechanical properties, a thermo- stability and accuracy in every detail, thereby rendering them suitable as visual-aid models and discussion models for design, architectural, constructional and other blueprints. The surface quality, the rigidity and the hardness of the elements can be improved by post-treatment. [0002] Various methods for producing three-dimensional objects having an arbitrary shape on the basis of data files (e.g., CAD) such as as a discussion model, a visual-aid model, a design model or a functional model are known under the term “rapid prototyping”. The three-dimensional objects are formed layer by layer in most of these methods. [0003] The following methods are of particular impor- tance: [0004] Stereolithography (SLA) (photopolymers are cured by irradiation with a suitable laser): Elements are obtained with a high resolution and mechanical properties, which are comparable to those of tech- nical plastics. However, the costs of the method (laser) and the sources of danger (toxic educts and use of the laser) are detrimental. [0005] Selective Laser Sintering (SLS) (metals, plas- tics or ceramics; in the case of ceramics, a powder is fused layer by layer by means of a laser): Using particularly suitable materials, the elements achieve approximately the same stability as elements of the same material obtained by injection molding. How- ever, the handling of the powder (typical particle sizes from 20 to 50 gm) requires considerable efforts in order to avoid contamination of the environment with the powder. [0006] 3-D-Printing (3DP) (a powder is formed into three-dimensional objects using liquid binders). The method is rapid, however, it leads to elements having a moderate resolution and frequently unsatisfying mechanical properties. However, these properties can optionally be improved by a post-treatment step. [0007] Fused Deposition Molding (FDM) (melts of waxes or low melting thermoplasts are deposited in strands or droplets to yield the desired molded articles and, subsequently, they solidify). For example, thermoplasts (such as polyamide or acry- lonitrile-butadiene-styrene-copolymers) can be employed. However, the resolution and the accuracy in every detail, respectively, are inferior. Sep. 29, 2005 [0008] A novel method requiring a relatively simple setup and thus being also suitable for use in the office or at home that does not require specific training of the users is described in WO 01/26885, claiming priority of DE 19948591 A1. It is based on the use of a liquid building material having a low viscosity that is deposited in a computer-controlled way onto specific positions on a build- ing support by means of a drop-on-demand technique (com- parable to an ink jet), and that thereby solidifies in a physical or chemical process. By depositing the building material layer by layer, a three-dimensional object having arbitrary shape is formed step by step. In this method, the building support is positioned in a bath. The bath fluid serves to fill the areas that are not filled by the building material and to act as a supporting material in the formation of overhanging structures. [0009] Suitable materials are not described in WO 01/26885 in more detail. It is merely mentioned that ther- moplastic or waxy materials having a viscosity of not more than 20 mPa~s at a temperature of not more than 130° C. can be employed, which cool down during deposition and, thus, solidify. Furthermore, it is mentioned that the solidification can also be caused by a chemical reaction by contacting an ingredient of the bath fluid or by thermically initiated crosslinking. [0010] Building materials such as the waxes mentioned in WO 01/26885 that solidify solely by cooling down from the processing temperature (according to the method described in WO 01/26885 130° C. at the most) to room temperature and, nevertheless, have the very low viscosity required for processing, exhibit an insufficient thermostability. Their softening already occurs at temperatures slightly above room temperature. As a result, they cannot serve as models to be touched. Furthermore, functional models cannot be produced using these materials because their mechanical properties are insufficient. [0011] The description in WO 01/26885 does not disclose the composition of suitable building materials fulfilling the requirement of having a low viscosity at the processing temperature, which can be solidified by a chemical reaction or by thermal crosslinking and, subsequently, have a suffi- cient thermostability and good mechanical properties. [0012] The successful application of the method described in WO 01/26885 poses very high demands on building material, bath and the combination thereof. Running systems of this kind are not known. The demands on such systems are as follows: The solidification has to proceed in a suffi- ciently rapid way in order to achieve a sufficient resolution of the structures produced, because flowing of the building material reduces the resolution due to a too slow curing. However, the curing has to proceed at the same time slowly enough in order to ensure an adhesion or a sticking of the droplets among each other and between subsequent layers. Moreover, it has to be ensured that the building material does not solidify until it contacts the bath fluid and not already in the outlet ports of the deposition device or in storage containers. For the application in the office or at home, when operated by untrained persons it is further required that the components, in particular the bath fluid are not toxic and the disposal of the bath fluid by way of the regular canalisation is possible without further action. Thus, for example the use of most of the known, technically US 2005/0215744 A1 employed monomers and initiators for the formation of polymers or for crosslinking, are practically excluded as ingredients of the bath fluid. The demands on the mechanical rigidity of the three-dimensional elements produced also excludes materials that result in powdery crystalline prod- ucts after solidification (e.g., solutions of low molecular or polymeric substances, which precipitate on contact with the bath fluid). In most cases waxy materials exhibit a too low thermostability. It is possible to produce three-dimensional molded elements according to the method described in WO 01/26885 using particular waxes. However, these elements already soften due to the body temperature upon contact with the hand. [0013] Therefore, there is the problem in applying the method described in WO 01/26885 for the production of three-dimensional elements, that there are presently no known suitable building materials and bath fluids, which result in elements having a sufficiently high thermostability and mechanical stability. [0014] Also WO 01/78968 discloses the formation of solid or semi-solid objects by applying droplets or strands layer by layer onto a support positioned in a bath fluid. However, the method described therein requires that the outlet port of the dosing device is under the surface of the bath fluid. The materials described therein (oligomers or polymers, which are liquid at room temperature, melts of oligomers or polymers, reactive oligomers or polymers, gels, pastes among others) exhibit either too high a viscosity for dosing, e.g., using an ordinary ink jet print head, or similar limita- tions as those for WO 01/26885 apply. That is, also WO 01/78968 does not give any hints how to prevent that a reactive material immediately hardens when being dosed into the bath fluid and, thus, plugs the dosing device. Particularly, in those cases, wherein a building material essentially consisting of a liquid-monomer is used in com- bination with an aqueous bath fluid, there is the problem that it cannot be avoided that a liquid monomer arbitrarily flows within the bath after dosing, when the method described in WO 01/78968 is applied using a dosage device having a port under the bath surface. Moreover, only very few monomers can be processed using water as a bath liquid, because their density has to be higher than 1 g/cm3 in order to avoid floating of the liquid monomer. These problems can only be solved, if the liquid monomer polymerises very rapidly, resulting in the problem that it already polymerises in the outlet port of the dosing device as well, thereby plugging it. In this context, the use of retarding substances (claims 21 to 23 of WO 01/78968) described in WO 01/78968 is counter- productive. Therefore, the materials described in WO 01/78968 cannot be used in the method described in WO 01/26885. [0015] Therefore, it is the object underlying the present invention to provide suitable low-viscosity building mate- rials and bath compositions for the production of three- dimensional models or elements by means of a method, preferably by means of the method described in WO 01/26885, wherein the building material is deposited in a computer-controlled way onto specific positions of a support layer by layer in form of single droplets, where it is chemically solidified in these positions in the presence of a bath fluid, the outlet port of the dosing device being located above the surface of the bath fluid in order to avoid plugging of the outlet port. Sep. 29, 2005 [0016] The building materials and the bath compositions shall be cost-efficient and shall not contain any toxic com- pounds. Moreover, their handling shall be easy in order to enable their use in the office or at home by a user without a specific training. [0017] The cured building material, i.e., the three-dimen- sional models obtained, shall have a good thermostability and further favourable mechanical and other physical prop- erties so that models which can be touched and functional models can be obtained. Finally, the three-dimensional mod- els obtained shall exhibit a good accuracy in every detail. In certain embodiments the elements shall also be suitable as scaffolds in tissue engineering. [0018] In principle, this object can be solved by using a combination of a building material and a bath fluid, the building material (“ink”) containing low-viscosity, low- molecular compounds capable of rapidly forming polymers having sufficient mechanical properties, when contacted with the bath fluid. This can be carried out either by polymerizing one or more monomers contained in the build- ing material upon contact with the bath fluid or by forming a branched or crosslinked polymer by reacting one or more low-viscosity multifunctional compounds contained in the building material with oligomeric or polymeric compounds contained in the bath fluid. [0019] Thereby, the deposition of the building material (“ink”) is carried out by means of a suitable dosing device, such as an ink jet print head, droplet by droplet into the bath fluid, that is, in layers corresponding to subsequent cross sections of the desired element. Thereby, the first layer is deposited onto a building platform or another suitable sup- port. Then each of the following layers can be applied onto the preceding layer or onto the bath surface depending on the shape of the desired element. Athree-dimensional element is obtained by the sequence of an adequate number of layers. [0020] The droplets are produced by a dosing system capable of producing single droplets or flows of droplets having a diameter in the range of 20 to 200 gm, preferably 50 to 90 gm and depositing these droplets at a predetermined position, for example, according to the principle of an ink jet print head. The building material must preferably have a viscosity of less than 200 mPa~s, particularly preferred less than 30 mPa~s in the processing state and further a suitable surface tension compared to the bath fluid for an accurate dosing. Furthermore, the building material must polymerise rapidly after deposition. Thereby, a good connection of the droplets among each other and to the building material of the preceding layer has to be achieved. At the same time it has to be ensured that the building material does not prematurely solidify in the storage container, in the dosing device, in the respective connections, in the die nor in another outlet port. [0021] In the case of monomer-based building materials, this can be achieved for example by incorporating into the bath fluid an initiator or a catalyst initiating the polymeri- sation of the monomers or the monomer mixture in the droplet of the building material. Alternatively, the building material itself can contain an initiator or a catalyst and, additionally, an inhibitor or a stabilizer, the inhibitor or the stabilizer being selected such that it can be deactivated by a compound contained in the bath. Furthermore, the initiator or catalyst system can also consist of several components, one or more of which are contained in the bath and the others US 2005/0215744 A1 are contained in the building material. In this case, the polymerisation is initiated upon contact between the build- ing material and the bath at the time when all components get into contact. Moreover, for building materials on the basis of crosslinking agents a defined start of the reaction can be ensured by selecting the multifunctional compounds in the building material such that these compounds are able to react only with multifunctional oligomers or polymers contained in the bath, and not with each other. [0022] The terms “initiator”, “catalyst”, “stabilizer” and “inhibitor” are used herein according to the definitions used in the literature in the field of polymer chemistry. [0023] According to the present invention a combination of at least one building material and a bath fluid for a method for directly printing elements and models is provided, char- acterized in that [0024] A) the building material contains at least one low-viscosity monomeric or oligomeric compound having a viscosity