JPH10292283A - Production of calcium carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce calcium carbonate excellent in whiteness, opacity, wearing properties of a plastic wire, and useful as a filler for papermaking by adding a green liquor to a specific milk, etc., of lime under a specified condition, and carrying out a caustification reaction thereof at a prescribed reaction temperature. SOLUTION: This method for producing calcium carbonate comprises a step for adding a green liquid to a calcined lime formed at a caustification step of a pulp manufacturing process and/or introduced from outside of the process, containing 0.1-10 wt.% calcium carbonate based on the weight of the calcined lime to regulate the concentration of the calcined lime so as to be 20-60 wt.%, and a step for slaking the calcined lime while stirring or kneading the calcined lime with the green liquid to form milk of the lime or mud of the lime, sequentially adding the green liquid formed at the caustification step of a prescribed amount required for producing a white liquid to the produced milk or mud of the lime at the adding rate of 0.02-50 cc (green liquid)/min/g (calcined lime) and carrying out the caustification reaction at 20-105 deg.C to provide the objective calcium carbonate of a spindle shape or a rice grain shape having 0.3-1.5 μm minor axis and 0.5-7 μm major axis.

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 calcium carbonate which gives useful properties as a filler for papermaking in a causticizing step of a pulp producing step by a sulfate method or a soda method, and more particularly to a method of using the same. The present invention relates to a method for producing quick lime and calcium carbonate which gives useful properties as a filler for papermaking by specifying slaking / causticizing conditions and the like.

[0002]

2. Description of the Related Art Generally, a filler is internally added to paper used for printing or writing for the purpose of improving whiteness, opacity, smoothness, writability, touch, printability and the like.
As this papermaking method, talc, clay, titanium oxide, or the like is used as a filler, and paper is made at around pH 4.5, so-called acidic papermaking, and paper is made at a pH of 7 to 8.5 in a neutral to weakly alkaline range. And so-called neutral papermaking. In neutral papermaking, it becomes possible to use domestically produced calcium carbonate as a filler instead of imported talc and clay which are expensive. recent years,
Neutral paper obtained by neutral papermaking has attracted attention due to problems such as paper storability.Besides, there are many advantages in terms of paper quality, cost, environmental measures, etc. The transition is progressing, and it is in a situation where its spread will continue to expand in the future.

[0003] In view of the recent demand for paper, commercial printing includes fields such as flyers, catalogs, brochures, and direct mail, and publishing printing involves computers, multimedia, and NES related to the progress of the information society. It is characterized by a large growth in the fields of books, magazines and photo books, mooks, and comic paper, and this has led to more cost-conscious thinking for paper users. Lightening is required.

[0004] As the demand for inexpensive and lightweight neutral paper increases as described above, the role of calcium carbonate as a filler is very important. Calcium carbonate used as a filler in this neutral papermaking includes heavy calcium carbonate obtained by mechanically pulverizing natural limestone in a dry or wet manner, and precipitated calcium carbonate (synthetic calcium carbonate) obtained by a chemical method. .

However, heavy calcium carbonate obtained from natural limestone using a crusher such as a ball mill is difficult to control its shape. Therefore, when it is used as an internal filler, the plastic wire is severely worn during papermaking. Let me do it. In addition, this filler can be used for regular high quality paper,
When a coated paper is manufactured by papermaking, the bulk, whiteness, opacity, smoothness, writability, touch, printability and the like are insufficient.

[0006] As the weight has been reduced recently, the above problem becomes more serious. Heretofore, conventional means for improving the opacity of lightweight printing paper include fillers having a large specific surface area (for example, finely ground silica, white carbon, etc.), fillers having a high refractive index (for example, titanium dioxide), or There is use of precipitated calcium carbonate (synthetic calcium carbonate).

The method of producing the precipitated calcium carbonate includes (1) a reaction between carbon dioxide gas obtained from a lime baking apparatus and the like and lime milk, (2) a reaction between ammonium carbonate and calcium chloride in the ammonia soda method, (3)
The reaction between milk of lime and sodium carbonate in the causticization of sodium carbonate is known. Of these methods,
In (2) and (3), little consideration has been given to a method of controlling the shape in order to be a by-product and to switch to a new method for obtaining the main product. On the other hand, (1) has a relatively simple reaction system (water,
Since it may be slaked lime or carbon dioxide), methods for producing various shapes have been widely studied, and there are some examples of actual production at a paper mill on site. However, since calcium carbonate is the only product, this method has a very high production cost, does not match the cost reduction desired by the user, and cannot be used for inexpensive paper, or the amount used is low. Severely restricted.

[0008] A possible method is to use calcium carbonate by-produced in the causticizing step of recovering and regenerating the cooking chemicals in the kraft pulp manufacturing process as a raw material for papermaking.

[0009] In the pulp production process by the sulfate method or the soda method, in order to isolate fibrous material in wood, the wood is digested at high temperature and high pressure using a chemical mixture of sodium hydroxide and sodium sulfide. The fibrous material is separated and refined as a solid phase to form pulp, and elution components other than fibrous material from the chemical solution and wood are collected as pulp waste liquid (black liquor) and concentrated and burned. At that time, the eluted components from the wood were recovered as a heat source, the inorganic substances in the chemical solution were recovered mainly as sodium carbonate and sodium sulfide, and the calcium carbonate sludge formed by the following reaction called a weak solution was washed. The white liquor component generated at this time is dissolved by a partially dissolved dilute chemical solution to become a green liquor.

[0010] Quick lime is mixed with this green liquor, [1],
[2] is to use the reaction by _{Ca0 + H 2 0 → Ca (} OH) 2 [1] Ca (OH) 2 + Na 2 C0 3 → CaC0 3 + 2NaOH [2] The resulting calcium carbonate represented by formula. Since this calcium carbonate is a by-product of producing the main product white liquor, it can be produced at a very low cost. In addition, calcium (calcium carbonate, quicklime, Slaked lime) Since calcium carbonate can be removed from the system from the circulation cycle to purify the system and to purify the circulated lime, it is possible to improve the reactivity of the above [1] and [2] and to improve the clarity of white liquor. Improvement and further reduction of waste can be expected.

However, the calcium carbonate obtained heretofore is difficult to control the shape, and therefore has various shapes such as a dice or a hexagon, a large particle size, and both are indefinite or massive, and the conventional weight is large. Since it is close to high-quality calcium carbonate, when using this filler to produce normal high-quality paper and coated paper, the whiteness, opacity, smoothness, writing properties, touch, printability, etc. are insufficient. Met. Further, in recent years, as the paper machine has been increased in size and the papermaking speed has been further increased, there has been a major problem in the abrasion of the plastic wire.

As described above, the plastic wire has good abrasion resistance at the time of paper making, and when it is used, a filler capable of obtaining high quality opaque high quality paper or coated paper while maintaining print quality. Alternatively, it has been difficult to efficiently and inexpensively produce calcium carbonate as a pigment.

[0013]

In view of the above-mentioned circumstances, wire abrasion is excellent when making paper, and when it is used in the production of paper, opacity is high and printing quality and the like are excellent. An object of the present invention is to provide an inexpensive calcium carbonate in which the shape of self-made light calcium carbonate is controlled and controlled using a causticizing process in order to provide high quality paper or coated paper.

[0014]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, a specific amount of pulp has been reduced by utilizing a causticizing step of a pulp manufacturing process by a sulfate method or a soda method. In the lime milk obtained by slaking reaction of quick lime containing calcium carbonate and green liquor, the white liquor is produced in the causticizing step of the pulp manufacturing process by the sulfate method or soda method, and in the conventional operation. The present inventors have found that the problem can be solved by continuously adding the same amount of green liquor as necessary for controlling the addition rate and the reaction temperature, and based on this finding, the present invention has been accomplished. According to the method of the present invention, it is possible to control the shape of calcium carbonate without greatly changing the conventional causticizing step, and the minor axis of the particles is 0.3 to 1.5 μm and the major axis is 0.5 to 7 μm. Spindle-shaped and rice-grained calcium carbonate are adjusted to improve whiteness, opacity and wire abrasion as a filler for papermaking, and to calcium carbonate obtained by the conventional method of reacting milk of lime with carbon dioxide. It can be manufactured at significantly lower cost. Further, as an attendant effect, by extracting calcium carbonate from the process, the kiln operation can be reduced, or the kiln can be stopped depending on the amount of calcium carbonate extracted from the process, thereby reducing the cost of the entire causticizing process.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Quicklime used in the slaking reaction, which is the first step of the present invention, is limestone containing calcium carbonate as a main component and / or causticization of pulp production by a sulfate method or a soda method. What is necessary is just to calcine calcium carbonate generated when sodium carbonate is converted to sodium hydroxide in the step. In addition, regarding the sintering apparatus at this time, a Beckenbach furnace, a Melz furnace, a rotary kiln, a Kunii type furnace, a KHD (Car Hardy) furnace, a Koma type furnace, a calmatic furnace, a fluidized sintering furnace, a mixed sintering furnace, etc. There is no particular limitation as long as it is a device that converts lime into quick lime (calcium oxide).

As to the content of impurities in the obtained calcium carbonate, a coloring component (Fe, Mn, etc.) is particularly problematic. However, it is obtained from raw limestone having a low coloring component content in accordance with the use of paper as a product. In the case of quicklime, which is appropriately selected, or in the case of recalcined quicklime in a rotary kiln or fluidized-bed kiln in the causticizing step, the coloring component is determined by the ratio of calcium carbonate extracted outside the system and calcium carbonate recycled in the system. Depending on the situation, the raw material lime having a small coloring component content to be replenished to the calcium circulation cycle in the causticizing step or the one obtained by adjusting the amount of calcined lime obtained by calcining the raw material lime may be used.

The calcium carbonate content in quicklime is 0.1 to 10% by weight based on the weight of quicklime. If it exceeds 10% by weight, the generated calcium carbonate will be irregular or lump, resulting in poor wire abrasion and no desired paper quality. Meanwhile,
In order to obtain 0.1% by weight or less, the energy required for firing is extremely increased, or a special device is required for the firing apparatus, which is uneconomical. There is no particular limitation on the particle size of quicklime,
1 to 30 mm is preferable, and when it is 0.01 mm or less, the cost for pulverization is increased, and at the same time, there is a problem of generation of dust and trouble in the transfer device. This is problematic in terms of uniform mixing, which is not preferable.

As the green liquor used for slaking quicklime, those generated from a causticizing step of a general sulfate method or soda method can be used, and a total alkali of 80 to 160 g / L is used.
(Of which 65 to 130 g / L of Na ₂ CO ₃ ), preferably 100 to 150 g / L of total alkali (of which,
(Na ₂ CO _3: 85 to 130 g / L).
If the total alkali is lower than 80 g / L (of which Na ₂ CO ₃ is 65 g / L), the concentration of the final white liquor will decrease, and it will be necessary to adjust the concentration when used for cooking. On the other hand, 160 g / L (of which Na ₂ CO ₃ is 130 g / L)
g / L), the wire abrasion of the generated calcium carbonate is inferior and the target paper quality cannot be obtained. The lime concentration at the time of slaking should be 20 to 60% by weight, preferably 25 to 55% by weight, based on quick lime before slaking. If it exceeds 60% by weight, the liquid viscosity is too high and stirring becomes difficult in practice, while if it is less than 20% by weight, the shape of the generated calcium carbonate becomes massive,
In addition to poor wire abrasion, the desired paper quality cannot be obtained.

The mixing of quicklime and green liquor at the time of slaking is performed by using a general stirring blade type, a pump type, an extruder, a kneader, or a kneader, for mixing the liquid or slurry at the time of mixing. The material may be appropriately selected and used according to the viscosity (see Chemical Engineering Handbook, published by Maruzen Co., Ltd. on March 18, 1988).

The temperature and time at the time of slaking are closely related. When the temperature of the aqueous solution used for slaking is high, a short time is sufficient, while when the temperature is low, a long time is required. The time is appropriately set according to the temperature of the quicklime used during slaking. One guideline is to allow time until the temperature rise due to heat generation during sloughing stops. actually,
Slaking at the highest possible temperature is effective.

As the green liquor in the causticization reaction which is the second step of the present invention, the green liquor generated from the causticizing step of a general sulfate method or soda method can be used.
0~160g / L (of which, in Na ₂ CO ₃ 65 to 130
g / L), preferably 100 to 150 total alkali
g / L (of which 85 to 130 g / L with Na ₂ CO ₃ ). If the total alkali is lower than 80 g / L (of which Na ₂ CO ₃ is 65 g / L), the concentration of the final white liquor will decrease, and it will be necessary to adjust the concentration when used for cooking. On the other hand, 160 g / L (of which Na
_{When 2} CO ₃ is higher than 130 g / L), the generated calcium carbonate has poor wire abrasion properties, and the desired paper quality cannot be obtained.

The mixing method of the lime milk and the green liquor adjusted in the first step is such that the addition rate of the green liquor to the lime milk is 0.02.
５０50 cc (green liquor) / min / g (quick lime), preferably 0.02 to 30 cc (green liquor) / min / g (quick lime)
Do with. 0.02cc (green liquor) / min / g (quicklime)
At lower addition rates, productivity is poor and unrealistic,
On the other hand, an addition rate of more than 30 cc (green liquor) / min / g (quick lime) requires a very large capacity pump, which is not practical.

Instead of lime milk prepared from quicklime in the first step, lime milk prepared by mixing calcium hydroxide and green liquor and adjusting to the same concentration as in the present method can be used. It is.

As for the causticization reaction temperature, the reaction temperature is 2
It is necessary to carry out at 0 to 105 ° C, preferably at 25 to 103 ° C. If the temperature is higher than 105 ° C., the temperature exceeds the boiling point under the atmospheric pressure, which requires a pressurized causticizer or the like, which is uneconomical. On the other hand, when the temperature is lower than 20 ° C.,
The shape of the calcium carbonate to be formed becomes a lump, which is inferior in wire abrasion, and a target paper quality cannot be obtained. Furthermore, the device for cooling and the accompanying cost are expensive and uneconomical.

The stirring at the time of the causticizing reaction can be performed by using a general stirring blade type, a pump type, an extruder, a Riwa machine, or a kneader, from the lime milk and the green lime adjusted in the first step. It is only necessary to appropriately select and use those which can uniformly mix the liquid (Showa 6
Published by Maruzen Co., Ltd. on March 18, 3rd, see Chemical Engineering Handbook).

Under the above conditions, spindle-shaped or rice-grained calcium carbonate having a short particle diameter of 0.3 to 1.5 μm and a long diameter of 0.5 to 7 μm can be adjusted.

The calcium carbonate of various shapes obtained by the present invention is superior in the wire abrasion property to the calcium carbonate obtained by the conventional causticizing process, and by adding it internally, white paper of high quality paper and coated paper can be obtained. Degree, opacity, smoothness, writability,
Gives excellent characteristics such as touch and printability. This includes newsprint, medium quality paper, printing paper, book paper, security paper, dictionary paper, Ryoko kraft paper, bleached kraft paper, tissue paper, rice paper, Indian paper, paperboard, carbonless paper, art paper, lightweight paper. When used for coated paper, cast-coated paper, wallpaper, heat-sensitive paper, etc., it is easily inferred that excellent characteristics such as whiteness, opacity, smoothness, writability, touch, printability and the like are provided. Furthermore, when used for various pigments, characteristics excellent in glossiness, smoothness, printability and the like are provided. In addition to papermaking, it can be used for rubber, plastic, paint, sealant, adhesive, fertilizer, and the like.

[0028]

Although the mechanism of the present invention has not been fully elucidated, the amount of calcium carbonate and green liquor in quicklime greatly affects the properties of lime milk, and the dissolved water when adding green liquor thereafter. It seems to affect the reaction state of calcium oxide and carbonate ion. The sequential addition of green liquor causes the concentration of dissolved calcium hydroxide and the proportion of carbonate ions to react at a low level of carbonate ions in the initial stage, thereby growing calcium carbonate crystals to become spindle-shaped and rice grain-shaped. It seems to be.

One of the characteristics of this calcium carbonate is that one has an effect of improving the abrasion property of a plastic wire at the time of high-speed papermaking, and the other has an effect of improving opacity and whiteness by making a paper. . The first reason is that, because the primary particles are spindle-shaped or rice-granular particles, the entanglement with the fiber increases, which is advantageous in improving the yield, and as a result, the filler passing through the wire part decreases, Since the particle shape is a spindle shape or a rice grain shape, the aspect ratio is large, and the sharp edge is small, so that the frictional resistance at the time of contact with the wire is low, which is advantageous for the improvement of abrasion resistance. The second reason is that from the observation of the surface and cross section of the paper by electron microscopy, spindle-shaped and rice-grained calcium carbonate fills the space between the pulp fibers as if they were fine fibers. It forms a lot and develops good opacity and whiteness.

[0030]

EXAMPLES The present invention will be described below in more detail with reference to Examples and Comparative Examples, but it goes without saying that the present invention is not limited to only Examples. [Test method] (1) Measurement of alkali: TAPP1624hm-85,
TAPM 625 hm-85 or measured according to this.

(2) Quicklime particle diameter: JISR9001-
It was measured by a dry operation according to 1993.

(3) Calcium carbonate content in quicklime: Carbon analyzer in metal (using HORIBA EMIA-110)
C0 ₂ was measured to measure calcium carbonate content than the amount by.

(4) Average particle diameter of the produced light calcium: The product was washed with water, filtered and diluted with water, and the average particle diameter was measured with a laser diffraction type particle size distribution analyzer (Model 715, manufactured by Cirrus Co.). The short diameter and the long diameter were measured with a scanning electron microscope (JSM-5300 manufactured by JEOL Ltd.) after drying, washing and filtering the product.

(5) Morphological observation: The product was washed with water, filtered, dried and then scanned with a scanning electron microscope (JSM-530 manufactured by JEOL Ltd.).
0).

(6) Crystal system: X-ray diffraction R manufactured by Rigaku
It was measured by AD-2C.

[Example 1] In a four-necked flask container of IL (the same container is used in the following Examples and Comparative Examples),
50 g of quicklime having a calcium carbonate content of 1.6% (particle size distribution is 150% to 4.0%, 150 to 75 μm 1
8.1%, 75-45 μm 19.4%, 45 μm or less 58.5%) and green liquor (composition: Na ₂ CO ₃ = 110 g)
/ L, Na ₂ S = 34 g / L, NaOH = 6 g / L. All were converted to Na ₂ 0, the same for the following Examples and Comparative Examples), mixed at a ratio of quick lime concentration of 30% by weight, slaked to form lime milk, and a green liquor (composition: Na
_{2 C0 3 = 110g / L,} Na 2 S = 34g / 1, NaO
H = 6 g / L. All of the values are in terms of Na ₂ O, and are the same for the following Examples and Comparative Examples.) Addition rate 0.22 cc / mi
n / g (quick lime), addition time 60 minutes, temperature 80 ° C., stirring speed 450 rpm (KYOEI POWERSTAIR)
The causticization reaction was carried out under the conditions of RR TYPE PS-2N and the same stirrer for the following Examples and Comparative Examples. As a result of observing the average particle diameter and the morphology of the produced reaction product, the average particle diameter was 3.8 μm, the average major axis was 3.8 μm,
Rice granular calcium carbonate having an average minor axis of 1.2 μm was observed. Table 1 shows the experimental conditions and results.

Example 2 50 g of quicklime having a calcium carbonate content of 3% (particle size distribution is 150 μm or more, 4.4%, 1%)
50-75 μm 17.4%, 75-45 μm 20.
1%, 58.1% for 45 μm or less) and the same green liquor as in Example 1, mixed with white liquor at a ratio of quick lime concentration of 40% by weight, then slaked to form lime milk, green liquor Addition speed 0.5 cc / min / g (quick lime), addition time 30 minutes,
The causticization reaction was performed under the conditions of a temperature of 85 ° C. and a stirring speed of 1000 rpm. In the product, rice granular calcium carbonate having an average particle diameter of 3.6 μm, an average major axis of 3.6 μm, and an average minor axis of 1.2 μm was observed. Table 1 shows the experimental conditions and results.

Example 3 50 g (average particle diameter: 10 mm) of calcined calcined lime having a calcium carbonate content of 7%;
Using the same green liquor as in Example 1 and mixing with the green liquor at a ratio of quick lime concentration of 50% by weight, slaked to form lime milk,
The same green liquor as in Example 1 was added at a rate of 28 cc / min / g.
Caustic reaction was performed under the conditions of (quick lime), addition time 0.5 minute, temperature 95 ° C., and stirring speed 600 rpm. The product was found to be granular rice carbonate having an average particle diameter of 4.0 μm, an average major axis of 4.0 μm, and an average minor axis of 1.2 μm. Table 1 shows the experimental conditions and results.

Example 4 The procedure was performed in the same manner as in Example 1 except that the temperature of the caustic reaction was changed to 30 ° C. The product had an average particle diameter of 6.1 μm, an average major axis of 1.2 μm, and an average minor axis of 0.1 μm.
It was found that the calcium carbonate was 3 μm in spindle shape. Table 1 shows the experimental conditions and results.

Example 5 The same procedure as in Example 2 was carried out except that the temperature of the caustic reaction was changed to 40 ° C. The product had an average particle diameter of 6.8 μm, an average major axis of 1.3 μm, and an average minor axis of 0.3 μm.
It was found that the calcium carbonate was 3 μm in spindle shape. Table 1 shows the experimental conditions and results.

Example 6 The procedure of Example 3 was repeated, except that the temperature of the caustic reaction was changed to 50 ° C. The product had an average particle diameter of 6.7 μm, an average major axis of 1.5 μm, and an average minor axis of 0.
4 μm was found to be spindle-shaped calcium carbonate. Table 1 shows the experimental conditions and results.

Comparative Example 1 Calcium carbonate content 13%
The procedure was performed in the same manner as in Example 3 except that quicklime was used. At this time, the reaction product was found to have massive particles having an average particle diameter of 12.5 μm. Table 2 shows the experimental conditions and results.

[Comparative Example 2] The quicklime concentration during slaking was 14%.
The procedure was performed in the same manner as in Example 2 except that At this time, the reaction product was found to have massive particles having an average particle diameter of 10.8 μm. Table 2 shows the experimental conditions and results.

Comparative Example 3 The temperature during the causticizing reaction was 15 ° C.
The procedure was performed in the same manner as in Example 3, except that At this time, the reaction product was found to have massive particles having an average particle diameter of 9.1 μm. Table 2 shows the experimental conditions and results.

Comparative Example 4 Commercially available heavy calcium carbonate S
S-1200 (manufactured by Shiraishi Kogyo, average particle 4.4 μm) was used.

[Application Example 1] Canadian standard type freeness is 300
ml of bleached chemical pulp alone slurry, 0.02% of internal sizing agent (alkyl ketene dimer) per pulp,
Sulfuric acid band 0.5%, cation modified starch 0.3%,
15% of each of the calcium carbonates obtained in Examples 1 to 6 and Comparative Examples 1 to 4, 200 ppm of a retention aid (polyacrylamide, anionic, molecular weight 4,000,000 to 500)
The slurry prepared by internally adding (10,000) was paper-made with a test machine. The basis weight, density, whiteness, and opacity of the paper thus obtained were measured at 20 ° C. and 65% RH for one day and night, and then measured according to JIS. In addition, a wire wear test was performed. The test method is shown below, and the obtained results are shown in Tables 1 and 2.

[Test Method] (1) Wire-Wear Measuring Method Tester: Nippon Filcon-type abrasion test equipment Wire: Nippon Filcon COS-60 polyester wire Slurry concentration: 2% by weight Load: 1250 g Wear time: 90 minutes ・ Abrasion: Wire weight loss before and after the wear test (mg)

[0048]

[Table 1]

[0049]

[Table 2]

[Application Example 2] Each paper produced in Application Example 1 was subjected to surface size pressing so that the weight after drying of the oxidized starch was 2 g / m ² by a size press, followed by drying.
After that, soft calendar processing (60, Minami-Senju Seisakusho)
At 50 ° C. and 50 kg / cm). Heavy calcium carbonate having an average particle diameter of 0.6 μm as a coating liquid composition (trade name: Hydrocarbo 90, manufactured by Shiraishi Calcium Co., Ltd.)
Kaolin (trade name: Ultra White 90, manufactured by Engelhard Co., Ltd.) of 60% by weight and an average particle size of 0.5 μm
40% by weight, phosphate esterified starch 4% by weight as adhesive, styrene / butadiene-based latex 10
Concentration 64% by weight and 0.3% by weight of dispersant.
% Coating solution with a test blade coater, 10 g per side
/ M ² was applied to both sides and dried. The quality evaluation method for the obtained product is shown below, and the obtained results are shown in Tables 3 and 4.

[Quality evaluation method] (1) Blank gloss: Measured according to JISP-8142 (2) Opacity: Measured according to JISP-8138 (3) Print gloss: Using a RI printer (manufactured by Meiji Seisakusho)
Using Sakata Inx Diatone GSL Red, printing at a constant ink amount of 0.35 cc, JIS P-8142
Measured at an angle of 75 degrees according to

[0052]

[Table 3]

[0053]

[Table 4]

[0054]

As shown in Examples 1 to 6, the calcium carbonate according to the present invention was spindle-shaped and rice-grained calcium carbonate. Further, the composition of the white liquor sampled from the inside of the process was not changed at all compared with the conventional conditions.

As a result of the paper quality test of Application Example 1, the calcium carbonate according to the present invention was excellent in whiteness, opacity, and abrasion resistance of plastic wires.

The coated paper of Application Example 2 gave excellent results in terms of opacity.

Further, according to the present method, calcium carbonate having a controlled shape can be produced by using the conventional causticizing step without major change, so that the production cost can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph showing a crystal particle structure of rice granular calcium carbonate obtained in Example 1.

FIG. 2 is a scanning electron micrograph showing the crystal particle structure of the spiky calcium carbonate obtained in Example 4.

FIG. 3 is a scanning electron micrograph showing the crystal particle structure of massive calcium carbonate obtained in Comparative Example 1.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasuhiro Okamoto 2-8-1 Iidacho, Iwakuni-shi, Yamaguchi Japan Japan Paper Manufacturing Co., Ltd.

Claims (5)

[Claims] 1. A method for producing calcium carbonate useful as a filler for papermaking in a causticizing step of a pulp manufacturing step by a sulfate method or a soda method, and (1) generated in the causticizing step, and / or Quicklime introduced from outside the process, and (2) 0.1 wt% based on the weight of the quicklime.
Green liquor is added to the quicklime containing 1 to 10% by weight of calcium carbonate so that the concentration of the quicklime becomes 20 to 60% by weight, and the liquid is slaked with stirring or kneading to obtain lime milk or lime. A first step for producing lime mud, and then adding a predetermined amount of green liquor generated in the causticizing step and required for producing white liquor to the lime ５０50 cc (green liquor) / min / g (quick lime) at a rate of 20 to 105 cc.
A method for producing calcium carbonate useful as a filler for papermaking, comprising carrying out a causticization reaction at a temperature of ° C. 2. Manufactured by the method of claim 1,
Calcium carbonate useful as a filler for papermaking or a coating pigment for coated paper. 3. A spindle or rice grain having a minor axis of 0.3 to 1.5 μm and a major axis of 0.5 to 7 μm.
The calcium carbonate as described. 4. A coating composition comprising the calcium carbonate according to claim 2 as a coating pigment. 5. A paper characterized by using the calcium carbonate according to claim 2 as a filler for papermaking, or a coated paper characterized by being used as a coating pigment.