JP7842669B2 - Dispersant for carbonate-containing cement compositions - Google Patents

Description

This invention relates to a dispersant for carbonate-containing cement compositions.

The cement industry is one of the largest emitters of carbon dioxide, second only to power and steel, making emission reduction an urgent issue. To address this challenge, companies, including those selected for NEDO's Green Innovation Fund program, are incorporating calcium carbonate into concrete (for example, Patent Document 1). This allows for the sequestration of carbon dioxide within the concrete, thereby reducing the total amount of carbon dioxide emitted during the cement manufacturing process.

Japanese Patent Publication No. 2022-40262 (Taisei Corporation)

While admixtures are typically added to concrete to improve its workability during production and placement, there is currently limited knowledge regarding cement admixtures suitable for cement compositions containing carbonates such as calcium carbonate.

The present invention aims to provide a dispersant capable of improving the dispersibility of carbonate-containing cement compositions.

The present invention provides the following:
[1] A dispersant for carbonate-based cement compositions, comprising a polycarboxylic acid copolymer containing 1 to 99% by weight of constituent unit (I) derived from a monomer represented by the following general formula (1), and 1 to 99% by weight of constituent unit (II) derived from a monomer represented by the following general formula (2).
[In the formula, ^R1 , ^R2 , and ^R3 each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, x represents a number from 0 to 3, y represents 0 or 1, R5O represents an oxyalkylene group having 2 to 18 carbon atoms, either identical or different, n is the average number of moles added by the oxyalkylene group and represents a number from 1 to 100, and ^R4 represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms];
[In the formula, ^R6 , ^R7 , and ^R8 each independently represent ^a hydrogen atom, a methyl group, or -( _CH2 ) _rCOOM2 , ^M1 and ^M2 are the same or different, representing a hydrogen atom, an alkali metal, an alkaline earth metal, an ammonium group, an alkylammonium group ^, or a substituted alkylammonium group, where r is an integer from 0 to 2, and where -( _CH2 ) ^rCOOM2 may form an anhydride with ^-COOM1 or other -( _CH2 ) _rCOOM2 , but if an anhydride is formed, ^M1 and ^M2 are not present in those groups ^. ]
[2] The dispersant according to [1], wherein the carbonate is calcium carbonate or magnesium carbonate.
[3] The dispersant described in [2], wherein the calcium carbonate is light calcium carbonate.
[4] The dispersant according to any one of [1] to [3], characterized in that the average particle size of the carbonate is 1.0 to 100 μm.
[5] The dispersant according to any one of [1] to [4], wherein the weight-average molecular weight of the polycarboxylic acid copolymer is 5,000 to 100,000.
[6] A dispersant according to any one of [1] to [5], wherein the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) (Mw/Mn) is 0.1 to 10.0.
[7] The dispersant according to any one of [1] to [6], wherein the carbonate content in the carbonate-containing cement composition is 10 to 100 parts by weight per 100 parts by weight of cement.
[8] The dispersant according to any one of [1] to [7], wherein the amount added is 0.01 to 5.0 parts by weight per 100 parts by weight of the total amount of the carbonate-containing cement composition.

According to the present invention, a dispersant capable of improving the dispersibility of carbonate-containing cement compositions is provided. Therefore, it is expected that the usability of carbonate-containing cement compositions will be improved, leading to a reduction in carbon dioxide emissions and contributing to the resolution of environmental problems in the cement industry.

Figure 1 is a graph showing the relationship between the flow value and the addition rate of polymer 1 in Example 1. Figure 2 is a graph showing the relationship between the flow value and the addition rate of polymer 2 in Example 2. Figure 3 is a graph showing the relationship between the flow value and the addition rate of polymer 3 in Example 3. Figure 4 is a graph showing the relationship between the flow value and the addition rate of polymer 4 in Comparative Example 1. Figure 5 is a graph showing the relationship between the flow value and the addition rate of polymer 1 (combination of polymers 1 and 4, or polymer 1 alone) in Example 4. Figure 6 is a graph showing the relationship between the flow value and the addition rate of polymer 2 (combined use of polymers 2 and 4, or polymer 2 alone) in Example 5. Figure 7 is a graph showing the relationship between the flow value and the addition rate of polymer 1 (polymer 1 alone in Example 6, and polymers 1 and 4 used together in Example 7) in Examples 6 and 7 (containing 55% light calcium carbonate). Figure 8 is a graph showing the relationship between the flow value and the addition rate of polymer 1 in Example 6 (containing 38% light calcium carbonate). Figure 9 is a graph showing the relationship between the flow value and the addition rate of polymer 2 in Example 8 (containing 55% light calcium carbonate). Figure 10 is a graph showing the relationship between the flow value and the addition rate of polymer 2 in Example 8 (containing 38% light calcium carbonate). Figure 11 is a graph showing the relationship between the flow value and the addition rate of polymer 4 in Comparative Example 3 (containing 55% light calcium carbonate). Figure 12 is a graph showing the relationship between the flow value and the addition rate of polymer 4 in Comparative Example 3 (containing 38% light calcium carbonate). Figure 13 is a graph showing the relationship between the flow value and the addition rate of polymer 1 in Examples 9 and 10 (polymer 1 alone in Example 9, and polymers 1 and 4 used together in Example 10). Figure 14 is a graph showing the relationship between the flow value and the addition rate of polymer 2 in Example 11. Figure 15 is a graph showing the relationship between the flow value and the addition rate of polymer 4 in Comparative Example 4.

[1. Polycarboxylic acid copolymers]
Polycarboxylic acid copolymers are copolymers containing constituent units (I) and (II).
[1-1. Constituent Units (I)]
The constituent unit (I) is a constituent unit derived from the monomer represented by general formula (1).

In general formula (1), ^R1 , ^R2 , and ^R3 each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. Examples of alkyl groups having 1 to 3 carbon atoms include a methyl group, an ethyl group, an n-propyl group, and an isopropyl group. The alkyl group having 1 to 3 carbon atoms may have substituents, but the number of carbon atoms in the substituents is not included in the number of carbon atoms of the alkyl group. ^R1 is preferably a hydrogen atom. ^R2 is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group. ^R3 is preferably a hydrogen atom.

In general formula (1), x represents an integer between 0 and 3, and y represents 0 or 1. When y is 0, x is preferably an integer between 1 and 3, more preferably 1 or 2. When y is 1, x is preferably 0.

In general formula (1), R ⁵ O represents an oxyalkylene group having 2 to 18 carbon atoms, which may be the same or different. Examples of the oxyalkylene group (alkylene glycol unit) include an oxyethylene group (ethylene glycol unit), an oxypropylene group (propylene glycol unit), and an oxybutylene group (butylene glycol unit), with the oxyethylene group and the oxypropylene group being preferred.

The phrase "may be the same or different" above means that when general formula (1) contains multiple ^R5O groups (when n is 2 or more), each ^R5O group may be the same oxyalkylene group, or they may be different oxyalkylene groups (two or more types). An example of when general formula (1) contains multiple ^R5O groups is when two or more oxyalkylene groups selected from the group consisting of oxyethylene groups, oxypropylene groups, and oxybutylene groups are mixed. Preferably, the mixture consists of oxyethylene groups and oxypropylene groups, or oxyethylene groups and oxybutylene groups, and more preferably, oxyethylene groups and oxypropylene groups are mixed. In the example where different oxyalkylene groups are mixed, the addition of two or more types of oxyalkylene groups may be in a block-like manner or in a random manner. In general formula (1), when y is 0, the alkylene group with x carbon atoms and R ⁵ O are bonded via an oxygen atom.

In general formula (1), n represents the average number of moles of oxyalkylene groups added, and is an integer from 1 to 100. n is preferably 5 or more, more preferably 7 or more, and even more preferably 10 or more. When y is 0, the lower limit of n is more preferably 20 or more, 30 or more, or 40 or more. The upper limit is preferably 90 or less, more preferably 80 or less, even more preferably 70 or less, and even more preferably 60 or less. When y is 1, the upper limit of n is more preferably 50 or less, 40 or less, or 30 or less. Therefore, 5 to 90 is preferred, 7 to 80 is more preferred, 10 to 70 is even more preferred, and 10 to 60 is even more preferred. The average number of moles added refers to the average number of moles of oxyalkylene groups added to 1 mole of monomer.

In general formula (1), ^R4 represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms. ^R4 is preferably a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, more preferably a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms, and even more preferably a hydrogen atom or a methyl group. Within this range, the number of carbon atoms does not become too large, which can improve the dispersibility of the hydraulic composition.

A method for producing the monomer represented by general formula (1) includes, for example, adding 1 to 100 moles of alkylene oxide to an alkylallyl alcohol such as allyl alcohol or methallyl alcohol, or an unsaturated alcohol such as 3-methyl-3-buten-1-ol.

Monomers that can be produced by this method include, for example, (poly)ethylene glycol allyl ether, (poly)ethylene glycol metharyl ether, (poly)ethylene glycol 3-methyl-3-butenyl ether, (poly)ethylene (poly)propylene glycol allyl ether, (poly)ethylene (poly)propylene glycol metharyl ether, (poly)ethylene (poly)propylene glycol 3-methyl-3-butenyl ether, (poly)ethylene (poly)butylene glycol allyl ether, (poly)ethylene (poly)butylene glycol metharyl ether, (poly)ethylene (poly)butylene glycol 3-methyl-3-butenyl ether, and methoxy(poly) Examples include ethylene glycol allyl ether, methoxy(poly)ethylene glycol metharyl ether, methoxy(poly)ethylene glycol 3-methyl-3-butenyl ether, methoxy(poly)ethylene(poly)propylene glycol allyl ether, methoxy(poly)ethylene(poly)propylene glycol metharyl ether, methoxy(poly)ethylene(poly)propylene glycol 3-methyl-3-butenyl ether, methoxy(poly)ethylene(poly)butylene glycol allyl ether, methoxy(poly)ethylene(poly)butylene glycol metharyl ether, and methoxy(poly)ethylene(poly)butylene glycol 3-methyl-3-butenyl ether.

Among these, (poly)ethylene glycol (meth)allyl ether, (poly)ethylene (poly)propylene glycol (meth)allyl ether, (poly)ethylene glycol 3-methyl-3-butenyl ether, and (poly)ethylene (poly)propylene glycol 3-methyl-3-butenyl ether are preferred due to their balance of hydrophilicity and hydrophobicity.

In this specification, the notation "(poly)" indicates whether the following component or raw material is present in multiple linked molecules or as a single molecule. "(meth)allyl" means methallyl and/or allyl; "(meth)acrylate" means methacrylate and/or acrylate; and "(meth)acrylic acid" means methacrylic acid and/or acrylic acid.

Another method for producing the monomer represented by general formula (1) is to esterify an unsaturated monocarboxylic acid such as acrylate or methacrylate with a (poly)alkylene glycol such as (poly)ethylene glycol, (poly)ethylene(poly)propylene glycol, (poly)ethylene(poly)butylene glycol, methoxy(poly)ethylene glycol, methoxy(poly)ethylene(poly)propylene glycol, or methoxy(poly)ethylene(poly)butylene glycol.

Examples of monomers that can be produced by this method include (poly)alkylene glycol (meth)acrylates such as (poly)ethylene glycol (meth)acrylate, (poly)ethylene (poly)propylene glycol (meth)acrylate, (poly)ethylene (poly)butylene glycol (meth)acrylate, methoxy (poly)ethylene glycol (meth)acrylate, methoxy (poly)ethylene (poly)propylene glycol (meth)acrylate, and methoxy (poly)ethylene (poly)butylene glycol (meth)acrylate.

Among these, (poly)alkylene glycol (meth)acrylate and methoxy(poly)alkylene glycol (meth)acrylate are preferred, and methoxy(poly)ethylene glycol (meth)acrylate is more preferred.

The constituent unit (I) may be one type or a combination of two or more types. In the case of a combination of two or more types, combinations of monomers where y in general formula (1) is 0, and combinations of monomers where y in general formula (1) is 1 are preferred. Furthermore, combinations where the difference in n in general formula (1) of each monomer is preferably within the range of 0 to 20, more preferably 0 to 15, and even more preferably 0 to 10 are preferred.

[1-2. Constituent Units (II)]
The constituent unit (II) is a constituent unit derived from the monomer represented by general formula (2).

In general formula (2), ^R6 , ^R7 , and ^R8 each independently represent a hydrogen atom, a methyl group ( _-CH3 ), or -( _CH2 ) _rCOOM2 . However, if ( _CH2 ) _rCOOM2 is ^present , it may form an anhydride ^{with -COOM1} or another -( _CH2 ) _rCOOM2 . If an anhydride is formed, ^{M1 and M2} of those groups are absent. ^R6 is preferably a hydrogen atom. ^R7 is preferably a hydrogen atom or _-CH3 . ^R8 is preferably a hydrogen atom.

^M1 and ^M2 may be the same or different, and represent a hydrogen atom, alkali metal, alkaline earth metal, ammonium group, alkylammonium group, or substituted alkylammonium group. Preferably, ^M1 and ^M2 are a hydrogen atom, alkali metal, and alkaline earth metal, respectively.

r represents an integer between 0 and 2, with 0 being preferred.

Examples of monomers represented by general formula (2) include unsaturated monocarboxylic acid monomers and unsaturated dicarboxylic acid monomers. Examples of unsaturated monocarboxylic acid monomers include acrylic acid, methacrylic acid, and crotonic acid; their monovalent metal salts, ammonium salts, and organic amine salts. Examples of unsaturated dicarboxylic acids include maleic acid, itaconic acid, citraconic acid, and fumaric acid; their monovalent metal salts, ammonium salts, and organic amine salts; and their anhydrides. Acrylic acid, methacrylic acid, and maleic acid are preferred monomers represented by general formula (2).

The constituent unit (II) may be a single type, or it may be two or more constituent units (II) derived from different monomers.

[1-3. Composition Ratio]
The content ratio of each constituent unit (if there are two or more, it is the sum of them, and the same applies to the content ratio of the copolymers below) is usually constituent unit (I) / constituent unit (II) = 1 to 99% by weight / 99 to 1% by weight, preferably 10 to 98% by weight / 90 to 2% by weight, more preferably 50 to 98% by weight / 50 to 2% by weight, even more preferably 60 to 95% by weight / 40 to 5% by weight, and even more preferably 70 to 95% by weight / 30 to 5% by weight.

[1-4. Arbitrary constituent unit (III)]
Polycarboxylic acid copolymers may further have a constituent unit (III) other than (I) and (II). Constituent unit (III) is a constituent unit derived from a monomer copolymerizable with monomers represented by general formulas (1) to (2). Monomers copolymerizable with monomers represented by general formulas (1) to (2) are structurally distinct from the monomers represented by general formulas (1) to (2). The monomers constituting constituent unit (III) are not particularly limited, but examples include the monomers listed below, which can be used individually or in combination of two or more.

Diallylbisphenols represented by the following general formula (III-1) (e.g., 4,4'-dihydroxydiphenylpropane, 4,4'-dihydroxydiphenylmethane, 4,4'-dihydroxydiphenylsulfone) with allyl substitutions at the 3 and 3'positions;

Allyl-substituted compounds at the 3-position of monoallylbisphenols represented by general formula (III-2) (e.g., 4,4'-dihydroxydiphenylpropane, 4,4'-dihydroxydiphenylmethane, 4,4'-dihydroxydiphenylsulfone);

Allylphenol represented by the following general formula (III-3);

Half-esters and diesters of unsaturated dicarboxylic acids such as maleic acid, maleic anhydride, fumaric acid, itaconic acid, and citraconic acid, and alcohols having 1 to 30 carbon atoms; half-amides and diamides of the same unsaturated dicarboxylic acids and amines having 1 to 30 carbon atoms;

Half-esters and diesters of alkyl (poly)alkylene glycols obtained by adding 1 to 500 moles of alkylene oxide with 2 to 18 carbon atoms to the above-mentioned alcohol or amine, and the above-mentioned unsaturated dicarboxylic acids;

Half-esters and diesters of the above-mentioned unsaturated dicarboxylic acids and glycols having 2 to 18 carbon atoms or polyalkylene glycols with 2 to 500 added moles of these glycols;

Halfamides of maleamic acid and polyalkylene glycols with 2 to 18 carbon atoms or 2 to 500 moles of these glycols added;

Esters of alkoxy(poly)alkylene glycols, obtained by adding 1 to 500 moles of alkylene oxide (containing 2 to 18 carbon atoms) to an alcohol (containing 1 to 30 carbon atoms), and unsaturated monocarboxylic acids such as (meth)acrylic acid;

(Poly)ethylene glycol monomethacrylate, (poly)propylene glycol monomethacrylate, (poly)butylene glycol monomethacrylate, etc., and 1 to 500 molar adducts of alkylene oxides having 2 to 18 carbon atoms to unsaturated monocarboxylic acids such as (meth)acrylic acid (excluding monomers represented by general formulas (1) to (3);

(Poly)alkylene glycol di(meth)acrylates such as triethylene glycol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, (poly)ethylene glycol (poly)propylene glycol di(meth)acrylate;

Polyfunctional (meth)acrylates such as hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and trimethylolpropane di(meth)acrylate;

(Poly)alkylene glycol dimalates such as triethylene glycol dimalate and polyethylene glycol dimalate;

Vinyl sulfonates, (meth)allyl sulfonates, 2-(meth)acryloxyethyl sulfonates, 3-(meth)acryloxypropyl sulfonates, 3-(meth)acryloxy-2-hydroxypropyl sulfonates, 3-(meth)acryloxy-2-hydroxypropyl sulfophenyl ethers, 3-(meth)acryloxy-2-hydroxypropyloxysulfobenzoate, 4-(meth)acryloxybutyl sulfonates, (meth)acrylamide methylsulfonic acid, (meth)acrylamide ethylsulfonic acid, 2-methylpropanesulfonic acid (meth)acrylamide, styrene sulfonic acid, and other unsaturated sulfonic acids, as well as their monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts;

Amides formed from unsaturated monocarboxylic acids such as methyl(meth)acrylamide and amines having 1 to 30 carbon atoms;
Vinyl aromatics such as styrene, α-methylstyrene, vinyltoluene, and p-methylstyrene;

Alkane diol mono(meth)acrylates such as 1,5-pentanediol mono(meth)acrylate and 1,6-hexanediol mono(meth)acrylate (excluding monomers represented by general formula (3));

Dienes such as butadiene, isoprene, 2-methyl-1,3-butadiene, and 2-chlor-1,3-butadiene;
Unsaturated amides such as (meth)acrylamide, (meth)acrylalkylamide, N-methylol(meth)acrylamide, and N,N-dimethyl(meth)acrylamide;

Unsaturated cyanides such as (meth)acrylonitrile and α-chloroacrylonitrile;
Unsaturated esters such as vinyl acetate and vinyl propionate;

Unsaturated amines such as (meth)acrylate aminoethyl, (meth)acrylate methylaminoethyl, (meth)acrylate dimethylaminoethyl, (meth)acrylate dimethylaminopropyl, (meth)acrylate dibutylaminoethyl, and vinylpyridine (excluding monomers represented by general formula (3));

Divinyl aromatic compounds such as divinylbenzene;
Cyanurates such as triallyl cyanurate;

Allyl compounds such as (meth)allyl alcohol and glycidyl (meth)allyl ether;
Vinyl ethers or allyl ethers such as methoxypolyethylene glycol monovinyl ether, polyethylene glycol monovinyl ether, methoxypolyethylene glycol mono(meth)allyl ether, polyethylene glycol mono(meth)allyl ether, etc. (excluding monomers represented by general formula (1)); and,

Siloxane derivatives such as polydimethylsiloxane-propylaminomaleamidoic acid, polydimethylsiloxane-aminopropyleneaminomaleamidoic acid, polydimethylsiloxane-bis-(propylaminomaleamidoic acid), polydimethylsiloxane-bis-(dipropyleneaminomaleamidoic acid), polydimethylsiloxane-(1-propyl-3-acrylate), polydimethylsiloxane-(1-propyl-3-methacrylate), polydimethylsiloxane-bis-(1-propyl-3-acrylate), and polydimethylsiloxane-bis-(1-propyl-3-methacrylate) (excluding monomers represented by general formula (3)).

If a constituent unit (III) is included, it may be just one type, or it may be two or more types derived from different monomers.

[1-5. Manufacturing method]
Polycarboxylic acid copolymers can be produced by copolymerizing each predetermined monomer using known methods. Examples of such methods include polymerization in a solvent and bulk polymerization.

- Reaction solvent -
Examples of solvents used in polymerization in a solvent include water; lower alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol; aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as cyclohexane and n-hexane; esters such as ethyl acetate; and ketones such as acetone and methyl ethyl ketone. From the viewpoint of solubility of the raw material monomers and the resulting copolymer, it is preferable to use at least one of water and a lower alcohol, and more preferably water.

When copolymerization is carried out in a solvent, each monomer and polymerization initiator may be added dropwise to the reaction vessel in a continuous manner, or a mixture of each monomer and a polymerization initiator may be added dropwise to the reaction vessel in a continuous manner. Alternatively, the solvent may be placed in the reaction vessel, and a mixture of monomers and solvent, along with a polymerization initiator solution, may be added dropwise to the reaction vessel in a continuous manner, or some or all of the monomers may be placed in the reaction vessel, and the polymerization initiator may be added dropwise.

- Initiator -
The polymerization initiators that can be used in copolymerization are not particularly limited. Examples of polymerization initiators that can be used when copolymerizing in an aqueous solvent include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate; and water-soluble peroxides such as t-butyl hydroperoxide and hydrogen peroxide. In this case, accelerators such as L-ascorbic acid, sodium bisulfite, and Mohr's salt may also be used in combination.

Polymerization initiators that can be used when copolymerizing in solvents such as lower alcohols, aromatic hydrocarbons, aliphatic hydrocarbons, esters, or ketones include, for example, peroxides such as benzoyl peroxide and lauryl peroxide; hydroperoxides such as cumene peroxide; and aromatic azo compounds such as azobisisobutyronitrile. In this case, accelerators such as amine compounds may also be used in combination. When copolymerizing in a water-lower alcohol mixed solvent, the polymerization initiator can be appropriately selected from the aforementioned polymerization initiators or combinations of polymerization initiators and accelerators.

The polymerization temperature varies depending on the polymerization conditions, such as the type of solvent and polymerization initiator used, but it is usually between 50 and 120°C.

- Chain transfer agent -
In copolymerization, the molecular weight can be adjusted using a chain transfer agent as needed. Examples of chain transfer agents that can be used include known thiol compounds such as mercaptoethanol, thioglycerol, thioglycolic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, thiomalic acid, octyl thioglycolate, and 2-mercaptoethanesulfonic acid; lower oxides and their salts such as phosphorous acid, hypophosphorous acid, and their salts (sodium hypophosphite, potassium hypophosphite, etc.), sulfurous acid, bisulfite, dithionite, metabisulfite, and their salts (sodium sulfite, potassium sulfite, sodium bisulfite, potassium bisulfite, sodium dithionite, potassium dithionite, sodium metabisulfite, potassium metabisulfite, etc.). These may be used alone or in combination of two or more.

To adjust the molecular weight of the copolymer, a monomer (IV) with high chain mobility, other than the monomers constituting the constituent units (I) to (III), may be used. Examples of monomers with high chain mobility (IV) include (meth)allyl sulfonic acid (salt) monomers.

-Neutralization-
When copolymerizing in an aqueous solvent to obtain copolymers, the pH during polymerization is usually strongly acidic due to the influence of monomers with unsaturated bonds, but this can be adjusted to a suitable pH. If pH adjustment is necessary during polymerization, it can be done using acidic substances such as phosphoric acid, sulfuric acid, nitric acid, alkyl phosphoric acid, alkyl sulfuric acid, alkyl sulfonic acid, or (alkyl)benzenesulfonic acid. Among these acidic substances, phosphoric acid is preferred due to its pH buffering properties.

Polymerization reactions are preferably carried out at a pH of 2 to 7 to eliminate the instability of the ester bonds in ester monomers. There are no particular limitations on the alkaline substances that can be used to adjust the pH, but alkaline substances such as NaOH and Ca(OH) _₂ are common. pH adjustment may be performed on the monomers before polymerization or on the copolymer solution after polymerization. Alternatively, some alkaline substances may be added before polymerization, and then the pH of the copolymer may be further adjusted.

[1-6. Physical Properties of Copolymers]
-Weight average molecular weight-
The weight-average molecular weight of the copolymer is preferably 5,000 or more, more preferably 7,000 or more, and even more preferably 9,000 or more. This allows the dispersibility of the hydraulic composition to be fully exhibited, enabling a water reduction rate exceeding that of AE water-reducing agents such as ligninsulfonic acid or oxycarboxylic acid, and improving fluidity or workability. The upper limit of the weight-average molecular weight is preferably 60,000 or less, more preferably 50,000 or less, and even more preferably 40,000 or less. This suppresses the aggregation of particles in the hydraulic composition, improving workability. The weight-average molecular weight is preferably 5,000 to 60,000, more preferably 7,000 to 50,000, and even more preferably 9,000 to 40,000.

-Mw/Mn-
The molecular weight distribution (dispersion: Mw/Mn) of the copolymer is preferably 1.0 or higher, more preferably 1.2 or higher. The upper limit is preferably 10.0 or lower, more preferably 5.0 or lower, and even more preferably 3.0 or lower. The molecular weight distribution is preferably 1.0 to 10.0, more preferably 1.2 to 5.0, and even more preferably 1.2 to 3.0.

The weight-average molecular weight and number-average molecular weight can be measured using a known method that converts them to polyethylene glycol equivalents via gel permeation chromatography (GPC). The molecular weight distribution can be calculated by dividing the measured weight-average molecular weight by the measured number-average molecular weight.

[2. Dispersants]
The above polycarboxylic acid copolymer can be used as a dispersant for carbonate-containing cement compositions. When a polyacrylic acid-based dispersant (a polymer consisting only of the above constituent unit (II)) is added to a "mixture" of carbonate and cement, the carboxyl groups of the polyacrylic acid-based dispersant repel each other by charge and aggregate, so it does not contribute to dispersion at all, at least at typical addition rates. In contrast, the above polycarboxylic acid-based copolymer, by containing constituent units (I) and (II), introduces nonionic, sterically repelling polyalkylene glycol chains to the polycarboxylic acid, thereby suppressing aggregation and exhibiting a dispersion effect. When used as a dispersant, the polycarboxylic acid-based copolymer may be used alone or in combination of two or more types.

[2-1. Carbonate-containing cement compositions]
In this specification, a carbonate-containing cement composition means a cement composition that contains carbonate.

-cement-
In this specification, cement includes not only cement but also other hydraulic materials such as gypsum (e.g., hemihydrate gypsum, dihydrate gypsum, etc.) and dolomite. Examples of cement include Portland cement (ordinary, rapid-hardening, ultra-rapid-hardening, moderate-heat, sulfate-resistant and their respective low-alkali forms), various blended cements (blast furnace cement, silica cement, fly ash cement), white Portland cement, alumina cement, ultra-rapid-hardening cement (1-clinker rapid-hardening cement, 2-clinker rapid-hardening cement, magnesium phosphate cement), grout cement, oil well cement, low-heat cement (low-heat blast furnace cement, fly ash-mixed low-heat blast furnace cement, beelite-high content cement), ultra-high-strength cement, cement-based solidifying agents, and eco-cement (cement manufactured using one or more of the following as raw materials: municipal solid waste incineration ash, sewage sludge incineration ash, etc.). The cement may also contain other components, such as fine powders like blast furnace slag, fly ash, cinder ash, clinker ash, husk ash, silica fume, silica powder, limestone powder, and gypsum.

-Carbonates-
The carbonate can be any compound containing carbonate ions ( _CO3-2 ⁾ , such as calcium carbonate, potassium carbonate, barium carbonate, magnesium carbonate, lithium carbonate, and ammonium carbonate. Calcium carbonate and magnesium carbonate are preferred, and calcium carbonate is more preferred due to its higher carbon dioxide fixation efficiency. Calcium carbonate is classified into light calcium carbonate (calcium carbonate produced artificially by methods such as carbon dioxide injection) and heavy calcium carbonate (calcium carbonate produced by crushing naturally occurring limestone minerals), and both can be used. Among these, light calcium carbonate is preferred because it has a higher carbon dioxide fixation efficiency than heavy calcium carbonate, is easily available as a by-product, and contributes to emission reduction through recycling.

Methods for producing light calcium carbonate include, for example, the following reactions: (1) the reaction of carbon dioxide-containing gas generated from a lime calcination apparatus, etc., with calcium hydroxide (slaked lime, lime milk); (2) the reaction of ammonium carbonate and calcium chloride in the ammonia-soda process; and (3) the reaction of calcium hydroxide and sodium carbonate. Of these, method (3) is preferred, and method (3) in the caustication process of the pulp manufacturing process is more preferred. This allows for the efficient production of calcium carbonate as a byproduct in pulp manufacturing. The caustication process in the pulp manufacturing process (e.g., sulfate process or soda process) is a process for recovering and regenerating digestion chemicals, and reaction (3) is a reaction that occurs during white liquor production.

The method for producing calcium carbonate in the pulp manufacturing process using the soda process (an example of the method described in (3) above) is described below. In the pulp manufacturing process, in order to extract pulp fibers from wood, a white liquor containing dissolved sodium hydroxide or sodium sulfide is added to wood chips and pulped in a boiler under high temperature and pressure. Along with the separation of the solid phase containing pulp fibers through pulping, a smelt mainly composed of a mixture of sodium carbonate, sodium sulfide, etc., is recovered as an inorganic component. A weak liquor (an aqueous solution in which some of the white liquor components are dissolved) is added to the smelt and dissolved to prepare crude green liquor. Crude green liquor contains inorganic components derived from the smelt (for example, including _Na₂CO₃ , _Na₂S , _and NaOH), as well as insoluble impurities such as unburned carbon particles generated in the boiler and wood components (components leached from the wood during pulping). Therefore, these impurities are separated from the system by separation methods such as sedimentation separation and filtration separation, and discharged, and other clarification treatments are performed as needed to obtain clarified green liquor. The clarified green liquor is sent to the causticization process, where calcium oxide (quicklime) is added and mixed. Through a two-step reaction of quenching and causticization, as shown in reactions 1 and 2 below, the sodium carbonate in the clarified green liquor is converted to sodium hydroxide (regeneration of the white liquor), and calcium carbonate is produced as a by-product.
Reaction 1: CaO + H ₂ O → Ca(OH) ₂
Reaction 2 _: Ca(OH) _₂ + _Na₂CO₃ → _CaCO₃ + 2NaOH

The amount of carbonate added is usually 5% or more by weight, or 7% or more by weight, and preferably 9% or more by weight, per 100 parts by weight of cement. When the carbonate is calcium carbonate, the lower limit may be 10 parts by weight or more, preferably 20 parts by weight or more, more preferably 30 parts by weight or more, and even more preferably 35 parts by weight or more. The upper limit is usually 100 parts by weight or less, preferably 90 parts by weight or less, more preferably 85 parts by weight or less, and even more preferably 80 parts by weight or less.

The average particle size of carbonates is typically 0.1 μm or more, 0.5 μm or more, or 1.0 μm or more, preferably 5.0 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. The upper limit is typically 100 μm or less, preferably 70 μm or less, more preferably 50 μm or less, and even more preferably 40 μm or less. Therefore, the average particle size is 0.1 to 100 μm, 0.5 to 100 μm, or 1.0 to 100 μm, preferably 5.0 to 100 μm, more preferably 10 to 70 μm, and even more preferably 15 to 50 μm. In this specification, the average particle size refers to the cumulative average particle size in the particle size distribution determined by laser diffraction.

In a cement composition containing carbonates, the carbonate may be added to the cement beforehand, or it may be added when mixing the cement with other components such as water and aggregate.

-aggregate-
A carbonate-containing cement composition typically further contains aggregate. The aggregate may be either fine aggregate or coarse aggregate. Examples of aggregate include sand, gravel, crushed stone; granulated slag; recycled aggregate, etc.; and refractory aggregates such as siliceous, clayey, zirconite, high-alumina, silicon carbide, graphite, chromite, chromomagnesia, and magnesia.

[2-2. Amount to add to carbonate-containing cement composition]
The amount of polycarboxylic acid copolymer added (blended amount) per 100 parts by weight of the carbonate-containing cement composition is usually 0.01 parts by weight or more, preferably 0.1 parts by weight or more, and more preferably 0.2 parts by weight or more. This allows for a sufficient dispersion promoting effect. The upper limit is usually 5.0 parts by weight or less, preferably 3.0 parts by weight or less, and more preferably 2.0 parts by weight or less. This allows the fluidity of the cement to be maintained within a suitable range that does not affect the actual construction. Therefore, it is usually 0.01 to 5.0 parts by weight, preferably 0.1 to 3.0 parts by weight, and more preferably 0.2 to 2.0 parts by weight.

[2-3. Optional components of dispersants]
The dispersant may, if necessary, contain components other than the polycarboxylic acid copolymer described above. Examples of other components include other cement dispersants, water-soluble polymers, polymer emulsions, air-entraining agents, cement wetting agents, expansive agents, waterproofing agents, retarders, thickeners, flocculants, drying shrinkage reducing agents, strength enhancers, hardening accelerators, defoamers, air-entraining agents, and other known concrete additives. These other components may be used individually or in combination of two or more. These other components may also be optional components of the cement composition.

As another cement dispersant, a polyacrylic acid polymer (a homopolymer of monomer (2) above) may be included. In that case, its content is preferably 3.0% by weight or less, and more preferably 2.0% by weight or less, relative to the cement. Furthermore, the weight ratio of the polyacrylic acid polymer to the polycarboxylic acid copolymer is preferably 3.0% or less, or 2.5% or less. This suppresses the occurrence of aggregation due to the inclusion of the polyacrylic acid polymer.

Examples of water-soluble polymers include polyalkylene glycols and cellulosic compounds. Specifically, examples include polyethylene polypropylene glycol, polyethylene polybutylene glycol, hydroxyethylcellulose, hydroxymethylcellulose, methylcellulose, and hydroxypropylmethylcellulose. The content of the water-soluble polymer is preferably 0.01% by weight or more relative to the weight of the polycarboxylic acid copolymer. The upper limit is preferably 50% by weight or less.

Examples of retarders include oxycarboxylic acids such as gluconic acid (salt) and citric acid (salt). The content of sugar alcohols is preferably 0.01% by weight or more relative to the weight of the polycarboxylic acid copolymer. The upper limit is preferably 50% by weight or less.

Examples of curing accelerators include soluble calcium salts such as calcium chloride, calcium nitrite, and calcium nitrate; chlorides such as iron chloride and magnesium chloride; thiosulfates; and formate salts such as formic acid and calcium formate. The content of the curing accelerator is preferably 0.01% by weight or more relative to the weight of the polycarboxylic acid copolymer. The upper limit is preferably 50% by weight or less.

Examples of thickening agents include hydroxypropyl methylcellulose, methylcellulose, carboxymethylcellulose, cellulose nanofiber, and cellulose nanocrystal. The content of the thickening agent is preferably 0.01% by weight or more, and preferably 50% by weight or less, relative to the weight of the polycarboxylic acid copolymer.

[2-4. Method of adding dispersant]
The dispersant can be used in the form of a dispersion of polycarboxylic acid copolymer, or in the form of a dried and powdered dispersion thereof. The dispersant may be added to the carbonate-containing cement composition at the time of use, or it may be pre-mixed with the cement, carbonate, and any optional components as needed to form a so-called premix product.

[2-5. Uses of cement after mixing]
By blending a dispersant into a carbonate-based cement composition, it is possible to obtain concrete such as ready-mixed concrete, concrete for precast concrete products, concrete for centrifugal molding, concrete for vibration compaction, steam-cured concrete, sprayed concrete, and other concretes that require high fluidity, such as medium-flow concrete (concrete with a slump value in the range of 22 to 25 cm), high-flow concrete (concrete with a slump value of 25 cm or more and a slump flow value in the range of 50 to 70 cm), self-compacting concrete, and self-leveling materials.

The present invention will be described in detail below with reference to examples. The following examples are intended to suitably illustrate the present invention and are not intended to limit it.

<Experiment 1> Polymer Preparation Example 1 (Preparation of Polymer 1)
In a glass reaction vessel equipped with a thermometer, stirrer, reflux apparatus, nitrogen inlet tube, and dropper, 245 parts water, 150 parts polyethylene glycol monometharyl ether (average number of moles of ethylene oxide added: 53), and 150 parts polyethylene glycol-3-methyl-3-butenyl ether (average number of moles of ethylene oxide added: 53) were added, and the reaction vessel was purged with nitrogen while stirring. After raising the temperature to 40°C under a nitrogen atmosphere, an aqueous solution of 2.4 parts hydrogen peroxide and 47 parts water was added dropwise to the reaction vessel over 30 minutes while the temperature was maintained at 40°C. Subsequently, an aqueous solution of 63 parts acrylic acid, 2.5 parts 3-mercaptopionic acid, and 106 parts water, and a mixture of 0.6 parts L-ascorbic acid and 89 parts water were each added dropwise to the reaction vessel over 2 hours. After the dropwise addition was complete, the reaction was carried out for 1 hour while maintaining the temperature at 40°C, then the temperature was raised to 60°C, and the polymerization termination reaction was carried out for another 1 hour to obtain an aqueous solution of copolymer (polymer 1) with a concentration of 40%. Analysis using gel permeation chromatography (GPC) under the following conditions revealed that the weight-average molecular weight of polymer 1 was 30,000 and the Mw/Mn ratio was 1.59.

[Weight-average molecular weight]: Measured in terms of polyethylene glycol by gel permeation chromatography (GPC). Details of the GPC measurement conditions are described below.
Measuring equipment: Manufactured by Tosoh Corporation. Columns used: Shodex Column OH-pak SB-806HQ, SB-804HQ, SB-802.5HQ.
Eluent: 0.05 mM sodium nitrate/acetonitrile 8/2 (v/v)
Standard material: Polyethylene glycol (manufactured by Tosoh or GL Science)
Detector: Differential refractometer (manufactured by Tosoh Corporation)

[Average Particle Size]: The cumulative average diameter (particle size × number of each particle / total number of particles) was measured from the particle size distribution using a laser diffraction particle size distribution analyzer (Malvern Mastersizer 3000), and this was defined as the average particle size.

Manufacturing Example 2 (Preparation of Polymer 2)
254 parts of water were placed in a glass reaction vessel equipped with a thermometer, stirrer, reflux apparatus, nitrogen inlet tube, and dropper, and the reaction vessel was purged with nitrogen while stirring. After raising the temperature to 100°C under a nitrogen atmosphere, the temperature was maintained at 100°C, and an aqueous monomer solution, a mixture of 206 parts methoxypolyethylene glycol methacrylate (average number of moles of ethylene oxide added: 25), 102 parts methoxypolyethylene glycol methacrylate (average number of moles of ethylene oxide added: 18), 14 parts methacrylic acid (MAA), 17 parts acrylic acid, and 307 parts water, was added dropwise over 2 hours. Simultaneously, a mixture of 7.4 parts sodium persulfate and 242 parts water was added dropwise to the reaction vessel over 2 hours. The reaction was carried out for another hour while maintaining the temperature at 100°C, then cooled to 70°C, and the pH was neutralized to 6 with sodium hydroxide while water was added to obtain an aqueous solution of copolymer (polymer 2) with a concentration of 43%. Analysis using GPC revealed that polymer 2 had a weight-average molecular weight of 16,500 and a Mw/Mn ratio of 1.45.

Manufacturing Example 3 (Preparation of Polymer 3)
254 parts of water were placed in a glass reaction vessel equipped with a thermometer, stirrer, reflux apparatus, nitrogen inlet tube, and dropper, and the reaction vessel was purged with nitrogen while stirring. After raising the temperature to 100°C under a nitrogen atmosphere, the temperature was maintained at 100°C, and an aqueous monomer solution, a mixture of 215 parts methoxypolyethylene glycol methacrylate (MPEG-MA, average number of moles of ethylene oxide added: 13.5), 3.1 parts 3-mercaptopionic acid, 33 parts methacrylic acid, and 42 parts water, was added dropwise over 2 hours. Simultaneously, a mixture of 2.7 parts ammonium persulfate and 38 parts water was added dropwise to the reaction vessel over 2.5 hours. The reaction was carried out for another hour while maintaining the temperature at 100°C, then cooled to 70°C, and the pH was neutralized with sodium hydroxide to 7 while water was added to obtain an aqueous solution of copolymer (polymer 3) with a concentration of 43%. Analysis using GPC revealed that polymer 3 had a weight-average molecular weight of 12,000 and a Mw/Mn ratio of 1.62.

Manufacturing Example 4 (Manufacturing of Polymer 4)
198 parts of water were placed in a glass reaction vessel equipped with a thermometer, stirrer, reflux apparatus, nitrogen inlet tube, and dropper. The reaction vessel was purged with nitrogen while stirring, and the temperature was raised to 100°C under a nitrogen atmosphere. While maintaining the temperature at 100°C, an aqueous monomer solution prepared by mixing 72 parts of acrylic acid, 70 parts of 31% NaOH aqueous solution, and 54 parts of water, and a mixture of 4 parts of ammonium persulfate and 37 parts of water were each added dropwise over 2 hours. The reaction was continued for another hour while maintaining the temperature at 100°C to obtain an aqueous solution of a homopolymer (polymer 4) with a concentration of 36%. Analysis using GPC revealed that the weight-average molecular weight of polymer 4 was 14000 and the Mw/Mn ratio was 1.71.

<Experiment 2> Mortar Test Examples 1-3, Comparative Examples 1 and 2 (Examples of polymer single-component formulations)
At ambient temperature (20°C), cement, water, and polymers 1-4 (added to water in a divided proportion) prepared in Experiment 1 were added in the mixing ratios listed in Table 1. The mixtures were then mechanically mixed using a mortar mixer at low speed for 60 seconds and at high speed for 90 seconds to obtain the standard mortars (cement compositions) of the examples and comparative examples. Similarly, calcium carbonate-added mortars (cement compositions) of the examples and comparative examples were obtained using the mixing ratios listed in Table 2 (adding heavy calcium carbonate (Furuta Lime Industry Co., Ltd.; average particle size: 15.8 μm)). Mortar flow values were measured using these mortars. Specifically, a slump test was performed referring to the method of JIS A1171, and the average value of measurements taken at two locations—the direction in which the diameter of the mortar after lateral spread was considered to be the maximum and the direction perpendicular to it—was defined as the mortar flow value. The test results are shown in Table 3 and Figures 1-4.

In Table 3 and Table 4 below, the addition rate is the percentage (%) of each polymer added relative to the weight of cement.

In conventional mortar, flow was observed in all of Examples 1-4 using polymers 1-3 and Comparative Example 2 using polymer 4. On the other hand, in heavy calcium carbonate-containing mortar, flow was not observed in Comparative Example 2 using polymer 4, while flow was observed in Examples 1-3 using polymers 1-3, similar to conventional mortar (Table 3, Figures 1-4).

Examples 4 and 5 (Examples of combined use of polymers)
Except for the use of polymer 4 in combination with either polymer 1 or 2 at their respective additive amounts, the mortar flow value of heavy calcium carbonate-based mortar was measured in the same manner as described above. The amount of polymer 4 added was 0.3% by weight relative to the cement. The test results are shown in Table 4 and Figures 5-6.

In Examples 4 and 5, the calcium carbonate-containing mortars with added polymers 1 and 2 all exhibited the flow characteristic of calcium carbonate-containing mortar, regardless of the presence or absence of polymer 4 (Table 4, Figures 4-5).

Examples 6-8 and Comparative Example 3 (Investigation of calcium carbonate content)
Except for using light calcium carbonate (manufactured by Nippon Paper Industries, average particle size 21.3 μm) instead of heavy calcium carbonate, adjusting the amounts of light calcium carbonate and aggregate as shown in Table 5 or Table 6, and using the mixing ratios of polymers 1, 2, and 4 as shown in Table 7, the mortar flow value of the calcium carbonate-containing mortar was measured in the same manner as above. The light calcium carbonate used was prepared by mixing quicklime and weak liquor, quenching, adding green liquor to the prepared lime milk, heating and stirring, and carrying out a causticization reaction to obtain causticized light calcium carbonate. The test results are shown in Table 7 and Figures 7 to 12.

In Examples 6 and 7, which used polymers 1 to 3 with light calcium carbonate-based cement, flow was observed with a smaller amount than in Comparative Example 3, which used polymer 4. Furthermore, in Example 8, which used polymers 1 and 4 in combination, good polymer flow was also observed (Table 7, Figures 7-12).

Examples 9-11, Comparative Example 4 (Magnesium Carbonate-Based Cement)
Using magnesium carbonate instead of calcium carbonate, the mortar flow value of the magnesium carbonate-containing mortar was measured in the same manner as above, except that magnesium carbonate (manufactured by LOOK, average particle size 9.95 μm) was added in the proportions shown in Table 8, and polymers 1, 2, and 4 were added at the rates shown in Table 9. The test results are shown in Table 9 and Figures 13-15.

The results were similar for magnesium carbonate-containing mortar as for calcium carbonate-containing mortar. Specifically, in Examples 9-10, which used polymers 1-3, flow was observed with a smaller amount than in Comparative Example 4, which used polymer 4. Furthermore, in Example 11, which used polymers 1 and 4 in combination, good polymer flow was also observed (Table 9, Figures 13-15).

These results demonstrate that the dispersant of the present invention, by using a polycarboxylic acid copolymer incorporating a PEG chain structure as an active ingredient, can suppress aggregation in carbonate-containing cement compositions and exhibit a dispersion effect.

Claims (8)

A dispersant for a carbonate-based cement composition, comprising a polycarboxylic acid copolymer containing 1 to 99% by weight of constituent unit (I) derived from a monomer represented by the following general formula (1), and 1 to 99% by weight of constituent unit (II) derived from a monomer represented by the following general formula (2),
A carbonate-containing cement composition is a cement composition containing 30 to 100 parts by weight of carbonate per 100 parts by weight of cement .
[In the formula, ^R1 , ^R2 , and ^R3 each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, x represents a number from 0 to 3, y represents 0 or 1, ^R5O represents an oxyalkylene group having 2 to 18 carbon atoms, either identical or different, n is the average number of moles added by the oxyalkylene group, representing a number from 1 to 90 , and ^R4 represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms];
[In the formula, ^R6 , ^R7 , and ^R8 each independently represent ^a hydrogen atom, a methyl group, or -( _CH2 ) _rCOOM2 , ^M1 and ^M2 are the same or different, representing a hydrogen atom, an alkali metal, an alkaline earth metal, an ammonium group, an alkylammonium group ^, or a substituted alkylammonium group, where r is an integer from 0 to 2, and where -( _CH2 ) _rCOOM2 may form an anhydride with ^-COOM1 or other -( _CH2 ) _rCOOM2 , but if an anhydride is formed, ^M1 and ^M2 are not present in those groups ^. ] The dispersant according to claim 1, wherein the carbonate is calcium carbonate or magnesium carbonate. The dispersant according to claim 2, wherein the calcium carbonate is light calcium carbonate. A dispersant according to any one of claims 1 to 3, characterized in that the average particle size of the carbonate is 0.1 to 100 μm. The dispersant according to claim 1 or 2, wherein the weight-average molecular weight of the polycarboxylic acid copolymer is 5,000 to 100,000. A dispersant according to claim 1 or 2, wherein the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) (Mw/Mn) is 1.0 to 10.0. The dispersant according to claim 1 or 2, wherein the carbonate content in the carbonate-containing cement composition is 35 to 100 parts by weight per 100 parts by weight of cement. The dispersant according to claim 1 or 2, wherein the amount added is 0.01 to 5.0 parts by weight per 100 parts by weight of the total amount of the carbonate-containing cement composition.