JP4601794B2 - Aqueous emulsion and method for producing the same - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、優れた耐水性および高温粘度安定性および低温放置安定性を有する水性エマルジョンおよび重合安定性に優れた水性エマルジョンの製造方法に関する。
【０００２】
【従来の技術】
従来、ポリビニルアルコール（以下、ＰＶＡと略記することがある）はエチレン性不飽和単量体、特に酢酸ビニルに代表されるビニルエステル系単量体の乳化重合用保護コロイドとして広く用いられており、これを保護コロイドとして用いて乳化重合して得られるビニルエステル系水性エマルジョンは紙用、木工用およびプラスチック用などの各種接着剤、含浸紙用および不織製品用などの各種バインダー、混和剤、打継ぎ材、塗料、紙加工および繊維加工などの分野で広く用いられている。
このような水性エマルジョンは、ＰＶＡ系重合体のけん化度を調整することにより、一般的に粘度が低く、ニュートニアン流動に近い粘性を有し、比較的耐水性の良好なものから、一般的に粘度が高く、比較的エマルジョン粘度の温度依存性が小さいものが得られることから、種々の用途に賞用されてきた。
しかしながら、該水性エマルジョンのあるものは、流動性（高速塗工性）が不足している、また耐水性が悪い、エマルジョン粘度の温度依存性が大きい、低温時のエマルジョン粘度の上昇が著しいなどの欠点を有しており、これらの性質は乳化重合に用いたＰＶＡ系重合体に依るところが大であることが知られている。
【０００３】
すなわち、乳化重合用分散剤としてのＰＶＡ系重合体は、一般的には鹸化度９８モル％程度のいわゆる“完全鹸化ＰＶＡ”と鹸化度８８モル％程度の“部分鹸化ＰＶＡ”があり、前者を使用した場合、比較的耐水性および流動性（高速塗工性）は良好なものの、低温放置時のエマルジョン粘度の上昇が著しく、ゲル化し易いという欠点があり、他方、後者のＰＶＡ系重合体を使用した場合、エマルジョンの低温時の粘度上昇やゲル化性向は改善されるものの耐水性に劣る欠点を有している。このような欠点を改良するために、両者のＰＶＡ系重合体の併用、両者の中間的な鹸化度のＰＶＡ系重合体の使用等が行われているが、耐水性、エマルジョン粘度の低温放置安定性を同時に満足することはできなかった。そこで、エチレン単位を含有するビニルアルコール系重合体が提案（特開平８−８１６６６号公報、特開平６−８０７０９号公報、特開平１０−２２６７７４号公報等）され、耐水性と低温放置安定性が大幅に改善された。しかしながら、このエマルジョンでも高温粘度安定性が十分満足すべきものではない、すなわち温度依存性があり、高温放置安定性も満足すべきものとはいえない。
【０００４】
【発明が解決しようとする課題】
本発明は、これらの従来技術の欠点を解消したものであり、高温粘度安定性の優れた（温度依存性が小さく、高温放置安定性に優れた）、しかも耐水性のより改善された、さらにまた低温放置安定性にも優れた水性エマルジョンを提供すること、および重合安定性に優れた水性エマルジョンの製造方法を提供することを目的とするものである。
【０００５】
【課題を解決するための手段】
すなわち、本発明は、分子内にエチレン単位を１〜１５モル％含有する、けん化度９５モル％以上のビニルアルコール系重合体を分散剤とし、ビニルエステル系単量体の重合体を分散質とする水性エマルジョンであって、該エマルジョンを製膜して得た皮膜を２０℃の水中に２４時間浸漬した時、溶出率が１．５％以下および吸水率が３０％以下を示し、かつ２０℃におけるエマルジョン粘度と、６０℃における粘度の比、Ｔ６０℃／Ｔ２０℃が２以下である水性エマルジョンである。ここで溶出率、吸水率とは後述する方法で測定される値であるが、溶出率が１．５％以下、吸水率が３０％以下を示すことは耐水性に優れていることを意味している。溶出率は１．１％以下であることがより好適であり、また吸水率は２７％以下であることがより好適である。また２０℃におけるエマルジョン粘度Ｔ２０℃と６０℃における粘度Ｔ６０℃の比、Ｔ６０℃／Ｔ２０℃とは後述する方法で測定される値であるが、 Ｔ６０℃／Ｔ２０℃が２以下を示すことは、エチレン含有ＰＶＡを分散剤として使用したビニルエステル系重合体エマルジョンは６０℃近辺で高い粘度を示すが、本発明では６０℃近辺で粘度の上昇を抑えることができること、すなわち温度依存性が小さいことを意味している。６０℃近辺で粘度の上昇を抑えることができるということは、エマルジョンの重合中にエマルジョンの高温保存、運搬、使用中の粘度の上昇を抑えることができることになり、作業性、取り扱い性は格段と向上することになる。
また、本発明においては、２０℃で調整し、１週間放置後のエマルジョン粘度Ｈ２０℃と６０℃で調整し、１週間放置後のエマルジョン粘度Ｈ６０℃の比、 Ｈ６０℃／Ｈ２０℃が、２．５以下のエマルジョンがより好ましい態様である。ここでＨ６０℃／Ｈ２０℃とは後述する方法で測定される値であるが、 Ｈ６０℃／Ｈ２０℃が２．５以下を示すということは、高温放置安定性に優れていることを意味し、１週間程度６０℃の高温下におかれても、粘度の上昇を抑えることができ、作業性、取り扱い性が損なわれることがない。
【０００６】
本発明の水性エマルジョンは、（１）分散剤として分子内にエチレン単位を１〜１５モル％含有する、けん化度９５モル％以上のビニルアルコール系重合体を用い、（２）過酸化水素、過硫酸アンモニウムおよび過硫酸カリウムから選ばれる少なくとも一種の重合開始剤をビニルエステル系単量体に対してモル比で０．００１〜０．０１使用し、さらに（３）重合初期にビニルエステル系単量体を単量体全量の５〜２０重量％仕込み、かつ上記重合開始剤を初期仕込みのビニルエステル系単量体に対してモル比で０．００５〜０．０２５一括添加する重合操作を行うことによって得られる。
【０００７】
【発明の実施の形態】
本発明の水性エマルジョンの分散剤として用いられる分子内にエチレン単位を１〜１５モル％含有し、けん化度９５モル％以上のＰＶＡ系重合体は、ビニルエステルとエチレンとの共重合体をけん化することにより得ることができる。
【０００８】
ここで、ビニルエステルとしては、蟻酸ビニル、酢酸ビニル、プロピオン酸ビニル、ピバリン酸ビニルなどが挙げられるが、酢酸ビニルが経済的にみて好ましい。
【０００９】
エチレン単位の含有量としては、１〜１５モル％であることが必要であり、好ましくは３〜１３％、さらに好ましくは５〜１２％である。エチレン単位の含有量が１モル％未満の場合には、後述する比較例１からも明らかなように、上述の耐水性（溶出率と吸水率）と高温粘度安定性を同時に満足する水性エマルジョンが得られないし、また低温放置安定性も悪い。また、１５モル％を越える場合には、水溶性が低下し、安定な水性エマルジョンが得られない懸念が生じる。
【００１０】
また、該分散剤は本発明の目的を損なわない範囲で共重合可能なエチレン性不飽和単量体を共重合したものでも良い。このようなエチレン性不飽和単量体としては、例えば、アクリル酸、メタクリル酸、フマル酸、（無水）マレイン酸、イタコン酸、アクリロニトリル、メタクリロニトリル、アクリルアミド、メタクリルアミド、トリメチル−（３−アクリルアミド−３−ジメチルプロピル）−アンモニウムクロリド、アクリルアミド−２−メチルプロパンスルホン酸およびそのナトリウム塩、エチルビニルエーテル、ブチルビニルエーテル、Ｎ−ビニルピロリドン、塩化ビニル、臭化ビニル、フッ化ビニル、塩化ビニリデン、フッ化ビニリデン、テトラフルオロエチレン、ビニルスルホン酸ナトリウム、アリルスルホン酸ナトリウムなどが挙げられる。
また、チオール酢酸、メルカプトプロピオン酸などのチオール化合物の存在下で、酢酸ビニルなどのビニルエステル系単量体を、エチレンと共重合し、それをけん化することによって得られる末端にメルカプト基またはカルボキシル基を有する変性物も用いることができる。
【００１１】
本発明の水性エマルジョンの分散剤として用いるエチレン変性ＰＶＡ系重合体のけん化度は、９５モル％以上であることが必要であり、より好ましくは、９６モル％以上、さらに好ましくは９７モル％以上である。けん化度が９５モル％未満の場合には、耐水性に優れた水性エマルジョンが得られない。本発明の目的とする水性エマルジョンを得るためには、該ＰＶＡ系重合体の重合度（粘度平均重合度）は、１００〜３０００が好ましく、３００〜３０００がより好ましい。
【００１２】
本発明の水性エマルジョンにおける分散質を構成するビニルエステル系単量体としては、蟻酸ビニル、酢酸ビニル、プロピオン酸ビニル、ピバリン酸ビニルなどが挙げられるが、酢酸ビニルが経済的にみて好ましい。
【００１３】
本発明では、単量体として、ビニルエステル系単量体が主に用いられるが、ビニルエステル系単量体とエチレンを併用することも好適な態様である。これらの単量体を乳化重合することにより、ビニルエステル系重合体またはビニルエステル−エチレン系共重合体を分散質とする水性エマルジョンが得られる。
【００１４】
また、本発明の目的を損なわない範囲で、エチレン性不飽和単量体およびジエン系単量体を共重合しても構わない。このような単量体としては、プロピレン、イソブチレンなどのオレフィン、塩化ビニル、フッ化ビニル、ビニリデンクロリド、ビニリデンフルオリドなどのハロゲン化オレフィン、アクリル酸、アクリル酸メチル、アクリル酸エチル、アクリル酸ブチル、アクリル酸２−エチルヘキシル、アクリル酸ドデシル、アクリル酸２−ヒドロキシエチルなどのアクリル酸およびそのエステル、メタクリル酸、メタクリル酸メチル、メタクリル酸エチル、メタクリル酸ブチル、メタクリル酸２−エチルヘキシル、メタクリル酸ドデシル、メタクリル酸２−ヒドロキシエチルなどのメタクリル酸およびそのエステル、アクリル酸ジメチルアミノエチル、メタクリル酸ジメチルアミノエチルおよびこれらの四級化物、さらには、アクリルアミド、メタクリルアミド、Ｎ−メチロールアクリルアミド、Ｎ，Ｎ−ジメチルアクリルアミド、アクリルアミド−２−メチルプロパンスルホン酸およびそのナトリウム塩などのアクリルアミド系単量体、スチレン、α−メチルスチレン、ｐ−スチレンスルホン酸およびナトリウム、カリウム塩などのスチレン系単量体、その他Ｎ−ビニルピロリドンなど、また、ブタジエン、イソプレン、クロロプレンなどのジエン系単量体が挙げられる。
【００１５】
本発明の水性エマルジョンは、前述したとおりビニルエステル系単量体を乳化重合するに際し、（１）分散剤として分子内にエチレン単位を１〜１５モル％含有する、けん化度９５モル％以上のビニルアルコール系重合体を用い、（２）過酸化水素、過硫酸アンモニウムおよび過硫酸カリウムから選ばれる少なくとも一種の重合開始剤をビニルエステル系単量体に対してモル比で０．００１〜０．０１使用し、さらに（３）重合初期にビニルエステル系単量体を単量体全量の５〜２０重量％仕込み、かつ上記重合開始剤を初期仕込みのビニルエステル系単量体に対してモル比で０．００５〜０．０２５一括添加する重合操作を行うことにより得られる。
【００１６】
本発明の水性エマルジョンを製造するにあたっては、過酸化水素、過硫酸アンモニウムおよび過硫酸カリウムから選ばれる少なくとも一種の重合開始剤を用いることは重要であり、この中でも、特に過酸化水素が好ましい。また、本発明においては、重合開始剤を使用する全ビニルエステル系単量体に対してモル比で０．００１〜０．０１使用して乳化重合することも極めて重要であり、好ましくは０．００２〜０．００７であり、さらに好ましくは０．００２５〜０．００５である。理由は明確ではないが、上記量の開始剤を用いることで、耐水性のより改善された、しかも高温粘度安定性に優れ、さらに低温放置安定性にも優れた水性エマルジョンが得られる。特開平８−８１６６６号公報の実施例１に記載されているように、重合開始剤が０．００１未満の場合、本発明の目的とする水性エマルジョンが得られない。このことは後述する比較例５から明らかである。また、重合開始剤が０．０１を越えると、本発明の目的とする耐水性の優れた、しかも高温粘度安定性に優れたエマルジョンが得られない。このことは後述する比較例３から明らかである。
【００１７】
また、前記重合開始剤は還元剤と併用し、レドックス系で用いられる場合もある。その場合、通常、過酸化水素は酒石酸、Ｌ−アスコルビン酸、ロンガリットなどとともに用いられる。また、過硫酸アンモニウム、過硫酸カリウムは亜硫酸水素ナトリウム、炭酸水素ナトリウムなどとともに用いられる。還元剤の使用量も特に限定されないが、通常、重合開始剤に対して、０．０５〜３当量用い、好ましくは０．１〜２当量、より好ましくは０．３〜１．５当量用いる。
【００１８】
前記重合開始剤の添加方法としては重合開始初期に重合開始剤を一括添加する方法を用いる。すなわち、ビニルエステル系単量体を、単量体全量の５〜２０％を重合初期に仕込み、重合開始剤を初期仕込みの単量体に対してモル比で０．００５〜０．０２５一括添加することが必要となり、好ましくは０．００８〜０．０２０であり、より好ましくは０．０１〜０．０１８である。
特開平８−８１６６６号の実施例１に記載されているように、重合開始剤の初期仕込量が０．００５未満の場合、本発明の目的とする水性エマルジョンが得られない。このことは後述する比較例５から明らかである。
また特開平６−８０７０９号の実施例１に記載されている様に重合開始剤の初期仕込量が０．０２５をこえる場合も本発明の目的とする耐水性および高温粘度安定性に優れたエマルジョンは得られない。このことは後述する比較例６から明らかである。
初期重合は重合開始剤を上記したとおり所定の量一括添加することにより上記したとおりの優れた効果が奏せられるが、さらに重合安定性も良好となり、重合後のろ過残量も少なくなる。
初期重合は、分散剤の水溶液に単量体、重合開始剤を加え、重合温度５０〜７０℃、好適には５５〜６５℃、重合時間１５〜６０分、好適には２０〜５０分の条件下で行われる。初期重合において単量体は一括添加することが好適である。
【００１９】
分散剤として使用するエチレン変性ＰＶＡ系重合体の使用量については特に制限はないが、単量体１００重量部に対して好ましくは３〜２０重量部、より好ましくは５〜１５重量部の範囲である。該使用量が３重量部未満および２０重量部をこえる場合には、重合安定性が低下したり、放置安定性が低下することがある。
【００２０】
初期重合はビニルエステルの残存濃度（生成ポリマーに対する重量％）が１０％以下、好適には５％以下、さらに好適には１％以下になった時点で終了する。初期重合後は、後期重合に入る。後期重合では重合開始剤は一括添加が好適であるが、連続添加あるいは断続添加でも良い。単量体は連続添加が好適であるが、一括添加（ショット添加）でも良い。また後期重合では、重合温度は初期重合温度よりも５〜３０℃高くすることが好適であり、５５〜１００℃、好適には６０〜９５℃、さらに好適には７０〜９０℃の範囲内で行われる。
【００２１】
重合圧力は、初期重合、後期重合とも常圧で良いが、必要に応じ加圧する必要がある。特にビニルエステルと他の単量体、例えばエチレンとの共重合体エマルジョンを製造する場合は、圧力下で行うことが必要である。
【００２２】
上記したとおりの方法を採用することにより、特に分散剤としてエチレン単位を１〜１５モル％含有する、けん化度９５モル％以上の変性ＰＶＡを使用すること、重合開始剤をビニルエステル系単量体に対してモル比で０．００１〜０．０１使用し、さらに重合初期にビニルエステル系単量体を単量体全量の５〜２０重量％仕込み、かつ上記重合開始剤を初期仕込みの単量体に対してモル比で０．００５〜０．０２５一括添加するすることにより、重合安定性が優れ、さらに耐水性の一段と改善された、しかも高温粘度安定性に優れた（温度依存性が小さく、高温放置安定性に優れた）水性エマルジョンが得られること、さらに得られた水性エマルジョンは低温放置安定性にも優れていることは驚くべきことであり、従来の特開平８−８１６６６号、特開平６−８０７０９号、特開平１０−２２６７７４号に記載された発明からはとうてい予測できないことである。特に本発明において重合開始剤量を特定量に規定したこと、重合初期において重合開始剤を一括添加するとともにその使用量を規定したことにより、本発明の目的とする優れた水性エマルジョンが得られるようになったことは驚くべきことであり、その工業的意味は大きい。
このようにして得られた本発明の水性エマルジョンは耐水性がより改善されているため、耐水性の要求される各種用途に好適に使用され、また本発明の水性エマルジョンは、温度依存性が小さく、特に６０℃に温度を上げたときエチレン変性PVAを分散安定剤とするビニルエステル系重合体エマルジョンでは通常粘度が大きく上昇するが、本発明の水性エマルジョンはその上昇が少ないため、エマルジョン重合時の粘度上昇を防ぐことができるし、６０℃前後の高温下での保存、運搬、使用においても粘度上昇を防ぐことができるので、作業性、取り扱い性は極めて優れている。
【００２３】
本発明で得られる水性エマルジョンは、上記の方法で得られる水性エマルジョンをそのまま用いることができるが、必要があれば、本発明の効果を損なわない範囲で、従来公知の各種エマルジョンを添加して用いることができる。
なお、本発明の水性エマルジョンにおける分散剤としては、前述のけん化度９５モル％以上のＰＶＡ系重合体あるいはけん化度９５モル％以上のエチレン変性ＰＶＡ系重合体が用いられるが、必要に応じて、従来公知のアニオン性、ノニオン性あるいはカチオン性の界面活性剤や、ＰＶＡ系重合体、ヒドロキシエチルセルロースなどを併用することもできる。
【００２４】
本発明の水性エマルジョンは、上記のような優れた特性を有していることから、紙管、製袋、合紙、段ボール用等の紙、パルプなどの紙加工用接着剤、フラッシュパネル、集成材、ツキ板、合板加工用、合板二次加工用（練り合わせ）、一般木工等の木工用接着剤および各種プラスチック用の接着剤、含浸紙用、不織製品用のバインダー、混和剤、打継ぎ材、塗料、紙加工および繊維加工などの分野で好適に用いられる。
【００２５】
【実施例】
次に、実施例および比較例により本発明をさらに詳細に説明する。なお、以下の実施例および比較例において「部」および「％」は、特に断らない限り重量基準を意味する。また、得られたエマルジョンの耐水性、放置安定性を、下記の要領で評価した。
【００２６】
（エマルジョンの評価）
（１）皮膜の耐水性
得られた水性エマルジョンを２０℃、６５％ＲＨの条件下に、ＰＥＴ上に流延し、７日間乾燥させて５００μｍの乾燥皮膜を得た。この皮膜を直径２．５ｃｍに打ち抜き、それを試料として２０℃水に２４時間浸漬した場合の、皮膜の吸水率、溶出率を求めた。
溶出率(%)：｛１−（浸漬後の皮膜絶乾重量／浸漬前の皮膜絶乾重量）｝×１００
吸水率(%)：｛（浸漬後の皮膜吸水重量／浸漬前の皮膜絶乾重量）−１｝×１００
＊浸漬前の皮膜絶乾重量；浸漬前の皮膜重量（含水）−｛浸漬前の皮膜重量（含水）× 皮膜含水率(%)／１００｝
＊皮膜含水率；皮膜（２０℃水に浸漬するサンプルとは別のサンプル）を、１０５℃、４時間で絶乾し、皮膜の含水率をあらかじめもとめる。
＊浸漬後の皮膜絶乾重量；浸漬後の皮膜を１０５℃、４時間で絶乾した重量。
浸漬後の皮膜重量；浸漬後の皮膜を水から引き上げた後、皮膜についた水をガーゼで拭き取り秤量。
（２）粘度安定性
低温放置安定性：５℃、９０日間放置後の粘度変化を測定
温度依存性：Ｔ６０℃／Ｔ２０℃（２０℃、６０℃に調整後測定）
高温放置安定性： Ｈ６０℃／Ｈ２０℃（２０℃、６０℃に調整し、１週間放置後粘度測定） （ Ｈ２０℃、Ｈ６０℃はそれぞれ２０℃、６０℃に調整し、１週間放置後の粘度）
粘度はＢ型粘度計（２０ｒｐｍ）を用いて測定。
（３）重合安定性
重合後、６０メッシュ金網でろ過し、ろ過残量（％）（対エマルジョン）を測定。ろ過残量が少ないほど重合安定性が優れていることを示す。
【００２７】
実施例１
還流冷却器、滴下ロート、温度計、窒素吹込口を備えた１リットルガラス製重合容器に、イオン交換水３００ｇ、ＰＶＡ−１（重合度１０００、けん化度９９．０モル％、エチレン変性量７．０モル%）２６ｇを仕込み９５℃で完全に溶解した。次に、このＰＶＡ水溶液を冷却、窒素置換後、２００ｒｐｍで撹拌しながら、６０℃に昇温した後、酒石酸の１０％水溶液を４．４ｇおよび５％過酸化水素水３ｇ（酢酸ビニルに対し、モル比で０．０１５）をショット添加後、酢酸ビニル２６ｇを仕込み重合を開始した。重合開始３０分後に初期重合終了（酢酸ビニルの残存量１重量％）を確認した。次に酒石酸の１０％水溶液を０．９ｇおよび５％過酸化水素水３ｇをショット添加後、酢酸ビニル２３４ｇを２時間にわたって連続的に添加し、重合温度８０℃に維持して重合を完結させた。冷却後、６０メッシュのステンレス製金網を用いてろ過した。ろ過残量が少ないほど重合安定性が優れ、多いほど重合安定性が悪いことを示す。
以上の結果、固形分濃度４７．３％のポリ酢酸ビニル系エマルジョン(Ｅｍ−１)が得られた。このエマルジョンの評価を前述の方法により行った。結果を表１に示す。
【００２８】
実施例２
還流冷却器、滴下ロート、温度計、窒素吹込口を備えた１リットルガラス製重合容器に、イオン交換水３００ｇ、ＰＶＡ−１ ２６ｇを仕込み９５℃で完全に溶解した。次に、このＰＶＡ水溶液を冷却、窒素置換後、２００ｒｐｍで撹拌しながら、６０℃に昇温した後、酒石酸の１０％水溶液を４．４ｇおよび５％過酸化水素水３ｇをショット添加後、酢酸ビニル２６ｇを仕込み重合を開始した。重合開始３０分後に初期重合終了（酢酸ビニルの残存量１重量％）を確認した。次に酒石酸の１０％水溶液を０．９ｇ添加し、１％過酸化水素水１５ｇおよび酢酸ビニル２３４ｇを２時間にわたって連続的に添加して、重合温度８０℃に維持して重合を完結させた。冷却後、６０メッシュのステンレス製金網を用いてろ過した。ろ過後のろ過残量により、実施例１と同様の方法で重合安定性を評価した。以上の結果、固形分濃度４７．２％のポリ酢酸ビニル系エマルジョン（Ｅｍ−２）が得られた。このエマルジョンの評価を前述の方法により行った。結果をあわせて表１に示す。
【００２９】
実施例３
還流冷却器、滴下ロート、温度計、窒素吹込口を備えた１リットルガラス製重合容器に、イオン交換水３００ｇ、ＰＶＡ−１ ２６ｇを仕込み９５℃で完全に溶解した。次に、このＰＶＡ水溶液を冷却、窒素置換後、２００ｒｐｍで撹拌しながら、６０℃に昇温した後、酒石酸の１０％水溶液１８ｇおよび酢酸ビニル２６ｇを仕込み、１％過酸化水素水８５ｇを２．５時間にわたって連続的に添加し、重合を開始した。重合開始３０分後に初期重合終了（酢酸ビニルの残存量１重量％）を確認した。次に酢酸ビニル２３４ｇを２時間にわたって連続的に添加した。酢酸ビニル添加終了後、１％過酸化水素水４．８ｇをショットで添加し、重合温度８０℃に維持して重合を完結させた。冷却後、６０メッシュのステンレス製金網を用いてろ過した。ろ過後のろ過残量により、実施例１と同様の方法で重合安定性を評価した。以上の結果、固形分濃度４７．６％のポリ酢酸ビニル系エマルジョン（Ｅｍ−３）が得られた。このエマルジョンの評価を前述の方法により行った。結果をあわせて表１に示す。
【００３０】
実施例４
実施例１において用いたＰＶＡ−１を用いる代わりにＰＶＡ−２（重合度１７００、けん化度９８．０モル％、エチレン変性量５．０モル%）を用いた他は実施例１と同様にして固形分濃度４７．５％のポリ酢酸ビニル系エマルジョン（Ｅｍ−４）が得られた。このエマルジョンの評価を前述の方法により行った。結果をあわせて表１に示す。
【００３１】
比較例１
実施例１において用いたＰＶＡ−１を用いる代わりにＰＶＡ−３（重合度１７００、けん化度９８．５モル％、クラレ製ＰＶＡ−１１７）を用いた他は、実施例１と同様にして固形分濃度４７．５％のポリ酢酸ビニル系エマルジョン（比較Ｅｍ−１）が得られた。このエマルジョンの評価を前述の方法により行った。結果をあわせて表１に示す。
【００３２】
実施例５
還流冷却器、滴下ロート、温度計、窒素吹込口を備えた１リットルガラス製重合容器に、イオン交換水３００ｇ、ＰＶＡ−１ ２６ｇを仕込み９５℃で完全に溶解した。次に、このＰＶＡ水溶液を冷却、窒素置換後、２００ｒｐｍで撹拌しながら、６０℃に昇温した後、亜硫酸水素ナトリウム１０％水溶液を２０ｇおよび酢酸ビニル２６ｇを仕込み、４％過硫酸アンモニウム２３．５ｇをショット添加して重合を開始し、３０分後に初期重合終了（酢酸ビニルの残存量１重量％）を確認した。次に酢酸ビニル２３４ｇを２時間にわたって連続的に添加し、重合温度を８０℃に維持して重合を完結させた。冷却後、６０メッシュのステンレス製金網を用いてろ過した。ろ過後のろ過残量により、実施例１と同様の方法で重合安定性を評価した。以上の結果、固形分濃度４７．３％のポリ酢酸ビニル系エマルジョン（Ｅｍ−５）が得られた。このエマルジョンの評価を前述の方法により行った。結果をあわせて表１に示す。
【００３３】
比較例２
実施例１において用いたＰＶＡ−１を用いる代わりにＰＶＡ−４（重合度１７００、けん化度８８．０モル％、クラレ製ＰＶＡ−２１７）を用いた他は実施例１と同様にして固形分濃度４７．５％のポリ酢酸ビニル系エマルジョン（比較Ｅｍ−２）が得られた。このエマルジョンの評価を前述の方法により行った。結果をあわせて表１に示す。
【００３４】
比較例３
還流冷却器、滴下ロート、温度計、窒素吹込口を備えた１リットルガラス製重合容器に、イオン交換水３００ｇ、ＰＶＡ−１ ２６ｇを仕込み９５℃で完全に溶解した。次に、このＰＶＡ水溶液を冷却、窒素置換後、２００ｒｐｍで撹拌しながら、６０℃に昇温した後、酒石酸の１０％水溶液を１２ｇおよび５％過酸化水素水３０ｇをショット添加後、酢酸ビニル２６ｇを仕込み重合を開始した。重合開始３０分後に初期重合終了（酢酸ビニルの残存量１重量％）を確認した。次に酒石酸の１０％水溶液を０．９ｇおよび５％過酸化水素水３０ｇをショット添加後、酢酸ビニル２３４ｇを２時間にわたって連続的に添加し、重合温度８０℃に維持しながら、重合を完結させた。冷却後、６０メッシュのステンレス製金網を用いてろ過した。ろ過後のろ過残量により、実施例１と同様の方法で重合安定性を評価した。以上の結果、固形分濃度４７．５％のポリ酢酸ビニル系エマルジョン（比較Ｅｍ−３）が得られた。このエマルジョンの評価を前述の方法により行った。結果をあわせて表１に示す。
【００３５】
比較例４
還流冷却器、滴下ロート、温度計、窒素吹込口を備えた１リットルガラス製重合容器に、イオン交換水３００ｇ、ＰＶＡ−１ ２６ｇを仕込み９５℃で完全に溶解した。次に、このＰＶＡ水溶液を冷却、窒素置換後、２００ｒｐｍで撹拌しながら、６０℃に昇温した後、酒石酸の１０％水溶液を０．１５ｇおよび５％過酸化水素水０．１ｇをショット添加後、酢酸ビニル２６ｇを仕込み重合を開始し、３０分後に初期重合の終了（酢酸ビニルの残存量１重量％）を確認した。次に酒石酸の１０％水溶液を０．１ｇおよび５％過酸化水素水０．１ｇをショット添加後、酢酸ビニル２３４ｇを２時間にわたって連続的に添加し、重合温度を８０℃に維持しながら重合を行ったが、途中でブロック化し、安定に水性エマルジョンが得られなかった。
【００３６】
比較例５
攪拌機、還流冷却器、滴下ロート、温度計、窒素導入口を備えた５リットルのガラス製容器にイオン交換水１４００ｇ、エチレン変性ＰＶＡ（重合度１４００、けん化度９８．０モル％、エチレン含有量５．５モル％）２２５ｇを仕込み９５℃で完全に溶解した。次に、変性ＰＶＡ水溶液を冷却後ｐＨを４に調整し、塩化第一鉄０．０５ｇを添加し、窒素置換した後、１４０ｒｐｍで攪拌しながら酢酸ビニル３５０ｇを仕込み、６０℃に昇温した。次に、０．７％の過酸化水素水を１５ｍｌ／ｈｒで、６％のロンガリット水溶液を１０ｍｌ／ｈｒで連続添加しながら、７０℃で重合を行い、３０分後に初期重合終了（酢酸ビニルの残存量１重量％）を確認した。次に、酢酸ビニル１４００ｇを３時間にわたって連続的に添加した。添加終了後、内温を８０℃に１時間保持し重合を完結させた。固形分濃度５０．４％のポリ酢酸ビニル水性エマルジョン（比較Ｅｍ−５）が得られた。このエマルジョンの評価結果を表１に示す。
【００３７】
比較例６
攪拌機、還流冷却器、滴下ロート、温度計、窒素導入口を備えた１リットルのガラス製容器中で、ＰＶＡ(重合度１２００、けん化度９０．０モル％、エチレン含有量７．２モル％)２０ｇを水２４０ｇに溶解した。次に、酢酸ビニル２０ｇを添加し、内温が７０℃に達したところで過酸化水素０．３ｇおよび酒石酸０．５ｇを添加し、重合を開始し、３０分後に初期重合終了（酢酸ビニルの残存量１重量％）を確認した。続いて、酢酸ビニル１８０ｇと過酸化水素０．３ｇを３時間かけて連続的に添加した。添加終了後、内温を８０℃に１時間保持し熟成を行い、ポリ酢酸ビニル水性エマルジョンを得た。このエマルジョンの評価結果を表１に示す。
【００３８】
比較例７
比較例５において、エチレン変性PVA（重合度１４００、けん化度９８．０モル％、エチレン含有量５．５モル％）の代わりにエチレン変性ＰＶＡ（重合度１０００，けん化度９９．７モル％、エチレン含有量７．５モル％）を使用する以外は比較例５と同様にしてポリ酢酸ビニル水性エマルジョン（Ｅｍ−７）を得た。このエマルジョンの評価結果を表１に示す。
前述の実施例および比較例で使用したＰＶＡ、重合開始剤の使用量、重合初期の単量体の仕込み量（重量％）（／全酢酸ビニル）等を表２にまとめて示す
【００３９】
【表１】
【表２】
実施例８〜１２および比較例８〜１３
Ｅｍ−１（実施例８）、 Ｅｍ−２（実施例９）、Ｅｍ−３（実施例１０）、 Ｅｍ−４（実施例１１）、Ｅｍ−５（実施例１２）、比較Ｅｍ−１（比較例８）、比較Ｅｍ−２（比較例９）、比較Ｅｍ−３（比較例１０）、比較Ｅｍ−５（比較例１１）、比較Ｅｍ−６（比較例１２）、比較Ｅｍ−７（比較例１３）をそれぞれ木工用接着剤に使用し、次の条件で評価を行った。その結果を表３に示す。
【００４２】
（４）常態接着力（カバ材）
得られた木工用接着剤をカバ材（柾目）に１５０ｇ／ｍ２塗布し、はりあわせて７ｋｇ／ｍ２の荷重で１６時間圧締し、その後、解圧し、２０℃６５％ＲＨ下で５日間養生した。この試験片の常態接着強度を２０℃、６５％ＲＨ下で測定した。
（５）耐温水接着力（カバ材）
得られた木工用接着剤をカバ材（柾目）に１５０ｇ／ｍ２塗布し、はりあわせて７ｋｇ／ｍ２の荷重で１６時間圧締し、その後、解圧し、２０℃６５％ＲＨ下で５日間養生した。養生後、６０℃の温水に３時間浸漬し、ぬれたままの状態で圧縮せん断強度を測定した。
（６）耐水接着力（合板二次加工）
得られた木工用接着剤をラワン合板（１類合板、五枚積層体）に２０００ｇ／ｍ２塗布し、はりあわせて７ｋｇ／ｍ２の荷重で３時間圧締し、その後、解圧し、２０℃６５％ＲＨ下で５日間養生した。養生後、６０℃の温水に３時間浸漬し、ぬれたままの状態で浸漬剥離試験を実施した。
【００４３】
【表３】
実施例１５〜１９および比較例１４〜１９
Ｅｍ−１（実施例１５）、 Ｅｍ−２（実施例１６）、Ｅｍ−３（実施例１７）、 Ｅｍ−４（実施例１８）、Ｅｍ−５（実施例１９）、比較Ｅｍ−１（比較例１４）、比較Ｅｍ−２（比較例１５）、比較Ｅｍ−３（比較例１６）、比較Ｅｍ−５（比較例１７）、比較Ｅｍ−６（比較例１８）、比較Ｅｍ−７（比較例１９）をそれぞれ紙加工用接着剤に使用し、次の条件で評価を行った。その結果を表４に示す。
【００４５】
（７）初期接着力
ＪＴ製初期接着力試験機（ＪＴ−１）を用い、得られた紙工用接着剤をクラフト紙に塗布して初期接着力を測定した（圧締時間１０秒間）。
（８）リングクラッシュ強度
紙管用原紙を２枚接着させた加工品を用い、ＪＩＳ−Ｐ８１２６にしたがって２０℃、６５％ＲＨ下の強度を測定した。
（９）耐水接着力
得られた紙工用接着剤をクラフト紙に３０ｇ／ｍ２塗布し、はりあわせてハンドロールで３回圧締した。乾燥後、得られた加工品を３０℃の水中に７２時間浸漬し、その後の接着状態を観察した。○紙破、△若干紙破、×剥離
【００４６】
【表４】
【発明の効果】
本発明の水性エマルジョンは、高温粘度安定性に優れ（温度依存性が小さく、高温放置安定性に優れ）、しかも耐水性がより改善され、さらにまた低温放置安定性にも優れており、紙用、木工用およびプラスチック用の接着剤、含浸紙用、不織製品用のバインダー、混和剤、打継ぎ材、塗料、紙加工および繊維加工などの分野で好適に用いられる。また、本発明の水性エマルジョンの製造方法は、重合安定性に優れている。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an aqueous emulsion having excellent water resistance, high-temperature viscosity stability and low-temperature storage stability, and a method for producing an aqueous emulsion excellent in polymerization stability.
[0002]
[Prior art]
Conventionally, polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) has been widely used as a protective colloid for emulsion polymerization of ethylenically unsaturated monomers, particularly vinyl ester monomers represented by vinyl acetate, Vinyl ester aqueous emulsions obtained by emulsion polymerization using this as a protective colloid are various adhesives for paper, woodworking and plastics, various binders, admixtures and punches for impregnated paper and non-woven products. Widely used in fields such as seams, paints, paper processing and textile processing.
Such an aqueous emulsion generally has a low viscosity by adjusting the degree of saponification of the PVA polymer, has a viscosity close to Newtonian flow, and has a relatively good water resistance. Since it has a high viscosity and relatively low temperature dependence of emulsion viscosity, it has been awarded for various uses.
However, some of the aqueous emulsions have insufficient fluidity (high-speed coating properties), poor water resistance, large temperature dependence of emulsion viscosity, and significant increase in emulsion viscosity at low temperatures. It is known that these properties largely depend on the PVA polymer used for emulsion polymerization.
[0003]
That is, PVA polymers as a dispersant for emulsion polymerization generally include so-called “fully saponified PVA” having a saponification degree of about 98 mol% and “partially saponified PVA” having a saponification degree of about 88 mol%. When used, the water resistance and fluidity (high-speed coating property) are relatively good, but the emulsion viscosity when standing at low temperature is remarkably increased and has the disadvantages of being easily gelled. On the other hand, the latter PVA polymer is used. When used, the emulsion has a disadvantage that it is inferior in water resistance, although the viscosity increase and gelation tendency at low temperatures are improved. In order to improve such drawbacks, the combined use of both PVA polymers and the use of PVA polymers having an intermediate saponification degree between the two have been carried out. I was not able to satisfy sex at the same time. Therefore, vinyl alcohol polymers containing ethylene units have been proposed (Japanese Patent Laid-Open Nos. 8-81666, 6-80709, 10-226774, etc.), and have water resistance and low-temperature storage stability. Greatly improved. However, even in this emulsion, the high temperature viscosity stability is not satisfactory, that is, it has temperature dependence, and the high temperature storage stability is not satisfactory.
[0004]
[Problems to be solved by the invention]
The present invention eliminates these disadvantages of the prior art, has excellent high-temperature viscosity stability (small temperature dependency, excellent high-temperature storage stability), and further improved water resistance. It is another object of the present invention to provide an aqueous emulsion excellent in low-temperature storage stability and to provide a method for producing an aqueous emulsion excellent in polymerization stability.
[0005]
[Means for Solving the Problems]
That is, the present invention uses a vinyl alcohol polymer having a saponification degree of 95 mol% or more containing 1 to 15 mol% of ethylene units in the molecule as a dispersant, and a vinyl ester monomer polymer as a dispersoid. When the film obtained by film-forming the emulsion is immersed in water at 20 ° C. for 24 hours, the dissolution rate is 1.5% or less and the water absorption is 30% or less, and 20 ° C. Ratio of emulsion viscosity at 60 ° C. to viscosity at 60 ° C., T 60 ° C / T 20 ° C Is an aqueous emulsion having 2 or less. Here, the elution rate and the water absorption rate are values measured by the method described later, but an elution rate of 1.5% or less and a water absorption rate of 30% or less means excellent water resistance. ing. The elution rate is more preferably 1.1% or less, and the water absorption rate is more preferably 27% or less. Emulsion viscosity T at 20 ° C 20 ° C And viscosity T at 60 ° C 60 ° C Ratio of T 60 ° C / T 20 ° C Is a value measured by the method described later. 60 ° C / T 20 ° C The vinyl ester polymer emulsion using ethylene-containing PVA as a dispersant shows a high viscosity around 60 ° C., but in the present invention, it is possible to suppress an increase in viscosity around 60 ° C. That is, the temperature dependency is small. The fact that the increase in viscosity can be suppressed at around 60 ° C. means that the increase in viscosity during high temperature storage, transportation and use of the emulsion can be suppressed during the polymerization of the emulsion. Will improve.
In the present invention, the emulsion viscosity H after adjustment at 20 ° C. and standing for 1 week 20 ° C And emulsion viscosity H after adjustment at 60 ° C for 1 week 60 ° C Ratio of H 60 ° C / H 20 ° C However, an emulsion of 2.5 or less is a more preferable embodiment. Where H 60 ° C / H 20 ° C Is a value measured by the method described later. 60 ° C / H 20 ° C Of 2.5 or less means that it is excellent in high-temperature storage stability, and even if it is kept at a high temperature of about 60 ° C. for about one week, an increase in viscosity can be suppressed. The handleability is not impaired.
[0006]
The aqueous emulsion of the present invention uses (1) a vinyl alcohol polymer having a saponification degree of 95 mol% or more, containing 1 to 15 mol% of ethylene units in the molecule as a dispersant. At least one polymerization initiator selected from ammonium sulfate and potassium persulfate is used in a molar ratio of 0.001 to 0.01 with respect to the vinyl ester monomer, and (3) a vinyl ester monomer at the initial stage of polymerization. By performing a polymerization operation in which 5 to 20% by weight of the total amount of monomers is added, and the polymerization initiator is collectively added in a molar ratio of 0.005 to 0.025 with respect to the vinyl ester monomer initially charged. can get.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
A PVA polymer containing 1 to 15 mol% of ethylene units in the molecule used as a dispersant for the aqueous emulsion of the present invention and having a saponification degree of 95 mol% or more saponifies a copolymer of vinyl ester and ethylene. Can be obtained.
[0008]
Here, examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, and vinyl pivalate. Vinyl acetate is preferable from the economical viewpoint.
[0009]
The ethylene unit content is required to be 1 to 15 mol%, preferably 3 to 13%, and more preferably 5 to 12%. When the ethylene unit content is less than 1 mol%, as is apparent from Comparative Example 1 described later, an aqueous emulsion satisfying the above water resistance (elution rate and water absorption rate) and high-temperature viscosity stability at the same time is obtained. It cannot be obtained, and the low temperature storage stability is poor. On the other hand, if it exceeds 15 mol%, the water solubility is lowered, and there is a concern that a stable aqueous emulsion cannot be obtained.
[0010]
The dispersant may be a copolymer of an ethylenically unsaturated monomer that can be copolymerized within a range that does not impair the object of the present invention. Examples of such ethylenically unsaturated monomers include acrylic acid, methacrylic acid, fumaric acid, (anhydrous) maleic acid, itaconic acid, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, trimethyl- (3-acrylamide). -3-dimethylpropyl) -ammonium chloride, acrylamido-2-methylpropanesulfonic acid and its sodium salt, ethyl vinyl ether, butyl vinyl ether, N-vinyl pyrrolidone, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, fluoride Examples include vinylidene, tetrafluoroethylene, sodium vinyl sulfonate, and sodium allyl sulfonate.
In addition, a vinyl ester monomer such as vinyl acetate is copolymerized with ethylene in the presence of a thiol compound such as thiolacetic acid or mercaptopropionic acid, and a mercapto group or carboxyl group is obtained at the terminal obtained by saponifying it. A modified product having can also be used.
[0011]
The saponification degree of the ethylene-modified PVA polymer used as a dispersant for the aqueous emulsion of the present invention needs to be 95 mol% or more, more preferably 96 mol% or more, and still more preferably 97 mol% or more. is there. When the saponification degree is less than 95 mol%, an aqueous emulsion excellent in water resistance cannot be obtained. In order to obtain the target aqueous emulsion of the present invention, the polymerization degree (viscosity average polymerization degree) of the PVA polymer is preferably 100 to 3000, and more preferably 300 to 3000.
[0012]
Examples of the vinyl ester monomer constituting the dispersoid in the aqueous emulsion of the present invention include vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, etc., but vinyl acetate is preferred from the economical viewpoint.
[0013]
In the present invention, a vinyl ester monomer is mainly used as the monomer, but it is also a preferred embodiment to use a vinyl ester monomer in combination with ethylene. By emulsion polymerization of these monomers, an aqueous emulsion having a vinyl ester polymer or a vinyl ester-ethylene copolymer as a dispersoid can be obtained.
[0014]
Moreover, you may copolymerize an ethylenically unsaturated monomer and a diene monomer in the range which does not impair the objective of this invention. Examples of such monomers include olefins such as propylene and isobutylene, halogenated olefins such as vinyl chloride, vinyl fluoride, vinylidene chloride, and vinylidene fluoride, acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, Acrylic acid and its esters such as 2-ethylhexyl acrylate, dodecyl acrylate, 2-hydroxyethyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, methacrylic acid Methacrylic acid and its esters such as 2-hydroxyethyl acid, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate and quaternized products thereof, acrylamide, methacrylic acid Acrylamide monomers such as amide, N-methylolacrylamide, N, N-dimethylacrylamide, acrylamide-2-methylpropanesulfonic acid and its sodium salt, styrene, α-methylstyrene, p-styrenesulfonic acid and sodium, potassium Examples thereof include styrene monomers such as salts, other N-vinylpyrrolidone, and diene monomers such as butadiene, isoprene and chloroprene.
[0015]
When the aqueous emulsion of the present invention emulsion-polymerizes a vinyl ester monomer as described above, (1) vinyl having 1 to 15 mol% of ethylene units in the molecule as a dispersant and having a saponification degree of 95 mol% or more. Using an alcohol polymer, (2) using at least one polymerization initiator selected from hydrogen peroxide, ammonium persulfate and potassium persulfate in a molar ratio of 0.001 to 0.01 with respect to the vinyl ester monomer. (3) The vinyl ester monomer is charged in an amount of 5 to 20% by weight of the total amount of monomers at the initial stage of polymerization, and the polymerization initiator is added in a molar ratio of 0 to the vinyl ester monomer charged initially. 0.005 to 0.025 can be obtained by performing a polymerization operation for batch addition.
[0016]
In producing the aqueous emulsion of the present invention, it is important to use at least one polymerization initiator selected from hydrogen peroxide, ammonium persulfate and potassium persulfate, and among these, hydrogen peroxide is particularly preferred. In the present invention, it is also extremely important to carry out emulsion polymerization by using 0.001 to 0.01 molar ratio with respect to all vinyl ester monomers using a polymerization initiator. It is 002-0.007, More preferably, it is 0.0025-0.005. Although the reason is not clear, by using the above-mentioned amount of the initiator, an aqueous emulsion having improved water resistance, excellent high-temperature viscosity stability, and excellent low-temperature storage stability can be obtained. As described in Example 1 of JP-A-8-81666, when the polymerization initiator is less than 0.001, the target aqueous emulsion of the present invention cannot be obtained. This is clear from Comparative Example 5 described later. On the other hand, when the polymerization initiator exceeds 0.01, an emulsion excellent in water resistance and excellent in high-temperature viscosity stability cannot be obtained. This is clear from Comparative Example 3 described later.
[0017]
Further, the polymerization initiator may be used in combination with a reducing agent and used in a redox system. In that case, hydrogen peroxide is usually used together with tartaric acid, L-ascorbic acid, Rongalite and the like. Ammonium persulfate and potassium persulfate are used together with sodium hydrogen sulfite, sodium hydrogen carbonate and the like. The amount of the reducing agent used is not particularly limited, but is usually 0.05 to 3 equivalents, preferably 0.1 to 2 equivalents, more preferably 0.3 to 1.5 equivalents, relative to the polymerization initiator.
[0018]
As a method for adding the polymerization initiator, a method of collectively adding a polymerization initiator at the beginning of polymerization is used. That is, 5 to 20% of the total amount of the vinyl ester monomer is charged at the initial stage of polymerization, and a polymerization initiator is added at a molar ratio of 0.005 to 0.025 at a molar ratio with respect to the initial charged monomer. It is necessary to do, Preferably it is 0.008-0.020, More preferably, it is 0.01-0.018.
As described in Example 1 of JP-A-8-81666, when the initial charge amount of the polymerization initiator is less than 0.005, the aqueous emulsion targeted by the present invention cannot be obtained. This is clear from Comparative Example 5 described later.
Further, as described in Example 1 of JP-A-6-80709, an emulsion excellent in water resistance and high-temperature viscosity stability, which is an object of the present invention, even when the initial charge amount of the polymerization initiator exceeds 0.025. Cannot be obtained. This is clear from Comparative Example 6 described later.
In the initial polymerization, by adding a predetermined amount of the polymerization initiator as described above, the excellent effects as described above can be obtained, but the polymerization stability is also improved and the remaining amount of filtration after polymerization is reduced.
In the initial polymerization, a monomer and a polymerization initiator are added to an aqueous solution of a dispersant, and the polymerization temperature is 50 to 70 ° C., preferably 55 to 65 ° C., the polymerization time is 15 to 60 minutes, preferably 20 to 50 minutes. Done under. In the initial polymerization, it is preferable to add the monomers all at once.
[0019]
Although there is no restriction | limiting in particular about the usage-amount of the ethylene modified PVA type polymer used as a dispersing agent, Preferably it is 3-20 weight part with respect to 100 weight part of monomers, More preferably, in the range of 5-15 weight part. is there. When the amount used is less than 3 parts by weight or more than 20 parts by weight, the polymerization stability may be lowered or the standing stability may be lowered.
[0020]
The initial polymerization is terminated when the residual concentration of vinyl ester (% by weight relative to the produced polymer) is 10% or less, preferably 5% or less, more preferably 1% or less. After the initial polymerization, the latter polymerization is started. In the latter polymerization, the polymerization initiator is preferably added all at once, but may be added continuously or intermittently. The monomer is preferably added continuously, but may be added all at once (shot addition). In the late polymerization, the polymerization temperature is preferably 5 to 30 ° C. higher than the initial polymerization temperature, 55 to 100 ° C., preferably 60 to 95 ° C., more preferably 70 to 90 ° C. Done.
[0021]
The polymerization pressure may be normal pressure for both initial polymerization and late polymerization, but it is necessary to increase the pressure as necessary. In particular, when producing a copolymer emulsion of a vinyl ester and another monomer such as ethylene, it is necessary to carry out under pressure.
[0022]
By adopting the method as described above, in particular, a modified PVA containing 1 to 15 mol% of ethylene units as a dispersant and having a saponification degree of 95 mol% or more is used, and the polymerization initiator is a vinyl ester monomer. Is used in a molar ratio of 0.001 to 0.01, and in the initial stage of polymerization, a vinyl ester monomer is charged in an amount of 5 to 20% by weight of the total amount of the monomer, and the polymerization initiator is a single amount of the initial charge. By adding 0.005 to 0.025 at a molar ratio to the body, the polymerization stability is excellent, the water resistance is further improved, and the high-temperature viscosity stability is excellent (the temperature dependence is small). It is surprising that an aqueous emulsion excellent in high-temperature storage stability is obtained, and that the obtained aqueous emulsion is also excellent in low-temperature storage stability. No. 6, JP-A-6-80709, it can not be hardly predicted from the invention described in JP-A-10-226774. In particular, in the present invention, the amount of the polymerization initiator is defined as a specific amount, and the polymerization initiator is collectively added at the initial stage of polymerization and the amount of the polymerization initiator is defined, so that an excellent aqueous emulsion intended by the present invention can be obtained. It is surprising that the industrial meaning is great.
Since the water-based emulsion of the present invention thus obtained has improved water resistance, it is suitably used for various applications requiring water resistance, and the water-based emulsion of the present invention has low temperature dependence. In particular, when the temperature is raised to 60 ° C., the viscosity of a vinyl ester polymer emulsion using ethylene-modified PVA as a dispersion stabilizer usually increases greatly. An increase in viscosity can be prevented, and an increase in viscosity can be prevented even during storage, transportation, and use at a high temperature of about 60 ° C., so that workability and handling are extremely excellent.
[0023]
As the aqueous emulsion obtained in the present invention, the aqueous emulsion obtained by the above method can be used as it is, but if necessary, various conventionally known emulsions are added and used within a range not impairing the effects of the present invention. be able to.
In addition, as the dispersant in the aqueous emulsion of the present invention, the PVA polymer having a saponification degree of 95 mol% or more or the ethylene-modified PVA polymer having a saponification degree of 95 mol% or more is used. Conventionally known anionic, nonionic or cationic surfactants, PVA polymers, hydroxyethyl cellulose, and the like can be used in combination.
[0024]
Since the aqueous emulsion of the present invention has the excellent properties as described above, it is a paper tube, bag making, interleaf, paper for corrugated board, paper processing adhesive such as pulp, flash panel, assembly. Wood, wood board, plywood processing, plywood secondary processing (kneading), woodworking adhesives for general woodworking and various plastics, impregnating paper, binders for non-woven products, admixtures, splicing It is suitably used in fields such as materials, paints, paper processing and fiber processing.
[0025]
【Example】
Next, the present invention will be described in more detail with reference to examples and comparative examples. In the following examples and comparative examples, “parts” and “%” mean weight basis unless otherwise specified. Further, the water resistance and storage stability of the obtained emulsion were evaluated in the following manner.
[0026]
(Emulsion evaluation)
(1) Water resistance of the film
The obtained aqueous emulsion was cast on PET under the conditions of 20 ° C. and 65% RH and dried for 7 days to obtain a dry film of 500 μm. This film was punched to a diameter of 2.5 cm, and the water absorption rate and elution rate of the film when the sample was immersed in water at 20 ° C. for 24 hours were determined.
Elution rate (%): {1- (Absolute dry weight after immersion / Absolute dry weight before immersion)} × 100
Water absorption rate (%): {(film water absorption weight after immersion / film absolute dry weight before immersion) -1} × 100
* Absolute dry weight of film before immersion; film weight before immersion (water content)-{film weight before immersion (water content) x film moisture content (%) / 100}
* Moisture content of film: The film (a sample different from the sample immersed in water at 20 ° C.) is completely dried at 105 ° C. for 4 hours to obtain the moisture content of the film in advance.
* Absolute dry weight after dipping; Weight obtained by dipping the dipped film at 105 ° C. for 4 hours.
Film weight after immersion: After lifting the film after immersion from the water, wipe the water on the film with gauze and weigh.
(2) Viscosity stability
Low temperature storage stability: 5 ° C , Measure viscosity change after 90 days
Temperature dependence: T 60 ° C / T 20 ° C (Measurement after adjustment to 20 ° C and 60 ° C)
High temperature storage stability: H 60 ° C / H 20 ° C (Adjusted to 20 ° C and 60 ° C, measured for viscosity after standing for 1 week) 20 ° C , H 60 ° C Are adjusted to 20 ° C and 60 ° C, respectively, and the viscosity after standing for 1 week)
Viscosity was measured using a B-type viscometer (20 rpm).
(3) Polymerization stability
After polymerization, the mixture was filtered through a 60 mesh wire net and the remaining amount of filtration (%) (vs. emulsion) was measured. The smaller the remaining amount of filtration, the better the polymerization stability.
[0027]
Example 1
In a 1 liter glass polymerization vessel equipped with a reflux condenser, a dropping funnel, a thermometer, and a nitrogen inlet, 300 g of ion exchange water, PVA-1 (degree of polymerization 1000, degree of saponification 99.0). Mole %, Ethylene modification amount 7.0 Mole %) 26 g was charged and completely dissolved at 95 ° C. Next, this PVA aqueous solution was cooled, purged with nitrogen, heated to 60 ° C. while stirring at 200 rpm, 4.4 g of a 10% aqueous solution of tartaric acid and 3 g of 5% aqueous hydrogen peroxide (relative to vinyl acetate, After adding 0.015) in a molar ratio, 26 g of vinyl acetate was charged and polymerization was started. The completion of initial polymerization (residual amount of vinyl acetate 1% by weight) was confirmed 30 minutes after the start of polymerization. Next, 0.9 g of a 10% aqueous solution of tartaric acid and 3 g of 5% hydrogen peroxide water were shot and then 234 g of vinyl acetate was continuously added over 2 hours, and the polymerization temperature was maintained at 80 ° C. to complete the polymerization. . After cooling, it was filtered using a 60 mesh stainless steel wire mesh. The smaller the remaining amount of filtration, the better the polymerization stability, and the larger the amount, the worse the polymerization stability.
As a result, a polyvinyl acetate emulsion (Em-1) having a solid content concentration of 47.3% was obtained. This emulsion was evaluated by the method described above. The results are shown in Table 1.
[0028]
Example 2
In a 1-liter glass polymerization vessel equipped with a reflux condenser, a dropping funnel, a thermometer, and a nitrogen blowing port, 300 g of ion-exchanged water and 26 g of PVA-1 were charged and completely dissolved at 95 ° C. Next, this PVA aqueous solution was cooled, purged with nitrogen, heated to 60 ° C. while stirring at 200 rpm, 4.4 g of a 10% aqueous solution of tartaric acid and 3 g of 5% aqueous hydrogen peroxide were added in a shot, and acetic acid was then added. 26 g of vinyl was charged and polymerization was started. The completion of initial polymerization (residual amount of vinyl acetate 1% by weight) was confirmed 30 minutes after the start of polymerization. Next, 0.9 g of a 10% aqueous solution of tartaric acid was added, 15 g of 1% hydrogen peroxide and 234 g of vinyl acetate were continuously added over 2 hours, and the polymerization temperature was maintained at 80 ° C. to complete the polymerization. After cooling, it was filtered using a 60 mesh stainless steel wire mesh. Polymerization stability was evaluated by the same method as in Example 1 based on the remaining amount after filtration. As a result, a polyvinyl acetate emulsion (Em-2) having a solid content concentration of 47.2% was obtained. This emulsion was evaluated by the method described above. The results are shown in Table 1.
[0029]
Example 3
In a 1-liter glass polymerization vessel equipped with a reflux condenser, a dropping funnel, a thermometer, and a nitrogen blowing port, 300 g of ion-exchanged water and 26 g of PVA-1 were charged and completely dissolved at 95 ° C. Next, this PVA aqueous solution was cooled, purged with nitrogen, heated to 60 ° C. while stirring at 200 rpm, and then charged with 18 g of a 10% aqueous solution of tartaric acid and 26 g of vinyl acetate, and 2. The polymerization was started by adding continuously over 5 hours. The completion of initial polymerization (residual amount of vinyl acetate 1% by weight) was confirmed 30 minutes after the start of polymerization. Next, 234 g of vinyl acetate was added continuously over 2 hours. After completion of the addition of vinyl acetate, 4.8 g of 1% hydrogen peroxide water was added by shot, and the polymerization temperature was maintained at 80 ° C. to complete the polymerization. After cooling, it was filtered using a 60 mesh stainless steel wire mesh. Polymerization stability was evaluated by the same method as in Example 1 based on the remaining amount after filtration. As a result, a polyvinyl acetate emulsion (Em-3) having a solid content concentration of 47.6% was obtained. This emulsion was evaluated by the method described above. The results are shown in Table 1.
[0030]
Example 4
Instead of using PVA-1 used in Example 1, PVA-2 (polymerization degree 1700, saponification degree 98.0) Mole %, Ethylene modification amount 5.0 Mole %) Was used in the same manner as in Example 1 to obtain a polyvinyl acetate emulsion (Em-4) having a solid concentration of 47.5%. This emulsion was evaluated by the method described above. The results are shown in Table 1.
[0031]
Comparative Example 1
Instead of using PVA-1 used in Example 1, PVA-3 (degree of polymerization 1700, degree of saponification 98.5) Mole %, A polyvinyl acetate emulsion (Comparative Em-1) having a solid content concentration of 47.5% was obtained in the same manner as in Example 1 except that Kuraray PVA-117) was used. This emulsion was evaluated by the method described above. The results are shown in Table 1.
[0032]
Example 5
In a 1-liter glass polymerization vessel equipped with a reflux condenser, a dropping funnel, a thermometer, and a nitrogen blowing port, 300 g of ion-exchanged water and 26 g of PVA-1 were charged and completely dissolved at 95 ° C. Next, this PVA aqueous solution was cooled, purged with nitrogen, heated to 60 ° C. with stirring at 200 rpm, charged with 20 g of a 10% aqueous solution of sodium hydrogensulfite and 26 g of vinyl acetate, and 23.5 g of 4% ammonium persulfate was added. Polymerization was started by adding shots, and after 30 minutes, the completion of initial polymerization (residual amount of vinyl acetate 1% by weight) was confirmed. Next, 234 g of vinyl acetate was continuously added over 2 hours, and the polymerization temperature was maintained at 80 ° C. to complete the polymerization. After cooling, it was filtered using a 60 mesh stainless steel wire mesh. Polymerization stability was evaluated by the same method as in Example 1 based on the remaining amount after filtration. As a result, a polyvinyl acetate emulsion (Em-5) having a solid content concentration of 47.3% was obtained. This emulsion was evaluated by the method described above. The results are shown in Table 1.
[0033]
Comparative Example 2
Instead of using PVA-1 used in Example 1, PVA-4 (polymerization degree 1700, saponification degree 88.0) Mole %, A polyvinyl acetate emulsion (Comparative Em-2) having a solid content concentration of 47.5% was obtained in the same manner as in Example 1, except that Kuraray PVA-217) was used. This emulsion was evaluated by the method described above. The results are shown in Table 1.
[0034]
Comparative Example 3
In a 1-liter glass polymerization vessel equipped with a reflux condenser, a dropping funnel, a thermometer, and a nitrogen blowing port, 300 g of ion-exchanged water and 26 g of PVA-1 were charged and completely dissolved at 95 ° C. Next, this PVA aqueous solution was cooled, purged with nitrogen, heated to 60 ° C. while stirring at 200 rpm, 12 g of a 10% aqueous solution of tartaric acid and 30 g of 5% aqueous hydrogen peroxide were shot, and then 26 g of vinyl acetate. The polymerization was started. The completion of initial polymerization (residual amount of vinyl acetate 1% by weight) was confirmed 30 minutes after the start of polymerization. Next, 0.9 g of a 10% aqueous solution of tartaric acid and 30 g of 5% hydrogen peroxide water were shot and then 234 g of vinyl acetate was continuously added over 2 hours to complete the polymerization while maintaining the polymerization temperature at 80 ° C. It was. After cooling, it was filtered using a 60 mesh stainless steel wire mesh. Polymerization stability was evaluated by the same method as in Example 1 based on the remaining amount after filtration. As a result, a polyvinyl acetate emulsion (Comparative Em-3) having a solid content concentration of 47.5% was obtained. This emulsion was evaluated by the method described above. The results are shown in Table 1.
[0035]
Comparative Example 4
In a 1-liter glass polymerization vessel equipped with a reflux condenser, a dropping funnel, a thermometer, and a nitrogen blowing port, 300 g of ion-exchanged water and 26 g of PVA-1 were charged and completely dissolved at 95 ° C. Next, this PVA aqueous solution was cooled, purged with nitrogen, heated to 60 ° C. with stirring at 200 rpm, and then shot with 0.15 g of a 10% aqueous solution of tartaric acid and 0.1 g of 5% hydrogen peroxide water. Then, 26 g of vinyl acetate was charged and polymerization was started. After 30 minutes, the completion of the initial polymerization (residual amount of vinyl acetate 1% by weight) was confirmed. Next, 0.1 g of a 10% aqueous solution of tartaric acid and 0.1 g of 5% hydrogen peroxide water were shot and then 234 g of vinyl acetate was continuously added over 2 hours, and polymerization was carried out while maintaining the polymerization temperature at 80 ° C. Although it went, it blocked on the way and the aqueous emulsion was not obtained stably.
[0036]
Comparative Example 5
In a 5 liter glass container equipped with a stirrer, reflux condenser, dropping funnel, thermometer, nitrogen inlet, 1400 g of ion-exchanged water, ethylene-modified PVA (polymerization degree 1400, saponification degree 98.0 mol%, ethylene content 5 .5 mol%) 225 g was charged and completely dissolved at 95 ° C. Next, after cooling the modified PVA aqueous solution, the pH was adjusted to 4, 0.05 g of ferrous chloride was added, and the atmosphere was replaced with nitrogen. Then, 350 g of vinyl acetate was charged while stirring at 140 rpm, and the temperature was raised to 60 ° C. Next, polymerization was carried out at 70 ° C. while continuously adding 0.7% hydrogen peroxide solution at 15 ml / hr and 6% Rongalite aqueous solution at 10 ml / hr, and after 30 minutes, the initial polymerization was completed (vinyl acetate Residual amount 1% by weight) was confirmed. Next, 1400 g of vinyl acetate was added continuously over 3 hours. After completion of the addition, the internal temperature was maintained at 80 ° C. for 1 hour to complete the polymerization. A polyvinyl acetate aqueous emulsion (Comparative Em-5) with a solids concentration of 50.4% was obtained. The evaluation results of this emulsion are shown in Table 1.
[0037]
Comparative Example 6
In a 1 liter glass container equipped with a stirrer, reflux condenser, dropping funnel, thermometer, nitrogen inlet, PVA (degree of polymerization 1200, degree of saponification 90.0 mol%, ethylene content 7.2 mol%) 20 g was dissolved in 240 g of water. Next, 20 g of vinyl acetate was added, and when the internal temperature reached 70 ° C., 0.3 g of hydrogen peroxide and 0.5 g of tartaric acid were added to start polymerization, and after 30 minutes, the initial polymerization was completed (remaining vinyl acetate remaining). 1% by weight). Subsequently, 180 g of vinyl acetate and 0.3 g of hydrogen peroxide were continuously added over 3 hours. After completion of the addition, the internal temperature was kept at 80 ° C. for 1 hour and ripening was performed to obtain an aqueous polyvinyl acetate emulsion. The evaluation results of this emulsion are shown in Table 1.
[0038]
Comparative Example 7
In Comparative Example 5, instead of ethylene-modified PVA (polymerization degree 1400, saponification degree 98.0 mol%, ethylene content 5.5 mol%), ethylene-modified PVA (polymerization degree 1000, saponification degree 99.7 mol%, ethylene A polyvinyl acetate aqueous emulsion (Em-7) was obtained in the same manner as in Comparative Example 5 except that the content was 7.5 mol%. The evaluation results of this emulsion are shown in Table 1.
Table 2 summarizes the PVA used in the above-described Examples and Comparative Examples, the amount of polymerization initiator used, the amount of monomer charged in the initial stage of polymerization (% by weight) (/ total vinyl acetate), and the like.
[0039]
[Table 1]
[Table 2]
Example 8 12 And Comparative Examples 8-13
Em-1 (Example 8), Em-2 (Example 9), Em-3 (Example 10), Em-4 (Example 11), Em-5 (Example 12) , Comparative Em-1 (Comparative Example 8), Comparative Em-2 (Comparative Example 9), Comparative Em-3 (Comparative Example 10), Comparative Em-5 (Comparative Example 11), Comparative Em-6 (Comparative Example 12), Comparative Em-7 (Comparative Example 13) was used as an adhesive for woodworking and evaluated under the following conditions. The results are shown in Table 3.
[0042]
(4) Normal adhesive strength (birch material)
150 g / m of the obtained woodworking adhesive for birch wood 2 Apply and paste 7kg / m 2 Then, the pressure was reduced for 16 hours, and then the pressure was released, followed by curing at 20 ° C. and 65% RH for 5 days. The normal adhesive strength of this test piece was measured at 20 ° C. and 65% RH.
(5) Warm water-resistant adhesive strength (birch material)
150 g / m of the obtained woodworking adhesive for birch wood 2 Apply and paste 7kg / m 2 Then, the pressure was reduced for 16 hours, and then the pressure was released, followed by curing at 20 ° C. and 65% RH for 5 days. After curing, the sample was immersed in warm water at 60 ° C. for 3 hours, and the compression shear strength was measured in a wet state.
(6) Water-resistant adhesive strength (plywood secondary processing)
The obtained adhesive for woodworking was applied to Lauan plywood (Class 1 plywood, five-layer laminate) at 2000 g / m. 2 Apply and paste 7kg / m 2 The mixture was clamped for 3 hours under a load of 3 hours, then decompressed and cured at 20 ° C. and 65% RH for 5 days. After curing, the film was immersed in warm water at 60 ° C. for 3 hours, and an immersion peeling test was performed in a wet state.
[0043]
[Table 3]
Example 15- 19 And Comparative Examples 14-19
Em-1 (Example 15), Em-2 (Example 16), Em-3 (Example 17), Em-4 (Example 18), Em-5 (Example 19) , Comparative Em-1 (Comparative Example 14), Comparative Em-2 (Comparative Example 15), Comparative Em-3 (Comparative Example 16), Comparative Em-5 (Comparative Example 17), Comparative Em-6 (Comparative Example 18), Comparative Em-7 (Comparative Example 19) was used as an adhesive for paper processing and evaluated under the following conditions. The results are shown in Table 4.
[0045]
(7) Initial adhesive strength
Using a JT initial adhesive strength tester (JT-1), the obtained adhesive for paperwork was applied to kraft paper, and the initial adhesive strength was measured (clamping time 10 seconds).
(8) Ring crush strength
Using a processed product obtained by bonding two paper tubes for paper tube, the strength under 20 ° C. and 65% RH was measured according to JIS-P8126.
(9) Water-resistant adhesive strength
30 g / m of the obtained paperwork adhesive on kraft paper 2 It was applied, bonded, and pressed three times with a hand roll. After drying, the obtained processed product was immersed in water at 30 ° C. for 72 hours, and the subsequent adhesion state was observed. ○ Paper break, △ Slight paper break, x peeling
[0046]
[Table 4]
【The invention's effect】
The aqueous emulsion of the present invention has excellent high-temperature viscosity stability (less temperature dependency, excellent high-temperature storage stability), improved water resistance, and excellent low-temperature storage stability. It is preferably used in the fields of adhesives for woodworking and plastics, binders for impregnated papers and nonwoven products, admixtures, jointing materials, paints, paper processing and fiber processing. Further, the method for producing an aqueous emulsion of the present invention is excellent in polymerization stability.
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0680709A (en) * | 1991-10-02 | 1994-03-22 | Kuraray Co Ltd | Dispersant |
| JPH0881666A (en) * | 1994-07-14 | 1996-03-26 | Kuraray Co Ltd | Aqueous emulsion |
| JPH09227748A (en) * | 1996-02-22 | 1997-09-02 | Kuraray Co Ltd | Aqueous emulsion |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0680709A (en) * | 1991-10-02 | 1994-03-22 | Kuraray Co Ltd | Dispersant |
| JPH0881666A (en) * | 1994-07-14 | 1996-03-26 | Kuraray Co Ltd | Aqueous emulsion |
| JPH09227748A (en) * | 1996-02-22 | 1997-09-02 | Kuraray Co Ltd | Aqueous emulsion |
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