JP5370360B2 - Dispersant for calcium carbonate - Google Patents

Description

The present invention relates to a pigment dispersant such as calcium carbonate. More specifically, particularly when used as a dispersant for inorganic pigments having a small particle size, the dispersion stabilizing effect is high and can be dispersed while maintaining good fluidity in the form of fine particles. A (meth) acrylic acid copolymer pigment dispersant that can be stably dispersed over a long period of time while suppressing the increase in viscosity over time in the solution is provided.
In the present invention, (meth) acrylic acid or a part or all of which is neutralized is referred to as (meth) acrylic acid (salt).

Conventionally, homopolymers of acrylic acid (salt) and copolymers of acrylic acid (salt) and other copolymerizable monomers are known as dispersants such as inorganic pigments. A homopolymer or copolymer of acrylic acid (salt) is adsorbed on the pigment particles and gives a repulsive action due to steric hindrance between the particles, whereby a stable pigment dispersion can be obtained. In particular, acrylic acid (salt) copolymers have advantages over acrylic acid (salt) homopolymers, and the following proposals have been made.
According to Patent Document 1 (Japanese Patent Laid-Open No. 61-69872), a monomer containing a monocarboxylic acid (salt), a monomer containing a dicarboxylic acid (salt), and a (meth) acrylic acid ester monomer Calcium carbonate is wet pulverized with a dispersant made of a copolymer.
According to Patent Document 2 (Japanese Patent Laid-Open No. 56-115630), a monomer containing a carboxylic acid (salt), a (meth) acrylic acid ester monomer having 1 to 8 carbon atoms, and a sulfonic acid (salt) The pigment is dispersed with a dispersant comprising a copolymer of a monomer containing

According to Patent Document 3 (Japanese Patent Laid-Open No. 49-130915), from a copolymer of a monomer containing a carboxylic acid (salt), a (meth) acrylic acid ester monomer having 1 to 4 carbon atoms. The pigment is dispersed with a dispersant.
According to Patent Document 4 (Japanese Patent Application Laid-Open No. 2004-306222), a monomer containing a carboxylic acid (salt) and a (meth) acrylic acid ester monomer having 1 to 20 carbon atoms are 97 to 99: 1. Light calcium carbonate is dispersed with a dispersant composed of a copolymer of ˜3.
According to Patent Document 5 (Japanese Patent Application Laid-Open No. 55-18423), a copolymer of (meth) acrylic acid (salt) and a (meth) acrylic acid ester monomer having 1 to 12 carbon atoms is used. The pigment is dispersed with a dispersant.

However, in recent years, inorganic pigments having a smaller particle size compared to conventional ones have been used, and it has become necessary for the dispersant to minimize the heat generated when performing wet grinding. . In addition, improvement of separation of media and slurry has been required.
Inorganic pigments having a small particle size have an increased surface area, so that the interaction between the particles becomes strong, so that the particles tend to aggregate and the viscosity of the dispersion tends to increase. In addition, during the wet pulverization, the particles repeatedly collide violently, so that heat generation increases. Furthermore, when the particle size is small, the separation between the media and the slurry tends to be poor, and the amount of slurry to be collected decreases.

In response to such demands, the conventional dispersants as described above do not provide satisfactory performance.
For example, Patent Document 1 (JP-A 61-69872), Patent Document 2 (JP-A 56-115630), Patent Document 3 (JP-A 49-130915) and Patent Document 4 (JP In the dispersant described in JP 2004-306222 A), there is a problem that the viscosity of the dispersion increases with time, and heat generation increases when wet pulverization is performed. In addition, there is a problem that the amount of slurry to be collected is reduced.
In addition, in the dispersant described in Patent Document 5 (Japanese Patent Application Laid-Open No. 55-18423), the emulsifier used also has an adverse effect on dispersibility. When wet pulverization is performed, there is a problem that heat generation increases. In addition, there is a problem that the amount of slurry to be collected is reduced.
Thus, even when the above acrylic acid (salt) copolymer is used, a dispersant that is sufficiently satisfied with respect to dispersion stability of inorganic pigments having a small particle size, suppression of heat generation during wet pulverization, and recovered amount of slurry. Not obtained.

JP-A 61-69872 Japanese Patent Laid-Open No. 56-115630 JP 49-130915 A JP 2004-306222 A Japanese Patent Laid-Open No. 55-18423

  The object of the present invention is to provide a (meth) acrylic acid-based pigment dispersant that satisfies the improvement in dispersibility of inorganic pigments having a small particle size and the effect of suppressing heat generation during wet pulverization, which are required for recent dispersants. There is to do.

  In order to solve the above-mentioned problems, the present inventor, in a conventionally known copolymer of (meth) acrylic acid and (meth) acrylic acid alkyl ester, has a carbon number as (meth) acrylic acid alkyl ester. A specific (meth) acrylic acid alkyl ester having 4 to 8 is selected, and the resulting (meth) acrylic acid copolymer and a dispersant having an alcohol having 4 to 8 carbon atoms, The present inventors have found that a pigment dispersant having a mass ratio of alcohol having 4 to 8 carbon atoms with respect to the (meth) acrylic acid copolymer of 1000 to 30000 ppm can solve the above problems, and has completed the present invention.

The invention for solving the above problems is described below.
1st invention is 60-95 mass% of (meth) acrylic acid monomers, 5-40 mass% of (meth) acrylic acid alkyl ester monomers whose carbon number of an alkyl group is 4-8 , and others. A (meth) acrylic acid copolymer consisting of 0 to 10% by mass of a copolymerizable monomer , and (meth) acrylic in which 15 to 100 mol% of carboxyl groups in the copolymer are in the form of a salt. Dispersant comprising an acid (salt) copolymer and an alcohol having 4 to 8 carbon atoms, and a mass ratio of the alcohol having 4 to 8 carbon atoms with respect to the (meth) acrylic acid copolymer Is a dispersant for calcium carbonate having 1000 to 30000 ppm.
2nd invention is a dispersing agent for calcium carbonates of 1st invention whose mass ratio of C4-C8 alcohol with respect to a (meth) acrylic-acid type copolymer is 2000-15000 ppm.
In the third invention, the (meth) acrylic acid alkyl ester monomer having 4 to 8 carbon atoms is butyl (meth) acrylate, and the alcohol having 4 to 8 carbon atoms is butyl alcohol. It is a dispersing agent for calcium carbonate in any one of invention or 2nd invention .
A fourth invention is the dispersant for calcium carbonate according to any one of the first to third inventions, which is a dispersant for wet grinding.
The fifth invention is a wet grinding method calcium carbonate, characterized in that calcium carbonate is used for dispersing agent according to any one of the first invention to fourth invention wet milling calcium carbonate.

When the pigment dispersant comprising the (meth) acrylic acid (salt) copolymer of the present invention is used as a dispersant such as an inorganic pigment having a small particle size, the viscosity of the dispersion does not increase with time. Moreover, since heat generation during wet pulverization can be reduced and the amount of recovered slurry is large, it is useful as a dispersant in various applications.
The manifestation of the effect as a pigment dispersant in the present invention is that, compared with conventional dispersants, the dispersant of the present invention adsorbs to the particles in the dispersion, and at the same time, slips between the particles and between the slurry and the media. It is presumed that

Hereinafter, embodiments of the present invention will be described in detail.
The pigment dispersant of the present invention comprises (meth) acrylic acid having a (meth) acrylic acid monomer and a (meth) acrylic acid alkyl ester monomer having 4 to 8 carbon atoms in the alkyl group as essential components. It is characterized by consisting of an alcohol having 4 to 8 carbon atoms and an alcohol having 4 to 8 carbon atoms in a mass ratio of 1000 to 30000 ppm with respect to the (meth) acrylic acid copolymer. It is characterized by being.

Examples of (meth) acrylic acid include acrylic acid and methacrylic acid, and may be in the form of a salt ((meth) acrylate) in which part or all of it is neutralized. Among these, acrylic acid and / or acrylate are preferable from the viewpoint of polymerizability and water solubility when producing the copolymer.
(Meth) acrylic acid salts include (meth) acrylic acid alkali metal salts (for example, sodium salts, potassium salts, lithium salts), ammonium salts, organic amine salts (for example, diethanolamine salts, triethanolamine salts, etc.) Can be mentioned. Among these, the form of the (meth) acrylate is preferably an alkali metal salt, particularly a sodium salt, from the viewpoint of the balance between production cost and performance.
The (meth) acrylate is produced by reacting (meth) acrylic acid with an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, or an organic amine such as ammonia or monoethanolamine. can do.

The (meth) acrylic acid-based copolymer in the present invention, (meth) 15 to 100 mole% of the mosquitoes carboxyl group of the acrylic acid are neutralized by a base, it is necessary to have the form of a salt, in particular Preferably it is 25-100 mol% . It is preferable that the carboxyl group is neutralized with a base as described above to be in the form of a salt because the water solubility of the (meth) acrylic acid copolymer is increased and the dispersion stabilizing effect is enhanced. .
In terms of pH, the carboxyl group is neutralized with a base at such a ratio that the pH of the aqueous solution of the (meth) acrylic acid copolymer is 3 to 9, particularly 4 to 8, The (meth) acrylic acid copolymer is preferable because the water solubility becomes high and the dispersion stabilization effect becomes high.

  It seems that at least 40 mol% (40 to 100 mol%) of the carboxyl group of (meth) acrylic acid is in an unneutralized state before and at the polymerization stage for producing the (meth) acrylic acid copolymer. Polymerization, and using a basic compound after the polymerization, 15 mol% or more, further 25 mol% or more of the carboxyl group of the (meth) acrylic acid copolymer may be converted into a salt form (meth) It is preferable from the point that the polymerization reaction for producing the acrylic acid copolymer proceeds smoothly.

Examples of the (meth) acrylic acid alkyl ester monomer having 4 to 8 carbon atoms in the alkyl group include n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, Examples include (meth) acrylic acid pentyl, (meth) acrylic acid hexyl, (meth) acrylic acid heptyl, (meth) acrylic acid 2-ethylhexyl, (meth) acrylic acid cyclohexyl, etc. Among these, (meth) acrylic acid n -Butyl, isobutyl (meth) acrylate and t-butyl (meth) acrylate are preferred, and (meth) acrylate butyl is particularly preferred, and n-butyl (meth) acrylate is particularly preferred.
A (meth) acrylic acid alkyl ester having 3 or less carbon atoms in the alkyl group is not preferred because the dispersion tends to thicken and heat generation during wet grinding tends to increase. Moreover, since the acquisition amount of the slurry to collect becomes small, it is not preferable. This is presumed to be due to the small slippage between the particles. On the other hand, (meth) acrylic acid alkyl esters having an alkyl group with 9 or more carbon atoms are not preferred because the dispersion tends to separate.

The mass proportion of (meth) acrylic acid (salt) and the alkyl group (meth) acrylic acid alkyl ester having 4 to 8 carbon atoms is (meth) acrylic acid (salt): (meth) acrylic acid alkyl ester. It must be 95: 5 to 60:40, and more preferably 90:10 to 70:30.
If the proportion of (meth) acrylic acid (salt) is less than 60% by mass, the pigment dispersant may be separated. On the other hand, if it exceeds 95% by mass, the viscosity of the dispersion tends to increase.

In the (meth) acrylic acid copolymer in the present invention, in addition to (meth) acrylic acid (salt) and (meth) acrylic acid alkyl ester, monomers copolymerizable with these may be copolymerized. . Examples of such monomers include unsaturated acids such as maleic acid and itaconic acid or salts thereof, unsaturated acid anhydrides such as maleic anhydride and itaconic anhydride, 2-acrylamido-2-methylpropanesulfonic acid, and styrene. Examples thereof include unsaturated sulfonic acids such as sulfonic acids or salts thereof, (meth) acrylic acid hydroxyalkyl esters, acrylamides, and (meth) acrylic acid esters containing a polyalkylene oxide skeleton in the ester. Two or more of these can be used in combination.
It is preferable that these monomers are 0-10 mass parts with respect to 100 mass parts of all monomers, and it is further more preferable that it is 0-5 mass parts. If the amount exceeds 10 parts by mass, the dispersion may increase in viscosity, which is not preferable.

The production method of the (meth) acrylic acid copolymer is not particularly limited, and can be produced by a solution polymerization method, an aqueous solution polymerization method, a high temperature high pressure polymerization method, a reverse phase suspension polymerization method, an emulsion polymerization, etc. However, the solution polymerization method and the aqueous solution polymerization method are preferable, and the aqueous solution polymerization method is particularly preferable.
According to the aqueous solution polymerization, the dispersant can be obtained as a uniform solution. On the other hand, in the case of producing by other polymerization methods such as emulsion polymerization, a uniform solution cannot be obtained, so that only non-uniform dispersion can be performed, and the resulting dispersion tends to increase in viscosity.
It is preferable to use a mixed solution of water and an organic solvent as the solvent for the aqueous solution polymerization. Use of only water as a solvent is not preferable because the (meth) acrylic acid alkyl ester is difficult to dissolve. On the other hand, when only an organic solvent is used, it is necessary to replace the organic solvent with water when used as a dispersant.
Preferable organic solvents include alcohols such as isopropyl alcohol and ketones such as acetone, and isopropyl alcohol is particularly preferable.

Moreover, as a polymerization initiator of a polymerization reaction, a well-known polymerization initiator can be used without a restriction | limiting especially, However, Especially a radical polymerization initiator is used preferably.
Examples of radical polymerization initiators include persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate, hydroperoxides such as t-butyl hydroperoxide, water-soluble peroxides such as hydrogen peroxide; Examples thereof include oil-soluble peroxides such as oxides and ketone peroxides such as cyclohexanone peroxide, and dialkyl peroxides such as di-t-butyl peroxide and t-butylcumyl peroxide.
The above peroxide-based radical polymerization initiators may be used alone or in combination of two or more.
Among the above-mentioned peroxide-based radical polymerization initiators, hydrogen peroxide and persulfate-based peroxides, which are easy to control the molecular weight and have a low decomposition temperature, are preferably used, particularly preferably sodium persulfate and Persulfates such as ammonium persulfate.

  The amount of the radical polymerization initiator used is not particularly limited, but is 0.1 to 15% by mass, particularly 0.5 to 10% by mass, based on the total mass of all monomers of the (meth) acrylic acid copolymer. It is preferable to use in the ratio. When the amount of the radical polymerization initiator used is less than 0.1% by mass, the copolymerization rate decreases, and when it exceeds 15% by mass, the stability of the (meth) acrylic acid copolymer decreases, May adversely affect performance.

  In some cases, the (meth) acrylic acid copolymer may be produced using a water-soluble redox polymerization initiator. Examples of the redox polymerization initiator may include a combination of an oxidizing agent (for example, the above-described peroxide), a reducing agent such as sodium bisulfite, sodium sulfite, and sodium hydrosulfite, and iron alum and potassium alum. .

  In the production of the (meth) acrylic acid copolymer, an appropriate amount of a chain transfer agent may be added to adjust the molecular weight. Examples of usable chain transfer agents include sodium phosphite, Examples thereof include sodium hypophosphite, sodium bisulfite, mercaptoacetic acid, mercaptopropionacetic acid, 2-propanethiol, 2-mercaptoethanol, thiophenol and the like.

The polymerization temperature for producing the (meth) acrylic acid copolymer is not particularly limited and can be carried out in a wide range, but the polymerization temperature is preferably 60 to 100 ° C.
When the polymerization temperature is less than 60 ° C., the polymerization reaction is slow, which is not preferable in terms of productivity. The reaction can also be carried out under pressure or reduced pressure, but it is preferable to carry out the reaction at normal pressure because of the cost required to make equipment for pressurized or reduced pressure reaction.
The polymerization time is preferably 2 to 20 hours, particularly about 3 to 10 hours.

  The weight average molecular weight of the (meth) acrylic acid copolymer in the present invention is preferably 2000 to 10000, more preferably 3000 to 8000. When the weight average molecular weight is less than 2,000, the dispersant tends to be desorbed from the particles in the dispersion, which tends to increase the viscosity of the dispersion. On the other hand, when the molecular weight exceeds 10,000, the dispersant itself becomes the dispersion. The viscosity of the dispersion tends to increase, which is not preferable. The measurement of the weight average molecular weight is a value assumed by GPC (gel permeation chromatography).

The organic solvent is removed from the solution containing the (meth) acrylic acid copolymer obtained above by distillation, vacuum distillation, drying, etc., and then neutralized with a basic compound as necessary. The (meth) acrylic acid copolymer is water-solubilized by converting the carboxyl group of the salt into a salt form. As described above, it is preferable that the degree of neutralization is 15 to 100 mol%, particularly 25 to 100 mol%, is neutralized with a base to form a salt.
Examples of basic compounds used for neutralization include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and organic amines such as aqueous ammonia, diethanolamine, and triethanolamine. Sodium and / or potassium hydroxide is preferred, and sodium hydroxide is particularly preferably used.

The water-solubilized (meth) acrylic acid-based copolymer obtained above is used for various dispersants by adding alcohol having 4 to 8 carbon atoms. As for the content of the alcohol having 4 to 8 carbon atoms, the mass ratio with respect to the (meth) acrylic acid copolymer is 1000 to 30000 ppm, preferably 1500 to 20000 ppm, particularly preferably 2000 to 15000 ppm. is there.
If the ratio of alcohol is less than 1000 ppm, the slipping between particles is small, so the dispersion tends to thicken and heat generation during wet grinding tends to increase, which is not preferable. Moreover, since the acquisition amount of the slurry to collect becomes small, it is not preferable. On the other hand, if it exceeds 30000 ppm, the particles tend to aggregate and the dispersion tends to thicken, which is not preferable.

Examples of the alcohol having 4 to 8 carbon atoms include n-butyl alcohol, isobutyl alcohol, t-butyl alcohol, pentyl alcohol, n-hexyl alcohol, heptyl alcohol, octyl alcohol and 2-ethylhexyl alcohol. Among these, n-butyl alcohol, isobutyl alcohol, and t-butyl alcohol are preferable from the viewpoint of performance as a dispersant, and n-butyl alcohol is particularly preferable.
Alcohols having 3 or less carbon atoms are not preferred because the dispersion tends to thicken and heat generation during wet grinding tends to increase. Moreover, since the acquisition amount of the slurry to collect becomes small, it is not preferable. On the other hand, an alcohol having 9 or more carbon atoms is not preferable because the dispersant tends to separate.

  The pigment dispersant of the present invention is usually prepared in a solid content concentration of 50 to 80% by mass, and preferably in the range of 60 to 78% by mass. In order to adjust the concentration, it is preferable to add water.

The pigment dispersant of the present invention exhibits an excellent effect on inorganic pigments. Specific examples include pigment clay, heavy calcium carbonate, light calcium carbonate, titanium oxide, alumina, and satin white.
The usage-amount of the pigment dispersant of this invention is 0.01-10 mass% normally with respect to a pigment, Preferably it is 0.05-5 mass%, Most preferably, it is 0.1-3 mass%. If it is less than 0.01% by mass, the dispersion effect is insufficient, and if it exceeds 10% by mass, the slurry tends to thicken, which is not preferable.

Hereinafter, the present invention will be described in more detail with reference to examples. Unless otherwise specified,% means mass%, and part means mass part.
Example 1
A tank reactor equipped with a stirrer and a condenser was charged with 170 kg of deionized water and 250 kg of isopropyl alcohol and maintained at 80 ° C. To this reactor, 330 kg of a monomer mixed with 255 kg of acrylic acid and 75 kg of n-butyl acrylate and 60 kg of a 15% ammonium persulfate aqueous solution were fed over 5 hours. After completion of dropping, the reaction solution was held at 80 ° C. for 1 hour. Subsequently, isopropyl alcohol was distilled off under reduced pressure while adding deionized water. Thereafter, the reaction solution was kept at 50 ° C. and neutralized by supplying a 48% aqueous sodium hydroxide solution over 4 hours. Here, when the liquid was analyzed by gas chromatography, 300 ppm of n-butanol was detected. Therefore, n-butanol was added and adjusted to 1500 ppm. In this way, a pigment dispersant having a solid content concentration of 40% by mass, a pH of 6, and 1500 ppm of n-butanol was obtained.
The weight average molecular weight (Mw) of the obtained pigment dispersant was measured by gel permeation chromatography (GPC). GPC was measured using an HLC8020 system (manufactured by Tosoh Corp.), and the column was connected to G4000PWxl, G3000PWxl, G2500PWxl (manufactured by Tosoh Corp.), and the eluent was 0.1M NaCl + phosphate buffer (PH7 The calibration curve was prepared using polyacrylic acid Na (manufactured by Sowa Kagaku Co., Ltd.). As a result of the measurement, Mw was 6000.

A cylindrical container was charged with 17 g of the pigment dispersant obtained above, 320 g of ion-exchanged water, and 900 g of heavy calcium carbonate (manufactured by Maruo Calcium Co., Ltd., Charcoal Cal A), and the mixture was lightly agitated and evenly blended. . Next, 3000 g of media (sand) was added and wet pulverized by stirring at 1000 rpm for 50 minutes. Here, when the liquid temperature at the end of stirring was measured with a thermometer, it was 79 ° C. Thereafter, the dispersion was recovered through a 200-mesh filter cloth. The obtained amount of the recovered dispersion was measured and found to be 390 g. Ion exchange water was added to this slurry to adjust the solid content to 75%, and a dispersion was obtained.
The fluidity of the heavy calcium carbonate slurry during the wet pulverization was evaluated according to the following evaluation criteria.
A: The slurry and media after pulverization are separated very quickly, and the fluidity of the slurry is extremely excellent.
○: Separation of the slurry and media after pulverization is rapid, and the fluidity of the slurry is excellent.
(Triangle | delta): Separation of the slurry and media after a grinding | pulverization does not advance rapidly, but the fluidity | liquidity of a slurry is low.

Further, the viscosity of the dispersion slurry on the wet pulverization day and the viscosity after standing at 25 ° C. for 7 days were measured using a BL viscometer at 25 ° C. and 60 rpm. The viscosity on the wet pulverization day was 250 mPa · s, and the viscosity after 7 days was 2200 mPa · s.
Further, the median diameter and 1.32 μm under integrated value of the dispersion immediately after production were measured using a laser diffraction / scattering particle size distribution measuring apparatus LA-910 (manufactured by Horiba, Ltd.). The median diameter was 0.67 μm, and the 1.32 μ under value was 100%.
These results are shown in Table 1.

Example 2
In Example 1, polymerization, vacuum distillation and neutralization were performed in the same manner as in Example 1 except that the monomers used were changed to 290 kg of acrylic acid and 40 kg of 2-ethylhexyl acrylate. When the liquid was analyzed here, 2-ethylhexanol was detected at 100 ppm. Therefore, 2-ethylhexanol was added and adjusted to 3000 ppm. In this way, a pigment dispersant containing a solid content concentration of 40 mass%, a pH of 6, and 3000 ppm of 2-ethylhexanol was obtained. The measured values of Mw and the results of wet grinding are shown in Table 1.

Example 3
In Example 1, polymerization and vacuum distillation were performed in the same manner as in Example 1 except that the monomers used were changed to 230 kg of acrylic acid and 100 kg of n-butyl acrylate. Thereafter, the reaction solution was kept at 80 ° C. and neutralized by supplying a 48% aqueous sodium hydroxide solution over 4 hours. When the liquid was analyzed here, 800 ppm of n-butanol was detected, so no additional alcohol was added. In this way, a pigment dispersant having a solid content concentration of 40% by mass, a pH of 6, and 800 ppm of n-butanol was obtained. The measured values of Mw and the results of wet grinding are shown in Table 1.

Example 4
In Example 1, polymerization and vacuum distillation were performed in the same manner as in Example 1 except that the monomer used was changed to 270 kg of acrylic acid and 60 kg of n-butyl acrylate. Thereafter, the reaction solution was kept at 70 ° C., and neutralized by supplying a 48% aqueous sodium hydroxide solution over 4 hours. When the liquid was analyzed here, 500 ppm of n-butanol was detected, but n-butanol was further added to adjust to 5000 ppm. In this way, a pigment dispersant having a solid content concentration of 40% by mass, a pH of 7, and 5000 ppm of n-butanol was obtained. The measured values of Mw and the results of wet grinding are shown in Table 1.

Example 5
In Example 1, polymerization, vacuum distillation and neutralization were performed in the same manner as in Example 1 except that the monomers used were changed to 290 kg of acrylic acid and 40 kg of isobutyl acrylate. When the solution was analyzed, isobutanol was detected at 100 ppm, so isobutanol was added and adjusted to 2000 ppm. In this way, a pigment dispersant having a solid content concentration of 40% by mass, a pH of 6, and 2000 ppm of isobutanol was obtained. The measured values of Mw and the results of wet grinding are shown in Table 1.

Example 6
In Example 1, polymerization and distillation under reduced pressure were performed in the same manner as in Example 1 except that the monomers used were changed to 255 kg of acrylic acid and 75 kg of n-butyl acrylate. Thereafter, the reaction solution was kept at 60 ° C., and neutralized by supplying a 48% aqueous sodium hydroxide solution over 4 hours. When the liquid was analyzed here, 400 ppm of n-butanol was detected, so n-butanol was added and adjusted to 500 ppm. In this way, a pigment dispersant having a solid content concentration of 40 mass%, a pH of 6, and 500 ppm of n-butanol was obtained. The measured values of Mw and the results of wet grinding are shown in Table 1.

Example 7
In Example 1, polymerization and distillation under reduced pressure were performed in the same manner as in Example 1 except that the monomers used were changed to 255 kg of acrylic acid and 75 kg of n-butyl acrylate. Thereafter, the reaction solution was kept at 60 ° C., and neutralized by supplying a 48% aqueous sodium hydroxide solution over 4 hours. When the liquid was analyzed here, 400 ppm of n-butanol was detected, but n-butanol was further added to adjust to 11000 ppm. In this way, a pigment dispersant having a solid content concentration of 40% by mass, a pH of 7, and 11000 ppm of n-butanol was obtained. The measured values of Mw and the results of wet grinding are shown in Table 1.

Comparative Example 1
In Example 1, polymerization, vacuum distillation and neutralization were performed in the same manner as in Example 1 except that the monomers used were changed to 255 kg of acrylic acid and 75 kg of methyl acrylate. When the liquid was analyzed, methanol was detected at 350 ppm, but alcohol having 4 to 8 carbon atoms was not detected. Therefore, n-butanol was added and adjusted to 1500 ppm. In this way, a pigment dispersant having a solid content concentration of 40% by mass, a pH of 6, and 1500 ppm of n-butanol was obtained. The measured values of Mw and the results of wet grinding are shown in Table 1.

Comparative Example 2
In Example 1, polymerization, vacuum distillation and neutralization were performed in the same manner as in Example 1 except that the monomers used were changed to 255 kg of acrylic acid and 75 kg of ethyl acrylate. When the liquid was analyzed, 350 ppm of ethanol was detected, but no alcohol having 4 to 8 carbon atoms was detected. Therefore, n-butanol was added and adjusted to 1500 ppm. In this way, a pigment dispersant having a solid content concentration of 40% by mass, a pH of 6, and 1500 ppm of n-butanol was obtained. The measured values of Mw and the results of wet grinding are shown in Table 1.

Comparative Example 3
In Example 1, polymerization, vacuum distillation and neutralization were attempted in the same manner as in Example 1 except that the monomers used were changed to 255 kg of acrylic acid and 75 kg of lauryl acrylate. However, the evaluation was stopped because a uniform solution could not be obtained.

Comparative Example 4
In Example 1, polymerization, vacuum distillation and neutralization were performed in the same manner as in Example 1 except that the monomers used were changed to 290 kg of acrylic acid and 40 kg of n-butyl acrylate. When the liquid was analyzed, n-butanol was detected at 100 ppm, and n-butanol was added to adjust to 300 ppm. In this manner, a pigment dispersant containing a solid content concentration of 40% by mass, a pH of 6, and 300 ppm of n-butanol was obtained. The measured values of Mw and the results of wet grinding are shown in Table 1.

Comparative Example 5
In Example 1, polymerization, vacuum distillation and neutralization were performed in the same manner as in Example 1 except that the monomers used were changed to 290 kg of acrylic acid and 40 kg of n-butyl acrylate. When the liquid was analyzed here, 100 ppm of n-butanol was detected. n-butanol was added and adjusted to 13000 ppm. In this way, a pigment dispersant containing a solid concentration of 40% by mass, a pH of 6, and 13000 ppm of n-butanol was obtained. The measured values of Mw and the results of wet grinding are shown in Table 1.

A (meth) acrylic acid-based copolymer using a (meth) acrylic acid alkyl ester having 4 to 8 carbon atoms in the alkyl group and an alcohol having 4 to 8 carbon atoms, and a (meth) acrylic acid-based material Examples 1 to 7 in which the mass ratio of the alcohol having 4 to 8 carbon atoms relative to the copolymer is 1000 to 30000 ppm are excellent in fluidity during wet pulverization, have a large amount of recovered slurry, and immediately after wet pulverization. The slurry temperature is low, and the viscosity change of the wet pulverized dispersion slurry is small, indicating that it is an extremely excellent pigment dispersant.
On the other hand, as shown in Comparative Examples 1 and 2, when a (meth) acrylic acid copolymer using a (meth) acrylic acid alkyl ester having an alkyl group with 3 or less carbon atoms is used, it is wet. It can be seen that the fluidity during pulverization is poor, the amount of recovered slurry is small, the slurry temperature immediately after wet pulverization is high, and the viscosity change of the wet pulverized dispersion slurry is large. Further, in Comparative Example 3 using lauryl acrylate having 12 carbon atoms, a uniform polymerization solution was not obtained.
On the other hand, about the comparative example 4 and the comparative example 5 whose mass ratio of the alcohol whose carbon number is 4-8 with respect to a (meth) acrylic-acid type copolymer is not the range of 1000-30000 ppm, it is in the fluidity | liquidity in wet grinding. Inferior, the amount of recovered slurry is small, the slurry temperature immediately after wet pulverization is high, and the viscosity change of the wet pulverized dispersion slurry is large, making it difficult to use as a pigment dispersant.

The pigment dispersant obtained by the present invention contains acrylic acid (salt) and a polymer of alkyl acrylate ester having 4 to 8 carbon atoms in alkyl and a specific amount of alcohol having 4 to 8 carbon atoms. This pigment dispersant is used to adsorb to particles in the liquid and at the same time provide slipping between the particles and between the slurry and the media. The viscosity of the dispersion over time can be reduced, and the amount of slurry to be recovered can be increased. Therefore, the dispersion liquid comprising the pigment dispersant of the present invention is easy to handle, and further, there is an effect that the storage period can be made longer than before. In addition, since heat generation during wet pulverization can be reduced, there is also an effect that a thermal load on equipment during pulverization is reduced.

Claims (5)

(Meth) acrylic acid (salt) monomer 60 to 95% by mass , alkyl group having 4 to 8 carbon atoms (meth) acrylic acid alkyl ester monomer 5 to 40% by mass, and other copolymers It is a (meth) acrylic acid (salt) -based copolymer comprising 0 to 10% by mass of possible monomers , and 15 to 100 mol% of the carboxyl groups in the copolymer is in the form of a salt (meth) A dispersant comprising an acrylic acid (salt) copolymer and an alcohol having 4 to 8 carbon atoms, and an alcohol having 4 to 8 carbon atoms relative to the (meth) acrylic acid (salt) copolymer An aqueous calcium carbonate dispersant having a mass ratio of 1000 to 30000 ppm. The dispersant for aqueous calcium carbonate according to claim 1, wherein the mass ratio of the alcohol having 4 to 8 carbon atoms relative to the (meth) acrylic acid (salt) copolymer is 2000 to 15000 ppm. A carbon number of 4-8 (meth) acrylic acid alkyl ester monomer is (meth) acrylate, butyl claim 1 or claim 2 carbon atoms 4-8 alcohol is butyl alcohol The dispersant for aqueous calcium carbonate according to any one of the above. The dispersant for aqueous calcium carbonate according to any one of claims 1 to 3 , which is a dispersant for wet grinding. Wet grinding method calcium carbonate, which comprises using an aqueous calcium carbonate dispersion agent according to any one of claims 1-4 for wet grinding of calcium carbonate