U.S. patent application number 10/295132 was filed with the patent office on 2004-05-20 for rapid prototyping material systems.
Invention is credited to Kasperchik, Vladek, Lambright, Terry M..
Application Number | 20040094058 10/295132 |
Document ID | / |
Family ID | 32297112 |
Filed Date | 2004-05-20 |
United States Patent
Application |
20040094058 |
Kind Code |
A1 |
Kasperchik, Vladek ; et
al. |
May 20, 2004 |
RAPID PROTOTYPING MATERIAL SYSTEMS
Abstract
A rapid prototyping system preferably includes a basic component
selected from the group consisting of a metal oxide, and one or
more aluminosilicate glasses; an acidic component (polymeric,
oligomeric or polymerizable low molecular weight acid or
hydrolyzable acidic metal salt); 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.
Inventors: |
Kasperchik, Vladek;
(Corvallis, OR) ; Lambright, Terry M.; (Corvallis,
OR) |
Correspondence
Address: |
HEWLETT-PACKARD COMPANY
Intellectual Property Administration
P.O. Box 272400
Fort Collins
CO
80527-2400
US
|
Family ID: |
32297112 |
Appl. No.: |
10/295132 |
Filed: |
November 14, 2002 |
Current U.S.
Class: |
101/483 |
Current CPC
Class: |
C04B 35/624 20130101;
Y10S 264/72 20130101; B33Y 70/00 20141201 |
Class at
Publication: |
101/483 |
International
Class: |
B41C 001/00; B41M
001/00 |
Claims
What is claimed is:
1. A rapid prototyping material system, which comprises: a basic
component selected from the group consisting of a metal oxide, and
one or more aluminosilicate glasses; an acidic component; and an
aqueous binder capable of initiating a crosslinking reaction
between said basic component and said acidic component to form a
three-dimensional printed object.
2. A rapid prototyping system according to claim 1, wherein said
acidic component is one or more acidic components selected from the
group consisting of an organic polyacid, a monomer acid, a monomer
having anions capable of forming hydrogel salts that are
cross-linkable with metal ions from said basic metal oxide, and a
hydrolyzable metal salt capable of forming an oxysalt polymer
matrix with said basic metal oxide.
3. A rapid prototyping system according to claim 1, wherein said
basic component is a metal oxide, and said acidic component is a
polycarboxylic acid.
4. A rapid prototyping system according to claim 3, wherein said
metal oxide is zinc oxide.
5. A rapid prototyping system according to claim 1, wherein said
basic component is a metal oxide, and said acidic component is at
least one component selected from the group consisting of
orthophosphoric acid and polyphosphoric acid.
6. A rapid prototyping system according to claim 5, wherein cations
from said metal in said metal oxide are capable of mediating
crosslinking of phosphate anionic species from said orthophosphoric
acid and/or said polyphosphoric acid.
7. A rapid prototyping system according to claim 5, wherein said
metal in said metal oxide is selected from the group consisting of
Be, Zn, Cu, Mg, Ca, Sr and Ba.
8. A rapid prototyping system according to claim 1, wherein said
basic component is one or more varieties of said aluminosilicate
glass, and said acidic component is at least one component selected
from the group consisting of orthophosphoric acid and
polyphosphoric acid.
9. A rapid prototyping system according to claim 1, wherein said
basic component is a metal oxide, and said acidic component is a
metal chloride or sulfate that forms an oxysalt bond with said
metal oxide.
10. A rapid prototyping system according to claim 9, wherein each
of said basic component and said acidic component includes Zn
and/or Mg.
11. A rapid prototyping system according to claim 1, wherein said
basic component is one or more varieties of said aluminosilicate
glass, and said acidic component is an organic polyacid and
contains one or more functional groups selected from the group
consisting of --COOH, --SO.sub.3H, and --PO.sub.3H.sub.2.
12. A rapid prototyping system according to claim 11, wherein said
basic and acidic components combine to form glass-ionomer cements,
and aid system further comprises a complexing agent for adjusting
reaction kinetics between said acidic component and said basic
component.
13. A rapid prototyping system according to claim 12, wherein said
complexing agent is L- or D-tartaric acid.
14. A rapid prototyping system according to claim 1, wherein said
acidic and said basic component are mixed together in a dry powder
form prior to the addition of said aqueous binder, said acidic
component being an organic polyacid of an average molecular weight
ranging from about 500 to about 1,000,000.
15. A rapid prototyping system according to claim 14, wherein said
organic polyacid is of an average molecular weight ranging from
about 2,000 to about 150,000.
16. A rapid prototyping system according to claim 1, wherein said
basic component is in a powder form, and said acidic component is
stored separately in a liquid form, and mixed with said aqueous
binder.
17. A rapid prototyping system according to claim 1, wherein said
acidic and said basic component are combined together in a dry
powder form prior to the addition of said aqueous binder, and said
aqueous binder is separately mixed with additional amounts of said
acidic component.
18. A rapid prototyping system according to claim 17, wherein said
acidic component in said dry powder has a higher average molecular
weight than said acidic component that is mixed with said aqueous
binder.
19. A rapid prototyping system according to claim 1, wherein said
acidic component further includes unsaturated covalently
polymerizable unsaturated acidic moieties of a monomeric or
oligomeric nature, and/or salts or other acid derivative groups of
said moieties; and said system further includes a polymerization
initiator.
20. A composition for rapid prototyping, which comprises: a basic
component and an acidic component mixed together in a dry powder
form, wherein said basic component is selected from the group
consisting of a metal oxide, and one or more aluminosilicate
glasses, and said acidic component is one or more acidic components
selected from the group consisting of an organic polyacid, a
monomer acid, a monomer having anions capable of forming hydrogel
salts that are cross-linkable with metal ions from said basic metal
oxide, and a hydrolyzable metal salt capable of forming an oxysalt
polymer matrix with said basic metal oxide.
21. A composition according to claim 20, wherein said acid
component is an organic polyacid of an average molecular weight
ranging from about 2,000 to about 1,000,000.
22. A composition according to claim 21, wherein said organic
polyacid is of an average molecular weight ranging from about
10,000 to about 150,000.
23. A composition according to claim 20, wherein said acid
component is an organic polyacid having a higher average molecular
weight than that of a separate acid component that is mixed with an
aqueous binder capable of stimulating a crosslinking reaction
between a basic component and said acidic component to form a
three-dimensional printed object.
24. A composition according to claim 20, wherein said acidic
component further includes unsaturated covalently polymerizable
acidic moieties of a monomeric or oligomeric nature, and/or salts
or other acid derivative groups of said moieties; and said
composition further includes a polymerization initiator.
25. A composition for rapid prototyping, which comprises: an acidic
component mixed with an aqueous binder capable of stimulating a
crosslinking reaction between a basic component and said acidic
component to form a three-dimensional printed object, the basic
component being selected from the group consisting of a metal
oxide, and one or more aluminosilicate glasses, and the acid
component being one or more acidic components selected from the
group consisting of an organic polyacid, a monomer acid, a monomer
having anions capable of forming hydrogel salts that are
cross-linkable with metal ions from said basic metal oxide, and a
hydrolyzable metal salt capable of forming an oxysalt polymer
matrix with said basic metal oxide.
26. A composition according to claim 25, wherein said acidic
component further includes unsaturated covalently polymerizable
acidic moieties of a monomeric or oligomeric nature, and/or salts
or other acid derivative groups of said moieties; and said
composition further includes a polymerization initiator.
27. A method for printing a three-dimensional object, which
comprises: iteratively infiltrating individual layers of powder
including a basic component with an aqueous binder solution capable
of stimulating a crosslinking reaction between said basic component
and an acidic component, the infiltrated powder layers being formed
adjacent to one another to form said three-dimensional printed
object, wherein said basic component is selected from the group
consisting of a metal oxide, and one or more aluminosilicate
glasses, and said acid component is mixed with said powder and/or
said aqueous binder solution.
28. A method according to claim 27, wherein said acid component is
selected from the group consisting of an organic polyacid, a
monomer acid, a monomer having anions capable of forming hydrogel
salts that are cross-linkable with metal ions from said basic metal
oxide, and a hydrolyzable metal salt capable of forming an oxysalt
polymer matrix with said basic metal oxide.
29. A method according to claim 27, wherein said basic component is
a metal oxide, and said acidic component is a polycarboxylic
acid.
30. A method according to claim 29, wherein said metal oxide is
zinc oxide.
31. A method according to claim 27, wherein said basic component is
a metal oxide, and said acidic component is at least one component
selected from the group consisting of orthophosphoric acid and
polyphosphoric acid.
32. A method according to claim 31, wherein cations from said metal
in said metal oxide are capable of crosslinking with phosphate
anions from said orthophosphoric acid and/or said polyphosphoric
acid.
33. A method according to claim 32, wherein said metal in said
metal oxide is selected from the group consisting of Be, Zn, Cu,
Mg, Ca, Sr and Ba.
34. A method according to claim 27, wherein said basic component is
one or more varieties of said aluminosilicate glass, and said
acidic component is at least one component selected from the group
consisting of orthophosphoric acid and polyphosphoric acid.
35. A method according to claim 27, wherein said basic component is
a metal oxide, and said acidic component is a metal chloride or
sulfate that forms an oxysalt bond with said metal oxide.
36. A method according to claim 35, wherein each of said basic
component and said acidic component includes Zn and/or Mg.
37. A method according to claim 27, wherein said basic component is
one or more varieties of said aluminosilicate glass, and said
acidic component is an organic polyacid and contains one or more
functional groups selected from the group consisting of --COOH,
--SO.sub.3H, and --PO.sub.3H.sub.2.
38. A rapid prototyping system according to claim 37, wherein said
basic and acidic components combine to form glass-ionomer cements,
and said system further comprises a complexing agent for adjusting
reaction kinetics between said acidic component and said basic
component.
39. A method according to claim 38, wherein said complexing agent
is L- or D-tartaric acid.
40. A method according to claim 27, wherein said acidic component
is mixed with said dry powder prior to the addition of said aqueous
binder, said acidic component being an organic polyacid of an
average molecular weight ranging from about 2,000 to about
1,000,000.
41. A method according to claim 40, wherein said organic polyacid
is of an average molecular weight ranging from about 10,000 to
about 150,000.
42. A method according to claim 27, wherein said acidic component
is entirely separate from said powder, and is mixed with said
aqueous binder.
43. A method according to claim 27, wherein said acidic component
is mixed with said dry powder prior to the addition of said aqueous
binder, and said aqueous binder is separately mixed with additional
amounts of said acidic component.
44. A method according to claim 43, wherein said acidic component
mixed with said dry powder has a higher average molecular weight
than said acidic component that is mixed with said aqueous
binder.
45. A method according to claim 44, wherein said acidic component
further includes unsaturated covalently polymerizable acidic
moieties of a monomeric or oligomeric nature, and/or salts or other
acid derivative groups of said moieties; and said system further
includes a polymerization initiator.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of rapid
prototyping.
[0002] More specifically, the present invention relates to a
material system for use in rapid prototyping.
BACKGROUND OF THE INVENTION
[0003] 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.
[0004] One form of rapid prototyping involves a process of
sequentially forming layers.
[0005] In this process, a powdery material is used to form each
individual layer of the desired product.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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
[0010] In one of many possible embodiments, the present invention
provides a rapid prototyping system that preferably includes a
basic component 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.
[0011] 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
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.sup.+z) as they are
replaced by the protons.
[0016] 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.
[0017] A representative (and the most simplified) example of this
chemical process involves glass-ionomer chemistry, where the acid
component in the rapid prototyping system is a polyacid such as
polyacrylic acid. The basic component in this example is
aluminosilicate glass, for example. The protons from the
polyacrylic acid release upon the dissolving of the polyacrylic
acid in the aqueous binder, and the protons attack the glass, which
releases multivalent cations. The cations then crosslink the
polyacid through formation of ionic bonds, and the bonding causes
the polyacid components to compress and solidify until the cement
is completely solidified and extremely hard.
[0018] There are three basic chemical components of the rapid
prototyping system, namely, an active acidic component, an active
basic component, and an aqueous binder. The basic component can be
a metal oxide, and can also be an aluminosilicate glass. The
aqueous binder must be capable of stimulating a crosslinking
reaction between the basic component and the acidic component to
form a three-dimensional printed object. The acidic component can
be one or more acidic components such as an organic polyacid, a
monomer acid, an oligomer acida monomer having anions capable of
forming hydrogel (or solvent-gel) salts that are cross-linkable
with metal ions from said basic metal oxide, and a hydrolyzable
metal salt capable of forming an oxysalt polymer matrix with said
basic metal oxide.
[0019] Examples of acid-base combinations that form a cement system
for rapid prototyping include the following.
[0020] a. Zinc oxide--polycarboxylic acid cements.
[0021] b. Metal oxide (i.e., oxides of Be, Zn, Cu, Mg, Ca, Sr, Ba,
or other metal oxides.)--orthophosphoric or poly (phosphoric acid)
cements. In this case, metal cations crosslink phosphate anions
resulting in the formation of a hydrogel matrix.
[0022] c. A mixture of reactive aluminosilicate glasses (i.e.,
xCaO*yAl.sub.2O.sub.3* zSiO.sub.2*nCaF2, and i.e. sometimes
containing fluorine) with orthophosphoric or poly (phosphoric
acid). In this case, setting of the cement involves the formation
of a hydrogel matrix of silica gel and ionically crosslinked
phosphate ions. The average particle size for the glass is
preferably approximately 30-50 .mu.m or less, as glass particles
with a smaller diameter can be difficult to spread.
[0023] d. Oxysalt-bonded cements. These are formed by acid-base
reactions of metal oxide powder such as ZnO or MgO, although the
metal oxide powder is not limited to these oxides, and a
concentrated solution of metal chloride or sulfate where the metal
is, for example, Zn or Mg.
[0024] e. Glass-ionomer cements. In this case, the basic component
of the system is reactive aluminosilicate glass (i.e.,
xCaO*yAl.sub.2O.sub.3*zSi- O.sub.2, and frequently containing
fluorine, i.e., in the form of CaF.sub.2, and the acidic component
of the system is organic polyacid containing functional groups such
as --COOH, --SO.sub.3H, and --PO.sub.3H.sub.2. The glass ionomer
mixture may also contain small amounts of low molecular weight
complexing agent such as L- or D-tartaric acid for adjusting the
kinetics of the cement setting process. In some cases, the
glass-ionomer cements should be pretreated to make the surface of
the polyacid powder less hydrophilic and therefore les susceptible
to clumping due to moisture absorption. A preferable pretreatment
includes the addition of some anti-caking hydrophobic agent to the
dry cement mix. The agent could include some stearate salts (Mg,
Ca, Zn) or lecithin at a concentration of between 0.01 and 13.0 wt
%.
[0025] The above types of cements provide superior compressive
strength and significantly better mechanical properties relative to
common systems typically used in rapid prototyping systems. Using
these cements, there is no need for any reinforcing post-treatment.
The cements have a very short setting/curing time. No drying is
necessary because water in the aqueous binder is consumed and
becomes part of the solid phase during the acid-base setting
reaction, which generally proceeds to completion much faster than
drying of the green object composed of the materials currently
present on the market. Further, the material produced by the cement
has a continuous texture.
[0026] The cements of the present invention cure by means of ionic
reactions like neutralization, salt formation, chelation,
crystallization, or ionic and covalent cross-linking, specifically
in the presence of water, or other polar solvent. As discussed
above, the components included in the system preferably include a
base such as a metal oxide or an aluminosilicate glass, an acidic
component, and an aqueous binder. The acidic component is usually a
polymeric acid (polycarboxylic, polysulfonic, polyphosphonic acids)
or other acid (phosphoric acid, derivatives of salicylic acid), or
a hydrolysable metal salt. The binder is not limited to an aqueous
one. Any polar solvent capable of interacting acid and base
components may be effective, so long as it can dissolve or
solubilize the components and promote the cross-linking
reaction.
[0027] In one of the embodiments of current invention, acid or
polymeric acid component of the acid-base cement could be partially
or fully substituted with unsaturated polymerizable acidic moieties
of a monomeric or oligomeric nature, as well as their salts or
other acid derivative groups. In such a case, a cross-linked
hydrogel formed after the acid-base interaction of the cement
components could be further fortified by polymerization and, hence,
covalent cross-linking of the unsaturated moieties. Examples of
polymerizable unsaturated monomers, oligomers or prepolymers with
acid groups or reactive acid-derivative groups may include:
[0028] unsaturated organic esters of phosphoric and phosphonic
acids (German AS No. 2 711 234 & German OS No. 3 150 285),
[0029] unsaturated organic esters of monofluorophosphoric acid
(U.S. Pat. No. 3,997,504),
[0030] unsaturated organic esters of phosphoric acids that contain
either chlorine or bromine bonded directly to the phosphorus (Eur.
Pat. No. 0 058 483),
[0031] unsaturated organic esters of phosphoric acid in the form of
pyrophosphates (anhydrides) (German OS No. 3 048 410),
[0032] unsaturated carboxylic acids,
[0033] unsaturated sulfur-containing organic acid moieties with
groups of --SO.sub.2H, --SO.sub.3H, --O--SO.sub.3H type,
[0034] unsaturated organic derivatives of boric acid i.e. the ones
containing groups: --B(OH).sub.2, B(OH)(OR), --O--B(OH).sub.2,
--O--B(OH)(OR) wherein R is H or alkyl,
[0035] unsaturated organic moieties containing cationic acid
radicals like NR.sub.2H.sup.+, --RR.sub.2H.sup.+ (wherein R is H or
alkyl), and/or
[0036] unsaturated organic moieties containing different
combinations of the acidic species listed in the a)-h).
[0037] The reactive acid derivatives can be substituted with acid
halides, with acid anhydrides, and with acid amides, nitriles, and
esters, that readily hydrolyze into acid in the presence of water
or other polar solvent, as such can enter into ion-exchange,
neutralization, salt formation, or chelation reactions with the
base component of the acid-base cement, i.e. metal oxides,
ceramics, zeolites or leachable reactive glasses. Especially
preferred are acid groups or reactive acid derivatives in the form
of carboxylate, phosphate, phosphonate, sulfonate, or borate acid
radicals or of their reactive derivatives.
[0038] The polymerizable unsaturated monomers, oligomers, or
prepolymers in the polymerizable cement mixtures in accordance with
the invention can carry alkenyl, alkenoxy, cycloalkenyl, aralkenyl,
or alkenaryl radicals, with acryl, methacryl, vinyl, or styryl
radicals being preferable and, of these, the acryl and methacryl
radicals which constitute the polymerizable groups in many monomers
are especially preferable. Especially appropriate are compounds
that contain at least two polymerizable groups or at least two acid
groups or acid-derivative groups. Examples are phosphoric-acid
esters of glycerine dimethacrylate or
1-methacryloxyethane-1,1-diphosphonic acid.
[0039] The presence of polymerizable unsaturated acidic moieties in
the acid-base cement systems is highly desirable, as well as the
presence of a polymerization initiator in the mixture. The role of
the initiator is to enable triggering of polymerization of the
unsaturated species after the initial setting caused by the
interaction of the acid and base components of the cement. The
covalent polymerization of the unsaturated component of the cement
could be initiated either by photoirradiation (light) or heat. An
example of the initiator used for the light-triggered
polymerization is mixture of a-diketones and tertiary amines.
Typical initiators used for the heat-triggered polymerization
include but are not limited to organic or inorganic peroxides such
as benzoyl peroxide or ammonium persulfate.
[0040] The major purpose for the aqueous or polar solvent-based
binder is to deliver and/or enable interaction of the acidic
component of the cement with the basic component. Apart from water
and/or solvent, the liquid binder may also contain:
[0041] a. surfactants/wetting agent to facilitate quick wetting of
the powder surface by the binder,
[0042] b. colorants such as dyes or pigments to provide color for
the printed object,
[0043] c. co-solvents to improve dye solubility in the binder,
[0044] d. soluble polymers to modify rheological behavior and
improve jettability of the binder,
[0045] e. complexing agent, i.e. tartaric acid or EDTA, to control
the setting behavior and rate of the acid-base reactive system.
[0046] In the case where the acidic part of the system contains
covalently polymerizable acidic moieties, the initial acid-base
interaction of the components is still used to print and produce
the so-called "green object." After the initial printing, the
mechanical properties, the ease of handling, and the resistance to
environmental factors (moisture and/or humidity) of the "green
object" is significantly enhanced by the post-treatment involving
curing material of the object through exposure to light or heat.
Polymerization of the unsaturated moieties in the "green object"
results in covalent cross-linking and further fortification of the
hydrogel salt matrix formed by the initial acid-base
interaction.
[0047] In another embodiment of the current invention, covalent
cross-linking of the unsaturated polymerizable moieties could be
initiated immediately after the delivery of the aqueous or polar
solvent-based binder into the powder. In this case covalent
cross-linking happens in parallel with ionic cross-linking cased by
acid-base interaction. The mechanical embodiment of this approach
implies the presence of a source of light in the visible or UV
range, or heat from, for example, IR radiation, above the printed
powder surface. The "green object" in this case is cured at the
same time as it is printed on the layer by layer basis.
[0048] An example reaction mixture involving reactive glass-ionomer
chemistry in one embodiment of the invention includes between about
60% and about 90% by weight of a reactive aluminosilicate glass. An
acidic powder having an average molecular mass of between about
2,000 about 1,000,000 is present at about 5 wt % to about 40 wt %.
It is preferred that in this case the acid component is a
polyacrylic acid having an average molecular weight that is between
about 10,000 and about 150,000. L- or D-tartaric acid is also
included. Finally, an ink-jettable aqueous binder is present at
between about 5 wt % and about 50 wt % of the dry mixture.
[0049] There are other cement systems that can be used in
accordance with the principles of the present invention. For
example, acid-base cements that have previously been used for
dental and surgical applications may be used with the present rapid
prototyping system, and include polycarboxylate cements such as
zinc oxide and polyacrylic acid-based surgical cements such as
those disclosed in U.S. Pat. No. 3,751,391 which is hereby
incorporated by reference, and glass-ionomer cements such as those
disclosed in U.S. Pat. No. 3,814,717 which is hereby incorporated
by reference, and in British Patent No. 1,316,129 which is also
hereby incorporated by reference.
[0050] Several applications can be created and modified using the
above-described materials in the present rapid prototyping system.
According to a first application, the acidic and the basic
component are mixed together in a dry powder form prior to the
addition of the aqueous binder. Preferably in this application, the
basic component is a metal oxide or a reactive glass as described
above, and the acidic component is an organic polyacid or a metal
salt. The surface of the powder is printed with ink-jettable
aqueous binder, which dissolves the acidic component and causes
initiation of the setting reaction. This approach is especially
useful when the acidic component is a high molecular weight
polyacid.
[0051] According to this first application and other applications,
the aqueous binder may be delivered by an inkjet and may contain
complexing agent(s) and coloring agent(s) as well. In the case
where the chemistry involves a glass-ionomer system, the polyacid
dissolves upon contact with the aqueous binder. A viscous liquid
phase is formed, binding together partially reacted glass
particles. When the polyacid is a high molecular weight compound
the mechanical properties of the final product are significantly
improved. The organic polyacid is preferably of an average
molecular weight ranging from about 10,000 to about 150,000,
although the range can be expanded to range from about 2,000 to
about 1,000,000. Most preferably, the organic polyacid is of a
molecular weight that is less than 100,000.
[0052] According to a second application of the present rapid
prototyping system, the acidic component is stored separately from
the powder, in a liquid form. Preferably, the acidic component is
mixed with the aqueous binder. While not so limited, this approach
could be typical for cases where the acidic component is of a
relatively low average molecular weight. In any respect, the acid
component is dissolved in the liquid binder and consequently is
delivered to the basic component-containing powder by an inkjet in
the case where inkjet printing is applied. One advantage of this
approach is a more efficient reaction as there is no need for the
acidic component to dissolve in the aqueous binder during
printing.
[0053] According to a third application of the printing system of
the present invention, the first two applications are combined, so
that while some of the acidic component and all of the basic
component are combined together in a dry powder form prior to the
addition of the aqueous binder. Further, the aqueous binder is
separately mixed with additional amounts of the acidic component
prior to printing. Under this approach, it is preferred that the
acidic component in the dry powder has a higher average molecular
weight than that of the acidic component that is mixed with the
aqueous binder. This approach combines the advantages of the first
and second approaches. Further, the integrity of the finally
produced object is improved because of the initial presence of the
acidic polymer in the binder, and the ability for a relatively high
average molecular weight acid polymer to mix with the powder. An
additional benefit of this approach is improved solubility of the
acidic component present in the powder. The acidic component
present in the liquid binder helps to solubilize the acidic binder
in the powder, and results in better structural uniformity of the
printed object.
EXAMPLE #1
[0054] Powder Mixture Composition:
1 Components Pts, weight Wt. % L-Tartaric Acid 0.015 1.23% Schott
Reactive Glass K1 1 81.30% Poly(acrylic acid) M .about.50,000
spray-dried 0.2 17.46%
[0055] Liquid Binder Composition (%, wt.):
2 2-Pyrrolidone 5.2% Tergitol-15-S-7 0.25% Tergitol-15-S-5 0.20%
Polyethyleneglycol (M .about.10K) 1.00% Dowfax-8390 0.15% Water
balance
[0056] The colorless binder of the above formulation was jetted
into the powder (glass-ionomer mixture). The binder/powder mass
ratio during the printing was 1.5:10. The initial setting of the
cement mixture was happening 2 min after the binder being jetted
into the powder mix. The printing produced white object. The object
had enough mechanical strength to be handled and cleaned from the
non-reacted powder immediately after the printing was finished.
EXAMPLE #2
[0057] Powder Mixture Composition:
3 Components Pts, weight Wt. % L-Tartaric Acid 0.015 1.23
Experimental Reactive Glass LG163* 1 85.27 Poly(acrylic acid) M
.about.50,000 spray-dried 0.2 13.50 *Composition of LG163 -
4.5SiO.sub.2 * Al.sub.2O.sub.3 * 1.5P.sub.2O.sub.5 * 4.5CaO *
0.5CaF.sub.2
[0058] Liquid Binders Composition (% wt.):
[0059] Clear
4 2-Pyrrolidone 5.2% Tergitol-15-S-7 0.25% Tergitol-15-S-5 0.20%
Polyethyleneglycol (M .about.10K) 1.00% Dowfax-8390 0.15% Water
balance
[0060] Yellow
5 2-Pyrrolidone 5.2% Tergitol-15-S-7 0.25% Tergitol-15-S-5 0.20%
Polyethyleneglycol (M .about.10K) 1.00% Dowfax-8390 0.15% Acid
Yellow 23 (yellow dye) 0.6% Water balance
[0061] Cyan
6 2-Pyrrolidone 5.2% Tergitol-15-S-7 0.25% Tergitol-15-S-5 0.20%
Polyethyleneglycol (M .about.10K) 1.00% Dowfax-8390 0.15% Direct
Blue 199 (cyan dye) 0.6% Water balance
[0062] Magenta
7 2-Pyrrolidone 5.2% Tergitol-15-S-7 0.25% Tergitol-15-S-5 0.20%
Polyethyleneglycol (M .about.10K) 1.00% Dowfax-8390 0.15% Ilford
M377 (magenta dye) 0.6% Water balance
[0063] The binders of the above formulation were jetted into the
powder (glass-ionomer mixture). The binder/powder mass ratio during
the printing was 1.7:10. The initial setting of the cement mixture
was happening 4 min after the binder being jetted into the powder
mix. The printing produced a colored object. The object had enough
mechanical strength to be handled and cleaned from the non-reacted
powder 5 min after the printing was finished.
[0064] The preceding description has been presented only to
illustrate and describe the invention. It is not intended to be
exhaustive or to limit the invention to any precise form disclosed.
Many modifications and variations are possible in light of the
above teaching.
[0065] The preferred embodiment was chosen and described in order
to best explain the principles of the invention and its practical
application. The preceding description is intended to enable others
skilled in the art to best utilize the invention in various
embodiments and with various modifications as are suited to the
particular use contemplated. It is intended that the scope of the
invention be defined by the following claims.
* * * * *