JP4270664B2 - Method for producing polyoxymethylene copolymer and polyoxymethylene copolymer composition - Google Patents

Description

〔但し、式中、Ｒ⁵ からＲ⁸ は、それぞれ独立して、水素原子、非置換又は１〜３個のハロゲン原子で置換された炭素数１〜５アルキル基を示し、各Ｒ⁹ は、それぞれ独立して、非置換のメチレン基、１〜２個の炭素数１〜Ｃアルキル基もしくは１〜２個のハロゲン原子で置換されているメチレン基又はオキシメチレン基（この場合、ｐは０から３の整数を表わす）、または、下記式（３）もしくは下記式（４）で表わされる２価の基を表わす（この場合式（２）のｐは１を表わし、式（３）及び（４）のｑは１から４の整数を表わす）。
―（ＣＨ₂ ）_q ―Ｏ―ＣＨ₂ ― （３）
―（ＯＣＨ₂ ＣＨ２）_q ―Ｏ―ＣＨ₂ ― （４） 〕
【００１３】
かかるコモノマーとしては、例えば、エチレンオキサイド、プロピレンオキサイド、１，３−ジオキソラン、１，３，５−トリオキセパン、ジエチレングリコールホルマール、１，４−ブタンジオールホルマール、１，３−ジオキサン等が挙げられる。中でも好ましいコモノマーはエチレンオキサイド、１，３−ジオキソラン、１，４−ブタンジオールホルマールである。特に好ましいコモノマーは１，３−ジオキソランであり、中でも、重合で得られたポリオキシメチレン共重合体の酸化分解抑制のため、２メチル−１，３−ジオキソランの含有量が５００重量ｐｐｍ以下好ましくは３００重量ｐｐｍ以下で、且つパーオキサイドの含有量が過酸化水素換算で１５重量ｐｐｍ以下、好ましくは５重量ｐｐｍ以下、更に少なくとも１種の立体障害性フェノールが１０〜５００重量ｐｐｍ、好ましくは５０〜３００重量ｐｐｍ添加された１，３−ジオキソランを用いることが好ましい。
【００１４】
１，３−ジオキソランに添加する立体障害性フェノールの内では、テトラキス［メチレン（３，５−ｔ−ブチル−４−ヒドロキシヒドロシンナメート）］メタンが特に好ましい。
これらコモノマーの使用量はトリオキサンに対し０．０２〜１５モル％が好ましく、０．１モル％〜１０モル％が更に好ましい。又、本発明の重合法において、ポリオキシメチレン共重合体の分子量調節のために、必要ならば適当な分子量調整剤、例えばメチラール等を使用しても良い。
【００１５】
また、ポリオキシメチレン共重合体には、トリオキサンやコモノマー中に含まれる活性水素（ＯＨの水素）を有する水、メチルアルコール、蟻酸等の不純物によって、重合時に不安定末端部分が生成する。そこで、重合時の不安定末端部分の生成を低減するために、トリオキサンやコモノマー中の水、メチルアルコール、蟻酸等の活性水素を有する不純物の濃度を蒸留及び吸着等によって極力減らす必要が有る。実用的には、活性水素を有する不純物濃度を水の濃度に換算し、その合計濃度をトリオキサンとコモノマーの合計量に対して２０ｐｐｍ以下にすることが好ましい。水濃度への換算は、具体的には、メチルアルコールの場合はメチルアルコール濃度の０．２８倍、蟻酸の場合は蟻酸濃度の０．２０倍することにより得られる。
【００１６】
本発明における重合触媒としては、ルイス酸、プロトン酸及びそのエステル又は無水物等のカチオン活性触媒が使用される。ルイス酸としては、例えば、ホウ酸、スズ、チタン、リン、ヒ素及びアンチモンのハロゲン化物が挙げられる。また、プロトン酸、そのエステル又は無水物の具体例としては、パークロル酸、トリフルオロメタンスルホン酸、パークロル酸−３級ブチルエステル、アセチルパークロラート、トリメチルオキソニウムヘキサフルオロホスフェート等が挙げられる。中でも、三フッ化ホウ素；三フッ化ホウ素水和物；及び酸素原子または硫黄原子を含む有機化合物と三フッ化ホウ素との配位錯化合物が好ましく、具体的には、三フッ化ホウ素ジエチルエーテラート、三フッ化ホウ素−ジ−ｎ−ブチルエーテラートを好適例として挙げることができる。これら三フッ化ホウ素系の重合触媒は、トリオキサンと環状エーテル及び／又は環状ホルマールとの混合物１モルに対し、５×１０^-6モル以上、５×１０^-5モル以下で用いることが好ましく、１×１０^-6モル以上、２×１０^-5モル以下で用いることが更に好ましい。
【００１７】
本発明の重合法は、従来公知のトリオキサンの重合法と同様の設備と方法で行うことができる。即ち、バッチ式、連続式、いずれも可能であり、又、溶液重合、塊状重合等何れにてもよいが、液体モノマーを用い、重合の進行とともに固体塊状のポリマーを得る連続式塊状重合方法が工業的には一般的であり好ましい。この場合、必要に応じて不活性媒体を共存させることもできる。本発明に用いられる重合装置としては、バッチ式では一般に用いられる攪拌機付きの反応槽が使用でき、また連続式としては、コニーダー、２軸スクリュー式連続押出混合機、２軸パドル型連続混合機等のセルフクリーニング型混合機が使用可能である。また、２種以上のタイプの重合装置を組み合わせて使用することも可能であるし、重合装置を直列に連結して使用することも可能である。また、重合反応によって生成する固体重合物が微細な形態で得られるような粉砕機能を備えたものが好ましい。
【００１８】
共重合反応は、常圧下で、好ましくは６０〜２００℃、より好ましくは６０〜１２０℃の温度範囲で行われる。また、重合時間は、特に制限はないが、一般に１０秒〜１００分以下が選ばれる。
重合を完了し、重合機から排出される粗ポリオキシメチレン共重合体は、次いで直ちに失活剤と混合接触させて重合触媒の失活化を行うことが必要である。本発明の特徴は失活剤として前記一般式（１）で表わされる第４級アンモニウム化合物を用いて、粗ポリオキシメチレン共重合体と接触させ重合触媒の失活を行う点に有る。
【００１９】
かかる失活剤の使用量は重合触媒量に対して０．５〜５００倍モル、好ましくは１〜２００倍モルである。本発明に用いる第４級アンモニウム化合物は、一般式（１）で表わされるものであれば特に制限はないが、一般式（１）におけるＲ¹ 、Ｒ² 、Ｒ³ 及びＲ⁴ が、各々独立して、炭素数１〜５のアルキル基又は炭素数２〜４のヒドロキシアルキル基であることが好ましく、この内、更に、Ｒ¹ 、Ｒ² 、Ｒ³ 及びＲ⁴ の少なくとも１つが、ヒドロキシエチル基であるものが特に好ましい。
【００２０】
具体的には、テトラメチルアンモニウム、テトラエチルアンモニウム、テトラプロピルアンモニウム、テトラ−ｎ−ブチルアンモニウム、セチルトリメチルアンモニウム、テトラデシルトリメチルアンモニウム、１，６−ヘキサメチレンビス（トリメチルアンモニウム）、デカメチレン−ビス−（トリメチルアンモニウム）、トリメチル−３−クロロ−２−ヒドロキシプロピルアンモニウム、トリメチル（２−ヒドロキシエチル）アンモニウム、トリエチル（２−ヒドロキシエチル）アンモニウム、トリプロピル（２−ヒドロキシエチル）アンモニウム、トリ−ｎ−ブチル（２−ヒドロキシエチル）アンモニウム、トリメチルベンジルアンモニウム、トリエチルベンジルアンモニウム、トリプロピルベンジルアンモニウム、トリ−ｎ−ブチルベンジルアンモニウム、
【００２１】
トリメチルフェニルアンモニウム、トリエチルフェニルアンモニウム、トリメチル−２−オキシエチルアンモニウム、モノメチルトリヒドロキシエチルアンモニウム、モノエチルトリヒドロキシエチルアンモニウム、オクダデシルトリ（２−ヒドロキシエチル）アンモニウム、テトラキス（ヒドロキシエチル）アンモニウム等の、水酸化物；塩酸、臭酸、フッ酸などの水素酸塩；硫酸、硝酸、燐酸、炭酸、ホウ酸、塩素酸、よう素酸、珪酸、過塩素酸、亜塩素酸、次亜塩素酸、クロロ硫酸、アミド硫酸、二硫酸、トリポリ燐酸などのオキソ酸塩；チオ硫酸などのチオ酸塩；蟻酸、酢酸、プロピオン酸、ブタン酸、イソ酪酸、ペンタン酸、カプロン酸、カプリル酸、カプリン酸、安息香酸、シュウ酸などのカルボン酸塩等が挙げられる。中でも、水酸化物（ＯＨ^- ）、硫酸（ＨＳＯ₄ ^- 、ＳＯ₄ ^2-）、炭酸（ＨＣＯ₃ ^- 、ＣＯ₃ ^2-）、ホウ酸（Ｂ（ＯＨ）₄ ^- ）、カルボン酸の塩が好ましい。カルボン酸の内、蟻酸、酢酸、プロピオン酸が特に好ましい。
【００２２】
これら第４級アンモニウム化合物は、単独でもあるいは２種以上を組み合わせて用いてもよい。また、従来から公知の失活剤である、アルキルアミン類、アルコキシアミン類、ヒンダードアミン類あるいはアルカリ金属、アルカリ土類金属の水酸化物、無機酸塩、有機酸塩、又は、三価の有機燐化合物やホウ酸化合物等と併用することも可能である。
【００２３】
本発明の失活剤と重合反応生成物との接触方法に関しては、特に制限はなく、前記第４級アンモニウム化合物を粗ポリオキシメチレン共重合体によく混合することによって得られるが、接触を充分に行い効率よく重合触媒の失活を行うためには第４級アンモニウム化合物を水及び／又は有機溶媒中に溶解した溶液とし、これと重合反応生成物を混合して、スラリー状で混合攪拌処理する方法が好ましい。この場合、重合機排出物が微細な粉粒体であれば好都合であるが、比較的粒径が大きい場合には、重合機排出後、速やかに粉砕することが好ましい。使用する粉砕機は特に限定されないが、例えば、ロータリーミル、ハンマーミル、ジョークラッシャー、フェザーミル、ロータリーカッターミル、ターボミル、ボールミルあるいは分級式衝撃粉砕機等が用いられる。粒径分布は、粉砕機の回転数、クリアランス、粉砕機に設けたスクリーンメッシュ及び／又は所望により別途設けた篩等により制御することができる。粉砕されたポリオキシメチレン共重合体は、下記（ａ）〜（ｄ）で規定する粒径分布を満足するものであることが好ましい。
【００２４】
（ａ）平均粒径０．２〜０．７ｍｍ
（ｂ）２０ｍｅｓｈを超えるものが０〜３０重量％
（ｃ）２００ｍｅｓｈを超え２０ｍｅｓｈ未満のものが３０〜１００重量％
（ｄ）２００ｍｅｓｈ未満のものが０〜４０重量％
（ただし、合計量は１００％）
ここで、粒径分布はＴｙｌｅｒ標準篩を用い、Ｒｏ−Ｔａｐシェーカーで１０分間振とうし篩い分けすることにより測定した。また、平均粒径は篩下累積度数（百分率で表わす）分布曲線において、累積度数が５０％になる粒径を平均粒径とした。この粒径分布は、粉砕し重合触媒の失活化を行うにことによって得られるポリオキシメチレン共重合体の品質、特にその不安定末端量と重合触媒によるポリオキシメチレン共重合体の主鎖分解の程度、及び失活後の後処理、具体的には不安定末端部分の分解除去操作や安定剤との溶融混錬処理における操作性の両者を満足させるという観点から見出したものである。
【００２５】
この内、（ａ）の平均粒径の上限（０．７ｍｍ）及び（ｂ）の２０ｍｅｓｈを超えるものの割合の上限は、主としてポリオキシメチレン共重合体の品質の鍵を握る重要な要件であり、（ａ）の平均粒径の下限（０．２ｍｍ）及び（ｄ）の２００ｍｅｓｈ未満のものの割合の上限は、主として不安定末端部分の分解除去操作や安定剤との溶融混錬処理における操作性の鍵を握る重要な要件である。ここで示した粒径分布より粒径が大きい方に偏った場合、例えば平均粒径がその上限を超えるか２０ｍｅｓｈを超えるものの割合がその上限を超えた場合、得られる粉砕ポリオキシメチレン共重合体のの品質、特に不安定末端部分の量は大きいものとなり、また重合触媒の失活化効率が低下し、不活性化されていない重合触媒による主鎖分解が発生する。
【００２６】
一方、この粒径分布より粒径が小さい方に偏った場合、例えば平均粒径がその下限未満あるいは２００ｍｅｓｈ未満のものの割合がその上限を超えた場合、ポリオキシメチレン共重合体の品質面では満足できるものの、押出機による不安定末端部分の溶融分解除去処理、あるいは、安定剤との溶融混錬処理等の操作性が著しく劣るものとなる。より具体的には粉砕されたポリオキシメチレン共重合体の押出機への食い込み性及びストランドの排出が不安定になり、また押出機のモーター電流値の変動及び押出機スクリュー先端直後に設置した樹脂圧力計の指示値変動が激しくなる等の問題が発生して安定した押出が不可能になり、安定化されたポリオキシメチレン共重合体を経済的に製造することが不可能になる。重合機から排出されたポリオキシメチレン共重合体は、直ちに第４級アンモニウムを含む水溶液等と接触させつつ、或いは、接触させた後に粉砕機によって湿式粉砕することも可能であるし、また、重合機から排出されたポリオキシメチレン共重合体を直ちに粉砕機で乾式粉砕した後第４級アンモニウムを含む水溶液等と接触させることも可能である。
【００２７】
本発明の重合触媒の失活化における温度及び処理時間は特に制限はないが、例えば、第４級アンモニウム化合物を水及び／又は有機溶媒中に溶解した溶液とし、これと重合反応生成物を混合して、スラリー状で混合攪拌処理することにより重合触媒の失活化を行う方法では、失活化促進のためスラリーを加熱して、４５℃以上ポリオキシメチレン共重合体の融点以下の温度で、好ましくは５０℃以上８０℃未満でポリオキシメチレン共重合体を溶融させずに実施することが好ましい。この場合失活化を完全に行うという観点では、処理時間は長い方が好ましいが、第４級アンモニウム化合物を失活剤に用いた場合は失活速度が早いため、実用的には５分以上６０分以下で処理される。また、重合反応生成物と第４級アンモニウム化合物を接触させた後、押出機等によってポリオキシメチレン共重合体の融点以上２３０℃以下の温度で、ポリオキシメチレン共重合を溶融させて重合触媒の失活化を行うことも可能である。この場合、実用的な処理時間は１分以上１０分以下である。
【００２８】
ポリオキシメチレン共重合体の粉砕並びに重合触媒の失活化は、ポリオキシメチレン共重合体の酸化分解抑制のため不活性ガス雰囲気下で行うことが好ましい。
本発明の失活剤により不安定末端部分が少なくしかも熱安定性の高いポリオキシメチレン共重合体が得られるのは、前記一般式（１）で表わされる第４級アンモニウム化合物が重合触媒を極めて速やかに失活化し、しかもその生成物の安定性がきわめて高いためと考えられる。
【００２９】
本発明において重合触媒の失活を行った共重合体は、必要に応じて、ろ過、乾燥を経た後、不安定末端部分の分解除去処理に付される。不安定末端部分の分解除去は、例えば、ベント付き単軸スクリュー式押出機やベント付き２軸スクリュー式押出機等を用いて、塩基性物質の存在下で溶融加水分解し、不安定末端部分を安定末端に変えるとともに、不安定末端部分の分解前のポリオキシメチレン共重合体に含まれる未反応モノマーや不安定末端部分の溶融加水分解で発生したホルムアルデヒド等をベントより減圧下除去することにより行うことができる。
【００３０】
不安定末端部分の分解除去に用いられる塩基性物質としてはアンモニア、トリエチルアミン、トリブチルアミン等の脂肪族のアミン化合物が挙げられる。他の塩基性物質としては、アルカリ金属又はアルカリ土類金属の水酸化物、無機弱酸塩、有機酸塩等が挙げられる。特に、アンモニア、トリエチルアミン、トリブチルアミン等の脂肪族のアミン化合物が好ましい。これらの塩基性物質の添加量はポリオキシメチレン共重合体に対して、アミン化合物では０．０１〜５重量％、アルカリ金属又はアルカリ土類金属の水酸化物、無機弱酸塩、有機酸塩では２〜５０００ｐｐｍ添加される。また、水及び／又はメタノール等の有機溶剤をこれら塩基性物質と共に添加することもできる。
【００３１】
不安定末端部分の分解除去されたポリオキシメチレン共重合体に、熱、光、酸化等に起因する分解に対する安定剤及びホルムアルデヒド補足剤、蟻酸中和剤、離型剤等の他の添加剤や補強剤、導電材、熱可塑性樹脂、熱可塑性エラストマー、顔料等を配合し、押出機等で溶融混錬することにより、最終の安定化ポリオキシメチレン共重合体の製品とする。本発明の方法によれば、重合触媒失活後のポリオキシメチレン共重合体の不安定末端部分が非常に少なく、また、重合触媒は完全に失活されている。したがって、不安定末端部分の分解除去処理の負荷は大幅に軽減されているため簡単な仕上げ処理で充分安定なポリオキシメチレン共重合体が得られる。
【００３２】
また、不安定末端部分が非常に少なく、また、重合触媒が完全に失活されているため、不安定末端部分の分解除去による末端安定化処理工程を実質的に経ること無く、各種安定剤、添加剤、補強剤と共に溶融混錬押出することによって、少量残存している不安定末端部分の分解除去を兼ねさせ、最終の安定化ポリオキシメチレン共重合体を製造することも可能である。この方法は、従来必須とされていた末端安定化処理工程を経ていないにもかかわらず、実用上十分安定な最終のポリオキシメチレン共重合体を得ることが可能で、且つ非常に経済的に有利な方法である。
【００３３】
また、本発明の重合触媒の失活方法により得られる第４級アンモニウム化合物を含有したポリオキシメチレン共重合体組成物は、上記したように、不安定末端部分が非常に少なく、重合触媒が完全に失活されている。したがって、本ポリオキシメチレン共重合体組成物は非常に安定で、例えば長期貯蔵時、あるいは、運搬時に分解によるホルムアルデヒドの発生やポリマー主鎖切断による分子量低下が発生しない。よって、本ポリオキシメチレン共重合体組成物はコンパウンド用の原料として好適に用いることができる。更に、本ポリオキシメチレン共重合体組成物に酸化防止剤、ホルムアルデヒド補足剤、蟻酸中和剤、紫外線吸収剤、光安定剤、離型剤、補強剤、導電材、熱可塑性樹脂、熱可塑性エラストマー、顔料等の配合剤の少なくとも一種以上を添加したポリオキシメチレン共重合体組成物もコンパウンド用の原料として好適に用いることができる。
【００３４】
【実施例】
以下実施例及び比較例によって、本発明をより具体的に説明するが、本発明はこれらによって何ら限定されるものではない。尚、実施例及び比較例中の用語、及び測定法は以下のとおりである。
＜２メチル−１，３−ジオキソラン、メチルアルコールの含有量＞
ガスクロパック５５（ジーエルサイエンス（株）製）を充填したガラスカラムを装着したガスクロマトグラフィーで水素炎イオン検出器により測定した。
＜水の濃度＞
カールフィッシャー水分計で測定した。
＜蟻酸の濃度＞
水酸化カリウムによる中和滴定で測定した。
【００３５】
＜１，３−ジオキソラン中のパーオキサイド含有量（過酸化水素換算）＞
フラスコ内にイソプロピルアルコール４０ｍｌ、ヨウ化ナトリウム飽和溶液（ＮａＩをイソプロピルアルコールで溶解）１０ｍｌ、酢酸２ｍｌ及び１，３−ジオキソラン２５ｇを加え、１００℃で約５分間還流する。その後直ちに０．０１Ｎチオ硫酸ナトリウムで、フラスコ内の混合物の色が黄色から無色になるまで滴定する（この時の滴定量をＡｍｌとする）。また、空滴定として、１，３−ジオキソランを用いず上記と同じ操作を行う（この時の滴定量をＢｍｌとする）。
【００３６】
１，３−ジオキソラン中のパーオキサイド量は、過酸化水素として、以下の式で求められる。
【式１】

【００３７】
＜粒径分布＞
Ｔｙｌｅｒ標準篩を用い、Ｒｏ−Ｔａｐシェーカーで１０分間振とうし篩い分けすることにより測定した。また、平均粒径は篩下累積度数（百分率で表わす）分布曲線において、累積度数が５０％になる粒径を平均粒径とした。
＜ＭＩ（メルトインデックス：ｇ／１０ｍｉｎ）＞
ＡＳＴＭ−Ｄ−１２３８により東洋精機製のＭＥＬＴ ＩＮＤＥＸＥＲを用いて１９０℃、２１６９ｇの条件下でメルトインデックス（ｇ／１０ｍｉｎ）を測定した。
【００３８】
＜不安定末端部の量（ｐｐｍ）＞
窒素気流下において、１９０℃、３０分間の条件下でオキシメチレン共重合体から発生するホルムアルデヒドを水に吸収した後適定し測定した。この条件下においては、発生するホルムアルデヒドの殆どはオキシメチレン共重合体の不安定末端部〔−（ＯＣＨ₂ ）ｎ−ＯＨ基〕からの分解による。
＜安定化ポリオキシメチレン共重合体の熱安定性（ｐｐｍ／ｍｉｎ）＞
窒素気流下において、２３０℃、９０分間にオキシメチレン共重合体から発生するホルムアルデヒドを水に吸収した後適定し測定する。測定した総ホルムアルデヒド量を９０分間で割って、１分間当たりの平均ホルムアルデヒド発生速度（ｐｐｍ／ｍｉｎ）を計算しこれを安定化ポリオキシメチレン共重合体の熱安定性とした。
【００３９】
【実施例１〜２０】
熱媒を通すことができるジャケット付きの２軸パドル型連続混合機を８０℃に調整し、３ｋｇ／Ｈｒのトリオキサンと、コモノマーとして１，３−ジオキソラン１１１ｇ／Ｈｒ（トリオキサン１モルに対して０．０４５モル）と、分子量調整剤としてメチラール１．８ｇ／Ｈｒ（トリオキサン１モルに対して０．７×１０^-3モル）とを連続的に添加した。１，３−ジオキソランは、２メチル−１，３−ジオキソランの含有量が１０５重量ｐｐｍ（ガスクロマトグラフィーで測定）、過酸化水素換算のパーオキサイド含有量が２．３重量ｐｐｍ、立体障害性フェノールとしてテトラキス［メチレン（３，５−ジ−ｔ−ブチル−４−ヒドロキシヒドロシンナメート）］メタン（チバガイギー製イルガノックス１０１０：商品名）が２００重量ｐｐｍ添加されているものを用いた。
【００４０】
また、トリオキサンと１，３−ジオキソランの混合物中の水、蟻酸、メチルアルコールの合計濃度は水換算濃度で１２ｐｐｍであった。重合触媒として、三フッ化ホウ素ジ−ｎ−ブチルエーテラートが、トリオキサン１モルに対して１．５×１０^-5モルになるように、三フッ化ホウ素ジ−ｎ−ブチルエーテラート１重量％のシクロヘキサン溶液９．９ｇ／Ｈｒを連続的に添加し重合を行った。混合機より排出されたポリオキシメチレン共重合体は、直ちに窒素雰囲気下で、表１に示す如く第４級アンモニウム化合物を含む水溶液と接触させながら、（株）奈良機械製作所製自由粉砕機Ｍ−２型で湿式粉砕し、粉砕機から排出された粉体状ポリオキシメチレン共重合体と第４級アンモニウム化合物を含むスラリーを貯留タンクに導入し失活化を行った。貯留タンクの温度は５０℃、貯留タンク中の平均滞留時間は３０分である。失活化の後、遠心分離機でろ過し、窒素下、１２０℃で乾燥し最終ポリオキシメチレン共重合体を得た。最終ポリオキシメチレン共重合体の粒径分布は以下のとおりであった。
（ａ）平均粒径０．３８ｍｍ
（ｂ）２０ｍｅｓｈを超えるものが４．２重量％
（ｃ）２００ｍｅｓｈを超え２０ｍｅｓｈ未満のものが８５．４重量％
（ｄ）２００ｍｅｓｈ未満のものが１０．４重量％
得られた最終ポリオキシメチレン共重合体の評価結果を表１に示す。
【００４１】
【実施例２１〜２４】
混合機より排出されたポリオキシメチレン共重合体を、直ちに、窒素雰囲気下で、（株）奈良機械製作所製自由粉砕機Ｍ−２型で乾式粉砕し、粉砕機から排出された粉体状ポリオキシメチレン共重合体を、表２に示す第４級アンモニウム化合物を含む水溶液の貯留タンクに導入し失活化を行ったこと以外は実施例１〜１３と全く同じ操作を行って最終ポリオキシメチレン共重合体を得た。最終ポリオキシメチレン共重合体の粒径分布は以下のとおりであった。
（ａ）平均粒径０．３７ｍｍ
（ｂ）２０ｍｅｓｈを超えるものが３．８重量％
（ｃ）２００ｍｅｓｈを超え２０ｍｅｓｈ未満８４．７重量％
（ｄ）２００ｍｅｓｈ未満のものが１１．５重量％
得られた最終ポリオキシメチレン共重合体の評価結果を表２に示す。
【００４２】
【実施例２５〜２８】
コモノマーとしてエチレンオキサイドを６６ｇ／Ｈｒ（トリオキサン１モルに対して０．０４５モル）、重合触媒として、三フッ化ホウ素ジ−ｎ−ブチルエーテラートが、トリオキサン１モルに対して４．５×１０^-5モルになるように、三フッ化ホウ素ジ−ｎ−ブチルエーテラート１重量％のシクロヘキサン溶液２９．７ｇ／Ｈｒを連続的に添加し重合を行ったこと以外は実施例１〜１３と全く同じ操作を行って最終ポリオキシメチレン共重合体を得た。トリオキサンとエチレンオキサイドの混合物中の水、蟻酸、メチルアルコールの合計濃度は水換算濃度で１０ｐｐｍであった。また、最終ポリオキシメチレン共重合体の粒径分布は以下のとおりであった。
（ａ）平均粒径０．３５ｍｍ
（ｂ）２０ｍｅｓｈを超えるものが３．５重量％
（ｃ）２００ｍｅｓｈを超え２０ｍｅｓｈ未満のものが８４重量％
（ｄ）２００ｍｅｓｈ未満のものが１２．５重量％
得られた最終ポリオキシメチレン共重合体の評価結果を表３に示す。
【００４３】
【実施例２９】
実施例１により得た粉粒状のポリオキシメチレン共重合体について、一般的に行われる不安定末端の分解除去工程を経ることなく、安定剤としてトリエチレングリコール−ビス［３−（３−ｔ−ブチル−５−メチル−４−ヒドロキシフェニル）プロピオネート］（チバガイギー社製イルガノックス２４５：商品名）を０．３重量％、ステアリン酸カルシウムを０．１５重量％、ナイロン６６を０．０５重量％混合し、ベント付き３０ｍｍ単軸押出機で溶融混錬することによりペレット状の安定化ポリオキシメチレン共重合体を得た。溶融温度は２００℃、押出機平均滞留時間は３分間、ベント真空度は３０Ｔｏｒｒである。得られたペレット状の安定化ポリオキシメチレン共重合体の評価結果を表４に示す。尚、３０ｍｍ単軸押出機での溶融混錬時の、粉粒状ポリオキシメチレン共重合体の食い込み性及びストランドの排出は安定しており、また、モーター電流値の変動、押出機スクリュー先端直後に設置した樹脂圧力計の指示値変動は殆ど無く安定した押出が可能であった。
【００４４】
【比較例１〜３】
第４級アンモニウム化合物に変えて、表５に示した失活剤を用いたこと以外は実施例１〜１３と全く同じ操作を行って最終ポリオキシメチレン共重合体を得た。得られた最終ポリオキシメチレン共重合体の評価結果を表５に示す。失活剤として第４級アンモニウム化合物を用いないと、失活化が不十分でポリオキシシメチレン共重合体の分解が進んで、ＭＩが増加し且つ不安定末端部の量が増加していることがわかる。
【００４５】
【比較例４】
比較例１により得た粉粒状のポリオキシメチレン共重合体を、３０ｍｍベント付き２軸押出機に供給し不安定末端の分解除去を行った。押出機の回転数は１００ｒｐｍ、温度は２００℃とした。不安定末端の分解除去に使用する塩基性物質として、トリエチルアミン水溶液を用い、その添加量は、ポリオキシメチレン共重合体１００重量部に対して３重量部（トリエチルアミン０．５重量部、水２．５重量部）とし、押出機の溶融したポリオキシメチレン共重合体に連続的に添加した。不安定末端が分解されたポリオキシメチレン共重合体は、ベント真空度３０Ｔｏｒｒの条件下で脱揮され、押出機ダイス部よりストランドとして押出されペレタイズされた。
【００４６】
このペレットに安定剤としてトリエチレングリコール−ビス［３−（３−ｔ−ブチル−５−メチル−４−ヒドロキシフェニル）プロピオネート］（チバガイギー社製イルガノックス２４５：商品名）を０．３重量％、ステアリン酸カルシウムを０．１５重量％、ナイロン６６を０．０５重量％混合し、ベント付き３０ｍｍ単軸押出機で溶融混錬することによりペレット状の安定化ポリオキシメチレン共重合体を得た。溶融温度は２００℃、ベント真空度は３０Ｔｏｒｒである。得られたペレット状の安定化ポリオキシメチレン共重合体の評価結果を表６に示す。実施例２２と比較すると、不安定末端部の分解除去を実施しているにもかかわらず、安定化後のポリオキシメチレン共重合体の熱安定性が悪い。また、安定化前と比較してＭＩが若干増加していることから、ポリオキシメチレン共重合体が分解していることがわかる。本発明の製造方法によれば、不安定部の分解除去を実施しなくても非常に熱安定性に優れたポリオキシメチレン共重合体を得ることができる。
【００４７】
【表１】

【００４８】
【表２】

【００４９】
【表３】

【００５０】
【発明の効果】
本発明の方法によって得られるポリオキシメチレン共重合体は、従来の方法と比べて、不安定末端部分の少ない共重合体が得られ、且つ、重合触媒の失活化が完全であるため、重合触媒起因のポリマー分解が引き起こされないので、失活処理後の後処理工程が簡略化でき、非常に経済的であると同時に最終製品の熱安定性も非常に高い。また、本発明のによって得られる第４級アンモニウム化合物を含有したポリオキシメチレン共重合体組成物はコンパウンド用の原料として好適である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a polyoxymethylene copolymer having improved thermal stability. More specifically, in the production of a polyoxymethylene copolymer using a cationically active catalyst of trioxane and cyclic ether and / or cyclic formal, a deactivation treatment of the polymerization catalyst using a quaternary ammonium compound is employed after the copolymerization. Thus, the present invention relates to an economical process for producing a polyoxymethylene copolymer having an improved thermal stability with few unstable terminals.
[0002]
[Prior art]
Polyoxymethylene copolymers have well-balanced mechanical properties and excellent fatigue properties, and are excellent in properties such as heat resistance, chemical resistance, electrical properties, and slidability, and in moldability. Therefore, they are used as engineering plastics in a wide range of applications such as machine parts, automobile parts, and electrical / electronic equipment parts. It is known that polyoxymethylene copolymers for practical use are generally produced by the following process. First, a cyclic acetal such as trioxane is used as the main monomer, a cyclic acetal or cyclic ether having an adjacent carbon atom as a comonomer, and a chain transfer agent for adjusting the degree of polymerization according to the purpose is added, and a cationically active catalyst is used. The crude polyoxymethylene copolymer is obtained by copolymerization. In general, such crude polyoxymethylene copolymers have a significant amount of unstable terminal moieties [-(OCH₂) N-OH group].
[0003]
This unstable end portion is easily decomposed by heating such as molding and generates a large amount of formaldehyde. Further, the polymerization catalyst remains in an active state, and when heat is applied, the main chain of the copolymer is decomposed or unstable terminal portions are increased. Accordingly, the crude polyoxymethylene copolymer as the polymerization product is then converted into an organic or inorganic basic compound such as an alkylamine, alkoxyamine, hindered amine, alkali metal, alkaline earth metal hydroxide or the like. Or, after neutralizing or deactivating the catalyst with a trivalent organic phosphorus compound, it is subjected to a step of decomposing and removing the unstable terminal portion, and a basic compound such as the above compound, etc., and optionally used in combination The unstable terminal portion is decomposed and removed by heating in the presence of water, alcohol or the like.
[0004]
The polyoxymethylene copolymer from which the unstable terminal portion has been decomposed and removed in this way is then blended with various stabilizers in order to impart heat stability, long-term stability, etc. A stabilized polyoxymethylene copolymer that can be put to practical use is obtained by blending and kneading various additives, reinforcing agents, and the like for imparting characteristics according to the above. As described above, in order to put the crude polyoxymethylene copolymer obtained by copolymerization into practical use, it is necessary to inactivate the polymerization catalyst and decompose and remove the unstable terminal portion. It was economically disadvantageous because it required more energy. If the crude polyoxymethylene copolymer before decomposing and removing the unstable terminal portion has few unstable portions, the stability of the final product will be better, and the process of decomposing and removing the unstable terminal portion There is an advantage that can be simplified.
[0005]
For this purpose, it is necessary to obtain a polyoxymethylene copolymer having a small number of unstable terminal portions and a completely deactivated polymerization catalyst in polymerization and / or deactivation of the polymerization catalyst. Of these, improvements with various deactivators have been proposed for catalyst deactivation, but the neutralization deactivation of polymerization catalysts with basic substances known in the past completely reduces the activity of the polymerization catalyst. It cannot be lost, and the main chain decomposition of the polyoxymethylene copolymer occurs during high-temperature drying after deactivation, melt pelletization, or product molding, resulting in a decrease in molecular weight and unstable terminal portions.
[0006]
Further, from the standpoint of deactivation efficiency of the polymerization catalyst and subsequent efficiency of decomposing and removing the unstable terminal portion, etc., a method of pulverizing and deactivating the crude polyoxymethylene copolymer after polymerization (JP-A-57-80414) And JP-A-58-34819) are known. Further, the crude polyoxymethylene copolymer is pulverized with a specific pulverizer and deactivated (Japanese Patent Laid-Open No. 10-101755), or pulverized to a specific particle size distribution and deactivated (Japanese Patent Laid-Open No. No. 10-101756) has also been proposed, but even with either method, there remains room for improvement in the deactivation of the polymerization catalyst, and there are few unstable terminal portions and the polymerization catalyst is completely A more economical method for deactivating a polymerization catalyst that can obtain an inactivated polyoxymethylene copolymer is desired.
[0007]
[Problems to be solved by the invention]
The present invention employs a deactivation treatment of a polymerization catalyst using a quaternary ammonium compound after copolymerization in the production of a polyoxymethylene copolymer using a cationically active catalyst of trioxane and cyclic ether and / or cyclic formal. Thus, the present invention provides an economical method for producing a polyoxymethylene copolymer having a small number of unstable end portions and an improved thermal stability, and the copolymer composition.
[0008]
[Means for Solving the Problems]
In view of the present situation, the present inventor has extremely few unstable terminal portions, significantly reduces the load in the subsequent step of decomposing and removing unstable terminal portions, and also sufficiently deactivates the polymerization catalyst to cause thermal degradation. As a result of earnest research for the purpose of obtaining an extremely stable crude polyoxymethylene copolymer, by using a quaternary ammonium compound represented by the following general formula (1) as a deactivator for the polymerization catalyst, The present invention has been completed.
[0009]
[R¹R²R^ThreeR^FourN⁺] NX^-n              (1)
(Wherein R¹, R², R^Three, R^FourAre each independently an unsubstituted alkyl group or substituted alkyl group having 1 to 30 carbon atoms; an aryl group having 6 to 20 carbon atoms; an unsubstituted alkyl group or substituted alkyl group having 1 to 30 carbon atoms; An aralkyl group substituted with an aryl group having 6 to 20 carbon atoms; or an alkylaryl group in which the aryl group having 6 to 20 carbon atoms is substituted with at least one unsubstituted alkyl group or substituted alkyl group having 1 to 30 carbon atoms The unsubstituted alkyl group or the substituted alkyl group is linear, branched, or cyclic. The substituent of the substituted alkyl group is a halogen, a hydroxyl group, an aldehyde group, a carboxyl group, an amino group, or an amide group. In the unsubstituted alkyl group, aryl group, aralkyl group, and alkylaryl group, a hydrogen atom may be substituted with a halogen. n represents an integer of 1 to 3. X represents a hydroxyl group or an acid residue of a carboxylic acid having 1 to 20 carbon atoms, a hydrogen acid, an oxo acid, an inorganic thioacid, or an organic thioacid having 1 to 20 carbon atoms. )
[0010]
  That is, the present invention produces a polyoxymethylene copolymer by copolymerizing trioxane as a main monomer and at least one cyclic ether and / or cyclic formal as a comonomer using at least one cationically active catalyst. In this method, after copolymerization, at least one quaternary ammonium compound represented by the general formula (1) is brought into contact with the copolymer to deactivate the polymerization catalyst.A method for producing a polyoxymethylene copolymer, wherein the deactivation of the polymerization catalyst satisfies the particle size distribution defined by the following (a) to (d) for the polyoxymethylene copolymer discharged from the polymerization machine To be pulverized into powderThe present invention relates to a method for producing a polyoxymethylene copolymer.
  (A) Average particle diameter of 0.2 to 0.7 mm
  (B) 0-30% by weight exceeds 20 mesh
  (C) 30 to 100% by weight exceeding 200 mesh and less than 20 mesh
  (D) 0 to 40% by weight of less than 200 mesh
  (However, the total amount is 100%)
  The feature of the present invention resides in that the quaternary ammonium compound represented by the general formula (1) is used as a deactivator for the polymerization catalyst, whereby the deactivation of the polymerization catalyst is extremely effectively performed. Is to obtain a crude polyoxymethylene copolymer having very few unstable terminal portions. Furthermore, the catalyst deactivated by the deactivator is no longer very stable, and the main chain decomposition promoting action in the post-process, that is, high temperature drying, melting decomposition removal of unstable parts, molding, etc. is remarkably suppressed. It was recognized that
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
The polyoxymethylene copolymer of the present invention is first copolymerized using trioxane as a main monomer and at least one of cyclic ether and / or cyclic formal as a comonomer in the presence of at least one cationically active catalyst. The cyclic ether or cyclic formal used here as a comonomer is a cyclic compound having at least one pair of linked carbon atoms and oxygen atoms represented by the following general formula (2).
[0012]
[Chemical 1]

[However, in the formula, R^FiveTo R⁸Each independently represents a hydrogen atom, an unsubstituted or substituted 1 to 5 alkyl group substituted with 1 to 3 halogen atoms, and each R⁹Each independently represents an unsubstituted methylene group, a methylene group substituted with 1 to 2 carbon atoms of 1 to C alkyl group or 1 to 2 halogen atoms, or an oxymethylene group (in this case, p is Represents an integer of 0 to 3) or a divalent group represented by the following formula (3) or the following formula (4) (in this case, p in formula (2) represents 1, the formula (3) and Q in (4) represents an integer of 1 to 4).
-(CH₂)_q-O-CH₂― (3)
-(OCH₂CH2)_q-O-CH₂― (4)]
[0013]
Examples of such comonomers include ethylene oxide, propylene oxide, 1,3-dioxolane, 1,3,5-trioxepane, diethylene glycol formal, 1,4-butanediol formal, 1,3-dioxane, and the like. Among them, preferred comonomers are ethylene oxide, 1,3-dioxolane, and 1,4-butanediol formal. A particularly preferred comonomer is 1,3-dioxolane. Among them, the content of 2methyl-1,3-dioxolane is preferably 500 ppm by weight or less in order to suppress oxidative degradation of the polyoxymethylene copolymer obtained by polymerization. 300 ppm by weight or less and the peroxide content is 15 ppm by weight or less in terms of hydrogen peroxide, preferably 5 ppm by weight or less, and at least one sterically hindered phenol is 10 to 500 ppm by weight, preferably 50 to 50 ppm. It is preferable to use 1,3-dioxolane added with 300 ppm by weight.
[0014]
Of the sterically hindered phenols added to 1,3-dioxolane, tetrakis [methylene (3,5-t-butyl-4-hydroxyhydrocinnamate)] methane is particularly preferred.
The amount of these comonomers used is preferably 0.02 to 15 mol%, more preferably 0.1 mol% to 10 mol%, based on trioxane. In the polymerization method of the present invention, an appropriate molecular weight adjusting agent such as methylal may be used if necessary for adjusting the molecular weight of the polyoxymethylene copolymer.
[0015]
In addition, in the polyoxymethylene copolymer, unstable terminal portions are generated during polymerization due to impurities such as water having active hydrogen (hydrogen of OH) contained in trioxane or a comonomer, methyl alcohol, formic acid and the like. Therefore, in order to reduce the generation of unstable terminal portions during polymerization, it is necessary to reduce the concentration of impurities having active hydrogen such as water, methyl alcohol, formic acid and the like in trioxane and comonomers as much as possible by distillation and adsorption. Practically, it is preferable that the concentration of impurities having active hydrogen is converted to the concentration of water, and the total concentration is 20 ppm or less with respect to the total amount of trioxane and comonomer. Specifically, the conversion to the water concentration is obtained by multiplying the methyl alcohol concentration by 0.28 times in the case of methyl alcohol and by 0.20 times the formic acid concentration in the case of formic acid.
[0016]
As the polymerization catalyst in the present invention, cationically active catalysts such as Lewis acids, proton acids and esters or anhydrides thereof are used. Examples of Lewis acids include boric acid, tin, titanium, phosphorus, arsenic, and antimony halides. Specific examples of the protonic acid, its ester or anhydride include perchloric acid, trifluoromethanesulfonic acid, perchloric acid-tertiary butyl ester, acetyl perchlorate, trimethyloxonium hexafluorophosphate, and the like. Among these, boron trifluoride; boron trifluoride hydrate; and a coordination complex compound of an organic compound containing an oxygen atom or a sulfur atom and boron trifluoride are preferable. Specifically, boron trifluoride diethyl ether Preferable examples include laurate and boron trifluoride-di-n-butyl etherate. These boron trifluoride-based polymerization catalysts are used in an amount of 5 × 10 5 with respect to 1 mol of a mixture of trioxane and cyclic ether and / or cyclic formal.^-6More than mole 5 × 10^-FiveIt is preferable to use at 1 mol or less.^-6More than mole 2 × 10^-FiveMore preferably, it is used at a mole or less.
[0017]
The polymerization method of the present invention can be carried out by the same equipment and method as those of conventionally known trioxane polymerization methods. That is, both batch type and continuous type are possible, and any of solution polymerization, bulk polymerization, etc. may be used, but there is a continuous bulk polymerization method using a liquid monomer to obtain a solid bulk polymer as the polymerization proceeds. It is general and preferred industrially. In this case, an inert medium can coexist if necessary. As a polymerization apparatus used in the present invention, a reaction vessel with a stirrer that is generally used in a batch type can be used, and as a continuous type, a kneader, a twin screw type continuous extrusion mixer, a twin axis paddle type continuous mixer, etc. The self-cleaning type mixer can be used. Two or more types of polymerization apparatuses can be used in combination, or the polymerization apparatuses can be connected in series. Moreover, what is provided with the grinding | pulverization function that the solid polymer produced | generated by a polymerization reaction is obtained with a fine form is preferable.
[0018]
The copolymerization reaction is performed under normal pressure, preferably in a temperature range of 60 to 200 ° C, more preferably 60 to 120 ° C. The polymerization time is not particularly limited, but generally 10 seconds to 100 minutes or less is selected.
The crude polyoxymethylene copolymer that has been polymerized and discharged from the polymerization machine must be immediately brought into contact with a deactivator to deactivate the polymerization catalyst. The feature of the present invention resides in that the quaternary ammonium compound represented by the general formula (1) is used as a deactivator to contact the crude polyoxymethylene copolymer to deactivate the polymerization catalyst.
[0019]
The amount of the deactivator used is 0.5 to 500 times mol, preferably 1 to 200 times mol for the amount of polymerization catalyst. The quaternary ammonium compound used in the present invention is not particularly limited as long as it is represented by the general formula (1), but R in the general formula (1)¹, R², R^ThreeAnd R^FourAre preferably each independently an alkyl group having 1 to 5 carbon atoms or a hydroxyalkyl group having 2 to 4 carbon atoms.¹, R², R^ThreeAnd R^FourParticularly preferred are those wherein at least one of is a hydroxyethyl group.
[0020]
Specifically, tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetra-n-butylammonium, cetyltrimethylammonium, tetradecyltrimethylammonium, 1,6-hexamethylenebis (trimethylammonium), decamethylene-bis- (trimethyl) Ammonium), trimethyl-3-chloro-2-hydroxypropylammonium, trimethyl (2-hydroxyethyl) ammonium, triethyl (2-hydroxyethyl) ammonium, tripropyl (2-hydroxyethyl) ammonium, tri-n-butyl (2 -Hydroxyethyl) ammonium, trimethylbenzylammonium, triethylbenzylammonium, tripropylbenzylammonium, tri-n-butyl Down Jill ammonium,
[0021]
Water such as trimethylphenylammonium, triethylphenylammonium, trimethyl-2-oxyethylammonium, monomethyltrihydroxyethylammonium, monoethyltrihydroxyethylammonium, okdadecyltri (2-hydroxyethyl) ammonium, tetrakis (hydroxyethyl) ammonium Oxides: Hydrochloric acid salts such as hydrochloric acid, odorous acid and hydrofluoric acid; sulfuric acid, nitric acid, phosphoric acid, carbonic acid, boric acid, chloric acid, iodic acid, silicic acid, perchloric acid, chlorous acid, hypochlorous acid, chloro Oxoacid salts such as sulfuric acid, amidosulfuric acid, disulfuric acid and tripolyphosphoric acid; thioic acid salts such as thiosulfuric acid; formic acid, acetic acid, propionic acid, butanoic acid, isobutyric acid, pentanoic acid, caproic acid, caprylic acid, capric acid, benzoic acid Examples thereof include carboxylates such as acid and oxalic acid. Among them, hydroxide (OH^-), Sulfuric acid (HSO_Four ^-, SO_Four ^2-), Carbonic acid (HCO_Three ^-, CO_Three ^2-), Boric acid (B (OH)_Four ^-), Salts of carboxylic acids are preferred. Of the carboxylic acids, formic acid, acetic acid, and propionic acid are particularly preferred.
[0022]
These quaternary ammonium compounds may be used alone or in combination of two or more. In addition, alkylamines, alkoxyamines, hindered amines, alkali metal, alkaline earth metal hydroxides, inorganic acid salts, organic acid salts, or trivalent organic phosphorus, which are conventionally known deactivators. It can also be used in combination with a compound, boric acid compound or the like.
[0023]
The method for contacting the deactivator of the present invention with the polymerization reaction product is not particularly limited and can be obtained by thoroughly mixing the quaternary ammonium compound into the crude polyoxymethylene copolymer. In order to efficiently deactivate the polymerization catalyst, a solution obtained by dissolving a quaternary ammonium compound in water and / or an organic solvent is mixed with the polymerization reaction product, and mixed and stirred in a slurry state. Is preferred. In this case, it is convenient if the polymer discharge is a fine powder, but if the particle size is relatively large, it is preferable to pulverize immediately after discharging the polymerization. Although the grinder to be used is not particularly limited, for example, a rotary mill, a hammer mill, a jaw crusher, a feather mill, a rotary cutter mill, a turbo mill, a ball mill, or a classification impact grinder is used. The particle size distribution can be controlled by the number of revolutions of the pulverizer, the clearance, the screen mesh provided in the pulverizer, and / or a sieve provided separately if desired. The pulverized polyoxymethylene copolymer preferably satisfies the particle size distribution defined by the following (a) to (d).
[0024]
(A) Average particle diameter of 0.2 to 0.7 mm
(B) 0-30% by weight exceeds 20 mesh
(C) 30 to 100% by weight exceeding 200 mesh and less than 20 mesh
(D) 0 to 40% by weight of less than 200 mesh
(However, the total amount is 100%)
Here, the particle size distribution was measured by shaking and sieving for 10 minutes with a Ro-Tap shaker using a Tyler standard sieve. Moreover, the average particle diameter was defined as the average particle diameter at a cumulative frequency of 50% in the distribution curve (expressed in percentage) under the sieve. This particle size distribution indicates the quality of the polyoxymethylene copolymer obtained by pulverization and deactivation of the polymerization catalyst, especially the main chain degradation of the polyoxymethylene copolymer by the unstable terminal amount and the polymerization catalyst. And a post-treatment after deactivation, specifically, from the viewpoint of satisfying both the operation for decomposing and removing the unstable terminal portion and the operability in the melt-kneading treatment with a stabilizer.
[0025]
Among these, the upper limit of the average particle diameter of (a) (0.7 mm) and the upper limit of the ratio of (b) exceeding 20 mesh are important requirements mainly holding the key to the quality of the polyoxymethylene copolymer, The lower limit (0.2 mm) of the average particle diameter of (a) and the upper limit of the ratio of less than 200 mesh of (d) are mainly for the operability in the operation of decomposing and removing unstable terminal portions and the melt-kneading treatment with a stabilizer. It is an important requirement that holds the key. When the particle size distribution is biased toward larger than the particle size distribution shown here, for example, when the average particle size exceeds the upper limit or the ratio of those exceeding 20 mesh exceeds the upper limit, the obtained pulverized polyoxymethylene copolymer is obtained. The quality of the polymer, particularly the amount of unstable terminal portions, is large, the deactivation efficiency of the polymerization catalyst is lowered, and the main chain is decomposed by the polymerization catalyst that is not inactivated.
[0026]
On the other hand, when the particle size is biased to be smaller than the particle size distribution, for example, when the average particle size is less than the lower limit or less than 200 mesh exceeds the upper limit, the quality of the polyoxymethylene copolymer is satisfactory. Although it can be performed, the operability such as the melt decomposition removal treatment of the unstable end portion by the extruder or the melt kneading treatment with the stabilizer is remarkably inferior. More specifically, the penetration of the pulverized polyoxymethylene copolymer into the extruder and the strand discharge become unstable, the motor current value of the extruder changes, and the resin installed immediately after the extruder screw tip Problems such as a large fluctuation in the indicated value of the pressure gauge occur and stable extrusion becomes impossible, making it impossible to economically produce a stabilized polyoxymethylene copolymer. The polyoxymethylene copolymer discharged from the polymerization machine can be wet-pulverized by a pulverizer while being brought into contact with an aqueous solution containing quaternary ammonium or the like immediately after the contact. The polyoxymethylene copolymer discharged from the machine can be immediately dry-pulverized by a pulverizer and then contacted with an aqueous solution containing quaternary ammonium.
[0027]
The temperature and treatment time for deactivation of the polymerization catalyst of the present invention are not particularly limited. For example, a solution in which a quaternary ammonium compound is dissolved in water and / or an organic solvent is mixed with the polymerization reaction product. Then, in the method of deactivating the polymerization catalyst by mixing and stirring in the form of a slurry, the slurry is heated to promote deactivation, and at a temperature not lower than 45 ° C. and not higher than the melting point of the polyoxymethylene copolymer. It is preferably carried out at 50 ° C. or more and less than 80 ° C. without melting the polyoxymethylene copolymer. In this case, from the viewpoint of complete deactivation, a longer treatment time is preferable. However, when a quaternary ammonium compound is used as a deactivator, the deactivation rate is fast, so practically 5 minutes or more. Processed in less than 60 minutes. Further, after contacting the polymerization reaction product with the quaternary ammonium compound, the polyoxymethylene copolymer is melted at a temperature not lower than the melting point of the polyoxymethylene copolymer and not higher than 230 ° C. by an extruder or the like. It is also possible to deactivate. In this case, the practical processing time is 1 minute or more and 10 minutes or less.
[0028]
The pulverization of the polyoxymethylene copolymer and the deactivation of the polymerization catalyst are preferably performed in an inert gas atmosphere in order to suppress oxidative decomposition of the polyoxymethylene copolymer.
The deoxygenating agent of the present invention provides a polyoxymethylene copolymer having a small number of unstable terminal portions and high thermal stability because the quaternary ammonium compound represented by the general formula (1) is extremely effective as a polymerization catalyst. This is considered to be due to the rapid deactivation and the extremely high stability of the product.
[0029]
In the present invention, the copolymer in which the polymerization catalyst has been deactivated is subjected to filtration and drying, if necessary, and then subjected to decomposition and removal treatment of the unstable terminal portion. Decomposition and removal of the unstable end portion is, for example, melt-hydrolyzed in the presence of a basic substance using a single screw extruder with a vent or a twin screw extruder with a vent to remove the unstable end portion. In addition to changing to a stable end, unreacted monomer contained in the polyoxymethylene copolymer before decomposition of the unstable end portion and formaldehyde generated by melt hydrolysis of the unstable end portion are removed from the vent under reduced pressure. be able to.
[0030]
Examples of basic substances used for decomposing and removing unstable terminal portions include aliphatic amine compounds such as ammonia, triethylamine, and tributylamine. Examples of other basic substances include alkali metal or alkaline earth metal hydroxides, inorganic weak acid salts, and organic acid salts. In particular, aliphatic amine compounds such as ammonia, triethylamine, and tributylamine are preferable. The addition amount of these basic substances is 0.01 to 5% by weight with respect to the polyoxymethylene copolymer, 0.01 to 5% by weight for amine compounds, and alkali metal or alkaline earth metal hydroxides, inorganic weak acid salts, and organic acid salts. 2 to 5000 ppm is added. Moreover, water and / or organic solvents, such as methanol, can also be added with these basic substances.
[0031]
To the polyoxymethylene copolymer from which the unstable terminal portion has been decomposed and removed, other additives such as a stabilizer against decomposition caused by heat, light, oxidation, etc. and formaldehyde supplement, formic acid neutralizer, mold release agent, etc. A final stabilized polyoxymethylene copolymer product is obtained by blending a reinforcing agent, a conductive material, a thermoplastic resin, a thermoplastic elastomer, a pigment, and the like, and melt-kneading with an extruder or the like. According to the method of the present invention, the unstable end portion of the polyoxymethylene copolymer after the deactivation of the polymerization catalyst is very small, and the polymerization catalyst is completely deactivated. Therefore, since the load of the decomposition and removal treatment of the unstable terminal portion is greatly reduced, a sufficiently stable polyoxymethylene copolymer can be obtained by a simple finishing treatment.
[0032]
In addition, since there are very few unstable terminal portions and the polymerization catalyst is completely deactivated, various stabilizers without substantially undergoing a terminal stabilization treatment step by decomposing and removing unstable terminal portions, It is also possible to produce a final stabilized polyoxymethylene copolymer by melting and kneading and extruding together with an additive and a reinforcing agent so as to decompose and remove the unstable terminal portion remaining in a small amount. This method makes it possible to obtain a final polyoxymethylene copolymer that is practically sufficiently stable, even though it has not undergone a terminal stabilization treatment step that has been essential in the past, and is very economically advantageous. It is a simple method.
[0033]
Further, as described above, the polyoxymethylene copolymer composition containing the quaternary ammonium compound obtained by the deactivation method of the polymerization catalyst of the present invention has very few unstable terminal portions and the polymerization catalyst is completely Has been deactivated. Accordingly, the present polyoxymethylene copolymer composition is very stable, and does not generate formaldehyde due to decomposition or decrease in molecular weight due to polymer main chain cleavage during long-term storage or transportation. Therefore, this polyoxymethylene copolymer composition can be suitably used as a raw material for a compound. Further, the present polyoxymethylene copolymer composition includes an antioxidant, a formaldehyde supplement, a formic acid neutralizer, an ultraviolet absorber, a light stabilizer, a release agent, a reinforcing agent, a conductive material, a thermoplastic resin, and a thermoplastic elastomer. A polyoxymethylene copolymer composition to which at least one compounding agent such as a pigment is added can also be suitably used as a raw material for the compound.
[0034]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. In addition, the term in an Example and a comparative example and a measuring method are as follows.
<Contents of 2 methyl-1,3-dioxolane and methyl alcohol>
The measurement was performed with a flame ion detector using a gas chromatography equipped with a glass column packed with Gasclopack 55 (manufactured by GL Sciences).
<Concentration of water>
Measured with a Karl Fischer moisture meter.
<Concentration of formic acid>
Measured by neutralization titration with potassium hydroxide.
[0035]
<Peroxide content in 1,3-dioxolane (in hydrogen peroxide conversion)>
Into the flask are added 40 ml of isopropyl alcohol, 10 ml of a saturated sodium iodide solution (NaI dissolved in isopropyl alcohol), 2 ml of acetic acid and 25 g of 1,3-dioxolane, and the mixture is refluxed at 100 ° C. for about 5 minutes. Immediately thereafter, titrate with 0.01N sodium thiosulfate until the color of the mixture in the flask changes from yellow to colorless (the titration amount at this time is Aml). In addition, as the empty titration, the same operation as described above is performed without using 1,3-dioxolane (the titration amount at this time is Bml).
[0036]
The amount of peroxide in 1,3-dioxolane is determined by the following formula as hydrogen peroxide.
[Formula 1]

[0037]
<Particle size distribution>
The measurement was carried out using a Tyler standard sieve and shaking and sieving for 10 minutes on a Ro-Tap shaker. Moreover, the average particle diameter was defined as the average particle diameter at a cumulative frequency of 50% in the distribution curve (expressed in percentage) under the sieve.
<MI (melt index: g / 10 min)>
The melt index (g / 10 min) was measured under the conditions of 190 ° C. and 2169 g using ASTM-D-1238 using a MELT INDEXER manufactured by Toyo Seiki.
[0038]
<Amount of unstable end (ppm)>
Under a nitrogen stream, formaldehyde generated from the oxymethylene copolymer was absorbed into water under conditions of 190 ° C. and 30 minutes, and then determined and measured. Under this condition, most of the formaldehyde generated is unstable end of the oxymethylene copolymer [-(OCH₂) N-OH group].
<Thermal stability of the stabilized polyoxymethylene copolymer (ppm / min)>
Under a nitrogen stream, formaldehyde generated from the oxymethylene copolymer is absorbed into water at 230 ° C. for 90 minutes, and then determined and measured. The measured total formaldehyde amount was divided by 90 minutes to calculate the average formaldehyde generation rate per minute (ppm / min), which was regarded as the thermal stability of the stabilized polyoxymethylene copolymer.
[0039]
Examples 1 to 20
A twin-screw paddle type continuous mixer with a jacket through which a heat medium can pass is adjusted to 80 ° C., and 3 kg / Hr of trioxane and 1,3-dioxolane 111 g / Hr as a comonomer (0. 045 mol) and 1.8 g / Hr of methylal as a molecular weight regulator (0.7 × 10 4 per 1 mol of trioxane).^-3Mol) was added continuously. 1,3-dioxolane has a 2-methyl-1,3-dioxolane content of 105 ppm by weight (measured by gas chromatography), a peroxide content of 2.3 ppm by weight in terms of hydrogen peroxide, and a sterically hindered phenol. As an example, tetrakis [methylene (3,5-di-t-butyl-4-hydroxyhydrocinnamate)] methane (Ciba Geigy's Irganox 1010: trade name) to which 200 ppm by weight was added was used.
[0040]
Further, the total concentration of water, formic acid and methyl alcohol in the mixture of trioxane and 1,3-dioxolane was 12 ppm in terms of water. As a polymerization catalyst, boron trifluoride di-n-butyl etherate is 1.5 × 10 5 per mole of trioxane.^-FivePolymerization was carried out by continuously adding 9.9 g / Hr of cyclohexane solution of 1% by weight of boron trifluoride di-n-butyl etherate so as to have a molar ratio. The polyoxymethylene copolymer discharged from the mixer was immediately brought into contact with an aqueous solution containing a quaternary ammonium compound as shown in Table 1 under a nitrogen atmosphere, while free milling machine M- manufactured by Nara Machinery Co., Ltd. The slurry containing the powdery polyoxymethylene copolymer and the quaternary ammonium compound discharged from the pulverizer was introduced into a storage tank and was deactivated. The temperature of the storage tank is 50 ° C., and the average residence time in the storage tank is 30 minutes. After deactivation, it was filtered with a centrifugal separator and dried at 120 ° C. under nitrogen to obtain a final polyoxymethylene copolymer. The particle size distribution of the final polyoxymethylene copolymer was as follows.
(A) Average particle size 0.38 mm
(B) 4.2% by weight exceeds 20 mesh
(C) 85.4% by weight is more than 200 mesh and less than 20 mesh
(D) Less than 200 mesh is 10.4% by weight
Table 1 shows the evaluation results of the final polyoxymethylene copolymer obtained.
[0041]
Examples 21 to 24
The polyoxymethylene copolymer discharged from the mixer is immediately dry-pulverized with a free crusher M-2 manufactured by Nara Machinery Co., Ltd. in a nitrogen atmosphere. The final polyoxymethylene was prepared in exactly the same manner as in Examples 1 to 13, except that the oxymethylene copolymer was introduced into a storage tank of an aqueous solution containing a quaternary ammonium compound shown in Table 2 and deactivated. A copolymer was obtained. The particle size distribution of the final polyoxymethylene copolymer was as follows.
(A) Average particle size 0.37 mm
(B) 3.8% by weight exceeds 20 mesh
(C) More than 200 mesh and less than 20 mesh 84.7% by weight
(D) Less than 200 mesh is 11.5% by weight
Table 2 shows the evaluation results of the final polyoxymethylene copolymer obtained.
[0042]
Examples 25-28
Ethylene oxide as a comonomer is 66 g / Hr (0.045 mol with respect to 1 mol of trioxane), and as a polymerization catalyst, boron trifluoride di-n-butyl etherate is 4.5 × 10 with respect to 1 mol of trioxane.^-FiveExactly the same operation as in Examples 1 to 13, except that 29.7 g / Hr of cyclohexane solution of 1% by weight of boron trifluoride di-n-butyl etherate was continuously added to carry out the polymerization to a molar ratio. To obtain a final polyoxymethylene copolymer. The total concentration of water, formic acid and methyl alcohol in the mixture of trioxane and ethylene oxide was 10 ppm in terms of water. The particle size distribution of the final polyoxymethylene copolymer was as follows.
(A) Average particle size of 0.35 mm
(B) More than 20 mesh is 3.5% by weight
(C) 84% by weight exceeding 200 mesh and less than 20 mesh
(D) Less than 200 mesh is 12.5% by weight
Table 3 shows the evaluation results of the final polyoxymethylene copolymer obtained.
[0043]
Example 29
The powdered polyoxymethylene copolymer obtained in Example 1 was subjected to triethylene glycol-bis [3- (3-t- (Butyl-5-methyl-4-hydroxyphenyl) propionate] (Irganox 245: trade name, manufactured by Ciba Geigy Co., Ltd.) 0.3 wt%, calcium stearate 0.15 wt%, and nylon 66 0.05 wt% Then, a pelletized stabilized polyoxymethylene copolymer was obtained by melt kneading with a vented 30 mm single screw extruder. The melting temperature is 200 ° C., the average residence time of the extruder is 3 minutes, and the vent vacuum is 30 Torr. Table 4 shows the evaluation results of the obtained pellet-shaped stabilized polyoxymethylene copolymer. In addition, the biting property of the granular polyoxymethylene copolymer and the strand discharge are stable during melt kneading in a 30 mm single screw extruder, and the motor current value fluctuates immediately after the extruder screw tip. Stable extrusion was possible with almost no change in the indicated value of the installed resin pressure gauge.
[0044]
[Comparative Examples 1-3]
The final polyoxymethylene copolymer was obtained in the same manner as in Examples 1 to 13, except that the quenching agent shown in Table 5 was used instead of the quaternary ammonium compound. Table 5 shows the evaluation results of the final polyoxymethylene copolymer obtained. If a quaternary ammonium compound is not used as a deactivator, the deactivation is insufficient, the polyoxysimethylene copolymer is decomposed, MI is increased, and the amount of unstable terminals is increased. I understand.
[0045]
[Comparative Example 4]
The granular polyoxymethylene copolymer obtained in Comparative Example 1 was supplied to a twin screw extruder with a 30 mm vent to decompose and remove unstable ends. The rotation speed of the extruder was 100 rpm, and the temperature was 200 ° C. An aqueous triethylamine solution was used as a basic substance used for decomposing and removing unstable terminals, and the amount added was 3 parts by weight (0.5 parts by weight of triethylamine, 2. 5 parts by weight) and continuously added to the melted polyoxymethylene copolymer of the extruder. The polyoxymethylene copolymer with the unstable terminal decomposed was devolatilized under a condition of a vent vacuum of 30 Torr, extruded as a strand from the extruder die, and pelletized.
[0046]
To this pellet, 0.3% by weight of triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] (Irganox 245: trade name, manufactured by Ciba Geigy) as a stabilizer, 0.15% by weight of calcium stearate and 0.05% by weight of nylon 66 were mixed and melt-kneaded with a vented 30 mm single screw extruder to obtain a pelletized stabilized polyoxymethylene copolymer. The melting temperature is 200 ° C., and the vent vacuum is 30 Torr. Table 6 shows the evaluation results of the obtained pellet-shaped stabilized polyoxymethylene copolymer. Compared to Example 22, the thermal stability of the stabilized polyoxymethylene copolymer is poor despite the decomposition and removal of the unstable terminal portion. Moreover, since MI slightly increases compared with before stabilization, it can be seen that the polyoxymethylene copolymer is decomposed. According to the production method of the present invention, it is possible to obtain a polyoxymethylene copolymer having excellent thermal stability without performing decomposition and removal of unstable parts.
[0047]
[Table 1]

[0048]
[Table 2]

[0049]
[Table 3]

[0050]
【The invention's effect】
The polyoxymethylene copolymer obtained by the method of the present invention provides a copolymer with less unstable terminal portions than the conventional method, and the polymerization catalyst is completely deactivated. Since the catalyst-induced polymer decomposition is not caused, the post-treatment process after the deactivation treatment can be simplified, and the thermal stability of the final product is very high while being very economical. Moreover, the polyoxymethylene copolymer composition containing the quaternary ammonium compound obtained by this invention is suitable as a raw material for compounds.

Claims (20)

In a method for producing a polyoxymethylene copolymer by copolymerizing trioxane as a main monomer and at least one cyclic ether and / or cyclic formal as a comonomer using at least one cationically active catalyst, A method for producing a polyoxymethylene copolymer comprising, after polymerization, contacting at least one quaternary ammonium compound represented by the following general formula (1) with the copolymer to deactivate the polymerization catalyst. The deactivation of the polymerization catalyst is performed while pulverizing the polyoxymethylene copolymer discharged from the polymerization machine into a granular material satisfying the particle size distribution defined by (a) to (d) below. A method for producing a polyoxymethylene copolymer.
[R ¹ R ² R ³ R ⁴ N ⁺ ] nX ⁻ⁿ (1)
(In the formula, R ¹ , R ² , R ³ , and R ⁴ each independently represent an unsubstituted alkyl group or substituted alkyl group having 1 to 30 carbon atoms; an aryl group having 6 to 20 carbon atoms; An aralkyl group having 30 unsubstituted alkyl groups or substituted alkyl groups substituted with at least one aryl group having 6 to 20 carbon atoms; or an aryl group having 6 to 20 carbon atoms having at least one carbon atom having 1 to 30 carbon atoms Represents an unsubstituted alkyl group or an alkylaryl group substituted with a substituted alkyl group, wherein the unsubstituted alkyl group or substituted alkyl group is linear, branched, or cyclic. An aldehyde group, a carboxyl group, an amino group, or an amide group, and the above-mentioned unsubstituted alkyl group, aryl group, aralkyl group, and alkylaryl group have a hydrogen atom as a halogen atom. N represents an integer of 1 to 3. X is a hydroxyl group, a carboxylic acid having 1 to 20 carbon atoms, a hydrogen acid, an oxo acid, an inorganic thioacid, or an organic thio having 1 to 20 carbon atoms. Represents the acid residue of the acid.)
(A) Average particle diameter of 0.2 to 0.7 mm
(B) 0-30% by weight exceeds 20 mesh
(C) 30 to 100% by weight exceeding 200 mesh and less than 20 mesh
(D) 0 to 40% by weight of less than 200 mesh
(However, the total amount is 100%)   The method for producing a polyoxymethylene copolymer according to claim 1, wherein X in the general formula (1) is a hydroxyl group or an acid residue of carbonic acid, boric acid, sulfuric acid or carboxylic acid.   The method for producing a polyoxymethylene copolymer according to claim 2, wherein the carboxylic acid is at least one selected from the group consisting of formic acid, acetic acid and propionic acid. R ¹ , R ² , R ³ and R ⁴ in the general formula (1) are each independently an alkyl group having 1 to 5 carbon atoms or a hydroxyalkyl group having 2 to 4 carbon atoms. Item 4. A method for producing a polyoxymethylene copolymer according to any one of Items 1 to 3. The method for producing a polyoxymethylene copolymer according to claim 4, wherein at least one of R ¹ , R ² , R ³ and R ⁴ in the general formula (1) is a hydroxyethyl group.   The deactivation of the polymerization catalyst is carried out by bringing the quaternary ammonium compound into contact with the polyoxymethylene copolymer as a solution of water and / or an organic solvent. A process for producing a polyoxymethylene copolymer. Cation-active catalyst is boron trifluoride, boron trifluoride hydrate, and to any one of claims 1 to 6, characterized in that at least one selected from the group comprising oxygen atom or a sulfur atom The manufacturing method of the polyoxymethylene copolymer of description. Cation-active catalyst concentration, relative to mixture 1 mole of trioxane and cyclic ether and / or cyclic formal, 5 × 10 ^-6 mol or more, according to claim 7, wherein a is 5 × 10 ^-5 mol or less A method for producing a polyoxymethylene copolymer. Cation-active catalyst concentration, relative to mixture 1 mole of trioxane and cyclic ether and / or cyclic formal, 1 × 10 ^-6 mol, 2 × claims 7-8, characterized in that at most 10 ^-5 mol or less A method for producing a polyoxymethylene copolymer according to any one of the above. The mixture of trioxane and cyclic ether and / or cyclic formal has a total concentration of water, formic acid, and methyl alcohol in the mixture of 20 ppm or less in terms of water , according to any one of claims 1 to 9. The manufacturing method of the polyoxymethylene copolymer of description. The method for producing a polyoxymethylene copolymer according to any one of claims 1 to 10, wherein the cyclic ether and / or the cyclic formal is 1,3-dioxolane. 1,3-dioxolane has a content of 2 methyl-1,3-dioxolane in the 1,3-dioxolane of 500 ppm by weight or less, and a peroxide content of 15 ppm by weight or less in terms of hydrogen peroxide, The method for producing a polyoxymethylene copolymer according to claim 11, further comprising 1,3-dioxolane having a content of at least one sterically hindered phenol of 10 to 500 ppm by weight. The method for producing a polyoxymethylene copolymer according to any one of claims 1 to 12, wherein the polymerization catalyst is deactivated under heat treatment. The method for producing a polyoxymethylene copolymer according to claim 13 , wherein the heat treatment is performed at a treatment temperature of 45 ° C or higher and below the melting point of the polyoxymethylene copolymer. The method for producing a polyoxymethylene copolymer according to claim 14 , wherein the heat treatment is performed at a treatment temperature of 50 ° C or higher and lower than 80 ° C. Deactivation of the polymerization catalyst, any of claims 1 to 15, characterized in line dividing it in a slurry state was charged quaternary ammonium water compounds and / or solution to the polyoxymethylene copolymer of an organic solvent The manufacturing method of the polyoxymethylene copolymer of description. The method for producing a polyoxymethylene copolymer according to claim 13 , wherein the heat treatment is performed at a treatment temperature of not less than the melting point of the polyoxymethylene copolymer and not more than 230 ° C and a treatment time of not less than 1 minute and not more than 10 minutes. . Deactivation of the polymerization catalyst, polyoxymethylene copolymer according to any one of claims 1 to 17, characterized in that is carried out using 0.5 to 500 moles of a polymerization catalyst a quaternary ammonium compound Manufacturing method. The method for producing a polyoxymethylene copolymer according to claim 18, wherein the deactivation of the polymerization catalyst is carried out using a quaternary ammonium compound in an amount of 1 to 200 times the molar amount of the polymerization catalyst. The oxymethylene copolymers deactivation of the catalyst was made by the method of any one of claims 1 to 19, stabilized oxymethylene copolymer, which comprises melt-kneading process with a stabilizer Manufacturing method.