JP2001240765A - Titanium dioxide-calcium carbonate composite, method for producing the same, and paper using the same - Google Patents

Abstract

(57) [Problem] To provide a titanium dioxide-calcium carbonate composite excellent in opacity, produced by utilizing a carbonation reaction, a method for producing the same, and a paper using the same. A titanium dioxide-calcium carbonate composite characterized by having titanium dioxide particles on a surface layer of calcium carbonate particles, which can be produced by utilizing a carbonation reaction,
When used as a filler or coating pigment to make paper,
Paper excellent in ash yield, whiteness, opacity, surface strength, etc. is obtained in a well-balanced manner.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a titanium dioxide-calcium carbonate composite, and more particularly to a method utilizing a carbonation reaction, and particularly to a titanium dioxide-calcium carbonate composite having excellent opacity. The present invention relates to a method for producing a body, and a paper and a coated paper having excellent opacity using the titanium dioxide-calcium carbonate composite as a filler or a coating pigment.

[0002]

2. Description of the Related Art In recent years, there has been a demand for the development of so-called lightweight paper which has the same weight and can be used more as a used area, for environmental protection measures, resource saving (saving) or economic reasons. In particular, the tendency is remarkable in fields such as catalogs, flyers, direct mail, and newsprint used in large quantities.

[0003] However, there are many problems associated with the reduction in weight. Above all, one of the major problems with the quality of lightweight paper is the reduction in opacity. In order to increase the opacity of lightweight paper, a method of using GP (mechanical pulp) or DIP (recycled paper deinked pulp), which has the effect of increasing opacity, as the main raw material fiber pulp, or opacity as an internal filler For example, it is possible to use a filler that is excellent in quality.

[0004] The method using mechanical pulp or DIP is limited in its application range because it cannot be applied to high quality paper. In addition, high-quality blending of medium-quality paper and recycled paper until the opacity is satisfied also causes problems such as a decrease in whiteness, an increase in impurities, and a decrease in print quality.

[0005] Generally, an internal filler is added to a pulp fiber-based paper stock for the purpose of improving opacity, whiteness, smoothness and formation of paper or sheet, etc., and papermaking is performed. Finished on paper. As the filler in that case, for example, talc, kaolin, heavy calcium carbonate, light calcium carbonate and the like are used. In addition, for special applications, the amount used is small but titanium dioxide, calcined clay,
A urea resin-based synthetic filler or gypsum is used. White carbon (amorphous synthetic silica) is widely used as a filler for newsprint. These fillers are used alone or in combination depending on the use and purpose. To improve the opacity, a method of adding a large amount of filler can be considered, but particularly in the case of lightweight paper, there is a disadvantage that the strength of the paper is reduced, and as a result, the operability during papermaking is reduced, In addition, during printing, there may be problems such as accumulation of paper powder and filler components on a blanket, and a decrease in print running performance such as cutting of paper.
Not much can be added.

[0006] The opacity of paper depends on the light absorption, scattering, and refractive index of the raw material, and among these, the opacity is greatly affected by the refractive index of light between air, filler, and pulp fibers. is there. Among the fillers exemplified above, titanium dioxide has the highest refractive index to light. Furthermore, in general,
The primary particle diameter of the titanium dioxide is 0.1 to 0.4.
μm, but the particle size of the filler is １ ／ of the wavelength of visible light.
Before and after, that is, about 0.3 μm, light scattering is maximum and opacity is highest. As described above, titanium dioxide is a material excellent in opacity improving effect because its refractive index and particle size are suitable for improving opacity of paper.

[0007] However, titanium dioxide is very expensive compared to other commonly used fillers, such as light calcium carbonate, talc, or kaolin. In addition, when used as a filler for papermaking, the average particle size is smaller than other fillers, and the yield to paper (retention in the wire part) is significantly lower than that of other fillers. However, there is a problem in that the operation is unstable due to an increase in the amount of filler in the white water and the load on the white water recovery system increases, and in fact, it is hardly used.

[0008] In recent years, as the demand for the preservability and durability of paper has increased, attention has been paid to a method of making paper in a pH range of neutral to weak alkali, that is, so-called neutral papermaking. In neutral papermaking, light calcium carbonate, which is relatively inexpensive, has high whiteness, and has excellent abrasion resistance to plastic wires, is preferably used. However, light calcium carbonate is less effective in improving opacity than titanium dioxide and the like, and must be added at a high rate in order to achieve a satisfactory level.In terms of quality, surface strength and paper strength decrease, and On the operation side, there are concerns about problems such as an increase in paper breakage and an increase in the load on the white water recovery system.

As described above, using expensive titanium dioxide alone as a filler pigment is not practical because the operation and economic burden are too large. On the other hand, titanium dioxide has the highest light scattering rate (excellent opacity)
If it is a material having high whiteness and titanium dioxide can be used efficiently and effectively, its application range is considered to be extremely increased. Therefore, a method of solving the problem of titanium dioxide by using titanium dioxide in combination with another filler has been proposed.

For example, Japanese Patent Application Laid-Open No. 2-51419 proposes a high concealing calcium carbonate in which calcium carbonate is grown from the surface with titanium dioxide or zinc oxide as a nucleus. Specifically, it is a method in which calcium chloride or calcium sulfate which is a soluble calcium carbonate salt is added to titanium dioxide or zinc oxide or the like, and ammonia and carbon dioxide gas are introduced. However, according to the method of this proposal, the high concealing calcium carbonate is covered with calcium carbonate with titanium dioxide having a high refractive index as a nucleus, so that the high concealing effect (high opacity) inherent in titanium dioxide is sufficiently achieved. There is a disadvantage that it cannot be obtained.

Japanese Patent Application Laid-Open No. Hei 6-93204 discloses that
After treating the surface of calcium carbonate particles with an alkali metal salt of polyacrylic acid as a binder, mixing and stirring the powders with titanium oxide to which an acrylic acid monomer has been adsorbed in advance to produce a titanium dioxide and calcium carbonate composite Has been proposed. The proposed method has the drawbacks of requiring a specific synthetic adhesive, which complicates the operation and increases the cost. Further, Japanese Patent Application Laid-Open
JP-A-217292 discloses a method in which titanium dioxide is mixed with a mixture of spindle-shaped light calcium carbonate and columnar light calcium carbonate to be used as a filler, and JP-T-2000-506205 discloses a method in which 30 to 100 nm of light calcium carbonate is mixed with titanium dioxide. There has been proposed a method in which titanium dioxide adhered to the surface by van der Waals force is used as a filler.

In these methods, the bond between titanium dioxide and light calcium carbonate is weak, and if a shear is applied, titanium dioxide and light calcium carbonate are separated, so that the drawbacks of titanium dioxide cannot be sufficiently solved. As described above, in the case of reducing the weight of paper, the current situation is that the paper is produced with reduced quality and operability.

Further, in the coated paper, in addition to the above countermeasures, a device using a coating liquid has been devised. For example, there is a method using light calcium carbonate or titanium dioxide, calcined clay, plastic pigment, or the like, which has excellent opacity as a coating pigment. The opacity can be improved by these methods, but the amount is limited by the quality of the coated paper, such as the glossiness of the white paper and the printing gloss, and it is difficult to increase the fluidity and high concentration of the coating liquid. And the addition amount cannot be increased to a point where opacity can be satisfied.

[0014]

DISCLOSURE OF THE INVENTION The present inventors have intensively studied fillers and coating pigments capable of solving operational problems while maintaining the quality characteristics of titanium dioxide. As a result, they found that the titanium dioxide-calcium carbonate composite obtained by utilizing the carbonation reaction could solve the problems in the operation of titanium dioxide and was excellent in opacity, and completed the present invention. Was.

[0015]

SUMMARY OF THE INVENTION The present invention provides a method for producing a titanium dioxide-calcium carbonate composite, comprising titanium dioxide particles on the surface layer of calcium carbonate particles by utilizing a carbonation reaction, and the titanium dioxide. -It relates to a high opacity paper characterized by using a calcium carbonate composite as a filler and a coating pigment. The titanium dioxide-calcium carbonate composite according to claim 1 has titanium dioxide particles on the surface layer of calcium carbonate particles. In the titanium dioxide-calcium carbonate composite according to the second aspect, the titanium dioxide-calcium carbonate composite preferably has an average particle diameter of 2 to 40 μm. The titanium dioxide-calcium carbonate composite according to claim 3, wherein the ratio of titanium dioxide in the titanium dioxide-calcium carbonate composite is 1 to 40 with respect to the total solid content of the composite.
% By weight. A method for producing a titanium dioxide-calcium carbonate composite according to a fourth aspect is characterized in that the above-described titanium dioxide-calcium carbonate composite according to the present invention is produced by utilizing a carbonation reaction. Further, in the method for producing a titanium dioxide-calcium carbonate composite according to claim 5, a carbon dioxide-containing gas is blown into an aqueous calcium hydroxide suspension to generate calcium carbonate,
When the carbonation ratio becomes 50 to 95%, an aqueous titanium dioxide suspension is added to continue the carbonation reaction. In addition, the method for producing a titanium dioxide-calcium carbonate composite according to claim 6 provides an aqueous calcium carbonate suspension,
After adding the aqueous suspension of calcium hydroxide and the aqueous suspension of titanium dioxide, a carbon dioxide-containing gas is blown into the mixed suspension to carry out the carbonation reaction. Aqueous calcium suspension /
The mixing ratio of the titanium dioxide aqueous suspension is 10
It is characterized by being controlled so as to be 0/4 to 75/1 to 130. In the method for producing a titanium dioxide-calcium carbonate composite according to claim 7, the weight ratio of the solid content of calcium hydroxide / titanium dioxide is controlled to 0.5 / 1 to 5/1 in the method of claim 6. It is characterized by.
The high opacity paper according to claim 8 is obtained by using the titanium dioxide-calcium carbonate composite according to any one of claims 1 to 3 as a filler. The high opacity paper according to the ninth aspect is characterized in that the high opacity paper according to the eighth aspect is used as a base paper, and both surfaces thereof are coated with a surface treatment agent containing an organic pigment and an adhesive as main components and dried. High opacity paper. A method for producing a titanium dioxide-calcium carbonate composite slurry according to claim 10 is the method for producing a titanium dioxide-calcium carbonate composite according to any one of claims 4 to 7, wherein the titanium dioxide-calcium carbonate composite is Further, the cake is dehydrated and concentrated by a filter press to obtain a cake, and at least a dispersant is added thereto, and the mixture is dispersed by a stirrer to form a slurry. The coated paper according to claim 11 is obtained by using the titanium dioxide-calcium carbonate composite according to any one of claims 1 to 3 as a coating pigment.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have studied the development of fillers and coating pigments utilizing the characteristics of titanium dioxide as a method of increasing opacity. As a result, titanium dioxide particles having titanium dioxide particles on the surface layer of calcium carbonate obtained by the carbonation reaction.
The calcium carbonate composite was found to be excellent in opacity. And by using the titanium dioxide-calcium carbonate composite as a filler or / and a coating pigment,
The present inventors have found that base paper, printing paper, high-quality paper, coated paper, and the like having excellent opacity can be stably produced, and have completed the present invention.

The titanium dioxide-calcium carbonate composite of the present invention is characterized in that titanium dioxide particles are fixed to the surface layer of calcium carbonate particles by utilizing a carbonation reaction.
That is, the titanium dioxide-calcium carbonate composite is
Without using an adhesive such as a synthetic resin such as acrylic, styrene, or styrene-butadiene, or a natural resin such as rubber or starch, titanium dioxide is added during the process of carbonating calcium hydroxide to form a composite. It is a thing.

The production method is not particularly limited, but in the step of blowing a carbon dioxide-containing gas into the aqueous calcium hydroxide solution to generate calcium carbonate, an aqueous suspension of titanium dioxide is produced during the carbonation reaction. A method of obtaining a titanium dioxide-calcium carbonate complex by adding a suspension to continue the carbonation reaction (hereinafter, referred to as method A), or an aqueous calcium carbonate suspension, an aqueous calcium hydroxide suspension, After adding the aqueous suspension of titanium dioxide, a method (hereinafter referred to as method B) obtained by blowing carbon dioxide-containing gas into the mixed suspension to carry out a carbonation reaction is exemplified.

The ratio of titanium dioxide in the titanium dioxide-calcium carbonate composite is preferably adjusted to 1 to 40% by weight based on the total solids of the composite. The ratio of titanium dioxide to the total solids of the composite is 1% by weight. %, It is difficult to obtain the desired opacity improving effect of the present invention, and according to experiments by the present inventors, if it exceeds 40% by weight, titanium dioxide is added further. However, the effect of improving opacity has reached saturation, which is economically undesirable. Further, titanium dioxide is easily separated from the composite, and there is a concern about operational problems such as a decrease in yield in a papermaking process. Considering the effect of opacity and cost as an internal filler or a coating pigment from the results of the experiment, the ratio of titanium dioxide in the titanium dioxide-calcium carbonate composite can be adjusted to 2 to 15% by weight. More preferred.

Hereinafter, the method for producing the titanium dioxide-calcium carbonate composite will be described in detail. First, in the production method by the method A, the solid content concentration is 5 to 20% by weight and the temperature is 10%.
While stirring the aqueous calcium hydroxide suspension at ~ 70 ° C, a carbon dioxide-containing gas is blown in to generate light calcium carbonate, and during the carbonation reaction, the aqueous titanium dioxide suspension is added, and the aqueous solution of the reaction system is added. PH value of the suspension is 7.5
The carbonation reaction is completed by blowing a carbon dioxide-containing gas until (below) to obtain a titanium dioxide-calcium carbonate composite in which titanium dioxide is fixed on the surface layer of calcium carbonate.

The time for adding the aqueous suspension of titanium dioxide is preferably such that the degree of carbonation is 50 to 95%, more preferably 80 to 95%. By the way, when the carbonation rate is less than 50% and the titanium dioxide aqueous suspension is added,
The ratio of coating the titanium dioxide particles with the generated calcium carbonate increases, and as a result, the ratio of the titanium dioxide particles existing in the surface layer of the composite particles decreases, and the original excellent optical suitability of titanium dioxide is exhibited. And the opacity improving effect is hardly obtained. On the other hand, when an aqueous suspension of titanium dioxide is added in a state where the carbonation reaction is almost completed (a state in which there is almost no unreacted calcium hydroxide), that is, a state in which the carbonation ratio exceeds 95%, the titanium dioxide The fixing rate to the composite decreases, and it is difficult to obtain the desired properties such as stable operation of the present invention. In any case, there is a problem that a composite having excellent opacity cannot be obtained. Here, the carbonation ratio is represented by the following equation. Carbonation rate (%) = (a / b) × 100 a: Weight of carbonated calcium hydroxide b: Weight of calcium hydroxide before carbonation reaction

On the other hand, in the production method by the method B, calcium hydroxide and titanium dioxide are added using calcium carbonate particles as a matrix, and a carbon dioxide-containing gas is blown into the mixed suspension to obtain a titanium dioxide-calcium carbonate composite. Things. The mixing ratio of calcium carbonate, calcium hydroxide, and titanium dioxide is not particularly limited, but preferably, an aqueous calcium hydroxide suspension is added so as to have a ratio corresponding to a carbonation rate of 50 to 95%, Further, the solid content of titanium dioxide is 1 to 4 per solid weight of the composite.
It is desirable to add an aqueous suspension of titanium dioxide so as to be 0%. That is, when specifically exemplified, the density 5
-20% by weight aqueous calcium carbonate suspension (solids 10
0 to 5 parts by weight of an aqueous suspension of calcium hydroxide having a concentration of 5 to 20% by weight in a solid content of 4 to 75 parts by weight and a concentration of 30 to 6 parts by weight.
An aqueous suspension of 5% by weight of titanium dioxide is solidified at 1 to 13%.
It is preferable to add and mix at a ratio of 0 parts by weight.

If the amount of calcium hydroxide is less than 4 parts by weight in terms of solid content, the fixing rate of titanium dioxide decreases, and it becomes difficult to obtain the desired properties of the present invention. On the other hand,
When the added amount of calcium hydroxide exceeds 75 parts by weight in solid content, the ratio of titanium dioxide particles present in the surface layer of the composite particles decreases, and the excellent optical suitability of titanium dioxide is not exhibited, and the opacity improving effect is not exhibited. May be difficult to obtain. On the other hand, if the added amount of titanium dioxide is less than 1 part by weight on a solid basis, it is difficult to obtain the desired opacity improving effect of the present invention, and if it exceeds 80 parts by weight, the opacity improving effect of titanium dioxide is saturated. And it is economically unfavorable. Furthermore, titanium dioxide is easily separated from the composite, and there is a concern that operation problems may occur.

In the method B, the solid content ratio of the calcium hydroxide suspension and the titanium dioxide suspension added to the calcium carbonate suspension is also an important factor for increasing the fixing rate of titanium dioxide. This solid content ratio is determined in consideration of the quality of the composite (high opacity effect), the amount of titanium dioxide added, the average particle size of titanium dioxide (primary particle size), and the like, but is more preferably. It is added while being adjusted in the range of 0.5 / 1 to 5/1. That is, when the content is controlled within this range, the titanium dioxide is sufficiently fixed even when the solid content ratio of the titanium dioxide is large. On the other hand, even when the solid content ratio of titanium dioxide is small, the coating of titanium dioxide with calcium carbonate is not so large, and a good opacity improving effect can be obtained.

If necessary, water or warm water is added to the aqueous suspension obtained by mixing calcium carbonate / calcium hydroxide / titanium dioxide to adjust the temperature to 10 to 70 ° C. and the concentration to 5 to 20% by weight. Then, while stirring the suspension, a carbon dioxide-containing gas is introduced, and the carbon dioxide-containing gas is blown until the pH value indicating the completion of the carbonation reaction, that is, the pH value becomes 7.5 or less, and the carbon dioxide-containing gas is blown. A titanium-calcium carbonate composite is obtained.

In the method B, as the calcium carbonate to be used, both light calcium carbonate and heavy calcium carbonate can be used, but light calcium carbonate is preferably used. The particle size of calcium carbonate and titanium dioxide is not particularly limited, but considering its use as a filler or a pigment, calcium carbonate has an average particle size of 2 to 30 μm and a primary particle size due to its quality characteristics. 0.3 to 15 μm, more preferably the average particle diameter is 3
It is desirable to use calcium carbonate having a primary particle diameter of 1 to 5 μm and a primary particle diameter of 1 to 5 μm.

The titanium dioxide used for producing the titanium dioxide-calcium carbonate composite of the present invention includes:
Primary particle diameter is 0.1 to 0.4 μm, preferably 0.2 to 0.4 μm
0.3 μm titanium dioxide is used. Incidentally, if the particle diameter of titanium dioxide is less than 0.1 μm or more than 0.4 μm, it is not preferable because the optical properties and the like are inferior. The crystal form of titanium dioxide used in the present invention may of course be any of rutile type, anatase type and brookite type, and particularly, rutile type and anatase type are preferably used.

Here, comparing method A and method B with respect to the addition time of the aqueous titanium dioxide suspension, in the case of method A, the addition time of the aqueous titanium dioxide suspension is restricted by the carbonation rate. However, there is a disadvantage that it is difficult to continuously determine the carbonation rate, and it is difficult to make the addition time of the aqueous titanium dioxide suspension constant. On the other hand, in the method B, in a state where a large amount of (light) calcium carbonate is already present, a method of starting the reaction by adding an aqueous suspension of calcium hydroxide and titanium dioxide is employed. The reaction can be performed regardless of the conversion. From this, compared to Method A, B
The method has an advantage that the operation for obtaining the titanium dioxide-calcium carbonate composite of the present invention is extremely easy, and a desired titanium dioxide-calcium carbonate composite is easily and stably obtained.

On the other hand, the concentration of carbon dioxide in the carbon dioxide-containing gas to be introduced during the carbonation reaction is not particularly limited, but preferably, the mixed volume of carbon dioxide (gas) is 10 to 35% by volume. Using a carbon dioxide-containing gas and blowing it into an aqueous suspension as carbon dioxide (gas) at a rate of 0.5 to 5 L / min per kg of calcium hydroxide to promote the carbonation reaction ,
In terms of the reaction time, the quality of the obtained titanium dioxide-calcium carbonate composite, etc., extremely efficient and stable carbonation reaction and complexation are promoted. By the way, if the introduced amount of carbon dioxide is less than 0.5 liter / min, the productivity is low. On the other hand, an amount exceeding 5 liter / min can be adopted, but such a large amount of carbon dioxide (gas) is introduced. Doing so results in an extremely large power load, and cannot be expected to have a corresponding effect.

Incidentally, the fact that the titanium dioxide particles in the titanium dioxide-calcium carbonate composite according to the present invention are fixed on the surface layer of calcium carbonate will be additionally described. That is, the present inventors have defined the expression "fixing" by considering as follows. That is, as a result of confirming the dried product of the composite obtained by the method of the present invention with a scanning electron microscope, the titanium dioxide particles were not present alone, but in a state where the composite was integrated with the calcium carbonate particles. It was judged based on what was observed and the result of measuring the particle size distribution of the titanium dioxide-calcium carbonate composite using a Microtrac HRA particle size analyzer (Nikkiso Co., Ltd.). This particle size distribution will be described in detail below. The peak (peak) of the particle size distribution of titanium dioxide particles and the peak (peak) of the particle size distribution of calcium carbonate are the average particle diameter (secondary particle diameter)
In the particle size distribution, peaks (peaks) are present at different particle diameter positions. Therefore, simply as a result of observing the particle size distribution of a mixture of an aqueous suspension of titanium dioxide and an aqueous suspension of calcium carbonate, it was found that both, namely, 2
Two peaks (mountains) were observed. On the other hand, when observing the particle size distribution of the titanium dioxide-calcium carbonate composite obtained by the method of the present invention, the particle size distribution (peak 1) of the composite obtained by the method A is almost the same as that of ordinary light calcium carbonate alone. G) is obtained, and also in the case of the method B, the particle size distribution slightly larger than the particle size distribution found in the calcium carbonate which is the parent added in the reaction tank in advance (1 peak)
Was observed.

Further, an aqueous suspension (concentration: 15% by weight, volume: 500 ml) of the titanium dioxide-calcium carbonate composite obtained by the method of the present invention is mixed with a mixer (trade name: TK Homodisper ... Clover blade). / Special Kika Kogyo Co., Ltd.)
After stirring at 5,000 rpm for 10 minutes, the particle size distribution of the composite was measured. As a result, a particle size distribution having one peak peak equivalent to that before strong stirring was observed. From the results of the above observations (experiments), in the titanium dioxide-calcium carbonate composite, titanium dioxide is not merely present on the surface of calcium carbonate, and at least its binding state is not clear, but calcium carbonate and titanium dioxide are considerably stronger. It is apparent that the titanium dioxide particles are attached to the surface layer of calcium carbonate having a large particle diameter after joining. In the present invention, such a state is expressed by the term fixing. Further, the titanium dioxide obtained by the method of the present invention-
It is clear from the fact that the effect of improving (improving) opacity is recognized by finishing the paper with the calcium carbonate composite as a filler. By the way, if titanium dioxide does not settle on calcium carbonate and is simply mixed, due to strong dehydration during papermaking, titanium dioxide, which is fine particles, is easily separated from the papermaking wire and hardly stays in the paper. However, it is estimated that the effect of improving the opacity is not recognized.

The titanium dioxide-calcium carbonate composite obtained in the present invention is used as a slurry as it is or dehydrated and used as a dry product as a filler for paper or a pigment for coating. It can also be used as a filler in the production of rubber and the like.

The particle size of the titanium dioxide-calcium carbonate composite obtained by the method of the present invention is not particularly limited, but is preferably an average particle size (secondary particle size).
The reaction conditions (calcium hydroxide concentration, reaction temperature, amount of carbon dioxide introduced, etc.) are adjusted so that the primary particle diameter is 2 to 40 μm and the primary particle diameter is 0.3 to 15 μm.

The thus obtained titanium dioxide-calcium carbonate composite is added as a filler to an aqueous suspension (paper stock) mainly composed of a cellulose fiber substance (wood pulp fiber). The high opacity paper of the present invention is produced by the papermaking method, and in this case, the addition ratio of the composite to the cellulose fiber substance is not particularly limited, but is generally 2 to 30% by weight as paper ash. %, Preferably in the range of 5 to 25% by weight.

The reason why the paper using the titanium dioxide-calcium carbonate composite of the present invention as a filler has excellent opacity and good operability of a paper machine is not necessarily clear, but it is speculated as follows. As described above, the titanium dioxide-calcium carbonate composite of the present invention fixes titanium dioxide to the surface layer of calcium carbonate by a carbonation reaction.
According to this method, it is considered that the opacity can be improved without impairing the optical characteristics of titanium dioxide. Also, by forming a complex with calcium carbonate, the particle size increases, and unlike calcium carbonate and titanium dioxide are simply mixed, they are separated into calcium carbonate and titanium dioxide by stirring and shear added during liquid sending. It is presumed that the operability of the paper machine such as the yield was improved without any occurrence. It is also found that the paper using the titanium dioxide-calcium carbonate composite light coal of the present invention as a filler has a better yield on a paper machine than when calcium carbonate is used as a filler, and can improve the operability of a white water recovery system and the like. Was.

Known cellulose fiber materials are used. Specifically, kraft pulp using wood chips as a raw material, sulphite pulp, chemical pulp such as soda pulp, semi-chemical pulp such as semi-mechanical pulp, semi-chemical pulp such as chemimechanical pulp, groundwood pulp, mechanical pulp such as thermomechanical pulp, or Non-wood fiber pulp made from mulberry, mitsumata, hemp, kenaf and the like, and deinked pulp made from waste paper are used, and at least one kind of these or two or more kinds are used by being appropriately mixed. The bleaching method for producing the above chemical pulp is not particularly limited, but the bleaching process does not use molecular chlorine such as chlorine gas, but bleached without using molecular chlorine such as chlorine gas, and chlorine-based compounds such as chlorine dioxide. TC bleached without using
Use of F pulp is preferable from the viewpoint of environmental conservation. When mechanical pulp or waste paper deinked pulp is used in combination with the titanium dioxide-calcium carbonate composite of the present invention, higher opacity can be expected.

In the present invention, when paper containing a titanium dioxide-calcium carbonate composite is internally added, it is a matter of course that calcium carbonate, talc, kaolin, clay, white carbon, amorphous silica, titanium dioxide, etc. It is also possible to add fillers, and papermaking chemicals used in normal neutral papermaking, for example, sizing agents such as reinforced rosin sizing agents and emulsion sizing agents, alkyl ketene dimers, etc., size fixing agents, dry paper strength Enhancer, wet paper strength enhancer, retention improver, drainage improver, waterproofing agent, defoamer,
Slime control agents, dyes and the like can be added as needed.

The paper machine used in the production of paper to which a titanium dioxide-calcium carbonate composite is added as a filler is not particularly limited, and known paper machines such as a fourdrinier paper machine and a circular net paper machine are available. The paper is made by a short-mesh paper machine or a twin-wire paper machine. The basis weight of the base paper is not particularly limited.
２５０250 g / m ² , preferably 35-100 g / m ² . Further, on the surface of this paper, starches such as oxidized modified starch, enzyme modified starch, cationized starch, carboxymethyl cellulose, methyl cellulose, water-soluble cellulose compounds such as hydroxyalkyl cellulose,
At least one of polyvinyl alcohols, polyacrylamides, and styrene-butadiene copolymer latexes can be applied as needed.

Further, on the surface of the paper obtained by the above method,
For the purpose of further improving print quality such as opacity and halftone dot reproducibility, a surface treatment agent containing an organic pigment or an inorganic pigment and an adhesive as main components can be applied as needed. The organic pigment used here is generally provided as particles of a styrene-acrylic copolymer, a polystyrene-based polymer, a styrene-butadiene-based copolymer, an acrylic polymer, or the like. Examples of the inorganic pigment include known materials such as kaolin, light calcium carbonate, heavy calcium carbonate, talc, and calcined clay. Examples of the adhesive include oxidized starch, enzyme-modified starch, starches such as cationized starch, carboxymethyl cellulose, methyl cellulose, water-soluble cellulose compounds such as hydroxyalkyl cellulose, water-soluble binders such as polyvinyl alcohols and polyacrylamides, In addition, styrene-butadiene copolymer, methyl methacrylate
Conjugated diene polymer latex such as butadiene copolymer, acrylic polymer latex such as acrylate and methacrylate polymer or copolymer, vinyl polymer latex such as ethylene / vinyl acetate copolymer, etc. Polymer latex binders, and these binders can be used alone or in combination. In the present invention, among these, a water-soluble binder is particularly preferably used from the viewpoint of operability and the like. Among them, organic pigments are preferable because they have a high effect of improving opacity and print quality. The structure of the organic pigment used in the present invention is not particularly limited, and may be hollow or solid. By the way, in order to improve the opacity, the organic pigment should have a hollow structure and a large particle size, but since the hollow organic pigment has a thin shell part, the particles are easily crushed by the drying process and calendering process When the particles are crushed, it is difficult to obtain the effect of improving the opacity. The organic pigment is provided as an aqueous dispersion of the above polymer, and has an effect of improving opacity and whiteness and an effect of reducing the weight of coated paper.
For this reason, it has been conventionally partially used in the field of coated paper for general printing such as art paper, coated paper and finely coated paper. However, since the printing strength is inferior and the cost is high, it is common to mix a small amount with commonly used pigments such as kaolin and calcium carbonate. In the present invention, when an organic pigment is used alone as a pigment and a water-soluble binder such as starch or polyvinyl alcohol or polyacrylamide is used as an adhesive, the effect of improving opacity or halftone dot reproducibility is obtained. It is more preferable to keep the texture of the base paper and the base paper easily.

Examples of the surface coating agent include, in addition to the above-mentioned adhesives and pigments, a surface sizing agent generally used in the papermaking field, a defoaming agent, a preservative, a thickener, and sodium carbonate as a conductive agent. Salts such as sodium hydrogen carbonate, sodium sulfate, sodium hydrogen sulfate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium chloride and the like are appropriately used in combination.

The surface treatment agent containing the adhesive and / or the organic pigment as described above is applied and dried as required, but the coating apparatus in this case is not particularly limited. For example, a conventionally known size press device such as a blade metering size press, a rod metering size press, a gate roll coater, a bill blade coater, and a two-roll size press is appropriately used. Among them, a two-roll size press, a gate roll coater, a blade metalling size press, and a rod metaling size press are preferably used.

The high opacity paper thus obtained is used as a printing paper by itself.
It can be used as PPC paper such as electrophotographic paper and copier paper, and base paper for printing and coated paper such as art paper, coated paper, lightweight coated paper, lightly coated paper, cast coated paper, etc. As base paper for information paper such as newsprint, thermal recording paper, inkjet paper, carbonless paper, etc.
It can be used to improve the opacity of these papers.

The titanium dioxide-calcium carbonate composite of the present invention can be used not only as a filler but also as a coating pigment. Although the titanium dioxide-calcium carbonate composite obtained after the carbonation reaction can be used as it is for coating, it has been subjected to concentration and pulverization because of its low concentration and large particle size. It is desirable to use That is, the composite light coal slurry obtained after the carbonation reaction is dehydrated and concentrated by a filter press to prepare a cake having a solid content of 60% by weight or more. Next, at least a dispersant is added to the cake and dispersed with a stirrer to prepare the titanium dioxide-calcium carbonate composite slurry having a solid content concentration of 58% by weight or more. The powder is pulverized by a wet pulverizer so as to have an average particle diameter of 2 μm or less, and provided as a coating pigment.

Incidentally, the average particle size after crushing was 2 μm.
If it exceeds, the quality such as gloss and smoothness of the coated paper may be deteriorated, which is not preferable. Further, the lower limit of the average particle size is not particularly limited, for example, when the average particle size is reduced to less than 0.5 μm,
A large amount of adhesive is required, which may affect the suitability for coating and may further deteriorate quality such as opacity, air permeability, or oil absorption. For this reason, the average particle diameter is generally appropriately adjusted in the range of 0.5 to 2 μm.

When used as a coating pigment, it is important to prepare a slurry with as high a concentration as possible in order to increase the concentration of the coating liquid. For that purpose, it is desirable to make the cake concentration of light calcium carbonate obtained by dehydration and concentration using a filter press as high as possible. When the cake concentration after dehydration and concentration by a filter press is less than 60% by weight, the slurry concentration of the obtained titanium dioxide-calcium carbonate composite is relatively low, and as a result, the concentration of the coating liquid is low, and the quality of the coated paper is low. Since the applicability of coating may be reduced, it is difficult to mix the titanium dioxide-calcium carbonate composite at a high rate. The concentration after the filter press does not particularly have an upper limit. However, based on experiments performed by the present inventors, the upper limit of the cake concentration is estimated to be approximately 76% by weight. It will be difficult to obtain.

As the apparatus used for the crushing treatment, any apparatus generally used for wet pulverization of pigments may be used, and examples thereof include a sand mill, a ball mill, a vibration mill, and a jet mill. The ball serving as the crushing medium is not particularly limited, but a spherical ball made of a hard material such as glass, ceramic, alumina, and zirconia is used, and the diameter thereof is preferably 0.5 to
Those having a diameter of 3.0 mm, more preferably 0.8 to 1.5 mm are used.

The thus-obtained titanium dioxide-calcium carbonate composite slurry is used as a coating pigment, but the method of use is not particularly limited, and may be a coating liquid for a single-layer coated paper. In addition, it can be used as both an undercoating liquid and a topcoating liquid of so-called double coated paper provided with two or more coating layers. The compounding amount is not particularly limited, and should be appropriately compounded according to the quality of the coated paper product. However, considering the purpose of obtaining the opacity improving effect, 5 to 100 parts by weight of the pigment component is required. 100 parts by weight,
Preferably it is used in the range of 10 to 100 parts by weight.

Examples of the pigment used in the present invention include, in addition to the titanium dioxide composite light coal of the present invention, kaolin, calcium hydroxide, satin white, barium sulfate, heavy calcium carbonate, conventionally known light calcium carbonate, talc and the like. ,
One or more kinds of pigments conventionally used in the field of coated paper, such as calcined clay and titanium dioxide, are appropriately used.

Further, the adhesive used in combination with the pigment of the above-mentioned coating liquid is not particularly restricted but includes, for example, proteins such as casein and soybean protein, styrene-butadiene copolymer, methyl methacrylate-butadiene. Conjugated diene polymer latex such as copolymer, acrylic polymer latex such as acrylate and methacrylate polymer or copolymer, vinyl polymer latex such as ethylene-vinyl acetate copolymer, or These various polymers and copolymers are functionally modified with a functional group-containing monomer such as a carboxyl group, and a functional group-modified alkali-soluble or alkali-insoluble polymer latex, polyvinyl alcohol, olefin-maleic anhydride resin,
For general coated paper, such as synthetic resin adhesives such as melamine resin, positive starch, oxidized starch, phosphate esterified starch, starches such as enzyme-modified starch, and cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose. Known and publicly known adhesives may be used alone or in combination. The amount of the adhesive is not particularly limited and is adjusted according to the quality of the coated paper. It is adjusted to 3 to 50 parts by weight, usually 5 to 35 parts by weight.

In the coating liquid, various water-proofing agents, printability improving agents, defoaming agents, coloring agents, lubricants, mold release agents, flow modifiers, preservatives, etc. may be used as necessary. It is also possible to add.

The coating liquid composed of the above-mentioned materials is generally adjusted to have a solid concentration of about 50 to 70% by weight.
Coating on base paper using a known and publicly used coating apparatus used in the general coated paper manufacturing field, for example, a blade coater, an air knife coater, a roll coater, a brush coater, a chaplex coater, a bar coater, a gravure coater, or the like. Is done.

The base paper at this time is not particularly limited. For example, ordinary high-quality paper, medium-quality paper, light-weight coated paper that has been finely coated in advance, or synthetic paper using synthetic fibers in combination is used. And a film are appropriately used. Of course, it is also possible to use base paper using the titanium dioxide composite light coal of the present invention as a filler.

[0053]

The present invention will be specifically described below with reference to examples. Of course, the present invention is not limited to them. Unless indicated otherwise, parts and% in the examples indicate parts by weight and% by weight, respectively.

[Preparation of Filler] Filler 1 (titanium dioxide-calcium carbonate composite) method A Aqueous suspension of 11% calcium hydroxide (solid content 50%)
While stirring 0 g), a carbon dioxide-containing gas of 20% by volume was blown in at a rate of 2.5 liter / min as carbon dioxide gas per 1 kg of calcium hydroxide to carry out carbonation. When the carbonation rate (carbonation reaction rate) became 55%, an aqueous suspension of titanium dioxide having a concentration of 45% (titanium dioxide = 60 g solid content [trade name: FR-44 / rutile type,
Water and a dispersing agent were added to the mixture to give an average particle diameter of 0.9 μm / primary particle diameter of 0.25 μm (made by Furukawa Kikai Metals Co., Ltd.), and the carbonation reaction was continued until the pH reached 7.5. , A
A titanium dioxide-calcium carbonate composite was obtained by the method.
The solid content of titanium dioxide in this composite was 8.2%.
Met.

Filler 2 (titanium dioxide-calcium carbonate composite) Method A In the production of the titanium dioxide-calcium carbonate composite of filler 1, when the carbonation rate reached 80%, an aqueous titanium dioxide suspension was added. Except for the above, a titanium dioxide-calcium carbonate composite was obtained in the same manner as in Filler 1. The solid content ratio of titanium dioxide in this composite was 8.2%.

Filler 3 (Titanium Dioxide-Calcium Carbonate Complex) Method A In the production of the titanium dioxide-calcium carbonate composite of Filler 1, when the carbonation rate reached 85%, the aqueous titanium dioxide suspension was solidified. A titanium dioxide-calcium carbonate composite was obtained in the same manner as in Filler 1, except that the mixture was added so that the amount became 350 g. The solid content ratio of titanium dioxide in the composite was 34.1%.

Filler 4 (Titanium dioxide-calcium carbonate composite) Method A In the production of the titanium dioxide-calcium carbonate composite of Filler 1, when the carbonation ratio reached 85%, the aqueous suspension of titanium dioxide was solidified. In the same manner as for Filler 1, except that 15 g was added, a titanium dioxide-calcium carbonate composite was obtained. The solid content ratio of titanium dioxide in this composite is
2.2%.

Filler 5 (titanium dioxide-calcium carbonate composite) Method A In the preparation of the titanium dioxide-calcium carbonate composite of filler 1, when the carbonation ratio reached 30%, an aqueous titanium dioxide suspension was added. Except for the above, a titanium dioxide-calcium carbonate composite was obtained in the same manner as in Filler 1. The solid content ratio of titanium dioxide in this composite was 8.2%.

Filler 6 (titanium dioxide-calcium carbonate complex) Method B While stirring 500 g (solid content) of an aqueous suspension of light calcium carbonate (average particle size (secondary particle size) 6.9 μm) having a concentration of 15%. Then, 50 g (solid content) of an aqueous suspension of calcium hydroxide having a concentration of 11% and 50 g (solid content) of an aqueous suspension of titanium dioxide having a concentration of 45% were added thereto. Subsequently, carbon dioxide-containing gas was blown under the same conditions as for Filler 1 to carry out a carbonation reaction, and the reaction was completed when the pH of the suspension reached 7.5, thereby obtaining a titanium dioxide-calcium carbonate composite. The solid content ratio of titanium dioxide in this composite is
It was 8.1%.

Filler 7 (titanium dioxide-calcium carbonate composite) Method B In the preparation of the titanium dioxide-calcium carbonate composite of filler 6, 25 g (solid content) of an aqueous suspension of calcium hydroxide and an aqueous suspension of titanium dioxide Was added in the same manner as for Filler 6, except that 25 g (solid content) was added to obtain a titanium dioxide-calcium carbonate composite. The titanium dioxide solid content ratio in this composite was 4.5%.

Filler 8 (titanium dioxide-calcium carbonate composite) Method B In the production of the titanium dioxide-calcium carbonate composite of filler 6, except that 35 g (solid content) of an aqueous calcium hydroxide suspension was used. Thus, a titanium dioxide-calcium carbonate composite was obtained in the same manner as described above. The solid content ratio of titanium dioxide in this composite was 8.4%.

Filler 9 (titanium dioxide-calcium carbonate complex) Method B In the preparation of the titanium dioxide-calcium carbonate complex of filler 6, 350 g (solid content) of an aqueous suspension of calcium hydroxide and an aqueous suspension of titanium dioxide Was changed to 500 g (solid content) to obtain a titanium dioxide-calcium carbonate composite in the same manner as for Filler 6. The solid content of titanium dioxide in the composite was 34.0%.

Filler 10 (Titanium dioxide-calcium carbonate composite) Method B In the production of the titanium dioxide-calcium carbonate composite of Filler 6, except that the aqueous calcium hydroxide suspension was changed to 400 g (solid content), Filler 6 was used. Thus, a titanium dioxide-calcium carbonate composite was obtained in the same manner as described above. The solid content ratio of titanium dioxide in this composite was 4.6%.

Filler 11 (titanium dioxide-calcium carbonate composite) B method In the production of the titanium dioxide-calcium carbonate composite of filler 6, titanium dioxide was trade name FA-55W / anatase type, average particle diameter 0.6 μm / primary Particle size 0.12
μm A titanium dioxide-calcium carbonate composite was obtained in the same manner as for Filler 6, except that the product was changed to Furukawa Machine Metal Co., Ltd. The solid content ratio of titanium dioxide in this composite was 8.
1%.

Filler 12 (titanium dioxide-calcium carbonate composite) Method B In the production of the titanium dioxide-calcium carbonate composite of filler 6, 40 g (solid content) of an aqueous suspension of calcium hydroxide and an aqueous suspension of titanium dioxide Was changed to 100 g (solid content) to obtain a titanium dioxide-calcium carbonate composite in the same manner as for Filler 6. The solid content of titanium dioxide in this composite was 15.3%.

Filler 13 (Titanium dioxide-calcium carbonate composite) Method B Except for changing the average particle diameter (secondary particle diameter) of light calcium carbonate to 2 μm in the production of the titanium dioxide-calcium carbonate composite of Filler 6 In the same manner as in Example 6, a titanium dioxide-calcium carbonate composite was obtained. The solid content ratio of titanium dioxide in this composite was 8.1%.

Filler 14 (Light Calcium Carbonate) While stirring an aqueous suspension of calcium hydroxide having a concentration of 11%, a gas containing 20% by volume of carbon dioxide was converted to carbon dioxide gas per kg of calcium hydroxide at a rate of 2.5 L / min. The carbonation reaction was terminated when the pH of the aqueous suspension became 7.5, and light calcium carbonate was obtained.

Examples 1 to 13 [Preparation of paper containing filler therein] 400 ml of freeness beforehand
C. S. F. (LB Canadian Standard Freeness)
While stirring 5 liters of a 1% slurry of KP (bleached hardwood kraft pulp), the aqueous suspension of the titanium dioxide-calcium carbonate composite obtained with the above fillers 1 to 13 was used as a filler so that the paper ash content became 10%. To obtain a stock having a solid content concentration of 0.5%. Separately, 0.
In preparing the 5% stock, the following chemicals were added to obtain the final stock. In addition, the addition rate of each chemical is all based on pulp (absolutely dry). Cationized starch (trade name: Ace K-100: Oji Cornstarch): 0.5% Neutral sizing agent (trade name: SPK-902: alkyl ketene dimer / Arakawa Chemical Industries): 0.1% sulfuric acid Band: 1.5% Yield improver (trade name: KW-504 ... anionic polyacrylamide resin / Arakawa Chemical Co., Ltd .: 0.03%) Using a sheet machine (Kumaya Rikisha), air-dry basis weight 60g / m
^2. A sheet having a paper ash content of 10% was prepared. Next, the sheet was conditioned (air-dried: 20 ° C., 65% RH for 24 hours), and then passed twice using an experimental calender (Yuri Roll Co., Ltd.) at a linear pressure of 10 kg / cm. After the treatment, a hand-made test paper was obtained. Then, 0.75 g of an oxidized modified starch (trade name: Ace A / Oji Cornstarch Co., Ltd.) as a surface treatment agent was applied on both sides of the test paper per one side.
/ m ² and dried to obtain test paper. The quality of the test paper thus obtained was measured, and the obtained results are summarized in Table 1.

Comparative Example 1 A test paper was obtained in the same manner as in Example 1, except that in place of Filler 1, Filler 14 was replaced by light calcium carbonate. Table 1 shows the quality results of the test paper.

Comparative Example 2 In preparing the handmade test paper of Example 1, instead of Filler 1, 92 parts by weight of light calcium carbonate of Filler 13 and titanium dioxide [trade name: FR-44 / rutile type] 8 Test paper was obtained in the same manner except that a mixture consisting of parts by weight was used. Table 1 shows the quality results of the test paper.

Comparative Example 3 In preparing the handmade test paper of Example 1, instead of Filler 1, 66 parts by weight of light calcium carbonate of Filler 13 and titanium dioxide [trade name: FR-44 / rutile type] 34 Test paper was obtained in the same manner except that a mixture consisting of parts by weight was used. Table 1 shows the quality results of the test paper.

Comparative Example 4 In the preparation of the handmade test paper of Example 1, instead of Filler 1, 92 parts by weight of light calcium carbonate of Filler 13 and titanium dioxide [trade name: FA-55W / anatase type] Test paper was obtained in the same manner except that a mixture consisting of 8 parts by weight was used. Table 1 shows the quality results of the test strips.
It was shown to.

Examples 14 and 15 In preparing the handmade test papers of Examples 1 and 6, the surface treatment agent was changed to 165 parts of oxidized modified starch (described above) with an average particle diameter of 0.6.
Except that the mixture was changed to a mixture of 100 parts of an organic pigment (grossdale 201-S: Mitsui Chemicals, Inc.) of 100 μm, and the coating amount was changed to 1.2 g / m ² per side, in the same manner as in each case. Test papers of Examples 13 and 14 were obtained. Table 1 shows the quality results of the test paper.

[0074]

[Table 1]

Each measurement value was measured by the following method. ● Average particle diameter: The median diameter of the aqueous suspension of the sample was measured using a Microtrac HRA particle size analyzer (Nikkiso Co., Ltd.). [Measurement of test paper quality] ● Ash content: Ash content in paper obtained by hand-sheeting (JIS
(Measured in accordance with P8204) was divided by the ash content in the paper stock provided for handsheeting. ● Whiteness: The paper obtained by hand-making is JIS P8123
It measured according to. ● Opacity: JIS P813
8 was measured. ● Surface strength: Printing was performed using an RI printing machine (manufactured by Meiji Seisakusho) using 0.4 ml of the sheet offset ink whose ink tack was adjusted to 13, and the printed surface was observed to determine the surface strength according to the following criteria. : No pick is seen. X: Picking is remarkably observed.

Preparation of Coated Paper (Preparation of Coating Pigment Slurry) The titanium dioxide-calcium carbonate composite obtained with Filler 2 was subjected to dehydration operation with a filter press to obtain a light calcium carbonate cake having a solid content of 70% or more. I got Next, the mixture is crushed to about several mm with a crusher, and a dispersant (Aron A-9 / Toa Gosei Co., Ltd.) and water are added to light calcium carbonate at a concentration of 1.0% using a Cores mixer, and the solid content concentration is increased. A 71.0% slurry was prepared. The high-concentration light calcium carbonate slurry obtained above was wet-crushed by a ball mill using zirconia beads having a diameter of 1 mm as a crushing medium, and the composite pigment slurry for coating was adjusted to an average particle diameter of 1.3 μm. 1 was obtained. The same treatment was performed for the slurry of the titanium dioxide-calcium carbonate composite obtained with Filler 3, Filler 6, and Filler 9 and the light calcium carbonate obtained with Filler 14, and the composite pigment slurries 2, 3, and 4 for coating, respectively. And a light calcium carbonate slurry was obtained.

Example 21 (Preparation of Coating Composition and Preparation of Coated Paper) 50 parts of a composite pigment slurry 1 for coating and 50 parts of kaolin (trade name: UW-90 / EC) in solid content, 6 parts of oxidized modified starch (Ace A / Oji Cornstarch) and 9 parts of styrene-butadiene copolymer latex (SN-307 / Nippon A & L Co., Ltd.) (each as a solid content) were mixed,
The mixture was dispersed using a Cores mixer, and water was further added to prepare a coating composition having a solid content of 60.0%. Next, the above coating composition was prepared in Comparative Example 1 to obtain a rice tsubo of 60 g / m2.
² of the base paper, performs coating and dried on both sides with coating a hot-air drying tester MLC-100 type to be 15 g / m ² on one surface per dry weight (Osugi Co.), and passed twice through a super calender A coated paper was obtained. Table 2 shows the quality measurement results of the coated paper thus obtained.

Example 22 In the preparation of the coated paper of Example 21, coating was performed in the same manner as in Example 21 except that the composite pigment slurry for coating 2 was used instead of the composite pigment slurry 1 for coating. Obtained paper. Table 2 shows the quality measurement results of the obtained coated paper.

Example 23 The procedure of Example 21 was repeated, except that the composite pigment slurry for coating 3 was used instead of the composite pigment slurry 1 for coating. Obtained paper. Table 2 shows the quality measurement results of the obtained coated paper.

Example 24 The procedure of Example 21 was repeated, except that the composite pigment slurry for coating 4 was used in place of the composite pigment slurry for coating 1 in the preparation of the coated paper of Example 21. Obtained paper. Table 2 shows the quality measurement results of the obtained coated paper.

Example 25 The procedure of Example 23 was repeated except that the base paper containing 10% as a filler the titanium dioxide-calcium carbonate composite obtained in Example 6 was used as the base paper in the preparation of the coated paper of Example 23. Coated paper was obtained in the same manner. Table 2 shows the quality measurement results of the obtained coated paper.

Comparative Example 21 A coated paper was obtained in the same manner as in Example 21 except that a light calcium carbonate slurry was used in place of the composite pigment slurry 1 for coating in the preparation of the coated paper of Example 21. Was. Table 2 shows the quality measurement results of the obtained coated paper.

Comparative Example 22 In the preparation of the coated paper of Example 21, 46 parts of light calcium carbonate slurry and 4 parts of titanium dioxide slurry were used instead of 50 parts of the composite pigment slurry for coating 1 as a pigment in solid content. Coated paper was obtained in the same manner as in Example 21 except that solid components were used. Table 2 shows the quality measurement results of the obtained coated paper.

Comparative Example 23 In the preparation of the coated paper of Example 21, 33 parts of a light calcium carbonate slurry and 17 parts of a titanium dioxide slurry were used instead of 50 parts of the composite pigment slurry 1 for coating as a pigment in solid content. Example 21 except that solid components were used.
A coated paper was obtained in the same manner as described above. Table 2 shows the quality measurement results of the obtained coated paper.

Comparative Example 24 The same procedure as in Example 22 was carried out except that the base paper containing the mixture of light calcium carbonate and titanium dioxide obtained in Comparative Example 2 as a filler was used for preparing the coated paper of Comparative Example 22. To obtain a coated paper. Table 2 shows the quality measurement results of the obtained coated paper.

[0086]

[Table 2]

[0087]

As is clear from Tables 1 and 2, when the titanium dioxide-calcium carbonate composite of the present invention is used as a filler or a pigment for coating to finish paper, ash retention, whiteness and opacity are obtained. It was found to be excellent in good balance of surface strength and the like. This indicates that sufficiently fine titanium dioxide particles are formed into a composite in a form capable of exerting its original function. Eventually, a titanium dioxide-calcium carbonate composite processed so that titanium dioxide particles, which are fine pigments having excellent opacity, can be effectively used as a filler for paper is obtained, and the fine titanium dioxide is fixed to calcium carbonate during papermaking. This has the effect that the filler yield in the wire part is excellent and the load on the white water recovery system is not increased in the preparation step.

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[Procedure amendment]

[Submission date] December 22, 2000 (200.12.
22)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

If the amount of calcium hydroxide is less than 4 parts by weight in terms of solid content, the fixing rate of titanium dioxide decreases, and it becomes difficult to obtain the desired properties of the present invention. On the other hand, if the added amount of calcium hydroxide exceeds 75 parts by weight in terms of solid content, the ratio of titanium dioxide particles present in the surface layer of the composite particles decreases, and the excellent optical aptitude of titanium dioxide is not exhibited and the opacity is not exhibited. There is a possibility that the improvement effect is hardly obtained. On the other hand, if the added amount of titanium dioxide is less than 1 part by weight on a solid basis, it is difficult to obtain the desired opacity improving effect of the present invention. If the added amount exceeds 130 parts by weight, the opacity improving effect of titanium dioxide is saturated. And it is economically unfavorable. Further, titanium dioxide is easily separated from the composite, and there is a concern that operation problems may occur.

Claims (11)

[Claims] 1. A titanium dioxide-calcium carbonate composite comprising titanium dioxide particles on the surface of calcium carbonate particles. 2. The method according to claim 1, wherein the average particle size is 2 to 40 μm.
The titanium dioxide-calcium carbonate composite according to the above. 3. The titanium dioxide-calcium carbonate composite has a titanium dioxide ratio of 1 to 4 with respect to the total solid content of the composite.
3. The titanium dioxide according to claim 1, which is 0% by weight.
Calcium carbonate complex. 4. The method for producing a titanium dioxide-calcium carbonate composite according to claim 1, wherein the composite is produced using a carbonation reaction. 5. An aqueous suspension of calcium hydroxide is blown with a carbon dioxide-containing gas to produce calcium carbonate. When the carbonation ratio reaches 50 to 95%, the aqueous suspension of titanium dioxide is added. The method for producing a titanium dioxide-calcium carbonate composite according to any one of claims 1 to 3, wherein the conversion reaction is continued. 6. An aqueous suspension of calcium carbonate, an aqueous suspension of calcium hydroxide and an aqueous suspension of titanium dioxide are added, and a carbon dioxide-containing gas is blown into the mixed suspension to carry out a carbonation reaction. In the squeezing, the mixing ratio of the aqueous calcium carbonate suspension / calcium hydroxide aqueous suspension / titanium dioxide aqueous suspension is 100/4 to 7 in terms of solid content weight.
The method for producing a titanium dioxide-calcium carbonate composite according to any one of claims 1 to 3, which is 5/1 to 130. 7. The method for producing a titanium dioxide-calcium carbonate composite according to claim 6, wherein the weight ratio of solid content of calcium hydroxide / titanium dioxide is 0.5 / 1 to 5/1. 8. A highly opaque paper comprising the titanium dioxide-calcium carbonate composite according to any one of claims 1 to 3 as a filler. 9. The high opacity paper according to claim 8, wherein a surface treating agent mainly composed of an organic pigment and an adhesive is applied to both sides of the base paper and dried. 10. The method for producing a titanium dioxide-calcium carbonate composite according to any one of claims 4 to 7, wherein the titanium dioxide-calcium carbonate composite is further dehydrated and concentrated by a filter press to obtain a cake. After adding a dispersant and dispersing with a stirrer to obtain a slurry, a wet crushing treatment is performed.
A method for producing a calcium carbonate composite slurry. 11. Coated paper using the titanium dioxide-calcium carbonate composite according to any one of claims 1 to 3 as a coating pigment.