JP2007070164A - Silica-calcium carbonate composite particle, its producing method and pigment, filler or paper containing it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a silica-calcium carbonate composite particle where the property of silica is added to that of calcium carbonate and which is suitable for an ink jet recording paper. <P>SOLUTION: In a carbonation reaction step to form calcium carbonate having a high specific surface area, typically a step to perform the carbonation reaction by introducing the mixed gas of carbon dioxide and air while stirring a calcium hydroxide slurry, an alkali silicate is added under the coexistence of an alkali metal ion between the initiation and the termination of the carbonation reaction. The mixed gas is continuously introduced and the carbonation reaction is continued and finished when the pH of the slurry reaches 7 and then the composite particle is produced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method for producing silica-calcium carbonate composite particles that can be suitably used as a pigment or filler for paper such as inkjet recording paper, the composite particles, or a pigment, filler, or paper containing the composite particles.
More specifically, by using an alkali silicate as a silica source and precipitating and fixing silica on the surface of calcium carbonate having a high specific surface area, the silica has a high specific surface area, high liquid absorption, vivid color development, etc. The present invention relates to a method for producing silica-calcium carbonate composite particles characterized by imparting an excellent function, or printing paper such as the composite particles, or a pigment, filler, or ink jet recording paper containing the composite particles.

Calcium carbonate, one of the main constituents of the composite particles of the present invention, is known in three types of calcite type, aragonite type and vaterite type due to the difference in crystal structure, and is used industrially There are two types of heavy calcium carbonate and synthetic (light) calcium carbonate depending on the production method.
The former heavy calcium carbonate is a finely pulverized product of crystalline white limestone (calcite type) that is naturally produced 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.

As the name implies, the latter synthetic calcium carbonate is chemically synthesized calcium carbonate, which is also called light or precipitated calcium carbonate, and includes calcite type and aragonite type.
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 gas compound method since 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 performed, the rate of carbonation, the production conditions such as coexisting ions, the particle shape, the particle diameter, It is possible to control physical properties such as specific surface area within a certain range.

Specifically, calcite-type colloidal, chain-like, cubic, spindle-shaped, and arbanite-type columnar calcium carbonate are well known, and their main uses are different.
That is, colloidal calcium carbonate is a colloidal particle having a particle diameter of 0.02 to 0.08 μm, and is used as a filler for plastics, rubber, paints and the like.
Chain-like calcium carbonate is formed by connecting crystal grains having a primary particle size of 0.02 to 0.08 μm in a long and thin chain, and serves as a filler for rubber, ink, and plastic.
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 has excellent 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 anhydrous silica, hydrous silica, colloidal silica, silica gel, etc., with high specific surface area, high gas adsorbing ability, fineness, penetrating power, adsorbing power, and adhesiveness in fine voids. 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, anhydrous silica is obtained by thermal decomposition of silicon tetrachloride and thermal reduction / oxidation of silica sand in an arc furnace, and it is used for reinforcing agents such as rubber, paint, ink, resin, and thixotropy imparting agents. Yes.
Hydrous silica is produced by decomposition of sodium silicate with sulfuric acid, and is used in rubber reinforcing fillers, paint matting agents, papermaking, resin films and the like.

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 a 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 and carrier, rubber filler, paint, It is used in applications such as thickening ink or anti-settling agents.

In this way, synthetic silica has a high specific surface area, high gas adsorption capacity, fineness, penetrating and adsorbing power into 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 the 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 it 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.
Thus, since calcium carbonate and synthetic silica each have unique features (advantages) and disadvantages, by combining calcium carbonate and silica, various technologies and solutions are available. Research on its use has been conducted for a long time and proposals have been made.

[Prior Art Document 1]
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

[Prior Art Document 2]
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

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. Amorphous silicic acid is produced by the above, and it is disclosed as a paper coating pigment mainly composed of vaterite 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 by paying attention to the use of a composite of silica and calcium carbonate, for example, a carrier for agricultural chemicals (Patent Document 8), a thermal recording material compounding agent (Patent Document 9), a pigment for ink jet recording paper ( Patent Document 10), reinforcing fillers such as rubber (Patent Document 11), and the like.
They are exemplified by production methods or structures different from those of the composites described above.
For example, in the calcium carbonate-silicic acid complex described in Patent Document 8, a metal such as Zn, Mg, Al is allowed to coexist during the carbonation reaction, and carbon dioxide gas is blown alone until the carbonation rate reaches 80%, and then silicic acid. It is manufactured by adding an alkali or silicic acid sol and blowing carbon dioxide gas 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, and the surface is not coated with silicic acid.

Further, 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 cause coprecipitation, 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. Although it is a manufacturing method that is different from the invention, it is not sufficient as can be understood from the fact that it is not put into practical use, and each of them has a problem (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 of Patent Document 3, titanium oxide is suitable as the fine particles, and even if 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 simple chain-like particle, and the silicon oxide-calcium carbonate complex disclosed in Patent Document 9 is obtained by binding silicon oxide and calcium carbonate in a molecular state or a state close thereto. It is believed that.

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, the particles obtained by these techniques are silica-calcium carbonate composite particles in which the surface of calcium carbonate having a specific shape, so-called spindle shape, colloidal shape, cubic shape, columnar shape, chain shape, etc., is coated with silica. Absent.

  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. 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 is disclosed.

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 remains difficult in terms of economy.

On the other hand, with the recent popularization of ink jet printers, market needs for printing paper suitable for printing, that is, ink jet recording paper, have increased, and many patents have been filed in order to meet the demand.
Inkjet recording paper includes non-coated paper that does not have a clear coating layer and coated paper that has a coating layer.
Coated paper is further divided into matte paper and glossy paper, and the base material is so-called paper, as well as synthetic paper, film, cloth, and non-woven fabric. The role of the coating layer in the coated paper is to absorb ink, It is to improve printability such as blur prevention, water resistance, weather resistance, color development, and color reproducibility.

In other words, coating-type inkjet recording paper is an inkjet-dedicated paper in which a porous pigment and a resin component such as PVA are applied to a base material such as paper, and is often used for color photographic printing. Therefore, extremely high levels of color developability and color reproducibility, water resistance and weather resistance, and ink absorbability are required.
As the porous pigment used here, silicas such as hydrous silica and colloidal silica are mainly used, and calcium carbonates are hardly used.
The reason is considered that general calcium carbonate not only has a lower ink absorption capacity than silica but also cannot exceed silica in terms of color development and color reproducibility.

In view of such circumstances, the present inventors have made extensive studies on the use of calcium carbonate as a porous pigment for papermaking, in particular, ink jet recording paper, and as a result, have excellent ink absorption capability, color development, We have succeeded in developing a material mainly composed of calcium carbonate that is excellent in color reproducibility.
That is, the present inventors use high-specific surface area calcium carbonate as a base material, use a relatively inexpensive alkali silicate, and carry or coat silica on the surface thereof, thereby containing hydrous silica or colloidal silica. Has succeeded in developing a method for producing silica-calcium carbonate composite particles that can impart printing suitability comparable to that of inkjet recording paper and that is also economically satisfactory.

Therefore, the present invention has a printability comparable to that of hydrous silica or colloidal silica by carrying or coating silica fine particles on the surface of a conventional synthetic calcium carbonate having a high specific surface area using a relatively inexpensive alkali silicate. It is a problem to be solved to provide a method for producing silica-calcium carbonate composite particles that can be imparted to inkjet recording paper and that is economically satisfactory.
Furthermore, another object of the present invention is to provide the composite particles or a pigment, filler or paper containing the composite particles.

The present invention provides a novel method for producing silica-calcium carbonate composite particles that solves the above-described problems.
In the carbonation reaction process, which is a process of forming calcium carbonate having a high specific surface area, an alkali silicate is added after the formation of crystal nuclei of calcium carbonate in the coexistence of alkali metal ions. The specific surface area by the BET method in which silica is fixed to the surface of calcium is 60 to 200 m ² / g, and the liquid absorption is 80 to 250 ml / 100 g.
The present invention also provides the composite particle, or a pigment, filler or paper containing the composite particle.
In addition, the liquid absorption amount here refers to the oil absorption amount and the water absorption amount, and at least one of them needs to be included in the above range.

In the silica-calcium carbonate composite particles obtained by the method for producing silica-calcium carbonate composite particles of the present invention, silica produced by a chemical precipitation reaction having an average particle size of 10 to 100 nm is dispersed on the surface of calcium carbonate having a high specific surface area. The specific surface area by the BET method is as high as 60 to 200 m ² / g as well as the oil absorption and water absorption. In contrast, it exhibits the same or better characteristics.
In addition, the composite particles of the present invention are porous pigments having excellent ink economy, vivid color development, and color reproducibility that are required for inkjet recording paper.

The silica-calcium carbonate composite particles obtained in this way are excellent not only in high specific surface area but also in high gas adsorbing ability, fineness, penetrating power and adsorbing power into fine voids, and high adhesive force. In addition to inkjet recording paper, other printing papers, as well as inks, paints, resins, pigments and fillers such as resin, rubber, etc. The use as a high-functional composite material is also promising.

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.
As described above, the silica-calcium carbonate composite particles of the present invention are produced in the carbonation reaction process, which is a process for forming calcium carbonate having a high specific surface area, in the presence of alkali metal ions until the carbonation reaction is completed. It is produced by adding an acid alkali to complete the carbonation reaction.

The carbonation reaction in the present invention is not particularly limited as long as calcium carbonate having a high specific surface area can be formed, and various methods such as a carbon dioxide compounding method, a calcium chloride soda method, a lime soda method or a water treatment method can be used. Although it can be adopted, the carbon dioxide compound method is suitable and economical in Japan.
Regarding calcium carbonate, which is one of the components constituting the composite particles of the present invention, if the calcium carbonate has a high specific surface area with a specific surface area of 50 m ² / g or more when not coated with silica, the production method thereof Is not particularly limited, and there is a method proposed in the following patent document.

[Prior Art Document 3]
JP-A-48-103100 JP 56-17925 A Japanese Patent Publication No. 5-55449 JP 2001-72413 A JP 2003-246617 A Gypsum and lime, no. 194, pp. 3-12, 1981

For example, Patent Document 13 discloses that lime milk containing 20% by weight or less of calcium hydroxide to which 5 to 30% by weight of calcium sulfite is added to calcium hydroxide is blown with carbon dioxide at a temperature of 0 to 40 ° C. A method for producing ultrafine calcium carbonate having a BET specific surface area of 90 to 100 m ² / g is disclosed.
Patent Document 14 discloses that an aqueous suspension of calcium hydroxide is mixed with 0.5 to 8 parts of sulfuric acid per 100 parts of calcium hydroxide, and then carbonized to have a minor axis of 0.02 to 0.03 μm and an aspect ratio. A method for producing fine particles of chain calcium carbonate with a ratio of 10 is disclosed.

Patent Document 15 discloses a method for producing fine precipitated calcium carbonate having a specific surface area of 60 m ² / g or more by blowing CO ₂ into an aqueous calcium hydroxide slurry containing an anionic organic polyphosphonate electrolyte.
In Patent Document 16, in the case of “more preferably”, calcium carbonate having a BET specific surface area of 50 m ² / g can be produced, and in the production method thereof, soluble metal salt, polyhydric alcohol, aluminum sulfate, magnesium sulfate, The use of various additives such as sulfuric acid, zinc sulfate, sodium hexametaphosphate and bisphosphonic acid is described.
And in the Example using these additives, it is described that a thing with a BET specific surface area of 71-130 m < ² > / g can be manufactured.

In Patent Document 17, a metal ion sequestering agent such as a hydroxycarboxylic acid such as citric acid or malic acid or a chelating agent such as ethylenediaminetetraacetic acid is added to the slaked lime suspension, and a carbon dioxide-containing gas is blown into the carbonic acid conversion rate of 20. After carbonation to ˜25%, further adding a sequestering agent in multiple stages and blowing a carbon dioxide-containing gas to terminate the reaction, the BET specific surface area is 100 to 200 m ² / g, the oil absorption amount Discloses a method for producing mesopore-carrying calcium carbonate of 150 to 200 ml / 100 g.

In the present invention, calcium carbonate having a high specific surface area can be produced by such a known method.
These calcium carbonates are all calcite type, but may be aragonite type, vaterite type, or amorphous calcium carbonate.
That is, in the present invention, in order to form calcium carbonate having a high specific surface area, it is convenient to use various additives for forming a high specific surface area, including the known additives.

As the auxiliary agent for forming the high specific surface area, sulfuric acid, zinc sulfate, aluminum sulfate, sulfate band, soluble metal salts represented by zinc chloride such as zinc sulfate, calcium sulfite, sodium silicate, phosphoric acid and Examples thereof include hydroxycarboxylic acids such as phosphate, citric acid, malic acid, tartaric acid, and gluconic acid, chelating agents such as ethylenediaminetetraacetic acid, anionic organic polyphosphonate electrolytes, and polyhydric alcohols.
These can be used alone or in combination of two or more.
The present inventors have also confirmed that it can be produced by adding sulfuric acid or sulfate, a method using them together, or a hydroxycarboxylic acid such as citric acid as an auxiliary for forming a high specific surface area during synthesis.

For example, in a carbon dioxide compounding method, after preparing lime milk, for example, sulfuric acid or sulfate, or a combination thereof, or a hydroxycarboxylic acid is added as an auxiliary agent for forming a high specific surface area before or after the introduction of carbon dioxide gas. As a result, fine calcium carbonate chain or fiber particles having a specific surface area of 50 to 170 m ² / g and a primary particle diameter of 20 to 40 nm can be produced.
In the carbon dioxide compounding method, the end of the carbonation reaction can be easily performed by measuring the pH, and the pH in the slurry decreases as the carbonation process proceeds, and reaches pH 7 when the carbonation reaction ends. Therefore, the end point of the carbonation reaction can be known by continuously measuring the change in pH.

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 a calcium carbonate formation process. Any alkali may be used as long as it reacts and precipitates as a solid on the surface of calcium carbonate, and it may be either silicon dioxide or its hydrate.

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.
Although this silica is presumed to be amorphous by powder X-ray diffraction at present, details of its structure or composition have not been confirmed.

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

In the present invention, the formation reaction of silica from alkali silicate must be performed in the presence of alkali metal ions, which is the greatest feature of the present invention. The method to do is not specifically 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 are prepared by adding alkali silicate in the presence of alkali metal ions between the formation of calcium carbonate crystal nuclei and the end of the carbonation reaction in the formation process of calcium carbonate having a high specific surface area. The alkali metal ions are allowed to exist in the reaction system by some method before adding the alkali silicate.

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, before the carbonation reaction start, or after the carbonation reaction start time, it is necessary to be before the addition of 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.
If the amount is too small, the surface of calcium carbonate cannot be uniformly coated, and silica single particles and aggregated particles increase.
On the other hand, if too much, a large amount of alkali metal compound is used, which not only decreases the economic efficiency, but also increases the anions such as alkali metal and chlorine ions remaining in the product, so that it can be used as a pigment or filler. May cause problems.

The timing of adding the alkali silicate is after the start of nucleation of calcium carbonate, preferably the carbonation reaction process in which the carbonation rate is 50% or more, and more preferably the crystals of synthetic calcium carbonate are formed. After the carbonation rate that has been generated and sufficiently grown reaches 75%, the carbonation rate is more preferably added in the vicinity of 90%.
Thus, silica-calcium carbonate composite particles in which silica is firmly and efficiently adhered and fixed to the surface of calcium carbonate having a high specific surface area can be obtained.
The carbonation rate here is represented by the following equation.
Carbonation rate = (calcium weight in calcium carbonate produced by carbonation reaction ÷ total weight of calcium present in reaction system and capable of becoming calcium carbonate by carbonation reaction) × 100

In addition, the start of crystal nucleation of calcium carbonate here can be easily known by continuously measuring the conductivity of the calcium hydroxide slurry in the carbon dioxide compounding method (see Non-Patent Document 1). However, the formation of crystal nuclei is often not confirmed, and at that time, it can be confirmed by sampling the suspension by a conventional method and using a powder X-ray diffraction method or an electron microscope.
In addition, when producing by a method other than the carbon dioxide compounding method, for example, when using a soluble carbonate such as sodium carbonate for the carbonation reaction, the formation of nuclei starts from the start of the addition, so the crystal nucleation starts to start carbonation. Sometimes coincides.

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. Silica (SiO ₂ ) is 0.1 to 100 parts by weight, desirably 1 to 30 parts by weight, and more desirably 5 to 30 parts by weight.
The added amount of alkali silicate here refers to the amount of anhydrous silicic acid contained in the added alkali silicate, not the amount of added alkali silicate itself.

When the amount added is less than 0.1 part by weight, the characteristics of silica are hardly exhibited, and the product is hardly different from the properties of calcium itself, so that the object of the present invention may not be achieved.
On the other hand, if the amount is too large, not only will it be economically disadvantageous, but it will also lead to a decrease in specific surface area and a decrease in the amount of oil absorbed and the amount of water absorbed, and the subject of the present invention may not be achieved.

Moreover, the silica-calcium carbonate composite particles of the present invention can also be produced by using synthetic calcium carbonate having a high specific surface area after completion of the carbonation reaction.
In that case, after adding an appropriate amount of a calcium source such as calcium hydroxide or calcium chloride to a synthetic calcium carbonate slurry having a specific surface area of 50 m ² / g or more, an alkali metal ion and an alkali silicate are added. Carbonation may be performed again with a carbon dioxide source such as carbon dioxide.
In this case, any alkali metal ions and alkali silicate may be added first as long as they are before the start of the recarbonation reaction.
However, when adding after the start of the recarbonation reaction, it is necessary to add an alkali metal ion before adding the alkali silicate.

By the above-described reaction operation, the average particle diameter of silica, that is, the surface of calcium carbonate is fixed on the surface of calcium carbonate particles having a high specific surface area by observing the surface shape with a scanning electron microscope or 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 of silica in the form of particles adhered to and fixed to the surface of high specific surface area calcium carbonate can be produced.
The silica-calcium carbonate composite particles thus obtained have a specific surface area that is usually 10 m ² / g or more higher than that of calcium carbonate alone, and the liquid absorption amount, that is, the oil absorption amount or the water absorption amount is also increased by 10 ml / 100 g or more.

The method for producing silica-calcium carbonate composite particles of the present invention can be easily carried out by a new and simple method of adding alkali silicate in the step of forming calcium carbonate having a high specific surface area. Are better.
The silica-calcium carbonate composite particles obtained in this manner are dispersed and uniformly adhered to the surface of calcium carbonate having a high specific surface area by dispersing silica produced by a chemical precipitation reaction having an average particle diameter of 10 to 100 nm. It is what.

The silica-calcium carbonate composite particles not only have a high specific surface area, but also have the same or better properties in terms of liquid absorbency such as oil absorbency and water absorbency compared with calcium carbonate of a base material not coated with silica. Is expressed.
In addition, since the composite particles of the present invention are coated with silica particles on the surface of calcium carbonate, the ink absorbency and vivid color development required for ink jet recording paper equivalent to or better than silica-based porous particles It becomes a porous pigment excellent in economy and color reproducibility.

[Examples and Comparative Examples]
Hereinafter, the present invention will be described more specifically with reference to a plurality of examples and comparative examples. However, the present invention is not limited to these examples and the like, and is specified by the description of the scope of claims. Needless to say, it is something.
In addition, the specific surface area by the BET method described below is measured by TECH K5101 using Mountech's Macsorb HM-1201, the water absorption is measured according to the JIS, In that case, water was used in place of the linseed oil used in the oil absorption measurement.

[Use of zinc sulfate + sulfuric acid as an auxiliary for forming a high specific surface area]
3 kg of quick lime for industrial use is hydrated with 15 liters of water to prepare 9.1% by weight lime milk (calcium hydroxide slurry), and 2.0 kg of this calcium hydroxide slurry is stirred at 450 rpm while adding sodium chloride. A total of 10% by weight solution of 15.0 g dissolved in water was added.
After the temperature was adjusted to 28 ° C., an aqueous solution of 24.2 g of zinc sulfate heptahydrate and sulfuric acid 16.2 were introduced while introducing a mixed gas of carbon dioxide gas amount 3.8 liters / minute and air amount 8.8 liters / minute. 7 g was added.

When the carbonation rate reached 90%, a 28 wt% solution of No. 3 sodium silicate in terms of SiO ₂ by weight, was added slowly such that the 10g to calcium carbonate 100g for generating, the slurry When the pH reached 7, the carbonation reaction was terminated.
According to observation with a scanning electron microscope (SEM), the obtained product is a silica in which silica fine particles of about 10 to 50 nm are adhered and fixed on the surface of fibrous calcium carbonate having a fiber length of about 0.5 μm. -Calcium carbonate composite particles.
The specific surface area by the BET method was 69.1 m ² / g, the oil absorption by linseed oil was 108 ml / 100 g, and the water absorption was 130 ml / 100 g.

While the temperature was adjusted to 28 ° C. while stirring 2.0 kg of the calcium hydroxide slurry prepared in Example 1 at 450 rpm, the mixed gas was 3.8 liters / minute of carbon dioxide and 8.8 liters / minute of air. Then, an aqueous solution of 22.7 g of zinc sulfate heptahydrate and 8.3 g of sulfuric acid were added.
When the carbonation rate reaches 90%, a total amount of 10% by weight aqueous solution in which 30 g of sodium chloride is dissolved is added, and a 28% by weight solution of No. 3 sodium silicate is converted into SiO ₂ weight to produce carbonic acid. Gradual addition was performed so that the amount became 20 g with respect to 100 g of calcium, and the carbonation reaction was terminated when the pH of the slurry reached 7.

According to observation with a scanning electron microscope (SEM), the obtained product is a silica in which silica fine particles of about 10 to 50 nm are adhered and fixed on the surface of fibrous calcium carbonate having a fiber length of about 0.3 μm. It was a calcium carbonate composite particle.
The specific surface area by the BET method was 76.2 m ² / g, the oil absorption by linseed oil was 105 ml / 100 g, and the water absorption was 140 ml / 100 g.

[Only zinc sulfate is used as an auxiliary for forming a high specific surface area]
While stirring 2.0 kg of calcium hydroxide slurry with a concentration of 7.3% by weight at 450 rpm, adjusting the temperature to 15 ° C., mixing carbon dioxide amount 1.5 liters / minute and air amount 2.1 liters / minute While introducing the gas, 5.7 g of zinc sulfate heptahydrate dissolved in water was added.
When the carbonation rate reached 60%, a total amount of 10 wt% solution in which 5.0 g of sodium chloride was dissolved in water was added, and a 28 wt% solution of No. 3 sodium silicate was converted to SiO ₂ weight. Then, it was gradually added so as to be 10 g per 100 g of produced calcium carbonate, 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), silica fine particles of about 10 to 50 nm adhere to the surface of calcium carbonate in which colloidal particles having a particle size of 20 nm are linked in a fixed manner. Silica-calcium carbonate composite particles.
The specific surface area by the BET method was 63.5 m ² / g, the oil absorption by linseed oil was 89 ml / 100 g, and the water absorption was 105 ml / 100 g.

[Use of citric acid as an auxiliary for forming a high specific surface area]
While stirring 1.8 kg of tap water, 200 g of industrial slaked lime was added to prepare a calcium hydroxide slurry having a concentration of 10% by weight.
An aqueous solution in which 3 g of citric acid was dissolved in tap water was added thereto, the slurry temperature was adjusted to 10 ° C., and carbon dioxide gas was introduced at a rate of 1.2 liters / minute.

10 minutes after the start of carbonation, an aqueous solution in which 3 g of citric acid was dissolved in tap water was added again, and in the same manner, it was added after 18 and 25 minutes.
50 minutes after the start of carbonation (carbonation rate 80%), a total amount of 10% by weight solution of 30 g of sodium chloride in water was added, and a 28% by weight solution of No. 3 sodium silicate was converted to SiO ₂ weight. Then, it was gradually added so as to be 20 g with respect to 100 g of produced calcium carbonate.
Carbonation was completed because the pH reached 7 65 minutes after the start of carbonation.

According to observation with a scanning electron microscope (SEM), the obtained product formed an aggregate of 3 to 7 μm of fibrous calcium carbonate having a fiber length of about 0.3 μm. It was silica-calcium carbonate composite particles having silica fine particles of about ˜70 nm adhered and fixed in a porous state.
The specific surface area by the BET method was 154.4 m ² / g, the oil absorption by linseed oil was 169 ml / 100 g, and the water absorption was 183 ml / 100 g.

[Use of potassium chloride as an additive for forming silica composites]
Silica-calcium carbonate composite particles were produced in the same manner as in Example 1 except that sodium chloride was changed to calcium chloride.
According to observation with a scanning electron microscope (SEM), the obtained product is a silica in which silica fine particles of about 10 to 70 nm are adhered and fixed on the surface of fibrous calcium carbonate having a fiber length of about 0.5 μm. -Calcium carbonate composite particles. The specific surface area by the BET method was 65.7 m ² / g, the oil absorption by linseed oil was 103 ml / 100 g, and the water absorption was 118 ml / 100 g.

[Comparative Example 1 (no use of sodium chloride as an additive for forming a silica composite)]
Under the same conditions as in Example 1, the carbonation reaction was terminated without adding sodium chloride.
When the obtained product is observed with a scanning electron microscope (SEM), fibrous calcium carbonate having a fiber length of about 0.5 μm is formed, and silica fine particles of about 10 to 50 nm are slightly observed on the surface. However, most of the silica particles are present in the form of aggregates, which is different from the silica-calcium carbonate composite particles of the present invention in which the surface of calcium carbonate is coated.
The specific surface area of this sample by the BET method was 63.6 m ² / g, the oil absorption by linseed oil was 102 ml / 100 g, and the water absorption was 117 ml / 100 g.

[Comparative Example 2 (No auxiliary agent for forming a high specific surface area (formation of spindle-shaped calcium carbonate))]
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.
The composite particles had a specific surface area by BET method of 12.9 m ² / g, an oil absorption by linseed oil of 81 ml / 100 g, and a water absorption of 88 ml / 100 g.
A small specific surface area indicates that there are few pores, which is insufficient as a porous pigment for ink jet recording paper.

[Comparative Example 3 (No use of auxiliary agent for forming high specific surface area (formation of columnar calcium carbonate))]
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.
The composite particles had a specific surface area of 12.9 m ² / g by BET method, an oil absorption by linseed oil of 70 ml / 100 g, and a water absorption of 102 ml / 100 g.
A small specific surface area indicates that there are few pores, which is insufficient as a porous pigment for ink jet recording paper.

Claims (9)

In the carbonation reaction process, which is the formation process of calcium carbonate having a high specific surface area, after the formation of calcium carbonate crystal nuclei, alkali silicate is added in the presence of alkali metal ions to fix silica to the surface of calcium carbonate. A method for producing silica-calcium carbonate composite particles, wherein the BET method has a specific surface area of 60 to 200 m ² / g and a liquid absorption of 80 to 250 ml / 100 g. The method for producing silica-calcium carbonate composite particles according to claim 1, wherein the average particle size 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 or 2, wherein the alkali silicate is sodium silicate. The method for producing silica-calcium carbonate composite particles according to any one of claims 1 to 3, wherein the alkali metal ion is sodium or potassium. 5. The silica-calcium carbonate composite particle according to claim 1, wherein the addition amount of the 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. The silica according to any one of claims 1 to 5, 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 to be added. A method for producing calcium carbonate composite particles. A process for forming calcium carbonate having a high specific surface area, wherein one or more auxiliary agents for forming a high specific surface area selected from sulfuric acid, soluble metal salts, hydroxycarboxylic acids, chelating agents and polyhydric alcohols are added. The method for producing silica-calcium carbonate composite particles according to any one of 1 to 6. Silica-calcium carbonate composite particles produced by the method according to any one of claims 1 to 7. A pigment, filler or paper containing silica-calcium carbonate composite particles produced by the method according to any one of claims 1 to 7.