U.S. patent application number 13/515664 was filed with the patent office on 2012-10-04 for liquid radiation curable resins for additive fabrication comprising a triaryl sulfonium borate cationic photoinitiator.
This patent application is currently assigned to DSM IP ASSETS, B.V.. Invention is credited to Ken Dake, Sam East, Kangtai Ren, John Edmund Southwell, Jigeng Xu.
Application Number | 20120251841 13/515664 |
Document ID | / |
Family ID | 43532791 |
Filed Date | 2012-10-04 |
United States Patent
Application |
20120251841 |
Kind Code |
A1 |
Southwell; John Edmund ; et
al. |
October 4, 2012 |
LIQUID RADIATION CURABLE RESINS FOR ADDITIVE FABRICATION COMPRISING
A TRIARYL SULFONIUM BORATE CATIONIC PHOTOINITIATOR
Abstract
Liquid radiation curable resins for additive fabrication
comprising an R-substituted aromatic thioetber triaryl sulfonmm
tetrakis(pentafluorophenyl)borate cationic photoinitiator is
disclosed. 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 are
also disclosed.
Inventors: |
Southwell; John Edmund;
(Glen Ellyn, IL) ; Xu; Jigeng; (South Elgin,
IL) ; Ren; Kangtai; (Geneva, IL) ; Dake;
Ken; (South Elgin, IL) ; East; Sam; (Lake in
the Hills, IL) |
Assignee: |
DSM IP ASSETS, B.V.
Heerlen
NL
|
Family ID: |
43532791 |
Appl. No.: |
13/515664 |
Filed: |
December 16, 2010 |
PCT Filed: |
December 16, 2010 |
PCT NO: |
PCT/US2010/060668 |
371 Date: |
June 13, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61287620 |
Dec 17, 2009 |
|
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|
Current U.S.
Class: |
428/704 ;
264/401; 522/15; 522/25; 522/31; 568/6 |
Current CPC
Class: |
B33Y 70/00 20141201;
B29C 2033/0005 20130101; G03F 7/038 20130101; G03F 7/0037 20130101;
G03F 7/0045 20130101; G03F 7/027 20130101; Y10T 428/31515 20150401;
B29C 2035/0827 20130101; G03F 7/029 20130101; B29C 64/135 20170801;
B33Y 10/00 20141201 |
Class at
Publication: |
428/704 ; 522/31;
522/15; 522/25; 568/6; 264/401 |
International
Class: |
C07F 5/02 20060101
C07F005/02; B29C 35/08 20060101 B29C035/08; B32B 9/00 20060101
B32B009/00; C08G 59/02 20060101 C08G059/02 |
Claims
1. A liquid radiation curable resin for additive fabrication
comprising an R-substituted aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator with a
tetrakis(pentafluorophenyl)borate anion and a cation of the
following formula (I): ##STR00007## 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.
2. The liquid radiation curable resin for additive fabrication of
claim 1 wherein the R-substituted aromatic thioether triaryl
sulfonium tetrakis(pentafluorophenyl)borate cationic photoinitiator
is present in an amount from about 0.1 wt % to about 20 wt %,
preferably from about 0.1 wt % to about 10 wt %, more preferably
from about 0.1 wt % to about 7 wt %, more preferably from about 0.2
wt % to about 4 wt % of the liquid radiation curable resin for
additive fabrication.
3. The liquid radiation curable resin for additive fabrication of
claim 2 further comprising: a. from 2 to 40 wt % of a radically
polymerizable compound b. from 10 to 80 wt % of a cationically
polymerizable compound and c. from 0.1 to 10 wt % of a radical
photoinitiator.
4. The liquid radiation curable resin for additive fabrication of
claim 1 wherein R is an acetyl group.
5. The liquid radiation curable resin for additive fabrication of
claim 1 wherein Y1, Y2, and Y3 are the same.
6. The liquid radiation curable resin for additive fabrication of
claim 1 wherein the R-substituted aromatic thioether triaryl
sulfonium tetrakis(pentafluorophenyl)borate cationic photoinitiator
is tris(4-(4-acetylphenyl)thiophenyl)sulfonium
tetrakis(pentafluorophenyl)borate.
7. The liquid radiation curable resin for additive fabrication of
claim 1 wherein the R-substituted aromatic thioether triaryl
sulfonium tetrakis(pentafluorophenyl)borate cationic photoinitiator
is present in an amount from 0.1 wt % to 2 wt %.
8. The liquid radiation curable resin for additive fabrication of
claim 1 further comprising a cationic photoinitiator that is not an
R-substituted aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator.
9. The liquid radiation curable resin for additive fabrication of
claim 1 further comprising a photosensitizer.
10. The liquid radiation curable resin for additive fabrication of
claim 1 further comprising an inorganic filler, preferably present
in an amount from about 5 wt % to about 90 wt %, more preferably
from about 10 wt % to about 75 wt %, more preferably from about 30
wt % to about 75 wt %.
11. The liquid radiation curable resin for additive fabrication of
claim 10 wherein the inorganic filler is silica nanoparticles
comprising at least 80 wt % silica, preferably 90 wt % silica, more
preferably 95 wt % silica.
12. The liquid radiation curable resin for additive fabrication of
claim 1 further comprising from about 0.1 to about 1 wt % of a
stabilizer.
13. The liquid radiation curable resin of claim 12 wherein the
stabilizer is a liquid Na.sub.2CO.sub.3 solution.
14. A liquid radiation curable resin for additive fabrication
comprising 5 wt % to about 90 wt %, preferably from 10 wt % to 75
wt %, more preferably from 30 to 75 wt % of inorganic filler, said
inorganic filler preferably comprising greater than 80 wt %,
preferably greater than 90 wt %, more preferably greater than 95 wt
% of silica, that has a Dp of from about 4.5 mils to about 7.0 mils
wherein the liquid radiation curable resin for additive
fabrication, when placed on a shaker table set at 240 rpm and
exposed to two 15 watt plant and aquarium lamps hung 8 inches above
the surface of the liquid radiation curable resin for additive
fabrication, has a gel time of greater than 200 hours, preferably
greater than 250 hours.
15. 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 for additive fabrication of
claim 1 with actinic radiation and repeating the steps of forming
and selectively curing a layer of the liquid radiation curable
resin composition for additive fabrication of claim 1 a plurality
of times to obtain a three-dimensional object.
16. The process of claim 15 wherein the source of actinic radiation
is one or more LEDs.
17. The process of claim 16 wherein the one or more LEDS emit light
at a wavelength of 200 nm-460 nm, preferably from 300 nm-400 nm,
more preferably from 340 nm to 370 nm, mire preferably having a
peak at 365 nm.
18. A three-dimensional object formed from the liquid radiation
curable resin of claim 1.
19. The use of an R-substituted aromatic thioether triaryl
sulfonium tetrakis(pentafluorophenyl)borate cationic photoinitiator
with a tetrakis(pentafluorophenyl)borate anion and a cation of the
following formula (I): ##STR00008## wherein Y1, Y2, and Y3 are the
same or different and where Y1, Y2, or Y3 are R-substituted
aromatic thioether with R being an acetyl or halogen group, on
metal and metal alloys, such as aluminum alloy, steels, stainless
steels, copper alloys, tin, or tin-plated steels.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to liquid radiation curable
resins for additive fabrication processes.
BACKGROUND OF THE INVENTION
[0002] Additive fabrication processes for producing three
dimensional objects are known in the field. 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.
[0003] 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 beam that traces the 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 beam 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 therefore may be subjected to post-curing, if
required. An example of an SL process is described in U.S. Pat. No.
4,575,330.
[0004] There are several types of lasers used in stereolithography,
ranging from 193 nm to 355 nm in wavelength. The use of bulky and
expensive gas lasers to cure liquid radiation curable resins 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.
[0005] 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.
LEDs consist of a semiconducting material doped with impurities to
create a p-n junction capable of emitting light as positive holes
join with negative electrons when voltage is applied. The
wavelength of emitted light is determined by the materials used in
the active region of the semiconductor. Typical materials used in
semiconductors of LEDs include, for example, elements from Groups
13 (III) and 15 (V) of the periodic table. These semiconductors are
referred to as III-V semiconductors and include, for example, GaAs,
GaP, GaAsP, AlGaAs, InGaAsP, AlGaInP, and InGaN semiconductors.
Other examples of semiconductors used in LEDs include compounds
from Group 14 (IV-IV semiconductor) and Group 12-16 (II-VI). The
choice of materials is based on multiple factors including desired
wavelength of emission, performance parameters, and cost.
[0006] Early LEDs used gallium arsenide (GaAs) to emit infrared
(IR) radiation and low intensity red light. Advances in materials
science have led to the development of LEDs capable of emitting
light with higher intensity and shorter wavelengths, including
other colors of visible light and UV light. It is possible to
create LEDs that emit light across a wide wavelength spectrum, for
example, from a low of about 100 nm to a high of about 900 nm.
Typically, LED UV light sources currently emit light at wavelengths
between 300 and 475 nm, with 365 nm, 390 nm, and 395 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.
[0007] Several manufacturers offer LED lamps for commercial curing
applications. For example, Phoseon Technology, Summit UV, Honle UV
America, Inc., IST Metz GmbH, Jenton International Ltd., Lumos
Solutions Ltd., Solid UV Inc., Seoul Optodevice Co., Ltd.,
Spectronics Corporation, Luminus Devices Inc., and Clearstone
Technologies, are some of the manufacturers offering LED lamps for
curing ink-jet printing compositions, PVC floor coating
compositions, metal coating compositions, plastic coating
composition, and adhesive compositions.
[0008] LED curing devices are used in dental work. An example of
such a device is the ELIPAR.TM. FreeLight 2 LED curing light from
3M ESPE. This device emits light in the visible region with a peak
irradiance at 460 nm. LED equipment is also being tested for use in
the ink-jet printing, including, for example, by IST Metz. Although
LED lamps are available, liquid radiation curable resins suitable
for additive fabrication and curable by the use of LED light are
not well known commercially.
[0009] Although LED lamps are available, photocurable compositions
suitable for additive fabrication and curable by the use of LED
light are not well known commercially. Laser curable resins are
more common. For example, U.S. Pat. No. 7,211,368 reportedly
discloses a liquid stereolithography resin comprising a first
urethane acrylate oligomer, a first acrylate monomer, a
polymerization modifier, a second urethane acrylate oligomer
different from the first urethane acrylate oligomer, and a
stabilizer. The first urethane acrylate oligomer is an aliphatic
polyester urethane diacrylate oligomer, the first acrylate monomer
is ethoxylated (3) trimethylolpropane acrylate, and the
polymerization modifier is selected from the group consisting of
isobornyl acrylate, ethoxylated (5) pentaerythritol tetraacrylate,
an aliphatic urethane acrylate, tris-(2-hydroxyethyl)isocyanurate
triacrylate, and mixtures thereof. The resin includes 5-35 weight %
of an aliphatic polyester urethane diacrylate oligomer and 0.5-25
weight % ethoxylated (3) trimethylolpropane acrylate, wherein the
resin includes 15-45 weight % ethoxylated (5) pentaerythritol
tetraacrylate. However, the '368 patent indicates that a laser is
used to cure the resin. Further, the '368 patent fails to disclose
the use of an acid generating photoinitiator, such as a cationic
photoinitiator.
[0010] More recently, some attention has been given to the use of
LEDs in additive fabrication processes. U.S. Pat. No. 6,927,018 and
U.S. Patent Application Publication No. 2005/0227186 purportedly
provide a method, article of manufacture and system for fabricating
an article using photo-activatable building material. The method
according to the '018 patent and the '186 publication includes the
steps of applying a layer of the photo-activatable building
material to a preselected surface, scanning the layer using a
plurality of light-emitting centers to photo-activate the layer of
photo-activatable building material in accordance with a
predetermined photo-initiation process to obtain polymerization of
the building material. Scanning is accomplished at a predetermined
distance using a predetermined light intensity, and repeating the
steps of applying the layer. Each layer is applied to an
immediately previous layer, and the layer is scanned with the
plurality of light-emitting centers to polymerize the building
material until the article is fabricated. While the '018 patent and
the '186 publication mention UV LEDs and laser diodes as suitable
light-emitting centers, they fail to disclose detailed information
on photo-activatable building material suitable for LED cure.
[0011] U.S. Pat. No. 7,270,528 purportedly discloses a flash curing
system for solid freeform fabrication which generates a plurality
of radiation emitting pulses that forms a planar flash. The planar
flash initiates curing of a curable material dispensed by a solid
freeform fabrication apparatus. The '528 patent, while mentioning
UV light-emitting diodes (LED) lamps in the specification, sets
forth examples where a flash lamp is used to cure the resin
composition. The resin composition illustrated in the '528 patent
does contain a cationically curable monomer or a cationic
photoinitiator.
[0012] U.S. Patent Application Publication No. 2008/0231731 or
2008/0169589 or European Patent Application No. EP 1950032
purportedly discloses a solid imaging apparatus that includes a
replaceable cartridge containing a source of build material and an
extendable and retractable flexible transport film for transporting
the build material layer-by-layer from the cartridge to the surface
of a build in an image plane. If desired, the apparatus can produce
a fully reacted build. A high intensity UV source is said to cure
the build between layers. The above publications state that the
solid imaging radiation that is used to cure the build material can
be "any actinic radiation which causes a photocurable liquid to
react to produce a solid, whether a visible or UV source or other
source,"
[0013] International Patent Publication No. WO 2008/118263 is
directed to a system for building a three-dimensional object based
on build data representing the three-dimensional object, wherein
the system includes an extrusion head that deposits a
radiation-curable material in consecutive layers at a high
deposition rate. The radiation-curable material of each of the
consecutive layers is cooled to a self-supporting state. The system
is said to include a radiation source that selectively exposes
portions of the consecutive layers to radiation at a high
resolution in accordance with the build data. It is stated that the
exposure head includes a linear array of high resolution, UV
light-emitting diodes (LEDs). P71-1464 CUREBAR.TM. and P150-3072
PRINTHEAD.TM. are described as examples of suitable UV-radiation
sources for the exposure head. The '263 publication fails to
describe exemplary photocurable formulations suitable for curing by
LED light in an additive fabrication process.
[0014] International Patent Publication No. WO 2005/103121,
entitled "Method for photocuring of Resin Compositions", assigned
to DSM IP Assets B.V., describes and claims Methods for Light
Emitting Diode (LED) curing of a curable resin composition
containing a photoinitiating system, characterized in that the
highest wavelength at which absorption maximum of the
photoinitiating system occurs (.lamda..sub.Max PIS) is at least 20
nm below, and at most 100 nm below, the wavelength at which the
emission maximum of the LED occurs (.lamda..sub.LED). The invention
in this PCT patent application relates to the use of LED curing in
structural applications, in particular in applications for the
lining or relining of objects, and to objects containing a cured
resin composition obtained by LED curing. This invention provides a
simple, environmentally safe and readily controllable method for
(re)lining pipes, tanks and vessels, especially for such pipes and
equipment having a large diameter, in particular more than 15 cm.
The specification does not describe LED radiation curable
photocurable resins.
[0015] U.S. Patent Application Publication No. 2007/0205528
reportedly discloses an optical molding process wherein the
radiation source used is a non-coherent source of radiation. The
'528 publication indicates that the photocurable compositions are
formulated so as to enable the production of three-dimensional
articles having better performance when irradiated with
conventional (non-coherent) UV rather than with Laser UV, and
states that the photocurable compositions disclosed are more
appropriate for UV non-coherent irradiation than for Laser UV.
While the '528 publication mentions that "the exposure system uses
irradiation from non-coherent light sources, e.g., a xenon fusion
lamp, or light emitting diode bars," the exemplified exposure was
reportedly carried out according to the method of WO 00/21735,
which is said to describe an apparatus and a method wherein the
photosensitive material is exposed to a light source illuminating a
cross-section of a material by at least two modulator arrangements
of individually controllable light modulators.
[0016] U.S. Patent Application Publication No. 2009/0267269A or WO
2009/132245 reportedly discloses a continuous-wave (CW) ultraviolet
(UV) curing system for solid freeform fabrication (SFF), wherein
the curing system is configured to provide an exposure of UV
radiation for one or more layers of UV-curable material. It is
reported that one or more UV exposures may initiate curing of a
curable material in the layer dispensed by a solid freeform
fabrication apparatus. According to the '269 or '245 publication,
one approach to provide the single or multiple UV exposures is the
use of one or more UV LEDs, which generate UV radiation without
generating any substantial amounts of infrared (IR) radiation at
the same time.
[0017] The foregoing shows that there is an unmet need to provide
photocurable resin compositions for additive fabrication which are
capable of curing by irradiation by LED light.
[0018] Regardless of which type of light source is used in an
additive fabrication process, it is well known in the field of
liquid radiation curable resins that hybrid liquid radiation
curable resins produce cured three-dimensional articles with the
most desirable combination of mechanical properties. A hybrid
liquid radiation curable resin is a liquid radiation curable resin
that comprises both free radical and cationic polymerizable
components and photoinitiators. It is also well known that the
cationically polymerizable components of a liquid radiation curable
resin primarily contribute to the desirable combination of
mechanical properties in a cured three-dimensional article,
however, the cationically polymerizable components of a liquid
radiation curable resin polymerize at a much slower rate than the
free-radically polymerizable components. Consequently, the
mechanical properties of the cured three-dimensional article
develop over time after the initial cure of the hybrid liquid
radiation curable resin. Liquid radiation curable resins for
additive fabrication that contain cationically polymerizable
components but no free-radical polymerizable components are known,
however, such resins are generally considered to be too slow for
use as rapid prototyping materials. Therefore, it is desired to
increase the speed of the cationic cure in a liquid radiation
curable resin for additive fabrication to enable the resin to
attain the most desirable combination of physical properties as
quickly as possible.
[0019] Since the cationic polymerizable components generally cure
at a much slower rate than free-radical polymerizable components,
it is highly desirable to speed the rate of cationic cure.
Moreover, it is desirable to attain a resin with a fast photospeed
that uses less photoinitiator so that the amounts of the components
that positively contribute to the mechanical properties of a
three-dimensional article formed from the liquid radiation curable
resin can occupy a greater percentage of the liquid radiation
curable resin. Furthermore, cationic photoinitiators that provide
excellent photospeed at a variety of wavelengths commonly used in
additive fabrication techniques are highly desirable.
[0020] Many cationic photoinitiators useful in additive fabrication
also have poor thermal-stability. Thermal-stability is the ability
of a liquid radiation curable resin to maintain its viscosity after
exposure to temperature over time or during storage. Cationic
photoinitiators are responsive to both light and temperature. At
elevated temperatures, or at ambient temperature for a long time
period, the cationic photoinitiators will be slowly activated and
initiate a small amount of polymerization in the liquid radiation
curable resin. Over time, this small amount of polymerization will
create an undesirable increase in the viscosity of the liquid
radiation curable resin for additive fabrication.
[0021] Hybrid liquid radiation curable resins that contain high
amounts of inorganic filler, so-called filled compositions, are
highly desirable because of the combination of strength and
stiffness of the fully cured objects. Silica filler has been the
most preferred inorganic filler for liquid radiation curable resins
for additive fabrication for a number of years. Please see for
example, US published applications 2006/0100301, assigned to DSM,
and 2005/0040562, assigned to 3D Systems. Silica particles are
predominately comprised of SiO.sub.2. Examples of commercial
embodiments of filled liquid radiation curable resins wherein
silica nanoparticles are present are NanoTool.TM. and NanoForm.TM.
15100 Series by DSM Somos.RTM. and Accura.RTM. BlueStone.TM. by 3D
Systems, Inc.
[0022] A high amount of inorganic filler is highly desirable in a
liquid radiation curable resin due to its impact on the strength
and stiffness of the three-dimensional object produced therefrom.
However, highly filled compositions represent several challenges to
the formulator of liquid radiation curable resins for additive
fabrication. As the amount of filler increases, the viscosity of
the liquid radiation curable resin also usually increases. A high
viscosity liquid radiation curable resin is not desirable in some
additive fabrication processes, for instance,
stereolithography.
[0023] Furthermore, certain highly filled compositions are usually
not as 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. Because liquid radiation curable
resins for additive fabrication include one or more photoinitiators
that are responsive to ambient light undesirable light scattering
that occurs in additive fabrication processes, partial
polymerization occurs in the liquid radiation curable resin after
it is exposed to light. This small amount of polymerization, over
time, causes the viscosity of the liquid radiation curable resin to
increase gradually. Achieving good photo-stability is particularly
challenging in highly filled liquid radiation curable resins
because of additional light scattering effects caused by the
filler.
[0024] The most used cationic photoinitiators for current liquid
radiation curable resins for additive fabrication are based upon
sulfonium or iodonium cations in combination with either
fluorophosphates or fluoroantimonate anions. Antimonate salts are
often preferred because of their fast rate of cure. However, in
some municipalities, objects fabricated from antimonate based
compositions must be disposed of as a hazardous waste or hazardous
constituent waste.
[0025] Furthermore, it is often desirable to have low antimony or
antimony-free radiation curable compositions due to the adverse
effect of antimonate salts on the desired applications of the
three-dimensional article. For example, antimonate salts can have
an undesirable effect in investment casting applications.
Iodonium-borate photoinitiators are available, but suffer from the
need to be sensitized at the wavelengths useful for
stereolithography and have low thermal-stability. Sulfonium
phosphate photoinitiators are available, but suffer from a poor
rate of curing.
[0026] It would be desirable to have a cationic photoinitiator for
additive fabrication that has fast photospeed, good photo-stability
in filled compositions, good thermal-stability, and is
antimony-free.
BRIEF SUMMARY OF THE INVENTION
[0027] The first aspect of the instant claimed invention is a
liquid radiation curable resin for additive fabrication comprising
an R-substituted aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator with a
tetrakis(pentafluorophenyl)borate anion and a cation of the
following formula (I):
##STR00001##
wherein Y1, Y2, and Y3 are the same or different and where Y1, Y2,
or Y3 are R-substituted aromatic thioether with R being an acetyl
or halogen group.
[0028] The second aspect of the instant claimed invention is a
process of forming a three-dimensional object comprising the steps
of forming and selectively curing a layer of a liquid radiation
curable resin for additive fabrication of the first aspect of the
instant claimed invention and repeating the steps of forming and
selectively curing a layer of a liquid radiation curable resin for
additive fabrication of the first aspect of the instant claimed
invention a plurality of times to obtain a three-dimensional
object.
[0029] The third aspect of the instant claimed invention is a
three-dimensional object formed from the liquid radiation curable
resin for additive fabrication of the first aspect of the instant
claimed invention.
[0030] The fourth aspect of the instant claimed invention is a
liquid radiation curable resin for additive fabrication comprising
5 wt % to about 90 wt %, preferably from 10 wt % to 75 wt %, more
preferably from 30 to 75 wt % of inorganic filler, said inorganic
filler preferably comprising greater than 80 wt %, preferably
greater than 90 wt %, more preferably greater than 95 wt % of
silica, that has a Dp of from about 4.5 mils to about 7.0 mils
wherein the liquid radiation curable resin for additive
fabrication, when placed on a shaker table set at 240 rpm and
exposed to two 15 watt plant and aquarium lamps hung 8 inches above
the surface of the liquid radiation curable resin for additive
fabrication, has a gel time of greater than 200 hours, preferably
greater than 250 hours.
[0031] The fifth aspect of the instant claimed invention is the use
of an R-substituted aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator with a
tetrakis(pentafluorophenyl)borate anion and a cation of the
following formula (I):
##STR00002##
wherein Y1, Y2, and Y3 are the same or different and where Y1, Y2,
or Y3 are R-substituted aromatic thioether with R being an acetyl
or halogen group, on metal and metal alloys.
DETAILED DESCRIPTION OF THE INVENTION
[0032] U.S. Provisional application 61/287,620 is hereby
incorporated by reference in its entirety.
[0033] The first aspect of the instant claimed invention is a
liquid radiation curable resin for additive fabrication comprising
an R-substituted aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator with a
tetrakis(pentafluorophenyl)borate anion and a cation of the
following formula (I):
##STR00003##
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.
[0034] R-Substituted Aromatic Thioether Triaryl Sulfonium
Tetrakis(Pentafluorophenyl)Borate Cationic Photoinitiator
[0035] In accordance with an embodiment, the liquid radiation
curable resin for additive fabrication comprises an R-substituted
aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator. The
cationic photoinitiator generates photoacids upon irradiation of
light. They generate Bronsted or Lewis acids upon irradiation.
[0036] Use of triaryl sulfonium salts in additive fabrication
applications is known. Please see U.S. Pat. No. 6,368,769, to Asahi
Denki Kogyo, which discusses 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.+MX.sub.n.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.
[0037] The inventors have discovered that using an R-substituted
aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator as the
cationic photoinitiator in a liquid radiation curable resin for
additive fabrication enables a liquid radiation curable resin that
attains a fast photospeed, attains good thermal-stability, and
attains good photo-stability.
[0038] In an embodiment, the R-substituted aromatic thioether
triaryl sulfonium tetrakis(pentafluorophenyl)borate cationic
photoinitiator has 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.
[0039] In an embodiment, Y1, Y2, and Y3 are the same. In another
embodiment, Y1 and Y2 are the same, but Y3 is different. 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.
[0040] 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.
[0041] The inventors have also discovered that an R-substituted
aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator, for
instance, tris(4-(4-acetylphenyl)thiophenyl)sulfonium
tetrakis(pentafluorophenyl)borate, is much more thermally-stable
than 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.
[0042] Furthermore, the inventors have surprisingly found excellent
performance in photo-stability of a liquid radiation curable resin
for additive fabrication that comprises an R-substituted aromatic
thioether triaryl sulfonium tetrakis(pentafluorophenyl)borate
cationic photoinitiator, for instance
tris(4-(4-acetylphenyl)thiophenyl)sulfonium
tetrakis(pentafluorophenyl)borate, in combination with high amounts
of inorganic filler, such as silica-based filler. The interaction
with light and inorganic filler, such as silica filler, creates
added stability problems in highly filled liquid radiation curable
resins for additive fabrication. However, use of R-substituted
aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator in a
liquid radiation curable resin enables the resin to attain
comparable critical energy (Ec, E10) and depth of penetration (Dp)
values to a resin incorporating a conventional cationic
photoinitiator while achieving much better photo-stability.
[0043] 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 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.
[0044] The liquid radiation curable resin for additive fabrication
of the invention are curable by one or more LEDs operating at the
appropriate wavelength. In an embodiment, the LEDs operate at a
wavelength of from 200 nm-460 nm, preferably from 300 nm-400 nm,
more preferably from 340 nm-375 nm.
[0045] The R-substituted aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator can be
present in any suitable amount. In embodiments, up to 20 wt %, more
preferably up to 10 wt %, more preferably up to about 7 wt %. In
embodiments, the R-substituted aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator is
present in an amount from about 0.1 wt % to about 20 wt %,
preferably from about 0.1 wt % to about 10 wt %, more preferably
from about 0.1 wt % to about 7 wt %, more preferably from about 0.2
wt % to about 4 wt %. In some embodiments, the R-substituted
aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator is
present in an amount from 0.1 wt % to 2 wt %, preferably from 0.1
wt % to 1.5 wt %.
[0046] Other Cationic Photo initiators and Photosensitizers
[0047] In accordance with an embodiment, the liquid radiation
curable resin for additive fabrication includes a cationic
photoinitiator in addition to 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. Thus, any residual
photoinitiator does not continue to cure after the removal of the
irradiating light. Cationic photoinitiators offer the advantage
that they are not sensitive to oxygen present in the
atmosphere.
[0048] 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).
[0049] In some embodiments it is desirable for the liquid radiation
curable resin for additive fabrication 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. 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.sup.-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,
methyl-2-benzoyl benzoate, 4-benzoyl-4'-methyl diphenyl sulphide,
4,4'-bis(diethylamino)benzophenone, and any combination
thereof.
[0050] 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).
[0051] 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
##STR00005##
and any combination thereof.
[0052] 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 composition, in certain embodiments, up to about 5%
by weight of the composition, and in further embodiments from about
0.05% to about 2% by weight of the composition.
[0053] 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). These photoinitiators when used in
combination with a photosensitizer are suitable for use with LED
light sources emitting at wavelengths from about 100 nm to about
300 nm.
[0054] 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.
[0055] 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
composition, in certain embodiments, from about 1 to about 8 wt %
of the composition, and in further embodiments from about 2 to
about 6 wt % of the composition. In an embodiment, the above ranges
are particularly suitable for use with epoxy monomers.
[0056] 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.
[0057] Cationically Polymerizable Component
[0058] 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.
[0059] 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.
[0060] Examples of 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--, --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, polyglycidyl ethers of polyether polyol obtained
by the addition of one or more alkylene oxides to aliphatic
polyhydric alcohols such as ethylene glycol, propylene glycol, and
glycerol, 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((1-ethyl(3-oxetanyl))methyl)ether,
3-ethyl-3-((2-ethylhexyloxy)methyl)oxetane,
3-ethyl-((triethoxysilylpropoxymethyl)oxetane,
3-(meth)-allyloxymethyl-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. Examples of polyfunctional materials that are cationically
polymerizable include 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.
[0061] In embodiments of the invention, the cationic polymerizable
component is at least one selected from the group consisting of a
cycloaliphatic epoxy and an oxetane. In a specific embodiment, the
cationic polymerizable component is an oxetane, for example, an
oxetane containing 2 or more than 2 oxetane groups. In another
specific embodiment, the cationic polymerizable component is a
cycloaliphatic epoxy, for example, a cycloaliphatic epoxy with 2 or
more than 2 epoxy groups.
[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 EPONEX.TM. 1510
from Hexion), 1,4-cyclohexanedimethanol diglycidyl ether (available
as HELOXY.TM. 107 from Hexion), 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.
[0064] The liquid radiation curable resin for additive fabrication
can include any suitable amount of the cationic polymerizable
component, for example, in certain embodiments, in an amount an
amount up to about 80 wt % of the composition, in certain
embodiments, from about 10 to about 80% by weight of the
composition, and in further embodiments from about 20 to about 70
wt % of the composition.
[0065] In accordance with an embodiment, the polymerizable
component of the liquid radiation curable resin for additive
fabrication 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 contain an
acrylate and an epoxy group, or an acrylate and an oxetane group,
on a same molecule.
[0066] In embodiments, the liquid radiation curable resin for
additive fabrication of the present invention includes a
photoinitiating system. The photoinitiating system can be a
free-radical photoinitiator or a cationic photoinitiator or 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.
[0067] Radical Photoinitiator
[0068] 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 Norrrish 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.
[0069] 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 composition to
determine if they will be activated by the LED light chosen to
provide the curing light.
[0070] 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.
[0071] 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]titan-
ium, and any combination thereof.
[0072] For LED 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.
[0073] 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).
[0074] It is possible for LED UV light sources to be designed to
emit light at shorter wavelengths. For LED light sources emitting
at wavelengths from between about 100 and about 300 nm, it is
desirable 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, and dimethoxybenzophenone, and,
1-hydroxyphenyl ketones, such as 1-hydroxycyclohexyl phenyl ketone,
phenyl (1-hydroxyisopropyl)ketone,
2-hydroxy-1-[4-(2-hroxyethoxy)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).
[0075] LED light sources can also be designed to emit visible
light. For LED light 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 (Irgacure 819 or
BAPO from Ciba), metallocenes such as bis(eta
5-2-4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titan-
ium (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.
[0076] In one embodiment of the instant claimed invention, the
light emitted by the LED 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 LED 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 LED is UVC radiation, which is
radiation with a wavelength between about 100 and about 280 nm.
[0077] The liquid radiation curable resin for additive fabrication
can include any suitable amount of the free-radical photoinitiator,
for example, in certain embodiments, in an amount up to about 10 wt
% of the composition, in certain embodiments, from about 0.1 to
about 10 wt % of the composition, and in further embodiments from
about 1 to about 6 wt % of the composition.
[0078] Radically Polymerizable Component
[0079] 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 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.
[0080] 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.
[0081] 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.
[0082] In accordance with an embodiment, the polyfunctional
(meth)acrylates of the polyfunctional component 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 hexa(meth)crylate, propoxylated
trimethylolpropane tri(meth)acrylate, and propoxylated neopentyl
glycol di(meth)acrylate, and any combination thereof.
[0083] 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.
[0084] 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 monohydroxypentaacrylate,
propoxylated trimethylolpropane triacrylate, and/or propoxylated
neopentyl glycol diacrylate.
[0085] The liquid radiation curable resin for additive fabrication
can include any suitable amount of the free-radical polymerizable
component, for example, in certain embodiments, in an amount up to
about 40 wt % of the composition, in certain embodiments, from
about 2 to about 40 wt % of the composition, in other embodiments
from about 10 to about 40 wt %, and in further embodiments from
about 10 to about 25 wt % of the composition.
[0086] Stabilizers
[0087] In embodiments of the invention, the liquid radiation
curable resins for additive fabrication include a stabilizer.
Stabilizers are often added to the compositions in order to 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. 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 compositions. A
15-23% sodium carbonate solution is preferred for formulations of
this invention with recommended amounts varying between 0.05 to
3.0% by weight of composition, more preferably from 0.05 to 1.0 wt
%, more preferably from 0.1 to 0.5% by weight of composition.
Alternative stabilizers include polyvinylpyrrolidones and
polyacrylonitriles.
[0088] Other Components
[0089] Other possible additives include dyes, pigments, talc, 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, titanium oxide, aluminum powder, bronze
powder, zinc powder, copper powder, lead powder, gold powder,
silver dust, glass fiber, titanic acid potassium whisker, carbon
whisker, sapphire whisker, beryllia whisker, boron carbide whisker,
silicon carbide whisker, silicon nitride whisker, glass beads,
hollow glass beads, metaloxides and potassium titanate whisker),
antioxidants, wetting agents, photosensitizers for the free-radical
photoinitiator, chain transfer agents, leveling agents, defoamers,
surfactants and the like.
[0090] In accordance with an embodiment, the liquid radiation
curable resin for additive fabrication can further include a chain
transfer agent, particularly a chain transfer agent for a cationic
monomer. The chain transfer agent has a functional group containing
active hydrogen. Examples of the active hydrogen-containing
functional group include an amino group, an amide group, a hydroxyl
group, a sulfo group, and a thiol group. In an embodiment, the
chain transfer agent terminates the propagation of one type of
polymerization, i.e., either cationic polymerization or
free-radical polymerization and initiates a different type of
polymerization, i.e., either free-radical polymerization or
cationic polymerization. In accordance with an embodiment, chain
transfer to a different monomer is a preferred mechanism. In
embodiments, chain transfer tends to produce branched molecules or
crosslinked molecules. Thus, chain transfer offers a way of
controlling the molecular weight distribution, crosslink density,
thermal properties, and/or mechanical properties of the cured resin
composition.
[0091] Any suitable chain transfer agent can be employed. For
example, the chain transfer agent for a cationic polymerizable
component is a hydroxyl-containing compound, such as a compound
containing 2 or more than 2 hydroxyl-groups. In an embodiment, the
chain transfer agent is selected from the group consisting of a
polyether polyol, polyester polyol, polycarbonate polyol,
ethoxylated or propoxylated aliphatic or aromatic compounds having
hydroxyl groups, dendritic polyols, hyperbranched polyols. An
example of a polyether polyol is a polyether polyol comprising an
alkoxy ether group of the formula [(CH.sub.2).sub.nO].sub.m,
wherein n can be 1 to 6 and m can be 1 to 100.
[0092] A particular example of a chain transfer agent is
polytetrahydrofuran such as TERATHANE.TM..
[0093] The liquid radiation curable resin for additive fabrication
can include any suitable amount of the chain transfer agent, for
example, in certain embodiments, in an amount up to about 50% by
weight of the composition, in certain embodiments, up to about 30%
by weight of the composition, and in certain other embodiments from
about 10% to about 20% by weight of the composition.
[0094] The liquid radiation curable resin 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, organic fillers, inorganic fillers, or
organic-inorganic hybrid fillers of sizes ranging from about 8
nanometers to about 50 microns.
[0095] Inorganic Filler
[0096] In embodiments, an inorganic filler is present in an amount
from 5 wt % to about 90 wt %, preferably from 10 wt % to 75 wt %,
more preferably from 30 to 75 wt %. The inorganic filler preferably
comprises silica (SiO.sub.2) nanoparticles or microparticles, or
nanoparticles or microparticles that are substantially silica
based, for instance, greater than 80 wt %, more preferably 90 wt %,
more preferably 95 wt % of silica. Preferred silica nanoparticles
are Nanopox products from Nanoresins, such as Nanopox A610.
Suitable examples of such silica microparticles are NP-30 and
NP-100 from AGC Chemicals, SUNSPACER.TM. 04.X and 0.4.times.ST-3
from Suncolor Corporation. Examples of such silica nanoparticles
are SUNSPHERES.TM. 200 nm such as 0.2 and 0.2-STP-10. Please see
U.S. Pat. No. 6,013,714 for further examples of silica particles.
However, depending on the size and other properties of the silica
nanoparticles or microparticles, the thermal-stability of the
liquid radiation curable resin may decrease when certain silica
nanoparticles or microparticles are added to the liquid radiation
curable resin due to the acidity of the silica.
[0097] As mentioned above, the inventors have found a surprising
combination of a triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator,
preferably, tris(4-(4-acetylphenyl)thiophenyl)sulfonium
tetrakis(pentafluorophenyl)borate, and high amounts of inorganic
filler, preferably silica filler which comprises greater than 80 wt
%, more preferably 90 wt %, more preferably 95 wt % of silica. The
combination yields liquid radiation curable resins for additive
fabrication that attain excellent photo-stability and
thermal-stability.
[0098] Nanoparticles are defined herein as particles having an
average particle diameter in the range from 1 nm to 999 nm as
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. Microparticles are defined
herein as particles that have an average particle diameter in the
range from 1 to about 100 microns as measured in accordance with
ISO13320:2009.
[0099] The second aspect of the instant claimed invention is a
process of forming a three-dimensional object comprising the steps
of forming and selectively curing a layer of a liquid radiation
curable resin for additive fabrication comprising a triaryl
sulfonium tetrakis(pentafluorophenyl)borate photoinitiator and
repeating the steps of forming and selectively curing a layer of a
liquid radiation curable resin for additive fabrication comprising
a triaryl sulfonium tetrakis(pentafluorophenyl)borate
photoinitiator a plurality of times to obtain a three-dimensional
object. The process can be performed using any suitable means of
imaging radiation, such as an LED, a lamp, or a laser. Moreover,
the process can be performed on a liquid radiation curable resin
contained in a vat or coated on a substrate. Preferably, the
process is performed by one or more LEDs. The LEDs preferably
operate from 200 nm-460 nm, preferably from 300 nm-400 nm, more
preferably from 340 nm-370 nm.
[0100] The third aspect of the instant claimed invention is a
three-dimensional object formed from a liquid radiation curable
resin for additive fabrication that comprises a triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator.
[0101] The fourth aspect of the instant claimed invention is a
liquid radiation curable resin for additive fabrication comprising
5 wt % to about 90 wt %, preferably from 10 wt % to 75 wt %, more
preferably from 30 to 75 wt % of inorganic filler, said inorganic
filler preferably comprising greater than 80 wt %, preferably
greater than 90 wt %, more preferably greater than 95 wt % of
silica, that has a Dp of from about 4.5 mils to about 7.0 mils,
preferably from 4.5 mils to about 6.0 mils, more preferably from
4.5 mils to about 5.5 mils, wherein the liquid radiation curable
resin for additive fabrication, when placed on a shaker table set
at 240 rpm and exposed to two 15 watt plant and aquarium lamps hung
8 inches above the surface of the liquid radiation curable resin
for additive fabrication, has a gel time of greater than 200 hours,
preferably greater than 250 hours.
[0102] The fifth aspect of the instant claimed invention is the use
of an R-substituted aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator with a
tetrakis(pentafluorophenyl)borate anion and a cation of the
following formula (I):
##STR00006##
wherein Y1, Y2, and Y3 are the same or different and where Y1, Y2,
or Y3 are R-substituted aromatic thioether with R being an acetyl
or halogen group, on metal and metal alloys, such as alluminum
alloy, steels, stainless steels, copper alloys, tin, or tin-plated
steels.
[0103] The following examples further illustrate the invention but,
of course, should not be construed as in any way limiting its
scope.
EXAMPLES
[0104] 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 Component Formula Chemical
Descriptor Supplier BYK A 501 Bubble breaker Naphtha/methoxy
propanol acetate BYK-Chemie NK Ester A-DOG Free radical
[2-[1,1-dimethyl-2-[(1- Kowa polymerizable
oxoallyl)oxy]ethyl]-5-ethyl-1,3-dioxan- compound 5-yl]methyl
acrylate CD 406 Free radical 1,4-Cyclohexanedimethanol diacrylate
Sartomer polymerizable compound Chivacure 1176 Cationic A mixture
of: bis[4- Chitec Photoinitiator diphenylsulfoniumphenyl]sulfide
bishexafluoroantimonate; thiophenoxyphenylsulfonium
hexafluoroantimonate and propylene carbonate. Chivacure BMS
Photosensitizing [4-[(4- Chitec agent
methylphenyl)thio]phenyl]phenyl- methanone DG-0071 Stabilizer 22%
of sodium carbonate solution Desotech DPHA Radical
Dipentaerythritol hexaacrylate Sigma Polymerizable Aldrich Compound
EPONOX 1510 Cationic Hydrogenated bisphenol A- Hexion Polymerizable
epichlorohydrin based epoxy resin Compound Heloxy 68 Cationic
Neopentylglycol diglycidylether Hexion Polymerizable Compound HQMME
Antioxidant Hydroquinone monomethyl ether Intermediate DG-0049
Pigment Pigment dispersion for color effects Desotech dispersion
Irgacure 184 Radical 1-Hydroxy-1-cyclohexyl phenyl ketone BASF
Photoinitiator Irgacure PAG-290 Cationic tris(4-(4- BASF
Photoinitiator acetylphenyl)thiophenyl)sulfonium
tetrakis(pentafluorophenyl)borate Longnox 10 Antioxidant
Pentaerythritol tetrakis[(3,5-di-tert- Longchem
butyl-4-hydroxyphenyl)propionate] C&S Int. Nanopox A610 Filler
in reactive 40% 15 nm of SiO.sub.2 Particle in epoxy Nanoresins
monomer monomer OXT-101 Cationic 3-Ethyl-3-oxetanemethanol Toagosei
Polymerizable Compound Polyvinyl pyrrolidone Acid
Poly[N-vinylpyrrolidinone]; PVP Sigma scavenger Aldrich Rhodorsil
2074 Photoacid Iodonium, [4-(1-methylethyl)phenyl](4- Rhodia
generator methylphenyl)-, tetrakis(pentafluorophenyl)borate
Rubidium carbonate Acid Dirubidium carbonate; Rb.sub.2CO.sub.3
Sigma scavenger Aldrich Silwet L 7600 Leveling Polyalkyleneoxide
modified Momentive agent polydimethylsiloxane SR-399LV, J Radical
Dipentaerythritol Sartomer Polymerizable monohydroxypentaacrylate
Compound SR-833S Radical Tricyclodecane Dimethanol Diacrylate
Sartomer Polymerizable Compound Sunspacer 4.0X-ST-3 Filler
SiO.sub.2 Particle (4 micron average particle Suncolor size)
TERATHANE 1000 Chain transfer Poly(tetramethylene ether) glycol
Invista agent for cationic monomers
Examples 1-7
[0105] Various liquid radiation curable resins for additive
fabrication were prepared using an R-substituted aromatic thioether
triaryl sulfonium tetrakis(pentafluorophenyl)borate cationic
photoinitiator. A similar composition was prepared using an
alternative antimony-free cationic photoinitiator. These samples
were tested according to the methods for working curve measurement
and dynamic mechanical analysis detailed below. Working curve data
was obtained using a single UV LED "bare bulb" (Model No. NCSU033A;
Nichia Corporation, Japan) having a peak wavelength of 365 nm in a
light curing apparatus, wherein the single LED light is
bottom-mounted on a flat surface inside a 30.degree. C. chamber and
positioned in an upward-looking arrangement and pointing vertically
according to the below method. Real-time dynamic mechanical
analysis was performed using a mercury lamp with a 365 nm
interference filter, respectively. The results are presented in
Table 2 and Table 3.
[0106] Working Curve Measurement
[0107] The photo cure speed test using 365 nm LED light is used to
measure values for Ec and Dp of the example and comparative example
compositions in Table 2 and Table 3. A single UV LED "bare bulb"
(Model No. NCSU033A; Nichia Corporation, Japan) having a peak
wavelength of 365 nm is used as the LED light source in a light
curing apparatus, wherein the single LED light is bottom-mounted on
a flat surface inside a 30.degree. C. chamber and positioned in an
upward-looking arrangement and pointing vertically. The LED light
is powered by a 3.30 V/0.050 A DC output from a Programmable Power
Supply (Model No. PSS-3203; GW Instek).
[0108] A 10-mil sheet of polyester film (Melinex #515, Polybase
Mylar D, 0.010 gauge) is placed at a distance of 12 mm above from
the bottom of the LED light bulb. A drop of the liquid resin is
placed on the polyester film over the center of the LED light. The
resin is exposed to the LED light through the polyester film for a
specific time interval. The process is repeated with fresh resin
for 2, 4, 6, 8, 10 second exposure times or up to 12, 16, or 20
seconds for slow curing resin formulations.
[0109] After exposure to the LED light, the sample is allowed to
age inside the 30.degree. C. chamber for at least 15 minutes, after
which time any uncured resin is removed from the exposed areas by
blotting with a Kimwipe EX-L (Kimberly Clark). A thickness
measurement is then taken on the center of the exposed area using
an ABSOLUTE Digimatic Indicator (Model ID-C112CE, Mitutoyo
Corporation, Japan). The measured thickness of each sample is
plotted as a function of the natural logarithm of the exposure
time. The depth of penetration (Dp; mil) of the resin composition
is the slope of the least squares fit line. The Ec (sec) is the
X-axis crossing point (Y=0) of the line. The E.sub.3, E.sub.4, or
E.sub.5 is, respectively, the time (in seconds) required to produce
a layer having a thickness of 3, 4, or 5 mils, respectively.
[0110] Alternatively, when the intensity of the incident light
(mW/cm.sup.2) from the light source on the resin surface is known,
the exposure energy (mJ/cm.sup.2) rather than the exposure time (in
seconds) is used for calculating the Dp and Ec values.
[0111] Measurement of Storage Shear Modulus (G) by Real Time
Dynamic Mechanical Analysis (RT-DMA)
[0112] Real Time Dynamic Mechanical Analysis (RT-DMA), including
the storage shear modulus (G'), is carried out under ambient lab
conditions (20-23.degree. C. and 25-35% RH), on compositions
undergoing curing using a StressTech Rheometer (Reologicia
Instruments AB, Sweden) with an 8 mm plate, a gap of 0.1 mm, and
modified to include a mercury lamp light source (OMNICURE Series
2000 available from EXFO), fitted with a 365 nm interference filter
(also available from EXFO) placed in the light path and a
liquid-filled light guide for conveying light from the source to
the rheometer. The 365 nm interference filter produces the spectral
output shown in FIG. 1. The samples are evaluated under the
following parameters: 10 s of equilibrium time; frequency of 10 Hz;
50 mW/cm2 light intensity by the IL 1400 radiometer with XRL140B
detector (International Light, Newburyport, Mass.); 1.0 s exposure
that starts at 2.1 seconds from the beginning of data collection;
FFT smoothing of curves; G' taken at 2.5, 2.7, 3, 4, and 6 s from
the beginning of data collection by using the accompanying software
for data analysis.
[0113] FIG. 2 shows a schematic of the RT-DMA apparatus. The liquid
radiation curable resin (1) is placed on a plane (2). The amount of
liquid resin used should be approximately the amount indicated in
the figure. The plane is a quartz plate that is sold with the
StressTech Rheometer. The 8 mm plate (3) is positioned with a 0.1
mm gap (4) between the plate and the plane. The gap is set via the
software accompanying the StressTech Rheometer. Light (5) is
provided though the plane (2). Please see the publication "Dynamic
Mechanical Analysis of UV-Curable Coatings While Curing" by Robert
W. Johnson available at
http://reologicainstruments.com/PDF%20files/BobJohnsonUVpaper.pdf,
and hereby incorporated by reference in its entirety, for more
information on RT-DMA.
TABLE-US-00002 TABLE 2 Ex1 Ex2 Ex3 EBECRYL-3700 25 17.237 24.449 CD
406 7 6.846 Celloxide 2021P 36 52.959 34.326 OXT-101 8.431
TERATHANE-1000 25 10.254 24.449 Chivacure 1176 3.998 3.325 Irgacure
PAG-290 4 2 2.2 Irgacure 184 3 4.9 4.401 PVP 0.005 Rubidium
carbonate 0.005 Silwet L 7600 0.196 BYK A 501 0.02 Total 100 100
100 Dp (mil) 3.53 5.69 5.42 Ec (s) 1.13 1.15 1.22 E3 (s) 2.64 1.96
2.13 E4 (s) 3.5 2.33 2.56 E5 (s) 4.65 2.78 3.08 G' 0.4 sec after
light on (Pa) 1270 1150 3060 G' 0.6 sec after light on (Pa) 5510
10700 76900 G' 0.9 sec after light on (Pa) 119000 99300 456000 G'
1.9 sec after light on (Pa) 627000 277000 1580000 G' 3.9 sec after
light on (Pa) 1030000 459000 2540000
TABLE-US-00003 TABLE 3 Ex4 Ex5 Ex6 Ex7 Comp1 Irgacure PAG 290 0.98
1.00 1.00 1.50 Rhodorsil PI-2074 2.00 Chivacure BMS 1.00 Irgacure
184 6.00 6.00 6.00 6.00 6.00 SR399J 6.24 5.74 4.94 DPHA 7.02 4.00
NK Ester A-DOG 20.00 20.00 15.57 15.57 15.57 Celloxide 2021P 45.84
45.84 Terathane1000 10.19 13.19 OXT-101 9.17 9.17 15.70 15.70 15.70
Longnox 10 0.50 0.50 1.00 1.00 0.50 PVP 0.01 0.01 DG-0049 0.30 0.30
0.20 0.20 Epon 1510 54.30 54.30 54.30 Total 100 100 100 100 100 G'
0.5 sec after light on (Pa) 18810 9884 809 2140 449 G' 0.7 sec
after light on (Pa) 195100 123000 44920 33620 21440 G' 1.0 sec
after light on (Pa) 742500 555100 360000 270900 219400 G' 2.0 sec
after light on (Pa) 1726000 1400000 1099000 866900 697800 G' 4.0
sec after light on (Pa) 2305000 1968000 1565000 1261000 1014000
Examples 8-11
[0114] Various liquid radiation curable resins were prepared
according to methods well known in the art. The amount and type of
the cationic photoinitiator was varied from Chivacure 1176
(Comparative Examples 8, 9, 10) to Irgacure PAG-290 (Examples 8, 9,
10, 11). Since Chivacure 1176 is a 50/50 mixture of cationic
photoinitiator and propylene carbonate, an amount of propylene
carbonate was added to some of the formulations containing PAG-290
in order to keep the amount of cationic photoinitiator plus
propylene carbonate constant. Working curve data was prepared using
a solid state laser operating at a wavelength of 354.7 nm in
accordance with the below method. Photo-stability data (hrs until
gel time), and thermal-stability data (initial viscosity, 15 day
viscosity, and 24 days viscosity) were measured in accordance with
the below methods. The details of the compositions of each example
(Ex) and comparative example (Comp) are specified in Table 4 with
each component represented as weight percent of the total
composition.
[0115] Working Curve Measurement
[0116] 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.
[0117] The exposure response for each formulation is measured using
a 20 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-C112CE Indicator
Micrometer. Film thickness is a linear function of the natural
logarithm of the exposure energy; the slope of the regression is Dp
(units of micron or mil) and Ec is the x-axis intercept of the
regression fit (units of mJ/cm.sup.2). E10 is the energy required
to cure a ten mil (254 micron) layer.
[0118] Photo-Stability Measurement
[0119] 45 g of each sample is added into 60 mL clear jars with a
wide open top, available from FlackTek, Inc. The sample containing
jars are placed uniformly across an Excella E5 platform shaker
available from New Brunswick Scientific Co., Inc. Each sample
containing jar is secured with clamps to the platform shaker. The
light bank containing two 15 watt plant & aquarium lamps
(General Electric, F15T8 PL/AQ) is hung 8 inches high over the
shaker platform. The shaker speed is set to 240 rpm. The samples
are exposed right under the lamps and rotated daily until the
liquid sample is gelled. The liquid sample is gelled when a solid
layer has formed on the surface of the liquid sample. The gel time
is collected to the nearest hour.
[0120] Thermal-Stability Measurement
[0121] After the liquid radiation curable resin is made, it is
allowed to sit for between 30 and 60 minutes or until it is
degassed. Light tapping of the container holding the liquid
radiation curable resin is performed to accelerate the degassing
process. The initial viscosity is then measured using a Rheometer
from Paar Physica (Rheolab, MC10, Z3 cup and 1/50 s shear rate).
The samples are held in the machine at the specified shear rate for
15 minutes before data is collected.
[0122] 45 g of each sample is added into 60 mL clear jars with a
wide open top available from FlackTek, Inc. The jar is capped
loosely. The sample containing jars are placed in a 55.degree. C.
oven for a specified number of days. The samples containing jars
are removed from the oven and allowed to cool to ambient
conditions. The samples are then remixed and the viscosity is
measured using the same equipment and technique mentioned
above.
[0123] The percentage change in viscosity is calculated by dividing
the viscosity at a specified day by the initial viscosity. The
result is then multiplied by 100.
TABLE-US-00004 TABLE 4 Component Comp 8 Ex 8 Comp 9 Ex 9 Comp 10 Ex
10 Ex 11 Nanopox A610 33.62 33.62 34.61 34.78 33.57 33.57 34.72
Heloxy 68 5.71 5.71 5.88 5.91 5.70 5.70 5.89 OXT-101 3.81 3.81 3.92
3.94 3.80 3.80 3.93 SR-399LV 3.42 3.42 3.52 3.54 3.42 3.42 3.54
SR-833S 2.29 2.29 2.36 2.37 2.29 2.29 2.39 Chivacure 1176 3.80 1.00
3.80 Irgacure PAG-290 1.90 0.50 1.90 0.50 Propylene carbonate 1.90
1.90 Irgacure 184 0.40 0.40 0.40 0.40 0.40 0.40 0.40 Sunspacer
4.0X-ST-3 46.93 46.93 48.29 48.54 46.85 46.85 48.46 HQMME 0.02 0.02
0.02 0.02 0.02 0.02 0.02 DG-0071 0.15 0.15 0.15 Total 100.00 100.00
100.00 100.00 100.00 100.00 100.00 Total fillers 60.38 60.38 62.13
62.45 60.28 60.28 62.35 Ec (mJ/cm2) 8.36 6.88 17.36 6.51 6.83 5.51
12.45 Dp (mils) 4.90 1.73 14.82 3.92 4.38 1.37 5.12 E10 (mJ/cm2)
64.29 2209 34.09 83.41 66.78 8177 87.75 Photo-stability (hrs, gel
time) 69 39 79 55 199 199 No gel Initial Viscosity (cps, 30.degree.
C.) 1693 1655 2014 2227 1618 1468 2089 15 Day Viscosity (cps,
30.degree. C.) 4249 2849 4084 3529 2549 2111 3120 15 Day Viscosity
increase (%) 250.97 172.15 202.78 158.46 157.54 143.80 149.35 24
Day Viscosity (cps, 30.degree. C.) 6642 3312 5743 3917 2927 2297
3388 24 Day Viscosity increase (%) 392.32 200.12 285.15 175.89
180.90 156.47 162.18 No gel = the sample did not gel after 300
hours. Comp = comparative example - not to be construed as an
example of the invention Ex = example of the invention
[0124] Discussion of Results
[0125] Improved reactivity of Examples 1-7 is demonstrated in
comparison to Comparative Example 1.
[0126] Comparative Example 8 uses a typical amount of a common
cationic photoinitiator used in many commercial liquid radiation
curable resins for additive fabrication. Consequently, an E10 and
Dp that is suitable for an additive fabrication process is
achieved.
[0127] Example 8 was designed to demonstrate the effects of a
direct swap of an R-substituted aromatic thioether triaryl
sulfonium tetrakis(pentafluorophenyl)borate cationic photoinitiator
for Chivacure 1176. Example 8 shows a very low Dp and very high E10
due to the increased absorbance of the R-substituted aromatic
thioether triaryl sulfonium tetrakis(pentafluorophenyl) borate
cationic photoinitiator over Chivacure 1176. The Dp is too low and
the E10 far too high compared to Comparative Example 8. Example 8
and Comparative Example 8 would thus not perform similarly in an
additive fabrication process. Consequently, the photo-stability of
Example 8 is less than the photo-stability of Comparative Example
8. However, the thermal-stability of Example 8 is greatly improved
over the thermal-stability of Comparative Example 8.
[0128] Example 9 and Comparative Example 9 use a much lower amount
of cationic photoinitiator. Again, the Dp is significantly lower
than in Comparative Example 8. The reduced amount of cationic
photoinitiators in Example 9 and Comparative Example 9 yield
additional improvement in the thermal-stability of the liquid
radiation curable resin over Example 8 and Comparative Example 8,
respectively.
[0129] A stabilizer is added in Example 10, Example 11, and
Comparative Example 10. The stabilizer greatly improves the
photo-stability of the liquid radiation curable resin for additive
fabrication. Despite the very low Dp and high E10, Example 10 is
able to achieve a photo-stability that is similar to Comparative
Example 10 which has a much more desirable Dp and E10. Example 11
demonstrates a Dp that is comparable to Example 8 and a greatly
improved photo-stability over any other example or Comparative
Example. Example 10 and Example 11 also demonstrate improved
thermal-stability over Comparative Example 10.
[0130] 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.
[0131] 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.
[0132] Preferred embodiments of this invention are described
herein, including the best mode known to the inventors 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 inventors expect skilled artisans to
employ such variations as appropriate, and the inventors intend 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.
[0133] 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.
* * * * *
References