U.S. patent application number 11/587976 was filed with the patent office on 2007-09-13 for flaky copper powder, method for producing the same, and conductive paste.
This patent application is currently assigned to Mitsui Mining & Smelting Co., Ltd.. Invention is credited to Yoshinobu Nakamura, Takahiko Sakaue, Hiroyuki Shimamura, Katsuhiko Yoshimaru.
Application Number | 20070209475 11/587976 |
Document ID | / |
Family ID | 35241489 |
Filed Date | 2007-09-13 |
United States Patent
Application |
20070209475 |
Kind Code |
A1 |
Sakaue; Takahiko ; et
al. |
September 13, 2007 |
Flaky Copper Powder, Method For Producing The Same, And Conductive
Paste
Abstract
It is an object of the present invention to provide a flaky
copper powder composed of fine particles having a sharp
distribution particle size, a large crystallite diameter and high
oxidation resistance. The flaky copper powder of the present
invention contains P and has a crystallite diameter/D.sub.1A ratio
of 0.01 or more to achieve the object. The method for producing the
flaky copper powder comprises four steps: a first step of preparing
an aqueous solution containing a copper salt and complexing agent;
a second step of adding an alkali hydroxide to the aqueous solution
to prepare a first slurry containing cupric oxide; a third step of
adding a first reducing agent which can reduce the cupric oxide
into cuprous oxide to the first slurry to prepare a second slurry
containing cuprous oxide; and a fourth step of adding a second
reducing agent which can reduce the cuprous oxide into copper to
the second slurry to provide a flaky copper powder, wherein
phosphoric acid and its salt are added in at least one of the first
to third steps and/or in the second slurry in the fourth step.
Inventors: |
Sakaue; Takahiko;
(Shimonoseki-shi, JP) ; Yoshimaru; Katsuhiko;
(Shimonoseki-shi, JP) ; Nakamura; Yoshinobu;
(Shimonoseki-shi, JP) ; Shimamura; Hiroyuki;
(Tokyo, JP) |
Correspondence
Address: |
ROTHWELL, FIGG, ERNST & MANBECK, P.C.
1425 K STREET, N.W.
SUITE 800
WASHINGTON
DC
20005
US
|
Assignee: |
Mitsui Mining & Smelting Co.,
Ltd.
11-1, Osaki 1-chome, Shinagawa-ku
Tokyo
JP
1418584
|
Family ID: |
35241489 |
Appl. No.: |
11/587976 |
Filed: |
April 26, 2005 |
PCT Filed: |
April 26, 2005 |
PCT NO: |
PCT/JP05/07877 |
371 Date: |
February 7, 2007 |
Current U.S.
Class: |
75/255 ;
75/373 |
Current CPC
Class: |
B22F 1/0062 20130101;
B22F 1/0014 20130101; H01B 1/22 20130101; B22F 9/24 20130101; B22F
1/0044 20130101; H05K 1/095 20130101; B22F 2001/0033 20130101; B22F
1/0055 20130101 |
Class at
Publication: |
075/255 ;
075/373 |
International
Class: |
B22F 9/24 20060101
B22F009/24 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 28, 2004 |
JP |
2004-134689 |
Claims
1. A flaky copper powder which is characterized in that comprising
P.
2. The flaky copper powder according to claim 1 which is
characterized in that comprising P at 10 to 200 ppm.
3. The flaky copper powder according to claim 1, which is
characterized in that an average particle diameter D.sub.50 of the
powder is in the range from 0.3 .mu.m to 7 .mu.m.
4. The flaky copper powder according to claim 1, which is
characterized in that crystallite diameter of the powder is 25 nm
or more.
5. The flaky copper powder according to claim 1 which is
characterized in that an aspect ratio D.sub.1A/t of the powder,
which is calculated by dividing an average particle diameter
D.sub.1A (.mu.m) by a flaky copper particle thickness t (.mu.m),
the average particle diameter D.sub.1A (.mu.m) and the thickness t
(.mu.m) are measured from analyzing SEM images directly observed by
a scanning electron microscope, is in the range from 2 to 50.
6. The flaky copper powder according to claim 1 characterized by
having an SD/D.sub.50 ratio of 0.45 or less, (where D.sub.50 is a
median diameter (.mu.m) calculated as 50% of volume cumulative
distributions examined by a laser diffraction scattering particle
size distribution measuring method).
7. The flaky copper powder according to claim 1 which is
characterized in that D.sub.90/D.sub.10 ratio of 3.0 or less,
(where D.sub.10 is diameter (.mu.m) at 10% of volume cumulative
distributions and D.sub.90 is diameter (.mu.m) at 90% of volume
cumulative distributions examined by a laser diffraction scattering
particle size distribution measuring method, and SD is a standard
deviation (.mu.m) of a particle size distribution examined by the
same measuring method respectively).
8. A method for producing a flaky copper powder comprising four
steps: a first step of preparing an aqueous solution comprising a
copper salt and a complexing agent; a second step of adding an
alkali hydroxide to the aqueous solution to prepare a first slurry
comprising cupric oxide; a third step of adding a first reducing
agent which can reduce cupric oxide into cuprous oxide to the first
slurry to prepare a second slurry comprising cuprous oxide; and a
fourth step of adding a second reducing agent which can reduce the
cuprous oxide into copper to the second slurry to provide a flaky
copper powder, which is characterized in that phosphoric acid and
its salt are added in at least one of the first to third steps
and/or phosphoric acid and its salt are added in the second slurry
in the fourth step.
9. The method for producing a flaky copper powder according to
claim 8, which is characterized in that the phosphoric acid and its
salt are added in at least one of the first to third steps and/or
in the second slurry in the fourth step to be a total amount of
0.001 to 3 moles as P per 1 mole of copper which present in the
above described aqueous solution, the first slurry or the second
slurry.
10. The method for producing a flaky copper powder according to
claim 8, which is characterized in that the first slurry contains
the alkali hydroxide at 1.05 to 1.50 equivalents per equivalent of
the copper salt.
11. The method for producing a flaky copper powder according to
claim 8, which is characterized in that the complexing agent is an
amino acid.
12. The method for producing a flaky copper powder according to
claim 8, which is characterized in that the first reducing agent is
a reducing sugar.
13. The method for producing a flaky copper powder according to
claim 8, which is characterized in that the second reducing agent
is at least one selected from the group consisting of hydrazine,
hydrated hydrazine, hydrazine sulfate, hydrazine carbonate and
hydrazine chloride.
14. The method for producing a flaky copper powder according to
claim 8, which is characterized in that the aqueous solution
comprises the complexing agent at 0.005 to 10 moles per 1 mole of
copper present in the aqueous solution itself, the first slurry or
the second slurry.
15. The flaky copper powder according to claim 1, which is
characterized in that an organic surface treatment layer is formed
on the surface.
16. The flaky copper powder according to claim 15, which is
characterized in that a coating rate of the organic surface
treatment layer is 0.05 to 2 wt % based on the flaky copper
powder.
17. A conductive paste comprising the flaky copper powder according
to claim 1 and a resin.
Description
TECHNICAL FIELD
[0001] The present invention relates to a flaky copper powder, a
method for producing the same and a conductive paste. More
specifically a flaky copper powder useful as a raw material for a
copper paste which is used for securing electrical continuity of
electrical circuits on printed circuit substrate and external
electrodes of ceramic condensers and the like, a method for
producing the same and a conductive paste.
BACKGROUND ART
[0002] One of the convertible methods for forming electrodes or
circuits in an electronic device or the like is, that printing a
conductive paste in which a copper powder is dispersed as a
conductive material on a substrate and then hardening by calcining
or curing the paste to obtain electrodes or circuits.
[0003] Recently, as the markets have required downsizing and higher
density for electronic devices for multi functional electronic
devices, so, a copper powder for a conductive paste is required to
have distribution sharper in particle size with finer size so that
it gives a well filling ability conductive paste.
[0004] A copper powder for a conductive paste may be oxidized on
contacting oxygen, e.g., in evaporation of volatile contents from
the conductive paste at the calcining, in particular. Copper
oxidation is an undesirable phenomenon, because it leads high
resistance of a thick copper film when it is used as conductive
paste. Therefore, the copper powder is preferred to have excellent
resistance to oxidation. It is said that the resistance can be
enhanced by increasing a diameter to decrease a grain boundaries of
crystallites in the powder. Therefore it is preferable to increase
the diameter of the crystallite in the copper powder as large as
possible.
[0005] One of a substrate on which a conductive paste is printed is
a ceramic material, for use of IC packages, where large quantities
of heat are generated. However, a ceramic substrate generally
differs in thermal expansion rate coefficient from a thick copper
film formed with a conductive paste, with the result that troubles,
e.g., separation of the film from the substrate and deformation of
the substrate itself, may occur when the paste is printed on the
substrate at the calcinations process. Therefore, thermal expansion
values are preferably as close to each other as possible.
[0006] One of the causes for thermal expansion of the thick copper
film by the calcinations may be minimized space of the copper
particles with each other by sintering, which are left between the
copper particles in evaporation of volatile contents from the
conductive paste. It is therefore necessary to minimize the spaces
remaining among the copper particles as small as possible in order
to have a copper-containing conductive paste of low thermal
expansion values. In other words, the copper particles preferably
have a shape which makes it easy to fill the paste densely. It is
also preferable that the copper particles in the conductive paste
have a shape which increases contact area between them to improve
conductivity of the thick copper film prepared by calcinating the
conductive paste. Particle shape anisotropy decreases as it
increases sphericity, or increases as it becomes flatter.
Therefore, a flaky copper powder instead of spherical one has been
studied to meet the copper particle requirements.
[0007] Moreover, a flaky copper powder preferably has a sharper
distribution particle size to be more dispersible in paste for a
conductive paste.
[0008] As discussed above, copper powder, in particular flaky
copper powder, for conductive paste is preferably finer, sharper
distribution in particle size and larger in crystallite
diameter.
[0009] Patent Document 1 (Japanese Patent Laid-Open No.
2003-119501) discloses flaky copper powder having the following
characteristics; particle diameter: 10 .mu.m or less, SD/D.sub.50
ratio: 0.15 to 0.35 (where, SD is standard deviation of particle
size distribution and D.sub.50 is 50% volumetric cumulative
particle diameter), and aspect ratio: 0.3 to 0.7 (i.e., ratio of
thickness of particles which constitute the powder to D.sub.50).
The invention gives a flaky copper powder composed of fine, flat
and flaky particles.
[0010] [Patent Document 1]: Japanese Patent Laid-Open No.
2003-119501 (Page 2)
DISCLOSURE OF THE INVENTION
[0011] However, the flaky copper powder disclosed by Patent
Document 1, although fine, is produced by breaking agglomerated
copper particles and then deforming the broken particles by
compression in a high-energy ball mill. As a result, it involves
problems that it tends to be oxidized or strained during the
compression deformation step and to have small crystallite
diameter.
[0012] It is therefore an object of the present invention to
provide a flaky copper powder composed of fine particles, having a
sharp distribution particle size, a large crystallite diameter and
high oxidation resistance. It is another object to provide a
conductive paste using the flaky copper powder.
[0013] The inventors of the present invention have found, after
having extensively studied to solve the above problems under these
situations, that a P-containing flaky copper powder, in particular
that composed of particles of specific shape, is suitable for a
conductive paste. The inventors have also found that a flaky copper
powder composed of small particle diameter, a large crystallite
diameter, and high oxidation resistance, a sharp distribution
particle size, can be produced without having to employ compression
deformation treatment, like the method disclosed by Patent Document
1, by a wet process, adding a specific phosphoric acid and its salt
in at least one of the steps, comprising a plurality of steps for
reducing the copper ion (II) present in a copper salt in a raw
material, achieving the present invention.
[0014] The present invention provides a flaky copper powder which
is characterized in that comprising P.
[0015] The present invention also provides a flaky copper powder
which is characterized in that comprising P at 10 to 200 ppm
(D.sub.50 is a median diameter (.mu.m) calculated as 50% of volume
cumulative distributions examined by a laser diffraction scattering
particle size distribution measuring method).
[0016] The flaky copper powder of the present invention preferably
has an average particle diameter D.sub.50 of the powder is in the
range from 0.3 to 7 .mu.m.
[0017] In addition, the flaky copper powder of the present
invention preferably has a crystallite diameter of the powder is 25
nm or more.
[0018] The flaky particles which constitute the flaky copper powder
of the present invention preferably have an aspect ratio
(D.sub.1A/t), obtained by dividing an aspect ratio D.sub.1A/t of
the powder, which is calculated by dividing an average particle
diameter D.sub.1A (.mu.m) by a flaky copper particle thickness t
(.mu.m), the average particle diameter D.sub.1A (.mu.m) and the
thickness t (.mu.m) are measured from analyzing SEM images directly
observed by a scanning electron microscope, is in the range from 2
to 50.
[0019] Moreover, the flaky copper powder of the present invention
preferably has an SD/D.sub.50 ratio of 0.45 or less, where D.sub.50
is a median diameter (.mu.m) calculated as 50% of volume cumulative
distributions examined by a laser diffraction scattering particle
size distribution measuring method.
[0020] Still more, the flaky copper powder of the present invention
preferably has a D.sub.90/D.sub.10 ratio of 3.0 or less, where
D.sub.10 is diameter (.mu.m) at 10% of volume cumulative
distributions and D.sub.90 is diameter (.mu.m) at 90% of volume
cumulative distributions examined by a laser diffraction scattering
particle size distribution measuring method, respectively, and SD
is a standard deviation (.mu.m) of a particle size distribution
examined by the same measuring method.
[0021] As a method of the present invention for producing a flaky
copper powder, a method comprising four steps: a first step of
preparing an aqueous solution comprising a copper salt and a
complexing agent; a second step of adding an alkali hydroxide to
the aqueous solution to prepare a first slurry comprising cupric
oxide; a third step of adding a first reducing agent which can
reduce cupric oxide into cuprous oxide to the first slurry to
prepare a second slurry comprising cuprous oxide; and a fourth step
of adding a second reducing agent which can reduce the cuprous
oxide into copper to the second slurry to provide a flaky copper
powder, which is characterized in that phosphoric acid and its salt
are added in at least one of the first to third steps and/or
phosphoric acid and its salt are added in the second slurry in the
fourth step is preferably adopted.
[0022] In the method of the present invention for producing the
flaky copper powder, which is characterized in that the phosphoric
acid and its salt are added in at least one of the first to third
steps and/or in the second slurry in the fourth step preferably to
be a total amount of 0.001 to 3 moles as P per 1 mole of copper
which present in the above described aqueous solution, the first
slurry or the second slurry.
[0023] Moreover, in the method of the present invention for
producing the flaky copper powder, the first slurry preferably
contains 1.05 to 1.50 chemical equivalents of the alkali hydroxide
against one chemical equivalent of the copper salt.
[0024] Still more, in the method of the present invention for
producing the flaky copper powder, the complexing agent is
preferably an amino acid.
[0025] Still more, in the method of the present invention for
producing the flaky copper powder, the first reducing agent is
preferably a reducing sugar.
[0026] Still more, in the method of the present invention for
producing the flaky copper powder, the second reducing agent is
preferably at least one selected from the group consisting of
hydrazine, hydrated hydrazine, hydrazine sulfate, hydrazine
carbonate and hydrazine chloride.
[0027] Still more, in the method of the present invention for
producing the flaky copper powder, the aqueous solution preferably
comprises the complexing agent at 0.005 to 10 moles per 1 mole of
copper present in the aqueous solution itself, first slurry or
second slurry.
[0028] The method of the present invention provides the flaky
copper powder characterized in that an organic surface treatment
layer is formed on the surface.
[0029] Moreover, the method of the present invention provides the
flaky copper powder characterized in that a coating rate of the
organic surface treatment layer is 0.05 to 2 wt % based on the
flaky copper powder.
[0030] The present invention also provides a method for producing a
conductive paste characterized by comprising the flaky copper
powder of the present invention and a resin.
ADVANTAGE OF THE INVENTION
[0031] The flaky copper powder is free from compression deformation
process. It is less oxidized or strained, fine, sharp distribution
in particle size, and has a large crystallite diameter. As such,
when used for a conductive paste, the powder is resistant to
oxidation in evaporation of volatile contents process from the
conductive paste, well dispersible in the paste, and densely fills
the conductive paste can downsize of electrodes, circuits or the
like formed by a thick copper film. The method of the present
invention can efficiently produce the flaky copper powder of the
present invention. The conductive paste of the present invention is
highly oxidation-resistant in evaporation of volatile contents
process from the conductive paste; densely filled with the flaky
copper powder; electrodes, circuits and or the like by a thick
copper film can be finer; and a thick copper film can be excellent
thermal expansion rate.
BEST MODE FOR CARRYING OUT THE INVENTION
(Flaky Copper Powder of the Present Invention)
[0032] The flaky copper powder of the present invention is composed
of particles of microscopically flaky shape. In the present
invention, the powder of flaky shape means that the primary
particles have a flaky shape and does not mean shape of the
secondary particles, i.e., agglomerated primary particles.
[0033] The flaky copper powder of the present invention normally
has a D.sub.50 value of 0.3 to 7 .mu.m, preferably 0.5 to 5 .mu.m,
more preferably 0.5 to 4 .mu.m. The flaky copper powder having a
D.sub.50 value in the above range is preferable, because it well
fills the conductive paste. On the other hand, the powder having a
D.sub.50 value below 0.3 .mu.m is not preferable, because it gives
the conductive paste of excessively high viscosity, and the powder
having a D.sub.50 value above 7 .mu.m is also not preferable,
because it is difficult to make thinner of the thick copper film or
produce a fine line with the conductive paste. In the present
invention, D.sub.10, D.sub.50 and D.sub.90 are diameter (.mu.m) at
10, 50 and 90% by volume cumulative distributions examined by a
laser diffraction scattering particle size distribution
measuring.
[0034] The flaky copper powder of the present invention has a
crystallite diameter of 25 nm or more, preferably 35 nm or more. It
is preferable that a crystallite diameter is within the
above-described range, because it gives a conductive paste
suffering to a small dimensional change in a thick copper film
forming process, the dimensional changes leading thermal expansion
rate more notably to separate the film from a ceramic substrate or
deformation of the film, and, moreover, it exhibits higher
oxidation resistance in evaporation of volatile contents process.
On the other hand, it is not preferable that a crystallite diameter
below 25 nm, because it gives a conductive paste more suffering
troubles resulting from dimensional changes in a thick copper film
forming process, the dimensional changes causing thermal expansion
rate more notably to separate the film from a ceramic substrate or
deformation of the film, and, moreover, it exhibits lower oxidation
resistance in evaporation of volatile contents process. The
crystallite diameter in this specification means the average
crystallite diameter obtained from the half-value width of the
diffraction angle of each crystal face obtained by conducting X-ray
diffraction for flaky copper powder sample.
[0035] The crystallite diameter/D.sub.1A ratio of the flaky copper
powder of the present invention is normally 0.01 or more,
preferably 0.015 or more. The crystallite diameter/D.sub.1A within
the above-described range is preferable because it gives small
dimensional changes in a thick copper film, which is produced with
the paste contained the flaky copper powder, forming process, the
dimensional changes causing thermal expansion rate more notably.
And, moreover, it exhibits higher oxidation resistance in
evaporation of volatile contents process. On the other hand, the
powder having the crystallite diameter/D.sub.1A ratio below 0.01 is
not preferable, because it gives a conductive paste suffering
troubles resulting from dimensional changes in a thick copper film
forming process by the paste, the dimensional changes causing
thermal expansion rate more notably. And, moreover, it exhibits
lower oxidation resistance in evaporation of volatile contents
process.
[0036] The flaky copper powder of the present invention normally
has a D.sub.1A value of 0.3 to 8 .mu.m. The flaky copper powder
having a D.sub.1A value in the above range is preferable, because
it gives high densely the conductive paste. On the other hand, the
flaky copper powder having a D.sub.1A value below 0.3 .mu.m is not
preferable, because it gives the conductive paste of excessively
high viscosity, and the powder having a D.sub.1A value above 8
.mu.m is also not preferable, because it is difficult to thinner of
the thick copper film or produce a fine line with the conductive
paste in which it is added. The D.sub.1A value in this
specification is an average major diameter (.mu.m) observed by a
scanning electron microscope (SEM, magnification: 5,000 to 20,000)
for 10 or more flaky copper particle samples, and differs from the
D.sub.50 value, which is a 50% volumetric cumulative particle
diameter (.mu.m) determined by laser diffraction-scattering
particle size distribution measuring method.
[0037] The flaky copper powder of the present invention normally
has an aspect ratio D.sub.1A/t, i.e., D.sub.1A divided by thickness
t (.mu.m) of the flaky copper powder, of 2 to 50, preferably 2 to
20, more preferably 3 to 10. The powder having the aspect ratio
D.sub.1A/t in the above range is preferable, because it has an
increased contact area between the copper particles in the
conductive paste and tends to decrease electrical resistance of the
thick copper film prepared with the paste. On the other hand, the
powder having an aspect ratio (D.sub.1A/t) below 2 has an
insufficient contact area between the copper particles in the
conductive paste and tends to be difficult to decrease thick copper
film resistance, and that having the ratio above 50 tends to
rapidly increase viscosity of the conductive paste. Thickness t
(.mu.m) of the flaky copper powder used in this specification is an
average value determined by processing SEM images directly observed
by a scanning electron microscope.
[0038] The flaky copper powder of the present invention contains P
normally at 10 to 200 ppm, preferably 30 to 100 ppm, more
preferably 50 to 80 ppm. The powder containing P at a content in
the above range is preferable, because it tends to have higher
oxidation resistance. The content beyond the above range is not
preferable; because the powder maybe insufficient in oxidation
resistance and difficult to be flattened at below 10 ppm, and tends
to have an excessive resistance at above 200 ppm. The "ppm" used in
this specification means parts per million by weight.
[0039] The flaky copper powder of the present invention normally
has an SD/D.sub.50 ratio of 0.45 or less, preferably 0.4 or less.
The flaky copper powder having an SD/D.sub.50 ratio in the above
range is preferable, because it shows the flaky copper powder
having a sharp distribution particle size so that the conductive
paste in which it is added tend to be high densely. The flaky
copper powder having an SD/D.sub.50 ratio beyond the above range is
not preferable, because it shows the flaky copper powder having a
broader particle size distribution, hence insufficiently filling
the conductive paste in which it is added. SD used in this
specification is a standard deviation (.mu.m) of the particle size
distribution, examined by a laser diffraction-scattering particle
size distribution laser diffraction scattering particle size
distribution measuring method.
[0040] The flaky copper powder of the present invention normally
has a D.sub.90/D.sub.10 ratio of 3.0 or less, preferably 2.5 or
less. The flaky copper powder having a D.sub.90/D.sub.10 ratio
beyond the above range is not preferable, because it shows the
flaky copper powder having a broader distribution particle size and
hence the conductive paste tends to be insufficiently filling.
[0041] The flaky copper powder of the present invention normally
has a specific surface area of 0.2 to 4.0 m.sup.2/g, preferably 0.3
to 2.2 m.sup.2/g. The powder having a specific surface area above
4.0 m.sup.2/g is not preferable, because it may gives an
excessively viscous conductive paste. The specific surface area in
this specification is BET-determined one.
[0042] The flaky copper powder of the present invention normally
has a tap density of 2.0 g/cm.sup.3 or more, preferably 3.3 to 5.0
g/cm.sup.3. The powder having a tap density in the above range is
preferable, because it is well dispersible in a paste thus easy
production of a conductive paste. Moreover, space formed adequately
among flaky copper powder during formation of a conductive paste
film may ease evaporate of a volatile contents from the conductive
paste film, and thereby to increase density of the calcined film
and hence decrease electrical resistance of the resulting thick
copper film.
[0043] The flaky copper powder of the present invention is
preferably surface-treated to have an organic layer on the
particles, because it is protected from oxidation with oxygen in a
calcination atmosphere while the conductive paste film in which it
is added is calcined to form a thick copper film, and thereby to
prevent temporal increase of electrical resistance of the film.
[0044] The organic surface layer is formed by coating the flaky
copper powder particles with an organic compound. The organic
compounds useful for the present invention can be selected from
saturated fatty acids, unsaturated fatty acids, nitrogen-containing
organic compounds, sulfur-containing organic compounds and silane
coupling agents or the like.
[0045] The saturated fatty acids useful for the present invention
can be selected from enanthic acid (C.sub.6H.sub.13COOH), caprylic
acid (C.sub.7H.sub.15COOH), pelargonic acid (C.sub.8H.sub.17COOH),
capric acid (C.sub.9H.sub.19COOH), undecylic acid
(C.sub.10H.sub.21COOH), lauric acid (C.sub.11H.sub.23COOH),
tridecylic acid (C.sub.12H.sub.25COOH), myristic acid
(C.sub.13H.sub.27COOH), pentadecylic acid (C.sub.14H.sub.29COOH),
palmitic acid (C.sub.15H.sub.31COOH), heptadecylic acid
(C.sub.16H.sub.33COOH), stearic acid (C.sub.17H.sub.35COOH),
nonadecanoic acid (C.sub.18H.sub.37COOH), arachidic acid
(C.sub.19H.sub.39COOH) and behenic acid (C.sub.21H.sub.43COOH) or
the like.
[0046] The unsaturated fatty acids useful for the present invention
can be selected from acrylic acid (CH.sub.2=CHCOOH), crotonic acid
(CH.sub.3CH=CHCOOH), isocrotonic acid (CH.sub.3CH=CHCOOH),
undecylenic acid (CH.sub.2=CH(CH.sub.2).sub.9COOH), oleic acid
(C.sub.17H.sub.33COOH), elaidic acid
(CH.sub.3(CH.sub.2).sub.7CH=CH(CH.sub.2).sub.7COOH), cetoleic acid
(CH.sub.3(CH.sub.2).sub.9CH=CH(CH.sub.2).sub.9COOH), blassidic acid
(C.sub.21H.sub.41COOH), erucic acid (C.sub.21H.sub.41COOH), sorbic
acid (C.sub.5H.sub.7COOH), linoleic acid (C.sub.17H.sub.31COOH),
linolenic acid (C.sub.17H.sub.29COOH), and arachidonic acid
(C.sub.13H.sub.31COOH) or the like.
[0047] The nitrogen-containing organic compounds useful for the
present invention can be selected from triazole compounds having a
substituent, e.g., 1,2,3-benzotriazole, carboxybenzotriazole,
N',N'-bis(benzotriazolylmethyl)urea, 1H-1,2,4-triazole and
3-amino-1H-1,2,4-triazole or the like.
[0048] The sulfur-containing organic compounds useful for the
present invention can be selected from mercaptobenzothiazole,
thiocyanuric acid and 2-benzimidazolethiol or the like.
[0049] The silane coupling agents useful for the present invention
can be selected from vinyl trimethoxysilane, aminosilane,
tetramethoxysilane, methyltrimethoxysilane and
diphenyldimethoxysilane or the like.
[0050] In the present invention, the above organic compounds, oleic
acid, capric acid and stearic acid are more preferable, because
they tend to give the flaky copper powder having higher oxidation
resistance and more densely filling the conductive paste in which
it is added. In the present invention, these organic compounds,
i.e., saturated fatty acids, unsaturated fatty acids,
nitrogen-containing organic compounds, sulfur-containing organic
compounds and silane coupling agents, may be used either
individually or in combination of two or more.
[0051] The flaky copper powder of the present invention, when
surface-treated to have the surface organic layer on the particles,
is normally coated at a coating rate of 0.05 to 2 wt % on the flaky
copper powder, preferably 0.1 to 1 wt %. The coating rate of the
organic surface layer used in this specification means ratio of
weight of the surface organic layer to that of the uncoated flaky
copper particles. The powder coated at a rate in the above range is
preferable, because it improves oxidation resistance of the
conductive paste in which it is added, and tends to improve
oxidation resistance of the powder itself. On the other hand, the
powder coated at a rate above 2 wt % is not preferable, because it
tends to deteriorate temporal viscosity stability of the conductive
paste.
[0052] The flaky copper powder of the present invention, when
coated with the surface organic layer, normally has a specific
surface area of 0.1 to 3.5 m.sup.2/g, preferably 0.2 to 2.0
m.sup.2/g. The powder having a specific surface area above 3.5
m.sup.2/g is not preferable, because it gives an excessively
viscous conductive paste.
[0053] The flaky copper powder of the present invention, when
coated with the surface organic layer, normally has a tap density
of 3.0 g/cm.sup.3 or more, preferably 3.5 to 5.5 g/cm.sup.3. The
powder having a tap density in the above range is preferable,
because it is well dispersible in the paste thus make it easy
production of the conductive paste. Moreover, it makes spaces
adequately in a printed paste, and thereby to help evaporation of
volatile contents from the conductive paste when the film is
calcined and thereby to make well density of the calcined film and
hence decrease electrical resistance of the resulting thick copper
film. The flaky copper powder of the present invention can be
produced by the following method, for example.
(Method for Forming the Flaky Copper Powder of the Present
Invention)
[0054] The method for forming a flaky copper powder of the present
invention comprises four steps; the first step prepares an aqueous
solution containing a copper salt and complexing agent (hereinafter
referred to as aqueous copper salt solution); the second step an
alkali hydroxide add to the aqueous solution to prepare a first
slurry containing cupric oxide; the third step a first reducing
agent which can reduce the cupric oxide into cuprous oxide add to
the first slurry to prepare a second slurry containing cuprous
oxide; and the fourth step a second reducing agent which can reduce
the cuprous oxide add to the second slurry to obtain the copper of
flaky shape, wherein phosphoric acid and its salt are added in at
least one of the first to third steps and/or in the second slurry
in the fourth step.
(First Step)
[0055] First, the first step prepares an aqueous copper salt
solution. The aqueous copper salt solution in this invention is the
aqueous solution prepared by adding a copper salt and complexing
agent, where the copper ion (II) derived from the copper salt is
bound to the complexing agent to form a Cu complex.
[0056] The copper salts useful for the present invention can be
selected from those soluble in water, e.g., copper sulfate, copper
nitrate, copper acetate and a hydrate thereof, of which copper
sulfate pentahydrate and copper nitrate are more preferable,
because they are highly soluble as a salt gives high copper content
and easy to make the flaky copper powder composed of the
uniformly-sized particles. The complexing agents for the present
invention are those reacting with the copper ion present in the
aqueous solution. In the present invention, the Cu complex with the
copper ion (II) derived from the copper salt works to uniformly
produce CuO in the presence of an alkali hydroxide in the second
step. The complexing agents can be use amino acid and tartaric acid
or the like. The amino acids can be use aminoacetic acid, alanine,
glutamic acid and or the like, of which aminoacetic acid is more
preferable because it tends to give the uniformly-sized flaky
copper powder. These complexing agents may be used either
individually or in combination of two or more.
[0057] The aqueous copper salt solution is prepared by dissolving a
copper salt and complexing agent in water. The procedure and order
of dissolving them in water are not limited. For example, a copper
salt and complexing agent are added to water kept stirred, and the
resulting mixture is stirred. Water for the solution is preferably
pure water, ion-exchanged water, superpure water or the like
because it dissolves fine flaky copper particles and helps large
crystallite diameter. When the solution is prepared, water is
normally kept at 50 to 90.degree. C., preferably 60 to 80.degree.
C. Keeping water at a temperature in the above range is preferable,
because it makes easily production of the uniformly-sized copper
oxide particles in the subsequent step.
[0058] The aqueous copper salt solution is added with a complexing
agent normally at 0.005 to 10 moles per 1 mole of copper present in
the solution, preferably 0.01 to 5 moles. The complexing agent
added at content in the above range is preferable, because it gives
the fine flaky copper particles of large crystallite diameter and
high flatness.
[0059] The aqueous copper salt solution is added with a copper salt
normally at 10 to 50 parts by weight per 100 parts by weight of
water, preferably 20 to 40 parts by weight. The copper salt added
at content in the above range is preferable, because it gives the
highly uniformly-sized flaky copper particles.
(Second Step)
[0060] The second step adding the aqueous copper salt solution with
an alkali hydroxide to prepare a first slurry containing cupric
oxide. The first slurry for the present invention is a slurry
prepared by adding an alkali hydroxide in the aqueous copper salt
solution, in which fine particles of cupric oxide (CuO) of
precipitate in the solution. An alkali hydroxide may be added in
the form of an aqueous solution in the aqueous copper salt solution
kept stirred, the resulting solution being continuously stirred,
for example. While the first slurry is prepared, the solution is
normally kept at 50 to 90.degree. C., preferably 60 to 80.degree.
C. Keeping the solution at a temperature in the above range is
preferable, because it facilitates production of the highly
uniformly-sized flaky copper particles, with the primary particles
being efficiently prevented from agglomerating with each other.
[0061] The alkali hydroxide for the present invention functions to
convert copper in the complex present in the aqueous copper salt
solution into cupric oxide (CuO). The alkali hydroxides useful for
the present invention can be used sodium hydroxide, potassium
hydroxide, ammonia, ammonia water and or the like, of which sodium
hydroxide is more preferable because it is inexpensive and can
easily control the reaction for forming cupric oxide. An alkali
hydroxide is preferable because it helps, when kept in the form of
aqueous solution, convert copper in the complex present in the
aqueous solution into cupric oxide (CuO), when added in the
solution, to reduce variations of the flaky copper particle
diameters.
[0062] The first slurry is added with the alkali hydroxide normally
at 1.05 to 1.50 equivalents per equivalent of the copper salt,
preferably 1.10 to 1.30 equivalents. The alkali hydroxide present
at content in the above range is preferable, because it facilitates
production of the highly uniformly-sized flaky copper particles.
Moles of the copper salt and alkali hydroxide are moles as acid and
base, respectively.
[0063] In the second step, the first slurry is stirred normally for
10 to 60 minutes, preferably 20 to 40 minutes, after it is prepared
by adding the aqueous copper salt solution with an alkali
hydroxide. Continued stirring of the solution added with the alkali
hydroxide is preferable, because it sufficiently converts copper in
the complex present in the aqueous copper salt solution into cupric
oxide (CuO), thereby can be produce of the highly uniformly-sized
flaky copper particles.
(Third Step)
[0064] The third step incorporates the first slurry with a first
reducing agent which can reduce the cupric oxide into cuprous oxide
to prepare a second slurry containing cuprous oxide. The second
slurry for the present invention is a slurry prepared by adding the
first reducing agent in the first slurry, in which cuprous oxide
(CuO) separates out in the solution. The first reducing agent may
be added in the first slurry kept stirred, the resulting solution
being continuously stirred. While the second slurry is prepared,
the solution is normally kept at 50 to 90.degree. C., preferably 60
to 80.degree. C. Keeping the solution at a temperature in the above
range is preferable, because it can be produce of the highly
uniformly-sized flaky copper particles, with the primary particles
being efficiently prevented from agglomerating with each other.
[0065] The first reducing agent for the present invention functions
to reduce cupric oxide (CuO) present in the first slurry into
cuprous oxide (Cu.sub.2O). The first reducing agents for the
present invention can be use reducing sugar and hydrazine or the
like. The reducing sugars can be use glucose, fructose, lactose or
the like, of which glucose is more preferable because it can
control the reaction more easily. The above compounds may be used
either individually or in combination of two or more. The first
reducing agent is preferable because it helps, when kept in the
form of aqueous solution, quickly reduce cupric oxide (CuO) present
in the first slurry into cuprous oxide (Cu.sub.2O), when added in
the first slurry, to reduce variations of the flaky copper particle
diameter.
[0066] The second slurry is added with the first reducing agent
normally at 0.1 to 3.0 moles per 1 mole of the copper salt present
in the first slurry, preferably 0.3 to 1.5 moles. The first
reducing agent present at a content in the above range is
preferable, because it allows the reduction of cupric oxide (CuO)
into cuprous oxide (Cu.sub.2O) to proceed sufficiently, thus
facilitating synthesis of the flaky copper powder with the primary
particles agglomerating with each other to a lesser extent.
[0067] In the third step, the second slurry is stirred normally for
10 to 60 minutes, preferably 20 to 40 minutes, after it is prepared
by adding the first reducing agent in the first slurry. It is
preferred to stir the solution after adding the alkali hydroxide is
preferable, because it sufficiently reduces cupric oxide (CuO) into
cuprous oxide (Cu.sub.2O), thus can make a synthesis of the flaky
copper powder with the primary particles agglomerating with each
other to a lesser extent.
(Fourth Step)
[0068] The fourth step adds a second reducing agent which can
reduce the cuprous oxide into copper to the second slurry for
producing flaky copper powder. In the present invention, phosphoric
acid and its salt are added in at least one of the first to third
steps and/or in the second slurry in the fourth step. Therefore,
the second slurry invariably contains phosphoric acid and its salt
when the second reducing agent is added in the fourth step.
[0069] The phosphoric acid and its salt for the present invention
are those capable of supplying the phosphate ion, e.g.,
orthophosphate, pyrophosphate, metaphosphate ion or the like in the
presence of water. It is considered that P added by them in the
flaky copper power of the present invention functions to decrease
copper particle diameter and increase crystallite diameter. The
phosphoric acids and the salts thereof useful for the present
invention can be selected from phosphoric acid; polyphosphoric
acids, e.g., pyrophosphoric acid; metaphosphoric acids, e.g.,
trimetaphosphoric acid; phosphates, e.g., sodium phosphate and
potassium phosphate; polyphosphates, e.g., sodium pyrophosphate and
potassium pyrophosphate; and metaphophates, e.g., sodium
trimetaphophate and potassium trimetaphosphate or the like.
[0070] The total quantity of the phosphoric acid and its salt added
in at least one of the first to third steps and/or in the second
slurry in the fourth step is normally 0.001 to 3 moles as P
(phosphorus) per mole of copper present in the aqueous copper salt
solution or first or second slurry, preferably 0.01 to 1 mole. The
flaky copper powder added with P at a content in the above range is
preferable because it can easily obtain the highly oxidation
resistance flaky copper powder. On the other hand, P content below
0.001 moles/mole is not preferable, because of insufficient
oxidation resistance and difficulty in flattening of the flaky
copper powder. P content above 3 moles/mole is also not preferable
because of excessively increased electric resistance of the
powder.
[0071] The method of adding the second reducing agent to the second
slurry, for example, the second reducing agent may be added in the
form of aqueous solution in the second slurry kept stirred, the
resulting solution being continuously stirred. When the second
reducing agent is added in the second slurry in the fourth step,
the solution is normally kept at 50 to 90.degree. C., preferably 60
to 80.degree. C. Keeping the solution at a temperature in the above
range is preferable, because it can be produce of the highly
uniformly-sized flaky copper particles, with the primary particles
being efficiently prevented from agglomerating with each other.
[0072] The second reducing agent used in the present invention acts
to reduce cuprous oxide (Cu.sub.2O) in the second slurry into Cu.
The second reducing agent is one or more selected for at least one
selected from the group consisting of hydrazine, hydrated hydrazine
(N.sub.2H.sub.4H.sub.2O), hydrazine sulfate, hydrazine carbonate
and hydrazine chloride.
[0073] It is preferable to incorporate the second reducing agent in
the first slurry slowly and little by little while taking
substantial time rather than all at once, because it can be easy to
keep diameter of the flaky copper particles within the range
described above. Time for which it is added is normally 1 to 60
minutes, preferably 3 to 40 minutes.
[0074] In the fourth step, the second slurry is added with the
second reducing agent normally at 0.5 to 6.0 moles per 1 mole of
the copper salt present in the second slurry, preferably 0.8 to 3.0
moles. The second reducing agent present at content in the above
range is preferable, because it allows the reduction of cuprous
oxide (Cu.sub.2O) into Cu to proceed sufficiently, thus it can be
produce of the highly uniformly-sized flaky copper powder.
[0075] In the fourth step, the second slurry is stirred normally
for 20 minutes to 2 hours, preferably 40 minutes to 1.5 hours,
after it is added with the second reducing agent. Continued
stirring of the solution added with the second reducing agent is
preferable, because it sufficiently reduces cuprous oxide
(Cu.sub.2O) into Cu, thus it can be produce of the flaky copper
powder with the primary particles agglomerating with each other to
a lesser extent.
[0076] The fourth step produces the flaky copper powder in the
slurry. The powder can be recovered by filtering the slurry by a
Buchner funnel or the like, and rinse the precipitate with pure
water and then rinsed with a methanol solution or the like
containing oleic acid or the like and drying the precipitate. The
mechanisms involved in production of the flaky copper powder only
by reduction are not fully substantiated. However, it is noted that
the powder is produced in the presence of phosphoric acid and its
salt before the second reducing agent is added, based on which it
is considered that phosphoric acid and its salt trigger some
functions when cuprons oxide is reduced to copper to produce the
flaky copper powder.
[0077] The organic surface layer, when provided on the flaky copper
particles, maybe formed by a known method, for example, dry or wet,
by coating the particles with an organic compound.
(Conductive Paste of the Present Invention)
[0078] The conductive paste of the present invention is composed of
the flaky copper powder of the present invention and a resin. The
resins useful for the present invention include acrylic resin,
epoxy resin, ethyl cellulose and carboxyethyl cellulose.
[0079] The conductive paste of the present invention contains the
flaky copper powder of the present invention normally at 30 to 98
wt %, preferably 40 to 90 wt %. The paste containing the flaky
copper powder in the above range is preferable, because it gives
copper interconnections of low electrical resistance.
[0080] The flaky copper powder of the present invention can be
used, either by itself or in combination with other spherical
powder or the like, as a raw material for electrodes made by
calcining or conductive paste. Moreover, it can give conductive
paste in which the flaky copper powder is well dispersed, when
mixed with a known paste used for production of conductive paste.
The conductive paste can be used to secure conductive passages,
e.g., in circuits on printed circuit substrate, external electrodes
of ceramic condensers and or the like, and as a copper paste for
measures against EMIs.
[0081] The present invention is described by Examples, which shall
not be construed to limit the present invention.
EXAMPLE 1
[0082] Pure water (6 L) kept at 70.degree. C. was added with 4 kg
of copper sulfate pentahydrate, 120 g of aminoacetic acid and 50 g
of sodium phosphate with stirring, and the resulting aqueous
solution was further added with pure water to 8 L and continuously
kept stirred for 30 minutes.
[0083] Next, the aqueous solution was added, while it was kept
stirred, with 5.8 kg of a 25 wt % aqueous solution of sodium
hydroxide, kept stirred for 30 minutes, and further added with 1.5
kg of glucose, and kept stirred for 30 minutes.
[0084] Then, the resulting aqueous solution was added, while it was
kept stirred, with 1 kg of 100 wt % hydrated hydrazine
(N.sub.2H.sub.4H.sub.2O) slowly taking 5 minutes, and kept stirred
for 1 hour to complete the reaction.
[0085] On completion of the reaction, the resulting slurry was
filtered using a Buchner funnel, and the precipitate was rinsed
with pure water and then rinsed with methanol, and dried to prepare
the flaky copper powder.
[0086] The flaky copper powder was analyzed to measurements
D.sub.10, D.sub.50, D.sub.90, D.sub.max, SD, crystallite diameter,
P content and aspect ratio by the procedures described below. At
the same time, SD/D.sub.50 ratio and crystallite diameter/D.sub.1A
ratio were also calculated. The results are given in Tables 2 and
3.
(Measurements of D.sub.10, D.sub.50, D.sub.90, D.sub.max and
SD)
[0087] First, 0.2 g of the flaky copper powder sample was mixed
with a 0.1 wt % aqueous solution of a dispersant (SN-Dispersant
5468, manufactured by Sannobuko co., Ltd.) and a nonionic
surfactant (polyoxyethyleneoctylphenyl ether, Triton X-100,
manufactured by Wako Pure Chemical Industries, Ltd.), and dispersed
by a supersonic homogenizer (US-300T, manufactured by Nippon Seiki
co., Ltd.) for 5 minutes. Next, the particle diameters (.mu.m) at
cumulative volumes of 10, 50, 90 and 100% were determined by a
laser diffraction/scattering analyzer (MicroTrack HRA9320-X100
Model, manufactured by Nikkiso Co., Ltd., (manufactured by
Leeds+Northrup co., Ltd.) to report them as D.sub.10, D.sub.50,
D.sub.90 and D.sub.max. The standard deviation (SD, .mu.m) was
determined from the distribution particle size, obtained by the
above analysis.
(Determination of D.sub.1A)
[0088] The copper powder sample was directly observed by an SEM
(magnification: 5,000 to 20,000), where the major diameter of the
circular cross-section was measured for 200 particles to determine
the average.
(Determination of Crystallite Diameter)
[0089] The crystallite diameter was determined by an X-ray
diffractometer (RINT200V, manufactured by Rigaku Corporation co.,
Ltd.) using a crystallite analysis software.
(Analysis of P Content)
[0090] The sample powder was dissolved in diluted nitric acid, and
the solution was analyzed by an ICP emission analyzer to determine
P content, from which P content in the powder was determined.
(Determination of Aspect Ratio)
[0091] The average thickness (t, .mu.m) of the particles was
measured by a scanning electron microscope and the aspect ratio by
is calculated dividing D.sub.1A by the thickness t.
EXAMPLE 2
[0092] Pure water (6 L) kept at 70.degree. C. was added with 4 kg
of copper sulfate pentahydrate, 120 g of aminoacetic acid and 75 g
of sodium phosphate with stirring, and the resulting aqueous
solution was further added with pure water to 8 L and continuously
kept stirred for 30 minutes.
[0093] Next, the aqueous solution was added, while it was kept
stirred, with 5.8 kg of a 25 wt % aqueous solution of sodium
hydroxide, kept stirred for 30 minutes, and further added with 1.5
kg of glucose, and kept stirred for 30 minutes.
[0094] Then, the resulting aqueous solution was added, while it was
kept stirred, with 1 kg of 100 wt % hydrated hydrazine
(N.sub.2H.sub.4H.sub.2O) slowly taking 30 minutes, and kept stirred
for 1 hour to complete the reaction.
[0095] On completion of the reaction, the resulting slurry was
filtered using a Buchner funnel, and the precipitate was rinsed
with pure water and then rinsed with methanol and dried to prepare
the flaky copper powder.
[0096] The flaky copper powder was analyzed to measure D.sub.10,
D.sub.50, D.sub.90, D.sub.max, SD, crystallite diameter, P content
and aspect ratio in the same manner as in Example 1. At the same
time, SD/D.sub.50 ratio and crystallite diameter/D.sub.1A ratio
were also calculated. The results are given in Tables 2 and 3.
[0097] Moreover, the flaky copper powder prepared was subjected to
thermogravimetric analysis (TG) by the following procedure, to
determine oxidation initiation temperature. The result is given in
Table 3.
(Thermogravimetric Analysis)
[0098] The flaky copper powder was heated in air at 10.degree.
C./minute to follow weight changes of the powder.
EXAMPLE 3
[0099] Pure water (6 L) kept at 70.degree. C. was added with 4 kg
of copper sulfate pentahydrate, 120 g of aminoacetic acid and 75 g
of sodium phosphate with stirring, and the resulting aqueous
solution was further added with pure water to 8 L and continuously
kept stirred for 30 minutes.
[0100] Next, the aqueous solution was added, while it was kept
stirred, with 5.8 kg of a 25 wt % aqueous solution of sodium
hydroxide, kept stirred for 30 minutes, and further added with 1.5
kg of glucose, and stirring was continued for 30 minutes.
[0101] Then, the resulting aqueous solution was added, while it was
kept stirred, with 1 kg of 100 wt % hydrated hydrazine
(N.sub.2H.sub.4H.sub.2O) slowly taking 30 minutes, and kept stirred
for 1 hour to complete the reaction.
[0102] On completion of the reaction, the resulting slurry was
filtered using a Buchner funnel, and the precipitate was rinsed
with pure water and then with methanol. The filtration residue was
immersed for one hour in a methanol solution which is obtained by
dissolving 1 g of oleic acid in 3 L of methanol, and then rinsed
with methanol and dried to prepare the flaky copper powder.
[0103] The resulting powder was put on filter paper placed on the
Buchner funnel basal plane, to which a solution with 1 g of oleic
acid dispersed in 1 L of methanol was added, allowed to stand for
30 minutes, and filtered under a vacuum by a vacuum pump.
[0104] The flaky copper powder left on the glass filter paper was
taken out, dried at 70.degree. C. for 5 hours, to prepare the flaky
copper powder coated with oleic acid.
[0105] The flaky copper powder was analyzed to measure D.sub.10,
D.sub.50, D.sub.90, D.sub.max, SD, crystallite diameter, P content
and aspect ratio in the same manner as in Example 1. At the same
time, SD/D.sub.50 ratio and crystallite diameter/D.sub.1A ratio
were also calculated. The results are given in Tables 2 and 3.
EXAMPLE 4
[0106] Pure water (6 L) kept at 70.degree. C. was added with 4 kg
of copper sulfate pentahydrate and 120 g of aminoacetic acid, and
the resulting aqueous solution was further added with pure water to
8 L and continuously kept stirred for 30 minutes.
[0107] Next, the aqueous solution was added, while it was kept
stirred, with 75 g of sodium phosphate and then with 5.8 kg of a 25
wt % aqueous solution of sodium hydroxide, kept stirred for 30
minutes, further added with 1.5 kg of glucose, and kept stirred for
30 minutes.
[0108] Then, the resulting aqueous solution was added, while it was
kept stirred, with 1 kg of 100 wt % hydrated hydrazine
(N.sub.2H.sub.4H.sub.2O ) slowly taking 30 minutes, and kept
stirred for 1 hour to complete the reaction.
[0109] On completion of the reaction, the resulting slurry was
filtered using a Buchner funnel, and the precipitate was rinsed
with pure water and then rinsed with methanol, and dried to prepare
the flaky copper powder.
[0110] The flaky copper powder was analyzed to measure D.sub.10,
D.sub.50, D.sub.90, D.sub.max, SD, crystallite diameter, P content
and aspect ratio in the same manner as in Example 1. At the same
time, SD/D.sub.50 ratio and crystallite diameter/D.sub.1A ratio
were also calculated. The results are given in Tables 2 and 3.
[0111] Moreover, the flaky copper powder prepared was subjected to
thermogravimetric analysis (TG) in the same manner as in Example2
to determine oxidation initiation temperature. The result is given
in Table 3.
EXAMPLE 5
[0112] Pure water (6 L) kept at 70.degree. C. was added with 4 kg
of copper sulfate pentahydrate, 120 g of aminoacetic acid with
stirring, and the resulting aqueous solution was further added with
pure water to 8 L and continuously kept stirred for 30 minutes.
[0113] Next, the aqueous solution was added, while it was kept
stirred, with 5.8 kg of a 25 wt % aqueous solution of sodium
hydroxide, kept stirred for 30 minutes, added with 75 g of sodium
phosphate and then with 1.5 kg of glucose, and kept stirred for 30
minutes.
[0114] Then, the resulting aqueous solution was added, while it was
kept stirred, with 1 kg of 100 wt % hydrated hydrazine
(N.sub.2H.sub.4H.sub.2O) slowly taking 30 minutes, and kept stirred
for 1 hour to complete the reaction.
[0115] On completion of the reaction, the resulting slurry was
filtered using a Buchner funnel, and the precipitate was rinsed
with pure water and then rinsed with methanol, and dried to prepare
the flaky copper powder.
[0116] The flaky copper powder was analyzed to measure D.sub.10,
D.sub.50, D.sub.90, D.sub.max, SD, crystallite diameter, P content
and aspect ratio in the same manner as in Example 1. At the same
time, SD/D.sub.50 ratio and crystallite diameter/D.sub.1A ratio
were also calculated. The results are given in Tables 2 and 3.
[0117] Moreover, the flaky copper powder prepared was subjected to
thermogravimetric analysis (TG) in the same manner as in Example
2to determine oxidation initiation temperature. The result is given
in Table 3.
EXAMPLE 6
[0118] Pure water (6 L) kept at 70.degree. C. was added with 4 kg
of copper sulfate pentahydrate, 120 g of aminoacetic acid with
stirring, and the resulting aqueous solution was further added with
pure water to 8 L and continuously kept stirred for 30 minutes.
[0119] Next, the aqueous solution was added, while it was kept
stirred, with 5.8 kg of a 25 wt % aqueous solution of sodium
hydroxide, kept stirred for 30 minutes, added with 1.5 kg of
glucose, and kept stirred for 30 minutes.
[0120] Then, the resulting aqueous solution was added, while it was
kept stirred, 75 g of sodium phosphate and then with 1 kg of 100 wt
% hydrated hydrazine (N.sub.2H.sub.4H.sub.2O) slowly taking 30
minutes, and kept stirred for 1 hour to complete the reaction.
[0121] On completion of the reaction, the resulting slurry was
filtered using a Buchner funnel, and the precipitate was rinsed
with pure water and then rinsed with methanol, and dried to prepare
the flaky copper powder.
[0122] The flaky copper powder was analyzed to measure D.sub.10,
D.sub.50, D.sub.90, D.sub.max, SD, crystallite diameter, P content
and aspect ratio in the same manner as in Example 1. At the same
time, SD/D.sub.50 ratio and crystallite diameter/D.sub.1A ratio
were also calculated. The results are given in Tables 2 and 3.
[0123] Moreover, the flaky copper powder prepared was subjected to
thermogravimetric analysis (TG) in the same manner as in Example 2
to determine oxidation initiation temperature. The result is given
in Table 3.
COMPARATIVE EXAMPLE 1
[0124] Pure water (6 L) kept at 70.degree. C. was added with 4 kg
of copper sulfate pentahydrate, 120 g of aminoacetic acid with
stirring, and the resulting aqueous solution was further added with
pure water to 8 L and continuously kept stirred for 30 minutes.
[0125] Next, the aqueous solution was added, while it was kept
stirred, with 5.8 kg of a 25 wt % aqueous solution of sodium
hydroxide, kept stirred for 30 minutes, added with 1.5 kg of
glucose, and kept stirred for 30 minutes.
[0126] Then, the resulting aqueous solution was added, while it was
kept stirred, with 1 kg of 100 wt % hydrated hydrazine
(N.sub.2H.sub.4H.sub.2O) slowly taking 30 minutes, and kept stirred
for 1 hour to complete the reaction.
[0127] On completion of the reaction, the resulting slurry was
filtered using a Buchner funnel, and the precipitate was rinsed
with pure water and then rinsed with methanol. The precipitate was
immersed in a methanol solution obtained by dissolving 1 g of oleic
acid in 3 L of methanol for one hour, and then rinsed with methanol
and dried to prepare the copper powder.
[0128] The copper powder was ball milled in the presence of 0.7 mm
zirconia beads as a medium and methanol as a solvent for 60 minutes
using a mill (DYNO-MILL KDL, manufactured by Willy A. Bachofen AG
Maschinenfabrik co., Ltd.) for plastic deformation of the copper
powder.
[0129] The copper powder was analyzed to measure D.sub.10,
D.sub.50, D.sub.90, D.sub.max, SD, crystallite diameter, P content
and aspect ratio in the same manner as in Example 1. At the same
time, SD/D.sub.50 ratio and crystallite diameter/D.sub.1A ratio
were also calculated. The results are given in Tables 2 and 3.
[0130] Moreover, the copper powder prepared was subjected to
thermogravimetric analysis (TG) in the same manner as in Example 2
to determine oxidation initiation temperature. The result is given
in Table 3. TABLE-US-00001 TABLE 1 25 wt % aqueous Copper Amino-
Sodium solution of 100 wt % Pure sulfate acetic phos- sodium
hydrated water pentahydrate acid phate hydroxide Glucose hydrazine
(L) (kg) (g) (g) (kg) (kg) (kg) Example 1 8 4 120 50 5.8 1.5 1
Example 2 8 4 120 75 5.8 1.5 1 Example 3 8 4 120 75 5.8 1.5 1
Example 4 8 4 120 75 5.8 1.5 1 Example 5 8 4 120 75 5.8 1.5 1
Example 6 8 4 120 75 5.8 1.5 1 Comparative 8 4 120 0 5.8 1.5 1
Example 1
[0131] TABLE-US-00002 TABLE 2 Plastic deformation D.sub.10 D.sub.50
D.sub.90 D.sub.max D.sub.90/ D.sub.IA treatment (.mu.m) (.mu.m)
(.mu.m) (.mu.m) D.sub.10 (.mu.m) Example 1 Not employed 0.72 1.02
1.46 10 2.03 1.2 Example 2 Not employed 1.42 2.08 2.96 7 2.08 2.2
Example 3 Not employed 1.41 2.10 2.99 7 2.12 2.3 Example 4 Not
employed 1.03 1.41 2.07 4 2.01 1.5 Example 5 Not employed 0.92 1.24
1.76 4 1.91 1.3 Example 6 Not employed 0.72 0.99 1.41 3 1.96 1.0
Comparative Employed 2.14 3.93 7.48 19 3.49 2.5 Example 1
[0132] TABLE-US-00003 TABLE 3 Crystallite Crystallite Oxidation SD
diameter diameter/ Aspect P content initiation (.mu.m) SD/D.sub.50
(nm) D.sub.1A ratio (ppm) temperature Example 1 0.26 0.25 44 0.037
5 55 --*.sup.1 Example 2 0.59 0.28 36 0.016 7 43 260 Example 3 0.60
0.29 36 0.016 7 43 --*.sup.1 Example 4 0.37 0.26 38 0.025 6 46 250
Example 5 0.31 0.25 40 0.031 6 33 230 Example 6 0.26 0.26 39 0.039
5 29 230 Comparative 2.01 0.51 19 0.008 6 0 180 Example 1
*.sup.1Not measured
[0133] As shown in Tables 1 to 3, the flaky copper powder prepared
from a raw material added with phosphoric acid and its salt is
fine, sharp in particle size distribution, large in crystallite
diameter, and can have a flaky shape without using plastic
deformation treatment, as employed in COMPARATIVE Example 1. The
smaller crystallite diameter observed in Comparative Example 1
results from plastic deformation treatment.
INDUSTRIAL APPLICABILITY
[0134] The present invention provides a flaky copper powder, a
method for producing the same and a conductive paste, can be used
for a copper paste or for material to the paste. The technology
used for formation of electrical circuits on printed circuit
substrate and securing electrical continuity of external electrodes
of ceramic condensers and or the like.
* * * * *