U.S. patent application number 12/666864 was filed with the patent office on 2010-08-05 for spherical copper fine powder and process for producing the same.
This patent application is currently assigned to NIPPON MINING & METALS CO., LTD.. Invention is credited to Takahiro Haga.
Application Number | 20100192728 12/666864 |
Document ID | / |
Family ID | 40185528 |
Filed Date | 2010-08-05 |
United States Patent
Application |
20100192728 |
Kind Code |
A1 |
Haga; Takahiro |
August 5, 2010 |
Spherical Copper Fine Powder and Process for Producing the Same
Abstract
Provided is spherical copper fine powder in which the average
grain size of copper fine powder is 0.05 .mu.m or more and 0.25
.mu.m or less. Additionally provided is a method of producing
spherical copper fine powder including the steps of preparing a
slurry by adding cuprous oxide to an aqueous medium containing an
additive of natural resin, polysaccharide or a derivative thereof,
adding 5 to 50% of an acid aqueous solution to the slurry at a time
within 15 minutes, and thereby performing disproportionation. The
process enables speedy, efficient and stable production of metallic
copper particles controlled in particle shape or particle size,
particularly copper fine powder having small particles in size.
Inventors: |
Haga; Takahiro; (Ibaraki,
JP) |
Correspondence
Address: |
HOWSON & HOWSON LLP
501 OFFICE CENTER DRIVE, SUITE 210
FORT WASHINGTON
PA
19034
US
|
Assignee: |
NIPPON MINING & METALS CO.,
LTD.
Tokyo
JP
|
Family ID: |
40185528 |
Appl. No.: |
12/666864 |
Filed: |
June 17, 2008 |
PCT Filed: |
June 17, 2008 |
PCT NO: |
PCT/JP2008/061033 |
371 Date: |
January 22, 2010 |
Current U.S.
Class: |
75/370 |
Current CPC
Class: |
B22F 9/20 20130101 |
Class at
Publication: |
75/370 |
International
Class: |
B22F 9/18 20060101
B22F009/18 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 28, 2007 |
JP |
2007-169869 |
Claims
1-2. (canceled)
3. A method of producing spherical copper fine powder, including
the steps of preparing a slurry by adding cuprous oxide to an
aqueous medium containing an additive of natural resin,
polysaccharide or a derivative thereof, adding 5 to 50% of an acid
aqueous solution to the slurry at a time within 15 minutes, and
thereby performing disproportionation.
4. The method of producing spherical copper fine powder according
to claim 3, further including the steps of performing solid-liquid
separation and water cleaning to the copper fine powder slurry
obtained after the disproportionation, additionally performing
alkali solution-based reduction treatment thereto, and repeating
the solid-liquid separation and water cleaning of the obtained fine
powder slurry to obtain copper powder.
5. The method of producing spherical copper fine powder according
to claim 4, wherein acid-based acidification treatment is performed
during the course of repeating the solid-liquid separation and
water cleaning of the fine powder slurry.
6. The method of producing spherical copper fine powder according
to claim 5, further including the steps of filtering the copper
powder after the final water cleaning treatment, and additionally
performing vacuum drying thereto in order to obtain the copper
powder.
7. The method of producing spherical copper fine powder according
to claim 6, wherein the average grain size of the copper fine
powder is 0.05 .mu.m or more and 0.25 .mu.m or less.
8. The method of producing spherical copper fine powder according
to claim 7, wherein the specific surface area (BET) of the copper
fine powder is 2.5 m.sup.2/g or more and 15.0 m.sup.2/g or
less.
9. The method of producing spherical copper fine powder according
to claim 8, wherein the average grain size of the copper fine
powder is 0.05 .mu.m or more and 0.21 .mu.m or less.
10. The method of producing spherical copper fine powder according
to claim 4, further including the steps of filtering the copper
powder after the final water cleaning treatment, and additionally
performing vacuum drying thereto in order to obtain the copper
powder.
11. The method of producing spherical copper fine powder according
to claim 4, wherein the average grain size of the copper fine
powder is 0.05 .mu.m or more and 0.25 .mu.m or less.
12. The method of producing spherical copper fine powder according
to claim 4, wherein the specific surface area (BET) of the copper
fine powder is 2.5 m.sup.2/g or more and 15.0 m.sup.2/g or
less.
13. The method of producing spherical copper fine powder according
to claim 4, wherein the average grain size of the copper fine
powder is 0.05 .mu.m or more and 0.21 .mu.m or less.
Description
TECHNICAL FIELD
[0001] The present invention relates to spherical metal copper
particles having a controlled grain shape or grain size, and in
particular to a method of producing spherical copper fine powder
which can achieve speedy, efficient and stable production of
metallic copper particles controlled in particle shape or particle
size, as well as to the spherical copper fine powder obtained
thereby.
BACKGROUND ART
[0002] As methods of producing copper powder, the electrolytic
method and the atomization method have been used conventionally.
The copper powder prepared based on these methods can be favorably
used in powder metallurgy of oil retaining bearings and electrical
brushes, but finer particles with controlled grain size and grain
shape are being demanded for use as conductive fillers such as
paint, paste and resin in which the demands thereof are expected to
increase in the near future.
[0003] The methods of producing such fine metal copper particles
that suit for the foregoing usage are: [0004] (1) hydrogen pressure
reduction method of copper salt aqueous solution; [0005] (2)
chemical additive reduction method of copper salt aqueous solution;
and [0006] (3) thermal decomposition method of organic copper
salt.
[0007] However, there are problems such as equipment costs and
operating costs being expensive, and there are drawbacks in the
yield is inferior upon controlling the particles to be of a
prescribed grain shape and grain size, surface oxidation occurs
easily, or the chemical costs are expensive, so these are no
satisfactory methods.
[0008] In light of the above, it has been known that the method of
reacting cuprous oxide particles and acid enables the favorable
control of the grain shape and grain size of the metal copper
particles to be created, and by additionally managing the reactive
conditions such as the pH, temperature, and average retention time,
it is possible to adjust the prescribed grain shape and grain size,
and produce high purity metal copper fine particles.
[0009] In addition, it has also become known that it is possible to
obtain chain-shaped agglomerated/bonded powder by selecting the
reactive condition (for instance, refer to Patent Document 1).
[0010] Patent Document 1 was published in 1985, and was extremely
high technology in terms copper powder production at that time.
[0011] The outline of the technology above is as follows: [0012] 1)
a method of collecting metal copper particles by reacting cuprous
oxide particles and acid to generate a copper salt aqueous solution
and metal copper particles, and performing solid-liquid separation,
including the steps of continuously pouring a diluted acid solution
into a reaction tank at a flow rate of obtaining a prescribed
average retention time corresponding to the target grain size of
the metal copper particles to be produced, adding cuprous oxide
particles at an adding rate of maintaining the pH of the reaction
tank at a prescribed value and causing a reaction at a liquid
temperature of 50.degree. C. or less, discharging a slurry of the
metal copper particles to be created at a rate that corresponds
with the flow rate of the solution, collecting the metal copper
particles via a solid-liquid separation means from the discharged
slurry of the metal copper particles slurry, and thereby producing
metal copper particles having a controlled grain size, and [0013]
2) a method of collecting metal copper particles by reacting
cuprous oxide particles and acid to generate a copper salt aqueous
solution and metal copper particles, and performing solid-liquid
separation, wherein reaction is performed while maintaining the
liquid temperature capable of obtaining the prescribed grain shape
and grain size.
[0014] Nevertheless, in recent years, even finer and more uniform
copper powder is being demanded, and technology for producing such
copper powder quickly is also being sought. In light of the above,
the present inventors proposed a method of producing copper fine
powder in which the disproportionation start temperature is set to
10.degree. C. or less upon producing copper fine powder by
performing acid-based disproportionation to cuprous oxide in an
aqueous solution containing an additive of natural resin,
polysaccharide or a derivative thereof (refer to Patent Document
2).
[0015] This method enables the speedy production of fine copper
fine powder, and is extremely effective. Nevertheless, the average
grain size of this copper fine powder is at a level of 0.5 .mu.m to
3.0 .mu.m, and the present inventors were searching for a method
for even finer copper powder. [0016] [Patent Document 1] Japanese
Patent Laid-Open Publication No. S60-33304 [0017] [Patent Document
2] Japanese Patent Laid-Open Publication No. 2005-256012
DISCLOSURE OF THE INVENTION
[0018] An object of the present invention is to provide a method of
producing spherical copper fine powder which provides speedy,
efficient and stable production of metallic copper particles
controlled in particle shape or particle size, particularly copper
fine powder having smaller particle sizes, as well as to provide
the spherical copper fine powder obtained thereby.
[0019] The present invention provides: [0020] 1) Spherical copper
fine powder, wherein the average grain size of copper fine powder
is 0.05 .mu.m or more and 0.25 .mu.m or less; and [0021] 2) The
spherical copper fine powder according to paragraph 1) above,
wherein the specific surface area (BET) of copper fine powder is
2.5 m.sup.2/g or more and 15.0 m.sup.2/g or less.
[0022] Here, the term "spherical" means a shape in which the ratio
of the short diameter and long diameter of the individual copper
particles is 150% or less, and in particular 120% or less. Thus, a
shape in which the ratio of the short diameter and long diameter
exceeds 150% is of a flat shape, and is not referred to as
"spherical."
[0023] With the present invention, even in cases where flat copper
fine powder gets mixed in, the amount thereof is 20% or less of the
overall amount, preferably 10% or less, and more preferably 5% or
less. In reality, desirably, such flat copper fine powder is not
contained.
[0024] The present invention additionally provides: [0025] 3) A
method of producing spherical copper fine powder, including the
steps of preparing slurry by adding cuprous oxide to an aqueous
medium containing an additive of natural resin, polysaccharide or a
derivative thereof, adding 5 to 50% of an acid aqueous solution to
the slurry at a time within 15 minutes, and thereby performing
disproportionation.
[0026] As the additive, natural rubber or gelatin may be used. As
specific examples of such an additive, pine resin, gelatin, glue,
carboxymethylcellulose (CMC), starch, dextrin, gum arabic, casein
and the like are effective.
[0027] Though the slurry concentration of the cuprous oxide is
suitably 500 g/L or less, the process is usually carried out at 300
g/L or less. This slurry concentration can be suitably selected
without any particular limitation. If the slurry concentration of
the cuprous oxide is made to be extremely low, since the reaction
will not progress, it will just increase costs.
[0028] The molar ratio (predetermined number of acids/number of
moles of slurry) is desirably 1.00 to 2.00 upon implementing the
process. There will be no problem with the reaction so long as the
molar ratio is equivalent (1.0) or higher. The effect will not
change even if acid is added excessively. Contrarily, if the acid
concentration is too high, the calorific value upon adding acid to
the cuprous oxide slurry will increase, the temperature of the
reaction system will increase, which is expected to be
disadvantageous in obtaining finer powder, and in terms of cost,
disadvantageous as well.
[0029] Meanwhile, if the acid concentration is low, the reaction
rate will consequently deteriorate, and this will be
disadvantageous in obtaining finer powder. In light of the above,
it is desirable to set the molar ratio (predetermined number of
acids/number of moles of slurry) to 1.00 to 2.00.
[0030] Desirably, the disproportionation start temperature is set
to 10.degree. C. or less in producing copper fine powder by
performing acid-based disproportionation in an aqueous medium. This
is effective in forming copper fine powder with fine particles.
[0031] Moreover, it is extremely important that this acid aqueous
solution be added at a time, namely, at a time within 15 minutes.
It is thereby possible to obtain spherical copper fine powder
having an average grain size of 0.25 .mu.m or less. The
disproportionation based on the speedy addition of acid aqueous
solution is able to achieve fine spherical copper powder. The
reason why this collective addition in a short time is effective in
producing copper fine powder is not necessarily clear.
[0032] Nevertheless, this short-period disproportionation is
considered effective on the growth of copper particles. Thus,
collective addition in a short time is effective in achieving finer
powder. Preferably, the adding time of the acid aqueous solution is
short, that is, 3 minutes or less, and more preferably 1 minute or
less.
[0033] The present invention further provides: [0034] 4) The method
of producing spherical copper fine powder according to paragraph 3)
above, further including the steps of performing solid-liquid
separation and water cleaning to the copper fine powder slurry
obtained after the disproportionation, additionally performing
alkali solution-based reduction treatment thereto, and repeating
the solid-liquid separation and water cleaning of the obtained fine
powder slurry to obtain copper powder. This alkali solution-based
reduction treatment yields the effect of achieving a uniform
chemical composition of the copper particles by reducing the
cuprous oxide that has not yet reacted with the oxide remaining in
the obtained copper fine powder. [0035] 5) The method of producing
spherical copper fine powder according to paragraph 3) or paragraph
4) above, wherein acid-based acidification treatment is performed
during the course of repeating the solid-liquid separation and
water cleaning of the fine powder slurry. This acid-based
acidification treatment is able to enhance effect of the rust
prevention in performing rust treatment. [0036] 6) The method of
producing spherical copper fine powder according to any one of
paragraphs 3) to 5) above, further including the steps of filtering
the copper powder after the final water cleaning treatment, and
additionally performing vacuum drying thereto in order to obtain
the copper powder; [0037] 7) The method of producing spherical
copper fine powder according to any one of paragraphs 3) to 6)
above, wherein the average grain size of the copper fine powder is
0.05 .mu.m or more and 0.25 .mu.m or less; and [0038] 8) The method
of producing spherical copper fine powder according to any one of
paragraphs 3) to 7) above, wherein the specific surface area (BET)
of the copper fine powder is 2.5 m.sup.2/g or more and 15.0
m.sup.2/g or less.
[0039] The method of producing copper fine powder according to the
present invention yields superior effects of achieving a spherical
grain shape and arbitrarily controlling the grain size, and
enabling speedy, efficient and stable production of copper fine
powder having smaller particle sizes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] [FIG. 1] A diagram showing the outline of the production
flow of the spherical copper fine powder
[0041] [FIG. 2] An FE-SEM photograph of the spherical copper fine
powder
BEST MODE FOR CARRYING OUT THE INVENTION
[0042] The cuprous oxide particles may be produced with a publicly
known method such as from a copper salt aqueous solution via
cuprous chloride. Specifically, since there is no direct
relationship between the grain size of the cuprous oxide particles
to be used and the grain size of the metal copper particles
obtained by the method of the present invention, coarse cuprous
oxide particles may be used.
[0043] Sulfuric acid is commonly used for acid, but nitric acid,
phosphoric acid, or acetic acid may be used. It is not necessary to
specify the type of acid. In case sulfuric acid is used,
disproportionation is to generate a copper sulfate aqueous solution
and metal copper particles based on the following reaction
formula.
Cu.sub.2O+H.sub.2SO.sub.4=Cu.dwnarw.+CuSO.sub.4+H.sub.2O
[0044] If the additive ratio of acid to the cuprous oxide is
increased, then the pH of the reaction system will decrease, and
the pH will increase in the opposite case. Thus, the pH can be
controlled based on the additive ratio of acid or cuprous
oxide.
[0045] The pH is maintained to be 2.5 or less, and desirably in the
vicinity of 1.0 in order to avoid the generation of precipitation
of impurities during the reaction and to promptly advance the
reaction without leaving any residual cuprous oxide.
[0046] Upon producing copper fine powder based on
disproportionation of cuprous oxide, acid-based disproportionation
is performed in an aqueous medium including an additive (protective
colloid) of natural resin, polysaccharide or a derivative thereof.
This is a major characteristic of this invention.
[0047] This additive (protective colloid) works to inhibit the
growth of particles, and also works to reduce the frequency that
the particles come in contact with each other. Accordingly, this is
effective in producing fine particles.
[0048] As the additive, natural rubber or gelatin may be used. As
specific examples of such an additive, pine resin, gelatin, glue,
carboxymethylcellulose (CMC), starch, dextrin, gum arabic, casein
and the like are effective. In particular, if glue is used, it is
possible to achieve fine powder having an average grain size of
0.25 .mu.m or less, and yield an agglomeration inhibiting
effect.
[0049] The liquid temperature during the reaction is set to
30.degree. C. or less, and preferably to 10.degree. C. or less upon
producing metal copper fine particles. If the liquid temperature
exceeds 30.degree. C., there is tendency of the metal copper fine
particles becoming agglomerated and bonded with each other. In
particular, it is desirable to set the disproportionation start
temperature to 10.degree. C. or less in order to seek finer powder.
As a result of lowering the reaction temperature, the growth of
particles can be effectively inhibited, and even finer powder can
be obtained.
[0050] With temperature of 10.degree. C. or less being maintained
till the end of the reaction, there will be a better effect. It is
also possible to set the reaction temperature to exceed 30.degree.
C. In the foregoing case, a special grain shape can be obtained by
leveraging the tendency of the metal copper particles becoming
agglomerated and bonded with each other. As described above, the
grain shape and grain size of the metal copper particles to be
generated can be controlled based on the reaction temperature. The
present invention covers this kind of temperature control.
[0051] Moreover, upon producing copper fine powder by performing
acid-based disproportionation of cuprous oxide in the present
invention, it is extremely important that this acid aqueous
solution be added at a time. Specifically, the acid aqueous
solution needs to be added at a time within 15 minutes, preferably
within 3 minutes and more preferably within 1 minute. It is thereby
possible to obtain spherical copper fine powder having an average
grain size of 0.25 .mu.m or less.
[0052] The disproportionation based on the speedy addition of acid
aqueous solution is able to achieve fine spherical copper powder.
Thus, by speeding up the adding rate of acid, nucleation will
prevail over the growth of particles, and a finer copper powder can
be obtained.
[0053] This short-period disproportionation is considered to have
an effect of inhibiting the growth of copper particles. Thus,
collective addition in a short time is essential in achieving finer
powder.
[0054] The average grain size of the present invention is desirably
a small value, but if the value is smaller than the average grain
size (D.sub.50), the actual value of D.sub.10 becomes 0.06 .mu.m,
and D.sub.min as the minimum value of grain size distribution will
become even smaller. However, with the disproportionation process,
which is a wet reaction, since 0.05 .mu.m is lower limit of
production, the average grain size is set to 0.05 .mu.m.
[0055] Since D.sub.min as the minimum value of the grain size
distribution is even smaller, much finer copper powder will be
included. In addition, with the disproportionation process, which
is a wet reaction, since 0.05 .mu.m is estimated to be lower limit
of production, the average grain size is set to 0.05 .mu.m.
[0056] Meanwhile, the smaller the average grain size becomes, the
larger the specific surface area tends to be, but they are not
necessarily proportional. In addition, the measured value and the
theoretical value of the specific surface area are different.
[0057] When presuming that the copper fine powder is a true
spherical shape, the true density of copper is 8.93 g/cm.sup.3, and
calculating the volume, surface area, and mass from the specific
surface area with the average grain size (D.sub.50) as the
diameter, D.sub.50=0.05 .mu.m, and the theoretical specific surface
area will be 13.44 m.sup.2/g.
[0058] Nevertheless, with respect to the relationship between the
average grain size (D.sub.50) and the specific surface area, the
tendency is: the smaller the average grain size becomes, the less
the difference between the theoretical value and the measured value
becomes. This is considered to be because the surface state
(irregularities on the outermost surface) will affect the specific
surface area when the average grain size is large, while in case
the average grain size becomes small, the influence of the size
itself becomes greater than the surface state and the difference
between the theoretical value and the measured value becomes
less.
[0059] In summary, if the lower limit of D.sub.50 is set to 0.05
.mu.m, it is anticipated that the upper limit of the specific
surface area will become approximately 15.0 m.sup.2/g. Thus, the
upper limit of the BET specific surface area was set to 15.0
m.sup.2/g.
[0060] The ultrafine spherical copper powder obtained as described
above could become agglomerated in the air or liquid. Nevertheless,
the agglomerate itself can be dispersed once again with a means
such as applying ultrasonic waves in the aqueous solution. It
should be understood that this is based on the premise that the
initial particles are spherical copper fine powder having an
average grain size of 0.25 .mu.m or less. This is because spherical
fine copper powder cannot be obtained by attempting to achieve
finer powder by way of pulverization.
[0061] When performing batch-type reaction, acid may be added to
the slurry of cuprous oxide particles, or contrarily cuprous oxide
particles or a slurry of cuprous oxide particles may be added to
the acid solution.
[0062] In all cases, the obtained metal copper particles are of
high purity and have abundant surface activity. Accordingly,
appropriate rust prevention treatment is performed to the metal
copper particles obtained from the solid-liquid separation, and the
metal copper particles are subsequently dried. FIG. 1 shows the
outline of the production flow of the spherical copper fine
powder.
[0063] The spherical copper fine powder is produced through the
processes as shown in FIG. 1: dissolving additive.fwdarw.obtaining
slurry (process of adding cuprous oxide into an aqueous medium
containing an additive to form a slurry).fwdarw.disproportionation
(addition of acid aqueous solution).fwdarw.cleaning.fwdarw.rust
prevention.fwdarw.filtering.fwdarw.drying.fwdarw.pulverizing.fwdarw.sorti-
ng.
Examples
[0064] The present invention is now explained in detail with
reference to the Examples. These Examples are merely illustrative,
and the present invention shall in no way be limited thereby. In
other words, various modifications and other embodiments based on
the technical spirit claimed in the claims shall be included in the
present invention as a matter of course.
Example 1
[0065] Glue of 8 g was dissolved in 7 liters of deionized water,
1000 g of cuprous oxide was added and suspended therein in mixing
the solution, and cuprous oxide slurry was cooled to 7.degree. C.
Cuprous oxide in the slurry was approximately 143 g/L.
[0066] Subsequently, 2000 cc of diluted sulfuric acid
(concentration 24%: 9N, molar ratio (acid aqueous solution/slurry):
1.5) cooled to 7.degree. C. was added in 1 minute. The created
copper fine powder was cleaned, subject to rust prevention
treatment, and thereafter dried to obtain 420 g of copper fine
powder.
[0067] The reaction ended approximately 1 minute after the
addition. The FE-SEM photograph of the spherical copper fine powder
obtained as described above is shown in FIG. 2. As shown in FIG. 2,
the average grain size of the copper fine powder was 0.09 .mu.m. It
is evident that the addition of cooled diluted sulfuric acid in 1
minute is extremely effective in attaining copper fine powder. The
specific surface area BET was 6.66 m.sup.2/g. This Example 1 is a
particularly favorable example even among the conditions of the
other Examples.
Example 2 to Example 8
[0068] Examples of cases using, as the additive, pine resin,
gelatin, carboxymethylcellulose (CMC), starch, dextrin, gum arabic,
and casein are shown. In the foregoing case, the copper powder was
created under all the same conditions as Example 1 other than
substituting the additive. Consequently, the foregoing additives
are all effective, but the addition of "glue" in Example 1 yielded
the most favorable result.
Comparative Example 1 and Comparative Example 2
[0069] The copper fine powder was inspected in each case with
polyethylene glycol (PEG) selected as the additive and without it.
The results are shown in Comparative Examples 1 and 2. Then, the
copper powder was created under the same conditions as Example 1
except the change of additive. Consequently, the additive of
Comparative Example 1 yielded no effect, and in the case without
additive showed inferior results as well; the grain size of the
copper powder increased and copper powder having a low BET specific
surface area was obtained.
[0070] The average grain size and the specific surface area of the
spherical copper fine powder pertaining to the foregoing Examples
and Comparative Examples were measured. The average grain size was
measured based on the laser diffraction/dispersion grain size
distribution measurement method, and the value of the weight
cumulative grain size D.sub.50 was adopted. The specific surface
area was measured based on the BET method.
[0071] The results of foregoing Example 1 to Example 8 and
Comparative Example 1 to Comparative Example 2 are shown in Table
1.
TABLE-US-00001 TABLE 1 Acid addition Reaction start Average grain
BET specific Additive time temperature(.degree. C.) size (.mu.m)
surface area (m.sup.2/g) Example 1 Glue 1 minute 7 0.09 6.66
Example 2 Pine resin Same as above Same as above 0.21 4.67 Example
3 Gelatin Same as above Same as above 0.20 4.56 Example 4 CMC Same
as above Same as above 0.18 5.05 Example 5 Starch Same as above
Same as above 0.19 4.95 Example 6 Dextrin Same as above Same as
above 0.20 4.66 Example 7 Gum Arabic Same as above Same as above
0.25 4.00 Example 8 Casein Same as above Same as above 0.19 4.85
Comparative Example PEG Same as above Same as above 7.32 6.46
Comparative Example No additive Same as above Same as above 4.90
4.50 CMC: carboxymethylcellulose, PEG: polyethylene glycol
Example 9 to Example 12, Example 16
[0072] Next, taking typical Example 1 as the reference, results
from changing the acid addition time are shown in Example 9 to
Example 12. Then, the acid addition time was changed from 5 seconds
to 15 minutes. Here, other than changing the acid addition time,
the copper powder was created under the same conditions as Example
1. Consequently, with the acid addition time being shorter, it was
possible to obtain copper powder having a small grain size and a
low BET specific surface area. Since the acid addition time also
affects the grain size and BET specific surface area, desirably the
acid addition time is as short as possible. Though there is no need
to take time in adding the acid, it is desirable to add the acid
within approximately 15 minutes. The results were the same even
when using the additives of pine resin, gelatin,
carboxymethylcellulose (CMC), starch, dextrin, gum arabic, and
casein.
Comparative Example 3 and Comparative Example 4
[0073] Next, the cases when the acid addition time was 16 minutes
and 80 minutes, which are outside the conditions of the present
invention, are shown in Comparative Example 3 and Comparative
Example 4. Then, conditions other than changing the acid addition
time and the copper powder, were the same as Example 1. In all
cases, the grain size of the copper powder increased and copper
powder having a low BET specific surface area was obtained, and
yielded inferior results.
[0074] The results of Example 9 to Example 12 and Comparative
Example 3 to Comparative Example 4 are shown in Table 2.
TABLE-US-00002 TABLE 2 BET specific Acid addition Average grain
surface area time size (.mu.m) (m.sup.2/g) Example 1 1 minute 0.09
6.66 Example 9 3 minutes 0.18 4.39 Example 10 2 minutes 0.15 4.94
Example 11 30 seconds 0.09 6.70 Example 12 5 seconds 0.08 6.75
Example 16 15 minutes 0.20 6.15 Comparative Example 3 16 minutes
0.40 3.80 Comparative Example 4 80 minutes 0.80 3.50 Additive:
glue, Reaction start temperature: 7.degree. C.
Example 13 to Example 17
[0075] Next, taking typical Example 1 as the reference, results
from changing the reaction start temperature are shown in Example
13 to Example 17. Then, the reaction start temperature was changed
from 0 to 30.degree. C. Here, other than changing the reaction
start temperature, the copper powder was created under the same
conditions as Example 1.
[0076] Consequently, with the reaction start temperature being
lower, it was possible to obtain copper powder having a small grain
size and a large BET specific surface area. The results were the
same even when using the additives of pine resin, gelatin,
carboxymethylcellulose (CMC), starch, dextrin, gum arabic, and
casein.
Comparative Example 5
[0077] Next, a case where the reaction start temperature was
50.degree. C., which is outside the conditions of the present
invention, is shown in Comparative Example 5. Then, other than
changing the reaction start temperature, the copper powder was
created under the same conditions as Example 1. In all cases, the
grain size of the copper powder increased and copper powder having
a low BET specific surface area was obtained, and yielded inferior
results.
[0078] The results of Example 13 to Example 17 and Comparative
Example 5 are shown in Table 3.
TABLE-US-00003 TABLE 3 Reaction start BET specific temperature
Average grain surface area (.degree. C.) size (.mu.m) (m.sup.2/g)
Example 1 7 0.09 6.66 Example 13 30 0.25 6.10 Example 14 20 0.18
6.00 Example 15 10 0.12 6.10 Comparative Example 5 50 1.20 5.76
Additive: glue, Acid addition time: 1 minute
[0079] As described above, by following the conditions of the
present invention, namely, adding cuprous oxide in an aqueous
medium including an additive of natural resin, polysaccharide or a
derivative thereof in order to prepare a slurry containing 10 to
300 g/L of cuprous oxide, adding 5 to 50% of an acid aqueous
solution at a molar ratio (predetermined number of acids/number of
moles of slurry) of 1.00 to 2.00 at a time to the slurry within 3
minutes, and thereby performing disproportionation, it is possible
to obtain favorable spherical copper fine powder.
[0080] Consequently, it is possible to obtain spherical copper fine
powder having an average grain size of 0.25 .mu.m or less.
Moreover, with this spherical copper fine powder, it is possible to
yield a specific surface area (BET) of 4.0 m.sup.2/g or more.
INDUSTRIAL APPLICABILITY
[0081] A spherical copper fine powder produced according to the
present invention is very effective since the grain size of the
powder is small and uniform. The powder is useful not only for oil
retaining bearings and electrical brushes, but also as conductive
fillers to be used as paint, paste, resin and the like.
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