U.S. patent application number 16/493800 was filed with the patent office on 2020-03-05 for fine copper particles, method for producing fine copper particles and method for producing sintered body.
The applicant listed for this patent is TAIYO NIPPON SANSO CORPORATION. Invention is credited to Takayuki FUJIMOTO, Hiroshi IGARASHI, Yuji SAKURAMOTO.
Application Number | 20200070244 16/493800 |
Document ID | / |
Family ID | 63585262 |
Filed Date | 2020-03-05 |
United States Patent
Application |
20200070244 |
Kind Code |
A1 |
SAKURAMOTO; Yuji ; et
al. |
March 5, 2020 |
FINE COPPER PARTICLES, METHOD FOR PRODUCING FINE COPPER PARTICLES
AND METHOD FOR PRODUCING SINTERED BODY
Abstract
One object of the present invention is to provide fine copper
particles which are less likely to be deteriorated by oxidation in
the atmosphere without being coated with an antioxidant or the like
and which can be sintered at a lower temperature. The present
invention provides fine copper particles wherein an entire surface
is covered with a coating film containing cuprous oxide and having
an average film thickness of 1.5 nm or less.
Inventors: |
SAKURAMOTO; Yuji;
(Kawasaki-shi, JP) ; IGARASHI; Hiroshi; (Kai-shi,
JP) ; FUJIMOTO; Takayuki; (Kawasaki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TAIYO NIPPON SANSO CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
63585262 |
Appl. No.: |
16/493800 |
Filed: |
March 7, 2018 |
PCT Filed: |
March 7, 2018 |
PCT NO: |
PCT/JP2018/008768 |
371 Date: |
September 13, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 1/0018 20130101;
B22F 3/1007 20130101; B22F 2301/10 20130101; B22F 1/02 20130101;
B22F 2302/25 20130101; B22F 2304/058 20130101 |
International
Class: |
B22F 1/02 20060101
B22F001/02; B22F 1/00 20060101 B22F001/00; B22F 3/10 20060101
B22F003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 24, 2017 |
JP |
2017-058593 |
Claims
1. Fine copper particles wherein an entire surface is covered with
a coating film containing cuprous oxide and having an average film
thickness of 1.5 nm or less.
2. The fine copper particles according to claim 1, wherein an
average particle diameter is 500 nm or less.
3. A method for producing fine copper particles in which fine
copper particles having a coating film containing cuprous oxide on
a surface are produced by heating copper or a copper compound in a
reducing flame formed by a burner, wherein the fine copper
particles are produced by adjusting a mixing ratio between a
combustible gas and a combustion supporting gas which form the
reducing flame such that a volume ratio of CO/CO.sub.2 is in a
range of 1.5 to 2.4.
4. A method for producing a sintered body, wherein fine copper
particles according to claim 1 are used as a raw material and
sintered them in a reducing atmosphere at 150.degree. C. or
lower.
5. A method for producing a sintered body, wherein fine copper
particles according to claim 2 are used as a raw material and
sintered them in a reducing atmosphere at 150.degree. C. or lower.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to fine copper particles, a
method for producing fine copper particles, and a method for
producing a sintered body.
DESCRIPTION OF RELATED ART
[0002] In recent years, for example, technological innovations such
as high-density wiring have become remarkable with the increase in
performance, miniaturization, and weight reduction of electronic
devices and printed wiring boards used in electronic component
devices. Examples of a material for forming such a high-density
wiring include a conductive ink and a conductive paste. These
materials contain fine silver particles in order to impart
conductivity. However, silver has problems such as high cost and
easy migration. For this reason, it is considered to use fine
copper particles which are low in cost and have the same
conductivity as that of silver instead of silver fine
particles.
[0003] On the other hand, metal fine particles have a problem that
they tend to deteriorate due to oxidation when left in the
atmosphere. In order to prevent such deterioration of metal fine
particles due to oxidation, for example, it is conceivable to coat
the surface of the fine particles with an antioxidant or the
like.
[0004] However, the thicker the coating, such as an antioxidant,
coated to the surface of the fine particles, the higher the
sintering temperature is required to sinter the fine particles
while reliably removing the coating.
[0005] Thus, when the sintering temperature of the metal fine
particles increases, for example, when a conductive ink or a
conductive paste containing the metal fine particles is used in a
printed wiring board or the like having a resin substrate, a resin
material having low heat resistance such as a PET film or the like
cannot be used.
[0006] For this reason, when using a conductive ink or a conductive
paste containing metal fine particles, it is necessary to use a
material having high heat resistance such as polyimide for the
resin substrate, which causes a cost increase.
[0007] For this reason, there is a demand for fine particles which
can be used in a resin substrate made of a material having low heat
resistance such as a PET film and sintered at low temperatures as
fine particles contained in a conductive ink and a conductive
paste.
[0008] In order to solve the problems when the surface of the metal
fine particles is coated with an antioxidant or the like as
described above, a technique for coating the surface of the fine
particles with an oxide has been proposed. For example, Patent
Document 1 below discloses fine copper particles of which the
surface is coated with copper oxide using copper as a raw material,
and a method for producing fine copper particles.
PRIOR ART DOCUMENTS
Patent Literature
[0009] Patent Document 1: Japanese Unexamined Patent Application,
First Publication No. 2016-028176
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0010] However, as a result of intensive studies by the present
inventors, it was revealed that the fine copper particles disclosed
in Patent Document 1 exhibit high conductivity when simply pressed,
so the coating layer containing copper oxide could not completely
cover the surface of the fine copper particles. In such a case,
deterioration of the fine copper particles due to oxidation
proceeds. For this reason, after all, there was a problem which it
was necessary to separately coat the surface of the fine copper
particles with an antioxidant or the like.
[0011] The present invention has been made in view of the problems
above, and an object of the present invention is to provide fine
copper particles which are less likely to be deteriorated by
oxidation in the atmosphere without being coated with an
antioxidant or the like and can be sintered at a lower temperature,
a method for producing fine copper particles, and a method for
producing a sintered body.
Means to Solve the Problem
[0012] In order to solve the problems above, the present invention
includes the following aspects.
[0013] The present invention provides fine copper particles wherein
an entire surface is covered with a coating film containing cuprous
oxide and having an average film thickness of 1.5 nm or less.
[0014] According to the present invention, since the entire surface
of the fine copper particles is covered with the coating film
containing cuprous oxide and having the average film thickness
above, it is possible to effectively suppress the deterioration due
to oxidation in the atmosphere. In addition, since the reduction of
the coating film is facilitated during sintering, the sintering
temperature can be lowered.
[0015] The fine copper particles of the present invention
preferably have an average particle diameter of 500 nm or less.
According to the present invention, the coating film is more easily
reduced during sintering, and the coating film is easily removed by
adjusting the average particle size to 500 nm or less, so the
sinterability is further improved.
[0016] Further, the present invention provides a method for
producing fine copper particles in which fine copper particles
having a coating film containing cuprous oxide on a surface are
produced by heating copper or a copper compound in a reducing flame
formed by a burner wherein the fine copper particles are produced
by adjusting a mixing ratio between a combustible gas and a
combustion supporting gas which form the reducing flame such that a
volume ratio of CO/CO.sub.2 is in a range of 1.5 to 2.4.
[0017] According to the present invention, the coating film
containing cuprous oxide can be formed on the entire surface of the
fine copper particles while adjusting the average film thickness to
1.5 nm or less by adjusting the mixing ratio between the
combustible gas and the combustion supporting gas which are
supplied to the burner. For this reason, the progress of the
oxidation in the atmosphere is suppressed and the deterioration
becomes difficult. Further, it is possible to produce fine copper
particles having a sintering temperature lower than that of prior
art by producing fine copper particles such that the coating film
containing cuprous oxide has the average film thickness above.
[0018] The present invention also provides a method for producing a
sintered body wherein the fine copper particles are used as a raw
material and sintered them in a reducing atmosphere at 150.degree.
C. or lower.
[0019] The production method of the present invention is a method
of using the fine copper particles with the coating film containing
cuprous oxide and having an average film thickness of 1.5 nm or
less on the entire raw material, and sintering the fine copper
particles. As a result, even when the sintering temperature is as
low as 150.degree. C., the coating film is easily reduced and
removed during sintering, and a sintered body can be produced with
excellent sinterability.
[0020] In the present description, "sintering in a reducing
atmosphere at 150.degree. C. or lower" refers to a state in which
the fine copper particles are sufficiently sintered in a reducing
atmosphere at 150.degree. C. or lower within 1 hour.
Effects of the Invention
[0021] According to the fine copper particles of the present
invention, since the entire surface is covered with the coating
film containing cuprous oxide film and an average film thickness of
1.5 nm or less, even when stored in the air, it is possible to
effectively suppress the deterioration due to oxidation. In
addition, when fine copper particles are sintered, the coating film
containing cuprous oxide is easily reduced, so the sintering
temperature can be lowered. Therefore, for example, since the fine
copper particles can be used in high-density wiring on the surface
of a resin substrate having low heat resistance, it is possible to
reduce the cost of electronic devices, printed wiring boards, and
the like.
[0022] In addition, according to the method for producing fine
copper particles of the present invention, a coating film can be
formed on the entire surface of the fine copper particles while
adjusting the coating film containing cuprous oxide to 1.5 nm or
less by adjusting the mixing ratio between the combustible gas and
the combustion supporting gas which are supplied to the burner.
Accordingly, oxidation is prevented from proceeding in the
atmosphere, and is difficult to deteriorate in the fine copper
particles produced by the production method according to the
present invention. Further, it is possible to produce the fine
copper particles having a sintering temperature lower than that of
prior art by producing fine copper particles such that the coating
film containing cuprous oxide has the average film thickness
above.
[0023] Moreover, the method for producing a sintered body according
to the present invention is a method for using the fine copper
particles according to the present invention having a low sintering
temperature as a raw material and sintering them in a reducing
atmosphere of 150.degree. C. or lower. Accordingly, for example,
the sintered body produced by the production method according to
the present invention can be easily used in high-density wiring or
the like on the surface of a resin substrate having low heat
resistance, and the cost of electronic devices, printed wiring
boards, and the like can be reduced.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1 is a figure for explaining the fine copper particles
which are one embodiment of the present invention, and is a
photograph of the fine copper particles by a scanning electron
microscope (SEM).
[0025] FIG. 2 is a figure for schematically illustrating the method
for producing fine copper particles which is one embodiment of the
present invention, and is a schematic block diagram for showing an
example of the producing apparatus used in producing the fine
copper particles.
[0026] FIG. 3 is a figure for schematically illustrating the method
for producing fine copper particles which is one embodiment of the
present invention, and is a planner view for showing one example of
a burner provided with the producing apparatus of the fine copper
particles shown in FIG. 2.
[0027] FIG. 4 is a figure for schematically illustrating the method
for producing fine copper particles which is one embodiment of the
present invention, and is a cross-sectional view taken along the
line A-A of the burner shown in FIG. 3.
[0028] FIG. 5 is a figure for explaining the method for producing a
sintered body which is one embodiment of the present invention, and
is the photograph of a sintered body produced by sintering the fine
copper particles by a scanning electron microscope (SEM).
[0029] FIG. 6 is a figure for explaining the fine copper particles
according to one embodiment of the present invention, and is a
graph showing an amount of increase in an oxygen concentration in
the fine copper particles when the fine copper particles produced
in Examples were left in the atmosphere.
[0030] FIG. 7 is a figure for explaining the fine copper particles
and the production method thereof according to an embodiment of the
present invention, and is a graph showing a relationship between a
volume ratio of CO/CO.sub.2 in a combustion exhaust gas of the
burner and the average film thickness of the coating film
containing cuprous oxide formed on the surface of the fine copper
particles.
DETAILED DESCRIPTION OF THE INVENTION
[0031] Hereinafter, fine copper particles, a production method for
fine copper particles, and a production method for a sintered body
of one embodiment according to the present invention will be
described with reference to FIGS. 1 to 7 as appropriate. Moreover,
in order to make the features easy to understand, there are cases
where the structure which become the features are enlarged for the
sake of convenience, and the dimensional ratios of the respective
structures are not always the same as the actual ones in the
drawings used in the following description. In addition, the
materials and the like exemplified in the following description are
mere examples, and the present invention is not limited to them,
and can be appropriately modified and implemented without changing
the gist thereof.
[0032] <Fine Copper Particles>
[0033] The fine copper particles of the present embodiment are, for
example, fine particles of a submicron scale or less, wherein the
entire surface is covered with a coating film containing cuprous
oxide and having an average film thickness of 1.5 nm or less as
shown in an observation photograph by a scanning electron
microscope (SEM) in FIG. 1.
[0034] In general, the surface of the fine copper particles is
oxidized to produce the coating film containing cuprous oxide.
Usually, the coating film produced has a non-uniform formation
position and a non-uniform thickness on the surface of the fine
copper particles, and at least a part of the surface of the fine
copper particles is exposed.
[0035] In contrast, the fine copper particles of the present
embodiment are covered with the coating film containing cuprous
oxide on the entire surface as described above. In particular,
since the coating film having the upper limit of the average film
thickness being formed without gaps, it is possible to effectively
suppress the deterioration due to oxidation in the atmosphere. In
addition, since the coating film is easily reduced during
sintering, the sintering temperature can be further reduced.
[0036] As described above, the fine copper particles of the present
embodiment have an average film thickness of 1.5 nm or less, more
preferably 1.3 nm or less, formed on the entire surface. By setting
the upper limit of the average film thickness of the coating film
containing cuprous oxide formed on the surface of fine copper
particles to 1.5 nm, while suppressing the progress of the
deterioration in the atmosphere, the coating film can be easily
reduced during sintering, so the effect of lowering the sintering
temperature can be reliably obtained.
[0037] In addition, the lower limit of the average film thickness
of the coating film containing cuprous oxide is not particularly
limited. However, since it is difficult for industrial production
to form the coating film having an average film thickness of less
than 0.3 nm on the surface of fine copper particles without gaps,
the lower limit is set to less than 0.3 nm.
[0038] The "average film thickness of the coating film" described
in the present embodiment can be obtained by, for example,
measuring the mass oxygen concentration of the fine copper
particles and converting the oxygen concentration and the average
particle diameter of the fine copper particles.
[0039] The film thickness of the coating film formed on the surface
of the fine copper particles will be described in detail in the
explanation of the production method described later. The film
thickness can be controlled to a desired range by adjusting the
volume ratio of CO/CO.sub.2 in the combustion exhaust gas generated
by the combustion of the burner within the optimum range.
[0040] The particle diameter of the fine copper particles of the
present embodiment is preferably 5 nm or more and 1000 nm or
less.
[0041] Further, the fine copper particles may have a uniform
particle diameter in the range above in the present embodiment.
However, the particle diameter may be distributed around the
average particle diameter, and the average particle diameter in
this case is preferably 500 nm or less. Thus, when the average
particle diameter is 500 nm or less, the coating film is more
easily reduced during sintering, and the coating film can be easily
removed, so the sinterability is further improved. When the average
particle diameter of the fine copper particles exceeds 500 nm, the
total particle size becomes too large and the total amount of the
coating film in each particle unit increases, so the coating film
is difficult to reduce during sintering and the sintering
temperature rises. In addition, the sinterability may be
decreased.
[0042] The average particle diameter of the fine copper particles
is more preferably in the range of 50 to 150 nm.
[0043] The average particle diameter of the fine copper particles
described in the present embodiment is a particle diameter which is
obtained by measuring a specific surface area per unit mass of the
fine copper particles using a specific surface area meter (for
example, Macsorb HM model-1201 etc., manufactured by Mountec Co.,
Ltd.), and converting based on the obtained specific surface
area.
[0044] When the specific surface area per unit mass is S
(m.sup.2/g) and the density is .rho. (g/cm.sup.3), the average
particle diameter Dave (nm) can be obtained from the following
equation.
Dave=6000/(.rho..times.S)
[0045] Further, the detailed composition of the fine copper
particles of the present embodiment is not particularly limited as
long as the fine copper particles contain copper (Cu), but the
copper element is preferably 95% by mass, and more preferably 97%
by mass or more with respect to the entire fine particles.
[0046] <Method for Producing Fine Copper Particles>
[0047] The production method for fine copper particles of the
present embodiment is a method for producing fine copper particles
having a coating film containing cuprous oxide on the surface by
heating copper or a copper compound in a reducing flame formed by a
burner. In the production method of the present embodiment, the
fine copper particles are produced by adjusting a mixing ratio
between the combustible gas and the combustion supporting gas such
that the volume ratio of CO/CO.sub.2 in the combustion exhaust gas
is in the range of 1.5 to 2.4
[0048] The producing apparatus used in the production method for
fine copper particles of this embodiment and the producing
procedure in the method for producing fine copper particles will be
described in detail below.
[0049] [Producing Apparatus for Fine Copper Particles]
[0050] One example of a producing apparatus used in the production
method for fine copper particles of this embodiment will be
described in detail below.
[0051] The producing apparatus 50 shown in FIG. 2 is schematically
configured to include a burner 3 which is configured to form a
high-temperature flame and a reaction furnace 6 which is configured
to produce fine copper particles P inside. Further, the producing
apparatus 50 shown in FIG. 1 further includes a combustible gas
supply unit 1 which is configured to supply a combustible gas G1, a
feeder 2 which is configured to supply a raw material to the burner
3 using the combustible gas G1 supplied from the combustible gas
supply unit 1 as a carrier gas, a combustion supporting gas supply
unit 4 which is configured to supply a combustion supporting gas G2
to the burner 3, a bug filter 8 which is configured to separate gas
(a combustion exhaust gas G3) and powder (the fine copper particles
P) generated inside the reaction furnace 6, a collection unit 9
which is configured to collect the fine copper particles P
separated by the bug filter 8, and a blower 10 which is configured
to suck the combustion exhaust gas G3.
[0052] The combustible gas supply unit 1 stores the combustible gas
G1 for forming a high-temperature flame, and transfers the
combustible gas G1 toward the feeder 2. Although detailed
illustration is abbreviated in figures, the combustible gas supply
unit 1 has a structure which can adjust the supply amount of the
combustible gas G1. For example, the combustible gas supply unit 1
is provided with a container which stores the combustible gas G1, a
flow regulator, and the like.
[0053] In the present embodiment, for example, methane, propane,
hydrogen, or a mixed gas of methane and hydrogen can be selected
and used as the combustible gas G1.
[0054] The feeder 2 quantitatively transfers the combustible gas G1
as a carrier gas (transferring gas) and the powder raw material M
as a raw material of the fine copper particles P toward the burner
3.
[0055] Since the production method in this embodiment is a method
for producing fine copper particles P, copper or a copper compound
is used as the powder raw material M supplied from the feeder
2.
[0056] The burner 3 is provided to the upper part of the reaction
furnace 6 to be described later, and the powder raw material M is
supplied into the reaction furnace 6 while ejecting the combustible
gas G1 into the reaction furnace 6, and forming a high temperature
reducing flame in the reaction furnace 6.
[0057] The burner 3 shown in FIGS. 3 and 4 is provided with a raw
material ejection passage 31 which is configured to eject the
powder raw material M as a raw material for the fine copper
particles P and the combustible gas G1 along the central axis. In
addition, a primary combustion supporting gas ejection passage 32
which is configured to eject the combustion supporting gas G2 is
provided in parallel to the central axis of the raw material
ejection passage 31 on the outer peripheral side of the raw
material ejection passage 31. Further, a secondary combustion
supporting gas ejection passage 33 which is configured to eject the
combustion supporting gas G2 toward one point on the extension line
of the central axis of the burner 3 is coaxially provided on the
outer peripheral side of the primary combustion supporting gas
ejection passage 32. Further, a water cooling jacket 34 is provided
on the outer peripheral side of the secondary oxygen supply passage
33 so that the burner 3 itself can be cooled with water.
[0058] Moreover, as shown in FIG. 3, the elliptical openings 31a,
which are the tip ends of the raw material ejection passage 31, are
provided at four locations, equally arranged on the
circumference.
[0059] Further, a plurality of small-diameter openings 32a, which
are the tip ends of the primary combustion supporting gas ejection
passage 32, are provided so as to be evenly arranged on the
circumference.
[0060] Further, a plurality of small-diameter openings 33a, which
are the tip ends of the secondary oxygen supply passage 33, are
provided evenly arranged on the circumference.
[0061] That is, the openings 31a of the raw material ejection
passage 31, the openings 32a of the primary combustion supporting
gas ejection passage 32, and the opening 33a of the secondary
combustion supporting gas ejection passage 33 are arranged
concentrically along the central axis of the burner 3,
respectively.
[0062] As shown in FIG. 4, the plurality of openings 31a which are
the tip ends of the raw material ejection passage 31 are inclined
with respect to the central axis of the burner 3 in a range of
5.degree. to 45.degree. so that the central axis of the raw
material ejection passage 31 is inclined toward the outer diameter
side of the burner 3 toward the tip end of the burner 3.
[0063] Further, the plurality of openings 32a which are the tip
ends of the primary combustion supporting gas ejection passage 32
are provided so as to eject the combustion supporting gas G2 in
parallel to the central axis of the burner 3.
[0064] In addition, the plurality of openings 33a which are tip
ends of the secondary combustion supporting gas ejection passage 33
are provided such that the central axis of each of the openings 33a
is inclined with respect to the central axis of the burner 3 in a
range of approximately 5 to 45 degrees so as to reach one point on
the extension line of the central axis of burner 3.
[0065] Since the burner 3 is configured as described above, the
combustible gas G1 and the powder raw material M from the feeder 2
are transferred into the raw material ejection passage 31. In
addition, the combustion supporting gas G2 such as air,
oxygen-enriched air, or oxygen is transferred into the primary
combustion supporting gas ejection passage 32 and the secondary
oxygen supply passage 33 from the combustion supporting gas supply
unit 4 which will be described later with the flow rate adjusted
individually.
[0066] As the material of the burner 3, for example, a stainless
material such as SUS316 can be used. However, the material is not
limited to this, and any material can be used as long as it is
durable to high temperatures.
[0067] The structure of the burner 3 is not limited to that shown
in FIGS. 3 and 4, and the nozzle arrangement, and the arrangement,
shape, angle, and number of the openings can be appropriately
adjusted.
[0068] The combustion supporting gas supply unit 4 supplies the
combustion supporting gas G2 for stably forming a high-temperature
flame to the burner 3. As the combustion supporting gas G2, air,
oxygen-enriched air, oxygen, or the like is used as described
above. Although not shown in detail in figures, the combustion
supporting gas supply unit 4 of the present embodiment can adjust
the flow rate or the like of the combustion supporting gas G2 so
that the ratio of the combustible gas G1 and the combustion
supporting gas G2 in the burner 3 can be adjusted.
[0069] The high-temperature reducing flame formed by the burner 3
is taken into the reaction furnace 6, and the copper or the copper
compound transferred by the combustible gas G1 evaporates in the
reducing flame. Thereby, the fine copper particles P of a submicron
scale or less are produced. As described above, the burner 3 is
provided to the upper portion of the reaction furnace 6 so that the
front end portion (flame formation side) of the burner 3 faces
downward.
[0070] Moreover, although detailed illustration is abbreviated in
figures, the reaction furnace 6 can cool internal combustion gas by
circulating a cooling water to the water cooling jacket with which
a surrounding wall part is equipped, and can block the atmosphere
in the reaction furnace from the outside of the reaction
furnace.
[0071] Although the reaction furnace 6 may be a metal furnace, it
may be a furnace using a refractory wall. In this case, the
combustion gas in the reaction furnace can be cooled by taking the
first cooling gas G3 such as nitrogen or argon into the reaction
furnace using a gas supply device such as a first cooling gas
supply unit that will be described later. Furthermore, the reaction
furnace 6 can be configured by a combination of a water-cooled wall
and a refractory wall.
[0072] Although the detailed illustration is abbreviated in
figures, the reaction furnace 6 may be configured such that, for
example, a cooling gas such as nitrogen or argon is taken into the
reaction furnace and a swirling flow is formed in the reaction
furnace. That is, a plurality of gas intake holes (not shown in
figures) are formed on the peripheral wall of the reaction furnace
6 in the circumferential direction and the height direction, and
the gas ejection direction of these gas intake holes is formed
along the inner peripheral surface of the reaction furnace 6.
Thereby, when cooling gas is taken into the reaction furnace 6, the
swirling flow of combustible gas G1 can be generated in the
reaction furnace.
[0073] The way how to generate the swirling flow of gas in the
reaction furnace 6 is not limited to the one having the
configuration above. For example, the swirling flow can be
generated by adjusting the position of the burner 3 to the reaction
furnace 6, the direction of the nozzle, or the shape and structure
of the nozzle opening of the burner 3.
[0074] The bug filter 8 catches the fine copper particles P as
products by separating the exhaust gas D discharged from the bottom
of the reaction furnace 6 into the fine copper particles P and the
combustion exhaust gas G3. As the bug filter 8, any one having a
configuration conventionally used in this technical field can be
employed without any limitations.
[0075] The fine copper particles P caught by the bug filter 8 are
transferred to the collection unit 9 which is configured to collect
and store the fine copper particles P, and the combustion exhaust
gas G3 is transferred, for example, to an exhaust gas treatment
device (not shown in figures) or the like by an intake action of
the blower 10 that will be described later.
[0076] In the present embodiment, an embodiment is described in
which the exhaust gas D is separated into the fine copper particles
P and the combustion exhaust gas G3 using the bug filter 8.
However, the present invention is not limited to this embodiment,
and it is also possible to employ a cyclone, a dust collector or
the like.
[0077] As described above, the blower 10 sends (discharges) the
combustion exhaust gas G3 separated by the bug filter 8 toward the
outside of the producing apparatus 50. As the blower 10, a general
blower including a motor and a fan can be used without any
limitations.
[0078] [Production of Fine Copper Particles]
[0079] A method for producing fine copper particles P using the
producing apparatus 50 having the configuration above will be
described in detail below.
[0080] As described above, the production method of the present
embodiment is a method in which copper or the copper compound is
heated in the reducing flame formed in the reaction furnace 6 by
the burner 3, and the fine copper particles P having the coating
film containing cuprous oxide on the surface is produced. In the
production method of the present embodiment, the mixing ratio
between the combustible gas G1 and the combustion supporting gas G2
is adjusted so that the volume ratio of CO/CO.sub.2 in the
combustion exhaust gas G3 is in the range of 1.5 to 2.4, and the
fine copper particles P are produced.
[0081] When producing the fine copper particles P using the
producing apparatus 50, first, the powder raw material M is set in
the feeder 2, and the combustible gas G is transferred from the
feeder 2 into the raw material ejection passage 31 of the burner 3.
Thereby, the combustible gas G1 is supplied, while transferring the
powder raw material M in the feeder 2. At this time, the powder raw
material M is quantitatively transferred from the feeder 2 toward
the burner 3 while being transferred to the combustible gas G1. In
addition, at the same time, the combustion supporting gas G2 is
transferred from the combustion supporting gas supply unit 4 into
the primary combustion supporting gas ejection passage 32 and the
secondary combustion supporting gas ejection passage 33 of the
burner 3, so that the combustible gas G1 and the combustion
supporting gas G2 are combusted by the burner 3, and the
high-temperature reducing flame is formed in the reactor 6.
[0082] At this time, as the combustible gas G1 supplied from the
combustible gas supply unit 1, for example, 100% methane gas, 80%
methane gas +20% hydrogen gas, 60% methane gas +40% hydrogen gas,
or 100% propane gas can be used without any limitations.
[0083] The combustible gas G1 is not limited to these gases, and
any gas can be used as long as it is a gas capable of forming a
reducing flame.
[0084] In the present embodiment, the flow rate of the combustible
gas G1 is not particularly limited, and may be set so that the gas
ratio of the combustion exhaust gas G3 falls within a predetermined
range as will be described later.
[0085] Further, the combustion supporting gas G2 is not
particularly limited. As described above, air, oxygen-enriched air,
oxygen (oxygen 100%), or the like can be appropriately used in
consideration of a necessary oxygen amount and the like.
[0086] In the production method of the present embodiment, the
mixing ratio between the combustible gas G1 and the combustion
supporting gas G2 is adjusted so that the volume ratio of
CO/CO.sub.2 in the combustion exhaust gas G3 is in the range of 1.5
to 2.4 described above.
[0087] At this time, the mixing ratio is adjusted by adjusting the
flow rate of the combustible gas G1 with the combustible gas supply
unit 1, the flow rate of the combustion supporting gas G3 with the
combustion supporting gas supply unit 4, or the mixing ratio
between the combustible gas G1 and the combustion supporting gas
G3.
[0088] More specifically, for example, it is preferable to control
the volume ratio of CO/CO.sub.2 in the combustion exhaust gas G3 to
be in the range above by adjusting the flow rate of the combustion
supporting gas G2, while keeping the composition and flow rate of
the combustible gas G1 constant from the viewpoint of ease of
control and the like. At this time, it is preferable that the
amount of the combustion supporting gas supplied from the
combustion supporting gas supply unit 4 to the burner 3, that is,
the amount of oxygen, be appropriately adjusted while taking into
consideration the amount of oxygen serving as a reducing
atmosphere.
[0089] In the present embodiment, it is possible to produce the
fine copper particles P such that the entire surface of the fine
copper particles P is covered with the coating film containing
cuprous oxide while suppressing the thickness of the coating film
containing cuprous oxide to 1.5 nm or less by adjusting the mixing
ratio between the combustible gas G1 and the combustion supporting
gas G2 which are supplied to the burner 3 so that the volume ratio
of CO/CO.sub.2 in the combustion exhaust gas G3 is in the range
above. Thereby, the sintering temperature of the fine copper
particles P produced can be set to a low temperature of 150.degree.
C. or lower. Further, the fine copper particles P produced by such
a method are covered with the coating film on the entire surface,
so that the oxidation is suppressed from progressing in the
atmosphere and hardly deteriorates.
[0090] When the volume ratio of CO/CO.sub.2 in the combustion
exhaust gas G3 is 1.5 or more, the thickness of the coating film
formed on the surface of the fine copper particles does not become
too large, and the coating film is easily reduced during sintering.
Therefore, it can be sintered at a low temperature and has
excellent sinterability. On the other hand, when the volume ratio
of CO/CO.sub.2 in the combustion exhaust gas G3 is 2.4 or less, the
thickness of the coating film formed on the surface of the fine
copper particles can be reduced. At the same time, even when the
ratio of CO in the combustion exhaust gas G3 is high, the fine
copper particles produced are easily dispersed in the organic
solvent. Thereby, the slurry for producing a sintered body can be
adjusted easily, and it becomes a preferable raw material of a
sintered body.
[0091] As described above, the fine copper particles P having the
coating film containing cuprous oxide formed on the surface having
an average film thickness of 1.5 nm or less, which are excellent
dispersibility in an organic solvent, and suitable for producing a
sintered body can be obtained by adjusting the mixing ratio between
the combustible gas G1 and the combustion supporting gas G2 so that
the volume ratio of CO/CO.sub.2 in the combustion exhaust gas G3 is
in the range of 1.5 to 2.4.
[0092] Moreover, as the powder raw material M supplied from the
feeder 2, powder of copper (metal copper) or a copper compound (for
example, copper oxide, and the like) is used in this
embodiment.
[0093] The particle diameter of the powder raw material M is not
particularly limited, but considering the preferable average
particle diameter range of the fine copper particles produced P, it
is preferable to use the powder raw material M having an average
particle diameter in the range of 1 to 50 .mu.m.
[0094] In addition, the average particle diameter of the powder raw
material M demonstrated in this embodiment means the value obtained
by conversion from the specific surface area above.
[0095] Moreover, as the powder raw material M used in the present
embodiment, in addition to the above, for example, any raw
materials such as copper nitrate and copper hydroxide which can
produce copper oxide by heating and has a high purity can be used
without any limitations.
[0096] As described above, the copper powder or the copper compound
powder introduced into the reducing flame by the burner 3 becomes
fine copper particles P having a particle diameter smaller than
that of the powder raw material M and smaller than a submicron
level by heating, evaporating, and reducing. Further, the coating
film containing cuprous oxide and having an average film thickness
of 1.5 nm or less is formed on the surface of the fine copper
particles P produced at this time.
[0097] When producing the fine copper particles P, for example, it
is possible to suppress increase in diameter due to the fine copper
particles P produced colliding with each other and fuse by passing
cooling water through a water cooling jacket (not shown in figures)
provided in the reaction furnace 6 to rapidly cool the reaction
furnace atmosphere.
[0098] Further, it is possible to prevent the fine copper particles
P from being combined to increase the diameter by taking the
cooling gas (not shown in figures) into the reaction furnace 6, and
forming a swirl flow in the reaction furnace, while controlling the
shape of the fine copper particles P to be produced into a
spherical shape.
[0099] The fine copper particles P produced in the reaction furnace
6 are taken out from the bottom of the reaction furnace 6 as the
exhaust gas D together with the combustion exhaust gas G3 and
introduced into the bug filter 8. Then, the fine copper particles P
caught in the bug filter 8 are collected and stored in the
collection unit 9.
[0100] At this time, the fine copper particles P having a desired
particle diameter distribution, for example, the average particle
diameter is 500 nm or less can be produced as a product by further
classifying the fine copper particles P caught in the bug filter 8
using a classifying device not shown in figures. At this time, the
remaining fine copper particles after classification (mainly fine
copper particles having a large particle diameter) can be recovered
and reused as a powder raw material.
[0101] In the present embodiment, an embodiment is described in
which the combustible gas G1 and the powder raw material M are
introduced into the burner 3 using the combustible gas G1 as a
carrier gas. However, the present invention is not limited to this
embodiment. For example, the powder raw material M may be directly
blown into the reducing flame formed by the burner from a portion
other than the burner. Alternatively, the powder raw material M may
be separately transferred to the burner using a gas other than a
fuel (for example, air) as a carrier gas.
[0102] Moreover, as the fuel for forming the reducing flame,
hydrocarbon fuel oil, and the like can also be used other than the
combustible gas, for example. In this case, it is desirable that
the powder raw material M be directly blown into the reducing flame
from a portion other than the burner.
[0103] <Method for Producing Sintered Body>
[0104] The production method for a sintered body of this embodiment
is a method for producing a sintered body using the fine copper
particles of the present embodiment as a raw material, and
sintering them in a reducing atmosphere at 150.degree. C. or
less.
[0105] Here, as described in the present embodiment, "sintering in
a reducing atmosphere of 150.degree. C. or lower" means that the
fine copper particles P are sufficiently sintered in a reducing
atmosphere of 150.degree. C. or lower within one hour as described
above.
[0106] Specifically, first, for example, an organic solvent is
added to the fine copper particles P produced by the production
method so that the weight ratio of the fine copper particles P
becomes a predetermined ratio, and stirring is performed at a
rotational speed of about 2000 rpm for a predetermined time.
[0107] Next, the mixture which has become a paste by stirring is
applied to, for example, a glass substrate.
[0108] Then, for example, the glass substrate coated with the
mixture is sintered at a temperature of 150.degree. C. or lower for
1 hour in a reducing atmosphere of nitrogen gas to which hydrogen
gas is added in a predetermined amount, and thereby a sintered body
can be produced.
[0109] Further, the sintered state of the sintered body can be
determined by measuring the volume resistivity of the sintered
body. The volume resistivity can be measured by a four-terminal
method using a commercially available volume resistivity meter (for
example, Lorester GP MCP-T610 manufactured by Mitsubishi Chemical
Analytech Co., Ltd.) or the like.
[0110] In general, when fine copper particles exhibit low
resistivity with a volume resistivity of 1.0.times.10.sup.-6
.OMEGA.m or less, it can be judged that the cuprous oxide on the
surface of the fine copper particles is reduced and combusted
sufficiently well.
[0111] As shown in an observation photograph by a scanning electron
microscope (SEM) in FIG. 5, the sintered body of this embodiment is
produced by sintering the fine copper particles P having the
configuration above. As described above, the fine copper particles
P have the coating film containing cuprous oxide and having a
thickness of 1.5 nm or less on the entire surface. The production
method for a sintered body of the present embodiment is a method of
sintering the fine copper particles P described above as a raw
material. For this reason, even at a sintering temperature as low
as 150.degree. C., the coating film is easily reduced during
sintering, and a sintered body can be produced with excellent
sinterability.
[0112] The method for producing a sintered body of this embodiment
can be used in the formation of high-density wirings and the like
on the surface of a resin substrate having low heat resistance, for
example, because the sintering temperature is suppressed to
150.degree. C. As described above, when the production method for a
sintered body of the present embodiment is used in the formation of
high-density wiring or the like on a resin substrate, it is
possible to further reduce the cost of electronic devices, printed
wiring boards, and the like.
[0113] <Effects>
[0114] As described above, the fine copper particles P of the
present embodiment are entirely covered with the coating film
containing cuprous oxide and having an average film thickness of
1.5 nm or less. For this reason, even when the fine copper
particles P of the present embodiment are stored in the atmosphere,
it is possible to effectively suppress the deterioration due to
oxidation. Further, when the fine copper particles P are sintered,
the coating film containing cuprous oxide is easily reduced, so
that the sintering temperature can be lowered.
[0115] Therefore, for example, since the fine copper particles P
can be used in high-density wiring on the surface of a resin
substrate having low heat resistance, it is possible to reduce the
cost of electronic devices, printed wiring boards, and the
like.
[0116] Further, according to the production method for fine copper
particles of the present embodiment, the coating film containing
cuprous oxide can be formed on the entire surface of the fine
copper particles P while suppressing the thickness of the coating
film containing cuprous oxide to 1.5 nm or less by adjusting the
mixing ratio between the combustible gas G1 and the combustion
supporting gas G2 which are supplied to the burner 3. For this
reason, the oxidation of the fine copper particles P is prevented
from proceeding in the atmosphere, and is difficult to deteriorate.
Moreover, it is possible to produce fine copper particles P having
a sintering temperature lower than that of the prior art by
producing fine copper particles P so that the coating film
containing cuprous oxide has the average film thickness.
[0117] Further, the production method for a sintered body of the
present embodiment is a method in which the fine copper particles P
of the present embodiment having a low sintering temperature as
described above are used as a raw material and sintered them in a
reducing atmosphere of 150.degree. C. or lower. Therefore, the
production method for a sintered body can be easily used in, for
example, high-density wiring on the surface of a resin substrate
having low heat resistance, and it is possible to reduce the cost
of electronic devices, printed wiring boards, and the like.
EXAMPLES
[0118] The fine copper particles, the production method for fine
copper particles, and the production method for a sintered body
according to the present invention will be described in more detail
with reference to examples. However, the present invention is not
limited to the following examples.
Example 1
[0119] In Example 1, fine copper particles P were produced by the
procedure explained below using a producing apparatus 50 as shown
in FIG. 2 (including the burner 3 shown in FIGS. 3 and 4) under
conditions shown in Tables 1 and 2 below (see also Example 1 in
Table 3).
[0120] In Example 1, 100% methane gas as shown in Table 1 below was
used as the combustible gas G1 supplied from the combustible gas
supply unit 1 to the burner 3 through the feeder 2, and the flow
rate was adjusted to 2.35 Nm.sup.3/h.
[0121] Moreover, 100% oxygen gas was used as the combustion
supporting gas G2 supplied from the combustion supporting gas
supply unit 4, the flow rate was adjusted to 2.82 Nm.sup.3/h, and
the oxygen ratio was adjusted to 0.60.
[0122] In Example 1, the mixing ratio between the combustible gas
G1 and the combustion supporting gas G2 was adjusted so that the
volume ratio of CO/CO.sub.2 in the combustion exhaust gas G3
generated by the combustion of the burner 3 was 1.78.
[0123] In Example 1, copper (I) oxide powder having an average
particle diameter of 10 .mu.m was used as the powder raw material M
which was the raw material. The powder raw material M was
quantitatively transferred from the feeder 2 at a flow rate of 0.72
kg/h using the combustible gas G1 as a carrier gas.
[0124] In Example 1, the copper (I) oxide powder transferred by the
combustible gas G1 into the reaction furnace 6 is evaporated in a
high-temperature reducing flame formed by the burner 3, and fine
copper particles P of submicron or less were produced. Thereafter,
the fine copper particles P contained in the exhaust gas D from the
water cooling path were caught by the bug filter 8 and collected by
the collection unit 9.
[0125] Then, it was confirmed that the coating film containing
cuprous oxide was formed on the surface of the fine copper
particles P produced by analyzing the fine copper particles P
produced in Example 1 by X-ray photoelectron spectroscopy
(XPS).
[0126] Further, the specific surface area of the fine copper
particles P produced was measured using a commercially available
specific surface area meter (manufactured by Mountech Co., Ltd.:
Macsorb HM model-1201), and the particle diameter was determined by
conversion from the specific surface area. The results were shown
in Tables 2 and 3 below.
[0127] Further, the mass oxygen concentration of the fine copper
particles produced P was measured with an oxygen/nitrogen analyzer
(manufactured by LECO: TC-600 type). From the mass oxygen
concentration and the average particle diameter of the fine copper
particles P, the thickness of the coating film containing cuprous
oxide formed on the surface was calculated. The results were shown
in Tables 2 and 3 below.
[0128] The observation photograph by the scanning electron
microscope (SEM) of the fine copper particles produced in Example 1
was shown in FIG. 1.
[0129] From FIG. 1, it could be understood that the fine copper
particles produced in Example 1 were fine particles having a good
shape without fusing each of the fine copper particles.
[0130] Furthermore, the fine copper particles P produced in Example
1 were left in the atmosphere at a temperature of 25.degree. C. and
a humidity of 65%, and the relationship between the standing time
and the increase in oxygen concentration in the fine copper
particles P was examined. The results were shown in the graph of
FIG. 6. At this time, the oxygen concentration was measured with
the oxygen/nitrogen analyzer (manufactured by LECO: TC-600 type) in
the same manner as described above, and the increase in oxygen
concentration with the passage of the standing time was
examined.
[0131] Next, 2-propanol was added to the fine copper particles P
produced in Example 1 so that the weight ratio of the fine copper
particles was 63% by mass, and the mixture was stirred by a
commercially available kneader (Shinky Corporation: Awatori
Neritaro (Registered trademark)) under the conditions of a rotation
speed of 2,000 rpm and a rotation time of 1 min to produce a
paste.
[0132] Next, the paste produced was applied to a glass substrate,
and the glass substrate with the paste was sintered at a constant
temperature of 150.degree. C. for 1 hour in a reducing atmosphere
in which 3% by volume of hydrogen gas was added to nitrogen gas.
The volume resistivity of the sintered body produced was measured
by a four-terminal method, and the volume resistivity is shown in
Table 3 below as an index of the sinterability (sintering
temperature) of the fine copper particles. As described above, it
could be judged that when the fine copper particles had a low
resistivity of volume resistivity of 1.0.times.10.sup.-6 .OMEGA.m
or less, the cuprous oxide on the surface of the fine copper
particles was reduced and sintered sufficiently well.
[0133] The SEM photograph of the sintered body after sintering the
fine copper particles P produced in Example 1 was shown in FIG.
5.
[0134] From FIG. 5, it could be understood that the sintered body
produced by sintering the fine copper particles produced in Example
1 was in a state in which each of the fine copper particles is
satisfactorily sintered.
[0135] Table 1 below shows the production conditions of the fine
copper particles P in Example 1, that is, each condition of the
combustible gas G1, the combustion supporting gas G2, the oxygen
ratio, and the volume ratio of CO/CO.sub.2 in the combustion
exhaust gas G3. Table 2 below shows the average particle diameter
of the fine copper particles P produced in Example 1 and the
average film thickness of the coating film formed on the surface.
Table 3 below shows a list of the average particle diameter of the
fine copper particles P and the average film thickness of the
coating film, and the volume resistivity of the sintered body
produced by sintering the fine copper particles P.
TABLE-US-00001 TABLE 1 Conditions for producing fine copper
particles Volume ratio Flow rate of of CO/CO.quadrature. Kind of
Flow rate of combustion Oxygen in combustion Combustible
combustible gas supporting gas ratio exhaust gas gas [Nm.sup.3/h]
[Nm.sup.3/h] [--] [--] Example 1 100% 2.35 2.82 0.6 1.78 Methane
gas
TABLE-US-00002 TABLE 2 Properties of fine copper particles Average
film thickness of coating film Average particle containing cuprous
oxide diameter formed on the surface [nm] [nm] Example 1 125
1.3
TABLE-US-00003 TABLE 3 Conditions for producing Properties of fine
copper fine copper particles particles Volume Average film ratio of
thickness of Properties of Examples CO/CO.quadrature. in Average
coating film sintered body or Kind of combustion particle formed on
the Volume Comparative Combustible exhaust gas diameter surface
resistivity Examples gas [--] [nm] [nm] [.OMEGA. m] Example 1 100%
1.78 125 1.3 6.70 .times. 10.sup.-7 Comparative Methane gas 0.5 118
4 7.03 .times. 10.sup.-4 Example 1 Comparative 0.86 121 4.2 6.21
.times. 10.sup.-4 Example 2 Comparative 1.1 123 4 5.17 .times.
10.sup.-4 Example 3 Comparative 1.33 124 3.2 9.65 .times. 10.sup.-5
Example 4 Example 2 2.04 129 1.4 5.69 .times. 10.sup.-7 Example 3
2.38 127 1.2 6.14 .times. 10.sup.-7 Comparative 2.54 128 1.2
Impossible to Example 5 produce Comparative 80% 1.23 123 4.4 5.28
.times. 10.sup.-4 Example 6 Methane gas + Comparative 20% 1.46 121
4.2 6.31 .times. 10.sup.-4 Example 7 Hydrogen Example 4 gas 2.07
126 1.2 6.25 .times. 10.sup.-7 Example 5 60% 2.35 124 1 5.79
.times. 10.sup.-7 Methane gas + 40% Comparative Hydrogen 2.78 125
1.3 Impossible to Example 8 gas produce Comparative 100% 0.75 114
3.8 8.17 .times. 10.sup.-4 Example 9 Propane gas Comparative 1.06
116 3 4.05 .times. 10.sup.-5 Example 10 Comparative 1.31 125 1.9
2.18 .times. 10.sup.-5 Example 11 Example 6 1.53 124 1.1 6.14
.times. 10.sup.-7 Example 7 1.75 127 1.2 5.32 .times. 10.sup.-7
Examples 2 to 7, and Comparative Examples 1 to 11
[0136] In Examples 2 to 7 and Comparative Examples 1 to 11, fine
copper particles P were produced and evaluated under the same
conditions and procedures as in Example 1, except that the
combustible gas shown in Table 3 was used, and the volume ratio of
CO/CO.sub.2 in the combustion exhaust gas G3 was adjusted shown in
Table 3. The results were shown in Table 3.
[0137] Specifically, in Examples 2 to 7 and Comparative Examples 1
to 11, any one of 100% methane gas, 80% methane gas +20% hydrogen
gas, 60% methane gas +40% hydrogen gas, and 100% propane gas was
used as the combustible gas G1. The volume ratio of CO/CO.sub.2 in
the combustion exhaust gas G3 was adjusted to satisfy the
conditions shown in Table 3 by changing the flow rate of the
combustion supporting gas G2 while maintaining the flow rate of the
combustible gas G1 constant.
[0138] In Examples 2 to 7 and Comparative Examples 1 to 11, a
sintered body was also produced by sintering the fine copper
particles P produced and evaluated under the same conditions and
procedures as in Example 1. The results were shown in Table 3.
[0139] <Evaluation Results>
[0140] As shown in Tables 1 to 3, the volume resistivity of the
sintered body produced by sintering the fine copper particles P of
Example 1 having the structure according to the present invention,
and produced by the production method according to the present
invention at 150.degree. C. was 6.70.times.10.sup.-7 .OMEGA.m. The
volume resistivity exhibited that the fine copper particles P of
Example 1 had a low resistivity significantly lower than a volume
resistivity of 1.0.times.10.sup.-6 .OMEGA.m, which is an index of
sinterability when fine copper particles were sintered. Thereby, it
was confirmed that the fine copper particles P of Example 1 had a
sintering temperature as low as 150.degree. C. or lower and were
extremely excellent in sinterability.
[0141] Further, as shown in the graph of FIG. 6, the fine copper
particles P of Example 1 had an oxygen concentration increase
amount of less than 10% after being left in the atmosphere for 15
days after production. In general, when the surface of fine copper
particles is not completely covered with the coating film
containing cuprous oxide, the oxygen concentration increase will
exceed 10% in about 2 hours and cannot be used as a material for a
sintered body. It was confirmed that the fine copper particles P of
Example 1 were sufficiently stable even when left in the
atmosphere, that the coating film containing cuprous oxide covered
the entire surface of the fine copper particles.
[0142] Further, as shown in Table 3, the volume resistivity of the
sintered body produced by sintering the fine copper particles P of
all Examples 2 to 7 having the structure according to the present
invention, and produced by the production method according to the
present invention at 150.degree. C. was significantly below
1.0.times.10.sup.-6 .OMEGA.m. As a result, it was confirmed that
the fine copper particles P of Examples 2 to 7 had a sintering
temperature as low as 150.degree. C. or lower as in Example 1, and
were extremely excellent in sinterability.
[0143] On the other hand, as shown in Table 3, the volume ratio of
CO/CO.sub.2 in the combustion exhaust gas G3 during the production
in the fine copper particles of Comparative Examples 1 to 11 was
outside the specified range of the present invention. Further, the
average film thickness of the coating film on the surface of the
fine copper particles produced was outside the specified range of
the present invention.
[0144] Among these Comparative Examples, Comparative Examples 1 to
4, 6, 7, and 9 to 11 had a volume ratio of CO/CO.sub.2 in the
combustion exhaust gas G3 of less than 1.5, which was below the
lower limit defined in the present invention. Further, the average
thickness of the coating film on the surface of the fine copper
particles produced was 1.9 to 4.4 nm, which exceeded the upper
limit defined in the present invention.
[0145] As shown in Table 3, the volume resistivity of the sintered
body produced by sintering the fine copper particles of Comparative
Examples 1 to 4, 6, 7, and 9 to 11 exceeded 1.0.times.10.sup.-6
.OMEGA.m. It could be judged that when fine copper particles of
Comparative Examples 1 to 4, 6, 7, and 9 to 11 were used as a raw
material and sintering was performed at 150.degree. C. for 1 hour,
the cuprous oxide on the surface of the fine copper particles could
not be reduced and the sintering was not sufficient.
[0146] In Comparative Examples 5 and 8 in which the volume ratio of
CO/CO.sub.2 in the combustion exhaust gas G3 exceeds 2.5, it was
confirmed that the coating film having a predetermined average film
thickness was formed on the surface of the fine copper particles.
However, the fine copper particles to which 2-propanol was added
did not become paste, and it was impossible to produce a sintered
body. This is presumably because in Comparative Examples 5 and 8,
the organic matter that becomes an impurity was generated due to
the too high ratio of CO in the combustion exhaust gas G3, and the
fine copper particles became difficult to be dispersed in
2-propanol.
[0147] A graph in which the volume ratio of CO/CO.sub.2 in the
combustion exhaust gas G3 and the average film thickness of the
coating film containing cuprous oxide formed on the surface of the
fine copper particles in each Example shown in Table 3 were
plotted, was shown in FIG. 7.
[0148] From FIG. 7, it was confirmed that even when the kind of the
gas of the combustible gas G1 was changed, it was possible to
control the thickness of the coating film formed on the surface of
the fine copper particles by adjusting the volume ratio of
CO/CO.sub.2 in the combustion exhaust gas G3 to be within the range
defined in the present invention.
[0149] Further, from the data shown in Table 3, it could be
understood that the production condition of the fine copper
particles P capable of producing a sintered body which had a volume
resistivity of less than 1.0.times.10.sup.-6 .OMEGA.m and was
determined that the sintered state was sufficiently good was that
the volume ratio of CO/CO.sub.2 in the combustion exhaust gas G3
was in the range of 1.5 to 2.4. In addition, it could be also
understood that the production condition which can reduce the
average film thickness of the coating film on the surface of the
fine copper particles P to 1.5 nm or less was that the volume ratio
of CO/CO.sub.2 in the combustion exhaust gas G3 was in the range
above.
[0150] In general, the higher the average film thickness of the
coating film containing cuprous oxide on the surface of the fine
copper particles, the higher the sintering temperature is required
to remove the coating film. That is, when the coating film on the
surface of the fine copper particles is too thick, it cannot be
sufficiently sintered at a temperature of 150.degree. C., and the
volume resistivity of the sintered body becomes a high value. On
the other hand, it was confirmed that the fine copper particles P
which had excellent sintering properties and could be sufficiently
sintered at a temperature of 150.degree. C. could be produced by
producing the fine copper particles P under conditions in which the
volume ratio of CO/CO.sub.2 in the combustion exhaust gas G3 was in
the range of 1.5 to 2.4 and controlling the average film thickness
of the coating film containing cuprous oxide formed on the surface
to 1.5 nm or less as in Examples 1 to 7.
INDUSTRIAL APPLICABILITY
[0151] The fine copper particles of the present invention can be
easily used in, for example, high-density wiring on the surface of
a resin substrate having low heat resistance, and is very suitable
for electronic devices, printed wiring boards, and the like.
EXPLANATION OF REFERENCE NUMERAL
[0152] 1 combustible gas supply unit
[0153] 2 feeder
[0154] 3 burner [0155] 31 raw material ejection passage [0156] 32
primary combustion supporting gas ejection passage [0157] 33
secondary combustion supporting gas ejection passage [0158] 34
water-cooled jacket
[0159] 4 combustion supporting gas supply unit
[0160] 6 reaction furnace
[0161] 8 bug filter
[0162] 9 collection unit
[0163] 10 blower
[0164] 50 producing apparatus (producing apparatus of fine copper
particles)
[0165] G1 combustible gas
[0166] G2 combustion supporting gas
[0167] G3 combustion exhaust gas
[0168] M powder raw material (copper or copper compound)
[0169] P fine copper particles
[0170] D exhaust gas (gas containing fine copper particles and fuel
exhaust gas)
* * * * *