U.S. patent application number 11/604429 was filed with the patent office on 2007-05-10 for high conductivity inks with low minimum curing temperatures.
This patent application is currently assigned to Parelec, Inc.. Invention is credited to Brian F. Conaghan, Paul H. Kydd, David L. Richard.
Application Number | 20070104884 11/604429 |
Document ID | / |
Family ID | 32736286 |
Filed Date | 2007-05-10 |
United States Patent
Application |
20070104884 |
Kind Code |
A1 |
Conaghan; Brian F. ; et
al. |
May 10, 2007 |
High conductivity inks with low minimum curing temperatures
Abstract
Conductive ink compositions which can be cured to highly
conductive metal traces by means of "chemical welding" include
additives which reduce the curing temperatures for use with
low-temperature substrates. Conductive ink compositions can be
deposited on a substrate coated with a cure temperature reducing
agent to reduce the curing temperatures.
Inventors: |
Conaghan; Brian F.;
(Princeton, NJ) ; Kydd; Paul H.; (Lawrenceville,
NJ) ; Richard; David L.; (Fanwood, NJ) |
Correspondence
Address: |
MCCARTER & ENGLISH, LLP
FOUR GATEWAY CENTER
100 MULBERRY STREET
NEWARK
NJ
07102
US
|
Assignee: |
Parelec, Inc.
|
Family ID: |
32736286 |
Appl. No.: |
11/604429 |
Filed: |
November 27, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10354154 |
Jan 29, 2003 |
7141185 |
|
|
11604429 |
Nov 27, 2006 |
|
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|
Current U.S.
Class: |
427/383.1 ;
427/256; 427/384 |
Current CPC
Class: |
C09D 11/30 20130101;
H05K 1/097 20130101; H05K 1/095 20130101; H01B 1/22 20130101; C09D
11/52 20130101 |
Class at
Publication: |
427/383.1 ;
427/256; 427/384 |
International
Class: |
B05D 5/00 20060101
B05D005/00; B05D 3/02 20060101 B05D003/02 |
Claims
1-34. (canceled)
35. A method for preparing a solid pure metal conductor on a
substrate comprising the steps of (a) mixing a reactive organic
medium, a metal powder, and a cure temperature lowering agent; (b)
applying the mixture formed in step (a) onto the substrate; and (c)
heating the substrate at a critical temperature less than
200.degree. C. for a time less than about 30 minutes; wherein the
applied mixture is converted into a well-consolidated pure metal
conductor.
36. The method of claim 35, further comprising roll milling the
mixture to produce a homogeneous composition.
37. The method of claim 35, wherein the metal powder has an average
particle size of from about 0.05 to 15 .mu.m.
38. The method of claim 35, wherein the reactive organic medium is
a metallo-organic decomposition compound, an organic reactive
reagent which can form a metallo-organic decomposition compound
upon reaction with the metal constituent or a mixture thereof.
39. The method of claim 35, wherein the mixture is applied by
printing.
40. The method of claim 39, wherein the printing technique is
selected from screen printing, rotary screen printing, gravure
printing, intaglio printing, flexographic printing, letterpress
printing, lithographic printing, ink jet printing or electrostatic
printing.
41. The method of claim 35, wherein the metal is silver.
42. The method of claim 41, wherein the temperature is between
120.degree. C. and 150.degree. C.
43. The method of claim 38, wherein the cure temperature lowering
agent is a polymer selected from polyvinylidene chloride, polyvinyl
chloride, polyethylene vinyl chloride, or copolymers thereof.
44. The method of claim 38, wherein the cure temperature lowering
agent is an organic glycol ether.
45. The method of claim 44, wherein the cure temperature lowering
agent is dipropylene glycol methyl ether.
46. A method for preparing a solid pure metal conductor on a
substrate comprising the steps of (a) mixing (i) a metallo-organic
decomposition compound; (ii) a metal powder in an amount 1 to 20
times the amount of the metallo-organic decomposition compound by
weight; and (iii) a cure temperature lowering agent in the amount
of 0.5 to 10% by weight; (b) printing the mixture formed in step
(a) onto the substrate; and (c) heating the substrate at a critical
temperature less than 200.degree. C. for a time less than about 30
minutes; wherein the printed mixture is converted into a
well-consolidated pure metal conductor.
47. The method of claim 46, further comprising roll milling the
mixture to produce a homogeneous composition.
48. The method of claim 46, wherein the metal powder has an average
particle size of from about 0.05 to 15 .mu.m.
49. The method of claim 46, wherein the mixture is printed by a
method selected from screen printing, rotary screen printing,
gravure printing, intaglio printing, flexographic printing,
letterpress printing, lithographic printing, ink jet printing or
electrostatic printing.
50. The method of claim 46, wherein the substrate is selected from
polyester, polyimide, epoxy or paper.
51. The method of claim 46, wherein the cure temperature lowering
agent is a polymer selected from polyvinylidene chloride, polyvinyl
chloride, polyethylene vinyl chloride, or copolymers thereof.
52. The method of claim 46, wherein the cure temperature lowering
agent is an organic glycol ether.
53. The method of claim 52, wherein the cure temperature lowering
agent is dipropylene glycol methyl ether.
54. The method of claim 46, wherein the metal powder is silver.
55. The method of claim 54, wherein the temperature is between
120.degree. C. and 150.degree. C.
56. A method for preparing a solid metal conductor on a substrate
comprising the steps of (a) mixing a reactive organic medium and a
metal powder; (b) coating the substrate with a cure temperature
lowering agent; (c) applying the mixture formed in step (a) onto
the coated substrate; and (d) heating the substrate at a critical
temperature less than 200.degree. C. for a time less than about 30
minutes; wherein the applied mixture is converted into a
well-consolidated pure metal conductor.
57. The method of claim 56, further comprising roll milling the
mixture to produce a homogeneous composition.
58. The method of claim 56, wherein the metal powder has an average
particle size of from about 0.05 to 15 .mu.m.
59. The method of claim 56, wherein the reactive organic medium is
a metallo-organic decomposition compound, an organic reactive
reagent which can form a metallo-organic decomposition compound
upon reaction with the metal constituent or a mixture thereof.
60. The method of claim 56, wherein the mixture is applied by
printing.
61. The method of claim 60, wherein the printing technique is
selected from screen printing, rotary screen printing, gravure
printing, intaglio printing, flexographic printing, letterpress
printing, lithographic printing, ink jet printing or electrostatic
printing.
62. The method of claim 56, wherein the metal powder is silver.
63. The method of claim 62, wherein the temperature is between
120.degree. C. and 150.degree. C.
64. The method of claim 56, wherein the cure temperature lowering
agent is a polymer selected from polyvinylidene chloride, polyvinyl
chloride, polyethylene vinyl chloride, or copolymers thereof.
65. A method for preparing a solid pure metal conductor on a
substrate comprising the steps of (a) mixing (i) a metallo-organic
decomposition compound; and (ii) a metal powder in an amount 1 to
20 times the amount of the metallo-organic decomposition compound
by weight; (b) coating the substrate with a cure temperature
lowering agent in the amount of 0.5 to 10% by weight; (c) printing
the mixture formed in step (a) onto the substrate; and (d) heating
the substrate at a critical temperature less than 200.degree. C.
for a time less than about 30 minutes; wherein the printed mixture
is converted into a well-consolidated pure metal conductor.
66. The method of claim 65, further comprising roll milling the
mixture to produce a homogeneous composition.
67. The method of claim 65, wherein the metal powder has an average
particle size of from about 0.1 to 15 .mu.m.
68. The method of claim 65, wherein the mixture is printed by a
method selected from screen printing, rotary screen printing,
gravure printing, intaglio printing, flexographic printing,
letterpress printing, lithographic printing, ink jet printing or
electrostatic printing.
69. The method of claim 65, wherein the substrate is selected from
polyester, polyimide, epoxy or paper.
70. The method of claim 65, wherein the cure temperature lowering
agent is a polymer selected from polyvinylidene chloride, polyvinyl
chloride, polyethylene vinyl chloride, or copolymers thereof.
71. The method of claim 65, wherein the metal powder is silver.
72. The method of claim 71, wherein the temperature is between
120.degree. C. and 150.degree. C.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to electrically conductive ink
compositions used in combination with agents which reduce the
curing temperature of the ink compositions, and methods of
producing these compositions. The compositions can be cured to form
highly conductive metal traces on low temperature substrates.
BACKGROUND OF THE INVENTION
[0002] Materials for printing electrical circuits on electrical
conductor substrates are disclosed in U.S. Pat. Nos. 5,882,722,
6,036,889, 6,143,356 and 6,379,745, the entire disclosures of which
are expressly incorporated herein by reference, and are known as
PARMOD.RTM. materials. PARMOD.RTM. materials have been developed
for printing conductive circuits on polymer or paper substrates
such as those used for printed wiring boards, flexible circuits and
RFID antennae. Using PARMOD.RTM. materials and a simple
print-and-heat process for "chemical welding" of pure metals,
electrical conductors made of a single-phase continuous well-bonded
metal trace are produced, rather than conductors made of individual
particles that may be in adventitious contact with each other, as
are found in polymer thick film containing materials. PARMOD.RTM.
materials provide a desirable alternative to the conventional
polymer thick film compositions that are cured at high temperatures
onto ceramic or glass based substrates. PARMOD.RTM. materials are
cured at temperatures which polymer and paper based substrates can
withstand, and provide electrical conductivity comparable to the
pure metal and at least a factor of five greater than most known
polymer thick films.
[0003] PARMOD.RTM. compositions have been printed on polyimide
films coated with various adhesive layers and thermally cured to
create flexible printed circuits. Suitable substrates are:
KAPTON.RTM. type FN with a FEP TEFLON.RTM. coating; KAPTON types KJ
and LJ with low melting polyimide coatings; and polyimide
substrates with a polyamic acid coating. PARMOD.RTM. compositions
have been printed directly on certain grades of FR-4 epoxy-glass
laminates and thermally cured to produce well-bonded rigid printed
circuits.
[0004] However, a significant problem in the manufacture of
PARMOD.RTM. products is that thermal treatment of PARMOD.RTM.
materials can damage low-temperature substrates such as polymer or
paper, and cause mechanical and dimensional instability to the
printed circuits. For example, the cure temperature for "chemically
welding" PARMOD.RTM. silver into circuit traces is 200.degree. C.
This curing temperature limits the choice of substrates to those
with high thermal resistance, such as polyimides and epoxies. Many
polymer and paper substrates cannot be processed at these
temperatures.
[0005] Although low temperature sintering of metal toners has been
observed on certain substrates, see, e.g., WO 01/45935, specific
temperature lowering additives to promote low temperature sintering
have not heretofor been defined or shown to be advantageous in the
manufacture of conductive ink compositions.
[0006] Thus, there is a need for PARMOD.RTM. methods and
compositions such as inks which have a minimum cure temperature
that is compatible with substrates of commercial interest and which
still retain the highly conductive properties of the PARMOD.RTM.
materials.
SUMMARY OF THE INVENTION
[0007] The present application provides ink compositions which
include agents that lower the minimum curing temperature of the ink
compositions. The ink compositions of the present invention may be
used on low-temperature substrates in the manufacture of highly
conductive electrical circuits.
[0008] It has been found that the minimum cure temperature for the
ink compositions can be reduced by adding the agents directly to
the ink compositions, or by coating the substrates onto which the
ink compositions are applied with the temperature lowering
agents.
[0009] Accordingly, in one embodiment the invention provides a
conductive ink composition comprising a reactive organic medium
(ROM), a metal powder or flake, and a cure temperature lowering
agent.
[0010] Preferably, the ROM comprises a metallo-organic
decomposition compound, an organic reactive reagent which can react
with the metal powder or flake to form a metallo-organic
decomposition compound, or a mixture thereof. The metal powder or
flake may be silver or other suitable metal.
[0011] The cure temperature lowering agent is selected from halogen
containing polymers including polyvinylidene chloride, polyvinyl
chloride, polyethylene vinyl chloride, or copolymers thereof; or
organic glycol ethers, including dipropylene glycol methyl ether
and the like.
[0012] The ink composition may also include an organic liquid
vehicle to facilitate mixing and application of the mixture to the
substrate.
[0013] The present invention also provides a method of preparing a
solid pure metal conductor on a substrate comprising the steps of
(a) mixing (i) a metallo-organic decomposition compound; (ii) a
metal flake or powder in an amount 1 to 20 times the amount of the
metallo-organic decomposition compound by weight; and (iii) a cure
temperature lowering agent; (b) printing the mixture formed in step
(a) onto the substrate; and (c) heating the substrate at a critical
temperature less than 200.degree. C. for a time sufficient to cure
the printed mixture; wherein the printed mixture is converted into
a well-consolidated well-bonded pure metal conductor.
[0014] The present invention further provides a method for
preparing a solid pure metal conductor on a substrate comprising
the steps of (a) mixing (i) a metallo-organic decomposition
compound; (ii) a metal flake or powder in an amount 1 to 20 times
the amount of the metallo-organic decomposition compound by weight;
(b) coating the substrate with a cure temperature lowering agent;
(c) printing the mixture formed in step (a) onto the substrate; and
(d) heating the substrate at a critical temperature less than
200.degree. C. for a time sufficient to cure the printed mixture;
wherein the printed mixture is converted into a well-consolidated
well-bonded pure metal conductor.
[0015] The composition of the invention is advantageously applied
to low-temperature polymer substrates, paper and polyimide-based
substrates using any suitable printing technique to provide circuit
traces of high electrical conductivity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 shows the resistivity versus time measured for the
circuit pattern comprising silver, and an epoxy-based substrate,
without a cure temperature lowering agent, as described in Example
1.
[0017] FIG. 2 shows the resistivity versus time measured for the
circuit pattern comprising silver, an epoxy-based substrate, and
dipropylene glycol methyl ether as the cure temperature lowering
agent, as described in Example 2.
[0018] FIG. 3 shows the resistivity versus time measured for the
circuit pattern comprising silver, a polyester-based substrate, and
SARAN.RTM. as the cure temperature lowering agent, as described in
Example 3.
[0019] FIG. 4 shows the resistivity versus time measured for the
circuit pattern comprising silver, a polyester-based substrate, and
DARAN.RTM. 8730 latex as the cure temperature lowering agent, as
described in Example 4.
[0020] FIG. 5 shows the resistivity versus time measured for the
circuit pattern comprising silver, a polyester-based substrate, and
DARAN.RTM. 8600 latex as the cure temperature lowering agent, as
described in Example 5.
[0021] FIG. 6 shows the resistivity versus time measured for the
circuit pattern comprising silver, a polyester-based substrate, and
AIRFLEX.RTM. 4530 as the cure temperature lowering agent, as
described in Example 6.
[0022] FIG. 7 shows the resistivity versus time measured for the
circuit pattern comprising silver, a paper-based substrate, and
DARAN.RTM. 8730 and polystyrene acrylate latex as the cure
temperature lowering agent, as described in Example 7.
[0023] FIG. 8 shows a comparison of the resistivity versus time
measured for the circuit pattern comprising a composition
comprising silver, a polyester-based substrate, and AIRFLEX.RTM.
4530, and a circuit pattern comprising a commercially available ink
composition without a cure temperature lowering agent, as described
in Example 8.
DETAILED DESCRIPTION OF THE INVENTION
[0024] PARMOD.RTM. mixtures contain a reactive organic medium (ROM)
and metal flakes and/or metal powders. The ROM comprises either a
metallo-organic decomposition compound or an organic reagent which
can form such a compound upon heating in the presence of the metal
flakes and/or metal powders, or a mixture thereof. The ingredients
are blended together with organic vehicles, if necessary, to
improve the viscosity or dispersibility of the ink composition.
These ink compositions can be printed on temperature-sensitive
substrates, and cured at commercially desirable temperatures low
enough so that the substrate is not damaged, to form
well-consolidated electrical conductors. The curing process occurs
in seconds at temperatures as much as 500.degree. C. below the
temperatures used for conventional sintering of thick film inks and
pastes. As used herein the term "critical temperature" means the
temperature at which the composition decomposes and is cured. Using
the PARMOD.RTM. process, the metal compositions decompose at
temperatures far below their known normal decomposition
temperatures. During the curing process, material deposited from
decomposition of the metallo-organic decomposition compound
"chemically welds" the powder constituents of the PARMOD.RTM.
mixture together into a solid. A porous but continuous metal trace
is produced which has a density approximately half that of bulk
metal and an electrical conductivity per unit mass which may be as
high as half that of the bulk metal.
[0025] The compositions of the present invention improve certain
PARMOD.RTM. materials by including a cure temperature lowering
agent. The cure temperature lowering agent is an agent that lowers
the minimum curing temperature required to "chemically weld" the
ink composition, thereby improving the application of the
PARMOD.RTM. materials to various low-temperature substrates,
especially those substrates which can only be exposed to
temperatures below 150.degree. C. during the curing process.
[0026] This invention provides a method for curing PARMOD.RTM.
compositions at temperatures compatible with polymer and paper
substrates while maintaining high metal conductivity after curing.
This approach has been demonstrated on a number of rigid and
flexible substrates such as FR4 epoxy-glass rigid board, various
high temperature flexible substrates such as KAPTON.RTM. H, but is
especially attractive in that it has also been demonstrated on low
temperature substrates such as polyester at heat treating
temperatures as low as 120.degree. C. to 125.degree. C. Thus, the
compositions of the present invention are suitable for use with low
temperature substrates such as polyester, as well as with
substrates that can withstand higher temperatures, such as paper,
and those that withstand even higher temperatures, such as
epoxies.
[0027] The concentration of the additive is low enough to maintain
significantly higher conductivity of the resulting metal circuit
traces than with polymer thick film inks.
[0028] The cure temperature lowering agent may be added directly to
the PARMOD.RTM. material. Alternatively, the temperature lowering
agent may be coated directly onto the substrate prior to
application of the conductive PARMOD.RTM. material. In either
embodiment, the ink composition is in direct contact with the
temperature lowering agent, which accelerates the chemical welding
of the PARMOD.RTM. material to the substrate at a lower minimum
curing temperature and does not significantly interfere with the
physical and chemical properties of the conductive PARMOD.RTM.
material, e.g., resistivity and conductivity.
[0029] Thus, in one embodiment, the compositions of the invention
comprise 1) a metal powder; 2) a ROM in which the consolidation of
the metal powder to a solid conductor takes place; and 3) a cure
temperature lowering agent.
[0030] The metal component is present in the composition in an
amount of about 1 to 20 times the amount of the metallo-organic
decomposition compound. The metal constituent comprises metal
powder. It will be understood in the art that "powder" is commonly
used to include both powder and flake. The metal powders suitable
for use in the invention preferably have an average particle size
in the range of from about 0.05 to 15 .mu.m. Commercially available
metal powders may be used. Suitable metals include copper, silver,
gold, zinc, cadmium, palladium, iridium, ruthenium, osmium,
rhodium, platinum, iron, cobalt, nickel, indium, tin, antimony,
lead, bismuth and mixtures thereof.
[0031] The ROM provides the environment in which the metal powder
mixture is bonded together to form well-consolidated conductors.
Many classes of organic compounds can function as the ROM. The
common characteristic which they share and which renders them
effective is that they have, or can form, a bond to the metal via a
heteroatom. The heteroatoms can be oxygen, nitrogen, sulfur,
phosphorous, arsenic, selenium and other nonmetallic elements,
preferably oxygen, nitrogen or sulfur. This bond is weaker than the
bonds holding the organic moiety together, and can be thermally
broken to deposit the metal. In most cases the reaction is
reversible, so that the acid or other organic residue can react
with metal to reform the metallo-organic compound. ROM compounds
are described, e.g., in U.S. Pat. No. 6,379,745.
[0032] The ROM preferably comprises any metallo-organic compound
which is readily decomposable to the corresponding metal, i.e., a
metallo-organic decomposition compound, an organic reagent which
can react with the metal to produce such a compound or mixtures
thereof. Examples are metal soaps and the corresponding fatty
acids. Other examples are metal amines and metal mercapto compounds
and their corresponding amino and sulfide precursors. Specific
examples of preferred ROM constituents are the carboxylic acids and
the corresponding metallic soaps of neodecanoic acid and 2-ethyl
hexanoic acid with silver and copper, such as silver
neodecanoate.
[0033] The ROM compositions can be made by methods well known in
the art and are capable of decomposition to the respective metals
at relatively low temperatures.
[0034] The present invention involves the addition of certain
agents to metal containing ink compositions which provide a
significantly lowered minimum curing temperature to the ink
compositions. The cure temperature lowering agent is added in an
amount sufficient to cure the printed mixture on the substrate. The
cure temperature lowering agent may be present in an amount of
about 1 to 10% by weight. However, amounts outside this range, for
example, as low as 0.5%, may also be used, or as are commercially
or practically possible. For example, higher amounts will increase
the thickness and increase decomposition time. The added cure
temperature lowering agent does not adversely affect the
PARMOD.RTM. cure chemistry process whereby the metal chemically
welds into a continuous metal network. As a result, the
conductivity of the PARMOD.RTM. materials remains significantly
higher than that of polymer thick film inks.
[0035] The agents that have been shown to lower the minimum curing
temperature of PARMOD.RTM. compositions to substrates include
polymers, such as polyvinylidene chloride, polyvinyl chloride,
polyethylene vinyl chloride, and copolymers thereof. Other halogen
containing compounds are suitable, for example, those containing Br
and F.
[0036] Preferred minimum cure temperature lowering agents also
include organic glycol ethers, for example dipropylene glycol
methyl ether, and may include dipropylene glycol butyl ether,
dipropylene glycol dimethyl ether, dipropylene glycol propyl ether,
and the like.
[0037] In some cases it may be convenient to add an organic liquid
vehicle in an amount of 0.05 to 100 times the amount of the
metallo-organic decomposition compound by weight to the
compositions of the invention to enhance the printing
characteristics of the compositions of the invention. Such organic
liquids may be used as diluents or rheology-enhancing agents to
produce a range of viscosities of printable compositions and are
not reactive in the consolidation process. However, organic liquid
vehicles that may additionally participate in the "welding"
reaction may also be used. For example, .alpha.-terpineol has been
used to reduce the viscosity of copper and silver compositions to
facilitate screen printing. .alpha.-terpineol also participates in
the consolidation reaction by virtue of the acid character of the
OH group bonded to an unsaturated ring. Other agents commonly used
in conductive ink compositions can also be added as desired to the
compositions of the invention.
[0038] The constituents of the compositions are weighed out in the
appropriate proportions, mixed with diluents or viscosity modifiers
if needed to provide the proper consistency, and milled together by
hand roll milling or machine roll milling to provide a homogeneous,
printable composition. The fineness of grind of the ink typically
is less than 1.mu..
[0039] Substrates to which these compositions can be applied
include those onto which conductive circuits are typically printed.
Suitable substrates include rigid epoxy laminates, polyimide films
for flexible circuits, other polymer-based electronic components,
paper, such as medium card stock from Wausau, metal pads and
semiconductor components. Preferred substrates include
polyester-based substrates such as polyethylene terephthalate,
e.g., Melinex.RTM. or Mylar.RTM., polyethylene naphthalate,
paper-based substrates, polyimide-based susbstrates, such as
Apical.RTM. or Kapton.RTM., and epoxy-based substrates, known as
FR-4.
[0040] The compositions of this invention may be applied to
substrates using any suitable printing technology including screen
printing, rotary screen printing, gravure printing, intaglio
printing, flexographic printing, letterpress printing, lithographic
printing, ink jet printing and electrostatic printing. The
thickness and viscosity of the applied compositions will vary
depending upon the printing technique used. The compositions may
range from a thickness of 350 nm with 1 centepoise (cp) viscosity
using electrostatic printing, 1 to 4 microns at 50 to 200 cp by
gravure printing, 4 to 50 microns by screen printing with
viscosities ranging from 30,000 to 100,000 cp, and 10 to 25 microns
by rotary screen printing at 3,000 cp.
[0041] According to the present invention, the agents that lower
the minimum curing temperature of PARMOD.RTM. compositions can also
be coated directly onto the substrate, as an alternative to being
added directly to the ink compositions. The cure temperature
lowering agents, including polymers such as polyvinylidene
chloride, polyvinyl chloride, polyethylene vinyl chloride, and
copolymers thereof, may be coated onto various substrates at a
thickness of from about 1 to 15.mu..
[0042] Accordingly, the ink compositions are prepared as described
above, however, without the addition of the cure temperature
lowering agent. The substrate is first coated with the cure
temperature lowering agent, allowed to dry, and then the ink
composition is applied to the substrate, using any of the printing
methods described above.
[0043] The ink compositions containing the cure temperature
lowering agents and the ink compositions on the substrates coated
with the cure temperature lowering agents are cured by exposure to
heat for a short period of time. The heating time depends upon the
temperature to which the substrate can be safely exposed and can
vary from about 10 seconds to 30 minutes to achieve a measurable
resistivity. The curing temperature will generally be below
200.degree. C., typically between about 120.degree. C. to
200.degree. C., however the temperature will depend upon the
decomposition temperature of the metallo-organic compound. For
example, for silver, the curing temperature of compositions of the
invention will range from 120.degree. C. to 180.degree. C.
Temperatures higher than 120.degree. C. generally shorten curing
times; thus the selection of curing temperature will be governed by
practical considerations of time and commercial requirements.
[0044] The examples described below indicate how the individual
constituents of the preferred compositions and the conditions for
applying them function to provide the desired results. The examples
will serve to further typify the nature of this invention but
should not be construed as a limitation to the scope thereof which
scope is defined solely in the appended claims.
EXAMPLES
[0045] Parmod.RTM. Silver Ink A (silver flake, silver necadecanoate
in neodecanoic acid with a 6 to 1 ratio of flake to silver
neodecanoate and 3 roll milling) was prepared as described in U.S.
Pat. No. 6,036,889. Parmod.RTM. Silver Ink B contains the
ingredients of Ink A with dipropylene glycol methyl ether added at
1.1 weight %. Roll milling was performed on a Ross.RTM. 3 roll
mill; screen printing on a Presco.RTM. screen printer; furnace was
a Hotpack.RTM. convection oven; cross-sectional area was measured
using a Dektak.RTM. II.
Example 1
[0046] TABLE-US-00001 PARMOD .RTM. Silver Ink A 100 wt %
[0047] The ink was screen printed into a resistivity pattern onto 3
mil KAPTON.RTM. H substrates. The samples were then thermally
treated at 1 to 30 minutes at temperatures of 190.degree. C. to
300.degree. C. in an air atmosphere. The resistance and
cross-sectional area of the pattern were measured and used to
calculate resistivity. .rho.=(R*A)/l
[0048] where R=resistance (ohms), A=cross-sectional area
(cm.sup.2), and l=length (cm)
[0049] The resistivity versus time data is shown in FIG. 1. The
results demonstrate that the minimum lowest cure temperature of the
ink which still provided measurable resistance in the circuit trace
was 200.degree. C. Above 200.degree. C., the resistivity of the ink
decreased asymptotically as the cure time and temperature were
increased.
Example 2
[0050] TABLE-US-00002 PARMOD .RTM. Silver Ink A 98.9 wt %
Di(propylene glycol)methyl ether 1.1 wt %
[0051] The ink was used to screen print a resistivity pattern onto
3 mil KAPTON.RTM. H substrates. The samples were then thermally
cured at 60 to 1,800 seconds and at temperatures of 140.degree. C.
to 350.degree. C. in an air atmosphere. The resistance and
cross-sectional area of the pattern were measured and used to
calculate resistivity.
[0052] The resistivity versus time data is shown in FIG. 2. The
results show that the addition of di(propylene glycol)methyl ether
lowered the minimum ink cure temperature. The lowest cure
temperature of the ink which still provided measurable resistance
in the circuit trace was 150.degree. C. The resistivity of the ink
decreased with increased cure time and temperature.
Example 3
[0053] TABLE-US-00003 PARMOD .RTM. Silver Ink B 100 wt %
[0054] Substrate [0055] SARAN.RTM. coated Polyester 2.5, 7.5, and
15 micron coating thicknesses
[0056] The ink was used to screen print a resistivity pattern onto
three SARAN.RTM. (Dow Chemcals) coated polyester substrates of
differing thicknesses. The SARAN.RTM. was coated on bare
Melinex.RTM. polyester (DuPont-Teijin) using different wire-wound
rods to provide the desired thicknesses. The samples were then
thermally cured at 15 and 30 minutes and at temperatures of
125.degree. C. and 150.degree. C. in an air atmosphere. The
resistance and cross-sectional area of the pattern were measured
and used to calculate resistivity.
[0057] The resistivity versus time data is shown in FIG. 3. The
results demonstrate that coating the polyester substrate with
SARAN.RTM. lowered the minimum ink cure temperature. The minimum
lowest cure temperature of the ink which still provided measurable
resistance in the circuit trace was 125.degree. C. The resistivity
of the ink was not time dependent under these conditions at
150.degree. C., but at 125.degree. C. only the samples cured for 30
minutes had measurable resistances. The thickness of the SARAN.RTM.
coating also had an effect on the resistivity of samples cured at
125.degree. C., with the thicker coatings providing samples with
lower resistivity.
Example 4
[0058] TABLE-US-00004 PARMOD .RTM. Silver Ink B 95 wt % DARAN .RTM.
8730 Latex 5 wt %
[0059] DARAN.RTM. (WR Grace) is a polymer of vinylidene chloride,
butyl acrylate and acrylonitrile polymer emulsion.
[0060] The ink and latex were mixed and rolled through a three roll
mill. The ink mixture was used to screen print a resistivity
pattern onto 3 mil Melinex.RTM. polyester substrates. The samples
were then thermally cured at 2 to 30 minutes and at temperatures of
135.degree. C. and 150.degree. C. in an air atmosphere. The
resistance and cross-sectional area of the pattern were measured
and used to calculate resistivity.
[0061] The resistivity versus time data is shown in FIG. 4. The
results demonstrate that the addition of the DARAN.RTM. polymer
reduced the minimum curing temperature of the ink. The lowest cure
temperature of the ink which still provided measurable resistance
in the circuit trace was 135.degree. C. when heated for 2 minutes,
a temperature suitable for the polyester substrate. The resistivity
of the ink decreased with increased cure time and temperature.
Example 5
[0062] TABLE-US-00005 PARMOD .RTM. Silver Ink A 95 wt % DARAN .RTM.
8600C Latex 5 wt %
[0063] The ink and latex were mixed and rolled through a three roll
mill. The ink mixture was used to screen print a resistivity
pattern onto 3 mil polyester substrates. The samples were then
thermally cured at 2 to 30 minutes and at temperatures of
135.degree. C. and 150.degree. C. in an air atmosphere. The
resistance and cross-sectional area of the pattern were measured
and used to calculate resistivity.
[0064] The resistivity versus time data is shown in FIG. 5. The
results demonstrate that the addition of the DARAN.RTM. polymer
reduced the minimum curing temperature of the ink. The lowest cure
temperature of the ink which still provided measurable resistance
in the circuit trace was 135.degree. C. when heated for 2 minutes.
The resistivity of the ink decreased with increased cure time and
temperature.
Example 6
[0065] TABLE-US-00006 Formulation PARMOD .RTM. Silver Ink B 95 wt %
AIR FLEX .RTM. EVC 4530 5 wt %
[0066] The ink and AIR FLEX.RTM. (polyethylene vinyl chloride
copolymer, Air Products and Chemicals) were mixed and rolled
through a three roll mill. The ink was used to screen print a
resistivity pattern onto 3 mil Melinex.RTM. polyester substrates.
The samples were then thermally cured at 2 to 30 minutes and at
temperatures of 135.degree. C. and 150.degree. C. in an air
atmosphere. The resistance and cross-sectional area of the pattern
were measured and used to calculate resistivity.
[0067] The resistivity versus time data is shown in FIG. 6. The
results demonstrate that the minimum lowest cure temperature of the
ink that still provided measurable resistance in the circuit trace
was 135.degree. C. when heated for 2 minutes. The resistivity of
the ink decreased with increased cure time and temperature.
Example 7
[0068] TABLE-US-00007 PARMOD .RTM. B 96 wt. % DARAN .RTM. 8730 3
wt. % polystyrene acrylate latex (Dow) 1 wt. %
[0069] The ink, DARAN.RTM. and latex were mixed and rolled through
a three roll mill. The ink mixture was printed on 175 g/m.sup.2
paper (Wausau Paper) and cured in a convection oven for 2 and 5
minutes at 135.degree. C. and 150.degree. C.
[0070] The resistivity vs. time and temperature data are shown in
FIG. 7. The results demonstrate that the minimum lowest cure
temperature of the ink that still provided measurable resistance in
the circuit trace was 135.degree. C. when heated for 2 minutes. The
resistivity of the ink decreased with increased cure time and
temperature.
Example 8
[0071] TABLE-US-00008 PARMOD .RTM. base Ink B 94 wt % AIRFLEX
.RTM.4530 5 wt % RODA 1 wt %
[0072] The ink, AIRFLEX.RTM. and RODA were mixed and rolled through
a three roll mill. The ink mixture was screen printed onto 5 mil
uncoated PET and heat-treated at 140.degree. C. for various lengths
of time between 1 and 20 minutes. As a comparison, resistivity
patterns were also printed with commercially available DuPont 5007
ink and heat-treated at 140.degree. C. for 4 and 8 minutes. FIG. 8
shows the plot of resistivity versus time data for both types of
ink compositions.
[0073] The data shown in FIG. 8 demonstrate that the compositions
of the present invention have lower resistivity and therefore
higher conductivity than the commercially available ink composition
that did not contain a cure temperature lowering agent.
* * * * *