JPS636492B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a highly concentrated slurry with good fluidity from synthetic calcium carbonate. Calcium carbonate is used as a filler for various plastics, as filler for paper, and as a coating agent.When making a highly concentrated slurry from it, natural products have good fluidity, but synthetic products have good fluidity. Since there is a problem that liquidity becomes inferior,
The upper limit for synthetic calcium carbonate slurry is approximately 60% concentration, which inevitably limits its uses. The present inventors have conducted extensive research to overcome these drawbacks of synthetic calcium carbonate and to develop a method for producing slurry from synthetic calcium carbonate with good fluidity and a high concentration of 65% or more. As a result of repeated research, it was unexpectedly discovered that the objective could be achieved by performing two-stage dispersion treatment with different shear rates using a specific dispersant, and based on this knowledge, the present invention was made. . That is, the present invention uses a dispersant having a weight average molecular weight of 8,000 to 1.0 μm for cubic synthetic calcium carbonate having a water content of 1% by weight or less and a particle size of 0.1 to 1.0 μm.
150,000 and an alkali metal salt or ammonium salt of an acrylic polymer or copolymer containing at least 90 mol% of acrylic acid units in a proportion of 0.5 to 5.0% by weight based on the total amount of synthetic calcium carbonate and 35% by weight based on the total amount of the final mixture. After adding an aqueous solution dissolved in water in an amount below %, first the shear rate is 10 ² ~ 10 ³ sec ^-1
Perform primary dispersion at a shear rate of 10 ⁵ ~
The present invention provides a method for producing a highly concentrated slurry with a solid content of 65% by weight or more and good fluidity, which is characterized by performing secondary dispersion at 10 ⁷ sec ^-1 . In the present invention, finely divided synthetic calcium carbonate having a cubic particle shape and a particle size of 0.1 to 1.0 μm, preferably 0.2 to 0.5 μm is used. Such synthetic calcium carbonate powder is usually provided with a water content of 1% by weight or less and is used as is in the method of the present invention, but this water content is not so important in the present invention. Further, the dispersant used in the method of the present invention is an alkali metal salt or ammonium salt of a polymer having a weight average molecular weight of 8,000 to 150,000 and containing at least 90 mol % of acrylic acid units. Such polymers include homopolymers of acrylic acid and acrylic acid 90
It includes a copolymer of mol% or more and 10 mol% or less of another copolymerizable monomer. Comonomers to be copolymerized with acrylic acid include, for example, ethylenically unsaturated mono- or polycarboxylic acids such as methacrylic acid, maleic acid, fumaric acid, and itaconic acid, and amide groups such as acrylamide, methacrylamide, and N-methylolacrylamide. Containing monomers, aliphatic or aromatic vinyl sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, vinyltoluenesulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, sulfopropyl (meth)acrylate; Esters such as methyl (meth)acrylate, butyl methacrylate, hydroxyethyl (meth)acrylate; styrene,
Examples include vinyltoluene, vinyl acetate and acrylonitrile. Among the above comonomers, those containing carboxyl groups or sulfonic acid groups can be subjected to copolymerization in the form of their alkali metal salts or ammonium salts; It is then neutralized.
These comonomers may be used alone or in combination of two or more. Among these comonomers, preferred are those containing carboxyl groups or sulfonic acid groups and their alkali metal salts, preferably sodium salts or ammonium salts. In copolymer dispersants, acrylic acid units are 90
If it is less than mol%, the fluidity is poor and the object of the present invention cannot be achieved, which is not preferable. Also,
The polymer or copolymer containing at least 90 mol% of acrylic acid units has a weight average molecular weight of 8000 to
It is important that the molecular weight be within the range of 150,000; even if the molecular weight is lower or higher, the performance as a dispersant will deteriorate and the object of the present invention cannot be achieved.
The preferred molecular weight is about 30,000 to 130,000, particularly about 40,000 to 100,000. The weight average molecular weight in the present invention can be easily measured using gel permeation chromatography using polyethylene glycol of known molecular weight as a standard substance. In the method of the present invention, such a dispersant is used in an amount of 0.5 to 5.0% by weight of the synthetic calcium carbonate, and is mixed with 35% by weight or less of water in the final slurry to be sheared. It performs two-stage dispersion treatment with different speeds, and due to these combined processing requirements, the solid content concentration can be reduced to 65% by weight.
As described above, a synthetic calcium carbonate aqueous slurry having practically desirable fluidity can be easily prepared. If the amount of dispersant used is less than 0.5% by weight of the synthetic calcium carbonate, the dispersing power will be insufficient and a slurry with good dispersion stability cannot be obtained, and if it exceeds 5% by weight, the fluidity of the slurry will decrease, which is not preferable. . In addition, the water used for slurry formation is
Matches the water concentration of the final slurry
An amount of up to 35% by weight is used, and when adding it, it is preferable to add the dispersant to be used in advance to the water and mix it with the synthetic calcium carbonate powder as an aqueous solution. However, some water can also be used for wetting the synthetic calcium carbonate powder. In the method of the present invention, a mixture of synthetic calcium carbonate powder and an aqueous dispersant solution is first subjected to a primary dispersion treatment at a shear rate of 10 ² to ^{10 3} sec ^-1 , and then subjected to a primary dispersion treatment at a shear rate of 10 ⁵ to 10 ⁷ sec ^-1. Combinatorial processing with quadratic distributed processing is extremely important. In this two-stage treatment with different shear rates, a combination of shear rates within the above ranges is most effective, and good slurry fluidity can be obtained. Examples of the dispersing machine used for the primary dispersion include dispersing machines that provide a high shear rate, such as a disk cavitation mixer, a stator rotor, a Kedem mill, a colloid mill, and a Coles mixer. To perform primary dispersion using these dispersing machines, the method is usually to fill a cylindrical container with a predetermined amount of water, add a predetermined dispersant, and add a predetermined amount of synthetic calcium carbonate powder while stirring with the dispersing machine. can be adopted with practical advantage, and after mixing 10 ² ~
Primary dispersion can be carried out by performing dispersion treatment at a shear rate of 10 ³ sec ^-1 for a time period of, for example, about 5 to 30 minutes. In the present invention, the slurry subjected to the primary dispersion treatment is subjected to the dispersion treatment using a secondary dispersion machine having a high shear rate, such as a sand mill type dispersion machine, at a shear rate higher than the shear rate in the primary dispersion. is important. For this secondary dispersion, it is advantageous to use a dispersion machine that is equipped with a stirring blade of any shape and a crushing medium such as glass beads in a container, and rotates these to stir and disperse the filled fine particles at a high shear rate. In such a dispersing machine, the primary dispersion treatment slurry is supplied at a constant rate, and the slurry is dispersed within the dispersion system for a residence time of, for example, 5 to 60 minutes. This distributed processing is 1
However, it is also possible to perform cyclic processing multiple times as necessary. When the shear rate in the primary dispersion treatment deviates from the above range, it is difficult to form a good fluidity slurry in the secondary dispersion treatment, and also when the shear rate in the secondary dispersion treatment deviates from the above range, it is difficult to form a slurry with good fluidity. This is not preferred because a slurry with good fluidity cannot be obtained. In this way, by combining a specific synthetic calcium carbonate with a specific dispersant and subjecting the highly concentrated water mixture to two-step dispersion treatment, we have created a product that could not be obtained with conventional synthetic calcium carbonate slurry.
It was a completely unexpected discovery that a practically fluid slurry with a high solid content concentration of 65% by weight or more could be provided. As described above, according to the method of the present invention, a slurry having a solid content concentration of 65% by weight or more and good fluidity can be easily obtained. The high-concentration slurry obtained by the method of the present invention has a good fluidity especially when agitated at high shear rate, and by utilizing this desirable property, synthetic calcium carbonate can be produced, which has not been possible for low-concentration slurries in the past. The high-density color formulation used can also be used in paper manufacturing coating processes, and the range of applications is expected to expand significantly. Next, the present invention will be explained in more detail with reference to Examples. Example 1 1.5 g of water was placed in a stainless steel (SUS304) container with a capacity of 3 of a Coles type mixer having a stirring blade with a blade diameter of 250 mmφ, and while stirring, 39.8 g of sodium polyacrylate was added and dissolved as a dispersant. . Then particle size 0.2~0.4μ
m cube-shaped synthetic calcium carbonate 4Kg (moisture content
0.6% by weight) and the stirring speed of the blade.
Primary dispersion treatment was performed for 20 minutes at 10000 rpm (shear rate 5×10 ² sec ⁻¹ ). The solid content concentration at this time is 71.3
It was %. Next, hard glass beads with a particle size of 1 to 1.5 mmφ
3500 g of the above primary dispersion treatment slurry was added to a 4.9 capacity attriter IS type (manufactured by Mitsui Miike Seisakusho) dispersion machine with a 4500 g filler and a 13.5 cm long rod-shaped stirring blade, and the rotational speed Dispersion treatment was carried out for 20 minutes at 260 rpm (shear rate 1×6 ⁶ sec ⁻¹ ). This treatment was carried out in the same manner for sodium salt dispersants of polyacrylic acid of various molecular weights.
The viscosity and high-speed shear viscosity of each of the obtained secondary dispersion treated slurries were measured. The viscosity of the slurry was determined using a B-type viscometer at the rotational speed.
The 1-minute value was measured at 60 rpm and a temperature of 25°C, and the high-speed shear viscosity was measured at 2200 rpm using a Hercules high-speed shear viscosity and a BBob. Table 1 summarizes the various molecular weights of sodium polyacrylate used as a dispersant and the respective results.

[Table] * Cannot be made into slurry Figures 1 and 2 of the attached drawings are graphs showing the relationship between the molecular weight of the dispersant and the slurry viscosity in Table 1. Figure 2 shows measurements taken using a Hercules high-speed shear viscometer. Example 2 A secondary dispersion treatment slurry was prepared in the same manner as in Example 1 using cubic synthetic calcium carbonate having a particle size of 0.5 to 0.8 μm and sodium polyacrylate having a molecular weight of 71,000 as a dispersant. The resulting slurry was measured using a B-type viscometer and a Hercules high-speed shear viscometer under the same conditions as in Example 1, and found to be 1350 cps and 95 cps, respectively. Example 3 2900 g of cubic synthetic carbon calcium with a particle size of 0.15 to 0.2 μm (water content), molecular weight 71000 as a dispersant
A primary dispersion treatment was performed using 29 g of sodium polyacrylate under the same conditions as in Example 1, with the solid content concentration of the slurry being 65% by weight. The resulting slurry was subjected to secondary dispersion treatment in the same manner as in Example 1, and its viscosity was measured to be 3100 cps.
(Type B) and 260 cps (Hercules) were obtained. Example 4 Put 1 m ³ of water into a stainless steel copper (SUS304) container with a capacity of 2 m ³ and add and dissolve 26.7 kg of sodium polyacrylate with a molecular weight of 71,000. Cubic synthetic calcium carbonate 2670Kg (moisture content 0.6% by weight)
using a Coles type mixer with a blade diameter of 508 mmφ at a rotation speed of 939 rpm (shear speed 4.2 ×
10 ² sec ^-1 ) for 30 minutes for primary dispersion. The obtained slurry having a solid content concentration of 71.5% by weight was subjected to secondary dispersion treatment as follows. Filled with 10 kg of hard glass beads with a particle size of 1 to 1.5 mmφ, a 200 mmφ disk-type stirring blade 5
Using a sand grinder with a capacity of 15 stages (manufactured by Igarashi Seisakusho), the blade rotation speed was 220 rpm.
(5.0×10 ⁵ sec ⁻¹ ), the above primary dispersion slurry was supplied at a rate of 2.3 Kg/min. The viscosity of the slurry subjected to the secondary dispersion treatment using a B-type viscometer and a Hercules high-speed shear viscometer was 1410 cps and 97 cps, respectively. Example 5 Various secondary dispersion slurries were prepared in the same manner as in Example 1 except for changing the type of dispersant. The dispersant used in the preparation is as follows. A Sodium polyacrylate with a molecular weight of 71,000 B Ammonium salt of a 92 mol% acrylic acid-8 mol% itaconic acid copolymer with a molecular weight of 72,000 C Ammonium salt of a 50 mol% acrylic acid-50 mol% itaconic acid copolymer with a molecular weight of 71,000 D Sodium salt of 92 mol% acrylic acid-8 mol% maleic acid copolymer with molecular weight 68,000 E Sodium salt of 95 mol% acrylic acid-5 mol% vinyl sulfonic acid copolymer with molecular weight 70,000 F Acrylic acid 92 with molecular weight 72,000 Mol% - Sodium salt of 8 mol% methacrylic acid copolymer G Sodium salt of 92 mol% acrylic acid - 8 mol% methacrylic acid copolymer with a molecular weight of 170000 Among the above dispersants, A, B, D, E, and F are These are related to the present invention, and C and G are outside the present invention. Table 2 shows the results of measuring the viscosity of the slurry prepared using each of these dispersants.

[Table] The slurries prepared using dispersants D and E were allowed to stand for 24 hours, but no hard cake precipitation was observed. Also, these 24
The viscosity after time was as shown in Table 3.

[Table] As shown, the viscosity hardly increases even after being left for 24 hours. Comparative Example A slurry for primary dispersion treatment was prepared in the same manner as in Example 1 using cubic synthetic calcium carbonate having a particle size of 0.2 to 0.4 μm and sodium polyacrylate having a molecular weight of 71,000 as a dispersant. The obtained slurry was measured using a B-type viscometer and a Hercules high-speed shear viscometer under the same conditions as in Example 1.
The viscosity was 1720 cps, and the viscosity could not be measured using a Hercules high-speed shear viscometer.

[Brief explanation of the drawing]

FIGS. 1 and 2 are graphs showing the relationship between the molecular weight of a sodium polyacrylate dispersant and the viscosity and high-speed shear viscosity of a secondary dispersion treatment slurry.

Claims (1)

[Claims] 1. For cubic synthetic calcium carbonate having a water content of 1% by weight or less and a particle size of 0.1 to 1.0 μm, an acrylic polymer having a weight average molecular weight of 8,000 to 150,000 and containing at least 90 mol% of acrylic acid units as a dispersant or The amount of alkali metal salt or ammonium salt of the copolymer is 0.5 to 5.0 per total amount of synthetic calcium carbonate.
After adding an aqueous solution dissolved in water in an amount of not more than 35% by weight based on the total amount of the final mixture in a proportion of % by weight, first a primary dispersion is carried out at a shear rate of 10 ² to ^{10 3} sec ^-1 ,
A method for producing a highly concentrated synthetic calcium carbonate slurry having a solid content of 65% by weight or more and having good fluidity, which comprises then performing secondary dispersion at a shear rate of 10 ⁵ to ^{10 7} sec ^-1 .