JP2004137400A - Method for manufacturing (meth)acrylic acid (salt) polymer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a (meth)acrylic acid (salt) polymer having good hue with excellent productivity. <P>SOLUTION: The (meth)acrylic acid (salt) polymer with a degree of neutralization of 50 mol% or lower is produced by controlling the U value defined by formula (1) to 10 to 30 and adding an initiator containing a persulfate to an aqueous solution containing (meth)acrylic acid (salt) monomer. <P>COPYRIGHT: (C)2004,JPO

Description

【０００９】
（２）重合時の最終固形分濃度が２０質量％以下の（メタ）アクリル酸（塩）系重合体溶液を８０℃以下で減圧濃縮し、濃縮後の固形分濃度が２５質量％以上であることを特徴とする上記（１）記載の（メタ）アクリル酸（塩）系重合体の製造方法。
【００１０】
上記Ｕ値における「重合時の最終固形分濃度」（質量％）は、（メタ）アクリル酸（塩）系単量体を重合させ、必要に応じて熟成させた後の、該反応液中のモノマー、ポリマー、開始剤等からなる固形分成分の濃度を言う。重合時の最終固形分濃度（質量％）は、投入される全量中の固形分量の割合を計算することにより算出することができ、具体的には、初期仕込みの水量及び重合時に添加される水量と、重合開始時の各種固形分材料の濃度、すなわち開始剤濃度、モノマー濃度等、を種々設定することにより、適宜設定することができる。
【００１１】
「添加する過硫酸塩の、モノマー１モル当たりの重量」（ｇ）は、重合反応において、反応液中に添加される全ての過硫酸塩の、モノマー１モル当たりの重量（ｇ）を言い、ここにおける「モノマー」とは、（メタ）アクリル酸（塩）系単量体のみならず、それ以外に添加される任意の単量体をも含むものである。
【００１２】
本発明における上記Ｕ値は１０〜３０、好ましくは１２〜２８である。Ｕ値がが３０を越えると、色が悪くなり好ましくない。Ｕ値が低いほど、色がきれいになり好ましい。一方で、Ｕ値が１０未満であると、生産性が悪くなり、好ましくない。
【００１３】
本発明においては、「（重合体固形分中に含まれる硫黄原子（Ｓ）の重量比）×（得られる重合体の重量平均分子量；Ｍｗ）」で定義されるＳ値が、５０〜２００の範囲であることが好ましい。Ｓ値がこの範囲において、良好な色相が得られるとともに、目標の分子量が得られ、好ましい。
【００１４】
また、本発明において、「｛^１Ｈ−ＮＭＲスペクトルにおける（３．３〜４．３ｐｐｍのシグナルの総積分比）／（０．３〜４．３ｐｐｍのシグナルの総積分比）｝×（得られる重合体の重量平均分子量；Ｍｗ）」で定義されるＴ値が、６０〜１００の範囲であることが好ましい。Ｔ値がこの範囲において、安定性が良好となり、好ましい。
【００１５】
更に、本発明において、重合時の最終固形分濃度は、５〜２０質量％の低濃度であることが好ましく、８〜１８質量％であることがより好ましく、１０〜１７質量％であることが更に好ましい。かかる低濃度で重合を行った後、さらに減圧濃縮を好ましくは８０℃以下、より好ましくは７５℃以下で行い、減圧濃縮後の固形分濃度を２５％以上、より好ましくは２８％以上の高濃度とすることが好ましい。これにより、色相が良く、しかも生産性良く、高濃度、低分子量の酸型の（メタ）アクリル酸（塩）系重合体を製造することができる。
なお、本発明の方法は、用いる装置の材質が、ＳＵＳ３０４又は３１６である時に、特に適している。
【００１６】
【発明の実施の形態】
以下、本発明を更に具体的に詳述する。
本発明の方法により得られる（メタ）アクリル酸（塩）系重合体は、重量平均分子量（Ｍｗ）が１，０００〜５０，０００、好ましくは２，０００〜４０，０００、より好ましくは３，０００〜３０，０００である。なお、本明細書における重量平均分子量、数平均分子量は、実施例の分子量測定の項で記載した方法によって測定した数値である。
【００１７】
本発明に従い得られる（メタ）アクリル酸（塩）系重合体は、炭素数３〜６のモノカルボン酸モノエチレン性不飽和単量体（ａ）由来の構造単位（Ｉ）を主とする重合体のことをいう。具体的には、炭素数３〜６のモノカルボン酸モノエチレン性不飽和単量体（ａ）由来の構造単位（Ｉ）１００〜７０モル％及びその他共重合可能な単量体（ｂ）由来の構造単位（ＩＩ）０〜３０モル％（但し、（Ｉ）と（ＩＩ）の合計量は１００モル％である）からなる重合体が挙げられ、好ましくは、炭素数３〜６のモノカルボン酸モノエチレン性不飽和単量体（ａ）由来の構造単位（Ｉ）１００〜８０モル％及びその他共重合可能な単量体（ｂ）由来の構造単位（ＩＩ）０〜２０モル％からなる。より好ましくは炭素数３〜６のモノカルボン酸モノエチレン性不飽和単量体（ａ）由来の構造単位（Ｉ）１００〜９０モル％及びその他共重合可能な単量体（ｂ）由来の構造単位（ＩＩ）０〜１０モル％からなる重合体である。さらに好ましくは、炭素数３〜６のモノカルボン酸モノエチレン性不飽和単量体（ａ）由来の構造単位（Ｉ）１００〜９５モル％及びその他共重合可能な単量体（ｂ）由来の構造単位（ＩＩ）０〜５モル％からなる（但し、（Ｉ）と（ＩＩ）の合計量は１００モル％である）重合体である。最も好ましくは炭素数３〜６のモノカルボン酸モノエチレン性不飽和単量体（ａ）由来の構造単位（Ｉ）１００モル％からなる重合体である。上記炭素数３〜６のモノカルボン酸モノエチレン性不飽和単量体（ａ）由来の構造単位（Ｉ）は、アクリル酸（塩）、メタクリル酸（塩）、クロトン酸（塩）由来の構造単位であり、好ましくはアクリル酸（塩）、メタクリル酸（塩）由来の構成単位であり、より好ましくはアクリル酸（塩）由来の構成単位である。これら単量体は１種または２種以上含んでもよい。
【００１８】
本明細書において「（メタ）アクリル酸（塩）」とは、（メタ）アクリル酸及び／または（メタ）アクリル酸塩である。（メタ）アクリル酸塩としては特に限定はされないが、（メタ）アクリル酸ナトリウム、（メタ）アクリル酸カリウム等の（メタ）アクリル酸アルカリ金属塩；（メタ）アクリル酸アンモニウム；（メタ）アクリル酸有機アミン塩等を１種または２種以上含んでいてもよい。
【００１９】
その他共重合可能な単量体（ｂ）由来の構造単位（ＩＩ）は、特に限定されるものではなく、必要に応じて併用してもよい。例えば、マレイン酸、フマル酸、イタコン酸、シトラコン酸、アコニット酸等の不飽和ジカルボン酸系単量体及び不飽和多価カルボン酸系不飽和単量体；（メタ）アクリルアミド、ｔ−ブチル（メタ）アクリルアミド等のアミド系単量体；（メタ）アクリル酸エステル、スチレン、２−メチルスチレン、酢酸ビニル等の疎水性単量体；ビニルスルホン酸、アリルスルホン酸、メタリルスルホン酸、スチレンスルホン酸、２−アクリルアミド−２−メチルプロパンスルホン酸、３−アリロキシ−２−ヒドロキシ−プロパンスルホン酸、スルホエチル（メタ）アクリレート、スルホプロピル（メタ）アクリレート、２−ヒドロキシスルホプロピル（メタ）アクリレート、スルホエチルマレイミド等の不飽和スルホン酸単量体；上記不飽和ジカルボン酸系単量体、上記不飽和多価カルボン酸系単量体または上記不飽和スルホン酸系単量体を、１価金属、２価金属、アンモニア、有機アミン等で部分中和または完全中和してなる中和物；２−ヒドキシエチル（メタ）アクリレート、２−ヒドロキシプロピル（メタ）アクリレート、α−ヒドロキシアクリル酸、ビニルアルコール、アリルアルコール、イソプレノール等の水酸基含有不飽和単量単量体及びこれらのアルキレンオキシド付加体；ジメチルアミノエチル（メタ）アクリレート等のカチオン性単量体、（メタ）アクリロニトリル等のニトリル系単量体、（メタ）アクリルアミドメタンホスホン酸等の含リン単量体、メチルビニルエーテル、エチルビニルエーテル等のアルキルビニルエーテル類、ビニルピロリドン等を挙げることができる。これらの単量体は、１種のみを用いてもよいし、２種以上を併用してもよい。
【００２０】
本発明の（メタ）アクリル酸（塩）系重合体の中和度は、重合体の全酸基の中和度が５０モル％以下、好ましくは３０モル％以下、より好ましくは１０モル％以下、さらに好ましくは５モル％以下、最も好ましくは１モル％以下である。この重合体の中和度が５０モル％を超えると添加剤の種類によっては、配合性や後反応による変性の制限等の問題がある。
【００２１】
上記（メタ）アクリル酸（塩）系重合体の製造方法としては、反応器内の単量体濃度と重合開始剤濃度とを所定範囲に調整しながら重合させることで製造することができる。例えば、（メタ）アクリル酸（塩）系単量体含有水溶液に重合開始剤を添加して重合する（メタ）アクリル酸（塩）系重合体の製法であって、反応器に該（メタ）アクリル酸（塩）系単量体含有水溶液の全量と該重合開始剤とを徐々に添加して重合を開始させる段階（Ａ）と、次いでこれに更に重合開始剤を添加しつつ重合を継続させる段階（Ｂ）と、該重合開始剤の全量添加後に該反応液を熟成させる段階（Ｃ）を経て、（メタ）アクリル酸（塩）系重合体を製造することが好ましい。この方法によれば、重合開始剤および単量体の残存量の少ない（メタ）アクリル酸（塩）系重合体を製造することができ、得られた重合体の保存安定性に優れる。
【００２２】
（メタ）アクリル酸（塩）系単量体含有水溶液を構成する溶媒は、水系溶媒が用いられ、特に好ましくは水単独で用いられるが、必要に応じて親水性有機溶媒を水に適宜添加してもよい。上記親水性有機溶媒としては、特に限定されないが、例えば、メタノール、エタノール、２−プロパノール等の低級アルコール；ジメチルホルムアミド等のアミド類；アセトン等のケトン類；１，４−ジオキサン等のエーテル類等が挙げられ、これらの中から１種または２種以上適宜選んで使用できる。親水性有機溶媒の添加割合は、水との混合溶媒全量に対し、好ましくは２０質量％以下、さらに好ましくは１０質量％以下、より好ましくは５質量％以下、最も好ましくは１質量％以下である。この割合が２０質量％を超えると、該重合体が分離及び／または沈殿するおそれがあり、好ましくない。
【００２３】
本発明の製造方法は、上記（メタ）アクリル酸（塩）を主成分とする単量体成分を水系溶媒にて重合し、（メタ）アクリル酸（塩）系重合体を得るものである。この際、段階（Ａ）として反応器に該（メタ）アクリル酸（塩）系単量体含有水溶液の全量と該重合開始剤の一部とを徐々に添加して重合を開始させることが好ましい。
（メタ）アクリル酸（塩）系単量体の添加方法は、単量体成分炭素数３〜６のモノカルボン酸モノエチレン性不飽和単量体（ａ）及びその他共重合可能な単量体（ｂ）の使用量の一部を反応器に初期に仕込み次いで残部を連続的に滴下するか、全量を連続的に滴下する。本発明では、全使用量の５０質量％以上、好ましくは７０質量％以上、より好ましくは９０質量％以上、さらに好ましくは９５質量％以上、最も好ましくは全量を、実質的に連続的に滴下することにより反応系に添加する。滴下の割合が５０質量％未満であると、重合初期に重合が急激に進行してしまい、温度及び分子量の制御が困難になり、好ましくない。
【００２４】
この方法では、反応器への（メタ）アクリル酸（塩）系単量体含有水溶液の全量の仕込み終了時までに重合開始剤を徐々に添加することが好ましい。この反応器への単量体の仕込みは、好ましくは６０分〜３００分、より好ましくは９０分〜２７０分、更に好ましくは１２０分〜２４０分、特に好ましくは１５０分〜２１０分で行なう。このように反応器への単量体の仕込みと重合開始剤の仕込みとを連続的に行なうことで、反応器内の重合体濃度と重合開始剤濃度とをほぼ一定に保つことができるため、得られる重合体の分子量が製造後も安定する。
【００２５】
本発明では、重合開始剤として過硫酸塩を少なくとも１種用いる。ここで、過硫酸塩としては、過硫酸ナトリウム、過硫酸アンモニウム、過硫酸カリウム等を挙げることができる。
本発明では、更に重合開始剤として、それ以外の重合開始剤を併用してもよい。併用できる重合開始剤は特に限定されるものではないが、過酸化物などを挙げることができ、例えば、過酸化水素；２，２’−アゾビス（２−アミノジプロパン）２塩酸塩、４，４’−アゾビス（４−シアノバレリン酸）、アゾビスイソブチルニトリル、２，２’−アゾビス（４−メトキシ−２，４−ジメチルバレロニトリル）等のアゾ系化合物；過酸化ベンゾイル、過酸化ラウロイル、過酢酸、過コハク酸、ジ−ｔ−ブチルパーオサイド、ｔ−ブチルヒドロパーオサイド、クメンヒドロパーオキサイド等の有機過酸化物等が挙げられる。これらは、の１種類のみであっても２種類以上含んでいてもよい。中でも、過酸化水素、有機過酸化物、２，２’−アゾビス（２−アミノジプロパン）２塩酸塩が好ましく、過酸化水素、２，２’−アゾビス（２−アミノジプロパン）２塩酸塩がより好ましく、２，２’−アゾビス（２−アミノジプロパン）２塩酸塩がさらに好ましい。
【００２６】
上記重合開始剤の添加量は、目的の分子量によって適宜設定すればよい。なお、滴下時の重合開始剤の濃度は、特に限定されないが、過硫酸塩が開始剤である場合には、好ましくは３〜５０質量％水溶液、より好ましくは５〜４０質量％水溶液、さらに好ましくは１０〜３０質量％水溶液である。アゾ系化合物を開始剤として併用する場合には、好ましくは０．１〜５質量％水溶液、より好ましくは０．３〜３質量％水溶液、さらに好ましくは０．５〜２質量％水溶液である。
【００２７】
また、重合開始剤として過酸化物と還元剤や金属塩等を組み合わせてもよい。還元剤や金属塩等は、特に限定されるものではないが、亜硫酸水素ナトリウムやＦｅ^２＋、Ｆｅ^３＋、Ｃｕ^＋、Ｃｕ^２＋、Ｖ^２＋、Ｖ^３＋、ＶＯ^２＋等が挙げられ、亜硫酸水素ナトリウム、Ｆｅ^２＋、Ｆｅ^３＋、Ｃｕ^＋、Ｃｕ^２＋が好ましく、Ｆｅ^２＋、Ｆｅ^３＋、Ｃｕ^＋、Ｃｕ^２＋がより好ましい。Ｆｅ^２＋、Ｆｅ^３＋、Ｃｕ^＋、Ｃｕ^２＋を併用することにより、分散度（重量平均分子量／数平均分子量）が狭くなり、好ましい。重合開始剤と還元剤や金属塩を組み合わせる時の還元剤や金属塩の添加量は特に限定されないが、金属塩の場合には重合終了時の（メタ）アクリル酸（塩）系重合体に対して０．１質量ｐｐｍ〜１，０００質量ｐｐｍが好ましく、０．５質量ｐｐｍ〜５００質量ｐｐｍがより好ましく、１質量ｐｐｍ〜３００質量ｐｐｍがさらに好ましい。金属塩の添加量が０．１質量ｐｐｍ未満であると分散度を狭くする効果がなく、１，０００質量ｐｐｍを超えるともはや添加の効果が無く、経済的面から好ましくない。
【００２８】
次いで、段階（Ｂ）として、該反応器に更に重合開始剤を添加しつつ重合を継続させることが好ましい。この際、添加する重合開始剤は、段階（Ａ）で使用できるものを添加することができる。段階（Ａ）と同じものであっても異なってもよい。また、重合開始剤量は、単量体水溶液に対して、好ましくは１００〜１０，０００質量ｐｐｍ、より好ましくは２００〜８，０００質量ｐｐｍ、更に好ましくは３００〜５，０００質量ｐｐｍ、特に好ましくは５００〜３，０００質量ｐｐｍとする。また、重合開始剤の添加時間は、段階（Ａ）の後、好ましくは１分以上３時間以下、より好ましくは５分以上３時間以下、更に好ましくは１０分以上２時間以下、特には１５分以上１時間半以下である。（メタ）アクリル酸（塩）単量体滴下終了後１分未満に重合開始剤の滴下を終了すると、（メタ）アクリル酸（塩）単量体が大量に残存し、重合体の重量平均分子量が変動しやすく、該重合体水溶液の粘度が上がる等の安定性が悪くなる。一方、重合開始剤の滴下を３時間を超えて行うと、該重合体の分散度（重量平均分子量／数平均分子量）が大きくなり、さらに生産性も低くなり経済的面から好ましくない。このように、単量体滴下終了後に更に重合開始剤を添加することで、残存する単量体成分を大幅に低減でき、得られる該重合体の安定性が高くなる。
【００２９】
本発明の（メタ）アクリル酸（塩）系重合体の製造方法では、必要に応じて、重合に悪影響を及ぼさない範囲内で、分子量調整剤として、重合開始剤と併用して連鎖移動剤を用いてもよい。連鎖移動剤としては、例えば、亜硫酸塩、亜硫酸水素塩、ジ亜リン酸、ジ亜リン酸塩、メルカプトプロピオン酸、チオグリコール酸等が挙げられるが特に限定されず、これらを単独で用いてもよく、２種以上の併用系でもよい。使用量としては、特に限定はないが、質量比で開始剤量の３倍以内であることが好ましい。３倍を超えて使用しても、もはや添加効果は現れず、該重合体の純分の低下を招き、好ましくない。また、連鎖移動剤の添加方法は適宜設定すればよい。
【００３０】
本発明の方法では、次いで段階（Ｃ）として、反応器への該重合開始剤の添加後に該反応液を熟成させることが好ましい。このように段階（Ｂ）の後に熟成時間を設けることで、重合開始剤の残存量を低減することができ、得られる重合体の重量平均分子量の変動を抑制することができる。「熟成」とは、段階（Ｂ）の後に、反応器に単量体と重合開始剤とを添加することなく、反応器内の単量体の重合反応を促進する工程をいう。この段階（Ｃ）で特定する熟成時間は、３０分以上５時間、好ましくは４０分〜３時間、特に好ましくは６０分〜２時間で十分である。なお、段階（Ｂ）と段階（Ｃ）との合計は５０分以上、好ましくは５５分〜５時間、特には６０分〜３時間である。
【００３１】
本発明の（メタ）アクリル酸（塩）系重合体の製造方法における中和度は５０モル％以下、好ましくは３０モル％以下、より好ましくは１０モル％以下、さらに好ましくは５モル％以下、最も好ましくは１モル％以下である。該単量体の中和剤としては、水酸化ナトリウム、水酸化カリウム等のアルカリ金属の水酸化物；水酸化カルシウム、水酸化マグネシウム等のアルカリ土類水酸化物；アンモニア；モノエタノールアミン、トリエタノールアミン等の有機アミンが挙げられる。これらは単独で用いてもよいし、２種以上の混合物として用いてもよい。
【００３２】
中和は単量体を反応器に供給する前に予め行われてもよいし、段階（Ａ）、（Ｂ）、（Ｃ）のいずれでも、更に熟成後、すなわち段階（Ｃ）の後であってもよい。重合開始から、重合終了時までの中和度は上記範囲内であれば、一定である必要は無く、重合前半の中和度と重合後半の中和度が異なってもよい。
【００３３】
本発明の（メタ）アクリル酸（塩）系重合体の製造方法における重合温度は、特に限定されるものではなく、分子量、重合濃度等によって適宜設定すればよ
い。好ましくは５０℃〜１５０℃、更に好ましくは８０℃〜１２０℃、特に好ましくは常圧下沸点である。
【００３４】
本発明の（メタ）アクリル酸（塩）系重合体の製造方法における重合時の最終固形分濃度は、好ましくは２０質量％以下、より好ましくは１８質量％以下であり、これに見合うように滴下物の濃度調整を行うことが好ましい。
【００３５】
本発明の（メタ）アクリル酸（塩）系重合体の製造方法における重合圧力は、特に限定されず、加圧、常圧（大気圧）、減圧いずれかでのよく、場合により適宜設定すればよいが、常圧が好ましい。
【００３６】
本発明では、段階（Ｃ）の後に、例えば反応器の温度が、７０℃以下、好ましくは５０℃以下、より好ましくは４０℃以下になったら、反応器に過酸化物分解促進剤を添加して、残存する重合開始剤を分解してもよい。７０℃を越えると過酸化物分解促進剤が消失してしまい、残存している重合開始剤を消失させることができない恐れがある。また、添加時間は、１分から２時間、好ましくは５〜９０分、より好ましくは１０〜６０分である。
【００３７】
このような促進剤としては還元剤が一般的に挙げられるが特に限定されるものではない。還元剤として、例えば、亜硫酸ナトリウム、亜硫酸水素ナトリウム等の亜硫酸塩類；チオ硫酸ナトリウム等のチオ硫酸塩；Ｌ−アスコルビン酸、Ｌ−アスコルビン酸ナトリウム等のＬ−アスコルビン酸類；亜硝酸ナトリウム等の亜硝酸塩；ホスホン酸ナトリウム、ホスホン酸カリウム等の酸塩類；ホスフィン酸ナトリウム、ホスフィン酸カリウム等のホスフィン酸類；鉄塩、銅塩等の重金属塩類が挙げられる。好ましくは亜硫酸水素ナトリウム、Ｌ−アスコルビン酸ナトリウムが挙げられ、さらに好ましくは亜硫酸水素ナトリウムが挙げられる。これらの１種類のみであっても２種類以上含んでいてもよい。
【００３８】
反応器に添加する過酸化物分解促進剤の量は、特に限定されないが、該水溶液に対して５，０００質量ｐｐｍ以下、好ましくは３，０００質量ｐｐｍ以下、より好ましくは２，０００質量ｐｐｍ以下、さらに好ましくは１，０００質量ｐｐｍ以下、最も好ましくは７００質量ｐｐｍ以下である。この過酸化物分解促進剤の量が５，０００質量ｐｐｍを超えるともはや添加量に見合う効果は得られず、不純物が増加する結果となり、使用する用途によっては、充分な性能が発揮されないといった問題を生じる。使用する促進剤は、固体でもよいが、水溶液に溶解してしようすることが簡便である。
【００３９】
本発明の製造方法によれば、得られた（メタ）アクリル酸（塩）系重合体に残存する重合開始剤の量は、該重合体調製後の水溶液に対して１０質量ｐｐｍ以下とすることができる。残存する重合開始剤の量は、好ましくは７質量ｐｐｍ以下、より好ましくは５質量ｐｐｍ以下、さらに好ましくは３質量ｐｐｍ以下、最も好ましくは１質量ｐｐｍ以下である。
【００４０】
本発明の製造方法で得られる（メタ）アクリル酸（塩）系重合体に含まれる残存する（メタ）アクリル酸（塩）単量体の量は、該重合体に対して３，０００質量ｐｐｍ以下とすることができる。好ましくは２，０００質量ｐｐｍ以下、より好ましくは１，０００質量ｐｐｍ以下、さらに好ましくは５００質量ｐｐｍ以下、最も好ましくは２００質量ｐｐｍ以下である。（メタ）アクリル酸（塩）単量体の量が３，０００質量ｐｐｍ以下とすることにより、保存時に分子量が上がったり、低分子量が増えたりする等、該重合体の安定性を悪化させることがなく、好ましい。
【００４１】
また、本発明に用られる反応器としては（メタ）アクリル酸（塩）系重合体製造用に通常用いられる反応器（例えば、ＳＵＳ３０４，３１６等）を使用することができる。
【００４２】
本発明の製造方法では、段階（Ａ）に次いで、上記段階（Ｃ）、または段階（Ｂ）および段階（Ｃ）を行なうことで、（メタ）アクリル酸（塩）系重合体を製造することができる。
【００４３】
反応器に該（メタ）アクリル酸（塩）系単量体含有水溶液の全量と該重合開始剤とを徐々に添加して重合を開始させる段階（Ａ）と、次いでこれに更に重合開始剤を添加しつつ重合を継続させる段階（Ｂ）と、該重合開始剤の全量添加後に該反応液を熟成させる段階（Ｃ）とを含むことで、残存単量体および残存重合開始剤量の少ない（メタ）アクリル酸（塩）系重合体を得ることができる。このため、該重合体に含まれる単量体の重合による分子量上昇を押さえ、低分子量物が増加するのを押さえる効果が絶大となり、該重合体の分子量分布が狭く均一な分子量の重合体を得ることができる。
【００４４】
上記のようにして得られた（メタ）アクリル酸（塩）系重合体溶液は、その最終固形分濃度が２０質量％以下の低濃度であることが好ましく、該低濃度の（メタ）アクリル酸（塩）系重合体溶液を、８０℃以下で減圧濃縮し、濃縮後の固形分濃度が２５質量％以上となるように高濃度化することが好ましい。これにより、色相が良く、しかも生産性良く、高濃度、低分子量の酸型の（メタ）アクリル酸（塩）系重合体を製造することができる。
上記減圧濃縮の方法としては、特に限定的ではなく、具体的には、重合体水溶液をそのまま減圧、加熱し、濃縮してもよいし、薄膜濃縮機等で連続的に濃縮してもよい。
【００４５】
本発明の（メタ）アクリル酸系重合体組成物の用途としては、水系の分散剤（顔料分散剤を含む）、スケール防止剤（スケール抑制剤）、洗剤ビルダー及びこれを用いた洗浄剤組成物などが挙げられるが、これらの制限されるべきものではなく、例えば、金属イオン封止剤、増粘剤、各種バインダーなどの用途などにも幅広く適用できるものである。
【００４６】
【実施例】
以下、本発明の実施例により具体的に説明する。
【００４７】
≪固形分濃度測定法≫
０．１ｍｇまで精秤したアルミ製カップにサンプルを約１ｇ採り、精秤した。上記アルミ製カップを１２０℃に設定した乾燥機に入れ、２時間乾燥させた。乾燥後、このアルミ製カップをデシケータに移し、１５分間室温放冷した後に精秤した。乾燥後のサンプルの重量を乾燥前のサンプルの重量で割った数値に１００を乗じた値を固形分濃度とした。
【００４８】
≪分子量測定≫
アクリル酸（塩）系重合体の重量平均分子量（Ｍｗ）および数平均分子量（Ｍｎ）は、ともにＧＰＣ（ゲルパーミュエーションクロマトグラフィー）により測定した。なお、測定条件、装置などは以下の通りである。
【００４９】
ＧＰＣのカラムとしては、昭和電工製のＧＦ−７ＭＨＱ（商品名）を用いた。
移動相としては、リン酸水素二ナトリウム１２水和物３４．５ｇおよびリン酸二水素ナトリウム２水和物４６．２ｇ（いずれも試薬特級）の純水を加えて全量を５０００ｇとし、その後０．４５μｍのメンブランフィルターでろ過した水溶液を用いた。
検出器としては、ウォーターズ製のモデル４８１型を用い、検出波長ＵＶ２１４ｎｍとした。
ポンプとしては、株式会社日立製作所製のＬ−７１１０（商品名）を用いた。
移動相の流量は、０．５ｍｌ／分とし、温度は３５℃とした。検量線は、創和科学製のポリアクリル酸ナトリウム標準サンプルを用いて作成した。
【００５０】
実施例１
還流冷却管及び攪拌機を備えた容量５ＬのＳＵＳ３１６製セパラブルフラスコにイオン交換水１６００ｇを仕込み、攪拌下１００℃に昇温した後、８０％アクリル酸水溶液（以下８０％ＡＡと称す）３６０ｇ（４モル）及び１５％過硫酸アンモニウム水溶液（以下１５％ＡＰＳと称す）２１３．３ｇ（８ｇ／アクリル酸１モル）をそれぞれ別の滴下口より滴下した。それぞれの滴下時間は、８０％ＡＡが１８０分間、１５％ＡＰＳが１８５分間とした。なお、滴下開始はすべて同時とした。この間、温度は系の沸点を維持した。さらに同温度を８０％ＡＡ滴下終了後３０分間にわたって維持して熟成を行い、重合を完結した。重合の完結後、反応溶液を放冷した。続いてこの反応容器に真空ポンプを接続して、２００ｍｍＨｇまで減圧、約６５℃で濃縮を行った。約９０分かけて所定量の水分を除去して固形分濃度４０％の重合体水溶液（１）を得た。
【００５１】
実施例２〜５
表１に示す重合処方とした以外は実施例１と同様にして、各重合反応を行った。各種測定結果を表２に示した。
【００５２】
比較例１
還流冷却器及び攪拌機を備えた容量２．５ＬのＳＵＳ製セパラブルフラスコに、イオン交換水１０００ｇを仕込み、攪拌下１００℃まで昇温した後、８０％ＡＡを３６０ｇ（４モル）及び１５％ＡＰＳを５３３．３ｇ（２０ｇ／アクリル酸１モル）をそれぞれ別の滴下口より滴下した。それぞれの滴下温度は、８０％ＡＡが１８０分間、１５％ＡＰＳが１８５分間とした。なお、滴下開始はすべて同時とした。この間、温度は系の沸点を維持した。更に同温度を８０％ＡＡ滴下終了後３０分間にわたって維持して熟成を行い、重合を完結した。重合の完結後、反応溶液を放冷した。続いてこの反応容器に真空ポンプを接続して２００ｍｍＨｇまで減圧、約６５℃で濃縮を行った。約９０分かけて所定量の水分を除去して固形分濃度４０％の比較重合体水溶液（１）を得た。この比較重合体（１）の測定結果も表２に併記した。
【００５３】
【表１】

【００５４】
【表２】

【００５５】
表２の結果から、各条件を満たす重合体水溶液は、色調に優れることが判る。
【００５６】
【発明の効果】
本発明の（メタ）アクリル酸（塩）系重合体の製造方法によれば、得られる重合体の色相が良く、優れている。更に、固形分濃度２０質量％以下の低濃度重合で、更に減圧濃縮を８０℃以下で行い、固形分濃度２５質量％以上の高濃度とすることにより、生産性良く、高濃度、低分子量の酸型の（メタ）アクリル酸系重合体を製造することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a (meth) acrylic acid (salt) -based polymer having a good hue and high productivity.
[0002]
[Prior art]
Many methods have been proposed for producing a (meth) acrylic acid-based water-soluble polymer. Numerous methods for producing a (meth) acrylic acid-based water-soluble polymer in the presence of hypophosphorous acid (salt) have been proposed, and for example, Patent Documents 1 to 3 disclose production methods.
[0003]
[Patent Document 1]
U.S. Pat. No. 2,789,099
[Patent Document 2]
JP-A-50-15881
[Patent Document 3]
JP-A-55-127413
[0004]
[Problems to be solved by the invention]
However, when phosphorus is introduced, it causes a problem of eutrophication and contains many impurities. Further, when hypophosphorous acid is not used, a large amount of persulfate is required, so that impurities may be increased, various performances may be reduced, and a problem that a hue is deteriorated may occur. In particular, when an attempt is made to obtain an acid-type (meth) acrylic acid-based polymer having a high concentration and a low molecular weight, there has been a problem that the color deteriorates.
[0005]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a high-concentration, high-purity, low-molecular-weight acid-type (meth) acryl having extremely low colorability and high productivity. An object of the present invention is to provide a method for producing an acid-based polymer.
[0006]
[Means to solve the problem]
The inventors have conducted intensive studies to solve the conventional problems, and as a result, added a persulfate to an aqueous solution containing a (meth) acrylic acid (salt) -based monomer to polymerize (meth) acrylic acid (salt). It has been found that the hue is remarkably improved by controlling the acid concentration in the polymerization defined by the following U value to a specific value of 10 to 30 in the production of a system polymer. Further, it is preferable that the U value is in the range of 10 to 30 and the final solid content concentration at the time of polymerization is low-concentration polymerization of 20% by mass or less. It has been found that by setting the concentration to 25% or more, a high-concentration, low-molecular-weight acid-type (meth) acrylic acid-based polymer can be obtained with high productivity. That is, the above problem is solved by the following (1) and (2).
[0007]
(1) A method for producing a (meth) acrylic acid (salt) -based polymer in which an initiator containing a persulfate is added to an aqueous solution containing a (meth) acrylic acid (salt) -based monomer and polymerized, The method for producing a (meth) acrylic acid (salt) -based polymer having a degree of neutralization of 50 mol% or less, characterized in that the U value defined in (1) is 10 to 30.
[0008]
(Equation 2)

[0009]
(2) A (meth) acrylic acid (salt) -based polymer solution having a final solid content concentration of 20% by mass or less during polymerization is concentrated under reduced pressure at 80 ° C or less, and the solid concentration after concentration is 25% by mass or more. The method for producing a (meth) acrylic acid (salt) -based polymer according to the above (1), characterized in that:
[0010]
The “final solid content concentration at the time of polymerization” (% by mass) in the above U value is defined as the value of the (meth) acrylic acid (salt) -based monomer in the reaction solution after polymerization and aging if necessary. It refers to the concentration of a solid component composed of a monomer, a polymer, an initiator and the like. The final solid content concentration (% by mass) at the time of polymerization can be calculated by calculating the ratio of the amount of solid content to the total amount charged, and specifically, the amount of water initially charged and the amount of water added during polymerization. And the concentration of various solid materials at the start of the polymerization, that is, the initiator concentration, the monomer concentration, and the like, can be appropriately set.
[0011]
“Weight of persulfate to be added per mole of monomer” (g) means the weight (g) of all persulfate added to the reaction solution in the polymerization reaction per mole of monomer, The term "monomer" used herein includes not only (meth) acrylic acid (salt) -based monomers but also any other added monomers.
[0012]
The U value in the present invention is 10 to 30, preferably 12 to 28. If the U value exceeds 30, the color deteriorates, which is not preferable. The lower the U value, the better the color becomes. On the other hand, when the U value is less than 10, productivity is deteriorated, which is not preferable.
[0013]
In the present invention, the S value defined by “(weight ratio of sulfur atom (S) contained in polymer solid content) × (weight average molecular weight of obtained polymer; Mw)” is 50 to 200. Preferably, it is within the range. When the S value is in this range, a good hue is obtained and a target molecular weight is obtained, which is preferable.
[0014]
In the present invention, “｛ ¹ (Total integral ratio of signals of 3.3 to 4.3 ppm) / (Total integral ratio of signals of 0.3 to 4.3 ppm) in the H-NMR spectrum｝ × (weight average molecular weight of obtained polymer; Mw) Is preferably in the range of 60 to 100. When the T value is in this range, the stability becomes favorable, which is preferable.
[0015]
Furthermore, in the present invention, the final solid content concentration during the polymerization is preferably a low concentration of 5 to 20% by mass, more preferably 8 to 18% by mass, and more preferably 10 to 17% by mass. More preferred. After the polymerization at such a low concentration, concentration under reduced pressure is further carried out preferably at 80 ° C. or lower, more preferably at 75 ° C. or lower, and the solid concentration after vacuum concentration is 25% or more, more preferably 28% or more. It is preferable that This makes it possible to produce an acid (meth) acrylic acid (salt) polymer having a good hue and high productivity, and having a high concentration and a low molecular weight.
The method of the present invention is particularly suitable when the material of the device to be used is SUS304 or 316.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail.
The (meth) acrylic acid (salt) -based polymer obtained by the method of the present invention has a weight average molecular weight (Mw) of 1,000 to 50,000, preferably 2,000 to 40,000, more preferably 3, 000 to 30,000. In addition, the weight average molecular weight and the number average molecular weight in the present specification are numerical values measured by the method described in the section of molecular weight measurement in Examples.
[0017]
The (meth) acrylic acid (salt) -based polymer obtained according to the present invention is a polymer mainly composed of a structural unit (I) derived from a monoethylenically unsaturated monomer (a) having 3 to 6 carbon atoms. Refers to coalescence. Specifically, 100 to 70 mol% of a structural unit (I) derived from a monocarboxylic unsaturated monocarboxylic acid monomer having 3 to 6 carbon atoms (a) and another copolymerizable monomer (b) derived A polymer comprising the structural unit (II) of 0 to 30 mol% (the total amount of (I) and (II) is 100 mol%), and preferably a monocarboxylic acid having 3 to 6 carbon atoms. It is composed of 100 to 80 mol% of the structural unit (I) derived from the acid monoethylenically unsaturated monomer (a) and 0 to 20 mol% of the structural unit (II) derived from the other copolymerizable monomer (b). . More preferably, 100 to 90 mol% of a structural unit (I) derived from a monoethylenically unsaturated monomer (a) having 3 to 6 carbon atoms and a structure derived from another copolymerizable monomer (b). It is a polymer composed of 0 to 10 mol% of the unit (II). More preferably, 100 to 95 mol% of a structural unit (I) derived from a monoethylenically unsaturated monomer (a) having 3 to 6 carbon atoms and a monomer (b) derived from another copolymerizable monomer. It is a polymer composed of 0 to 5 mol% of the structural unit (II) (however, the total amount of (I) and (II) is 100 mol%). Most preferably, it is a polymer comprising 100 mol% of a structural unit (I) derived from a monocarboxylic unsaturated monocarboxylic acid monomer (a) having 3 to 6 carbon atoms. The structural unit (I) derived from the monocarboxylic unsaturated monocarboxylic acid monomer having 3 to 6 carbon atoms (a) is a structure derived from acrylic acid (salt), methacrylic acid (salt), and crotonic acid (salt). It is a unit, preferably a constituent unit derived from acrylic acid (salt) or methacrylic acid (salt), and more preferably a constituent unit derived from acrylic acid (salt). One or more of these monomers may be contained.
[0018]
In the present specification, “(meth) acrylic acid (salt)” is (meth) acrylic acid and / or (meth) acrylate. The (meth) acrylate is not particularly limited, but alkali metal (meth) acrylates such as sodium (meth) acrylate and potassium (meth) acrylate; ammonium (meth) acrylate; (meth) acrylic acid One or more organic amine salts may be contained.
[0019]
Other structural units (II) derived from the copolymerizable monomer (b) are not particularly limited, and may be used in combination as needed. For example, unsaturated dicarboxylic acid monomers such as maleic acid, fumaric acid, itaconic acid, citraconic acid, aconitic acid and unsaturated polycarboxylic acid unsaturated monomers; (meth) acrylamide, t-butyl (meth) ) Amide monomers such as acrylamide; hydrophobic monomers such as (meth) acrylate, styrene, 2-methylstyrene, and vinyl acetate; vinyl sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, and styrene sulfonic acid , 2-acrylamide-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxy-propanesulfonic acid, sulfoethyl (meth) acrylate, sulfopropyl (meth) acrylate, 2-hydroxysulfopropyl (meth) acrylate, sulfoethylmaleimide Unsaturated dicarboxylic acid such as unsaturated sulfonic acid monomer; Partial or complete neutralization of an acid monomer, the unsaturated polycarboxylic acid monomer or the unsaturated sulfonic acid monomer with a monovalent metal, a divalent metal, ammonia, an organic amine or the like. Neutralized products obtained from the above; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, α-hydroxyacrylic acid, vinyl alcohol, allyl alcohol, isoprenol, and other hydroxyl-containing unsaturated monomeric monomers; Alkylene oxide adducts; cationic monomers such as dimethylaminoethyl (meth) acrylate; nitrile monomers such as (meth) acrylonitrile; phosphorus-containing monomers such as (meth) acrylamide methanephosphonic acid; methyl vinyl ether And alkyl vinyl ethers such as ethyl vinyl ether, and vinylpyrrolidone. You. These monomers may be used alone or in combination of two or more.
[0020]
The degree of neutralization of the (meth) acrylic acid (salt) -based polymer of the present invention is such that the degree of neutralization of all acid groups of the polymer is 50 mol% or less, preferably 30 mol% or less, more preferably 10 mol% or less. , More preferably at most 5 mol%, most preferably at most 1 mol%. If the degree of neutralization of this polymer exceeds 50 mol%, there are problems such as limitations on mixability and modification by post-reaction depending on the type of additive.
[0021]
The (meth) acrylic acid (salt) -based polymer can be produced by performing polymerization while adjusting the monomer concentration and the polymerization initiator concentration in the reactor within a predetermined range. For example, a method for producing a (meth) acrylic acid (salt) -based polymer in which a polymerization initiator is added to an aqueous solution containing a (meth) acrylic acid (salt) -based monomer and polymerization is performed, and the (meth) Step (A) of gradually adding the total amount of the acrylic acid (salt) -based monomer-containing aqueous solution and the polymerization initiator to start the polymerization, and then continuing the polymerization while further adding the polymerization initiator thereto It is preferable to produce a (meth) acrylic acid (salt) -based polymer through a step (B) and a step (C) in which the reaction solution is aged after the total amount of the polymerization initiator is added. According to this method, a (meth) acrylic acid (salt) -based polymer having a small amount of the polymerization initiator and the residual amount of the monomer can be produced, and the obtained polymer has excellent storage stability.
[0022]
As the solvent constituting the aqueous solution containing the (meth) acrylic acid (salt) -based monomer, an aqueous solvent is used, and particularly preferably water is used alone. However, if necessary, a hydrophilic organic solvent may be appropriately added to water. You may. The hydrophilic organic solvent is not particularly limited, but includes, for example, lower alcohols such as methanol, ethanol, and 2-propanol; amides such as dimethylformamide; ketones such as acetone; ethers such as 1,4-dioxane; And one or more of these can be appropriately selected and used. The addition ratio of the hydrophilic organic solvent is preferably 20% by mass or less, more preferably 10% by mass or less, more preferably 5% by mass or less, and most preferably 1% by mass or less, based on the total amount of the mixed solvent with water. . If this ratio exceeds 20% by mass, the polymer may be separated and / or precipitated, which is not preferable.
[0023]
In the production method of the present invention, a monomer component containing (meth) acrylic acid (salt) as a main component is polymerized in an aqueous solvent to obtain a (meth) acrylic acid (salt) polymer. At this time, it is preferable to gradually add the whole amount of the (meth) acrylic acid (salt) -based monomer-containing aqueous solution and a part of the polymerization initiator to the reactor to start the polymerization as the step (A). .
The method of adding the (meth) acrylic acid (salt) -based monomer includes a monomer component having 3 to 6 carbon atoms, a monocarboxylic acid monoethylenically unsaturated monomer (a), and other copolymerizable monomers. A part of the used amount of (b) is initially charged into the reactor and then the remaining portion is continuously dropped, or the whole amount is continuously dropped. In the present invention, 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and most preferably the whole amount is dripped substantially continuously based on the total amount used. To the reaction system. If the dropping ratio is less than 50% by mass, the polymerization proceeds rapidly in the early stage of the polymerization, and it becomes difficult to control the temperature and the molecular weight, which is not preferable.
[0024]
In this method, it is preferable to gradually add the polymerization initiator by the time when the entire amount of the aqueous solution containing the (meth) acrylic acid (salt) monomer is charged into the reactor. The charging of the monomer into the reactor is preferably performed for 60 minutes to 300 minutes, more preferably 90 minutes to 270 minutes, still more preferably 120 minutes to 240 minutes, and particularly preferably 150 minutes to 210 minutes. By continuously charging the monomer and the polymerization initiator into the reactor in this manner, the polymer concentration and the polymerization initiator concentration in the reactor can be kept almost constant, The molecular weight of the resulting polymer is stable after production.
[0025]
In the present invention, at least one persulfate is used as a polymerization initiator. Here, examples of the persulfate include sodium persulfate, ammonium persulfate, potassium persulfate, and the like.
In the present invention, another polymerization initiator may be used in combination as the polymerization initiator. The polymerization initiator that can be used in combination is not particularly limited, and examples thereof include peroxides, such as hydrogen peroxide; 2,2′-azobis (2-aminodipropane) dihydrochloride, Azo compounds such as 4'-azobis (4-cyanovaleric acid), azobisisobutylnitrile, and 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile); benzoyl peroxide, lauroyl peroxide, Organic peroxides such as acetic acid, persuccinic acid, di-t-butyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide and the like. These may be only one kind or two or more kinds. Among them, hydrogen peroxide, an organic peroxide, and 2,2′-azobis (2-aminodipropane) dihydrochloride are preferable, and hydrogen peroxide and 2,2′-azobis (2-aminodipropane) dihydrochloride are preferable. Is more preferable, and 2,2′-azobis (2-aminodipropane) dihydrochloride is further preferable.
[0026]
The amount of the polymerization initiator to be added may be appropriately set depending on the desired molecular weight. The concentration of the polymerization initiator at the time of dropping is not particularly limited, but when a persulfate is the initiator, preferably a 3 to 50% by mass aqueous solution, more preferably a 5 to 40% by mass aqueous solution, and further more preferably Is an aqueous solution of 10 to 30% by mass. When an azo compound is used as an initiator, the aqueous solution is preferably a 0.1 to 5% by mass aqueous solution, more preferably a 0.3 to 3% by mass aqueous solution, and still more preferably a 0.5 to 2% by mass aqueous solution.
[0027]
Further, a peroxide, a reducing agent, a metal salt or the like may be combined as a polymerization initiator. Although the reducing agent and the metal salt are not particularly limited, sodium bisulfite and Fe ²⁺ , Fe ³⁺ , Cu ⁺ , Cu ²⁺ , V ²⁺ , V ³⁺ , VO ²⁺ And the like, sodium hydrogen sulfite, Fe ²⁺ , Fe ³⁺ , Cu ⁺ , Cu ²⁺ Is preferable, and Fe ²⁺ , Fe ³⁺ , Cu ⁺ , Cu ²⁺ Is more preferred. Fe ²⁺ , Fe ³⁺ , Cu ⁺ , Cu ²⁺ Is preferred because the degree of dispersion (weight average molecular weight / number average molecular weight) becomes narrower. The amount of the reducing agent or the metal salt added when the polymerization initiator is combined with the reducing agent or the metal salt is not particularly limited. However, in the case of the metal salt, the amount added to the (meth) acrylic acid (salt) -based polymer at the end of the polymerization 0.1 ppm by mass to 1,000 ppm by mass, more preferably 0.5 ppm by mass to 500 ppm by mass, still more preferably 1 ppm by mass to 300 ppm by mass. If the addition amount of the metal salt is less than 0.1 ppm by mass, there is no effect of narrowing the degree of dispersion, and if it exceeds 1,000 ppm by mass, there is no longer any effect of addition, which is not preferable from an economic viewpoint.
[0028]
Next, as step (B), it is preferable to continue the polymerization while further adding a polymerization initiator to the reactor. At this time, as the polymerization initiator to be added, those which can be used in step (A) can be added. It may be the same as step (A) or may be different. The amount of the polymerization initiator is preferably 100 to 10,000 mass ppm, more preferably 200 to 8,000 mass ppm, still more preferably 300 to 5,000 mass ppm, particularly preferably, based on the monomer aqueous solution. Is 500 to 3,000 mass ppm. Further, the addition time of the polymerization initiator is preferably 1 minute or more and 3 hours or less, more preferably 5 minutes or more and 3 hours or less, still more preferably 10 minutes or more and 2 hours or less, particularly 15 minutes after the step (A). More than one and a half hours. When the dropping of the polymerization initiator is completed within 1 minute after the dropping of the (meth) acrylic acid (salt) monomer, a large amount of the (meth) acrylic acid (salt) monomer remains, and the weight average molecular weight of the polymer is reduced. Tend to fluctuate, and the stability of the polymer aqueous solution such as the viscosity is increased. On the other hand, if the addition of the polymerization initiator is carried out for more than 3 hours, the degree of dispersion (weight average molecular weight / number average molecular weight) of the polymer increases, and the productivity also decreases, which is not preferable from an economic viewpoint. As described above, by further adding the polymerization initiator after completion of the dropping of the monomer, the remaining monomer component can be significantly reduced, and the stability of the obtained polymer is increased.
[0029]
In the method for producing a (meth) acrylic acid (salt) -based polymer of the present invention, if necessary, a chain transfer agent may be used in combination with a polymerization initiator as a molecular weight modifier within a range that does not adversely affect polymerization. May be used. Examples of the chain transfer agent include, but are not limited to, sulfites, bisulfites, diphosphorous acid, diphosphites, mercaptopropionic acid, thioglycolic acid, and the like. Alternatively, a combination of two or more types may be used. The amount used is not particularly limited, but is preferably within 3 times the amount of the initiator by mass ratio. Even if it is used more than three times, the effect of addition is no longer exhibited, and the pure content of the polymer is reduced, which is not preferable. The method of adding the chain transfer agent may be set as appropriate.
[0030]
In the method of the present invention, it is preferable that the reaction liquid is aged after the addition of the polymerization initiator to the reactor as step (C). By providing the aging time after the step (B), the remaining amount of the polymerization initiator can be reduced, and the fluctuation of the weight average molecular weight of the obtained polymer can be suppressed. "Aging" refers to a step of accelerating the polymerization reaction of the monomers in the reactor without adding the monomers and the polymerization initiator to the reactor after step (B). The aging time specified in this step (C) is 30 minutes or more and 5 hours, preferably 40 minutes to 3 hours, particularly preferably 60 minutes to 2 hours. The total of the step (B) and the step (C) is 50 minutes or more, preferably 55 minutes to 5 hours, particularly 60 minutes to 3 hours.
[0031]
The degree of neutralization in the method for producing a (meth) acrylic acid (salt) -based polymer of the present invention is 50 mol% or less, preferably 30 mol% or less, more preferably 10 mol% or less, and still more preferably 5 mol% or less. Most preferably, it is 1 mol% or less. Examples of the neutralizing agent for the monomer include hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide; alkaline earth hydroxides such as calcium hydroxide and magnesium hydroxide; ammonia; Organic amines such as ethanolamine are exemplified. These may be used alone or as a mixture of two or more.
[0032]
Neutralization may be carried out before the monomer is fed to the reactor, or in any of steps (A), (B) and (C), after further aging, ie after step (C). There may be. The degree of neutralization from the start of polymerization to the end of polymerization need not be constant as long as it is within the above range, and the degree of neutralization in the first half of polymerization and the degree of neutralization in the second half of polymerization may be different.
[0033]
The polymerization temperature in the method for producing a (meth) acrylic acid (salt) -based polymer of the present invention is not particularly limited, and may be appropriately set depending on the molecular weight, the polymerization concentration, and the like.
No. The boiling point is preferably 50 ° C to 150 ° C, more preferably 80 ° C to 120 ° C, and particularly preferably a normal boiling point.
[0034]
The final solid content concentration at the time of polymerization in the method for producing a (meth) acrylic acid (salt) -based polymer of the present invention is preferably 20% by mass or less, more preferably 18% by mass or less. It is preferable to adjust the concentration of the substance.
[0035]
The polymerization pressure in the method for producing a (meth) acrylic acid (salt) -based polymer of the present invention is not particularly limited, and may be pressurized, normal pressure (atmospheric pressure), or reduced pressure, and may be appropriately set as the case may be. Good, but normal pressure is preferred.
[0036]
In the present invention, after the step (C), for example, when the temperature of the reactor becomes 70 ° C. or less, preferably 50 ° C. or less, more preferably 40 ° C. or less, a peroxide decomposition accelerator is added to the reactor. Thus, the remaining polymerization initiator may be decomposed. When the temperature exceeds 70 ° C., the peroxide decomposition accelerator is lost, and there is a possibility that the remaining polymerization initiator cannot be lost. The addition time is 1 minute to 2 hours, preferably 5 to 90 minutes, more preferably 10 to 60 minutes.
[0037]
Examples of such an accelerator generally include a reducing agent, but are not particularly limited. Examples of the reducing agent include sulfites such as sodium sulfite and sodium hydrogen sulfite; thiosulfates such as sodium thiosulfate; L-ascorbic acids such as L-ascorbic acid and sodium L-ascorbate; nitrites such as sodium nitrite Acid salts such as sodium phosphonate and potassium phosphonate; phosphinic acids such as sodium phosphinate and potassium phosphinate; heavy metal salts such as iron salts and copper salts. Preferred are sodium bisulfite and sodium L-ascorbate, and more preferred are sodium bisulfite. These may be only one type or may include two or more types.
[0038]
The amount of the peroxide decomposition accelerator to be added to the reactor is not particularly limited, but is 5,000 mass ppm or less, preferably 3,000 mass ppm or less, more preferably 2,000 mass ppm or less based on the aqueous solution. , More preferably 1,000 ppm by mass or less, and most preferably 700 ppm by mass or less. When the amount of the peroxide decomposition accelerator exceeds 5,000 ppm by mass, the effect corresponding to the added amount can no longer be obtained, resulting in an increase in impurities, and a problem that sufficient performance is not exhibited depending on the use application. Is generated. The accelerator used may be a solid, but it is convenient to dissolve it in an aqueous solution.
[0039]
According to the production method of the present invention, the amount of the polymerization initiator remaining in the obtained (meth) acrylic acid (salt) -based polymer should be 10 mass ppm or less based on the aqueous solution after the preparation of the polymer. Can be. The amount of the remaining polymerization initiator is preferably at most 7 ppm by mass, more preferably at most 5 ppm by mass, still more preferably at most 3 ppm by mass, most preferably at most 1 ppm by mass.
[0040]
The amount of the remaining (meth) acrylic acid (salt) monomer contained in the (meth) acrylic acid (salt) -based polymer obtained by the production method of the present invention is 3,000 mass ppm with respect to the polymer. It can be: It is preferably at most 2,000 ppm by mass, more preferably at most 1,000 ppm by mass, still more preferably at most 500 ppm by mass, most preferably at most 200 ppm by mass. When the amount of the (meth) acrylic acid (salt) monomer is 3,000 mass ppm or less, the stability of the polymer may be deteriorated, for example, the molecular weight may increase during storage or the low molecular weight may increase. Not preferred.
[0041]
Further, as the reactor used in the present invention, a reactor (eg, SUS304, 316, etc.) that is generally used for producing a (meth) acrylic acid (salt) -based polymer can be used.
[0042]
In the production method of the present invention, the step (A) is followed by the step (C) or the steps (B) and (C) to produce a (meth) acrylic acid (salt) -based polymer. Can be.
[0043]
Step (A) of gradually adding the total amount of the (meth) acrylic acid (salt) -based monomer-containing aqueous solution and the polymerization initiator to a reactor to start polymerization, and then further adding a polymerization initiator By including the step (B) of continuing the polymerization while adding and the step (C) of ripening the reaction solution after adding the entire amount of the polymerization initiator, the amount of the residual monomer and the residual polymerization initiator is small ( A (meth) acrylic acid (salt) polymer can be obtained. For this reason, the effect of suppressing the increase in the molecular weight due to the polymerization of the monomers contained in the polymer, and the effect of suppressing the increase in the low-molecular-weight product becomes enormous, and a polymer having a narrow molecular weight distribution and a uniform molecular weight is obtained. be able to.
[0044]
The (meth) acrylic acid (salt) -based polymer solution obtained as described above preferably has a final solid content concentration of 20% by mass or less, and the low concentration of (meth) acrylic acid The (salt) -based polymer solution is preferably concentrated under reduced pressure at a temperature of 80 ° C. or less, and the concentration is preferably increased so that the concentration of the solid content after concentration is 25% by mass or more. This makes it possible to produce an acid (meth) acrylic acid (salt) polymer having a good hue and high productivity, and having a high concentration and a low molecular weight.
The method of concentration under reduced pressure is not particularly limited, and specifically, the polymer aqueous solution may be concentrated under reduced pressure and heated as it is, or may be continuously concentrated using a thin film concentrator or the like.
[0045]
Uses of the (meth) acrylic acid-based polymer composition of the present invention include aqueous dispersants (including pigment dispersants), scale inhibitors (scale inhibitors), detergent builders, and detergent compositions using the same. Examples thereof include, but are not limited to, those which can be widely applied to applications such as metal ion sealants, thickeners, and various binders.
[0046]
【Example】
Hereinafter, the present invention will be described specifically with reference to examples.
[0047]
≪Solid content concentration measurement method≫
About 1 g of a sample was placed in an aluminum cup precisely weighed to 0.1 mg and weighed accurately. The aluminum cup was placed in a dryer set at 120 ° C. and dried for 2 hours. After drying, the aluminum cup was transferred to a desiccator, allowed to cool to room temperature for 15 minutes, and then precisely weighed. The value obtained by dividing the weight of the sample after drying by the weight of the sample before drying and multiplying by 100 was defined as the solid concentration.
[0048]
≪Molecular weight measurement≫
Both the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the acrylic acid (salt) polymer were measured by GPC (gel permeation chromatography). The measurement conditions, equipment, and the like are as follows.
[0049]
As a column of GPC, GF-7MHQ (trade name) manufactured by Showa Denko was used.
As the mobile phase, pure water of 34.5 g of disodium hydrogen phosphate dodecahydrate and 46.2 g of sodium dihydrogen phosphate dihydrate (each of which is a special grade of reagent) was added to make the total amount 5000 g. An aqueous solution filtered with a 45 μm membrane filter was used.
As the detector, Model 481 manufactured by Waters was used, and the detection wavelength was UV 214 nm.
As the pump, L-7110 (trade name) manufactured by Hitachi, Ltd. was used.
The flow rate of the mobile phase was 0.5 ml / min, and the temperature was 35 ° C. The calibration curve was created using a standard sample of sodium polyacrylate manufactured by Souwa Kagaku.
[0050]
Example 1
1600 g of ion-exchanged water was charged into a 5 L SUS316 separable flask equipped with a reflux condenser and a stirrer, heated to 100 ° C. with stirring, and then 360 g of an 80% aqueous acrylic acid solution (hereinafter referred to as 80% AA). Mol) and 213.3 g (8 g / 1 mol of acrylic acid) of a 15% aqueous solution of ammonium persulfate (hereinafter referred to as 15% APS) were respectively dropped from different dropping ports. Each dropping time was 180 minutes for 80% AA and 185 minutes for 15% APS. The start of the dropping was all the same. During this time, the temperature maintained the boiling point of the system. Further, the same temperature was maintained for 30 minutes after the completion of the 80% AA dropping to carry out aging to complete the polymerization. After the completion of the polymerization, the reaction solution was allowed to cool. Subsequently, a vacuum pump was connected to the reaction vessel, and the pressure was reduced to 200 mmHg and concentration was performed at about 65 ° C. A predetermined amount of water was removed over about 90 minutes to obtain a polymer aqueous solution (1) having a solid content of 40%.
[0051]
Examples 2 to 5
Each polymerization reaction was carried out in the same manner as in Example 1 except that the polymerization recipes shown in Table 1 were used. Table 2 shows the results of various measurements.
[0052]
Comparative Example 1
Into a 2.5 L SUS separable flask equipped with a reflux condenser and a stirrer was charged 1000 g of ion-exchanged water, and the temperature was raised to 100 ° C. with stirring. Then, 360 g (4 mol) of 80% AA and 15% APS were added. 533.3 g (20 g / acrylic acid 1 mol) were respectively dropped from different dropping ports. The respective dropping temperatures were 80% AA for 180 minutes and 15% APS for 185 minutes. The start of the dropping was all the same. During this time, the temperature maintained the boiling point of the system. Further, the same temperature was maintained for 30 minutes after the completion of the 80% AA dropping to carry out aging to complete the polymerization. After the completion of the polymerization, the reaction solution was allowed to cool. Subsequently, a vacuum pump was connected to the reaction vessel, and the pressure was reduced to 200 mmHg and the concentration was performed at about 65 ° C. A predetermined amount of water was removed over about 90 minutes to obtain a comparative polymer aqueous solution (1) having a solid content of 40%. Table 2 also shows the measurement results of the comparative polymer (1).
[0053]
[Table 1]

[0054]
[Table 2]

[0055]
From the results in Table 2, it is understood that the aqueous polymer solution satisfying each condition has excellent color tone.
[0056]
【The invention's effect】
According to the method for producing a (meth) acrylic acid (salt) -based polymer of the present invention, the obtained polymer has a good hue and is excellent. Furthermore, by performing low-concentration polymerization at a solid concentration of 20% by mass or less and further performing concentration under reduced pressure at 80 ° C. or less to obtain a high concentration of a solid concentration of 25% by mass or more, high productivity, high concentration and low molecular weight An acid type (meth) acrylic acid-based polymer can be produced.

Claims (2)

A method for producing a (meth) acrylic acid (salt) -based polymer in which an initiator containing a persulfate is added to an aqueous solution containing a (meth) acrylic acid (salt) -based monomer and polymerized, and is defined as follows: The method for producing a (meth) acrylic acid (salt) -based polymer having a degree of neutralization of 50 mol% or less, wherein the U value is 10 to 30.

A (meth) acrylic acid (salt) -based polymer solution having a final solid content concentration of 20% by mass or less during polymerization is concentrated under reduced pressure at 80 ° C or less, and the solid content concentration after concentration is 25% by mass or more. The method for producing a (meth) acrylic acid (salt) polymer according to claim 1.