U.S. patent application number 15/870552 was filed with the patent office on 2018-05-17 for electrical, plating and catalytic uses of metal nanomaterial compositions.
This patent application is currently assigned to NCC NANO, LLC. The applicant listed for this patent is NCC NANO, LLC. Invention is credited to Wayne Furlan, Denny Hamill, Karl Martin, Steve McCool, Kurt A. Schroder, Kevin Walter, Darrin Willauer, Dennis Wilson.
Application Number | 20180139850 15/870552 |
Document ID | / |
Family ID | 42781362 |
Filed Date | 2018-05-17 |
United States Patent
Application |
20180139850 |
Kind Code |
A1 |
Schroder; Kurt A. ; et
al. |
May 17, 2018 |
ELECTRICAL, PLATING AND CATALYTIC USES OF METAL NANOMATERIAL
COMPOSITIONS
Abstract
This invention relates generally to uses of novel nanomaterial
composition and the systems in which they are used, and more
particularly to nanomaterial compositions generally comprising
carbon and a metal, which composition can be exposed to pulsed
emissions to react, activate, combine, or sinter the nanomaterial
composition. The nanomaterial compositions can alternatively be
utilized at ambient temperature or under other means to cause such
reaction, activation, combination, or sintering to occur.
Inventors: |
Schroder; Kurt A.;
(Coupland, TX) ; McCool; Steve; (Austin, TX)
; Hamill; Denny; (Austin, TX) ; Wilson;
Dennis; (Austin, TX) ; Furlan; Wayne; (Austin,
TX) ; Walter; Kevin; (Austin, TX) ; Willauer;
Darrin; (Austin, TX) ; Martin; Karl; (Austin,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NCC NANO, LLC |
Dallas |
TX |
US |
|
|
Assignee: |
NCC NANO, LLC
Dallas
TX
|
Family ID: |
42781362 |
Appl. No.: |
15/870552 |
Filed: |
January 12, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15285927 |
Oct 5, 2016 |
9907183 |
|
|
15870552 |
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11720171 |
May 24, 2007 |
7820097 |
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15285927 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 1/0022 20130101;
B29C 35/10 20130101; H05K 2203/0502 20130101; B29C 35/0805
20130101; H05K 3/1283 20130101; C23C 18/1658 20130101; C23C 30/00
20130101; C23C 18/1667 20130101; B22F 3/10 20130101; B41M 3/001
20130101; B41M 5/0064 20130101; C23C 18/31 20130101; C23C 18/143
20190501; B41M 5/0035 20130101; B41M 2205/12 20130101; D21H 19/02
20130101; H05K 2203/10 20130101; H05K 2203/1131 20130101; B22F
2998/10 20130101; B41M 7/0072 20130101; C23C 18/1692 20130101; B22F
2001/0033 20130101; H05K 1/097 20130101; B41M 7/0081 20130101; B41M
5/0047 20130101; C09D 1/04 20130101; H05K 3/12 20130101; B41M 3/006
20130101; B22F 2998/10 20130101; B22F 2007/042 20130101; B22F 9/24
20130101; B22F 2202/11 20130101; B22F 2202/13 20130101 |
International
Class: |
H05K 3/12 20060101
H05K003/12; B22F 3/10 20060101 B22F003/10; D21H 19/02 20060101
D21H019/02; B29C 35/08 20060101 B29C035/08; B29C 35/10 20060101
B29C035/10; B41M 3/00 20060101 B41M003/00; C23C 18/31 20060101
C23C018/31; C23C 30/00 20060101 C23C030/00; C23C 18/16 20060101
C23C018/16; C23C 18/14 20060101 C23C018/14; C09D 1/04 20060101
C09D001/04; B22F 1/00 20060101 B22F001/00; B41M 7/00 20060101
B41M007/00 |
Claims
1. A system for sintering materials, said system comprising: a
flashlamp generates a plurality of electromagnetic emission pulses
for irradiating a film on a substrate in ambient air in order to
sinter said film on said substrate such that the conductivity of
said film on said substrate increases by at least two-fold, wherein
said film includes at least one metal less than 1 micrometer; and a
control circuit controls said flashlamp to limit a duration of each
of said electromagnetic emission pulses to be between one
microsecond and one hundred milliseconds.
2. The system of claim 1, wherein said system further includes a
printer for printing said film on said substrate using a
formulation having said one metal less than 1 micrometer.
3. The system of claim 2, wherein said one metal is copper.
4. The system of claim 1, wherein said substrate has a
decomposition temperature below 450 degrees Celsius.
5. The system of claim 1, wherein said substrate includes a
substance selected from the group consisting of PET, polyester,
plastics, polymers, resins, paper products, laminates and
combinations thereof.
6. The system of claim 1, wherein said flashlamp is a xenon
flashlamp.
7. The system of claim 1, wherein said system further includes a
conveyor for moving said substrate.
Description
RELATED PATENT APPLICATIONS
[0001] The present application is a divisional application of U.S.
patent application Ser. No. 11/720,171 (filed May 24, 2007). This
patent application claims the benefit of the earlier filing dates
of U.S. Patent Application No. 60/630,988 (filed Nov. 24, 2004),
which application is entitled "Electrical, Plating and Catalytic
Uses of Metal Nanomaterial Compositions," having Kurt A. Schroder,
Karl M. Martin, Dennis E. Wilson, Darrin L. Willauer, Dennis W.
Hamill, and Kevin C. Walter as inventors and U.S. Patent
Application No. 60/668,240 (filed Apr. 4, 2005), which application
entitled "Method and System for Reacting, Activating and Sintering
Nanomaterials," having Steven C. McCool, Kurt A. Schroder and
Dennis E. Wilson as inventors.
[0002] This application is also related to the following patent
applications:
[0003] PCT Patent Application No. PCT/US2005/027711, filed Aug. 4,
2005, entitled "Carbon And Metal Nanomaterial Composition And
Synthesis" having Kurt Schroder and Karl Matthew Martin as
inventors (the "PCT 05/027711 Application"), and claiming benefits
of the earlier filing dates of U.S. Patent Application Nos.
60/598,784 (filed Aug. 4, 2005) and 60/620,181 (filed on Oct. 19,
2004), which two provisional patent applications have the same
title and named inventors as the PCT 05/027711 Application.
[0004] U.S. patent application Ser. No. 10/669,858, filed on Sep.
24, 2003, entitled "Nanopowder Synthesis Using Pulsed Arc Discharge
and Applied Magnetic Field," having Kurt Schroder and Doug Jackson
as inventors.
[0005] U.S. Pat. No. 6,777,639, issued on Aug. 17, 2004, entitled
"Radial Pulsed Arc Discharge Gun For Synthesizing Nanopowders,"
having Kurt Schroder and Doug Jackson as inventors.
[0006] Each of the applications and patents identified above are
assigned to the Assignee of the present invention and are
incorporated herein by reference.
FIELD OF THE INVENTION
[0007] This invention relates generally to uses of novel
nanomaterial composition and the systems in which they are used,
and more particularly to nanomaterial compositions generally
comprising carbon and a metal, which composition can be exposed to
pulsed emissions to react, activate, combine, or sinter the
nanomaterial composition. The nanomaterial compositions can
alternatively be utilized at ambient temperature or under other
means to cause such reaction, activation, combination, or sintering
to occur.
BACKGROUND
[0008] In the field of material processing, materials are often
heated to cause a particular change in material morphology, a
particular reaction to occur, or to cause a phase change. For
example, in the area of conductive patterning, formulations or inks
containing silver flakes or powder are laid down on a substrate and
then heated to cause the particles to fuse and form a conductive
line. In such case, the formulation is required to be fluid and
often is nonconductive in order to print the pattern while at the
end of the processing it must be solid and highly conductive. The
heat changes the morphology of the silver to give the desired
results. For silver inks, the temperature that the ink and
substrate must be heated to in order to cure the ink is a function
of the sintering temperature of the silver. For silver, the melting
temperature is approximately 960.degree. C. and the sintering
temperature is approximately 800.degree. C. This high temperature
limits the substrates to materials that are unaffected by the high
temperature. Many of the lower cost or flexible substrates such as
cellulose (paper), Polyethylene Terephthalate (PET), Polyester and
many other plastics cannot withstand these temperatures. Similarly,
other components on the substrate, such as organic semiconductors
may also decompose at elevated temperatures.
[0009] One approach to addressing this limitation is to use higher
temperature substrates such as polyimide films. While this does
provide a moderately high temperature flexible substrate, it is not
necessarily high enough to form highly conductive films.
Furthermore, it is expensive and not suitable for low cost
applications.
[0010] Another approach to solve this problem is to use high
loading of silver flakes in a resin or polymer that contracts
during curing. This forces the silver flakes together causing them
to make electrical contact. This approach has been demonstrated by
Dow Corning under the trade name PI-2000 Highly Conductive Silver
Ink. While this product appears to work in some applications, it
does have some limitations in that it cannot be inkjetted.
[0011] Another approach to solving this temperature limitation is
to use nanometals that exhibit a reduction in sintering temperature
because of their small size. This approach has shown improvements
by reducing the processing temperature to approximately 300.degree.
C. to approximately 700.degree. C. Generally, to take advantage of
the depressed sintering temperature, the particles must be
discrete. Most nanometal synthesis processes such as SOL-GEL
require chemical surface functionalization of the particles to keep
the particles discrete and to prevent them from spontaneously
fusing. This chemical surface functionalization generally needs to
be volatilized at an elevated temperature that may be higher than
the sintering temperature of the silver. Even if the surface
functionalization is designed to evaporate below the sintering
temperature, the sintering temperature may still be too high to use
some of the lower temperature substrates. As the industry tries to
lower the processing temperature, it is often done at the expense
of the conductivity of the pattern. While it may be possible to use
lower processing temperatures, the result is usually a pattern with
less than adequate conductivity.
[0012] While the above example has been described in the context of
conductive inks, there are similar applications where the same
problems exist. For example, in catalytic applications, the
catalyst is usually bonded to a high temperature substrate. In
order for the reaction to occur at an acceptable rate, the catalyst
must be at elevated temperatures. These high temperature substrates
are often expensive and it is desirable to replace them with lower
temperature substrates. Nanomaterials have begun to be used in
these applications, because of their high reactivity and lower
reaction temperatures. However, they still must operate at
temperatures typically above the lower cost substrate's operating
temperatures.
[0013] Therefore, in the field there exists a need to process
materials at lower temperatures to allow more economical substrates
to be used. More specifically, there is a need in the conductive
patterning market to produce high conductivity patterns on low
temperature substrates.
SUMMARY OF THE INVENTION
[0014] This invention relates generally to uses of novel
nanomaterials composites comprised of relatively unaggregated
metals particles. The processes described in the PCT 05/027711
Application produce the new materials in which some of the
composites are composed of carbon and a metal while others are
composed of an oxide and a metal. These materials, while being
unique and novel unto themselves, can be used in unique and novel
applications. Additionally, some of the uses have been shown to
work with other nanomaterials. The new uses are accomplished by
exploiting the unique material properties that exist in
nanomaterials. Specifically, it has been observed that
nanomaterials have a unique combination of attributes and
properties that allow them to be used for electrical and catalytic
applications.
[0015] The current invention can exploit these properties and
reveals novel uses in the area of conductive patterning. For
example, the current invention can relate to creating conductive
patterns using nanometals at room or relatively low temperatures,
using a photonic curing process in conjunction with nanometals to
create highly conductive patterns and using nanometals in
conjunction with xerographic printing techniques.
[0016] One embodiment of the current invention uses the
carbon/metal composite to create conductive patterns at room
temperature. This is accomplished by either a simple dispersion of
the material in water and then printing the dispersion on a paper
substrate. Forming conductive patterns on other substrates at room
temperature has also been accomplished using other dispersion
techniques.
[0017] Another embodiment of the current invention relates
generally to a novel method for reacting, activating or sintering
nanomaterials and combinations thereof. For example, the invention
can relate to the processing of nanometal powders, such as
nanometals. Metals, such as, but not limited to, silver, copper,
gold, platinum, palladium, tin, antimony, indium and lead are
examples of materials that may be used. In the current invention
nano refers to at least one aspect of the material having
dimensions less than about 1 micron. Generally, this dimension is
less than about 500 nm, and even more so less than about 100
nm.
[0018] Applicants have observed that some nanoparticles, including
most metal nanoparticles, are generally very absorbent of photonic
radiation. That is, the particles behave as good blackbodies and
have high absorptivity of electro-magnetic radiation. Additionally,
nanoparticles tend to have lower reflectivity and poorer thermal
conductivity as compared to the bulk materials. Nanoparticles also
have a much larger surface area to mass ratio and have a low
thermal mass individually than micron or larger sized particles.
These qualities suggest irradiation of the nanoparticles with a
pulsed photonic source, more specifically a broadcast photonic
source, could momentarily heat the particles to a very high
temperature. (A "photonic source" is a radiation source in the
electromagnetic spectrum including, but not limited, to gamma rays,
x-rays, ultraviolet, visible, infrared, microwaves, radio waves, or
combinations thereof) This effect is very advantageous, as noted in
several examples listed below.
[0019] The current invention addresses the limitations described in
the prior art by providing a novel method and system for processing
nanomaterial. The current invention uses a high powered, pulsed
photonic source to process the nanoparticles while minimally
affecting the substrate. By such process, this overcomes
limitations of the prior art. In the current invention, a film or
pattern containing nanomaterial is fabricated on a surface. Such
film or pattern may be fabricated using techniques such as inkjet,
screen-printing, gravure printing, xerography, stamping,
flexography, offset printing, painting, airbrushing, etc. Once the
film or pattern has dried on the substrate, the pattern is
subjected to a high-powered, pulsed photonic emission source. The
high absorptivity of the nanomaterials and low thermal mass of
particles causes them to be rapidly heated while the poor thermal
conductivity and short pulse length retards the nanoparticles
ability to transfer heat to their surroundings. The result is that
the particle temperature is increased quickly to temperatures that
cause them to fuse. The poor conductivity, low absorptivity and
high thermal mass of the substrate insures that much of the energy
from the photonic pulse goes into heating up the particles and
minimal energy is transferred to the substrate or surrounding
components.
[0020] By using a method and system that focuses the energy
delivery on the film or pattern, the current invention overcomes
the limitations of the prior art.
[0021] In yet another embodiment, the nanometal is used in
conjunction with a photonic source for catalytic applications.
Specifically, this can be accomplished at much lower temperatures
than current technologies.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 reflects a portion of a conductive film on PET that
was processed using the current invention.
[0023] FIG. 2 shows another film with a cured central region.
[0024] FIG. 3 shows an example where only the right half of the
film has been photonically cured.
[0025] FIG. 4 shows a sample of the present invention obtained by
optimizing the particle oxide layer and photonic conditions such
that conductive of bulk copper is approached.
[0026] FIG. 5 shows a process diagram of an embodiment of the
invention.
[0027] FIG. 6 shows a schematic of the production system.
DETAILED DESCRIPTION
Ambient Cure Conductive Ink
[0028] One novel use that is particularly enabled by the
carbon/metal nanocomposite material is electroless
deposition/plating/printing. In an embodiment of the invention, a
conductive ink has been made with the silver/carbon nanocomposite
material that will cure and possess metallic conduction without
requiring a thermal cure (i.e. ambient room temperature). Such ink
can be used for producing metal patterns.
[0029] In one embodiment, the silver/carbon composite is combined
with de-ionized water and then mixed using zirconia beads in a
gyroscopic mixer. The dispersion or ink is then printed on a paper
substrate. As the dispersion dries, the material will turn from
black to silver in color. Additionally, the resistivity will go
from infinite down to approximately 5 times bulk silver. Once
dried, the pattern has good adhesion and long-term
conductivity.
[0030] It is hypothesized that the unique combination of carbon,
silver and paper enable the highly conductive pattern to be
produced. It is believed that the wicking of the water into the
paper creates high hydrostatic pressure gradients that force the
particles into intimate contact. Additionally, the carbon which
keeps the silver particles apart appears to be more dispersible in
the water and tends to wick out with the water leaving the bare
silver particles in contact with the paper fibers. When in contact
with one another, the bare silver nanoparticles will reduce their
surface energy by fusing and thus form a highly conductive pattern
that is bonded to the paper fibers. The following example
illustrates an embodiment of the invention.
Example 1
[0031] Ambient temperature cure silver ink. The ink is comprised of
the following components: [0032] Nano Ag Particle Dispersion for
ambient cure [0033] Ag nano particles (25-150 nm BET) 15-45 g
[0034] Deionied Water 85-65 g [0035] Zirconia Milling Beads 0.1-1.2
mm 100-150 g [0036] Mix with Gyroscopic Mixing action 30-120
minutes
[0037] The ink was drawn down on Epson Photo Quality paper with a
#10 wire wound rod (1.0 mil wet) to achieve a 0.09 mil (2.3 micron)
dry film thickness. Conductivity as shown in Table 1A is achieved
within 10-30 minutes.
TABLE-US-00001 TABLE 1A Conductivity of Ag dispersion on porous
substrate such as paper, gloss paper and photo paper microohm-cm
ohm/.quadrature. ohm/.quadrature./mil Rho Film/Bulk 18.06 0.08 0.01
11.28
[0038] This method was applied to other non-porous substrates such
as PET, however conductivity was not obtained, as illustrated in
Table 1B.
TABLE-US-00002 TABLE 1B Conductivity on Non-porous substrates
microohm-cm ohm/.quadrature. ohm/.quadrature./mil Rho Film/Bulk
Open Circuit OC OC OC
[0039] To address this conductivity issue of coating on non-porous
substrates another embodiment is used. In this embodiment, the
silver/carbon composite was suspended in a suitable solvent, such
as an alcohol. The suspension was treated with an acid, such as
HCL. The HCL can etch any oxide that may exist on the surface of
the silver and aid in electrostatically stabilizing of the
particles. The solution was then sonicated and painted or printed
with a variety of printing techniques--such as inkjet, screen
transfer, gravure--onto a nonconducting surface, such as paper,
plastic, or glass. At ambient temperatures, the solution can dry
within a couple minutes and the deposited material can become
conductive. Resistivities as low as 36 microohm-cm (around 23 times
more resistive than solid silver) have been achieved with this
process. Further improvements can be made by slightly heating the
sample to about 90.degree. C. for 30 minutes. Tests were conducted
over the temperature range of about 25.degree. C. to about
150.degree. C., with improvements seen over the entire temperature
range. An advantage of this process is that the solvents evaporate
at ambient temperature leaving bare silver particles, which
ultimately sinter, at ambient temperatures to form a conductive
path.
Example 2
[0040] The process can be improved by applying low temperature,
much lower than 700.degree. C., which is currently required to
sinter flake silver. Results from this embodiment on Mylar are
illustrated by Example 2 shown in Tables 2A-2C.
TABLE-US-00003 TABLE 2A Formulations of Ag in Isopropyl Alcohol
with small amounts of Hydrochloric acid Formulation 31-90 31-91
31-92 31-93 31-94 Ag30ST3 (g) 6.48 6.51 6.55 6.58 6.61 IPA (g)
12.97 13.03 13.09 13.16 13.22 HCl (28%) (g) 0.55 0.46 0.36 0.26
0.17 Total (g) 20.00 20.00 20.00 20.00 20.00 Milling Beads 20.00
20.00 20.00 20.00 20.00
TABLE-US-00004 TABLE 2B Typical Particle size data on the Horbia
910 Horiba 910 EXP 31-94 Particle size SLS nm D10 135 D50 270 D90
51 D95 603 D95 1140
TABLE-US-00005 TABLE 2C Conductivity of Ag in Isopropyl Alcohol
with small amounts of Hydrochloric acid on PET sheet sheet
Rho_film/ % Acid thickness resistivity resistance resistance
Rho_bulk Sample (HCl) (mils) (microOhm-cm) (ohm/.quadrature.)
(ohms/.quadrature./mil) Ratio 31-90-avg 2.80 0.017 32000 7500
1.3E+02 ~20,000 31-91-avg 2.30 0.043 63 0.582 2.5E-02 39 31-92-avg
1.80 0.046 50 0.423 2.0E-02 31 31-93-avg 1.30 0.058 36 0.248
1.4E-02 23 31-94-avg 0.80 0.039 45 0.457 1.8E-02 28
[0041] An embodiment of present invention can also be used to plate
metal, such as copper or steel. When plating a metal, an advantage
of the HCL is that the substrate is pickled and plated in a single
step. Another advantage of this process was the thickness of the
plating can be very thick, if desired. 100-micron thick layers have
been deposited in a single pass. However, higher conductivity can
be achieved with multiple thinner depositions. Since the silver can
form a porous, three-dimensional sintered network, the plated
material can slightly compress or deform to conform to a surface.
This may form a superior electrical or thermal contact. When a vial
containing the silver dispersion was allowed to dry, a porous
silver "sponge" remained.
[0042] In yet another embodiment, other material or particles were
placed in this network, to give a coating with unique properties.
An example can be dispersing other particles or fibers, such as
alumina or zirconia, with the silver solution. The final coating
was both electrically conducting and scratch resistant. This was
desirable for sliding electrical contacts.
[0043] It should be noted that this carbon/silver composite was
well suited for ambient thermal cure conducting ink application, as
the particles are comparatively devoid of organic ligands, and as
compared to other metallic nanoparticle conductive inks. This means
the evaporation of the solvent was all that was needed to induce
the particles to begin fusing together. With inks that have
organics attached to them, a thermal source, typically greater than
300.degree. C., was ordinarily needed to drive off or volatilize
the organic before sintering of the nanoparticles can ensue. This
is generally undesirable as it adds an additional process step. The
heat also potentially damages the substrate and other components
(such as organic based devices) in the circuit. Any ink containing
particles made by other processes that are comparatively clean on
the surface could be used to make a no or low thermal cure ink.
[0044] From the aforementioned information, one skilled in the art
would recognize the impact of the current invention in that it
allows the use of low temperature substrates not currently
available for use with common thermal cure processes. This opens a
new market by substantially reducing both production and product
costs. Generally, the low temperature substrates are less expensive
than high temperature substrates. Additionally, the cost associated
with purchasing and operating thermal ovens at elevated
temperatures was eliminated. The following examples illustrate
embodiments of the invention.
Example 3
[0045] Ambient cure silver paint was created using 1 g of 30 nm
silver with 2% carbon content was poured into a vial containing 2 g
of isopropanol and 0.25 g of 37% hydrochloric acid (remainder
water). This mixture was shaken and sonicated in a bath for 30
seconds. A 1/4'' wide artist brush was used to paint the dispersion
onto a piece of photocopy paper or similar porous substrate. The
trace painted was about 4 microns thick (when dry), a few inches
long, and about 7 mm wide. The resistance of the trace immediately
after application was greater than 20 megaohms (out of range on the
ohmmeter). Over the next two to three minutes, the isoproponal and
hydrochloric acid began to evaporate. During this time, the
resistance monotonically went down to a few ohms per inch of trace.
The conductivity came within 50% its final value 20 minutes after
application; and the resistance continued to drop down to about 0.6
ohms per inch of trace over a period of several hours. This
corresponded to a resistivity of about 67 microohm-cm or about 45
times more resistive than a solid silver trace. In other units, the
resistance of this trace was about 30 milliohm/sq/mil. The
temperature during this entire time was about 25.degree. C. No
thermal cure was required. The trace appeared to be bonded to the
paper and only delaminated when the bend radius of the paper became
less than a millimeter, i.e., a sharp edge. Scotch tape could not
pull the trace off the paper. The liquid dispersion used to paint
the trace gave consistent conductivity results for at least 3 days
after it was synthesized. This example is similar to a screen or
gravure printing process.
Example 4
[0046] Multiple layers. A thin film of silver nanoparticles was
laid down with the technique and ink dispersion of Example 1. After
a few hours, the resistance of the 4-inch long trace was 7.6 ohms.
A similar trace was painted directly on top of that trace. After a
few hours, the resistance of the 4-inch long trace was only 1.0
ohm.
Example 5
[0047] No thermal cure ink jet printing. Same recipe as Example 1,
except 4 g of isoproponal was used to reduce the viscosity to
refill an inkjet cartridge for an Epson Stylus Photo 925 printer.
Silver lines as narrow as 100 microns were printed with this
printer.
[0048] One skilled in the art would recognize that this process can
be applied to other metals. Copper is a good example. In this
embodiment, two processes formed unaggregated nanopowders; one
using the carbon and the other by introducing trace amounts of
oxygen during the production process to create an oxide shell
around the copper particles. In both cases, the nanoparticles are
relatively unaggregated. In this case, the films as produced were
not conductive but were conductive when heated at about 150.degree.
C. in an inert atmosphere. In the case of copper, the material
readily oxidizes such that if an inert atmosphere is not used,
non-conductive copper oxide is formed.
Xerographic Printing
[0049] While the previous embodiments can use the nanometal
dispersed in a solvent which is then printed, there are other
methods of printing that use dry powders. For example, laser
printing or xerographic printing typically uses powders or toners
that are electrostatically deposited onto a substrate and then
heated to fuse the particles of the powder to create the desired
image. One material attribute for the preset process was that the
powders have a high resistivity so that it can be electrostatically
charged. Hence, metal powders are not used in this process.
[0050] Nanometal powders and in particular the carbon/metal
composite material are well suited for this application because the
powder has a very high and controllable resistivity. This allows it
to be electrostatically transferred in a xerographic process to
directly print the metal powder. After the nanoparticles have been
transferred to the printer, they can be sintered to folio.
conductive paths with a variety of means such heat, laser, ion beam
or ultraviolet, infrared or photonic curing (described below).
Hence, a new method of creating patterns is enabled by the
nanomaterials. The following examples demonstrate different
embodiments of the current invention.
Example 6
[0051] The toner from a cartridge from an IBM Laser printer E by
Lexmark Type 4019-E01 laser printer was removed and replaced with
10 nm silver with 30% carbon content. The bulk silver powder had
very high resistance. Two probes from an ohmmeter were immersed
into a jar of the powder with 3/8 inch probe spacing and 1/2 inch
probe depth, the resistance was greater then 20 megaohms (the
maximum range of the ohmmeter). The thermal heating element of the
printer was disabled to prevent premature burning of the silver.
Successful transfer of silver powder was noted on a regular sheet
of copy paper. This silver on this sheet of paper would then need
to be sintered in order to be conductive. This can be done with a
variety of techniques including, but not limited to, mechanical
pressure, microwaves, resistance welding, ultrasonic welding, or
radiative means such as laser sintering or a flashlamp described in
the Photonic Activation of Metallic Nanoparticles section below.
Objects such as plastic, wood, textiles and other metals have been
plated with this powder using these sintering techniques.
[0052] Although the carbon metal composite nanomaterial is
particularly amenable to being a xerographic printing toner
component for printing conductive paths, other materials may be
amenable if they can be made very resistive while in bulk powder
form and be made to become conductive after printing. Examples may
include metallic particle powder coated with a thin dielectric
material that could be volatilized or reacted off after printing to
form conductive paths. An example is copper nanoparticles with an
oxide layer. Note that this would need to be cured in an inert
atmosphere to prevent copper oxide from forming. Fortunately, the
techniques described below enable the curing of the film in
air.
Photonic Activation of Metallic Nanoparticles
[0053] Another embodiment of the current invention includes a
method and system for processing nanomaterials to create conductive
patterns. The method and system of processing the nanomaterials
takes advantage of the unique properties of nanoparticles, as
compared to micron or the bulk material. For example, nanoparticles
tend to have low reflectivity, high absorptivity, reduced sintering
temperatures, higher reactivity and poor thermal conductivity, as
compared to the bulk material property. The current invention uses
a high-powered, pulsed, broadcast photonic source to process the
nanoparticles while minimally affecting the substrate, thus
overcoming the limitations of the prior art.
[0054] In the current invention, a film or pattern containing
nanomaterial was fabricated on a surface. Such film or pattern may
be fabricated using techniques such as inkjet, screen-printing,
gravure printing, xerography, stamping, flexography, offset
printing, painting, airbrushing, etc. Once the film or pattern had
dried on the substrate, the pattern was subjected to a
high-powered, pulsed photonic emission source. The high
absorptivity of the nanomaterials and low thermal mass of particles
causes them to be rapidly heated while the poor conductivity and
short pulse length retards the nanoparticles ability to transfer
heat to their surroundings. The result was that the particles'
temperature is increased quickly to temperatures enabling them to
fuse. The poor conductivity, low absorptivity and high thermal mass
of the substrate insured that much of the energy from the photonic
pulse went into heating up the particles and minimal energy was
transferred to the substrate or surrounding components. In summary,
the energy delivered to the particles happened so quickly that the
particles fused before they have time to transfer their heat to the
substrate. This natural discrimination capability of the
nanoparticles allows a pulsed, broadcast emission to cure a large
complex printed pattern in a single flash without damaging the
substrate. Typically, this technique deposits of order 1 J/cm.sup.2
on the substrate. This is generally below the damage level for the
substrate at the pulse lengths used. For systems which use a
continuous laser to sinter metal nanoparticle films of order 100
J/cm.sup.2 is needed. Since this involves depositing a much higher
areal energy density, the laser generally needs to be focused only
on the printed pattern of the substrate adjacent to the pattern or
the substrate will be damaged. Furthermore, the laser curing is a
serial process and requires expensive equipment and critically
aligned optics. It is possible to use a pulsed laser to accomplish
the above as the required areal energy density would be low, and
such a technique may even be preferable when curing a small area in
a repetitive fashion. A pulsed laser system is less desirable as
the area to be cured becomes larger. In this case the pulsed
emission from a gas discharge, such as a xenon flash lamp, becomes
more desirable. A reason for this is largely economic, as the
hardware for gas discharge lamp system is cheap and has a high
electrical to light conversion efficiency. This is demonstrated by
the fact that a flash lamp is often used to optically pump a laser
system. Furthermore, a gas discharge lamp system does not require
complex optics and critical alignment as a laser-based system does.
Still, pulsed solid-state and other pulsed emission sources are
continually becoming more and more economical. Multiple emission
sources could be used in parallel to achieve a broadcast effect.
Since this curing technology does not place a significant thermal
load on the substrate or surrounding components, multi-layer
circuits, even with embedded devices, are more practical on
thermally fragile substrates such as paper or plastic.
Photonic Curing Process
[0055] A method of an embodiment of the invention is to expose the
nanoparticles to a pulsed emission source, so as to cause their
morphology or phase to change and/or cause the material to react
without substantially affecting the substrate that they are
contained within or reside on. Several tests were performed to
evaluate the effectiveness of curing nanoparticle formulations for
conductive inks. In the tests, formulations were prepared by mixing
different nanomaterials with various solvents, surfactants and
dispersants and producing films or patterns with the formulations.
The films and patterns were applied to substrates, subjected to the
pulsed emission source and the conductivity, adhesion, surface
morphology and curing depth were measured. The conductivity was
determined using a four-point probe and thickness gauge. In some
cases, the films or patterns were allowed to dry prior to being
subjected to the pulsed emission source.
[0056] When the film or pattern was subjected to the pulsed
emission source, the particles heated-up and sintered. When this
happens, it was found that the absorptivity of that portion of the
pattern decreased and its reflectivity and thermal conductivity
increased. Hence the process was self-limiting. This may imply, in
some cases, that it was better to apply a single intense pulse
rather than multiple lower intensity pulses. In developing the
current invention, the effects of pulse duration and pulse energy
were investigated. The total power delivered to the pattern was a
function of the pulse energy, pulse duration and optical footprint
area. Tests were performed with pulse lengths from 0.7
microseconds-100 milliseconds using xenon flash lamps.
[0057] In development, a mixture of approximately 30% mass of
Nanotechnologies, Inc. 30 nm silver, 60% mass isoproponal and 10%
mass hydrochloric acid was used as the formulation to produce a
conductive film on PET. As the pattern dries its conductivity
increases to about 1/20.sup.th of bulk silver. The films were
applied to a 3.5 mil matte PET substrate with a "2.5" wire wound
draw down bar and allowed to dry. In some cases, multiple passes
were made. Typically, three passes yielded a 2-3 micron thick dried
film. After subjecting the film to the pulse, in all cases the
conductivity increased. Increases in conductivity to approximately
1/10 and in some cases 1/3 to 1/2 the conductivity of silver was
observed. In testing, it was generally found that for a given total
energy, the patterns processed using a higher power and a shorter
pulse length gave better conductivity. Testing also showed that
there was a threshold areal energy density, which if exceeded,
blows the film off of the PET surface. Tests performed at a given
energy above the threshold showed that the samples processed with a
long pulse length had substantial thermal damage to the substrate,
whereas the samples subjected to the shorter pulse lengths showed
minimal or even undetectable thermal damage to the substrate. In
this series of tests, the samples subjected to the shorter pulse
lengths showed visibly cured silver around the edges of the blown
off pattern, whereas the longer pulse length samples did not.
[0058] This evidence suggested that the shorter pulse lengths
worked better. This information has far reaching implications. For
short pulse lengths, it is possible to fully cure a sample without
causing significant damage to the substrate. This can remove the
thermal limitations of the substrate and allows a wide range of new
substrates to be used such as PET, polyester, plastics, polymers,
resins, fabrics, non-woven fabrics, paper products and organic
compounds. While this process works for low temperature substrates,
it is also applicable to high temperature substrates such as
ceramics, composites, laminates, glass, silicon and most materials
currently being used in the conductive patterning market. One
aspect of the substrate that should be reviewed is its absorptivity
in the wavelength of the flash emission. Generally, the substrate
should not have a high absorptivity in the wavelength range of the
flash because if it absorbs the energy of the flash it maybe
damaged. If needed, filters can be used to remove the undesirable
emission bands. One method to test whether the substrate is
affected by the emission is to subject it to the cure conditions
without any pattern. The substrate can then be inspected to
determine if it has been adversely affected.
Example 7
[0059] FIG. 1 shows a portion of a conductive film on PET that was
processed using the current invention. The top film shows several
places where the film was photonically cured. The lower film shows
several places where sufficient energy was used to blow the film
off the substrate. Notice, that substantially more damage occurs at
the longer pulses.
Example 8
[0060] FIG. 2 shows another film with a cured central region where
the conductivity was 1/3 to 1/2 that of bulk silver. Note the
indentations from the four-point probe used to measure its
resistivity. This process was also performed on formulations of
silver and isoproponal using different size particles ranging from
25 nm to 200 nm. In these cases, the pattern had infinite
resistance, greater than 40 Megaohms, or a non-detectable
conductivity after drying. In all cases, once the pattern was
subjected to the photonic curing, the conductivity increased to
within several orders of magnitude and generally within two orders
of magnitude of bulk silver. In some cases the conductivity was
within an order of magnitude of bulk silver. FIG. 3 shows an
example where only the right half of the film has been photonically
cured.
Example 9
[0061] A thin film of silver nanoparticles (with the ink recipe
from Example 1 of Section 1 (No Thermal Cure Conductive Ink) above,
but with 10% ethylene glycol by weight, was laid down onto a
cellulose substrate (paper) and allowed to dry. The electrical
resistance of the film was approximately 612 ohms. When a flash of
light from the xenon flash bulb of a disposable photographic camera
(Studio 35 Single Use Camera [27 exposures] distributed by Walgreen
Co, Deerfield, Ill. 60015-4681) is initiated about 1/2'' from the
film, the resistance immediately goes down to 440 ohms. Subsequent
flashes approximately 1-minute apart yielded resistances of 401,
268, 224, and 221 ohms respectively.
Example 10
[0062] Similar films of nanosilver (with the ink recipe from
Example 1 of Section 1 Ambient Cure Conductive Ink) above, were
laid down on a cellulose substrate and allowed to dry for about 25
minutes. The film #1 had an initial resistance of about 3.7 ohms.
One flash from a camera flash (described above) at 1/4 inch to 1/2
inch immediately dropped the resistance down to 3.3 ohms. A second
flash one-minute later dropped the resistance down to 2.5 ohms. A
subsequent flash one-minute later did not drop the resistance
noticeably. The second film was placed in an oven at 140 degrees
centigrade for 15 minutes. Its resistance dropped from 5.3 to 4.0
ohms. Two subsequent flashes from the camera dropped the resistance
of the film down to 3.9 and 3.8 ohms, respectively. In effect, a
few strobe flashes on the substrate appear to be a desirable
substitute for a low temperature thermal cure.
Example 11
[0063] A film of silver nanoparticles was made and allowed to dry
at approximately 25 degrees centigrade for 10 days. One flash from
the camera at 1/2 inch from the surface dropped the resistance from
about 67 to about 61 ohms instantly.
Example 12
[0064] When the camera strobe was placed within 1/8 inch from the
substrate 15 minutes after applying the silver film and 10 minutes
after the film appeared dry, there was audible pop when the strobe
is initiated. In this case, a finger placed on the opposite side of
the paper can feel a pop when the camera is initiated. When viewed
under the microscope, portions of the film have been blown off.
Presumably, this is due to the rapid expansion of gas next to the
surface of the heated nanoparticles. Since a loud pop and
associated pressure pulse on the paper is also noticed on 4-day-old
film, the source for the gas is likely not unevaporated solvent.
This suggests that if intense photonic sources are used, the laid
down film should be thin or the substrate should be flooded with
the photonic source in a vacuum.
Example 13
[0065] Several silver inks were produced using different solvents
and the subjected to the photonic curing process. Additionally, the
effects of adding binders to promote adhesion of the ink to the
substrate where tested. The first example was shown in Table 3A in
which a silver ink was made from Methyl Ethyl Ketone. The film
thicknesses were drawn down on PET to a thickness of 0.09 mil or
2.29 microns. The results of various areal energy densities and
pulse width were explored using a prototype photonic cure system.
The data shows that there is an optimal combination of areal energy
density and pulse length to give the best conductivity.
TABLE-US-00006 TABLE 3A Photonically cured Ag films made from Ag
Methyl Ethyl Ketone dispersions Areal Pulse Energy Length Rho
Density (micro- MicroOhm- ohm/ ohm/.quadrature./ Film/ (J/cm.sup.2)
second) cm .quadrature. mil Bulk 0.86 300 97 0.42 0.04 60 1.03 300
63 0.27 0.03 39 1.12 300 51 0.22 0.02 32 1.22 300 49 0.21 0.02 30
1.42 300 56 0.24 0.02 35 0.38 300 1230000 5300 480 768000 0.63 300
2400 10.6 0.96 1500 1.65 100 133 0.58 0.05 83 1.38 100 64 0.28 0.03
40 1.13 100 49 0.21 0.02 31 0.90 100 61 0.27 0.02 38 0.70 100 87
0.38 0.03 54 0.48 100 254 1.10 0.10 59 0.31 100 590000 2600 230
370000 0.88 30 150 0.67 0.06 97 1.32 30 90 0.39 0.04 56 1.42 30 70
0.30 0.03 44 0.69 30 1140 0.63 0.06 90 0.53 30 290 1.27 0.12 183
0.39 30 4800 20 1.90 3000 1.05 30 130 0.56 0.05 80
[0066] Another example shown in Table 13B uses silver dispersed in
water on Photo grade InkJet paper at 2.3 microns, with various
types of curing, about 25.degree. C. for 30 minutes, about
90.degree. C. for 30 minutes, and Photonic cure. In this example,
three films were created from the same formulation. One film was
subjected to a temperature cure of 93.degree. C. for 30 minutes and
the other the photonic cure process. The last sample was used as a
baseline. Notice that the photonic cure sample obtained
approximately 5.times. bulk silver resistivity and was slightly
better than the thermal cure. Additionally, the thermal cure
results are quite good for this low temperature.
TABLE-US-00007 TABLE 3B uses silver dispersed in water on Photo
grade InkJet Areal Pulse Energy Length Rho Density (micro-
MicroOhm- ohm/ ohm/.quadrature./ Film/ Cure (J/cm.sup.2) second) cm
.quadrature. mil Bulk 25.degree. C. 0 0 19 0.09 0.01 12 93.degree.
C. 0 0 10 0.05 0.004 6.5 Photonic 0.73 30 8 0.04 0.001 5.1 Cure
[0067] Yet another example shown in Table 3C shows silver dispersed
at 10% binder loading coated on Mylar at 2.3 microns. In this
example different binders were incorporated to improve adhesion to
the substrate. The samples were then subjected to the photonic cure
process. A significant result is that the binders allow high power
to be applied to the samples before they blow off the film. The
higher power also increases the ability of the ink to cure.
[0068] This example shows silver dispersed at 10% binder loading
coated on Mylar at 2.3 microns. In this example, different binders
were incorporated to improve adhesion to the substrate. The samples
were then subjected to the photonic cure process. A significant
result is that the binders allow high power to be applied to the
samples before they blow off the film. The higher power also
increases the ability of the ink to cure.
TABLE-US-00008 TABLE 3C Ag dispersed at 10% binder loading coated
on Mylar at 2.3 microns Areal Pulse Energy Length Rho Polymer
Density (micro- MicroOhm- ohm/ ohm/.quadrature./ Film/ System
(J/cm.sup.2) second) cm .quadrature. mil Bulk Acrylic 0.56 300 78.7
0.344 0.014 49 Pressure Sensitive Adhesive H.sub.20 Vinyl Acetate
0.65 300 37 0.285 0.015 23 Ethylene Adhesive H.sub.20 Acrylic Clear
1.12 300 84 0.363 0.033 52 Coat Solvent Urethane Clear 0.78 300 47
0.365 0.019 30 Coat Solvent
[0069] While the tests were performed using Nanotechnologies,
Inc.'s dry silver powder, the process should also be effective on
silver synthesized with a surface functionalization such as
material from a SOL-GEL process. In this case, the photonic process
will heat the particles to a high temperature, which will volatize
the surface organic compounds and allow the particles to sinter.
Furthermore, the photonic process could be used to augment the
conductivity of a film that has already been partially or
completely cured with a thermal process. The photonic process
overcomes the limitations of the prior art by separating the
heating of the formulation from the heating of the substrate and
allows the surface functionalization to be volatilized by the
heated particles.
[0070] The photonic curing process has other unique benefits.
Materials, such as copper and zinc, that readily oxidize, are
typically not used to make conductive patterns. If an ink or
formulation is created using materials such as these metals and
then heated to cure the pattern, the metal will oxidize in the
presence of oxygen and form a poorly conductive or nonconductive
metal oxide pattern. During the heating process, the oxidation of
the particles occurs at a lower temperature than sintering, hence
the particles convert to the metal oxide before they sinter. This
issue is typically addressed by processing in a vacuum or in an
inert or reducing atmosphere such as hydrogen. All of these options
are expensive and make these materials unattractive to the
conductive patterning market.
[0071] The current invention overcomes the limitation of using
readily oxidizing and or reactive material by allowing the
nanomaterials to be processed without a controlled environment.
Tests were performed using copper nanoparticles in the range of 30
nm-100 nm. Tests were performed on copper with an oxide passivation
layer as well as a copper/carbon composite material.
Example 14
[0072] In the tests, the nanocopper was dispersed in isoproponal,
spread onto a sheet of PET and allowed to dry. The coating was
black in color and had almost infinite resistivity. The coating was
subjected to a 2.3 ms xenon broadcast flash and the material
immediately turned copper in color and the conductivity increased
to 1/100.sup.th that of bulk copper. Another sample subjected to a
higher-powered flash showed conductivity results that were
1/40.sup.th that of bulk copper. Better results should be obtained
by optimizing the particle oxide layer and photonic conditions such
that conductive of bulk copper is approached. One such sample is
shown in FIG. 4, which shows uncured copper film and film after
photo curing. It is speculated that because of the inherent
properties of the nanocopper, the particles are heated and sintered
in a time scale that is much faster than the time scale for
oxidation such that minimal oxidation occurs. This has significant
and far-reaching implications. The current invention allows
inexpensive materials that had previously been discounted because
of oxidation issues to be used in existing and new applications.
Material, such as but not limited to metals and transition metals
like copper, iron, zinc, titanium, zirconium, magnesium, tin,
aluminum, nickel, cobalt, indium, antimony, and lead tray be
usable. In addition these materials can be used on low temperature
substrates as well as high temperature substrate.
[0073] With this process it may also be useful to use combinations
of materials or alloys of materials. Combinations of materials may
allow expensive and inexpensive materials and highly conductive and
moderately conductive materials to be processed to tailor costs and
conductivity. Additionally, it may be possible to mix two or more
compounds such that when they are heated they react or form an
alloy.
[0074] Some alloys when formed may release energy that helps to
further sinter the material. For example a test was performed using
copper with an oxide layer and a small amount of nano-aluminum. In
this case, the copper oxide and aluminum when heated will result in
a thermitic reaction. This reaction releases a substantial amount
of heat that aids in further heating and sintering the copper. A
side benefit is that the products of the reaction are copper and
alumina. Hence the copper oxide on the surface of the particles in
converted to copper resulting in better conductivity.
[0075] In yet another embodiment, it is recognized that larger
particles may be able to be used if they have a favorable
morphology such as being highly agglomerated, possess nanopores or
have extreme surface roughness that makes them highly absorptive.
Also, one could mix a small amount of tiny particles with larger
ones to increase the effective absorptivity. Mixing a small amount
of nanoaluminum with some micron-sized copper, laying a film of the
mix on paper, and photonically curing it to render the film
electrically conductive demonstrated an embodiment of this concept.
In this case, it was very difficult to photonically cure the
micron-sized copper alone as the copper had a low surface area to
mass ratio and had low absorptivity of the radiation emitted from
the xenon strobe. The combustion of the nanoaluminum provided the
additional energy needed to sinter the copper. The photonic
initiation of aluminum is disclosed in PCT Patent Application No.
PCT/US2005/038557, filed Oct. 25, 2005, entitled "System for
Photonic Initiation of Nanoenergetic Materials" having Dennis E.
Wilson and Kurt A. Schroder as inventors, which application is
incorporated herein by reference. Other variants include adding
additional oxidizer such as copper oxide or iron oxide to the mix,
passivating the copper to provide oxidizer for the aluminum
directly on the particles to be sintered, or adding carbon black,
or some other nanoscale emissive material, to the mix to make the
film absorptive of the photonic radiation.
Example 15
[0076] A conductive pattern was successfully producing using a film
comprised of 10 micron silver flake (which has very low
absorptivity) with 5-10% by weight, 40 nm silver. Specifically, the
resistance of the trace went from infinite to 3 ohms with a single
2.3 ms strobe flash. In this case, it is believed that the
nanopowder acts as a sintering aid.
[0077] While most of the processed conductive films have been
fairly thin, less than 10 mils, it may be possible to use the
current invention for thicker films. In these cases, a longer
wavelength and possibly longer duration pulse would be
desirable.
[0078] Most nanopowders and/or nanoparticle dispersions often have
a discrete particle distribution that may be log normal, narrow,
broad or modal. Since the sintering temperature is a function of
the particle size, there may be a range of temperatures that cause
the particles to sinter for a given powder. When the film is
subjected to the emission source, it is possible that some of the
particles are vaporized, some are melted, some are sintered and
some are just heated. Recognizing this, another embodiment of the
current invention uses multiple emissions to cure the sample. In
this embodiment, the emissions are controlled to moderate the
amount of sintering. For example, the film is subjected to a lower
powered pulse to sinter the smaller particles and then followed by
higher powered pulse or sequence of pulses to sinter the larger
particles. If a high intensity pulse is used initially, it is
possible that the smaller particles are vaporized which would
result in poor film uniformity such as voids and performance. A
test was performed to determine if multiple pulses work. The sample
was subjected to multiple pulses of increasing intensity. After
each pulse, the conductivity was measured and found to increase
after the first several pulses. After approximately 5 pulses, the
conductivity no longer increased.
[0079] It was observed in the initial testing that an audible pop
can be heard when a strobe is flashed near the nanomaterial sample.
This occurred with the loose nanoaluminum powder or loose
nanosilver powder. The pop becomes louder as the strobe becomes
closer to the substrate. Additionally, the audible pop can be used
as a feedback mechanism for the strobe intensity for curing the
film. Here, a fresh film pops more easily, as it has a very high
emissivity and a very low thermal conductivity. As the film is
cured, the particles begin to sinter, which makes the emissivity
lower and the thermal conductivity higher. Thus, a flash from a
strobe of the same intensity makes less of a pop. The resulting
film is now able to take a higher intensity pulse without being
destroyed. Likewise, a higher intensity pulse is needed to further
cure the film. Since the gas is the primary reason the intensity of
the strobe can be high initially, an alternative approach would be
to flash the substrate in a vacuum. In this environment, the
ultimate conductivity may become higher as convection is eliminated
as an energy transfer mechanism. In this case the film can stay hot
longer and sinter more fully.
[0080] This photonic cure technique may be used in parallel with
thermal curing means to augment the results and achieve the same
results at a lower cure temperature than without the photonic
curing.
Photonic Curing System
[0081] The following describes a commercial photonic curing system
capable of high-volume processing of conductive patterns on
low-temperature substrates including flexible circuit boards, flat
panel displays, interconnects, RF-ID tags, and other disposable
electronics. The commercial system described is capable of
processing products spanning 34'' in width moving at a rate of 100
feet per minute. The same design scales to higher speeds and wider
formats with a cost that increases less than linearly with area
processed per unit time.
[0082] FIG. 5 shows a process diagram of an embodiment of the
invention, and FIG. 6 shows a schematic of the production system.
The photonic curing system cures metallic nano-inks on a wide
variety of substrates. The multi-strobe head is driven by a high
voltage power supply and trigger circuit, which is mounted in a
standalone relay rack. The height of the strobe head can be
adjusted to control the strobe footprint. The exposure level is
adjusted electronically via the strobe power supply. Both the
strobe energy and pulse duration are adjustable to allow optimum
curing without substrate damage depending on the uncured ink
emissivity, material properties, and ink thickness.
[0083] The system is comprised of a process for making films and
patterns 601 that will be processed to produce conductive patterns
and a system for curing the films and patterns to create a
conductive film or pattern. The system for creating the film or
pattern 601 on the substrate could be one or combinations of
existing technologies such as screen printing, inkjet printing,
gravure, laser printing, xerography, pad printing, painting, dip
pen, syringe, airbrush, lithography that are capable of applying
nanoparticles to a surface. The system would then move the
substrates with the pattern to the photonic curing system 602 where
the film is cured. An embodiment of the invention is capable of
operating with various substrates. The system is capable of
continuously processing samples at 100 ft/min. with uniform
coverage or double that rate with reduced uniformity.
[0084] This system uses a method of moving the samples 603 past the
strobe head 620, although it may be possible to move the strobe
head 620 relative to the samples. The current invention uses a
conveyor belt system 610 with a width capable of handling samples
of approximately 90 cm.times.times.150 cm. It is used to move the
samples under the photonic cure device. The conveyer belt 610
operates at speeds from 5 to 200 ft/min and is controlled by the
conveyor controller 632. One skilled in the art would recognize
that other conveyance methods such as robotics and pneumatics could
be used to move the samples.
[0085] The photonic cure system 602 contains a photon emission
source such as a xenon flash lamp 621 in the strobe head 620
connected to an adjustable power supply 630. The adjustable power
supply has an energy capability of 5-600 Joules with a pulse
duration of 1 microsecond-100 milliseconds. While there are some
"flash" technologies that use pulses in the 2 seconds to several
minutes to cure resins, one skilled in the art would recognize that
if the pulse is too short in these applications there is little if
any effect or the entire product, substrate and film is heated. The
current invention distinguishes itself from these systems by using
pulses that are orders on magnitude shorter than current systems
and are designed to interact with the nanomaterials. The flash lamp
621 or array of flash lamps is configured to produce a 90 cm wide
by 1-3 cm strobe pattern. The intensity of the strobe is varied by
changing the height from the sample from approximately 1-30 cm. The
adjustable power supply 630 is controlled by the strobe control 631
to provide a single pulse to pulses at a frequency of approximately
40 Hz. A blower 622 or other cooling means such as liquid is
connected to the strobe head to cool and extend the life.
[0086] One skilled in the art will recognize that there are other
options for creating the pulse emission. Devices such as a pulsed
laser, chopping an intense light source, light deflection methods
such as mechanical or electrical deflection, pulsed arc, etc. can
be used to create the emission. While the current invention shows
the samples 603 being subjected to the emission source from the
top, it is possible to subject the film from the bottom or
combination of top and bottom. The current invention also shows
that the samples are subjected to the emission after they have
dried. It may be beneficial to submit the films to the emission
source when they are wet. Additionally, the system may be
configured to automatically determine the optimal settings by
progressing through a series of production parameters and measuring
the conductivity of each configuration. The product settings would
then be set to the parameters that give the best film
properties.
[0087] In operation, the products 603 are produced by the film and
pattern printer 601 and moved on to the conveyor 610. The conveyor
610 moves the product 603 under the strobe head 620 where they are
photonically cured by rapid pulses from the flash lamp 621. The
strobe power, duration and repetition rate are controlled by the
strobe control 631 whereas the conveyor control 630 determines the
speed at which the products are moved past the strobe head 620. The
samples are then removed from the conveyor 610 for the next step of
processing.
[0088] One skilled in the art would recognize that the current
invention could be used in conjunction with other curing methods.
This technique may be used in parallel with thermal curing means in
order to achieve the same results at a lower cure temperature and
at faster rates. In fact, a test was performed on several
conductive patterns that had been printed and cured. The patterns
were subjected to a xenon flash and the conductivity increased by a
factor of two.
Photon Activated Catalysis
[0089] Applicants have observed that some nanoparticle powders,
including most metal nanopowders, are generally very absorbent of
photonic radiation. That is, the powder is a good blackbody. The
nanoparticles also have a much larger surface area to mass ratio
than micron or larger sized particles. Finally, the thermal
conductivity of a bulk nanopowder is very poor as compared to the
bulk material. These three qualities suggest that irradiation of
the nanoparticles with a pulsed photonic source could momentarily
heat the particles to a very high temperature. (A "photonic source"
is a radiation source in the electromagnetic spectrum including,
but not limited to gamma rays, x-rays, ultraviolet, visible
infrared, microwaves, radio waves, or combinations thereof) This
effect is very advantageous as noted in several new applications
listed below.
[0090] In general, the catalytic activity of a material increases
as the surface area and the temperature of the material increase. A
natural result of the first item is that catalytic materials tend
to have high surface area. One way to do this is to have catalytic
materials with nanoscale dimensions. As a result of the second
item, many catalytic processes are performed at high temperature.
Many catalytic materials are manometer-sized metals and are
therefore very absorbent of radiation. By flooding the catalysts
with a photonic source, they will absorb the radiation and heat up
to a higher temperature than the rest of the system. Thus, higher
catalytic activity can be attained without significantly changing
the temperature of the system. This is especially true if a pulsed
photonic source is used.
Example 16
[0091] "Instant on" or cold start catalysis: A significant portion
of the pollution generated by an internal combustion engine comes
from the first minute or two of operation. Thus, during the first
minute of operation, an automobile's catalytic converter does very
little catalytic converting since it is cold. Preheating the whole
catalytic converter may require the need for an additional battery,
which would somewhat defeat the purpose of the doing it in the
first place. However, a repetitive, pulsed intense photonic source
could instantly preheat the catalytic material with very little
input energy until the entire engine is heated up resulting in
dramatically lower emissions from the engine.
Example 17
[0092] High catalysis rates in low temperature environments.
Environments in which high temperature cannot be tolerated or is
not desired, such as a liquid environment, can have increased
catalytic activity of being flooded by a photonic source. This can
be done without significantly changing the temperature of the
system. High yield catalytic cracking of water could be done at
temperatures below the boiling point of water.
Example 18
[0093] Modulated catalysis. By controlling the intensity of the
impinging photonic source, the catalytic activity of a catalyst can
be controlled on a short time scale and done so independent of the
temperature of the system. The control of the catalytic activity
could be from a feedback from another subsystem. This results in an
"on demand" chemical reaction such as that which would be desired
from a fuel cell or an industrial chemical synthesis process.
Example 19
[0094] Cleaning poisoned catalysts. By exposing nanomaterial
catalysts to an intense pulsed photonic source the nanoparticles
will momentarily be heated. Any adsorbed materials on the surfaces
will be driven off or reacted to reactivate the catalyst.
Example 20
[0095] Pulsed broadcast irradiation of a nanoparticle aerosol for
catalytic synthesis. By exposing nanopowders suspended in a gas to
irradiation, the gas in which the particles are suspended may
catalytically react with the particles. This may be an effective
method for cracking hydrocarbon gases.
[0096] While many of the tests were performed with silver, the
applicants recognize that other metals will exhibit the same
effects and have similar performance. Other metals include but are
not limited to copper, aluminum, zirconium, niobium, gold, iron,
nickel cobalt, magnesium, tin, zinc, titanium, hafnium, tantalum,
platinum, palladium, chromium, vanadium and alloys of the metals.
Additionally, non-metallic compounds such as carbon also exhibit
these attributes.
[0097] It should be appreciated by those of skill in the art that
the techniques disclosed herein represent techniques discovered by
the inventors to function well in the practice of the invention,
and thus can be considered to constitute exemplary modes for its
practice. However, those of skill in the art should, in light of
the present disclosure, appreciate that many changes can be made in
the specific embodiments that are disclosed and still obtain a like
or similar result without departing from the spirit and scope of
the invention.
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