JP4563057B2 - Dispersant for inorganic pigment - Google Patents

Description

  The present invention relates to an inorganic pigment dispersant suitably used when an inorganic pigment is dispersed in water or the like to obtain a slurry, and a pigment dispersion composition containing the dispersant.

  In dispersing an inorganic pigment in an aqueous medium to form a slurry, a polycarboxylate-based dispersant is used. For example, a slurry obtained by dispersing an inorganic pigment such as calcium carbonate in water with a polycarboxylate-based dispersant can impart smoothness and gloss to the surface by applying it to the surface of paper. . It is desirable that the slurry has a high concentration and a low viscosity so that the slurry can be uniformly and easily applied or can be easily mixed with other inorganic pigments.

  Further, in recent years, the above-described slurry has been demanded to reduce the viscosity under high shear in order to realize high-speed coating on the paper surface. In addition, in order to further improve the smoothness and gloss after the slurry is applied, the inorganic pigments such as calcium carbonate to be used are further finely divided, and the slurry has a higher concentration. However, it has been difficult to reduce the viscosity of a high-concentration slurry of finely divided pigments with a conventional polycarboxylate-based dispersant. For example, Patent Document 1 discloses an acrylic acid-maleic acid copolymer having a weight average molecular weight of 45,000 to 85000 and a viscosity of 25 to 50 mPa · s at 25 ° C. in a 20 wt% aqueous solution as a dispersant for an inorganic pigment. Although salt is disclosed, it is difficult to reduce the viscosity of light calcium carbonate having an average particle size of 0.5 μm or less as a slurry having a solid content of 70% by weight or more with such a dispersant. The viscosity under high shear has not reached a satisfactory level.

On the other hand, a dispersant having a high calcium ion and / or magnesium ion scavenging ability tends to lower the dispersibility of the inorganic pigment when the water contains a large amount of calcium ions and / or magnesium ions. Patent Documents 2 and 3 disclose salts of acrylic acid-maleic acid copolymers that are not easily affected by the metal ions. However, the copolymer disclosed in Patent Document 2 has a clay dispersibility, which is an evaluation index as a detergent composition, of 60% or more (in the presence of magnesium ions), and is disclosed in Patent Document 3. In the copolymer, the clay dispersibility is 50% or more (in the presence of calcium ions). However, in the copolymer having the clay dispersibility, it is possible to reduce the viscosity of the high-concentration slurry of the atomized pigment. It was impossible.
JP 2000-327946 A Japanese Patent No. 311454 JP 2000-53729 A

  The problem of the present invention is that it is possible to reduce the viscosity even in a high-concentration slurry of finely divided pigment, and is excellent in long-term dispersion stability of the low-viscosity slurry, and further, the viscosity of the slurry under high shear is reduced. An object of the present invention is to provide a dispersant for an inorganic pigment that can be kept small and a pigment dispersion composition containing the dispersant.

The present invention has a clay dispersibility of 35 to 45% in the presence of calcium ions 80 mg / L, a clay dispersibility of 50 to 59% in the presence of 21 mg / L magnesium ions, and a calcium ion scavenge capacity of 290 to 370 mgCaCO. ₃ / g, a salt of a copolymer of methacrylic acid and at least one unsaturated dibasic acid selected from maleic acid and fumaric acid or its anhydride (hereinafter referred to as methacrylic acid-unsaturated dibasic acid copolymer). Disclosed is a dispersant for inorganic pigments containing a polymer salt), and a pigment dispersion composition containing the dispersant for inorganic pigments, particularly a pigment dispersion composition for coated paper.

  The dispersant for inorganic pigments of the present invention is capable of lowering viscosity even in a high-concentration slurry of finely divided pigments as compared with conventional dispersants for inorganic pigments, and long-term dispersion of low-viscosity slurry. It is also excellent in stability, and furthermore, the viscosity of the slurry under high shear can be kept small.

The salt of the methacrylic acid-unsaturated dibasic acid copolymer used in the present invention lowers the viscosity of the high-concentration pigment slurry, stabilizes the low-viscosity slurry for a long period of time, and keeps the slurry viscosity under high shear low. In view of the above, the clay dispersibility in the presence of 80 mg / L of calcium ions is 35 to 45%, preferably 40 to 45%, and the clay dispersibility in the presence of 21 mg / L of magnesium ions is 50 to 59%, preferably is 51 to 56%, calcium ion capturing ability is 290~370mgCaCO ₃ / g, preferably 300~360mgCaCO ₃ / g, more preferably from 310~350mgCaCO ₃ / g.

  The “clay dispersibility” and “calcium ion scavenging ability” as used in the present invention are measured by the measurement methods described in the examples, and are values used as indicators of the properties of the dispersant for inorganic pigments. is there.

  The dispersant of the present invention contains a salt of a methacrylic acid-unsaturated dibasic acid copolymer having a clay dispersibility and a calcium ion scavenging ability within the above specified range, thereby increasing the fineness of the finely divided pigment. It is possible to lower the viscosity of the concentration slurry, stabilize the low viscosity slurry for a long period of time, and keep the viscosity of the slurry under high shear low. The reason for expressing such a remarkably excellent effect is not clear, but it is probably an inorganic pigment from the viewpoint of reducing the viscosity of a high-concentration slurry of finely divided pigments and stabilizing the low-viscosity slurry for a long period of time. It is thought that it is based on the excellent repulsive force (electrostatic and / or steric) by the dispersant adsorbed on the inorganic pigment and the viscosity of the slurry under high shear. From this viewpoint, it is probably based on the excellent steric repulsion due to the dispersant adsorbed on the inorganic pigment.

  Therefore, the dispersant of the present invention is appropriately defined by the clay dispersibility and the calcium ion scavenging ability. In addition, in the case of a dispersant containing a salt of a methacrylic acid-unsaturated dibasic acid copolymer whose clay dispersibility and calcium ion scavenging ability are outside the scope of the present invention, adsorption power and repulsive force (electrostatic and / or steric) ) Cannot be satisfied together, and the effects of the present invention cannot be obtained.

  The salt of the methacrylic acid-unsaturated dibasic acid copolymer of the present invention is a viewpoint that lowers the viscosity of a high-concentration slurry of pigment, stabilizes the low-viscosity slurry for a long period of time, and keeps the viscosity of the slurry under high shear low. Therefore, the methacrylic acid / unsaturated dibasic acid (molar ratio) is preferably 74/26 to 91/9, and the weight average molecular weight (Mw) is preferably 25,000 to 60,000.

  Further, from the viewpoint of reducing the viscosity of the high-concentration slurry of pigment and stabilizing the low-viscosity slurry for a long period of time, the methacrylic acid / unsaturated dibasic acid (molar ratio) is more preferably 74/26 to 87/13, and the weight The average molecular weight (Mw) is more preferably from 30000 to 55000, particularly preferably from 35000 to 50000, and most preferably from 40000 to 50000. Furthermore, from the viewpoint of keeping the viscosity of the slurry under high shear small, the methacrylic acid / unsaturated dibasic acid (molar ratio) is more preferably 80/20 to 91/9, and the weight average molecular weight (Mw) is 25,000 to 55000. Is more preferable, and 25000-50000 is particularly preferable.

  Therefore, the salt of the methacrylic acid-unsaturated dibasic acid copolymer of the present invention reduces the viscosity of the high-concentration pigment slurry, stabilizes the low-viscosity slurry for a long period of time, and keeps the slurry viscosity under high shear low. Therefore, the best methacrylic acid / unsaturated dibasic acid (molar ratio) is 80/20 to 87/13, and the weight average molecular weight (Mw) is 40000 to 50000.

  Here, the weight average molecular weight (Mw) is a value measured by the measuring method described in Examples.

  The salt of the methacrylic acid-unsaturated dibasic acid copolymer of the present invention is a viewpoint that lowers the viscosity of a high-concentration slurry of pigment, stabilizes the low-viscosity slurry for a long period of time, and keeps the viscosity of the slurry under high shear low. Therefore, the number average molecular weight (Mn) is preferably 20,000 to 40,000, the ratio of the weight average molecular weight to the number average molecular weight, and Mw / Mn is preferably 3 or less. Further, from the viewpoint of lowering the viscosity of a high-concentration slurry of pigment and stabilizing the low-viscosity slurry for a long period of time, the number average molecular weight (Mn) is more preferably 25000 to 35000, particularly preferably 27000 to 35000, and Mw / Mn is 1.25 to 3 is more preferable, and 1.25 to 2.5 is particularly preferable. Furthermore, the number average molecular weight (Mn) is more preferably 20000 to 35000 from the viewpoint of keeping the viscosity of the slurry under high shear small.

  Therefore, the salt of the methacrylic acid-unsaturated dibasic acid copolymer of the present invention reduces the viscosity of the high-concentration pigment slurry, stabilizes the low-viscosity slurry for a long period of time, and keeps the slurry viscosity under high shear low. Therefore, the best number average molecular weight (Mn) is 27000 to 35000, and Mw / Mn is 1.25 to 2.5.

  From the viewpoint of lowering the viscosity of a high-concentration slurry of pigment, stabilizing the dispersion of the low-viscosity slurry for a long period of time, and maintaining the viscosity of the slurry under high shear to be small, the salt of the methacrylic acid-unsaturated dibasic acid copolymer of the present invention The viscosity at 20 ° C. of the 20 wt% aqueous solution is preferably 9 to 24 mPa · s.

  Further, from the viewpoint of lowering the viscosity of the high-concentration slurry of pigment and stabilizing the low-viscosity slurry for a long period of time, the viscosity is more preferably 13 to 20 mPa · s, and particularly preferably 13.8 to 18.5 mPa · s. preferable. Furthermore, 9 to 18.5 mPa · s is more preferable from the viewpoint of keeping the viscosity of the slurry under high shear small.

  Therefore, from the viewpoint of reducing the viscosity of the high-concentration slurry of the pigment, stabilizing the dispersion of the low-viscosity slurry for a long period of time, and keeping the viscosity of the slurry low under high shear, the best viscosity is 13.8 to 18.5 mPa · s.

  The viscosity at 20 ° C. of a 20% by weight aqueous solution of a salt of a methacrylic acid-unsaturated dibasic acid copolymer is a value measured by the measurement method described in the examples.

  The salt of the methacrylic acid-unsaturated dibasic acid copolymer of the present invention is preferably at least one selected from alkali metal salts, alkaline earth metal salts, quaternary ammonium salts, ammonium salts, and organic amine salts.

  Examples of the alkali metal constituting the salt include sodium, potassium, and lithium. Examples of the alkaline earth metal include magnesium, calcium, and barium. Examples of the quaternary ammonium include tetramethylammonium hydroxide and triethylmethylammonium hydroxide. Examples of the organic amine include diethanolamine, triethanolamine, ethylenediamine, diethylenetriamine, triethylamine, and tributylamine.

  Among these, preferred are alkali metal salts, and sodium salts and potassium salts are more preferable from the viewpoint of lowering the viscosity of a high-concentration slurry of pigment and stabilizing the low-viscosity slurry for a long period of time. Ammonium salts are preferred for use in applications where ash content remains, such as electronic materials.

  The degree of neutralization of the salt of the methacrylic acid-unsaturated dibasic acid copolymer of the present invention is not particularly limited, but is usually preferably 50 to 99%, more preferably 70 to 99%.

  The content of the salt of the methacrylic acid-unsaturated dibasic acid copolymer in the dispersant of the present invention is preferably 97 to 100% by weight, and 98 to 100% in a category where the viscosity of the high-concentration slurry of pigment can be reduced. Is more preferable, and 99 to 100% is particularly preferable. In addition to this, unreacted methacrylic acid, maleic acid, fumaric acid and the like may be contained.

  Although the manufacturing method of the salt of the methacrylic acid-unsaturated dibasic acid copolymer of this invention is not specifically limited, For example, it can manufacture by the method shown below.

  Maleic acid or maleic anhydride and ion-exchanged water are charged into a reaction vessel so that the maleic acid concentration is 37% by weight or more, heated to 75 ° C., and then NaOH aqueous solution is twice the number of moles of maleic acid charged. To obtain maleic acid Na salt. Next, after heating to about 100 ° C., the aqueous methacrylic acid solution is adjusted so that the methacrylic acid / maleic acid (molar ratio) is 74/26 to 91/9, and the aqueous hydrogen peroxide solution is hydrogenated with methacrylic acid. Each is added dropwise over 3 to 5 hours so as to be 17 to 50 mol% with respect to the total charged moles of acid and maleic acid, and a polymerization reaction is performed. After completion of dropping, the mixture is aged at 100 ° C. for 1 to 10 hours. After completion of the reaction, the reaction solution is cooled to about 60 ° C., and an aqueous NaOH solution is added so that the pH is 8 to 9, thereby obtaining a Na salt of a methacrylic acid-maleic acid copolymer.

  The salt of the methacrylic acid-unsaturated dibasic acid copolymer of the present invention can also be produced by replacing maleic acid with fumaric acid in the above production method.

  Inorganic pigments of interest in the present invention are calcium carbonate, calcium phosphate, zinc phosphate, clay, bentonite, satin white, zinc white, bengara, ferrite, titanium oxide, alumina, magnesium oxide, talc, white carbon, cement, gypsum, Examples thereof include carbon black, titanate, and silicate, and calcium carbonate and titanate such as barium titanate are preferable.

  Specifically, the dispersant of the present invention is effective as a dispersant for light calcium carbonate production process, calcium carbonate wet grinding, paper coating paint, ferrite production process or electronic materials such as barium titanate. . It is also effective for ceramic pigments such as alumina.

  The dispersant of the present invention can be used effectively when obtaining a pigment dispersion composition for coated paper, electronic materials, ceramics, etc., and is particularly preferably used for coated paper. The pigment dispersion composition can be obtained by dispersing an inorganic pigment powder, powder ore or coarse particles in an aqueous medium using the dispersant of the present invention. Examples of the aqueous medium include water or a mixed solution of water and a water-soluble organic solvent such as ethyl alcohol or ethylene glycol, preferably water.

  The content of the pigment in the pigment dispersion composition is not particularly limited, but is preferably 65 to 85% by weight. Further, the content of the dispersant of the present invention in the pigment dispersion composition is not particularly defined, but is usually preferably 0.01 to 10% by weight, more preferably 0.05 to 5% by weight, based on the inorganic pigment. 0.05 to 3% by weight is particularly preferable.

  As a method for obtaining a pigment dispersion composition using the dispersant of the present invention, a usual slurrying method is used. For example, a method of adding a pigment to an aqueous solution in which a dispersant is dissolved and stirring and mixing, a method of adding water and a dispersant to the pigment, stirring and mixing, and the like can be mentioned. As a method of stirring and mixing, for example, a generally used stirring device such as a high-speed disper, a homomixer, or a ball mill can be used.

  In addition, when slurrying the pigment ore or coarse particles at the same time as pulverization, a method of adding water and a dispersant to the pigment ore or coarse particles and slurrying at the same time as the pulverization may be mentioned. A generally used wet pulverizer such as a bead mill can be used as a method of slurrying simultaneously with pulverization.

  In the following examples, the physical properties of the dispersant for inorganic pigment were measured by the following methods.

<Weight average molecular weight>
It measured by GPC (gel permeation chromatography) on the following conditions.
Column: TSK PWXL + G4000PWXL + G2500PWXL (both manufactured by Tosoh Corporation)
Column temperature: 40 ° C
Detector: RI or UV (210 nm)
Eluent: 0.2 mol / L phosphate buffer / acetonitrile (9/1)
Flow rate: 1.0 mL / min
Injection volume: 0.1 mL
Standard: Polyethylene glycol <Viscosity>
Using a BL type viscometer of Tokyo Keiki Co., Ltd., 20 mL of a 20% by weight aqueous solution of a dispersant was set in a BL adapter and allowed to stand in a constant temperature bath at 20 ° C. for 1 hour, and then measured at 30 rpm or 15 rpm. Hereinafter referred to as BL viscosity.

<Clay dispersibility>
The following procedure was followed. It should be noted that the method using calcium chloride dihydrate has the ability to disperse clay in the presence of 80 mg / L calcium ion, and the method using magnesium chloride hexahydrate has the ability to use 21 mg / L magnesium ion. Shows clay dispersibility.
1) Prepare a glycine buffer solution by adding ion exchange water to 60.56 g of glycine, 52.6 g of sodium chloride and 60 mL of 1N NaOH aqueous solution to make 600 g.
2) Add ion-exchanged water to 1000 g of calcium chloride dihydrate 0.3268 g or magnesium chloride hexahydrate 0.1937 g and 60 g of the prepared solution of 1) to prepare a dispersion.
3) Prepare 20 g of 0.1 wt% (solid content conversion) inorganic pigment dispersant aqueous solution.
4) Put 0.3g of JIS test powder 1,8 types (Kanto loam, fine particles: Japan Powder Industrial Technology Association) into the test tube, and add 2g of preparation liquid 27g and 3g of preparation liquid 3g. To do.
5) After sealing the test tube with parafilm, shake the test tube and check that there is no lump at the bottom of the test tube, then shake the test tube up and down 20 times.
6) Leave the test tube of 5) in a place not exposed to direct sunlight for 20 hours.
7) After 20 hours, collect 5 mL of the supernatant of the dispersion with a whole pipette into a 20 mL screw tube.
8) Measure the transmittance (T%) with a UV spectrometer (wavelength 380 nm, 1 cm cell).
The value obtained by subtracting the value of T% from 100 is defined as clay dispersibility (turbidity).

<Calcium ion scavenging ability>
1) Prepare a standard calcium ion solution.

0.01 mol / L calcium ion aqueous solution: a solution obtained by dissolving 1.4701 g of calcium chloride dihydrate in 1 kg of ion exchange water 0.001 mol / L calcium ion aqueous solution: ion exchange water to 100 g of the above 0.01 mol / L calcium ion aqueous solution Added to make 1 kg 0.0001 mol / L calcium ion aqueous solution: 100 g obtained by adding ion-exchanged water to 10 g of the above 0.001 mol / L calcium ion aqueous solution
2) Into a 100 mL beaker, add 10 mg of the inorganic pigment dispersant and 50 g of 0.001 mol / L calcium ion aqueous solution in terms of solid content.
3) Stir 50 g of each aqueous solution of 1) and the aqueous solution of 2) with a magnetic stirrer.
4) Add 4.8 wt% NaOH aqueous solution to each aqueous solution of 3) so that the pH is 9-11.
5) Add 1 mL of 4M-KCl aqueous solution to each aqueous solution of 4).
6) Using an Orion ion analyzer EA920, measure the amount of calcium ions with an Orion calcium ion electrode 93-20.
7) Measure the amount of calcium ions captured by the dispersant for inorganic pigment from the calibration curve, express the amount captured per gram of the solid content of the dispersant in mg in terms of calcium carbonate, and use that value as the calcium ion scavengeability. .

Production Example 1
[(A) Maleic anhydride 49.0 g] and [(B) ion-exchanged water 54.3 g] were charged in a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a nitrogen introduction tube, and a dropping funnel, and 75 ° C. After heating, [(C) 30 wt% NaOH aqueous solution 133.3 g] was added dropwise to obtain [(D) maleic acid Na salt aqueous solution]. Next, after heating to 100 ° C. under a nitrogen stream, while maintaining this temperature, [(E) 215.2 g of methacrylic acid] and [(F) 355.7% by weight aqueous hydrogen peroxide solution 125.7 g] were separately added. It dropped from the dropping funnel over [(G) 3 hours], and the polymerization reaction was performed. After completion of the dropping, aging was carried out at 100 ° C. [(H) 7 hours] to complete the polymerization reaction. After completion of the reaction, the reaction mixture was cooled and neutralized with [(I) 30 wt% NaOH aqueous solution] so that the pH was 8 to 9 while maintaining about 60 ° C., and [(J) methacrylic acid-maleic acid co-polymerized]. Combined sodium salt] was obtained. This is referred to as Dispersant 1.

Production Examples 2 to 10
(A) to (J) of Production Example 1 were changed as shown in Table 1 to produce a methacrylic acid-maleic acid copolymer salt. These are referred to as dispersants 2 to 10, respectively.

Comparative Production Examples 1-3
(A) to (J) of Production Example 1 were changed as shown in Table 1 to produce a methacrylic acid-maleic acid copolymer salt. These are referred to as comparative dispersants 1 to 3, respectively.

  In the table, MA represents maleic acid, MAA represents methacrylic acid, and% represents% by weight.

Comparative production example 4
In a reaction vessel similar to Production Example 1, 125.0 g of ion exchange water was charged, heated to 95 ° C., 363.5 g of methacrylic acid, 249.6 g of 49 wt% NaOH aqueous solution, 147.4 g of 35 wt% aqueous hydrogen peroxide solution, And 41.6 g of 30% sodium persulfate aqueous solution was dropped from another dropping funnel over 4 hours to carry out the polymerization reaction. After completion of the dropping, the mixture was aged at 100 ° C. for 7 hours to complete the polymerization reaction. After completion of the reaction, the reaction mixture was cooled and neutralized with a 49 wt% NaOH aqueous solution so as to have a pH of 8 to 9 while maintaining about 60 ° C to obtain a sodium salt of polymethacrylic acid. This is referred to as comparative dispersant 4.

  Methacrylic acid / maleic acid (molar ratio), weight average molecular weight (Mw), number average molecular weight of dispersants 1-10 and comparative dispersants 1-4 obtained in Production Examples 1-10 and Comparative Production Examples 1-4 ( Mn), Mw / Mn, BL viscosity, clay dispersibility in the presence of calcium ions or magnesium ions, and calcium ion scavengeability are summarized in Table 2.

Example 1
Dispersion beaker 500 mL, spindle-shaped calcite light calcium carbonate cake having a mean particle size of 0.45 μm (water content 28 wt%) 243.06 g, ion-exchanged water 1.11 g and dispersant 1-10 or comparative dispersant 1 -4 (diluted with ion-exchanged water and adjusted to a solid content of 30% by weight) was charged with 5.83 g, kneaded and then stirred with a homodisper manufactured by Tokushu Kika Kogyo Co., Ltd. (2500 rpm x 2 minutes) A primary dispersion slurry of calcium was prepared. Next, 1 mm glass beads were charged into this slurry at a ratio of 1.5 times the total charged amount, and further stirred while being kept at about 25 ° C. with a homodisper (7600 rpm × 15 minutes) to prepare a secondary dispersion slurry.

  After filtering out the glass beads, the B viscosity (25 ° C.) of the secondary dispersion slurry was measured after 1 minute at a rotational speed of the rotor of 60 rpm using a B-type viscosity measuring device manufactured by Tokyo Keiki Co., Ltd. In addition, this secondary dispersion slurry was allowed to stand at 250C for 30 days with 250 mL of polybin, and then shaken about 30 to 40 times. Thereafter, the B viscosity was measured in the same manner as described above. Further, the H viscosity (25 ° C.) of the secondary dispersion slurry after standing for 30 days was measured with an E-Bob at 4400 rpm and a sweep time of 5 seconds using a high shear viscosity measuring device manufactured by Kumagai Riki Kogyo Co., Ltd. . These results are shown in Table 3.

  In addition, as for secondary dispersion | distribution slurry, B viscosity (after the first day and 30 days) is 300 mPa * s or less, and what is H viscosity (after 30 days) is 100 mPa * s or less is favorable.

Example 2
Dispersion beaker 500 mL, spindle shaped calcite light calcium carbonate cake (water content 28% by weight) 243.06 g having an average particle size of 0.5 μm, 2.27 g of ion-exchanged water and dispersants 1 to 10 or comparative dispersant 1 ˜4 (diluted with ion-exchanged water and adjusted to a solid content of 30% by weight) was charged with 4.67 g. After kneading, the mixture was stirred (2500 rpm × 2 minutes) with a homodisper manufactured by Tokushu Kika Kogyo Co. A primary dispersion slurry of calcium was prepared. Next, 1 mm glass beads were charged into this slurry at a ratio of 1.5 times the total charged amount, and further stirred while being kept at about 25 ° C. with a homodisper (7600 rpm × 15 minutes) to prepare a secondary dispersion slurry.

  The B viscosity (first day and 30 days later) and H viscosity (30 days later) of the secondary dispersion slurry were measured in the same manner as in Example 1. These results are shown in Table 4.

  In addition, as for secondary dispersion | distribution slurry, B viscosity (after the first day and 30 days) is 300 mPa * s or less, and what is H viscosity (after 30 days) is 100 mPa * s or less is favorable.

Example 3
Disposable beaker 300mL, barium titanate 148g with an average particle size of 0.5μm, ion-exchanged water 49.04g and dispersant 1-10 or comparative dispersant 1-4 (diluted with ion-exchanged water and adjusted to 30% solid content) 2.96 g of the mixture was charged, and then stirred with a homodisper manufactured by Tokushu Kika Kogyo Co., Ltd. (2000 rpm × 2 minutes) to prepare a 74 wt% slurry. The obtained slurry was measured for B viscosity at 25 ° C. using a B-type viscometer manufactured by Tokyo Keiki Co., Ltd. after 1 minute at a rotational speed of the rotor of 60 rpm. Further, this slurry was allowed to stand at 250C for 30 days with 250 mL of polybin, and then shaken about 30 to 40 times. Thereafter, the B viscosity was similarly measured under the above conditions. These results are shown in Table 5.

  A slurry having a B viscosity (on the first day and after 30 days) of 150 mPa · s or less is good.

Claims (5)

The clay dispersibility in the presence of 80 mg / L calcium ions is 35 to 45%, the clay dispersibility in the presence of 21 mg / L magnesium ions is 50 to 59%, and the calcium ion scavenging ability is 290 to 370 mg CaCO ₃ / g. A salt of a copolymer of methacrylic acid and at least one unsaturated dibasic acid or anhydride selected from maleic acid and fumaric acid (hereinafter referred to as methacrylic acid-unsaturated dibasic acid copolymer salt) The methacrylic acid-unsaturated dibasic acid copolymer salt has a methacrylic acid / unsaturated dibasic acid (molar ratio) of 74/26 to 87/13 and a weight average molecular weight (Mw) Is 25000-60000, the number average molecular weight (Mn) is 20000-40000, and Mw / Mn ≦ 3 . Methacrylic acid - 20% by weight aqueous solution of a salt of an unsaturated dibasic acid copolymer, an inorganic pigment dispersant of claim 1 Symbol mounting a viscosity at 20 ° C. is 9~24mPa · s. The inorganic pigment dispersant according to claim 1 or 2 , wherein the inorganic pigment is at least one selected from calcium carbonate and titanate. Claim 1-3 pigment dispersion composition containing an inorganic pigment dispersant according to any one. The pigment dispersion composition according to claim 4 , which is for coated paper.