U.S. patent application number 11/167427 was filed with the patent office on 2005-10-27 for silica-calcium carbonate composite particles.
This patent application is currently assigned to Nittetsu Mining Co., Ltd.. Invention is credited to Mitsuhashi, Kouhei, Tanabe, Katsuyuki.
Application Number | 20050235872 11/167427 |
Document ID | / |
Family ID | 18578889 |
Filed Date | 2005-10-27 |
United States Patent
Application |
20050235872 |
Kind Code |
A1 |
Tanabe, Katsuyuki ; et
al. |
October 27, 2005 |
Silica-calcium carbonate composite particles
Abstract
Silica-calcium carbonate composite particles having the
characteristics of both synthetic silica and calcium carbonate are
described along with paper having the particles internally filled
therein and a method for making the particles. In the carbonation
reaction, which typically involves a step of forming calcium
carbonate, while agitating a calcium hydroxide slurry, a mixed gas
of carbon dioxide and air is introduced thereinto and synthetic
silica, such as colloidal silica or the like, is added before the
carbonation rate arrives at 95% but after commencement of the
carbonation reaction, followed by further introduction of the mixed
gas to continue the carbonation reaction and completion of the
carbonation reaction at the time when the pH of the slurry reaches
7, thereby providing the composite particles.
Inventors: |
Tanabe, Katsuyuki; (Tokyo,
JP) ; Mitsuhashi, Kouhei; (Tokyo, JP) |
Correspondence
Address: |
FLYNN THIEL BOUTELL & TANIS, P.C.
2026 RAMBLING ROAD
KALAMAZOO
MI
49008-1631
US
|
Assignee: |
Nittetsu Mining Co., Ltd.
|
Family ID: |
18578889 |
Appl. No.: |
11/167427 |
Filed: |
June 27, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11167427 |
Jun 27, 2005 |
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10204532 |
Aug 20, 2002 |
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10204532 |
Aug 20, 2002 |
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PCT/JP01/01614 |
Mar 2, 2001 |
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Current U.S.
Class: |
106/463 ;
106/482 |
Current CPC
Class: |
C01F 11/181 20130101;
C01F 11/182 20130101; D21H 17/675 20130101 |
Class at
Publication: |
106/463 ;
106/482 |
International
Class: |
D21C 009/00; C09C
001/02; C04B 014/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 3, 2000 |
JP |
2000-058272 |
Claims
What is claimed is:
1. Silica-calcium carbonate composite particles comprising fine
particles of silica having an average size of from 1 to 100 nm
attached to and affixed on the outer surface of calcium carbonate
particles, said silica-calcium carbonate being formed by a method
comprising the steps of: conducting a carbonation reaction in a
reaction system in which crystal nuclei of calcium carbonate are
formed; adding colloidal or anhydrous silica to the reaction system
until the carbonation reaction is about 95% complete; and
completing the carbonation reaction to form the silica-calcium
carbonate composite particles.
2. A filler material containing the silica-calcium carbonate
composite particles of claim 1.
3. A pigment material containing the silica-calcium carbonate
composite particles of claim 1.
4. A printing paper containing the silica-calcium carbonate
composite particles of claim 1.
5. A rubber material containing the silica-calcium carbonate
composite particles of claim 1.
6. A plastic material containing the silica-calcium carbonate
composite particles of claim 1.
7. Silica-calcium carbonate composite particles comprising fine
particles of silica having an average size of from 1 to 100 nm
attached to and affixed on calcium carbonate particles having
ground calcium carbonate as a core portion and precipitated calcium
carbonate as a surface portion, said fine particles of silica being
formed from colloidal or anhydrous silica.
Description
[0001] This is a division of Ser. No. 10/204,532, filed Aug. 20,
2002, which was the national stage of International Application No.
PCT/JP01/01614, filed Mar. 2, 2001, which International Application
was not published in English.
TECHNICAL FIELD
[0002] This invention relates to silica-calcium carbonate composite
particles having both excellent characteristics of synthetic silica
and excellent characteristics of calcium carbonate, paper wherein
the particles are internally filled therein and/or coated thereon,
and also to a method for making the particles. More particularly,
the invention relates to silica-calcium carbonate composite
particles having a novel structure, characterized in that synthetic
silica is fixed on the surfaces of calcium carbonate particles as
it is while keeping the characteristics of the synthetic silica
that has good properties such as a high specific surface area, high
gas absorbability, a high oil absorption and the like, and also to
paper wherein the particles are internally filled therein and/or
coated thereon, and a method for making the particles.
TECHNICAL BACKGROUND
[0003] With respect to calcium carbonate that is one of the
constituents forming the composite particles of the invention,
there are known ground calcium carbonate and precipitated calcium
carbonate. The former ground calcium carbonate is a finely
pulverized product of limestone which naturally occurs and has high
whiteness, and can be made according to relatively simple processes
such as pulverization, classification and the like. The particles
have an irregular form inherent to a physically pulverized product
and thus a wide size distribution, and can be widely used as a
filler or pigment for plastics, rubbers and resins and also for
paper-making while making use of their high whiteness and
economy.
[0004] The latter synthetic calcium carbonate is chemically
synthesized calcium carbonate. For the methods of preparing the
particles, there are known a carbonation process wherein carbon
dioxide is introduced into a calcium hydroxide (slaked lime) slurry
for chemical precipitation, a calcium chloride soda process wherein
the reaction between calcium chloride and sodium carbonate is used
for the precipitation, a soda ash-lime process where the reaction
between calcium hydroxide and sodium carbonate is used for the
precipitation, and a water treating process wherein the reaction
between calcium hydroxide and calcium bicarbonate is used for the
precipitation.
[0005] Such known processes as mentioned above are now in use for
the process of preparing precipitated calcium carbonate. In our
country, a starting limestone material of good quality occurs
richly, eventually leading to the production using a carbonation
process in most cases. In the preparation of precipitated calcium
carbonate, it is possible to control a particulate form, a particle
size and the like within certain ranges by controlling the
preparation conditions including a concentration of calcium in a
starting slaked lime slurry, a temperature at which the carbonation
reaction is carried out, a rate of carbonation and the like.
[0006] It is well known that the particles take various forms
particularly including colloidal, cubic, spindle-shaped, columnar
and the like forms, and these are, respectively, used for different
main applications. More particularly, the colloidal calcium
carbonate is in the form of colloidal particles having a particle
diameter of 0.04.about.0.08 .mu.m and has been used as a filler for
plastics, rubbers, paints and the like. The cube-shaped calcium
carbonate is in the form of cubic particles with a particle
diameter of 0.1.about.0.2 .mu.m and is excellent, particularly, as
a pigment for paper-making.
[0007] The spindle-shaped calcium carbonate is in the form of
spindle-shaped particles with a major axis of 0.5.about.5.0 .mu.m
and a minor axis of 0.1.about.1.0 .mu.m and are widely utilized as
a filler for paper-making. The columnar calcium carbonate is in the
form of columnar particles having a major axis of 1.0.about.20
.mu.m and a minor axis of 0.1.about.1.0 .mu.m, and mention is made
of its application as a pigment, filler for paper-making or the
like.
[0008] This precipitated calcium carbonate is produced by
relatively simple preparation process as set out hereinabove and
has prominent properties with respect to physical stability,
diversity, the economy in particulate form, whiteness and the like,
thus being used in various industrial applications.
[0009] The synthetic silica that is the other constituent forming
the composite particles of the invention is now described below.
For industrial silica materials, mention is made of colloidal
silica, silica gel, anhydrous silica, white carbon and the like,
which are used in a variety of fields while making use of excellent
characteristics such as a high specific surface area, high gas
absorptivity, fineness, infiltration or adsorption power into fine
interstices, high adhesion, high oil absorption, uniformity of
particles, high dispersability and the like.
[0010] Of these, colloidal silica consists of amorphous silica,
which is obtained by removing impurities from a silicic acid
compound to provide a sol of silicic anhydride and controlling the
pH and concentration to stabilize the sol and which has spherical,
chain-shaped and irregular forms. These have been applied as a
processability improver of a resin, a wax, a sizing agent, a
quality improver of a latex, a binder, a printability improver for
printing paper, a metal surface treating agent, or the like.
[0011] A silica gel consists of anhydrous silicic acid obtained by
decomposing sodium silicate with an inorganic acid and has been
used for applications as a desiccant for foods, medicines, fibers,
gases or air, a catalyst or a carrier therefor, a filler for
rubbers, or a thickening or precipitation inhibitor for paints or
inks. Anhydrous silica is obtained by hydrolyzing silicon
tetrachloride and is utilized for a filler or reinforcing agent for
paints, inks, resins, rubbers and the like.
[0012] Among inorganic materials for industry, calcium carbonate
and silica materials are those materials that are most widely
employed, and, respectively, have excellent characteristics, also
have demerits. For instance, where calcium carbonate is used as a
filler for rubber, its surface is so inert as to be poor in
affinity for rubber molecules physically and chemically, thus
little reinforcing effect on rubber products is obtained.
[0013] When used as a pigment or filler for paper-making,
particularly for printing paper, the carbonate is lower in ink
absorption than synthetic silica, with the possibility that
troubles may occur with respect to the ink setting property,
strike-through of an ink and opacity of a printed portion. In
addition, because of the poor resistance to an acid, it is
difficult to use it in combination with an acidic substance such as
in an acidic paper-making procedure using aluminum sulfate.
[0014] Moreover, where the silica material is employed as a pigment
for paper-making, it causes a coating agent to be increased in
viscosity, thus making it difficult to formulate in the coating
agent at a high concentration. It has been indicated that upon use
as a filler for rubber, the viscosity of the resultant rubber
composition becomes very high.
[0015] Colloidal silica may produce problems with respect to the
variations in the temperature, pH, concentration of an electrolyte
of a solution, the long-term storage, the stability against organic
solvents and the like. In addition, colloidal silica is more
expensive than calcium carbonate, thus disenabling one to formulate
the colloidal silica in a product in high concentration or use it
in large amounts.
[0016] Hence, in order to solve or reduce the deficiencies of
calcium carbonate, studies have been made from old on the
techniques of making a composite product of calcium carbonate and
silica and also on applications thereof, under which many proposals
have been made.
[0017] For instance, Japanese Patent Publication No. Sho 60-72963
proposes a composite improved pigment wherein the surfaces of
calcium carbonate particles are activated with an inorganic acid,
and silicic acid or a silicate is reacted on the surfaces to form a
covering layer of silicic acid or the silicate via CaSiO.sub.3
formed by the reaction.
[0018] Japanese Patent Publication No. Hei 4-63007 proposes a
method of making a specific type of composite powder made of a
powder, such as of calcium carbonate and hydrous silicic acid,
which is obtained according to a physical technique wherein a
mixture of a powder, such as of calcium carbonate and hydrous
silicic acid, is ground and which is provided with an
ink-strike-through preventing property and is thus suitable as a
filler for paper. Japanese Patent Publication No. Hei 11-107189
proposes a method of making composite particles wherein fine
particles of calcium carbonate or the like are dispersed in an
alkali silicate solution, to which a mineral acid is added under
specific conditions to cause the fine particles of calcium
carbonate or the like to be uniformly incorporated in the particles
of the hydrous silicic acid.
[0019] Moreover, applications of the composite product of silica
and calcium carbonate include, for example, a carrier for
agricultural chemicals (Japanese Laid-open Patent Publication No.
Sho 60-222402), a formulating agent for thermal paper (Japanese
Laid-open Patent Application No. Sho 61-118287), a pigment for ink
jet recording paper (Japanese Patent Publication No. Hei 8-1038), a
filler for reinforcing rubber or the like (Japanese Laid-open
Patent Application No. Hei 11-29319), and the like. In these
publications, there may be exemplified preparation methods or
structures different from those of the above-stated composite
product.
[0020] For instance, the composite material set out in Japanese
Laid-open Patent Application No. Sho 60-222402 is such that a metal
such as Zn, Mg, Al or the like is caused to co-exist in the course
of a carbonation reaction, thereby permitting the metal to co-exist
in the resultant composite material, and the composed material
described in Japanese Laid-open Patent Application No. Sho
61-118287 is one obtained by co-precipitation of sodium silicate
and a water-soluble calcium compound, such as calcium hydroxide,
through a carbonation reaction. The composition material of
Japanese Patent Publication No. Hei 8-1038 is one obtained by
sodium silicate and calcium chloride, followed by carbonation
reaction.
[0021] These techniques can achieve an effect to some extent in
respect of the fact that the defects of calcium carbonate are
covered up while making use of the characteristics inherent to
silica. However, except for the physical technique disclosed in
Japanese Laid-open Patent Application No. Hei 4-63007 or Japanese
Laid-open Patent Application No. Hei 11-29319, the composite
materials are ones wherein silica is precipitated on the surface of
calcium carbonate in a system for coverage with the silica film,
calcium carbonate and silica are subjected to co-precipitation, and
calcium carbonate is formed, followed by carbonation. There are no
cases such that fine particles of silica are added to from outside
the system to permit the fine particles of silica to be attached to
and fixed on the surfaces of the calcium carbonate.
PROBLEMS TO SOLVE
[0022] Under the circumstances stated hereinabove, the formation of
the composite material by the chemical techniques known up to now
differs from the manner of fixing silica particles on the surfaces
of calcium carbonate particles as they are. Eventually, it cannot
be expected that the excellent characteristics of fine particles of
silica are imparted thereto, and thus, such characteristics can be
shown only within a limited range.
[0023] We have made intensive studies on the formation of a
composite material of synthetic silica and calcium carbonate for
the purpose of realizing the high functionality of calcium
carbonate, with the result that the composite material of the
invention can be developed.
[0024] Accordingly, the invention has for the problem to be solved
the provision of novel silica-calcium carbonate composite particles
without a sacrifice of excellent characteristics of silica, such as
a high specific surface area, high gas adsorbability, fineness,
high infiltration into fine interstices and high adsorption, high
adhesion, uniformity of particles, high dispersability and the
like, and excellent characteristics of calcium carbonate, a paper
sheet having the particles internally filled therein or coated
therewith, and a method for making the particles.
[0025] More particularly, the invention has for its object the
provision of novel silica-calcium carbonate composite particles
having excellent characteristics inherent to both synthetic silica
and calcium carbonate, a paper sheet having the particles
internally filled therein and/or coated therewith, and a method for
making the particles.
DISCLOSURE OF THE INVENTION
[0026] The invention contemplates the provision of novel
silica-calcium carbonate composite particles, a paper sheet in
which the particles are internally filled therein and/or coated
thereon, and a method for making the particles. The composite
particles are characterized in that the fine particles of synthetic
silica are added before completion of the carbonation reaction so
that the fine particles of synthetic silica having an average size
ranging 1 nm.about.100 nm are attached to and fixed on the surfaces
of calcium carbonate.
[0027] The paper having the particles internally filled therein is
one wherein at least a part of a filler is made of the composite
particles by mixing the composite particles with pulp and other
chemicals for paper-making upon preparation of a paper stock in the
course of a paper-making step, followed by making paper from the
stock as a starting material. The paper coated with the particles
means paper wherein at least a part of a pigment contained in a
coating layer of the coated paper is made of the composite
particles, and is made by mixing the composite particles with a
binder and other pigments upon preparation of a coating in the
course of a coating step, followed by applying the coating on base
paper.
[0028] The method for making silica-calcium carbonate composite
particles is characterized in that fine particles of synthetic
silica are added to in the course of a carbonation reaction which
is a step of forming calcium carbonate, followed by completion of
the carbonation reaction.
[0029] In the invention, since the fine particles of synthetic
silica are fixed on the surfaces of calcium carbonate, the
composite material has the excellent characteristics of both
without lowering the characteristics of synthetic silica, such as a
high specific surface area, high gas absorbability, infiltration
into fine interstices and adsorption, high adhesion, high oil
absorption, particulate uniformity, high dispersability and the
like, and also the characteristics of calcium carbonate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a scanning electron microscopic (SEM) photograph
(.times.20,000) showing a particulate structure of silica-calcium
carbonate composite particles obtained in Example 1.
BEST MODE FOR CARRYING OUT THE INVENTION
[0031] The invention is now described in detail including the best
mode for carrying out the invention, which should not be construed
as limiting the invention thereto. Thus, it is to be understood
that the true spirit and scope of the invention is as defined in
the appended claims.
[0032] The silica-calcium carbonate composite particles of the
invention are prepared by adding synthetic silica particles in the
course of a carbonation reaction forming calcium carbonate as set
forth hereinbefore and completing the carbonation reaction.
[0033] The calcium carbonate, which is a first component of the two
components constituting the composite particles of the invention,
should preferably consist of precipitated calcium carbonate and is
not limited thereto. For instance, there may be used one which
includes precipitated calcium carbonate as a surface portion and
ground calcium carbonate as a core portion. In this connection, a
major proportion may be made either of ground calcium carbonate or
of synthetic calcium carbonate. These may be arbitrarily selected
depending on the characteristics required for the intended
silica-calcium carbonate composite particles.
[0034] It is known that precipitated calcium carbonate has various
shapes and sizes of particles, and especially, when such
precipitated calcium carbonate is used as calcium carbonate, the
shape and size of precipitated calcium carbonate can be selected
depending on the characteristics required for the intended
silica-calcium carbonate composite particles, thus being suited for
achieving the purposes of the invention. Among them, spindle-shaped
calcium carbonate is preferred in view of the fact that not only
can it be prepared in the vicinity of normal temperatures and the
control of preparation conditions is relatively easy, but also the
efficiency of adhesion of synthetic silica is most excellent in the
practice of the invention.
[0035] For the synthetic silica, which is the other constituent of
the composite particles of the invention, silicas which are
artificially prepared through some chemical reactions may be used
without limitation, but except naturally occurring silica, and
include colloidal silica, silica gel, anhydrous silica, white
carbon and the like. These silicas, i.e. silica materials, have
been widely used in various fields while making use of excellent
characteristics thereof such as a high specific surface area, high
gas absorbability, fineness, high infiltration into fine
interstices and adsorption, high adhesion, high oil absorption,
uniformity of particles, high dispersability and the like.
[0036] Among these synthetic silicas, colloidal silica is made of
amorphous silica having a round, chain-like, irregular or the like
form and obtained by removing impurities from a silicic acid
compound to provide a sol of silicic acid anhydride and controlling
its pH and concentration to stabilize the sol. Silica gel consists
of hydrous silicic acid obtained by decomposing sodium silicate
with an inorganic acid. Anhydrous silica is one obtained by
hydrolyzing silicon tetrachloride. White carbon is made of finely
powdered hydrous silicic acid obtained by decomposing an
organosilicon compound or sodium silicate.
[0037] As having stated hereinbefore, various types of synthetic
silicas are usable in the practice of the invention without
limitation. In order to obtain silica-calcium carbonate composite
particles of the invention, synthetic silica suited therefor should
be selected, and it is necessary to use synthetic silica whose
average size of the primary particles is in the range of
1.about.100 nm. In respect of the adsorption on and fixing to
calcium carbonate, colloidal silica and anhydrous silica are most
preferred among various silica materials. Anyway, the selection
should depend on the characteristics required for intended
silica-calcium carbonate composite particles.
[0038] Next, the method for making silica-calcium carbonate
composite particles of the invention is described in detail. The
silica-calcium carbonate composite particles of the invention are
made by adding synthetic silica in the course of the carbonation
reaction of the calcium in the step of forming calcium carbonate.
The calcium source includes slaked lime (calcium hydroxide)
obtained by hydrating the quick lime (calcium oxide) prepared by
firing limestone, calcium chloride, calcium nitrate or the like.
For the carbonation, there may be used a carbon dioxide-containing
gas such as an exhaust gas discharged upon the preparation of quick
lime as mentioned above, pure carbon dioxide, and soluble
carbonates such as sodium carbonate, sodium bicarbonate, calcium
bicarbonate and the like.
[0039] The addition of synthetic silica may be before the beginning
of the carbonation reaction or at a time between the commencement
and completion of the carbonation reaction, preferably before the
carbonation rate is up to 95%. Especially, with the formation of
composite particles with synthetic calcium carbonate, it is
preferred in view of synthetic silica being strongly, efficiently
attached to and fixed on the surfaces of the calcium carbonate that
the addition is in the course of the carbonation reaction and at
the time after the formation of crystal nuclei of calcium carbonate
commences but before the carbonation rate is up to 95%.
[0040] The commencement with respect to the formation of crystal
nuclei of calcium carbonate can be readily determined by
continuously measuring the electrical conductivity of a calcium
hydroxide slurry when using a carbonation process. With colloidal
calcium carbonate, for instance, a point of time at which the
primary drop of electrical conductivity is converted to rise is
coincident with the time of commencement for the formation of
crystal nuclei of calcium carbonate ("Gypsum and Lime", No. 194,
pp. 3-12, 1981). In case of spindle-shaped calcium carbonate, a
small primary drop of electrical conductivity can also be
recognized at the initial stage of the carbonation reaction.
[0041] Where the preparation of silica calcium carbonate particles
is by methods other than the carbonation process, e.g., a soluble
carbonate such as sodium carbonate is used for the carbonation
reaction, the nuclei addition, so that the formation of the crystal
nuclei coincides with the commencement of carbonation.
[0042] The carbonation rate used herein is expressed according to
the following equation.
Carbonation rate=(weight of calcium in calcium carbonate formed by
the carbonation reaction.div.total weight of calcium existing in
the reaction system).times.100
[0043] The amount of added synthetic silica is not critical and can
be determined depending on the extent of synthetic silica-derived
characteristics required for silica-calcium carbonate composite
particles. Preferably, the amount is at 0.01 g or over per 100 g of
calcium carbonate. If the amount is smaller than 0.01 g, few
characteristics of synthetic silica are shown, and the resultant
product has almost the same properties as calcium carbonate per se,
so that the purposes of the invention may not be achieved in some
cases. Although the upper limit is not critical, limitation is
placed on, the amount of deposition by virtue of the specific
surface area of calcium carbonate, under which if the amount of
synthetic silica is in excess, free synthetic silica increases in
amount. This entails not only poor economy, but also the drawbacks
of synthetic silica being emphasized in some cases.
[0044] Ground calcium carbonate may be used as the calcium
carbonate for the silica-calcium carbonate composite particles of
the invention. In this case, it is necessary that a carbonic acid
source be introduced into a ground calcium carbonate slurry after
addition of a calcium source in order to carry out the carbonation
reaction, like the formation of synthetic calcium carbonate, during
which synthetic silica is added thereto to obtain silica-calcium
carbonate composite particles.
[0045] The addition of synthetic silica may be before the
carbonation reaction, during the time of or immediately after
commencement of the reaction till completion thereof, preferably
during a time at which the carbonation rate of a calcium source
such as calcium hydroxide, calcium chloride, calcium nitrate or the
like, is added to the ground calcium carbonate slurry, ranges from
0.about.95%.
[0046] The carbonation rate used herein is expressed according to
the following equation.
Carbonation rate=(weight of calcium in calcium carbonate formed by
the carbonation reaction.div.weight of calcium in calcium source
added to ground calcium carbonate slurry).times.100
[0047] The amount of added synthetic silica is not critical and can
be determined depending on the extent of synthetic silica-derived
characteristics required for silica-calcium carbonate composite
particles. Preferably, the amount is at 0.01 g or over per 100 g of
calcium carbonate at the point of time when the carbonation is
completed, like the case using synthetic calcium carbonate.
According to the above-stated reaction procedure, there can be
prepared silica-calcium carbonate composite particles of the
invention wherein synthetic silica having a size of 1.about.100 nm
are attached to and fixed on the surfaces of calcium carbonate
particles.
[0048] Further, the method for making silica-calcium carbonate
composite particles of the invention can be readily carried out by
the novel and simple procedure wherein synthetic silica is added in
the step of forming calcium carbonate.
[0049] The resultant silica-calcium carbonate composite particles
have the features including, aside from excellent characteristics
of calcium carbonate, characteristics inherent to silica, such as
high oil absorption, affinity for plastics, rubbers and the like,
gas adsorbability, catalytic activity and the like.
[0050] Accordingly, where the silica-calcium carbonate composite
particles of the invention are used as a filler or pigment, effects
of improving printability of printing paper and improving strength
of rubber and plastics can be expected.
[0051] It can also be expected that the composite particles exhibit
excellent performances as highly functional calcium carbonate in a
wide variety of fields, such as impartment of an acid-proofing to
calcium carbonate, utilization as a carrier caused by the formation
of porous surfaces of calcium carbonate, removal by adsorption of
acidic substances, harmful gases of calcium carbonate based on the
catalytic action of silica or improvement in the removability, and
the like.
[0052] In the practice of the invention since fine particles of
synthetic silica are fixed on the surfaces of calcium carbonate,
the composite product has the excellent characteristics of both
without lowering the characteristics of synthetic silica, such as a
high specific surface area, high gas adsorbability, fineness,
infiltration power into fine interstices or adsorption power, high
adhesion, high oil absorption, uniformity of particles, high
dispersability and the like, and the characteristics of calcium
carbonate.
[0053] The silica-calcium carbonate composite particles of the
invention have such excellent characteristics as set out
hereinabove and show an excellent performance when applied to paper
seats wherein the composite particles are internally filled therein
or coated thereon.
[0054] The paper seats having the composite particles internally
filled therein are ones wherein at least a part of the fillers
contained therein is made of the composite particles. The composite
particles are mixed with pulp and other chemicals for paper-making
upon preparation of a paper stock in a paper-making process, and
the paper stock is subjected to paper-making to provide the paper.
The paper coated with the particles is one wherein at least part of
the pigments contained in a coating layer of coated paper is made
of the composite particles, and is made by mixing with a binder and
other types of pigments upon preparation of a coating solution in a
coating step and applying the coating solution onto a paper stock.
The paper which is internally filled or coated with these
silica-calcium carbonate composite particles is excellent in ink
receptivity due to the high oil absorption characteristics of the
composite particles, thus being very effective in preventing a
printed portion from striking-through and improving printing
capacity.
[0055] The method for making silica-calcium carbonate composite
particles is characterized in that in the course of a carbonation
reaction, which is the step of forming calcium carbonate, fine
particles of synthetic silica is added and the carbonation reaction
is subsequently completed.
[0056] In the practice of the invention, the fine particles of
synthetic silica are fixed on the surfaces of the calcium
carbonate, so that the resultant composite product has the
excellent characteristics of both without lowering the
characteristics of the synthetic silica, such as a high specific
surface area, high gas adsorbability, fineness, infiltration power
into fine interstices or adsorption power, high adhesion, high oil
absorption, uniformity of particles, high dispersability and the
like, and the characteristics of calcium carbonate.
EXAMPLES AND COMPARATIVE EXAMPLES
[0057] The invention is more particularly described by way of
examples and comparative examples, which should not be construed as
limiting the invention thereto. As a matter of course, the
invention is defined only by the appended claims.
Example 1
[0058] While agitating 2.0 kg of a calcium hydroxide slurry whose
temperature was controlled at 30.degree. C. and which had a
concentration of 7.4 wt %, a mixed gas of carbon dioxide having a
concentration of 25 vol % and air was fed into the slurry at a rate
of 1.2 liters/minute per 100 g of calcium hydroxide, thereby
causing a carbonation reaction to commence. At the time when the
carbonation rate reached 20%, 300 g (calculated as the weight of
SiO.sub.2 and corresponding to 30 g per 100 g of calcium carbonate
formed) of a 20 wt % solution of colloidal silica (with an average
particle size of 45 nm and a spherical shape) was added and the
mixed gas was subsequent fed so as to continue the carbonation
reaction, followed by completing the carbonation reaction at the
time when the pH of the slurry arrived at 7.
[0059] According to observation through a scanning electron
microscope (SEM), the resultant product was made of silica-calcium
carbonate composite particles wherein the colloidal silica was
attached to and fixed on the surfaces of spindle-shaped calcium
carbonate particles having a major axis of 2.0 .mu.m and a minor
axis of 0.4 .mu.m. About 90% of the surfaces of the spindle-shaped
calcium carbonate was covered with the colloidal silica, with the
particles made solely of silica being recognized only in a slight
amount. These are as shown in FIG. 1.
Example 2
[0060] While agitating 2.0 kg of a calcium hydroxide slurry whose
temperature was controlled at 30.degree. C. and which had a
concentration of 7.3 wt %, a mixed gas of carbon dioxide having a
concentration of 25 vol % and air was fed at a rate of 1.2
liters/minute per 100 g of calcium hydroxide, thereby causing a
carbonation reaction to commence. At the time when the carbonation
rate reached 80%, 300 g (calculated as the weight of SiO.sub.2 and
corresponding to 30 g per 100 g of calcium carbonate formed) of a
20 wt % colloidal silica (with an average particle size of 45 nm
and a spherical shape) solution was added, and the mixed gas was
further fed so as to continue the carbonation reaction, followed by
completing the carbonation reaction at the time when the pH of the
slurry arrived at 7.
[0061] According to observation through a SEM, the resultant
product was made of silica-calcium carbonate composite particles
wherein the colloidal silica was attached to and fixed on the
surfaces of spindle-shaped calcium carbonate particles having a
major axis of 2.0 .mu.m and a minor axis of 0.4 .mu.m. About 40% of
the surfaces of the spindle-shaped calcium carbonate was covered
with the colloidal silica, with the particles made solely of silica
being recognized therearound only in a very small amount.
Example 3
[0062] While agitating 2.0 kg of a calcium hydroxide slurry whose
temperature was controlled at 35.degree. C. and which had a
concentration of 5.6 wt %, 150 g (calculated as the weight of
SiO.sub.2 and corresponding to 20 g per 100 g of calcium carbonate
formed) of a 20 wt % colloidal silica (with an average particle
size of 20 nm and a round shape) solution was added. Subsequently,
pure carbon dioxide gas having a concentration of 100 vol % was fed
from a gas cylinder at a rate of 0.3 liters/minute per 100 g of the
calcium hydroxide, thereby causing a carbonation reaction to start,
and the carbonation reaction was stopped when the pH of the slurry
arrived at 7.
[0063] According to observation through a SEM, the resultant
product was made of silica-calcium carbonate composite particles
wherein the colloidal silica was attached to and fixed on the
surfaces of spindle-shaped calcium carbonate particles having a
major axis of 1.5.about.2.0 .mu.m and a minor axis of 0.3.about.0.4
.mu.m. All the surfaces of the spindle-shaped calcium carbonate
were covered with the colloidal silica, with particles made solely
of silica not being recognized at all.
Example 4
[0064] While agitating 2.0 kg of a calcium hydroxide slurry whose
temperature was controlled at 70.degree. C. and which had a
concentration of 11.1 wt %, a mixed gas of carbon dioxide having a
concentration of 25 vol % and air was fed at a rate of 0.3
liters/minute per 100 g of calcium hydroxide, thereby causing a
carbonation reaction to commence. At the time when the carbonation
rate reached 50%, 75 g (calculated as the weight of SiO.sub.2 and
corresponding to 5 g per 100 g of calcium carbonate formed) of a 20
wt % colloidal silica (in an elongated form having a width of 15 nm
and a major axis of 100 nm) solution was added, and the mixed gas
was further fed so as to continue the carbonation reaction,
followed by completing the carbonation reaction at the time when
the pH of the slurry arrived at 7.
[0065] According to observation through a SEM, the resultant
product was made of silica-calcium carbonate composition particles
wherein the colloidal silica was attached to and fixed on the
surfaces of column-shaped calcium carbonate particles having a
major axis of 1.5.about.2.0 .mu.m and a minor axis of 0.2 .mu.m.
About 50% of the surfaces of the column-shaped calcium carbonate
was covered with the colloidal silica, with particles made solely
of silica being recognized only in a slight amount.
Example 5
[0066] While agitating 2.0 kg of a calcium hydroxide slurry whose
temperature was controlled at 10.degree. C. and which had a
concentration of 5.3 wt %, a pure gas made of carbon dioxide having
a concentration of 100 vol % was fed from a gas cylinder at a rate
of 1.0 liter/minute per 100 g of calcium hydroxide, thereby causing
a carbonation reaction to commence. At the time when the
carbonation rate reached 80%, 300 g (calculated as the weight of
SiO.sub.2 and corresponding to 42 g per 100 g of calcium carbonate
formed) of a 20 wt % colloidal silica (with an average particle
size of 20 nm and a spherical shape) solution was added, and the
mixed gas was further fed so as to continue the carbonation
reaction, followed by completing the carbonation reaction at the
time when the pH of the slurry arrived at 7. This slurry was heated
to 60.degree. C. and maintained at 60.degree. C. over 3 days.
[0067] According to observation through a SEM, the resultant
product was made of silica-calcium carbonate composite particles
wherein the colloidal silica was attached to and fixed on the
surfaces of colloidal calcium carbonate particles. Although the
particles made solely of the colloidal silica were found around the
composite particles, about 40% of the surface of the colloidal
calcium carbonate was covered with the colloidal silica.
Example 6
[0068] While agitating 2.0 kg of a calcium hydroxide slurry whose
temperature was controlled at 30.degree. C. and which had a
concentration of 7.5 wt %, a mixed gas of carbon dioxide having a
concentration of 25 vol % and air was fed at a rate of 1.2
liters/minute per 100 g of calcium hydroxide, thereby causing a
carbonation reaction to commence. At the time when the carbonation
rate reached 20%, 100 g (calculated as the weight of SiO.sub.2 and
corresponding to 2 g per 100 g of calcium carbonate formed) of a 4
wt % anhydrous silica (Aerosil, with an average particle size of 12
nm) solution was added, and the mixed gas was further fed so as to
continue the carbonation reaction, followed by completing the
carbonation reaction at the time when the pH of the slurry arrived
at 7.
[0069] According to observation through a SEM, the resultant
product was made of silica-calcium carbonate composite particles
wherein the anhydrous silica was attached to and fixed on the
surfaces of spindle-shaped calcium carbonate particles having a
major axis of 2.0 .mu.m and a minor axis of 0.4 .mu.m. About 30% of
the surfaces of the spindle-shaped calcium carbonate was covered
with the colloidal silica, with the particles made solely of
anhydrous silica being not recognized at all.
Example 7
[0070] While agitating 2.0 kg of a ground calcium carbonate (with
an average particle size of 5.1 pm and a specific surface area of
11.300 cm/g) slurry which had a concentration of 20 wt %, 50 g of
slaked lime for industry was added and, after controlling a slurry
temperature at 70.degree. C., a mixed gas of carbon dioxide having
a concentration of 25 vol % and air was fed at a rate of 0.1
liter/minute per 100 g of calcium hydroxide, thereby causing a
carbonation reaction to commence. At the time when the carbonation
rate reached 40%, 200 g (calculated as the weight of SiO.sub.2 and
corresponding to 10 g per 100 g of calcium bicarbonate) of a 20 wt
% colloidal silica (with an average particle size of 20 nm)
solution was added, and the mixed gas was further fed so as to
continue the carbonation reaction, followed by completing the
carbonation reaction at the time when the pH of the slurry arrived
at 7.
[0071] According to observation through a SEM, the resultant
product was made of silica-calcium carbonate composite particles
wherein about 80% of the surfaces of the ground calcium carbonate
was attached and fixed thereon with the colloidal silica particles.
Although particles made solely of silica were recognized, the
amount was only slight. It was recognized that the calcium
carbonate formed through the carbonation reaction of calcium
hydroxide formed fresh particles with a size of 0.04.about.0.06
.mu.m and attached to the surfaces of the ground calcium carbonate.
Besides, the surface profile of the ground calcium carbonate
particles after completion of the reaction was changed into a
relatively smooth profile in comparison with an irregular,
fragmentary shape prior to the reaction, from which it was assumed
that the calcium carbonate was crystallized on the surfaces of the
calcium bicarbonate.
Example 8
[0072] A reagent-grade sodium carbonate solution having a
concentration of 10 wt % was dropped in 2.0 kg of a reagent-grade
calcium chloride solution, controlled at 25.degree. C. and having a
concentration of 5.0 wt %, at a rate of 8.0 ml/minute, thereby
causing a carbonation reaction to start. At the time when the
carbonation rate reached 15%, 100 g (calculated as the weight of
SiO.sub.2 and corresponding to 22 g per 100 g of calcium carbonate
formed) of a 20 wt % colloidal silica (in an elongated form having
a minor axis of 15 nm and a major axis of 100 nm) solution was
added, and the sodium carbonate solution was further fed so as to
continue the carbonation reaction, followed by completing the
carbonation reaction at the time when the pH of the slurry arrived
at 9.
[0073] According to observation through a SEM, the resultant
product was made of silica-calcium carbonate composite particles
wherein the colloidal silica was attached to and fixed on
substantially all the surfaces of the calcium carbonate round
particles with a particle size of 10.about.20 .mu.m, with no
particles made solely of silica being observed.
Example 9
[0074] 80 g of reagent-grade calcium chloride was added to 2.0 kg
of a ground calcium carbonate (with an average particle size of 5.1
.mu.m and a specific surface area of 11,300 cm/g) slurry, followed
by controlling at 25.degree. C. While agitating the slurry, a 10 wt
% solution of reagent-grade sodium carbonate was dropped at a rate
of 8.0 ml/minute, thereby causing carbonation to start. At the time
when the carbonation rate reached 10%, 100 g (calculated as the
weight of SiO.sub.2 and corresponding to 5 g per 100 g of ground
calcium carbonate) of a 20 wt % colloidal silica (in an elongated
form having a minor axis of 15 nm and a major axis of 100 nm)
solution was added, and the sodium carbonate solution was further
fed so as to continue the carbonation reaction, followed by
completing the carbonation reaction at the time when the pH of the
slurry arrived at 9.
[0075] According to observation through a SEM, the resultant
product was made of silica-calcium carbonate composite particles
wherein the colloidal silica particles were attached to and fixed
on about 70% of the surfaces of the calcium bicarbonate having a
particle size of 0.2.about.20 .mu.m, with no particles made solely
of silica being observed. It was confirmed that the calcium
carbonate formed through the carbonation reaction of calcium
chloride formed fresh particles having a size of 0.04.about.0.06
.mu.m and deposited on the surfaces of the ground calcium
carbonate. Besides, the surface profile of the calcium bicarbonate
particles after completion of the reaction was changed into a
relatively smooth profile in comparison with an irregular,
fragmentary shape prior to the reaction, from which it was assumed
that the calcium carbonate was crystallized on the surfaces of the
calcium bicarbonate.
Comparative Example 1
[0076] A mixed gas of carbon dioxide having a concentration of 25
vol % and air was introduced into 2.0 kg of a 7.8 wt % slurry of
calcium hydroxide, controlled at 30.degree. C., at a rate of 1.2
liters/minute per 100 g of calcium hydroxide to cause a carbonation
reaction to start. At the time when the carbonation rate reached
20%, 63 g (calculated as the weight of SiO.sub.2 and corresponding
to 30 g per 100 g of calcium carbonate formed) of fine powder
(naturally occurring quartz pulverized to an extent that an average
particle size was at 2.8 .mu.m) of silica sand, which is natural
silica, was added, and the mixed gas was further introduced so as
to continue the carbonation reaction, followed by completing the
carbonation reaction. Observation of the resultant product through
a SEM revealed that no natural silica was found on the surfaces of
spindle-shaped calcium carbonate particles having a major axis of
2.0 .mu.m and a minor axis of 0.4 .mu.m, but independent particles
were formed.
Comparative Example 2
[0077] A mixed gas of carbon dioxide having a concentration of 25
vol % and air was introduced into 2.0 kg of a 7.4 wt % slurry of
calcium hydroxide, controlled at 30.degree. C., at a rate of 1.2
liters/minute per 100 g of calcium hydroxide to cause a carbonation
reaction to start, followed by completing the carbonation reaction
when the pH of the slurry arrived at 7. While agitating the calcium
carbonate slurry, 300 g (calculated as the weight of SiO.sub.2 and
corresponding to 30 g per 100 g of calcium carbonate formed) of a
20 wt % solution of colloidal silica (with an average size of 45 nm
and a round shape) was added, and the mixed gas was again
introduced over 30 minutes. Observation of the resultant product
through SEM revealed that no colloidal silica was found on the
surfaces of spindle-shaped calcium carbonate particles having a
major axis of 2.0 .mu.m and a minor axis of 0.4 .mu.m, but
independent particles were formed.
Comparative Example 3
[0078] While agitating 2.0 kg of a calcium bicarbonate (with an
average particle size of 5.1 .mu.m and a specific surface area of
11.300 cm/g) slurry which had a concentration of 20 wt %, 200 g
(calculated as the weight of SiO.sub.2 and corresponding to 10 g
per 100 g of calcium bicarbonate formed) of a 20 wt % solution of
colloidal silica (with an average size of 20 nm) was added, and a
mixed gas of carbon dioxide having a concentration of 25 vol % and
air was fed over 30 minutes. Observation of the resultant product
through a SEM revealed that no colloidal silica was found on the
surfaces of the calcium bicarbonate particles, but was observed as
independent discrete particles.
[0079] The composite particles of the invention has an excellent
oil absorption as stated hereinbefore. In order to prove this, an
oil absorption measuring test was carried out using the
silica-calcium carbonate composite particles made in Example 1 and
the like. The results are shown in Table 1. From the results of the
test, it will be seen that the composite particles of the invention
have a higher oil absorption than the particles of calcium
carbonate alone or a mixture of calcium carbonate and silica. It
will be noted that the oil adsorption measuring test was effected
according to "JIS K 5101".
1 TABLE 1 Sample Oil Absorption (ml/100 g) Composite particles of
65.0 Example 1 Mixture of calcium carbonate 51.5 and silica
Spindle-shaped calcium 45.0 carbonate
INDUSTRIAL UTILITY
[0080] As stated hereinbefore, the silica-calcium carbonate
composite particles of the invention are ones wherein synthetic
silica having an average particle size of 1.about.100 .mu.m is
attached to and fixed on the surfaces of calcium carbonate and have
both the excellent characteristics of silica and excellent
characteristics of calcium carbonate. The making method is a novel
and simple technique wherein synthetic silica is added in the
course of a carbonation step of calcium carbonate, and can be
readily carried out.
[0081] Where the silica-calcium carbonate composite particles of
the invention are used as a filler or pigment in various fields,
not only the effects of improving the printability of printing
paper and improving the strength of rubbers and plastics are
obtained, but also excellent performance as a calcium carbonate of
high functionality in wide fields can be expected including
impartment of an acid resistance to calcium carbonate, utilization
as a carrier caused by establishing porous surfaces of calcium
carbonate, removal by adsorption of acidic substances and harmful
gases with calcium carbonate based on the catalyst action of silica
or improvement in the removability, and the like.
* * * * *