JPH07316999A - Pigment dispersing agent for coated paper - Google Patents

Abstract

PURPOSE:To obtain the subject dispersing agent, comprising a water-soluble salt of a copolymer comprising specific components and capable of well dispersing a pigment for coated paper and manifesting sufficient dispersing effects by addition thereof in a small amount thereto. CONSTITUTION:This pigment dispersing agent comprises a water-soluble salt (e.g. an alkali metallic salt or an ammonium salt) of a copolymer, obtained by copolymerizing (A) acrylic acid with (B) maleic anhydride at a molar ratio within the range of (50/50) to (95/5), especially (78/22) to (90/10) in the presence of a persulfate and a reducing agent and having 5-10 molecular weight distribution [Mw/Mn (weight-average/number-average molecular weights of the copolymer)] thereof. The dispersing agent is capable of manifesting sufficient effects on a pigment for coated paper such as heavy or light calcium carbonate, kaolin, clay, aluminum hydroxide or titanium oxide by addition thereof in a small amount thereto.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a dispersant for pigments for coated paper such as heavy and light calcium carbonate, kaolin, clay, aluminum hydroxide, satin white, titanium oxide, talc, and mixtures thereof.

[0002]

2. Description of the Related Art In producing coated paper such as art paper and coated paper, first, a so-called pigment for coated paper such as kaolin, clay and calcium carbonate is dispersed in water together with a dispersant, and a binder is added to the dispersion. As synthetic latex, starch, polymer such as casein is added to prepare a coating solution,
A method of coating and drying the coating liquid on the base paper is generally used. Various pigments are mixed and used for the purpose of improving printability. Therefore, the pigment dispersant for coated paper is required to have the following characteristics. To show effective dispersing effect for various pigments and mixed pigments. From the viewpoints of economy and quality of coated paper, it is possible to prepare a highly concentrated pigment dispersion with good dispersibility using a small amount. The stability of the viscosity of the pigment dispersion over time is excellent. Conventionally, as a pigment dispersant for coated paper, a phosphoric acid-based soda salt such as sodium tripolyphosphate and sodium hexametaphosphate, and an organic polymer-based dispersant such as sodium polyacrylate are used. However, such a dispersant is not yet satisfactory in terms of dispersion effect and stability over time.

To solve these drawbacks, Japanese Patent Publication No. 54-361
Japanese Patent Publication No. 66 and Japanese Patent Publication No. 56-47131 propose to use a copolymer of acrylic acid and maleic acid as a dispersant for coated paper. However, even with these dispersants, the dispersibility of the mixed pigment in the required quality of is insufficient, and also in the point that a high-concentration pigment dispersion liquid can be prepared with a small amount, which is the required quality of Was not.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the problems of dispersibility of these conventional dispersants, and provides a sufficient dispersing effect to various pigments for coated paper with a small addition amount. It is an object of the present invention to provide a dispersant for the pigment for coated paper shown below.

[0005]

The present invention provides a water-soluble salt of a copolymer of acrylic acid and (anhydrous) maleic acid,
This is made based on the finding that the above problems can be completely solved by setting the copolymerization ratio and the molecular weight distribution (Mw / Mn) within a specific range. That is,
In the present invention, the molar ratio of (a) acrylic acid to (b) (anhydrous) maleic acid is (a) / (b) = 50/50 to 95/5.
And a molecular weight distribution (Mw / Mn) of 3.5 to 10, which is composed of a water-soluble salt of the copolymer. Hereinafter, the present invention will be described in more detail. The monomer composition molar ratio of (a) acrylic acid and (b) maleic anhydride and / or maleic acid is (a) / (b) = 50/50 to 95/5, preferably 60/40 to 90/10, More preferably 78/22
~ 90/10. Molar ratio (a) / (b) is 50/5
When it becomes smaller than 0, the reaction rate of maleic acid becomes low,
The pigment dispersibility of the copolymer also deteriorates. On the other hand, the molar ratio is 95
Even if it becomes larger than / 5, the pigment dispersibility of the copolymer decreases.

The molecular weight distribution of the copolymer is 3.5 to 10, preferably 3.5 to 7. If the molecular weight distribution is smaller than 3.5, the versatility is lowered, and especially the dispersion performance for the mixed pigment is lowered. On the other hand, if it exceeds 10, the required addition amount increases. The number average molecular weight of the copolymer is 1000 to 200.
00 is suitable, and preferably 1000 to 10,000. If it is less than 1000, the pigment dispersion performance is poor, and it is 2000
If it exceeds 0, the viscosity of the aqueous solution of the copolymer increases and the handling property deteriorates. A method for producing a copolymer of acrylic acid and maleic acid is described in JP-B-56-54005 and JP-A-60-21241.
Various methods described in Japanese Patent Laid-Open No. 2-124711 and Japanese Patent Laid-Open No. 3-124711 are known. In particular, according to the production example described in JP-B-54-36166, a copolymer having the same acrylic acid / maleic acid molar ratio and molecular weight as that of the present invention can be obtained. However, these methods cannot provide the one which satisfies the condition of the molecular weight distribution of 3.5 to 10, which is an important requirement of the present invention. That is, the salt of the copolymer of acrylic acid and maleic acid produced by each of the above production methods is essentially different from that of this patent. That is, the method for obtaining the copolymer having the molecular weight and the range of the molecular weight distribution, which is the object of the present invention, is limited, and specifically, the method described below is preferable.

That is, maleic acid, water, and an alkali metal hydroxide or an aqueous solution thereof and / or ammonia or aqueous ammonia are charged into a container, and 50 to 80 equivalent% of the carboxyl group of maleic acid is converted to a salt-form concentration 1
It is advisable to prepare a maleic acid salt aqueous solution of 0 to 50% by weight, and polymerize while dropwise adding a 50 to 80% by weight aqueous solution of acrylic acid or its salt. As the polymerization initiator,
Persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate are preferably used in combination with a reducing agent such as phosphorous acid, hypophosphorous acid, or salts thereof. As the reducing agent, hypophosphorous acid is particularly preferable. Sodium acid is preferred. The persulfate and the reducing agent are preferably used in an amount of 1 to 6 mol% with respect to the monomer, and the total amount of the persulfate and the reducing agent is preferably less than 10 mol% with respect to the monomer.

The salt of the copolymer in the present invention is preferably an alkali metal salt such as sodium salt or potassium salt or an ammonium salt, but a part thereof is substituted with an alkaline earth metal salt such as magnesium or calcium. Well,
Further, the unneutralized portion may remain, and it may be water-soluble as a whole. If necessary, other copolymerizable monomers such as styrene sulfonic acid, hydroxypropyl acrylate, hydroxyethyl acrylate, methoxy polyethylene glycol methacrylate, phenoxy polyethylene glycol acrylate, and itaconic acid may be copolymerized within a range that does not impair the effects of the present invention. It may be polymerized, in which case the other copolymerizable monomer is 10% of the total monomer.
It is preferably within mol%. The dispersant thus obtained is usually used as an aqueous solution of 10 to 60% by weight. In use, water and a dispersant are added, and then a predetermined amount of pigment is added, followed by stirring and mixing with a stirrer equipped with stirring blades such as paddle type blades and turbine blades, a homomixer, etc. % By weight, preferably 65-80
A weight% pigment aqueous dispersion is obtained. The amount of the dispersant used is preferably 0.01 to 3.0% by weight based on the pigment. The order of adding the pigment, water, and the aqueous dispersant solution can be appropriately changed depending on the circumstances.

[0009]

INDUSTRIAL APPLICABILITY The dispersant of the present invention is applied to coated paper pigments such as heavy and light calcium carbonate, kaolin, clay, satin white, aluminum hydroxide, titanium oxide, and other pigments and mixtures thereof. In addition, it exhibits an excellent dispersion effect, and by using a small amount, a high-concentration and low-viscosity pigment dispersion liquid can be realized, and a high pigment concentration of 70% by weight or more is possible. In particular, it has a high versatility that it exerts its effect on various mixed pigments with a small addition amount.
Moreover, the viscosity of the pigment dispersion liquid is excellent in stability over time, and even if the pigment dispersion liquid is prepared and left standing for a long time, an increase in the viscosity can be suppressed. Next, production examples and examples of the salt of the acrylic acid / maleic acid copolymer of the present invention will be described.
The present invention is not limited to these production examples and examples.

[0010]

【Example】

Production Example 1: Production of Copolymer A-1 A device equipped with a stirrer, a thermometer, a reflux condenser, a dropping funnel, and a nitrogen introducing tube was used. 47.1 g (0.48 mol) of maleic anhydride, 127.7 g of water, and 48 40.0 g (0.48 mol; 50% maleic anhydride neutralization rate) of 4% by weight aqueous sodium hydroxide solution was charged and dissolved and neutralized, and further sodium hypophosphite (1
13.6 g (0.128 mol; 4 mol% relative to monomer) were dissolved and then heated to 100 ° C. under a nitrogen stream. Then, while maintaining the temperature at 100 ° C. under stirring, 245.0 g (2.72 mol) of an acrylic acid 80% by weight aqueous solution and 36.5 g (1 mol% of monomer) of an ammonium persulfate 20% by weight aqueous solution were taken from different nozzles for 3 hours. Dropped. Further, the temperature was kept at the same temperature for 1 hour to complete the polymerization reaction. After cooling, the solution was neutralized with a 48% by weight aqueous solution of sodium hydroxide to a pH of 7.5, and further diluted with water to obtain a copolymer aqueous solution with a concentration of 35% by weight.

Production Examples 2-10: Copolymers A-2 to A-1
Production of 0 As shown in Table 1, under substantially the same polymerization conditions as in Production Example 1 except that the monomer composition, the type and amount of the polymerization initiator, the amount of the reducing agent, and the type and amount of the alkali were changed. The same operation was performed to obtain a copolymer aqueous solution. In Production Example 8, a 80% by weight aqueous solution of acrylic acid neutralized by half with a 48% by weight aqueous solution of sodium hydroxide was added dropwise. Further, in Production Example 9, sodium hypophosphite (monohydrate) was dissolved in an acrylic acid 80% by weight aqueous solution and added dropwise with the acrylic acid aqueous solution. Production Examples 11 and 12: Comparative Copolymers B-1 and B-2 As shown in Table-1, the monomer composition, the type and amount of the polymerization initiator, the amount of the reducing agent, and the amount of the alkali were changed. Except for the above, substantially the same operations were performed under substantially the same polymerization conditions as in Production Example 1 to obtain an aqueous copolymer solution.

Production Example 13: Comparative Copolymer B-3 In the apparatus shown in Production Example 1, 125.5 g (1.28 mol) of maleic anhydride, 124.9 g of water, and 106.7 g (1.28 mol of 48% by weight aqueous sodium hydroxide solution) were added. A maleic anhydride neutralization rate of 50%) was charged, dissolved and neutralized, and then heated to 70 ° C. under a nitrogen stream. Then, while maintaining the temperature at 70 ° C. under stirring, 173.0 g (1.92 mol) of 80% by weight acrylic acid aqueous solution, 121.7 g of 30% by weight ammonium persulfate aqueous solution (5 mol per monomer), and 22.0 g of 10% by weight hydrogen peroxide aqueous solution ( 3 mol% monomer) was added dropwise from separate nozzles over 5 hours. Further, the temperature was kept at the same temperature for 1 hour to complete the polymerization reaction. After cooling, the pH is adjusted with a 48% by weight aqueous solution of sodium hydroxide.
The solution was neutralized to 7.5 and further diluted with water to obtain a copolymer aqueous solution having a concentration of 35% by weight. Production Example 14: Comparative Copolymer B-4 156.9 g of maleic anhydride (1.60 mol, 176.4 g of water, and 48% by weight aqueous solution of sodium hydroxide) were added to the apparatus shown in Production Example 1.
After 200.0 g (2.40 mol; maleic anhydride neutralization rate: 75%) was charged and dissolved / neutralized, the mixture was heated to 100 ° C. under a nitrogen stream. Next, while maintaining the temperature at 100 ° C. under stirring, 144.1 g (1.60 mol) of an acrylic acid 80% by weight aqueous solution and 73.0 g (2 mol% of monomer) of an ammonium persulfate 20% by weight aqueous solution were respectively taken from different nozzles for 3 hours. Dropped. Further, the temperature was kept at the same temperature for 1 hour to complete the polymerization reaction. After cooling, the pH is adjusted with a 48% by weight aqueous solution of sodium hydroxide.
The solution was neutralized to 7.5 and further diluted with water to obtain a copolymer aqueous solution having a concentration of 35% by weight.

Production Example 15: Comparative Copolymer B-5 As shown in Table 1, except that the monomer composition, the kind and amount of the polymerization initiator, the amount of the reducing agent, and the amount of the alkali were changed. Under substantially the same polymerization conditions as in Example 1, substantially the same operation was carried out to obtain an aqueous copolymer solution. Table 1 collectively shows the monomer composition and production conditions used in Production Examples 1 to 15. The number average molecular weight (Mn) and molecular weight distribution (Mw / Mn) of each of the obtained copolymers were measured under the following conditions using a GPC system (8000 series) manufactured by Tosoh Corporation. Column: Tosoh PW6000XL + PW3000XL Mobile phase: Phosphate buffer + 0.1M saline Standard substance: Sodium polyacrylate (POLYSCIENCE)
(Made)

[0014]

[Table 1] Table-1 Sun monomer composition Initiator type Reducing agent Alkali type Polymerization pull (mol%) and amount used SPH and MA initial temperature Production example name AA MA IA (mol%) ^{* 1} (mol%) ^{* 1} Neutralization rate (% ) (℃) 1 A-1 85 15-APS, 1.0 4.0 48% NaOH, 50 100 2 A-2 80 20-NPS, 1.0 4.0 48% NaOH, 75 100 3 A-3 95 5-APS, 2.0 2.0 48% NaOH, 75 100 4 A-4 80 20-APS, 1.0 3.0 25% NH3, 50 100 shots 5 A-5 95 5-NPS, 3.0 1.0 48% NaOH, 75 100 6 A-6 60 40-NPS, 3.0 5.0 48% NaOH, 50 100 7 A-7 80 20-APS, 1.0 2.0 48% NaOH, 50 100 bright 8 A-8 50 50-NPS, 2.0 2.0 48% NaOH, 75 100 9 A-9 60 40- NPS, 2.0 1.0 48% NaOH, 75 70 10 A-10 47.5 7.5 5 APS, 3.0 1.0 48% NaOH, 75 100 11 B-1 98 2-APS, 2.0 2.0 48% NaOH, 50 100 Ratio 12 B-2 45 55-NPS, 3.0 1.0 48% NaOH, 75 100 13 B-3 60 40-APS, 5.0 − 48% NaOH, 50 70 Compare H ₂ O ₂ , 3.0 14 B-4 50 50-APS, 2.0 − 48% NaOH , 75 100 Examples 15 B-5 95 5-NPS, 4.0 6.0 48% NaOH, 75 100 [abbreviation in table] * 1 pair monomer AA: acrylic acid (80% aqueous solution) MA: maleic anhydride IA: itaconic acid SPH: sodium hypophosphite (monohydrate) APS: ammonium persulfate NPS: sodium persulfate

Table 2 shows the measurement results of the number average molecular weight and the molecular weight distribution.

[0016]

[Table 2] Table-2 Sample name Mn Mw / Mn A-1 2600 4.1 book A-2 3000 5.0 A-3 5000 4.0 shot A-4 3500 6.0 A-5 4300 10.0 Mear A-6 1300 3. 7 A-7 6200 3.5 Product A-8 3000 4.3 A-9 18000 5.5 A-10 3200 4.8 B-1 4800 4.0 Ratio B-2 3700 5.1 Comparison B-3 5000 12.0 Goods B-4 6000 3.0 B-5 800 3.8

Example 1 The properties of the various copolymers produced as described above as a pigment dispersant were investigated by the following methods. The various pigments shown in Table-3, water, and the copolymer shown in the production example were charged into a container, and the mixture was mixed with TK Auto Homo Mixer manufactured by Tokushu Kika Kogyo Co., Ltd.
The mixture was stirred at 3000 rpm for 20 minutes to prepare 500 g of a pigment aqueous dispersion having the pigment concentration shown in Table-3. The copolymer was added to the pigment so that the solid content was 0.2% or 0.5%. 25 ° C. of the pigment aqueous dispersion thus prepared
Viscosity was measured by a B-type rotational viscometer manufactured by Tokyo Keiki Co., Ltd. Furthermore, in order to confirm the stability of the prepared aqueous pigment dispersion over time, the viscosity was measured under the same conditions after standing for 1 week. The results are shown in Table-4.

[0018]

[Table 3] Table-3 Pigment composition (wt%) Pigment water dispersion heavy calcium carbonate * 1 Light calcium carbonate * 2 Kaolin clay * 3 Pigment concentration (wt%) Pigment 1 0 100 0 66 Pigment 2 0 0 100 55 55 Pigment 3 600 40 68 Pigment 4 60 20 20 70 * 1 Average particle size 1.5 μm, irregular shape * 2 Average particle size 0.3 μm, cube * 3 Particle size 2 μm or less 95% or more, hexagonal plate shape

[0019]

[Table 4] Table-4 (Part 1) Co-polymer Pigment water dispersion viscosity (cP) Sample name Addition amount Pigment 1 Pigment 3 (wt%) Initial 1 week later Initial 1 week A-1 0.2 350 420 420 80 150 0.5 0.5 80 90 135 150 A-2 0.2 500 580 85 85 150 0.5 70 75 130 140 140 Actual A-3 0.2 300 390 75 75 160 0.5 85 100 140 140 160 A-4 0.2 650 840 145 250 250 0.5 110 130 150 180 A-5 0.2 700 910 170 270 0.5 130 155 140 140 170 A-6 0.2 700 920 120 120 210 0.5 140 180 120 160 160 A-7 0.2 450 540 85 150 150. 5 70 80 135 150 A-8 0.2 750 990 200 320 320 0.5 150 180 180 125 150 Example A-9 0.2 700 850 130 130 230 0.5 110 130 140 140 170 A-10 0.2 750 950 180 180 300 0.5 135 135 170 135 170 B-1 0.2 500 1050 150 380 Ratio 0.5 130 260 220 370 B-2 0.2 Not slurried-Not slurried-0.5 500 1000 1000 160 340 Comparison B-3 0.2 1200 2300 250 510 510 0.5 120 150 150 200 310 B-4 0.2 Not slurried-800 1700 Example 0.5 220 220 370 230 400 B-5 0.2 1100 1800 620 1400 0.5 180 180 260 180 300

[0020]

[Table 5] Table-4 (Part 2) Copolymer Pigment water dispersion viscosity (cP) Sample name Addition amount Facial agent 2 (wt%) Initial 1 week later A-1 0.5 320 380 A-2 0.5 300 350 350 A-3. 5 370 480 A-4 0.5 360 460 A-5 0.5 370 490 Application A-6 0.5 230 300 A-7 0.5 290 350 A-8 0.5 150 200 Example A-9 0. 5 210 260 A-10 0.5 170 220 220 B-1 0.5 480 1000 B-2 0.5 No slurry-Comparison B-3 0.5 350 670 B-4 0.5 700 1500 B-5 0.5 560 920

[0021]

[Table 6] Table-4 (Part 3) Copolymer Pigment water dispersion viscosity (cP) Sample name Addition amount Facial agent 4 (wt%) Initial period 1 week later A-1 0.2 90 165 0.5 0.5 145 160 A-2 0.2 90 90 1600 .5 140 150 Actual A-3 0.2 80 80 170 0.5 155 180 A-4 0.2 160 280 0.5 0.5 170 200 A-5 0.2 230 230 360 0.5 160 185 Application A-6 0. 2 135 240 0.5 125 165 A-7 0.2 95 170 0.5 140 155 A-8 0.2 220 350 350 0.5 140 170 Example A-9 0.2 145 260 0.5 0.5 150 180 A- 10 without 0.2 200 335 0.5 150 190 B- 1 0.2 195 490 ratio 0.5 290 460 B-2 0.2 slurried - 0.5 210 500 compare B-3 0.2 320 50 0.5 260 440 B-4 0.2 1000 2200 Example 0.5 300 510 B-5 0.2 800 1800 0.5 230 360

Claims (3)

[Claims] 1. A molar ratio of (a) acrylic acid to (b) (anhydrous) maleic acid is (a) / (b) = 50/50 to 95.
A pigment dispersant for coated paper, comprising a water-soluble salt of a copolymer of / 5 and having a molecular weight distribution (Mw / Mn) of 3.5 to 10. 2. The number average molecular weight (Mn) of the copolymer is 10
The dispersant according to claim 1, which is from 0 to 20000. 3. The water-soluble salt of a copolymer of acrylic acid and (anhydrous) maleic acid is a carboxyl group of maleic acid.
To a maleic acid salt aqueous solution having a concentration of 0 to 80% and a concentration of 10 to 50% by weight, in the presence of a persulfate and a reducing agent, a 50 to 80% by weight aqueous solution of acrylic acid or a salt thereof is added dropwise. The dispersant according to claim 1 or 2, which is produced by polymerization.