Use of CO2-soluble materials as transient coatings

Details Use of CO2-soluble materials as transient coatings Use of CO2-soluble materials as transient coatings

1998-12-14

2001-10-09

Lin, Kuang Y. (Department: 1722)

Metal founding

Process

Shaping liquid metal against a forming surface

C164S005000, C164S014000, C134S038000, C156S345420

Reexamination Certificate

active

06298902

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to methods of employing CO
2
-soluble materials as transient spacers, templates, molds, adhesives, binders, and coatings. More particularly, the invention relates to methods of employing CO
2
to remove and dissolve the CO
2
-soluble materials.
BACKGROUND OF THE INVENTION
Transient spacers, templates, adhesives, binders, coatings, and molds are used in numerous industrial applications. In many applications, it is desirable to remove these materials during or after a manufacturing process. For example, in lost foam and lost wax metal casting technologies, a premade form/template pattern of a part is typically made out of plastic or wax.
The form/template is then used to prepare a casting mold, such as a metal casting mold. Metal casting typically involves one of two different processes. In one process, the form/template is removed leaving a cavity suitable to subsequently receive the molten metal. The cavity is typically created by burning out the form/template by firing the casting mold, or by dissolving the form/template in an appropriate solvent. In the other process, the molten metal is poured into the casting mold, contacting the plastic or wax form/template so as to displace the form/template from the mold. During this process, the form/template burns off from the mold as the molten material causes the form/template to decompose at elevated temperatures.
In spite of the wide spread use of these processes, potential environmental risks exist. For example, when the form/template is burned from the mold, noxious gases are generated and emitted. Moreover, when the form/template is dissolved in a solvent, potentially hazardous organic liquids are often employed as the solvent. It would be desirable to utilize techniques in forming molds and the like which employ materials capable of being displaced which do not utilize the above potentially hazardous techniques.
It is therefore an object of the present invention to provide a method of removing material used in applications such as forming molds, which do not require potentially environmentally hazardous techniques.
SUMMARY OF THE INVENTION
To the above end and others, a first aspect of the present invention relates to a method for forming a three-dimensional cavity in a corresponding structure. The method comprises providing a structure comprising a CO
2
-insoluble material which has a three-dimensional object positioned therein. The object comprises CO
2
-soluble material. The object is then contacted with a fluid comprising carbon dioxide to dissolve the object therein, and then the fluid is removed to form a cavity in the structure. The cavity has a shape corresponding to the shape of the three-dimensional object.
Carbon dioxide may be employed in liquid, gaseous, or supercritical form, with supercritical and liquid carbon dioxide being preferred. The CO
2
-soluble material may be selected from various components including fluorinated components, siloxane containing components, and mixtures thereof.
In a second aspect, the present invention relates to a method of removing an adhesive material from two separate substrates.
In a third aspect, the present invention relates to a method of removing a coating material from a substrate surface portion.
In a fourth aspect, the present invention relates to a method of removing a binder from a plurality of particles.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will now be described more fully hereinafter with reference to preferred embodiments of the invention. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
The present invention is directed to a method of forming a three-dimensional cavity in a corresponding structure. Specifically, the method includes providing a structure comprising CO
2
-insoluble material, wherein the structure has a three-dimensional object positioned therein. The three-dimensional object comprises CO
2
-soluble material. The object is then contacted with a fluid comprising carbon dioxide to dissolve the object in the fluid. The fluid is then removed to form a cavity in the structure. The cavity has a shape corresponding to the shape of the three-dimensional object.
For the purpose of the present invention, the fluid includes carbon dioxide in a liquid, gaseous,. or supercritical phase. If liquid CO
2
is used, the temperatures employed during the process are preferably below 31° C. If gaseous CO
2
is used, it is preferred that the phase be employed at high pressure. As used here-in, the term “high pressure” generally refers to CO
2
having a pressure from about 5 to about 1000 bar. In a preferred embodiment, the CO
2
is utilized in a “supercritical” phase. As used herein, “supercritical” means that a fluid medium is at a temperature that is sufficiently high that it cannot be liquefied by pressure. The thermodynamic properties of CO
2
are reported in Hyatt,
J. Org. Chem
. 49: 5097-5101 (1984); therein, it is stated that the critical temperature of CO
2
is about 31° C.
The fluid can include components other than carbon dioxide, the selection of which can be ascertained by the skilled artisan. Other components may include, but are not limited to, aqueous and organic liquid co-solvents.
The three-dimensional object may exist in any suitable shape or figure. Preferably, the object is present as a form or template. The object includes material which is CO
2
-soluble (i.e., “CO
2
-philic”). The CO
2
soluble material may contain various substituents such as a fluorinated component, a siloxane-containing component, or a mixture of the above. Exemplary fluorinated components include, for example, fluorinated polymers or oligomers. As used herein, a fluoropolymer has its conventional meaning in the art and should also be understood to include low molecular weight oligomers (degree of polymerization greater than or equal to 2). See generally Banks et al.
Organofluorine Compounds: Principles and Applications
(1994) and fluorine-containing polymers, 7 Encyclopedia of Polymer Science and Engineering 256 (H. Mark et al. Eds., 2d Ed. 1985). Exemplary fluoropolymers and their oligomers are those formed from monomers such as fluoroacrylate monomers including 2-(N-ethylperfluoro octanesulfonamido) ethyl acrylate (EtFOSEA), 2-(N-ethylperfluorooctane-sulfonamido) ethyl methacrylate (EtFOSEMA), 2-(N-methyl- perfluorooctanesulfonamido) ethyl acrylate (MeFOSEA), 2-(N-methylperfluorooctanesulfonamido) ethyl acrylate (MeFOSEA), 2-(N-methylperf luorooctane sulfonamido) ethyl methacrylate (MeFOSEMA), 1,1′-dihydro perfluorooctyl acrylate (FOA), 1,1′-dihydro perfluorooctyl methacrylate (FOMA): 1,1′,2,2′-tetrahydro perfluoroalkyl acrylates and methacrylates; fluorostyrene monomers such as &agr;-fluorostyrene, and 2,4,6-trifluoromethylstyrene; fluoroalkylene oxide monomers such as a hexaf luoropropylene oxide and perfluorocyclohexene oxide; fluoroolefins such as tetrafluoroethylene, vinylidine fluoride, and chlorotrifluoroethylene; fluorinated alkyl vinyl ether monomers such as perfluoro(propyl vinyl ether) and perfluoro (methylvinyl ether); and the copolymers thereof with suitable comonomers (e.g. oxygen as in the photooxidative polymerization of fluorinated monomers) wherein the it comonomers may be fluorinated or unfluorinated. Mixtures of any of the above can be used. Copolymers formed from any of the monomers recited herein may also be employed. Exemplary copolymers include, for example, copolymers of FOMA and methyl methacrylate.
Siloxane-containing segments may include, for example, poly(dimethyl siloxane) or its derivatives. Exemplary siloxane containing compounds include, but are not limited to, alkyl, fluoroalkyl, and chloroalkyl siloxanes, along with mixtures thereof. Copolymers of any of the above may also be utilized.
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