U.S. patent application number 14/951743 was filed with the patent office on 2017-10-05 for stabilized matrix-filled liquid radiation curable resin compositions for additive fabrication.
The applicant listed for this patent is DSM IP Assets B.V.. Invention is credited to Mingbo He, Tai Yeon Lee, Caroline Liu, Kangtai Ren, Beth Rundlett.
Application Number | 20170283580 14/951743 |
Document ID | / |
Family ID | 51845350 |
Filed Date | 2017-10-05 |
United States Patent
Application |
20170283580 |
Kind Code |
A9 |
He; Mingbo ; et al. |
October 5, 2017 |
STABILIZED MATRIX-FILLED LIQUID RADIATION CURABLE RESIN
COMPOSITIONS FOR ADDITIVE FABRICATION
Abstract
Matrix-filled liquid radiation curable resin compositions for
additive fabrication are described and claimed. Such resins include
a cationically polymerizable component that is an aliphatic
epoxide, a multifunctional (meth)acrylate component, a cationic
photoinitiator, a free-radical photo initiator, and a matrix of
inorganic fillers, wherein the matrix further constitutes
prescribed ratios of at least one microparticle constituent and at
least one nanoparticle constituent. Also described and claimed is a
process for using the matrix-filled liquid radiation curable resins
for additive fabrication to create three dimensional parts, and the
three-dimensional parts made from the liquid radiation curable
resins for additive fabrication.
Inventors: |
He; Mingbo; (Gilberts,
IL) ; Rundlett; Beth; (West Des Moines, IA) ;
Ren; Kangtai; (Geneva, IL) ; Liu; Caroline;
(Barrington, IL) ; Lee; Tai Yeon; (Crystal Lake,
IL) |
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Applicant: |
Name |
City |
State |
Country |
Type |
DSM IP Assets B.V. |
Heerlen |
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NL |
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Prior
Publication: |
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Document Identifier |
Publication Date |
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US 20170145184 A1 |
May 25, 2017 |
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Family ID: |
51845350 |
Appl. No.: |
14/951743 |
Filed: |
November 25, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14533238 |
Nov 5, 2014 |
9228073 |
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14951743 |
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61900044 |
Nov 5, 2013 |
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62074735 |
Nov 4, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03F 7/0047 20130101;
B33Y 70/00 20141201; B29C 64/135 20170801; C08F 2/50 20130101; G03F
7/027 20130101; Y10T 428/31511 20150401; C08L 33/10 20130101; B29K
2063/00 20130101; C08K 2201/011 20130101; C08K 3/36 20130101; G03F
7/0045 20130101; C08F 222/1006 20130101; G03F 7/0037 20130101; G03F
7/038 20130101; B29K 2105/0088 20130101; B29K 2105/246 20130101;
B29K 2509/02 20130101 |
International
Class: |
C08K 3/36 20060101
C08K003/36 |
Claims
1-18. (canceled)
19. A liquid radiation curable composition for additive fabrication
comprising: (a) a cationically polymerizable component; (b) a
(meth)acrylate component; (c) a cationic photoinitiator; (d) a
free-radical photoinitiator; (e) a filled matrix, further
comprising a filled particle dispersion containing a nanoparticle
constituent made up of a plurality of silica nanoparticles having
an average particle size of at least about 50 nanometers, and a
solvent, and a microparticle constituent made up of a plurality of
inorganic microparticles; wherein the ratio by weight of the
microparticle constituent to the nanoparticle constituent is from
about 1:1 to about 12:1, wherein the filled particle dispersion has
a particle dispersion pH of greater than about 5.5.
20. The liquid radiation curable composition for additive
fabrication of claim 19, wherein said plurality of silica
nanoparticles have ara average particle size of from about 50
nanometers to about 100 nanometers; said plurality of inorganic
microparticles have an average particle size of from about 0.2
microns to 20 microns; and wherein the particle dispersion pH of
the filled particle dispersion is from 6.0 to about 7.5.
21. The liquid radiation curable composition for additive
fabrication of claim 20, wherein the filled matrix is present in an
amount by weight, relative to the entire composition, of from about
50 wt % to about 70 wt %.
22. The liquid radiation curable composition for additive
fabrication of claim 21, wherein the ratio of the average particle
size of the inorganic microparticles in the microparticle
constituent to the average particle size of the silica
nanoparticles in the nanoparticle constituent is from about 6.46:1
to about 100:1; and the ratio by weight of the microparticle
constituent to the nanoparticle constituent is from about 4:1 to
about 8:1.
23. The liquid radiation curable composition for additive
fabrication of claim 22, wherein the solvent is selected from one
or more of the group consisting of methyl ethyl ketone,
isopropanol, an epoxide, an oxetane, and an acrylate.
24. The liquid radiation curable composition for additive
fabrication of claim 23, wherein the solvent is a
3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexanecarboxylate.
25. The liquid radiation curable composition for additive
fabrication of claim 24, wherein component (c) is an R-substituted
aromatic thioether triaryl sulfonium or iodonium
tetrakis(pentafluorophenyl) borate cationic photoinitiator with a
tetrakis(pentafluorophenyl)borate anion and a cation of the
following formula (I): ##STR00004## wherein Y1, Y2, and Y3 are the
same or different and wherein Y1, Y2, or Y3 are R-substituted
aromatic thioether with R being an acetyl or halogen group.
26. The liquid radiation curable composition for additive
fabrication of claim 24, wherein component (c) is a
fluoroalkyl-substituted fluorophosphate with a cation of the
following general formula (II): ##STR00005## wherein R.sup.1,
R.sup.2, R.sup.3, R.sup.5 and R.sup.6 each independently represent
an alkyl group, a hydroxy group, an alkoxy group, an alkylcarbonyl
group, an arylcarbonyl group, an alkoxycarbonyl group, an
aryloxycarbonyl group, an arylthiocarbonyl group, an acyloxy group,
an arylthio group, an alkylthio group, an aryl group, a
heterocyclic hydrocarbon group, an aryloxy group, an alkylsulfinyl
group, an arylsulfinyl group, an alkylsulfonyl group, an
arylsulfonyl group, a hydroxy(poly)alkyleneoxy group, an optionally
substituted amino group, a cyano group, a nitro group, or a halogen
atom, R.sup.4 represents an alkyl group, a hydroxy group, an alkoxy
group, an alkylcarbonyl group, an alkoxycarbonyl group, an acyloxy
group, an alkylthio group, a heterocyclic hydrocarbon group, an
alkylsulfinyl group, an alkylsulfonyl group, a
hydroxy(poly)alkyleneoxy group, an optionally substituted amino
group, a cyano group, a nitro group, or a halogen atom, m.sup.1 to
m.sup.6 each represent the number of occurrences of each of R.sup.1
to R.sup.6, m.sup.1, m.sup.4, and m.sup.6 each represent an integer
of 0 to 5, and m.sup.2, m.sup.3, and m.sup.5 each represent an
integer of 0 to 4.
27. The liquid radiation curable composition for additive
fabrication of claim 1, wherein the nanoparticle constituent
comprising a plurality of nanoparticles is present in a filled
particle dispersion further comprising a solvent, wherein the
filled particle dispersion has a particle dispersion pH of greater
than about 5.5.
28. The liquid radiation curable composition for additive
fabrication of claim 27, wherein said plurality of silica
nanoparticles have an average particle size of from about 50
nanometers to about 100 nanometers, wherein said plurality of
inorganic microparticles have an average particle size of from
about 0.2 microns to 20 microns, and wherein the particle
dispersion pH of the filled particle dispersion is from 6.0 to
about 7.5.
29. The liquid radiation curable composition for additive
fabrication of claim 28, wherein the ratio of the average particle
size of the inorganic microparticles in the microparticle
constituent to the average particle size of the silica
nanoparticles in the nanoparticle constituent is from about 6.46:1
to about 100:1; the ratio by weight of the microparticle
constituent to the nanoparticle constituent is from about 4:1 to
about 8:1, and the filled matrix is present in an amount by weight,
relative to the entire composition, of from about 50 wt % to about
70 wt %.
30. The liquid radiation curable composition for additive
fabrication of claim 29, wherein the solvent is selected from one
or more of the group consisting of methyl ethyl ketone,
isopropanol, an epoxide, an oxetane, and an acrylate.
31. The liquid radiation curable composition for additive
fabrication of claim 30, wherein the solvent is a
3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexanecarboxylate.
32. The liquid radiation curable composition for additive
fabrication of claim 28, wherein the particle dispersion pH of the
filled particle dispersion is alkaline.
33. The liquid radiation curable composition for additive
fabrication of claim 19, wherein the filled matrix further
comprises a settling additive.
34. The liquid radiation curable composition for additive
fabrication of claim 32, wherein the settling additive is a fumed
silica.
35. The liquid radiation curable composition for additive
fabrication of claim 33, wherein the fumed silica settling additive
is hydrophilic.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Applications No. 61/900,044 filed 5 Nov. 2013 and No. 62/074,735
filed 4 Nov. 2014, each of which are hereby incorporated by
reference in their entirety as if fully set forth herein.
TECHNICAL FIELD
[0002] The present invention relates to matrix-filled liquid
radiation curable compositions for additive fabrication
processes.
BACKGROUND
[0003] Additive fabrication processes for producing three
dimensional objects are well known. Additive fabrication processes
utilize computer-aided design (CAD) data of an object to build
three-dimensional parts. These three-dimensional parts may be
formed from liquid resins, powders, or other materials.
[0004] A non-limiting example of an additive fabrication process is
stereolithography (SL). Stereolithography is a well-known process
for rapidly producing models, prototypes, patterns, and production
parts in certain applications. SL uses CAD data of an object
wherein the data is transformed into thin cross-sections of a
three-dimensional object. The data is loaded into a computer which
controls a laser that traces a pattern of a cross section through a
liquid radiation curable resin composition contained in a vat,
solidifying a thin layer of the resin corresponding to the cross
section. The solidified layer is recoated with resin and the laser
traces another cross section to harden another layer of resin on
top of the previous layer. The process is repeated layer by layer
until the three-dimensional object is completed. When initially
formed, the three-dimensional object is, in general, not fully
cured, and is called a "green model." Although not required, the
green model may be subjected to post-curing to enhance the
mechanical properties of the finished part. An example of an SL
process is described in U.S. Pat. No. 4,575,330, which is hereby
incorporated by reference.
[0005] There are several types of lasers used in stereo
lithography, traditionally ranging from 193 nm to 355 nm in
wavelength, although other wavelength variants exist. The use of
gas lasers to cure liquid radiation curable resin compositions is
well known. The delivery of laser energy in a stereolithography
system can be Continuous Wave (CW) or Q-switched pulses. CW lasers
provide continuous laser energy and can be used in a high speed
scanning process. However, their output power is limited which
reduces the amount of curing that occurs during object creation. As
a result the finished object will need additional post process
curing. In addition, excess heat could be generated at the point of
irradiation which may be detrimental to the resin. Further, the use
of a laser requires scanning point by point on the resin which can
be time-consuming.
[0006] Other methods of additive fabrication utilize lamps or light
emitting diodes (LEDs). LEDs are semiconductor devices which
utilize the phenomenon of electroluminescence to generate light. At
present, LED UV light sources currently emit light at wavelengths
between 300 and 475 nm, with 365 nm, 390 nm, 395 nm, 405 nm, and
415 nm being common peak spectral outputs. See textbook,
"Light-Emitting Diodes" by E. Fred Schubert, 2.sup.nd Edition,
.COPYRGT. E. Fred Schubert 2006, published by Cambridge University
Press, for a more in-depth discussion of LED UV light sources.
[0007] Many additive fabrication applications require a
freshly-cured part, aka the "green model" to possess high
mechanical strength (modulus of elasticity, fracture strength).
This property, often referred to as "green strength," constitutes
an important property of the green model and is determined
essentially by the nature of the liquid radiation curable resin
composition employed in combination with the type of apparatus used
and degree of exposure provided during part fabrication. Other
important properties of a stereolithographic resin composition
include a high sensitivity for the radiation employed in the course
of curing and a minimum amount of curl or shrinkage deformation,
permitting high shape definition of the green model. Of course, not
only the green model but also the final cured article should have
sufficiently optimized mechanical properties.
[0008] For select additive fabrication applications in the
aerospace or automotive industries, for example, three-dimensional
solid parts are subjected to the high force loads of a wind tunnel,
or the extreme temperatures of a location proximate to
heat-generating componentry. In such applications, designers and
engineers require a three-dimensional solid part created via
additive fabrication to maintain its structural integrity and
minimize deflection. Thus three-dimensional parts made from
photopolymerizable compositions must possess ceramic-like material
properties, such as high strength, stiffness, and heat
resistance.
[0009] "Filled" liquid radiation curable resins have long been used
in the field in an attempt to meet these specialized application
design criteria. That is, high amounts of inorganic filler, such as
silica (SiO.sub.2) have been imparted into traditional "unfilled"
liquid radiation curable resins due to the filler's positive impact
on the strength and stiffness of the three-dimensional object
produced therefrom. Such filled liquid radiation curable
compositions are known in the art of additive fabrication, and are
disclosed in, e.g., U.S. Pat. No. 5,972,563 (Issued Oct. 26, 1999),
U.S. Pat. No. 5,989,475 (Issued Nov. 23, 1999), U.S. Pat. No.
6,287,745 (Issued Sep. 11, 2001), U.S. Pat. No. 6,742,456 (Issued
Jun. 1, 2004), U.S. Pat. Pub. No. 20020045126, U.S. Pat. Pub. No.
20040077745, and U.S. Pat. Pub. No. 20050101684, all of which are
hereby incorporated by reference. While the aforementioned patents
disclose fundamental filled liquid radiation curable compositions,
none discuss or teach compositions sufficiently and simultaneously
overcoming the several drawbacks typically associated with their
use.
[0010] Thus, highly filled compositions present several challenges
to the formulator of liquid radiation curable resins for additive
fabrication. Heretofore no filled liquid radiation curable
composition for additive fabrication existed that could both yield
three-dimensional parts possessing excellent mechanical properties,
yet simultaneously avoid: (1) a high initial viscosity, (2) a poor
viscosity stability, and (3) a tendency to phase separate,
resulting in phenomena known as either "soft pack" or "hard
pack."
[0011] The first long-felt problem with filled liquid radiation
curable resin compositions for additive fabrication is that as the
amount of filler increases, the viscosity of the resin also usually
increases, resulting in decreased workability and processing speed.
Highly viscous resins particularly retard the processing speed in
vat-based additive fabrication systems such as stereolithography.
Existing resins are sufficiently flow-resistant such that they will
not readily form a smooth layer of liquid photo curable resin over
the just formed solid layer to ensure accurate cure by actinic
radiation. Consequently, a recoating operation has traditionally
been used to simultaneously place and mechanically smooth a fresh
layer of resin over a previously cured layer prior to exposure with
actinic radiation. In one non-limiting example, this recoating
operation has traditionally been performed by means of a "recoating
blade." A recoating blade design is discussed in, for example,
Chapman et al., U.S. Pat. No. 5,626,919, assigned to DSM IP Assets,
B.V.
[0012] Even with a recoating operation, however, low viscosity
remains an important characteristic of the resin. The filled liquid
radiation curable resin composition's viscosity affects the time it
takes to equilibrate as a smooth, even surface after the recoating
step. Consequently, a programmed "dwell time" has been
traditionally used between the end of the recoating operation and
the beginning of the exposure of the next layer of resin to
appropriate imaging radiation. Both the recoating operation and the
dwell time dramatically increase the process time of a typical
vat-based additive fabrication process.
[0013] Additionally, the viscosity of the liquid radiation curable
resin also affects the time and difficulty associated with
preparing a recently-cured part for post processing operations. In
a vat-based additive fabrication process, upon build completion of
a three-dimensional solid part, the solidified portions are removed
from the liquid uncured resin. A highly viscous resin will be more
difficult to separate from the cured part, wherein a resin of
substantially low viscosity will be removed without significant
effort. Thus, low viscosity resins reduce the time required to
clean a part in order to prepare it for post processing
operations.
[0014] Second, while the importance of filled liquid radiation
curable compositions for additive fabrication with a sufficiently
low initial viscosity is significant, it is equally as important to
conduct additive fabrication processes with a resin having
sufficient viscosity stability over time. Filled liquid radiation
curable resins for additive fabrication possess a well-known
amplified tendency to increase in viscosity over time than versus
traditional unfilled resins. This exacerbates the aforementioned
problems associated with the high initial viscosities of filled
compositions, resulting in increasingly less efficient, more costly
additive fabrication processes over time.
[0015] Additionally, highly filled compositions are usually not as
thermal- or photo-stable as non-filled liquid radiation curable
resins for additive fabrication. Photo stability is the ability of
a liquid radiation curable resin to maintain its viscosity after
exposure to ambient light and undesirable light scattering in
additive fabrication machines. Thermal stability is the ability of
a liquid radiation curable resin to maintain its viscosity after
exposure to elevated temperatures, which are known to accelerate
cationic polymerization. Because liquid radiation curable resins
for additive fabrication include reactive species that are
responsive to undesirable ambient light scattering that occurs as a
result of contact with crystallized filled particles, partial
uncontrolled polymerization occurs in the liquid radiation curable
resin after it is exposed to light. This small amount of
uncontrolled polymerization, over time, is accelerated if the resin
is stored at elevated temperatures. These factors cause the
viscosity of the liquid radiation curable resin to increase
gradually--but significantly--over time. Thus achieving sufficient
viscosity stability is particularly challenging in highly filled
liquid radiation curable resins because of additional light
scattering effects caused by the filler.
[0016] A third problem traditionally associated with filled liquid
radiation curable compositions for additive fabrication is their
tendency to phase separate in storage or a vat over time. This
phase separation, whereby the inorganic filler loses its state of
homogeneous suspension in the surrounding liquid radiation curable
resin, results in a vat made up of a bifurcated composition: (1) a
low-viscosity, largely unfilled top portion, and (2) a
supersaturated, high-viscosity bottom portion. The resin in the top
portion of a vat is not able to produce cured parts possessing
sufficient strength and stiffness (because of a lack of filled
component present in the composition), while the bottom portion is
devoid of any suitability for additive fabrication at all (due to
an excess of filled particles). Despite the historical inclusion of
inorganic particles designed for anti-sedimentation, existing
filled liquid radiation curable compositions for additive
fabrication invariably eventually settle, either into a "soft pack"
or a "hard pack." In the more benign settling phenomenon, a soft
pack, the settled filler forms a waxy portion at the bottom of a
storage container or vat. The settled filler is frequently
surrounded by partially polymerized resin, resulting in the
wax-like consistency. Although re-assimilation into the liquid
radiation curable resin as a whole is possible, it requires
frequent and often vigorous recirculation. This is a time- and
energy-consuming maintenance process, and still does not obviate a
resin's eventual viscosity increase, due to the rampant partial
polymerization.
[0017] Still other filled liquid radiation curable compositions for
additive fabrication settle into an undesirable "hard pack." Hard
pack occurs whereby the inorganic filler settles to the bottom of a
storage container or vat, forming a concrete-like piece or pieces.
These pieces must be broken up by a drill or similar apparatus, and
are typically unable to be re-assimilated into the liquid radiation
curable resin as a whole. This shortens the shelf-life of such
resins, or results in changing and inconsistent properties in the
cured parts made therefrom, due to the changing amounts of filler
component which are not re-miscible into the solution. Thus, it is
especially desirable to formulate a liquid radiation curable resin
composition for additive fabrication which, in addition to the
other required performance characteristics mentioned above,
possesses superior anti-sedimentation capabilities.
[0018] Various other patents or patent publications also describe
using inorganic filled compositions comprising, inter alia, silica
microparticles and/or nanoparticles, among them:
[0019] U.S. Pat. No. 6,013,714 (Haruta et al.), assigned to DSM IP
Assets, B.V., which describes additive fabrication processes that
utilizes filled resins to performing a combination of steps,
including (1) applying a thin layer of resin on a supporting stage;
(2) selectively irradiating the thin layer of resin as to cure a
selected part of said resin; (3) applying a further thin layer of
resin; and repeating steps (2) and (3) as to obtain a three
dimensional shape of a plurality of cured layers, optionally
combined with either one of the steps of washing and post-curing
the three dimensional shape, as to obtain the mold, wherein the
resin composition is formulated from constituents comprises at
least one photoreaction monomer at least one photoinitiator at
least one filler.
[0020] U.S. Pat. Pub. No. 20050040562 (Steinmann et al.), assigned
to 3D Systems, Inc., which describes a process for forming a
three-dimensional article by stereolithography, said process
comprising the steps: 1) coating a thin layer of a liquid
radiation-curable composition onto a surface of said composition
including at least one filler comprising silica-type nano-particles
suspended in the radiation-curable composition: 2) exposing said
thin layer imagewise to actinic radiation to form an imaged
cross-section, wherein the radiation is of sufficient intensity to
cause substantial curing of the thin layer in the exposed areas; 3)
coating a thin layer of the composition onto the previously exposed
imaged cross-section; 4) exposing said thin layer from step (3)
imagewise to actinic radiation to form an additional imaged
cross-section, wherein the radiation is of sufficient intensity to
cause substantial curing of the thin layer in the exposed areas and
to cause adhesion to the previously exposed imaged cross-section;
5) repeating steps (3) and (4) a sufficient number of times in
order to build up the three-dimensional article.
[0021] U.S. Pat. Pub. No. 20120251841 (Southwell et al.), assigned
to DSM IP Assets B.V., which describes liquid radiation curable
resins for additive fabrication comprising an R-substituted
aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator and
silica nanoparticles. Also disclosed is a process for using the
liquid radiation curable resins for additive fabrication and
three-dimensional articles made from the liquid radiation curable
resins for additive fabrication.
[0022] From the foregoing, it is evident that no filled liquid
radiation curable compositions for additive fabrication exist that
are suitable for producing cured components having adequate
application-specific heat resistance and structural rigidity, while
simultaneously overcoming the long-felt but unsolved industry needs
of providing the requisite low initial viscosity, high viscosity
stability, and high phase-separation resistance.
BRIEF SUMMARY
[0023] The first aspect of the claimed invention is a liquid
radiation curable composition for additive fabrication comprising:
[0024] (a) a cationically polymerizable aliphatic epoxide; [0025]
(b) a multifunctional (meth)acrylate component; [0026] (c) a
cationic photoinitiator; [0027] (d) a free-radical photoinitiator;
and [0028] (e) a filled matrix comprising [0029] a nanoparticle
constituent comprising a plurality of inorganic nanoparticles, and
[0030] a microparticle constituent comprising a plurality of
inorganic microparticles; [0031] wherein the ratio by weight of the
microparticle constituent to the nanoparticle constituent is from
about 1:1 to about 12:1, more preferably from about 4:1 to about
8:1, and wherein the ratio of the average particle size of the
inorganic microparticles in the microparticle constituent to the
average particle size of the inorganic nanoparticles in the
nanoparticle constituent is from about 2.41:1 to about 200:1, more
preferably from about 6.46:1 to about 100:1.
[0032] The second aspect of the claimed invention is a process of
forming a three-dimensional object comprising the steps of forming
and selectively curing a layer of the liquid radiation curable
resin composition according to the present invention as described
herein with actinic radiation and repeating the steps of forming
and selectively curing a layer of the liquid radiation curable
resin composition for additive fabrication as described herein a
plurality of times to obtain a three-dimensional object.
[0033] The third aspect of the claimed invention is the
three-dimensional object formed from the liquid radiation curable
resin of the first aspect of the present invention by the process
of the second aspect of the claimed invention.
[0034] The fourth aspect of the claimed invention is a liquid
radiation curable resin for additive fabrication comprising: [0035]
(a) a cationically polymerizable component; [0036] (b) a
(meth)acrylate component; [0037] (c) a cationic photoinitiator;
[0038] (d) a free-radical photoinitiator; and [0039] (e) a filled
matrix, further comprising [0040] a filled particle dispersion
containing [0041] a nanoparticle constituent made up of a plurality
of silica nanoparticles having an average particle size of at least
about 50 nanometers, and a solvent, and [0042] a microparticle
constituent made up of a plurality of inorganic microparticles;
[0043] wherein the ratio by weight of the microparticle constituent
to the nanoparticle constituent is from about 1:1 to about 12:1;
and [0044] wherein the filled particle dispersion has a particle
dispersion pH of greater than about 5.5.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] FIG. 1 depicts a two-dimensional cross-sectional view of an
embodiment of a square configuration filled matrix of the present
invention.
[0046] FIG. 2 depicts a two-dimensional cross-sectional view of an
embodiment of a triangular configuration filled matrix of the
present invention.
DETAILED DESCRIPTION
[0047] An embodiment of the claimed invention is a liquid radiation
curable composition for additive fabrication, comprising: [0048]
(a) a cationically polymerizable aliphatic epoxide; [0049] (b) a
multifunctional (meth)acrylate component; [0050] (c) a cationic
photoinitiator; [0051] (d) a free-radical photoinitiator; and
[0052] (e) a filled matrix comprising [0053] a nanoparticle
constituent comprising a plurality of inorganic nanoparticles, and
[0054] a microparticle constituent comprising a plurality of
inorganic microparticles; [0055] wherein the ratio by weight of the
microparticle constituent to the nanoparticle constituent is from
about 1:1 to about 12:1, more preferably from about 4:1 to about
8:1, and wherein the ratio of the average particle size of the
inorganic microparticles in the microparticle constituent to the
average particle size of the inorganic nanoparticles in the
nanoparticle constituent is from about 2.41:1 to about 200:1, more
preferably from about 6.46:1 to about 100:1.
Cationically Polymerizable Component
[0056] In accordance with an embodiment, the liquid radiation
curable resins for additive fabrication of the invention comprise
at least one cationically polymerizable component; that is a
component which undergoes polymerization initiated by cations or in
the presence of acid generators. The cationically polymerizable
components may be monomers, oligomers, and/or polymers, and may
contain aliphatic, aromatic, cycloaliphatic, arylaliphatic,
heterocyclic moiety(ies), and any combination thereof. Suitable
cyclic ether compounds can comprise cyclic ether groups as side
groups or groups that form part of an alicyclic or heterocyclic
ring system.
[0057] The cationic polymerizable component is selected from the
group consisting of cyclic ether compounds, cyclic acetal
compounds, cyclic thioethers compounds, spiro-orthoester compounds,
cyclic lactone compounds, and vinyl ether compounds, and any
combination thereof.
[0058] Suitable cationically polymerizable components include
cyclic ether compounds such as epoxy compounds and oxetanes, cyclic
lactone compounds, cyclic acetal compounds, cyclic thioether
compounds, spiro orthoester compounds, and vinylether compounds.
Specific examples of cationically polymerizable components include
bisphenol A diglycidyl ether, bisphenol F diglycidyl ether,
bisphenol S diglycidyl ether, brominated bisphenol A diglycidyl
ether, brominated bisphenol F diglycidyl ether, brominated
bisphenol S diglycidyl ether, epoxy novolac resins, hydrogenated
bisphenol A diglycidyl ether, hydrogenated bisphenol F diglycidyl
ether, hydrogenated bisphenol S diglycidyl ether,
3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate,
2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)-cyclohexane-1,4-dioxane,
bis(3,4-epoxycyclohexylmethyl)adipate, vinylcyclohexene oxide,
4-vinylepoxycyclohexane, vinylcyclohexene dioxide, limonene oxide,
limonene dioxide, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate,
3,4-epoxy-6-methylcyclohexyl-3',4'-epoxy-6'-methylcyclohexanecarboxylate,
.epsilon.-caprolactone-modified
3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylates,
trimethylcaprolactone-modified
3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylates,
.beta.-methyl-.delta.-valerolactone-modified
3,4-epoxycyclohexcylmethyl-3',4'-epoxycyclohexane carboxylates,
methylenebis(3,4-epoxycyclohexane), bicyclohexyl-3,3'-epoxide,
bis(3,4-epoxycyclohexyl) with a linkage of --O--, --S--, --SO--,
--SO.sub.2--, --C(CH.sub.3).sub.2--, --CBr.sub.2--,
--C(CBr.sub.3).sub.2--, --C(CF.sub.3).sub.2--,
--C(CCl.sub.3).sub.2--, or --CH(C.sub.6H.sub.5)--,
dicyclopentadiene diepoxide, di(3,4-epoxycyclohexylmethyl) ether of
ethylene glycol, ethylenebis(3,4-epoxycyclohexanecarboxylate),
epoxyhexahydrodioctylphthalate, epoxyhexahydro-di-2-ethylhexyl
phthalate, 1,4-butanediol diglycidyl ether, 1,6-hexanediol
diglycidyl ether, neopentylglycol diglycidyl ether, glycerol
triglycidyl ether, trimethylolpropane triglycidyl ether,
polyethylene glycol diglycidyl ether, polypropylene glycol
diglycidyl ether, diglycidyl esters of aliphatic long-chain dibasic
acids, monoglycidyl ethers of aliphatic higher alcohols,
monoglycidyl ethers of phenol, cresol, butyl phenol, or polyether
alcohols obtained by the addition of alkylene oxide to these
compounds, glycidyl esters of higher fatty acids, epoxidated
soybean oil, epoxybutylstearic acid, epoxyoctylstearic acid,
epoxidated linseed oil, epoxidated polybutadiene,
1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene,
3-ethyl-3-hydroxymethyloxetane,
3-ethyl-3-(3-hydroxypropyl)oxymethyloxetane,
3-ethyl-3-(4-hydroxybutyl)oxymethyloxetane,
3-ethyl-3-(5-hydroxypentyl)oxymethyloxetane,
3-ethyl-3-phenoxymethyloxetane,
bis((l-ethyl(3-oxetanyl))methyl)ether,
3-ethyl-3-((2-ethylhexyloxy)methyl)oxetane,
3-ethyl-((triethoxysilylpropoxymethyl)oxetane,
3-(meth)-allyloxymethyl-3-ethyloxetane,
3-hydroxymethyl-3-ethyloxetane,
(3-ethyl-3-oxetanylmethoxy)methylbenzene,
4-fluoro-[1-(3-ethyl-3-oxetanylmethoxy)methyl]benzene,
4-methoxy-[1-(3-ethyl-3-oxetanylmethoxy)methyl]-benzene,
[1-(3-ethyl-3-oxetanylmethoxy)ethyl]phenyl ether,
isobutoxymethyl(3-ethyl-3-oxetanylmethyl)ether,
2-ethylhexyl(3-ethyl-3-oxetanylmethyl)ether, ethyldiethylene
glycol(3-ethyl-3-oxetanylmethyl)ether, dicyclopentadiene
(3-ethyl-3-oxetanylmethyl)ether,
dicyclopentenyloxyethyl(3-ethyl-3-oxetanylmethyl)ether,
dicyclopentenyl(3-ethyl-3-oxetanylmethyl)ether,
tetrahydrofurfuyl(3-ethyl-3-oxetanylmethyl)ether,
2-hydroxyethyl(3-ethyl-3-oxetanylmethyl)ether,
2-hydroxypropyl(3-ethyl-3-oxetanylmethyl)ether, and any combination
thereof.
[0059] The cationically polymerizable component may optionally also
contain polyfunctional materials including dendritic polymers such
as dendrimers, linear dendritic polymers, dendrigraft polymers,
hyperbranched polymers, star branched polymers, and hypergraft
polymers with epoxy or oxetane functional groups. The dendritic
polymers may contain one type of polymerizable functional group or
different types of polymerizable functional groups, for example,
epoxy and oxetane functions.
[0060] In an embodiment, the composition of the present invention
also comprises one or more mono or poly glycidylethers of aliphatic
alcohols, aliphatic polyols, polyesterpolyols or polyetherpolyols.
Examples of preferred components include
1,4-butanedioldiglycidylether, glycidylethers of polyoxyethylene
and polyoxypropylene glycols and triols of molecular weights from
about 200 to about 10,000; glycidylethers of polytetramethylene
glycol or poly(oxyethylene-oxybutylene) random or block copolymers.
In a specific embodiment, the cationically polymerizable component
comprises a polyfunctional glycidylether that lacks a cyclohexane
ring in the molecule. In another specific embodiment, the
cationically polymerizable component includes a neopentyl glycol
diglycidyl ether. In another specific embodiment, the cationically
polymerizable component includes a 1,4 cyclohexanedimethanol
diglycidyl ether.
[0061] Examples of commercially available preferred polyfunctional
glycidylethers are Erisys.TM. GE 22 (Erisys.TM. products are
available from Emerald Performance Materials.TM.), Heloxy.TM. 48,
Heloxy.TM. 67, Heloxy.TM. 68, Heloxy.TM. 107 (Heloxy.TM. modifiers
are available from Momentive Specialty Chemicals), and
Grilonit.RTM. F713. Examples of commercially available preferred
monofunctional glycidylethers are Heloxy.TM. 71, Heloxy.TM. 505,
Heloxy.TM. 7, Heloxy.TM. 8, and Heloxy.TM. 61.
[0062] In an embodiment, the epoxide is
3,4-epoxycyclohexylmethyl-3',4-epoxycyclohexanecarboxylate
(available as CELLOXIDE.TM. 2021P from Daicel Chemical, or as
CYRACURE.TM. UVR-6105 from Dow Chemical), hydrogenated bisphenol
A-epichlorohydrin based epoxy resin (available as EPON.TM. 1510
from Momentive), 1,4-cyclohexanedimethanol diglycidyl ether
(available as HELOXY.TM. 107 from Momentive), a hydrogenated
bisphenol A diglycidyl ether (available as EPON.TM. 825 from
Momentive) a mixture of dicyclohexyl diepoxide and nanosilica
(available as NANOPDX.TM.), and any combination thereof.
[0063] The above-mentioned cationically polymerizable compounds can
be used singly or in combination of two or more thereof. In
embodiments of the invention, the cationic polymerizable component
further comprises at least two different epoxy components. In a
specific embodiment, the cationic polymerizable component includes
a cycloaliphatic epoxy, for example, a cycloaliphatic epoxy with 2
or more than 2 epoxy groups. In another specific embodiment, the
cationic polymerizable component includes an epoxy having an
aromatic or aliphatic glycidyl ether group with 2 (difunctional) or
more than 2 (polyfunctional) epoxy groups.
[0064] The liquid radiation curable resin for additive fabrication
can therefore include suitable amounts of the cationic
polymerizable component, for example, in certain embodiments, in an
amount from about 10 to about 80% by weight of the resin
composition, in further embodiments from about 20 to about 70 wt %
of the resin composition, and in further embodiments from about 25
to about 65 wt % of the resin composition.
[0065] In other embodiments of the invention, the cationic
polymerizable component also optionally comprises an oxetane
component. In a specific embodiment, the cationic polymerizable
component includes an oxetane, for example, an oxetane containing
1, 2 or more than 2 oxetane groups. If utilized in the composition,
the oxetane component is present in a suitable amount from about 5
to about 30 wt % of the resin composition. In another embodiment,
the oxetane component is present in an amount from about 10 to
about 25 wt % of the resin composition, and in yet another
embodiment, the oxetane component is present in an amount from 20
to about 30 wt % of the resin composition.
[0066] In accordance with an embodiment, the liquid radiation
curable resin composition for additive fabrication contains a
component that is polymerizable by both free-radical polymerization
and cationic polymerization. An example of such a polymerizable
component is a vinyloxy compound, for example, one selected from
the group consisting of bis(4-vinyloxybutyl)isophthalate,
tris(4-vinyloxybutyl) trimellitate, and combinations thereof. Other
examples of such a polymerizable component include those containing
an acrylate and an epoxy group, or an acrylate and an oxetane
group, on a same molecule.
Radically Polymerizable Component
[0067] In accordance with an embodiment of the invention, the
liquid radiation curable resin for additive fabrication of the
invention comprises at least one free-radical polymerizable
component, that is, a component which undergoes polymerization
initiated by free radicals. The free-radical polymerizable
components are monomers, oligomers, and/or polymers; they are
monofunctional or polyfunctional materials, i.e., have 1, 2, 3, 4,
5, 6, 7, 8, 9, 10 . . . 20 . . . 30 . . . 40 . . . 50 . . . 100, or
more functional groups that can polymerize by free radical
initiation, may contain aliphatic, aromatic, cycloaliphatic,
arylaliphatic, heterocyclic moiety(ies), or any combination
thereof. Examples of polyfunctional materials include dendritic
polymers such as dendrimers, linear dendritic polymers, dendrigraft
polymers, hyperbranched polymers, star branched polymers, and
hypergraft polymers; see, e.g., US 2009/0093564 A1. The dendritic
polymers may contain one type of polymerizable functional group or
different types of polymerizable functional groups, for example,
acrylates and methacrylate functions.
[0068] Examples of free-radical polymerizable components include
acrylates and methacrylates such as isobornyl (meth)acrylate,
bornyl (meth)acrylate, tricyclodecanyl (meth)acrylate,
dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate,
cyclohexyl (meth)acrylate, benzyl (meth)acrylate, 4-butylcyclohexyl
(meth)acrylate, acryloyl morpholine, (meth)acrylic acid,
2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,
2-hydroxybutyl (meth)acrylate, methyl (meth)acrylate, ethyl
(meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate,
butyl (meth)acrylate, amyl (meth)acrylate, isobutyl (meth)acrylate,
t-butyl (meth)acrylate, pentyl (meth)acrylate, caprolactone
acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, heptyl
(meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate,
2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl
(meth)acrylate, isodecyl (meth)acrylate, tridecyl (meth)acrylate,
undecyl (meth)acrylate, lauryl (meth)acrylate, stearyl
(meth)acrylate, isostearyl (meth)acrylate, tetrahydrofurfuryl
(meth)acrylate, butoxyethyl (meth)acrylate, ethoxydiethylene glycol
(meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate,
polyethylene glycol mono(meth)acrylate, polypropylene glycol
mono(meth)acrylate, methoxyethylene glycol (meth)acrylate,
ethoxyethyl (meth)acrylate, methoxypolyethylene glycol
(meth)acrylate, methoxypolypropylene glycol (meth)acrylate,
diacetone (meth)acrylamide, beta-carboxyethyl (meth)acrylate,
phthalic acid (meth)acrylate, dimethylaminoethyl (meth)acrylate,
diethylaminoethyl (meth)acrylate, butylcarbamylethyl
(meth)acrylate, n-isopropyl (meth)acrylamide fluorinated
(meth)acrylate, 7-amino-3,7-dimethyloctyl (meth)acrylate.
[0069] Examples of polyfunctional free-radical polymerizable
components include those with (meth)acryloyl groups such as
trimethylolpropane tri(meth)acrylate, pentaerythritol
(meth)acrylate, ethylene glycol di(meth)acrylate, bisphenol A
diglycidyl ether di(meth)acrylate, dicyclopentadiene dimethanol
di(meth)acrylate,
[2-[1,1-dimethyl-2-[(1-oxoallyl)oxy]ethyl]-5-ethyl-1,3-dioxan-5-yl]methyl
acrylate;
3,9-bis(1,1-dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro[5.5-
]undecane di(meth)acrylate; dipentaerythritol
monohydroxypenta(meth)acrylate, propoxylated trimethylolpropane
tri(meth)acrylate, propoxylated neopentyl glycol di(meth)acrylate,
tetraethylene glycol di(meth)acrylate, polyethylene glycol
di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol
di(meth)acrylate, neopentyl glycol di(meth)acrylate, polybutanediol
di(meth)acrylate, tripropyleneglycol di(meth)acrylate, glycerol
tri(meth)acrylate, phosphoric acid mono- and di(meth)acrylates,
C.sub.7-C.sub.20 alkyl di(meth)acrylates,
tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate,
tris(2-hydroxyethyl)isocyanurate di(meth)acrylate, pentaerythritol
tri(meth)acrylate, pentaerythritol tetra(meth)acrylate,
dipentaerythritol hexa(meth)crylate, tricyclodecane diyl dimethyl
di(meth)acrylate and alkoxylated versions (e.g., ethoxylated and/or
propoxylated) of any of the preceding monomers, and also
di(meth)acrylate of a diol which is an ethylene oxide or propylene
oxide adduct to bisphenol A, di(meth)acrylate of a diol which is an
ethylene oxide or propylene oxide adduct to hydrogenated bisphenol
A, epoxy (meth)acrylate which is a (meth)acrylate adduct to
bisphenol A of diglycidyl ether, diacrylate of polyoxyalkylated
bisphenol A, and triethylene glycol divinyl ether, and adducts of
hydroxyethyl acrylate.
[0070] In accordance with an embodiment, the radically
polymerizable component is a polyfunctional (meth)acrylate. The
polyfunctional (meth)acrylates may include all methacryloyl groups,
all acryloyl groups, or any combination of methacryloyl and
acryloyl groups. In an embodiment, the free-radical polymerizable
component is selected from the group consisting of bisphenol A
diglycidyl ether di(meth)acrylate, ethoxylated or propoxylated
bisphenol A or bisphenol F di(meth)acrylate, dicyclopentadiene
dimethanol di(meth)acrylate,
[2-[1,1-dimethyl-2-[(1-oxoallyl)oxy]ethyl]-5-ethyl-1,3-dioxan-5-yl]methyl
acrylate, dipentaerythritol monohydroxypenta(meth)acrylate,
dipentaerythritol penta(meth)acrylate, dipentaerythritol
hexa(meth)crylate, propoxylated trimethylolpropane
tri(meth)acrylate, and propoxylated neopentyl glycol
di(meth)acrylate, and any combination thereof.
[0071] In a preferred embodiment, the polyfunctional (meth)acrylate
has more than 2, more preferably more than 3, and more preferably
greater than 4 functional groups.
[0072] In another preferred embodiment, the radically polymerizable
component consists exclusively of a single polyfunctional
(meth)acrylate component. In further embodiments, the exclusive
radically polymerizable component is tetra-functional, in further
embodiments, the exclusive radically polymerizable component is
penta-functional, and in further embodiments, the exclusive
radically polymerizable component is hexa-functional.
[0073] In another embodiment, the free-radical polymerizable
component is selected from the group consisting of bisphenol A
diglycidyl ether diacrylate, dicyclopentadiene dimethanol
diacrylate,
[2-[1,1-dimethyl-2-[(1-oxoallyl)oxy]ethyl]-5-ethyl-1,3-dioxan-5-yl]methyl
acrylate, dipentaerythritol monohydroxypentaacrylate, propoxylated
trimethylolpropane triacrylate, and propoxylated neopentyl glycol
diacrylate, and any combination thereof.
[0074] In specific embodiments, the liquid radiation curable resins
for additive fabrication of the invention include one or more of
bisphenol A diglycidyl ether di(meth)acrylate, dicyclopentadiene
dimethanol di(meth)acrylate, dipentaerythritol
monohydroxypenta(meth)acrylate, propoxylated trimethylolpropane
tri(meth)acrylate, and/or propoxylated neopentyl glycol
di(meth)acrylate, and more specifically one or more of bisphenol A
diglycidyl ether diacrylate, dicyclopentadiene dimethanol
diacrylate, dipentaerythritol pentaacrylate, propoxylated
trimethylolpropane triacrylate, and/or propoxylated neopentyl
glycol diacrylate.
[0075] The above-mentioned radically polymerizable compounds can be
used singly or in combination of two or more thereof. The liquid
radiation curable resin for additive fabrication can include any
suitable amount of the free-radical polymerizable components, for
example, in certain embodiments, in an amount up to about 40 wt %
of the resin composition, in certain embodiments, from about 2 to
about 40 wt % of the resin composition, in other embodiments from
about 5 to about 30 wt %, and in further embodiments from about 10
to about 20 wt % of the resin composition.
Hydroxy Functional Components
[0076] Many of the known liquid radiation curable resin
compositions for additive fabrication use hydroxy-functional
compounds to enhance the properties of the parts made from the
resin compositions.
[0077] In certain embodiments of the invention, the resin
composition may optionally contain a hydroxy-functional component.
The hydroxyl-containing material which can be used in the present
invention may be any suitable organic material having a hydroxyl
functionality of at least 1. If present, the material is preferably
substantially free of any groups which interfere with the curing
reactions or which are thermally or photolytically unstable.
[0078] If present, any hydroxy group may be employed for the
particular purpose. If present, the hydroxyl-containing material
preferably contains one or more primary or secondary aliphatic
hydroxyl. The hydroxyl group may be internal in the molecule or
terminal. Monomers, oligomers or polymers can be used. The hydroxyl
equivalent weight, i.e., the number average molecular weight
divided by the number of hydroxyl groups, is preferably in the
range of 31 to 5000.
[0079] Representative examples of hydroxyl-containing materials
having a hydroxyl functionality of 1 include alkanols, monoalkyl
ethers of polyoxyalkyleneglycols, mohoalkyl ethers of
alkyleneglycols, and others, and combinations thereof.
[0080] Representative examples of monomeric polyhydroxy organic
materials include alkylene and arylalkylene glycols and polyols,
such as 1,2,4-butanetriol, 1,2,6-hexanetriol, 1,2,3-heptanetriol,
2,6-dimethyl-1,2,6-hexanetriol,
(2R,3R)-(-)-2-benzyloxy-1,3,4-butanetriol, 1,2,3-hexanetriol,
1,2,3-butanetriol, 3-methyl-1,3,5-pentanetriol,
1,2,3-cyclohexanetriol, 1,3,5-cyclohexanetriol,
3,7,11,15-tetramethyl-1,2,3-hexadecanetriol,
2-hydroxymethyltetrahydropyran-3,4,5-triol,
2,2,4,4-tetramethyl-1,3-cyclobutanediol, 1,3-cyclopentanediol,
trans-1,2-cyclooctanediol, 1,16-hexadecanediol,
3,6-dithia-1,8-octanediol, 2-butyne-1,4-diol, 1,3-propanediol,
1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol,
1,8-octanediol, 1,9-nonanediol, 1-phenyl-1,2-ethanediol,
1,2-cyclohexanediol, 1,5-decalindiol,
2,5-dimethyl-3-hexyne-2,5-diol,
2,7-dimethyl-3,5-octadiyne-2-7-diol, 2,3-butanediol,
1,4-cyclohexanedimethanol, and combinations thereof.
[0081] Representative examples of oligomeric and polymeric
hydroxyl-containing materials include polyoxyethylene and
polyoxypropylene glycols and triols of molecular weights from about
200 to about 10,000; polytetramethylene glycols of varying
molecular weight; poly(oxyethylene-oxybutylene) random or block
copolymers; copolymers containing pendant hydroxy groups formed by
hydrolysis or partial hydrolysis of vinyl acetate copolymers,
polyvinylacetal resins containing pendant hydroxyl groups;
hydroxy-terminated polyesters and hydroxy-terminated polylactones;
hydroxy-functionalized polyalkadienes, such as polybutadiene;
aliphatic polycarbonate polyols, such as an aliphatic polycarbonate
diol; and hydroxy-terminated polyethers, and combinations
thereof.
[0082] If present, preferred hydroxyl-containing monomers include
1,4-cyclohexanedimethanol and aliphatic and cycloaliphatic
monohydroxy alkanols. Such preferred hydroxyl-containing oligomers
and polymers include hydroxyl and hydroxyl/epoxy functionalized
polybutadiene, polycaprolactone diols and triols, ethylene/butylene
polyols, and monohydroxyl functional monomers. Preferred examples
of polyether polyols are polypropylene glycols of various molecular
weights and glycerol propoxylate-B-ethoxylate triol. If present,
especially preferred are linear and branched polytetrahydrofuran
polyether polyols available in various molecular weights, such as
in the range of 150-4000 g/mol, preferably in the range of 150-1500
g/mol, more preferably in the range of 150-750 g/mol.
[0083] If present, the resin composition preferably comprises,
relative to the total weight of the resin composition, at most 10
wt % of one or more non-free radical polymerizable
hydroxy-functional compounds, more preferably at most 5 wt %, and
most preferably at most 2 wt %.
[0084] In embodiments, the liquid radiation curable resin for
additive fabrication of the present invention includes a
photoinitiating system. The photoinitiating system can include a
free-radical photoinitiator and/or a cationic photoinitiator. In
accordance with an embodiment, the liquid radiation curable resin
composition includes a photoinitiating system contains at least one
photoinitiator having a cationic initiating function, and at least
one photoinitiator having a free radical initiating function.
Additionally, the photoinitiating system can include a
photoinitiator that contains both free-radical initiating function
and cationic initiating function on the same molecule. The
photoinitiator is a compound that chemically changes due to the
action of light or the synergy between the action of light and the
electronic excitation of a sensitizing dye to produce at least one
of a radical, an acid, and a base.
Cationic Photoinitiator
[0085] In accordance with an embodiment, the liquid radiation
curable resin composition includes a cationic photoinitiator. The
cationic photoinitiator initiates cationic ring-opening
polymerization upon irradiation of light.
[0086] In an embodiment, any suitable cationic photoinitiator can
be used, for example, those with cations selected from the group
consisting of onium salts, halonium salts, iodosyl salts, selenium
salts, sulfonium salts, sulfoxonium salts, diazonium salts,
metallocene salts, isoquinolinium salts, phosphonium salts,
arsonium salts, tropylium salts, dialkylphenacylsulfonium salts,
thiopyrilium salts, diaryl iodonium salts, triaryl sulfonium salts,
ferrocenes, di(cyclopentadienyliron)arene salt compounds, and
pyridinium salts, and any combination thereof.
[0087] In another embodiment, the cation of the cationic
photoinitiator is selected from the group consisting of aromatic
diazonium salts, aromatic sulfonium salts, aromatic iodonium salts,
metallocene based compounds, aromatic phosphonium salts, and any
combination thereof. In another embodiment, the cation is a
polymeric sulfonium salt, such as in U.S. Pat. No. 5,380,923 or
U.S. Pat. No. 5,047,568, or other aromatic heteroatom-containing
cations and naphthyl-sulfonium salts such as in U.S. Pat. No.
7,611,817, U.S. Pat. No. 7,230,122, US2011/0039205, US2009/0182172,
U.S. Pat. No. 7,678,528, EP2308865, WO2010046240, or EP2218715. In
another embodiment, the cationic photoinitiator is selected from
the group consisting of triarylsulfonium salts, diaryliodonium
salts, and metallocene based compounds, and any combination
thereof. Onium salts, e.g., iodonium salts and sulfonium salts, and
ferrocenium salts, have the advantage that they are generally more
thermally stable.
[0088] In a particular embodiment, the cationic photoinitiator has
an anion selected from the group consisting of BF.sub.4.sup.-,
AsF.sub.6.sup.-, SbF.sub.6.sup.-, PF.sub.6.sup.-,
[B(CF.sub.3).sub.4].sup.-, B(C.sub.6F.sub.5).sub.4.sup.-,
B[C.sub.6H.sub.3-3,5 (CF.sub.3).sub.2].sub.4.sup.-,
B(C.sub.6H.sub.4CF.sub.3).sub.4.sup.-,
B(C.sub.6H.sub.3F.sub.2).sub.4.sup.-,
B[C.sub.6F.sub.4-4(CF.sub.3)].sub.4.sup.-,
Ga(C.sub.6F.sub.5).sub.4.sup.-,
[(C.sub.6F.sub.5).sub.3B--C.sub.3H.sub.3N.sub.2--B(C.sub.6F.sub.5).sub.3]-
.sup.-,
[(C.sub.6F.sub.5).sub.3B--NH.sub.2--B(C.sub.6F.sub.5).sub.3].sup.--
, tetrakis(3,5-difluoro-4-alkyloxyphenyl)borate,
tetrakis(2,3,5,6-tetrafluoro-4-alkyloxyphenyl)borate,
perfluoroalkylsulfonates, tris[(perfluoroalkyl)sulfonyl]methides,
bis[(perfluoroalkyl)sulfonyl]imides, perfluoroalkylphosphates,
tris(perfluoroalkyl)trifluorophosphates,
bis(perfluoroalkyl)tetrafluorophosphates,
tris(pentafluoroethyl)trifluorophosphates, and
(CH.sub.6B.sub.11Br.sub.6).sup.-, (CH.sub.6B.sub.11Cl.sub.6).sup.-
and other halogenated carborane anions.
[0089] A survey of other onium salt initiators and/or metallocene
salts can be found in "UV Curing, Science and Technology", (Editor
S. P. Pappas, Technology Marketing Corp., 642 Westover Road,
Stamford, Conn., U.S.A.) or "Chemistry & Technology of UV &
EB Formulation for Coatings, Inks & Paints", Vol. 3 (edited by
P. K. T. Oldring).
[0090] In an embodiment, the cationic photoinitiator has a cation
selected from the group consisting of aromatic sulfonium salts,
aromatic iodonium salts, and metallocene based compounds with at
least an anion selected from the group consisting of
SbF.sub.6.sup.-, PF.sub.6.sup.-, B(C.sub.6F.sub.5).sub.4.sup.-,
[B(CF.sub.3).sub.4].sup.-,
tetrakis(3,5-difluoro-4-methoxyphenyl)borate,
perfluoroalkylsulfonates, perfluoroalkylphosphates,
tris[(perfluoroalkyl)sulfonyl]methides, and
[(C.sub.2F.sub.5).sub.3PF.sub.3].sup.-.
[0091] Examples of cationic photoinitiators useful for curing at
300-475 nm, particularly at 365 nm UV light, without a sensitizer
include
4-[4-(3-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfonium
hexafluoroantimonate,
4-[4-(3-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfonium
tetrakis(pentafluorophenyl)borate,
4-[4-(3-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfonium
tetrakis(3,5-difluoro-4-methyloxyphenyl)borate,
4-[4-(3-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfonium
tetrakis(2,3,5,6-tetrafluoro-4-methyloxyphenyl)borate,
tris(4-(4-acetylphenyl)thiophenyl)sulfonium
tetrakis(pentafluorophenyl)borate (Irgacure.RTM. PAG 290 from
BASF), tris(4-(4-acetylphenyl)thiophenyl)sulfonium
tris[(trifluoromethyl)sulfonyl]methide (Irgacure.RTM. GSID 26-1
from BASF), tris(4-(4-acetylphenyl)thiophenyl)sulfonium
hexafluorophosphate (Irgacure.RTM. 270 from BASF), and HS-1
available from San-Apro Ltd.
[0092] Preferred cationic photoinitiators include, either alone or
in a mixture: bis[4-diphenylsulfoniumphenyl]sulfide
bishexafluoroantimonate; thiophenoxyphenylsulfonium
hexafluoroantimonate (available as Chivacure 1176 from Chitec),
tris(4-(4-acetylphenyl)thiophenyl)sulfonium
tetrakis(pentafluorophenyl)borate (Irgacure.RTM. PAG 290 from
BASF), tris(4-(4-acetylphenyl)thiophenyl)sulfonium
tris[(trifluoromethyl)sulfonyl]methide (Irgacure.RTM. GSID 26-1
from BASF), and tris(4-(4-acetylphenyl)thiophenyl)sulfonium
hexafluorophosphate (Irgacure.RTM. 270 from BASF),
[4-(1-methylethyl)phenyl](4-methylphenyl) iodonium
tetrakis(pentafluorophenyl)borate (available as Rhodorsil 2074 from
Rhodia),
4-[4-(2-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfon-
ium hexafluoroantimonate (as SP-172 from Adeka), SP-300 from Adeka,
and aromatic sulfonium salts with anions of
(PF.sub.6-m(C.sub.nF.sub.2n+1).sub.m).sup.- where m is an integer
from 1 to 5, and n is an integer from 1 to 4 (available as CPI-200K
or CPI-200S, which are monovalent sulfonium salts from San-Apro
Ltd., TK-1 available from San-Apro Ltd., or HS-1 available from
San-Apro Ltd.).
[0093] In various embodiments, the liquid radiation curable resin
composition for additive fabrication may be irradiated by laser or
LED light operating at any wavelength in either the UV or visible
light spectrum. In particular embodiments, the irradiation is from
a laser or LED emitting a wavelength of from 340 nm to 415 nm. In
particular embodiments, the laser or LED source emits a peak
wavelength of about 340 nm, 355 nm, 365 nm, 375 nm, 385 nm, 395 nm,
405 nm, or 415 nm.
[0094] In an embodiment of the invention, the liquid radiation
curable resin for additive fabrication comprises an aromatic
triaryl sulfonium salt cationic photoinitiator.
[0095] Use of aromatic triaryl sulfonium salts in additive
fabrication applications is known. Please see US 20120251841 to DSM
IP Assets, B.V. (which is hereby incorporated in its entirety),
U.S. Pat. No. 6,368,769, to Asahi Denki Kogyo, which discusses
aromatic triaryl sulfonium salts with tetraryl borate anions,
including tetrakis(pentafluorophenyl)borate, and use of the
compounds in stereolithography applications. Triarylsulfonium salts
are disclosed in, for example, J Photopolymer Science & Tech
(2000), 13(1), 117-118 and J Poly Science, Part A (2008), 46(11),
3820-29. Triarylsulfonium salts Ar.sub.3S.sup.+MXn.sup.- with
complex metal halide anions such as BF.sub.4.sup.-,
AsF.sub.6.sup.-, PF.sub.6.sup.-, and SbF.sub.6.sup.-, are disclosed
in J Polymr Sci, Part A (1996), 34(16), 3231-3253.
[0096] The use of aromatic triaryl sulfonium salts as the cationic
photoinitiator in liquid radiation curable resins is desirable in
additive fabrication processes because the resulting resin attains
a fast photospeed, good thermal-stability, and good
photo-stability.
[0097] In a preferred embodiment, the cationic photoinitiator is an
aromatic triaryl sulfonium salt that is more specifically an
R-substituted aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator, having a
tetrakis(pentafluorophenyl)borate anion and a cation of the
following formula (I):
##STR00001##
[0098] wherein Y1, Y2, and Y3 are the same or different and wherein
Y1, Y2, or Y3 are R-substituted aromatic thioether with R being an
acetyl or halogen group.
[0099] In an embodiment, Y1, Y2, and Y3 are the same. In another
embodiment, Y1 and Y2 are the same, but Y3 is different. In another
embodiment, Y1, Y2, or Y3 are an R-substituted aromatic thioether
with R being an acetyl or halogen group. Preferably Y1, Y2, or Y3
are a para-R-substituted aromatic thioether with R being an acetyl
or halogen group.
[0100] A particularly preferred R-substituted aromatic thioether
triaryl sulfonium tetrakis(pentafluorophenyl)borate cationic
photoinitiator is tris(4-(4-acetylphenyl)thiophenyl)sulfonium
tetrakis(pentafluorophenyl)borate.
Tris(4-(4-acetylphenyl)thiophenyl)sulfonium
tetrakis(pentafluorophenyl)borate is known commercially as
IRGACURE.RTM. PAG-290 (formerly known by the development code
GSID4480-1) and is available from Ciba/BASF.
[0101] An R-substituted aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator, for
instance, tris(4-(4-acetylphenyl)thiophenyl)sulfonium
tetrakis(pentafluorophenyl)borate, is also more thermally-stable
than some other cationic photoinitiators. The improved
thermal-stability allows liquid radiation curable resins for
additive fabrication incorporating a triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator instead
of other conventional cationic photoinitiators to retain their
viscosity at elevated temperatures for long periods of time.
[0102] In another embodiment, the cationic photoinitiator is an
aromatic triaryl sulfonium salt that possesses an anion represented
by SbF.sub.6.sup.-, PF.sub.6.sup.-, BF.sub.4.sup.-,
(CF.sub.3CF.sub.2).sub.3PF.sub.3.sup.-,
(C.sub.6F.sub.5).sub.4B.sup.-,
((CF.sub.3).sub.2C.sub.6H.sub.3).sub.4B.sup.-,
(C.sub.6F.sub.5).sub.4Ga.sup.-,
((CF.sub.3).sub.2C.sub.6H.sub.3).sub.4Ga.sup.-,
trifluoromethanesulfonate, nonafluorobutanesulfonate,
methanesulfonate, butanesulfonate, benzenesulfonate, or
p-toluenesulfonate, and a cation of the following formula (II):
##STR00002##
[0103] wherein in formula (II), R.sup.1, R.sup.2, R.sup.3, R.sup.5
and R.sup.6 each independently represent an alkyl group, a hydroxy
group, an alkoxy group, an alkylcarbonyl group, an arylcarbonyl
group, an alkoxycarbonyl group, an aryloxycarbonyl group, an
arylthiocarbonyl group, an acyloxy group, an arylthio group, an
alkylthio group, an aryl group, a heterocyclic hydrocarbon group,
an aryloxy group, an alkylsulfinyl group, an arylsulfinyl group, an
alkylsulfonyl group, an arylsulfonyl group, a
hydroxy(poly)alkyleneoxy group, an optionally substituted amino
group, a cyano group, a nitro group, or a halogen atom, R.sup.4
represents an alkyl group, a hydroxy group, an alkoxy group, an
alkylcarbonyl group, an alkoxycarbonyl group, an acyloxy group, an
alkylthio group, a heterocyclic hydrocarbon group, an alkylsulfinyl
group, an alkylsulfonyl group, a hydroxy(poly)alkyleneoxy group, an
optionally substituted amino group, a cyano group, a nitro group,
or a halogen atom, m.sup.1 to m.sup.6 each represent the number of
occurrences of each of R.sup.1 to R.sup.6, m.sup.1, and m.sup.6
each represent an m.sup.4, integer of 0 to 5, m.sup.2, m.sup.3, and
m.sup.5 each represent an integer of 0 to 4. Such photoinitiators
are described in, for example, U.S. Pat. No. 8,617,787.
[0104] A particularly preferred aromatic triaryl sulfonium cationic
photoinitiator has an anion that is a fluoroalkyl-substituted
fluorophosphate. Commercial examples of an aromatic triaryl
sulfonium cationic photoinitiator having a fluoroalkyl-substituted
fluorophosphate anion is the CPI-200 series (for example
CPI-200K.RTM. or CPI-2105.RTM.) or 300 series, available from
San-Apro Limited.
[0105] In accordance with embodiments of the invention, the liquid
radiation curable resin for additive fabrication includes a
cationic polymerizable component in addition to an R-substituted
aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate or fluoroalkyl-substituted
fluorophosphate cationic photoinitiator. In other embodiments, the
liquid radiation curable resins for additive fabrication include
cationic polymerizable components, free-radical photoinitiators,
and free-radical polymerizable components. In some embodiments, the
liquid radiation curable resins for additive fabrication include an
R-substituted aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator and
additional cationic photoinitiators and/or photosensitizers, along
with a cationic polymerizable component and, optionally,
free-radical polymerizable components and free-radical
photoinitiators.
[0106] The liquid radiation curable resin composition can include
any suitable amount of the cationic photoinitiator, for example, in
certain embodiments, in an amount up to about 15% by weight of the
resin composition, in certain embodiments, up to about 5% by weight
of the resin composition, and in further embodiments from about 2%
to about 10% by weight of the resin composition, and in other
embodiments, from about 0.1% to about 5% by weight of the resin
composition. In a further embodiment, the amount of cationic
photoinitiator is from about 0.2 wt % to about 4 wt % of the total
resin composition, and in other embodiments from about 0.5 wt % to
about 3 wt %.
[0107] In some embodiments, depending on the wavelength of light
used for curing the liquid radiation curable resin, it is desirable
for the liquid radiation curable resin composition to include a
photosensitizer. The term "photosensitizer" is used to refer to any
substance that either increases the rate of photoinitiated
polymerization or shifts the wavelength at which polymerization
occurs; see textbook by G. Odian, Principles of Polymerization,
3.sup.rd Ed., 1991, page 222. A variety of compounds can be used as
photosensitizers, including heterocyclic and fused-ring aromatic
hydrocarbons, organic dyes, and aromatic ketones. Examples of
photosensitizers include those selected from the group consisting
of methanones, xanthenones, pyrenemethanols, anthracenes, pyrene,
perylene, quinones, xanthones, thioxanthones, benzoyl esters,
benzophenones, and any combination thereof. Particular examples of
photosensitizers include those selected from the group consisting
of [4-[(4-methylphenyl)thio]phenyl]phenyl-methanone,
isopropyl-9H-thioxanthen-9-one, 1-pyrenemethanol,
9-(hydroxymethyl)anthracene, 9,10-diethoxyanthracene,
9,10-dimethoxyanthracene, 9,10-dipropoxyanthracene,
9,10-dibutyloxyanthracene, 9-anthracenemethanol acetate,
2-ethyl-9,10-dimethoxyanthracene,
2-methyl-9,10-dimethoxyanthracene,
2-t-butyl-9,10-dimethoxyanthracene, 2-ethyl-9,10-diethoxyanthracene
and 2-methyl-9,10-diethoxyanthracene, anthracene, anthraquinones,
2-methylanthraquinone, 2-ethylanthraquinone,
2-tertbutylanthraquinone, 1-chloroanthraquinone,
2-amylanthraquinone, thioxanthones and xanthones, isopropyl
thioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone,
1-chloro-4-propoxythioxanthone, methyl benzoyl formate (Darocur MBF
from BASF), methyl-2-benzoyl benzoate (Chivacure OMB from Chitec),
4-benzoyl-4'-methyl diphenyl sulphide (Chivacure BMS from Chitec),
4,4'-bis(diethylamino) benzophenone (Chivacure EMK from Chitec),
and any combination thereof.
[0108] The novel mixtures may also contain various photoinitiators
of different sensitivity to radiation of emission lines with
different wavelengths to obtain a better utilization of a UV light
source. The use of known photoinitiators of different sensitivity
to radiation of emission lines is well known in the art of additive
fabrication, and may be selected in accordance with radiation
sources of, for example, 351, nm 355 nm, 365 nm, 385 nm, and 405
nm. In this context it is advantageous for the various
photoinitiators to be selected such, and employed in a
concentration such, that equal optical absorption is produced with
the emission lines used.
[0109] The liquid radiation curable resin composition for additive
fabrication can include any suitable amount of the photosensitizer,
for example, in certain embodiments, in an amount up to about 10%
by weight of the resin composition, in certain embodiments, up to
about 5% by weight of the resin composition, and in further
embodiments from about 0.05% to about 2% by weight of the resin
composition.
Other Cationic Photoinitiators and Photosensitizers
[0110] In accordance with an embodiment, the liquid radiation
curable resin for additive fabrication includes a cationic
photoinitiator in addition to, or in lieu of, an R-substituted
aromatic thioether triaryl sulfonium tetrakis(pentafluorophenyl)
borate cationic photoinitiator. Any suitable cationic
photoinitiator can be used, for example, those selected from the
group consisting of onium salts, halonium salts, iodosyl salts,
selenium salts, sulfonium salts, sulfoxonium salts, diazonium
salts, metallocene salts, isoquinolinium salts, phosphonium salts,
arsonium salts, tropylium salts, dialkylphenacylsulfonium salts,
thiopyrilium salts, diaryl iodonium salts, triaryl sulfonium salts,
sulfonium antimonate salts, ferrocenes,
di(cyclopentadienyliron)arene salt compounds, and pyridinium salts,
and any combination thereof. Onium salts, e.g., iodonium salts,
sulfonium salts and ferrocenes, have the advantage that they are
thermally-stable.
[0111] Preferred mixtures of cationic photoinitiators include a
mixture of: bis[4-diphenylsulfoniumphenyl]sulfide
bishexafluoroantimonate; thiophenoxyphenylsulfonium
hexafluoroantimonate (available as Chivacure 1176 from Chitec);
tris(4-(4-acetylphenyl)thiophenyl)sulfonium
tetrakis(pentafluorophenyl)borate (Irgacure PAG-290 or GSID4480-1
from Ciba/BASF), iodonium,
[4-(1-methylethyl)phenyl](4-methylphenyl)-,
tetrakis(pentafluorophenyl)borate (available as Rhodorsil 2074 from
Rhodia),
4-[4-(2-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfon-
ium hexafluoroantimonate (as SP-172) and SP-300 (both available
from Adeka).
[0112] Additionally, photosensitizers are useful in combination
with photoinitiators in effecting cure with LED light sources
emitting in the wavelength range of 300-475 nm. Examples of
suitable photosensitizers include: anthraquinones, such as
2-methylanthraquinone, 2-ethylanthraquinone,
2-tertbutylanthraquinone, 1-chloroanthraquinone, and
2-amylanthraquinone, thioxanthones and xanthones, such as isopropyl
thioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, and
1-chloro-4-propoxythioxanthone, methyl benzoyl formate (Darocur MBF
from Ciba), methyl-2-benzoyl benzoate (Chivacure OMB from Chitec),
4-benzoyl-4'-methyl diphenyl sulphide (Chivacure BMS from Chitec),
4,4'-bis(diethylamino) benzophenone (Chivacure EMK from
Chitec).
[0113] In an embodiment, the photosensitizer is a fluorone, e.g.,
5,7-diiodo-3-butoxy-6-fluorone, 5,7-diiodo-3-hydroxy-6-fluorone,
9-cyano-5,7-diiodo-3-hydroxy-6-fluorone, or a photosensitizer
is
##STR00003##
and any combination thereof.
[0114] The liquid radiation curable resin for additive fabrication
can include any suitable amount of the photosensitizer, for
example, in certain embodiments, in an amount up to about 10% by
weight of the resin composition, in certain embodiments, up to
about 5% by weight of the resin composition, and in further
embodiments from about 0.05% to about 2% by weight of the resin
composition.
[0115] When photosensitizers are employed, other photoinitiators
absorbing at shorter wavelengths can be used. Examples of such
photoinitiators include: benzophenones, such as benzophenone,
4-methyl benzophenone, 2,4,6-trimethyl benzophenone, and
dimethoxybenzophenone, and 1-hydroxyphenyl ketones, such as
1-hydroxycyclohexyl phenyl ketone, phenyl
(1-hydroxyisopropyl)ketone, 2-hydroxy-1-[4-(2-hydroxyethoxy)
phenyl]-2-methyl-1-propanone, and
4-isopropylphenyl(1-hydroxyisopropyl)ketone, benzil dimethyl ketal,
and oligo-[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]
propanone] (Esacure KIP 150 from Lamberti).
[0116] A photosensitizer or co-initiator may be used to improve the
activity of the cationic photoinitiator. It is for either
increasing the rate of photoinitiated polymerization or shifting
the wavelength at which polymerization occurs. The sensitizer used
in combination with the above-mentioned cationic photoinitiator is
not particularly limited. A variety of compounds can be used as
photosensitizers, including heterocyclic and fused-ring aromatic
hydrocarbons, organic dyes, and aromatic ketones. Examples of
sensitizers include compounds disclosed by J. V. Crivello in
Advances in Polymer Science, 62, 1 (1984), and by J. V. Crivello
& K. Dietliker, "Photoinitiators for Cationic Polymerization"
in Chemistry & technology of UV & EB formulation for
coatings, inks & paints. Volume III, Photoinitiators for free
radical and cationic polymerization. by K. Dietliker; [Ed. by P. K.
T. Oldring], SITA Technology Ltd, London, 1991. Specific examples
include polyaromatic hydrocarbons and their derivatives such as
anthracene, pyrene, perylene and their derivatives, thioxanthones,
.alpha.-hydroxyalkylphenones, 4-benzoyl-4'-methyldiphenyl sulfide,
acridine orange, and benzoflavin.
[0117] The liquid radiation curable resin for additive fabrication
can include any suitable amount of the other cationic
photoinitiator or photosensitizer, for example, in certain
embodiments, in an amount an amount from 0.1 to 10 wt % of the
resin composition, in certain embodiments, from about 1 to about 8
wt % of the resin composition, and in further embodiments from
about 2 to about 6 wt % of the resin composition. In an embodiment,
the above ranges are particularly suitable for use with epoxy
monomers.
[0118] In accordance with an embodiment, the liquid radiation
curable resin for additive fabrication includes a photoinitiating
system that is a photoinitiator having both cationic initiating
function and free radical initiating function.
Free-Radical Photoinitiator
[0119] Typically, free radical photoinitiators are divided into
those that form radicals by cleavage, known as "Norrish Type I" and
those that form radicals by hydrogen abstraction, known as "Norrish
type II". The Norrish type II photoinitiators require a hydrogen
donor, which serves as the free radical source. As the initiation
is based on a bimolecular reaction, the Norrish type II
photoinitiators are generally slower than Norrish type I
photoinitiators which are based on the unimolecular formation of
radicals. On the other hand, Norrish type II photoinitiators
possess better optical absorption properties in the near-UV
spectroscopic region. Photolysis of aromatic ketones, such as
benzophenone, thioxanthones, benzil, and quinones, in the presence
of hydrogen donors, such as alcohols, amines, or thiols leads to
the formation of a radical produced from the carbonyl compound
(ketyl-type radical) and another radical derived from the hydrogen
donor. The photopolymerization of vinyl monomers is usually
initiated by the radicals produced from the hydrogen donor. The
ketyl radicals are usually not reactive toward vinyl monomers
because of the steric hindrance and the delocalization of an
unpaired electron.
[0120] To successfully formulate a liquid radiation curable resin
for additive fabrication, it is necessary to review the wavelength
sensitivity of the photoinitiator(s) present in the resin
composition to determine if they will be activated by the radiation
source chosen to provide the curing light.
[0121] In accordance with an embodiment, the liquid radiation
curable resin for additive fabrication includes at least one free
radical photoinitiator, e.g., those selected from the group
consisting of benzoylphosphine oxides, aryl ketones, benzophenones,
hydroxylated ketones, 1-hydroxyphenyl ketones, ketals,
metallocenes, and any combination thereof.
[0122] In an embodiment, the liquid radiation curable resin for
additive fabrication includes at least one free-radical
photoinitiator selected from the group consisting of
2,4,6-trimethylbenzoyl diphenylphosphine oxide and
2,4,6-trimethylbenzoyl phenyl, ethoxy phosphine oxide,
bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide,
2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1,2-benzyl-2-(dim-
ethylamino)-1-[4-(4-morpholinyl) phenyl]-1-butanone,
2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-o-
ne, 4-benzoyl-4'-methyl diphenyl sulphide, 4,4'-bis(diethylamino)
benzophenone, and 4,4'-bis(N,N'-dimethylamino) benzophenone
(Michler's ketone), benzophenone, 4-methyl benzophenone,
2,4,6-trimethyl benzophenone, dimethoxybenzophenone,
1-hydroxycyclohexyl phenyl ketone, phenyl
(1-hydroxyisopropyl)ketone, 2-hydroxy-1-[4-(2-hydroxyethoxy)
phenyl]-2-methyl-1-propanone,
4-isopropylphenyl(1-hydroxyisopropyl)ketone,
oligo-[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl] propanone],
camphorquinone, 4,4'-bis(diethylamino) benzophenone, benzil
dimethyl ketal, bis(eta 5-2-4-cyclopentadien-1-yl)
bis[2,6-difluoro-3-(1H-pyrrol-1-yl) phenyl] titanium, and any
combination thereof.
[0123] For light sources emitting in the 300-475 nm wavelength
range, especially those emitting at 365 nm, 390 nm, or 395 nm,
examples of suitable free-radical photoinitiators absorbing in this
area include: benzoylphosphine oxides, such as, for example,
2,4,6-trimethylbenzoyl diphenylphosphine oxide (Lucirin TPO from
BASF) and 2,4,6-trimethylbenzoyl phenyl, ethoxy phosphine oxide
(Lucirin TPO-L from BASF),
bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide (Irgacure 819 or
BAPO from Ciba),
2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1 (Irgacure
907 from Ciba), 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)
phenyl]-1-butanone (Irgacure 369 from Ciba),
2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-o-
ne (Irgacure 379 from Ciba), 4-benzoyl-4'-methyl diphenyl sulphide
(Chivacure BMS from Chitec), 4,4'-bis(diethylamino) benzophenone
(Chivacure EMK from Chitec), and 4,4'-bis(N,N'-dimethylamino)
benzophenone (Michler's ketone). Also suitable are mixtures
thereof.
[0124] Additionally, photosensitizers are useful in conjunction
with photoinitiators in effecting cure with LED light sources
emitting in this wavelength range. Examples of suitable
photosensitizers include: anthraquinones, such as
2-methylanthraquinone, 2-ethylanthraquinone,
2-tertbutylanthraquinone, 1-chloroanthraquinone, and
2-amylanthraquinone, thioxanthones and xanthones, such as isopropyl
thioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, and
1-chloro-4-propoxythioxanthone, methyl benzoyl formate (Darocur MBF
from Ciba), methyl-2-benzoyl benzoate (Chivacure OMB from Chitec),
4-benzoyl-4'-methyl diphenyl sulphide (Chivacure BMS from Chitec),
4,4'-bis(diethylamino) benzophenone (Chivacure EMK from
Chitec).
[0125] It is possible for UV radiation sources to be designed to
emit light at shorter wavelengths. For light sources emitting at
wavelengths from between about 100 and about 300 nm, it is possible
to employ a photosensitizer with a photoinitiator. When
photosensitizers, such as those previously listed are present in
the formulation, other photoinitiators absorbing at shorter
wavelengths can be used. Examples of such photoinitiators include:
benzophenones, such as benzophenone, 4-methyl benzophenone,
2,4,6-trimethyl benzophenone, dimethoxybenzophenone, and
1-hydroxyphenyl ketones, such as 1-hydroxycyclohexyl phenyl ketone,
phenyl (1-hydroxyisopropyl)ketone, 2-hydroxy-1-[4-(2-hydroxyethoxy)
phenyl]-2-methyl-1-propanone, and
4-isopropylphenyl(1-hydroxyisopropyl)ketone, benzil dimethyl ketal,
and oligo-[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]
propanone] (Esacure KIP 150 from Lamberti).
[0126] Radiation sources can also be designed to emit at higher
wavelengths. For radiation sources emitting light at wavelengths
from about 475 nm to about 900 nm, examples of suitable free
radical photoinitiators include: camphorquinone,
4,4'-bis(diethylamino) benzophenone (Chivacure EMK from Chitec),
4,4'-bis(N,N'-dimethylamino) benzophenone (Michler's ketone),
bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide ("BAPO," or
Irgacure 819 from Ciba), metallocenes such as bis (eta
5-2-4-cyclopentadien-1-yl) bis [2,6-difluoro-3-(1H-pyrrol-1-yl)
phenyl] titanium (Irgacure 784 from Ciba), and the visible light
photoinitiators from Spectra Group Limited, Inc. such as H-Nu 470,
H-Nu-535, H-Nu-635, H-Nu-Blue-640, and H-Nu-Blue-660.
[0127] In one embodiment of the instant claimed invention, the
light emitted by the radiation source is UVA radiation, which is
radiation with a wavelength between about 320 and about 400 nm. In
one embodiment of the instant claimed invention, the light emitted
by the radiation source is UVB radiation, which is radiation with a
wavelength between about 280 and about 320 nm. In one embodiment of
the instant claimed invention, the light emitted by the radiation
source is UVC radiation, which is radiation with a wavelength
between about 100 and about 280 nm.
[0128] The liquid radiation curable resin for additive fabrication
can include any suitable amount of the free-radical photoinitiator
as component (d), for example, in certain embodiments, in an amount
up to about 10 wt % of the resin composition, in certain
embodiments, from about 0.1 to about 10 wt % of the resin
composition, and in further embodiments from about 1 to about 6 wt
% of the resin composition.
Fillers
[0129] The liquid radiation curable composition for additive
fabrication according to the present invention also comprises at
least one filler. Inorganic substances are especially preferred as
fillers because of their tendency to impart water-resistance,
heat-resistance, and robust mechanical properties into the cured,
solid three-dimensional parts made therefrom.
[0130] In an embodiment, a filler of which the particles are
spherical--herein defined as having a sphericity of 0.80 or
greater--is used, because of the improved molding properties and
accuracy they impart into three dimensional objects made of the
prepared resin composition of the present invention.
[0131] Sphericity, also known as the "degree of circularity", is a
ratio that measures the deviation of a spherical object from being
a perfect sphere, and is defined by formula (III). When the shape
of a projected image is exactly spherical, the sphericity is
defined as 1. Sphericity may be calculated by the following formula
(III):
Sphericity = 4 .pi.S p C = d pa d pc ( III ) ##EQU00001##
[0132] wherein S.sub.p is a projection area, C is the peripheral
length of the projected image, d.sub.pa is the diameter of a circle
having the same area as that of the projection area, and d.sub.pc
is the diameter of a circle having the same peripheral length as
the projected image of the particle.
[0133] This sphericity can be measured using an image analyzer
which can analyze a microphotograph taken by a scanning electron
microscope (SEM). The average sphericity can be measured by
calculating the average sphericity of 100 particles arbitrarily
selected from a multitude of particles appearing in the
microphotograph.
[0134] In an embodiment of the invention, the filler is inorganic
and comprises ceramics such as silica (SiO.sub.2) nanoparticles,
i.e., those particles having a mean particle size of from between 1
nanometer (nm) to 999 nm, or microparticles, i.e., those particles
having a mean particle size of between 1 micrometer (.mu.m) to 999
.mu.m. Average particle size may be measured using laser
diffraction particle size analysis in accordance with
ISO13320:2009. A suitable device for measuring the average particle
diameter of nanoparticles is the LB-550 machine, available from
Horiba Instruments, Inc, which measures particle diameter by
dynamic light scattering.
[0135] The nanoparticles or microparticles may be substantially
silica based powders, for instance, greater than 85 wt %, more
preferably 90 wt %, more preferably 95 wt % of silica (SiO.sub.2).
Certain non-limiting examples of commercially available silica
powder products include Crystallite 3K-S, Crystallite NX-7,
Crystallite MCC-4, Crystallite CMC-12, Crystallite A-1, Crystallite
AA, Crystallite C, Crystallite D, Crystallite CMC-1, Crystallite
C-66, Crystallite 5X, Crystallite 2A-2, Crystallite VX-S2,
Crystallite VX-SR, Crystallite VX-X, Crystallite VX-S, HUSELEX
RD-8, HUSELEX RD-120, HUSELEX MCF-4, HUSELEX GP-200T, HUSELEX
ZA-30, HUSELEX RD-8, HUSELEX Y-40, HUSELEX E-2, HUSELEX Y-60,
HUSELEX E-1, HUSELEX E-2, HUSELEX FF, HUSELEX X, HUSELEX ZA-20,
IMSIL A-25, IMSIL A-15, IMSIL A-10, and IMSIL A-8, (Ryushin Co.,
Ltd.); ORGANOSILICASOL.TM. MEK-EC-2102, ORGANOSILICASOL.TM.
MEK-EC-2104, ORGANOSILICASOL.TM. MEK-AC-2202, ORGANOSILICASOL.TM.
MEK-AC-4101, ORGANOSILICASOL.TM. MEK-AC-5101, ORGANOSILICASOL.TM.
MIBK-SD, ORGANOSILICASOL.TM. MIBK-SD-L, ORGANOSILICASOL.TM.
DMAC-ST, ORGANOSILICASOL.TM. EG-ST, ORGANOSILICASOL.TM. IPA-ST,
ORGANOSILICASOL.TM. IPA-ST-L, ORGANOSILICASOL.TM. IPA-ST-L-UP,
ORGANOSILICASOL.TM. IPA-ST-ZL, ORGANOSILICASOL.TM. MA-ST-M,
ORGANOSILICASOL.TM. MEK-ST, ORGANOSILICASOL.TM. MEK-ST-L,
ORGANOSILICASOL.TM. MEK-ST-UP, ORGANOSILICASOL.TM. MIBK-ST,
ORGANOSILICASOL.TM. MT-ST, ORGANOSILICASOL.TM. NPC-ST-30,
ORGANOSILICASOL.TM. PMA-ST, SUNSPHERE H-31, SUNSPHERE H-32,
SUNSPHERE H-51, SUNSPHERE H-52, SUNSPHERE H-121, SUNSPHERE H-122,
SUNSPHERE L-31, SUNSPHERE L-51, SUNSPHERE L-121, SUNSPHERE NP-30,
SUNSPHERE NP-100, and SUNSPHERE NP-200 (Asahi Glass Co., Ltd.);
Silstar MK-08 and MK-15 (Nippon Chemical Industrial Co., Ltd.);
FB-48 (Denki Kagaku Kogyo K.K.); Nipsil SS-10, Nipsi:L SS-15,
Nipsil SS-10A, Nipsil SS-20, Nipsil SS-30P, Nipsil SS-30S, Nipsil
SS-40, Nipsil SS-50, Nipsil SS-50A, Nipsil SS-70, Nipsil SS-100,
Nipsil SS-10F, Nipsil SS-50F, Nipsil SS-50B, Nipsil SS-50C, Nipsil
SS-72F, Nipsil SS-170X, Nipsil SS-178B, Nipsil E150K, Nipsil
E-150J, Nipsil E-1030, Nipsil ST-4, Nipsil E-170, Nipsil E-200,
Nipsil E-220, Nipsil E-200A, Nipsil E-1009, Nipsil E-220A, Nipsil
E-1011, NipsilE-K300, Nipsil HD, Nipsil HD-2, Nipsil N-300A, Nipsil
L-250, Nipsil G-300, Nipsil E-75, Nipsil E-743, and Nipsil E-74P
(Nippon Silica Industry, Ltd.). Please see U.S. Pat. No. 6,013,714
for further examples of silica particles.
[0136] In other embodiments of the invention, alternative inorganic
filler substances may be used, such as those containing glass or
metal particles. Certain non-limiting examples of such substances
include: glass powder, alumina, alumina hydrate, magnesium oxide,
magnesium hydroxide, barium sulfate, calcium sulfate, calcium
carbonate, magnesium carbonate, silicate mineral, diatomaceous
earth, silica sand, silica powder, oxidation titanium, aluminum
powder, bronze, zinc powder, copper powder, lead powder, gold
powder, silver dust, glass fiber, titanic acid potassium whiskers,
carbon whiskers, sapphire whiskers, verification rear whiskers,
boron carbide whiskers, silicon carbide whiskers, and silicon
nitride whiskers.
[0137] Certain non-limiting examples of such other commercially
available inorganic filler products include Glass bead GB210,
GB210A, GB210B, GB210C, GB045Z, GB045ZA, GB045ZB, GB045ZC, GB731,
GB731A, GB731B, GB731C, GB731M, GB301S, EGB210, EGB210A, EGB210B,
EGB210C, EGB045Z, EGB045ZA, EGB045ZB, EGB045ZC, MB-10, MB-20,
EMB-10, EMB-20, HSC070Q, HSC-024X, HSC-0805, HSC-070G, HSC-075L,
HSC-110, HSC-110A, HSC-110B, and HSC-110C (Toshiba Balotini Co.,
Ltd.); Radiolite #100, Radiolite Fine Flow B, Radiolite Fine Flow
A, Radiolite Sparkle Flow, Radiolite Special Flow, Radiolite #300,
Radiolite #200, Radiolite Clear Flow, Radiolite #500, Radiolite
#600, Radiolite #2000, Radiolite #700, Radiolite #500S, Radiolite
#800, Radiolite #900, Radiolite #800S, Radiolite #3000, Radiolite
Ace, Radiolite Superace, Radiolite High Ace, Radiolite PC-1,
Radiolite Delux P-5, Radiolite Delux W50, Radiolite Microfine,
Radiolite F, Radic)lite SPF, Radiolite GC, Topco #31, Topco #34,
Topco #36, Topco #38, and Topco #54 (Showa Chemical Industry Co.,
Ltd.); Higilite H-X, Higilite H-21, Higilite H-31, Higilite H-32,
Higilite H-42, Higilite H-42M, Higilite H-43, Higilite H-32ST,
Higilite H-42STV, Higilite H-42T, Higilite H-34, Higilite H-34HL,
Higilite H-32I, Higilite H-42I, Higilite H-425, Higilite H-210,
Higilite H-310, Higilite H-320, Higilite H-141, Higilite H-241,
Higilite H-341, Higilite H-3201, Higilite H-320ST, Higilite HS-310,
Higilite HS-320, Higilite HS-341, Alumina A-426, alumina A-42-1,
Alumina A-42-2, Alumina A-42-3, Alumina A-420, Alumina A-43M,
Alumina A-43-L, Alumina A-50-K, Alumina A-50-N, Alumina A-50-F,
Alumina AL-45-H, Alumina AL-45-2, Alumina AL-45-1, Alumina AL-43-M,
Alumina AL-43-L, Alumina AL-43PC, Alumina AL-150SG, Alumina AL-170,
Alumina A-172, Alumina A-173, Alumina AS10, Alumina AS-20, Alumina
AS-30, Alumina AS-40, and Alumina AS-50 (Showa Denko K.K.);
Starmague U, Starmague M, Starmague L, Starmague P, Starmague C,
Starmague CX, High purity magnesia HP-10, High purity magnesia
HP-10N, High purity magnesia HP-30, Star brand-200, Star brand-10,
Star brand-10A, Star brand magnesium carbonate Venus, Star brand
magnesium carbonate two stars, Star brand magnesium carbonate one
star, Star brand magnesium carbonate S, Star brand magnesium
carbonate Fodder, Star brand heavy magnesium carbonate, High purity
magnesium carbonate GP-10, High purity magnesium carbonate 30, Star
brand light calcium carbonate general use, Star brand light calcium
carbonates EC, and Star brand light calcium carbonate KFW-200
(Konoshima Chemical Industry Co., Ltd.); MKC Silica GS50Z and MKC
Silica SS-15 (Mitsubishi Chemical Corp.), Admafine SOE-E3, Admafine
SO-C3, Admafine AO-800, Admafine AO-809, Admafine AO-500, and
Admafine AO-509 (Adomatex Co., Ltd.); M. S. GEL D-560A, M. S. GEL
D-5120A, M. S. GEL D-5300A, M. S. GEL D-2060A, M. S. GEL D-20120A,
M. S. GEL D-20-300A, SILDE-X H-31, SELDEX H-32, SILDEX H-51, SILDEX
H-52, SILDEX H-121, SILDEX H-122, SILDEX L-31, SILDEX L-51, SILDEX
L-121, SILD EX F-51, and SILDEX F-121 (Asahi Glass); SYLYSIA 250,
SYLYSIA 250N, SYLYSIA 256, SYLYSIA 256N, SYLYSIEA 310, SYLYSIA 320,
SYLYSIA 350, SYLYSIA 358, SYLYSIA 430, SYLYSIA 431, SYLYSIA 440,
SYLYSIA 450, SYLYSIA 470, SYLYSIA 435, SYLYSIA 445, SYLYSIA 436,
SYLYSIA 446, SYLYSIA 456, SYLYSIA 530, SYLYSIA 540, SYLYSIA 550,
SYLYSIA 730, SYLYSIA 740, SYLYSIA 770, SYLOPHOBIC100, and
SYLOPHOBIC 200 (Fuji Silysia Chemical Co., Ltd.); and Tismo-D,
Tismo-L, Tofica Y, Tofica YN, Tofica YB, Dendol WK-200, Dendol
WK-200B, Dendol WK-300, Dendol BK-200, Dendol BK-300, Swanite, and
Barihigh B Super Dendol(Otsuka Chemical Co., Ltd.).
[0138] The inorganic fillers may also be surface treated with a
silane coupling agent. Silane coupling agents which can be used for
this purpose include vinyl triclorosilane, vinyl tris
(.beta.-methoxyethoxy) silane, vinyltriethoxy silane,
vinyltrimethoxy silane, .gamma.-(methacryloxypropyl) trimethoxy
silane, .beta.-(3,4-epoxycyclohexyl)ethyltrimethoxy silane,
.gamma.-glycydoxypropyltrimethoxy silane,
.gamma.-glycydoxypropylmethyl diethoxy silane,
N-.beta.(aminoethyl)yaminopropyltrimethoxy silane,
N-.beta.-(aminoethyl)-.gamma.-aminopropylmethyldimethoxy silane,
.gamma.-aminopropyltriethoxysilane, N-phenyl-.gamma.-amino propyl
trimethoxy silane, .gamma.-mercaptopropyl trimethoxysilane, and
.gamma.-chloropropyltrimethoxy silane.
[0139] The condition of the surface of the particles of the filler
used and the impurities contained in filler from the fabrication
process can affect the curing reaction of the resin composition. In
such cases, it is preferable to wash the filler particles or coat
the particles with an appropriate primer as a method of improving
the curing properties. The inventors have also noted that certain
fillers tend to contribute to a particularly marked reduction in
viscosity stability. Without wishing to be bound by any particular
theory, a hypothesized cause for this phenomenon is the presence of
residual acids present amongst the particles of such fillers, which
are an unwanted but often unavoidable byproduct of the
manufacturing process used to create them. These residual acids
will react with cationically polymerizable components in the
surrounding resin, resulting in partial polymerization and an
increase in viscosity over time.
[0140] The liquid radiation curable resin for additive fabrication
can include any suitable amount of inorganic filler or combination
of fillers as component (e), for example, in an amount up to about
80 wt % of the resin composition, in certain embodiments from about
30 to about 80 wt % of the resin composition, and in further
embodiments from about 50 to about 70 wt % of the resin
composition. If the amount of the component (e) is too small, the
water and heat resistant properties, durability, and structural
rigidity of the molds made of the prepared resin composition do not
increase sufficiently. On the other hand, if the amount of the
component (e) is too large, the fluidity of the prepared resin
composition becomes too low, rendering it difficult or even
un-workable in additive fabrication processes. The excessive amount
of the component (e) can also affect the time needed for radiation
curing of the resin composition, causing the processing time to
increase substantially.
Filled Matrix
[0141] The above inorganic fillers may be used singly or in
combination of two or more. As has been generally known to those
skilled in the art, by using inorganic fillers with different
properties in combination, it is possible to impart certain
properties derived from the fillers to the prepared resin
composition. Further, the prepared resin composition can have
different viscosities if the average grain size or fiber length, or
the grain size or fiber length distribution of the inorganic filler
used is different, though the substance and amount are the same.
Therefore, by appropriately determining not only the average
particle size or fiber length but also the particle size or fiber
length distribution, or by using inorganic fillers of the same
substance with different average particle sizes or fiber lengths in
combination, the necessary amount of the filler and the fluidity
and other properties of the prepared resin can be controlled as
desired.
[0142] Presently, inventors have now surprisingly found that
certain filled "matrices" are able to contribute to the formation
of sufficiently robust three-dimensional solid parts yet stabilize
the liquid radiation curable composition for additive fabrication
to impart improved resistance to: (1) an unwanted particle settling
into a soft pack or hard pack, and (2) an increase in viscosity
over time. Such compositions are henceforth referred to as
"optimally stabilized". For the purposes herein, "matrices" are
defined as arrangements of inorganic filler constituents of varying
sizes, substances, and/or size distributions which form a suspended
solid lattice or backbone in a liquid radiation curable composition
for additive fabrication. A matrix of the present invention
contains at least two constituents: (1) a microparticle constituent
that comprises a plurality of inorganic particles largely defining
the structure of the matrix; and (2) a nanoparticle constituent
that comprises a plurality of inorganic particles which fill gaps
between successive microparticles in order to form a more fully
filled matrix.
[0143] The microparticle constituent contains inorganic
microparticles having an average particle size or fiber length of
from about 1 to about 999 micrometers (.mu.m), more preferably from
about 1 to about 50 .mu.m, more preferably from about 1 to about 10
.mu.m, as measured in accordance with ISO13320:2009. In an
embodiment of the invention, the microparticle constituent is
spherical silica powder, such as of fused or crystal silica. In an
embodiment of the invention, the microparticles of the
microparticle constituent possess an average particle size or fiber
length of from about 2 to about 8 .mu.m.
[0144] The nanoparticle constituent contains inorganic
nanoparticles having an average particle size or fiber length of
from about 1 to about 999 nanometers (nm), more preferably from
about 20 to about 200 nm, more preferably from about 50 to about
100 nm, as measured in accordance with ISO13320:2009. In an
embodiment of the invention, the nanoparticle constituent is
spherical silica powder, such as fused or crystal silica, and
possesses an average particle size or fiber length of from about 50
to about 100 nm.
[0145] The microparticle constituent or nanoparticle constituent of
the present invention may possess any particle size distribution.
Thus, a constituent may be deemed to fall within a range as herein
described even though the "tails" of a particular particle size
distribution fall outside that stated range, so long as the mean
particle size falls within it.
[0146] Such particle sizes notwithstanding, inventors have
discovered that optimally stabilized compositions may be achieved
by selecting appropriately-sized microparticle and nanoparticle
constituents relative to each other. A derivation of the lower
bound of the ratio of average particle size of the microparticles
in the microparticle constituent to the nanoparticles in the
nanoparticle constituent in an embodiment of the invention is
depicted in FIGS. 1 and 2. As FIGS. 1 and 2 represent specific
matrix configurations, they are merely examples and are not
intended to limit the scope of the invention. FIG. 1 depicts a
two-dimensional cross section of a square configuration filled
matrix 1. The square configuration filled matrix 1 includes a
microparticle constituent 3 and a nanoparticle constituent 4. The
microparticle constituent 3 further comprises individual spherical
microparticles 7, 8, 9, and 10, whereas the nanoparticle
constituent 4 comprises spherical nanoparticles 11, 12, and 13. An
imaginary square 2 encompasses the centerpoints of the
microparticles 7, 8, 9, and 10 to demonstrate more clearly the
square configuration of the filled matrix. In order to ensure the
possibility of a tightly packed, stabilized matrix, the
nanoparticle radius 6 can only be large enough to form a
nanoparticle which is tangential to the four surrounding,
contacting microparticles. Thus the minimum ratio of the
microparticle radius 5 to the nanoparticle radius 6 in such a
configuration can be derived using the Pythagorean Theorem
a.sup.2+b.sup.2=c.sup.2, where a and b are equal to the
microparticle radius 5, and c is equal to combined value of the
microparticle radius 5 and the nanoparticle radius 6. Simplifying
the expression yields c= {square root over (2)}, or further that
the nanoparticle radius 6 is equal to ( {square root over (2)}-1)
times the value of the microparticle radius 5. Thus in this
configuration, the minimum ratio of the average particle size of
the microparticle constituent to the average particle size of the
nanoparticle constituent is 1/ {square root over (2)}-1, or
approximately 2.41:1.
[0147] An alternative, more tightly-packed embodiment is depicted
in FIG. 2. FIG. 2 involves a two-dimensional cross section of a
triangular configuration filled matrix 14. The triangular
configuration filled matrix 14 includes a microparticle constituent
16 and a nanoparticle constituent 17. The microparticle constituent
16 further comprises spherical microparticles 18, 19, and 20,
whereas the nanoparticle constituent 17 comprises spherical
nanoparticles 21, 22, 23, and 24. An imaginary equilateral triangle
15 encompasses the centerpoints of the microparticles 18, 19, and
20, to demonstrate more clearly the triangular configuration of the
filled matrix. In order to ensure the possibility of a tightly
packed, stabilized matrix, the nanoparticle radius 26 can only be
large enough to form a nanoparticle which is tangential to the
three surrounding, contacting microparticles. Thus the minimum
ratio of the microparticle radius 25 to the nanoparticle radius 26
in such a configuration can be derived using trigonometry, wherein
the nanoparticle radius 26 is equal to the expression
r cos 30 .degree. - r , ##EQU00002##
where r is equal to the microparticle radius 25. Thus in this
configuration, the minimum ratio of the average particle size of
the microparticles in the microparticle constituent to the
nanoparticles in the nanoparticle constituent is
1 r cos 30 .degree. - r , ##EQU00003##
or approximately 6.46:1.
[0148] Thus, in an embodiment according to the present invention,
the ratio of the average particle size of the microparticles in the
microparticle constituent to the nanoparticles in the nanoparticle
constituent is from about 2.41:1 to about 2,000:1, more preferably
from about 2.41 to about 200:1, more preferably from about 6.46:1
to about 200:1, even more preferably from about 6.46:1 to about
100:1. Ratios whereby the size of the average particle size of the
microparticles in the microparticle constituent to the
nanoparticles in the nanoparticle constituent exceeds these figures
tend to produce unwieldy matrices that raise the viscosity of the
overall composition with which they are associated, or, due to an
excessive average microparticle size, they do not enable sufficient
resolution of solid parts cured therefrom. They may also contribute
to unstable filled matrices which readily disintegrate into a soft
pack.
[0149] The inventors have also surprisingly discovered that liquid
radiation curable resin compositions for additive fabrication may
become optimally stabilized when the ratio by weight of the
microparticle constituent to the nanoparticle constituent is from
greater than about 1:1 to about 12:1, more preferably from about
4:1 to about 8:1. Compositions having lower weight ratios tend not
to form a matrix imparting sufficient mechanical rigidity and
strength to the solid part upon curing. Conversely, those
compositions having a microparticle constituent which comprises too
large a weight percentage of the total filled matrix tend to form
an unstable matrix which rapidly breaks down, causing the inorganic
filler to settle into an unwanted hard or soft pack.
[0150] Additionally, inventors have discovered that the density of
the constituents of the filled matrices also can contribute to
formulation of an optimally stabilized composition. Thus, inventors
have also discovered that liquid radiation curable resin
compositions for additive fabrication may also become optimally
stabilized when the ratio by volume of the microparticle
constituent to the nanoparticle constituent is from greater than
about 1:1 to about 12:1, more preferably from about 4:1 to about
8:1. Compositions having lower volume ratios tend not to form a
matrix imparting sufficient mechanical strength to the mold upon
curing. Conversely, those compositions having a microparticle
constituent which comprises too large a percentage by volume of the
total filled matrix tend to form an unstable matrix which rapidly
breaks down, causing the inorganic filler to settle into an
unwanted hard or soft pack.
[0151] Furthermore, the inventors have discovered that the
respective numbers of particles of the constituents of the filled
matrices also can contribute to formulation of an optimally
stabilized composition. Although matrices of the present invention
may possess a greater amount of the microparticle constituent than
the nanoparticle constituent by weight, they often possess a
greater number of individual nanoparticles than microparticles, due
to the markedly smaller weight of each nanoparticle. Thus,
inventors have also discovered that filled liquid radiation curable
compositions for additive fabrication may also become optimally
stabilized when the ratio by number of the total amount of
nanoparticles in the nanoparticle constituent to the total amount
of microparticles in the microparticle constituent present is from
about 50:1 to about 1,000,000:1, more preferably from about 5,000:1
to about 50,000:1. Compositions having too few or too many relative
number of nanoparticles to microparticles tend to form an unstable
matrix which can break down, causing the inorganic filler to settle
into a hard or soft pack.
[0152] It is understood that the number of particles and overall
volume of a matrix constituent may vary depending on the matrix
constituent's particle size distribution. It is nonetheless assumed
herein that for purposes of calculating the "ratio by volume" or
"ratio by number" that all of the particles present for a given
constituent possess the mean particle size for that constituent, as
determined by ISO13320:2009.
[0153] The aforementioned fillers, sizes, combinations, and ratios
of filled constituents form optimally stabilized compositions
because they prescribe filled matrices which maintain their
original structure over time, and resist ancillary polymerization.
Although not wishing to be bound by any theory, it is hypothesized
that such filled matrices achieve this technical effect because
they are stabilized both mechanically and chemically. That is,
certain ratios of filled inorganic constituents in a matrix prevent
the matrix from disintegrating because the individual particles are
physically prevented from significant movement or sedimentation due
to proper arrangements of interlocking microparticles and
nanoparticles. Additionally, such sedimentation is further
prevented because the constituents of the filled matrices of the
present invention are arranged so as to optimize the chemical bonds
formed both between successive constituent particles, and also
between the constituent particles and the surrounding liquid. This
equilibrium of chemical bonds imparts additional stability and
rigidity to the overall filled matrix. The inventors have
discovered that such optimally stabilized resins exhibit improved
resistance to settling and viscosity increase versus all other
previously known filled liquid radiation curable compositions
suitable for certain additive fabrication applications.
[0154] In addition to the aforementioned factors, inventors have
also discovered the surprisingly significant effect that the
particle dispersion pH further has on polymerization efficacy and
viscosity stability of the resulting photocurable composition for
additive fabrication into which it is ultimately incorporated.
Particle dispersion pH is herein defined as the pH of the filled
particle dispersion--that is, the pH of the solution incorporating
two elements: the filler constituent (for example, the nanoparticle
constituent or microparticle constituent) and the solvent into
which the solid filler constituent is incorporated. Non-limiting
examples of commonly-used such solvents include inert agents such
as methyl ethyl ketone or isopropanol, or polymerizable agents such
as epoxies, oxetanes, or (meth)acrylates. Such solvents may be
employed singularly or in combination of two or more. Particle
dispersion pH is measured prior to the incorporation of the filled
particle dispersion into the liquid radiation curable resin
composition for additive fabrication as a whole.
[0155] Inventors have discovered that if the particle dispersion pH
falls within certain ranges, in particular the thermal stability of
a liquid radiation curable composition for additive fabrication can
be markedly improved. This is because the alkaline or acidic (as
the case may be) nature of the filled particle dispersion causes it
to interact with the pH of the entire surrounding resin, thereby
influencing the efficacy and speed of the cationic polymerization
reaction during an additive fabrication process. If the particle
dispersion pH is too low, the resulting resin may become too
acidic, thereby initiating polymerization reactions amongst the
cationically curable components in the surrounding resin (such as
epoxies and oxetanes) even in the absence of exposure to radiation.
This unwanted effect in additive fabrication applications is
particularly increased at elevated temperatures, and greatly
contributes to an increase in viscosity of the resultant resin over
time.
[0156] Conversely, if the particle dispersion pH is too high, the
resulting resin becomes too alkaline, thereby inhibiting
photopolymerization reactions altogether. In this scenario, the
Bronsted acid species generated by the cationic photoinitiator
component become neutralized by the basic nature of the filled
particle dispersion before said Bronsted acid species can initiate
any photopolymerization reaction. Because the presence of such
Bronsted acid-generating species are necessary to initiate and
propagate the ring-opening reaction which is emblematic of cationic
polymerization, it is important that the particle dispersion pH is
maintained sufficiently low.
[0157] In an embodiment, the particle dispersion pH is from 4.0 to
8.0. In another embodiment, the particle dispersion pH is from 5.5
to 7.5. In another embodiment, the particle dispersion pH is from
6.0 to 7.5. In another embodiment, the particle dispersion pH is
greater than 5.5. In another embodiment, the particle dispersion pH
is neutral, or about 7.0.
[0158] Notably, in prescribing filled matrices of the present
invention, the inventors have arrived at liquid radiation curable
compositions for additive fabrication that also possess lower
initial viscosities than those previously contemplated as
practical. Particularly, no compositions heretofore have been
described that successfully combine a decreased initial viscosity
with improved anti-sedimentation characteristics, given the
longstanding belief of the inversely proportional relationship
between those characteristics as they pertain to liquid radiation
curable compositions for additive fabrication. Prior compositions
might have been formulated for either low initial viscosity or
anti-settling, but not both. Thus, it has heretofore been thought
that formulating a low-viscosity composition was diametrically
opposed to creating one that minimized or eliminated filler
settling behavior, because of the belief that the relatively high
density inorganic particles would rapidly phase separate when
situated in a surrounding liquid medium of significantly lower
density.
[0159] All things being equal, the viscosity of a liquid radiation
curable composition for additive fabrication is inversely
proportional to the average particle size of the filled particles
immersed therein. Recognizing this principle, the inventors have
contravened the longstanding belief that precipitation of the
filler occurs when the viscosity of the prepared resin into which
it is immersed becomes too low by prescribing particle sizes and
ratios of the nanoparticle and microparticle constituents in a way
according to the present invention so as to create a low-viscosity,
yet optimally stable matrix. Thus, inventors have been able to
formulate a matrix filled, liquid radiation curable resin for
additive fabrication that surprisingly achieves a low initial
viscosity, imparts sufficient mechanical properties in the cured
parts derived therefrom, while simultaneously demonstrating
improved anti-sedimentation and viscosity stability.
Stabilizers and Other Components
[0160] Stabilizers are often added to the resin compositions in
order to further prevent a viscosity build-up, for instance a
viscosity build-up during usage in a solid imaging process. Useful
stabilizers include those described in U.S. Pat. No. 5,665,792, the
entire disclosure of which is hereby incorporated by reference. In
the instant claimed invention, the presence of a stabilizer is
optional. In a specific embodiment, the liquid radiation curable
resin composition for additive fabrication comprises from 0.1 wt %
to 3% of a stabilizer.
[0161] If present, such stabilizers are usually hydrocarbon
carboxylic acid salts of group IA and IIA metals. Most preferred
examples of these salts are sodium bicarbonate, potassium
bicarbonate, and rubidium carbonate. Solid stabilizers are
generally not preferred in filled resin compositions. If present, a
15.about.23% sodium carbonate solution is preferred for
formulations of this invention with recommended amounts varying
between 0.05 to 3.0% by weight of resin composition, more
preferably from 0.05 to 1.0 wt %, more preferably from 0.1 to 0.5%
by weight of resin composition. Alternative stabilizers include
polyvinylpyrrolidones and polyacrylonitriles.
[0162] Other possible additives include dyes, pigments,
antioxidants, wetting agents, photosensitizers for the free-radical
photoinitiator, chain transfer agents, leveling agents, defoamers,
surfactants and the like.
[0163] The liquid radiation curable resin composition for additive
fabrication of the invention can further include one or more
additives selected from the group consisting of bubble breakers,
antioxidants, surfactants, acid scavengers, pigments, dyes,
thickneners, flame retardants, silane coupling agents, ultraviolet
absorbers, resin particles, core-shell particle impact modifiers,
soluble polymers and block polymers.
[0164] The second aspect of the claimed invention is a process of
forming a three-dimensional object comprising the steps of forming
and selectively curing a layer of the liquid radiation curable
resin composition according to the present invention as described
herein with actinic radiation and repeating the steps of forming
and selectively curing a layer of the liquid radiation curable
resin composition for additive fabrication as described herein a
plurality of times to obtain a three-dimensional object.
[0165] As noted previously herein, it is preferred that filled
liquid radiation curable compositions for additive fabrication have
a low initial viscosity in order to maximize workability and
minimize processing time. Therefore, it is preferred that liquid
radiation curable compositions for additive fabrication according
to the present invention have a viscosity, when measured at 30
degrees Celsius, of between 200 centipoise (cPs) and 2000 cPs, more
preferably between 500 cPs and 1500 cPs, even more preferably
between 600 cPs and 1200 cPs.
[0166] Furthermore, the filled composition must be able to impart
sufficient strength and stiffness into the three dimensional solid
objects which they form upon curing. Therefore, it is preferred
that liquid radiation curable compositions for additive fabrication
according to the present invention have a flexural modulus, after
full cure with actinic radiation and a 60 minute UV and thermal
postcure according to processes well-known in the art of additive
fabrication and stereolithography (ASTM D648-98c), of at least
6,000 MPa, more preferably at least about 8,000 MPa, and even more
preferably at least about 10,000 MPa. In an embodiment of the
present invention, the flexural modulus achieved is between about
8,000 MPa and about 12,000 MPa.
[0167] Additionally, the filled composition must be able to impart
sufficient resilience and integrity into three dimensional solid
objects which they form upon curing, even after exposure to high
heat conditions. Thus, it is preferred that the liquid radiation
curable composition for additive fabrication according to the
present invention, after full cure with actinic radiation and 60
minute UV and thermal postcure according to processes well-known in
the art of additive fabrication and stereolithography (ASTM
D648-98c), has a heat distortion temperature at 1.82 MPa of at
least about 80 degrees Celsius, more preferably at least about 100
degrees Celsius, and more preferably at least about 110 degrees
Celsius. In an embodiment of the present invention, the heat
distortion temperature at 1.82 MPa is between about 80 degrees
Celsius and about 120 degrees Celsius.
[0168] The third aspect of the claimed invention is the
three-dimensional object formed from the liquid radiation curable
resin of any one of the first aspect of the present invention, by
the process of the second aspect of the claimed invention.
[0169] The fourth aspect of the claimed invention is a liquid
radiation curable resin for additive fabrication comprising: [0170]
(f) a cationically polymerizable component; [0171] (g) a
(meth)acrylate component; [0172] (h) a cationic photoinitiator;
[0173] (i) a free-radical photoinitiator; and [0174] (j) a filled
matrix, further comprising [0175] a filled particle dispersion
containing [0176] a nanoparticle constituent made up of a plurality
of silica nanoparticles having an average particle size of at least
about 50 nanometers, and [0177] a solvent, and [0178] a
microparticle constituent made up of a plurality of inorganic
microparticles; [0179] wherein the ratio by weight of the
microparticle constituent to the nanoparticle constituent is from
about 1:1 to about 12:1; and [0180] wherein the filled particle
dispersion has a particle dispersion pH of greater than about
5.5.
[0181] The following examples further illustrate the invention but,
of course, should not be construed as in any way limiting its
scope.
EXAMPLES
[0182] These examples illustrate embodiments of the liquid
radiation curable resins for additive fabrication of the instant
invention. Table 1 describes the various components of the liquid
radiation curable resins for additive fabrication used in the
present examples.
TABLE-US-00001 TABLE 1 Function in Supplier/ Component Formula
Chemical Descriptor Manufacturer 4-methoxyphenol Antioxidant
4-methoxyphenol Sigma- Aldrich DG-0071 Stabilizer Saturated sodium
carbonate in water DSM solution Desotech Aerosil 200 Settling
Hydrophilic fumed silica Evonik additive Industries Chivacure 1176
Cationic A mixture of: bis[4- Chitec Photoinitiator
diphenylsulfoniumphenyl]sulfide bishexafluoroantimonate;
thiophenoxyphenylsulfonium hexafluoroantimonate and propylene
carbonate. Irgacure 184 Radical 1-Hydroxy-1-cyclohexyl phenyl BASF
Photoinitiator ketone DPHA Radically Dipentaerythritol hexaacrylate
Sigma- Polymerizable Aldrich Compound Heloxy 68 Cationically
Neopentylglycol diglycidyl ether Momentive Polymerizable compound
Erisys GE 22 Cationically 1,4 Cyclohexanedimethanol Emerald
Polymerizable Diglycidyl Ether Performance Compound Materials
Celloxide 2021P Cationic 3,4-Epoxycyclohexylmethyl 3',4'- Daicel
Polymerizable epoxycyclohexanecarboxylate Corporation Compound
HQMME Synthetic Hydroquinone monomethyl ether Nova intermediate,
International uv inhibitor SR 351 Radically Trimethylolpropane
triacrylate Sartomer Polymerizable Compound ORGANO- Filled particle
30% colloidal silica nanoparticles in Nissan SILICASOL dispersion
70% methyl ethyl ketone solvent; 10-15 nm Chemical MEK-AC-2101
including particle size distribution nanoparticle constituent
ORGANO- Filled particle 30% colloidal silica nanoparticles in
Nissan SILICASOL dispersion 70% methyl ethyl ketone solvent; 40-50
nm Chemical MEK-AC-4101 including particle size distribution
nanoparticle constituent ORGANO- Filled particle 30% colloidal
silica nanoparticles in Nissan SILICASOL dispersion 70% methyl
ethyl ketone solvent; 70-100 nm Chemical MEK-AC-5101 including
particle size distribution; 80 nm nanoparticle avg. particle size
constituent ORGANO- Filled particle 30% colloidal silica
nanoparticles in Nissan SILICASOL dispersion Isopropanol solvent;
70-100 nm Chemical IPA-ST-ZL including particle size distribution
nanoparticle constituent DZ-0077 Filled particle 40% colloidal
silica nanoparticles in Nanoparticles dispersion 60%
3,4-epoxycyclohexylmethyl from Nissan including
3',4'-epoxycyclohexanecarboxylate; Chemical; nanoparticle 80 nm
avg. particle size Epoxy from constituent Daicel Nanopox A 610
Filled particle 40% spherical silica nanoparticles in Evonik
dispersion 60% 3,4-epoxycyclohexylmethyl Industries including
3',4'-epoxycyclohexanecarboxylate; nanoparticle 20 nm avg. particle
size constituent Sunspacer 04.X Filled particle SiO2 Particle (4
.mu.m average particle Suncolor dispersion size) including
microparticle constituent NP-30S Filled particle Spherical
SiO.sub.2 microparticles; 4 .mu.m AGC dispersion avg. particle size
Chemicals including microparticle constituent
Examples 1-12
[0183] Various filled liquid radiation curable resins for additive
fabrication were prepared according to well-known methods in the
art, employing a hybrid cure photoinitiating package, a
cationically polymerizable package, a radically polymerizable
package, and select additives. The MEK-AC-5101 nanoparticles are
supplied in a methyl ethyl ketone solvent, which was exchanged for
a cycloaliphatic epoxide--resulting in a 40% nanoparticle/60%
epoxide solution--using standard techniques. Other resin
compositions utilizing varying filled matrices were then prepared
by alternating the type and/or quantity of microparticle
constituent and nanoparticle constituent.
[0184] These samples were tested according to the methods for
viscosity, settling behavior, shelf life thermal stability, and
physical property testing, as detailed below. Finally, filled
matrix characteristics were determined by calculating the ratio by
weight, size, and volume of the microparticle constituent to the
nanoparticle constituent, and the ratio by particle number of the
nanoparticle constituent to the microparticle constituent. The
results are presented in Table 2.
Viscosity
[0185] The viscosity of each sample was taken with an Anton Paar
Rheoplus Rheometer (S/N 80325376) using a Z3/Q1 measuring cylinder
(S/N 10571) with a 25 mm diameter. The temperature was set at
30.degree. Celsius with a shear rate of 50 s.sup.-1. The rotational
speed was set at 38.5 min.sup.-1. The measuring container was a
H-Z3/SM cup (diameter 27.110 mm) which was filled with 21.4 grams
of sample (enough to the spindle). Measurements were recorded in
millipascal-seconds (mPas), but converted and reported herein as
centipoise (cPs).
Settling Behavior of Filled Materials
[0186] Forty grams of each sample was measured into a glass petri
dish and placed in a 50 degrees Celsius (C).+-.2 degrees C. oven.
At the appropriate interval each sample was removed from the oven,
and qualitatively examined for settling behavior. The behaviors
observed were no settling, soft pack, or hard pack. Samples were
then placed back into the oven to resume the test for the duration
of the prescribed allotted time (typically 28 days). The duration
at which the first indication of soft pack or hard pack settling
behavior was observed was then recorded.
Viscosity Stability--Shelf Life Thermal Stability Test
[0187] Forty grams of each sample was measured and placed in a 50
degrees Celsius (C)+2 degrees C. oven. At the appropriate interval
each sample was removed from the oven, then placed in a centrifuge
at 2500 rpm for 1 minute (to remix any separation that might have
occurred) and had the viscosity taken according the viscosity
method. Samples were then placed back into the oven to resume the
test for the duration of the prescribed allotted time (typically 28
days). Measurements were recorded in millipascal-seconds (mPas),
but converted and reported herein as centipoise (cPs). Sections
marked with an asterisk (*) indicates that because partial gelling
of the sample had occurred, accurate readings were not
obtainable.
Physical Property Testing
[0188] Samples were built by viper SLA machine (S/N 03FB0244 or S/N
02FB0160) to the standard Type I dogbone shape for tensile testing
where the overall length is 6.5 inches, the overall width is 0.75
inch and the thickness is 0.125 inches and standard bar shape for
the Flexural testing where the length is 5 inches, the overall
width is 0.5 inch and the thickness is 0.125 inches. Samples were
conditioned 7 days at 23.degree. C. at 50% relative humidity. The
tensile properties were tested according to the ASTM D638-10 test
method. The flexural strength & modulus properties were tested
according to the ASTM D 0790 test method. Both tests were performed
on the 5G Sintech tensile tester (S/N 34359).
Ratios by Size, Weight, Volume, and Number
[0189] The ratio by size was derived by dividing the mean particle
size of the microparticle constituent in a given composition by the
mean particle size of the nanoparticle constituent in that
composition. Mean particle sizes were determined from
ISO13329:2009. Values expressed do not possess units.
[0190] The ratio by weight was derived by dividing the total amount
by weight of the microparticle constituent in a given composition
by the total amount by weight of the nanoparticle constituent in
that composition. Values expressed do not possess units.
[0191] The ratio by volume was derived by dividing the total volume
of the microparticle constituent in a given composition by the
total volume of the nanoparticle constituent present in that
composition. Volume for a constituent was determined by dividing
the weight of that constituent by its density. Where, as in the
examples below, both the microparticle constituent and nanoparticle
constituent possess the same density, it should be noted that the
ratio by volume does not differ from the ratio by weight. Values
expressed do not possess units.
[0192] The ratio by number was derived by dividing the total number
of nanoparticles present in the nanoparticle constituent by the
total number of microparticles present in the microparticle
constituent. Where, as in the examples below, spherical particles
were used, for the sake of calculation, it was assumed that each
matrix constituent was comprised entirely of spherical particles
possessing a symmetric particle size distribution about the mean
particle size. Thus, calculations were performed by first
determining the volume of each spherical particle, which can be
derived by the formula V=4/3.pi.r.sup.3, where r is the radius of
the spherical particle. Next, the weight of each spherical particle
was determined by multiplying the volume of each particle by its
density. Where, as in the examples below, both the microparticle
constituent and nanoparticle constituent possess the same density,
the relative value of the density is immaterial to the ratio
calculation. Finally, the value of the weight of each particle was
divided by the total weight in the entire composition of the
constituent of which that particle was included, to obtain the
total number of particles present in the composition. Calculations
were similarly performed on the other matrix constituents to
determine the ratio of particles by number. Values expressed do not
possess units.
TABLE-US-00002 TABLE 2 Values are listed in parts by weight
Component\Formula Example 1 Example 2 Example 3 Example 4 Example 5
Example 6 Aerosil 200 0.37 0.37 0.37 0.37 0.37 0.37 Chivacure 1176
3.80 3.80 3.80 3.80 3.80 3.80 DPHA 2.07 2.07 2.07 2.07 2.07 2.07
Heloxy 68 7.500 7.500 7.500 7.500 7.500 7.500 HQMME 0.018 0.018
0.018 0.018 0.018 0.018 IRGACURE 184 0.400 0.400 0.400 0.400 0.400
0.400 SR 351 3.350 3.350 3.350 3.350 3.350 3.350 DZ-0077 0 34.610
27.000 19.500 10.000 10.000 Nanopox A 610 34.610 0 0 0 0 0
Celloxide 2021P 0 0 4.61 9.11 14.85 18.61 NP-30 47.890 47.890 50.89
53.89 57.65 53.89 TOTAL 100.00 100.00 100.00 100.00 100.00 100.00
Ratio by size 200:1 50:1 50:1 50:1 50:1 50:1 (micro/nano) Ratio by
weight 3.46:1 3.46:1 4.71:1 6.91:1 14.41:1 13.47:1 (micro/nano)
Ratio by volume 3.46:1 3.46:1 4.71:1 6.91:1 14.41:1 13.47:1
(micro/nano) Ratio by # 2,312,633:1 36,135:1 26,528:1 18,092:1
8,673:1 9,278:1 (nano/micro) Initial Viscosity 2712 1171 1132 1225
1556 1315 Viscosity, 1 week 3698 1646 1630 1767 2307 1926
Viscosity, 2 weeks 4333 1733 1755 1721 * * Viscosity, 3 weeks 5072
* * 1921 * * Viscosity, 4 weeks 6203 * * * * * Settling Behavior,
Soft Pack Soft Pack Soft Pack Soft Pack Hard Pack Hard Pack type
Settling Behavior, 3 15 15 11 11 11 timing (days) Example Example
Example Component\Formula Example 7 Example 8 Example 9 10 11 12
Aerosil 200 0.37 0.37 0.37 0.37 0.37 0.37 Chivacure 1176 3.80 3.80
3.80 3.80 3.80 3.80 DPHA 2.07 2.07 2.07 2.07 2.07 2.07 Heloxy 68
7.500 7.500 7.500 7.500 7.500 7.500 HQMME 0.018 0.018 0.018 0.018
0.018 0.018 Irgacure 184 0.400 0.400 0.400 0.400 0.400 0.400 SR 351
3.350 3.350 3.350 3.350 3.350 3.350 DZ-0077 10.000 10.000 27.000
19.500 0 0 Nanopox A 610 0 0 0 0 0 0 Celloxide 2021P 21.61 24.61
7.61 15.11 24.85 34.61 NP-30 50.89 47.89 47.89 47.89 57.65 47.890
TOTAL 100.00 100.00 100.00 100.00 100.00 100.00 Ratio by size 200:1
50:1 50:1 50:1 Undefined Undefined (micro/nano) Ratio by weight
12.72:1 11.97:1 4.43:1 6.14:1 Undefined Undefined (micro/nano)
Ratio by volume 12.72:1 11.97:1 4.43:1 6.14:1 Undefined Undefined
(micro/nano) Ratio by # 9,825:1 10,441:1 28,190:1 20,359:1 0 0
(nano/micro) Initial Viscosity 1133 918.3 1036 936 2182 1098
Viscosity, 1 week 1619 1307 1408 1286 3370 1590 Viscosity, 2 weeks
* * 1428 * * * Viscosity, 3 weeks * * * * * * Viscosity, 4 weeks *
* * * * * Settling Behavior, Hard Pack Hard Soft Pack Soft Pack
Hard Pack Hard Pack type Pack Settling Behavior, 11 11 15 15 11 11
timing
Examples 13-20
[0193] Various base filled resin compositions for additive
fabrication were prepared according to well-known methods in the
art by combining a photoinitiating package, a cationically
polymerizable package, a radically polymerizable package, and
select additives. Other resin compositions utilizing varying filled
matrices were then prepared by alternating the type and/or quantity
of microparticle constituent and nanoparticle constituent.
Additionally, a cationically polymerizable component was varied.
These samples were tested according to the methods prescribed
herein for viscosity and settling behavior. Finally, filled matrix
characteristics were determined by calculating the ratio by weight
and volume of the microparticle constituent to the nanoparticle
constituent, and the ratio by particle number of the nanoparticle
constituent to the microparticle constituent. The results are
presented in Table 3.
TABLE-US-00003 TABLE 3 Values are listed in parts by weight
Component Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18 Ex. 19 Ex. 20
Aerosil 200 0.370 0.370 0.370 0.370 0.370 0.370 0.370 0.370 DPHA
2.070 2.070 2.070 2.070 2.070 2.070 2.070 2.070 Heloxy 68 7.500
7.500 7.500 7.500 Nanopox A 34.610 34.610 10.000 10.000 610 NP-30
47.890 47.890 57.570 47.890 47.890 57.570 57.570 57.570 SR 351
3.350 3.350 3.350 3.350 3.350 3.350 3.350 3.350 Celloxide 14.810
14.810 14.810 14.810 2021P DZ-0077 34.610 34.610 10.000 10.000
Erisys GE 7.500 7.500 7.500 7.500 22 Chivacure 4.210 4.210 4.330
4.210 4.210 4.330 4.330 4.330 1176 + Irgacure 184 TOTALS 100.00
100.00 100.00 100.00 100.00 100.00 100.00 100.00 Ratio by 200:1
200:1 200:1 50:1 50:1 50:1 200:1 50:1 size (micro/nano) Ratio by
3.46:1 3.46:1 14.39:1 3.46:1 3.46:1 14.39:1 14.39:1 14.39:1 weight
(micro/nano) Ratio by 3.46:1 3.46:1 14.39:1 3.46:1 3.46:1 14.39:1
14.39:1 14.39:1 volume (micro/nano) Ratio by # 2,312,633:1
2,312,633:1 555,845:1 36,135:1 36,135:1 8,685:1 555,845:1 8,685:1
(nano/micro) Settling Soft Pack Soft Pack Hard Soft Soft Hard Hard
Hard Behavior, Pack Pack Pack Pack Pack Pack type Settling 11 11 18
28 18 7 11 2 Behavior, timing
Examples 21-24
[0194] Various filled particle dispersions were evaluated to
determine the particle dispersion pH of the raw material
(nanoparticle constituent plus solvent). Readings for each
respective filled particle dispersion were taken at 20.degree. C.
Before use, the electrode probe of a Beckman Coulter .PHI.250 pH
meter (Series #3527) was soaked in a pH 4 buffer solution
overnight. The pH meter was calibrated with three standard pH
buffer solutions (pH 4.0, 7.0, and 10.01) before taking
measurements. The calibration method and pH reading were performed
according to the meter's operation instructions (Beckman .PHI.200
Series Operation Manual, pp. 19-21). After calibration, the probe
was cleaned with distilled water and then was gently tapped to
remove any water residue. The glass was not wiped vigorously in
order to avoid scratches and dehydration.
[0195] In order to accurately measure the particle dispersion pH of
the raw material, it was necessary to first dissolve the filled
particle dispersion into a testing carrier (itself consisting of a
3:2 ratio of distilled water to methanol). Thus, 8.33 g of each
filled particle dispersion was dissolved into 43.75 g of the
testing carrier.
[0196] Next, the electrode probe of the Beckman .PHI. 250 pH meter
was inserted into the above solution (filled particle dispersion
plus testing carrier) to establish a first particle dispersion pH
reading. With the reading recorded, the electrode probe was cleaned
with a solution of 50% acetone and 50% isopropanol (IPA) followed
by distilled water. This cleaning procedure was repeated between
each of five separate readings taken for each sample. The above
process was repeated for each of four samples. The average value of
the five readings for each of the four samples is reproduced in
Table 4 below.
TABLE-US-00004 TABLE 4 Particle Size Particle Filled particle
Distribution dispersion dispersion Solvent SiO.sub.2 % (nm) pH Ex.
21 MEK-AC-2101 MEK 30 10-15 6.71 Ex. 22 MEK-AC-4101 MEK 30 40-50
4.59 Ex. 23 IPA-ST-ZL IPA 30 70-100 4.03 Ex. 24 MEK-AC-5101 MEK 30
70-100 7.34
Examples 25-29
[0197] New samples were then prepared by exchanging the original
solvent in the same four commercially available filled particle
dispersions used in examples 21-24 with a 3,4-epoxycyclohexylmethyl
3',4'-epoxycyclohexanecarboxylate solvent. This solvent exchange,
accomplished according to standard techniques, resulted in a 40%
silica nanoparticle/60% epoxide solution. The pH of these resulting
filled particle dispersions were then recorded for each sample
according to the technique illustrated in the discussion of
Examples 21-24, supra, with the exception that instead of creating
a 8.33:43.75 filled particle dispersion to test carrier solution,
6.25 g of the resulting filled particle dispersion was dissolved
into 43.75 g of the testing carrier.
[0198] Next, the samples were subjected to a thermal aging test. To
effectuate this test, the initial viscosity was first measured
according to the viscosity testing procedure outlined in the
discussion of examples 1-12, supra. After 7 days of aging in a
55.degree. C. oven, samples were cooled to room temperature and
remixed if nanoparticle settling was observed. Viscosity was then
again measured according to the viscosity testing procedure
outlined in the discussion of examples 1-12, supra.
TABLE-US-00005 TABLE 5 Component Ex. 25 Ex. 26 Ex. 27 Ex. 28 Ex. 29
Celloxide 2021P 0 60 60 60 60 Nanopox A610 100 0 0 0 0 MEK-AC-2101
0 40 0 0 0 (nanoparticle constituent only) MEK-AC-4101 0 0 40 0 0
(nanoparticle constituent only) IPA-ST-ZL 0 0 0 40 0 (nanoparticle
constituent only) MEK-AC-5101 0 0 0 0 40 (nanoparticle constituent
only) Resulting particle 6.63 6.71 5.36 4.79 7.19 dispersion pH
(post solvent exchange) Initial Viscosity 2750 1553 Gelled during
505 Viscosity, 7 days 5325 31000 solvent exchange 526 Viscosity
Change (%) 94% 1922% 4%
Examples 30-31
[0199] Two filled liquid radiation curable resins for additive
fabrication were prepared according to well-known methods in the
art, employing an identical hybrid cure photoinitiating package,
cationically polymerizable package, radically polymerizable
package, and select additives. The only difference between the two
samples was the identity of the nanoparticle constituent. E.sub.c,
D.sub.p, and E.sub.10 values were measured according to the working
curve measurement procedure outlined below. Further, the samples
were subjected to the thermal aging test outlined in the
description of Examples 25-29, supra. Viscosity measurements were
taken (according to the procedure outlined in the discussion of
examples 1-12 herein, supra) at the beginning of the test, then
again at 7 and 14 days at 55.degree. C., with the results recorded
in Table 6 below.
Working Curve Measurement
[0200] Working curve data (E.sub.c, D.sub.p, and E.sub.10) was
prepared using a solid state laser operating at a wavelength of
354.7 nm in accordance with the below method.
[0201] The working curve is a measure of the photospeed of the
particular material. It represents the relationship between the
thickness of a layer of liquid radiation curable resin produced as
a function of the exposure given. For all formulations, the
exposure-working curve of the formula is determined using methods
well known in the art.
[0202] The exposure response for each formulation is measured using
a 21.7 g sample of the formulation in a 100 mm diameter petri dish
held at 30.degree. C. and 30% RH. The surface of the formulation is
exposed with the indicated light source. The exposures are made in
half-inch squares (exposure regions) which are scanned out by
drawing consecutive parallel lines approximately 25.4 microns apart
on the surface of the liquid in the petri dish at 72 mW. Different
exposure regions are exposed to different levels of known incident
energy to obtain different cured thicknesses. The spot diameter at
the liquid surface is approximately 0.0277 cm in diameter. After
waiting at least 15 minutes for the exposed panels to harden, the
panels are removed from the petri dish and excess, uncured resin is
removed by blotting with a Kimwipe EX-L (Kimberly Clark). Film
thickness is measured with a Mitutoyo Model ID-C 1 12CE Indicator
Micrometer. Film thickness is a linear function of the natural
logarithm of the exposure energy; the slope of the regression is
D.sub.p (units of micron or mil) and E.sub.c is the x-axis
intercept of the regression fit (units of mJ/cm.sup.2). E.sub.10 is
the energy required to cure a ten mil (254 micron) layer.
TABLE-US-00006 TABLE 6 Component Ex. 30 Ex. 31 Nanopox A 610 34.61
Dispersion of Example 29 34.61 Erysis GE-20 7.5 7.5 SR-351 3.36
3.36 DPHA 2.07 2.07 Irgacure 184 0.4 0.4 Chivacure 1176 3.8 3.8
4-methoxyphenol 0.02 0.02 Aerosil 200 0.22 0.22 Sunspacer 04.X
47.87 47.87 DG-0071 0.15 0.15 Total 100.00 100.00 Total fillers
61.71 61.71 Ec (mJ/cm2) 12.22 10.86 Dp (mils) 5.15 4.75 E.sub.10
(mJ/cm2) 85 89.1 Initial Viscosity (30.degree. C., cps) 2282 1306
Viscosity (30.degree. C., cps) (55.degree. C., 7 days) 3899 1835
Viscosity (30.degree. C., cps) (55.degree. C., 14 days) 5405
2034
Discussion of Results
[0203] Examples 1-31 are matrix filled liquid radiation curable
resin compositions demonstrating increased suitability for additive
fabrication. It is apparent from Tables 2 and 3 that the ratio of
the microparticle constituent to the nanoparticle constituent (by
weight and/or volume), is critical to creating filled matrices
which can resist the hard pack settling phenomenon. Particularly,
it is noted that below approximately a 12:1 weight or volume ratio
of the microparticle constituent to nanoparticle constituent,
filled matrices display a surprisingly improved tendency to
withstand disintegration into a hard pack. The hard pack phenomenon
is similarly evident in Examples 11 and 12, wherein the
nanoparticle constituent is removed from the filled matrix
entirely. Thus, in an embodiment of the present invention, the
presence of both a nanoparticle constituent and a microparticle
constituent is necessary to prevent unwanted hard pack phase
separation.
[0204] Furthermore, Examples 1-20 demonstrate that when the ratio
by number of the nanoparticles present in the nanoparticle
constituent to the microparticles present in the microparticle
constituent becomes too large, the filled matrix can possess an
undesirably high viscosity and quickly break down into a soft pack.
Particularly, it is hypothesized, drawing upon support from the
Examples in Tables 2 and 3, that filled matrices become unwieldy
and break down into a soft pack when the ratio of nanoparticles
present in the nanoparticle constituent to the number of
microparticles present in the microparticle constituent is exceeds
about 1,000,000:1.
[0205] Additionally, Examples 21-31 demonstrate the effect that
both the particle dispersion pH and the particle size of the filled
particle dispersion have on the resulting liquid radiation curable
composition's thermal stability. It is surmised from an
extrapolation of the data in Tables 4-5 that below a particle
dispersion pH of about 5.5, the acidic filled particle dispersion
imparts poor thermal stability into the photocurable composition
for additive fabrication into which it is incorporated, such that
even a routine solvent exchange is impractical. Furthermore, from
Table 6, it is shown that compositions possessing a nanoparticle
constituent with nanoparticles having an average particle size of
above 50 nm exhibit improved thermal stability versus those having
nanoparticles with an average size of below 50 nm, even where the
particle dispersion pH is in an otherwise acceptable range.
[0206] All references, including publications, patent applications,
and patents, cited herein are hereby incorporated by reference to
the same extent as if each reference were individually and
specifically indicated to be incorporated by reference and were set
forth in its entirety herein.
[0207] The use of the terms "a" and "an" and "the" and similar
referents in the context of describing the invention (especially in
the context of the following claims) are to be construed to cover
both the singular and the plural, unless otherwise indicated herein
or clearly contradicted by context. The terms "comprising,"
"having," "including," and "containing" are to be construed as
open-ended terms (i.e., meaning "including, but not limited to,")
unless otherwise noted. Recitation of ranges of values herein are
merely intended to serve as a shorthand method of referring
individually to each separate value falling within the range,
unless otherwise indicated herein, and each separate value is
incorporated into the specification as if it were individually
recited herein. All methods described herein can be performed in
any suitable order unless otherwise indicated herein or otherwise
clearly contradicted by context. The use of any and all examples,
or exemplary language (e.g., "such as") provided herein, is
intended merely to better illuminate the invention and does not
pose a limitation on the scope of the invention unless otherwise
claimed. No language in the specification should be construed as
indicating any non-claimed element as essential to the practice of
the invention.
[0208] Preferred embodiments of this invention are described
herein, including the best mode known to the inventor for carrying
out the invention. Variations of those preferred embodiments may
become apparent to those of ordinary skill in the art upon reading
the foregoing description. The inventor expects skilled artisans to
employ such variations as appropriate, and the inventor intends for
the invention to be practiced otherwise than as specifically
described herein. Accordingly, this invention includes all
modifications and equivalents of the subject matter recited in the
claims appended hereto as permitted by applicable law. Moreover,
any combination of the above-described elements in all possible
variations thereof is encompassed by the invention unless otherwise
indicated herein or otherwise clearly contradicted by context.
[0209] While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent to
one of ordinary skill in the art that various changes and
modifications can be made therein without departing from the spirit
and scope of the claimed invention.
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