JP2009242598A - Polyacrylic acid-based polymer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyacrylic acid-based polymer product usable as a pigment dispersant, and also to provide a pigment dispersant using the polyacrylic acid-based polymer product. <P>SOLUTION: The polyacrylic acid-based polymer product is obtained by polymerization of unsaturated monomers containing acrylic acid and/or a salt thereof using an initiator and an alcohol-based chain transfer agent, and the polyacrylic acid-based polymer product contains a polyacrylic acid-based polymer having a structure (A) derived from the alcohol-based chain transfer agent, and the percentage of the structure (A) derived from the alcohol-based chain transfer agent in the polyacrylic acid-based polymer in term of structure unit of the structure (A) derived from the alcohol-based chain transfer agent in the polyacrylic acid-based polymer is at least 1.5 mol% against the structure unit derived from the unsaturated monomer comprising the polyacrylic acid-based polymer, and the content of inorganic ion derived from the initiator against solid component of the polyacrylic acid-based polymer product is not more than 12,000 mass ppm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polyacrylic acid polymerization product.

  Polyacrylic acid-based polymers mainly composed of sodium polyacrylate are used for applications such as detergent builders, pigment dispersants, and water treatment agents (scale component adhesion inhibitors). In these markets, a polyacrylic acid polymer having higher performance is required.

  As a method for meeting such a demand, for example, a technique for reducing the molecular weight distribution of a polyacrylic acid polymer as described in Patent Documents 1 to 3 is known.

In addition, for example, when a polyacrylic acid polymer is used as a detergent builder, it exerts an effect of dispersing mud dirt, etc. In addition, development of a polyacrylic acid polymer that exhibits dispersive power over time is desired.
JP 2004-143402 A JP 2000-31888 A JP 59-223702

  However, even the polyacrylic acid polymer produced by the above technique has not yet been able to be said to sufficiently meet the above requirements. That is, it was not possible to obtain a polyacrylic acid polymer having higher performance and stability over time.

  Therefore, an object of the present invention is to provide a desired polyacrylic acid polymer as described above.

  In view of the above situation, the present inventors have conducted intensive research. First, in the process, the inventors investigated in detail as follows why the polyacrylic acid polymer exhibiting dispersibility over time could not be obtained by the technique of the above-mentioned patent document.

  By the way, since a polyacrylic acid polymer generally shows a good dispersibility in a region having a small molecular weight, the polyacrylic acid polymer used for the above-mentioned use is controlled to have a low molecular weight.

  As a method for adjusting the molecular weight of a polymer, generally, the amount of a polymerization initiator (also referred to simply as “initiator” in the present specification) when starting radical polymerization is adjusted, and the concentration of a monomer mixture. Adjustment of the temperature and time of the polymerization reaction, selection of a polymerization solvent, use of a chain transfer agent, use of a monomer having a molecular weight adjusting effect, and the like. In particular, when obtaining a polymer having a low molecular weight, a large amount of a polymerization initiator is usually used.

  The present inventors pay attention to such means that those skilled in the art normally perform, and it is not possible to obtain a polyacrylic acid polymer that exhibits dispersibility over time. Due to the fact that many polymer molecules are used, the polymer molecules due to the influence of inorganic ions derived from the remaining polymerization initiator shrink, and the polymer is likely to be detached from the particle surface such as mud stains and pigments. I thought.

  The inventors have also studied to mainly modify the polymer terminal that does not affect the adsorbing group of the polyacrylic acid polymer as much as possible.

  Even if the hydrophilicity of the polyacrylic acid polymer is too high or the hydrophobicity is too high, the dispersibility with time tends to decrease. In view of such a tendency, if a “hydrophilic / hydrophobic balanced substituent” such as an isopropyl alcohol structure or a secondary butyl alcohol structure is introduced at the terminal, the polyacrylic acid polymer molecule can We thought that it would adsorb more stably on the surface of particles such as pigments. Based on this idea, intensive research was conducted and the present invention was completed.

  That is, the present invention is a polyacrylic acid polymerization product obtained by polymerizing an unsaturated monomer containing acrylic acid and / or a salt thereof using a polymerization initiator and an alcohol chain transfer agent. The polyacrylic acid-based polymerization product includes a polyacrylic acid-based polymer having a structure (A) derived from an alcohol-based chain transfer agent, and the polyacrylic acid-based polymer has a structure derived from an alcohol-based chain transfer agent. The proportion of (A) is the structure of the structure (A) derived from the alcohol chain transfer agent of the polyacrylic acid polymer relative to the structural unit derived from the unsaturated monomer constituting the polyacrylic acid polymer. The unit is 1.5 mol% or more, and the content of inorganic ions derived from the polymerization initiator is 12,000 ppm by mass or less based on the solid content of the polyacrylic acid-based polymerization product. It is acrylic acid polymer product.

  According to the present invention, it is possible to obtain a polyacrylic acid-based polymerization product including a polyacrylic acid-based polymer that exhibits mud dirt and pigment dispersion power and has higher performance and stability over time.

  Hereinafter, the present invention will be described in detail.

  The present invention is a polyacrylic acid polymerization product obtained by polymerizing an unsaturated monomer containing acrylic acid and / or a salt thereof using a polymerization initiator and an alcohol chain transfer agent, The polyacrylic acid-based polymerization product includes a polyacrylic acid-based polymer having a structure (A) derived from an alcohol-based chain transfer agent, and the polyacrylic acid-based polymer has a structure (A The proportion of the structural unit derived from the unsaturated monomer constituting the polyacrylic acid polymer is the structural unit of the structure (A) derived from the alcohol chain transfer agent of the polyacrylic acid polymer. , 1.5 mol% or more, and the content of inorganic ions derived from the polymerization initiator is 12,000 mass ppm or less based on the solid content of the polyacrylic acid-based polymerization product. The polymerization product.

  As used herein, the phrase “polyacrylic acid-based polymerization product” is an unsaturated monomer containing acrylic acid and / or a salt thereof using a polymerization initiator and an alcohol-based chain transfer agent. Refers to a product obtained by polymerizing That is, since it means the product obtained by these, the state may be a solid state from which the solvent is removed, or a solution state dissolved in water and / or a water-soluble organic solvent described later. Good.

  Further, the “product” means that the polyacrylic acid-based polymerization product of the present application contains an unsaturated monomer containing acrylic acid and / or a salt thereof using a polymerization initiator and an alcohol-based chain transfer agent. This is because it is a product obtained by polymerization and may contain not only a polyacrylic acid polymer but also inorganic ions derived from a polymerization initiator as a raw material. From another point of view, the “polyacrylic acid polymerization product” can be said to be a “polyacrylic acid polymer composition” in that it consists of two or more components.

[Unsaturated monomer containing acrylic acid and / or salt thereof]
The unsaturated monomer containing acrylic acid and / or a salt thereof that can be used in the present invention is a polymer having a repeating unit derived from acrylic acid and / or a salt thereof in the main chain. The polyacrylic acid polymerization product includes a polyacrylic acid polymer having a structure (A) derived from an alcohol chain transfer agent.

  In light of the tendency of the dispersibility over time to decrease even when the hydrophilicity of the polyacrylic acid polymer is too high or too high in hydrophobicity, the present inventors have found that “the balance between hydrophilicity / hydrophobicity is balanced. As a result of the ingenuity of introducing a “substituent” at the terminal, it was surprisingly possible to obtain a polyacrylic acid polymer product having desired characteristics.

  Here, “having a structure (A) derived from an alcohol chain transfer agent” specifically means having a structure derived from an alcohol chain transfer agent mainly at the terminal of the polyacrylic acid polymer, It also includes a structure derived from an alcohol-based chain transfer agent introduced into the main chain or side chain by chain transfer reaction after abstracting the hydrogen radical of the polymer main chain or esterification of the side chain carboxyl group.

  Here, “the ratio of the structure (A) derived from the alcohol chain transfer agent of the polyacrylic acid polymer is higher than the structural unit derived from the unsaturated monomer constituting the polyacrylic acid polymer. The structural unit of the structure (A) that the coalescence has is 1.5 mol% or more, and the polyacrylic acid type of the structural unit of the structure (A) derived from the alcohol chain transfer agent of the polyacrylic acid polymer The ratio (mol%) with respect to the structural unit derived from the unsaturated monomer constituting the polymer is also referred to as “molar ratio of structure (A)” in this specification.

["Molar ratio of structure (A)"]
“Molar ratio of structure (A)” is

Can be expressed as A specific method for measuring (calculating) the “molar ratio of the structure (A)” is described in detail in the column of Examples.

  A polyacrylic acid polymer is obtained by polymerizing an unsaturated monomer containing acrylic acid and / or a salt thereof using a polymerization initiator and an alcohol chain transfer agent. As described above, the alcohol-based chain transfer agent is introduced into the terminal of the polyacrylic acid polymer obtained by polymerization, the main chain of the polyacrylic acid polymer, and / or the side-chain carboxy group. The polyacrylic acid polymer has a structure (A) derived from an alcohol chain transfer agent. That is, the “molar ratio of the structure (A)” is an index indicating how many alcohol chain transfer agent-derived structures are introduced into the polyacrylic acid polymer in the polymer product. In other words, it is the ratio of the skeleton derived from the chain transfer agent in the polyacrylic acid polymer.

  Here, the meaning of the “molar ratio of the structure (A)” will be described with a specific example.

  “Mole ratio of structure (A)” indicates how much alcohol-based chain transfer agent is introduced into the polymer with respect to the monomer units constituting the polymer. If a large amount of an alcohol chain transfer agent is introduced into the polyacrylic acid polymer obtained by polymerization, the “molar ratio of the structure (A)” increases accordingly.

  The polyacrylic acid-based polymer of the present invention is not particularly limited as long as the “molar ratio of the structure (A)” is 1.5 mol% or more, but is preferably 1 from the viewpoint of mud stain and pigment dispersibility. It is 0.5-3.5 mol%, More preferably, it is 1.6-3.0 mol%, More preferably, it is 1.7-2.8 mol%. If it is less than 1.5 mol%, the dispersion stability of the dispersion force may decrease.

Here, the “molar ratio of the structure (A)” can be calculated by ¹ HNMR as described later. For example, if it is a homopolymer of acrylic acid, it can be calculated as follows. The “structural unit derived from an unsaturated monomer” in a homopolymer of acrylic acid is naturally a unit derived from acrylic acid. Here, “unit derived from acrylic acid” represents a structure (—CH ₂ —CH (COOH) —) after acrylic acid (CH ₂ ═CHCOOH) is polymerized. That is, in the ¹ HNMR chart, the value obtained by dividing the peak area of the structure (A) by the number of protons of the structure (A) is the proton of the methine group of the structural unit derived from acrylic acid (the methine proton in the structural unit derived from acrylic acid). (The number is 1)) is divided by the value obtained by dividing the peak area by the number of protons of the methine group, the “molar ratio of the structure (A)” can be calculated.

  The peak areas may be compared by cutting out a peak from a printed chart and measuring the mass.

  In the present invention, when calculating “the number of moles of the structural unit derived from the unsaturated monomer constituting the polymer”, the structural unit derived from the monomer has a methine group in the portion corresponding to the main chain. For the calculation, the proton peak of the methine group is used in the calculation. When the monomer-derived structural unit does not have a methine group in the part corresponding to the main chain, the proton peak of the methylene group or the peak of the side chain proton is used in the calculation. To do.

¹ HNMR is measured by dissolving the polymer product in a measurement solvent after drying. However, if the measurement is difficult due to the polymer product containing a large amount of impurities such as residual monomers, the polymer product is removed by a known method such as dialysis treatment. After drying, it may be measured by dissolving in a measurement solvent.

  The polyacrylic acid-based polymer may have a structure copolymerized with other copolymerizable monomers within a range not impairing the effects of the present invention.

  The acrylic acid and / or salt thereof is at least one of acrylic acid and acrylate. Although it does not specifically limit as acrylate, For example, acrylic acid alkali metal salts, such as sodium acrylate and potassium acrylate; Ammonium acrylate; Acrylic acid organic amine salt etc. are mentioned. These may be used alone or in combination of two or more.

  The other copolymerizable monomer is not particularly limited and may be used in combination as necessary, but those described below are preferably used.

  That is, other copolymerizable monomers include, for example, unsaturated carboxylic acid monomers such as methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, and aconitic acid; (meth) acrylamide, t Amide monomers such as butyl (meth) acrylamide; Hydrophobic monomers such as (meth) acrylic acid ester, styrene, 2-methylstyrene, vinyl acetate; Vinyl sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid , Styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxy-propanesulfonic acid, sulfoethyl (meth) acrylate, sulfopropyl (meth) acrylate, 2-hydroxysulfopropyl (meth) acrylate , Unsaturated sulfonic acid monomers such as sulfoethylmaleimide; Partially neutralizing the unsaturated dicarboxylic acid monomer, the unsaturated polycarboxylic acid monomer or the unsaturated sulfonic acid monomer with a monovalent metal, divalent metal, ammonia, organic amine or the like Neutralized product obtained by complete neutralization; hydroxyl group-containing unsaturated monomer such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, α-hydroxyacrylic acid, vinyl alcohol; dimethylaminoethyl ( Cationic monomers such as (meth) acrylate; nitrile monomers such as (meth) acrylonitrile; phosphorus-containing monomers such as (meth) acrylamide methanephosphonic acid; alkyl vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; vinyl Pyrrolidone; ethylene oxide adduct of (meth) allyl alcohol, ethylene of isoprenol Examples thereof include oxide adducts and (alkoxy) polyethylene glycol esters of (meth) acrylic acid. These may be used alone or in combination of two or more.

  In this case, the ratio of the other copolymerizable monomer may be within a range that does not impair the characteristics of the polyacrylic acid polymer that can be obtained (such as stability over time, low viscosity at a high concentration, and dispersibility). Although not particularly limited, it is 0 to 30% by mass, more preferably 0 to 10% by mass, based on the entire unsaturated monomer.

  Further, at this time, the ratio of the unsaturated monocarboxylic acid and unsaturated dicarboxylic acid in the unsaturated monomer is preferably 90 mol% or more from the viewpoint of mud stain and pigment dispersibility, more preferably 95 mol% or more. More preferably, it is 97 mol% or more, and particularly preferably 100 mol%.

  The polyacrylic acid polymer of the present invention may be composed of the same repeating unit or different repeating units. In the latter case, the bonding form of the repeating unit is a block. The shape may be random or random.

  The molecular structure of the polyacrylic acid polymer of the present invention may be branched or linear, but is preferably linear.

  The weight average molecular weight of the polyacrylic acid polymer of the present invention is in the range of 1500 to 50,000, more preferably 1800 to 20,000, and even more preferably 2000 to 15,000. Such a range is preferable because the dispersibility is exhibited in a region having a small molecular weight. In addition, in this specification, a weight average molecular weight shall say the value obtained by the method as described in the column of an Example.

[Content of remaining inorganic ions]
A polyacrylic acid polymerization product obtained by polymerizing an unsaturated monomer containing acrylic acid and / or a salt thereof using a polymerization initiator and an alcohol chain transfer agent, and derived from the polymerization initiator The inorganic ion content (also referred to as “content of remaining inorganic ions” in the present specification) is 12,000 ppm by mass or less based on the solid content of the polyacrylic acid-based polymerization product.

  When the content of the remaining inorganic ions exceeds 12,000 ppm by mass, when the polyacrylic acid-based polymerization product is used in a detergent builder or the like, it leads to a result that viscosity and stability over time are lowered. Therefore, in consideration of viscosity and stability over time when the polyacrylic acid-based polymerization product of the present invention is used for a detergent builder or the like, it is preferably 9,300 mass ppm or less, more preferably 8,200 or less. Yes, more preferably 7,000 or less. In consideration of the actual situation, it is 2,000 mass ppm or more.

  As described above, the present inventors have surprisingly found that, as a result of conducting research to formulate to reduce the amount of remaining inorganic ions in addition to introducing a predetermined amount of a specific structure into the polymer, Thus, a polyacrylic acid-based polymerization product capable of obtaining an aqueous dispersion having a higher concentration and a lower viscosity can be obtained.

  Inorganic ions derived from the remaining polymerization initiator include those containing sulfur atoms such as sulfate ion and sulfite ion, those containing phosphorus atoms such as hypophosphite ion, phosphite ion and phosphate ion, nitrite ion And those containing nitrogen atoms such as nitrate ions. Of these, those containing sulfur atoms have the greatest influence. The method for measuring the content of the remaining inorganic ions derived from the polymerization initiator will be described in detail in the Examples section.

  In the polyacrylic acid polymerization product obtained by polymerizing an unsaturated monomer containing acrylic acid and / or a salt thereof using a polymerization initiator and an alcohol chain transfer agent, residual unsaturation The fewer monomers (also referred to herein as “residual monomers”), the better.

  Specifically, the content of the residual monomer is preferably 5000 ppm by mass or less with respect to the solid content of the polyacrylic acid-based polymerization product, and when the content of the residual monomer exceeds 12,000 ppm by mass, There is a risk of deterioration. Therefore, in consideration of exhibiting more excellent dispersant performance, it is preferably 8,200 ppm by mass or less, more preferably 7,000 or less, and further preferably 4,500 or less. In consideration of the actual situation, it is 2,000 mass ppm or more.

  In the present specification, the residual monomer detected and analyzed under the same conditions as in the molecular weight measurement method described later was quantified.

  Further, the molecular weight distribution of the polyacrylic acid polymerization product of the present invention is preferably 1.2 to 3.0. More preferably, it is 1.3-2.8, More preferably, it is 1.5-2.5. Here, the molecular weight distribution is a numerical value represented by weight average molecular weight / number average molecular weight. Such a range is preferable from the viewpoint of improving the dispersibility of the inorganic substance.

[Method for Producing Polymerization Product of the Present Invention]
As described above, the present invention is a polyacrylic acid polymerization product obtained by polymerizing an unsaturated monomer containing acrylic acid and / or a salt thereof using a polymerization initiator and an alcohol chain transfer agent. The polyacrylic acid-based polymerization product includes a polyacrylic acid-based polymer having a structure (A) derived from an alcohol-based chain transfer agent, and the polyacrylic acid-based polymer has an alcohol-based chain transfer agent-derived The ratio of the structure (A) is the structure derived from the alcohol chain transfer agent of the polyacrylic acid polymer (A) relative to the structural unit derived from the unsaturated monomer constituting the polyacrylic acid polymer. The polymer unit is 1.5 mol% or more, and the content of inorganic ions derived from the polymerization initiator is 12,000 ppm by mass or less based on the solid content of the polyacrylic acid polymerization product. Acrylic acid-based polymer product.

  In the present specification, a polyacrylic acid polymer obtained by polymerization is also simply referred to as “polymer” or “polymer”.

  The present invention is characterized not only by introducing a predetermined amount of a specific structure into a polymer using the concept of reversal but also by the technical idea of reducing the amount of remaining inorganic ions. Therefore, “the structural unit derived from the alcohol-based chain transfer agent of the polyacrylic acid polymer is 1 in relation to the structural unit derived from the unsaturated monomer constituting the polyacrylic acid polymer. A specific method in which the content of the inorganic ion derived from the polymerization initiator is 12,000 ppm by mass or less based on the solid content of the polyacrylic acid polymerization product will be described below.

  The method for producing the polyacrylic acid-based polymerization product of the present invention is particularly preferably carried out using a polymerization initiator in a solvent (also referred to as “polymerization solvent”).

  As the polymerization solvent for the polyacrylic acid-based polymerization product, water is preferably used, and a water-soluble organic solvent may be appropriately added as necessary. That is, the polymerization solvent may be in the form of a mixed solvent.

  The water is not particularly limited and may be tap water, ion exchange water, distilled water, or pure water (distilled after ion exchange), but from the viewpoint of removing inorganic ions, Pure water is preferred.

  Although it does not specifically limit as a water-soluble organic solvent, For example, lower alcohols, such as methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol, 2-butanol, t-butanol; Dimethylformamide etc. Amides; Ketones such as acetone; Ethers such as 1,4-dioxane and the like, and one or more of these may be appropriately selected and used. Of these, isopropanol is preferable because of its chain transfer effect. From the viewpoint of partially neutralizing the polymerization liquid, causing phase separation, transferring a low molecular weight product to the upper layer, and obtaining a polymerization product having a narrow molecular weight distribution, 2-propanol (isopropanol), 2-butanol, t- Butanol and the like are more preferable. Of these, isopropanol is preferable because of its chain transfer effect.

  Examples of the alcohol chain transfer agent include secondary alcohols such as 2-propanol (isopropanol) and 2-butanol, and t-butanol. These may also be used as a polymerization solvent.

  When the polymerization solvent is in the form of a mixed solvent, the addition ratio of the water-soluble organic solvent is preferably 10 to 95% by mass, more preferably 20 to 90% by mass, and further preferably 25 to 75% by mass with respect to the total amount of the mixed solvent. %. When it exceeds 95 mass%, there exists a possibility that the superposed | polymerized polymerization product may precipitate.

  In order to produce the polymer of the present invention, before adding the unsaturated monomer and the polymerization initiator, one of water, a water-soluble organic solvent and a mixed solvent of water-soluble organic solvent (polymerization solvent) is added. It is good to reflux. Preferably, the mixed solvent (polymerization solvent) of the water-soluble organic solvent is refluxed.

  Although it does not specifically limit as a polymerization initiator at the time of manufacturing the said polyacrylic-acid type polymerization product, For example, a peroxide etc. are mentioned.

  The peroxide is not particularly limited, and examples thereof include hydrogen peroxide; persulfates such as sodium persulfate, ammonium persulfate, and potassium persulfate; 2,2′-azobis (2-aminodipropane) dihydrochloride, Azo compounds such as 4,4′-azobis (4-cyanovaleric acid), azobisisobutylnitrile, 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile); benzoyl peroxide, lauroyl peroxide Organic peroxides such as peracetic acid, persuccinic acid, di-t-butyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, and the like.

  Of these, persulfate is preferable from the viewpoint of reducing the content of the remaining unsaturated monomer. Among the above peroxides, hydrogen peroxide and organic peroxides are particularly preferable from the viewpoint of removing sulfate ions. From the viewpoint of the production cost of the resulting polymer, or a polymer having a desired molecular weight. From the viewpoint that it is easy to obtain, it is preferable to use a persulfate in a range that allows the use of the polymer to be affected. These polymerization initiators may be used alone or in combination of two or more.

  In the polyacrylic acid-based polymerization product of the present invention, in consideration of controlling the content of remaining inorganic ions to 5000 ppm by mass or less, the amount of the polymerization initiator added is the unsaturated monomer used. On the other hand, it is preferably 0.5 to 3.0% by mass, more preferably 0.7 to 2.5% by mass, and still more preferably 1.0 to 2.0% by mass. If it exceeds 3.0% by mass, the content of the remaining inorganic ions derived from the polymerization initiator may exceed 12,000 ppm by mass, and if it is less than 0.5% by mass, the unsaturated monomer is a polymer. There is a risk that it will not be fully converted. Thus, by significantly reducing the amount of the polymerization initiator to be added, the amount of the remaining inorganic ions can be significantly reduced, and the molar ratio of the structure (A) can be increased.

  In addition, the polymerization initiator may be added in any form, such as batch addition, continuous addition by dropping or the like, or divided and intermittent addition. However, when added all at once, the unsaturated monomer polymerizes rapidly, and immediately after the addition, the reaction control becomes difficult due to a large amount of reaction heat, or a large amount of unreacted monomer remains. The molecular weight distribution may be widened. Therefore, in this invention, it is preferable that a polymerization initiator is dripped continuously.

  The dropping conditions for continuously dropping the persulfate are not particularly limited, but considering the molecular weight and molecular weight distribution of the polyacrylic acid polymer to be obtained, the persulfate is preferably 60 ° C to It is preferable to continuously drop at 100 ° C., more preferably at a temperature of 70 ° C. to 100 ° C., preferably 2 to 4 hours, more preferably 2.5 to 3.5 hours. When the above range is exceeded, the molar ratio of the structure (A) tends to decrease. As a result, the temporal stability of the dispersion force may be reduced.

  The polymerization initiator may be added simultaneously with the unsaturated monomer, or may be added before or after the unsaturated monomer is added. Preferably, the polymerization initiator is added first from the viewpoint of increasing the heat generation start time.

  By the way, when the amount of the polymerization initiator to be added is reduced, the molecular weight of the produced polymer tends to increase. As described above, the polyacrylic acid-based polymerization product is in a low molecular weight region (for example, 1000 to 1000). Dispersibility is exhibited at a weight average molecular weight as low as 50,000). Therefore, a method for suppressing the increase in molecular weight by a method other than increasing the amount of the polymerization initiator to be added (that is, a method for suppressing the molecular weight that can exhibit dispersibility) will be described. That is, it is preferable that the polymerization initiator and the acrylate are continuously dropped. Thereby, even if it reduces the total addition amount of an initiator, while it becomes possible to hold down the molecular weight of a polymer low, it exists in the tendency for the molar ratio of a structure (A) to increase.

  In the above case, it is preferable that the total dropping time of the initiator is 1 to 30 minutes longer than the total dropping time of acrylic acid. More preferably, it is 3 to 15 minutes longer. Particularly preferably, it is preferably 4 to 10 minutes longer. Thereby, even if it reduces the total addition amount of an initiator, while it becomes possible to hold down the molecular weight of a polymer low, it exists in the tendency for the molar ratio of a structure (A) to increase.

  In the above case, it is preferable to continuously drop the polymerization initiator over 1 minute or more after completion of dropping of acrylic acid. Preferably, it is preferably dripped continuously for 3 minutes or more, more preferably 4 minutes or more. Preferably it is 10 minutes or less, More preferably, it is good to add continuously over 7 minutes or less. Thereby, even if it reduces the total addition amount of an initiator, while it becomes possible to hold down the molecular weight of a polymer low, it exists in the tendency for the molar ratio of a structure (A) to increase.

  Thus, in order to reduce the molecular weight of the polymer obtained, by adopting the above method without increasing the amount of polymerization initiator to be added, the increase in molecular weight is significantly suppressed, and The dispersibility of the coalescence is improved. Such ingenuity is characterized not only by introducing a specific amount of a specific structure into the polymer using the concept of reversal, but also by the technical idea of reducing the amount of remaining inorganic ions. It is none other than.

  Moreover, in order to manufacture the polymer of this invention, it is good to suppress the production | generation of a low molecular weight compound or a low molecular weight polymer. In the present specification, the “low molecular compound” specifically includes unsaturated monomers and charged raw materials, and the “low molecular weight polymer” refers to a polyacrylic acid polymerization product. Refers to the oligomer of The weight average molecular weight of the polyacrylic acid oligomer is, for example, 1,500 or less.

  Therefore, it is good to control the polymerization conditions in producing the polymer contained in the polyacrylic acid-based polymerization product. Specific polymerization conditions will be described below.

  The amount of the unsaturated monomer present in the polymerization solvent is not limited as long as the (co) polymerization of the unsaturated monomer can sufficiently proceed. However, the monomer / solvent mass ratio is preferably 0.2. -1.5, more preferably 0.3-1.3, particularly preferably 0.4-1.0. If it is such quantity, a desired polymer can be obtained efficiently and sufficient productivity can be secured.

  The unsaturated monomer may be added to the mixed solvent in any form such as batch addition, continuous addition by dropping or the like, or intermittent addition in divided portions. However, when added all at once, the unsaturated monomer polymerizes rapidly, and immediately after the addition, the reaction control becomes difficult due to a large amount of reaction heat, or a large amount of unreacted monomer remains. The molecular weight distribution may be widened. Therefore, in this invention, it is preferable that an unsaturated monomer is dripped continuously.

  In addition, the dropping conditions when the unsaturated monomer is continuously dropped are not particularly limited, but in consideration of the molecular weight and molecular weight distribution of the resulting polyacrylic acid polymer, the unsaturated monomer is preferably used. Is preferably dropped continuously at a temperature of 60 to 100 ° C, more preferably 70 to 100 ° C, preferably 2 to 4 hours, more preferably 2.5 to 3 hours.

  The polymerization conditions are appropriately determined depending on the solvent used, the type of the polymerization initiator, and the like. For example, the polymerization temperature is usually preferably 60 to 100 ° C., more preferably 70 to 100 ° C. or more. Especially preferably, it is 80-100 degreeC. The polymerization time is suitably in the range of 2 to 5 hours, preferably 2.5 to 4 hours, more preferably 2.5 to 3.5 hours. If the polymerization time is too long or too short from this range, the polymerization rate may be lowered or the productivity may be lowered.

  In the present invention, the polymerization time is the time when both the at least one initiator and at least one monomer are added to the polymerization kettle, and the end points are the initiator and the monomer. This is the point when all of the dripping is completed.

  Moreover, it is preferable to provide an aging step after completing the addition of the unsaturated monomer.

  Here, the aging conditions in the aging step are not particularly limited as long as a polyacrylic acid polymer having a predetermined molecular weight can be efficiently produced from an unsaturated monomer. Specifically, after adding the unsaturated monomer, the mixture is preferably 0.5 to 2.0 hours, more preferably 0.5 to 1.0 hours, preferably 70 to 100 ° C., more preferably Is preferably maintained at a temperature of 80 to 100 ° C. Moreover, after the said aging process, temperature is adjusted to the range of 30-80 degreeC, a polymerization terminator etc. are added as needed and a polymerization reaction is stopped.

  Thus, a mixed solvent containing the polyacrylic acid polymer according to the present invention is obtained. At this time, considering the operability of the subsequent steps, the polyacrylic acid polymer in the mixed solvent is obtained. The concentration is preferably about 20 to 70% by mass, more preferably about 30 to 60% by mass.

  By adjusting the polymerization conditions as described above, it is possible to suppress the formation of low molecular weight compounds and low molecular weight polymers that can adversely affect the dispersion performance, thereby making the dispersion performance of the polyacrylic acid polymer remarkable. To improve.

  In order to produce the polyacrylic acid-based polymerization product of the present invention, as described above, it is preferable to perform polymerization using a polymerization initiator in a polymerization solvent. Further preferred.

  Even if the polymerization conditions are adjusted, low molecular weight compounds or low molecular weight polymers may be contained. In such cases, at the laboratory level, low molecular weight compounds and other impurities may usually be removed by a reprecipitation method by introducing the polymer solution into a poor solvent for the polymer. However, in this method, there is a problem in actual production that costs are increased and a process for treating a poor solvent is increased.

  In the present invention, polymerization is carried out in a mixed solvent of water and a water-soluble organic solvent, and the neutralization degree of the polymer is utilized to reduce the solubility of the partially neutralized polymer in the water-soluble organic solvent. A method of phase separation from the solvent is utilized. At this time, since the low molecular weight polymer and impurities partially migrate to the layer having a high water-soluble organic solvent ratio at the same time, they can be reduced or removed.

  This mechanism will be described more specifically.

  That is, immediately after polymerization, the mixed solvent is uniform without causing layer separation. Here, when a basic substance is added to the mixed solvent of water in which the polymer is dissolved and the water-soluble organic solvent, the solubility of the partially neutralized polymer in the water-soluble organic solvent is lowered.

  As a result, the solvent can no longer maintain uniformity, and the solvent is separated into an aqueous layer and a water-soluble organic solvent layer. In this case, the polymer is present in each layer with water and a water-soluble organic solvent. Most polymers with extremely low solubility in water-soluble organic solvents such as high molecular weight polymers are present in layers with a high water ratio (also referred to as “highly water-containing layers” or “aqueous layers”), and low molecular weight polymers The polymer having relatively high solubility, such as the above, moves to a layer having a high water-soluble organic solvent ratio (also referred to as “highly water-soluble organic solvent layer” or “organic layer”). At this time, the low molecular weight polymer and impurities are also partially transferred to the layer having a high water-soluble organic solvent ratio, so that these are reduced or removed.

  In addition, the said mechanism is only inventors' estimation, and it cannot be overemphasized that the technical scope of invention is not restrict | limited by this mechanism.

  As an alkaline substance (basic substance) used for liquid-liquid separation, for example, a monovalent alkali metal hydroxide such as sodium hydroxide, lithium hydroxide, cesium hydroxide, or a water-soluble organic solvent is relatively Examples include highly soluble aliphatic amines and aromatic amines. Particularly preferred is sodium hydroxide because it is easily available and relatively inexpensive.

  Since the amount of the alkaline substance to be added varies depending on the molecular weight of the unsaturated monomer (monomer) and basic substance used, the molar amount of the carboxyl group (acid type) of the polymer after neutralization rather than the mass ratio is indicated. The ratio is important. That is, the basic substance may be added so that the total amount of the carboxyl group (acid type) and the carboxylate is 100 mol%, and the ratio of the carboxylate is preferably 20 to 95 mol%. However, it is more preferably 30 to 90 mol%, still more preferably 30 to 80 mol%. If it exceeds 95 mol%, there is a possibility that the solubility in a water-soluble organic solvent is almost lost, so that the separation of the low molecular weight polymer may be deteriorated. On the other hand, if it is less than 20 mol%, the layer separation itself may not occur.

  Subsequently, specific conditions in the step of liquid-liquid separation (layer separation) will be described in more detail below.

  While stirring the polymerization product (polymerized solution) at a predetermined temperature, a predetermined amount of a basic substance is dropped, and after completion of the dropping, neutralization is completed. Continue stirring for 0 hour.

  In the meantime, layer separation occurs, but each layer is transferred to a liquid separation device and allowed to stand at a predetermined temperature for a predetermined time to complete the separation.

  The temperature of the predetermined temperature is preferably 30 to 70 ° C., more preferably 40 to 60 ° C., considering the temporal stability of the dispersion force of the polymer obtained. If it is less than 30 degreeC, since it takes time until the composition of an upper layer, a lower layer, etc. become constant, the performance of a product may vary. On the other hand, when it exceeds 70 ° C., there is a possibility that low molecular weight substances and the like cannot be removed.

  Inorganic ions are distributed to the highly water-containing layer (aqueous layer). As described above, since the amount of the polymerization initiator to be added is significantly reduced, a desired polyacrylic acid-based polymerization product is formed. Things can be manufactured.

  The polyacrylic acid polymer contained in the high water content layer thus obtained can be used for various purposes as it is, but usually a water-soluble organic solvent is distilled off by distillation operation or the like. In general, it is used for various applications in a state that does not contain a water-soluble organic solvent.

  In addition, the water-soluble organic solvent distilled and recovered from each layer (“highly water-containing layer” and “organic layer”) should be reused for polymerization by adjusting the water / water-soluble organic solvent ratio again to reduce costs. Is also possible.

  Although the content rate after the organic solvent removal of the water-soluble organic solvent of a highly water-containing layer is not specifically limited, Preferably it is 1 mass% or less, More preferably, it is 5000 mass ppm or less, More preferably, it is 1000 mass ppm or less. The smaller the number, the higher the recovery rate, so that the cost ratio of the water-soluble organic solvent can be suppressed.

  In addition, the content of the unsaturated monomer remaining in the high water content layer after performing these operations is preferably 12,000 ppm by mass or less, based on the solid content of the polyacrylic acid polymerization product, More preferably, it is 9,300 ppm by mass or less. In view of the actual situation, it is 1,000 ppm by mass or more.

  Moreover, the amount of residual inorganic ions in the high water content layer after these operations is 12,000 ppm by mass or less with respect to the solid content of the polyacrylic acid polymerization product. More preferably, it is 9,300 ppm by mass or less. In consideration of the actual situation, it is 2000 mass ppm or more.

  The polymer product of the present invention can be preferably used as a detergent builder.

  Specifically, the detergent builder of the present invention may consist solely of the polymer product of the present invention or may comprise a mixture with any other suitable detergent builder. In the above case, the polymer product of the present invention may be in the form of an aqueous solution or in a dried form.

  Examples of other optional cleaning builders include, for example, sodium tripolyphosphate, sodium pyrophosphate, sodium silicate, bow glass, sodium carbonate, sodium nitrilotriacetate, sodium ethylenediaminetetraacetate and potassium, zeolite, carboxyl derivatives of polysaccharides, And water-soluble polymers such as (meth) acrylic acid (co) polymer salts and fumaric acid (co) polymer salts.

  The detergent builder may be for liquid cleaning or powder detergent. The detergent builder of the present invention is excellent in compatibility with a surfactant. For this reason, the liquid detergent is preferred in that it can be a highly concentrated liquid detergent composition.

  The said detergent builder can set arbitrary appropriate kinds and compounding ratios within the range which does not impair the effect of this invention.

  The detergent builder is excellent in dispersion stability with time and excellent in properties such as anti-recontamination ability.

  As above-mentioned, the polymer product of this invention can be preferably used as a raw material of a detergent composition. A detergent builder, preferably comprised of the polymer product of the present invention, is included.

  The detergent composition may be a powder detergent composition or a liquid detergent composition. The detergent composition may contain any suitable additive that is typically used in detergents. Examples of the additive include an anti-redeposition agent for preventing re-deposition of contaminants such as alkali builder, chelate builder, sodium carboxymethyl cellulose, stain inhibitor such as benzotriazole and ethylene-thiourea, and a soil release agent. , Color transfer inhibitor, softener, alkaline substance for pH adjustment, fragrance, solubilizer, fluorescent agent, colorant, foaming agent, foam stabilizer, polish, bactericidal agent, bleaching agent, bleaching aid, Enzymes, contamination, solvents and the like are preferred. In the case of a powder detergent composition, it is preferable to blend zeolite.

  The content ratio of the polymer product of the present invention in the detergent builder (compared as the mass excluding moisture in the polymer product and the detergent builder) is 0.1 to 100 mass% of the detergent builder. It is preferable that it is 80 mass%, More preferably, it is 1-70 mass%, More preferably, it is 5-65 mass%. If the content of the polymer product of the present invention is less than 0.1% by mass, the cleaning power when used as a cleaning composition may be insufficient. When the content ratio of the polymer product of the present invention exceeds 80% by mass, there is a risk of becoming uneconomical.

  The detergent builder containing the polymer product of the present invention in the detergent composition may be liquid or solid. What is necessary is just to determine according to the form (for example, liquid substance or solid substance) at the time of sale of a detergent. Moreover, you may mix | blend with the form of the aqueous solution after superposition | polymerization, and you may mix | blend in the state which reduced the water | moisture content of the aqueous solution to some extent and concentrated.

  The above products are detergents used only for specific purposes such as synthetic detergents for household detergents, textile industry and other industrial detergents, hard surface cleaners, and bleaching cleaners that enhance one of the components. Including. Since the polymerization product of the present invention is excellent in chelating ability, it can be suitably used because it can stabilize hydrogen peroxide by capturing trace metals and is excellent in bleaching agent stabilization ability.

  The detergent composition preferably contains a surfactant in addition to the polymerization product. The surfactant preferably contained in the cleaning composition is at least one selected from the group consisting of an anionic surfactant, a nonionic surfactant, a cationic surfactant, and an amphoteric surfactant. These surfactants may be used alone or in combination of two or more.

  When two or more surfactants are used in combination, the combined amount of the anionic surfactant and the nonionic surfactant is preferably 50% by mass or more, more preferably 100% by mass of the total surfactant. 60 mass% or more, More preferably, it is 70 mass% or more, Most preferably, it is 80 mass% or more.

  The polymer product of the present invention can be preferably used as a pigment dispersant.

  According to the present invention, it is possible to provide a paper slurry having a low viscosity and stability over time and having a high concentration. And as a result, without applying coating defects when coating with the slurry, it provides good base paper coverage, printing gloss, blister resistance, uniform printing surface, and the inherent whiteness of the pigment. Further, it becomes possible to provide a coated paper for printing having superiority in opacity and ink acceptability.

  The pigment used in the present invention is not particularly limited, and examples thereof include kaolin, clay, heavy calcium carbonate, light calcium carbonate, titanium dioxide, satin white, talc, aluminum hydroxide, and plastic pigment.

  In the present invention, as a method for preparing the pigment, conventionally known methods can be referred to as appropriate or can be carried out in combination. Examples thereof include a method of performing primary dispersion and wet-grinding. This method is preferable in that a high-concentration pigment slurry having a low viscosity and excellent dispersion stability can be obtained. Furthermore, of course, the method for preparing the pigment in the present invention is not limited to this wet pulverization method, and it is not limited to take a preparation method without performing the wet pulverization treatment. In the method for preparing the pigment, the primary dispersion method is not particularly limited, but it is preferably mixed with a mixer, for example, a shear force such as a high-speed disperser, a homomixer, a ball mill, a coreless mixer, a stirring disperser, etc. It is preferable to use one having a high value.

  In the wet pulverization treatment, the polyacrylic acid-based polymerization product obtained as described in the first aspect of the present invention may be charged into a pulverizer and pulverized. In such a case, the polyacrylic acid polymerization product also serves as a grinding aid.

  The average particle size of the pigment contained in the papermaking pigment slurry is preferably 1.5 μm or less, more preferably 1.0 μm or less. In addition, as a method for controlling the particle size, pulverization is performed with the above-described apparatus and the like, and the particle size is measured with a laser particle size distribution meter as used in Examples described later, and the desired particle size is preferably 93. %, More preferably 95% or more.

  The total amount of the above-mentioned paper dispersant for papermaking and the amount of the polyacrylic acid polymerization product of the present invention is preferably 0.05 to 1.0% by mass with respect to the total amount of the pigment.

  The pigment slurry in the present invention preferably has a solid content concentration of 65% by mass or more.

  The viscosity of the pigment slurry is not particularly limited, but is preferably 1000 mPa · s or less, more preferably 600 mPa · s or less. When it is higher than 1000 mPa · s, when the coating liquid prepared mainly from the slurry is applied while receiving high shearing force at high speed, coating defects such as streak, bleeding and sarcophagus are likely to occur. There is a possibility that an excellent coated paper texture cannot be obtained.

  The pigment slurry viscosity is measured using a B-type viscometer. The value measured at 3, 60 rpm for 1 minute.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples. Unless otherwise specified, “part” means “part by mass” and “%” means “% by mass”.

<Quantification method of “molar ratio of structure (A)” (by ¹ HNMR analysis)>
An NMR chart (measured in heavy water) was prepared. And the baseline of the three peaks derived from the chain transfer agent was drawn. In the case of IPA (isopropanol), a peak of 1.1 mass ppm, a peak of 1.2 mass ppm, and a peak of 1.3 mass ppm are peaks of methyl groups derived from IPA which is a chain transfer agent. The sum of these three peaks is taken as the peak derived from IPA.

  The peak of the CH group in the polymer main chain was used for comparison. It was separated from other peaks by drawing a line perpendicular to the baseline from 1.7 ppm and 2.35 ppm. This was the peak of the CH group. The peak was cut out from the chart paper and the mass was measured.

The sum of the three peak masses is divided by the number of protons used for comparison in the structure (A) (in the above case, 6 derived from the methyl group of IPA, which is an alcohol chain transfer agent) (W _A ). On the other hand, the peak of the methine group of the polymer main chain is divided by the number of protons (1 if the polymer is a homopolymer of acrylic acid) (referred to as W _M ). Here, the "number of moles / polymer structural units derived from an unsaturated monomer contained in the structures (A) contained in the polymer" is calculated by W A _/ W _M. Therefore,

<Measurement method of molecular weight and molecular weight distribution>
The molecular weight of the water-soluble resin was measured under the following measurement conditions using GPC (gel permeation chromatography).

<Measurement method of inorganic ions>
It measured on the following measuring conditions with the ion chromatography (suppressor method).

<Solid content of polymer product (polymer aqueous solution)>
About 1 g of the polymer product is accurately weighed together (Bg) in an aluminum cup (Ag) that has been accurately weighed in advance. Dry under nitrogen atmosphere at 120 ° C. for 1 hour. The dried aluminum cup is cooled in a desiccator and weighed (Cg). The solid content is calculated from the volatile content measured by weighing.

<Example 1>
A 5 L stainless steel (SUS316) separable flask equipped with a reflux condenser, two dripping devices, and paddle blades was charged with 400 g of ion exchange water (initial charge solution) and 400 g of isopropyl alcohol. To the two dropping devices, 540 g of an 80% aqueous solution of acrylic acid (hereinafter referred to as AA) and 60 g of a 15% aqueous solution of sodium persulfate were separately added as dropping solutions.

  The temperature was raised to the reflux temperature while stirring to start refluxing, and then the dropping of each of the aqueous solutions into the flask was simultaneously started. AA 80% aqueous solution was added dropwise over 180 minutes and sodium persulfate 15% aqueous solution over 185 minutes. Further, the temperature of the reaction system (reaction temperature) at the time of dropping, that is, at the time of polymerization was adjusted to 80 to 83 ° C. so as to maintain the reflux. After all the aqueous solutions had been dropped, the mixture was further stirred for 1 hour at the boiling point and aged. Further, the reaction solution was cooled to obtain a polymer.

  500 g of the obtained polymer and 333 g of water are put into a 1 L separable flask equipped with a stirrer and a 500 ml dropping funnel, and 126 g of 48% NaOH aqueous solution is gradually dropped and neutralized while paying attention to heat generation from this dropping funnel. did. After stirring for 30 minutes, the mixture was transferred to a 1 L separatory funnel and left at 40 ° C. The contents were immediately separated into two layers, and the amount of liquid in the upper layer gradually increased. However, the change in the amount of liquid became almost constant in one hour, so that the contents were collected separately in an upper layer of 273 g and a lower layer of 677 g. Furthermore, the lower layer is put into a 500 ml separable flask equipped with a Dean-Stark trap, heated to 120 to 140 ° C. in an oil bath, and isopropyl alcohol and water in the liquid are distilled off. Finally, an aqueous polymer solution (polymer formation) 220 g of product) was obtained.

  When the weight average molecular weight (Mw) and molecular weight distribution D were determined by the molecular weight measurement method described above, Mw was 6070 and D was 2.26.

  In addition, the chain transfer agent ratio in one molecule of the polymer was 2.1 mol%, and the sulfate ion amount by ion chromatography was 9,200 mass ppm.

<Example 2>
A 5 L stainless steel (SUS316) separable flask equipped with a reflux condenser, two dripping devices, and paddle blades was charged with 320 g of ion-exchanged water (initial charge solution) and 480 g of isopropyl alcohol. To the two dropping devices, 540 g of 80% aqueous solution of acrylic acid (hereinafter referred to as AA) and 40 g of 15% aqueous solution of sodium persulfate were separately charged as dropping solutions. The temperature was raised to the reflux temperature while stirring to start refluxing, and then the dropping of each of the aqueous solutions into the flask was simultaneously started. AA 80% aqueous solution was added dropwise over 180 minutes and sodium persulfate 15% aqueous solution over 185 minutes. Further, the temperature of the reaction system (reaction temperature) at the time of dropping, that is, at the time of polymerization was adjusted to 80 to 83 ° C. so as to maintain the reflux. After all the aqueous solutions had been dropped, the mixture was further stirred for 1 hour at the boiling point and aged. Further, the reaction solution was cooled to obtain a polymer.

  40 g of the obtained polymer and 27 g of water were put into a 100 ml separable flask equipped with a stirrer and a 20 ml dropping funnel, and 10.2 g of 48% NaOH aqueous solution was gradually dropped from the dropping funnel while paying attention to heat generation. Neutralized. After stirring for 30 minutes, the mixture was transferred to a 100 ml separatory funnel and left at 40 ° C. The contents were immediately separated into two layers, and the amount of liquid in the upper layer gradually increased. However, the change in the amount of liquid became almost constant over 1 hour, so that it was divided into 45.8 g for the upper layer and 30.1 g for the lower layer. Furthermore, the lower layer is put into a 100 ml separable flask equipped with a Dean-Stark trap, heated to 120-140 ° C. in an oil bath, isopropyl alcohol and water in the liquid are distilled off, and finally an aqueous polymer solution (polymer formation) 22.6 g of product) was obtained.

  When the weight average molecular weight (Mw) and the molecular weight distribution D were determined by the above molecular weight measurement method, Mw was 6306 and D was 2.16.

  Further, the ratio of the chain transfer agent in one molecule of the polymer was 2.3 mol%, and the amount of sulfate ion by ion chromatography was 8,300 mass ppm.

<Comparative Example 1>
A 5 L stainless steel (SUS316) separable flask equipped with a reflux condenser, two dripping devices, and a paddle blade was charged with 600 g of ion exchange water (initial charge solution) and 200 g of isopropyl alcohol. To the two dropping devices, 540 g of an 80% aqueous solution of acrylic acid (hereinafter referred to as AA) and 100 g of a 15% aqueous solution of sodium persulfate were separately added as dropping solutions.

  After the temperature was increased while stirring and refluxing was started, dropping of each of the aqueous solutions into the flask was simultaneously started. AA 80% aqueous solution was added dropwise over 180 minutes, and sodium persulfate 15% aqueous solution was added dropwise over 185 minutes. Further, the temperature of the reaction system (reaction temperature) at the time of dropping, that is, at the time of polymerization was adjusted to 80 to 83 ° C. so as to maintain the reflux. After all the aqueous solutions had been dropped, the mixture was further stirred for 1 hour at the boiling point and aged. Further, the reaction solution was cooled to obtain 1440 g of a polymerization solution.

  400 g of the obtained polymer and 40 g of water are put into a 1 L separable flask equipped with a stirrer and a 200 ml dropping funnel, and 100 g of 48% NaOH aqueous solution is gradually dropped and neutralized while paying attention to heat generation from this dropping funnel. did. After stirring for 30 minutes, the mixture was transferred to a 1 L separatory funnel and left at 40 ° C. The contents were immediately separated into two layers, and the amount of liquid in the upper layer gradually increased. However, since the change in the amount of liquid became almost constant in one hour, the contents were collected separately in the upper layer 210 g and the lower layer 375 g. The obtained lower layer was put into a 500 ml separable flask equipped with a Dean-Stark trap, adjusted to pH 7.3 with 48% NaOH aqueous solution, heated to 120-140 ° C. in an oil bath, Isopropyl alcohol and water were distilled off, and finally 190 g of an aqueous polymer solution was obtained.

  When the weight average molecular weight (Mw) and the molecular weight distribution D were determined by the molecular weight measurement method described above, Mw was 6800 and D was 2.5.

  Further, the ratio of the chain transfer agent in one molecule of the polymer was 1.3 mol%, and the amount of sulfate ion by ion chromatography was 20,100 ppm by mass.

<Performance confirmation>
A calcium carbonate dispersion (slurry) was prepared using the polymer as an inorganic pigment dispersant. A 500 ml SUS separable flask was charged with 200 g of calcium carbonate (commercially available), and a stirring blade and a glass three-necked upper lid were set and fixed.

  While stirring at 400 rpm, 9.5 g of the 10% solution of the polymer obtained above was gradually added to the inside and dispersed uniformly. Further, 500 g of 2 mm diameter ceramic beads were gradually added. Carefully so as not to decelerate the stirrer against the torque of the internal mixture, gradually increase the rotation speed, and simultaneously add 9.5 g of 10% polymer solution in portions, and finally rotate the rotation speed to 1500 rpm. The calcium carbonate was pulverized in about 110 to 120 minutes. By the above operation, a calcium carbonate aqueous dispersion (slurry) having a concentration of 75% was obtained.

  The dispersion performance of the water-soluble resin was determined by measuring the viscosity with time of the slurry (dispersion) using a B-type viscometer. It was measured at 3, 60 rpm for 1 minute. Viscosity measurement was performed immediately after slurry preparation and after one week. The measurement results are shown in Table 2.

Claims (2)

A polyacrylic acid polymerization product obtained by polymerizing an unsaturated monomer containing acrylic acid and / or a salt thereof using a polymerization initiator and an alcohol chain transfer agent,
The polyacrylic acid polymerization product includes a polyacrylic acid polymer having a structure (A) derived from an alcohol chain transfer agent,
The ratio of the structure (A) derived from the alcohol chain transfer agent in the polyacrylic acid polymer is such that the polyacrylic acid-based structure unit is derived from the unsaturated monomer-derived structural unit constituting the polyacrylic acid polymer. The structural unit of the structure (A) derived from the alcohol chain transfer agent in the polymer is 1.5 mol% or more,
The polyacrylic acid polymerization product, wherein the content of inorganic ions derived from the polymerization initiator is 12,000 ppm by mass or less based on the solid content of the polyacrylic acid polymerization product.   The polyacrylic acid polymerization product according to claim 1, wherein a ratio of unsaturated monocarboxylic acid and unsaturated dicarboxylic acid in the unsaturated monomer is 90 mol% or more.