Printing – Processes
Reexamination Certificate
2002-11-14
2004-06-01
Eickholt, Eugene H. (Department: 2854)
Printing
Processes
C101S401100, C264S308000, C264SDIG007, C106S162900, C156S305000
Reexamination Certificate
active
06742456
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of rapid prototyping. More specifically, the present invention relates to a material system for use in rapid prototyping.
BACKGROUND OF THE INVENTION
Rapid prototyping is fast becoming a popular process for manufacturing three-dimensional objects including prototype parts and working tools such as structural ceramics and ceramic shell molds. One form of rapid prototyping involves a process of sequentially forming layers.
In this process, a powdery material is used to form each individual layer of the desired product.
Such a printing process offers the advantages of speedy fabrication and low materials cost. It is considered one of the fastest rapid prototyping methods, and can be performed using a variety of colors as well.
However, there are several disadvantages in conventional powder based rapid prototyping processes including the fragility of the resulting product. Poor mechanical properties in the final product are characterized by a low modulus of elasticity and low fracture strength. Weakness in compression and tensile failures at low stress may be due to low density, poor adhesion between powder particles, low density of particles, and the presence of voids. In both the intralayer and interlayer levels, the powder particles are only loosely glued together. More particularly, powders that are presently being used in the market are based on gypsum and/or water swellable polymers such as starches, PVA, etc. Interaction of these powders with an aqueous binder results in poor mechanical strength as well as high porosity of the green object. Also, parts made by powder based rapid prototyping as well as jetted, direct build-up type rapid prototyping suffer from poor strength. The latter is due to the fact that only lower molecular weight polymers (namely their solutions) can be jetted since high molecular weight polymers have viscosities that are too high.
Further, the poor mechanical properties in the resulting product lead to the fact that the base or “green” object, which is fabricated by printing layers in a powder bed, must be subjected to labor intensive post-processing. This post-processing often involves reinforcing the printed object by soaking it in binding or strengthening agents such as cyanoacrylate glue, etc. which penetrate the surface and fill the interconnected pores within the bulk. Gypsum based powders and water swellable polymers currently available have long swelling times, which can be thirty minutes or more. Another disadvantage of this and similar processes is that the resulting products can have a poor resolution, represented by a grainy texture of the product.
While post-processing drying of the resulting article improves the mechanical properties slightly, the improvements are minimal and the drying process is very slow. Other post-processing measures include reinforcing with polymerizable glues such as cyanoacrylate, or surface finishing, but these measures are costly and labor intensive as well. Ultimately the mechanical properties and surface finish depend on the properties of the system of materials in concert with their ability to intermix uniformly and react sufficiently.
SUMMARY OF THE INVENTION
In one of many possible embodiments, the present invention provides a rapid prototyping system including a basic component in powder form selected from the group consisting of a metal oxide, and one or more aluminosilicate glasses; an acidic component; and an aqueous binder capable of stimulating a crosslinking reaction between the basic component and the acidic component to form a three-dimensional printed object.
Additional advantages and novel features of the invention will be set forth in the description which follows or may be learned by those skilled in the art through reading these materials or practicing the invention. The advantages of the invention may be achieved through the means recited in the attached claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In a wide variety of embodiments, the present invention provides a system for rapid prototyping, the compositions included in the system, and a rapid prototyping method incorporating the system. The system for rapid prototyping is preferably leveraged from so-called acid-base cements. The components included in the system preferably include a base such as a metal oxide or an aluminosilicate glass, a polymeric acid or other acid, and an aqueous binder. The basic powder interacts with the acid in the presence of water, causing the formation of an ionically crosslinked hydrogel salt. Formation of the crosslinked hydrogel causes setting of the mixture.
There are three general possibilities for implementation of the system and the materials included in rapid prototyping systems according to the present invention. First, both reactive components, i.e., the acid component and the basic component, can be present in a dry powder mixture. The powder is then inkjet printed with an aqueous or polar solvent binder solution that does not contain any of the reactive components that form the cement. Second, a dry powder mixture can contain only the basic component. An aqueous or polar solvent binder solution that includes the acid component is then jetted onto the powder bed during the printing process. Third, a dry powder can contain the basic component as well as some of the acid component as a mixture. An aqueous or polar solvent binder solution is then used that includes some of the acid component dissolved therein, so that both the powder mixture and the aqueous binder include some of the reactive acid component. The aqueous or polar solvent binder solution and acid component mixture is then jetted onto the powder bed containing the mixture of the acid and basic components.
Apart from the chemical aspects of the present invention, the printing process is similar to the conventional mechanics associated with rapid prototyping that uses a printing process. Multiple planar layers are printed and adjoined together to form a three-dimensional object. Printing is performed layer-by-layer, with each layer representing a cross section of a portion of the final desired product. The powder material forms each individual layer, and is evenly distributed and compressed by compression means such as a roller. When the printer used in the rapid prototyping method is an ink jet printer, a printer head deposits the binder onto the powder in a two-dimensional pattern, and the powder is bonded in the areas,where the adhesive is deposited, thereby forming a printed layer of the final object to be produced. Predetermined portions of the adjacent printed layers are adhered one to another by the use of an aqueous binder, resulting in the joining of the individual cross sections of the final product. The binder is applied simultaneously with the printing of each individual layer. The “un-printed” regions where no adhesive has been applied are then separated from the printed regions where adhesive binder has been applied, leaving a three-dimensional printed base or “green” product.
Next, the chemical aspects of the present invention will be described. The acid component of the rapid prototyping system is water/solvent soluble, and is acidic relative to water/solvent. Consequently, contact of the acidic component with the aqueous or polar solvent binder solution causes protons to dissociate from the acidic component. The free protons are immediately attracted to the basic component of the rapid prototyping system, and the basic component releases multivalent cations (Me
+Z
) as they are replaced by the protons.
The released cations from the basic component of the rapid prototyping system mediate the crosslinking of the compounds that make up the acid component. Ionic crosslinking of the acidic compounds reduces the mobility of the acid component. Eventually the crosslinking process results in solidification of the acid in the solution because of formation salt hydro (or solvent) gel, followed by setting and further hardening of the cement product.
A
Kasperchik Vladek
Lambright Terry M.
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