U.S. patent number 7,087,109 [Application Number 10/255,139] was granted by the patent office on 2006-08-08 for three dimensional printing material system and method.
This patent grant is currently assigned to Z Corporation. Invention is credited to James F. Bredt, Sarah Clark, Grieta Gilchrist.
United States Patent |
7,087,109 |
Bredt , et al. |
August 8, 2006 |
Three dimensional printing material system and method
Abstract
The present invention is directed to a three-dimensional
printing system and method, and an article made therefrom. The
method of the present invention includes building cross-sectional
portions of a three dimensional article, and assembling the
individual cross-sectional areas in a layer-wise fashion to form a
final article. The individual cross-sectional areas are built using
an ink-jet printhead to deliver an aqueous fluid to a particle
material that includes a first particulate material, a second
particulate material, and a third particulate material, wherein the
first and second particulate materials react in the presence of the
fluid in a period of time, and the third particulate material
reacts in the presence of the fluid to form a solid in a longer
period of time.
Inventors: |
Bredt; James F. (Watertown,
MA), Clark; Sarah (Somerville, MA), Gilchrist; Grieta
(Albuquerque, NM) |
Assignee: |
Z Corporation (Burlington,
MA)
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Family
ID: |
31993437 |
Appl.
No.: |
10/255,139 |
Filed: |
September 25, 2002 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040056378 A1 |
Mar 25, 2004 |
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Current U.S.
Class: |
106/691; 106/690;
106/31.13 |
Current CPC
Class: |
C04B
28/30 (20130101); C04B 28/34 (20130101); B28B
7/465 (20130101); B33Y 70/00 (20141201); C04B
28/14 (20130101); B29C 64/165 (20170801); B28B
1/001 (20130101); C04B 28/34 (20130101); C04B
14/02 (20130101); C04B 14/30 (20130101); C04B
22/064 (20130101); C04B 24/122 (20130101); C04B
2103/0092 (20130101); C04B 28/30 (20130101); C04B
14/02 (20130101); C04B 24/122 (20130101); C04B
2103/0092 (20130101); C04B 28/14 (20130101); C04B
2103/0092 (20130101); C04B 2103/10 (20130101); B33Y
80/00 (20141201); C04B 2111/00181 (20130101) |
Current International
Class: |
C04B
28/10 (20060101) |
Field of
Search: |
;106/683,689,690,691,31.13 ;524/4,5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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19853834 |
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May 2000 |
|
DE |
|
101 58 233 |
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Mar 2003 |
|
DE |
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0 431 924 |
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Jun 1991 |
|
EP |
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2001-162351 |
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Jun 2001 |
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JP |
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93/25336 |
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Dec 1993 |
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WO |
|
95/30503 |
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Nov 1995 |
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WO |
|
97/26302 |
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Jul 1997 |
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WO |
|
98/09798 |
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Mar 1998 |
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WO |
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98/28124 |
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Jul 1998 |
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WO |
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WO 00 26026 |
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May 2000 |
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WO |
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WO 01 34371 |
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May 2001 |
|
WO |
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Other References
Borland, "Characterization of Fundamental and Reticulated
Biomedical Polymer Structures Fabricated by Three Dimensional
Printing," Thesis, MIT,(Jun. 1995.). cited by other .
Ederer, "A 3D Print Process for Inexpensive Plastic Parts,"
Presentation for the Austin Solid Freeform Conference (1995.), no
month provided. cited by other .
Khanuja, "Origin and Control of Anisotropy in Three Dimensional
Printing of Structural Ceramics," Thesis, MIT,(Feb. 1996.). cited
by other .
International Search Report for PCT/US03/29714,(Feb. 10, 2004.)6
pages. cited by other .
Boyer et al., "Metals Handbook," American Society for Metals, pp.
23-25 and 23-8-13, (1985), no month provided. cited by other .
German, Powder Injection Molding, (1990), no month provided, pp.
32-43 and 92-95. cited by other.
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Primary Examiner: Brunsman; David M
Attorney, Agent or Firm: Goodwin Procter LLP
Claims
The invention claimed is:
1. A solid article comprising: a product of a mixture of a
plurality of particles of: a first particulate material comprising
monocalcium phosphate, anhydrous; a second particulate material
comprising magnesium oxide; and a third particulate material
comprising polyvinyl alcohol, wherein the first particulate
material and the second particulate material can react to form a
solid in a period of time, and the third particulate material can
solidify in a longer period of time when the mixture is contacted
by a fluid during three-dimensional printing, the article having
been formed by three-dimensional printing and comprising a
plurality of layers of the mixture.
2. The article of claim 1, wherein the first particulate material
and the second particulate material react in the presence of the
fluid.
3. The article of claim 2, wherein at least one of the first
particulate material and the second particulate material is
substantially soluble in the fluid.
4. The article of claim 2, wherein the fluid is aqueous.
5. The article of claim 1, wherein the mixture of plurality of
particles further comprises a filler.
6. The article of claim 5, wherein the filler is selected from the
group consisting of: limestone, staurolite, silica sand, zircon
sand, olivine sand, chromite sand, magnesite, alumina silicate,
calcium silicate, fused silica, calcium phosphate, rutile,
bentonite, montmorillonite, glass, chamotte, fireclay, and mixtures
thereof.
7. A compound used in three-dimensional printing, comprising: a dry
particulate mixture of: a first dry particulate material comprising
monocalcium phosphate, anhydrous; a second dry particulate material
comprising magnesium oxide; and a third dry particulate material
comprising polyvinyl alcohol, wherein the dry particulate mixture
can be used in three-dimensional printing to form an article
comprised of a plurality of layers, the first particulate material
and the second particulate material can react to form a solid in a
period of time, and the third particulate material can solidify in
a longer period of time when the mixture is contacted by a fluid
during three-dimensional printing.
8. The compound of claim 7, wherein the first particulate material
and the second particulate material react in the presence of the
fluid.
9. The compound of claim 8, wherein at least one of the first
particulate material and the second particulate material is
substantially soluble in the fluid.
10. The compound of claim 7, wherein the mixture of plurality of
particles further comprises a filler.
11. The compound of claim 10, wherein the filler is selected from
the group consisting of: limestone, staurolite, silica sand, zircon
sand, olivine sand, chromite sand, magnesite, alumina silicate,
calcium silicate, fused silica, calcium phosphate, rutile,
bentonite, montmorillonite, glass, chamotte, fireclay, and mixtures
thereof.
12. The compound of claim 8, wherein the fluid is aqueous.
13. A dry particulate mixture of solids used for three-dimensional
printing that, when contacted by a fluid during three-dimensional
printing to form an article comprised of a plurality of layers,
undergoes a first solidification reaction beginning with the fluid
contact and occurring at a first rate, and also undergoes a second
solidification reaction beginning with the fluid contact and
occurring at a second rate slower than the first rate, wherein the
dry particulate mixture comprises: a first dry particulate material
comprising monocalcium phosphate, anhydrous; a second dry
particulate material comprising magnesium oxide; and a third dry
particulate material comprising polyvinyl alcohol.
Description
BACKGROUND
This application relates generally to rapid prototyping techniques
and, more particularly to a Three Dimensional Printing material and
method using particulate mixtures.
The field of rapid prototyping involves the production of prototype
articles and small quantities of functional parts, as well as
structural ceramics and ceramic shell molds for metal casting,
directly from computer-generated design data.
Two well-known methods for rapid prototyping include a selective
laser sintering process and a liquid binder Three Dimensional
Printing process. The techniques are similar to the extent that
they both use layering techniques to build three-dimensional
articles. Both methods form successive thin cross sections of the
desired article. The individual cross sections are formed by
bonding together grains of a granular material on a flat surface of
a bed of the granular material. Each layer is bonded to a
previously formed layer to form the desired three-dimensional
article at the same time as the grains of each layer are bonded
together. The laser-sintering and liquid binder techniques are
advantageous because they create parts directly from
computer-generated design data and can produce parts having complex
geometries. Moreover, Three Dimensional Printing can be quicker and
less expensive than conventional machining of prototype parts or
production of cast or molded parts by conventional "hard" or "soft"
tooling techniques which can take from a few weeks to several
months, depending on the complexity of the item.
Three Dimensional Printing has been used to make ceramic molds for
investment casting, thereby generating fully-functional metal
parts. Additional uses have been contemplated for Three Dimensional
Printing.
For example, three Dimensional Printing may be useful in
design-related fields where it is used for visualization,
demonstration and mechanical prototyping. It may also be useful for
making patterns for molding processes. Three Dimensional Printing
techniques may be further useful, for example, in the fields of
medicine and dentistry, where expected outcomes may be modeled
prior to performing procedures. Other businesses that could benefit
from rapid prototyping technology include architectural firms, as
well as others in which visualization of a design is useful.
A selective laser sintering process is described in U.S. Pat. No.
4,863,538 to Deckard, which is incorporated herein by reference for
all purposes. The selective laser sintering process was
commercialized by DTM and acquired by 3D Systems. The selective
laser sintering process involves spreading a thin layer of powder
onto a flat surface. The powder is spread using a tool developed
for use with the selective laser sintering process, known in the
art as a counter-rolling mechanism (hereinafter "counter-roller").
Using the counter-roller allows thin layers of material to be
spread evenly, without disturbing previous layers. After the layer
of powder is spread onto the surface, a laser directs laser energy
onto the powder in a predetermined two-dimensional pattern. The
laser sinters or fuses the powder together in the areas struck by
its energy. The powder can be plastic, metal, polymer, ceramic or a
composite. Successive layers of powder are spread over previous
layers using the counter-roller, followed by sintering or fusing
with the laser. The process is essentially thermal, requiring
delivery by the laser of a sufficient amount of energy to sinter
the powder together, and to previous layers, to form the final
article.
U.S. Pat. No. 5,639,402 to Barlow, incorporated herein by reference
for all purposes, discloses a method for selectively fusing calcium
phosphate particles that are coated, or alternatively mixed with, a
polymeric binder material.
U.S. Pat. No. 5,204,055, to Sachs et al. incorporated herein by
reference for all purposes, describes an early Three Dimensional
Printing technique which involves the use of an ink-jet printing
head to deliver a liquid or colloidal binder material to layers of
powdered material. The Three Dimensional ink-jet printing technique
(hereafter "liquid binder method") involves applying a layer of a
powdered material to a surface using a counter-roller. After the
powdered material is applied to the surface, the inkjet printhead
delivers a liquid binder to the layer of powder. The binder
infiltrates into gaps in the powder material, hardening to bond the
powder material into a solidified layer. The hardened binder also
bonds each layer to the previous layer. After the first
cross-sectional portion is formed, the previous steps are repeated,
building successive cross-sectional portions until the final
article is formed. Optionally, the binder can be suspended in a
carrier which evaporates, leaving the hardened binder behind. The
powdered material can be ceramic, metal, plastic or a composite
material, and can also include fiber. The liquid binder material
can be organic or inorganic. Typical organic binder materials used
are polymeric resins, or ceramic precursors such as
polycarbosilazane. Inorganic binders are used where the binder is
incorporated into the final articles; silica is typically used in
such an application.
U.S. Pat. No. 5,490,962 to Cima, incorporated herein by reference
for all purposes, discloses solid free-form techniques for making
medical devices for controlled release of bioactive agents.
U.S. Pat. No. 6,397,922 to Sachs et al., incorporated herein by
reference for all purposes, discloses a layered fabrication
technique used to create a ceramic mold and is incorporated herein
by reference for all purposes.
One advantage of using an ink-jet printhead rather than a laser is
that a plurality of spray nozzles used to deliver binder to the
powder can be arranged side-by-side in a single printhead. In
selective laser sintering machines, only one laser, which delivers
energy to the powder, is conventionally used. The combination of
several spray nozzles increases the speed of liquid binder printing
compared to laser-sintering by allowing a wider area to be printed
at one time. In addition, the liquid binder printing equipment is
much less expensive than the laser equipment due to the high cost
of the laser and the high cost of the related beam deflection
optics and controls.
However, three-dimensional printing materials may be susceptible to
deformation during and after the printing process if sufficient
bond strength within and between layers has not adequately
developed.
In addition, the powders, especially metallic powders, used in both
selective laser sintering and liquid binder techniques present
safety issues that render them undesirable for use in an office
environment. These safety issues may require special clothing and
processing facilities to prevent, for example, skin contact or
inhalation of toxic materials. In addition, more expense may be
incurred through complying with regulations for the disposal of
toxic materials.
SUMMARY
One aspect of the invention is directed to an article comprising a
product of a mixture of a plurality of particles of a first
particulate material, a second particulate material and a third
particulate material. The first particulate material and the second
particulate material can react to form a solid in a period of time,
and the third particulate material can solidify in a longer period
of time. In another embodiment, the mixture of the plurality of
particles may also include a filler. In another embodiment, the
first particulate material is a phosphate. In another embodiment,
the second particulate material is an alkaline oxide. In yet
another embodiment, the first particulate material is a plaster. In
another embodiment, the second particulate material is an
accelerator. In yet another embodiment, the third particulate
material is an adhesive.
Another aspect of the invention is directed to a compound used in
three dimensional printing. The compound comprises a first
particulate material, a second particulate material, and a third
particulate, wherein the first particulate material and the second
particulate material can react to form a solid in a period of time,
and the third particulate material can solidify in a longer period
of time. In another embodiment, the compound may also include a
filler. In another embodiment, the first particulate material is a
phosphate. In another embodiment, the second particulate material
is an alkaline oxide. In yet another embodiment, the first
particulate material is a plaster. In another embodiment, the
second particulate material is an accelerator. In yet another
embodiment, the third particulate material is an adhesive.
Another aspect of the invention is directed to a method of
three-dimensional printing, comprising providing a layer of a dry
particulate material comprising a first particulate material, a
second particulate material, and a third particulate material and
dispensing a fluid onto a region of the first layer. The fluid
causes a reaction between the first and second particulate
materials to occur, the reaction causing a solidified material to
form in the region, and causes the third particulate material to
solidify in the region. The reaction between the first and second
particulate materials occurs in a period of time, and the third
particulate material solidifies in a longer period of time. In
another embodiment, the layer of dry particulate material may also
include a filler. In another embodiment, the first particulate
material is a phosphate. In another embodiment, the second
particulate material is an alkaline oxide. In yet another
embodiment, the first particulate material is a plaster. In another
embodiment, the second particulate material is an accelerator. In
yet another embodiment, the third particulate material is an
adhesive.
Another aspect of the invention is directed to a mixture of solids
used in three dimensional printing that, when contacted by a fluid,
undergoes a first solidification reaction occurring at a first
rate, and simultaneously undergoes a second solidification reaction
occurring at a second rate slower than the first rate.
Other advantages, novel features, and objects of the invention will
become apparent from the following detailed description of
non-limiting embodiments of the invention when considered in
conjunction with the accompanying drawings, which are schematic and
which are not intended to be drawn to scale. In the figures, each
identical or nearly identical component that is illustrated in
various figures typically is represented by a single numeral. For
purposes of clarity, not every component is labeled in every
figure, nor is every component of each embodiment of the invention
shown where illustration is not necessary to allow those of
ordinary skill in the art to understand the invention. In cases
where the present specification and a document incorporated by
reference include conflicting disclosure, the present specification
shall control.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred non limiting embodiments of the present invention will be
described by way of example with reference to the accompanying
drawings, in which:
FIG. 1 illustrates schematically a first layer of a mixture of
particulate material of the invention deposited onto a downwardly
movable surface on which an article is to built, before any fluid
has been delivered;
FIG. 2 illustrates schematically an ink-jet nozzle delivering a
fluid to a portion of the layer of particulate material of FIG. 1
in a predetermined pattern;
FIG. 3 illustrates schematically a view of a final article made
from a series of steps illustrated in FIG. 2 enclosed in the
container while it is still immersed in the loose unactivated
particles;
FIG. 4 illustrates schematically a view of the final article from
FIG. 3.
FIG. 5 illustrates schematically a cross-sectional view of a mold,
including a support structure, for fabricating a casting.
DETAILED DESCRIPTION
The present invention relates to a Three Dimensional Printing
material system useful, among other things, for preparing molds for
casting, such as molds for metal casting. A large number of metal
castings are made by pouring molten metal into a ceramic mold. For
sand casting, the mold may be made of sand held together with
binders. For investment casting, the mold may be made of
refractories, such a alumina powder, held together by silica.
Molds prepared for casting should be sufficiently strong to
withstand pouring of a molten material, such as metal, into a mold
cavity. However, the mold should also be able to break during the
cooling process, or be broken after the cooling process, to allow
removal of the molded product.
In a Three Dimensional Printing material system, it is desired to
have good depowderablility, sufficient strength, and a quick
solidification mechanism when preparing a mold or an appearance
model. As used herein, the term "depowderability" is defined as the
ability to clean loose powder from a printed article after it has
solidified. While the exemplary embodiments described herein are
particularly advantageous for molds because of their strength, heat
resistance and other characteristics, they can also be used to make
appearance models and other articles.
The present invention relates to a Three Dimensional Printing
material system comprising a mixture of a first particulate
material, a second particulate material, a third particulate
material, and a filler. A fluid causes the first particulate
material and the second particulate material to react to form a
solid in a first period of time, and causes the third particulate
material to solidify in a second period of time that is longer than
the first period of time. The reaction between the first
particulate material and the second particulate material provides
initial strength to the printed part during and after the printing
process and may promote high accuracy, allow for a shorter time
from the end of the print stage to handling and may reduce or
eliminate part deformation. Solidification of the third particulate
material provides strength to the final product. As used herein,
the term "solid" is intended to mean a substance that has a
definite volume and shape and resists forces that tend to alter its
volume or shape, as well as to include solid-like substances, such
as gels. The present invention also relates to a method of use for
such a materials system, and to an article made by the method of
the invention.
Referring now to FIG. 1, a schematic representation of a printing
method using the materials system of the present invention is
presented. According to the method, a layer or film of particulate
material 20 is applied on a downwardly movable surface 22 of a
container 24. The layer or film of particulate material can be
formed in any manner, and preferably is applied using a
counter-roller. The particulate material applied to the surface
includes a first particulate material, a second particulate
material, a third particulate material, and a filler. As used
herein, "filler" is meant to define an inert material that is solid
prior to application of the fluid, which is substantially insoluble
in the fluid, and which gives structure to the final article. The
first and second particulate materials react in the presence of a
fluid to provide initial bond strength to the part being built,
while the third particulate material solidifies in a longer period
of time to provide final part strength.
For purposes of the present invention, "particulate material" is
meant to define any dry material containing significant amounts of
particulate material. The particulate material may be soluble in,
or interact with the fluid material, or any portion thereof,
depending upon the particular embodiment of the invention that is
being practiced. For example, in certain embodiments, it may be
desirable that the particulate material dissolve in the fluid
material.
Generally, the size of the particles in the particulate material is
limited by the thickness of the layers to be printed. That is, the
particles are preferably approximately smaller than the thickness
of the layers to be printed. The particulate materials may have any
regular or irregular shape. Using smaller particles may provide
advantages such as smaller feature size, the ability to use thinner
layers, and the ability to reduce what is known in the art as a
"stair stepping" effect. In preferred embodiments, the material
systems include particulate material having particles with a mean
diameter ranging from about 1 .mu.m to about 300 .mu.m, preferably
ranging from about 2 .mu.m to about 250 .mu.m, more preferably
ranging from about 10 .mu.m to about 100 .mu.m, and more preferably
ranging from about 10 .mu.m to about 50 .mu.m.
The particulate material may include impurities and/or inert
particles. The inert particles or any portion of the particulate
material can comprise granular, powdered or fibrous materials.
Classes of inert particles include a polymer, a ceramic, a metal,
an organic material, an inorganic material, a mineral, clay and a
salt.
Choosing a suitable particulate material for the material systems
of the present invention involves various qualitative evaluations,
which may easily be accomplished through routine experimentation by
those of ordinary skill in the art. First, a small mound of
particulate material is formed, a small depression is formed in the
mound, and a small amount of fluid is placed in the depression.
Visual observations are made regarding, among other things, the
rate at which the fluid diffuses into the particulate material, the
viscosity of the particulate material introduction of the fluid,
and whether a membrane is formed around the fluid. Next, line
testing is performed by filling a syringe filled with fluid and
strafing the mounds of particulate material. After a period of
about 24 hours, the mounds of particulate material are examined.
Those in which pebbles of particulate material have formed are
suitable, as it means that the particulate material and fluid react
more quickly than the fluid can evaporate or diffuse into the
surrounding dry powder. Those in which both pebbles and rods of
hardened material have formed are the yet more suitable, indicating
that the rate at which the fluid and particulate material harden is
greater than the rate at which fluid evaporates or diffuses into
the surrounding dry powder. In some instances, the rods of hardened
material will shrink, indicating that the particulate material may
give rise to problems with distortions. As described above, various
additives may be included in the particulate material and/or fluid
to accelerate the rate at which the particulate material
hardens.
The particulate material may also be evaluated to determine the
ease of spreading. Simple test parts may also be formed to
determine, inter alias, the flexural strength, the distortion, the
rate of hardening, the optimum layer thickness, and the optimum
ratio of fluid to particulate material. Material systems suitable
for use in the three-dimensional printing method include those
hardening with minimal distortion, in addition to relatively high
flexural strength. Hardened products with high flexural strength
values may not be suitable for use in the three-dimensional
printing method, if distortions compromise the accuracy of the
final printed articles; this is especially applicable where
relatively fine features are desired.
After a material has been identified as a potential material
through line testing, the formula may be further developed by
printing test patterns on a three dimensional printer. The
strength, accuracy, and degree of difficulty in handling may all be
characterized with a set of test parts (e.g., breaking bars for
strength and gauge blocks for accuracy). These tests may be
repeated as much as necessary, and powder formulas are iterated
until optimum characteristics are obtained.
According to aspects of embodiments of the present invention, an
additional criterion for selecting the particulate materials are
the relative rates of reaction and/or solidification in the
presence of a fluid. The first particulate material and the second
particulate material are selected to react and solidify in the
presence of the fluid in a period of time shorter than the
solidification of the third particulate material in the presence of
the fluid. Solidification of the reaction product of the first and
second particulate materials in the presence of the fluid could
occur within about 20 minutes. In another embodiment, the first
particulate material and the second particulate material react to
form a solid within about 10 minutes, preferably within about 5
minutes, more preferably within about 2 minutes, and most
preferably within about 1 minute of application of the fluid. The
solidification of the third particulate material occurs at a time
longer than the reaction between the first particulate material and
the second particulate material. In one embodiment, the third
particulate material solidifies in a time ranging from about 10
minutes to about 2 hours or more. The absolute period of time for
the solidification of the first and second particulate materials
and the absolute period of time for solidification of the third
particulate material can each vary over a wide range, however, the
period of time for solidification of the third particulate material
will be at least longer than period of time for solidification of
the first particulate material and the second particulate
material.
In one embodiment, the first particulate material may be an acid
and second particulate material may be a base that react with one
another in the presence of a fluid. For example, the first
particulate material may be a phosphate while the second
particulate material may be an alkaline oxide, and/or an alkaline
hydroxide. When an aqueous fluid is printed on a powder that
contains these materials, the phosphate dissolves and acts on the
alkaline oxide and/or an alkaline hydroxide to form a cement.
The phosphates used in the embodiments of the invention include a
salt of an oxygen acid of phosphorus including salts of phosphoric
acids such as orthophosphoric acid, polyphosphoric acid,
pyrophosphoric acid, and metaphosphoric acid.
As used herein, the term "phosphate" is generic and includes both
crystalline and amorphous inorganic phosphates. Further,
"phosphate" includes, but is not limited to, orthophosphates and
condensed phosphates. Orthophosphates are compounds having a
monomeric tetrahedral ion unit (PO.sub.4).sup.3-. Typical
orthophosphates include sodium orthophosphates, such as, monosodium
phosphate, disodium phosphate, trisodium phosphate, potassium
orthophosphates and ammonium orthophosphates. Phosphates are
further described in U.S. Pat. No. 6,299,677 to Johnson et al. and
incorporated by reference in its entirety for all purposes.
Examples of acid phosphates that may be used in embodiments of the
invention include, but are not limited to, monoammonium phosphate;
sodium aluminum phosphate, acidic; monocalcium phosphate,
anhydrous; monopotassium phosphate; monosodium phosphate; and
aluminum acid phosphate. Examples of acid polyphosphates that may
be used in embodiments of the invention include, but are not
limited to, sodium tripolyphosphate; sodium hexametaphosphate;
sodium polyphosphate, anhydrous; and ammonium polyphosphate.
Examples of acid pyrophosphates that may be used in embodiments of
the invention include, but are not limited to, sodium acid
pyrophosphate; tetrasodium pyrophosphate; tetrapotassium
pyrophosphate. Examples of other phosphates that may be used in
embodiments of the invention include, but are not limited to,
diammonium phosphate; dipotassium phosphate; disodium phosphate;
monocalcium phosphate, monhydrate; dicalcium phosphate, dihydrate;
dicalcium phosphate, anhydrous; tricalcium phosphate; disodium
phosphate; and tripotassium phosphate. In a preferred embodiment,
the phosphate is a phosphate salt, such as, monocalcium phosphate,
anhydrous; sodium aluminum phosphate, acidic; aluminum acid
phosphate; monoammonium phosphate; monopotassium phosphate; and
combinations thereof.
Alkaline oxides that may be used as the second particulate material
include, but are not limited to, zinc oxide; magnesium oxide;
calcium oxide; copper oxide; beryllium oxide; bismuth oxide;
cadmium oxide; tin oxide; red lead oxide; and combinations thereof.
Examples of alkaline hydroxides that may be used as the second
particulate material include, but are not limited to, magnesium
hydroxide, beryllium dihydroxide, cobalt trihydroxide, and
combinations thereof. In one embodiment, the second particulate
material is an alkaline oxide. In a preferred embodiment, the
alkaline oxide is magnesium oxide. Magnesium oxide may react with
phosphate compounds to form magnesium phosphate cement. In one
embodiment, the ratio of magnesium oxide and acid phosphate salt
may be varied to accommodate a variety of resin, filler, and binder
chemistries.
In another embodiment, magnesium oxide may react with sulfate
containing compounds to form magnesium oxysulfate cement, or react
with chloride containing compounds to form magnesium oxychloride
cement. In another embodiment, zinc oxide may react with sulfate
containing compounds or chloride containing compounds. Examples of
sulfate containing compounds include, but are not limited to,
magnesium sulfate and zinc sulfate. Examples of chloride containing
compounds include, but are not limited to, magnesium chloride, zinc
chloride, and calcium chloride.
In another embodiment, the first particulate material may be
plaster, and the second particulate material may be an accelerator.
Plaster is frequently called "Plaster of Paris," a name derived
from the earths of Paris and its surrounding regions, which contain
an abundance of the mineral gypsum, from which Plaster of Paris is
manufactured. Plaster is also referred to by many other names,
including, but not limited to, sulphate of lime, semihydrate of
calcium sulfate, casting plaster, gypsum plaster, hydrated sulphate
of lime, hydrated calcium sulphate, and dental plaster, as well as
a variety of trade names. The term "plaster," as used herein, is
meant to define any variety of material including a substantial
amount of CaSO.sub.4.1/2H.sub.2O that is in powder form prior to
the application of an aqueous fluid. The terms "hydrated plaster"
and "set plaster" are used interchangeably herein, and are meant to
include any variety of plaster that includes a substantial amount
of CaSO.sub.42H.sub.2O after setting, or rehydration. Many
varieties of plaster are commercially available, varying, for
example, in structural strength, the time required for setting, and
in volume changes that occur during the setting. Typically,
commercially available plasters include other ingredients such as,
but not limited to, silica, powdered limestone, starch, Terra Alba,
and lime. Examples of commercially available plaster materials that
may be suitable for the embodiments of the present invention
include, but are not limited to, white hydrocal cement, durabond
90, and drystone (each available from U.S. Gypsum, located in
Chicago, Ill.), as well as most brands of casting plaster, molding
plaster, and spackling compound.
An accelerator may be used as the second particulate material.
"Accelerator," as used herein, is meant to define any material that
increases the rate at which plaster sets. Examples of ways to
accelerate the rate of plaster include, but are not limited to,
increasing the solubility of plaster in water, by providing
additional nucleation sites for crystal formation or increasing the
growth rate of crystals. Accelerators are generally used sparingly
in conventional plaster processing, as they may adversely affect
the strength characteristics of the plaster. However, accelerators
are preferred in some embodiments of the present invention because
they help produce a relatively quick set during printing and
further processing. The potential adverse effect to the strength
characteristics of the plaster is of less importance since the
third particulate material is present to provide strength to the
final part. Suitable accelerators include, but are not limited to,
Terra Alba, potassium sulfate, barium sulfate, ammonium sulfate,
sodium chloride, under calcined-plaster, alum, potassium alum,
lime, calcined lime, and combinations thereof. Terra Alba, which is
raw ground gypsum, is a preferred accelerator, and works by
providing additional nucleation sites for gypsum crystal formation.
Another preferred accelerator is potassium sulfate, which is
thought to work by increasing the solubility of the plaster in the
water. Both Terra Alba and potassium sulfate also increase the
final strength of the article. In one embodiment, at least one
accelerator is preferably used as a second particulate material in
order to increase the rate at which the plaster sets. Plaster
chemistry is further described in U.S. patent application Ser. No.
09/832,309 filed Apr. 10, 2001 which is a continuation of U.S.
patent application Ser. No. 09/182,295 filed Oct. 29, 1998, and is
incorporated herein by reference in its entirety for all purposes.
The third particulate material of the embodiments of the invention
reacts in the presence of an fluid to solidify at a rate slower
than that of the reaction between the first particulate material
and the second particulate material, and imparts strength to the
final part. In one embodiment, the third particulate material is an
adhesive. In another embodiment, the third particulate material is
a filler coated with an adhesive.
The adhesive is a compound selected for the characteristics of high
solubility in the fluid, low solution viscosity, low
hygroscopicity, and high bonding strength. The adhesive should be
highly soluble in the fluid in order ensure that it is incorporated
rapidly and completely into the fluid. Low solution viscosity is
preferred to ensure that once dissolved in the fluid, the solution
migrates quickly to sites in the powder bed to adhesively bond
together the reinforcing materials. The adhesive is preferably
milled as finely as possible prior to admixture with the filler
and/or prior to coating the filler particles in order to increase
the available surface area, enhancing dissolution in the solvent,
without being so fine as to cause "caking," an undesirable article
characteristic. Typical adhesive particle grain sizes are about 10
40 .mu.m. Low hygroscopicity of the adhesive avoids absorption of
excessive moisture from the air and evaporating fluid in printed
regions of the powder bed which causes "caking", in which
unactivated powder spuriously adheres to the outside surface of the
part, resulting in poor surface definition.
Water-soluble compounds are preferred for the adhesive in
embodiments of the present invention, although other compounds can
be used. Compounds suitable for use as the adhesive in embodiments
of the present invention may be selected from the following
non-limiting list: water-soluble polymers, carbohydrates, sugars,
sugar alcohols, proteins, and some inorganic compounds.
Water-soluble polymers with low molecular weights dissolve more
quickly because smaller molecules diffuse more rapidly in solution.
Suitable water-soluble polymers include but are not limited to,
polyethylene glycol, sodium polyacrylate, polyacrylic acid,
polyvinyl alcohol, polyvinyl pyrrolidone, sodium polyacrylate
copolymer with maleic acid, polyvinyl alcohol copolymer with
polyvinyl acetate, and polyvinyl pyrrolidone copolymer with vinyl
acetate, a copolymer of octylacrylamide/acrylate/butylaminoethyl
methacrylate, polyethylene oxide, sodium polystyrene sulfonate,
polyacrylic acid, polymethacrylic acid, copolymers of polyacrylic
acid and methacrylic acid with maleic acid, and alkali salts
thereof, maltodextrine, hydrolyzed gelatin, sugar, polymethacrylic
acid, polyvinyl sulfonic acid, sulfonated polyester,
poly(2-ethyl-2-oxazoline), polymers incorporating maleic acid
functionalities, and combinations thereof. Carbohydrates include,
but are not limited to, acacia gum, locust bean gum, pregelatinized
starch, acid-modified starch, hydrolyzed starch, sodium
carboxymethylcellulose, sodium alginate and hydroxypropyl
cellulose. Suitable sugars and sugar alcohols include sucrose,
dextrose, fructose, lactose, polydextrose, sorbitol and xylitol.
Organic compounds including organic acids and proteins can also be
used, including citric acid, succinic acid, polyacrylic acid,
gelatin, rabbit-skin glue, soy protein, and urea. Inorganic
compounds include plaster, bentonite, sodium silicate and salt.
In another embodiment, a mixture of solid material is contacted by
a fluid, and undergoes a first solidification beginning with the
fluid contact and occurring at a first rate, and also undergoes a
second solidification reaction beginning with the fluid contact and
occurring at a second rate slower than the first rate. As used
herein, the term "solid material" includes particulate material,
aggregates, and the like. In one embodiment of the invention, a
solid material may include more than one type of material, such as,
a particulate material having a coating that is activated by the
fluid causing a solidification reaction to occur within the solid
material and among adjacent solid material. As used herein, the
term "solidification reaction" is defined as any chemical, thermal,
or physical process wherein free flowing solid material are
hardened, bonded, or firmly fixed in relation to other adjacent
solids.
In one embodiment, the mixture may be a mixture of two solid
materials, wherein one of the solid materials is present in excess
of a quantity that will react with the other solid material. In
this embodiment, when contacted by a fluid, the two solids
materials react and solidify in a first period of time, and the
excess of one of the solid materials left over from the reaction
with the other solid material reacts when contacted by a fluid in a
second period of time that is longer than the first period of time.
For example, the mixture may comprise an alkaline oxide, such as
magnesium oxide, and at least one of polyacrylic acid,
polymethacrylic acid, copolymers of polyacrylic acid and
methacrylic acid with maleic acid, and alkali salts thereof. In the
presence of a fluid, the alkaline oxide reacts with a portion of
the at least one of polyacrylic acid, polymethacrylic acid, citric
acid, succinic acid, malic acid, copolymers of polyacrylic acid and
methacrylic acid with maleic acid, and alkali salts thereof to form
a solid. The remaining portion of the at least one of polyacrylic
acid, polymethacrylic acid, citric acid, succinic acid, malic acid,
copolymers of polyacrylic acid and methacrylic acid with maleic
acid, and alkali salts thereof left over from the reaction with the
alkaline oxide may then solidify in the presence of a fluid in a
longer period of time.
In another embodiment, the mixture may comprise two solids, wherein
one solid material solidifies in the presence of a fluid in one
period of time, while the other particulate material solidifies in
the presence of a fluid in a second period of time that is longer
than the first period of time.
In another embodiment, the mixture may comprise three solid
materials, wherein a first and second solid material react in the
presence of a fluid to form a solid in one period of time, and the
third solid material solidifies in the presence of a fluid in a
longer period of time. In an alternative embodiment, a first solid
material may solidify in the presence of a fluid in one period of
time, and a second solid material and third solid material may
react to form a solid in the presence of a fluid in a second period
of time that is longer than the first period of time.
In another embodiment, the mixture may comprise a first coated
particulate material and a second particulate material. In one
embodiment, the first coated particulate material reacts to form a
solid in one period of time when contacted by a fluid and the
second particulate material solidifies when contacted by a fluid in
longer period of time. In another embodiment, a first coated
particulate material reacts to form a solid in one period of time
when contacted by a fluid and a second particulate material
solidifies when contacted by a fluid in a shorter period of time.
In another embodiment, one or more particulate material may be
encapsulated, or present in an aggregate.
The fluid in embodiments of the present invention is selected to
comport with the degree of solubility required for the various
particulate components of the mixture, as described above. The
fluid comprises a solvent in which the third particulate material
and at least one of the first particulate material and the second
particulate material are active, preferably soluble, and may
include processing aids such as a humectant, a flowrate enhancer,
and a dye. An ideal solvent is one in which the third particulate
material and at least one of the first particulate material, the
second particulate material, and the third particulate material is
highly soluble, and in which the filler is insoluble or
substantially less soluble. The fluid can be aqueous or
non-aqueous. In a preferred embodiment, an aqueous fluid comprises
at least one cosolvent. Suitable solvents and cosolvents may be
selected from the following non-limiting list: water; methyl
alcohol; ethyl alcohol; isopropyl alcohol; acetone; methylene
chloride; acetic acid; ethyl acetoacetate; dimethylsulfoxide;
n-methyl pyrrolidone; 2-amino-2-methyl-1-propanol;
1-amino-2-propanol; 2-dimethylamino-2-methyl-1-propanol;
N,N-diethylethanolamine; N-methyldiethanolamine;
N,N-dimethylethanolamine; triethanolamine; 2-aminoethanol;
1-[bis[3-(dimethylamino)propyl]amino]-2-propanol;
3-amino-1-propanol; 2-(2-aminoethylamino)ethanol;
tris(hydroxymethyl)aminomethane; 2-amino-2-ethyl-1,3-propanediol;
2-amino-2-methyl-1,3-propanediol; diethanolamine;
1,3-bis(dimethylamino)-2-propanol; and combinations thereof. Other
polar organic compounds will be obvious to one skilled in the art.
In a preferred embodiment, the fluid is an aqueous solution of
2-amino-2-methyl-1-propanol, with isopropanol, ethanol, or a
combination of both.
The filler in embodiments of the present invention is a compound
selected for the characteristics of insolubility, or extremely low
solubility in the fluid, rapid wetting, low hygroscopicity, and
high bonding strength. The filler provides mechanical structure to
the hardened composition. Sparingly soluble filler material may be
used, but insoluble filler material is preferred. The filler
particles become adhesively bonded together when the first
particulate material and the second particulate material interact
upon application of the fluid. The filler particles are further
bonded together when the third particulate material dries/hardens
after the fluid has been applied. Preferably, the filler includes a
distribution of particle grain sizes, ranging from the practical
maximum of about 250 300 .mu.m downward, to the practical minimum
of about 1 .mu.m. Large grain sizes appear to improve the final
article quality by forming large pores in the powder through which
the fluid can migrate rapidly, permitting production of a more
homogeneous material. Smaller grain sizes serve to reinforce
article strength.
Compounds suitable for use as the filler in embodiments of the
present invention may be selected from the same general groups from
which the third particulate material is selected, provided that the
solubility, hygroscopicity and bonding strength criteria described
above are met. Examples of fillers include, but are not limited to,
limestone, olivine, zircon, alumina, staurolite, and fused silica.
In one embodiment, the filler may be a granular refractory
particulate, including, but not limited to, limestone, staurolite,
silica sand, zircon sand, olivine sand, chromite sand, magnesite,
alumina silicate, calcium silicate, fused silica, calcium
phosphate, rutile, bentonite, montmorillonite, glass, chamotte,
fireclay, and mixtures thereof. In a preferred embodiment, the
filler is olivine, a mineral used for foundry sand
((Mg--Fe).sub.2SiO.sub.4) that is low in crystalline silica and
possesses a low coefficient of thermal expansion. In another
preferred embodiment, the filler is zircon (ZrSiO.sub.4).
Various processing aids may be added to the particulate material,
the fluid, or both, including, but not limited to, accelerators,
adhesives, flowrate enhancers, humectants, visible dyes, fiber,
filler, and combinations thereof. Examples of these and other
additives may be found in U.S. Pat. No. 5,902,441 to Bredt et al.
and U.S. Pat. No. 6,416,850 to Bredt et al., both incorporated by
reference in their entirety for all purposes
FIG. 2 is a schematic representation of an ink-jet nozzle 28
delivering fluid 26 to a portion 30 of the layer or film 20 of the
particulate mixture in a two-dimensional pattern. According to the
method, the fluid 26 is delivered to the layer or film of
particulate material in any predetermined two-dimensional pattern
(circular, in the figures, for purposes of illustration only),
using any convenient mechanism, such as a Drop-On-Demand
(hereinafter "DOD") printhead driven by customized software which
receives data from a computer-assisted-design (hereinafter "CAD")
system, a process which is known in the art. The first portion 30
of the particulate mixture is by the fluid, causing the first
particulate material and the second particulate material to adhere
together and the third particulate material to adhere to form an
essentially solid circular layer that becomes a cross-sectional
portion of the final article. As used herein, "activates" is meant
to define a change in state from essentially inert to adhesive.
When the fluid initially comes into contact with the particulate
mixture, it immediately flows outward (on the microscopic scale)
from the point of impact by capillary action, dissolving the
adhesive within the first few seconds. A droplet of fluid,
typically having a volume of about 100 pl, may spread to a surface
area of about 100 .mu.m once it comes into contact with the
particulate mixture. As the solvent dissolves the third particulate
material and at least one of the first particulate material and
second particulate material, the fluid viscosity increases
dramatically, arresting further migration of the fluid from the
initial point of impact. Within a few minutes, the fluid with
dissolved particulate material therein infiltrates the less soluble
and slightly porous particles, forming bonds between the filler
particles. The fluid is capable of bonding together the particulate
mixture in an amount that is several times the mass of a droplet of
the fluid. As volatile components of the fluid evaporate, the
adhesives harden, joining the filler into a rigid structure, which
becomes a cross-sectional portion of the finished article.
Any unactivated particulate mixture 32 that was not exposed to the
fluid remains loose and free-flowing on the movable surface.
Preferably, the unactivated particulate mixture is left in place
until formation of the final article is complete. Leaving the
unactivated, loose particulate mixture in place ensures that the
article is supported during processing, allowing features such as
overhangs, undercuts, and cavities (not illustrated, but
conventional) to be defined without using support structures. After
formation of the first cross-sectional portion of the final
article, the movable surface is indexed downward.
Using, for example, a counter-rolling mechanism, a second film or
layer of the particulate mixture is then applied over the first,
covering both the rigid first cross-sectional portion, and any
loose particulate mixture by which it is surrounded. A second
application of fluid follows in the manner described above,
dissolving the adhesive and forming adhesive bonds between a
portion of the previous cross-sectional portion, the filler, and,
optionally, fiber of the second layer, and hardening to form a
second rigid cross-sectional portion added to the first rigid
cross-sectional portion of the final article. The movable surface
is again indexed downward.
Applying a layer of particulate mixture, including the adhesive,
applying the fluid, and indexing the movable surface downward are
repeated until the final article is completed. FIG. 3 is a
schematic representation of the final cylindrical article after it
has been completely formed. At the end of the process, only the top
surface 34 of a final article 38 is visible in the container. The
final article is preferably completely immersed in a bed 36 of
unactivated particulate material. Alternatively, those skilled in
this art would know how to build an article in layers upward from
an immovable platform, by successively depositing, smoothing and
printing a series of such layers.
FIG. 4 is a schematic representation of the final cylindrical
article 38. The unactivated particulate material is preferably
removed by blown air or a vacuum. After removal of the unactivated
particulate material from the final article 38, post-processing
treatment may be performed, including cleaning, infiltration with
stabilizing materials, painting, etc.
FIG. 5 illustrates a mold prepared using the three-dimensional
printing techniques of on embodiment of the present invention. Mold
40 comprises an inner shell 42, an outer shell 44, and supports 46
to provide added strength to the inner shell during the casting
process. After three-dimensional printing is completed, unactivated
particulate material is removed from cavity 48, thus providing a
casting surface. Unactivated particulate material may, but need not
be, removed from interstitial spaces 50. Unactivated particulate
material remaining in the interstitial spaces may provide
additional strength to the inner shell during subsequent
casting.
Embodiments of the present invention is further illustrated by the
following Examples which in no way should be construed as further
limiting. The following representative formulas are directed to
preparing molds for investment casting.
Particulate Formulation I
67% Olivine sand (-140 mesh) 29.6% Plaster 3% PVA 0.3% Terra alba
0.1% K.sub.2SO.sub.4.
In Formulation I, Olivine is a mineral used for foundry sand
((Mg--Fe).sub.2 SiO.sub.4) that is low in crystalline silica and
possesses a low coefficient of thermal expansion. Olivine sand
(-140 mesh) is bonded with plaster (Hydrocal) and PVA, but the bond
between PVA and olivine is sufficiently strong that much less resin
is needed. The reduced organic content causes molds made with the
formulation of Example II, to emit less smoke during casting. This
improves the environmental conditions during casting, and leads to
higher quality castings due to the formation of less gas bubbling.
The mold resulting from this formulation is suitable for
low-temperature casting, such as casting Aluminum, Magnesium and
Zinc.
Fluid I
92.6% Water 6.0% glycerol 0.5% isopropanol 0.5% polyvinyl
pyrrolidone 0.2% 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate
0.2% potassium sorbate
Fluid I is a preferred fluid for particulate formulation I.
Particulate Formulations II and III are intended for high
temperature material casting such as for brass, cast iron, and
steel. Because plaster decomposes at around 1200.degree. C. and
releases sulfur dioxide, it is not desirable to use it for high
temperature casting.
Particulate Formulation II
83.9% Zircon 2.5% octacrylamide/acrylate/butylaminoethyl
methacrylate copolymer 1.5% Zinc oxide 10% limestone 1.28% MgO
0.72% monocalcium phosphate, anhydrate 0.1% ethylene glycol
octyl/decyl diester
Magnesium phosphate cement forms bonds early in the curing process
to resist the drying stresses and attendant part distortion. The
active cement filler is formed by the combination of magnesium
oxide with monocalcium phosphate, anhydrate. Any commercially
available grade of magnesium oxide or monocalcium phosphate,
anhydrate may be used. This material rapidly forms a gel that
maintains the dimensional stability of the part while the
octylacrylamide/acrylate/butylaminoethyl methacrylate copolymer,
having a particle size of less than about 70 .mu.m, dissolves and
deposits itself into the pores of the granular solid, forming
stronger bonds that support the material during handling up the
casting stage. Zircon (ZrSiO.sub.4) having a 140 mesh particle size
is a very refractory (foundry sand) filler that has a very low
coefficient of thermal expansion. The remaining ingredients: Zinc
oxide having a particle size of about 10 microns, limestone having
a particle size of less than about 40 microns, and ethylene glycol
octyl/decyl diester are added in order to control the flow of
powder during spreading and printing. Any commercially available
grade of ethylene glycol octyl/decyl diester may be used.
Particulate Formulation III
75.9% Olivine 2.0% octacrylamide/acrylate/butylaminoethyl
methacrylate copolymer 2.4% ZnO 15.9% fused silica (SiO.sub.2) 2.2%
MgO 1.4% monocalcium phosphate, anhydrous 0.18% ethylene glycol
octyl/decyl diester 0.02% sorbitan trioleate (SPAN 85 )
In this formula, olivine replaces zircon as the refractory filler.
Olivine has a slightly higher thermal expansion than zircon, but
since it is lower density, the printed parts are lighter and easier
to manipulate. The magnesium oxide/monocalcium phosphate cement
enables parts to be built and removed from the machine rapidly, and
placed in a drying oven to harden the organic copolymer to full
strength. Zinc oxide and fused silica, having a particle size of
about 200 mesh, are fine powdered additives. Ethylene glycol
octyl/decyl diester and sorbitan trioleate are oily liquids that
give the powder a small degree of cohesion, further improving the
friction characteristics.
Fluid II
86.5% water 10.0% isopropanol 2.5% 2-amino-2-methyl-1-propanol 1%
2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate
In Fluid II, the water component dissolves the phosphate allowing
the phosphate to act on the magnesium oxide to form a cement. Fluid
II includes 2-amino-2-methyl-1-propanol, an organic alkali that is
compatible with the octylacrylonitrile/acrylate/butylaminoethyl
methacrylate copolymer and dissolves the copolymer. Isopropanol and
2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate facilitate wetting
of the fluid in the powder.
Further considerations when selecting the adhesive, filler and
fiber depend on the desired properties of the final article. The
final strength of the finished article depends largely on the
quality of the adhesive contacts between the particles of the
mixture, and the size of the empty pores that persist in the
material after the adhesive has hardened; both of these factors
vary with the grain size of the particulate material. In general,
the mean size of the grains of particulate material is preferably
not larger than the layer thickness. A distribution of grain sizes
increases the packing density of the particulate material, which in
turn increases both article strength and dimensional control.
The materials and method of the illustrative embodiments of the
present invention present several advantages over prior Three
Dimensional Printing methods. The particulate materials provide a
relatively rapid binding reaction in addition to a relatively
longer reaction time for preparing the final part. The additional
rapid binding mechanism may provide high accuracy, allow for
shorter printing and handling time and may reduce or eliminate part
deformation. The materials used in embodiments of the present
invention are relatively non-toxic and inexpensive. Because the
binding particles are added directly to the particulate mixture,
adhesive, particularly adhesive including high levels of suspended
solids, need not be sprayed through the printhead. Instead,
embodiments of the present invention involves spraying preferably
an aqueous solvent, which overcomes problems such as clogging
associated with prior art methods that involve spraying a binder to
a layer of powder.
Those skilled in the art will readily appreciate that all
parameters listed herein are meant to be exemplary and actual
parameters depend upon the specific application for which the
methods and materials of the present invention are used. It is,
therefore, to be understood that the foregoing embodiments are
presented by way of example only and that, within the scope of the
appended claims and equivalents thereto, the invention can be
practiced otherwise than as specifically described.
While several embodiments of the invention have been described and
illustrated herein, those of ordinary skill in the art will readily
envision a variety of other means and structures for performing the
functions and/or obtaining the results or advantages described
herein, and each of such variations or modifications is deemed to
be within the scope of the present invention. More generally, those
skilled in the art would readily appreciate that all parameters,
dimensions, materials, and configurations described herein are
meant to be exemplary and that actual parameters, dimensions,
materials, and configurations will depend upon specific
applications for which the teachings of the present invention are
used. Those skilled in the art will recognize, or be able to
ascertain using no more than routine experimentation, many
equivalents to the specific embodiments of the invention described
herein. It is, therefore, to be understood that the foregoing
embodiments are presented by way of example only and that, within
the scope of the appended claims and equivalents thereto, the
invention may be practiced otherwise than as specifically
described. The present invention is directed to each individual
feature, system, material and/or method described herein. In
addition, any combination of two or more such features, systems,
materials and/or methods, if such features, systems, materials
and/or methods are not mutually inconsistent, is included within
the scope of the present invention.
In the claims (as well as in the specification above), all
transitional phrases such as "comprising", "including", "carrying",
"having", "containing", "involving", and the like are to be
understood to be open-ended, i.e. to mean including but not limited
to. Only the transitional phrases "consisting of" and "consisting
essentially of" shall be closed or semi-closed transitional
phrases, respectively, as set forth in the United States Patent
Office Manual of Patent Examining Procedures, section 2111.03.
* * * * *