WO2014189020A1

WO2014189020A1 - Dispersant for calcium carbonate and method for producing same

Info

Publication number: WO2014189020A1
Application number: PCT/JP2014/063270
Authority: WO
Inventors: 正裕藤原
Original assignee: 東亞合成株式会社
Priority date: 2013-05-24
Filing date: 2014-05-20
Publication date: 2014-11-27
Also published as: JPWO2014189020A1; JP6119850B2

Abstract

This dispersant for calcium carbonate is capable of providing a calcium carbonate slurry, which has a sufficiently low viscosity and good long-term stability, both by wet pulverization and by stirring dispersion. This dispersant contains a (meth)acrylic acid polymer which is composed of 80-100% by mass of one or more monomers that are selected from among (meth)acrylic acid, potassium (meth)acrylate and magnesium (meth)acrylate and 0-20% by mass of another monomer, and wherein 20-65 mol% of the carboxyl groups of the (meth)acrylic acid polymer is in the form of a potassium salt and 35-70 mol% thereof is in the form of a magnesium salt.

Description

Dispersant for calcium carbonate and method for producing the same

The present invention relates to a dispersant for calcium carbonate and a method for producing the same. More specifically, the present invention relates to a calcium carbonate dispersant useful for producing a calcium carbonate slurry by wet pulverization or stirring and dispersion and a method for producing the same.

Calcium carbonate slurry obtained by dispersing calcium carbonate in an aqueous medium is widely used in paper coating agents, paint pigments, and the like.
As a method for producing a calcium carbonate slurry, a wet pulverization method is widely employed in which a slurry is obtained by stirring and pulverizing calcium carbonate, a dispersant and the like together with media in water. According to this method, it is possible to produce a calcium carbonate slurry having a small particle diameter with an average particle diameter of 1 μm or less.
There is also a method of obtaining a slurry by stirring and mixing calcium carbonate and a dispersant in water without using a medium (hereinafter also referred to as “mixing dispersion”). This method does not require a special apparatus and is suitable for obtaining a calcium carbonate slurry having a relatively large particle size.

The calcium carbonate slurry is required to have a sufficiently low viscosity from the viewpoint of handling during transportation and coating. Further, it is required that the viscosity of the slurry does not increase greatly with time and that the viscosity stability is also good.
Therefore, the dispersant used in the calcium carbonate slurry is required to exhibit excellent dispersibility in order to satisfy the demand for such a slurry.

As the dispersing agent for calcium carbonate, a dispersing agent containing a (meth) acrylic acid polymer is widely used, and studies on improving the dispersing performance of the dispersing agent are being widely promoted.
Patent Document 1 discloses a pigment dispersant comprising a polymer neutralized product mainly composed of an α, β-unsaturated carboxylic acid having a specific terminal group.
Patent Documents 2 to 5 disclose pigment dispersants containing a (meth) acrylic acid polymer having a specific range of alkali metal salts and alkaline earth metal salts.
Furthermore, Patent Document 6 proposes an acrylic acid (co) polymer having a specific end group and a weight average molecular weight as a dispersant for wet grinding of calcium carbonate.

Japanese Patent Laid-Open No. 2005-307023 JP 54-82416 A JP 2006-193418 A JP 2000-212371 A JP 2011-105853 A JP 2000-281959 A

However, although the dispersants described in Patent Documents 1 and 3 to 6 have a good effect on the dispersion of the calcium carbonate slurry obtained by wet grinding, the viscosity of the slurry is sufficiently reduced in the case of stirring dispersion. In some cases, the viscosity of the slurry may increase with time.
Moreover, although the dispersing agent described in patent document 2 shows favorable dispersibility when this is used for stirring dispersion of calcium carbonate, a satisfactory slurry cannot be obtained when it is used for wet grinding. There was a case.

Thus, the present condition is that the dispersing agent which shows favorable dispersibility has not yet been obtained in any method of wet grinding and stirring dispersion.
An object of the present invention is a dispersant for a calcium carbonate slurry, which is capable of obtaining a calcium carbonate slurry having a sufficiently low viscosity and good stability over time, regardless of the method for producing the slurry, and its production Is to provide a method.

As a result of intensive studies in view of the above problems, the present inventors have shown that a (meth) acrylic acid polymer in which the specific amount of carboxyl group is in the form of potassium salt and magnesium salt exhibits excellent performance as a dispersant for calcium carbonate. That is, the present invention has been completed.

The present invention is as follows.
1. From 80 to 100% by mass of one or more monomers selected from (meth) acrylic acid, potassium (meth) acrylate and magnesium (meth) acrylate, and from 0 to 20% by mass of other monomers (Meth) acrylic acid polymer, wherein 20 to 65 mol% of the carboxyl group of the (meth) acrylic acid polymer is a potassium salt and 35 to 70 mol% is a magnesium salt. Dispersant for calcium carbonate containing a polymer.
2. 2. The calcium carbonate dispersant as described in 1 above, wherein the (meth) acrylic acid polymer has a weight average molecular weight of 3000 to 10,000.
3. The (meth) acrylic acid polymer polymerizes a monomer containing (meth) acrylic acid in the presence of a phosphorous acid compound and / or a hypophosphorous acid compound using an aqueous isopropyl alcohol solution as a solvent. Is obtained by
1 or 2, wherein the phosphorous acid compound and / or the hypophosphorous acid compound is used in an amount of 1.0 to 4.5 parts by mass with respect to 100 parts by mass of the monomer. The dispersing agent for calcium carbonate as described.
4). A method for producing a dispersant for calcium carbonate containing a (meth) acrylic acid polymer,
One kind selected from (meth) acrylic acid, potassium (meth) acrylate and magnesium (meth) acrylate in the presence of a phosphite compound and / or a hypophosphite compound using an aqueous isopropyl alcohol solution as a solvent Or a polymerization step of polymerizing two or more monomers of 80 to 100% by mass and other monomers of 0 to 20% by mass,
In the polymerization step, a phosphorous acid compound and / or a hypophosphorous acid compound is used in an amount of 1.0 to 4.5 parts by mass with respect to 100 parts by mass of the monomer.
If necessary, neutralization is performed so that 20 to 65 mol% of the carboxyl group of the (meth) acrylic acid polymer is a potassium salt and 35 to 70 mol% is a magnesium salt. Method for producing a dispersing agent.

According to the dispersant for calcium carbonate of the present invention, a calcium carbonate slurry having a sufficiently low viscosity and good temporal stability can be obtained even when the calcium carbonate slurry is produced by any of wet pulverization and stirring and dispersion methods. Can be obtained.

The present invention relates to a (meth) acrylic acid polymer, in which 20 to 65 mol% of the carboxyl group of the polymer is a potassium salt and 35 to 70 mol% is a magnesium salt. The present invention relates to a calcium carbonate dispersant containing a coalescence and a method for producing the same.
The present invention will be described in detail below. In the present specification, acrylic acid and / or methacrylic acid is represented as (meth) acrylic acid.

The (meth) acrylic acid polymer according to the present invention is an essential structural unit of one or more monomers selected from (meth) acrylic acid, potassium (meth) acrylate and magnesium (meth) acrylate. It is what. The use ratio of these in all structural units is 80 to 100% by mass, preferably 90 to 100% by mass, and particularly preferably 100% by mass.
Water of the resulting polymer when the proportion of one or more monomers selected from (meth) acrylic acid, potassium (meth) acrylate and magnesium (meth) acrylate is 80% by mass or more The solubility in can be made sufficient.
Further, among (meth) acrylic acid, potassium (meth) acrylate and magnesium (meth) acrylate, acrylic acid and its potassium salt or magnesium salt are used from the viewpoint that the obtained polymer exhibits good water solubility. It is preferable. Among these, acrylic acid is preferable from the viewpoint of good polymerizability and the need for a separate neutralization facility or the like when preparing the raw material monomer.

Monomers other than (meth) acrylic acid, potassium (meth) acrylate and magnesium (meth) acrylate (hereinafter also referred to as “other monomers”) are monomers copolymerizable with these. If there is, it will not be specifically limited. Specifically, a vinyl monomer (polymerizable unsaturated compound) having radical polymerizability is exemplified. Examples of the vinyl monomer include, for example, ethylenically unsaturated carboxylic acids other than (meth) acrylic acid, neutralized salts of ethylenically unsaturated carboxylic acids, (meth) acrylic acid alkyl ester compounds, aromatic vinyl compounds, Acid anhydride, amino group-containing vinyl compound, amide group-containing vinyl compound, sulfonic acid group-containing vinyl compound, polyoxyalkylene group-containing vinyl compound, alkoxyl group-containing vinyl compound, cyano group-containing vinyl compound, cyanide vinyl compound, vinyl ether compound , Vinyl ester compounds, conjugated dienes and the like. These can be used alone or in combination of two or more.
Of these, a (meth) acrylic acid alkyl ester compound and a polyoxyalkylene group-containing vinyl compound are preferred from the viewpoint of excellent dispersion stability and coloring suppression performance of the resulting dispersant.

Examples of the ethylenically unsaturated carboxylic acid other than (meth) acrylic acid include ethacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, phthalic anhydride half-esterified with alkyl alcohol, and itaconic anhydride And those obtained by half-esterification with alkyl alcohol.

As the neutralized salt of the ethylenically unsaturated carboxylic acid, (meth) acrylic acid includes alkali metal salts other than potassium salts, alkaline earth metal salts other than magnesium salts, ammonium salts, and organic amine salts. Can be mentioned. Other alkali metal salts such as ethacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, phthalic anhydride half-esterified with alkyl alcohol, and itaconic anhydride half-esterified with alkyl alcohol , Alkaline earth metal salts, ammonium salts, and organic amine salts.

Examples of the (meth) acrylic acid alkyl ester compounds include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, and n-butyl (meth) acrylate. , Isobutyl (meth) acrylate, sec-butyl (meth) acrylate, tert-butyl (meth) acrylate, n-pentyl (meth) acrylate, isoamyl (meth) acrylate, n-hexyl (meth) acrylate 2-methylpentyl (meth) acrylate, n-octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-decyl (meth) acrylate, n-dodecyl (meth) acrylate, (meth) N-octadecyl acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate (Meth) acrylate, phenyl include benzyl (meth) acrylate and the like. Among these, a (meth) acrylic acid alkyl ester compound having an alkyl group having 1 to 4 carbon atoms is preferable from the viewpoint of the balance between solubility in water and good dispersibility.

Examples of the aromatic vinyl compound include styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, α-methylstyrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene, and 4-tert-butylstyrene. Tert-butoxystyrene, vinyltoluene, vinylnaphthalene, halogenated styrene, styrenesulfonic acid, α-methylstyrenesulfonic acid, and the like.

Examples of the acid anhydride monomer include maleic anhydride, itaconic anhydride, citraconic anhydride, and the like.

Examples of the amino group-containing vinyl compound include dimethylaminomethyl (meth) acrylate, diethylaminomethyl (meth) acrylate, 2-dimethylaminoethyl (meth) acrylate, 2-diethylaminoethyl (meth) acrylate, (meth) 2- (di-n-propylamino) ethyl acrylate, 2-dimethylaminopropyl (meth) acrylate, 2-diethylaminopropyl (meth) acrylate, 2- (di-n-propylamino) (meth) acrylate And propyl, 3-dimethylaminopropyl (meth) acrylate, 3-diethylaminopropyl (meth) acrylate, 3- (di-n-propylamino) propyl (meth) acrylate, and the like.

Examples of the amide group-containing vinyl compound include (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, N-methylol (meth) acrylamide and the like.

Examples of the sulfonic acid group-containing vinyl compound include methallylsulfonic acid, acrylamide-2-methyl-2-propanesulfonic acid, styrenesulfonic acid, 3-allyloxy-2-hydroxy-1-propanesulfonic acid, and the like. Salt.

Examples of the polyoxyalkylene group-containing vinyl compound include (meth) acrylic acid esters of alcohols having a polyoxyethylene group and / or a polyoxypropylene group.

Examples of the alkoxyl group-containing vinyl compound include 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 2- (n-propoxy) ethyl (meth) acrylate, and 2- (meth) acrylic acid 2- (N-butoxy) ethyl, 3-methoxypropyl (meth) acrylate, 3-ethoxypropyl (meth) acrylate, 2- (n-propoxy) propyl (meth) acrylate, 2- (n) (meth) acrylate -Butoxy) propyl and the like.

Examples of the (meth) acrylic acid ester compound having a cyano group include cyanomethyl (meth) acrylate, 1-cyanoethyl (meth) acrylate, 2-cyanoethyl (meth) acrylate, 1-cyanopropyl (meth) acrylate, (Meth) acrylic acid 2-cyanopropyl, (meth) acrylic acid 3-cyanopropyl, (meth) acrylic acid 4-cyanobutyl, (meth) acrylic acid 6-cyanohexyl, (meth) acrylic acid 2-ethyl-6- And cyanohexyl and 8-cyanooctyl (meth) acrylate.

Examples of the vinyl cyanide compound include acrylonitrile, methacrylonitrile, ethacrylonitrile and the like.

Examples of the vinyl ether compound include vinyl methyl ether, vinyl ethyl ether, vinyl-n-butyl ether, vinyl phenyl ether, vinyl cyclohexyl ether and the like. These may be used alone or in combination of two or more.
Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, and vinyl propionate.

Examples of the conjugated dienes include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 4, Examples include 5-diethyl-1,3-octadiene, 3-butyl-1,3-octadiene, chloroprene and the like.

Other maleimide compounds such as maleimide, N-methylmaleimide, N-butylmaleimide, N-phenylmaleimide, N-cyclohexylmaleimide; maleic acid ester compounds; itaconic acid ester compounds; N-vinyl heterocyclic compounds such as vinylpyridine Is mentioned.

Of these other monomers, maleic acid, acrylamido-2-methyl-2-propanesulfonic acid, and salts thereof are preferable. By using these together with (meth) acrylic acid, a dispersant having excellent initial viscosity of a slurry obtained by stirring and dispersing can be obtained.

The (meth) acrylic acid polymer of the present invention has a carboxyl group derived from the structural unit (meth) acrylic acid, and 20 to 65 mol% of the carboxyl group is a potassium salt. The preferred range of the potassium salt is 25 to 60 mol%, more preferably 30 to 50 mol%.
When the potassium salt is less than 20 mol%, there is a tendency that the viscosity of the calcium carbonate slurry by stirring and dispersing cannot be sufficiently reduced. Moreover, when it exceeds 65 mol%, the temporal stability of the calcium carbonate slurry by stirring and dispersion may be insufficient.

In the (meth) acrylic acid polymer of the present invention, 35 to 70 mol% of the carboxyl group is a magnesium salt. The preferred range of the magnesium salt is 40 to 65 mol%, more preferably 45 to 65 mol%.
When the magnesium salt is less than 35 mol%, the temporal stability of the calcium carbonate slurry by wet pulverization may not be sufficient. Moreover, when it exceeds 70 mol%, the solubility of a dispersing agent may become inadequate.

The (meth) acrylic acid polymer of the present invention is one kind selected from (meth) acrylic acid, potassium (meth) acrylate and magnesium (meth) acrylate in the presence of a polymerization initiator or the like in a polymerization solvent. It can be obtained by polymerizing a monomer mixture containing 80 to 100% by mass of two or more monomers and neutralizing the carboxyl group of the polymer obtained as necessary. When potassium (meth) acrylate and magnesium (meth) acrylate are used as monomers, the ratio of the potassium salt and magnesium salt of the obtained (meth) acrylic acid polymer is within the range specified in the present application. The obtained polymer may not be further neutralized.
Further, the carboxyl group of the (meth) acrylic acid polymer of the present invention may include forms such as alkali metal salts, alkaline earth metal salts, ammonium salts and organic amine salts other than the potassium salt and magnesium salt.

The neutralization rate of the (meth) acrylic acid polymer of the present invention is 55 to 100 mol%, preferably 60 to 98 mol%, more preferably 60 to 95 mol%.
In order to adjust the neutralization rate in the polymerization reaction of the (meth) acrylic acid polymer and in the final product, and the pH of the solution, an alkali agent (neutralizing agent) is used. Specifically, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide, ammonia, monoethanolamine, diethanolamine, triethanolamine, etc. Organic amines etc. are mentioned, Among these, 1 type (s) or 2 or more types can be used.

The polymerization method of the (meth) acrylic acid polymer is not particularly limited, but a solution polymerization method is preferable. According to the solution polymerization, the dispersant can be obtained as a uniform solution.
Water or a mixed solution of water and an organic solvent can be used as a polymerization solvent in the solution polymerization. Preferred organic solvents when using a mixed solution of water and an organic solvent include alcohols such as isopropyl alcohol and ketones such as acetone, with isopropyl alcohol being particularly preferred.
When a mixed liquid of water and isopropyl alcohol (hereinafter also referred to as “isopropyl alcohol aqueous solution”) is used as a polymerization solvent, isopropyl alcohol also acts as a chain transfer agent. Therefore, the isopropyl alcohol aqueous solution is used as a reaction solvent and a chain transfer agent.

The isopropyl alcohol concentration of the aqueous isopropyl alcohol solution is preferably 30% by mass to 60% by mass, and more preferably 35-50% by mass.
When the concentration of isopropyl alcohol is 30% by mass or more, the chain transfer effect as a chain transfer agent possessed by isopropyl alcohol works effectively. Moreover, since the reaction liquid during superposition | polymerization will be kept uniformly if it is 60 mass% or less, it is easy to obtain a polymer with narrow molecular weight distribution.

Further, the amount of isopropyl alcohol used in the polymerization is preferably 30 to 95 parts by mass, more preferably 40 to 85 parts by mass with respect to 100 parts by mass of the monomer. When the amount of isopropyl alcohol used is 30 parts by mass or more, the chain transfer effect of isopropyl alcohol works effectively. Further, when it is 95 parts by mass or less, the time required for solvent distillation described later can be shortened, so that a polymer solution with less coloring is obtained.

When an isopropyl alcohol aqueous solution is used at the time of polymerization, the reaction system is decompressed and / or heated after the polymerization is completed to distill isopropyl alcohol out of the system and distill off the isopropyl alcohol from the reaction solution. preferable.
The isopropyl alcohol distilled off is usually an azeotrope with water. Therefore, isopropyl alcohol is distilled off from the reaction solution as an aqueous solution, resulting in a concentrated composition in which isopropyl alcohol and water are reduced.

The method for distilling off isopropyl alcohol is not particularly limited. For example, water and isopropyl alcohol can be distilled out of the system by subjecting the reaction system to reduced pressure and keeping its internal temperature at or above the azeotropic temperature of isopropyl alcohol. Further, water and isopropyl alcohol may be distilled out of the system by passing the reaction solution through a thin film evaporator under reduced pressure.

When isopropyl alcohol is distilled off, the content of isopropyl alcohol contained in the resulting concentrated composition is preferably 1% by mass or less, more preferably 5000 ppm by mass or less, still more preferably 2000 ppm by mass or less, Especially preferably, it is 1000 mass ppm or less.

In the polymerization, a known polymerization initiator can be used, and a radical polymerization initiator is particularly preferably used.
Examples of the radical polymerization initiator include persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate, hydroperoxides such as t-butyl hydroperoxide, water-soluble peroxides such as hydrogen peroxide, methyl ethyl ketone, and the like. Oil-soluble peroxides such as ketone peroxides such as peroxide and cyclohexanone peroxide, dialkyl peroxides such as di-t-butyl peroxide and t-butylcumyl peroxide, 2,2′-azobis (2- And azo compounds such as methylpropionamidine) dihydrochloride.
The peroxide radical polymerization initiator may be used alone or in combination of two or more.
Among the peroxide-based radical polymerization initiators, persulfates and azo compounds are preferable from the viewpoint that the polymerization reaction can be easily controlled, and persulfates are particularly preferable.
The radical polymerization initiator is diluted with, for example, an aqueous medium and supplied to the reactor from a supply port different from that of the monomer.
The ratio of the radical polymerization initiator used is not particularly limited, but is a ratio of 0.1 to 15% by weight, particularly 0.5 to 10% by weight, based on the total weight of all monomers constituting the acrylic acid polymer. Is preferably used. By making this proportion 0.1% by weight or more, the (co) polymerization rate can be improved, and by making it 15% by weight or less, the stability of the resulting polymer is improved and used for a dispersant or the like. When it is done, it will have excellent performance.
In some cases, a water-soluble redox polymerization initiator may be used as a polymerization initiator. As a redox polymerization initiator, a combination of an oxidizing agent (for example, the above-described peroxide) and a reducing agent such as sodium bisulfite, ammonium bisulfite, sodium sulfite, sodium hydrosulfite, iron alum, potassium alum, etc. Can be mentioned.

In the production of the (meth) acrylic acid polymer, a chain transfer agent may be appropriately added to the polymerization system in order to adjust the molecular weight. Examples of the chain transfer agent include phosphite compounds such as sodium phosphite and potassium phosphite; hypophosphite compounds such as sodium hypophosphite and potassium hypophosphite; sodium bisulfite, mercaptoacetic acid, Examples include mercaptopropionic acid, 2-propanethiol, 2-mercaptoethanol, thiophenol and isopropyl alcohol.
The above chain transfer agents may be used alone or in combination of two or more.
Among the chain transfer agents described above, phosphite compounds, hypophosphite compounds and isopropyl alcohol are preferred because the molecular weight can be easily controlled.
The chain transfer agent may be supplied to the reactor from a supply port different from that of the monomer or polymerization initiator, but may be mixed with the monomer immediately before being supplied to the reactor. The preferred amount of use is 0.3 to 50 mol%, more preferably 1.0 to 25 mol%, based on the amount of monomer (number of moles).

In the present invention, it is preferable that the polymerization solvent is an isopropyl alcohol aqueous solution and a phosphorous acid compound and / or a hypophosphorous acid compound is used as a chain transfer agent in terms of low initial viscosity of a slurry obtained by wet pulverization.
The amount of the phosphorous acid compound and / or hypophosphorous acid compound used is preferably 1.0 to 4.5 parts by mass, more preferably 1.5 to 4. The amount is 0 parts by mass, more preferably 1.7 to 3.8 parts by mass. If the usage-amount of a phosphorous acid compound and / or a hypophosphorous acid compound is 1.0 mass part or more, adjustment of the molecular weight of the (meth) acrylic acid type polymer obtained will become easy. Moreover, since there are few inorganic salts byproduced if it is 4.5 mass parts or less, the time-dependent stability of a calcium carbonate dispersion liquid will become favorable.

The reaction temperature during the polymerization is preferably 60 to 95 ° C, more preferably 65 to 90 ° C, and further preferably 70 to 85 ° C.
As the polymerization method, any of a batch polymerization method and a continuous polymerization method can be adopted. In the case of the batch polymerization method, the time required for supplying the raw material (raw material composition) containing the monomer is preferably 2 to 12 hours, more preferably 3 to 8 hours. If the required time is 2 hours or more, it is easy to remove the heat of polymerization, and if it is 12 hours or less, the productivity is increased.
In the case of a continuous polymerization method, the process is preferably performed by a multistage CSTR (continuous stirred tank reactor having a plurality of reaction tanks). In this case, the average residence time in each reaction tank is preferably 60 to 240 minutes, more preferably 80 to 180 minutes. When the average residence time is 60 minutes or longer, unreacted monomers can be reduced. Moreover, the size of a reaction tank can be made small as it is 240 minutes or less.

The weight average molecular weight (Mw) of the acrylic acid polymer in the present invention is preferably in the range of 3000 to 10,000, and more preferably in the range of 4000 to 8000. When the weight average molecular weight is 3000 or more, the temporal stability of the dispersion by stirring dispersion and wet grinding is improved. Moreover, the viscosity of the calcium carbonate slurry by wet grinding is reduced as it is 10,000 or less. The weight average molecular weight can be measured by a gel permeation chromatography (GPC) using a standard substance such as sodium polyacrylate.

The pH and solid content concentration of the dispersant of the present invention are not particularly limited. The pH is preferably 5 to 10, and more preferably 6 to 9. The solid content concentration is preferably 30 to 55%, more preferably 35 to 50%.

Moreover, the dispersing agent of this invention can contain other components, such as an antifoamer and a preservative, further.
Examples of the antifoaming agent include polyether, mineral oil, silicone, and amide. When the dispersant of the present invention contains the antifoaming agent, the content thereof is preferably 0.01 to 1.0% by mass with respect to 100 parts by mass of the acrylic polymer.

Examples of the preservative include isothiazoline and parabens. When the dispersant of the present invention contains the preservative, the content thereof is preferably 0.001 to 1.0% by mass with respect to 100 parts by mass of the acrylic polymer.

The dispersant of the present invention may be a solution or dispersion in which the (meth) acrylic polymer and the other components to be blended as necessary are contained in an aqueous medium.
Moreover, when the dispersing agent of this invention contains the said other component, another component is added and mixed. In addition, the said mixing is not specifically limited, It can carry out by a well-known method.

When a calcium carbonate slurry is obtained using the dispersant of the present invention, the amount of the dispersant is not particularly limited, but the (meth) acrylic polymer is 0.1 to 10 per 100 parts by mass of calcium carbonate. It is preferable to add 0.0 parts by mass and 20 to 100 parts by mass of the aqueous medium.
The dispersant may be added all at once, or may be added in two or more portions. Moreover, you may add continuously. Among these, from the viewpoint of easily obtaining a low-viscosity calcium carbonate slurry, a method of adding in a divided manner or a method of adding continuously is preferable.
When obtaining a calcium carbonate slurry, the dispersing agent of this invention can be used 1 type (s) or 2 or more types. Moreover, when adding a dispersing agent separately, you may use together dispersing agents other than the dispersing agent of this invention.
And a calcium carbonate slurry can be obtained by wet-grinding or stirring and dispersing a mixture of a dispersant containing calcium carbonate and a (meth) acrylic polymer blended as described above by a known method.

The dispersant of the present invention is excellent in the dispersibility of calcium carbonate, and is suitably used as a dispersant for calcium carbonate in the case of obtaining a calcium carbonate slurry by wet pulverizing or stirring and dispersing calcium carbonate. The calcium carbonate slurry obtained using the dispersant of the present invention has a low initial viscosity, a remarkable increase in viscosity with time is suppressed, and a slurry having excellent long-term dispersion stability can be obtained.

Further, when the dispersant of the present invention contains the other components, the (meth) acrylic polymer and other components added as necessary can be mixed. Moreover, when the dispersing agent of this invention is the aqueous solution or dispersion liquid by the aqueous medium containing a (meth) acrylic-type polymer, another component is added and mixed with this aqueous solution and dispersion liquid as needed. In addition, the said mixing is not specifically limited, It can carry out by a well-known method.

Hereinafter, the present invention will be specifically described based on examples. In the following description, “part” means part by mass, and “%” means mass%.
Moreover, solid content concentration, such as a polymer obtained in each case, was measured by the method as described below.

<Solid content>
About 1 g of the measurement sample was weighed (a), then the residue after drying at 155 ° C. for 30 minutes in the ventilation dryer was measured (b) and calculated from the following formula. A weighing bottle was used for the measurement. Other operations were in accordance with JIS K 0067-1992 (chemical product weight loss and residue test method).
Solid content (%) = (b / a) × 100

<Molecular weight measurement (GPC)>
The weight average molecular weight (Mw) and number average molecular weight (Mn) of the polymer were measured by gel permeation chromatograph (GPC).
As a GPC apparatus, an HLC8020 system (manufactured by Tosoh Corporation) was used, and G4000PWxl, G3000PWxl, and G2500PWxl (all of which are manufactured by Tosoh Corporation) were used as columns. The eluent was 0.1M NaCl + phosphate buffer (pH 7), and the calibration curve was prepared using polyacrylic acid Na (manufactured by Sowa Kagaku Co., Ltd.).

<Viscosity>
It measured on 25 degreeC and 60 rpm conditions using the B-type viscosity meter.
<Particle size of calcium carbonate slurry>
The 2 μm under integrated value of the calcium carbonate slurry was measured using a particle size distribution measuring device Sedygraph 5120 (manufactured by Micromeritic).

Example 1
<Production of Dispersant E1>
A flask equipped with a stirrer and a condenser was charged with 300 g of an aqueous solution having an isopropyl alcohol (hereinafter referred to as “IPA”) concentration of 44% and maintained at 75 ° C. A solution prepared by mixing 500 g of acrylic acid (hereinafter referred to as “AA”), 18 g of sodium hypophosphite, and 250 g of an aqueous solution with an IPA concentration of 44%, and 33 g of a 15% aqueous solution of sodium persulfate are supplied to this flask over 4 hours. Then, a polymerization reaction was performed. After completion of the supply, the reaction solution was further kept at 75 ° C. for 1 hour to be reacted. Subsequently, about the obtained reaction liquid, IPA was depressurizingly distilled, throwing in deionized water until IPA density | concentration became 1000 mass ppm or less. Subsequently, the reaction solution obtained by distilling off IPA under reduced pressure was maintained at 75 ° C., and 100 g of magnesium hydroxide (corresponding to 49 mol% of used AA) and 370 g of 48% potassium hydroxide aqueous solution (corresponding to 46 mol% of used AA) And deionized water was supplied. As a result, a dispersant E1 containing a (meth) acrylic polymer E1 and having a solid content concentration of 40% and a pH of 7.0 was obtained.
Moreover, Mw of the (meth) acrylic-type polymer E1 was 4900, and Mw / Mn was 2.1.

<Wet grinding test of calcium carbonate>
7 g of dispersant E1, 320 g of ion exchange water and 900 g of heavy calcium carbonate (manufactured by Maruo Calcium Co., Ltd., trade name “No. A heavy charcoal”) are put into a cylindrical container, and lightly stirred to be evenly blended. It was. Next, 3000 g of media (1 mmφ ceramic beads) was put into the cylindrical container, and wet pulverization was performed by stirring at 1000 rpm for 50 minutes. Thereafter, the slurry was recovered through a 200-mesh filter cloth, and ion exchange water was added to adjust the solid content to 75%, thereby obtaining a heavy calcium carbonate slurry. And when the viscosity immediately after wet grinding of this slurry and the viscosity after standing for 7 days at 25 ° C. were measured as described above, the viscosity immediately after wet grinding was 190 mPa · s, and the viscosity after 7 days was 1700 mPa · s. s.
The 2 μm under value of the slurry immediately after wet pulverization was 99%. These results are shown in Table 1.

<Calculation dispersion test of calcium carbonate>
6.3 g of the dispersant E1, 330 g of ion-exchanged water and 1000 g of heavy calcium carbonate (No. A heavy coal) were put into a cylindrical container equipped with a stirrer and dispersed by stirring at 4000 rpm for 10 minutes. When the viscosity immediately after dispersion of this slurry and the viscosity after standing for 7 days at 25 ° C. were measured, the viscosity immediately after stirring and dispersion was 150 mPa · s, and the viscosity after 7 days was 1000 mPa · s.

Examples 2 to 15 and Comparative Examples 1 to 4
Dispersion containing (meth) acrylic polymers E2 to E15 and C1 to C4 in the same manner as in Example 1 except that the raw materials used for the polymerization reaction and subsequent neutralization were as shown in Tables 1 to 3. Agents E2-E15 and C1-C4 were obtained.
Thereafter, a wet pulverization test for calcium carbonate and an agitation dispersion test for calcium carbonate were carried out in the same manner as in Example 1 except that the dispersants E2 to E15 and C1 to C4 were used instead of the dispersant E1. The results are shown in Tables 1 to 3.

In Tables 1 to 3, the symbols (a) to (c) attached to the special remarks column mean the following states.
(A): The aqueous polymer solution was colored brown.
(B): Turbidity occurred in the aqueous polymer solution.
(C): The aqueous polymer solution was separated. For this reason, the wet pulverization test and the stirring dispersion test were not performed.

In each of the (meth) acrylic acid polymers E1 to E15 shown in Examples 1 to 15, the carboxyl group of the (meth) acrylic acid polymer has a potassium salt and a magnesium salt in the range defined in the present application. It is what has become. When these (meth) acrylic acid polymer aqueous solutions were used as a dispersant, a slurry having a low viscosity was obtained in both wet pulverization and stirring dispersion, and no significant increase in viscosity with time was observed.
In Example 7, the amount of IPA used was relatively large, and it took a longer time than other experimental examples to distill it off after polymerization. For this reason, the obtained polymer aqueous solution was colored brown. In Example 11 where the proportion of magnesium salt was relatively high and Example 12 where the proportion of potassium salt was relatively low, turbidity was observed in the aqueous polymer solution.

On the other hand, Comparative Example 1 is an example in which a (meth) acrylic acid polymer having a low magnesium salt ratio was used as a dispersant, but the stability of slurry viscosity was poor particularly in wet grinding. Further, in Comparative Example 2 in which a (meth) acrylic acid polymer having a high magnesium salt ratio was used as a dispersant, the wet pulverization test and the stirring dispersion test could not be performed because the polymer aqueous solution was separated.
On the other hand, Comparative Examples 3 and 4 in which the proportion of the potassium salt of the (meth) acrylic acid polymer is outside the range specified in the present application resulted in a high slurry viscosity particularly in the stirring dispersion test.

According to the dispersant for calcium carbonate containing the (meth) acrylic acid polymer of the present invention, it is possible to produce a slurry having a low viscosity and good dispersion stability regardless of a dispersion method such as wet grinding or stirring dispersion. It is.

Claims

From 80 to 100% by mass of one or more monomers selected from (meth) acrylic acid, potassium (meth) acrylate and magnesium (meth) acrylate, and from 0 to 20% by mass of other monomers (Meth) acrylic acid polymer, wherein 20 to 65 mol% of the carboxyl group of the (meth) acrylic acid polymer is a potassium salt and 35 to 70 mol% is a magnesium salt. Dispersant for calcium carbonate containing a polymer.
2. The calcium carbonate dispersant according to claim 1, wherein the (meth) acrylic acid polymer has a weight average molecular weight of 3000 to 10,000.
The (meth) acrylic acid polymer polymerizes a monomer containing (meth) acrylic acid in the presence of a phosphorous acid compound and / or a hypophosphorous acid compound using an aqueous isopropyl alcohol solution as a solvent. Is obtained by
The amount of the phosphorous acid compound and / or hypophosphorous acid compound used is 1.0 to 4.5 parts by mass with respect to 100 parts by mass of the monomer. Dispersant for calcium carbonate as described in 1.
A method for producing a dispersant for calcium carbonate containing a (meth) acrylic acid polymer,
One kind selected from (meth) acrylic acid, potassium (meth) acrylate and magnesium (meth) acrylate in the presence of a phosphite compound and / or a hypophosphite compound using an aqueous isopropyl alcohol solution as a solvent Or a polymerization step of polymerizing two or more monomers of 80 to 100% by mass and other monomers of 0 to 20% by mass,
In the polymerization step, a phosphorous acid compound and / or a hypophosphorous acid compound is used in an amount of 1.0 to 4.5 parts by mass with respect to 100 parts by mass of the monomer.
If necessary, neutralization is performed so that 20 to 65 mol% of the carboxyl group of the (meth) acrylic acid polymer is a potassium salt and 35 to 70 mol% is a magnesium salt. Method for producing a dispersing agent.