U.S. patent application number 13/741873 was filed with the patent office on 2014-02-27 for silica particles and method of preparing the same.
This patent application is currently assigned to FUJI XEROX CO., LTD.. The applicant listed for this patent is FUJI XEROX CO., LTD.. Invention is credited to Takeshi IWANAGA, Yasunobu KASHIMA, Yuka ZENITANI.
Application Number | 20140057107 13/741873 |
Document ID | / |
Family ID | 50148233 |
Filed Date | 2014-02-27 |
United States Patent
Application |
20140057107 |
Kind Code |
A1 |
ZENITANI; Yuka ; et
al. |
February 27, 2014 |
SILICA PARTICLES AND METHOD OF PREPARING THE SAME
Abstract
Provided are silica particles having two maximum values in
number particle size distribution, wherein in the two maximum
values, a particle size ratio (a maximum value of a small-size
side/a maximum value of a large-size side) between a maximum value
of a large-size side and a maximum value of a small-size side is
from 0.02 to 0.3, and a number ratio (a number of silica particles
having a maximum value of the small-size side/number of silica
particles having a maximum value of the large-size side) is from 1
to 100, and particles within a range of 10% from the large-size
side of the silica particles have an average circularity of from
0.65 to 0.90 and an average shrinkage ratio of from 10 to 50.
Inventors: |
ZENITANI; Yuka; (Kanagawa,
JP) ; IWANAGA; Takeshi; (Kanagawa, JP) ;
KASHIMA; Yasunobu; (Kanagawa, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJI XEROX CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
FUJI XEROX CO., LTD.
Tokyo
JP
|
Family ID: |
50148233 |
Appl. No.: |
13/741873 |
Filed: |
January 15, 2013 |
Current U.S.
Class: |
428/402 ;
423/335 |
Current CPC
Class: |
Y10T 428/2982 20150115;
C09C 1/30 20130101; C01P 2004/53 20130101; C01B 33/12 20130101;
C01P 2004/32 20130101; C01B 33/145 20130101; C01B 33/148 20130101;
C01P 2004/62 20130101 |
Class at
Publication: |
428/402 ;
423/335 |
International
Class: |
C01B 33/12 20060101
C01B033/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 24, 2012 |
JP |
2012-185694 |
Claims
1. Silica particles having two maximum values in number particle
size distribution, wherein in the two maximum values, a particle
size ratio (a maximum value of a small-size side/a maximum value of
a large-size side) is from 0.02 to 0.3, and a number ratio (a
number of silica particles having a maximum value of the small-size
side/number of silica particles having a maximum value of the
large-size side) is from 1 to 100, and particles within a range of
10% from the large-size side of the silica particles have an
average circularity of from 0.65 to 0.90 and an average shrinkage
ratio of from 10 to 50.
2. The silica particles according to claim 1, wherein the particle
size ratio is from 0.03 to 0.2.
3. The silica particles according to claim 1, wherein the particle
size ratio is from 0.04 to 0.1.
4. The silica particles according to claim 1, wherein a particle
size of the maximum value of the large-size side is from 50 nm to
500 nm.
5. The silica particles according to claim 1, wherein a particle
size of the maximum value of the large-size side is from 80 nm to
400 nm.
6. The silica particles according to claim 1, wherein a particle
size of the maximum value of the large-size side is from 100 nm to
300 nm.
7. The silica particles according to claim 1, wherein a particle
size of the maximum value of the small-size side is from 5 nm to 80
nm.
8. The silica particles according to claim 1, wherein the number
ratio is from 10 to 80.
9. The silica particles according to claim 1, wherein a number
average particle diameter is from 100 nm to 200 nm.
10. A method of preparing silica particles, comprising: preparing
an alkaline catalyst solution in which an alcohol-containing
solvent contains an alkaline catalyst at a concentration of from
0.6 mol/L to 1.0 mol/L; and supplying tetraalkoxysilane and an
alkaline catalyst into the alkaline catalyst solution, wherein the
supplying satisfies the following conditions, within a range of
from A/2 to A, there is a part where C/B is from 15
(mol/L)/{(mol/min)L} to 60 (mol/L)/{(mol/min)L}, wherein, A
represents the total amount of the tetraalkoxysilane supplied, B
represents (a flow rate of the tetraalkoxysilane supplied)/(a total
amount of a solution formed when the tetraalkoxysilane and an
alkaline catalyst are supplied into the alkaline catalyst
solution), and C represents a concentration of water in a reaction
system.
11. The method of preparing silica particles according to claim 10,
wherein a concentration of the alkaline catalyst is in a range of
from 0.63 mol/L to 0.78 mol/L.
12. The method of preparing silica particles according to claim 10,
wherein C/B is from 20 (mol/L)/{(mol/min)L} to 50
(mol/L)/{(mol/min)L}.
13. The method of preparing silica particles according to claim 10,
wherein C/B is from 25 (mol/L)/{(mol/min)L} to 40
(mol/L)/{(mol/min)L}.
14. The method of preparing silica particles according to claim 10,
wherein the amount of the tetraalkoxysilane supplied is 0.002
mol/(molmin) or more and less than 0.006 mol/(molmin) based on the
mole number of the alcohol in the alkaline catalyst solution.
15. The method of preparing silica particles according to claim 10,
wherein the tetraalkoxysilane is selected from tetramethoxysilane,
tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane.
16. The method of preparing silica particles according to claim 10,
wherein the alkaline catalyst is selected from ammonia, urea,
monoamine, and a quaternary ammonium salt.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based on and claims priority under 35
USC 119 from Japanese Patent Application No. 2012-185694 filed Aug.
24, 2012.
BACKGROUND
[0002] 1. Technical Field
[0003] The present invention relates to silica particles and a
method of preparing the same.
[0004] 2. Related Art
[0005] As an attempt at improving properties of materials, two or
more same kinds of inorganic particles differing in size, shape, or
the like are mixed together.
SUMMARY
[0006] According to an aspect of the invention, there is provided
silica particles having two maximum values in number particle size
distribution, wherein in the two maximum values, a particle size
ratio (a maximum value of a small-size side/a maximum value of a
large-size side) is from 0.02 to 0.3, a number ratio (number of
silica particles having a maximum value of the small-size
side/number of silica particles having a maximum value of the
large-size side) is from 1 to 100, and particles within a range of
10% from the large-size side of the silica particles have an
average circularity of from 0.65 to 0.90 and an average shrinkage
ratio of from 10 to 50.
DETAILED DESCRIPTION
[0007] Hereinafter, exemplary embodiments as an example of the
present invention will be described.
[0008] Silica Particles
[0009] The silica particles according to the present exemplary
embodiment are silica particles having two maximum values in number
particle size distribution, wherein in the two maximum values, a
particle size ratio (a maximum value of a small-size side/a maximum
value of a large-size side) between a maximum value of a large-size
side and a maximum value of a small-size side is from 0.02 to 0.3,
a number ratio (a number of silica particles having a maximum value
of the small-size side/number of silica particles having a maximum
value of large-size side) is from 1 to 100, and particles within a
range of 10% from the large-size side of the silica particles have
an average circularity of from 0.65 to 0.90 and an average
shrinkage ratio of from 10 to 50.
[0010] The silica particles according to the present exemplary
embodiment improve the fluidity of a substance to which the
particles are to be attached.
[0011] Though unclear, the reason is considered to be as below.
[0012] The silica particles having two maximum values (large-size
side and small-size side) in the number particle size distribution
are silica particles having two different types of particle sizes
and numbers of particles. The silica particles having the above
particle size ratio and number ratio are considered to be particles
in which the particle size of the particles of the large-size side
is larger than that of the particles of the small-size side by 10/3
times to 50 times, and the number of the particles of the
small-size side is larger than that of the particles of the
large-size side by 1 time to 100 times.
[0013] It is considered that, among such silica particles, when the
particles of the large-size side are attached to a substance to
which the particles are to be attached, this makes the particles of
the small-size side be easily attached onto the surface of the
substance exposed between the attached particles of the large-size
side, whereby a coverage ratio of the substance is improved. It is
considered that since the particles of the large-size side function
as a spacer, and exposure of the substance to which the particles
are to be attached is inhibited by the particles of the small-size
side, substances to which the particles are to be attached are
inhibited from adhering to each other.
[0014] In addition, the silica particles within a range 10% from
the large-size side of the silica particles have many concavities
and convexities and an irregular shape overall as silica particles
compared to spherical silica particles, the degree of surface
smoothness of these silica particles is low compared to spherical
silica particles, and the surface area thereof is large.
Accordingly, it is considered that in a state where such silica
particles having these characteristics are attached to a substance
to which the particles are to be attached, the particles are
inhibited from moving (showing uneven distribution) to or being
embedded in concavities of the substance, whereby the state where
the silica particles are attached to the substance is maintained.
It is also considered that loss of the silica particles resulting
from stress concentration caused when a mechanical load is applied
to the silica particles is inhibited.
[0015] For the above reasons, the silica particles according to the
present exemplary embodiment are considered to improve the fluidity
of a substance to which the particles are to be attached.
[0016] Hereinafter, the silica particles of the present exemplary
embodiment will be described.
[0017] --Particle Size Ratio--
[0018] In the silica particles according to the present exemplary
embodiment, among the two maximum values in number particle size
distribution, a particle size ratio (a maximum value of a
small-size side/a maximum value of a large-size side) between a
maximum value of large-size side and a maximum value of a
small-size side is from 0.02 to 0.3, preferably from 0.03 to 0.2,
and even more preferably from 0.04 to 0.1.
[0019] If the particle size ratio of the silica particles is less
than 0.02, this makes it difficult for the silica particles to
cover a substance to which the particles are to be attached, and
substances to which the particles are to be attached easily adhere
to each other. Consequently, it is difficult for the silica
particles to improve the fluidity of the substance.
[0020] On the other hand, if the particle size ratio of the silica
particles exceeds 0.3, this makes it difficult for the silica
particles to cover a substance to which the particles are to be
attached, and substances to which the particles are to be attached
easily adhere to each other. Consequently, it is difficult for the
silica particles to improve the fluidity of the substance.
[0021] The particle size in the maximum value of the large-size
side of the silica particles is preferably from 50 nm to 500 nm,
more preferably from 80 nm to 400 nm, and even more preferably from
100 nm to 300 nm. The particle size in the maximum value of the
small-size side is preferably from 2 nm to 100 nm, more preferably
from 5 nm to 80 nm, and even more preferably from 10 nm to 50
nm.
[0022] The particle size ratio of the silica particles is defined
by the ratio of the particle size of the maximum value of the
small-size side to the particle size in the maximum value of the
large-size side in the number particle size distribution of the
silica particles. In addition, the particle size ratio of the
silica particles is calculated as follows. First, in a body of
resin particles (for example, polyester resin, a weight average
molecular weight Mw=50000) having a volume average particle
diameter of 100 .mu.m, specific silica particles are dispersed, and
then the particles are observed using a Scanning Electron
Microscope. The obtained image of the particles is analyzed,
thereby obtaining a number particle size distribution of the silica
particles. Subsequently, based on the distribution pattern, the
size of particles in the large-size side and the size of particles
in the small-size side are obtained respectively from the maximum
value of the large-size side and the maximum value of small-size
side. Finally, from the size of particles of the small-size side
and the size of particles of the large-size side, the particle size
ratio of the silica particles is calculated.
[0023] --Number Ratio--
[0024] In the silica particles according to the present exemplary
embodiment, among the two maximum values in the number particle
size distribution, a number ratio (a number of silica particles
having a maximum value of the small-size side/a number of silica
particles having a maximum value of the large-size side) between
the maximum value of the large-size side and the maximum value of
the small-size side is from 1 to 100, preferably from 10 to 80, and
more preferably from 30 to 60.
[0025] If the number ratio of the silica particles is less than 1,
this makes it difficult for the silica particles to cover a
substance to which the particles are to be attached, and substances
to which the particles are to be attached easily adhere to each
other. Consequently, it is difficult for the silica particles to
improve the fluidity of the substance.
[0026] On the other hand, if the number ratio of the silica
particles exceeds 100, the number of particles of the large-size
side becomes extremely small compared to the number of particles of
the small-size side. This makes it difficult for the particles of
large-size side to function as a spacer, and substances to which
the particles are to be attached easily adhere to each other.
Consequently, it is difficult for the silica particles to improve
the fluidity of the substance.
[0027] The number ratio of the silica particles is defined by the
ratio of the number of the particle sizes in the maximum value of
the small-size side to the number of the particle sizes in the
maximum value of the large-size side in the number particle size
distribution obtained by the particle size ratio of the silica
particles. In addition, the number ratio of the silica particles is
obtained as follows. First, specific silica particles are dispersed
in a body of resin particles (for example, a polyester resin,
weight average molecular weight Mw=50000) having a volume average
particle diameter of 100 .mu.m, and then the particles are observed
using a Scanning Electron Microscope. The obtained image of the
particles is analyzed, thereby obtaining a number distribution of
the particle sizes. Subsequently, the number of particles of which
the particle size is within maximum particle size.+-.10% (within a
range of from -10% to +10%) of the large-size side and the number
of particles of which the particle size is within maximum particle
size.+-.10% (within a range of from to +10%) of the small-size side
are calculated. Finally, from the obtained number of particles of
the large-size side and the number of particles of the small-size
side, the number ratio of the silica particles is calculated.
[0028] --Average Circularity--
[0029] The average circularity of primary particles within a range
of 10% from the large-size side of the silica particles of the
present exemplary embodiment is from 0.65 to 0.90, preferably from
0.70 to 0.85, and even more preferably from 0.75 to 0.80.
[0030] If the average circularity of the silica particles is less
than 0.65, the silica particles have a shape of a sphere in which a
ratio of length/width is large. Therefore, when a mechanical load
is applied to the silica particles, stress concentration is caused,
so the loss of particles is easily caused. Moreover, a substance to
which the particles are to be attached does not easily maintain
fluidity. Further, when the silica particles according to the
present exemplary embodiment are prepared by a sol-gel method, it
is difficult to prepare silica particles having an average
circularity of primary particles of less than 0.65.
[0031] On the other hand, if the average circularity of the silica
particles exceeds 0.90, the shape of the silica particles becomes
close to a sphere. Accordingly, when the silica particles are
attached to a substance to which the particles are to be attached,
the particles show uneven distribution and become embedded in
concavities, and this makes it difficult to improve the fluidity of
the substance.
[0032] In addition, in order to obtain the circularity of the
silica particles, primary particles obtained after the silica
particles are dispersed in resin particles (polyester, a weight
average molecular weight Mw=50000) having a particle size of 100
.mu.m are observed by a Scanning Electron Microscope. From the
result of the analysis performed on the obtained image of the
primary particles, the circularity is obtained as "100/SF2"
calculated from the following formula.
Circularity (100/SF2)=4.pi..times.(A/I.sup.2)
[0033] In the above formula, I represents a perimeter of the
primary particles in the image, and A represents a projected area
of the primary particles.
[0034] Moreover, the average circularity of the primary particles
of the silica particles is obtained as a 50% circularity in
cumulative frequency of circle-equivalent diameters of 100 primary
particles obtained by the above image analysis.
[0035] --Average Shrinkage Ratio--
[0036] An average shrinkage ratio of the primary particles within a
range of 10% from the large-size side of the silica particles of
the present exemplary embodiment is from 10 to 50, preferably from
20 to 45, and more preferably from 30 to 40.
[0037] If the average shrinkage ratio of the silica particles is
less than 10, the surface of the silica particles becomes smooth,
and the amount of silanol groups on the surface of the silica
particles becomes smaller than the amount of silanol groups of the
silica particles of which the surface is not smooth, whereby the
amount of water held in the surface becomes small. Moreover, the
state where the silica particles are attached to a substance to
which the particles are to be attached is not easily maintained.
Consequently, it is difficult for the silica particles to improve
the fluidity of the substance.
[0038] On the other hand, if the average shrinkage ratio of the
silica particles exceeds 50, this makes it difficult to prepare the
silica particles according to the present exemplary embodiment by a
sol-gel method. In addition, attaching the silica particles to the
substance to which the particles are to be attached becomes
difficult. Consequently, it is difficult for the silica particles
to improve the fluidity of the substance.
[0039] In order to obtain the shrinkage ratio of the silica
particles, the silica particles are dispersed in resin particles
(polyester, a weight average molecular weight Mw=50000) having a
volume average particle diameter of 100 .mu.m, and then primary
particles of the silica particles are observed by a Scanning
Electron Microscope. From the result of analysis performed on the
obtained planar image of the primary particles, the shrinkage ratio
is calculated by the following formula.
Shrinkage ratio=(1-H/I).times.100
[0040] In the above formula, H represents an envelope perimeter of
the silica particles in the image, and I represents a perimeter of
the silica particles in the image. The envelope perimeter refers to
a perimeter that is obtained when the apexes of convexities of the
silica particles in the planar image are connected to each other
with a shortest distance. The perimeter refers to a length of the
outline itself of the silica particles in the planar image. The
shrinkage ratio is an index indicating to what degree the particle
has shrunk compared to a convex hull. The greater the shrinkage
ratio, the rougher the surface and the larger the surface area.
[0041] In addition, the average shrinkage ratio of the silica
particles is calculated as an average of the shrinkage ratio of
each of 100 silica particles that is calculated by the above
formula.
[0042] In order to determine the average circularity and average
shrinkage ratio of the particles within a range of 10% from the
large-size side of the silica particles, based on the number
particle size distribution measured by image analysis, a cumulative
distribution is drawn from the large-size side for divided particle
size ranges (channels), the particle sizes of which the number is
within a range of cumulative 10% from the large-size side is
measured, and the average circularity and average shrinkage ratio
of the particles within a range of cumulative 10% are measured.
[0043] --Number Average Particle Diameter--
[0044] The number average particle diameter of whole silica
particles is, for example, preferably from 100 nm to 200 nm, more
preferably from 105 nm to 180 nm, and even more preferably from 110
nm to 160 nm.
[0045] In order to define a number average particle diameter
D.sub.50p, based on the measured particle size distribution, a
cumulative distribution is drawn from the small-size side in terms
of the number of particles for divided particle size ranges
(channels), and the particle size which is cumulative 50% in terms
of the number is defined as D.sub.50p. Specifically, the number
average particle diameter D.sub.50p is obtained as follows. By
using a number distribution obtained by image analysis, a
cumulative distribution is drawn, and a particle size D.sub.50p
which is cumulative 50% in terms of the number is obtained.
[0046] Method of Preparing Silica Particles
[0047] The method of preparing silica particles according to the
present exemplary embodiment is a preparation method for obtaining
the silica particles according to the above exemplary embodiment.
Specifically, the method is as follows.
[0048] The method of preparing silica particles according to the
present exemplary embodiment is a method including a step of
preparing an alkaline catalyst solution in which an
alcohol-containing solvent contains an alkaline catalyst at a
concentration of 0.6 mol/L to 1.0 mol/L (hereinafter, called "a
step of preparing an alkaline catalyst solution" in some cases),
and a step of supplying tetraalkoxysilane and an alkaline catalyst
into the alkaline catalyst solution (hereinafter, called "a
supplying step" in some cases), wherein provided that a total
amount of the tetraalkoxysilane supplied is A, a flow rate of the
tetraalkoxysilane supplied/a total amount of a solution formed when
the tetraalkoxysilane and the alkaline catalyst are supplied into
the alkaline catalyst solution is B, and a concentration of water
in a reaction system is C, at any point in time when the amount of
the tetraalkoxysilane supplied falls within a range of from A/2 to
A, a state where C/B is from 15 (mol/L)/{(mol/min)/L} to 60
(mol/L)/{(mol/min)/L} is created.
[0049] That is, the method of preparing silica particles according
to the present exemplary embodiment is a method in which while each
of the tetraalkoxysilane as a raw material and the alkaline
catalyst as a catalyst is being separately supplied in the above
relationship in the presence of alcohol containing the alkaline
catalyst at the above concentration, the tetraalkoxysilane is
reacted to generate the silica particles by a sol-gel method.
[0050] In the method of preparing silica particles according to the
present exemplary embodiment, by the above technique, the silica
particles which have two maximum values (large-size side and
small-size side) in number particle size distribution and of which
the particles of the large-size side have an irregular shape are
easily obtained. Specifically, for example, it is easy to obtain
silica particles having two maximum values in number particle size
distribution, wherein among the two maximum values, a particle size
ratio (a maximum value of a small-size side/a maximum value of a
large-size side) between the maximum value of a large-size side and
the maximum value of the small-size side is from 0.02 to 0.3, a
number ratio (a number of silica particles having a maximum value
of the small-size side/a number of silica particles having a
maximum value of the large-size side) is from 1 to 100, and the
particles within a range of 10% from the large-size side of the
silica particles have an average circularity of from 0.65 to 0.90
and an average shrinkage ratio of from 10 to 50. Though unclear,
the reason is considered to be as below.
[0051] In the method of preparing silica particles according to the
present exemplary embodiment, the supplying step is divided into
two stages. The two stages include a stage where the amount of the
tetraalkoxysilane supplied is 0 or more and less than A/2, and a
stage where the amount is from A/2 to A.
[0052] First, the stage where the amount of the tetraalkoxysilane
supplied is 0 or more and less than A/2 will be described.
[0053] In the alcohol-containing solvent, when the
tetraalkoxysilane and an alkaline catalyst are supplied
respectively into the alkaline catalyst solution containing an
alkaline catalyst, the tetraalkoxysilane supplied into the alkaline
catalyst solution reacts, whereby core particles are formed. It is
considered that, at this time, if the concentration of the alkaline
catalyst in the alkaline catalyst solution falls within the above
range, core particles having an irregular shape are generated while
the generation of coarse aggregates such as secondary aggregates is
being inhibited. The reason is considered to be as follows. The
alkaline catalyst not only has a catalytic action, but also
contributes to the shape and dispersion stability of the core
particles by being coordinated to the surface of the generated core
particles. However, if the amount of the alkaline catalyst is
within the above range, the alkaline catalyst does not evenly cover
the surface of the core particles (that is, the alkaline catalyst
shows uneven distribution and becomes attached to the surface of
the core particles). Accordingly, though the dispersion stability
of the core particles is maintained, the surface tension and
chemical affinity of the core particles are unevenness in some
parts, so core particles having an irregular shape are
generated.
[0054] In addition, if the supply of the tetraalkoxysilane and the
supply of the alkaline catalyst are continued respectively, the
generated core particles grow due to the reaction of the
tetraalkoxysilane, whereby the silica particles are obtained. It is
considered that, at this time, if the tetraalkoxysilane and the
alkaline catalyst are supplied while their amounts supplied is
being maintained in the above relationship, the generation of
coarse aggregates such as secondary aggregates is inhibited, and at
the same time, the core particles having an irregular shape grow
while retaining the irregular shape. The reason is considered to be
as below. If the amount of the tetraalkoxysilane and alkaline
catalyst supplied is set in the above relationship, while the
dispersed state of the core particles is being maintained, the
partial concentration of the surface tension and the chemical
affinity on the surface of the core particles is maintained.
Accordingly, growth of the core particles while maintaining the
irregular shape is caused.
[0055] Next, the stage where the amount of the tetraalkoxysilane
supplied is from A/2 to A will be described.
[0056] At the stage where the particles of the large-size side that
have an irregular shape have grown, in a state where C/B is from 15
(mol/L)/{(mol/min)/L} to 60 (mol/L)/{(mol/min)/L}, that is, in a
state where the concentration of water in the solution in which the
silica particles are generated is set to be low compared to a case
of generating spherical silica particles, and the amount of the
tetraalkoxysilane supplied into the alkaline catalyst solution is
set to be large compared to the initial stage of the supplying
step, the tetraalkoxysilane and the alkaline catalyst are supplied.
If the tetraalkoxysilane and the alkaline catalyst are supplied in
this state, since the amount of water is small in this state, a
hydrolysis reaction is caused slowly. Consequently, it is
considered that the concentration of unreacted monomers
(tetraalkoxysilane) increases, so a probability that the monomers
may collide with each other increases. Therefore, it is considered
that new core particles to be an origin of the particles of the
small-size side are formed easily. In addition, it is considered
that at any point in time at the stage where the amount is from A/2
to A, if the tetraalkoxysilane and the alkaline catalyst are
supplied in the above state, new core particles to be an origin of
the particles of the small-size side are formed easily.
[0057] That is, it is considered that, in the present exemplary
embodiment, by generating the core in two stages, and by generating
the core of the particles of the large-size side before generating
the core of the particles of the small-size side, two types of
silica particles (particles of large-size side and particles of
small-size side) differing in the particle size are generated.
[0058] As described above, in the method of preparing silica
particles according to the present exemplary embodiment, by the
above technique, it is easy to obtain silica particles which have
two maximum values (large-size side and the small-size side) in
number particle size distribution and in which the particles of the
large-size side have an irregular shape.
[0059] In addition, it is considered that, in the method of
preparing silica particles according to the present exemplary
embodiment, the generated core particles having an irregular shape
grow while maintaining the irregular shape, and the silica
particles are obtained in this manner, whereby the silica particles
which are resistant to a mechanical load and not easily broken are
obtained.
[0060] Further, in the method of preparing silica particles
according to the present exemplary embodiment, the
tetraalkoxysilane and the alkaline catalyst are respectively
supplied into the alkaline catalyst solution, and the
tetraalkoxysilane is reacted to generate particles. Accordingly,
compared to the case of preparing silica particles having an
irregular shape by a sol-gel method of the related art, the total
amount of the alkaline catalyst used is reduced, and consequently,
a step of removing the alkaline catalyst may be omitted. It is
considered that this is particularly advantageous for the case
where the silica particles are applied to products requiring a high
purity.
[0061] Hereinafter, the respective step will be described.
[0062] First, the step of preparing an alkaline catalyst solution
will be described.
[0063] In the step of preparing an alkaline catalyst solution, an
alcohol-containing solvent is prepared, and an alkaline catalyst is
added thereto to prepare an alkaline catalyst solution.
[0064] The alcohol-containing solvent may be, for example, a
solvent consisting only of alcohol, or a mixed solvent containing
another solvent like water, ketones such as acetone, methyl ethyl
ketone, and methyl isobutyl ketone, cellosolves such as methyl
cellosolve, ethyl cellosolve, butyl cellosolve, and cellosolve
acetate, and ethers such as dioxane and tetrahydrofuran, if
necessary. In the case of the mixed solvent, the amount of alcohol
based on another solvent is preferably 80% by weight or more and
more preferably 90% by weight or more.
[0065] In addition, examples of the alcohol include lower alcohols
such as methanol and ethanol.
[0066] The alkaline catalyst refers to a catalyst for accelerating
the reaction (a hydrolysis reaction and a condensation reaction) of
tetraalkoxysilane, and examples thereof include basic catalysts
such as ammonia, urea, monoamines, and quaternary ammonium salts.
Among these, ammonia is particularly preferable.
[0067] The concentration (content) of the alkaline catalyst is
preferably from 0.6 mol/L to 1.0 mol/L, more preferably from 0.63
mol/L to 0.78 mol/L, and even more preferably from 0.66 mol/L to
0.75 mol/L.
[0068] If the concentration of the alkaline catalyst is less than
0.6 mol/L, dispersibility of the core particles in the process of
growth among the generated core particles becomes unstable.
Accordingly, coarse aggregates such as secondary aggregates are
generated, or the particles are gelated, so silica particles are
not obtained.
[0069] On the other hand, if the concentration of the alkaline
catalyst exceeds 1.0 mol/L, the generated core particles are
stabilized too much. Accordingly, spherical core particles are
generated, and core particles with an irregular shape having an
average circularity of 0.90 or less are not obtained. As a result,
silica particles having an irregular shape are not obtained.
[0070] In addition, the concentration of the alkaline catalyst
refers to a concentration based on the alcohol catalyst solution
(alkaline catalyst+alcohol-containing solvent).
[0071] Next, the supplying step will be described.
[0072] The supplying step is a step of generating silica particles
by supplying the tetraalkoxysilane and the alkaline catalyst
respectively into the alkaline catalyst solution and reacting (a
hydrolysis reaction and a condensation reaction) the
tetraalkoxysilane in the alkaline catalyst solution.
[0073] Further, this supplying step is divided into two stages
including a stage where the amount of the tetraalkoxysilane
supplied is 0 or more and less than A/2 and a stage where the
amount is from A/2 to A. Hereinafter, the two stages in the
supplying step will be described.
[0074] 1) Stage where Amount of Tetraalkoxysilane Supplied is 0 or
More and Less than A/2
[0075] In this stage, at the initial stage of supplying
tetraalkoxysilane, core particles to be an origin of the particles
of the large-size side are generated by the reaction of the
tetraalkoxysilane (stage of core particle generation), and then the
core particles grow (stage of core particle growth). In this stage,
C/B is preferably in a state where C/B exceeds 60
(mol/L)/{(mol/min)/L}.
[0076] 2) Stage where Amount of Tetraalkoxysilane Supplied is from
A/2 to A
[0077] In this stage, the tetraalkoxysilane and the alkaline
catalyst are continuously supplied into the alkaline catalyst
solution respectively, and at any point in time when the amount of
the tetraalkoxysilane supplied falls within the above range, C/B is
placed in a state where C/B is from 15 (mol/L)/{(mol/min)/L} to 60
(mol/L)/{(mol/min)/L}. After core particles to be an origin of
particles of the small-size side are generated (stage of core
particle generation), these particles grow (stage of core particle
growth). In addition, core particles to be particles of the
large-size side also grow. Thereafter, silica particles are
generated.
[0078] C/B is defined as a ratio of C (concentration of water) in
the reaction system to B (flow rate of the tetraalkoxysilane
supplied based on the total amount of the solution into which the
tetraalkoxysilane and the alkaline catalyst have been supplied) in
the alkaline catalyst solution in which silica particles are
generated. The value of C/B is an index showing the ratio of water
to the tetraalkoxysilane supplied into the reaction system by being
newly supplied dropwise in a certain reaction scale.
[0079] Herein, the each value of C and B is a value at each point
in time when each of the values of C/B is obtained, and the total
amount of the solution is an amount of the solution, in which the
supplied alkaline catalyst has been dissolved in a solvent,
including the solvent. In addition, the words "in the reaction
system" refers to the alkaline catalyst solution for preparing
silica particles of the present exemplary embodiment.
[0080] C/B is from 15 (mol/L)/{(mol/min)/L} to 60
(mol/L)/{(mol/min)/L}, preferably from 20 (mol/L)/{(mol/min)/L} to
50 (mol/L)/{(mol/min)/L}, and more preferably from 25
(mol/L)/{(mol/min)/L} to 40 (mol/L)/{(mol/min)/L}.
[0081] When C/B is less than 15, dispersibility of the silica
particles becomes unstable, so the silica slurry is gelated. On the
other hand, if C/B exceeds 60, the stage of core generation is not
divided into two stages. Accordingly, the obtained silica particles
do not have two maximum values in number particle size
distribution.
[0082] Herein, as methods of setting C/B within the above range, 1)
increasing the amount of tetraalkoxysilane supplied dropwise, 2)
decreasing the concentration of water during the reaction by
increasing the concentration of aqueous ammonia supplied dropwise,
3) decreasing the amount of water charged initially, and the like
are exemplified.
[0083] In the method of preparing silica particles according to the
present exemplary embodiment, at any point in time when the amount
of the tetraalkoxysilane supplied is from A/2 to A, a state where
C/B is within the above range is created. The rate at which C/B is
within the above range is preferably 20% or higher, preferably 50%
or higher, more preferably 80% or higher, and most preferably 100%,
when the amount of the tetraalkoxysilane supplied is from A/2 to
A.
[0084] In addition, the rate at which the state where C/B is within
the above range is calculated at any point in time when the amount
of the tetraalkoxysilane supplied is from A/2 to A. For example,
the points may be continuous or intermittent. Specifically, for
example, when the rate at which C/B is within the above range is
50%, examples of the points include continuous points in time of
the initial stage where the amount of the tetraalkoxysilane
supplied is from A/2 to A (for example, from A/2 to 3 A/4),
continuous points in time after this stage (for example, from 3 A/4
to A), continuous points in time in the middle of the stage (for
example, from 5 A/8 to 7 A/8 and the like), and the like.
[0085] Examples of the tetraalkoxysilane supplied into the alkaline
catalyst solution include tetramethoxysilane, tetraethoxysilane,
tetrapropoxysilane, tetrabutoxysilane, and the like. Among these,
in view of the controllability of the reaction rate and the shape,
particle size, and particle size distribution of the silica
particles obtained, tetramethoxysilane (TMOS) and tetraethoxysilane
are preferable.
[0086] The amount of the tetraalkoxysilane supplied is preferably
0.002 mol/(molmin) or more and less than 0.006 mol/(molmin), and
more preferably from 0.002 mol/(molmin) to 0.0033 mol/(molmin),
based on the mole number of the alcohol in the alkaline catalyst
solution.
[0087] If the amount of the tetraalkoxysilane supplied is in the
above range, the average circularity of the primary particles
within a range of 10% from the large-size side of the number
particle size distribution easily becomes from 0.65 to 0.90.
[0088] Moreover, if the amount of the tetraalkoxysilane supplied is
less than 0.002 mol/(molmin), the probability that the
tetraalkoxysilane supplied dropwise may contact the core particles
is more reduced. However, it takes a long time until the dropwise
supply of the total amount of tetraalkoxysilane ends, so production
efficiency deteriorates in some cases.
[0089] On the other hand, if the amount of the tetraalkoxysilane
supplied is 0.006 mol/(molmin) or more, it is considered that the
reaction between tetraalkoxysilane molecules is caused before the
tetraalkoxysilane supplied dropwise reacts with the core particles.
Consequently, this encourages the tetraalkoxysilane to be unevenly
supplied to the core particles, and the core particles formed show
variation. As a result, the width of distribution of the particle
size and shape is enlarged, and it is difficult to prepare silica
particles of which the primary particles within a range of 10% from
the large-size side of the number particle size distribution have
an average circularity of from 0.65 to 0.90.
[0090] In addition, the amount of the tetraalkoxysilane supplied
refers to a mole number of the tetraalkoxysilane supplied per
minute, per 1 mol of alcohol in the alkaline catalyst solution.
[0091] Meanwhile, examples of the alkaline catalyst supplied into
the alkaline catalyst solution include those exemplified above. The
alkaline catalyst supplied may be the same types as the alkaline
catalyst contained in advance in the alkaline catalyst solution or
a different type of catalyst, but the catalyst is preferably the
same type of catalyst.
[0092] The amount of the alkaline catalyst supplied is preferably
from 0.1 mol to 0.4 mol, more preferably from 0.14 mol to 0.35 mol,
and even more preferably from 0.18 mol to 0.30 mol, per 1 mol as
the total amount of the tetraalkoxysilane supplied per minute.
[0093] When the amount of the alkaline catalyst supplied is less
than 0.1 mol, the dispersibility of core particles in the process
of growth among the generated core particles becomes unstable.
Accordingly, coarse aggregates such as secondary aggregates are
generated, or the particles are gelated, so the particle size
distribution deteriorates in some cases.
[0094] On the other hand, when the amount of the alkaline catalyst
supplied exceeds 0.4 mol, the generated core particles are
stabilized too much. Accordingly, even if the core particles having
an irregular shape are generated in the stage of core particle
generation, the core particles grow into spherical particles in the
stage of core particle growth, which makes it difficult to obtain
silica particles having an irregular shape.
[0095] Herein, in the supplying step, though the tetraalkoxysilane
and alkaline catalyst are supplied respectively into the alkaline
catalyst solution, the supply method may be a method of continuous
supply or a method of intermittent supply.
[0096] In the supplying step, the temperature of the alkaline
catalyst solution (temperature at the time of supply) is, for
example, preferably from 5.degree. C. to 50.degree. C. and more
preferably from 15.degree. C. to 40.degree. C.
[0097] In addition, A/B is preferably from 1 mol/((mol/min)/L) to 5
mol/((mol/min)/L). If A/B is less than 1 mol/((mol/min)/L), the
core generation stage is not divided into two stages, and the
silica particles do not have two maximum values in number particle
size distribution in some cases. On the other hand, if A/B exceeds
5 mol/((mol/min)/L), the dispersibility of the silica particles
becomes unstable, so the silica slurry is gelated in some
cases.
[0098] A/B is defined as a ratio of A (total amount of the
tetraalkoxysilane supplied) to B (flow rate of the
tetraalkoxysilane supplied, based on the total amount of the
solution into which the tetraalkoxysilane and the alkaline catalyst
have been supplied) in the alkaline catalyst solution in which the
silica particles are generated. The value of A/B is an index
showing the amount of monomers supplied dropwise based on the
scale.
[0099] Through the steps described above, the silica particles are
obtained. In this state, the silica particles are obtained in a
state of a dispersion. The silica particles may be used as is as
the silica particle dispersion, or used by being taken as silica
particle powder by removing the solvent.
[0100] When the silica particles are used as the silica particle
dispersion, if necessary, the dispersion may be diluted with water
or alcohol or concentrated to adjust the solid content
concentration of the silica particles. In addition, the silica
particle dispersion may be used after the solvent is replaced with
another water-soluble organic solvent such as alcohols, esters, or
ketones.
[0101] On the other hand, when the silica particles are used as
silica particle powder, the solvent needs to be removed from the
silica particle dispersion. Examples of the method of removing the
solvent include known methods such as 1) a method of removing the
solvent by filtration, centrifugation, distillation, or the like
and then drying the resultant with a vacuum drier, a shelf drier,
or the like, and 2) a method of directly drying the slurry by using
a fluid-bed drier, a spray drier, or the like. Though not
particularly limited, the drying temperature is preferably
200.degree. C. or lower. If the temperature is higher than
200.degree. C., due to the condensation of silanol groups remaining
on the surface of the silica particles, the primary particles
easily bind to each other, or coarse particles are easily
generated.
[0102] If necessary, it is preferable that the dried silica
particles be pulverized and sieved to remove the coarse particles
or aggregates. Though not particularly limited, the pulverizing
method is implemented using a dry-type pulverizing instrument such
as a jet mill, a vibration mill, a ball mill, or a pin mill. The
sieving method is implemented using a known instrument such as a
vibration sieve or a wind classifier.
[0103] The silica particles obtained by the method of preparing
silica particles according to the present exemplary embodiment may
be used after the surface of the silica particles undergoes
hydrophobizing treatment by using a hydrophobizing agent.
[0104] Examples of the hydrophobizing agent include known organic
silicon compounds having an alkyl group (for example, a methyl
group, an ethyl group, a propyl group, or a butyl group), and
specific examples thereof include silane compounds (for example,
methyltrimethoxysilane, dimethyldimethoxysilane,
trimethylchlorosilane, and trimethylmethoxysilane) and silazane
compounds such as hexamethyldisilazane, tetramethyldisilazane, and
the like. One kind of the hydrophobizing agent may be used, or
plural kinds thereof may be used.
[0105] Among these hydrophobizing agents, organic silicon compounds
having a trimethyl group, such as trimethylmethoxysilane and
hexamethyldisilazane are preferable.
[0106] The amount of the hydrophobizing agent used is not
particularly limited. However, in order to obtain effects of
hydrophobizing, the amount is, for example, preferably from 1% by
weight to 100% by weight and more preferably from 5% by weight to
80% by weight based on the silica particles.
[0107] As the method of obtaining a hydrophobic silica particle
dispersion having under gone hydrophobizing treatment by the
hydrophobizing agent, a method is exemplified in which the
hydrophobizing agent is added in a necessary amount to the silica
particle dispersion and reacted in a temperature range of from
30.degree. C. to 80.degree. C. under stirring to perform the
hydrophobizing treatment on the silica particles, thereby obtaining
the hydrophobic silica particle dispersion. If the reaction
temperature is lower than 30.degree. C., it is difficult to cause
the hydrophobizing reaction. If the temperature exceeds 80.degree.
C., due to self-condensation of the hydrophobizing agent, the
dispersion is easily gelated, or the silica particles are easily
aggregated with each other.
[0108] Meanwhile, examples of the method of obtaining the
hydrophobic silica particles as powder include a method of
obtaining a hydrophobic silica particle dispersion by the above
method and then drying the dispersion by the above method to obtain
powder of hydrophobic silica particles, a method of obtaining
powder of hydrophilic silica particles by drying the silica
particle dispersion, and then performing the hydrophobizing
treatment by adding the hydrophobizing agent to obtain powder of
hydrophobic silica particles, a method of obtaining a hydrophobic
silica particle dispersion, drying the dispersion to obtain powder
of hydrophobic silica particles, and then performing hydrophobizing
treatment by adding the hydrophobizing agent to obtain powder of
hydrophobic silica particles, and the like.
[0109] Herein, as the method of performing the hydrophobizing
treatment on the silica particles as powder, a method is
exemplified in which the hydrophilic silica particles as powder are
stirred in a treatment vessel such as a Henschel mixer or
fluidized-bed, the hydrophobizing agent is added thereto, and the
inside of the treatment vessel is heated to gasify the
hydrophobizing agent such that the hydrophobizing agent is allowed
to react with the silanol groups on the surface of the silica
particles as powder. Though not particularly limited, the treatment
temperature is, for example, preferably from 80.degree. C. to
300.degree. C. and more preferably from 120.degree. C. to
200.degree. C.
EXAMPLES
[0110] Hereinafter, the present invention will be described in more
detail based on examples. Here, the respective examples do not
limit the present invention. In addition, "part(s)" and "%" are
based on weight unless otherwise specified.
[0111] In addition, the molecular weight of the respective
components used below is methanol: 32.04, NH.sub.3: 17.03, and
tetramethoxysilane (TMOS): 152.22. Moreover, the specific gravity
of methanol is 0.79 and the specific gravity of 10% aqueous ammonia
is 1.00.
Example 1
Step of Preparing Alkaline Catalyst Solution
[0112] As an experimental instrument, a glass reaction container
having a volume of 1 L provided with a metallic stirring rod, a
dripping nozzle (a micro tube pump made of Teflon (registered
trademark)), and a thermometer is prepared.
[0113] As an initial charge amount, 210.50 parts of methanol and
25.68 parts of 13.4% aqueous ammonia are put in the reaction
container of the experimental instrument, followed by mixing under
stirring, thereby obtaining an alkali catalyst solution (1). At
this time, the concentration of the ammonia catalyst in the
alkaline catalyst solution, that is, NH.sub.3
(mol)/[NH.sub.3+methanol+water (L)] is 0.70 mol/L.
[0114] --Supplying Step (Generation of Silica Particles 1)--
[0115] The temperature of the alkaline catalyst solution (1) is
adjusted to 25.degree. C., and nitrogen purging is performed on the
alkaline catalyst solution (1). Thereafter, while the alkaline
catalyst solution (1) is being stirred, 92.16 parts of
tetramethoxysilane (TMOS) and 21.75 parts of aqueous ammonia with a
catalyst (NH.sub.3) concentration of 9.70% by weight are started to
be supplied dropwise thereto simultaneously at the following supply
rate, thereby obtaining a suspension of silica particles (silica
particle suspension (1)).
[0116] Herein, the supply rate of the tetramethoxysilane (TMOS) is
set to 8.06 parts/min, based on the total mole number of methanol
in the alkaline catalyst solution (1).
[0117] In addition, the supply rate of the 9.70% by weight aqueous
ammonia is set to 1.90 parts/min, based on the total amount of the
tetraalkoxysilane supplied per minute (8.06 parts/min). This rate
corresponds to 0.205 mol/min based on 1 mol as the total amount of
the tetraalkoxysilane supplied per minute.
[0118] Herein, the values of C/B at points in time when the amount
of the TMOS supplied in the supplying step is A/8, A/4, A/2, 5 A/8,
6 A/8, 7 A/8, and A are calculated. The value of C/B is calculated
as follows. First, assuming that 100% of the tetraalkoxysilane has
reacted, the value of a water concentration (C) in the reaction
system is calculated from the amount of water charged and the
amount of tetraalkoxysilane and the aqueous ammonia supplied
dropwise. Thereafter, from the flow rate of the tetraalkoxysilane
supplied (flow rate at each point in time) and the amount of the
alkaline catalyst solution (the total amount of the solution into
which TMOS and the alkaline catalyst have been supplied at each
point in time), B is calculated. Subsequently, from the obtained C
and B, C/B is calculated. The obtained values of C/B are shown in
Table 2.
[0119] --Step of Hydrophobizing Treatment--
[0120] Subsequently, trimethylsilane is added to the obtained
suspension, and the resultant is heated and dried on a hot plate at
100.degree. C., thereby generating powder particles.
Example 2
[0121] Silica particles are prepared in the same manner as in
Example 1, except that the concentration and amount of the
initially charged aqueous ammonia are set to 18.1% and 27.15 parts
respectively in the step of preparing silica particles.
Example 3
[0122] Silica particles are prepared in the same manner as in
Example 1, except that the concentration and amount of the
initially charged aqueous ammonia are set to 11.8% and 25.20 parts
respectively in the step of preparing silica particles.
Example 4
[0123] Silica particles are prepared in the same manner as in
Example 1, except that the amount of the aqueous ammonia supplied
dropwise is set to 60.00 parts, and the flow rate of the aqueous
ammonia supplied dropwise is set to 5.25 parts/min in the step of
preparing silica particles.
Example 5
[0124] Silica particles are prepared in the same manner as in
Example 1, except that the amount of aqueous ammonia supplied
dropwise is set to 4.73 parts, and the flow rate of aqueous ammonia
supplied dropwise is set to 0.41 part/min in the step of preparing
silica particles.
Example 6
[0125] Silica particles are prepared in the same manner as in
Example 1, except that the flow rate of the tetramethoxysilane
supplied dropwise is set to 4.09 parts/min, and the flow rate of
the aqueous ammonia supplied dropwise is set to 0.97 part/min in
the step of preparing silica particles.
Example 7
[0126] Silica particles are prepared in the same manner as in
Example 1, except that the flow rate of the tetramethoxysilane
supplied dropwise is set to 12.68 parts/min, and the flow rate of
the aqueous ammonia supplied dropwise is set to 2.99 parts/min in
the step of preparing silica particles.
Example 8
[0127] Silica particles are prepared in the same manner as in
Example 1, except that the flow rate of the tetramethoxysilane
supplied dropwise is set to 7.00 parts/min, the amount of the
aqueous ammonia supplied dropwise is set to 30.00 parts, and the
flow rate of aqueous ammonia is set to 2.28 parts/min in the step
of preparing silica particles.
Comparative Example 1
[0128] Silica particles are prepared in the same manner as in
Example 1, except that the concentration and amount of the
initially charged aqueous ammonia are set to 8.82% and 60.00 parts
respectively in the step of preparing silica particles.
Comparative Example 2
[0129] Silica particles are prepared in the same manner as in
Example 1, except that the concentration and amount of the
initially charged aqueous ammonia are set to 17.5% and 14.55 parts
respectively in the step of preparing silica particles.
Comparative Example 3
[0130] Silica particles are prepared in the same manner as in
Example 1, except that the amount of the aqueous ammonia supplied
dropwise is set to 96.25 parts, and the flow rate of the aqueous
ammonia supplied dropwise is set to 8.42 parts/min in the step of
preparing silica particles.
Comparative Example 4
[0131] Silica particles are prepared in the same manner as in
Example 1, except that the amount of the aqueous ammonia supplied
dropwise is set to 0.00 part, and the flow rate of the aqueous
ammonia supplied dropwise is set to 0 part/min in the step of
preparing silica particles.
Comparative Example 5
[0132] Silica particles are prepared in the same manner as in
Example 1, except that the flow rate of the tetramethoxysilane
supplied dropwise is set to 3.77 parts/min, and the flow rate of
the aqueous ammonia supplied dropwise is set to 1.13 parts/min in
the step of preparing silica particles.
Comparative Example 6
[0133] Silica particles are prepared in the same manner as in
Example 1, except that the flow rate of the tetramethoxysilane
supplied dropwise is set to 24.50 parts/min, and the flow rate of
the aqueous ammonia supplied dropwise is set to 5.78 parts/min in
the step of preparing silica particles.
Comparative Example 7
[0134] Silica particles are prepared in the same manner as in
Example 1, except that the flow rate of the tetramethoxysilane
supplied dropwise is set to 16.00 parts/min, and the flow rate of
the aqueous ammonia supplied dropwise is set to 3.78 parts/min in
the step of preparing silica particles.
Comparative Example 8
[0135] Silica particles are prepared in the same manner as in
Example 1, except that the amount of the aqueous ammonia charged
initially is set to 25.61 parts, the flow rate of the
tetramethoxysilane supplied dropwise is set to 10.00 parts/min, the
amount of the aqueous ammonia supplied dropwise is set to 4.00
parts, and the flow rate of the aqueous ammonia supplied dropwise
is set to 0.43 part/min in the step of preparing silica
particles.
[0136] The conditions in the method of preparing silica particles
in each example are shown in Tables 1 and 2.
[0137] Evaluation
[0138] Physical Properties of Silica Particles
[0139] The particle size ratio (particles of small-size
side/particles of large-size side), number ratio (particles of
small-size side/particles of large-size side), and the average
circularity and average shrinkage ratio within a range of 10% from
the large-size side in number particle size distribution of the
hydrophobized silica particles obtained in each example are
calculated by the method described above.
[0140] Function of Silica Particles
[0141] --Preparation of Body of Resin Particles (Preparation of
Amorphous Resin Particles A)--
[0142] 23 mol % of dimethyl terephthalate, 10 mol % of isophthalic
acid, 15 mol % of dodecenyl succinic anhydride, 3 mol % of
trimellitic anhydride, 5 mol % of a bisphenol A ethylene oxide 2
mol adduct, and 45 mol % of a bisphenol A propylene oxide 2 mol
adduct are put in a reaction container provided with a stirrer, a
thermometer, a condenser, and a nitrogen gas-introducing tube, and
the inside of the reaction container is purged with dry nitrogen
gas. Thereafter, 0.06 mol % of dibutyltin oxide as a catalyst is
added thereto, and the mixture is reacted under stirring for about
7 hours at about 190.degree. C. under a nitrogen gas flow. The
temperature is raised to about 250.degree. C. to react the mixture
under stirring for about 5.0 hours, and then the internal pressure
of the reaction container is reduced to 10.0 mmHg to react the
mixture under stirring for about 0.5 hour under reduced pressure,
thereby obtaining a polyester resin having a polar group in the
molecule.
[0143] Thereafter, 100 parts of the polyester resin is melted and
kneaded by a Banbury mixer-type kneader. The kneaded material is
molded into a plate shape having a thickness of 1 cm by using a
rolling roll, roughly ground with a Fitz mill-type grinder to have
a size of about several millimeters, and then finely pulverized by
an IDS-type pulverizer. Subsequently, the resultant is sequentially
classified by an elbow-type classifier, thereby obtaining amorphous
resin particles having a volume average particle diameter of 7
.mu.m.
[0144] --Attaching Step--
[0145] The hydrophobized silica particles obtained in the
respective examples are added to 20 parts of the amorphous resin
particles having a volume average particle diameter of 7 that are
obtained in the above preparation method, such that the coverage
ratio becomes 50%, and the particles are mixed for 30 seconds at
15000 rpm by a 0.4 L sample mill, thereby obtaining resin particles
containing the hydrophobized silica particles. At this time, the
specific gravity of the amorphous resin particles as the body of
resin particles is 1.05, and the specific gravity of the
hydrophobized silica particles as the silica particles obtained in
the respective examples is 1.5.
[0146] The dispersibility of the silica particles obtained in the
respective examples that is exhibited when the silica particles are
dispersed in the resin particles, and the fluidity and mechanical
strength (resistance to stress such as stirring) of the resin
particles to which the silica particles are attached are evaluated
in the following manner.
[0147] --Dispersibility Evaluation--
[0148] The surface of the prepared resin particles containing the
hydrophobized silica particles is observed by using a SEM. In
addition, by image analysis, an attachment area of the
hydrophobized silica particles is measured. The coverage ratio of
the hydrophobized silica particles is calculated from the ratio of
a total attachment area D of specific silica particles to a surface
area C of the body of resin particles [(D/C).times.100] to conduct
evaluation based on the following criteria.
A: Silica particles exhibit a coverage ratio of 45% or more and are
attached onto the surface of the body of resin particles without
showing uneven distribution, and almost no aggregates are observed.
B: Though aggregates of silica particles are observed to a slight
extent, the silica particles exhibit a coverage ratio of 40% or
more and less than 45% and are attached onto the surface of the
body of resin particles without showing uneven distribution. C:
Aggregates of silica particles are found here and there, and the
coverage ratio of silica particles on the surface of the body of
resin particles is less than 40% which indicates dispersion
defects.
[0149] --Fluidity Evaluation--
[0150] For the resin particles containing the hydrophobized silica
particles, an apparent specific gravity in a loosened state and an
apparent specific gravity in a packed state of the resin particles
are measured using a powder tester manufactured by Hosokawa Micron
Limited. From the ratio between the apparent specific gravity in a
loosened state and the apparent specific gravity in a packed state,
a compression ratio is calculated using the following formula, and
from the calculated compression ratio, the fluidity of the resin
particles is evaluated.
Compression ratio=[(apparent specific gravity in packed
state)-(apparent specific gravity in loosened state)]/(apparent
specific gravity in packed state)
[0151] The "apparent specific gravity in a loosened state" is a
measurement value obtained by filling the resin particles in a
sample cup having a volume of 100 cm.sup.3 and weighing the
particles, and refers to a packing specific gravity obtained in a
state where the resin particles are allowed to fall into the sample
cup by gravity. The "apparent specific gravity in a packed state"
refers to an apparent specific gravity obtained by tapping the
sample cup to remove air from the state of the apparent specific
gravity in a loosened state, such that the resin particles are
rearranged and more densely fill the cup.
[0152] In addition, in the fluidity evaluation, the particles are
mixed for 60 minutes using a Turbula shaker before measurement to
apply a mechanical load, just like the evaluation of dispersion
maintainability.
[0153] The evaluation criteria are as follows.
AA: a compression ratio of less than 0.3 A: a compression ratio of
0.3 or more and less than 0.4 C: a compression ratio of 0.4 or
more
[0154] --Mechanical Strength Evaluation--
[0155] The resin particles containing the hydrophobized silica
particles are mixed by being shaken for 10 minutes using a shaker,
and then a sample is collected for SEM observation. The collected
sample is named sample (1). After the sample (1) is further shaken
for 30 minutes using a shaker, a sample is collected from the
sample and named sample (2). For each of the obtained samples (1)
and (2), the circle-equivalent diameter of 100 primary particles is
measured by SEM observation and image analysis so as to compare the
circle-equivalent diameters of the samples with each other, and
evaluation is performed based on the following criteria.
A: There is no difference in the circle-equivalent diameter between
the samples (1) and (2), and loss of silica particles is not
caused. B: The circle-equivalent diameter of the sample (2)
decreases slightly, but this is unproblematic in practical use. C:
The circle-equivalent diameter of the sample (2) decreases
markedly, and the strength is insufficient.
[0156] --Chargeability--
[0157] The chargeability of the obtained silica particles is
evaluated as follows. 19.8 g of an iron powder carrier and 0.2 g of
the resin particles containing the hydrophobized silica particles
are accurately weighed and put into a sample bottle. While the cap
is opened, the resultant is humidified for 3 hours or longer in
each of a thermohygrostat (C) that has been adjusted in advance to
10.degree. C. and 50% RH and a thermohygrostat (A) that has been
adjusted in advance to 28.degree. C. and 85% RH. After
humidification, the bottle is capped, and the resultant is mixed by
being shaken for 30 minutes using a shaker. 1.00 g of the mixed
sample is taken by being weighed accurately, and the charge amount
of the sample humidified in each of the thermohygrostats (C) and
(A) is measured using a charge amount measuring instrument, a
blow-off powder charge amount measuring instrument. The
chargeability at the time when a charge amount of the
thermohygrostat (C) is denoted as c, and a charge amount of the
thermohygrostat (A) is denoted as a is evaluated based on the
following criteria.
c/a=1 AA:
1>c/a.gtoreq.0.8 A:
0.8>c/a.gtoreq.0.5 B:
0.5>c/a C:
[0158] Table 3 shows the characteristics of the silica particles
and the evaluation results in a list.
[0159] In addition, in Comparative Examples 2, 4, and 6, the silica
particles are gelated, so evaluation fails to be conducted.
TABLE-US-00001 TABLE 1 Alkaline catalyst solution (Step of
preparing alkaline catalyst solution) Tetraalkoxysilane and
alkaline catalyst supplied dropwise Weight Total Total amount of
amount of aqueous Flow rate Weight of Concentration aqueous
Concentration of TMOS Flow rate Concentration ammonia of aqueous
methanol of NH.sub.3 ammonia of NH.sub.3 supplied of TMOS of
NH.sub.3 supplied ammonia (part) (% by weight) (part) (mol/L)
(part) (part/min) (% by weight) (part) (part/min) Example 1 210.50
13.4 25.68 0.70 92.16 8.06 9.70 21.75 1.90 Example 2 210.50 18.1
27.15 0.99 92.16 8.06 9.70 21.75 1.90 Example 3 210.50 11.8 25.20
0.60 92.16 8.06 9.70 21.75 1.90 Example 4 210.50 13.4 25.68 0.70
92.16 8.06 9.70 60.00 5.25 Example 5 210.50 13.4 25.68 0.70 92.16
8.06 9.70 4.73 0.41 Example 6 210.50 13.4 25.68 0.70 92.16 4.09
9.70 21.75 0.97 Example 7 210.50 13.4 25.68 0.70 92.16 12.68 9.70
21.75 2.99 Example 8 210.50 13.4 25.68 0.70 92.16 7.00 9.70 30.00
2.28 Comparative 210.50 8.82 60.00 1.06 92.16 8.06 9.70 21.75 1.90
Example 1 Comparative 210.50 17.5 14.55 0.54 92.16 8.06 9.70 21.75
1.90 Example 2 Comparative 210.50 13.4 25.68 0.70 92.16 8.06 9.70
96.25 8.42 Example 3 Comparative 210.50 13.4 25.68 0.70 92.16 8.06
0.00 0.00 0 Example 4 Comparative 210.50 13.4 25.68 0.70 92.16 3.77
9.70 21.75 1.13 Example 5 Comparative 210.50 13.4 25.68 0.70 92.16
24.50 9.70 21.75 5.78 Example 6 Comparative 210.50 13.4 25.68 0.70
92.16 16.00 9.70 21.75 3.78 Example 7 Comparative 210.50 13.4 25.61
0.70 92.16 10.00 9.70 4.00 0.43 Example 8
TABLE-US-00002 TABLE 2 C/B [(mol/L)/{(mol/min)/L}] Supplied
amount.sup.1) A/8 A/4 A/2 5A/8 6A/8 7A/8 A Example 1 32.7 30.5 26.7
25.1 23.7 22.3 21.1 Example 2 32.7 30.5 26.7 25.1 23.6 22.3 21.1
Example 3 32.8 30.5 26.7 25.1 23.7 22.3 21.1 Example 4 38.3 40.9
45.0 46.7 48.2 49.5 50.7 Example 5 30.2 25.6 17.6 14.2 11.0 8 5.3
Example 6 64.5 60.2 52.7 49.5 46.6 44.0 41.6 Example 7 20.8 19.4
17.0 16.0 15.0 14.2 13.4 Example 8 40.0 43.9 50.2 52.7 54.9 56.9
58.6 Comparative 87.3 82.9 75.0 71.6 68.5 65.6 62.9 Example 1
Comparative 17.8 16.3 13.9 12.9 12.0 11.1 10.3 Example 2
Comparative 43.3 49.9 61.0 64.0 67.4 70.4 73.1 Example 3
Comparative 29.4 24.1 14.9 10.8 7.1 3.6 0.4 Example 4 Comparative
75.8 72.9 68.1 66.1 64.2 62.5 61.0 Example 5 Comparative 10.8 10.0
8.8 8.3 7.8 7.3 6.9 Example 6 Comparative 16.5 15.4 13.5 12.7 11.9
11.2 10.6 Example 7 Comparative 24.2 20.4 13.8 10.9 8.3 5.9 3.6
Example 8 .sup.1)Amount of TMOS supplied at the time when the total
amount of TMOS supplied dropwise is denoted as A
TABLE-US-00003 TABLE 3 Characteristics of silica particles Maximum
Maximum value of value of Characteristics at the time when Number
particles particles silica particles are average of of attached to
resin particles Number of particle large-size small-size Average
Particle Mechan- maximum diameter side side Average shrinkage size
Number Dispersi- ical Charge- value.sup.1) (nm) (nm) (nm)
circularity.sup.2) ratio.sup.2) ratio.sup.3) ratio.sup.3) bility
Fluidity strength ability Example 1 2 135 145 15 0.75 34 0.103 71 A
AA A AA Example 2 2 127 130 10 0.88 15 0.077 50 A AA A A Example 3
2 140 148 18 0.66 35 0.120 68 A AA A AA Example 4 2 149 150 10 0.78
21 0.067 18 A AA A A Example 5 2 123 135 39 0.77 48 0.289 91 A AA A
AA Example 6 2 142 146 14 0.79 18 0.096 16 A AA A A Example 7 2 120
143 14 0.68 45 0.098 98 A AA A AA Example 8 2 192 190 4 0.89 16
0.021 13 A A A AA Comparative 2 125 128 10 0.95 2 0.078 48 C A B B
Example 1 Comparative --.sup.4) -- -- -- -- -- -- -- -- -- -- --
Example 2 Comparative 1 151 151 0 0.87 1 0 0 B C A B Example 3
Comparative --.sup.4) -- -- -- -- -- -- -- -- -- -- -- Example 4
Comparative 1 150 150 0 0.81 2 0 0 A C A B Example 5 Comparative
--.sup.4) -- -- -- -- -- -- -- -- -- -- -- Example 6 Comparative 2
130 135 42 0.85 46 0.310 96 B C C A Example 7 Comparative 2 132 136
13 0.84 45 0.096 108 C B C B Example 8 .sup.1)Number of maximum
value of number particle size distribution .sup.2)Particles within
a range of 10% from large-size side of number particle size
distribution .sup.3)Particles of small-size side/particles of
large-size side .sup.4)Gelation
[0160] From the above results, it is understood that the present
examples yield excellent results in all of the respective
evaluations of dispersibility, fluidity, mechanical strength, and
chargeability.
[0161] The foregoing description of the exemplary embodiments of
the present invention has been provided for the purposes of
illustration and description. It is not intended to be exhaustive
or to limit the invention to the precise forms disclosed.
Obviously, many modifications and variations will be apparent to
practitioners skilled in the art. The embodiments were chosen and
described in order to best explain the principles of the invention
and its practical applications, thereby enabling others skilled in
the art to understand the invention for various embodiments and
with the various modifications as are suited to the particular use
contemplated. It is intended that the scope of the invention be
defined by the following claims and their equivalents.
* * * * *