JP3910616B2 - Method for producing polymer - Google Patents

Description

  The present invention relates to a method for producing a polymer that can be suitably used as, for example, a detergent builder or an inorganic pigment dispersant.

Conventionally, in a method for producing a polymer, a polymerization initiator or a chain transfer agent is dropped during the polymerization period (when the polymerization reaction proceeds). For example, Patent Document 1 discloses a method of obtaining a polymer such as a poly (meth) acrylic acid (salt) -based polymer by dropping hypophosphorous acid (salt) as a chain transfer agent during the polymerization period. It is disclosed. Patent Document 2 discloses a method for obtaining a polymer such as an unsaturated carboxylic acid (salt) polymer by dropping a polymerization initiator and a chain transfer agent during the polymerization period as a method for producing a dispersant. ing. In Patent Document 3, a polymerization initiator and a chain transfer agent are added dropwise during the polymerization period, and a basic compound such as sodium hydroxide is added dropwise to keep the pH in the polymerization system within a specific range. Discloses a method for obtaining a poly (meth) acrylic acid (salt) polymer.
JP-A-6-287208 JP 2000-169654 A JP-A-5-86125

  In general, the dropping operation is performed by dropping various liquids at a constant speed (a constant speed). In each of the above conventional production methods, a polymerization initiator or a chain transfer agent is dropped at a constant rate during the polymerization period. However, each of the conventional manufacturing methods that perform the dropping operation has the following problems. That is, the method described in Patent Document 1 has a problem that the amount of residual monomer (monomer) is large. The method described in Patent Document 2 has a problem that the dispersion performance of the resulting dispersant is insufficient because the molecular weight distribution of the polymer is wide. In addition, in the method described in Patent Document 3, since the basic compound is dropped together with the polymerization initiator and the chain transfer agent, labor is required for removing heat from the polymerization system, and the reaction solution may foam. There is a problem that the monomer concentration in the liquid cannot be increased and the productivity of the polymer is lowered.

  That is, in the above conventional production method, the amount of residual monomer cannot be reduced; the monomer concentration in the reaction solution cannot be increased; the molecular weight distribution of the resulting polymer is narrowed It cannot be done; etc.

  The present invention has been made in view of the above-described conventional problems, and its purpose is to reduce the amount of residual monomer and to increase the concentration of monomer in the reaction solution. It is also possible to provide a method for producing a water-soluble polymer that can narrow the molecular weight distribution of the obtained polymer.

Method for producing a water-soluble polymer of the present invention, in order to solve the above problems, the predetermined period during the polymerization, a process for the preparation of the water-soluble polymer that continuous addition of a chain transfer agent, monomer The body component is continuously added to the reaction solution for a period at least partially overlapping with the period in which the chain transfer agent is continuously added to the reaction solution, and the addition rate of the same chain transfer agent is set to the overlap period. It is characterized by changing at least once within. Furthermore, the method for producing a water-soluble polymer of the present invention is characterized by changing the addition rate so as to decrease the above-mentioned problem. Moreover, it is preferable to change this addition speed | velocity | rate by the method of decreasing once in steps, the method of decreasing several times in steps, or the method of decreasing continuously.

  Moreover, in order to solve said subject, the manufacturing method of the water-soluble polymer of this invention is characterized by the monomer component to be used containing an unsaturated carboxylic acid (salt) type monomer. The content of the unsaturated carboxylic acid (salt) monomer in the monomer component is preferably 50% by weight or more.

  According to said structure, since the addition rate with respect to the monomer of a chain transfer agent is changed at least once, the amount of residual monomers can be reduced. Therefore, the safety of the obtained water-soluble polymer can be improved. Moreover, the monomer concentration in the reaction solution can be increased by changing the addition rate of the chain transfer agent to be small. Thereby, the productivity of the water-soluble polymer can be improved, and therefore the water-soluble polymer can be produced at low cost. Furthermore, since the molecular weight distribution of the obtained water-soluble polymer can be narrowed, when the water-soluble polymer is used as, for example, a detergent builder or an inorganic pigment dispersant, excellent performance (dispersion performance, etc.) is obtained. It can be demonstrated.

  That is, according to the above configuration, the amount of residual monomer can be reduced, the monomer concentration in the reaction solution can be increased, and the molecular weight of the resulting water-soluble polymer can be increased. A method for producing a water-soluble polymer capable of narrowing the distribution can be provided.

As described above, the method for producing a water-soluble polymer of the present invention continuously reacts during a period at least partially overlapping with a period in which the monomer component is continuously added to the reaction liquid. It is the structure which adds to a liquid and changes the addition rate of the same chain transfer agent at least once within the said overlap period . Moreover, the manufacturing method of the water-soluble polymer of this invention is the structure which changes so that this addition rate may become small as mentioned above. Further, it is preferable that the addition rate is changed by a method of decreasing the addition once in a stepwise manner, a method of decreasing it a plurality of times in a stepwise manner, or a method of decreasing it continuously.

  Moreover, the manufacturing method of the water-soluble polymer of this invention is a structure in which the monomer component to be used contains 50 weight% or more of unsaturated carboxylic acid (salt) type monomers as mentioned above.

  Thereby, since the amount of residual monomers can be reduced, the safety of the water-soluble polymer obtained can be improved. Moreover, since the monomer concentration in the reaction solution can be made higher, the productivity of the water-soluble polymer can be improved, and therefore the water-soluble polymer can be produced at low cost. Furthermore, since the molecular weight distribution of the obtained water-soluble polymer can be narrowed, when the water-soluble polymer is used as, for example, a detergent builder or an inorganic pigment dispersant, excellent performance (dispersion performance, etc.) is obtained. It can be demonstrated.

  That is, according to the above configuration, the amount of residual monomer can be reduced, the monomer concentration in the reaction solution can be increased, and the molecular weight of the resulting water-soluble polymer can be increased. There exists an effect that the manufacturing method of the water-soluble polymer which can narrow distribution can be provided.

  An embodiment of the present invention will be described as follows. In the present invention, “changing the addition rate at least once” includes “making the addition rate zero”, that is, “adding at a constant rate and then ending the addition”. Make it not exist. In the present invention, the “polymerization period” refers to a point in time when at least a part of the monomer component and at least a part of the polymerization initiator are mixed and a polymerization operation such as a temperature raising operation is started. The period from the (polymerization start time) to the time when the polymerization operation is completed (polymerization end time) by performing, for example, a cooling operation is shown. Accordingly, the “predetermined period during the polymerization period” refers to at least a part of the period from the polymerization start point to the polymerization end point.

  A monomer component suitable for polymerization by applying the production method according to the present invention is not particularly limited, but a monomer component containing an unsaturated carboxylic acid (salt) monomer is more preferable. Preferably, a monomer component containing (meth) acrylic acid (salt) and a monomer component containing maleic acid (salt) are more preferred, and (meth) acrylic acid (salt) as the main component (50% by weight or more) And a monomer component containing maleic acid (salt) as a main component (50% by weight or more). Further, when the monomer component contains (meth) acrylic acid (salt) or maleic acid (salt) as a main component, the content is more preferably 60% by weight or more, and 90% by weight or more. Is more preferable, and 100% by weight is particularly preferable. A water-soluble polymer can be obtained by polymerizing a monomer component containing (meth) acrylic acid (salt) or maleic acid (salt) as a main component. Examples of the unsaturated carboxylic acid (salt) monomer include (meth) acrylic acid (salt) and maleic acid (salt), as well as unsaturated monocarboxylic acid (salt) monomers and unsaturated monomers described below. Examples thereof include saturated dicarboxylic acid (salt) monomers.

  Specific examples of (meth) acrylic acid (salt) include acrylic acid; monovalent metal salts of acrylic acid such as sodium acrylate and potassium acrylate; divalent acrylic acid such as magnesium acrylate and calcium acrylate. Metal salts; Acrylic acid (salt) such as ammonium acrylate; and methacrylic acid; Monovalent metal salts of methacrylic acid such as sodium methacrylate and potassium methacrylate; Divalent metals such as magnesium methacrylate and calcium methacrylate Examples thereof include, but are not particularly limited to, methacrylic acid (salt) such as salt; ammonium methacrylate; These (meth) acrylic acids (salts) may be used alone or in combination of two or more.

  Specific examples of maleic acid (salt) include maleic acid and maleic anhydride; compounds containing monovalent metals such as sodium and potassium; compounds containing divalent metals such as magnesium and calcium; ammonia and amines And a neutralized product obtained by partially neutralizing or completely neutralizing maleic acid. These maleic acids (salts) may be used alone or in combination of two or more.

  Specific examples of the monomer that can be used as a monomer component in addition to the above (meth) acrylic acid (salt) and maleic acid (salt) include unsaturated monocarboxylic acids such as crotonic acid (salt). Acid (salt) monomers; fumaric acid (salt), itaconic acid (salt), unsaturated dicarboxylic acid (salt) monomers such as citraconic acid (salt); (meth) acrylamide, t-butyl (meta ) Amide monomers such as acrylamide; Hydrophobic monomers such as (meth) acrylic acid esters such as methyl (meth) acrylate and ethyl (meth) acrylate, styrene, 2-methylstyrene, vinyl acetate; Vinyl Sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-allyloxy-2-hydroxypropane sulfonic acid, Unsaturated sulfonic acid monomers such as foethyl (meth) acrylate, sulfopropyl (meth) acrylate, 2-hydroxysulfopropyl (meth) acrylate, sulfoethylmaleimide; Compounds containing monovalent metals such as potassium, compounds containing divalent metals such as magnesium and calcium, neutralized products obtained by partial or complete neutralization with a base such as ammonia or amine; 3-methyl-2-butene -1-ol (prenol), 3-methyl-3-buten-1-ol (isoprenol), 2-methyl-3-buten-2-ol (isoprene alcohol), 2-hydroxyethyl (meth) acrylate, polyethylene glycol Mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, Liethylene glycol monoisoprenol ether, polypropylene glycol monoisoprenol ether, polyethylene glycol monoallyl ether, polypropylene glycol monoallyl ether, glycerol monoallyl ether, α-hydroxyacrylic acid, N-methylol (meth) acrylamide, glycerol mono (meth) Hydroxyl group-containing unsaturated monomers such as acrylate and vinyl alcohol; cationic monomers such as dimethylaminoethyl (meth) acrylate and dimethylaminopropyl (meth) acrylamide; nitrile monomers such as (meth) acrylonitrile; (Meth) acrylamide methanephosphonic acid, (meth) acrylamide methanephosphonic acid methyl ester, 2- (meth) acrylamide-2-methylpropanephosphone Phosphorus-containing monomers and the like; but like, but is not particularly limited. Only one kind of these monomers may be used, or two or more kinds may be used in combination.

  Specific examples of a polymerization initiator that can be suitably used for polymerization by applying the production method according to the present invention include hydrogen peroxide; ammonium peroxodisulfate (ammonium persulfate), sodium peroxodisulfate ( Sodium persulfate), peroxodisulfate (persulfate) such as potassium peroxodisulfate (potassium persulfate); 2,2′-azobis- (2-amidinopropane) dihydrochloride, 4,4′-azobis- Azo compounds such as (4-cyanovaleric acid), 2,2′-azobisisobutyronitrile, 2,2′-azobis- (4-methoxy-2,4-dimethylvaleronitrile); benzoyl peroxide, Lauroyl oxide, peracetic acid, persuccinic acid, di-t-butyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide Organic peroxide; and the like. However, the invention is not particularly limited. These polymerization initiators may be used alone or in combination of two or more. Of the polymerization initiators exemplified above, peroxides such as hydrogen peroxide, peroxodisulfate, and organic peroxides are more preferred, and peroxodisulfate is more preferred. Although the usage-amount of the polymerization initiator with respect to 1 mol of monomer components is not specifically limited, The inside of the range of 0.0001 mol-0.05 mol is suitable. In order to further accelerate the polymerization, the polymerization initiator may be used in combination with a reducing agent such as (bi) sulfite or transition metal salt.

  Specific examples of the chain transfer agent that can be suitably used for polymerization by applying the production method according to the present invention include sulfur-containing compounds such as thioglycolic acid, thioacetic acid, and mercaptoethanol; Phosphorous acid (salt) such as acid and sodium phosphite; hypophosphorous acid (salt) such as hypophosphorous acid and sodium hypophosphite; lower alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, and butyl alcohol ; However, it is not particularly limited. Only one type of these chain transfer agents may be used, or two or more types may be used in combination. Of the chain transfer agents exemplified above, hypophosphorous acid (salt) is more preferred, and sodium hypophosphite is more preferred. Although the usage-amount of the chain transfer agent with respect to 1 mol of monomer components is not specifically limited, The inside of the range of 0.005 mol-0.15 mol is suitable.

  Specific examples of the solvent that can be suitably used for polymerization by applying the production method according to the present invention include water; an aqueous solvent compatible with water; a mixed solvent of water and an aqueous solvent. Non-aqueous solvents such as aromatic hydrocarbons such as benzene, toluene and xylene, but are not particularly limited. Specific examples of the aqueous solvent include lower alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol and butyl alcohol; lower ketones such as acetone and methyl ethyl ketone; lower ethers such as dimethyl ether, diethyl ether and methyl ethyl ether; Etc. Of the above exemplified solvents, water is more preferred. Moreover, the ratio of water in the case of using the above mixed solvent as a solvent is not particularly limited, but is more preferably 40% by weight or more. The amount of the solvent used with respect to 1 mol of the monomer component is not particularly limited. When a lower alcohol is used as a solvent, the lower alcohol also serves as a chain transfer agent.

  The method for producing a polymer according to the present invention is (1) a method for producing a polymer in which a polymerization initiator is continuously added for a predetermined period during the polymerization period, and the addition rate of the polymerization initiator is changed at least once. And (2) a method for producing a polymer in which a chain transfer agent is continuously added for a predetermined period during the polymerization period, wherein the addition rate of the chain transfer agent is changed at least once. In the present invention, “add continuously” includes not only literally adding continuously but also adding intermittently at a predetermined (short) interval, such as dropping. Suppose that Further, in the present invention, “changing the addition rate at least once” specifically means, for example, that the dropping rate is changed at least once when the addition method is dropping.

  The reaction conditions for the polymerization reaction are not particularly limited, but the reaction temperature is more preferably in the range of 50 ° C to 120 ° C, more preferably in the range of 60 ° C to 115 ° C, and 90 ° C to 110 ° C. Within the range is particularly preferred. When the reaction temperature is less than 50 ° C., an ultra-high molecular weight polymer is likely to be formed, and the gel resistance of the resulting polymer may be reduced. When the reaction temperature exceeds 120 ° C., a low molecular weight polymer is likely to be formed, so that the chelating ability of the resulting polymer may be reduced. The reaction time may be set according to the addition rate of the polymerization initiator or chain transfer agent, the composition of the monomer component, the reaction temperature, etc., and is not particularly limited.

  When employing the method (1) above, a part of the polymerization initiator may be charged into the reactor before starting the polymerization operation such as a temperature raising operation, if necessary. Moreover, when employ | adopting the method of said (2), some chain transfer agents may be charged into the reactor before starting superposition | polymerization operation | movement, such as temperature rising operation as needed.

  When employing the method (1), a chain transfer agent may or may not be used. In the case of using a chain transfer agent, the chain transfer agent may be charged into the reactor all at once before starting the polymerization operation (before the polymerization starts), a part of the chain transfer agent is charged into the reactor, and the rest is polymerized. It may be continuously added to the reaction liquid (polymerization system) for a predetermined period in the period, or the entire amount may be continuously added to the reaction liquid for a predetermined period in the polymerization period. Further, when adopting the method of (2) above, the polymerization initiator may be charged into the reactor all at once before the start of polymerization, a part of the polymerization initiator is charged into the reactor, and the rest is a predetermined period in the polymerization period, You may add to a reaction liquid continuously, and you may add the whole quantity to a reaction liquid continuously for the predetermined period in a superposition | polymerization period. Therefore, the production method according to the present invention can use the method (1) and the method (2) in combination. When both methods are used in combination, the period in which the polymerization initiator is continuously added to the reaction liquid and the period in which the chain transfer agent is continuously added to the reaction liquid are at least partially overlapping each other. It is particularly desirable to do so.

  When employing the above method (1) or (2), it is sufficient that at least a part of the solvent is charged in the reactor before the start of polymerization. In addition, the monomer component may be charged into the reactor all at once before the start of polymerization, a part of the monomer component may be charged into the reactor, and the remainder may be continuously added to the reaction solution for a predetermined period during the polymerization period. Well, the entire amount may be continuously added to the reaction solution for a predetermined period during the polymerization period, but in particular, it is more preferable to add at least a part thereof to the reaction liquid continuously for a predetermined period during the polymerization period. Desirably, it is particularly desirable to continuously add the polymerization initiator and the chain transfer agent to the reaction solution for a period at least partially overlapping with the period of continuous addition to the reaction solution. Moreover, it is more preferable that the monomer component is completely added before the polymerization initiator and the chain transfer agent are completely added to the reaction solution.

  In the method (1) and the method (2), as a method of changing the addition rate of the polymerization initiator or the chain transfer agent at least once, specifically, the case where the method of adding is dropwise. For example, (i) a method of dropping at a speed A and then dropping at a speed B larger than the speed A (increasing the speed stepwise); (ii) after dropping at a speed C; A method in which the velocity is gradually increased and finally dropped at a velocity D greater than the velocity C (the velocity is continuously increased); (iii) after dropping at the velocity E, a velocity F smaller than the velocity E (Iv) After dropping at a speed G, the speed is gradually decreased, and finally dropping at a speed H smaller than the speed G (the speed is continuously increased). Method). Furthermore, (v) a method of repeatedly performing the above (i) (increasing the speed a plurality of times in steps); (vi) a method of repeatedly performing the above (iii) (increasing the speed a plurality of times in steps); ) A method in which (i) is performed at least once, and then (iii) is performed at least once; (viii) a method in which (iii) is performed at least once and then (i) is performed at least once; ) A method of performing (iv) after performing (i) at least once; (x) a method of performing (ii) after performing at least one of the above (iii); (xi) a method of performing (ii) above (Iii) After performing (iii) at least once; (xii) After performing (iv) above, (i) at least once; (xiii) After performing (ii) above (iv) (Xiv) A method in which the above methods (i) to (iv) are appropriately combined, such as a method in which (ii) is performed after the above (iv) is performed, can also be employed.

  Among the methods exemplified above, as a method for changing the addition rate of the polymerization initiator at least once, for example, when the methods (i), (ii), (v) and (viii) are employed, the residual monomer ( The amount of monomer) can be reduced, and the molecular weight distribution of the resulting polymer can be narrowed (sharp). Therefore, the safety of the polymer can be improved, and when the polymer is used as, for example, a detergent builder or an inorganic pigment dispersant, excellent performance can be exhibited. Further, since the monomer concentration in the reaction solution can be made higher, the productivity of the polymer can be improved, and therefore the polymer can be produced at a low cost.

  On the other hand, among the methods exemplified above, for example, when the method of (iii), (iv), (vi), (vii), (xi) is adopted as a method of changing the addition rate of the polymerization initiator at least once. As compared with the case where the same amount of the polymerization initiator is dropped at a constant speed (a constant speed), the amount of residual monomer can be reduced. Therefore, the safety of the polymer can be improved.

  In the production method according to the present invention, as a method of changing the addition rate of the polymerization initiator at least once, the above methods (i), (ii), (v), that is, the addition rate is increased. The method of changing is particularly preferred.

  Among the methods exemplified above, as a method of changing the addition rate of the chain transfer agent at least once, for example, when the methods (iii), (iv), (vi), (vii) are employed, the amount of residual monomers And the molecular weight distribution of the resulting polymer can be narrowed (sharpened). Therefore, the safety of the polymer can be improved, and when the polymer is used as, for example, a detergent builder or an inorganic pigment dispersant, excellent performance can be exhibited. Further, since the monomer concentration in the reaction solution can be made higher, the productivity of the polymer can be improved, and therefore the polymer can be produced at a low cost.

  On the other hand, among the methods exemplified above, as a method of changing the addition rate of the chain transfer agent at least once, for example, when adopting the method (i), (ii), (v), (viii), (xi) Compared with the case where the same amount of chain transfer agent is dropped at a constant speed (a constant speed), the amount of residual monomer can be reduced. Therefore, the safety of the polymer can be improved.

  In the production method according to the present invention, as a method of changing the addition rate of the chain transfer agent at least once, the above methods (iii), (iv), (vi), that is, the addition rate is made small. The method of changing is particularly preferred.

  As described above, according to the production method of the present invention, since the addition rate of the polymerization initiator is changed at least once, or because the addition rate of the chain transfer agent is changed at least once, the amount of residual monomers Can be reduced. Therefore, the safety of the obtained polymer can be improved. In addition, the monomer concentration in the reaction solution can be increased by changing the polymerization initiator addition rate to be larger or by changing the chain transfer agent addition rate to be smaller. be able to. Thereby, the productivity of the polymer can be improved, and therefore the polymer can be produced at a low cost. Furthermore, since the molecular weight distribution of the obtained polymer can be narrowed, when the polymer is used as, for example, a detergent builder or an inorganic pigment dispersant, excellent performance (dispersion performance, etc.) can be exhibited. it can.

  EXAMPLES Hereinafter, although an Example, a reference example, and a comparative example demonstrate this invention further more concretely, this invention is not limited at all by this. In the examples, reference examples and comparative examples, “part” represents “part by weight” and “%” represents “% by weight”.

In Examples, Reference Examples and Comparative Examples, the molecular weight (weight average molecular weight and number average molecular weight) of the polymer, and the molecular weight distribution are as follows.
Pump: L-7110 (manufactured by Hitachi, Ltd.)
Carrier liquid: An aqueous solution prepared by adding ultrapure water to 34.5 g of disodium hydrogen phosphate.12 hydrate and 46.2 g of sodium dihydrogen phosphate.dihydrate to adjust the total amount to 5000 g. Flow rate: 0.5 ml / min
Column: Water-based GPC column TSK-GEL G3000PWXL (manufactured by Tosoh Corporation), 1 detector: UV detector L-7400 (manufactured by Hitachi, Ltd.), wavelength 214 nm
Molecular weight standard sample: Sodium polyacrylate (manufactured by Soka Science Co., Ltd.)
Was measured.

[Reference Example 1]
A 5 L SUS316 separable flask equipped with a reflux condenser, a thermometer, a plurality of dropping funnels, and a stirrer was used as the reactor. The reactor was charged with 287.3 parts of ion-exchanged water as a solvent and 717.4 parts of maleic anhydride, and was charged with 1037.0 parts of a 48% aqueous sodium hydroxide solution in a dropping funnel. Then, while stirring the contents, the aqueous solution was dropped at a constant rate over 60 minutes, and then the contents were heated to the boiling point of the system (so as to be in a reflux state).

  Next, 658.6 parts of an 80% aqueous acrylic acid solution (526.9 parts of acrylic acid and 131.7 parts of ion-exchanged water), 650.2 parts of ion-exchanged water, and 35 as a polymerization initiator were placed in separate dropping funnels. % Hydrogen peroxide solution 160.9 parts (hydrogen peroxide 56.32 parts and ion-exchanged water 104.58 parts), and 170.6 parts of a 15% aqueous sodium peroxodisulfate solution as a polymerization initiator (sodium peroxodisulfate) 25.59 parts and ion-exchanged water 145.01 parts).

  Then, while stirring the contents, the acrylic acid aqueous solution was dropped at a constant rate over 120 minutes, and hydrogen peroxide was dropped at a constant rate over 90 minutes to initiate a polymerization reaction. The ion-exchanged water was dropped at a constant rate over 80 minutes after 50 minutes had elapsed from the start of dropping of the acrylic acid aqueous solution. The sodium peroxodisulfate aqueous solution was dropped from 24.4 parts (14% of the total) over 60 minutes at a constant speed after 10 minutes from the start of dropping of the acrylic acid aqueous solution, and then the remaining amount over 60 minutes. 146.2 parts were added dropwise at a constant speed. That is, the dropping rate of the sodium peroxodisulfate aqueous solution was changed in two steps so that the dropping rate in the latter half was larger (approximately 6 times) than the dropping rate in the first half. The reaction temperature was maintained at the boiling point of the system (100 ° C. to 110 ° C.) during the dropping period of each of the aqueous solutions.

  After completion of the dropping operation, that is, after completion of dropping of the sodium peroxodisulfate aqueous solution, the mixture was further agitated at the same temperature for 20 minutes for aging to complete the polymerization reaction. As a result, a water-soluble polymer as a polymer was obtained. The weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (D value = Mw / Mn) of the water-soluble polymer were measured under the above measurement conditions. Further, the residual monomer amount (ppm) was measured by a predetermined method. The results are shown in Table 1.

[Reference Example 2]
The polymerization reaction was carried out in the same manner as in Reference Example 1 except that the 35% hydrogen peroxide solution dropping method was changed to the following method. That is, 352.6% hydrogen peroxide solution was dropped at a constant rate of 112.6 parts (70% of the whole) over 50 minutes, and then the remaining 48.3 parts were dropped at a constant rate over a further 40 minutes. A water-soluble polymer was obtained. That is, for the hydrogen peroxide solution, the dropping rate was changed in two stages so that the dropping rate in the latter half was smaller (approximately 0.5 times) than the dropping rate in the first half. Various measurement results are shown in Table 1.

[Example 1]
In the same reactor as in Reference Example 1, 805.5 parts of ion-exchanged water was charged, and the temperature was raised to the boiling point (100 ° C.) while stirring. Next, in each separate dropping funnel, 216.1 parts of 80% aqueous acrylic acid solution (1700.9 parts of acrylic acid and 425.2 parts of ion-exchanged water) and 112.4 parts of 15% aqueous sodium peroxodisulfate solution (peroxo 16.86 parts of sodium sulfate and 95.54 parts of ion-exchanged water) and 200.3 parts of 45% sodium hypophosphite / monohydrate aqueous solution (sodium hypophosphite / monohydrate as a chain transfer agent) Product 90.14 parts and ion-exchanged water 110.16 parts).

  Then, while stirring the contents, the acrylic acid aqueous solution was dropped at a constant rate over 180 minutes, and the sodium peroxodisulfate aqueous solution was dropped at a constant rate over 185 minutes to initiate the polymerization reaction. Sodium hypophosphite monohydrate aqueous solution was dripped 40.1 parts (20% of the whole) at a constant speed over 18 minutes, and then the remaining 160.2 parts at a constant speed over another 162 minutes. It was dripped. That is, the dropping rate of the sodium hypophosphite monohydrate aqueous solution was changed in two steps so that the dropping rate in the latter half was smaller (approximately 0.4 times) than the dropping rate in the first half. The reaction temperature was maintained at the boiling point of the system (100 ° C. to 105 ° C.) during the dropwise addition of each aqueous solution.

  After completion of the dropping operation, that is, after completion of dropping of the sodium peroxodisulfate aqueous solution, the mixture was further agitated at the same temperature for 5 minutes for aging to complete the polymerization reaction. Thereby, a water-soluble polymer was obtained. Various measurement results are shown in Table 1.

  Next, the obtained water-soluble polymer was neutralized with a 48% aqueous sodium hydroxide solution so as to have a pH of 9.0 to obtain a neutralized product. And the superiority or inferiority of the inorganic pigment dispersibility (dispersion performance) of the neutralized product was determined based on the following measurement method. That is, 0.6 g of the above neutralized product, 128.0 g of ion-exchanged water, and 300 g of calcium carbonate (Super # 2000; manufactured by Maruo Calcium Co., Ltd.), which is an inorganic pigment, are placed in a 450 ml mayonnaise bottle. The mixture was stirred and liquefied. Next, after putting 150 g of glass beads having a diameter of 3.5 mm into the mayonnaise bottle, the calcium carbonate was sufficiently dispersed in ion-exchanged water by shaking for 30 minutes using a paint shaker. Thereby, a 70% calcium carbonate aqueous dispersion, that is, a slurry was obtained.

  The viscosity (cP) immediately after production of this slurry and the viscosity (cP) after storage at 50 ° C. for 30 days were measured using a B-type viscometer. The better the dispersion performance of the neutralized product, the smaller the viscosity immediately after production and the smaller the difference between the viscosity immediately after production and the viscosity after 30 days. Therefore, by measuring these viscosities, it is possible to determine the superiority or inferiority of the inorganic pigment dispersibility of the neutralized product. The results are also shown in Table 1.

[Example 2]
The same method as in Example 1 except that the amount of ion-exchanged water charged to the reactor was reduced to 625.4 parts and the monomer component concentration was adjusted to a higher concentration reaction solution. The polymerization reaction was performed by the method. Various measurement results are shown in Table 1.

Example 3
Instead of dropping the 80% acrylic acid aqueous solution, the polymerization reaction was carried out in the same manner as in Example 1, except that 2126.1 parts of the 80% acrylic acid / methacrylic acid aqueous solution was dropped. The molar ratio (acrylic acid / methacrylic acid) between acrylic acid and methacrylic acid in the aqueous solution was 8/2. Various measurement results are shown in Table 1.

Example 4
A polymerization reaction was carried out in the same manner as in Example 1 except that the dropping method of the 45% sodium hypophosphite monohydrate aqueous solution was changed to the following method. That is, after 45% sodium hypophosphite monohydrate aqueous solution was added dropwise over 8 minutes at a constant speed over 90 minutes, the remaining 120.2 parts over 90 minutes. Was dropped at a constant speed to obtain a water-soluble polymer. That is, the dropping rate of the sodium hypophosphite monohydrate aqueous solution was changed in two steps so that the dropping rate in the latter half was larger (approximately 1.5 times) than the dropping rate in the first half. Various measurement results are shown in Table 1.

[Reference Example 3]
The polymerization reaction was carried out in the same manner as in Reference Example 1 except that the dropping method of the 15% sodium peroxodisulfate aqueous solution was changed to the following method. That is, a 15% aqueous solution of sodium peroxodisulfate was added dropwise at a dropping rate of 0.41 part / minute (constant speed) over 50 minutes after 10 minutes from the start of dropping of the acrylic acid aqueous solution. Thereafter, the drop rate is gradually increased by 0.102 parts / minute in increments of 1 minute (every minute), and after changing the drop speed, 20 minutes have elapsed to become 2.44 parts / minute. Adjusted. Thereafter, the remaining aqueous solution was added dropwise at a dropping speed of 2.44 parts / minute (constant speed) over 50 minutes to obtain a water-soluble polymer. That is, in the sodium peroxodisulfate aqueous solution, the dropping rate was changed to 21 steps so that the dropping rate increased stepwise. Various measurement results are shown in Table 1.

Example 5
A polymerization reaction was carried out in the same manner as in Example 1 except that the dropping method of the 45% sodium hypophosphite monohydrate aqueous solution was changed to the following method. That is, 40.1 parts of 45% sodium hypophosphite monohydrate aqueous solution was dropped at a dropping speed of 2.23 parts / minute (constant speed) over 18 minutes. Thereafter, 130.2 parts were added dropwise at a dropping speed of 0.89 parts / minute (constant speed) over 147 minutes. Thereafter, the remaining 30.0 parts were added dropwise at a dropping speed of 2.00 parts / minute (constant speed) over 15 minutes. Thereby, a water-soluble polymer was obtained. That is, the dropping rate of the sodium hypophosphite monohydrate aqueous solution was changed in three stages so that the dropping rate was reduced midway. Various measurement results are shown in Table 1.

[Comparative Example 1]
A 15% sodium peroxodisulfate aqueous solution was subjected to a polymerization reaction in the same manner as in Reference Example 1 except that it was dropped at a constant rate over 120 minutes after 10 minutes from the start of dropping of the acrylic acid aqueous solution, A comparative water-soluble polymer was obtained. Various measurement results are shown in Table 1.

[Comparative Example 2]
A water-soluble polymer for comparison was obtained by performing a polymerization reaction in the same manner as in Example 1 except that 45% sodium hypophosphite monohydrate aqueous solution was added dropwise at a constant rate over 180 minutes. It was. Various measurement results are shown in Table 1.

  Subsequently, the obtained comparative water-soluble polymer was neutralized with a 48% aqueous sodium hydroxide solution so that the pH became 9.0, thereby obtaining a neutralized product. And the superiority or inferiority of the inorganic pigment dispersibility of the neutralized product was determined by the same method as the method of Example 1. That is, the viscosity immediately after production of the slurry and the viscosity after storage at 50 ° C. for 30 days were measured using a B-type viscometer. The results are also shown in Table 1.

[Comparative Example 3]
The polymerization reaction was carried out in the same manner as in Example 1 except that the addition method of the 45% sodium hypophosphite monohydrate aqueous solution was changed to the following method. That is, out of 200.3 parts of 45% sodium hypophosphite monohydrate aqueous solution, 100.2 parts were charged into the reactor before the start of polymerization (initial charge), and the remaining 100.1 parts were charged for 180 minutes. It was dripped at constant speed. As a result, a comparative water-soluble polymer was obtained. Various measurement results are shown in Table 1.

  As is apparent from the results in Table 1, by adopting the production method according to the present invention, the amount of residual monomer can be reduced; the monomer concentration in the reaction solution can be made higher. It was found that the molecular weight distribution of the obtained polymer can be narrowed. Furthermore, from comparison between Example 1 and Comparative Example 2, it was found that a polymer excellent in dispersion performance can be obtained by employing the production method according to the present invention.

Claims (5)

A method for producing a water-soluble polymer in which a chain transfer agent is continuously added for a predetermined period during the polymerization period, wherein the monomer component is at least as long as the chain transfer agent is continuously added to the reaction solution. A method for producing a water-soluble polymer , which is continuously added to a reaction solution for a partially overlapping period, and the addition rate of the same chain transfer agent is changed at least once within the overlapping period . 2. The method for producing a water-soluble polymer according to claim 1, wherein the addition rate is changed to be small . 3. The water-soluble polymer according to claim 2 , wherein the rate of addition is changed by a method of decreasing it once in steps, a method of decreasing it a plurality of times in steps, or a method of decreasing it continuously . Production method.   The method for producing a water-soluble polymer according to any one of claims 1 to 3, wherein the monomer component used contains an unsaturated carboxylic acid (salt) monomer.   The method for producing a water-soluble polymer according to claim 4, wherein the content of the unsaturated carboxylic acid (salt) monomer in the monomer component is 50% by weight or more.