JP2000327946A - Dispersant for inorganic pigment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a dispersant which is used for inorganic pigments, can lower the viscosity of a high concentration inorganic pigment slurry and can stabilize the dispersion of the slurry for a long period, by specifying the copolymerization ratio, mol.wts., component (for each mol.wt.) ratio, salt kind and neutralization degree of acrylic acid-maleic acid copolymer. SOLUTION: This dispersant for inorganic pigments comprises 5 to 15 wt.% of a polymer component having a 20 wt.% aqueous solution viscosity of 25 to 50 mPa.s at 25 deg.C and a weight-average mol.wt.(MW) of <10,000, 60 to 80 wt.% of a polymer component having a MW of 10,000 to 100,000, and 10 to 25 wt.% of a polymer component having a MW of >=100,000. The polymer components are expressed by the formula [A, B are each H, a molecular terminal group caused by a radical polymerization or the like; M is H, an alkali metal or the like; (m), (n) are each >=0, provided that (m), (n) are simultaneously not 0; (m)/9>=(n); α/' is 0 to 0.053 (α is the number of carboxyl groups in the molecule; β is the number of carboxylate salt groups)], have a MW of 45,000 to 85,000, and a MW/MN (number-average mol.wt.) of 1.7 to 2.8. The dispersant of the formula can be obtained by a conventional method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a dispersant for an inorganic pigment.

[0002]

2. Description of the Related Art A low molecular weight polycarboxylic acid (salt) -based dispersant is effective for dispersing and slurrying an inorganic pigment in an aqueous medium. For example, a salt of a copolymer of acrylic acid and maleic acid (JP-A-48-79230, JP-A-53-129200) is proposed.

[0003]

However, Japanese Unexamined Patent Publication No.
20% at 25 ° C. as disclosed in 8-79230
Acrylic acid maleate copolymer having an aqueous solution having a viscosity of 8.5 to 9.2 mPa · s, and an acrylic acid maleate copolymer having a molecular weight of 1,000 to 20,000 disclosed in JP-A-53-129200. In any polymer, it is possible to produce an inorganic pigment slurry excellent in fluidity with high concentration and low viscosity, but the long-term dispersion stability of the slurry is extremely poor,
When the slurry is stored for a long period of time, the pigment particles settle, forming a strong coagulate and cannot be redispersed. From such a background, it is possible to produce a high-concentration, low-viscosity slurry having excellent fluidity, and there is little sedimentation of pigment particles over time, or even if sedimentation occurs, a hard cake is not formed and redispersion is performed. There is a long-felt need to develop a dispersant capable of producing a pigment slurry having excellent long-term dispersion stability.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve these problems, and as a result, have found that the copolymerization ratio of maleic acid acrylate, the acrylic acid polymer and / or the maleic acid acrylate copolymer. Polymers whose molecular weight, molecular weight distribution, component composition ratio by molecular weight, type of salt, and neutralization ratio are within a specific range are used to reduce viscosity at high concentration of inorganic pigment slurry as well as to provide long-term dispersion stability of the slurry. The inventors have found that they are remarkably excellent, and have reached the present invention. That is, the present invention provides a compound represented by the general formula (I) having a weight average molecular weight of 45,000 to 85,000 and an MW (weight average molecular weight) / MN (number average molecular weight) of 1.7 to 2.8. , A 20% by weight aqueous solution of the polymer having a viscosity at 25 ° C. of 25 to 50 mPa · s, a component having a weight average molecular weight of less than 10,000 in the polymer being 5 to 15% by weight, a weight average molecular weight of 10, A dispersant for an inorganic pigment in which a component having a weight average molecular weight of 100 to 100% is 10 to 25% by weight. [In the formula, A and B are a molecular terminal group resulting from a polymerization initiator of radical polymerization, a terminal group generated by hydrolysis thereof, a hydrogen atom or a hydroxyl group, respectively. M is a hydrogen atom,
Alkali metals, alkaline earth metals, ammonium or amines. m and n are integers of 0 or more, and m / 9 ≧
n. However, m and n do not become 0 at the same time.
If the number of carboxylic acid groups in the molecule is α and the number of carboxylic acid groups is β, then 0 ≦ α / β ≦ 0.053. ]

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The dispersant of the present invention is a homopolymer (salt) of acrylic acid (meaning a polymer or a salt thereof, the same applies hereinafter), acrylic acid and maleic acid and / or various copolymerization ratios. A mixture of a block and / or random copolymer (salt) of fumaric acid, a homopolymer (salt) of acrylic acid and a block and / or random copolymer (salt) of acrylic acid and maleic acid at various copolymerization ratios Either. In the dispersant of the present invention, m / 9 ≧ n, and m / 9 <n
In the case of the above, the long-term dispersion stability of the inorganic pigment slurry becomes poor.

The dispersant of the present invention has a polymer having a weight average molecular weight of 45,000 to 85,000, of which 5 to 15% by weight has a component having a molecular weight of less than 10,000, and a weight average molecular weight of 10,000 to 100,000. 60 components less than 000
It is necessary that the components having a weight average molecular weight of 100,000 or more have a content of 10 to 25% by weight. If a dispersant outside of these ranges is used, the fluidity of the inorganic pigment slurry deteriorates significantly, and the long-term dispersion stability of the slurry deteriorates.

[0007] MW (weight average molecular weight) of the dispersant of the present invention
/ MN (number average molecular weight) is 1.7 to 2.8. MW
When / MN is 2.8 or more, the long-term dispersion stability of the inorganic pigment slurry is excellent, but the fluidity of the slurry is poor. If the MW / MN is 1.7 or less, the object of the present invention cannot be achieved because the inorganic pigment slurry lacks long-term dispersion stability.

MW (weight average molecular weight) of the dispersant of the present invention
And MN (number average molecular weight) were measured by gel permeation chromatography using polyethylene glycol of known molecular weight as a standard substance.

In the dispersant of the present invention, M is a hydrogen atom, an alkali metal, an alkaline earth metal, ammonium or an amine. Examples of the alkali metal include lithium, sodium, and potassium. Examples of the alkaline earth metal include calcium and magnesium. Examples of the amine include triethylamine, diethanolamine, diethylamine and the like. Preferred among these are sodium, ammonium and lithium.

In the dispersant of the present invention, 0 ≦ α / β ≦ 0.
053, preferably 0 <α / β ≦ 0.031. If α / β is 0.053 or more, the fluidity of the inorganic pigment slurry deteriorates, which is not preferable.

The viscosity of the dispersant of the present invention must be 25 to 50 mPa · s in a 20% aqueous solution. If the viscosity is lower than this, the inorganic pigment slurry lacks long-term stability, and if the viscosity is more than 50 mPa · s, the slurry lacks fluidity and the object of the present invention cannot be achieved.

In the dispersant of the present invention, A and B are a molecular terminal group resulting from radical polymerization and a terminal group formed by hydrolysis thereof. For example, it is a residue of an azo compound (eg, azoisobutyronitrile) or a persulfate (eg, sodium persulfate, potassium persulfate, ammonium persulfate, etc.) which is a polymerization initiator. It is a hydrogen atom or a hydroxyl group.

As a method for producing the dispersant of the present invention, generally known methods can be used. For example, acrylic acid and, if necessary, maleic acid and / or fumaric acid are converted into a known polymerization initiator, a azo compound (eg, azobisisobutyronitrile), a persulfate (eg, sodium persulfate, potassium persulfate, ammonium persulfate). ), Redox initiators such as ascorbic acid-hydrogen peroxide, etc. in water and / or alcoholic solvents in the presence of｝.
And a polymerization method in which polymerization is performed at 1 ° C. for 1 to 12 hours. As the polymerization method, the entire amount of the monomer may be charged into a polymerization tank and polymerization may be performed, or an appropriate drop polymerization method may be used. Further, a method in which a part of the monomer is charged into the polymerization tank and the remaining monomer is dropped may be used. The polymerization initiator may be present in the polymerization tank in advance before the polymerization, or a method of continuously introducing the polymerization initiator during the polymerization may be used. The dispersant of the present invention is usually produced by a solution polymerization method in water and / or an alcohol-based solvent, and is dissolved in a hydrophobic organic solvent such as mineral oil, naphtha, n-hexane, or isoparaffin in the presence of an emulsifier. It can also be produced by an emulsion polymerization method in which an aqueous solution of a monomer is added. If necessary, components having a specific molecular weight may be separated by a liquid separation extraction method or the like.

The dispersant of the present invention is particularly (1) rutile type titanium oxide having a large sedimentation property, and (2) an average minor axis of 0.1 to 1.0.
μm, average major axis 1.0-3.0 μm, BET specific surface area 1
Spindle-shaped light calcium carbonate having a spindle shape of 1 to 10 m ² / g, (3) cubic calcite light calcium carbonate having a BET specific surface area of 5 to 15 m ² / g and an average particle diameter of 0.1 to 2.0 μm; 4) BET specific surface area 20-50m2
/ G, an average particle size of 0.01 to 1.0 μm, has a remarkable effect on colloidal calcium carbonate.
It has a good effect on light calcium carbonate having a T specific surface area and shape. Also natural calcium carbonate, clay,
Titanium oxide, ferrite, alumina, satin white,
It is also effective for other pigments for ceramics.

In producing an inorganic pigment slurry using the dispersant of the present invention, a known dispersing machine such as a homogenizer, a disk cavitation mixer, a stator roller, a Keddy mill, a colloid mill, a Cores mixer, an attritor, a sand mill and a bead mill is used. Machine can be used. It is also possible to perform multi-stage dispersion processing for performing multi-order dispersion using a combination of these dispersers.

The amount of the dispersant added is preferably 0.1 to the inorganic pigment.
01-5.0% by weight, more preferably 0.05-3.0%
% By weight. If the amount of the dispersant is less than 0.01% by weight, the dispersing power is insufficient and a slurry having excellent fluidity and long-term dispersion stability cannot be obtained. Also, when it exceeds 5% by weight, the fluidity and long-term dispersion stability of the slurry deteriorate.

[0017]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which, however, are not intended to restrict the scope of the present invention. Table 1 shows examples and comparative examples. Production Example 1 (Example 1) A stainless steel flask for polymerization (1) equipped with a thermometer, a stirrer, a condenser, and two dropping pumps
300.0 g of ion-exchanged water (referred to as initial ion-exchanged water) was added to L), and the mixture was heated to 95 ° C. with stirring. Thereafter, a monomer aqueous solution (300.0 g of acrylic acid + 75.0 g of ion-exchanged water) under reflux is added for 120 minutes (referred to as monomer dropping time).
Of the mixed catalyst solution (9.5 g of sodium persulfate, 3
41.2 g of 5% hydrogen peroxide solution, 15.1 g of ion-exchanged water
Was also dropped at a constant rate over 120 minutes (referred to as catalyst dropping time) to cause a reaction. 6 more after the end of dropping
The same temperature was maintained for 0 minutes (referred to as aging time) to complete the polymerization reaction. The mixture was cooled to 50 ° C. or lower and neutralized with 333.9 g of a 48.5% aqueous sodium hydroxide solution. Neutralization temperature is 50
C. or less. The obtained polymer aqueous solution is solid content 20%
To obtain Example 1 in Table 1.

Example 2 Example 2 was obtained using the same method as in Production Example 1 except for the following changes. Changes: The initial ion exchanged water was changed to 310.0 g.

Example 3 Example 3 was obtained using the same method as in Production Example 1 except for the following changes. Changes: The initial ion exchanged water was changed to 330.0 g.

Example 4 Example 4 was obtained using the same method as in Production Example 1 except for the following changes. Changes: The initial ion exchanged water was changed to 270.0 g.

Example 5 Example 5 was obtained using the same method as in Production Example 1 except for the following changes. Modification: Initial ion exchange water was changed to 350.0 g.

Example 6 Example 6 was obtained using the same method as in Production Example 1 except for the following two changes. Modification 1: Initial ion exchanged water was changed to 330.0 g. Modification 2: monomer drop time and catalyst drop time are 10
Changed to 0 minutes.

Example 7 Example 7 was obtained using the same method as in Production Example 1 except for the following changes. Change point: The amount of the aqueous sodium hydroxide solution to be neutralized is 326.3 g.
Changed to

Example 8 Example 8 was obtained using the same method as in Production Example 1 except for the following changes. Change: The amount of the aqueous sodium hydroxide solution to be neutralized is 343.7 g.
Changed to

Example 9 Example 9 was obtained using the same method as in Production Example 1 except for the following changes. Modification point: The initial ion exchange water was changed to 250.0 g.

Example 13 Example 13 was obtained using the same method as in Production Example 1 except for the following changes. Changes: Neutralized with 97.0 g of lithium hydroxide.

Example 14 Example 14 was obtained using the same method as in Production Example 1 except for the following changes. Modification: neutralized with 275.3 g of a 25% aqueous ammonia solution.

Comparative Example 1 Comparative Example 1 was obtained using the same method as in Production Example 1 except for the following two changes. Modification 1: Initial ion exchanged water was changed to 360.0 g. Modification 2: After the temperature of the initial ion-exchanged water was raised, the catalyst solution was added all at once.

Comparative Example 2 Comparative Example 2 was obtained using the same method as in Production Example 1 except for the following changes. Changes: Initial ion exchanged water was changed to 230.0 g.

Comparative Example 3 Comparative Example 3 was obtained using the same method as in Production Example 1 except for the following changes. Modifications: After the polymerization, a part of the polymer on the high molecular weight side and the low molecular weight side of the product was removed using acetone.

Comparative Example 4 Comparative Example 4 was obtained using the same method as in Production Example 1 except for the following two changes. Modification 1: The monomer dropping time and the catalyst dropping time were changed to 90 minutes. Modification 2: The catalyst solution was dropped at once after the temperature of the initial ion-exchanged water was raised.

Comparative Example 5 Comparative Example 5 was obtained using the same method as in Production Example 1 except for the following two changes. Modification 1: Initial ion exchanged water was changed to 350.0 g. Modification 2: A part of the polymer on the high molecular weight side of the product was removed using acetone after polymerization.

Comparative Example 6 Comparative Example 6 was obtained using the same method as in Production Example 1 except for the following two changes. Modification 1: Initial ion exchanged water was changed to 250.0 g. Modification 2: The catalyst solution was added all at once after the temperature of the initial ion-exchanged water was raised.

Comparative Example 7 Comparative Example 7 was obtained using the same method as in Production Example 1 except for the following changes. Modification 1: Initial ion exchanged water was changed to 230.0 g. Modification 2: After the temperature of the initial ion-exchanged water was raised, the catalyst solution was added all at once.

Comparative Example 9 An actual comparative example 9 was obtained using the same method as in Production Example 1 except for the following changes. Changes: The amount of the aqueous sodium hydroxide solution was changed to 292.0 g.

Production Example 2 (Example 11) A polymerization stainless steel flask (1) equipped with a thermometer, a stirrer, a condenser, and two dropping pumps
In L), 40.8 g of maleic anhydride and 30 parts of ion-exchanged water were added.
0.0 g (referred to as initial ion-exchanged water) is charged and stirred 9
Heated to 5 ° C. Thereafter, 120.0 g of acrylic acid aqueous solution (270.0 g of acrylic acid + 75.0 g of ion-exchanged water) was refluxed.
The mixture was dropped from the dropping pump over 0 minutes (referred to as monomer dropping time), and at the same time, the mixed catalyst solution (9.5 g of sodium persulfate, 35% hydrogen peroxide 4
1.2 g of ion-exchanged water and 15.1 g of ion-exchanged water) were dropped at a constant rate over a period of 120 minutes (catalyst dropping time) to cause a reaction. After the completion of the dropwise addition, the same temperature was maintained for another 90 minutes (referred to as aging) to complete the polymerization reaction. The mixture was cooled to 50 ° C. or lower and neutralized with 366.5 g of a 48.5% aqueous sodium hydroxide solution. Neutralization temperature was kept below 50 ° C. The obtained aqueous polymer solution was diluted to a solid content of 20% to obtain Example 11 in Table 1.

Example 10 Example 10 was obtained using the same method as in Production Example 2 except for the following three changes. Modification 1: The amount of maleic anhydride was changed to 20.4 g. Modification 2: The amount of acrylic acid was changed to 285.0 g. Modification 3: The amount of the aqueous sodium hydroxide solution was changed to 350.6 g.

Example 12 Example 12 was obtained using the same method as in Production Example 2 except for the following changes. Modification point: The initial ion exchange water was changed to 250.0 g.

Example 15 Example 15 was obtained using the same method as in Production Example 2 except for the following three changes. Modification 1: Maleic anhydride (40.8 g) was converted to fumaric acid (24.
Changed to 2g. Modification 2: The amount of acrylic acid was changed to 285.0 g. Modification 3: The amount of aqueous sodium hydroxide solution was changed to 357.1 g.

Comparative Example 8 Comparative Example 8 was obtained using the same method as in Production Example 2 except for the following changes. Modification: Initial ion exchange water was changed to 350.0 g.

Comparative Example 10 A comparative example 10 was obtained by using the same method as that of Production Example 2 except for the following two changes. Modification 1: The initial ion exchange water was changed to 400.0 g. Modification 2: The catalyst solution (ammonium persulfate 19.1 g) was used.
g, 35% hydrogen peroxide solution 82.4 g, ion-exchanged water 1
5.1 g).

Comparative Example 11 Comparative Example 11 was obtained using the same method as in Production Example 2 except for the following changes. Changes: Initial ion exchange water was changed to 230.0.

Comparative Example 12 Example 12 was obtained using the same method as in Production Example 2 except for the following two changes. Modification 1: The amount of acrylic acid was changed to 255.0 g. Modification 2: The amount of maleic anhydride was changed to 61.3 g.

[0044]

[Table 1]

Evaluation method 1 Into a stainless steel beaker having a capacity of 500 ml, 120 g of water was charged, and 0.84 g of a dispersant prepared as a 40% by weight aqueous solution and 2.0 g of a defoamer (Dehydran 1620: manufactured by San Nopco) were prepared.
Input. Then, while gently stirring with a homogenizer having a blade diameter of 40 mm, the average particle diameter is 0.2 ~ 0.5μ
After charging 280 g of rutile-type titanium dioxide, 3,0
The mixture was stirred at 00 rpm for 10 minutes to prepare a slurry having a solid concentration of 70% by weight. The temperature of the obtained slurry was adjusted to 25 ° C., and the viscosity of the slurry was immediately measured using a B-type viscometer at a rotation speed of 60 rpm. After the viscosity-measured slurry was allowed to stand at 25 ° C. for one month, the presence or absence of a hard cake was measured using a glass rod. After shaking only 30 times without the hard cake, the viscosity was measured under the same conditions as immediately after the preparation of the slurry. Table 2 shows the results.

[0046]

[Table 2]

Evaluation method 2 1.7 kg of water was placed in a 3 L stainless steel (SUS304) container of a Coreless mixer having a stirring blade having a blade diameter of 50 mm, and the mixture was stirred at 40% by weight.
99.4 g of an aqueous dispersant was added and dissolved. Next, the average minor axis is 0.1 to 1.0 μm, and the average major axis is 1.2 to 2.8.
4.0 kg (calcium content of 0.6% by weight) of calcite-based light calcium carbonate hydrate having a spindle shape of μm was added, and the rotation speed was 1
Dispersion treatment was performed at 000 rpm for 20 minutes. The temperature of the obtained slurry was adjusted to 25 ° C., and the viscosity of the slurry was measured immediately. Furthermore, after leaving still at 25 ° C. for 7 days, the viscosity was measured at the same temperature. The viscosity was measured using a B-type viscometer at a rotation speed of 60 rpm. Table 3 shows the results.

[0048]

[Table 3]

Evaluation Method 3 Light calcium carbonate was hydrated with a cubic calcite-based light calcium carbonate having an average particle diameter of 0.1 to 0.6 μm.
The evaluation was performed in the same manner as in Evaluation method 2 except that g (water content: 0.6% by weight) was changed. Table 4 shows the results.

[0050]

[Table 4]

Evaluation method 4 2.0 kg of water was put into a 3 L stainless steel (SUS304) container of a Coreless mixer having stirring blades having a blade diameter of 50 mm, and this was stirred to form a 40% by weight aqueous dispersant 100. 0 g was added and dissolved.
Next, 2.0 kg of hydrated colloidal calcium carbonate having an average particle size of 0.01 to 0.3 μm (water content: 0.6% by weight) was added,
The dispersion treatment was carried out at a stirring speed of 10,000 rpm for 20 minutes. Immediately after the dispersion treatment, the temperature was adjusted to 25 ° C., and the viscosity of the slurry was measured using a B-type viscometer at a rotation speed of 60 rpm. After standing at 25 ° C. for 7 days, the viscosity was measured under the same conditions. Table 5 shows the results.

[0052]

[Table 5]

The weight average molecular weight and number average molecular weight in the present invention were measured under the following conditions using gel permeation chromatography (GPC) using polyethylene glycol of known molecular weight as a standard substance. Equipment used: Tosoh Corporation, Model HLC-8120GPC,
Column: Tosoh Corporation, Model G5000PWXL and Model G3000PWXL, Detector: RI detector, Data processor: Tosoh Corporation, Model SC-8020, Column temperature: 40 ° C., Eluent: 0.1- MPB disodium hydrogen phosphate aqueous solution and sodium dihydrogen phosphate aqueous solution, flow rate: 0.6 ml / min., Sample concentration: 0.4% by weight eluent solution, sample solution injection volume: 50 μl, standard substance: Tosoh Corporation ) TSK standard polyethylene oxide (SE-150: weight average molecular weight 885,000, SE
-70: weight average molecular weight 510,000, SE-30:
Weight average molecular weight 340,000, SE-15: weight average molecular weight 170,000, SE-8: weight average molecular weight 9
5,000, SE-5: weight average molecular weight 46,000,
SE-2: weight average molecular weight 26,000), a reagent manufactured by Wako Pure Chemical Industries, Ltd. (polyethylene glycol 6000 having passed the first grade of Wako standard: weight average molecular weight 7,500, special grade ethylene glycol: weight average molecular weight 62).

[0054]

The inorganic pigment slurry dispersed by using the dispersant of the present invention has good fluidity even at a high concentration and excellent long-term dispersion stability.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C08L 33/02 C08L 33/02 C09C 1/02 C09C 1/02 1/36 1/36 F-term (reference) 4D077 AB04 AC05 BA01 BA02 BA07 BA13 CA12 CA13 CA15 DD05X DD09X DD17X DD20X DE02X DE10X 4J002 BG011 DE136 DE236 FA116 FD096 4J037 AA10 AA22 CC16 CC17 DD02 DD05 DD08 EE28 EE43 DAFF4 4100 100

Claims (5)

[Claims] 1. A water-soluble polymer represented by the formula (I) having a weight average molecular weight of 45,000 to 85,000 and a MW (weight average molecular weight) / MN (number average molecular weight) of 1.7 to 2.8. A 20% by weight aqueous solution of the polymer, having a viscosity at 25 ° C. of 25 to 50 mPa · s, a component having a weight average molecular weight of less than 10,000 in the polymer being 5 to 15% by weight, and a weight average molecular weight of 10,000 or more 6 components less than 100,000
0 to 80% by weight, and a dispersant for an inorganic pigment, wherein a component having a weight average molecular weight of 100,000 or more is 10 to 25% by weight. [In the formula, A and B are a molecular terminal group resulting from radical polymerization, a terminal group generated by hydrolysis thereof, a hydrogen atom or a hydroxyl group, respectively. M is a hydrogen atom, an alkali metal, an alkaline earth metal, ammonium or an amine. m and n are integers of 0 or more, and m / 9 ≧ n.
However, m and n do not become 0 at the same time. If the number of carboxylic acid groups in the molecule is α and the number of carboxylic acid groups is β
0 ≦ α / β ≦ 0.053. ] 2. An inorganic pigment having an average particle size of 0.3 to 0.4 μm.
2. The dispersant according to claim 1, which is a rutile type titanium dioxide. 3. An inorganic pigment having a BET specific surface area of 1 to 10 m ² /
g, average minor axis 0.1-1.0 μm, average major axis 1.0-
The dispersant according to claim 1, which is a spindle-shaped calcite light calcium carbonate having a diameter of 3.0 µm. 4. An inorganic pigment having a BET specific surface area of 5 to 15 m ² /
g, a cubic calcite-based light calcium carbonate having an average particle size of 0.1 to 2.0 μm. 5. An inorganic pigment having a BET specific surface area of 20 to 50 m
^2. The dispersant according to claim 1, wherein the dispersant is a colloidal calcium carbonate having a particle size of ² / g and an average particle size of 0.01 to 1.0 μm.