Note: Descriptions are shown in the official language in which they were submitted.
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DISPERSIONS FOR ADDITIVE MANUFACTURING COMPRISING DISCRETE
CARBON NANOTUBES
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. continuation-in-part
application no.
17/212,612 filed on March 25, 2021. This application also related to U.S.
Serial No.
17/187,658, filed Feb. 26, 2021, which itself is a continuation in part of
U.S. Serial No.
16/012,265 filed June 19, 2018, now U.S. Patent 10,934,447, which is a
continuation in part of
U.S. Serial No. 15/288,553 filed October 7, 2016, now United States Patent No.
9,636,649,
which was a continuation-in-part application of U.S. Serial No. 15/225,215
filed August 1,
2016, allowed September 12, 2016 and issued as U.S. Patent No. 9,493,626 which
was a
continuation-in-part application of U.S. Serial No. 15/166,931 filed May 27,
2016 and issued
as U.S. Patent No. 9,422,413 which was a continuation of U.S. Serial No.
14/924,246, Filed
October 27, 2015 and issued as U.S. Patent No. 9,353,240, which is a
continuation of U.S.
Serial No. 13/993,206, filed June 11, 2013 and issued as U.S. Patent No.
9,212,273, which
claims priority to PCT/EP2011/072427, filed December 12, 2011, which claims
benefit of U.S.
provisional application 61/423,033, filed December 14, 2010. All of the afore-
mentioned U.S.
applications and/or granted patents are expressly incorporated herein by
reference. This
application is also related to U.S. Serial Nos. 62/319,599; 14/585,730;
14/628,248; and
14/963,845.
FIELD OF INVENTION
[0002] The present invention is directed to additive manufacturing
compositions and
methods for producing additive manufacturing composite blends with oxidized
discrete carbon
nanotubes with dispersion agents bonded to at least one sidewall of the
oxidized discrete carbon
nanotubes. Such compositions are especially useful when radiation cured,
sintered or melt
fused.
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BACKGROUND OF THE INVENTION
[0003] Additive Manufacturing (AM) is an appropriate name to describe the
technologies that build 3D objects by adding layer-upon-layer of material, the
material
generally being crosslinkable monomers or oligomers, polymers, metals,
ceramics, and
biocompatible materials. Common to AM technologies is the use of a computer,
3D modeling
software (Computer Aided Design or CAD), machine equipment and layering
material. Once
a CAD sketch is produced, the AM equipment reads in data from the CAD file and
lays downs
or adds successive layers of liquid, powder, sheet material or others such
tape, in a layer-upon-
layer fashion to fabricate a 3D object. The term AM encompasses many
technologies including
subsets like 3D Printing, Rapid Prototyping (RP), Direct Digital Manufacturing
(DDM),
layered manufacturing and additive fabrication.
[0004] Liquid radiation curable resins are selectively cross-linked (or cured)
by an
energy source such as lasers. Photocurable resin formulation efforts have
focused on
mechanical performance enhancement to simulate properties of commodity
plastics and
engineered polymers. Improving mechanical performance of photo-curable resins
can be
accomplished through development of special monomers and curing agents,
altering chain
growth mechanisms, utilization of mixed modes of polymerization and inclusion
of additives
and fillers. However, there remains many limitations as their balance of
properties such as heat
distortion resistance, rigidity, and impact strength.
[0005] Addition of fillers have been utilized to meet specific performance
requirements
for select AM applications, such as stiffness. Inorganic fillers such as SiO2
and A1203 have
shown to improve the strength and stiffness of the components fabricated via
vat
photopolymerization, but often with much longer undesirable cure times. In
addition, these
fillers often cause high initial resin viscosity, poor viscosity stability,
and exhibit a tendency of
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filler to separate from the base resin. There is a continued need for fillers
which do not cause
undesirable additional cure times to the base cross-linkable resin
formulation.
[0006] Hence there is a need for radiation curable resins that produce parts
with
enhanced mechanical, thermal, electrical, magnetic and chemical properties and
satisfy
stringent polymerization resin requirements such as high rates of curing, low
viscosity,
exceptional stability, and high green strength. In particular, it has been a
challenge to reach a
resistance of at least 10 billion ohm per square with conductive carbon blacks
because of the
above-mentioned rate of curing requirements.
[0007] For AM methods utilizing powdered material (metal, ceramic, or polymer)
it is
desired to improve their ability to sinter and also their green strength
before secondary
processing. Binder selection is considered essential for successful part
fabrication. First, the
binder must be jettable. An ideal binder has low viscosity, is stable under
shear stresses, has
good interaction with powdered feedstock, has a clean bum-out, has long shelf-
life. Common
in-liquid binding agents are butyral resins, polyvinyls, polysiloxanes,
polyacrylic acids, and
polyether-urethanes. It is desirable in some cases for a higher strength
polymeric binder
particularly where the sintering is occurring at higher temperatures.
[0008] Binders for metallic and ceramic powders are typically aqueous or non-
aqueous
dispersions of inorganic particles such as silica, aluminum nitrate or film
forming polymer
dispersions. The incorporation of nanoparticles into the binder system fills
the voids in the
packed powder bed and therefore improves sinterability, increases part density
and reduces
shrinkage. The melting point of nanoparticles decreases exponentially with a
decrease in
nanoparticle size. Therefore, nanoparticles in the binder will sinter at lower
temperature than
the feedstock powder and can fuse the large particles, thus improving green
strength of the
component. It is desirable to have a binder that has low ash residual content
at the temperature
of sintering or curing for metals, cermats or ceramics.
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[0009] Binder for polymeric powders, typically consist of the solvent or a
solvent
mixture that promote swelling of the polymeric feedstock leading to particle
coalescence by
interdiffusion and entanglement. Solutions of film forming polymeric
dispersions can be used
as binders as well. Processing hydrophilic powders such as starch; plaster,
and cement require
aqueous binders. Hydrophobic polymer powders (e.g., polylactic acid or PLA)
can be
processed using organic solvents. These types of binders for polymeric powders
can also be
used to coat thermoplastic filaments for fusion into parts.
[0010] Carbon nanotubes can be classified by the number of walls in the tube,
single-
wall, double wall and multiwa11. Each wall of a carbon nanotube can be further
classified into
chiral or non-chiral forms. Some of the carbon atoms of the carbon nanotube
may be
substituted by nitrogen atoms. Carbon nanotubes are currently manufactured as
agglomerated
carbon nanotube balls or bundles which have very limited commercial use. Use
of carbon
nanotubes as a reinforcing agent in polymer composites is an area in which
carbon nanotubes
are predicted to have significant utility. However, utilization of carbon
nanotubes in these
applications has been hampered due to the general inability to reliably
produce individualized
carbon nanotubes. To reach the full potential of performance enhancement of
carbon
nanotubes as composites in polymers the aspect ratio, that is length to
diameter ratio, should
be greater than 10. The maximum aspect ratio for a given tube length is taken
to be reached
when each tube is fully separated from another. A bundle of carbon nanotubes,
for example,
has an effective aspect ratio in composites of the average length of the
bundle divided by the
bundle diameter.
100111 Various methods have been developed to debundle or disentangle carbon
nanotubes in solution. For example, carbon nanotubes may be shortened
extensively by
aggressive oxidative means and then dispersed as individual nanotubes in
dilute solution.
These tubes have low aspect ratios not suitable for high strength composite
materials. Carbon
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nanotubes may also be dispersed in very dilute solution as individuals by
sonication in the
presence of a surfactant. Illustrative surfactants used for dispersing carbon
nanotubes in
aqueous solution include, for example, sodium dodecyl sulfate, or
cetyltrimethyl ammonium
bromide. In some instances, solutions of individualized carbon nanotubes may
be prepared
from polymer-wrapped carbon nanotubes. Individualized single-wall carbon
nanotube
solutions have also been prepared in very dilute solutions using
polysaccharides, polypeptides,
water-soluble polymers, nucleic acids, DNA, polynucleotides, polyimides, and
polyvinylpyrrolidone, but these dilute solutions are unsuitable for additive
manufacturing.
SUMMARY OF INVENTION
[0012] The present invention relates to novel compositions and methods for
producing
additive manufacturing dispersions and parts thereof.
[0013] In one embodiment the composition of this invention comprises an
Additive
Manufacturing dispersion, wherein the dispersion comprises at least one
portion of a cross-
linkable moiety, and oxidized, discrete carbon nanotubes with a bonded
dispersing agent on at
least one sidewall of the oxidized discrete carbon nanotubes wherein the
oxidized, discrete
carbon nanotubes are present in the range of greater than zero and up to about
30% by weight
based on the total weight of the dispersion and a plurality of the carbon
nanotubes present in
the dispersion are discrete.
[0014] Preferably, the oxidized, discrete carbon nanotubes comprise an
interior and
exterior surface, each surface comprising an interior surface oxidized species
content and an
exterior surface oxidized species content, wherein the interior surface
oxidized species content
differs from the exterior surface oxidized species content by at least about
20%, and as high as
100%.
100151 The oxidized discrete carbon nanotubes can comprise a mixture of
oxidized
discrete carbon nanotubes with a bimodal or trimodal distribution of the
diameters of the
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oxidized discrete carbon nanotubes formed from combinations of oxidized
discrete single wall,
oxidized discrete double wall and oxidized discrete multiwall carbon
nanotubes.
[0016] The bonded dispersing agent on the sidewall of the oxidized discrete
carbon
nanotubes is preferably covalently bonded.
[0017] The bonded dispersing agent on the sidewall of the oxidized discrete
carbon
nanotubes preferably comprises an average molecular weight in the range of
about 50 to about
20,000 daltons and the weight fraction of bonded dispersing agent on the
sidewall of the
discrete carbon nanotubes relative to the oxidized discrete carbon nanotubes
is greater than
about 0.02 and less than about 0.8.
[0018] The bonded dispersing agent on the sidewall of the oxidized discrete
carbon
nanotubes is preferably miscible with a material in contact with the bonded
dispersing agent.
[0019] A second embodiment of the invention is an Additive Manufacturing
dispersion, wherein the dispersion comprises at least one portion of a cross-
linkable acrylate
moiety and oxidized, discrete carbon nanotubes with a bonded dispersing agent
on at least one
sidewall of the oxidized discrete carbon nanotubes wherein the bonded
dispersing agent on the
sidewall of the discrete carbon nanotubes comprises molecular units selected
from the group
of ethers.
[0020] The molecular units of the second embodiment preferably comprise
ethylene
oxide.
[0021] The first or second embodiments can further comprise fillers in the %
weight
from about 0.1% to about 30% by weight of the dispersion, preferably wherein
the fillers are
selected from the group consisting of carbon black, graphene, oxidized
graphene, reduced
graphene, carbon fibers, silicas, silicates, halloysite, clays, calcium
carbonate, wollastonite,
glass, fire-retardants and talc.
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[0022] The first or second embodiments can further comprise a member of the
group
consisting of thermoplastics, thermosets, and elastomers.
[0023] The first or second embodiments can further comprise a core shell
elastomer,
wherein the elastomer preferably comprises particles having diameters from
about 0.01 to
about 1 micrometer.
[0024] The first or second embodiments can further comprise semi-conductor,
metallic,
or ceramic powders, wherein the powders comprise particle diameters from about
1 nm to about
20 micrometers.
[0025] The first or second embodiments can further comprise at least one
additional
dispersing agent attached to the sidewall of the oxidized discrete carbon
nanotubes selected
from the group consisting of anionic, cationic, nonionic and zwitterionic
surfactants, polyvinyl
alcohols, copolymers of polyvinyl alcohols and polyvinyl acetates,
polyvinylpyrrolidones and
their copolymers, carboxymethyl cellulose, carboxypropyl cellulose,
carboxymethyl propyl
cellulose, hydroxyethyl cellulose, polyetherimines, polyethers, starch, and
mixtures thereof
100261 The first or second embodiments wherein the oxidized discrete carbon
nanotubes comprise about 0.1% to about 20% by weight of nitrogen atoms.
[0027] A third embodiment of the invention is an Additive Manufacturing
dispersion
wherein the dispersion comprises at least one portion of a thermoplastic
moiety and discrete
carbon nanotubes with a bonded dispersing agent on at least one sidewall of
the discrete carbon
nanotubes wherein the discrete carbon nanotubes are present in an amount
greater than zero
and up to about 30% by weight based on the total weight of the dispersion.
100281 The third embodiment can comprise a bonded dispersing agent on the
sidewall
of the oxidized discrete carbon nanotubes at least partially thermally
decomposes at less than
about 500 C in nitrogen with less than about 5% weight ash content.
[0029] The third embodiment can comprise a plurality of discrete carbon
nanotubes.
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[0030] Any of the three embodiments can comprise a part made by Additive
Manufacturing having an electrical resistance less than about 10 billion ohms
per square.
[0031] Any of the three embodiments can comprise a dispersion having a UV-
visible
absorption at 500 nm greater than about 0.5 units of absorbance for a
concentration of oxidized
discrete carbon nanotubes in the dispersion of 2.5 x10-5 g/ml.
[0032] Any of the three embodiments can further comprise a filler selected
from the
group of thermally conducting materials, such as but not limited to metals and
metal alloys,
boron nitride, aluminum oxide, silicon nitride, aluminum nitride, diamond,
graphite and
graphene.
[0033] Any of the three embodiments can further comprise a biologically
reactive
species selected from the group consisting of species that can interact with
bacteria, virus,
fungi, and biological agents.
[0034] Oxidized carbon nanotubes are those carbon nanotubes that have been
subjected
to oxidizing media, such as but not limited to, concentrated nitric acid,
peroxides and
persulfates, that introduces chemical units such as carboxylic acids,
hydroxyls, ketones and
lactones. The oxidized discrete carbon nanotubes are selected from the group
consisting of
oxidized discrete single wall, oxidized discrete double wall, or oxidized
discrete multiwall
carbon nanotubes.
[0035] The oxidized, discrete carbon nanotubes can also comprise an interior
and
exterior surface, each surface comprising an interior surface oxidized species
content (also
called interior oxygen containing species content because the interior oxygen
species may
differ from the exterior oxygen species) and an exterior surface oxidized
species content (also
called exterior oxygen containing species content because the interior oxygen
species may
differ from the exterior oxygen species), wherein the interior surface
oxidized species content
differs from the exterior surface oxidized species content by at least 20%,
and as high as 100%,
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preferably wherein the interior surface oxidized species content is less than
the exterior surface
oxidized species content. The interior surface oxidized species content can be
up to 3 weight
percent relative to carbon nanotube weight, preferably from about 0.01 to
about 3 weight
percent relative to carbon nanotube weight, more preferably from about 0.01 to
about 2, most
preferably from about 0.01 to about 1. Especially preferred interior surface
oxidized species
content is from zero to about 0.01 weight percent relative to carbon nanotube
weight. The
exterior surface oxidized species content can be from about 0.1 to about 65
weight percent
relative to carbon nanotube weight, preferably from about 1 to about 40, more
preferably from
about 1 to about 20 weight percent relative to carbon nanotube weight. This is
determined by
comparing the exterior oxidized species content for a given plurality of
nanotubes against the
total weight of that plurality of nanotubes.
[0036] The oxidized, discrete carbon nanotubes can further comprise a mixture
of
oxidized discrete carbon nanotubes with a bimodal or trimodal distribution of
the diameters of
the oxidized discrete carbon nanotube formed from combinations of oxidized
discrete single
wall, oxidized discrete double wall and oxidized discrete multiwall carbon
nanotubes.
Preferably, the dispersion of oxidized discrete carbon nanotubes comprises a
majority of
oxidized discrete multiwall carbon nanotubes, more preferably a majority of
oxidized discrete
double wall carbon nanotubes and even more preferably a majority of oxidized
discrete single
wall carbon nanotubes. The meaning of majority is more than 50% by weight of
all the carbon
nanotubes present in the dispersion.
[0037] In another embodiment of this invention the Additive Manufacturing
dispersion
the bonded dispersing agent on the sidewall of the oxidized discrete carbon
nanotubes is
hydrogen bonded, preferably ionically bonded and more preferably covalently-
bonded.
[0038] In another embodiment the oxidized discrete carbon nanotubes further
have a
bonded dispersing agent on the sidewall of the oxidized discrete carbon
nanotubes consisting
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of a molecular weight in the range of about 50 to about 20,000 daltons.
Preferably the
molecular weight range of the bonded dispersing agent is from about 60 to
about 5000 daltons
and more preferably from about 70 to about 1000 daltons. The bonded dispersing
agent on the
sidewall of the oxidized discrete carbon nanotubes consists of chemical units
selected from the
group of carbon-carbon bonds, carbon-nitrogen bonds, carbon-oxygen bonds,
carbon-sulfur
bonds and silicon-oxygen bonds. In the presence of cross-linkable matrices the
chemical units
of the bonded dispersing agent are preferred to be able to be crosslinked into
the matrices.
[0039] The weight fraction of bonded dispersing agent on the sidewall of the
discrete
carbon nanotubes relative to the oxidized discrete carbon nanotubes is greater
than about 0.02
and less than about 0.8. Preferably the weight fraction of bonded dispersing
agent from about
0.03 to about 0.6, more preferably from about 0.05 to about 0.5 and most
preferably from about
0.06 to about 0.4.
[0040] The bonded dispersing agent on the sidewall of the oxidized discrete
carbon
nanotubes is selected such that it has good compatibility with a material in
contact with the
dispersing agent. Good compatibility here is to mean a sufficient amount of
electronic, van der
Waals, ionic or dipole interactions such that the oxidized carbon nanotube can
be dispersed as
individual or discrete carbon nanotubes. Preferably the bonded dispersing
agent on the
sidewall of the oxidized discrete carbon nanotubes is selected such that it is
thermodynamically
miscible, i.e., forms a homogeneous mixture with a material in contact with
the dispersing
agent.
[0041] The bonded dispersing agent on the sidewall of the discrete carbon
nanotubes
can further comprise ethylene oxide molecular units. More preferred is the
bonded dispersion
agent comprise a mixture of propylene oxide and ethylene oxide molecular
units. There may
be a mixture of bonded dispersing agents on the sidewall of the discrete
carbon nanotubes or a
mixture of oxidized discrete carbon nanotubes with different types of bonded
dispersion agents.
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[0042] In another embodiment of this invention the bonded dispersing agent on
the
sidewall of the oxidized discrete carbon nanotubes may be further selected to
have a thermal
decomposition such that at less than 500 C in nitrogen there is less than
about 5% weight ash
content of the dispersing agent. Preferably the bonded dispersing agent on the
sidewall of the
oxidized discrete carbon nanotubes has a thermal decomposition such that at
less than about
500 C in nitrogen there is less than about 1% weight ash content of the
dispersing agent and
more preferably the bonded dispersing agent on the sidewall of the oxidized
discrete carbon
nanotubes has a thermal decomposition such that at less than about 400 C in
nitrogen there is
less than about 1% weight ash content of the dispersing agent.
[0043] The oxidized discrete carbon nanotubes with a bonded dispersing agent
on the
sidewall of the oxidized discrete carbon nanotubes consist of an aspect ratio,
known as the ratio
of the length to diameter of the oxidized discrete carbon nanotube, from about
10 to about
10000. For oxidized discrete single wall carbon nanotubes the aspect ratio is
preferred to be
from about 300 to about 10000, for oxidized discrete double wall carbon
nanotubes the aspect
ratio is preferred to be from about 150 to about 5000 and for oxidized
discrete multiwall carbon
nanotubes the aspect ratio is preferred from about 40 to about 500.
[0044] The aspect ratio of the oxidized discrete carbon nanotubes can be a
unimodal
distribution, or a multimodal distribution (such as a bimodal or trimodal
distribution). The
multimodal distributions can have evenly distributed ranges of aspect ratios
(such as 50% of
one L/D range and about 50% of another L/D range). The distributions can also
be
asymmetrical ¨ meaning that a relatively small percent of discrete nanotubes
can have a
specific L/D while a greater amount can comprise another aspect ratio
distribution.
[0045] An embodiment of this invention is that the oxidized discrete carbon
nanotubes
with a bonded dispersing agent on the sidewall of the oxidized discrete carbon
nanotubes are
present in the weight range greater than zero and up to about 30% by weight
based on the total
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weight of the dispersion. Preferably the weight range of oxidized discrete
carbon nanotubes
with a bonded dispersing agent on the sidewall of the oxidized discrete carbon
nanotubes
present in the dispersion is from about 0.01 to about 10% by weight and more
preferably from
about 0.01 to about 5% by weight based on the total weight of the dispersion.
[0046] In yet another embodiment of this invention is that a plurality of the
carbon
nanotubes present in the dispersion are discrete. Preferably at least about
51% by weight of
oxidized carbon nanotubes with a bonded dispersing agent on the sidewall of
the oxidized
carbon nanotubes present in the dispersion are discrete, preferably at least
about 65% by weight
of oxidized carbon nanotubes with a bonded dispersing agent on the sidewall of
the oxidized
carbon nanotubes present in the dispersion are discrete, more preferably at
least about 75% by
weight of oxidized carbon nanotubes with a bonded dispersing agent on the
sidewall of the
oxidized carbon nanotubes present in the dispersion are discrete and most
preferably at least
about 85% by weight of carbon nanotubes present in the dispersion are
discrete.
[0047] In another embodiment of this invention the dispersion of oxidized
discrete
carbon nanotubes with a bonded dispersing agent on the sidewall of the
oxidized discrete
carbon nanotubes comprises fillers in the % weight from about 0.05% to about
80% relative to
the total weight of the dispersion. Preferably the % weight of fillers is from
about 0.05% to
about 30% and most preferably from about 0.1% to about 10% relative to the
total weight of
the dispersion.
[0048] The fillers are selected from the group consisting of carbon black,
graphene,
oxidized graphene, reduced graphene, carbon fibers, silicas, silicates,
halloysite, clays, calcium
carbonate, wollastonite, glass, flame retardants and talc. The fillers may be
in the shapes of
roughly spherical particles, rods, fibers or plates. Preferably the fillers
have at least one scale
of dimension greater than about 1 nm and less than about 10 micrometers, more
preferably
have at least one scale of dimension greater than about 5 nm and less than
about 2 micrometers
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and most preferably have at least one scale of dimension greater than about 10
nm and less
than about 1 micrometer.
[0049] In some embodiments the dispersion comprising of oxidized discrete
carbon
nanotubes further comprises a mixture of at least two different fillers. In
some embodiments
the dispersion comprising oxidized discrete carbon nanotubes further comprises
a mixture of a
different species of a single filler which may vary by particles size, thermal
conductivity,
packing, or molecular weight.
[0050] In further embodiments of this invention the dispersion further
comprises photo-
crosslinkable monomers, oligomers or polymers. The cross-linkable monomers,
oligomers or
polymers contain molecular units selected from the group of carbon-carbon
double bonds,
carbon-carbon triple bonds, urethanes, acrylates, alkvlacrylates,
cyanonitriles, cyanoacrylates,
nitriles, epoxies, amides, amines, alcohols, ethers and esters.
[0051] In another embodiment the dispersion of the oxidized discrete carbon
nanotubes
with a bonded dispersing agent on the sidewall of the oxidized discrete carbon
nanotubes
further comprises a thermoplastic. The dispersion of oxidized discrete carbon
nanotubes with
a bonded dispersing agent on the sidewall of the oxidized discrete carbon
nanotubes may coat
the thermoplastic or oxidized discrete carbon nanotubes with a bonded
dispersing agent on the
sidewall of the oxidized discrete carbon nanotubes may be dispersed within the
thermoplastic.
A preferred thermoplastic is selected from the group of amorphous and semi-
crystalline
thermoplastics, including, but not limited to, Polylactic acid (PLA),
Acrylonitrile butadiene
styrene (ABS), Polycarbonate (PC), Polycarbonate - Acrylonitrile butadiene
styrene blend (PC-
ABS), P oly etherimi de (PEI), Polyphenylsulfone (PPSF), Polyethylene
terephthal ate (PET),
Polyethylene terephthalate glycol (PETG), Polyether ether ketone (PEEK),
Polyamides, such
as but not limited to Nylon 12, Nylon 11, Nylon 6, and Nylon 6,6, polyvinyl
alcohol and
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copolymers, polyvinylbutyrate and copolymers, polyvinylpyrrolidone and
copolymers,
polyether and copolymers. The thermoplastic may be a linear, grafted, comb or
block polymer.
[0052] In yet another embodiment of this invention the dispersion of the
oxidized
discrete carbon nanotubes with a bonded dispersing agent on the sidewall of
the oxidized
discrete carbon nanotubes further comprises elastomers. The elastomers can be
selected from
the group consisting of, but not limited to, natural rubber, polyisobutylene,
polybutadiene,
styrene-butadiene, hydrogenated styrene-butadiene, butyl rubber, polyisoprene,
styrene-
isoprene rubber, ethylene propylene diene, silicones, polyurethanes,
polyester, polyether,
polyacrylates, hydrogenated and non-hydrogenated nitrile rubbers, halogen
modified
elastomers, polyolefin elastomers fluoroelastomers, and combinations thereof
The elastomers
may be non-crosslinked or crosslinked, grafted or copolymers.
[0053] In another embodiment the dispersion of the oxidized discrete carbon
nanotubes
with a bonded dispersing agent on the sidewall of the oxidized discrete carbon
nanotubes
further comprises polymeric impact modifiers with a glass transition
temperature of less than
about 25 C. The impact modifiers are selected from the group of polyethers,
polyesters,
vinylpolymers, polyvinylcopolymers, polyolefins polyacrylates, polyurethanes,
poly-amides
and polysiloxanes, blends and copolymers thereof They may be further
functionalized with
reactive groups, such as but not limited to epoxy, hydroxyl, isocyanate, and
carboxylic groups.
[0054] The impact modifiers are preferred to be phase-separated from the main
matrix
material of the dispersion yet have good cohesion or thermodynamic
interaction. More
preferred is that the composition of the impact modifiers that are block
copolymers or core-
shell polymers. Examples of core shell polymers are PARALOIDTM Impact
Modifiers which
are acrylate or butadiene based. More preferred is that the impact modifiers
have a refractive
index value at least within 0.03 units of the refractive index value of the
matrix, more preferably
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within 0.02 units, so as to minimize the scattering of radiation in the UV-
visible wavelength
range.
[0055] The core-shell particles can include more than one core and/or more
than one
shell. In addition, mixtures of core-shell particles with elastomer particles
can be used. In an
embodiment, two different diameters of impact modifiers are used in a certain
ratio. The use
of two different impact modifiers with different diameters has the effect of
lowering the
viscosity of the liquid radiation curable resin. In an embodiment, the
composition of impact
modifiers is about a 7 to 1 ratio of diameter (e.g. 140 nm particles vs. a 20
nm particles) and
about a 4 to 1 ratio of wt%. In another embodiment, the composition of impact
modifiers is
about a 5 to 1 ratio of diameter and about a 4 to 1 ratio of wt%. In another
embodiment the
composition of impact modifiers is about a 5 to 1 ratio of diameter and about
a 6 to 1 ratio of
wt%.
[0056] The phase-separated domain size of the impact modifier in the
dispersion of the
oxidized discrete carbon nanotubes with a bonded dispersing agent on the
sidewall of the
oxidized discrete carbon nanotubes can be greater than about 0.005 micrometers
and less than
about 1 micrometer in diameter, preferably greater than 0.01 micrometers and
less than about
0.8 micrometer in diameter and most preferably greater than about 0.05
micrometers and less
than about 0.6 micrometer in diameter.
[0057] The impact modifier may be present in the dispersion of the oxidized
discrete
carbon nanotubes with a bonded dispersing agent on the sidewall of the
oxidized discrete
carbon nanotubes from at least about 0.1% to less than about 30% by weight of
the dispersion,
preferably at least greater than about 0.5% to less than about 15% and most
preferably at least
about 2% to less than about 10%.
[0058] In another embodiment the dispersion of the oxidized discrete carbon
nanotubes
with a bonded dispersing agent on the sidewall of the oxidized discrete carbon
nanotubes
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further comprises metallic powders. The metallic powders can contain any of
those metal
elements listed in the Periodic Table of Elements The metals may also be in
the form of metal
oxides, carbides, silicides or nitrides, or alloys with other elements.
Preferred metallic powders
can be selected, but not limited to, the class of stainless steel, Inconel,
bronze, copper, silver,
platinum, tungsten, Aluminum, cobalt, platinum, and tungsten carbide. More
preferred is that
the metallic powders have a particle diameter greater than about 1 nm and less
than about 20
micrometers. For more effective sintering it may be further preferred to have
a bimodal
metallic powder particle diameter distribution. Yet further preferred is that
in the metallic
powder particle distribution the number of larger particle size be in the
majority.
[0059] In another embodiment the dispersion of the oxidized discrete carbon
nanotubes
with a bonded dispersing agent on the sidewall of the oxidized discrete carbon
nanotubes
further comprises ceramic powders. The ceramic powders can be selected from,
but not limited
to, the class of aluminum oxide, zirconium oxide, silica, boron nitride and
silicon carbide and
blends thereof Preferred is that the ceramic powders have a particle diameter
greater than
about 1 nm and less than about 20 micrometers. For more effective sintering of
the ceramic it
may be further preferred to have a bimodal ceramic powder particle diameter
distribution. Yet
further preferred that in the ceramic powder particle distribution that the
number of larger
particle size be in the majority.
[0060] In another embodiment the dispersion of the oxidized discrete carbon
nanotubes
with a bonded dispersing agent on the sidewall of the oxidized discrete carbon
nanotubes
further comprises a mixture of ceramic powders and metallic powders which when
sintered
form cermets. The preferred cermets which are based on carbides, nitrides,
borides, and
silicides of the fourth to sixth element groups of the Periodic Table of
Elements.
[0061] In another embodiment of this invention the dispersion of the oxidized
discrete
carbon nanotubes with a bonded dispersing agent on the sidewall of the
oxidized discrete
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carbon nanotubes further comprising at least one additional dispersing agent
attached to the
sidewall of the oxidized discrete carbon nanotubes selected from the group
consisting of
anionic, cationic, nonionic and zwitterionic surfactants, polyvinyl alcohols,
copolymers of
polyvinyl alcohols and polyvinyl acetates, polyvinylpyrrolidones and their
copolymers,
carboxymethyl cellulose, carboxypropyl cellulose, carboxymethyl propyl
cellulose,
hydroxyethyl cellulose, polyetherimines, polyethers, starch, and mixtures
thereof. Preferred
are the non-covalently attached polymeric dispersion agents be selected from
the group of
amphiphilic polymers.
[0062] The molecular weight of the additional dispersing agent attached to the
sidewall
of the oxidized discrete carbon nanotubes is preferred to be in the range of
about 100 to about
400,000 daltons, more preferably in the range of about 1000 to about 200,000
daltons and most
preferably in the range of about 10,000 to about 100,000 daltons.
[0063] The additional dispersing agents attached to the sidewall of the
oxidized discrete
carbon nanotubes with a bonded dispersing agent on the sidewall of the
oxidized discrete
carbon nanotubes can be present in the dispersion in the weight ratio of
attached additional
dispersing agent to oxidized discrete carbon nanotubes with a bonded
dispersing agent on the
sidewall of the oxidized discrete carbon nanotubes from about 0.01 to about 2.
Preferably the
weight ratio is from about 0.1 to about 1 and most preferably from about 0.2
to about 0.75.
[0064] Another embodiment of this invention is that the dispersion of the
oxidized
discrete carbon nanotubes with a bonded dispersing agent on the sidewall of
the oxidized
discrete carbon nanotubes further comprises an organic solvent. A preferred
organic solvent
is selected from the group of alcohols, ethers, ketones, dioxolane, acetates,
glycols, and
mixtures thereof.
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[0065] Yet another embodiment of this invention is that the dispersion of the
oxidized
discrete carbon nanotubes with a bonded dispersing agent on the sidewall of
the oxidized
discrete carbon nanotubes further comprises water.
100661 In an embodiment of this invention the dispersion of the oxidized
discrete
carbon nanotubes with a bonded dispersing agent on the sidewall of the
oxidized discrete
carbon nanotubes is electrostatic-dissipative. Preferably the dispersion has a
surface resistivity
of less than 10 billion ohms per square, more preferably less than 10 million
ohms per square.
[0067] In yet another embodiment of this invention the dispersion of the
oxidized
discrete carbon nanotubes with a bonded dispersing agent on the sidewall of
the oxidized
discrete carbon nanotubes further comprises about 0.1% to about 20% by weight
of nitrogen
atoms.
[0068] In one embodiment of this invention the UV-visible absorption at 500 nm
for
the dispersion of the oxidized discrete carbon nanotubes with a bonded
dispersing agent on the
sidewall of the oxidized discrete carbon nanotubes is above 0.5 units of
absorbance for a
concentration of oxidized discrete carbon nanotubes with a bonded dispersing
agent in the
dispersion of 2.5 x10-5 g/ml. Preferably the unit of absorption is above 0.75
at the same
concentration of oxidized carbon nanotubes and wavelength of measurement, most
preferably
above 1 unit of absorbance at the same concentration of oxidized carbon
nanotubes and
wavelength of measurement.
[0069] In yet another embodiment of this invention the filler can be selected
from the
group of fire retardants consisting of char formation agents, intumescent
agents, and reactions
in the gas phase such but not limited to organic halides (haloalkanes).
[0070] In one embodiment the dispersion of the oxidized discrete carbon
nanotubes
with a bonded dispersing agent on the sidewall of the oxidized discrete carbon
nanotubes
comprises a filler selected from the group of thermally conducting materials
such as but not
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limited to metals and metal alloys, boron nitride, aluminum oxide, silicon
nitride, aluminum
nitride, diamond, graphite.
[0071] In another embodiment the dispersion of the oxidized discrete carbon
nanotubes
with a bonded dispersing agent on the sidewall of the oxidized discrete carbon
nanotubes
comprises a filler selected from the group of magnetic and ferromagnetic
materials, such as but
not limited to those materials containing atoms of nickel, iron, cobalt and
their alloys and
oxides.
[0072] An embodiment of this invention is the dispersion of the oxidized
discrete
carbon nanotubes with a bonded dispersing agent further comprising magnetic or
ferromagnetic
particles provide electromagnetic absorbance or shielding at frequencies
greater than about 1
MHz, preferably at frequencies greater than about 1GHz. The dispersion of the
oxidized
discrete carbon nanotubes with a bonded dispersing agent further comprising
electron
conducting filler particles are al so desirable for shielding of radio
frequencies.
[0073] In yet another embodiment the dispersion comprising at least one
portion of a
cross-linkable moiety, and oxidized, discrete carbon nanotubes with a bonded
dispersing agent
on at least one sidewall of the oxidized discrete carbon nanotubes is
crosslinked at least
partially by radiation followed by post-curing comprises at least one portion
of a cross-linkable
moiety, and oxidized, discrete carbon nanotubes with a bonded dispersing agent
on at least one
sidewall of the oxidized discrete carbon nanotubes to achieve final desired
part performance
by thermal or irradiative methods wherein the time to post cure to achieve the
final desired part
performance is 10% less than the dispersion without oxidized discrete carbon
nanotubes,
preferably 25% less time and more preferably 50% less time.
[0074] In another embodiment the dispersion comprising at least one portion of
a cross-
linkable moiety, and oxidized, discrete carbon nanotubes with a bonded
dispersing agent on at
least one sidewall of the oxidized discrete carbon nanotubes is jettable.
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[0075] In another embodiment the dispersion comprising at least one portion of
a cross-
linkable moiety, and oxidized, discrete carbon nanotubes with a bonded
dispersing agent on at
least one sidewall of the oxidized discrete carbon nanotubes further
comprising materials which
can be sintered using about 10% less radiation power than a similar dispersion
not containing
oxidized discrete carbon nanotubes, preferably using about 25% less radiation
power, more
preferably using about 50% less radiation power than a similar dispersion not
containing
oxidized discrete carbon nanotubes.
[0076] In one embodiment the dispersion of oxidized discrete carbon nanotubes
with
bonded dispersion agent further comprises an elastomer wherein the final part
exhibits at least
about 20% higher resistance to fracture under cyclic fatigue, preferably at
least about 50% and
most preferably at least about 100% higher resistance to fracture than a
similar dispersion
without the oxidized discrete carbon nanotubes with bonded dispersion agent.
[0077] Other embodiments
[0078] Embodiment 1. An Additive Manufacturing dispersion wherein the
dispersion
comprises at least one portion of a cross-linkable moiety, and oxidized,
discrete carbon
nanotubes with a bonded dispersing agent on at least one sidewall of the
oxidized discrete
carbon nanotubes wherein the oxidized, discrete carbon nanotubes are present
in the range of
greater than zero and up to about 30% by weight based on the total weight of
the dispersion
and a plurality of the carbon nanotubes present in the dispersion are
discrete.
[0079] Embodiment 2. The dispersion of Embodiment 1 wherein the oxidized,
discrete
carbon nanotubes comprise an interior and exterior surface, each surface
comprising an interior
surface oxidized species content and an exterior surface oxidized species
content, wherein the
interior surface oxidized species content differs from the exterior surface
oxidized species
content by at least about 20%, and as high as 100%.
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[0080] Embodiment 3. The dispersion of Embodiment 1 wherein the oxidized
discrete
carbon nanotubes comprise a mixture of oxidized discrete carbon nanotubes with
a bimodal or
trimodal distribution of the diameters of the oxidized discrete carbon
nanotubes formed from
combinations of oxidized discrete single wall, oxidized discrete double wall
and oxidized
discrete multiwall carbon nanotubes.
[0081] Embodiment 4. The dispersion of Embodiment 1 wherein the bonded
dispersing agent on the sidewall of the oxidized discrete carbon nanotubes is
covalently
bonded.
[0082] Embodiment 5. The dispersion of Embodiment 1 wherein the bonded
dispersing agent on the sidewall of the oxidized discrete carbon nanotubes
comprises an
average molecular weight in the range of about 50 to about 20,000 daltons and
the weight
fraction of bonded dispersing agent on the sidewall of the discrete carbon
nanotubes relative to
the oxidized discrete carbon nanotubes is greater than about 0.02 and less
than about 0.8.
[0083] Embodiment 6. The dispersion of Embodiment 1 wherein the bonded
dispersing agent on the sidewall of the oxidized discrete carbon nanotubes is
miscible with a
material in contact with the bonded dispersing agent.
[0084] Embodiment 7. An Additive Manufacturing dispersion wherein the
dispersion
comprises at least one portion of a cross-linkable acrylate moiety and
oxidized, discrete carbon
nanotubes with a bonded dispersing agent on at least one sidewall of the
oxidized discrete
carbon nanotubes wherein the bonded dispersing agent on the sidewall of the
discrete carbon
nanotubes comprises molecular units selected from the group of ethers.
[0085] Embodiment 8. The dispersion of Embodiment 7 wherein the molecular
units
comprise ethylene oxide.
[0086] Embodiment 9. The dispersion of Embodiment 1 further comprising fillers
in
the % weight from about 0.1% to about 30% by weight of the dispersion selected
from the
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group consisting of carbon black, graphene, oxidized graphene, reduced
graphene, carbon
fibers, silicas, silicates, halloysite, clays, calcium carbonate,
wollastonite, glass, fire-retardants
and talc.
100871 Embodiment 10. The dispersion of Embodiment 1 further comprising a
member
of the group consisting of thermoplastics, thermosets, and elastomers.
[0088] Embodiment 11. The dispersion of Embodiment 1 further comprising a core
shell elastomer further comprising particles diameters from about 0.01 to
about 1 micrometer.
[0089] Embodiment 12. The dispersion of Embodiment 1 further comprising semi-
conductor, metallic and, or ceramic powders with particle diameters from about
1 nm to about
20 micrometers.
[0090] Embodiment 13. The dispersion of Embodiment 1 further comprising at
least
one additional dispersing agent attached to the sidewall of the oxidized
discrete carbon
nanotubes selected from the group consisting of anionic, cationic, nonionic
and zwitterionic
surfactants, polyvinyl alcohols, copolymers of polyvinyl alcohols and
polyvinyl acetates,
polyvinylpyrrolidones and their copolymers, carboxymethyl cellulose,
carboxypropyl
cellulose, carboxymethyl propyl cellulose, hydroxy ethyl cellulose,
polyetherimines,
polyethers, starch, and mixtures thereof
[0091] Embodiment 14. The composition of Embodiment 1 wherein the oxidized
discrete carbon nanotubes comprise about 0.1% to about 20% by weight of
nitrogen atoms.
[0092] Embodiment 15. An Additive Manufacturing dispersion wherein the
dispersion
comprises at least one portion of a thermoplastic moiety and discrete carbon
nanotubes with a
bonded dispersing agent on at least one sidewall of the discrete carbon
nanotubes wherein the
discrete carbon nanotubes are present in an amount greater than zero and up to
about 30% by
weight based on the total weight of the dispersion.
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[0093] Embodiment 16. The dispersion of Embodiment 15 wherein a bonded
dispersing agent on the sidewall of the oxidized discrete carbon nanotubes at
least partially
thermally decomposes at less than about 500 C in nitrogen with less than
about 5% weight
ash content.
[0094] Embodiment 17. The Additive Manufacturing dispersion of Embodiment 15
wherein a plurality of carbon nanotubes is discrete.
[0095] Embodiment 18. The dispersion of Embodiment 1 wherein a part made by
Additive Manufacturing has an electrical resistance less than 10 billion ohms
per square.
[0096] Embodiment 19. The dispersion of Embodiment 1 wherein the dispersion
has
a UV-visible absorption at 500 nm greater than about 0.5 units of absorbance
for a
concentration of oxidized discrete carbon nanotubes in the dispersion of 2.5
x10-5 g/ml.
[0097] Embodiment 20. The dispersion of Embodiment 1 further comprises a
filler
selected from the group of thermally conducting materials, such as but not
limited to metals
and metal alloys, boron nitride, aluminum oxide, silicon nitride, aluminum
nitride, diamond,
graphite and graphene.
[0098] Embodiment 21. An additive manufacturing dispersion
for at least
partially encapsulating electronic components, wherein the dispersion
comprises:
at least one portion of a cross-linkable moiety; and
oxidized, discrete carbon nanotubes;
wherein the oxidized, discrete carbon nanotubes comprise a dispersing agent
bonded on a sidewall of the oxidized, discrete carbon nanotubes; and
wherein the oxidized, discrete carbon nanotubes are present in the range of
greater than zero and up to about 30% by weight based on the total weight of
the
dispersion; and
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wherein a plurality of the carbon nanotubes present in the dispersion are
discrete.
DETAILED DESCRIPTION OF THE INVENTION
[0099] In the following description, certain details are set forth such as
specific
quantities, sizes, etc., so as to provide a thorough understanding of the
present embodiments
disclosed herein. However, it will be evident to those of ordinary skill in
the art that the present
disclosure may be practiced without such specific details. In many cases,
details concerning
such considerations and the like have been omitted inasmuch as such details
are not necessary
to obtain a complete understanding of the present disclosure and are within
the skills of persons
of ordinary skill in the relevant art.
101001 While most of the terms used herein will be recognizable to those of
ordinary
skill in the art, it should be understood, however, that when not explicitly
defined, terms should
be interpreted as adopting a meaning presently accepted by those of ordinary
skill in the art.
In cases where the construction of a term would render it meaningless or
essentially
meaningless, the definition should be taken from Webster's Dictionary, 3rd
Edition, 2009.
Definitions and/or interpretations should not be incorporated from other
patent applications,
patents, or publications, related or not, unless specifically stated in this
specification or if the
incorporation is necessary for maintaining validity.
[0101] In various embodiments a dispersion is disclosed comprising oxidized,
discrete
carbon nanotubes with a bonded dispersing agent on the sidewall of the
oxidized discrete
carbon nanotubes wherein the oxidized, discrete carbon nanotubes are present
in an amount
greater than zero and up to about 30% by weight based on the total weight of
the dispersion
and a plurality of the oxidized carbon nanotubes present in the dispersion are
discrete.
[0102] As-made carbon nanotubes using metal catalysts such as iron, aluminum
or
cobalt can retain a significant amount of the catalyst associated or entrapped
within the carbon
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nanotube, as much as five weight percent or more. These residual metals can be
deleterious in
such applications as electronic devices because of enhanced corrosion or can
interfere with the
vulcanization process in curing elastomer composites. Furthermore, these
divalent or
multivalent metal ions can associate with carboxylic acid groups on the carbon
nanotube and
interfere with the discretization of the carbon nanotubes in subsequent
dispersion processes. In
an embodiment a dispersion is disclosed comprising oxidized, discrete carbon
nanotubes with
a bonded dispersing agent on the sidewall of the oxidized discrete carbon
nanotubes comprising
a residual metal concentration of less than about 50,000 parts per million,
ppm, and preferably
less than about 10,000 parts per million. The residual catalyst concentration
can be
conveniently determined by using thermogravimetry by heating at 5 C/min in
nitrogen from
25 C to 800 C then switching the gas to air and holding at 800 C for 30
minutes. The %
residual ash is determined by the weight of material remaining compared to the
weight of the
starting material. The ash can then be analyzed for metal type using energy
dispersive X-ray
and a scanning electron microscope. Alternatively, the oxidized discrete
carbon nanotubes can
be separation from the dispersion medium and analyzed using atomic absorption
techniques.
[0103] The oxidation level of the oxidized discrete carbon nanotubes is
defined as the
amount by weight of oxygenated species covalently bound to the carbon
nanotube. The
thermogravimetric method for the determination of the percent weight of
oxygenated species
on the carbon nanotube involves taking about 5 mg of the dried oxidized carbon
nanotube and
heating at 5 C/minute from room temperature to 800 degrees centigrade in a
dry nitrogen
atmosphere. The percentage weight loss from 200 to 600 degrees centigrade is
taken as the
percent weight loss of oxygenated species. The oxygenated species can also be
quantified
using Fourier transform infra-red spectroscopy, FTIR, particularly in the
wavelength range
from 1680 to 1730 cm1
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[0104] The oxidized carbon nanotubes can have oxidation species comprising of
carboxylic acid or derivative carbonyl containing species. The derivative
carbonyl species can
include ketones, quaternary amines, amides, esters, acyl halogens, monovalent
metal salts and
the like. Alternatively, or in addition, the carbon nanotubes may comprise an
oxidation species
selected from hydroxyl or derived from hydroxyl containing species, ketones
and lactones.
[0105] The term discrete, alternatively known by the term exfoliated, is taken
here to
mean individual carbon nanotubes separated substantially along their length,
i.e., not bundled.
Aspect ratio is defined as the length to diameter ratio of the carbon
nanotube. If a bundle of
carbon nanotubes are present the aspect ratio is taken as the length to
diameter ratio of the
bundle. For a spherical ball of entangled carbon nanotubes the aspect ratio is
taken as 1.
[0106] Based on the desired application the aspect ratio of the oxidized
discrete carbon
nanotubes can be a unimodal distribution, or a multimodal distribution (such
as a bimodal or
trimodal distribution). The multimodal distributions can have evenly
distributed ranges of
aspect ratios (such as 50% of one L/D range and about 50% of another L/D
range). The
distributions can also be asymmetrical ¨ meaning that a relatively small
percent of discrete
nanotubes can have a specific L/D while a greater amount can comprise another
aspect ratio
distribution. The aspect ratio of the oxidized discrete carbon nanotubes can
be determined, for
example, using dilutions of the dispersion in organic solvent and scanning
electron microscopy.
[0107] Manufacturers of carbon nanotubes that may be suitable for use in the
applications described herein include, for example, Southwest
Nanotechnologies, Zeonano or
Zeon, CNano Technology, Nanocyl, ACS Materials, American Elements, Chasm
Technologies, Haoxin Technology, Hanwha Nanotech Group, Hyperion Catalysis, KB
Chemical, Klean Commodities, LG Chem, Nano-C, NTP Shenzhen Nanotech Port,
Nikkiso,
Raymor, Saratoga Energy, SK Global, Solid Carbon Products, Sigma Aldrich, Sun
Nanotech,
Thomas Swan, TimesNano, Tokyo Chemical Industry, XF Nano, and OCSiAl.
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[0108] A method to obtain discrete carbon nanotubes is to subject the carbon
nanotubes
to high mechanical forces. During shearing, samples may be subjected to
intensely disruptive
forces generated by shear (turbulent) and/or cavitation with process equipment
capable of
producing energy densities as high as of 106 to 108 Joules/m3. Equipment that
meets this
specification includes but is not limited to ultrasonicators, cavitators,
mechanical
homogenizers, pressure homogenizers and microfluidizers. One such homogenizer
is shown
in U.S. Patent 756,953, the disclosure of which is incorporated herein by
reference. Additional
shearing equipment includes, but is not limited to, HAAKETM mixers, Brabender
mixers, Omni
mixers, SiIverson mixers, Colloidal mills, Gaullin homogenizers, and/or twin-
screw extruders.
After shear processing, the carbon nanotubes bundles have been loosened,
thereby exposing
the surface of a greater number of nanotubes and/or a greater portion of the
surface of the
nanotubes to the surrounding environment. Typically, based on a given starting
amount of
entangled as-received and as-made carbon nanotubes, a plurality of high-
surface area oxidized
carbon nanotubes results from this process, preferably at least about 60%,
more preferably at
least about 75%, most preferably at least about 95% and as high as 100%, with
the minority of
the tubes, usually the vast minority of the tubes remaining tightly bundled
and with the surface
of such tightly bundled nanotubes substantially inaccessible.
[0109] Bosnyak et al., in various patent applications (e.g.. US 2012-0183770
Al and
US 2011-0294013 Al), have made discrete carbon nanotubes through judicious and
substantially simultaneous use of oxidation and shear forces, thereby
oxidizing both the inner
and outer surface of the nanotubes, typically to approximately the same
oxidation level on the
inner and outer surfaces, resulting in individual or discrete tubes.
[0110] In many embodiments, the present inventions differ from those earlier
Bosnyak
et al. applications and disclosures. In the process of oxidizing the carbon
nanotubes and
bonding the dispersing agent on the sidewall of the oxidized discrete carbon
nanotubes, the
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degree of fibrillation of the carbon nanotubes can influence the population of
carbon nanotubes
that differ by extent or type of oxygen containing species and also the bonded
dispersing agent
on the sidewall of the oxidized carbon nanotubes. For example, if many of the
tubes are aligned
as trunks then the tubes within the core of the trunk are less likely to
contain oxygenated species
on reaction with say nitric acid than the tubes on the outermost portion of
the trunk. For a more
homogeneous population of modified carbon nanotubes it is desired to have
discrete or open
structure of carbon nanotubes during the reaction to modify the carbon
nanotube. For some
applications such as, but not limited to electrical conductivity in biphasic
materials it may be
desirable to control the degree of fibrillation of the carbon nanotube bundle
to obtain a
distribution of bonded dispersing agent on the sidewall of the oxidized
discrete carbon
nanotubes.
[0111] The dispersion comprising oxidized discrete carbon nanotubes with a
bonded
dispersing agent on the sidewall of the oxidized discrete carbon nanotubes can
be made by first
making oxidized discrete carbon nanotubes then bonding the dispersing agent on
the sidewall
or ends of the oxidized discrete carbon nanotubes, or alternatively making
oxidized carbon
nanotubes, then bonding the dispersing agent on the sidewall or ends of the
oxidized carbon
nanotubes, then making the carbon nanotubes with bonded dispersion agent
discrete.
[0112] Although not limited by the chemistry of covalently bonding dispersion
agents
to the carbon nanotubes, it is convent to use the carboxylic acid groups on
the carbon nanotubes
to react with amine functional groups of the selected dispersion agent.
Examples, but not
limited by, of suitable dispersion agents are commercial products from
Huntsman Corporation
which are amine terminated polyethers, Jeffamine. The Jeffamine series can
differ in their
propylene oxide to ethylene oxide ratio as well as the degree of amination.
Alternatively,
hydroxyl groups present on the carbon nanotubes can be reacted with carboxyl,
isocyanate, or
glycidyl groups of the selected dispersion agent. Other useful chemical
moieties for covalently
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bonding molecules to the sidewall of carbon nanotubes include, but not limited
to, azides, acyl
halides and silane moieties.
[0113] The dispersion of oxidized discrete carbon nanotubes with bonded
dispersion
agent can be used advantageously in Additive Manufacturing to improve the
processing and
part performance by employing near infra-red to radio frequency radiation up
to 1 Terahertz
which is absorbed rapidly by the carbon nanotubes to create heat. This effect
can be used to
improve the time required to fully cure cross-linkable molecules, improve the
sintering of
materials and reduced part warpage.
[0114] Examples of suitable impact modifiers are elastomers and, more
preferably,
prefabricated elastomer particles. These elastomers have a glass transition
temperature (Tg)
lower than 0 C, preferably lower than -20 C.
[0115] Particle size of the impact modifying component can be accomplished by
using,
for example, a dynamic light scattering nanoparticle size analysis system. An
example of such
a system is the LB-550 machine, available from Horiba Instruments, Inc. A
preferred method
of measuring particle size is laser diffraction particle size analysis in
accordance with
IS013320:2009. Information regarding such analysis can be found in Setting New
Standards
for Laser Diffraction Particle Size Analysis. Alan Rawle and Paul Kippax,
Laboratory
Instrumentation News, January 21, 2010.
[0116] Monomers from a liquid radiation curable resin or solvents used in
analysis can
affect the measured average particle size. Additionally, analysis by laser
diffraction may
require the use of a solvent or other low viscosity dispersant. These solvents
may affect
measured average particle size. For the purposes of this work, dispersed
average particle size
refers to those particles that have been exposed to the listed monomers of a
given formulation,
dispersed, and then analyzed using propylene carbonate as solvent for laser
diffraction particle
size analysis. Dispersions of impact modifier particles were subjected to
particle size analysis
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while in dilute propylene carbonate solution, typically used was a
concentration of 0.1-0.4g
dispersion in lOg propylene carbonate.
[0117] Suitable impact modifying components, which can be mixed into the
dispersion
of oxidized discrete carbon nanotubes with bonded dispersion agent are
elastomers based on
copolymers of ethylene or propylene and one or more C2 to C12 olefin monomers.
[0118] Examples of such are ethylene/propylene copolymers or
ethylene/propylene
copolymers. optionally containing a third copolymerizable diene monomer
(EPDM), such as 1
,4-hexadiene, dicyclopentadiene, di-cyclooctadiene, methylene norbomene,
ethylidene
norbomene and tetrahydroindene; ethylene/a-olefin copolymers, such as ethylene-
octene
copolymers and ethylene/a- olefin/polyene copolymers.
[0119] Other suitable elastomers are polybutadiene, polyisoprene,
styrene/butadiene
random copolymer, styrene/isoprene random copolymer, acrylic rubbers (e.g.,
polybutylacry I ate), poly (h ex amethyl en e carbonate), ethyl en e/acry I
ate random copolymers and
acrylic block copolymers, styrene/butadiene/(meth)acrylate (SBM) block-
copolymers,
styrene/butadiene block copolymer (styrene- butadiene-styrene block copolymer
(SBS),
styrene-isoprene-styrene block copolymer (SIS) and their hydrogenated
versions, SEBS,
SEPS), and (SIS) and ionomers.
[0120] Suitable commercial elastomers are Kraton (SBS, SEBS, SIS, SEBS and
SEAS)
block copolymers produced by Shell, Nanostrength block copolymers E20, E40
(SBM type)
and M22 (full- acrylic) as produced by Arkema, Lotryl ethyl/acrylate random
copolymer
(Arkema) and Surlyn ionomers (Dupont).
[0121] Optionally, the elastomer may be modified to contain reactive groups
such as
e.g. epoxy, oxetane, carboxyl or alcohol. This modification can e.g. be
introduced by reactive
grafting or by copolymerization. Commercial examples of the latter are the
Lotader random
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ethylene/acrylate copolymers AX8840 (glycidyl methacrylate/GMA modified),
AX8900 and
AX8930 (GMA and maleic anhydride modified/MA) produced by Arkema.
[0122] Optionally, the elastomer may be crosslinked after mixing into a
dispersion of
oxidized discrete carbon nanotubes with bonded dispersion agent. The
crosslinking structure
may be introduced via a conventional method. As examples of crosslinking
agents used in
such a materials peroxide, sulfur, cresol and the like, optionally in
combination with
multifunctional monomers like divinylbenzene, ethylene glycol
di(meth)acrylate,
diallylmaleate, triallylcyanurate, triallylisocyanurate, diallylphthalate,
trimethylolpropane
triacrylate, allyl methacrylate and the like can be given.
[0123] In an embodiment the impact modifiers that can be mixed into the
dispersion of
oxidized discrete carbon nanotubes with bonded dispersion agent are pre-
fabricated elastomer
particles. Elastomer particles may be prepared by a variety of means,
including those obtained
by isolation from latex made via emulsion polymerization, or preparation in-
situ in another
component of the composition.
101241 Suitable commercial sources of such pre-fabricated elastomer particles
are PB
(polybutadiene) or PBA (polybutylacrylate) lattices available with varying
average particle size
from various producers, or lattices obtained by emulsification of EPDM, SBS,
S1S or any other
rubber.
[0125] Optionally, the elastomer may contain a crosslinking structure.
The
crosslinking structure may be introduced by a conventional method. As examples
of
crosslinking agents used in such a material peroxide, sulfur, cresol and the
like, optionally in
combination with multifunctional monomers like divinylbenzene, ethylene glycol
di(meth)acrylate, diallylmaleate, triallylcyanurate, triallylisocyanurate,
diallylphthalate,
trimethylolpropane triacrylate, allyl methacrylate, and the like can be given.
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[0126] Optionally, a shell may be present on the particles that can e.g. be
introduced
via grafting or during a second stage of emulsion polymerization. Examples of
such particles
are core-shell impact modifier particles that contain a rubber core and a
glassy shell. Examples
of core materials are polybutadiene, polyisoprene, acrylic rubber (e.g.
polybutylacrylate
rubber), styrene/butadiene random copolymer, styrene/isoprene random
copolymer, or
polysiloxane. Examples of shell materials or graft copolymers are (co)polymers
of vinyl
aromatic compounds (e.g. styrene) and vinyl cyanides (e.g. acrylonitrile) or
(meth)acrylates,
(e.g. methylmethacrylate).
[0127] Optionally, reactive groups can be incorporated into the shell by
copolymerization, such as copolymerization with glycidyl methacrylate, or by
treatment of the
shell to form reactive functional groups. Suitable reactive functional groups
include, but are
not limited to, epoxy groups, oxetane groups, hydroxyl groups, carboxyl
groups, vinyl ether
groups, and/or acrylate groups.
[0128] Suitable commercially available products of these core-shell type
elastomer
particles are, for example but not limited to, Resinous Bond RKB (dispersions
of core-shell
particles in epoxy manufactured by Resinous Chemical Industries Co., Ltd.),
Durastrength
D400, Durastrength 400R (manufactured by Arkema Group), Paraloid EXL-2300 (non-
functional shell), Paraloid EXL-2314 (epoxy functional shell), Paraloid EXL-
2600, Paraloid
KM 334, and Paraloid EXL 2300G. Paraloid core shell elastomers are
manufactured by Dow
Chemical Co., Genioperl P53, Genioperl P23, Genioperl P22 are manufactured by
Wacker
Chemical, Kane Ace MX products (manufactured by Kaneka).
[0129] Other examples of such elastomer particles are crosslinked
polyorganosiloxane
rubbers that may include dialkylsiloxane repeating units, where "alkyl" is Ci
to C6 alkyl. Such
particles may be made by the method disclosed in U.S. Pat. No. 4,853,434 to
Block,
incorporated in its entirety herein by reference. The particles may be
modified to include
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reactive groups such as oxirane, glycidyl, oxetane, hydroxyl, vinyl ester,
vinyl ether, or
(meth)acrylate groups, or combinations thereof, preferably on the surface of
the particles.
Examples of polyorganosiloxane elastomer particles that are commercially
available are
Albidur.
[0130] EP 2240(A), Albidur EP 2640, Albidur VE 3320, Albidur EP 5340, Albidur
EP
5640, and Albiflex 296 (dispersions of particles in epoxy or vinyl ether
resins, Hanse Chemie,
Germany), Genioperl M41C (dispersion in epoxy, Wacker Chemical), Chemisnow MX
Series
and MP Series (Soken Chemical and Engineering Co.). Other materials that can
be used to
make the core-shell particles for use in the present invention can be found in
for example:
Nakamura et al, J Appl. Polym. Sci. v 33 n 3 Feb. 20, 1987 p 885-897, 1987,
which discloses
a core-shell material with a poly(butyl acrylate) core and poly(methyl
methacrylate) shell. The
shell has been treated so that it contains epoxide groups; Saij a, L. M. and
Uminski, M., Surface
Coatings International Part B 2002 85, No.B2, June 2002, p. 149-53, which
describes a core
shell material with core and shell prepared from poly(methyl methacrylate-co-
butyl acrylate),
and treated with MMA or AMPS to produce material with carboxylic acid groups
on the
surface; Aerdts, A. M et al, Polymer 1997 38, No. 16, 1997, p. 4247-52, which
describes a
material using polystyrene, poly(methyl methacrylate) or polybutadiene as its
core. An
epoxidized poly(methyl methacrylate) is used for the shell. The epoxide sites
are reactive sites
on the shell of this material. In another embodiment, glycidyl methacrylate
and methyl
methacrylate are used as a co-monomer in the shell.
[0131] The core-shell particles can include more than one core and/or more
than one
shell. In addition, mixtures of core-shell particles with elastomer particles
can be used. Two
different diameters of impact modifiers can be used in a certain ratio to
lower the viscosity of
the dispersion comprising a cross-linkable monomer or oligomer. For example,
the
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composition of impact modifiers can be about a 7 to 1 ratio of diameters i.e.
140 nm diameter
particles vs 20 nm diameter particles and about a 4 to 1 ratio of wt%.
[0132] Another desirable feature of selection of the elastomer or impact
modifier is to
select a composition of the elastomer or impact modifier that has a refractive
index value at
least within 0.03 units of the refractive index value of the material it is
dispersed in, more
preferably within 0.02 units, so as to minimize the scattering of radiation in
the UV-visible
wavelength range. An example of such a mixture is Paraloid KM 334, refractive
index 1.47,
and Dymax BR-952- a urethane dimethacrylate, refractive index 1.48.
[0133] The dispersion of oxidized discrete carbon nanotubes with bonded
dispersion
agent further comprises fillers in the % weight from about 0.1% to about 30%
by weight of the
dispersion selected from the group consisting of carbon black, graphene,
oxidized graphene,
reduced graphene, carbon fibers, silicas, silicates, halloysite, clays,
calcium carbonate,
wollastonite, glass, fire-retardants and talc. The fillers can also be surface
modified to improve
their bonding and distribution within the dispersion. An example of a surface
treatment is the
use of a silane coupling agent to silica particles.
[0134] A general method to determine the thermal conductivity of the
dispersion is to
apply a known heat flux to a sample and once the sample's steady-state
temperature is reached,
the difference in temperature across the thickness of the sample is measured.
After assuming
one-dimensional heat flow and an isotropic medium, Fourier's Law is then used
to calculate
the measured thermal conductivity,
Example 1 - Oxidizing TuballTm (OCSiAl)
101351 500 grams of 67% weight nitric acid is heated to 95 degrees C in a 1
liter glass
reactor fitted with a stirrer and condensor. To the acid, 5 grams of as-
received, single-walled
carbon nanotubes (Tubaltrm) are added. The as-received fluffy carbon nanotubes
have the
morphology of tightly bundled tree-trunks which can be several millimeters in
length and a
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millimeter in diameter. The mixture of acid and carbon nanotubes are mixed
while the solution
is kept at about 95 degrees Celsius for 5 hours. At the end of the reaction
period, the oxidized
single wall carbon nanotubes are filtered to remove the acid and washed with
reverse osmosis
(RO) water to pH of 3-4. The resulting CNTs were oxidized to about 3.6% and
contained 4.4%
metal residue.
Example 2¨ Oxidizing multiwall carbon nanotubes, CNano Flotube 9000
[0136] 4 liters of concentrated nitric acid containing 65% nitric acid are
added into a
liter temperature controlled reaction vessel fitted with a sonicator and
stirrer. 40 grams of
non-discrete multiwall carbon nanotubes, grade Flowtube 9000 from CNano
corporation, are
loaded into the reactor vessel while stirring the acid mixture and the
temperature maintained at
85 C. The sonicator power is set at 130-150 watts and the reaction is
continued for three hours.
After 3 hours the viscous solution is transferred to a filter with a 5
micrometer filter mesh and
much of the acid mixture removed by filtering using a 100psi pressure. The
filter cake is
washed one time with four liters of deionized water followed by one wash of
four liters of an
ammonium hydroxide solution at pH greater than 9 and then two more washes with
four liters
of deionized water. The resultant pH of the final wash is 4.5. A small sample
of the filter cake
is dried in vacuum at 100 C for four hours and a thermogravimetric analysis
taken as described
previously. The amount of oxidized species on the fiber is 2.4 percent weight
and the average
aspect ratio as determined by scanning electron microscopy to be 60. The
residual catalyst
content is determined as 2,500 ppm.
Example 3 ¨ Covalently attaching a dispersing agent to oxidized single wall
carbon
nanotube.
[0137] Using oxidized single wall carbon nanotubes from example 1 in the form
of a
wet cake with water of solids content 6.6% weight. 30.3 g of wet cake is mixed
with 30g of
isopropanol then 3g of Jeffamine M2005 monoamine terminated polyether
dissolved in 350g
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of isopropanol and 622g water is added with stirring. Stirring is continued
for 10 minutes. The
slurry is transferred to a Waring Blender and blended at high speed for 10
minutes.
[0138] The slurry is then passed through a laboratory scale homogenizer
keeping the
temperature below 45 C until no large structures > 20 micrometers in scale
are observed by
optical microscopy.
[0139] The resultant mixture is then filtered using a Buchner filter and
number 2
Whatman filter paper at 13 and washed 4 times with 100 cm3 of 35% wt aqueous
isopropyl
alcohol. The washed wet cake is then dried first in a convection oven at 120
C to 95% solids,
then in a vacuum oven at 150 C for 1 hour. This is termed SWNT MB in Table 1.
[0140] The TGA analysis run in nitrogen at 5 C/min in the range 200-600 C
gave
47% covalently bound polyether.
Example 4 ¨ Covalently attaching a dispersing agent to oxidized multiwall
carbon
nanotube.
[0141] Using oxidized multiwall carbon nanotubes from example 2 in the form of
a wet
cake with water of solids content 5% weight. 40 g of wet cake is mixed with
30g of isopropanol
then 2g ofJeffamine M2005 monoamine terminated polyether dissolved in 350g of
isopropanol
and 622g water is added with stirring. Stirring is continued for 10 minutes.
The slurry is
transferred to a Waring Blender and blended at high speed for 10 minutes.
[0142] The slurry is then passed through a laboratory scale homogenizer
keeping the
temperature below 45 C until no large structures > 20 micrometers in scale
are observed by
optical microscopy.
[0143] The resultant mixture is then filtered using a Buchner filter and
number 2
Whatman filter paper at 13 and washed 4 times with 100 cm3 of 35% wt. aqueous
isopropyl
alcohol. The washed wet cake is then dried first in a convection oven at 120
C to 95% solids,
then in a vacuum oven at 150 'C for 1 hour.
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[0144] The TGA analysis run in nitrogen at 5 C/min in the range 200-600 C
gave
18% covalently bound polyether.
Example 5¨ Coating a Nylon powder
[0145] Nylon 11 is ground into small powder granules less than 10 micrometers
in
diameter. A dispersion is made by taking lg of the carbon nanotubes of Example
4 in 200g
aqueous isopropanol alcohol (50/50) together with lg of polyvinylpyrrolidone,
Molecular
weight about 24,000 daltons (Sigma Aldrich). 100g of the Nylon 11 powder is
stirred into the
modified carbon nanotube dispersion and stirred for 1 hour. The material is
then dried in a
convection oven at 110 C. The dried material is placed in a ball mill for 1
hour to give a fine
dispersion of Nylon 11 with a coating of the dried dispersion.
101461 The powder can then be used in an SLS additive manufacturing process to
create
strong parts with enhanced electrical conductivity with resistance less than
10 billion ohm per
square. The coating of oxidized discrete carbon nanotubes with covalently
attached dispersing
agent allows for improved post sinter annealing of parts by infra-red or radio
frequency
radiation.
Example 6¨ Coating a ceramic powder
[0147] Using aluminum oxide powder granules less than 10 micrometers in
diameter.
A dispersion is made by taking lg of the carbon nanotubes of Example 4 in 200g
isopropanol
alcohol together with lg Molecular weight about 24,000 daltons (Sigma Aldrich)
and mixing
in a Thinky mixer at 2000 rpm for 5 minutes. The dispersion is jetted
selectively onto the layer
of aluminum oxide powder and the alcohol is removed by drying.
[0148] The powder is bound by the dried dispersion of oxidized discrete carbon
nanotubes and can then be sintered to create strong parts. The dispersion of
oxidized discrete
carbon nanotubes with covalently attached dispersing agent significantly
improves the green
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strength of the ceramic part and the during sintering the covalently bound
dispersing agent is
removed. The oxidized discrete carbon nanotubes can be used to induce heating
by
electric/magnetic fields, or infra-red or radio frequency radiation.
Example 7- Mixing of radiation curable resin
[0149] Radiation curable compositions for vat photopolymerization are prepared
by
weighing ingredient and loading into a container. The mixture is mechanically
stirred at room
temperature or elevated temperatures (up to 80 C) until a homogeneous resin
mixture is
obtained. The prepared compositions are processed in the vat
photopolymerization equipment
and fabricated specimens are analyzed in accordance with the test methods
described below.
[0150] Fabrication of three-dimensional specimens.
101511 The general procedure used for preparing three-dimensional specimens
with vat
photopolymerization equipment is as follows. The radiation curable resin is
poured into a vat.
The fabrication parameters were set as standard-black resin and 25 .m layer
thickness. In that
mode, the resin is heated to 31 C prior to part fabrication. Depending on the
composition of
the resin, a sufficient number of laser passes were employed to provide the
desired
polymerization energy. The material was exposed to a laser emitting in the
range of 405 nm.
Initially a -green part" is formed, in which layers are not completely cured.
Under curing
allows for the successive layers to better adhere by bonding when further
cured. The fabricated
"green part" is removed from the machine, washed with isopropyl alcohol, dried
in air and
post-cured in a curing chamber equipped with 405 nm multi-directional LED
lamps. All
specimens were post-cured in the curing chamber at room temperature for 30
minutes unless
specified otherwise.
[0152] Test methods
[0153] The resin is prepared to satisfy desired viscosity and wetting behavior
requirements. Viscosity and wetting behavior directly affect the recoating
depth (layer
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thickness before radiation exposure), which in turn influences the build
resolution in z-
direction. Viscosity data was collected on freshly prepared resins using HR20
Discovery
Hybrid Rheometer (TA Instruments). The 40 mm 2.002 Stainless Steel Peltier
plate was used
for the flow sweep experiment. The logarithmic sweep was performed by sweeping
the shear
rate from 1.0e' to 8000 1/s at room temperature. Additional flow temperature
ramp testing
was conducted at a shear rate of 6 1/s and temperature ramp from 25 C to 80 C
at ramp rate of
2 C/min. Table 2 shows the viscosity at zero shear rate for three example
compositions. Data
shows that viscosity increases exponentially with increase in oxidized
discrete carbon nanotube
with bonded dispersion agent content in the final resin formulation.
Temperature ramp results
are shown in Table 3 and provide comparison points at 25 C, 50 C, and 80 C.
The results
show that with increase in temperature the viscosity reduces exponentially at
the constant shear
rate.
[0154]
Table 4
Example Viscosity at 25 C, [cP]
7.1 2,093
7.2 14,084
CONTROL 1 2,284
Table 5
Example Viscosity at Viscosity at
Viscosity at
25 C, [cP] 50 C, [cP] 80 C, [cP]
7.1 770 161 63
7.2 778 219 105
CONTROL 1 2073 267 50
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Table 6 lists the components of each photocurable composition labeled as
Examples 7.1,7.2
and Control 7.1. NOTE: TPO and OB amounts do not count towards total
composition
percentage.
Table 7
Component Example 7.1, Example 7.2, Control 1,
[% by weight] [% by weight] [% by
weight]
BR-952 47.00 37.00 67.00
BR-371 7.00 7.00 7.00
HEMA 26.00 26.00 26.00
TPO 1.00 1.00 1.00
OB 0.00 0.00 0.06
SWCNT MB 20.00 30.00 0
Tensile data was collected by testing tensile Type IV specimens (ASTM D638)
fabricated using
vat photopolymerization equipment. All specimens were fabricated vertically.
Tensile
strength, Young's modulus, and elongation at break tests were conducted 24
hours or more
after post-curing. The tensile tests were conducted in accordance with ASTM
D638, which is
hereby incorporated in its entirety by reference, except that no provision was
made for
controlling the room temperature and humidity and the bars were not
equilibrated for 2 days.
The testing was performed on an Instron testing machine (model 5985). The
reported data is
an average of three measurements. Table 8 shows the Ultimate tensile strength,
yield strength,
and young's modulus for example 7.1 and 7.2 compared to control that does not
have oxidized
discrete carbon nanotubes with bonded dispersing agent added to the
composition. These
examples show that addition of oxidized discrete carbon nanotubes with bonded
dispersing
agent increases both tensile and yield strength as well as Young's modulus
compared to resin
without the oxidized discrete carbon nanotubes.
Table 9
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Example Tensile Yield Strength, Young's
Strength, [MP a] [MPa] Modulus,
[GPa]
7.1 69 0.1 53.0 1.5 2.9 0.05
7.2 67 0.4 48.6 0.6 2.8 0.04
CONTROL 1 63.7 + 1 34.7 + 0.8 2.1 + 0.03
Cured specimens for determining the Izod impact strength were prepared in the
same manner
as for the tensile bars, except the specimens were designed in accordance with
ASTM D-256A
standard and had dimensions of 3.2 mm x 12.7 minx 63.5 mm (thickness x width x
length).
Specimens were notched using a motorized notching cutter from Ray-Ran. lzod
Impact was
measured using Universal Pendulum Impact System by Ray-Ran equipped with 2.75
J
pendulum. The reported data is the average of three measurements.
Impact strength of examples 7.1 to 7.4 is shown in Table 10. These examples
show that
addition of discrete oxidized carbon nanotubes with bonded dispersing agent
significantly
enhance the impact strength of the fabricated specimens compared to resin
without the oxidized
discrete carbon nanotubes.
Table 11
Example Impact Average, [/m] A Increase
7.1 19.8 32
7,2 15.7 4
7.3 19.8 75
7.4 28.5 151
CONTROL 1 15.0 **
CONTROL 2 11.3 **
Table 12 lists the components of each photocurable composition labeled as
Examples 7.3, 7.4
and Control 2,
Table 13
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Component Example 7.3, Example 7.4, Control 2,
[% by weight] [% by weight] [% by
weight]
Formlabs 99.95 99.80 100.00
Clear
MWCNT 0.05 0.20 0.00
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