| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | April 2, 2002 |
| PATENT TITLE |
Polymer gel molds |
| PATENT ABSTRACT | A polymer gel is formed into a mold defining a preselected shape. A flowable composition may be formed into a preselected shape via contact with the polymer gel mold |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | December 15, 1998 |
| PATENT GOVERNMENT INTERESTS | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A method of forming a flowable composition into a preselected shape comprising the steps of: a. forming an irreversible polymer gel into a mold which defines a preselected shape, said polymer gel comprising at least one of the group consisting of a gel produced by vinyl polymerization of at least one monomer, a gel produced by condensation polymerization of at least one monomer, a gel produced from a solution of at least one naturally occurring polymer, and a gel produced from a solution of at least one synthetic polymer; b. contacting a flowable composition with said mold to form said flowable composition into said preselected shape; and, c. solidifying said flowable composition to produce a formed article. 2. A method in accordance with claim 1 wherein said polymer gel produced by vinyl polymerization of monomers comprises at least one of the group consisting of a gel made by polymerizing at least one monofunctional vinyl monomer and at least one multifunctional vinyl monomer, a gel made by polymerizing at least one multifunctional vinyl monomer, a gel made by polymerizing hydroxymethylacrylamide in H.sub.2 O, and a gel made by polymerizing hydroxymethylacrylamide and a water-soluble comonomer in H.sub.2 O. 3. A method in accordance with claim 1 wherein said polymer gel produced by condensation polymerization of a monomer comprises at least one polymer system selected from the group consisting of epoxies, urethanes, phenolics, furans, and melamines. 4. A method in accordance with claim 1 wherein said polymer gel produced from a solution of a natural polymer comprises at least one polysaccharide. 5. A method in accordance with claim 1 wherein said polymer gel produced from a solution of a natural polymer comprises at least one protein. 6. A method in accordance with claim 5 said protein comprises albumin. 7. A method in accordance with claim 1 wherein said polymer gel produced from a solution of a synthetic polymer comprises at least one polymer selected from the group consisting of cellulose, a cellulose derivative, poly (vinyl alcohol), poly (acrylic acid), and poly (acrylamide). 8. A method in accordance with claim 1 wherein said polymer gel body further comprises a reinforcement material. 9. A method in accordance with claim 8 wherein said reinforcement material further comprises at least one of the group consisting of particles, plates and fibers. 10. A method in accordance with claim 1 wherein said flowable composition further comprises a particulate phase, a solvent, a monomer system soluble in said solvent, and an initiator system for polymerizing said monomer system, said solvent, said monomer system, and said initiator system comprising a binder phase. 11. The method of claim 10 further comprising the additional steps of: d. volatilizing said binder phase; and, e. sintering said particulate phase to form a dense sintered article. 12. The method of claim 10, wherein said particulate phase is selected from the group comprising metals, ceramics, carbon, and mixtures thereof. 13. A method in accordance with claim 1 wherein said flowable composition further comprises at least one of the group consisting of a chemically bonded ceramic composition, a silicone rubber based composition, and a fluid polymer based composition. 14. A method in accordance with claim 13, wherein said chemically bonded ceramic composition further comprises at least one of the group consisting of a plaster composition, a cementitious composition, a phosphoric acid bonded alumina composition, and a calcium aluminiate-based composition. 15. A method in accordance with claim 14 wherein said plaster composition further comprises plaster of paris. 16. A method in accordance with claim 14 wherein said cementitious composition further comprises a portland cement-based composition. 17. A method in accordance with claim 13 wherein said a fluid polymer based composition further comprises at least one of the group consisting of a urethane, an epoxy, and an unsaturated polyester. 18. The method of claim 1 wherein at least a portion of said polymer gel forms a core defining an internal surface of said preselected shape. 19. The method of claim 18 wherein said core is removed via volatilization from said solidified article. 20. A method of forming a flowable composition into a preselected shape comprising the steps of: a. forming a polymer gel into a mold which defines a preselected shape; b. isotropically reducing said gel mold in size by a preselected percentage by at least partially driving said gel mold; c. contacting a flowable composition with said mold to form said flowable composition into said preselected shape; and, d. solidifying said flowable composition to produce a formed article. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION The present invention relates to forms, patterns molds, and the like for forming flowable compositions, and more particularly to the same which comprise polymer gels. BACKGROUND OF THE INVENTION The process of forming flowable compositions into preselected shapes involves the use of patterns (usually positive shape), molds (usually negative shape), cores (including fugitive cores), plates, forms, templates, dies, components of the foregoing, and the like. The term "mold" is defined and used hereinafter as an inclusive term and, unless otherwise specified, means any or all of the foregoing and any equivalents thereof. Flowable compositions are brought into contact with a mold, take on the shape thereof, and subsequently solidified. Mold materials are generally nonporous and rigid, and are often machined into a preselected mold shape. There is a significant cost involved in preparing machined molds which could be avoided if suitable castable materials were available. Also, rigid molds are prone to problems (due to, for example, friction stress) associated with removal of formed product from the mold. Of particular interest are molds for forming gelcasting compositions, especially for prototyping and small lot production runs. A simple and inexpensive molding system is needed for such forming tasks. Research has shown that many castable mold materials are unsuitable for gelcasting. For example, silicone, urethane, and various waxes have disadvantageous surface reactions with gelcasting compositions which distort the formed product. Conventional plaster of paris molds are porous and draw water and other liquid solvents and/or vehicles out of the gelcasting slurry. In order to provide comparison data, silicone elastomer and mold wax were evaluated as molds for gelcast aluminum oxide. The effect of mold release agents generally considered to be superior with respect to gelcasting aluminum oxide was shown to be of little use with silicones such as RTV (Trade name of silicones manufactured by GE Silicones, General Electric Company, Waterford, N.Y. 12188) and wax mold material such as BW2260 (available from Blended Waxes, Inc.) As shown in Table I, no material in this series of trials yielded an acceptable level of surface feature retention. As cast samples were characterized by ungelled (unpolymerized) surface layers or poor feature retention. Dried samples were characterized by surface flaking or poor surface features. TABLE I Mold Result Result Material Condition Mold Release (as cast) (dried) RTV-11 As cast -- Ungelled Flaking Silicone layer* RTV-11 60.degree. C. -- Thin ungelled Thin Silicone overnight layer# flaking RTV-11 Vacuum -- Thin ungelled Thin Silicone overnight layer# flaking RTV-11 As cast AZN Mold Wiz Thin ungelled Thin Silicone layer# flaking RTV-11 As cast Polyester Parfilm Thin ungelled Thin Silicone layer# flaking RTV-11 As cast AXEL FFIH-15R Ungelled Flaking Silicone layer* RTV-60 As cast -- Ungelled Flaking Silicone layer* RTV-60 60.degree. C. -- Thin ungelled Thin Silicone overnight layer# flaking RTV-60 Vacuum -- Thin ungelled Thin Silicone overnight layer# flaking RTV-60 As cast AZN Mold Wiz Thin ungelled Thin Silicone layer# flaking RTV-60 As cast Polyester Parfilm Thin ungelled Thin Silicone layer# flaking RTV-60 As cast AXEL FFIH-15R Ungelled Flaking Silicone layer* BW2260 As cast -- Poor feature Poor Wax Retention surface BW2260 As cast Polyester Parfilm Poor feature Poor Wax Retention surface *Ungelled layer was approximately 1/8" to 1/6" thick. #Thin ungelled layer was approximately 1/16" to 1/32" thick. *#Ungelled layers were not uniform in thickness over the surface of the cast part. OBJECTS OF THE INVENTION Accordingly, objects of the present invention include the provision of non-rigid molds which are inexpensively and easily fabricated, are not prone to problems due to friction stress associated with removal of formed product from the mold, and do not have surface reactions with gelcasting compositions which distort the formed product. Further and other objects of the present invention will become apparent from the description contained herein. SUMMARY OF THE INVENTION In accordance with one aspect of the present invention, the foregoing and other objects are achieved by a mold which includes a polymer gel body which defines a preselected shape so that a flowable composition may be formed into the preselected shape via contact with the mold. In accordance with another aspect of the present invention, a method of forming a flowable composition into a preselected shape which includes the steps of Step 1. forming a polymer gel into a mold which defines a preselected shape; Step 2. contacting a flowable composition with the mold to form the flowable composition into the preselected shape; and, Step 3. solidifying the flowable composition to produce a formed article. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional side view illustrating a layered gelcasting process in accordance with the present invention. FIG. 2 is a view through section A A' of FIG. 1. For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is prepared to the following disclosure and appended claims in connection with the above-described drawings. DETAILED DESCRIPTION OF THE INVENTION By casting or otherwise forming and hardening a monomer solution in contact with an article of a preselected shape or a positive pattern of the article having the preselected shape, the gelled monomer solution forms a negative gel mold of the preselected shape. The mold is then useful for casting a flowable composition, generally via conventional methods. Technology of particular interest involves gelcasting compositions, both for mold materials and for flowable composition materials, some of which are disclosed in the following patents: 1. U.S. Pat. No. 4,894,194 issued on Jan. 16, 1990 to M. A. Janney, the entire disclosure of which is incorporated herein by reference; 2. U.S. Pat. No. 5,028,362 issued on Jul. 2, 1991 to M. A. Janney and O. O. Omatete, the entire disclosure of which is incorporated herein by reference; and 3. U.S. Pat. No. 5,145,908 issued on Sep. 8, 1992 to M. A. Janney and O. O. Omatete, the entire disclosure of which is incorporated herein by reference. Glossary of terms used herein: APS 10% Ammonium Persulfate Solution in H.sub.2 O HMAM Hydroxymethylacrylamide, n-metholylacrylamide MAM Methacrylamide MBAM N,N'-Methylenebisacrylamide PEG (n) Polyethylene glycol (mol. wt.) PEGDMA Polyethylene glycol (1000) dimethacrylate Raw Gel A gel that is not loaded with particles, also called a neat gel TEMED Tetramethylethylenediamine The terms "polymer gel" and "gel", as used herein, are defined as a polymer-solvent interpenetrating network that is derived from at least one of: a solution or mixture of a monomer and solvent and/or vehicle by a polymerization reaction; and a solution of a polymer and solvent (and optionally a chemical additive) by changing the temperature of the solution. Hereinafter, solvents and vehicles are referred to as solvent(s) because of their similar function. The solvent can be either aqueous or non-aqueous. Expressly excluded in the foregoing definition are rubbery materials formed by plasticizing brittle polymers, for example, plasticized poly (vinyl chloride). Some examples of gels that fulfill this definition include (but are not limited to) the following: 1a) Free radical polymerization mechanism. A gel made by polymerizing a solution of MAM, MBAM, and H.sub.2 O using a free radical initiator to polymerize the monomers. 1b) Free radical polymerization mechanism. A gel made by polymerizing a solution of HMAM in H.sub.2 O using a free radical initiator. 1c) Condensation polymerization. A gel made by polymerizing a solution of a commercial two part epoxy resin (with hardener) and acetone. 2a) Gelation on cooling. A gel made by cooling a solution of agar in H.sub.2 O from above its melting point to below its melting point. 2b) Gelation on cooling. A gel made by cooling a solution of poly (vinyl alcohol), borax (or Congo Red), and H.sub.2 O from above its melting point to below its melting point. 2c) Gelation on heating. A gel made by heating a solution of methylcellulose and H.sub.2 O from below its critical solution temperature to above its critical solution temperature. A polymer gel can be derived from any of a variety of sources, for example, vinyl polymerization of at least one monomer, condensation polymerization of at least one monomer, a solution of at least one naturally occurring polymer, and a gel produced from a solution of at least one synthetic polymer. A polymer gel produced by vinyl polymerization of monomers may include at least one of, for example, a gel made by polymerizing at least one monofunctional vinyl monomer and at least one multifunctional vinyl monomer, a gel made by polymerizing at least one multifunctional vinyl monomer, and a gel made by polymerizing hydroxymethylacrylamide and a water-soluble comonomer in H.sub.2 O. A polymer gel produced by condensation polymerization of a monomer may include at least one of, for example, epoxies, urethanes, phenolics, furans, and melamines. A polymer gel produced from a solution of a natural polymer may include at least one polysaccharide, for example, agar, xanthan gun, starch, and locust bean gum. Moreover, a polymer gel produced from a solution of a natural polymer may include at least one protein, for example, gelatin and albumin. A gel produced from a solution of a synthetic polymer may include at least one polymer, for example, cellulose, a cellulose derivative, poly (vinyl alcohol), poly (acrylic acid), and poly (acrylamide). The polymer mold can be plasticized via a conventional plasticizing method to prevent drying. Monomer combinations designed to dry very slowly once polymerized can be used to extend working time and mold assembly time. Humidity controls can be used to further slow the drying process. Non-aqueous or aqueous solvents can be used in neat gel formulations, and can be specifically tailored to slow drying and extend working time of the mold gels. Mold release agents can be used between the mold gel and the flowable composition to prevent bonding of the mold gel to the flowable composition. Moreover, monomer formulations can be selected for the mold which do not bond to the flowable composition. Polymers which are reversible such as agarose and/or gelatin based polymers can be used as molds for the gelcasting of flowable monomer solutions. Via reversible gelation, molds based on aragose or gelatin can be removed before firing by dissolving in warm or hot H.sub.2 O. Reinforcement materials in the form of particles, plates and/or fibers such as fibrous carbon can be added to increase the strength or rigidity of mold gels. For fugitive molds such as cores, reinforcement materials are preferably selected from materials that will burn out easily with conventional gelcasting binder burn out and/or sintering schedules known to and used by the skilled artisan for the specific material being processed. Suitable reinforcement materials may be reactive or relatively inert, and may include polymer compositions, metal compositions, ceramic compositions, and biologically obtained compositions such as fibers. Layered, sequential casting of flowable compositions can be combined with gel molds to form complex internal or external features in parts, as is described further hereinbelow. A gel mold can be isotropically reduced in size by a preselected percentage by partially or completely drying the gel mold after it is formed. A shrinkage factor can be easily targeted within the limits of the organic content of the gel. Thus, a positive mold for the negative gel mold can be fabricated oversize for ease of creating precise features. A monolithic billet of gel can be shaped via carving or machining to form a positive pattern from which a plaster of paris (or other suitable material) slip casting mold can be formed. A negative mold can also be carved or machined. A plurality of shaped monoliths of gel can be assembled into a positive mold or a negative mold. It is not generally necessary to match the monomer solution from which the mold is made with the flowable composition that is molded therewith. Flowable compositions suitable for processing according to the present invention include all known gelcasting compositions. Also suitable are chemically bonded inorganic compositions, for example, plasters such as plaster of paris, cementitious compositions such as portland cement-based compositions, phosphoric acid-bonded alumina compositions, and calcium aluminate-based compositions. Other suitable flowable compositions include silicone rubber-based compositions, fluid polymer-based compositions such as urethanes, epoxies, and unsaturated polyesters, and all other known flowable compositions suitable for molding at temperatures not exceeding the useful limits of the gel mold composition. A suitable flowable composition may also include a reinforcement phase such as a polymer, a metal, a ceramic, and/or a biologically obtained material. The reinforcement phase may be in the form of powder, fibers, plates, etc., as is well known in the art of molding flowable compositions. Processing temperatures are not critical to the invention, and temperatures may be selected which are within the useful ranges of the mold composition and the flowable composition. For most applications, the selected flowable composition can be contacted with a gel mold at room temperature, and the flowable composition can be subsequently solidified at a temperature not exceeding the boiling point of the solvent. |
| PATENT EXAMPLES | This data is not available for free |
| PATENT PHOTOCOPY | Available on request |
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