JP3905165B2 - Polyfunctional aqueous block polyisocyanate composition - Google Patents

Description

【００２２】
（２）２５℃における粘度は５，０００〜１００，０００ｍＰａ・ｓである。粘度が１００，０００ｍＰａ・ｓを超えると塗膜外観に悪影響を及ぼす場合があり、５，０００ｍＰａ・ｓ未満であると、本発明で規定するイソシアネート平均官能基数の範囲が得られない。
（３）数平均分子量は１，０００〜５，０００、好ましくは１，５００〜４，０００である。１，０００未満では、前記イソシアネート平均官能基数の好ましい範囲を得ることが出来ず、５，０００を越えると粘度上昇により塗膜外観に悪影響を及ぼす場合がある。
（４）イソシアネート濃度は２〜２３重量％である。２重量％未満では、架橋密度が小さく、良好な機械的物性の塗膜を得ることが出来ず、２３重量％を越えると、塗膜がもろくなるなど好ましくない。
【００２３】
特公昭５８−３４９１号公報に水分散ブロックドポリイソシアネートの製法が開示されている。その明細書には分子量８００以下、２〜４官能性のポリイソシアネートが記載されているが、本発明に用いるような高多官能、高分子量のポリイソシアネート組成物の効果も、示唆もない。
かくして得られた前駆体としてのポリイソシアネート組成物のイソシアネート基と、ブロック剤を反応させ、熱解離性ブロックイソシアネート基を得ることが出来る。
【００２４】
本発明に用いるブロック剤としては、例えば、フェノール系、活性メチレン、メルカプタン系、酸アミド系、酸イミド系、イミダゾール系、尿素系、オキシム系、アミン系、イミド系化合物等があり、これらを単独あるいは、混合して使用してもよい。より具体的なブロック剤の例を下記に示す。
（１）フェノール系；フェノール、クレゾール、エチルフェノール、ブチルフェノール等。
（２）活性メチレン系；マロン酸ジエステル（マロン酸ジメチル、マロン酸ジエチル、マロン酸ジｎ−ブチル、マロン酸ジ２−エチルヘキシル、マロン酸メチルｎ−ブチル、マロン酸エチルｎ−ブチル、マロン酸メチルｓｅｃ−ブチル、マロン酸エチルｓｅｃ−ブチル、マロン酸メチルｔ−ブチル、マロン酸エチルｔ−ブチル、メチルマロン酸ジエチル、マロン酸ジベンジル、マロン酸ジフェニル、マロン酸ベンジルメチル、マロン酸エチルフェニル、マロン酸ｔ−ブチルフェニル、イソプロピリデンマロネート等）、アセト酢酸エステル（アセト酢酸メチル、アセト酢酸エチル、アセト酢酸ｎ−プロピル、アセト酢酸イソプロピル、アセト酢酸ｎ−ブチル、アセト酢酸ｔ−ブチル、アセト酢酸ベンジル、アセト酢酸フェニル等）、アセチルアセトン等。
（３）メルカプタン系；ブチルメルカプタン、ドデシルメルカプタン等
（４）酸アミド系；アセトアニリド、酢酸アミド、ε−カプロラクタム、δ−バレロラクタム、γ−ブチロラクタム等。
（５）酸イミド系；コハク酸イミド、マレイン酸イミド等。
（６）イミダゾール系；イミダゾール、２−メチルイミダゾール等。
（７）尿素系；尿素、チオ尿素、エチレン尿素等。
（８）オキシム系；ホルムアルドオキシム、アセトアルドオキシム、アセトオキシム、メチルエチルケトオキシム、シクロヘキサノンオキシム等。
（９）アミン系；ジフェニルアミン、アニリン、カルバゾール等。
（１０）イミン系；エチレンイミン、ポリエチレンイミン等。
（１１）重亜硫酸塩；重亜硫酸ソーダ等。
（１２）ピラゾール系；ピラゾール、３−メチルピラゾール、３，５−ジメチルピラゾール等。
（１３）トリアゾール系；１，２，４−トリアゾール等。
【００２５】
上記のうち、活性メチレン系、オキシム系、酸アミド系が好ましく、更に好ましくは、アセトオキシム、メチルエチルケトオキシム、マロン酸ジエステル、アセト酢酸エステルが好ましく、特に、マロン酸ジエステル１種以上とアセト酢酸エステル１種以上を併用することが好ましい。その併用割合は、モル比でマロン酸ジエステル／アセト酢酸エステル＝５／１〜１／５が好ましく、前記値が５／１を越えると、ブロックポリイソシアネートの結晶化が生ずる場合があり、１／５未満であると、塗膜の硬化時の黄変などを生ずる場合がある。
【００２６】
ポリイソシアネート組成物とブロック剤との反応は溶剤の存在の有無に関わらず行うことができる。溶剤を用いる場合、イソシアネート基に対して不活性な溶剤を用いるのが好ましい。
ブロック化反応に際して、触媒として前記イソシアネート環状３量化反応触媒を用いることが出来る。用いた触媒が塗料物性に悪影響を及ぼす可能性がある場合は、該触媒を酸性化合物などで中和することが好ましい。この場合の酸性化合物としては、例えば、塩酸、亜燐酸、燐酸などの無機酸、メタンスルホン酸、ｐ−トルエンスルホン酸、ｐ−トルエンスルホン酸メチルエステル、ｐ−トルエンスルホン酸エチルエステル等のスルホン酸またはその誘導体、燐酸エチル、燐酸ジエチル、燐酸イソプロピル、燐酸ジイソプロピル、燐酸ブチル、燐酸ジブチル、燐酸２−エチルヘキシル、燐酸ジ（２エチルヘキシル）、燐酸イソデシル、燐酸ジイソデシル、オレイルアシッドホスフェート、テトラコシルアシッドホスフェート、エチレングリコールアシッドホスフェート、ピロリン酸ブチル、亜燐酸ブチル等があり、２種以上を併用しても良い。
【００２７】
反応は、一般に−２０〜１５０℃で行うことが出来るが、好ましくは０〜１００℃である。１５０℃を越えると副反応を起こす可能性があり、他方、あまり低温になると反応速度が小さくなり不利である。
本発明における非イオン性親水基とは、片末端に活性水素を有し、かつ、ポリエチレンオキサイド鎖を有する化合物（以下、エチレンオキサイド付加物と言う）である。
【００２８】
エチレンオキサイド付加物は、メタノール、エタノール、ブタノール等のモノアルコールにエチレンオキサイドを付加して得られ、エチレンオキサイド含有量は５０重量％以上が好ましく、数平均分子量は２００〜２，０００が好ましい。エチレンオキサイド付加物はプロピレンオキサイド単位を含んでも良い。
エチレンオキサイド付加化合物とポリイソシアネートの反応は、溶剤を用いて行うこともできる。この場合に使用する溶剤は、イソシアネートに対して不活性なものが好ましい。反応温度は、４０〜１５０℃、好ましくは６０〜１２０℃である。必要に応じてジブチル錫ジラウレート等の錫化合物等の塩基性化合物を反応触媒に使用しても良い。
【００２９】
イソシアネート基とブロック剤の反応、イソシアネート基とエチレンオキサイド付加物の反応は、いずれか一方を先行させることもできるし、同時に行うことも出来る。
ポリイソシアネートのイソシアネート基は、前記のブロック剤及びエチレンオキサイド付加物の反応によりすべてが消費される。この場合のブロック剤とエチレンオキサイド付加物（ポリエーテル鎖単位）のモル比は９８／２〜６０／４０であり、好ましくは９８／２から７０／３０である。９８／２を越えるとブロックポリイソシアネートの水分散性が低下し、６０／４０未満であると塗膜物性が低下する傾向がある。
【００３０】
更に水分散性の向上などの目的に応じて、ノニオン系、アニオン系、カチオン系、両性界面活性剤を添加することができる。界面活性剤の具体例としては、例えば、ポリエチレングリコール、多価アルコール脂肪酸エステル等のノニオン系、脂肪酸塩、アルキル硫酸エステル、アルキルベンゼンスルホン酸塩、アルキルリン酸塩等のアニオン系、アルキルアミン塩、アルキルベタイン等のカチオン系、カルボン酸アミン塩、スルホン酸アミン塩、硫酸エステル塩等の界面活性剤が挙げられる。
【００３１】
本発明においては、貯蔵安定性を向上するために１価アルコール系化合物を含むことが好ましい。該１価アルコール系化合物としては、脂肪族、脂環族、芳香族などがあり、脂肪族が好ましい。炭素数１〜２０が好ましく、例えば、メタノール、エタノール、ｎ−プロパノール、イソプロパノール、ｎ−ブタノール、ｓｅｃ−ブタノール、ｔｅｒｔ−ブタノール、２−メチル−１−プロパノール、ｎ−アミルアルコール、２−ペンタノール、３−ペンタノール、２−メチル−１−ブタノール、３−メチル−１−ブタノール、２−メチル−２−ブタノール、３−メチル−２−ブタノール、２，２，−ジメチル−１−プロパノール等の飽和アルコール、２−メトキシエタノール、２−エトキシエタノール、２−ブトキシエタノール、３，６−ジオキサ−１−ヘプタノール等のエーテルアルコール等がある。その添加量は、熱解離性ブロックイソシアネート基に対して０．２〜１０倍モル量が好ましい。
【００３２】
この様にして調整された低温硬化性多官能水性ブロックポリイソシアネート組成物は、水親和性ポリオールと共に混合され水性塗料組成物の主要構成成分を形成する。
本発明に使用する水親和性ポリオールとは、通常、水性塗料用に用いられているものであれば特に制限なく使用可能であり、アニオン系、カチオン系、両性イオン系でも、またイオン性を持たないものであってもよい。アルキド系、ポリエステル系、エポキシ系、フッ素系、アクリル系等がある。樹脂分水酸基価は１０〜３００ｍｇＫＯＨ／ｇであり、水を主たる成分とする分散媒に、溶解または分散されているものである。樹脂分水酸基価１０ｍｇＫＯＨ／ｇ未満の場合には、イソシアネート成分との反応によるウレタン架橋の密度が減少して、本発明の目的とする物性を必ずしも十分には達成することが出来ず、樹脂水酸基価が３００ｍｇＫＯＨ／ｇを超えると、逆に架橋密度が増大し、塗膜の機械的物性が低下する傾向がある。
【００３３】
溶解型のポリオールとしては、数平均分子量２，０００〜５０，０００であり、例えば、特開昭６３−２９５６８０号公報、特開昭６３−１７５０５９号公報、特開昭６２−２１６６７１号公報、特開平２−１９１６９２号公報等にその製造方法が開示されている。分散型のポリオールとは、水酸基を含有するラテックスであり、その製法としては例えば、特開昭５６−１５７３５８等がある。
【００３４】
ヒドロキシル基を有するフッ素共重合体であるフッ素ポリオールとしては、特開昭５７−３４１０７号公報、特開昭６１−２３１０４４号公報、特開平３−３７２５２号公報等にその製造方法が開示されている。アクリル樹脂としては、特開昭６３−２９５６８０号公報、特開昭６３−１７５０５９号公報、特開昭５６−１５７３５８号公報等に開示されている。
【００３５】
本発明の水性塗料組成物において、熱解離性ブロックイソシアネート基と水親和性ポリオールの水酸基の当量比は、通常１０：１〜１：１０に設定される。
硬化剤としてメラミン系硬化剤を併用することもできる。メラミン系硬化剤としては、ヘキサメトキシメチロールメラミン、メチル・ブチルエーテル化メラミン等が代表的なものとして例示される。
【００３６】
また、必要に応じて酸化防止剤、紫外線吸収剤、顔料、アルミ等の金属粉顔料、ジブチル錫ジラウレート等の有機金属化合物等の架橋促進剤、レベリング剤、レオロジーコントロール剤、溶剤等を添加してもよい。
通常は、水親和性ポリオール、硬化剤、添加剤等を混合し、水を主成分とする媒体を添加し、塗装方法に応じた塗料粘度に調整することにより水性塗料組成物となる。
【００３７】
この様にして調整された水系塗料は、スプレー塗装、ロール塗装、シャワー塗装、浸漬塗装等の方法で金属、プラスチック、無機材料等に塗装され、耐チッピング塗料、プレコートメタル用塗料等としても有用である。
本発明の低温硬化性多官能水性ブロックポリイソシアネート組成物は、塗料以外に、インキ、接着剤、繊維、フィルム、セラミック等の無機材料、紙、木材、樹脂等の改質剤、表面処理剤、バインダーとしても有用である。
【００３８】
【発明の実施の形態】
以下に、実施例に基づいて本発明を更に詳細に説明するが、本発明は、以下の実施例に限定されるものではない。
尚、％は重量％、部は重量部を示す。評価は下記に従い行った。
（数平均分子量の測定）
数平均分子量は下記の装置を用いたゲルパーミエーションクロマトグラフ測定によるポリスチレン基準の数平均分子量である。

（粘度測定）
エミラ型回転粘度計を用いて２５℃で測定した。
（貯蔵安定性）
５℃で２週間貯蔵し、溶液状態が結晶化、沈殿などを生じ変化したものを×、変化しないものを○と評価した。
（ゲル分率）
硬化塗膜を、アセトンに２０℃で２４時間浸漬した時の未溶解部分重量の浸漬前対する値を計算し、８５％未満は×、８５％以上は○で表した。
（ブロックポリイソシアネートの水分散性評価）
ブロックポリイソシアネートと純水を重量比２：１０で混合し、その後の溶液状態を肉眼で観察した。混合液が均一で沈降物のない状態を「良好」と評価した。
【００３９】
【製造例１】
（ポリイソシアネート組成物の製造）
撹拌機、温度計、還流冷却管、窒素吹き込み管、滴下ロートを取り付けた４ツ口フラスコ内を窒素雰囲気にし、ＨＭＤＩを６００部、３価アルコールであるポリカプロラクトン系ポリエステルポリオール「プラクセル３０３」（ダイセル化学の商標、分子量３００）３０部を仕込み、撹拌下反応器内温度を９０℃１時間保持しウレタン化反応を行った。その後反応器内温度を６０℃に保持し、イソシアヌレート化触媒テトラメチルアンモニウムカプリエートを加え、収率が４８％になった時点で燐酸を添加し反応を停止した。
【００４０】
反応液をろ過した後、薄膜蒸発缶を用いて未反応のＨＭＤＩを除去した。得られたポリイソシアネート組成物の２５℃における粘度は９５００ｍＰａ・ｓ、イソシアネート含有量は１９．２％、数平均分子量は１１００、平均イソシアネート官能基数は５．１であった。
【００４１】
【製造例２、３】
（ポリイソシアネート組成物の製造）
製造例１と同様な装置を用いて表１に示す反応条件で製造した。得られたポリイソシアネート組成物の物性を表１に示す。
【００４２】
【比較製造例１】
製造例１と同様な装置を用いて表１に示す反応条件で製造した。得られた生成物の物性を表１に示す。
【００４３】
【実施例１】
（水性ブロックポリイソシアネート組成物の製造）
撹拌機、温度計、還流冷却管、窒素吹き込み管、滴下ロートを取り付けた４ツ口フラスコ内を窒素雰囲気にし、製造例１で得られたポリイソシアネート組成物１００部、分子量４００のメトキシポリエチレングリコール（日本油脂の商標「ユニオックスＭ４００」）１９部（ポリイソシアネートの全イソシアネート基の１０％と反応する）、プロピレングリコールモノメチルエーテルアセテート３７部を仕込み、８０℃で７時間保持した。その後反応液温度を５０℃に保持し、メチルエチルケトオキシム３８部を滴下した。反応液の赤外スペクトルを測定した結果、イソシアネート基が消失し、固形分濃度８０重量％の水性ブロックポリイソシアネート組成物が得られた。水分散性、貯蔵安定性の評価結果を表２に示す。
【００４４】
【実施例２】
（水性ブロックポリイソシアネート組成物の製造）
実施例１と同様の反応装置を用いて、フラスコ内を窒素雰囲気にし、製造例１で得られたポリイソシアネート組成物１００部、分子量４００のメトキシポリエチレングリコール（日本油脂の商標「ユニオックスＭ４００」）３８部（ポリイソシアネートの全イソシアネート基の２０％と反応する）、プロピレングリコールモノメチルエーテルアセテート３５部を仕込み、８０℃で７時間保持した。その後反応液温度を６０℃に保持し、マロン酸ジエチル２９部、アセト酢酸エチル２４部、２８％ナトリウムメチラート０．７８部を添加し、４Ｈｒ保持した。ｎ−ブタノール２９部を添加し、反応液温度８０℃で２Ｈｒ保持した。２−エチルヘキシルアシッドホスフェート０．７６部を添加した。反応液の赤外スペクトルを測定した結果、イソシアネート基が消失し、固形分濃度７５重量％の水性ブロックポリイソシアネート組成物が得られた。水分散性、貯蔵安定性の評価結果を表２に示す。
【００４５】
【実施例３〜５】
（水性ブロックポリイソシアネート組成物の製造）
表２に示す以外は実施例２と同様に行った。結果を表２に示す。
【００４６】
【比較例１】
比較製造例１で得られたポリイソシアネート組成物を用い、表２に示す以外は実施例１と同様に行った。水分散性、貯蔵安定性の評価結果を表２に示す。
【００４７】
【比較例２】
表２に示す以外は実施例２と同様に行った。水分散性、貯蔵安定性の評価結果を表２に示す。
【００４８】
【実施例６】
（水性塗料組成物の調製）
ジメチルエタノールアミンで中和された水溶性アクリルポリオール（日本触媒（株）の商標「アロロン７６」、樹脂分水酸基価６４ｍｇＫＯＨ／ｇ、樹脂分濃度５０重量％）と実施例１で得られた水性ブロックポリイソシアネート組成物を、ブロックイソシアネート基／水酸基の当量比が１／１になるように混合し、ジブチル錫ジラウレート０．３６部加えた。更に水を添加して、塗料粘度が、フォードカップＮｏ．４で３０秒になるように調整した。この塗料をアプリケータ塗装し、表３に示す焼き付け条件で硬化させた。塗膜評価結果を表３に示す。
【００４９】
【実施例７〜１０】
（水性塗料組成物の調製）
表３に示す以外は実施例６と同様に行った。塗膜評価結果を表３に示す。
【００５０】
【比較例３、４】
表３に示す以外は実施例６と同様に行った。塗膜評価結果を表３に示す。
【００５１】
【表１】

【００５２】
【表２】

【００５３】
【表３】

【００５４】
【発明の効果】
本発明の低温硬化性多官能水性ブロックポリイソシアネート組成物、及びそれを含む水性塗料組成物は、耐候性、低温硬化性に極めて優れた性能を有する。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an aqueous block polyisocyanate composition obtained from aliphatic and alicyclic diisocyanates and an aqueous coating composition using the same.
[0002]
[Prior art]
In recent years, water-based paints have attracted attention from the viewpoints of the global environment, safety, and hygiene. It has come to be used for industrial coatings from building exteriors to industrial products such as food cans and coil coatings. Furthermore, there are many proposals regarding one-component paints for automobiles that require high quality such as weather resistance, chemical resistance, impact resistance, etc., as disclosed in JP-A-56-157358, JP-A-63-175079, Japanese Patent Application Laid-Open No. 63-193968 discloses a water-based paint. Many of the curing agents used here are alkyl etherified melamines.
[0003]
In addition, the coating film obtained from isocyanate-crosslinked urethane-based paints has excellent wear resistance, chemical resistance, and stain resistance, and aliphatic and alicyclic diisocyanates as isocyanate components. By using non-yellowing polyisocyanate as a raw material, the weather resistance is further improved, and the demand is increasing.
Therefore, development of water-based urethane paints capable of crosslinking with isocyanate has been actively conducted. When a one-component property such as a line coating is required, the isocyanate group of the polyisocyanate is usually blocked with a heat dissociable blocking agent and used as a blocked polyisocyanate.
[0004]
As an aqueous technology for block polyisocyanate, for example, JP-A-52-59657 uses a surfactant to make the block polyisocyanate aqueous. JP-A-56-151753 uses polyethylene oxide containing a higher fatty acid having 7 to 26 carbon atoms, and block polyisocyanate can be made aqueous by blocking the isocyanate group of polyisocyanate with sodium bisulfite. I have to.
[0005]
Japanese Patent Application Laid-Open No. 61-31422 discloses a technique for reacting a specific polyoxyethylene, which is a hydrophilic group, with polyisocyanate to prevent elution of a hydrophilic component and to make it aqueous using a high-speed stirring group or the like. .
Japanese Patent Application Laid-Open No. 62-151419 and Japanese Patent Application Laid-Open No. 2-3465 disclose techniques for making a polyisocyanate block having a heat resistant isocyanurate structure aqueous.
[0006]
In JP-A-62-151419, a polyoxyethylene group is added to a part of a polyisocyanate, and a water-soluble polymer compound such as polyethylene glycol, a copolymer of ethylene oxide and propylene oxide is further mixed.
In JP-A-2-3465, hydrophilicity is imparted by hydroxycarboxylic acid.
[0007]
However, when using these water-based blocked polyisocyanates to form cross-linked coatings, high-temperature baking is required, and there are restrictions on the use of plastics that do not have heat resistance, and high-temperature baking requires a large energy cost. And
[0008]
[Problems to be solved by the invention]
An object of the present invention is to provide an aqueous block polyisocyanate composition having excellent weather resistance and low temperature curability and a coating composition containing the same.
[0009]
[Means for Solving the Problems]
The inventors of the present invention have arrived at the present invention as a result of intensive studies to solve the above problems. That is, the present invention is as follows.
1) With thermally dissociable blocked isocyanate groups An ethylene oxide adduct obtained by adding ethylene oxide to methanol, ethanol, or butanol having a number average molecular weight of 200 to 2,000. Nonionic hydrophilic groups In the range of molar ratio of thermally dissociable blocked isocyanate group and ethylene oxide adduct (polyether chain unit) in one molecule of 98/2 to 70/30. A low-temperature curable polyfunctional aqueous block polyisocyanate composition, the precursor of which is aliphatic And / or After reacting at least one alicyclic diisocyanate with a polyhydric alcohol, or in the presence of the alcohol Any state of After the isocyanate cyclic trimerization reaction, the low-temperature curing is characterized in that the unreacted diisocyanate monomer and the solvent are substantially removed, and the polyisocyanate composition is the following (1) to (4): Polyfunctional aqueous block polyisocyanate composition.
(1) Isocyanate group average functional group number; 4.5-20
(2) Viscosity at 25 ° C .; 5,000 to 100,000 mPa · s
(3) Number average molecular weight; 1,000 to 5,000
(4) Isocyanate concentration: 2 to 23% by weight
2) The above, wherein the polyhydric alcohol is a trihydric or higher alcohol 1) The low-temperature curable polyfunctional aqueous block polyisocyanate composition described.
3) The above number of isocyanate group average functional groups is 5-8 1) Or 2) The low-temperature curable polyfunctional aqueous block polyisocyanate composition described.
4) Thermally dissociable blocked isocyanate groups Ki The above consisting of a reaction product with at least one selected from shim and active methylene compounds 1) 2) Or 3) The low-temperature curable polyfunctional aqueous block polyisocyanate composition described.
5) The above wherein the active methylene compound comprises at least two or more 4) The low-temperature curable polyfunctional aqueous block polyisocyanate composition described.
6) The above containing a monohydric alcohol compound 1) ~ 5) The low-temperature curable polyfunctional aqueous block polyisocyanate composition according to any one of the above.
7) Water affinity polyol and above 1) ~ 6 A water-based coating composition comprising the low-temperature curable polyfunctional water-based block polyisocyanate composition described in any of the above.
[0010]
Hereinafter, the present invention will be described in detail.
The low-temperature curable polyfunctional aqueous block polyisocyanate composition of the present invention can be obtained by introducing a nonionic hydrophilic group and blocking the polyisocyanate composition as a precursor.
First, the polyisocyanate composition that is a precursor will be described.
[0011]
In order to obtain a polyisocyanate composition which is a precursor, diisocyanate and a polyhydric alcohol are used.
Diisocyanates include aliphatic and alicyclic diisocyanates. Aliphatic diisocyanates having 4 to 30 carbon atoms are preferred, and alicyclic diisocyanates having 8 to 30 carbon atoms are preferred. For example, 1,4-tetramethylene diisocyanate, 1,5-pentamethylene diisocyanate, 1 , 6-hexamethylene diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, 1,3-bis (isocyanatomethyl) -cyclohexane, 4,4′-dicyclohexylmethane diisocyanate, etc. Can be mentioned. Among these, 1,6-hexamethylene diisocyanate (hereinafter referred to as HMDI) and isophorone diisocyanate (hereinafter referred to as IPDI) are preferable from the viewpoint of weather resistance and industrial availability. May be.
[0012]
The polyisocyanate composition used as a precursor in the present invention can be obtained by reacting the diisocyanate with a polyhydric alcohol or in the presence of the alcohol by cyclic trimerization of the isocyanate, that is, isocyanurate.
The polyhydric alcohol is preferably a trihydric or higher alcohol, and the low molecular weight polyhydric alcohol includes, for example, trimethylolpropane, glycerin, pentaerythritol and the like. Examples of the high molecular weight polyhydric alcohol include aliphatic hydrocarbon polyols, polyether polyols, polyester polyols, epoxy resins, fluorine polyols, and acrylic polyols.
[0013]
Specific examples of the aliphatic hydrocarbon polyols include terminal hydroxylated polybutadiene and hydrogenated products thereof. Polyether polyols include, for example, polyether polyols obtained by adding an alkylene oxide such as ethylene oxide or propylene oxide alone or in a mixture to polyhydric alcohols such as glycerin and propylene glycol. Tetramethylene glycols, further polyether polyols obtained by reacting alkylene oxide with polyfunctional compounds such as ethylenediamine and ethanolamine, and so-called obtained by polymerizing acrylamide or the like using these polyethers as a medium. Polymer polyols and the like are included.
[0014]
Polyester polyols include, for example, dibasic acids selected from the group of carboxylic acids such as succinic acid, adipic acid, sebacic acid, dimer acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid or the like. Polyester polyol resins obtained by a condensation reaction of a polyhydric alcohol selected from the group of ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, trimethylolpropane, glycerin and the like alone or a mixture thereof, and, for example, ε -Polycaprolactones obtained by ring-opening polymerization of caprolactone using a polyhydric alcohol.
[0015]
Epoxy resins include glycidyl ether type epoxy resins (for example, bisphenol A type, bisphenol F type, bisphenol AD type, phenol novolac type, cresol novolac type, etc.), cyclic aliphatic epoxy resins (for example, alicyclic diepoxy acetal). , Alicyclic diepoxy adipates, etc.), glycidyl ester resins (phthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, diglycidyl-p-oxybenzoic acid, dimer acid glycidyl ester, etc.) Glycidylamine resins (N, N-diglycidylaniline, tetraglycidyldiaminodiphenylmethane, triglycidyl-p-aminophenol, etc.), heterocyclic epoxy resins (for example, diglycidyl Hydantoin, hydantoin type epoxy resins such as glycidyl glycidoxy alkyl hydantoin, such as triglycidyl isocyanurate), and an amino compound these epoxy resins, modified resins like polyamide compounds and the like.
[0016]
Examples of the acrylic polyol include acrylic acid esters having active hydrogen, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-hydroxybutyl acrylate, or monoester or methacrylic acid glycerol. Acid monoester, trimethylolpropane acrylic acid monoester, or methacrylic acid monoester alone or in a mixture with methyl acrylate, ethyl acrylate, isopropyl acrylate, acrylic acid-n-butyl, acrylic Acrylic acid esters such as 2-ethylhexyl acid, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 3-hydroxypropyl methacrylate, methacrylate Methacrylic acid ester having active hydrogen such as acid-4-hydroxybutyl, or methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, methacrylate-n-butyl, isobutyl methacrylate, methacrylate-n-hexyl, methacrylic acid A single component or a mixture selected from the group of methacrylic esters such as lauryl is an essential component, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, acrylamide, N-methylol acrylamide, diacetone acrylamide, etc. In the presence or absence of an unsaturated amide, and glycidyl methacrylate, styrene, vinyl toluene, vinyl acetate, acrylonitrile, dibutyl fumarate and other polymerizable monomers. It is allowed and acrylic polyol resin obtained.
[0017]
Among these polyols, preferred are the above-mentioned low molecular weight polyhydric alcohols, polyether polyols and polyester polyols, and particularly preferred are polyester polyols of polycaprolactones. These may be used alone or in combination of two or more.
In the isocyanate cyclic trimerization reaction, a catalyst is usually used. The catalyst used here is generally preferably one having basicity. (1) For example, tetraalkylammonium hydroxide such as tetramethylammonium and tetraethylammonium, weak organic acid salts such as acetic acid and capric acid, and (2) For example, hydroxyalkylammonium hydroxides such as trimethylhydroxypropylammonium, trimethylhydroxyethylammonium, triethylhydroxypropylammonium, triethylhydroxyethylammonium, etc., organic weak acid salts such as acetic acid and capric acid, and (3) alkylcarboxylic acid For example, alkyl metal salts such as tin, zinc and lead; (4) metal alcoholates such as sodium and potassium; and (5) aminosilyl groups such as hexamethyldisilazane. Compound, ▲ 6 ▼ Mannich bases, ▲ 7 ▼ combination with tertiary amines with epoxy compounds, ▲ 8 ▼ example, there is a phosphorus compound such as tributylphosphine.
[0018]
The reaction may or may not use a solvent. When using a solvent, it is preferable to use a solvent inert to the isocyanate group.
The reaction temperature is usually 20 to 160 ° C, preferably 40 to 130 ° C. The reaction end point varies depending on the polyhydric alcohol used, but the yield is generally 30% to 70%.
[0019]
When the reaction reaches the target yield, the catalyst is deactivated with, for example, sulfonic acid, phosphoric acid, and the reaction is stopped.
Unreacted substances and the solvent are removed, and a polyisocyanate composition having an isocyanurate structure formed by an isocyanate cyclic trimerization reaction, which is used in the present invention, can be obtained.
[0020]
The characteristics of the polyisocyanate composition substantially free of unreacted monomer and solvent are as follows.
(1) The number of isocyanate average functional groups is 4.5 to 20, preferably 5 to 8. If it is less than 4.5, the low-temperature curability is inferior, and if it exceeds 20, it adversely affects the appearance of the coating film. The number of isocyanate average functional groups is the number of isocyanate functional groups statistically possessed by one molecule of polyisocyanate, and is calculated from the following formula 1.
[0021]
[Expression 1]

[0022]
(2) The viscosity at 25 ° C. is 5,000 to 100,000 mPa · s. When the viscosity exceeds 100,000 mPa · s, the coating film appearance may be adversely affected. When the viscosity is less than 5,000 mPa · s, the range of the number of isocyanate average functional groups defined in the present invention cannot be obtained.
(3) The number average molecular weight is 1,000 to 5,000, preferably 1,500 to 4,000. If it is less than 1,000, the preferable range of the said isocyanate average functional group number cannot be obtained, and if it exceeds 5,000, the coating film appearance may be adversely affected due to an increase in viscosity.
(4) The isocyanate concentration is 2 to 23% by weight. If it is less than 2% by weight, the crosslinking density is small and a coating film having good mechanical properties cannot be obtained, and if it exceeds 23% by weight, the coating film becomes brittle.
[0023]
Japanese Patent Publication No. 58-3491 discloses a method for producing a water-dispersed blocked polyisocyanate. The specification describes polyisocyanates having a molecular weight of 800 or less and 2 to 4 functionalities, but there is no effect or suggestion of a highly polyfunctional, high molecular weight polyisocyanate composition used in the present invention.
The isocyanate group of the polyisocyanate composition as a precursor thus obtained can be reacted with a blocking agent to obtain a thermally dissociable blocked isocyanate group.
[0024]
Examples of the blocking agent used in the present invention include phenolic, active methylene, mercaptan, acid amide, acid imide, imidazole, urea, oxime, amine, and imide compounds. Or you may use it, mixing. Examples of more specific blocking agents are shown below.
(1) Phenol type; phenol, cresol, ethylphenol, butylphenol and the like.
(2) Active methylene type; malonic acid diester (dimethyl malonate, diethyl malonate, di-n-butyl malonate, di-2-ethylhexyl malonate, methyl n-butyl malonate, ethyl n-butyl malonate, methyl malonate sec-butyl, ethyl sec-butyl malonate, methyl t-butyl malonate, ethyl t-butyl malonate, diethyl methyl malonate, dibenzyl malonate, diphenyl malonate, benzyl methyl malonate, ethyl phenyl malonate, malonic acid t-butylphenyl, isopropylidene malonate, etc.), acetoacetate (methyl acetoacetate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, n-butyl acetoacetate, t-butyl acetoacetate, benzyl acetoacetate, Phenyl acetoacetate), acetyl Acetone and the like.
(3) Mercaptans: butyl mercaptan, dodecyl mercaptan, etc.
(4) Acid amide system: acetanilide, acetic acid amide, ε-caprolactam, δ-valerolactam, γ-butyrolactam, and the like.
(5) Acid imide type; succinimide, maleic imide and the like.
(6) Imidazole type; imidazole, 2-methylimidazole and the like.
(7) Urea type; urea, thiourea, ethylene urea, and the like.
(8) Oxime series: formaldoxime, acetaldoxime, acetoxime, methyl ethyl ketoxime, cyclohexanone oxime and the like.
(9) Amine-based: diphenylamine, aniline, carbazole and the like.
(10) Imine type; ethyleneimine, polyethyleneimine and the like.
(11) Bisulfite; sodium bisulfite and the like.
(12) Pyrazole type; pyrazole, 3-methylpyrazole, 3,5-dimethylpyrazole and the like.
(13) Triazole type; 1,2,4-triazole and the like.
[0025]
Of the above, active methylene, oxime, and acid amide are preferable, and acetooxime, methyl ethyl ketoxime, malonic acid diester, and acetoacetate are preferable. Particularly, one or more malonic acid diesters and acetoacetate 1 are preferable. It is preferable to use more than one species in combination. The molar ratio of malonic acid diester / acetoacetic acid ester is preferably 5/1 to 1/5. If the above value exceeds 5/1, crystallization of block polyisocyanate may occur. If it is less than 5, yellowing or the like may occur when the coating film is cured.
[0026]
The reaction between the polyisocyanate composition and the blocking agent can be performed regardless of the presence or absence of a solvent. When using a solvent, it is preferable to use a solvent inert to the isocyanate group.
In the blocking reaction, the above-mentioned isocyanate cyclic trimerization reaction catalyst can be used as a catalyst. When the used catalyst may adversely affect the physical properties of the paint, it is preferable to neutralize the catalyst with an acidic compound or the like. Examples of acidic compounds in this case include inorganic acids such as hydrochloric acid, phosphorous acid, and phosphoric acid, and sulfonic acids such as methanesulfonic acid, p-toluenesulfonic acid, p-toluenesulfonic acid methyl ester, and p-toluenesulfonic acid ethyl ester. Or its derivatives, ethyl phosphate, diethyl phosphate, isopropyl phosphate, diisopropyl phosphate, butyl phosphate, dibutyl phosphate, 2-ethylhexyl phosphate, di (2 ethylhexyl) phosphate, isodecyl phosphate, diisodecyl phosphate, oleyl acid phosphate, tetracosyl acid phosphate, There are ethylene glycol acid phosphate, butyl pyrophosphate, butyl phosphite, etc., and two or more of them may be used in combination.
[0027]
The reaction can be generally carried out at -20 to 150 ° C, preferably 0 to 100 ° C. If the temperature exceeds 150 ° C., side reactions may occur. On the other hand, if the temperature is too low, the reaction rate is low, which is disadvantageous.
The nonionic hydrophilic group in the present invention is a compound having an active hydrogen at one end and a polyethylene oxide chain (hereinafter referred to as an ethylene oxide adduct).
[0028]
The ethylene oxide adduct is obtained by adding ethylene oxide to a monoalcohol such as methanol, ethanol, or butanol. The ethylene oxide content is preferably 50% by weight or more, and the number average molecular weight is preferably 200 to 2,000. The ethylene oxide adduct may contain propylene oxide units.
The reaction of the ethylene oxide addition compound and the polyisocyanate can also be performed using a solvent. In this case, the solvent used is preferably inert to the isocyanate. The reaction temperature is 40 to 150 ° C, preferably 60 to 120 ° C. If necessary, a basic compound such as a tin compound such as dibutyltin dilaurate may be used for the reaction catalyst.
[0029]
Either the reaction of the isocyanate group and the blocking agent, or the reaction of the isocyanate group and the ethylene oxide adduct can be preceded or can be performed simultaneously.
The isocyanate groups of the polyisocyanate are all consumed by the reaction of the blocking agent and the ethylene oxide adduct. In this case, the molar ratio of the blocking agent to the ethylene oxide adduct (polyether chain unit) is 98/2 to 60/40, preferably 98/2 to 70/30. If it exceeds 98/2, the water dispersibility of the block polyisocyanate is lowered, and if it is less than 60/40, the physical properties of the coating film tend to be lowered.
[0030]
Further, nonionic, anionic, cationic and amphoteric surfactants can be added depending on the purpose such as improvement of water dispersibility. Specific examples of the surfactant include, for example, nonionics such as polyethylene glycol and polyhydric alcohol fatty acid esters, fatty acid salts, alkyl sulfates, alkylbenzene sulfonates, alkyl phosphates and other anionics, alkylamine salts, alkyls Examples include surfactants such as cationic compounds such as betaine, carboxylic acid amine salts, sulfonic acid amine salts, and sulfate ester salts.
[0031]
In the present invention, it is preferable to include a monohydric alcohol compound in order to improve storage stability. Examples of the monohydric alcohol compound include aliphatic, alicyclic, and aromatic, with aliphatic being preferred. C1-C20 is preferable, for example, methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, 2-methyl-1-propanol, n-amyl alcohol, 2-pentanol, Saturation of 3-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 2-methyl-2-butanol, 3-methyl-2-butanol, 2,2, -dimethyl-1-propanol There are ether alcohols such as alcohol, 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, and 3,6-dioxa-1-heptanol. The amount added is preferably 0.2 to 10 times the molar amount of the thermally dissociable blocked isocyanate group.
[0032]
The low-temperature curable polyfunctional aqueous block polyisocyanate composition prepared in this way is mixed with a water-affinity polyol to form the main component of the aqueous coating composition.
The water-affinity polyol used in the present invention can be used without particular limitation as long as it is usually used for water-based paints, and has an ionic property even in anionic, cationic and zwitterionic systems. It may not be. There are alkyd, polyester, epoxy, fluorine, acrylic and the like. The resin hydroxyl value is 10 to 300 mgKOH / g, and is dissolved or dispersed in a dispersion medium containing water as a main component. When the resin hydroxyl value is less than 10 mgKOH / g, the density of urethane cross-linking due to the reaction with the isocyanate component is reduced, and the desired physical properties of the present invention cannot be achieved sufficiently. When it exceeds 300 mgKOH / g, on the contrary, the crosslink density increases and the mechanical properties of the coating film tend to decrease.
[0033]
Soluble polyols have a number average molecular weight of 2,000 to 50,000. For example, JP-A 63-295680, JP-A 63-175059, JP-A 62-216671, A manufacturing method thereof is disclosed in, for example, Japanese Laid-Open Patent Application No. 2-191692. The dispersion type polyol is a latex containing a hydroxyl group, and its production method includes, for example, JP-A-56-157358.
[0034]
As a fluoropolyol which is a fluorocopolymer having a hydroxyl group, its production method is disclosed in JP-A-57-34107, JP-A-61-231044, JP-A-3-37252 and the like. . Acrylic resins are disclosed in JP-A 63-295680, JP-A 63-175059, JP-A 56-157358, and the like.
[0035]
In the water-based coating composition of the present invention, the equivalent ratio of the thermally dissociable blocked isocyanate group to the hydroxyl group of the water-soluble polyol is usually set to 10: 1 to 1:10.
A melamine-based curing agent can be used in combination as a curing agent. Typical examples of the melamine curing agent include hexamethoxymethylol melamine and methyl / butyl etherified melamine.
[0036]
If necessary, add antioxidants, ultraviolet absorbers, pigments, metal powder pigments such as aluminum, cross-linking accelerators such as organometallic compounds such as dibutyltin dilaurate, leveling agents, rheology control agents, solvents, etc. Also good.
Usually, an aqueous coating composition is obtained by mixing a water-affinity polyol, a curing agent, an additive, and the like, adding a medium containing water as a main component, and adjusting the coating viscosity according to the coating method.
[0037]
Water-based paints prepared in this way are applied to metals, plastics, inorganic materials, etc. by spray coating, roll coating, shower coating, dip coating, etc., and are also useful as anti-chipping coatings and pre-coated metal coatings. is there.
The low-temperature curable polyfunctional aqueous block polyisocyanate composition of the present invention includes, in addition to paints, inorganic materials such as inks, adhesives, fibers, films, ceramics, modifiers such as paper, wood, and resins, surface treatment agents, It is also useful as a binder.
[0038]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the following examples.
In addition,% shows weight% and a part shows a weight part. Evaluation was performed according to the following.
(Measurement of number average molecular weight)
The number average molecular weight is a polystyrene-based number average molecular weight measured by gel permeation chromatography using the following apparatus.

(Viscosity measurement)
It measured at 25 degreeC using the Emira type | formula rotational viscometer.
(Storage stability)
The sample was stored at 5 ° C. for 2 weeks, and when the solution state changed due to crystallization, precipitation or the like, the change was evaluated as x, and the change was evaluated as ◯.
(Gel fraction)
When the cured coating film was immersed in acetone at 20 ° C. for 24 hours, the value of the undissolved partial weight before immersion was calculated, and less than 85% was represented by x, and 85% or more was represented by ◯.
(Evaluation of water dispersibility of block polyisocyanate)
Block polyisocyanate and pure water were mixed at a weight ratio of 2:10, and the subsequent solution state was observed with the naked eye. A state in which the liquid mixture was uniform and no precipitate was evaluated as “good”.
[0039]
[Production Example 1]
(Production of polyisocyanate composition)
A four-necked flask equipped with a stirrer, thermometer, reflux condenser, nitrogen blowing tube, and dropping funnel was placed in a nitrogen atmosphere, 600 parts of HMDI, a polycaprolactone-based polyester polyol “PLAXEL 303” (Daicel) Chemical brand, molecular weight 300) 30 parts were charged, and the temperature in the reactor was kept at 90 ° C. for 1 hour with stirring to conduct urethanization reaction. Thereafter, the temperature in the reactor was kept at 60 ° C., the isocyanuration catalyst tetramethylammonium capriate was added, and when the yield reached 48%, phosphoric acid was added to stop the reaction.
[0040]
After the reaction solution was filtered, unreacted HMDI was removed using a thin film evaporator. The resulting polyisocyanate composition had a viscosity at 25 ° C. of 9500 mPa · s, an isocyanate content of 19.2%, a number average molecular weight of 1100, and an average isocyanate functional group number of 5.1.
[0041]
[Production Examples 2 and 3]
(Production of polyisocyanate composition)
Using the same apparatus as in Production Example 1, production was carried out under the reaction conditions shown in Table 1. Table 1 shows the physical properties of the obtained polyisocyanate composition.
[0042]
[Comparative Production Example 1]
Using the same apparatus as in Production Example 1, production was carried out under the reaction conditions shown in Table 1. Table 1 shows the physical properties of the obtained product.
[0043]
[Example 1]
(Production of aqueous block polyisocyanate composition)
A 4-necked flask equipped with a stirrer, thermometer, reflux condenser, nitrogen blowing tube, and dropping funnel was placed in a nitrogen atmosphere, and 100 parts of the polyisocyanate composition obtained in Production Example 1, a methoxypolyethylene glycol having a molecular weight of 400 ( 19 parts (reacted with 10% of all isocyanate groups of polyisocyanate) and 37 parts of propylene glycol monomethyl ether acetate were added and maintained at 80 ° C. for 7 hours. Thereafter, the reaction solution temperature was maintained at 50 ° C., and 38 parts of methyl ethyl ketoxime was added dropwise. As a result of measuring the infrared spectrum of the reaction solution, the isocyanate group disappeared and an aqueous block polyisocyanate composition having a solid content concentration of 80% by weight was obtained. Table 2 shows the evaluation results of water dispersibility and storage stability.
[0044]
[Example 2]
(Production of aqueous block polyisocyanate composition)
Using the same reaction apparatus as in Example 1, the inside of the flask was put into a nitrogen atmosphere, and 100 parts of the polyisocyanate composition obtained in Production Example 1 and methoxypolyethylene glycol having a molecular weight of 400 (trademark “Niox M400” from NOF Corporation) 38 parts (reacted with 20% of all isocyanate groups of polyisocyanate) and 35 parts of propylene glycol monomethyl ether acetate were charged and held at 80 ° C. for 7 hours. Thereafter, the temperature of the reaction solution was maintained at 60 ° C., 29 parts of diethyl malonate, 24 parts of ethyl acetoacetate, and 0.78 part of 28% sodium methylate were added and maintained for 4 hours. 29 parts of n-butanol was added and the reaction solution temperature was maintained at 80 ° C. for 2 hours. 0.76 part of 2-ethylhexyl acid phosphate was added. As a result of measuring the infrared spectrum of the reaction solution, the isocyanate group disappeared and an aqueous block polyisocyanate composition having a solid content concentration of 75% by weight was obtained. Table 2 shows the evaluation results of water dispersibility and storage stability.
[0045]
Examples 3 to 5
(Production of aqueous block polyisocyanate composition)
The procedure was the same as in Example 2 except that it was shown in Table 2. The results are shown in Table 2.
[0046]
[Comparative Example 1]
The same procedure as in Example 1 was performed except that the polyisocyanate composition obtained in Comparative Production Example 1 was shown in Table 2. Table 2 shows the evaluation results of water dispersibility and storage stability.
[0047]
[Comparative Example 2]
The procedure was the same as in Example 2 except that it was shown in Table 2. Table 2 shows the evaluation results of water dispersibility and storage stability.
[0048]
[Example 6]
(Preparation of aqueous coating composition)
Water-soluble acrylic polyol neutralized with dimethylethanolamine (trade name “Allolon 76” of Nippon Shokubai Co., Ltd., resin hydroxyl value of 64 mg KOH / g, resin concentration of 50% by weight) and aqueous block obtained in Example 1 The polyisocyanate composition was mixed so that the equivalent ratio of blocked isocyanate group / hydroxyl group was 1/1, and 0.36 part of dibutyltin dilaurate was added. Further, water was added and the viscosity of the paint was changed to Ford Cup No. 4 was adjusted to 30 seconds. This paint was applied with an applicator and cured under the baking conditions shown in Table 3. The coating film evaluation results are shown in Table 3.
[0049]
Examples 7 to 10
(Preparation of aqueous coating composition)
The same operation as in Example 6 was carried out except that shown in Table 3. The coating film evaluation results are shown in Table 3.
[0050]
[Comparative Examples 3 and 4]
The same operation as in Example 6 was carried out except that shown in Table 3. The coating film evaluation results are shown in Table 3.
[0051]
[Table 1]

[0052]
[Table 2]

[0053]
[Table 3]

[0054]
【The invention's effect】
The low-temperature curable polyfunctional aqueous block polyisocyanate composition of the present invention and the aqueous coating composition containing the same have extremely excellent performance in weather resistance and low-temperature curability.

Claims (7)

Thermally dissociable blocked isocyanate group and nonionic hydrophilic group of ethylene oxide adduct in which ethylene oxide is added to methanol, ethanol or butanol having a number average molecular weight of 200 to 2,000 in one molecule. A low-temperature curable polyfunctional aqueous block polyisocyanate composition having a molar ratio of a group and an ethylene oxide adduct (polyether chain unit) in the range of 98/2 to 70/30 , wherein the precursor is aliphatic and / or or after reacting the at least one and polyhydric alcohols alicyclic diisocyanate, or after the isocyanate cyclic trimeric reaction either in the state of presence of the alcohol, substantially unreacted diisocyanate monomers and solvents Is removed, and the polyisocyanates (1) to (4) below: Is over preparative composition, temperature curing polyfunctional aqueous blocked polyisocyanate composition characterized.
(1) Isocyanate group average functional group number; 4.5 to 20 (2) Viscosity at 25 ° C .; 5,000 to 100,000 mPa · s (3) Number average molecular weight; 1,000 to 5,000 (4) Isocyanate concentration 2-23% by weight   The low-temperature curable polyfunctional aqueous block polyisocyanate composition according to claim 1, wherein the polyhydric alcohol is a trihydric or higher alcohol.   The low-temperature curable polyfunctional aqueous block polyisocyanate composition according to claim 1 or 2, wherein the number of isocyanate group average functional groups is 5 to 8. Thermally dissociative blocked isocyanate group, isocyanate group and take care shim system, low-temperature curable comprises a reaction product of at least one selected from active methylene compound according to claim 1, 2 or 3 wherein the multifunctional aqueous bromide poke polyisocyanate Composition.   The low-temperature curable polyfunctional aqueous block polyisocyanate composition according to claim 4, wherein the active methylene compound comprises at least two kinds.   The low-temperature curable polyfunctional aqueous block polyisocyanate composition according to any one of claims 1 to 5, which contains a monohydric alcohol compound.   An aqueous coating composition comprising a water-compatible polyol and the low-temperature curable polyfunctional aqueous block polyisocyanate composition according to any one of claims 1 to 6.