JP4421343B2 - Method for producing silica-calcium carbonate composite particles - Google Patents

Description

The present invention relates to a method for producing silica-calcium carbonate composite particles having both the excellent characteristics of synthetic silica and the excellent characteristics of calcium carbonate.
More specifically, it is characterized by imparting excellent functions of silica such as high specific surface area and high oil absorption to calcium carbonate by using alkali silicate as a silica source and precipitating and fixing silica on the surface of calcium carbonate. The present invention relates to a method for producing silica-calcium carbonate composite particles.

In the composite particles of the present invention, calcium carbonate is one of the main constituents, and those used industrially include heavy calcium carbonate and synthetic (light) calcium carbonate.
The former heavy calcium carbonate is a finely pulverized product of naturally occurring crystalline limestone with high whiteness, and can be produced by a relatively simple process of pulverization and classification.
The particles have an indefinite shape unique to physical pulverized products and have a wide particle size distribution, but they are widely used as fillers and pigments for plastics, rubber, resin, papermaking, taking advantage of high whiteness and economy. It has been.

The latter synthetic calcium carbonate is chemically synthesized calcium carbonate as the name suggests, and is also called light or precipitated calcium carbonate.
The production method includes a carbon dioxide gas compound method in which carbon dioxide is introduced into a calcium hydroxide slurry and chemically precipitated, a calcium chloride soda method in which precipitation is caused by a reaction between calcium chloride and sodium carbonate, and a combination of calcium hydroxide and sodium carbonate. A lime soda method for precipitation by reaction, a water treatment method for precipitation by reaction of calcium hydroxide and calcium hydrogen carbonate, and the like are known.

Although there are known methods for producing synthetic calcium carbonate as described above, most of them are produced by the carbon dioxide compound method because high quality limestone raw materials are produced in Japan.
In the production of the synthetic calcium carbonate, by adjusting the concentration of calcium in the raw slaked lime slurry, the temperature at which the carbonation reaction is carried out, the rate of carbonation, the production conditions such as coexisting ions, the particle shape, particle diameter, etc. Can be controlled within a certain range.

Specifically, colloidal shapes, cubic shapes, spindle shapes, columnar shapes, and the like are well known as the forms, and the main uses are different for each.
That is, colloidal calcium carbonate is a colloidal particle having a particle size of 0.04 to 0.08 μm, and is used as a filler for plastics, rubber, paints and the like.
Cubic calcium carbonate is a cubic particle having a particle size of 0.1 to 0.2 μm, and is particularly excellent as a pigment for papermaking or coating.

Spindle-like calcium carbonate is spindle-shaped particles having a major axis of 0.5 to 5.0 μm and a minor axis of 0.1 to 2.0 μm, and usually forms aggregates of several μm. As widely used.
Columnar calcium carbonate is a columnar particle having a major axis of 1.0 to 20 μm and a minor axis of 0.1 to 1.0 μm, and is excellent in dispersibility. Typical examples of the columnar calcium carbonate include papermaking pigments and fillers.
As described above, these synthetic calcium carbonates have a simple manufacturing process compared to other materials, and have excellent characteristics such as economy, physical stability, variety of particle shapes, and high whiteness. Therefore, it is used in various industrial applications.

On the other hand, the other major component of the composite particles of the present invention is silica, which is generally referred to as silicon dioxide or silicic anhydride having a chemical composition of SiO ₂ , although it is often hydrated. (Hydrogen-containing) Silicon dioxide SiO ₂ · nH ₂ O may be referred to as silica.
Industrial synthetic silica-based materials include colloidal silica, silica gel, anhydrous silica, white carbon, etc., which have high specific surface area, high gas adsorption capacity, fineness, permeability to fine voids, adsorption power, and adhesion. Utilizing excellent properties such as height, high oil absorbency, particle uniformity, and high dispersibility, it is used in a wide range of fields.

Among them, colloidal silica is a silicic acid sol obtained by removing impurities from silicic acid compounds, and adjusting the pH and concentration to stabilize the sol. Silica is used as a resin processability improver, wax, sizing agent, latex quality improver, binder, printing paper printability improver, metal surface treatment agent, and the like.
Silica gel is hydrous silicic acid obtained by decomposing sodium silicate with an inorganic acid, and is a dehumidifying desiccant such as food, medicine, fiber, gas or air, catalyst or carrier thereof, rubber filler, or It is used in applications such as thickening of paints and inks or anti-settling agents.
Anhydrous silica is obtained by hydrolysis of silicon tetrachloride, and is used for fillers and reinforcing agents for paints, inks, resins, rubbers and the like.

These synthetic silicas have high specific surface area, high gas adsorbing ability, fineness, penetrating and adsorbing power to fine voids, high adhesion, high oil absorption, particle uniformity, high dispersibility, etc. Taking advantage of its excellent properties, it is used in a wide range of fields such as rubber, papermaking, paints and petroleum refining catalysts.
As described above, among the industrial inorganic materials, calcium carbonate and silica materials are the most widely used materials, but each has excellent characteristics, but also has disadvantages.
For example, when calcium carbonate is used as a filler for rubber, its surface is inactive and has a poor chemical and physical affinity for rubber molecules, and therefore lacks the reinforcing effect of rubber products.

And when used as a pigment or filler for paper, especially for printing paper, the ink absorbency is lower than that of synthetic silica, causing problems in terms of ink setting, ink back-through, and opacity of the printed area. There is.
Moreover, since it is poor in resistance to acids, it is difficult to use in combination with acidic substances such as acidic papermaking using sulfuric acid bands.
On the other hand, when a silica-based material is used as a papermaking pigment, it causes a rise in the viscosity of the coating agent, so that it is not easy to add a high amount to the coating agent.
It has been pointed out that the viscosity of the rubber composition is remarkably increased as a rubber filler.

Colloidal silica may cause problems in terms of fluctuations in solution temperature, pH, electrolyte concentration, etc., long-term storage, and stability against organic solvents.
Furthermore, it is expensive compared with calcium carbonate or the like, which hinders high blending in products and mass use.
As described above, calcium carbonate and synthetic silica each have unique features and disadvantages. Therefore, by combining calcium carbonate and silica, various techniques and applications are used to eliminate these disadvantages. Research has been done for a long time and proposals have been made.

[Prior art documents]
Japanese Examined Patent Publication No. 2-56376 Japanese Examined Patent Publication No. 4-63007 JP-A-11-107189 U.S. Pat. No. 3,373,134 Japanese Patent Publication No.43-3487 Japanese Patent Publication No. 44-5330 Japanese Patent Publication No. 44-14699 JP 60-222402 A JP 61-118287 A Japanese Patent Publication No.8-1038 JP-A-11-29319 Japanese Patent No. 3392099 Gypsum and lime, no. 194, pp. 3-12, 1981

For example, in Patent Document 1, the surface of calcium carbonate particles is activated with an inorganic acid, and a coating layer of silicic acid or silicate is formed via CaSiO ₃ produced by reacting the surface with silicic acid or silicate. A composite modified pigment in which is formed has been proposed.
Patent Document 2 discloses a powder such as calcium carbonate that is suitable for a paper filler having an anti-through-through performance of ink by a physical method of pulverizing a mixture of powder such as calcium carbonate and hydrated silicic acid. Patent Document 3 discloses a method for producing a unique composite powder of a body and hydrated silicic acid, in which fine particles such as calcium carbonate are dispersed in an alkali silicate solution, and mineral acid is added thereto under specific conditions. A method for producing composite particles in which fine particles such as calcium carbonate are uniformly combined in hydrated silicate particles by adding them has been proposed.

In addition to the above-described techniques, synthetic calcium carbonate having a specific shape and characteristics produced by using colloidal silicic acid or activated silicic acid during the carbonation reaction is known.
For example, in Patent Document 4, carbon dioxide gas or ammonium carbonate is reacted in the presence of a predetermined amount of colloidal silicic acid in an aqueous calcium chloride solution in which an alkali having a pH of 8 or more is maintained by adding ammonium hydroxide. Produces amorphous silicic acid, which is a complex dispersed within the calcium carbonate grains.
In Patent Document 5, a highly dispersible carbonic acid having an irregular calcite structure and a non-dense secondary structure by reacting a CO ₂ -containing gas with an aqueous suspension of calcium hydroxide in the presence of active silicic acid. A method for producing calcium is disclosed.

In Patent Document 6, calcium chloride and carbon dioxide or / and ammonium carbonate are reacted in an aqueous solution having a liquid temperature of less than 35 ° C. and a pH of 8 or more with ammonium hydroxide in the presence of colloidal silicic acid or water-soluble silicic acid. As a result, amorphous silicic acid is produced, which is disclosed as a paper coating pigment mainly composed of vaterite-based calcium carbonate which is the core of calcium carbonate.
Patent Document 7 discloses a method for producing finely dispersed calcium carbonate by starting a carbonation reaction of a calcium hydroxide aqueous suspension with a carbon dioxide-containing gas in the presence of active silicic acid.

Furthermore, there is a technique disclosed as a use of a composite of silica and calcium carbonate, for example, an agrochemical carrier (Patent Document 8), a heat-sensitive recording material compounding agent (Patent Document 9), an ink jet recording paper pigment (Patent Document 10). ), Reinforcing fillers such as rubber (Patent Document 11), and the like.
There are exemplified production methods or structures different from the above-mentioned composites.
The calcium carbonate-silicic acid composite described in Patent Document 8 coexists metals such as Zn, Mg, and Al during the carbonation reaction, and blows carbon dioxide alone until the carbonation rate reaches 80%, and then alkali silicate. Alternatively, silicic acid sol is added and carbon dioxide is blown to complete carbonation.
The calcium carbonate-silicic acid composite thus obtained is a chain-like particle having a diameter of 0.01 × length of 0.05 to 1.00 μm.

Patent Document 9 is a solution in which carbon dioxide gas is blown into an aqueous solution of sodium silicate and calcium chloride or calcium hydroxide to coprecipitate, and silicon oxide and calcium carbonate are combined in a molecular state or a state close thereto. It is believed that.
In Patent Document 10, calcium carbonate composite silica obtained by blowing carbon dioxide into calcium silicate obtained by reacting calcium chloride with sodium silicate is used.
These technologies described above can be used to compensate for the shortcomings of calcium carbonate and take advantage of the characteristics of silica. However, as described below, this technique is a physical technique different from the present invention. As is apparent from the fact that the manufacturing method is different from the invention and the method has not been put into practical use, each has a problem.

For example, the method for producing a composite disclosed in Patent Document 2 or Patent Document 11 is based on a physical technique.
In the method disclosed in Patent Document 3, titanium oxide is suitable as the fine particles, and even when calcium carbonate is used, composite particles that uniformly cover the surface of the calcium carbonate particles cannot be obtained.
The calcium carbonate-silicic acid complex described in Patent Document 8 is a chain-like particle, and the silicon oxide-calcium carbonate complex disclosed in Patent Document 9 is considered that silicon oxide and calcium carbonate are bound in a molecular state or a state close thereto. None of these are obtained by coating silica with a specific shape of calcium carbonate such as a spindle shape or a column shape.

Further, even if it is a synthetic calcium carbonate produced using colloidal silicic acid or active silicic acid during the carbonation reaction, Patent Document 4 is a composite in which amorphous silicic acid is dispersed inside calcium carbonate particles. In Patent Document 5, calcium carbonate has an irregular calcite structure and a non-dense secondary structure.
In Patent Document 6, amorphous silicic acid is vaterite-based calcium carbonate in which calcium carbonate is the nucleus, and in Patent Document 7, it is finely dispersed calcium carbonate and not a composite.
That is, these techniques are not silica-calcium carbonate composite particles in which the surface of calcium carbonate having a specific shape, such as a so-called spindle shape, colloidal shape, cubic shape, or columnar shape, is coated with silica.

There is a method disclosed in Patent Document 12 as a technique that has been distinguished from these techniques and solved the above-mentioned problems. In the carbonation reaction process, which is a calcium carbonate formation process, colloidal after the formation of calcium carbonate crystal nuclei. There is disclosed a method for producing silica-calcium carbonate composite particles in which silica or anhydrous silica is added and then the carbonation reaction is completed, and silica fine particles are adhered and fixed on the surface of calcium carbonate.
This method is epoch-making in terms of the simplicity of the production process in which silica fine particles are added from outside the system, and the silica fine particles are adhered and fixed to the calcium carbonate surface.
However, since this production method uses particulate colloidal silica or anhydrous silica, which is relatively expensive for calcium carbonate, as a raw material, the produced silica-calcium carbonate composite is slightly more expensive than general synthetic calcium carbonate. Thus, the use as a general-purpose powder for papermaking, paints and resin applications has become difficult in terms of economy.

  In view of such circumstances, the present inventors can improve the economic efficiency, that is, the particulate colloidal silica used as a silica source in Patent Document 12 so that it can be widely used in papermaking, paints, resins, and the like. Instead of anhydrous silica, repeated investigations to produce a composite equivalent to or higher than the composite obtained by the method disclosed in Patent Document 12 using a less expensive siliceous raw material, The present invention has been successfully developed by using an inexpensive alkali silicate.

Therefore, the present invention can maintain the unique shape of the conventional synthetic calcium carbonate as it is and also has the characteristics of the silica-calcium carbonate composite particles produced by the method of the above patent, that is, high specific surface area and gas adsorption capacity. It has the same or better properties in terms of height, fineness, penetration and adsorption power into fine voids, high adhesion, high oil absorption, particle uniformity, high dispersibility, etc. It is an object to be solved to provide a more satisfactory method for producing silica-calcium carbonate composite particles.

The present invention is a novel method for producing silica-calcium carbonate composite particles that achieves the above-mentioned problems, and also includes a silica-calcium carbonate composite particle produced together or a composite composition or composite containing the composite particle. In the carbonation reaction process, which is a calcium carbonate formation process, an alkali silicate is added in the coexistence of alkali metal ions until the end of the carbonation reaction. The silica is fixed on the surface of calcium carbonate.

Silica-calcium carbonate composite particles obtained by the method for producing silica-calcium carbonate composite particles of the present invention are uniformly dispersed by dispersing silica produced by a chemical precipitation reaction with an average particle size of 10 to 100 nm on the surface of calcium carbonate. It is adhered and fixed and has both the excellent properties of silica and calcium carbonate.
In addition, the calcium carbonate in the produced composite can have existing specific shapes as represented by columnar calcium carbonate and spindle-shaped calcium carbonate. You can take over as it is.

As a result, the calcium carbonate in the composite particles produced in the present invention can maintain the unique shape of the conventional synthetic calcium carbonate as it is, and has the silica-calcium carbonate composite particles produced by the method of the above patent. Equivalent to or equivalent to characteristics such as high specific surface area, high gas adsorbing capacity, fineness, penetrating and adsorbing power to fine voids, high adhesion, high oil absorption, particle uniformity, and high dispersibility It has the above performance.
In particular, with respect to oil absorption and water absorption, characteristics similar to or higher than those of conventional ones, especially composites produced by the method described in the above patent, are exhibited.
Furthermore, since a relatively inexpensive alkali silicate is used as the silica source, the economy is more satisfactory.

The silica-calcium carbonate composite particles thus obtained are not only suitable as pigments and fillers for papermaking, inks, paints, resins, rubbers, etc., but also have high functionality when used in composite compositions and composites. Use as a composite material is also promising.
For example, when the composite particles are used as various fillers and pigments, not only the effects of improving the printability of printing paper and the strength of paints, rubbers, plastics, etc., but also imparting acid resistance to calcium carbonate, calcium carbonate Excellent in a wide range of fields as highly functional calcium carbonate, such as use as a support by making the surface porous, or the acidic substance of calcium carbonate based on the catalytic action of silica, adsorption removal of harmful gases or improvement of its removal capability Performance can be expected.
In addition, since silica forms a complex with calcium carbonate and is bonded to the surface of calcium carbonate having a large particle size, an increase in viscosity that occurs when used alone as a coating agent or a filler for rubber can be avoided.

In the following, embodiments including the best mode for carrying out the present invention will be described. However, the present invention is not limited thereto, and is specified by the description of the scope of claims. Needless to say.
The silica-calcium carbonate composite particles of the present invention are added with alkali silicate in the carbonation reaction process, which is a calcium carbonate formation process as described above, in the presence of alkali metal ions until the carbonation reaction is completed. Thus, it is produced by completing the carbonation reaction.
The carbonation reaction in the present invention is not particularly limited, and various methods such as a carbon dioxide gas compound method, a calcium chloride soda method, a lime soda method, or a water treatment method can be adopted, but the carbon dioxide gas compound method is economical. It is preferable.
In addition, the carbonation reaction in the present invention can be simply completed by measuring pH.
For example, in the carbon dioxide compounding method, the pH in the slurry decreases as the carbonation process progresses, and becomes pH 7 when the carbonation reaction is completed. By using this, the end point of the carbonation reaction is known. Can do.

Of the two components constituting the composite particles of the present invention, calcium carbonate, which is the first component, is preferably synthetic calcium carbonate, but is not limited thereto, and part of it is synthetic calcium carbonate and the rest is heavy. It may be calcium carbonate.
In that case, most of them may be either heavy calcium carbonate or synthetic calcium carbonate.
About this point, it can select freely according to the characteristic requested | required of the target silica-calcium carbonate composite particle.

In particular, when the total amount of calcium carbonate is assumed to be synthetic calcium carbonate, various particle shapes and particle diameters are known for synthetic calcium carbonate, so that the characteristics required for the target silica-calcium carbonate composite particles are achieved. It can be selected accordingly, and is suitable for achieving the object of the present invention.
Among these, spindle-shaped calcium carbonate is suitable not only because it can be produced at around room temperature and the production conditions are relatively easy to control, but it is also preferred in the present invention because of its excellent silica deposition efficiency.
Further, the columnar calcium carbonate is preferable in that the silica deposition efficiency is the highest as compared with the spindle-shaped calcium carbonate.

The raw material of silica, which is another component constituting the composite particles of the present invention, is not particularly limited as long as it is an alkali silicate, and examples thereof include sodium silicate (soda) and potassium silicate.
In the present invention, silica refers to a substance that is fixed to the surface of calcium carbonate by adding alkali silicate in the carbonation reaction process, which is the formation process of calcium carbonate. As long as it reacts and precipitates as a solid on the surface of calcium carbonate, which may be either silicon dioxide or its hydrate.
At present, silica is estimated to be amorphous by powder X-ray diffraction, but details of its structure or composition have not been confirmed.

The average particle diameter of silica precipitated and fixed on the surface of calcium carbonate according to the present invention is in the range of 10 nm to 100 nm when observed with a scanning electron microscope.
The silica particle diameter is the diameter of silica particles in the form of particles fixed on the surface of calcium carbonate (if the form is not a sphere, the average value of the major axis and the minor axis), and a scanning electron microscope It was measured by observation of the surface shape by, and observation of a transmission electron image in a transmission electron microscope.

As for the alkali silicate of the silica raw material used in the present invention, sodium silicate is represented by the general formula Na ₂ O.nSiO ₂ .nH ₂ O, and is a liquid product or powdered anhydride which is also called water glass. It is possible to use sodium silicate glass and flaky sodium orthosilicate.
Further, potassium silicate has a composition of K ₂ O.nSiO ₂ and is usually an aqueous solution.
In addition to general industrial potassium silicate, high-purity potassium silicate used as a fluorescent material binder for cathode ray tubes can be used.

In the present invention, the silica formation reaction from the alkali silicate needs to be carried out in the presence of alkali metal ions, but the type of alkali metal ions and the method of adding them are not particularly limited.
For the addition of alkali metal ions, chlorides, hydroxides, sulfates, nitrates, and the like can be used. Among them, sodium chloride, potassium chloride, sodium hydroxide, potassium hydroxide, sodium sulfate, etc., which are easily available, can be used. The method of adding seeds or more as they are or as an aqueous solution is the simplest and desirable industrially.

Next, a method for producing the silica-calcium carbonate composite particles of the present invention will be described in detail.
The silica-calcium carbonate composite particles of the present invention can be produced by coexistence of an alkali metal ion and an alkali silicate in the calcium carbonation reaction process including the start of the carbonation reaction in the calcium carbonate formation step. After the start, before adding the alkali silicate, alkali metal ions are allowed to exist in the reaction system by some method.

As the calcium source, slaked lime (calcium hydroxide) obtained by hydrating quick lime (calcium oxide) produced by firing limestone is suitable, but calcium chloride, calcium nitrate, or the like may be used.
In addition to the carbon dioxide-containing gas such as exhaust gas during the production of quicklime and carbon dioxide pure gas, soluble carbonates such as sodium carbonate, sodium bicarbonate, and calcium bicarbonate can be used for the carbonation.

About the addition time of an alkali metal ion, if it is before the carbonation reaction start, it may be before and after addition of an alkali silicate, and the order is not ask | required.
If it is after the start of the carbonation reaction, the time must be before the addition of the alkali silicate.
The addition amount is preferably 0.1 to 100 parts by weight as alkali metal ions with respect to 100 parts by weight of anhydrous silicic acid (SiO ₂ ) contained in the alkali silicate.
When the amount is small, the surface of calcium carbonate cannot be uniformly coated, and the aggregated particles of silica increase.
On the other hand, if the amount is too large, a large amount of an alkali metal compound is used, and not only the cost is lowered, but also the anions such as alkali metal and chlorine ions remaining in the product may increase, resulting in a problem.

The timing for adding the alkali silicate may be before the carbonation reaction starts.
However, in that case, silica particles can be fixed to the surface of calcium carbonate, but it is difficult to obtain calcium carbonate having a conventional shape.
In order to obtain a silica-bonded surface of a conventional form of calcium carbonate, called columnar or spindle-shaped, it is desirable that the carbonation reaction be started, and more preferably, the crystal nucleation of calcium carbonate during the carbonation reaction If it is after the start and if not only the shape but also liquid absorbency, that is, high oil absorbency and high water absorbency are required, it is added after the carbonation rate of 75% when the calcium carbonate crystals are formed and sufficiently grown. Good to do.
Thus, silica-calcium carbonate composite particles in which silica is firmly and efficiently adhered and fixed to the surface of calcium carbonate having a desired shape are obtained.

In this case, in the case of the carbon dioxide compounding method, the start of crystal nucleation of calcium carbonate can be easily known by continuously measuring the conductivity of the calcium hydroxide slurry.
For example, in colloidal calcium carbonate, the point at which the first drop in conductivity is converted to an increase coincides with the beginning of nucleation of calcium carbonate (
reference). In addition, even in the case of spindle-shaped calcium carbonate, a primary drop in weak conductivity can be confirmed at the initial stage of the carbonation reaction, and by using these, the start of crystal nucleation can be known. In addition, completion | finish of the carbonation reaction in this invention can be simply performed by measuring pH as above-mentioned. As for the carbonation process, the pH in the slurry decreases as the reaction proceeds, and becomes pH 7 when the carbonation reaction is completed. By using this, the end point of the carbonation reaction can be known. .

When producing by a method other than the carbon dioxide compounding method, for example, when a soluble carbonate such as sodium carbonate is used for the carbonation reaction, the formation of nuclei starts from the start of addition, so that the crystal nucleation coincides with the start of carbonation. To do.
Moreover, the carbonation rate here is represented by the following formula.
Carbonation rate = (calcium weight in calcium carbonate produced by carbonation reaction ÷ total weight of calcium present in reaction system) × 100

The amount of alkali silicate added is not particularly limited and can be determined according to the degree of characteristics derived from synthetic silica required for silica-calcium carbonate composite particles, but is anhydrous with respect to 100 parts by weight of calcium carbonate at the end of the carbonation reaction. It is desirable that it is 0.1 parts by weight or more as silicic acid (SiO ₂ ).
The amount of alkali silicate added refers to the amount of anhydrous silicic acid contained in the alkali silicate to be added, not the amount of alkali silicate itself added.

If the amount added is less than 0.1 parts by weight, the properties of silica are hardly exhibited, and the product is hardly different from the properties of calcium itself, so the object of the present invention may not be achieved.
On the other hand, the upper limit is not particularly limited, but if the amount added is too large, free silica that does not adhere to calcium carbonate increases, and the features of calcium carbonate disappear.
Accordingly, not only is it disadvantageous economically, but also the disadvantages of synthetic silica are emphasized, so that 100 weight parts of silicic acid (SiO ₂ ) is added to 100 weight parts of calcium carbonate at the end of the carbonation reaction. Parts or less are desirable.

Regarding the silica-calcium carbonate composite particles of the present invention, as described above, it is possible to use heavy calcium carbonate as a part of the calcium carbonate constituting the silica-calcium carbonate composite particle. As in the case of forming synthetic calcium carbonate in the slurry, after adding a calcium source, a carbonic acid source is introduced to perform a carbonation reaction.
Here again, the alkali metal ion may be added before or after the addition of the alkali silicate as long as it is before the start of the carbonation reaction, as in the absence of heavy calcium carbonate.
If it is after the carbonation reaction start time, it is necessary to be before the addition of alkali silicate.
The timing for adding the alkali silicate may be before the start of the carbonation reaction.
When adding after the start of carbonation, it is necessary to coexist an alkali metal ion before that.

That is, in this case, the alkali silicate may be added at a carbonation rate of 0 to 95% until the carbonation reaction is completed, but preferably the hydroxylation added to the heavy calcium carbonate slurry. It is preferred after the start of carbonation of calcium sources such as calcium, calcium chloride, calcium nitrate.
In addition, the carbonation rate here is represented by the following formula.
Carbonation rate = (calcium weight in calcium carbonate produced by carbonation reaction ÷ calcium weight in calcium source added to heavy calcium carbonate slurry) × 100

The addition amount of the alkali silicate is not particularly limited, and the addition amount can be determined depending on the degree of characteristics derived from the synthetic silica required for the silica-calcium carbonate composite particles, but the total calcium carbonate at the time when the carbonation is completed. The amount of silicic acid (SiO ₂ ) is preferably 0.1 parts by weight or more and 100 parts by weight or less based on 100 parts by weight when producing a complex with synthetic calcium carbonate in the absence of heavy calcium carbonate. It is the same.

By the above reaction operation, the average particle diameter of the silica, that is, the particles fixed to the calcium carbonate surface was observed on the surface of the calcium carbonate particles by observation of the surface shape with a scanning electron microscope or observation of the transmission electron image with a transmission electron microscope. The silica-calcium carbonate composite particles of the present invention in which synthetic silica having an average particle diameter of 10 to 100 nm attached to and fixed to the surface of calcium carbonate can be produced.
The method for producing silica-calcium carbonate composite particles of the present invention can be easily carried out by a new and simple technique of adding alkali silicate in the calcium carbonate formation step, and is excellent in economic efficiency.

The silica-calcium carbonate composite particles obtained in this way can maintain the conventional columnar shape or spindle shape of calcium carbonate as it is. It can be used as a high-performance product.
Furthermore, in addition to the excellent properties derived from shapes such as columnar and spindle shapes, it also has characteristics that are unique to silica, such as high oil absorption, affinity with plastics, rubber, etc., gas adsorption, and catalytic action. Therefore, new applications can be expected.

The silica-calcium carbonate composite particles of the present invention can be used as various composite compositions and composites as typical examples of the above-described applications.
As used herein, the composite composition refers to powders having indeterminate fluidity, paints such as slurries or pastes, inks, coating agents, paper coating agents, cosmetics, dentifrices, and the like. Yes, a composite is a block, film, fiber, special shape such as various tanks, cases, tires, etc. that are maintained in the form of a molded body under normal circumstances. It refers to rubber, metal with a coating film and wood board.

When the silica-calcium carbonate composite particles of the present invention are used as a component of such a composite composition or composite, various characteristics derived from the composite fine particles can be imparted thereto.
For example, when used as a filler or pigment for printing paper, the printability can be improved. When used as a filler for rubber, plastic, paint, etc., the strength can be improved and the matte effect can be obtained.
The composite fine particles are not only calcium carbonate having acid resistance, but also use as a support by making the surface of the calcium carbonate porous, or an acidic substance or harmful gas of calcium carbonate based on the catalytic action of silica. Excellent performance can be expected in a wide range of fields as high-functional calcium carbonate or high-functional silica, such as improved adsorption removal capability.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the examples and the like, and is specified by the description of the claims. Needless to say.

While stirring 2.0 kg of a calcium hydroxide slurry having a concentration of 6.2 wt% adjusted to a temperature of 26 ° C., a total amount of 10 wt% solution of 33.5 g of sodium chloride dissolved in water was added.
Thereafter, a mixed gas of carbon dioxide and air having a concentration of 25% by volume was introduced at a rate of 0.35 liter per minute per 100 g of calcium hydroxide to start the carbonation reaction.
When the carbonation rate of the carbonation reaction reaches 90%, 33.5 g of a 28 wt% solution of sodium silicate No. 3 (20 g per 100 g of calcium carbonate formed in terms of SiO ₂ weight) is added. At the same time, the mixed gas was continuously introduced to continue the carbonation reaction, and when the pH of the slurry reached 7, the carbonation reaction was terminated.

According to the observation with a scanning electron microscope (SEM), the obtained product is around 10 to 50 nm on the surface of spindle-shaped calcium carbonate particles having a major axis of 1.0 to 2.0 μm and a minor axis of 0.3 to 0.5 μm. It was a silica-calcium carbonate composite particle to which the silica fine particles adhered and fixed.
Further, about 80% of the spindle-shaped calcium carbonate surface was covered with silica fine particles, and silica single particles were only slightly recognized.

While stirring 2.0 kg of calcium hydroxide slurry having a concentration of 12.1 wt% adjusted to a temperature of 40 ° C., a total amount of 10 wt% solution obtained by dissolving 1.63 g of sodium chloride in water was added.
Thereafter, a mixed gas of carbon dioxide and air having a concentration of 25% by volume was introduced at a rate of 0.17 liter per minute per 100 g of calcium hydroxide to start the carbonation reaction.
When the carbonation rate of the carbonation reaction reaches 90%, 130.8 g of a 28 wt% solution of No. 3 sodium silicate (40 g per 100 g of calcium carbonate produced in terms of SiO ₂ weight) is added. At the same time, the mixed gas was continuously introduced to continue the carbonation reaction, and when the pH of the slurry reached 7, the carbonation reaction was terminated.

When the obtained product is observed with an SEM, silica fine particles of about 20 to 80 nm adhere to the surface of the columnar calcium carbonate particles having a major axis of 1.0 to 3.0 μm and a minor axis of 0.1 to 0.3 μm. Silica-calcium carbonate composite particles.
Further, about 90% of the surface of the columnar calcium carbonate was covered with silica fine particles, but a small amount of silica single particles were observed around the surface.
These are as shown in FIG.

Silica-calcium carbonate composite particles were obtained under the same reaction conditions as in Example 2.
The added sodium chloride was a 10% by weight solution in which 14.6 g was dissolved in water.
According to the observation by SEM, the obtained product is fixed by attaching silica fine particles of 20 to 50 nm on the surface of columnar calcium carbonate particles having a major axis of 1.0 to 3.0 μm and a minor axis of 0.1 to 0.3 μm. Silica-calcium carbonate composite particles.
Further, about 90% of the surface of the columnar calcium carbonate was covered with silica fine particles, but a small amount of silica single particles were observed around the surface.

While stirring 2.0 kg of a 10.6 wt% calcium hydroxide slurry adjusted to a temperature of 30 ° C., a total amount of 10 wt% solution of 14.6 g of potassium chloride dissolved in water was added.
Thereafter, a mixed gas of carbon dioxide and air having a concentration of 25% by volume was introduced at a rate of 0.17 liter per minute per 100 g of calcium hydroxide to start the carbonation reaction.
When the carbonation rate of the carbonation reaction reaches 95%, 114.6 g of a 28 wt% solution of No. 3 sodium silicate (40 g per 100 g of calcium carbonate produced in terms of SiO ₂ weight) is added. At the same time, the mixed gas was continuously introduced to continue the carbonation reaction, and when the pH of the slurry reached 7, the carbonation reaction was terminated.

According to the observation with a scanning electron microscope (SEM), the obtained product was about 20 to 40 nm on the surface of columnar calcium carbonate particles having a major axis of 1.0 to 3.0 μm and a minor axis of 0.1 to 0.2 μm. It was silica-calcium carbonate composite particles to which silica fine particles were adhered and fixed.
Further, about 80% of the columnar calcium carbonate surface was covered with silica fine particles, and silica single particles were slightly recognized.

While stirring 2.0 kg of a calcium hydroxide slurry having a concentration of 6.5 wt% adjusted to a temperature of 26 ° C., a total amount of 10 wt% solution obtained by dissolving 17.6 g of potassium chloride in water was added.
Thereafter, a mixed gas of carbon dioxide and air having a concentration of 25% by volume was introduced at a rate of 0.35 liter per minute per 100 g of calcium hydroxide to start the carbonation reaction.
When the carbonation rate of the carbonation reaction reaches 90%, 35.1 g of a 28 wt% solution of No. 3 sodium silicate (20 g per 100 g of calcium carbonate formed in terms of SiO ₂ weight) is added. At the same time, the mixed gas was continuously introduced to continue the carbonation reaction, and when the pH of the slurry reached 7, the carbonation reaction was terminated.

According to the observation with a scanning electron microscope (SEM), the obtained product is around 10 to 40 nm on the surface of spindle-shaped calcium carbonate particles having a major axis of 1.0 to 2.0 μm and a minor axis of 0.3 to 0.5 μm. It was a silica-calcium carbonate composite particle to which the silica fine particles adhered and fixed.
Further, about 60% of the spindle-shaped calcium carbonate surface was covered with silica fine particles, and the silica agglomerated particles were slightly conspicuous.

While stirring 2.0 kg of a 6.2 wt% calcium hydroxide slurry adjusted to a temperature of 26 ° C., a total of 10 wt% solution of 33.5 g of sodium chloride dissolved in water was added.
Thereafter, a mixed gas of carbon dioxide and air having a concentration of 25% by volume was introduced at a rate of 0.35 liter per minute per 100 g of calcium hydroxide to start the carbonation reaction.
When the carbonation rate of the carbonation reaction reaches 10%, 33.5 g of a 28 wt% solution of sodium silicate No. 3 (20 g per 100 g of calcium carbonate produced in terms of SiO ₂ weight) is added. At the same time, the mixed gas was introduced to continue the carbonation reaction, and when the pH of the slurry reached 7, the carbonation reaction was terminated.

According to observation with a scanning electron microscope (SEM), the obtained product was around 20 to 40 nm on the surface of spindle-shaped calcium carbonate particles having a major axis of 0.4 to 0.8 μm and a minor axis of 0.1 to 0.2 μm. It was a silica-calcium carbonate composite particle to which the silica fine particles adhered and fixed.
In addition, about 50% of the spindle-like calcium carbonate surface was covered with silica fine particles, and a little more agglomerated particles of silica were observed.

While stirring 2.0 kg of a 6.2 wt% calcium hydroxide slurry adjusted to a temperature of 26 ° C., a total of 10 wt% solution of 33.5 g of sodium chloride dissolved in water was added.
Thereafter, a mixed gas of carbon dioxide and air having a concentration of 25% by volume was introduced at a rate of 0.35 liter per minute per 100 g of calcium hydroxide to start the carbonation reaction.
When the carbonation rate of the carbonation reaction reaches 50%, 33.5 g of a 28 wt% solution of No. 3 sodium silicate (20 g per 100 g of calcium carbonate formed in terms of SiO ₂ weight) is added. At the same time, the mixed gas was introduced to continue the carbonation reaction, and when the pH of the slurry reached 7, the carbonation reaction was terminated.

According to the observation with a scanning electron microscope (SEM), the obtained product was around 20 to 40 nm on the surface of spindle-shaped calcium carbonate particles having a major axis of 0.5 to 1.0 μm and a minor axis of 0.2 to 0.4 μm. It was a silica-calcium carbonate composite particle to which the silica fine particles adhered and fixed.
In addition, about 70% of the spindle-shaped calcium carbonate surface was covered with silica fine particles, and a little more agglomerated particles of silica were observed.

While stirring 2.0 kg of a calcium hydroxide slurry having a concentration of 6.3 wt% adjusted to a temperature of 40 ° C., a total amount of 10 wt% solution in which 1.7 g of sodium sulfate was dissolved in water was added.
Thereafter, a carbon dioxide and air mixed gas having a concentration of 25% by volume was introduced at a rate of 0.35 liter per minute per 100 g of calcium hydroxide to start the carbonation reaction.
When the carbonation rate of the carbonation reaction reaches 90%, 34.1 g of a 28 wt% solution of sodium silicate No. 3 (20 g per 100 g of calcium carbonate produced in terms of SiO ₂ weight) is added. At the same time, the mixed gas was introduced to continue the carbonation reaction, and when the pH of the slurry reached 7, the carbonation reaction was terminated.

When the obtained product is observed with an SEM, silica fine particles of about 20 to 60 nm adhere to the surface of spindle-shaped calcium carbonate particles having a major axis of 1.0 to 2.0 μm and a minor axis of 0.3 to 0.5 μm. The silica-calcium carbonate composite particles were fixed.
In addition, about 90% of the spindle-shaped calcium carbonate surface was covered with silica fine particles, and a small amount of silica single particles were observed around the surface.

While stirring 2.0 kg of calcium hydroxide slurry having a concentration of 6.1 wt% adjusted to a temperature of 40 ° C., a total amount of 10 wt% solution obtained by dissolving 1.6 g of sodium nitrate in water was added.
Thereafter, a carbon dioxide and air mixed gas having a concentration of 25% by volume was introduced at a rate of 0.35 liter per minute per 100 g of calcium hydroxide to start the carbonation reaction.
When the carbonation rate of the carbonation reaction reaches 90%, 33.0 g of a 28 wt% solution of No. 3 sodium silicate (20 g per 100 g of calcium carbonate produced in terms of SiO ₂ weight) is added. At the same time, the mixed gas was introduced to continue the carbonation reaction, and when the pH of the slurry reached 7, the carbonation reaction was terminated.

When the obtained product is observed by SEM, silica fine particles of about 10 to 60 nm adhere to the surface of spindle-shaped calcium carbonate particles having a major axis of 1.0 to 2.0 μm and a minor axis of 0.3 to 0.7 μm. The silica-calcium carbonate composite particles were fixed.
Further, about 60% of the spindle-shaped calcium carbonate surface was covered with silica fine particles, and a small amount of silica single particles were observed around the surface.

While stirring 2.0 kg of a calcium hydroxide slurry having a concentration of 6.2% by weight adjusted to a temperature of 40 ° C., a total amount of 10% by weight solution of 1.7 g of potassium nitrate dissolved in water was added.
Thereafter, a carbon dioxide and air mixed gas having a concentration of 25% by volume was introduced at a rate of 0.35 liter per minute per 100 g of calcium hydroxide to start the carbonation reaction.
When the carbonation rate of the carbonation reaction reaches 90%, 33.5 g of a 28 wt% solution of sodium silicate No. 3 (20 g per 100 g of calcium carbonate formed in terms of SiO ₂ weight) is added. At the same time, the mixed gas was introduced to continue the carbonation reaction, and when the pH of the slurry reached 7, the carbonation reaction was terminated.

When the obtained product is observed with an SEM, silica fine particles of about 20 to 40 nm adhere to the surface of spindle-shaped calcium carbonate particles having a major axis of 1.0 to 2.0 μm and a minor axis of 0.3 to 0.7 μm. The silica-calcium carbonate composite particles were fixed.
Further, about 60% of the spindle-shaped calcium carbonate surface was covered with silica fine particles, and a small amount of silica single particles were observed around the surface.

While stirring 2.0 kg of a 6.1 wt% calcium hydroxide slurry, the entire 10 wt% solution of 1.6 g sodium chloride dissolved in water was added.
Thereafter, 33.0 g of a 28 wt% solution of No. 3 sodium silicate (20 g per 100 g of calcium carbonate produced in terms of SiO ₂ weight) was added, and the slurry temperature was adjusted to 30 ° C.
While stirring this slurry, a mixed gas of carbon dioxide and air having a concentration of 25% by volume is introduced at a rate of 0.33 liters per minute per 100 g of calcium hydroxide to start the carbonation reaction, and the pH of the slurry becomes 7. When reached, the carbonation reaction was terminated.

When the obtained product is observed with a scanning electron microscope (SEM), rice grains having a major axis of 0.3 to 0.5 μm, a major axis of 1.0 to 3.0 μm, and a minor axis of 0.1 to 0.2 μm. Columnar calcium carbonate was mixed, and silica-calcium carbonate composite particles in which silica fine particles of about 20 to 40 nm were adhered and fixed on the surface of these calcium carbonate particles.
Further, about 60% of the spindle-shaped calcium carbonate surface was covered with silica fine particles, and a small amount of silica single particles were observed around the surface.

[Comparative Example 1] (Example 3 of Patent Document 12)
While stirring 2.0 kg of calcium hydroxide slurry having a concentration of 5.6% by weight adjusted to 35 ° C., 150 g of a 20% by weight solution of colloidal silica (average particle diameter 20 nm, spherical) (in terms of SiO ₂ weight, produced) 20 g) per 100 g of calcium carbonate to be added.
Subsequently, a carbon dioxide pure gas having a CO ₂ concentration of 100% by volume was introduced from a cylinder at a rate of 0.3 liters per minute per 100 g of calcium hydroxide to start the carbonation reaction, and when the slurry pH reached 7 The carbonation reaction was terminated.

The obtained product, as observed by SEM, is a silica in which colloidal silica is adhered and fixed to the surface of spindle-shaped calcium carbonate particles having a major axis of 1.5 to 2.0 μm and a minor axis of 0.3 to 0.4 μm. -Calcium carbonate composite particles.
Further, the entire surface of the spindle-shaped calcium carbonate was covered with colloidal silica, and no single particles of silica were observed.
The composite particles were dried at 105 ° C. and the liquid absorption was measured. The oil absorption was 67.5 g / 100 g, and the water absorption was 70.0 g / 100 g.
These values are slightly smaller than those in Example 1 in which the same amount of silica is coated on calcium carbonate.

[Comparative Example 2] (in the absence of sodium chloride)
While stirring 2.0 kg of calcium hydroxide slurry at a concentration of 6.8% by weight adjusted to a temperature of 30 ° C., a mixed gas of carbon dioxide and air at a concentration of 25% by volume is added every 0.33 liters per 100 g of calcium hydroxide. The carbonation reaction was started at a rate of minutes.
Thereafter, when the carbonation rate reached 90%, 36.7 g of a 28 wt% solution of No. 3 sodium silicate (20 g per 100 g of calcium carbonate produced in terms of SiO ₂ weight) was added. The mixed gas was introduced to continue the carbonation reaction, and when the pH of the slurry reached 7, the carbonation reaction was terminated.

  The obtained product, when observed with a scanning electron microscope (SEM), aggregates on a part of the surface of spindle-shaped calcium carbonate particles having a major axis of 1.0 to 2.0 μm and a minor axis of 0.3 to 0.5 μm. Silica fine particles adhered and fixed, and many agglomerated single particles of silica were observed.

[Comparative Example 3] (Addition of sodium silicate before carbonation, in the absence of sodium chloride)
Add 72.4 g of a 28 wt% solution of sodium silicate 3 to 2.0 kg of calcium hydroxide slurry at a concentration of 6.7 wt% (40 g per 100 g of calcium carbonate produced in terms of SiO ₂ weight) The temperature was adjusted to 30 ° C.
While stirring this slurry, a mixed gas of carbon dioxide and air having a concentration of 25% by volume is introduced at a rate of 0.33 liters per minute per 100 g of calcium hydroxide to start the carbonation reaction, and the pH of the slurry becomes 7. When reached, the carbonation reaction was terminated.

  When the obtained product is observed with a scanning electron microscope (SEM), it is formed on the surface of cubic calcium carbonate particles having a minor axis of 0.2 to 0.3 μm, a major axis of 0.6 to 1 μm, and a spindle of 0.5 to 1 μm. Although a small amount of silica fine particles were adhered and fixed, many single particles of aggregated silica were also observed.

[Comparative Example 4] (in the presence of MgCl ₂ )
While stirring 2.0 kg of a calcium hydroxide slurry having a concentration of 6.4 wt% adjusted to a temperature of 40 ° C., a total amount of 10 wt% solution in which 3.6 g of magnesium chloride hexahydrate was dissolved in water was added.
Thereafter, a carbon dioxide and air mixed gas having a concentration of 25% by volume was introduced at a rate of 0.35 liter per minute per 100 g of calcium hydroxide to start the carbonation reaction.
When the carbonation rate of the carbonation reaction reaches 90%, 35.0 g of a 28 wt% solution of No. 3 sodium silicate (20 g per 100 g of calcium carbonate produced in terms of SiO ₂ weight) is added. At the same time, the mixed gas was continuously introduced to continue the carbonation reaction, and when the pH of the slurry reached 7, the carbonation reaction was terminated.

  When the obtained product is observed with a scanning electron microscope (SEM), spindle-shaped calcium carbonate having a major axis of 1.0 to 2.0 μm and a minor axis of 0.3 to 0.7 μm, a major axis of 1.0 to 3.0 μm. A silica-calcium carbonate composite particle in which a small amount of silica fine particles of about 10 to 40 nm are adhered and fixed to the surface of columnar calcium carbonate particles having a minor axis of 0.1 to 0.2 μm, and aggregated particles of silica are surrounded by the silica-calcium carbonate composite particles. Many were observed.

[Comparative Example 5] (in the presence of CaCl ₂ )
While stirring 2.0 kg of a calcium hydroxide slurry having a concentration of 6.4 wt% adjusted to a temperature of 40 ° C., a total amount of 10 wt% solution in which 1.7 g of calcium chloride was dissolved in water was added.
Thereafter, a carbon dioxide and air mixed gas having a concentration of 25% by volume was introduced at a rate of 0.35 liter per minute per 100 g of calcium hydroxide to start the carbonation reaction.
When the carbonation rate of the carbonation reaction reaches 90%, 35.0 g of a 28 wt% solution of No. 3 sodium silicate (20 g per 100 g of calcium carbonate produced in terms of SiO ₂ weight) is added. At the same time, the mixed gas was continuously introduced to continue the carbonation reaction, and when the pH of the slurry reached 7, the carbonation reaction was terminated.

When the obtained product is observed with a scanning electron microscope (SEM), spindle-shaped calcium carbonate having a major axis of 1.0 to 2.0 μm and a minor axis of 0.3 to 0.7 μm, a major axis of 1.0 to 3.0 μm. On the surface of the columnar calcium carbonate particles having a minor axis of 0.1 to 0.2 μm, silica fine particles were hardly adhered and fixed, and many silica agglomerated particles were observed.

[Comparative Example 6]
While stirring 2.0 kg of a calcium hydroxide slurry having a concentration of 6.3% by weight, 34.1 g of a 28 wt% solution of sodium silicate No. 3 (20 g per 100 g of calcium carbonate produced in terms of SiO ₂ weight) was added. And the slurry temperature was adjusted to 30 ° C.
While stirring the slurry, a mixed gas of carbon dioxide and air having a concentration of 25% by volume was introduced at a rate of 0.35 liter per minute per 100 g of calcium hydroxide to start the carbonation reaction, and the pH of the slurry was 7 The carbonation reaction was terminated when the value reached.

When the obtained product is observed with a scanning electron microscope (SEM), a 10- to 50-nm silica particle is formed on a surface of spindle-shaped calcium carbonate having a major axis of 0.2 to 0.5 μm and a major axis of 1.0 to 2.0 μm. Silica-calcium carbonate composite particles to which a small amount of fine particles adhered and fixed were confirmed.
However, it was confirmed that the silica-calcium carbonate composite particles were present in a mixture with the silica aggregates, and it was difficult to distinguish them under an electron microscope.

The silica-calcium carbonate composite particles obtained in the above examples and comparative examples were measured for oil absorption and water absorption in order to compare their properties, and the results are summarized in Table 1.
The oil absorption in Table 1 is measured according to JIS K5101.
The water absorption was measured according to the JIS, and water was used in place of the linseed oil used in the oil absorption measurement.
The amount of alkali silicate added in Table 1 refers to the amount of anhydrous silicic acid contained in the alkali silicate to be added, not the amount of alkali silicate itself added as described above.

Regarding Examples 1, 6 and 7 in Table 1, the lime milk concentration, the alkali metal compound and the addition amount thereof, the alkali silicate and the addition amount thereof, and the shape of the generated calcium carbonate are all the same. Only the addition time of sodium silicate is different in each example.
Specifically, the carbonation rate at the time of sodium silicate addition in each Example of Example 6, Example 7, and Example 1 is 10%, 50%, and 90%, and the obtained silica-calcium carbonate It can be understood from Table 1 that the oil absorption and water absorption of the composite particles increase as the carbonation rate increases.

Moreover, in Example 1 and Comparative Example 2, the lime milk concentration, the alkali silicate and its addition amount, the addition time of sodium silicate, and the shape of the generated calcium carbonate are all the same or almost the same, In Example 1, sodium chloride coexists in the carbonation reaction process, whereas in Comparative Example 2, there is a difference in that sodium chloride does not coexist, and even if there is a difference, the oil absorption amount is almost the same. On the other hand, it can be understood from Table 1 that the water absorption is inferior.
Furthermore, the product of Example 1 has few silica single particles and most are silica-calcium carbonate composite particles, whereas the product of Comparative Example 2 shows not only silica-calcium carbonate composite particles. It can be seen that there are also a large number of aggregated silica single particles that cause an increase in viscosity when used as a coating agent or a filler for rubber.

In addition, although Comparative Example 6 is common to Comparative Example 2 in that sodium chloride does not coexist in the carbonation reaction process, sodium silicate is added before the carbonation reaction is started. It is different from Example 2, and as a result, although the amount of oil absorption is inferior to that of Example 1, it is understood that the amount of water absorption is superior to that of Example 1.
However, the produced silica-calcium carbonate composite particles are mixed with silica aggregates, which is clearly inferior to Example 1 in this respect.

In Comparative Examples 4 and 5, the substance coexisting in the carbonation reaction process is replaced with sodium chloride, which is an alkali metal compound of Example 1, and magnesium chloride and calcium chloride, which are alkaline earth metal compounds, are used. Although the water absorption amount is higher than that in Example 1 using sodium chloride, the oil absorption amount is inferior.
Furthermore, in the case of both comparative examples, oil absorption and water absorption are almost the same as in Examples 8, 9 and 10 using sodium sulfate, sodium nitrate and potassium nitrate as alkali metal compounds.
However, in both comparative examples, a large number of silica agglomerated particles not adhered to the surface of the calcium carbonate particles are observed. In this respect, the silica-calcium carbonate produced in the cases of Examples 8, 9 and 10 was observed. It is inferior to the composite particles.

Further, Comparative Example 1 was obtained by producing silica-calcium carbonate composite particles by the method of Patent Document 12, and Example 1 was produced by the method of the present invention. In both cases, the composite particles are produced under suitable conditions in the respective production methods.
When the oil absorption amount and the water absorption amount are compared with respect to the produced composite particles, Example 1 is much better, and the present invention is a silica-calcium carbonate composite particle that is more excellent in oil absorption and water absorption than the method of Patent Document 12. It can be seen that can be manufactured.
In addition, when Comparative Example 1 is compared with Examples 6 and 7, Comparative Example 1 is slightly better than Example 7 in oil absorption, and much better than Example 6, but both examples are suitable conditions. Since the carbonation reaction is not performed below, the present invention is not inferior to the method of Patent Document 12 with this result.

2 is a scanning electron microscope (SEM) photograph showing the particle structure of silica-calcium carbonate composite particles obtained in Example 2 (× 25,000).

Claims (7)

In the carbonation reaction process is a process of forming calcium carbonate, adding an alkali metal ion, and by adding an alkali silicate until carbonation reaction was completed, to fix the silica to the surface of the calcium carbonate, moreover when the The method for producing silica-calcium carbonate composite particles, wherein the addition amount of alkali metal ions is 0.1 to 100 parts by weight with respect to 100 parts by weight of anhydrous silicic acid contained in the alkali silicate . The method for producing silica-calcium carbonate composite particles according to claim 1, wherein alkali silicate is added after the formation of crystal nuclei of calcium carbonate in the carbonation reaction process. The method for producing silica-calcium carbonate composite particles according to claim 1 or 2, wherein the average particle diameter of silica fixed to the surface of calcium carbonate is in the range of 10 nm to 100 nm. The method for producing silica-calcium carbonate composite particles according to claim 1, 2 or 3, wherein the calcium carbonate is columnar calcium carbonate or spindle-shaped calcium carbonate. The method for producing silica-calcium carbonate composite particles according to any one of claims 1 to 4, wherein the alkali silicate is sodium silicate. The method for producing silica-calcium carbonate composite particles according to any one of claims 1 to 5, wherein the alkali metal ion is sodium or potassium. The silica-calcium carbonate composite particles according to any one of claims 1 to 6, wherein the addition amount of alkali silicate is 0.1 to 100 parts by weight in terms of anhydrous silicic acid with respect to 100 parts by weight of calcium carbonate. Production method.

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