JP3286678B2 - Dispersant for calcium carbonate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a dispersant for calcium carbonate. More specifically, the present invention relates to a dispersant that imparts dispersibility and dispersion stability to calcium carbonate when producing a high-concentration aqueous calcium carbonate slurry.

[0002]

2. Description of the Related Art Calcium carbonate is used as an aqueous slurry dispersed in water in the fields of paper, paint and the like. Aqueous slurry of calcium carbonate is excellent in dispersibility, that is, it is low in viscosity at high concentration, and excellent in aging stability in order to make high quality product raw materials and easy handling. Need to be something. For example, when a white pigment is applied to paper or the like, it is preferable that the aqueous slurry has as little moisture as possible, that is, a high concentration and low viscosity, in order to increase the efficiency in the drying process after the application. Further, an aqueous slurry having excellent dispersibility and dispersion stability has been demanded from the viewpoint of coating workability and coating film properties. In addition, in terms of transportation and storage, in order to reduce costs, an aqueous slurry having a high concentration and a low viscosity, and at the same time, having excellent dispersion stability that does not settle in the transportation and storage tanks and form a hard cake is required. It has been. Therefore, it has been expected to provide a dispersant that can be used to prepare a high-concentration aqueous slurry having excellent dispersibility and dispersion stability with a small amount of addition.

[0003] Calcium carbonate is roughly classified into, for example, lime milk by adding water to quick lime and reacting it with carbon dioxide gas to obtain light calcium carbonate having a small particle size (about 0.01 to 1 µm) and natural calcium carbonate. There is heavy calcium carbonate having a relatively large particle diameter (about 1 to 10 μ) produced by grinding calcium carbonate. In recent years, demand for calcium carbonate having a small particle size has increased with the improvement in quality of products, and the amount of light calcium carbonate used has increased. However, the smaller the particle size, the worse the dispersibility and dispersion stability, and thus a better dispersant is required.

Conventionally, dispersants for this purpose include inorganic phosphates such as condensed phosphates such as pyrophosphate and hexametaphosphate, as well as zinc salts and silicates. On the other hand, as organic dispersants, polyacrylates and polycarboxylates such as maleic acid / isobutene copolymer salts (for example, JP-A-60-99334 and JP-A-62-132730) are known. is there.

[0005]

However, among these dispersants, the inorganic dispersants have a problem in dispersion stability of the obtained aqueous slurry and require a large amount of addition. As a result, there were serious drawbacks such as an increase in cost and a decrease in the performance of the coating film. Organic dispersants have relatively better performance than the above-mentioned inorganic dispersants. However, particularly when used for dispersion of light calcium carbonate having an average particle size of 1 μm or less, both dispersibility and dispersion stability have room for improvement.

Accordingly, an object of the present invention is to provide a dispersant for calcium carbonate which can obtain a low viscosity even in a high-concentration slurry by adding a small amount thereof and has excellent dispersion stability.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a dispersant for calcium carbonate comprising a salt of a hydrolyzate of a copolymer of maleic anhydride and an aliphatic conjugated diene.

[0008] The aliphatic conjugated diene constituting the copolymer of the present invention is, for example, an aliphatic conjugated diene having 4 to 7 carbon atoms, preferably 4 to 5 carbon atoms. Specifically, 1,3-butadiene,
Examples thereof include 1,3-pentadiene, isoprene, 1,3-hexadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, and 1,3-pentadiene. In particular, 1,3-butadiene and isoprene are preferred. One or more of these aliphatic conjugated dienes may be used in combination.

The copolymer of the present invention has a maleic anhydride unit content of 30 to 90 mol%, preferably 40 to 80 mol%, more preferably 45 to 75 mol%.
It is suitable for obtaining an excellent dispersion effect. The content of the maleic anhydride unit in the copolymer can be determined using CHN elemental analysis or CHN elemental analysis and NMR analysis. Further, the weight average molecular weight of the copolymer is 10
It is suitable for obtaining an excellent dispersing effect to be from 50,000 to 50,000, preferably from 2,000 to 30,000. Here, the weight average molecular weight can be determined by measurement by gel permeation chromatography (GPC).

The dispersant of the present invention is a salt of a hydrolyzate of the above copolymer. The hydrolyzate of the copolymer is usually a complete hydrolyzate, but may be a partial hydrolyzate in some cases. The compound used for preparing the salt of the hydrolyzate of the copolymer may be any compound that converts the hydrolyzate into a water-soluble salt, such as sodium, alkali metal compounds such as potassium, calcium, and barium. Examples include basic substances such as alkaline earth metal compounds, ammonia, and alkylamines. Among them, sodium hydroxide or ammonia is preferable.

Hereinafter, the method for producing the dispersant of the present invention will be described. The copolymer used for the dispersant of the present invention is obtained by subjecting maleic anhydride and an aliphatic conjugated diene to a radical copolymerization reaction in a solvent in the presence of a radical generator.

In the polymerization, the aliphatic conjugated diene is preferably continuously added to a mixture of maleic anhydride and a solvent. This is because if the aliphatic conjugated diene is previously charged together with maleic anhydride and the reaction solvent, the Diels-Alder reaction proceeds during the temperature increase or at the beginning of the polymerization reaction, and the yield may decrease. By continuously supplying the aliphatic conjugated diene, the polymerization reaction can be prioritized over the Diels-Alder reaction. The radical generator may be added in advance to a mixture of maleic anhydride and the reaction solvent, or may be added continuously as in the case of the aliphatic conjugated diene.

The radical generator used is determined in consideration of its half-life. For example, when the initiator is continuously supplied, it is preferable to use a radical generator having a half-life of 1 hour or less in the reaction temperature range. If the half-life is too long, the amount of radicals generated per unit time will decrease, and the Diels-Alder reaction will proceed preferentially over the polymerization reaction, possibly leading to a decrease in yield.

Examples of the radical generator include peroxyesters such as t-butylperoxy (2-ethylhexanoate) and t-butylperoxybenzoate;
Dialkyl peroxides such as di-t-butyl peroxide and dicumyl peroxide; 1,1-bis (t
-Butylperoxy) -3,3,5-trimethylcyclohexane and other peroxyketals.

The amount of the radical generator used is 0.05 to 15% by weight, preferably 0.5 to 10% by weight, based on maleic anhydride.
It is appropriate to set the weight%. If the amount is too small, the polymerization reaction will not proceed effectively. If the amount is too large, the molecular weight will be too low, and it is not preferable from the viewpoint of safety and economy.

Examples of the solvent include hydrocarbons such as benzene, toluene, xylene and cyclohexane; ketones such as acetone, cyclohexanone and methyl ethyl ketone; esters such as ethyl acetate and isopropyl acetate; ethers such as dibutyl ether, tetrahydrofuran and dioxane; Alternatively, dimethylsulfoxide, dimethylformamide, gamma-butyrolactone and the like can be used. These solvents can be classified into those in which maleic anhydride is dissolved but the copolymer is insoluble, and those in which both maleic anhydride and the copolymer are soluble. With the former type of solvent, the polymerization proceeds as a precipitation polymerization or a suspension polymerization in the presence of a suitable dispersant. On the other hand, when the latter type of solvent is used, it proceeds as solution polymerization. Solvents such as amines and alcohols are not suitable for reacting with maleic anhydride or the resulting copolymer.

The amount of the solvent used is not particularly limited, but is preferably such that maleic anhydride, aliphatic conjugated diene and radical generator are dissolved to form a homogeneous system.

When the radical generator is continuously supplied, the reaction temperature is preferably 90 ° C. or higher. If the temperature is lower than this, the average molecular weight of the copolymer becomes too high than a desired value, or three-dimensional cross-linking easily occurs, and the copolymer cannot be used as a water-soluble copolymer. On the other hand, the upper limit of the reaction temperature is not particularly limited. However, in order to set the average molecular weight of the obtained copolymer to a desired value, 1 is required.
The temperature is preferably lower than 80 ° C. Considering the average molecular weight of the copolymer and the reaction time, the reaction temperature is 100 to 1
More preferably, it is in the range of 60 ° C.

Since the polymerization reaction has been substantially completed after the addition of the aliphatic conjugated diene and the radical generator, the polymerization reaction may be terminated upon completion of the addition, but the unreacted monomer and the radical generator are completely consumed. Therefore, it is preferable to continue the reaction for a certain period of time.

After completion of the reaction, the copolymer obtained is hydrolyzed and neutralized with a basic substance such as an alkali metal compound, an alkaline earth metal compound, ammonia or an alkylamine to form a water-soluble salt. At this time, the copolymer precipitated in the precipitation or suspension polymerization is recovered by filtration or decantation of the supernatant. If necessary, it can be further washed with a poor solvent. On the other hand, in solution polymerization, a copolymer is precipitated by adding a reaction solution to a large amount of a poor solvent, and the copolymer is recovered by filtration separation or decantation of a supernatant.

The copolymer thus recovered is heated to reflux with water or water to which a basic substance such as an alkali metal compound is added, or steam is introduced after the completion of the reaction, and the residual solvent is distilled off by steam distillation. The solvent is distilled off and hydrolyzed to obtain an aqueous solution. further,
The aqueous solution of this hydrolyzate is adjusted to a degree of neutralization with a basic substance such as an alkali metal compound, and finally becomes a water-soluble salt. At this time, it is preferable that the aqueous solution be in a neutral to weakly alkaline region.

The dispersant of the present invention exhibits an excellent dispersing effect in the range of 0.05 to 5% by weight, preferably 0.1 to 2% by weight, based on calcium carbonate.

The dispersant of the present invention can be used for light calcium carbonate and heavy calcium carbonate, and can impart particularly excellent dispersibility and dispersion stability to light calcium carbonate as compared with conventional dispersants.

In preparing an aqueous slurry of calcium carbonate using the dispersant of the present invention, other inorganic or organic pigments, latexes and emulsions can be added. In some cases, other dispersants or surfactants can be used in combination.

[0025]

By using the dispersant of the present invention, it is possible to obtain a high-concentration aqueous calcium carbonate slurry having a smaller amount of addition to calcium carbonate than before and having excellent dispersibility. The obtained aqueous calcium carbonate slurry has low viscosity and high fluidity, and also has excellent stability over time. Further, by using the dispersant of the present invention, it is possible to provide a slurry having a higher concentration than before. The aqueous calcium carbonate slurry containing the dispersant of the present invention can be effectively used for various fields such as paper and paint.

[0026]

The present invention will be further described with reference to the following examples.

Production Example 1 An autoclave was charged with 30 parts by weight of maleic anhydride and 47 parts by weight of toluene, and heated to 115 ° C. in a nitrogen atmosphere. A mixture of 1.5 parts by weight of di-t-butyl peroxide and 40 parts by weight of toluene and 8,3-butadiene in 8.
A mixture of 3 parts by weight and 33 parts by weight of toluene were separately added over 4 hours. Thereafter, the mixture was aged at 115 ° C. for 1 hour to complete the reaction. After cooling, the supernatant solvent was removed, followed by washing and drying to obtain 20 parts by weight of a copolymer. Next, hydrolysis is carried out with an aqueous sodium hydroxide solution to adjust the pH to 9
To obtain a copolymer aqueous solution having a solid content concentration of 30% by weight. The content of maleic anhydride units in the copolymer was determined by CHN elemental analysis, and the molecular weight was determined by GPC measurement. Table 1 shows the results.

Production Example 2 100 parts by weight of maleic anhydride and 271 parts by weight of toluene were charged into an autoclave and heated to 150 ° C. in a nitrogen atmosphere. A mixed solution of 5 parts by weight of di-t-butyl peroxide and 99 parts by weight of toluene and a mixed solution of 55.1 parts by weight of 1,3-butadiene and 30 parts by weight of toluene were separately added thereto over 4 hours. Thereafter, the mixture was aged at 150 ° C. for 1 hour to terminate the reaction. After cooling, the supernatant solvent was removed, washed and dried to obtain 107 parts by weight of a copolymer. Next, hydrolysis is carried out with an aqueous sodium hydroxide solution,
The pH was adjusted to 9 to obtain a copolymer aqueous solution having a solid content of 30% by weight. The content of maleic anhydride units in the copolymer is C
The molecular weight was determined by HN elemental analysis, and the molecular weight was determined by GPC measurement. Table 1 shows the results.

Production Example 3 An autoclave was charged with 30 parts by weight of maleic anhydride and 56 parts by weight of cyclohexanone, and heated to 100 ° C. in a nitrogen atmosphere. Separately, a mixture of 1.5 parts by weight of t-butylperoxy (2-ethylhexanoate) and 44 parts by weight of cyclohexanone and a mixture of 16.5 parts by weight of 1,3-butadiene and 20 parts by weight of cyclohexanone were separately added. To 2
Added over time. Thereafter, the reaction was aged at 100 ° C. for 1 hour to terminate the reaction. After cooling, the reaction solution was poured into an excess of toluene, and the copolymer was precipitated and separated by filtration.
After washing and drying, 30 parts by weight of a copolymer was obtained. next,
Hydrolysis was carried out with an aqueous sodium hydroxide solution, the pH was adjusted to 9, and a copolymer aqueous solution having a solid content of 30% by weight was obtained.
The content of maleic anhydride units in the copolymer was determined by CHN elemental analysis, and the molecular weight was determined by GPC measurement.
Table 1 shows the results.

Production Example 4 100 parts by weight of maleic anhydride and 366 parts by weight of toluene were charged into an autoclave and heated to 120 ° C. in a nitrogen atmosphere. This is followed by t-butyl peroxybenzoate 10
A mixture of 48.6 parts by weight, 48.6 parts by weight of isoprene and 34 parts by weight of toluene was added over 2 hours. Then, at 120 ° C
For 1 hour to complete the reaction. After cooling, the supernatant solvent was removed, washed and dried to obtain 101 parts by weight of a copolymer. Next, hydrolysis was carried out with an aqueous sodium hydroxide solution, the pH was adjusted to 9, and a copolymer aqueous solution having a solid concentration of 30% by weight was obtained. The content of maleic anhydride units in the copolymer was determined by CHN elemental analysis, and the molecular weight was determined by GPC measurement. Table 1 shows the results.

Production Example 5 100 parts by weight of maleic anhydride and 393 parts by weight of toluene were charged into an autoclave and heated to 120 ° C. in a nitrogen atmosphere. This is followed by t-butyl peroxybenzoate 10
A mixed solution of 69.5 parts by weight, 69.5 parts by weight of isoprene and 7 parts by weight of toluene was added over 2 hours. Thereafter, the reaction was aged at 120 ° C. for 1 hour to terminate the reaction. After cooling, the supernatant solvent was removed, and washing and drying were performed to obtain 92 parts by weight of a copolymer. Next, hydrolysis is carried out with an aqueous sodium hydroxide solution,
The pH was adjusted to 9 to obtain a copolymer aqueous solution having a solid content of 30% by weight. The content of maleic anhydride units in the copolymer is C
The molecular weight was determined by HN elemental analysis, and the molecular weight was determined by GPC measurement. Table 1 shows the results.

Production Example 6 An autoclave was charged with 25 parts by weight of maleic anhydride and 40 parts by weight of toluene, and heated to 150 ° C. in a nitrogen atmosphere. A mixture of 0.25 parts by weight of di-t-butyl peroxide and 33 parts by weight of toluene and a mixture of 14.3 parts by weight of isobutene and 27 parts by weight of toluene were separately added to 4 parts each.
Added over time. Thereafter, the mixture was aged at 150 ° C. for 1 hour to terminate the reaction. After cooling, remove the supernatant solvent,
After washing and drying, 38 parts by weight of the copolymer were obtained. next,
Hydrolysis was carried out with an aqueous sodium hydroxide solution, the pH was adjusted to 9, and a copolymer aqueous solution having a solid content of 30% by weight was obtained.
The content of maleic anhydride units in the copolymer was determined by CHN elemental analysis, and the molecular weight was determined by GPC measurement.
Table 1 shows the results.

Production Example 7 An autoclave was charged with 100 parts by weight of maleic anhydride and 310 parts by weight of toluene, and heated to 130 ° C. in a nitrogen atmosphere. A mixed solution of 1 part by weight of di-t-butyl peroxide and 83 parts by weight of toluene and a mixed solution of 57.1 parts by weight of isobutene and 7 parts by weight of toluene were separately added thereto over 4 hours. Then aged at 130 ° C for 1 hour,
The reaction was terminated. After cooling, the supernatant solvent was removed, followed by washing and drying to obtain 155 parts by weight of a copolymer. Next, hydrolysis was carried out with an aqueous sodium hydroxide solution, the pH was adjusted to 9, and a copolymer aqueous solution having a solid concentration of 30% by weight was obtained. The content of maleic anhydride units in the copolymer was determined by CHN elemental analysis, and the molecular weight was determined by GPC measurement. Table 1 shows the results.

Examples 1-5 120 parts by weight of light calcium carbonate (average particle size 0.15 μm) were placed in a beaker having a capacity of 200 ml, and water (an amount at which the solid content concentration of calcium carbonate became 60% by weight) was prepared. A water-soluble salt of the copolymer obtained in Examples 1 to 5 (0.6% by weight based on calcium carbonate) was added. Next, the mixture was stirred at 3000 rpm for 10 minutes using a homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) to prepare a calcium carbonate aqueous slurry having a solid content concentration of 60% by weight. The viscosity of the slurry
Using a viscometer (DLV-B type, manufactured by Tokyo Keiki Co., Ltd.)
The measurement was performed at 0 rpm (rotor No. 4). Table 1 shows the obtained results.

Comparative Examples 1 to 3 Comparative Example 1 is a water-soluble salt of the copolymer obtained in Production Example 6, Comparative Example 2 is a water-soluble salt of the copolymer obtained in Production Example 7, and Comparative Example 3 is a commercially available polymer. Aqueous calcium carbonate slurries were prepared in the same manner as in Examples 1 to 5, using acrylates as dispersants, and their viscosities were measured. Comparative Examples 1 and 2
The dispersant used in the above corresponds to the dispersant described in JP-A-60-99334. Table 1 shows the obtained results.

[0036]

[Table 1]

From the results shown in Table 1, the dispersant of the present invention can provide a low-viscosity light calcium carbonate high-concentration slurry.
And this slurry was still low in viscosity after one week. On the other hand, the slurry of the comparative example had a relatively low viscosity, but had a higher viscosity than the slurry using the dispersant of the present invention.

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshiaki Kano 2-1504-67 Miyukigaoka, Yokkaichi-shi, Mie (56) References JP-A-63-162766 (JP, A) JP-A-2-52032 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) B01F 17/52 C01F 11/18

Claims (2)

(57) [Claims] (1) a maleic anhydride unit content of 30 to 90;
A dispersant for calcium carbonate, which is a mol% of a salt of a hydrolyzate of a copolymer of maleic anhydride and an aliphatic conjugated diene. 2. The dispersant according to claim 1, which is a dispersant for an aqueous calcium carbonate slurry.