U.S. patent application number 10/901057 was filed with the patent office on 2005-02-03 for mesoporous silica particles and production process thereof.
This patent application is currently assigned to Tokuyama Corporation. Invention is credited to Fukuda, Kentaro, Fukunaga, Kenji, Yamashita, Hiroya.
Application Number | 20050025690 10/901057 |
Document ID | / |
Family ID | 33543567 |
Filed Date | 2005-02-03 |
United States Patent
Application |
20050025690 |
Kind Code |
A1 |
Fukuda, Kentaro ; et
al. |
February 3, 2005 |
Mesoporous silica particles and production process thereof
Abstract
A process for wet pulverizing mesoporous silica particles while
a surfactant exists in mesopores, and mesoporous silica particles
having an average particle diameter of 1 .mu.m or less, wherein the
volume of mesopores having a diameter of 2 to 50 nm is 0.7 mL/g or
more and the geometric standard deviation of a mesopore
distribution is 2.0 or less. In the above process, mesoporous
silica particles having a particle diameter in a submicron order
can be obtained at a high yield without causing the marked collapse
of mesopores and can be produced efficiently by using an ordinary
pulverizer and safely by using an aqueous medium. The mesoporous
silica particles having an average particle diameter of 1 .mu.m or
less are useful as an ink absorbent for ink jet recording paper,
low-dielectric film, catalyst support, separating agent, adsorbent
and medical carrier for medicines.
Inventors: |
Fukuda, Kentaro; (Yamaguchi,
JP) ; Fukunaga, Kenji; (Yamaguchi, JP) ;
Yamashita, Hiroya; (Yamaguchi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Tokuyama Corporation
Yamaguchi-Ken
JP
|
Family ID: |
33543567 |
Appl. No.: |
10/901057 |
Filed: |
July 29, 2004 |
Current U.S.
Class: |
423/335 |
Current CPC
Class: |
B41M 5/5218 20130101;
C01B 33/193 20130101 |
Class at
Publication: |
423/335 |
International
Class: |
C01B 033/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 29, 2003 |
JP |
2003-203206 |
Sep 17, 2003 |
JP |
2003-324750 |
Claims
1. A process for producing fine mesoporous silica particles,
comprising wet pulverizing mesoporous silica particles while a
surfactant exists in mesopores.
2. The process according to claim 1, wherein the amount of the
surfactant is 20 to 300 parts by weight based on 100 parts by
weight of the mesoporous silica particles.
3. The process according to claim 1 or 2, wherein the pH of a
solution processed by wet pulverizing is within a range of pH at
which mesoporous silica particles are formed from silica
source.+-.2.
4. The process according to claim 1, wherein wet pulverizing is
carried out to ensure that the fine mesoporous silica particles
have an average particle diameter of 1 .mu.m or less.
5. A process for producing fine mesoporous silica particles,
comprising the steps of: a reaction step for forming mesoporous
silica particles in a polar solvent by precipitating silica in the
presence of a surfactant; a pulverizing step for wet pulverizing
the mesoporous silica particles contained in a reaction mixture
obtained in the above reaction step as a solution to be processed;
and a removing step for removing at least part of the surfactant
existent in the mesopores of the mesoporous silica particles.
6. Mesoporous silica particles having an average particle diameter
of 1 .mu.m or less, wherein the volume of mesopores having a
diameter of 2 to 50 nm is 0.7 mL/g or more and the geometric
standard deviation of a mesopore distribution is 2.0 or less.
7. The mesoporous silica particles according to claim 6, wherein
the geometric standard deviation of a particle size distribution is
1 to 3.
8. The mesoporous silica particles according to claim 6 or 7,
wherein the average diameter of mesopores is 5 nm or more.
9. The mesoporous silica particles according claim 1 which have an
X-ray diffraction peak corresponding to a d value of 2 to 50
nm.
10. The mesoporous silica particles according to claim 6 which are
produced by wet pulverizing while a surfactant exists in
mesopores.
11. A mesoporous silica particle dispersion containing the
mesoporous silica particles of claim 6.
12. A mesoporous silica granulated product prepared by granulating
the mesoporous silica particles of claim 6.
13. Use of the mesoporous silica particles of claim 6 as an ink
absorbent for ink jet recording paper.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to mesoporous silica and a
production process thereof. More specifically, it relates to
mesoporous silica particles having a particle diameter in a
submicron order and useful as a catalyst support, separating agent,
adsorbent, low-dielectric film or ink absorbent for ink jet
recording paper and to a process for producing the above particles
efficiently at a high yield.
DESCRIPTION OF THE PRIOR ART
[0002] Mesoporous silica is a new material having pores with a
diameter of 2 to 50 nm (to be referred to as "mesopores"
hereinafter) and expected to be used in various fields such as
catalyst support and separating agents. Like other inorganic
materials, it is preferably in the form of fine particles in most
cases when it is actually used.
[0003] For example, when it is used as thin film like an ink
absorbent for ink jet recording paper or low-dielectric thin film,
to obtain a flat homogeneous film, mesoporous silica must be
particulate and submicron-sized mesoporous silica particles are
needed.
[0004] In the fields of catalyst support, separating agents,
adsorbents and medical carriers for medicines, mesoporous silica is
granulated, molded or dispersed uniformly in a matrix. To improve
the mechanical strength of a granulated or molded product or
dispersibility in the matrix, mesoporous silica must be
particulate.
[0005] Under the above situation, mesoporous silica must be
particulate. However when mesoporous silica is pulverized into fine
particles, mesopores that are the greatest feature of mesoporous
silica collapse, resulting in a greatly reduced value as a
material.
[0006] Particularly when mesoporous silica is pulverized into
submicron-sized fine particles, the collapse of mesopores is marked
and the volume of mesopores in mesoporous silica greatly
decreases.
[0007] In view of the above problems, the inventors of the present
invention propose a process for obtaining particulate mesoporous
silica by processing a mixed solution of mesoporous silica and a
cationic resin dissolved in an aqueous solvent with a high-pressure
homogenizer (JP-A 2002-356621) (the term "JP-A" as used herein
means an "unexamined published Japanese patent application").
[0008] However, to make mesoporous silica fully particulate by the
above process, the mixed solution must be processed with the
high-pressure homogenizer many times in most cases, leaving room
for the improvement of production efficiency. Since mesoporous
silica produced by the above process contains the cationic resin
for the prevention of the collapse of its mesoporous structure, its
application is limited and there is a problem with uniformity in
mesopore size due to a wide mesopore distribution. Therefore, it is
difficult to use it as a catalyst support or separating agent which
is used for a specific-sized substance.
[0009] As means of pulverizing mesoporous silica while the collapse
of its mesoporous structure is prevented, wet pulverizing using an
organic solvent as a dispersion medium is proposed (JP-A
2000-44227).
[0010] Although the above method provides a certain measure of
effect, in order to prevent the collapse of mesopores, mesoporous
silica can be pulverized into particles of a size only about 10
.mu.m. When it is pulverized into submicron-sized fine particles,
the volume of mesopores in mesoporous silica greatly decreases.
SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to provide a
process capable of obtaining mesoporous silica particles having a
particle diameter in a submicron order at a high yield without
causing the marked collapse of mesopores and of producing them
efficiently by using an ordinary pulverizer.
[0012] It is another object of the present invention to provide
mesoporous silica particles having a particle diameter in a
submicron order, a satisfactory mesopore volume and uniformity in
mesopore diameter.
[0013] It is still another object of the present invention to
provide a dispersion and granulated product of the mesoporous
silica particles of the present invention.
[0014] Other objects and advantages of the present invention will
become apparent from the following description.
[0015] According to the present invention, firstly, the above
objects and advantages of the present invention are attained by a
process for producing pulverized mesoporous silica particles,
comprising wet pulverizing mesoporous silica particles while a
surfactant exists in mesopores.
[0016] According to the present invention, secondly, the above
objects and advantages of the present invention are attained by
mesoporous silica particles having an average particle diameter of
1 .mu.m or less, wherein the volume of mesopores having a diameter
of 2 to 50 nm is 0.7 mL/g or more, and the geometric standard
deviation of a mesopore distribution is 2.0 or less.
[0017] According to the present invention, thirdly, the above
objects and advantages of the present invention are attained by a
dispersion containing the above mesoporous silica particles of the
present invention and a granulated product obtained by granulating
the above mesoporous silica particles of the present invention.
BRIEF DESCRIPTION OF THE DRAWING
[0018] FIG. 1 is a graph showing the mesopore distribution curves
of mesoporous silica particles obtained in Example 1, Comparative
Example 1 and Comparative Example 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0019] The mesoporous silica particles of the present invention are
obtained by using an aggregate of a surfactant as template for
mesopores when silica is formed.
[0020] The mesoporous structure of the mesoporous silica particles
is not particularly limited and is, for example, a mesoporous
structure that tubular mesopores are arranged in a honeycomb-like
form or a 3-D net-like mesoporous structure that spherical
mesopores are arranged regularly and communicate with one another,
depending on the type of the surfactant and others.
[0021] The mesopore diameter of the mesoporous silica particles is
not particularly limited and may be selected according to
application purpose. The mesopore diameter of the mesoporous silica
particles can be controlled according to the type of the surfactant
and others.
[0022] As a typical method for preparation of the mesoporous silica
particles, a method which comprises precipitating silica from a
silica source in the presence of surfactant as a template, then
removing the surfactant from the resulting mixture is
mentioned.
[0023] A detailed description is subsequently given of a typical
process for producing mesoporous silica particles by using an
aggregate of the molecules of a surfactant.
[0024] The silica source and the surfactant are first mixed
together in a polar solvent. To improve the structural regularity
of the obtained mesoporous silica particles, an appropriate amount
of an acid or alkali is preferably added.
[0025] Examples of the above polar solvent include water, organic
solvents such as alcohols including methanol, ethanol and
isopropanol, ethers and ketones, and mixed solvents thereof. Out of
these, it is the most preferred to use water alone from the
viewpoint of handling ease.
[0026] Examples of the above silica source include particulate
silica such as fumed silica, precipitated silica and colloidal
silica, alkali metal silicates and silicon alkoxides. Out of these,
alkali metal silicates and active silica sols obtained by
dealkalizing these alkali metal silicates are the most preferred
because mesoporous silica can be obtained under mild reaction
conditions and they are inexpensive.
[0027] The above surfactant is a compound which forms a micellar or
lamellar aggregate and may be a cationic, anionic or nonionic
surfactant or polymer having surface activity. A surfactant capable
of forming a micelle is selected according to the above polar
solvent.
[0028] Specific examples of the surfactant include
alkyltrimethylammonium and polyoxyethylene alkyl ethers having a
linear alkyl group having 8 to 20 carbon atoms, and block copolymer
of ethylene glycol and propylene glycol.
[0029] Out of the above surfactants, polyoxyethylene alkyl ethers
having a linear alkyl group having 8 to 20 carbon atoms and block
copolymer of ethylene glycol and propylene glycol are preferred
because they are inexpensive and have low toxicity and
biodegradability.
[0030] The amount of the above surfactant is not particularly
limited but preferably 50 to 200 parts by weight based on 100 parts
by weight of the silica source in terms of SiO.sub.2.
[0031] To expand the mesopore diameter of mesoporous silica, a
hydrophobic compound such as 1,3,5-trimethylbenzene or
1,3,5-tributylbenzene may further be added.
[0032] Thereafter, the above silica source are reacted under
specific reaction conditions to obtain mesoporous silica having a
structure that a micellar or lamellar aggregate of the surfactant
is imprinted. The reaction conditions are not particularly limited
and reaction conditions suitable for a reaction system can be
selected.
[0033] Stated specifically, when particulate silica is used as the
above silica source, it is preferably reacted in an alkaline
reaction solution at 100 to 150.degree. C. under pressure. When an
alkali metal silicate or silicon alkoxide is used as the silica
source, it is preferably reacted in an alkaline or acid solution at
20 to 100.degree. C. under atmospheric pressure.
[0034] The greatest feature of the process of the present invention
is that mesoporous silica particles produced by the above process
are wet pulverized while the surfactant is existent in
mesopores.
[0035] In all the processes for producing particulate mesoporous
silica of the prior art, mesoporous silica particles obtained by
the above production process are pulverized after the surfactant is
substantially removed from the particles. According to the
processes, when the mesoporous silica particles are pulverized into
submicron-sized fine particles, mesopores collapse and the
characteristic properties of mesoporous silica greatly deteriorate
unless a special pulverizing technique is used.
[0036] In contrast to this, according to the process of the present
invention in which mesoporous silica particles are wet pulverized
while a surfactant exists in mesopores, even when mesoporous silica
particles are pulverized into submicron-sized fine particles with
an ordinary pulverizer, mesopores rarely collapse and the specific
surface area and the volume of mesopores can be maintained.
[0037] The process in which wet pulverizing is carried out while a
surfactant exists in mesopores was first proposed by the present
invention and provides an extremely marked effect that mesoporous
silica particles can be finely pulverized while mesopores are
protected at a high ratio.
[0038] The reason why the collapse of mesopores in mesoporous
silica particles can be suppressed by wet pulverizing the
mesoporous silica particles in the presence of the surfactant is
unknown but the inventors of the present invention assume as
follows.
[0039] That is, it is assumed that when mesoporous silica particles
are wet pulverized in a dispersion medium, partial hydrolysis of
silica is caused by mechanical stress and then silica
re-precipitates.
[0040] When the surfactant does not exist at this point, regular
mesopores disappear through repetitions of hydrolysis and
precipitation and mesoporous silica changes into ordinary
silica.
[0041] Characteristic mesopores are formed in the mesoporous silica
particles by the function of the surfactant when the silica source
precipitates as silica. Therefore, it is presumed that when the
surfactant exists during the above wet pulverizing, even if
hydrolysis and precipitation are repeated many times, the
characteristic mesopores are retained by the function of the
surfactant.
[0042] In the present invention, to make the surfactant exist in
mesopores, surfactant can be added to the mesoporous silica
particles produced by the process of the prior art. However, to
obtain the effect of the present invention with the most certainty,
in the above process for producing mesoporous silica particles, it
is preferred that the surfactant used as a template for the
mesopores of the mesoporous silica particles should remain in the
mesopores and not be removed from the mesopores.
[0043] In the present invention, the amount of the surfactant which
exists during wet pulverizing is preferably 20 to 300 parts by
weight, particularly preferably 50 to 200 parts by weight based on
100 parts by weight of the mesoporous silica particles. When the
amount of the surfactant is 20 parts or more by weight, the
collapse of mesopores can be effectively suppressed. When the
amount is 300 parts or less by weight, cost required for the
surfactant can be reduced and the surfactant can be easily removed
after pulverizing.
[0044] Examples of the dispersion medium used for wet pulverizing
in the present invention include water, organic solvents such as
alcohols including methanol, ethanol and isopropanol, ethers and
ketones, and mixed solvents thereof. Out of these, it is the most
preferred to use water alone from the viewpoint of handling
ease.
[0045] In a more preferred embodiment of the present invention, the
pH of the solution to be processed by wet pulverizing while the
surfactant exists in mesopores is adjusted to a range of pH at
which mesoporous silica particles formed from silica
source.+-.2.
[0046] The collapse of mesopores by wet pulverizing can be
particularly effectively suppressed by controlling the pH. Even
when the mesoporous silica particles are wet pulverized into
submicron-sized particles, the retainability of mesopores (volume
of mesopores after wet pulverizing/volume of mesopores before wet
pulverizing) can be adjusted to 90% or more.
[0047] In the most preferred embodiment of the present invention,
the surfactant and the silica source are reacted with each other in
an aqueous solvent to obtain mesoporous silica particles containing
the surfactant, and then the mesoporous silica particles are wet
pulverized by using part or all of the reaction solution as a
dispersion medium.
[0048] When the reaction solution is used as a dispersion medium,
the amount of the surfactant and pH at the time of wet pulverizing
can be adjusted without taking special means and a series of
production steps can be greatly simplified.
[0049] That is, according to the present invention, there is
provided a process for producing pulverized mesoporous silica
particles, comprising a reaction step for forming mesoporous silica
particles in a polar solvent by precipitating silica in the
presence of a surfactant, a pulverizing step for wet pulverizing
the mesoporous silica particles contained in a reaction solution
obtained in the above reaction step as the solution to be
processed, and a removing step for removing at least part of the
surfactant existent in the mesopores of the mesoporous silica
particles.
[0050] In the present invention, to enhance the structural
regularity of mesoporous silica, aging at normal temperature or
under heating may be carried out after wet pulverizing.
[0051] In the present invention, the above wet pulverizing method
is not particularly limited and any known method may be employed.
For example, wet pulverizing with a wet medium type dispersion
device such as a bead mill or pot mill, ultrasonic dispersion
device, high-pressure homogenizer or a medium-free dispersion
device, such as a colloid mill in which particles are pulverized by
passing through the gap (several .mu.m to several tens of .mu.m)
between a fixed disk and a rotary disk is employed. Out of these, a
wet medium type dispersion device is preferred because it has high
pulverizing efficiency and can easily pulverize mesoporous silica
into submicron-sized fine particles.
[0052] The content of the mesoporous silica particles in the
solution to be processed by wet pulverizing is preferably 1 to 40
wt %, more preferably 3 to 20 wt %. When the content of mesoporous
silica particles is 1 wt % or more, wet pulverizing efficiency can
be improved and when the content is 40 wt % or less, the mesoporous
silica particles can be uniformly and easily pulverized into fine
particles.
[0053] Since wet pulverizing is carried out in the presence of the
surfactant in the present invention, the solution to be processed
may foam and the pulverizing efficiency may lower. In this case, it
is preferred to take a measure for preventing the inclusion of foam
into the solution, for example, the elimination of a dead volume in
a vessel for pulverizing. The addition of a small amount of an
anti-foaming agent is also effective. Preferred examples of the
anti-foaming agent include acetylene glycol-based anti-foaming
agents and silicone-based anti-foaming agents.
[0054] The pulverized mesoporous silica particles can be obtained
by removing at least part of the surfactant from the pulverized
mesoporous silica particles containing the surfactant obtained by
the above wet pulverizing.
[0055] The method of removing the surfactant is not particularly
limited, for example, extraction with a suitable solvent,
extraction with a supercritical fluid such as carbon dioxide, or
calcinations at 400 to 600.degree. C. are mentioned.
[0056] For the removal of the above surfactant, the surfactant is
preferably removed completely but the surfactant residue may be
contained in limits that do not impair the characteristic
properties of the mesopores of the mesoporous silica particles.
[0057] In the present invention, the method of extracting the
surfactant using an extraction solvent is preferred because the
extracted surfactant can be recycled and the re-agglomeration of
mesoporous silica particles after wet pulverizing can be easily
suppressed.
[0058] In order to extract the surfactant using an extraction
solvent, preferably, the pulverized mesoporous silica particles
containing the surfactant are dispersed into the extraction
solvent, stirred at normal temperature or under heating for a
specific period of time and subjected to solid-liquid
separation.
[0059] Any extraction solvent may be used if it can extract the
surfactant from the pulverized mesoporous silica particles.
Examples of the extraction solvent include alcohols such as
methanol, ethanol and propanol and ketones such as acetone, from
which a suitable solvent may be selected.
[0060] The above solid-liquid separation is not particularly
limited but it is preferably carried out by filtration with a
filter press, centrifugation with a centrifugal separator or a
decanter, or ultrafiltration.
[0061] In the present invention, impurities other than the
surfactant such as an acid, alkali and salt may be contained in the
processed solution after wet pulverizing. These impurities may be
removed simultaneously with the removal of the surfactant. When it
is difficult to remove them simultaneously with the removal of the
surfactant, it may be removed by washing separately.
[0062] Out of the pulverized mesoporous silica particles having a
particle diameter in a submicron order obtained by the above
production process, mesoporous silica particles having an average
particle diameter of 1 .mu.m or less, a volume of mesopores having
a diameter of 2 to 50 nm of 0.7 mL/g or more and a geometric
standard deviation of a mesopore distribution of 2.0 or less can be
particularly advantageously used in the fields of catalyst
supports, separating agents, adsorbents, low-dielectric films and
ink absorbents for ink jet recording paper.
[0063] The mesoporous silica particles provided by the present
invention have an average particle diameter of 1 .mu.m or less. The
mesoporous silica particles having the above average particle
diameter can form a flat homogeneous film in fields in which a film
formed from mesoporous silica particles is used. Since a granulated
or molded product obtained from the mesoporous silica particles has
high mechanical strength, it is also useful in the fields of
catalyst supports, separating agents and adsorbents.
[0064] Out of the mesoporous silica particles having the above
average particle diameter, mesoporous silica particles having an
average particle diameter of 0.5 .mu.m or less are preferred, and
mesoporous silica particles having an average particle diameter of
0.3 .mu.m or less are particularly preferred. The lower limit of
the average particle diameter is not particularly limited but
generally 0.01 .mu.m, preferably 0.03 .mu.m.
[0065] The mesoporous silica particles of the present invention are
characterized in that the volume of mesopores is 0.7 mL/g or more
though they are fine particulate as described above. When a film is
formed from mesoporous silica particles having the above volume of
mesopores, the porosity of the obtained film grows, thereby making
it possible to increase the amount of ink absorbed into ink jet
recording paper and to reduce the dielectric constant of a
low-dielectric film. Mesoporous silica particles having the above
volume of mesopores are excellent in improving the catalytic
activity, the separation efficiency, the adsorption capacity and
the holding amount of a medicine.
[0066] Out of the mesoporous silica particles having the above
volume of mesopores, mesoporous silica particles having a mesopore
volume of 1.0 mL/g or more are particularly preferred. The upper
limit of mesopore volume is not particularly limited but generally
3 mL/g.
[0067] The mesoporous silica particles of the present invention are
also characterized in that the geometric standard deviation of a
mesopore distribution (to be referred to as ".sigma..sub.p"
hereinafter) is 2.0 or less.
[0068] .sigma..sub.p is an index of uniformity in mesopore
diameter. As .sigma..sub.p becomes smaller, the mesopores become
more uniform in diameter.
[0069] Since mesoporous silica particles having the above
.sigma..sub.p are extremely uniform in mesopore diameter, a
substance having a specific size can be selectively treated in the
fields of catalyst supports, separating agents and adsorbents.
[0070] Out of the mesoporous silica particles having the above
.sigma..sub.p, mesoporous silica particles having a geometric
standard deviation of 1.7 or less are particularly preferred. The
lower limit of .sigma..sub.p of the mesoporous silica particles is
not particularly limited but generally 1.
[0071] The mesoporous silica particles of the present invention are
preferably amorphous silica particles. That is, crystalline silica
often forms a crystalline silica dust in process of making and use,
and the crystalline silica dust causes silicosis which is difficult
to be cured. Therefore, special attention must be paid to the
crystalline silica. In contrast to this, as amorphous silica does
not form a crystalline silica dust, it is extremely advantageous in
terms of safety.
[0072] The mesoporous silica particles of the present invention
have a geometric standard deviation of a particle size distribution
(to be referred to as ".sigma..sub.d" hereinafter) of preferably 1
to 3, particularly preferably 1.5 to 2.5.
[0073] .sigma..sub.d is an index of uniformity in particle
diameter. As .sigma..sub.d becomes smaller, the fine particles
become more uniform in particle diameter.
[0074] Mesoporous silica particles having a .sigma..sub.d of 1 or
more have a high packing density when they are granulated or
molded. This is because the porosity of a packed layer decreases as
the particle size distribution becomes wider as described in Kagaku
Kogaku Ronbunshuu (Papers on Chemical Engineering), vol. 11, No. 4,
pp. 438, 1985. Therefore, when the mesoporous silica particles
having .sigma..sub.d of 1 or more are granulated or molded, they
tend to become dense, whereby a granulated or molded product having
high mechanical strength can be formed with a small amount of a
binder. When the mesoporous silica particles are filled into a
container and used, the container can be made compact. Since
mesoporous silica particle shaving a .sigma..sub.d of more than 3
include coarse particles and extremely fine particles, they may
cause a handling problem.
[0075] The mesoporous silica particles of the present invention
preferably have an average mesopore diameter of 5 nm or more. That
is, the mesoporous silica particles having an average mesopore
diameter of 5 nm or more are useful for not only the above
application purposes but also other application purposes because
they can adsorb, separate or carry a polymer substance such as
protein.
[0076] The mesoporous silica particles of the present invention
preferably have an X-ray diffraction peak corresponding to a d
value of 2 to 50 nm. Since the mesoporous silica particles having
the above diffraction peak have mesopores uniform in diameter and
arranged regularly, they can be used as a functional material for
an optical device, electronic device or others. They can also
display more stable performance in other application fields.
[0077] Although the process for producing the mesoporous silica
particles of the present invention is not particularly limited,
they can be advantageously produced by the following process.
[0078] First, an alkali metal silicate, surfactant and acid are
mixed together to precipitate silica, mesoporous silica particles
are obtained by using a micellar or lamellar aggregate of the
molecules of the surfactant as a template, the mesoporous silica
particles are wet pulverized, and the surfactant is extracted and
removed from the pulverized mesoporous silica particles.
[0079] The amount of the above surfactant is preferably 100 parts
or more by weight based on 100 parts by weight of silica. When the
amount of the surfactant is 100 parts or more by weight, the volume
of mesopores can be increased. Mesoporous silica particles having a
small .sigma..sub.p and a uniform mesopore diameter can be
obtained.
[0080] The above surfactant is preferably a block copolymer of
ethylene glycol and propylene glycol. By using this block
copolymer, mesoporous silica particles having a small .sigma..sub.p
and an average mesopore diameter of 5 nm or more can be obtained.
When a surfactant other than the above block copolymer is used and
mesoporous silica particles are wet pulverized, .sigma..sub.p tends
to become large and it is difficult to obtain mesoporous silica
particles having an average mesopore diameter of 5 nm or more.
[0081] To precipitate silica, the reaction mixture is preferably
maintained at 20 to 40.degree. C. for 0.5 to 10 hours and then at
80 to 100.degree. C. for 5 to 20 hours. According to this process,
the mesopores become uniform in diameter and are arranged
regularly, thereby making it possible to obtain mesoporous silica
particles having an X-ray diffraction peak.
[0082] The above wet pulverizing is preferably carried out without
removing the surfactant used as a template for the mesopores of the
mesoporous silica particles. According to this process, mesoporous
silica particles can be easily pulverized into fine particles
without impairing pore volume and uniformity in the diameter of the
mesopores of the mesoporous silica particles. The above wet
pulverizing is the most preferably carried out by using part or all
of the reaction solution as a dispersion medium.
[0083] The pulverizer used for the above wet pulverizing is
preferably a wet medium type pulverizer such as boad mill or pot
mill. The wet medium type pulverizer has high pulverizing
efficiency and can pulverize mesoporous silica particles into fine
particles having a particle diameter of 1 .mu.m or less
efficiently.
[0084] When a wet medium type pulverizer is used, the average
particle diameter and .sigma..sub.d of the obtained pulverized
mesoporous silica particles can be controlled by suitably selecting
the particle diameter of beads as a medium and the processing time
(residence time in the pulverizing unit of a continuous
pulverizer).
[0085] That is, when the particle diameter of beads is small, the
average particle diameter tends to become small and when the
processing time is long, .sigma..sub.d tends to become small.
Therefore, when small beads are used for processing for a long
time, for example, mesoporous silica particles having a small
average particle diameter and a small .sigma..sub.d are obtained
and when large beads are used for processing for a short time,
mesoporous silica particles having a large average particle
diameter and a large .sigma..sub.d are obtained.
[0086] To remove the surfactant from the mesoporous silica
particles by extraction, preferably, the mesoporous silica
particles containing the surfactant are dispersed in an extraction
solvent and stirred under heating for a specific period of time,
followed by solid-liquid separation. The extraction solvent is
preferably an alcohol such as methanol, ethanol or propanol, and
the solid-liquid separation is preferably carried out by
centrifugation, ultrafiltration or precision filtration.
[0087] The mesoporous silica dispersion of the present invention is
obtained by dispersing the mesoporous silica particles of the
present invention into a dispersion medium. The mesoporous silica
dispersion can form a flat homogeneous film and is useful as a
coating solution for forming a thin film such as the ink absorbing
layer of ink jet recording paper or a low-dielectric film.
[0088] In the present invention, any dispersion medium of the
mesoporous silica dispersion may be used without restriction if it
can disperse the mesoporous silica particles. Examples of the
dispersion medium include water, organic solvents such as alcohols
including methanol, ethanol and isopropanol, ethers and ketones,
and mixed solvents thereof. Out of these, it is the most preferred
to use water alone from the viewpoint of handling ease.
[0089] The content of the mesoporous silica particles in the
mesoporous silica dispersion is not particularly limited but
preferably 5 to 50 wt %, particularly preferably 10 to 40 wt %.
[0090] That is, when the content of the mesoporous silica particles
in the mesoporous silica dispersion is higher than 50 wt %, the
fluidity of the dispersion is apt to be lower and when the content
is lower than 5 wt %, it is difficult to obtain a film having a
desired thickness and energy cost required for drying after
application is apt to become high.
[0091] A dispersant may be added to the mesoporous silica
dispersion of the present invention in order to enhance the
dispersion stability of the mesoporous silica particles.
[0092] Preferred examples of the dispersant include cationic,
anionic and nonionic resins and surfactants. Out of these, cationic
resins having a primary, secondary or tertiary amine or quaternary
ammonium salt are particularly preferred.
[0093] Particularly when it is used in ink jet recording paper, the
fixability of an anionic dye contained in ink for ink jet printing
can be improved by the function of the cationic resin and ink jet
recording paper which is excellent in water resistance and printing
density can be obtained.
[0094] The mesoporous silica granulated product of the present
invention can be obtained by granulating the mesoporous silica
particles of the present invention.
[0095] Mesoporous silica particles having a large particle diameter
of the prior art have pores all of which are mesopores and it is
difficult for a certain substance to diffuse into a mesopore and
reach the inside of a particle. Therefore, the inside of each
particle cannot be effectively used.
[0096] In contrast to this, as the mesoporous silica granulated
product of the present invention has macropores between fine
particles, a substance diffuses into the macropores and easily
reaches the inside of each particle. Therefore, the inside of the
mesoporous silica granulated product can be effectively used,
whereby it is useful as a catalyst support, separating agent,
adsorbent or medical carrier for medicines.
[0097] Further, the mesoporous silica particles can be granulated
to a size of several .mu.m to several tens of mm according to
application purpose. Compared with a case where the mesoporous
silica particles are used as they are, the mesoporous silica
granulated product is extremely advantageous in handling ease when
it is separated or collected.
[0098] The method of obtaining the above mesoporous silica
granulated product is not particularly limited and any known method
can be employed without restriction. Specifically, spray
granulation for granulating a dispersion of mesoporous silica
particles by spraying and drying, rolling granulation for powdery
mesoporous silica particles, fluidized bed granulation, stirring
granulation, compression granulation or extrusion granulation may
be employed.
[0099] To further enhance the mechanical strength of the mesoporous
silica granulated product, a binder may be added during
granulation. Preferred examples of the binder include gelatin,
polyvinyl pyrrolidone, polyvinyl alcohol, cellulose and derivatives
thereof.
EXAMPLES
[0100] The following examples are provided for the purpose of
further illustrating the present invention but are in no way to be
taken as limiting.
[0101] The physical properties of the mesoporous silica particles
were measured by the following methods.
[0102] (1) Measurement of Specific Surface Area of Mesoporous
Silica Particles, and Volume, Average Diameter and .sigma..sub.p of
Mesopores
[0103] A nitrogen adsorption isotherm at 75K of fully dried
mesoporous silica particles was taken by using a high-speed
specific surface area/pore distribution measuring instrument
(ASAP2010 of Micromeritics Co., Ltd.), and from the isotherm,
specific surface area and mesopore distribution was calculated by
BET method and BJH method respectively. The mesopore diameter axis
of the mesopore distribution curve was a logarithmic scale.
[0104] The volume, retainability, average diameter (av.sub.p) and
.sigma..sub.p of mesopores having a diameter of 2 to 50 nm were
calculated from the above mesopore distribution curve. For the
calculation of the retainability, av.sub.p and .sigma..sub.p of the
mesopores, the following equations (1), (2) and (3) were used,
respectively.
Retainability of mesopores=volume of mesopores after
pulverizing/volume of mesopores before pulverizing (1)
log av.sub.p=.SIGMA.{v.sub.ilog p.sub.i}/.SIGMA.v.sub.i (2)
log .sigma..sub.p=[.SIGMA.{v.sub.i(log p.sub.i-log
av.sub.p).sup.2}/.SIGMA- .v.sub.i].sup.0.5 (3)
[0105] In the above equations (2) and (3), "i" denotes an i-th
section when the mesopore diameter axis is divided into an N number
of sections, with the proviso that 1 to N are natural numbers.
v.sub.i denotes the volume of mesopores having a diameter in the
i-th section and p.sub.i is a geometric mean between the lower
limit and the upper limit of mesopore diameter in the i-th
section.
[0106] (2) Measurement of Average Particle Diameter and
.sigma..sub.d of Mesoporous Silica Particles
[0107] Mesoporous silica particles were dispersed in ion exchange
water to a concentration of 3 wt % and processed with an ultrasonic
dispersion device (UT-205 of Sharp Co., Ltd.) at 200 W for 5.
minutes to prepare a sample. The volume-based particle size
distribution of the sample was measured with a laser diffraction
particle size analyzer (Coulter LS-230 of Coulter Co., Ltd.) at a
dispersion medium (water) refractive index as 1.332 and a silica
refractive index as 1.458. The particle diameter axis of the
particle size distribution curve was a logarithmic scale.
[0108] The average particle diameter (av.sub.d) and .sigma..sub.d
were calculated from the above particle size distribution curve.
For the calculation of av.sub.d and .sigma..sub.d, the following
equations (4) and (5) were used, respectively.
log av.sub.d=.SIGMA.{v.sub.i log d.sub.i}/.SIGMA.v.sub.i (4)
log .sigma..sub.d=[.SIGMA.{v.sub.i(log d.sub.i-log
av.sub.d).sup.2}/.SIGMA- .v.sub.i].sup.0.5 (5)
[0109] In the above equations (4) and (5), "i" denotes an i-th
section when the mesopore diameter axis is divided into an N number
of sections, with the proviso that 1 to N are natural numbers.
v.sub.i denotes the volume of particles having a diameter in the
i-th section and d.sub.i is a geometric mean between the lower
limit and the upper limit of particle diameter in the i-th
section.
[0110] (3) Evaluation of Mesoporous Structure of Mesoporous Silica
Particles
[0111] Mesoporous silica particles were dispersed in ion exchange
water to a concentration of 0.1 wt % and processed with an
ultrasonic dispersion device for 5 minutes to prepare a sample. The
sample was dropped to a grid and dried at room temperature under
reduced pressure. The mesoporous silica particles on the grid were
observed through a transmission electron microscope to evaluate the
mesoporous structure of the particles.
[0112] (4) Determination of the Amount of Surfactant Existent in
the Mesopores of Mesoporous Silica Particles
[0113] Fully dried mesoporous silica particles were calcined at
500.degree. C. for 6 hours to measure a weight change before and
after calcination to obtain the amount of a surfactant existent in
the mesopores of the mesoporous silica particles.
[0114] (5) X-Ray Diffraction Measurement of Mesoporous Silica
Particles
[0115] Mesoporous silica particles powders were filled into a
measurement holder and measured at a CuK.alpha.-ray with an X-ray
diffraction device (RINT-1400 of Rigaku Denki Co., Ltd.).
Example 1
[0116] A block copolymer of ethylene glycol and propylene glycol
(Pluronic-P123 of BASF Co., Ltd.) was dissolved in ion exchange
water to prepare a 20 wt % surfactant solution. 150 g of the
surfactant solution, 44 g of 25 wt % sulfuric acid and 73 g of ion
exchange water were mixed together to prepare a transparent
solution. 133 g of sodium silicate (containing 15 wt % of SiO.sub.2
and 5.1 wt % of Na.sub.2O) was added dropwise to this solution
under stirring to obtain a cloudy reaction mixture. The pH of the
reaction mixture was 2.7.
[0117] The reaction mixture was maintained at 30.degree. C. for 1
hour under stirring, heated at 95.degree. C. and maintained at that
temperature for 12 hours to produce mesoporous silica particles
having the surfactant existent in mesopores.
[0118] Thereafter, a polyethylene pot was filled with 390 g of the
above reaction mixture and 1,520 g of zirconia balls having a
diameter of 2 mm and sealed up without a dead volume in the pot to
wet pulverize the mixture with a pot mill. The amount of the
surfactant existent in the mesopores was 150 parts by weight based
on 100 parts by weight of silica, the pH of the solution to be
processed was 2.8, and the content of the mesoporous silica
particles in the solution was 5 wt %.
[0119] After particles were collected by centrifuging the wet
pulverized reaction mixture, dispersing particles in ion exchange
water and re-centrifugation were repeated to remove sulfuric acid
and sodium sulfate.
[0120] Then, the mesoporous silica particles were dispersed in
ethanol to a concentration of 1 wt %, stirred under heating and
centrifuged to collect particles. Stirring in ethanol and the
collection of particles by centrifugation were repeated to remove
the surfactant, and the particles were dried to obtain mesoporous
silica particles of the present invention.
[0121] Since three diffraction peaks corresponding to d values of
9.2, 5.8 and 5.2 were seen by the X-ray diffraction measurement of
the obtained mesoporous silica particles, it was confirmed that the
mesoporous silica particles had a regular mesoporous structure.
Since only a broad halo was seen and no peak derived from
crystalline silica was seen on a high angle region, it was
confirmed that the mesoporous silica particles were amorphous.
[0122] As a sharp peak was seen at a mesopore diameter of about 8
nm in the mesopore distribution curve of the mesoporous silica
particles, it was verified that the mesoporous silica particles had
uniform mesopores.
[0123] The physical properties of the mesoporous silica particles
are shown in Table 1 and the mesopore distribution curve is shown
in FIG. 1.
Comparative Examples 1 and 2
[0124] A block copolymer of ethylene glycol and propylene glycol
(Pluronic-P123 of BASF Co., Ltd.) was dissolved in ion exchange
water to prepare a 20 wt % surfactant solution. 150 g of the
surfactant solution, 44 g of 25 wt % sulfuric acid and 73 g of ion
exchange water were mixed together to prepare a transparent
solution. 133 g of sodium silicate (containing 15 wt % of SiO.sub.2
and 5.1 wt % of Na.sub.2O) was added dropwise to this solution
under stirring to obtain a cloudy reaction mixture. The pH of the
reaction mixture was 2.7.
[0125] The reaction mixture was maintained at 30.degree. C. for 1
hour under stirring, heated at 95.degree. C. and maintained at that
temperature for 12 hours to produce mesoporous silica particles
having the surfactant existent in mesopores.
[0126] After particles were collected by centrifuging the reaction
mixture, dispersing particles in ion exchange water and
re-centrifugation were repeated to remove sulfuric acid and sodium
sulfate from the reaction mixture.
[0127] Then, the mesoporous silica particles were dispersed in
ethanol to a concentration of 1 wt %, stirred under heating and
centrifuged to collect particles. Stirring in ethanol and the
collection of particles by centrifugation were repeated to remove
the surfactant so as to obtain mesoporous silica particles as
Comparative Example 1.
[0128] Since three diffraction peaks corresponding to d values of
9.2, 5.8 and 5.2 were seen by the X-ray diffraction measurement of
the obtained mesoporous silica particles of Comparative Example 1,
it was confirmed that the mesoporous silica particles had a regular
mesoporous structure.
[0129] As a sharp peak was seen at a mesopore diameter of about 8
nm in the mesopore distribution curve of the mesoporous silica
particles, it was confirmed that the mesoporous silica particles
had uniform mesopores.
[0130] Then, the mesoporous silica particles were dispersed in ion
exchange water to prepare a dispersion containing 5 wt % of
mesoporous silica particles. A polyethylene pot was filled with 390
g of the above dispersion and 1,520 g of zirconia balls having a
diameter of 2 mm and sealed up without a dead volume in the pot to
wet pulverize the dispersion with a pot mill. The amount of the
surfactant existent in the mesopores was 8 parts by weight based on
100 parts by weight of silica, and the pH of the processed solution
was 5.6.
[0131] A precipitate was collected from the processed solution by
centrifugation after wet pulverizing to obtain mesoporous silica
particles as Comparative Example 2.
[0132] Since no distinct peak was seen by the X-ray diffraction
measurement of the obtained mesoporous silica particles of
Comparative Example 2, it was confirmed that the regular mesoporous
structure collapsed.
[0133] As no distinct peak was seen in the mesopore distribution
curve of the mesoporous silica particles, it was verified that the
mesopores were lost.
[0134] The physical properties of the mesoporous silica particles
of Comparative Examples 1 and 2 are shown in Table 1 and the
mesopore distribution curves are shown in FIG. 1.
Example 2
[0135] A block copolymer of ethylene glycol and propylene glycol
(Pluronic-F127 of BASF Co., Ltd.) was dissolved in ion exchange
water to prepare a 10 wt % surfactant solution. 210 g of the
surfactant solution, 59 g of 25 wt % sulfuric acid and 291 g of ion
exchange water were mixed together to prepare a transparent
solution. 140 g of sodium silicate (containing 15 wt % of SiO.sub.2
and 5.1 wt % of Na.sub.2O) was added dropwise to this solution
under stirring to obtain a cloudy reaction mixture. The pH of the
reaction mixture was 1.0.
[0136] The reaction mixture was maintained at 30.degree. C. for 10
hours under stirring, heated at 80.degree. C. and maintained at
that temperature for 12 hours to produce mesoporous silica
particles having the surfactant existent in mesopores.
[0137] Thereafter, part of the solution was removed from the above
reaction mixture by decantation, and the content of the mesoporous
silica particles in the reaction mixture was adjusted to 5 wt
%.
[0138] A polyethylene pot was filled with 390 g of the above
reaction mixture containing 5 wt % of the mesoporous silica
particles and 1,520 g of zirconia balls having a diameter of 2 mm
and sealed up without a dead volume in the pot to wet pulverize the
mixture with a pot mill. The amount of the surfactant existent in
the mesopores was 100 parts by weight based on 100 parts by weight
of silica, and the pH of the processed solution was 1.1.
[0139] After particles were collected by centrifuging the processed
solution, dispersing particles in ion exchange water and
re-centrifugation were repeated to remove sulfuric acid and sodium
sulfate from the processed solution.
[0140] Then, the mesoporous silica particles were dispersed in
ethanol to a concentration of 1 wt %, stirred under heating and
centrifuged to collect particles. Stirring in ethanol and the
collection of particles by centrifugation were repeated to remove
the surfactant, and the particles were dried to obtain mesoporous
silica particles of the present invention.
[0141] Since three diffraction peaks corresponding to d values of
12.2, 8.6 and 7.0 were seen by the X-ray diffraction measurement of
the obtained mesoporous silica particles, it was confirmed that the
mesoporous silica particles had a regular mesoporous structure.
Since only a broad halo was seen and no peak derived from
crystalline silica was seen on a large angle side, it was confirmed
that the mesoporous silica particles were amorphous.
[0142] As a sharp peak was seen at a mesopore diameter of about 9
nm in the mesopore distribution curve of the mesoporous silica
particles, it was verified that the mesoporous silica particles had
uniform mesopores.
[0143] The physical properties of the obtained mesoporous silica
particles are shown in Table 1.
Comparative Examples 3 and 4
[0144] A block copolymer of ethylene glycol and propylene glycol
(Pluronic-F127 of BASF Co., Ltd.) was dissolved in ion exchange
water to prepare a 10 wt % surfactant solution. 210 g of the
surfactant solution, 59 g of 25 wt % sulfuric acid and 291 g of ion
exchange water were mixed together to prepare a transparent
solution. 140 g of sodium silicate (containing 15 wt % of SiO.sub.2
and 5.1 wt % of Na.sub.2O) was added dropwise to this solution
under stirring to obtain a cloudy reaction mixture. The pH of the
reaction mixture was 1.0.
[0145] The reaction mixture was maintained at 30.degree. C. for 10
hours under stirring, heated at 80.degree. C. and maintained at
that temperature for 12 hours to produce mesoporous silica
particles having the surfactant existent in mesopores.
[0146] After a precipitate was obtained by centrifuging the
reaction mixture, dispersing particles in ion exchange water and
re-centrifugation were repeated to remove sulfuric acid and sodium
sulfate from the reaction mixture.
[0147] Then, the mesoporous silica particles were dispersed in
ethanol to a concentration of 1 wt %, stirred under heating and
centrifuged to collect particles. Stirring in ethanol and the
collection of particles by centrifugation were repeated to remove
the surfactant so as to obtain mesoporous silica particles as
Comparative Example 3.
[0148] Since three diffraction peaks corresponding to d values of
12.2, 8.6 and 7.0 were seen by the X-ray diffraction measurement of
the obtained mesoporous silica particles of Comparative Example 3,
it was confirmed that the mesoporous silica particles had a regular
mesoporous structure.
[0149] As a sharp peak was seen at a mesopore diameter of about 9
nm in the mesopore distribution curve of the mesoporous silica
particles, it was verified that the mesoporous silica particles had
uniform mesopores.
[0150] Then, the mesoporous silica particles were dispersed in ion
exchange water to prepare a dispersion containing 5 wt % of the
mesoporous silica particles. A polyethylene pot was filled with 390
g of the above dispersion and 1,520 g of zirconia balls having a
diameter of 2 mm and sealed up without a dead volume in the pot to
wet pulverize the dispersion with a pot mill. The amount of the
surfactant existent in the mesopores was 7 parts by weight based on
100 parts by weight of silica, and the pH of the processed solution
was 5.6.
[0151] A precipitate was collected from the processed solution by
centrifugation after wet pulverizing to obtain mesoporous silica
particles as Comparative Example 4.
[0152] Since no distinct peak was seen by the X-ray diffraction
measurement of the obtained mesoporous silica particles of
Comparative Example 4, it was confirmed that the regular mesoporous
structure collapsed.
[0153] As no distinct peak was seen in the mesopore distribution
curve of the mesoporous silica particles, it was verified that
mesopores were lost.
[0154] The physical properties of the mesoporous silica particles
of Comparative Examples 3 and 4 are shown in Table 1.
Example 3
[0155] A block copolymer of ethylene glycol and propylene glycol
(Pluronic-P123 of BASF Co., Ltd.) was dissolved in ion exchange
water to prepare a 20 wt % surfactant solution. 100 g of the
surfactant solution, 44 g of 25 wt % sulfuric acid and 123 g of ion
exchange water were mixed together to prepare a transparent
solution. 133 g of sodium silicate (containing 15 wt % of SiO.sub.2
and 5.1 wt % of Na.sub.2O) was added dropwise to this solution
under stirring to obtain a cloudy reaction mixture. The pH of the
reaction mixture was 2.7.
[0156] The reaction mixture was maintained at 30.degree. C. for 10
hours under stirring to produce mesoporous silica particles having
the surfactant existent in mesopores.
[0157] Thereafter, a polyethylene pot was filled with 390 g of the
above reaction mixture and 1,520 g of zirconia balls having a
diameter of 2 mm and sealed up without a dead volume in the pot to
wet pulverize the mixture with a pot mill. The amount of the
surfactant existent in the mesopores was 100 parts by weight based
on 100 parts by weight of silica, the pH of the processed solution
was 2.8, and the content of the mesoporous silica particles in the
processed solution was 5 wt %.
[0158] The above processed solution after wet pulverizing was
maintained at 80.degree. C. for 12 hours to age the mesoporous
silica particles.
[0159] After particles were collected by centrifuging the above
processed solution after aging, dispersing particles in ion
exchange water and re-centrifugation were repeated to remove
sulfuric acid and sodium sulfate from the processed solution.
[0160] Then, the mesoporous silica particles were dispersed in
ethanol to a concentration of 1 wt %, stirred under heating and
centrifuged to collect particles. Stirring in ethanol and the
collection of particles by centrifugation were repeated to remove
the surfactant, and the-particles were dried to obtain mesoporous
silica particles of the present invention.
[0161] Since three diffraction peaks corresponding to d values of
9.4, 5.9 and 5.2 were seen by the X-ray diffraction measurement of
the obtained mesoporous silica particles, it was confirmed that the
mesoporous silica particles had a regular mesoporous structure.
Since only a broad halo was seen and no peak derived from
crystalline silica was seen on a large angle side, it was confirmed
that the mesoporous silica particles were amorphous.
[0162] As a sharp peak was seen at a mesopore diameter of about 8
nm in the mesopore distribution curve of the mesoporous silica
particles, it was verified that the mesoporous silica particles had
uniform mesopores.
[0163] The physical properties of the obtained mesoporous silica
particles are shown in Table 1.
Example 4
[0164] A block copolymer of ethylene glycol and propylene glycol
(Pluronic-P123 of BASF Co., Ltd.) was dissolved in ion exchange
water to prepare a 20 wt % surfactant solution. 100 g of the
surfactant solution, 44 g of 25 wt % sulfuric acid and 123 g of ion
exchange water were mixed together to prepare a transparent
solution. 133 g of sodium silicate (containing 15 wt % of SiO.sub.2
and 5.1 wt % of Na.sub.2O) was added dropwise to this solution
under stirring to obtain a cloudy reaction mixture. The pH of the
reaction mixture was 2.7.
[0165] The reaction mixture was maintained at 30.degree. C. for 10
hours under stirring, heated at 80.degree. C. and maintained at
that temperature for 12 hours to produce mesoporous silica
particles having the surfactant existent in mesopores.
[0166] After particles were collected by centrifuging the above
mixture solution, dispersing particles in ion exchange water and
re-centrifugation were repeated to remove sulfuric acid and sodium
sulfate from the reaction mixture.
[0167] Ion exchange water was added to the above precipitate
obtained by centrifugation and stirred to obtain a dispersion
containing 5 wt % of mesoporous silica particles.
[0168] A polyethylene pot was filled with 390 g of the above
dispersion and 1,520 g of zirconia balls having a diameter of 2 mm
and sealed up without a dead volume in the pot to wet pulverize the
dispersion with a pot mill. The amount of the surfactant existent
in the mesopores was 85 parts by weight based on 100 parts by
weight of silica, and the pH of the processed solution was 5.8.
[0169] A precipitate was collected from the processed solution
after wet pulverizing by centrifugation.
[0170] Then, the mesoporous silica particles were dispersed in
ethanol to a concentration of 1 wt %, stirred under heating and
centrifuged to collect particles. Stirring in ethanol and the
collection of particles by centrifugation were repeated to remove
the surfactant, and the particles were dried to obtain mesoporous
silica particles.
[0171] Since three diffraction peaks corresponding to d values of
9.2, 5.8 and 5.2 were seen by the X-ray diffraction measurement of
the obtained mesoporous silica particles, it was confirmed that the
mesoporous silica particles had a regular mesoporous structure.
Since only a broad halo was seen and no peak derived from
crystalline silica was seen on a large angle side, it was confirmed
that the mesoporous silica particles were amorphous.
[0172] As a sharp peak was seen at a mesopore diameter of about 8
nm in the mesopore distribution curve of the mesoporous silica
particles, it was verified that the mesoporous silica particles had
uniform mesopores but the area of the peak slightly decreased.
[0173] The physical properties of the obtained mesoporous silica
particles are shown in Table 1.
Example 5
[0174] An active silica solution was obtained by treating sodium
silicate (containing 4.0 wt % of SiO.sub.2 and 1.4 wt % of
Na.sub.2O) with a strong acid cationic exchange resin. This active
silica solution was added dropwise to an aqueous solution
containing 150 parts by weight of hexadecyltrimethylammonium
hydroxide and 200 parts by weight of 1,3,5-trimethylbenzene based
on 100 parts by weight of silica under stirring with a propeller
mixer. Then, sodium hydroxide was added to adjust the pH of the
reaction solution to 8.5. Stirring was continued to carry out a
reaction at 80.degree. C. for 3 hours to obtain a cloudy reaction
mixture. The pH of the reaction mixture was 8.4.
[0175] Part of the solution was removed from the above reaction
mixture by decantation to adjust the content of the mesoporous
silica particles in the reaction mixture to 5 wt %.
[0176] Thereafter, a polyethylene pot was filled with 390 g of the
above reaction mixture containing 5 wt % of mesoporous silica
particles and 1,520 g of zirconia balls having a diameter of 2 mm
and sealed up without a dead volume in the pot to wet pulverize the
mixture with a pot mill. The amount of the surfactant existent in
the mesopores was 150 parts by weight based on 100 parts by weight
of silica, the pH of the processed solution was 8.4, and the
content of the mesoporous silica particles in the processed
solution was 5 wt %.
[0177] After particles were collected by centrifuging the processed
solution, dispersing particles in ion exchange water and
re-centrifugation were repeated to remove sodium hydroxide from the
processed solution.
[0178] Then, the mesoporous silica particles were dispersed in
ethanol to a concentration of 1 wt %, stirred under heating and
centrifuged to collect particles. Stirring in ethanol and the
collection of particles by centrifugation were repeated to remove
the surfactant so as to obtain mesoporous silica particles.
[0179] Since a diffraction peak corresponding to a d value of 7.7
was seen by the X-ray diffraction measurement of the obtained
mesoporous silica particles, it was confirmed that the mesoporous
silica particles had a regular mesoporous structure. Since only a
broad halo was seen and no peak derived from crystalline silica was
seen on a large angle side, it was confirmed that the mesoporous
silica particles were amorphous.
[0180] As a sharp peak was seen at a mesopore diameter of about 7
nm in the mesopore distribution curve of the mesoporous silica
particles, it was verified that the mesoporous silica particles had
uniform mesopores.
[0181] The physical properties of the mesoporous silica particles
are shown in Table 1.
Comparative Example 5
[0182] An active silica solution was obtained by treating sodium
silicate (containing 4.0 wt % of SiO.sub.2 and 1.4 wt % of
Na.sub.2O) with a strong acid cationic exchange resin. This active
silica solution was added little by little to an aqueous solution
containing 150 parts by weight of hexadecyltrimethylammonium
hydroxide and 200 parts by weight of 1,3,5-trimethylbenzene based
on 100 parts by weight of silica under stirring with a-propeller
mixer. Then, sodium hydroxide was added to adjust the pH of the
reaction solution to 8.5. Stirring was continued to carry out a
reaction at 80.degree. C. for 3 hours to obtain a precipitate which
was then filtered and rinsed to obtain mesoporous silica particles
having the surfactant existent in mesopores.
[0183] Thereafter, the mesoporous silica particles were dispersed
in ethanol to a concentration of 1 wt %, stirred under heating and
centrifuged to collect a precipitate. Stirring in ethanol and the
collection of a precipitate by centrifugation were repeated to
remove the surfactant.
[0184] 20 parts by weight of the mesoporous silica particles from
which the above surfactant had been removed, 1 part by weight of
diallyl dimethylammonium chloride polymer and 79 parts by weight of
ion exchange water were mixed together and pre-dispersed with a
homogenizer (Ultra-Turrax T-50 of Ika Co., Ltd.) to obtain a
mesoporous silica particle dispersion having a silica content of 20
wt %.
[0185] The above dispersion was let pass through an orifice
repeatedly by a high-pressure homogenizer (Nanomizer LA-31 of
Nanomizer Co., Ltd.) at processing pressure of 80 MPa to obtain
mesoporous silica particles as Comparative Example 5.
[0186] Since a diffraction peak corresponding to a d value of 7.7
was seen by the X-ray diffraction measurement of the obtained
mesoporous silica particles, it was confirmed that the mesoporous
silica particles had a regular mesoporous structure. However, as
the diffraction peak was broader than that of Example 5, the
mesoporous silica particles of Comparative Example 5 were inferior
to the mesoporous silica particles of Example 5 in structural
regularity.
[0187] As a peak was seen at a mesopore diameter of about 7 nm in
the mesopore distribution curve of the mesoporous silica particles
and broader than that of Example 5, it was verified that the
mesoporous silica particles of Comparative Example 5 were inferior
to the mesoporous silica particles of Example 5 in the uniformity
of mesopores.
[0188] The physical properties of the obtained mesoporous silica
particles are shown in Table 1.
1 TABLE 1 physical properties of mesopores particle diameter
specific average average surface Mesopore mesopore geometric
mesopore particle geometric area volume diameter standard
retainability mesoporous diameter standard (m.sup.2/g) (mL/g) (nm)
deviation (%) structure (.mu.m) deviation Example 1 830 1.11 7.0
1.6 94 Honeycomb-like 0.22 1.9 C. Ex. 1 850 1.18 7.0 1.6 100
Honeycomb-like 16 2.0 C. Ex. 2 390 0.59 17 1.8 50 Irregular 0.27
2.0 Example 2 680 0.86 6.7 1.5 100 3-D net-like 0.33 1.8 C. Ex. 3
680 0.86 6.7 1.5 100 3-D net-like 41 2.4 C. Ex. 4 390 0.52 15 1.9
61 Irregular 0.39 1.9 Example 3 850 1.17 7.1 1.6 99 Honeycomb-like
0.22 1.8 Example 4 750 0.94 7.5 1.7 80 Honeycomb-like 0.21 1.9
Example 5 860 1.08 5.8 1.5 95 Honeycomb-like 0.32 1.8 C. Ex. 5 820
1.05 5.9 2.1 95 Honeycomb-like 0.42 1.3 C. Ex.: Comparative
Example
Example 6
[0189] Ion exchange water was added to the mesoporous silica
particles obtained in Example 1 to a concentration of 15 wt % and
agitated violently to obtain the mesoporous silica particle
dispersion of the present invention.
[0190] 60 g of the mesoporous silica particle dispersion and 45 g
of a 10 wt % polyvinyl alcohol solution were mixed together to
prepare a coating solution for forming a thin film. This coating
solution was applied to a hydrophilized PET film and dried to form
a thin film.
[0191] The thin film had a glossy surface. When its section was
observed through an optical microscope, it was confirmed that it
was a flat homogenous film.
Comparative Example 6
[0192] A thin film was obtained in the same manner as in Example 6
except that the mesoporous silica particles obtained in Comparative
Example 1 were used.
[0193] The thin film had a rough surface. When its section was
observed through an optical microscope, it was found that the
surface was very rough and coarse particles were contained in the
film.
Example 7
[0194] A dispersion containing 10 wt % of mesoporous silica
particles was prepared by adding ion exchange water to the
mesoporous silica particles obtained in Example 1. The dispersion
was introduced into a spray dryer and granulated by spraying to
obtain the mesoporous silica particle granulated product of the
present invention.
[0195] When the obtained mesoporous silica particle granulated
product was observed through a scanning electron microscope, the
granulated product was composed of agglomerates of fine particles
each of which was as large as about 120 .mu.m. A large number of
macropores having a diameter of about 100 to 300 nm derived from
the gap between fine particles were existent in the granulated
product.
[0196] When the mesopore volume, average mesopore diameter,
.sigma..sub.p and X-ray diffraction of the mesoporous silica
particle granulated product were measured, the same results as
those of Example 1 were obtained and it was confirmed that the
product was a granulated product having macropores for facilitating
the dispersion in particles of a substance while retaining the
characteristic properties of mesoporous silica particles.
Comparative Example 7
[0197] Spray granulation was carried out in the same manner as in
Example 7 except that the mesoporous silica particles obtained in
Comparative Example 1 were used. The obtained granulated product
was fragile and got powdered immediately.
[0198] When the powdered granulated product was observed through a
scanning electron microscope, it was composed of particles as large
as about 10 to 100 .mu.m each of which was just a mass, and the
existence of macropores was not observed.
[0199] As described above, according to the production process of
the present invention, even when an aqueous dispersion medium is
used, mesoporous silica particles can be pulverized into
submicron-sized fine particles while the collapse of mesopores is
suppressed.
[0200] According to the present invention, there are provided novel
mesoporous silica particles having a particle diameter of 1 .mu.m
or less which could not be achieved in the prior art, a
satisfactory mesopore volume and uniformity in mesopore diameter.
When the mesoporous silica particles are used as an ink absorbent
for ink jet recording paper, they greatly improve the gloss and
printing density of the ink jet recording paper, compared with
those of the prior art. The mesoporous silica particles of the
present invention are useful as a low-dielectric film, catalyst
support, separating agent, adsorbent and medical carrier for
medicines in addition to the above applications.
* * * * *