JPH10226517A - Production of calcium carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fusiform or rice-like granular calcium carbonate excellent in whiteness, opacity and wire wearing property by adding a green liquor generated in a caustification process in a prescribed quantity necessary to produce a white liquor into a specific lime milk or lime mud. SOLUTION: The lime milk or lime mud is obtained by adding the white liquor having 80-160g/l total alkali (expressed in term of Na2 O, the same hereafter) and <=30g/l Na2 CO3 into a quick lime having 0.01-30mm particle diameter and containing 0.1-10wt.% calcium carbonate so as to be 0.5-60wt.% in the concentration of the quick lime and slaking while stirring or kneading. The green liquor generated in the caustification process and having 80-160g/l total alkali (in which Na2 CO3 is 65-130g/l) is added into the lime milk and/or the lime mud at the adding rate of 0.02-50cc (green liquor)/min/g (quick lime) to perform caustification reaction at 20-105 deg.C.

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 recent demand for paper, in commercial printing, fields such as flyers, catalogs, brochures, and direct mails, and in publishing printing, computers, multimedia, and NES related to the advance 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 by using a natural limestone using a pulverizer such as a ball mill is difficult to control the shape. Therefore, when 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 produced, 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, as a usual means for improving the opacity of lightweight printing paper, fillers having a large specific surface area (for example, finely divided silica, white carbon, etc.) and fillers having a high refractive index (for example, titanium dioxide),
Or precipitated calcium carbonate (synthetic calcium carbonate)
There is use of

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 are collected as a heat source, the inorganic substances in the chemical are collected mainly as sodium carbonate and sodium sulfide, and the calcium carbonate sludge formed by the following reaction called water or weak liquid is washed. The white liquor component generated at this time is dissolved by a partially dissolved dilute chemical solution to become a green liquor. Quicklime mixed with the green liquor, [1], [2] by the reaction shown by the formula _{CaO + H 2 O → Ca (} OH) 2 [1] Ca (OH) 2 + Na 2 CO 3 → CaCO 3 + 2NaOH [2] The generated calcium carbonate is used. 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, conventionally, calcium carbonate obtained here has a variety of various shapes such as a dice or a hexagon, and has a large particle size because of the difficulty in controlling the shape. 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 become larger and the papermaking speed has been further increased, there has been a great problem in the abrasion of the plastic wire.

[0011] Thus, at the time of papermaking, the abrasion of the plastic wire is good, 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.

[0012]

In view of the above-mentioned circumstances, wire abrasion is excellent at the time of paper making, and when used in paper production, the opacity is high and the printing quality is 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.

[0013]

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. The lime milk obtained by slaking reaction of quick lime containing calcium carbonate and white liquor, which is generated in the causticizing step of the pulp manufacturing process by the sulfate method or the soda method, produces white liquor 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 0.1 μm.
Spindle-shaped or rice-grained calcium carbonate of 5 to 7 μm is prepared, whiteness, opacity and wire abrasion can be improved as a filler for papermaking, and can be obtained by a conventional method by reaction of milk of lime and carbon dioxide. It can be manufactured at a significantly lower cost than calcium carbonate. As an additional effect, by extracting calcium carbonate from the causticizing process,
The kiln operation can be reduced, or the kiln can be stopped depending on the amount of calcium carbonate withdrawn from the process, thereby reducing the cost of the entire causticizing process.

[0014]

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).

With respect to the content of impurities in the obtained calcium carbonate, there is a problem particularly with regard to coloring components (Fe, Mn, etc.), but it is obtained from raw limestone having a low coloring component content in accordance with the use of paper as a product. Choose quicklime as appropriate or
Alternatively, in the case of recalcined calcined lime in a rotary kiln or fluidized kiln in a causticizing process, the content of coloring components and the like change depending on the ratio of calcium carbonate extracted outside the system and calcium carbonate recirculated in the system. In addition, a raw limestone having a low coloring component content to be supplied to the calcium circulation cycle in the causticizing step or a raw limestone obtained by calcining the raw limestone 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 massive, resulting in poor wire abrasion and a light weight coated paper of the target paper quality cannot be obtained. On the other hand, 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. The particle size of quicklime is not particularly limited, but is preferably 0.01 to 30 mm, and 0.01 mm
In the following cases, the cost for pulverization is high, and at the same time, there is a problem of generation of dust and trouble in the transfer device.
If it is not less than m, there is a problem in terms of uniform mixing in stirring during slaking, which is not preferable.

The white liquor used for slaking quicklime is a total alkali of 80 to 160 g / L (calculated as Na ₂ O, the same applies hereinafter), a Na ₂ CO ₃ of 30 g / L or less, preferably a total alkali of 100 to 150 g / L. L, ₂ with Na ₂ CO ₃
It is necessary to carry out at 5 g / L or less. 8 total alkalis
If it is lower than 0 g / L, the concentration of the final white liquor will decrease, and it will be necessary to adjust the concentration when it is used for cooking. On the other hand, when it is higher than 160 g / L, the wire abrasion of the generated calcium carbonate is inferior and the target paper quality cannot be obtained. Also, when Na ₂ CO ₃ is higher than 30 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 is 0.5 to 60% by weight, preferably 3.5% by weight based on quick lime before slaking.
It needs to be performed at ~ 55% by weight. If it exceeds 60% by weight, the liquid viscosity is so high that it becomes difficult to stir it in practice.
If it is less than 5% by weight, the productivity of calcium carbonate is very poor and not practical.

The mixing of quicklime and liquid at the time of slaking includes:
Any of general stirring blade type, pump type, extruder, kneader and kneader may be appropriately selected and used according to the viscosity of the liquid or slurry at the time of mixing (Showa 63
Published by Maruzen Co., Ltd. on March 18, 2003, see Chemical Engineering Handbook).

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 to 160 g / L (of which Na ₂ CO ₃ is 65 to 130 g / L)
g / L), preferably 100 to 150 total alkali
g / L (of which Na ₂ CO ₃ is 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, when it is higher than 160 g / L (Na ₂ CO ₃ is 130 g / L), the abrasion resistance of the generated calcium carbonate wire is inferior and the target 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). At an addition rate of less than 0.02 cc (green liquor) / min / g (quick lime), the productivity is poor and impractical, while an addition rate of more than 50 cc (green liquor) / min / g (quick lime) is extremely low. Requires a large capacity pump, which is not practical.

Here, instead of lime milk adjusted from quicklime in the first step, it is also possible to use lime milk adjusted to the same concentration of calcium hydroxide as in the present method.

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 generated calcium carbonate becomes irregular or lump, resulting in poor 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 may be performed by using a general stirring blade type, a pump type, an extruder, a kneader, or a kneader, from the lime milk and the green prepared 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 abrasion property of the wire as compared with the calcium carbonate conventionally obtained in the causticizing step, and by adding it internally, the white paper of the high quality paper and the 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, thermal paper, etc., it is easy to guess that strong stiffness and excellent characteristics such as whiteness, opacity, smoothness, writability, touch, and printability can be easily provided. You.
Furthermore, when used for various pigments, characteristics excellent in glossiness, smoothness, printability and the like are provided. In addition to papermaking,
It can also be used for rubber, plastic, paint, sealant, adhesive, fertilizer, etc.

[0028]

Although the mechanism of the present invention has not been sufficiently elucidated, the amount of calcium carbonate in quicklime and the total amount of alkali in white liquor greatly affect the properties of lime milk. It seems to affect the reaction state of dissolved calcium hydroxide and carbonate ion. The sequential addition of the green liquor causes the concentration of dissolved calcium hydroxide and the proportion of carbonate ions to react in a state with a small amount of carbonate ions in the initial stage, thereby growing crystals of calcium carbonate to form a spindle-shaped,
It seems that rice grains will be present.

One of the features of this calcium carbonate is that it has an effect of improving the abrasion of plastic wires during high-speed papermaking, and the other has an effect of improving opacity and whiteness by papermaking. The first reason is that, because the primary particles are spindle-shaped or rice-granular, entanglement with the fiber increases, which is advantageous for improving the yield, and as a result, the filler passing through the wire part decreases, Since the particle shape is spindle-shaped or rice-grain-shaped, 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 improving the abrasion property.
The second reason is from the electron microscope observation of the surface and cross section of the paper,
Spindle-shaped or rice-grained calcium carbonate fills the pulp fibers as if they were fine fibers, and because they are rigid, they form many fine voids and have good opacity,
Develop 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: TAPPI 624hm-8
5 or according to this.

(2) Quicklime particle diameter: JIS R900
It measured by dry operation according to 1-193.

(3) Calcium carbonate content in quicklime: CO _{2 was} measured by a carbon-in-metal analyzer (EMIA-110, Horiba Seisakusho), and the calcium carbonate content was measured from the amount.

(4) Average particle size of formed calcium carbonate:
The product was washed with water, filtered and diluted with water, and the average particle size was measured with a laser diffraction particle size distribution analyzer (Cirrus model 715). For the minor axis and major axis, the product was washed with water, filtered, dried, and then scanned with a scanning electron microscope (JSM-530 manufactured by JEOL Ltd.).
0).

(5) Morphological observation: The product was washed with water, filtered, dried, and observed with a scanning electron microscope (JEOL JSM-5300).

(6) Crystal system: X-ray diffraction R manufactured by Rigaku
It was measured by AD-2C. [Example 1] 50 g of quicklime having a calcium carbonate content of 1.6% (particle size distribution was 150 µm) was placed in a 1-L four-necked flask container (the same container was used in the following Examples and Comparative Examples).
m or more 4.0%, 150-75 μm 18.1%, 7
5 to 45 μm 19.4%, 45 μm or less 58.5
%) And a white liquor (composition: Na ₂ CO ₃ = 24 g / L, Na ₂
S = 31 g / L, NaOH = 71 g / L. Both are Na
Using the same value as in the following Examples and Comparative Examples in terms of ₂ O, the mixture was mixed at a ratio of quick lime concentration of 7% by weight, and then slaked to form lime milk, and a green liquor (composition: Na ₂ CO ₃₎ = 11
0 g / L, Na ₂ S = 34 g / L, NaOH = 6 g / L
L. All of them are in terms of Na ₂ O and are the same for the following Examples and Comparative Examples.) Addition rate: 0.22 cc / min / g (quick lime), Addition time: 60 minutes, Temperature: 80 ° C., Stirring speed: 450 r
pm (using KYOEI POWER STAIRRER TYPE PS-2N, using 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, rice granulated calcium carbonate having an average particle diameter of 3.5 μm, an average major axis of 3.5 μm, and an average minor axis of 1.2 μm was observed. Table 1 shows the experimental conditions and results. [Example 2] Quicklime 5 having a calcium carbonate content of 3.0%
0 g (particle size distribution is 150% or more, 4.4%, 150 to
75 μm 17.4%, 75-45 μm 20.1%,
45 μm or less (58.1%) and the same white liquor as in Example 1, mixed with the white liquor at a ratio of quick lime concentration of 14% by weight, slaked to form lime milk, and the same green as in Example 1. Green liquor addition rate 0.5 cc / min / g (quick lime)
Addition time 30 minutes, temperature 85 ° C, stirring speed 1000rpm
Caustic reaction was performed under the following conditions. The product had an average particle size of 3.6 μm, an average major axis of 3.6 μm, and an average minor axis of 1.2 μm.
m, that is, rice granulated calcium carbonate. Table 1 shows the experimental conditions and results. Example 3 Using 50 g (average particle diameter: 10 mm) of calcined regenerated calcined lime having a calcium carbonate content of 7% and the same white liquor as in Example 1, after mixing with the white liquor at a ratio of quick lime concentration of 30% by weight The liquor was made by slaking and using the same green liquor as in Example 1, the green liquor was added at a rate of 28 cc / min / g (quick lime), an addition time was 0.5 minutes, a temperature was 95 ° C., and a stirring rate was 60.
Caustic reaction was performed under the condition of 0 rpm. The product was found to be granular calcium carbonate having an average particle diameter of 4.0 μm, an average major axis of 4.0 μm, and an average minor axis of 1.1 μm. Table 1 shows the experimental conditions and results. [Example 4] Except that the causticization reaction temperature was changed to 30 ° C,
Performed in the same manner as in Example 1. The product has an average particle size of 5.1.
It was found to be spindle-shaped calcium carbonate having an average major axis of 5.1 μm and an average minor axis of 0.7 μm. Table 1 shows the experimental conditions and results. [Example 5] Except that the causticization reaction temperature was changed to 40 ° C,
Performed in the same manner as in Example 2. The product has an average particle size of 4.8.
It was found to be spindle-shaped calcium carbonate having an average major axis of 4.8 μm and an average minor axis of 0.7 μm. Table 1 shows the experimental conditions and results. [Example 6] Except that the causticization reaction temperature was changed to 50 ° C,
Performed in the same manner as in Example 3. The product has an average particle size of 4.7.
It was found to be spindle-shaped calcium carbonate having an average major axis of 4.7 μm and an average minor axis of 0.6 μm. Table 1 shows the experimental conditions and results. [Comparative Example 1] The same operation as in Example 3 was performed except that quicklime having a calcium carbonate content of 13% was used. The reaction product at this time was found to be amorphous or massive calcium carbonate having an average particle size of 12.5 μm. Table 2 shows the experimental conditions and results. Comparative Example 2 Green liquid (composition: Na ₂ CO ₃₎
= 110 g / L, Na ₂ S = 34 g / L, NaOH = 6
g / L) was carried out in the same manner as in Example 2.
The reaction product at this time was found to be amorphous or massive calcium carbonate having an average particle diameter of 10.8 μm. Table 2 shows the experimental conditions and results. [Comparative Example 3] The same operation as in Example 3 was carried out except that the temperature during the causticization reaction was set to 15 ° C. The reaction product at this time is
It was confirmed that the particles were amorphous or massive calcium carbonate having an average particle size of 9.1 μm. Table 2 shows the experimental conditions and results. [Comparative Example 4] Commercially available heavy calcium carbonate SS-1200
(Manufactured by Shiraishi Kogyo Co., Ltd., average particle diameter 4.4 μm) was used. [Application Example 1] Canadian standard freeness (hereinafter CSF) 3
Internal sizing agent (alkyl ketene dimer) per pulp in a slurry of 00 ml of hardwood bleached chemical pulp
0.02%, sulfuric acid band 0.5%, cation-modified starch 0.3%, 15% of each calcium carbonate obtained in Examples 1 to 6 and Comparative Examples 1 to 4, and 200 ppm of a yield improver (poly Acrylamide and an anionic molecular weight of 4,000,000 to 5,000,000) were internally added and adjusted to prepare a slurry using a test machine. The basis weight, density, whiteness, and opacity of the paper thus obtained were measured at 20 ° C. and 65% R.
After controlling the humidity with H for one day and night, the measurement was performed according to JIS. Also,
A wire abrasion test was performed. The test method is shown below, and the obtained results are shown in Tables 1 and 2. [Test method] (1) Wire abrasion measurement method ・ Tester: Japan Filcon abrasion test device ・ Wire: Nippon Filcon COS-60 polyester wire ・ Slurry concentration: 2% by weight ・ Load: 1250 g ・ Abrasion time: 90 minutes ・ Abrasion Amount: Wire weight loss before and after abrasion test (mg)

[Table 1]

[Application Example 2] Each paper prepared 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, and dried. After that, soft calender treatment (Minami-Senju, 60 ℃, 50kg / cm
(Constant processing). As a coating liquid composition, 60% by weight of heavy calcium carbonate having an average particle diameter of 0.6 μm (trade name: Hydrocarbo 90, manufactured by Shiraishi Calcium Co.), and kaolin having an average particle diameter of 0.5 μm (trade name: Ultra White 9)
0, 40% by weight of Engelhard Co.) and a coating of 64% concentration containing 4% by weight of a phosphate esterified starch, 10% by weight of a styrene-butadiene latex and 0.3% by weight of a dispersant as an adhesive. The working solution was applied on both sides at 10 g / m ² per one side by a test blade coater and dried. The quality evaluation methods for the obtained products are shown below, and the obtained results are shown in Tables 3 and 4. [Quality evaluation method] (1) Blank gloss: Measured according to JIS P-8142 (2) Opacity: Measured according to JIS P-8138 (3) Print gloss: Diamond tone manufactured by Sakata Inx using an RI printing machine (Meiji Seisakusho) Using GSL red, print at a constant ink amount of 0.35 cc and measure at an angle of 75 degrees according to JIS P-8142

[Table 3]

[Table 4]

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.

Further, 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 a plastic wire.

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 any 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 a crystal particle structure of spindle-shaped calcium carbonate obtained in Example 4.

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

[Table 1]

[Table 2]

[Table 3]

[Table 4]

 ────────────────────────────────────────────────── ─── 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 producing step by a sulfate method or a soda method, wherein (i) generated in the causticizing step, and / or And quicklime introduced from outside the process, and (ii) 0.1 wt% based on the weight of quicklime.
A white liquor is added to the quicklime containing 1 to 10% by weight of calcium carbonate so that the concentration of the quicklime becomes 0.5 to 60% by weight, and the white lime is slaked with stirring or kneading. A first step for producing milk or lime mud, and then adding to the lime milk and / or lime mud a predetermined amount of green liquor generated in the causticizing step and required for producing white liquor with respect to quicklime. 0.02 to 50 cc (green liquor) / min / g (quick lime) at a rate of 20 to 105 ° C.
A method for producing calcium carbonate useful as a filler for papermaking, comprising performing a causticization reaction at 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 using 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.