JP2004267991A - Method of manufacturing gas phase process silica aqueous dispersion and inkjet recording material using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a high concentration gas phase process silica dispersion extremely superior in process by shortening the time required for dispersion and to provide an inkjet recording material having a high ink absorbency and a gloss using the same. <P>SOLUTION: The method of manufacturing the gas phase process silica dispersion comprises two processes of a first dispersion process obtaining a coarse dispersed material of a gas phase process silica, and a second dispersion process finely dispersing the coarse dispersed material obtained through the first dispersion process to adjust a particle size distribution. In the first dispersion process, a flow type vacuum dispersing agitator continuously supplying and dispersing the gas phase process silica to a mixture of a dispersing agent and an aqueous dispersing medium, and a batch type dispersing tank having a rotary-blade type agitator are used together, and also dispersion is carried out under a reduced pressure. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２５】
【化２】

【００２６】
【化３】

【００２７】
【化４】

【００２８】
一般式（１）、（２）、（３）及び（４）において、Ｒ_１及びＲ_２は各々、水素原子、メチル基、エチル基等のアルキル基、またはヒドロキシエチル基等の置換アルキル基を表し、Ｙはラジカル重合可能なモノマー（例えば、スルホニル、アクリルアミド及びその誘導体、アクリル酸エステル、メタクリル酸エステル等）を表す。また、一般式（３）及び（４）において、ｎ／ｍ＝９／１〜２／８、ｌ＝５〜１００００である。Ｘはアニオンを表す。
【００２９】
一般式（３）又は（４）で示されるポリジアリルアミンの誘導体の具体的な例としては、特開昭６０−８３８８２号公報記載のＳＯ_２基を繰り返し単位に含む もの、特開平１−９７７６号公報に記載されているアクリルアミドとの共重合体等が挙げられる。本発明に用いられるポリジアリルアミン誘導体のカチオンポリマーの平均分子量は、２，０００〜５万程度がより好ましい。
【００３０】
水溶性金属化合物としては、例えば水溶性の多価金属塩が挙げられる。カルシウム、バリウム、マンガン、銅、コバルト、ニッケル、アルミニウム、鉄、亜鉛、ジルコニウム、クロム、マグネシウム、タングステン、モリブデンから選ばれる金属の水溶性塩が挙げられる。具体的には例えば、酢酸カルシウム、塩化カルシウム、ギ酸カルシウム、硫酸カルシウム、酢酸バリウム、硫酸バリウム、リン酸バリウム、塩化マンガン、酢酸マンガン、ギ酸マンガンニ水和物、硫酸マンガンアンモニウム六水和物、塩化第二銅、塩化アンモニウム銅（ＩＩ）ニ水和物、硫酸銅、塩化コバルト、チオシアン酸コバルト、硫酸コバルト、硫酸ニッケル六水和物、塩化ニッケル六水和物、酢酸ニッケル四水和物、硫酸ニッケルアンモニウム六水和物、アミド硫酸ニッケル四水和物、硫酸アルミニウム、亜硫酸アルミニウム、チオ硫酸アルミニウム、ポリ塩化アルミニウム、硝酸アルミニウム九水和物、塩化アルミニウム六水和物、臭化第一鉄、塩化第一鉄、塩化第二鉄、硫酸第一鉄、硫酸第二鉄、フェノールスルホン酸亜鉛、臭化亜鉛、塩化亜鉛、硝酸亜鉛六水和物、硫酸亜鉛、酢酸ジルコニウム、塩化ジルコニウム、塩化酸化ジルコニウム八水和物、ヒドロキシ塩化ジルコニウム、酢酸クロム、硫酸クロム、硫酸マグネシウム、塩化マグネシウム六水和物、クエン酸マグネシウム九水和物、りんタングステン酸ナトリウム、クエン酸ナトリウムタングステン、１２タングストりん酸ｎ水和物、１２タングストけい酸２６水和物、塩化モリブデン、１２モリブドりん酸ｎ水和物等が挙げられる。
【００３１】
分散助剤の添加量は、好ましくは気相法シリカの０．１〜１５質量％、より好ましくは１〜１０質量％である。多すぎると最終のインクジェット記録材料表面にひび割れが発生しやすく、少なすぎると分散安定性の効果が得られない。
【００３２】
本発明の水系分散媒は主として水が好適に用いられるが、イオン交換水が特に好適である。粘度調整等の目的で必要に応じて水にメチルアルコール、エチルアルコール、イソプロピルアルコール、ｎ−プロピルアルコール、酢酸メチル、酢酸エチル等の低沸点溶剤を添加することもできる。低沸点有機溶剤を添加する場合の添加量は水の３０質量％程度以下が一般的である。
【００３３】
本発明において、一次分散工程では分散助剤と水系分散媒の混合物に気相法シリカ粉体を連続的に供給及び分散するフロー式吸引分散撹拌機と、回転翼式撹拌機を備えたバッチ式分散タンクを併用し、且つ１００ｍｍａｑ以上の減圧にて分散することを特徴とする。図１は本発明の一次分散工程を示す概略構成図である。分散助剤と水系分散媒は、回転翼式撹拌機（３）を備えたバッチ式分散タンク（２）に所定量溜められ、気相法シリカ粉体（６）は粉体供給経路（５）を経由してフロー式吸引分散撹拌機（１）より連続的に供給される。回転翼式撹拌機（３）を備えたバッチ式分散タンク（２）は循環経路（４）を介してフロー式吸引分散撹拌機（１）と連結されており、分散助剤と水系分散媒の混合物はこのルートを循環しながら（１）部において剪断力を受けながら気相法シリカ粉体と混合・分散される。分散助剤と水系分散媒の混合物が（２）→（４）→（１）→（４）→（２）と循環する際循環系内は負圧となり、気相法シリカ粉体は（５）、（１）を通して円滑に循環系内に引き込まれるが、粉体搬送を補助する目的で（５）の途中にダイヤフラムポンプ等のポンプを配置する事は何等差し支えない。本発明の様な設備構成とすることで気相法シリカ粉体の一次分散を閉鎖系で行う事が出来、従って粉体が飛散して作業環境を悪化させたり外部から異物が混入するリスクを排除する事が出来る事は非常に大きな利点の一つである。
【００３４】
所定量の気相法シリカ粉体の投入が終了した後にフロー式吸引分散撹拌機と、回転翼式撹拌機を備えたバッチ式分散タンクを含む循環経路は真空ポンプ（７）を使用した減圧下で分散を継続する。これにより撹拌中の気泡の発生を抑制したり、それまでの段階で発生した気泡を脱泡することが出来、分散効率が格段に上昇して分散時間を短縮する事が出来る他、分散系の温度上昇の抑止効果も併せ持つ。減圧レベルは０．０２ＭＰａ以上、０．０７ＭＰａ以下の範囲にあることが好ましい。０．０２ＭＰａ未満の場合は気泡発生の抑制が不十分となる。０．０７ＭＰａを越える場合は、分散に悪影響を及ぼすものではないが、気泡の抑制や脱泡の効果が頭打ちとなり、それ以上の減圧にする意味がない。減圧はロータリーポンプ、オイルディフュージョンポンプ等の公知の減圧／真空ポンプを用いて行うことができる。
【００３５】
本発明のフロー式吸引分散撹拌機は主要部分としては混合／分散チャンバ、ロータ、ステータより構成される。ロータには内ブレードと外ブレードが付いているが、循環する液体はロータの内ブレードにより吸引加速されステータに向かう。一方、分散チャンバに吸引された気相法シリカ粉体はロータ表面で加速され、裏面から導入された液体と共にステータを通過し、その際に液体と粉体が瞬時に混合され、外ブレードにより加速されて液出口に向かう。液体と粉体は分散チャンバ内での剪断力と衝撃力により、強力な粉砕・混合・分散作用を受ける。かかるフロー式吸引分散撹拌機としては、例えばイーストラル社より市販されているＣｏｎｔｉ−ＴＤＳ（商品名）を使用することができる。
【００３６】
本発明の回転翼式撹拌機を備えたバッチ式分散タンクにおいて、回転翼式撹拌翼として好適に使用されるのは、特開２００２−２７４０１８号公報に開示されているものと同様の形状のノコギリ歯状ブレードやプロペラ型羽根であり、より好ましくはより剪断力の強いノコギリ歯状ブレードである。該回転翼は分散効率か、周速は２０ｍ／秒以上であることが好ましく、又、１軸であっても良いが２軸である方がより好ましい。又、同じ軸に２つ以上の撹拌翼を取り付ることも可能である。回転翼の好ましい直径はバッチ式分散タンクの直径の１０〜４０％である。
【００３７】
本発明において、一次分散工程で得られる気相法シリカの粗分散物とは、一次粒子の平均粒径の数倍〜１万倍以下程度の粒径の凝集物が水系分散媒、及び分散助剤と混合分散された状態であり、好ましい粘度は概略１０〜数千ｍＰａ・ｓである。一次分散工程で得られた気相法シリカの粗分散物は、必要であれば更に適度の水、低沸点溶剤等を添加して二次分散工程に適した液性に整えても良い。
【００３８】
本発明では、一次分散工程で気相法シリカ微粒子をより均一に分散することで二次分散工程での分散が容易になり、得られる分散物を使用したインクジェット記録材料は優れた白紙部光沢性とインク吸収性を有する。特に、一次分散工程で水系分散媒、及び分散助剤中で分散することで二次分散工程で均一な二次粒子の分散が容易になり、得られる分散物を使用したインクジェット記録材料はより優れた白紙部光沢性とインク吸収性を有する。
【００３９】
本発明において、一次分散工程で得られた気相法シリカの粗分散物を微細分散処理する二次分散工程では、好ましくは高圧ホモジナイザー、超高圧ホモジナイザー、超音波分散機、及び薄膜施回型分散機から選ばれる少なくとも１つを用いる。高圧ホモジナイザーはバルブ／バルブシート間の間隙を高圧・高速で被処理物を通過させる際の剪断力を利用した分散機でゴウリンタイプとして広く知られており、ＡＰＶゴウリン社、ラニー社、ＮＩＲＯ ＳＯＡＶＩ社、（株）日本精機製作所、三和機械（株）等から市販されているものを使用できる。超高圧ホモジナイザーは高圧ホモジナイザーでは達成できないような更に高圧の処理ができる分散機であり、チャンバー中の折れ曲がった細い経路内を高圧・高速で被処理物を通過させる際の剪断力や衝撃力を利用したタイプや、対向するノズルから被処理液を高圧・高速で噴射して被処理液同士を衝突させる際の剪断力を利用した対向衝突型ジェット粉砕タイプが知られており、（株）スギノマシン、みづほ工業（株）、ナノマイザー社等からアルティマイザー、マイクロフルイダイザー、ナノマイザー等の商品名で市販されているものを使用できる。超音波分散機は超音波発振器より発生する超音波振動エネルギーを利用した分散機であり（株）日本精機製作所等から市販されているものを使用できる。薄膜施回型分散機はブラシを備えた高速回転軸を有するチャンバー内に被処理液を導入し、被処理液が薄膜となってチャンバー内壁を上部に移動する際のずり応力を利用したタイプであり、特殊機化工業（株）からフィルミックスという商品名で市販されているものを用いることができる。一次分散工程や二次分散工程の剪断により、添加していた分散助剤が劣化して粒子の分散安定化効果が低下するのを補う目的で、必要に応じて二次分散処理を行う前に分散助剤を追加しても差し支えない。
【００４０】
本発明において、一次分散工程後に得られる気相法シリカの最終分散物は、一次粒子の平均粒径の数倍〜２００倍以下程度の粒径の凝集物が水系分散媒、及び分散助剤と混合分散された状態であり、ハンドリング性から、好ましい粘度は概略１０００ｍＰａ・ｓ以下であり、より好ましくは５００ｍＰａ・ｓである。また、品質の安静性の観点から経時後の粘度上昇は少ない方が好ましい。
【００４１】
本発明において、好ましい一次分散工程の処理条件や二次分散工程の処理条件は、二次分散工程処理後の気相法シリカ分散物の粒度分布測定、電子顕微鏡観察等ににより粗粒の存在有無を評価したり、粘度測定を行ったり、分散物を使用したインクジェット記録材料の特性評価により決定される。
【００４２】
本発明のインクジェット記録材料は、かかる方法にて分散液とした気相法シリカを主成分とする塗布液を支持体に塗布し、インク受容層を形成することによって得られる。気相法シリカは、インク受容層の主たる割合、すなわちインク受容層の全固形分に対して気相法シリカを５０質量％以上、好ましくは６０質量％以上、より好ましくは６５質量％以上含有することが好ましい。インク受容層には、気相法シリカ固形分を８ｇ／ｍ^２以上含有するのが好ましく、１０〜３５ｇ／ｍ^２の範囲で用いるのがより好ましい。この範囲より少ないとインク吸収性が劣り、多すぎると強度が劣る傾向となる。
【００４３】
本発明のインクジェット記録材料のインク受容層において気相法シリカを結着する目的でバインダーを用いる。バインダーとしては、デンプン類、ヒドロキシエチルセルロース、メチルセルロース、エチルセルロース、カルボキシメチルセルロース等のセルロース誘導体、カゼイン、ゼラチンなどのプロテイン、酸化デンプン、エステル化合物デンプン等の水性天然高分子化合物、ポリビニルアルコール、変性ポリビニルアルコール、ポリビニルピロリドン、ポリアクリル酸、アクリル酸アミド／アクリル酸エステル共重合体、アクリル酸アミド／アクリル酸エステル／メタクリル酸３元共重合体、スチレン／無水マレイン酸共重合体のアルカリ塩、ポリアクリルアミド、スチレン／無水マレイン酸共重合体、エチレン／無水マレイン酸共重合体のアルカリ塩、ポリ酢酸ビニル、ポリウレタン、ポリアクリル酸エステル、スチレン／ブタジエン共重合体、アクリロニトリル／ブタジエン共重合体、アクリル酸メチル／ブタジエン共重合体、アクリロニトリル／ブタジエン／アクリル酸共重合体、エチレン／酢酸ビニル共重合体等の水溶性合成高分子化合物や水分散性合成高分子化合物の水系分散物が挙げられるが、透明性が高くインクのより高い浸透性が得られる親水性バインダーが好ましく用いられる。親水性バインダーの使用に当たっては、親水性バインダーがインクの初期の浸透時に膨潤して空隙を塞いでしまわないことが重要であり、この観点から比較的室温付近で膨潤性の低い親水性バインダーが好ましく用いられる。特に好ましい親水性バインダーは完全または部分ケン化のポリビニルアルコールまたはカチオン変性ポリビニルアルコールである。
【００４４】
ポリビニルアルコールの中でも特に好ましいのは、ケン化度が８０％以上の部分または完全ケン化したものである。平均重合度２００〜５０００のものが好ましい。
【００４５】
また、カチオン変性ポリビニルアルコールとしては、例えば特開昭６１−１０４８３号に記載されているような、第１〜３級アミノ基や第４級アンモニウム基をポリビニルアルコールの主鎖あるいは側鎖中に有するポリビニルアルコールである。
【００４６】
バインダー量は、気相法シリカに対して４０質量％以下、好ましくは３０質量％以下である。このようにバインダーの比率を小さくすることによって、インク吸収性は向上するが、ひび割れや粉落ちが発生しやすく、下限は８質量％である。
【００４７】
上記親水性バインダーを用いる際は架橋剤（硬膜剤）と共に用いることが好ましい。架橋剤の具体的な例としては、ホルムアルデヒド、グルタルアルデヒドの如きアルデヒド系化合物、ジアセチル、クロルペンタンジオンの如きケトン化合物、ビス（２−クロロエチル尿素）−２−ヒドロキシ−４，６−ジクロロ−１，３，５トリアジン、米国特許第３，２８８，７７５号記載の如き反応性のハロゲンを有する化合物、ジビニルスルホン、米国特許第３，６３５，７１８号記載の如き反応性のオレフィンを持つ化合物、米国特許第２，７３２，３１６号記載の如きＮ−メチロール化合物、米国特許第３，１０３，４３７号記載の如きイソシアナート類、米国特許第３，０１７，２８０号、同２，９８３，６１１号記載の如きアジリジン化合物類、米国特許第３，１００，７０４号記載の如きカルボジイミド系化合物類、米国特許第３，０９１，５３７号記載の如きエポキシ化合物、ムコクロル酸の如きハロゲンカルボキシアルデヒド類、ジヒドロキシジオキサンの如きジオキサン誘導体、クロム明ばん、硫酸ジルコニウム、ほう酸及びほう酸塩の如き無機架橋剤等があり、これらを１種または２種以上組み合わせて用いることができる。これらの中でも、特にほう酸またはほう酸塩が好ましい。
【００４８】
本発明のインクジェット記録材料を構成するインク受容層にインク定着用の媒染剤としてカチオン性化合物を添加するほうが好ましい。かかるカチオン性化合物としては、カチオン性ポリマーや水溶性金属化合物が挙げられる。カチオン性ポリマーとしては、ポリアリルアミン、アルキルアミン重合物、１〜３級アミノ基、４級アンモニウム塩基、あるいはホスホニウム塩基を有するポリマーが好ましく用いられる。
【００４９】
水溶性金属化合物としては、例えば前記の分散助剤で使用されるのと同様の水溶性の多価金属塩が挙げられる。これらの水溶性金属化合物の中でも特に水溶性アルミニウム化合物あるいは周期表４Ａ族元素を含む水溶性化合物が好ましい。水溶性アルミニウム化合物は、例えば無機塩としては塩化アルミニウムまたはその水和物、硫酸アルミニウムまたはその水和物、アンモニウムミョウバン等が知られている。さらに、無機系の含アルミニウムカチオンポリマーである塩基性ポリ水酸化アルミニウム化合物がある。特に、塩基性ポリ水酸化アルミニウム化合物が好ましい。
【００５０】
前記塩基性ポリ水酸化アルミニウム化合物とは、主成分が下記の一般式１、２又は３で示され、例えば［Ａｌ_６（ＯＨ）_１５］^３＋、［Ａｌ_８（ＯＨ）_２０］^４＋、［Ａｌ_１３（ＯＨ）_３４］^５＋、［Ａｌ_２１（ＯＨ）_６０］^３＋、等のような塩基性で高分子の多核縮合イオンを安定に含んでいる水溶性のポリ水酸化アルミニウムである。
【００５１】
［Ａｌ_２（ＯＨ）_ｎＣｌ_６−ｎ］_ｍ 一般式１
［Ａｌ（ＯＨ）_３］_ｎＡｌＣｌ_３ 一般式２
Ａｌ_ｎ（ＯＨ）_ｍＣｌ_{（３ｎ−ｍ）} ０＜ｍ＜３ｎ 一般式３
【００５２】
これらのものは多木化学（株）よりポリ塩化アルミニウム（ＰＡＣ）の名で水処理剤として、浅田化学（株）よりポリ水酸化アルミニウム（Ｐａｈｏ）の名で、また、（株）理研グリーンよりピュラケムＷＴの名で、また他のメーカーからも同様の目的を持って上市されており、各種グレードの物が容易に入手できる。本発明ではこれらの市販品をそのままでも使用できるが、ｐＨが不適当に低い物もあり、その場合は適宜ｐＨを調節して用いることも可能である。
【００５３】
本発明に用いられる周期表４Ａ族元素を含む水溶性化合物は水溶性で有れば特に制限はないがチタンまたはジルコニウムを含む水溶性化合物が好ましい。例えばチタンを含む水溶性化合物としては塩化チタン、硫酸チタンが、ジルコニウムを含む水溶性化合物としては酢酸ジルコニウム、塩化ジルコニウム、オキシ塩化ジルコニウム、ヒドロキシ塩化ジルコニウム、硝酸ジルコニウム、塩基性炭酸ジルコニウム、水酸化ジルコニウム、炭酸ジルコニウム・アンモニウム、炭酸ジルコニウム・カリウム、硫酸ジルコニウム、フッ化ジルコニウム化合物等が知られている。これらの化合物はｐＨが不適当に低い物もあり、その場合は適宜ｐＨを調節して用いることも可能である。本発明に於いて、水溶性とは常温常圧下で水に１質量％以上溶解することを目安とする。
【００５４】
本発明において、インクの媒染剤として使用するカチオン性化合物の添加量は気相法シリカに対して１〜１０質量％が好ましい。カチオン性化合物は２種以上を併用することができる。媒染剤として使用する場合、カチオン性ポリマーと水溶性金属化合物を併用するのが好ましい。
【００５５】
本発明において、気相法シリカを含有するインク受容層の膜面ｐＨが２〜６であることが好ましく、特に３〜５が好ましい。インク受容層の膜面ｐＨは、Ｊ．ＴＡＰＰＩ紙パルプ試験方法Ｎ０．４９に記載の方法に従って、蒸留水を用い、３０秒後に測定した表面ｐＨである。
【００５６】
インク受容層のｐＨは、塗布液の段階で調整するのが好ましいが、塗布液のｐＨと塗布乾燥された状態での膜面ｐＨとは必ずしも一致しないため、塗布液と膜面ｐＨとの関係を予め実験等によって求めておくことが所定の膜面ｐＨにするために必要である。インク受容層塗布液のｐＨは、酸またはアルカリを適当に組み合わせて行われる。酸としては、塩酸、硝酸、硫酸、リン酸等の無機酸、酢酸、クエン酸、コハク酸等の有機酸が用いられ、アルカリとしては、水酸化ナトリウム、アンモニア水、炭酸カリウム、リン酸三ナトリウム、または弱アルカリとして、酢酸ナトリウム等の弱酸のアルカリ金属塩が用いられる。
【００５７】
本発明のインク受容層は、更に皮膜の脆弱性を改良するために各種油滴を含有することができる。そのような油滴としては室温における水に対する溶解性が０．０１質量％以下の疎水性高沸点有機溶媒（例えば、流動パラフィン、ジオクチルフタレート、トリクレジルホスフェート、シリコンオイル等）や重合体粒子（例えば、スチレン、ブチルアクリレート、ジビニルベンゼン、ブチルメタクリレート、ヒドロキシエチルメタクリレート等の重合性モノマーを一種以上重合させた粒子）を含有させることができる。そのような油滴は好ましくは親水性バインダーに対して１０〜５０質量％の範囲で用いることができる。
【００５８】
本発明において、インク受容層に界面活性剤を添加することができる。用いられる界面活性剤はアニオン系、カチオン系、ノニオン系、ベタイン系のいずれのタイプでもよく、また低分子のものでも高分子のものでもよい。１種もしくは２種以上界面活性剤をインク受理層塗液中に添加するが、２種以上の界面活性剤を組み合わせて使用する場合は、アニオン系のものとカチオン系のものとを組み合わせて用いることは好ましくない。界面活性剤の添加量はインク受容層を構成するバインダー１００ｇに対して０．００１〜５ｇが好ましく、より好ましくは０．０１〜３ｇである。
【００５９】
本発明において、インク受容層には更に、着色染料、着色顔料、インク染料の定着剤、紫外線吸収剤、酸化防止剤、顔料の分散剤、消泡剤、レベリング剤、防腐剤、蛍光増白剤、粘度安定剤、ｐＨ調節剤などの公知の各種添加剤を添加することもできる。
【００６０】
本発明に用いられる支持体としては、一般紙、アート紙、コート紙等の吸水性支持体、合成紙、ポリエチレンテレフタレート等のポリエステル樹脂、ジアセテート樹脂、トリアセテート樹脂、アクリル樹脂、ポリカーボネート樹脂、ポリ塩化ビニル、ポリイミド樹脂、セロハン、セルロイド等のプラスチック樹脂フィルム、及び紙の両面にポリオレフィン樹脂をラミネートした樹脂被覆紙等の耐水性支持体が挙げられる。特に樹脂被覆紙が好ましく用いられる。
【００６１】
本発明において好ましく用いられる樹脂被覆紙を構成する原紙は、特に制限はなく、一般に用いられている紙が使用できるが、より好ましくは例えば写真用支持体に用いられているような平滑な原紙が好ましい。原紙を構成するパルプとしては天然パルプ、再生パルプ、合成パルプ等を１種もしくは２種以上混合して用いられる。この原紙には一般に製紙で用いられているサイズ剤、紙力増強剤、填料、帯電防止剤、蛍光増白剤、染料等の添加剤が配合される。
【００６２】
さらに、表面サイズ剤、表面紙力剤、蛍光増白剤、帯電防止剤、染料、アンカー剤等が表面塗布されていてもよい。
【００６３】
また、原紙の厚みに関しては特に制限はないが、紙を抄造中または抄造後カレンダー等にて圧力を印加して圧縮するなどした表面平滑性の良いものが好ましく、その坪量は３０〜２５０ｇ／ｍ^２が好ましい。
【００６４】
樹脂被覆紙の樹脂としては、ポリオレフィン樹脂等の熱可塑性樹脂や電子線や紫外線で硬化する樹脂を用いることができる。ポリオレフィン樹脂としては、低密度ポリエチレン、高密度ポリエチレン、ポリプロピレン、ポリブテン、ポリペンテンなどのオレフィンのホモポリマーまたはエチレン−プロピレン共重合体などのオレフィンの２つ以上からなる共重合体及びこれらの混合物であり、各種の密度、溶融粘度指数（メルトインデックス）のものを単独にあるいはそれらを混合して使用できる。
【００６５】
電子線や紫外線で硬化する樹脂として用いることのできる樹脂としてはエチレン性不飽和結合を有する化合物が挙げられるが、より具体的には以下の樹脂が挙げられる。
【００６６】
（１）脂肪族、脂環族、芳香族、芳香脂肪族の多価アルコール及びポリアルキレングリコールのポリ（メタ）アクリレート
（２）脂肪族、脂環族、芳香族、芳香脂肪族の多価アルコールにアルキレンオキサイドを付加させた多価アルコールのポリ（メタ）アクリレート
（３）ポリエステルポリ（メタ）アクリレート
（４）ポリウレタンポリ（メタ）アクリレート
（５）エポキシポリ（メタ）アクリレート
（６）ポリアミドポリ（メタ）アクリレート
（７）ポリ（メタ）アクリロイルオキシアルキルリン酸エステル
（８）（メタ）アクリロイルオキシ基を側鎖、又は末端に有するビニル系又はジエン系化合物
（９）単官能（メタ）アクリレート、ビニルピロリドン、（メタ）アクリロイル化合物
（１０）エチレン性不飽和結合を有するシアノ化合物
（１１）エチレン性不飽和結合を有するモノあるいはポリカルボン酸、およびそれらのアルカリ金属塩、アンモニウム塩、アミン塩など
（１２）エチレン性不飽和（メタ）アクリルアミド又はアルキル置換（メタ）アクリルアミドおよびその多量体
（１３）ビニルラクタムおよびポリビニルラクタム化合物
（１４）エチレン性不飽和結合を有するポリエーテルおよびそのエステル
（１５）エチレン性不飽和結合を有するアルコールのエステル
（１６）エチレン性不飽和結合を有するポリアルコールおよびそのエステル
（１７）スチレン、ジビニルベンゼンなど１個以上のエチレン性不飽和結合を有する芳香族化合物
（１８）（メタ）アクリロイルオキシ基を側鎖、又は末端に有するポリオルガノシロキサン系化合物
（１９）エチレン性不飽和結合を有するシリコーン化合物
（２０）上記（１）〜（１９）記載の化合物の多量体あるいはオリゴエステル（メタ）アクリレート変性物
【００６７】
これらの樹脂は、単独で使用できるし他の樹脂と混合して使うこともできる。又、無溶剤で塗工することもできるし有機溶剤に溶解して塗工するか、水あるいは不溶解性の有機溶剤に乳化させて塗工、乾燥、硬化して用いることもできる。
【００６８】
また、樹脂被覆紙の樹脂中には、酸化チタン、酸化亜鉛、タルク、炭酸カルシウムなどの白色顔料、ステアリン酸アミド、アラキジン酸アミドなどの脂肪酸アミド、ステアリン酸亜鉛、ステアリン酸カルシウム、ステアリン酸アルミニウム、ステアリン酸マグネシウムなどの脂肪酸金属塩、イルガノックス１０１０、イルガノックス１０７６などの酸化防止剤、コバルトブルー、群青、セシリアンブルー、フタロシアニンブルーなどのブルーの顔料や染料、コバルトバイオレット、ファストバイオレット、マンガン紫などのマゼンタの顔料や染料、蛍光増白剤、紫外線吸収剤などの各種の添加剤を適宜組み合わせて加えるのが好ましい。
【００６９】
本発明において好ましく用いられる支持体である樹脂被覆紙は、走行する原紙上にポリオレフィン樹脂の場合は、加熱溶融した樹脂を流延する、いわゆる押出コーティング法により製造され、その両面が樹脂により被覆される。また、電子線や紫外線により硬化する樹脂の場合は、グラビアコーター、マイクログラビアコーター、ロールコーター、コンマコーター、ブレードコーター、キャストコーターなど一般に用いられるコーターにより樹脂を塗布した後、電子線や紫外線を照射し、樹脂を硬化させて被覆する。また、樹脂を原紙に被覆する前に、原紙にコロナ放電処理、火炎処理などの活性化処理を施すことが好ましい。支持体のインク受容層が塗布される面（表面）は、その用途に応じて光沢面、マット面などを有し、特に光沢面が優位に用いられる。裏面に樹脂を被覆する必要はないが、カール防止の点から樹脂被覆したほうが好ましい。裏面は通常無光沢面であり、表面あるいは必要に応じて表裏両面にもコロナ放電処理、火炎処理などの活性処理を施すことができる。また、樹脂被覆層の厚みとしては特に制限はないが、一般に５〜５０μｍの厚味に表面または表裏両面にコーティングされる。
【００７０】
本発明における支持体には帯電防止性、搬送性、カール防止性などのために、各種のバックコート層を塗設することができる。バックコート層には無機帯電防止剤、有機帯電防止剤、親水性バインダー、ラテックス、硬化剤、顔料、界面活性剤などを適宜組み合わせて含有せしめることができる。
【００７１】
本発明において、インク受容層の塗布方法は任意の方法が用いられ、例えばスライドリップ方式、カーテン方式、エクストルージョン方式、エアナイフ方式、ロールコーティング方式、ロッドバーコーティング方式等があるが、好ましくはカーテン方式である。カーテン塗布により支持体の表面形状によらない均一なインク受容層が得られるため、均一な表面と優れたインク吸収性のインクジェット記録材料が得られる。
【００７２】
本発明でカーテン方式で塗布するインク受容層塗布組成物の塗液粘度は一般的には４０〜２５００ｍＰａ・ｓであり、好ましくは１００〜２０００ｍＰａ・ｓである。４０ｍＰａ・ｓより低いとカーテン膜の延伸時の乱れが発生して均一な塗布膜が得られない。２５００ｍＰａ・ｓより高いとカーテン膜の落下点が下流に移動するので空気同伴により塗布むらが発生しやすい。インク受容層塗布組成物の塗布液固形分濃度は、上記の粘度範囲内に調整されるが、一般的には１４〜４０質量％である。塗布液を高濃度で塗布することで乾燥効率が向上するのに加えて水等が蒸発するときの表面の荒れを抑えることができるので好ましい。
【００７３】
本発明において、インクジェット記録材料には、気相法シリカを含有するインク受容層に加え、さらに別のインク受容層、インク定着層、中間層、保護層等を設けてもよい。
【００７４】
【実施例】
以下、実施例により本発明を詳しく説明するが、本発明の内容は実施例に限られるものではない。なお、部とは固形分質量部を意味する。
【００７５】
実施例１
「シリカの一次分散工程」
分散助剤として固形分３．５ｋｇ分のカチオン性ポリマー（ポリジメチルジアリルアンモニウムクロライド、分子量９０００）を含むカチオン性ポリマーとイオン交換水の混合液４００ｋｇをバッチ式分散タンクに仕込み、該混合液をバッチ式分散タンクとフロー式吸引分散撹拌機の間を循環経路を介して循環させながら、フロー式吸引分散撹拌機部より平均一次粒径７ｎｍの気相法シリカ（トクヤマ社製、ＢＥＴ比表面積３００ｍ^２／ｇ）１００ｋｇを徐々に投入した。同時にバッチ式分散タンクに備えたノコギリ歯状ブレードを有する１軸の回転翼式撹拌機を周速２０ｍ／秒で運転した。全ての気相法シリカを投入し終わってから３０分間、０．０２５ＭＰａの減圧にて分散を行い、気相法シリカ分が２０質量％の気相法シリカの粗分散物を得た。
「シリカの二次分散工程」
一次分散工程で得られたシリカ粗分散物を高圧ホモジナイザーにより、処理量１５００ｌ／時間、圧力４０ＭＰａの条件で２回分散して目的とする気相法シリカ分散液を得た。
【００７６】
実施例２
「シリカの一次分散工程」においてノコギリ歯状ブレードを有する回転翼式撹拌機を１軸から２軸に換え、気相法シリカ投入後の分散時間を２０分とした以外は実施例１と同様にして目的とする気相法シリカ分散液を得た。
【００７７】
実施例３
「シリカの一次分散工程」においてノコギリ歯状ブレードを有する回転翼式撹拌機の周速を２０ｍ／秒から１８ｍ／秒に変更し、気相法シリカ投入後の分散時間を５０分とした以外は実施例１と同様にして目的とする気相法シリカ分散液を得た。
【００７８】
実施例４
「シリカの一次分散工程」において、減圧のレベルを０．０１５ＭＰａとした以外は実施例１と同様にして気相法シリカ分散液を得た。
【００７９】
実施例５
分散助剤のカチオン性ポリマーを３．５ｋｇから４．２ｋｇに変更し、又、気相法シリカを１００ｋｇから１２０ｋｇに変更して気相法シリカ分散液の濃度を２４質量％とし、気相法シリカ投入後の分散時間を３５分とした以外は実施例２と同様にして目的とする気相法シリカ分散液を得た。
【００８０】
実施例６
「シリカの二次分散工程」において、高圧ホモジナイザーに代えて超音波分散機（日本精機製作所社製、循環式超音波ホモジナイザー出力３００Ｗ）により処理量１０ｌ／時間で３回処理した以外は実施例１と同様にして目的とする気相法シリカ分散液を得た。
【００８１】
実施例７
「シリカの二次分散工程」において、高圧ホモジナイザーに代えて薄膜旋回型分散機（特殊機化工業社製、フィルミックス）により周速４０ｍ／秒で処理した以外は実施例１と同様にして目的とする気相法シリカ分散液を得た。
【００８２】
実施例８
「シリカの二次分散工程」において、高圧ホモジナイザーに代え対向衝突式の超高圧ホモジナイザー（スギノマシン社製、アルティマイザー）により１００ＭＰａで１回処理した以外は実施例１と同様にして目的とする気相法シリカ分散液を得た。
【００８３】
実施例９
気相法シリカとして平均一次粒径１２ｎｍの気相法シリカ（日本アエロジル社製、ＢＥＴ比表面積２００ｍ^２／ｇ）を用いた以外は実施例１と同様にして目的とする気相法シリカ分散液を得た。
【００８４】
比較例１
「シリカの一次分散工程」において、フロー式吸引分散撹拌機及び循環経路を用いずに、カチオン性ポリマーとイオン交換水の混合液を仕込んだバッチ式分散タンクに気相法シリカ粉体を直接手投入した以外は実施例１と同様にして気相法シリカ分散液を得た。
【００８５】
比較例２
「シリカの一次分散工程」において、回転翼式撹拌機の代わりにロータ／ステータ型ミキサーを３０００ｒｐｍで用いた以外は実施例１と同様にして気相法シリカ分散液を得た。
【００８６】
比較例３
「シリカの一次分散工程」において、減圧を行わず、大気圧にて一次分散を行った以外は実施例１と同様にして気相法シリカ分散液を得た。
【００８７】
比較例４
実施例１と同様に一次分散を行い、二次分散は行わなずに気相法シリカ分散液を得た。
【００８８】
実施例１０
支持体として、ＬＢＫＰ（５０部）とＬＢＳＰ（５０部）のパルプ配合からなる１２０ｇ／ｍ^２の基紙の表面に低密度ポリエチレン（７０部）と高密度ポリエ チレン（２０部）と酸化チタン（１０部）からなる樹脂組成物を２５ｇ／ｍ^２塗 布し、裏面に高密度ポリエチレン（５０部）と低密度ポリエチレン（５０部）からなる樹脂組成物を２５ｇ／ｍ^２塗布してなる樹脂被覆紙を用意した。この支持体上に、実施例１で作製した気相法シリカ分散液を用いて、下記組成の固形分濃度１３質量％のインク受容層塗液を調製し、気相法シリカの塗布量が固形分で１９ｇ／ｍ^２となるようにカーテン塗布装置で塗布、乾燥して実施例１０のインクジェット記録材料を作成した。尚、インク受容層の膜面ｐＨが４．２になるように調整した。
【００８９】
＜インク受容層塗液＞
気相法シリカ分散物（固形分として） １００部
ポリビニルアルコール ２５部
（商品名：ＰＶＡ２３５、（株）クラレ製、ケン化度８８％、平均重合度３５００）
ほう酸 ４部
両性界面活性剤 ０．３部
（商品名：ＳＷＡＭ ＡＭ−２１５０、日本サーファクタント社製）
【００９０】
実施例１１
実施例１で作製した気相法シリカ分散液の代わりに実施例２で作製した気相法シリカ分散液用いた以外は実施例１０と同様にしてインクジェット記録材料を作成した。
【００９１】
実施例１２
実施例１で作製した気相法シリカ分散液の代わりに実施例３で作製した気相法シリカ分散液用いた以外は実施例１０と同様にしてインクジェット記録材料を作成した。
【００９２】
実施例１３
実施例１で作製した気相法シリカ分散液の代わりに実施例４で作製した気相法シリカ分散液用いた以外は実施例１０と同様にしてインクジェット記録材料を作成した。
【００９３】
実施例１４
実施例１で作製した気相法シリカ分散液の代わりに実施例５で作製した気相法シリカ分散液用いた以外は実施例１０と同様にしてインクジェット記録材料を作成した。
【００９４】
実施例１５
実施例１で作製した気相法シリカ分散液の代わりに実施例６で作製した気相法シリカ分散液用いた以外は実施例１０と同様にしてインクジェット記録材料を作成した。
【００９５】
実施例１６
実施例１で作製した気相法シリカ分散液の代わりに実施例７で作製した気相法シリカ分散液用いた以外は実施例１０と同様にしてインクジェット記録材料を作成した。
【００９６】
実施例１７
実施例１で作製した気相法シリカ分散液の代わりに実施例８で作製した気相法シリカ分散液用いた以外は実施例１０と同様にしてインクジェット記録材料を作成した。
【００９７】
実施例１８
実施例１で作製した気相法シリカ分散液の代わりに実施例９で作製した気相法シリカ分散液用いた以外は実施例１０と同様にしてインクジェット記録材料を作成した。
【００９８】
比較例５
実施例１で作製した気相法シリカ分散液の代わりに比較例１で作製した気相法シリカ分散液用いた以外は実施例１０と同様にしてインクジェット記録材料を作成した。
【００９９】
比較例６
実施例１で作製した気相法シリカ分散液の代わりに比較例２で作製した気相法シリカ分散液用いた以外は実施例１０と同様にしてインクジェット記録材料を作成した。
【０１００】
比較例７
実施例１で作製した気相法シリカ分散液の代わりに比較例３で作製した気相法シリカ分散液用いた以外は実施例１０と同様にしてインクジェット記録材料を作成した。
【０１０１】
比較例８
実施例１で作製した気相法シリカ分散液の代わりに比較例４で作製した気相法シリカ分散液用いた以外は実施例１０と同様にしてインクジェット記録材料を作成した。
【０１０２】
実施例１〜９、比較例１〜４で得られた気相法シリカ分散液について、一次分散所要時間、粘度、経時粘度変化、粒度分布、作業環境を評価した。その結果を表１に示す。
【０１０３】
＜一次分散所要時間＞
粉体投入開始より一次分散が終了するまでの時間を測定した。一次分散の終了は、一次分散液のＢ型粘度が２５００ｍＰａ・ｓ未満となった時点とした。所要時間が短いほど工業的に優位である。
【０１０４】
＜粘度＞
気相法シリカ分散液の粘度を、分散終了直後に（株）東京計器製のＢ型粘度計を用いて２５℃にて測定した。好ましくは１０００ｍＰａ・ｓ以下、より好ましくは５００ｍＰａ・ｓ以下である。
【０１０５】
＜経時粘度変化＞
２５℃で１５日間経時させた気相法シリカ分散液の粘度を上記と同様の方法で粘度測定を行い、分散終了直後からの粘度変化を算出した。この値が小さいほど分散液の安定性が高い。
【０１０６】
＜粒度分布＞
レーザー散乱／回折式粒度分布計（（株）堀場製作所製ＬＡ−９１０）にて測定を行い、体積基準で１μｍ以上の粒子の比率（％）を求めた。この数値が大きいほど粗大粒子が残存していることになる。
【０１０７】
＜作業環境＞
一連の分散作業中の周辺への粉体の飛散の有無を目視観察した。
【０１０８】
実施例１０〜１８、比較例５〜８で得られたインクジェット記録材料について、インク吸収性、及び光沢度を評価した。その結果を表２に示す。
【０１０９】
＜インク吸収性＞
インクジェットプリンター（セイコーエプソン社製ＰＭ−８８０Ｃ）を用いて、Ｃ，Ｍ，Ｙをそれぞれ１２０％で印字して、印字直後にＰＰＣ用紙を印字部に重ねて軽く圧着し、ＰＰＣ用紙に転写したインク量の程度を目視で観察し、下記の基準で評価した。
○：全く転写しない、又は僅かに転写するが実使用上全く支障無い。
△：転写するが実使用下限。
×：転写する。
【０１１０】
＜光沢度＞
ＪＩＳ Ｐ−８１４２（紙及び板紙の７５度鏡面光沢度試験方法）に記載の方法に従って測定した。
【０１１１】
【表１】

【０１１２】
【表２】

【０１１３】
上記結果から明らかなように、実施例１〜９に示した様な本発明に提案の方法に従った気相法シリカスラリーの分散方法によれば、分散効率が極めて良好となって一次分散工程における所要時間が短縮されると共に作業環境も良好という工業的な意義が大きいものとなり、得られた気相法シリカ分散液の粘度が適当で経時安定性にも優れ、１μｍを越えるような凝集粒子も検出されない或いは検出されても微量な分散液が得られた。但し、実施例１と３の比較から判る様に一次分散所要時間から回転翼式撹拌機の周速は２０ｍ／秒以上であることが好ましく、実施例１と４の比較から判る様に粒度分布から減圧のレベルの下限は０．０２ＭＰａ以上であることが好ましい。又、実施例１と２の比較から判るように回転翼式撹拌機は１軸より２軸とした方がより効率的となる。
【０１１４】
これに対して、比較例１はフロー式吸引分散撹拌機を使用しなかった場合、比較例２は回転翼式撹拌機の代わりにロータ／ステータ型ミキサーを使用した場合、比較例３は減圧せずに大気圧にて一次分散を行った場合であるが何れの場合も実施例と比較して一次分散所要時間が長く工業的に不利であり、得られた気相法シリカ分散液の粘度も実施例より高めで且つ粘度の経時安定性も実施例より劣り、粒度分布的にも１μｍ以上の粒子が多めの分散液となった。又、特に比較例１ではフロー式吸引分散撹拌機を使用していないため、作業環境も劣るものであった。比較例４は二次分散を実施しなかったものであるが、粘度、粘度の経時安定性、粒度分布が何れも劣る分散液となった。
【０１１５】
また、本発明の実施例１〜９で得られた気相法シリカスラリーを用いた実施例１０〜１８のインクジェット記録材料は良好なインク吸収性と光沢度を有した。これに対し比較例１〜４で得られた気相法シリカスラリーを用いた比較例５〜８のインクジェット記録材料は、インク吸収性は使用可或いは使用下限レベルであったが、光沢度については実施例より劣るものであった。
【０１１６】
【発明の効果】
本発明で提案の気相法シリカ分散液の製造方法に従えば、分散所要時間が短縮され、作業環境も良好で、粘度的にハンドリング性も良好であると共に経時安定性にも優れた、微粒化分散された気相法シリカ分散液を高い固形分濃度で得ることができる。またこれによって得られた気相法シリカ分散液を使用して得たインクジェット記録材料は、高いインク吸収性及び光沢が得られる。
【図面の簡単な説明】
【図１】本発明の一次分散工程を示す概略構成図
【符号の説明】
１ フロー式吸引分散撹拌
２ バッチ式分散タンク
３ 回転翼式撹拌機
４ 循環経路
５ 粉体供給経路
６ 気相法シリカ粉体
７ 真空ポンプ
図中矢印 液体又は粉体の流れ方向を示す[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing an aqueous dispersion of fumed silica fine particles, and an ink jet recording material having excellent gloss and ink absorbability produced using a fumed silica dispersion produced according to the production method. is there.
[0002]
[Prior art]
The ink jet recording method is a method in which fine droplets of ink are ejected onto a recording material such as paper and adhere to the recording material to perform recording. It has the advantages of high speed, low noise, easy multicolor recording, and low cost. The characteristics required of the recording material include print density, sharpness of color tone, ink absorption from repelling and unevenness, and ink drying from stain.
[0003]
As a recording material used in the ink jet recording method, a porous ink absorbing layer made of a water-soluble binder such as polyvinyl alcohol is coated with a pigment such as amorphous silica on a support called ordinary paper or ink jet recording paper. A recording material provided is known.
[0004]
For example, JP-A Nos. 55-51583, 56-157, 57-107879, 57-107880, 59-230787, 62-160277, 62-184879, and 62-183382. And JP-A 64-11877, there has been proposed a recording material obtained by applying a silicon-containing pigment such as silica to a paper support together with an aqueous binder.
[0005]
In addition, Japanese Patent Publication No. 3-56552, JP-A-2-188287, JP-A-10-81064, JP-A-10-119423, JP-A-10-175365, JP-A-10-193776, JP-A-10-203006, JP-A-10-217601, JP-A-11-20300, JP-A-11-20306, and JP-A-11-34481 disclose synthetic silica fine particles by a gas phase method (hereinafter, referred to as gas phase silica). It is disclosed for use. This fumed silica is an ultrafine particle having an average primary particle diameter of several nm to several tens of nm, and is characterized by high gloss. In recent years, as photo-like recording sheets have been demanded, glossiness has become increasingly important, and water resistance of polyolefin resin-coated paper (a laminate of polyolefin resin such as polyethylene on both sides of paper) and polyester film There has been proposed a recording material in which an ink receiving layer mainly composed of fumed silica is provided on a support.
[0006]
JP-A-62-174183, JP-A-2-276670, JP-A-5-32037 and JP-A-6-199034 disclose recording materials using alumina or alumina hydrate. However, the glossiness of blank paper was good, but the ink absorbency was insufficient.
[0007]
JP-A-10-86509 discloses that an ink receiving layer has an amorphous silica and / or alumina silicate having a primary particle size of 3 to 40 nm, a secondary aggregated particle having an average particle size of 10 to 200 nm, and an ink receiving layer. Has a haze of 4 to 65%.
[0008]
Conventionally, a paper support that has been generally used has its own role as an ink absorbing layer, but a water-resistant support such as the above-mentioned polyolefin resin-coated paper is different from a paper support. Since the ink cannot be absorbed, the ink absorbing property of the ink receiving layer provided on the support is important, and it is necessary to increase the porosity of the ink receiving layer. Therefore, it was necessary to increase the amount of application of fumed silica and the like, and to further reduce the ratio of the binder.
[0009]
However, the coating liquid used to provide a porous ink absorbing layer of amorphous silica such as fumed silica or alumina hydrate on a water-resistant support is made of amorphous silica or alumina hydrate. It greatly affects the characteristics of the ink jet recording material obtained by the dispersion method and the treatment method, and particularly has a great influence on the glossiness of the recording material surface and the ink absorbency.
[0010]
Dispersion methods of inorganic fine particles such as fumed silica are disclosed in JP-A-11-321079, JP-A-2000-239536, JP-A-2001-19421, and the like by adding inorganic fine particles to an aqueous solution containing a water-soluble cationic polymer. Although a method of adding and dispersing is disclosed, no detailed description of dispersion other than homogenization by a high-pressure disperser or an ultrasonic disperser is made. However, the step of obtaining the coarse dispersion before the final homogenization (the primary dispersion step in the present invention) has a considerable effect on the quality, and the quality may be deteriorated unless an appropriate method is used.
[0011]
Japanese Patent Application Laid-Open No. 2000-94830 discloses a method in which inorganic fine particles dispersed without a dispersing aid are mixed with a cationic dispersing aid aqueous solution. However, since the inorganic fine particle dispersion is surface anionic, There has been a problem that when mixed with the aqueous solution of the cationic dispersing aid, the viscosity is remarkably increased and aggregates are generated.
[0012]
JP-A-2002-47454 and JP-A-2002-105356 disclose a method of performing final dispersion while continuously supplying an inorganic fine particle powder such as fumed silica and an aqueous dispersant without performing batch dispersion. However, in this method, the mechanical load applied to the final disperser is increased, the solid content concentration of the obtained dispersion is unstable, and the stability of quality when used as an inkjet recording material is And other problems.
[0013]
In order to solve these problems, the present inventors firstly disperse inorganic fine particles such as fumed silica using a two- or more-axis disperser, and then atomize the primary dispersion using a high-pressure homogenizer or the like. It has been found and proposed that an inorganic fine particle dispersion suitable for use in an ink jet recording material can be obtained through secondary dispersion for sizing (Patent Document 1). However, in a high-concentration dispersion in which the solid content concentration of the fumed silica is 17% by mass or more, the time required for the dispersion may be long, or the powder may be scattered when the powder is charged, thereby deteriorating the working environment. In fact, further improvement was required.
[0014]
[Patent Document 1]
JP-A-2002-274018 (pages 3 to 6, FIG. 1)
[0015]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a method for producing a high-concentration fumed silica dispersion which is extremely advantageous in the process by shortening the time required for dispersion, and also provides a fumed silica obtained by such means. An object of the present invention is to provide an ink jet recording material having high gloss and high ink absorption using a dispersion liquid.
[0016]
[Means for Solving the Problems]
The above object of the present invention, as a result of intensive study of the dispersion conditions of fumed silica, a primary dispersion step of obtaining a coarse dispersion of fumed silica, finely dispersing the coarse dispersion obtained in the primary dispersion step A flow-type suction dispersion stirrer for continuously supplying and dispersing fumed silica to a mixture of a dispersing aid and an aqueous dispersion medium in the primary dispersion step, comprising a secondary dispersion step of adjusting the particle size distribution, By using a batch type dispersion tank equipped with a rotary blade type stirrer and dispersing under reduced pressure, there is no scattering of the powder material during the dispersion operation, the time required for dispersion is short, the process is extremely superior, and Production of high concentration dispersion liquid became possible. Further, an ink jet recording material having excellent gloss and ink absorbability was obtained by applying the fumed silica dispersion thus obtained to a support.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
Synthetic silica includes those obtained by a wet method and those obtained by a gas phase method. Examples of the wet process silica include: (1) a silica sol obtained by double decomposition of sodium silicate with an acid or the like through an ion exchange resin layer; (2) a colloidal silica obtained by heating and aging this silica sol; and (3) a gelation of the silica sol. By changing the formation conditions, silica gel in which primary particles of several microns to 10 microns have become siloxane-bonded three-dimensional secondary particles, and (4) silica sol, sodium silicate, sodium aluminate, etc. And synthetic silicate compounds mainly composed of silicic acid, such as those obtained by heat-generating. The silica used in the present invention is preferably fumed silica, and the object of the present invention can be more effectively achieved by a combination of the dispersion method of the present invention and fumed silica.
[0018]
The fumed silica is also called a dry method, and is generally produced by a flame hydrolysis method. Specifically, a method of making silicon tetrachloride by burning it with hydrogen and oxygen is generally known, but instead of silicon tetrachloride, silanes such as methyltrichlorosilane and trichlorosilane may be used alone or in silicon tetrachloride. And can be used in a mixed state. The fumed silica is commercially available as Aerosil from Nippon Aerosil Co., Ltd. and Reolosil QS type from Tokuyama Co., Ltd. and can be obtained. The fumed silica referred to in the present invention is SiO 2 ₂ In addition to a single pure grade, Al ₂ O ₃ Is also included in a mixed grade containing at an arbitrary ratio.
[0019]
The specific surface area of the fumed silica of the present invention by the BET method is 80 m. ² / G or more, and a specific surface area by the BET method of 130 m ² / G or more, especially 200 m ² / G or more. The BET method referred to in the present invention is one of the methods for measuring the surface area of a powder by a gas phase adsorption method, and is a method for determining the total surface area of 1 g of a sample, that is, the specific surface area from an adsorption isotherm. Usually, nitrogen gas is often used as the adsorption gas, and a method of measuring the amount of adsorption from the change in pressure or volume of the gas to be adsorbed is most often used. The most prominent expression of the isotherm for multimolecular adsorption is the Brunauer, Emmett, and Teller equation, which is called the BET equation and is widely used for determining the surface area. The amount of adsorption is determined based on the BET equation, and the surface area is obtained by multiplying the area occupied by one adsorbed molecule on the surface.
[0020]
The average primary particle size of the fumed silica of the present invention is 5 to 50 nm. Those outside this range are difficult to produce industrially stably.
[0021]
The fumed silica aqueous dispersion of the present invention is obtained by charging and dispersing fumed silica in an aqueous dispersion medium containing a dispersing aid. Here, the solid content concentration of the fumed silica in the dispersion is preferably 17% by mass or more and 25% by mass or less. When the concentration is 17% by mass or less, dispersion can be performed relatively easily without following the dispersion method described in the present invention. On the other hand, an inkjet recording material is manufactured using a fumed silica aqueous dispersion. When preparing the coating liquid of the above, it is industrially disadvantageous, for example, it is difficult to increase the concentration of the coating liquid, or the productivity and the transport efficiency are deteriorated. On the other hand, if the concentration exceeds 25%, the bulky secondary aggregation structure peculiar to fumed silica is destroyed, and an effective void structure, which is important when producing an ink jet recording material, cannot be maintained.
[0022]
As the dispersion aid of the present invention, a cationic compound is preferably used. Examples of such a cationic compound include a cationic polymer and a water-soluble metal compound.
[0023]
As the cationic polymer, a polymer having a primary to tertiary amino group, a quaternary ammonium base or a phosphonium base is used. Among them, a water-soluble polymer is preferable, and a polymer having an average molecular weight of 50,000 or less is particularly preferable. Particularly, a cationic polymer having a structural unit of a polydiallylamine derivative is preferable, and examples thereof include a cationic polymer having a structural unit represented by the following general formula (1), (2), (3) or (4). These derivatives are obtained by cyclocondensation of a diallylamine compound, and are obtained as Charol DC902P (Daiichi Kogyo Seiyaku), Jetfix 110 (Satoda Kako), Unisense CP-101 to 103 (Senka), and PAS-H (Nitto Boseki). It is commercially available.
[0024]
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[0025]
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[0026]
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[0027]
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[0028]
In the general formulas (1), (2), (3) and (4), R ₁ And R ₂ Each represents a hydrogen atom, an alkyl group such as a methyl group or an ethyl group, or a substituted alkyl group such as a hydroxyethyl group, and Y represents a radically polymerizable monomer (for example, sulfonyl, acrylamide and its derivatives, acrylate, methacrylic) Acid ester). In the general formulas (3) and (4), n / m = 9/1 to 2/8 and l = 5 to 10,000. X represents an anion.
[0029]
Specific examples of the polydiallylamine derivative represented by the general formula (3) or (4) are described in JP-A-60-83882. ₂ Examples thereof include those containing a group in a repeating unit, and copolymers with acrylamide described in JP-A-1-9776. The average molecular weight of the cationic polymer of the polydiallylamine derivative used in the present invention is more preferably about 2,000 to 50,000.
[0030]
Examples of the water-soluble metal compound include a water-soluble polyvalent metal salt. Water-soluble salts of metals selected from calcium, barium, manganese, copper, cobalt, nickel, aluminum, iron, zinc, zirconium, chromium, magnesium, tungsten, and molybdenum. Specifically, for example, calcium acetate, calcium chloride, calcium formate, calcium sulfate, barium acetate, barium sulfate, barium phosphate, manganese chloride, manganese acetate, manganese formate dihydrate, manganese ammonium sulfate hexahydrate, chloride Copper, ammonium copper (II) chloride dihydrate, copper sulfate, cobalt chloride, cobalt thiocyanate, cobalt sulfate, nickel sulfate hexahydrate, nickel chloride hexahydrate, nickel acetate tetrahydrate, nickel sulfate Ammonium hexahydrate, nickel amidosulfate tetrahydrate, aluminum sulfate, aluminum sulfite, aluminum thiosulfate, polyaluminum chloride, aluminum nitrate nonahydrate, aluminum chloride hexahydrate, ferrous bromide, chloride Ferrous, ferric chloride, ferrous sulfate, ferric sulfate, zinc phenolsulfonate, odor Zinc, zinc chloride, zinc nitrate hexahydrate, zinc sulfate, zirconium acetate, zirconium chloride, zirconium chloride octahydrate, zirconium hydroxychloride, chromium acetate, chromium sulfate, magnesium sulfate, magnesium chloride hexahydrate, citrate Magnesium silicate nonahydrate, sodium phosphotungstate, sodium tungsten citrate, 12-tungstophosphoric acid n-hydrate, 12-tungstosilicic acid 26-hydrate, molybdenum chloride, 12-molybdophosphoric acid n-hydrate and the like .
[0031]
The addition amount of the dispersing aid is preferably 0.1 to 15% by mass of the fumed silica, more preferably 1 to 10% by mass. If the amount is too large, cracks tend to occur on the surface of the final inkjet recording material, and if the amount is too small, the effect of dispersion stability cannot be obtained.
[0032]
As the aqueous dispersion medium of the present invention, water is mainly preferably used, and ion-exchanged water is particularly preferable. If necessary, a low-boiling solvent such as methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, methyl acetate, or ethyl acetate can be added to water for the purpose of adjusting viscosity or the like. When adding a low-boiling organic solvent, the amount of addition is generally about 30% by mass or less of water.
[0033]
In the present invention, in the primary dispersion step, a flow type suction dispersion stirrer for continuously supplying and dispersing the fumed silica powder to a mixture of a dispersing aid and an aqueous dispersion medium, and a batch type equipped with a rotary blade type stirrer It is characterized by using a dispersion tank in combination and dispersing under reduced pressure of 100 mmaq or more. FIG. 1 is a schematic diagram showing the primary dispersion step of the present invention. A predetermined amount of the dispersing aid and the aqueous dispersion medium is stored in a batch type dispersion tank (2) equipped with a rotary blade type stirrer (3), and the fumed silica powder (6) is supplied to a powder supply path (5). And is continuously supplied from a flow type suction dispersion stirrer (1). A batch type dispersion tank (2) equipped with a rotary blade type stirrer (3) is connected to a flow type suction dispersion stirrer (1) through a circulation path (4), and a dispersion aid and an aqueous dispersion medium are dispersed. The mixture is mixed and dispersed with the fumed silica powder while receiving a shearing force in part (1) while circulating through this route. When the mixture of the dispersing aid and the aqueous dispersion medium circulates in the order of (2) → (4) → (1) → (4) → (2), the pressure in the circulation system becomes negative, and the fumed silica powder becomes (5). ) And (1) are smoothly drawn into the circulation system, but there is no problem in arranging a pump such as a diaphragm pump in the middle of (5) for the purpose of assisting powder conveyance. With the equipment configuration as in the present invention, the primary dispersion of the fumed silica powder can be performed in a closed system, and therefore, there is a risk that the powder is scattered, thereby deteriorating the working environment and mixing foreign substances from the outside. Being able to eliminate is one of the great advantages.
[0034]
After the addition of a predetermined amount of the fumed silica powder, the circulation path including the flow-type suction-dispersion stirrer and the batch-type dispersion tank equipped with the rotary blade-type stirrer is operated under reduced pressure using a vacuum pump (7). Continue dispersion with. In this way, it is possible to suppress the generation of bubbles during agitation, to remove bubbles generated in the previous stage, to significantly increase the dispersion efficiency and shorten the dispersion time, and to reduce the dispersion time. It also has the effect of suppressing temperature rise. The reduced pressure level is preferably in the range of 0.02 MPa or more and 0.07 MPa or less. If it is less than 0.02 MPa, the suppression of bubble generation will be insufficient. If the pressure exceeds 0.07 MPa, the dispersion is not adversely affected, but the effect of suppressing and defoaming air bubbles has leveled off, and there is no point in reducing the pressure further. The decompression can be performed using a known decompression / vacuum pump such as a rotary pump and an oil diffusion pump.
[0035]
The flow-type suction dispersion stirrer of the present invention is mainly composed of a mixing / dispersion chamber, a rotor and a stator. The rotor is provided with an inner blade and an outer blade, and the circulating liquid is sucked and accelerated by the inner blade of the rotor toward the stator. On the other hand, the fumed silica powder sucked into the dispersion chamber is accelerated on the rotor surface and passes through the stator together with the liquid introduced from the back surface, at which time the liquid and the powder are instantaneously mixed and accelerated by the outer blade. And headed to the liquid outlet. Liquids and powders undergo strong pulverizing, mixing and dispersing actions due to shear and impact forces in the dispersion chamber. As such a flow-type suction / dispersion stirrer, for example, Conti-TDS (trade name) commercially available from Eastral Co., Ltd. can be used.
[0036]
In the batch type dispersion tank provided with the rotary blade type agitator of the present invention, a saw blade having the same shape as that disclosed in JP-A-2002-274018 is preferably used as a rotary blade type agitator. It is a toothed blade or a propeller type blade, and more preferably a sawtooth blade having a higher shearing force. The rotating blade preferably has a dispersion efficiency or a peripheral speed of 20 m / sec or more, and may have one axis, but more preferably has two axes. It is also possible to mount two or more stirring blades on the same shaft. The preferred diameter of the rotor is 10 to 40% of the diameter of the batch dispersion tank.
[0037]
In the present invention, the coarse dispersion of fumed silica obtained in the primary dispersion step means that an aggregate having a particle diameter of several times to about 10,000 times or less the average particle diameter of the primary particles is an aqueous dispersion medium and a dispersion aid. It is in a state of being mixed and dispersed with the agent, and the preferable viscosity is approximately 10 to several thousand mPa · s. The crude dispersion of fumed silica obtained in the primary dispersion step may be further adjusted to a liquid property suitable for the secondary dispersion step by adding an appropriate amount of water, a low boiling point solvent, and the like, if necessary.
[0038]
In the present invention, dispersion in the secondary dispersion step is facilitated by dispersing the fumed silica fine particles more uniformly in the primary dispersion step, and the ink jet recording material using the obtained dispersion has excellent white paper gloss. And ink absorbency. In particular, the dispersion in the aqueous dispersion medium in the primary dispersion step, and the dispersing aid facilitates uniform dispersion of the secondary particles in the secondary dispersion step, and the inkjet recording material using the obtained dispersion is more excellent. It has glossiness of white paper and ink absorbency.
[0039]
In the present invention, in the secondary dispersion step of finely dispersing the coarse dispersion of the fumed silica obtained in the primary dispersion step, preferably a high-pressure homogenizer, an ultra-high-pressure homogenizer, an ultrasonic disperser, and a thin-film spinning dispersion At least one selected from the machines is used. A high-pressure homogenizer is widely known as a goulin type dispersing machine that uses a shearing force when a workpiece is passed through a gap between a valve and a valve seat at a high pressure and at a high speed, and is known as an APV Goulin Co., Runny Co., and NIRO SOAVI. Commercially available from Nippon Seiki Seisakusho, Sanwa Kikai Co., Ltd. or the like can be used. An ultra-high pressure homogenizer is a disperser that can process even higher pressure than can be achieved with a high pressure homogenizer, and uses the shearing force and impact force when passing an object to be processed at high pressure and high speed in a bent narrow path in a chamber. And the opposite collision type jet pulverization type that uses the shearing force when the liquids to be treated are collided by injecting the liquids to be treated from the opposed nozzles at high pressure and high speed, is known as Sugino Machine Co., Ltd. And those commercially available from Mizuho Industry Co., Ltd., Nanomizer Co., etc. under the trade names such as Ultimizer, Microfluidizer, and Nanomizer. The ultrasonic disperser is a disperser utilizing ultrasonic vibration energy generated from an ultrasonic oscillator, and a commercially available one from Nippon Seiki Seisakusho or the like can be used. The thin-film spinning disperser is a type that utilizes shear stress when a liquid to be treated is introduced into a chamber having a high-speed rotating shaft equipped with a brush and the liquid to be treated becomes a thin film and moves up the inner wall of the chamber. Yes, a product commercially available from Tokushu Kika Kogyo Co., Ltd. under the trade name of "FILMIX" can be used. Before the secondary dispersion treatment, if necessary, for the purpose of compensating for the decrease in the dispersion stabilizing effect of the particles due to the deterioration of the added dispersion aid due to the shearing of the primary dispersion step or the secondary dispersion step. A dispersing aid may be added.
[0040]
In the present invention, the final dispersion of the fumed silica obtained after the primary dispersion step is an aqueous dispersion medium having an aggregate having a particle diameter of several times to about 200 times or less the average particle diameter of the primary particles, and a dispersing aid. In a mixed and dispersed state, from the viewpoint of handling properties, a preferable viscosity is approximately 1000 mPa · s or less, and more preferably 500 mPa · s. In addition, it is preferable that the increase in viscosity after aging is small from the viewpoint of quality stability.
[0041]
In the present invention, the preferable processing conditions of the primary dispersion step and the processing conditions of the secondary dispersion step are determined by the particle size distribution measurement of the fumed silica dispersion after the secondary dispersion step treatment, the presence or absence of coarse particles by electron microscope observation, etc. Is determined, the viscosity is measured, or the properties of an ink jet recording material using a dispersion are determined.
[0042]
The ink jet recording material of the present invention can be obtained by applying a coating liquid containing fumed silica as a dispersion liquid as a main component to a support by such a method to form an ink receiving layer. The fumed silica contains 50% by mass or more, preferably 60% by mass or more, more preferably 65% by mass or more of the fumed silica based on the main proportion of the ink receiving layer, that is, the total solid content of the ink receiving layer. Is preferred. In the ink receiving layer, the solid content of fumed silica was 8 g / m 2. ² More preferably, the content is 10 to 35 g / m ² It is more preferable to use in the range of. If the amount is less than this range, the ink absorbency tends to be poor, and if it is too large, the strength tends to be poor.
[0043]
A binder is used for the purpose of binding fumed silica in the ink receiving layer of the ink jet recording material of the present invention. As the binder, starches, hydroxyethylcellulose, methylcellulose, ethylcellulose, cellulose derivatives such as carboxymethylcellulose, casein, proteins such as gelatin, oxidized starch, aqueous natural polymer compounds such as ester compound starch, polyvinyl alcohol, modified polyvinyl alcohol, polyvinyl Pyrrolidone, polyacrylic acid, acrylamide / acrylate copolymer, acrylamide / acrylate / methacrylic acid terpolymer, alkali salt of styrene / maleic anhydride copolymer, polyacrylamide, styrene / Maleic anhydride copolymer, ethylene / maleic anhydride alkali salt, polyvinyl acetate, polyurethane, polyacrylate, styrene / butadiene copolymer Water-soluble synthetic polymer compounds such as acrylonitrile / butadiene copolymer, methyl acrylate / butadiene copolymer, acrylonitrile / butadiene / acrylic acid copolymer, ethylene / vinyl acetate copolymer, and water-dispersible synthetic polymer compounds Although an aqueous dispersion is mentioned, a hydrophilic binder which has high transparency and can obtain higher permeability of the ink is preferably used. In using the hydrophilic binder, it is important that the hydrophilic binder does not swell during the initial permeation of the ink and does not block the voids. From this viewpoint, a hydrophilic binder having a relatively low swelling property at around room temperature is preferable. Used. Particularly preferred hydrophilic binders are fully or partially saponified polyvinyl alcohols or cationically modified polyvinyl alcohols.
[0044]
Particularly preferred among polyvinyl alcohols are those partially or completely saponified with a saponification degree of 80% or more. Those having an average polymerization degree of 200 to 5000 are preferred.
[0045]
Further, as the cation-modified polyvinyl alcohol, for example, as described in JP-A-61-10483, a tertiary amino group or a quaternary ammonium group is contained in the main chain or side chain of the polyvinyl alcohol. Polyvinyl alcohol.
[0046]
The amount of the binder is at most 40% by mass, preferably at most 30% by mass, based on the fumed silica. By reducing the ratio of the binder in this way, the ink absorbency is improved, but cracks and powder drop are likely to occur, and the lower limit is 8% by mass.
[0047]
When using the above-mentioned hydrophilic binder, it is preferable to use it together with a crosslinking agent (hardening agent). Specific examples of the crosslinking agent include aldehyde compounds such as formaldehyde and glutaraldehyde, ketone compounds such as diacetyl and chloropentanedione, bis (2-chloroethylurea) -2-hydroxy-4,6-dichloro-1, 3,5 Triazine, a compound having a reactive halogen as described in U.S. Pat. No. 3,288,775, divinyl sulfone, a compound having a reactive olefin as described in U.S. Pat. No. 3,635,718, U.S. Pat. N-methylol compounds as described in U.S. Pat. No. 2,732,316, isocyanates as described in U.S. Pat. No. 3,103,437, and N-methylol compounds as described in U.S. Pat. Nos. 3,017,280 and 2,983,611. Aziridine compounds, carbodiimide compounds described in U.S. Pat. No. 3,100,704, US Pat. No. 3,091,537, epoxy compounds, halogen carboxaldehydes such as mucochloric acid, dioxane derivatives such as dihydroxydioxane, and inorganic crosslinking agents such as chrome alum, zirconium sulfate, boric acid and borate. Can be used alone or in combination of two or more. Among these, boric acid or borate is particularly preferred.
[0048]
It is preferable to add a cationic compound as a mordant for fixing the ink to the ink receiving layer constituting the ink jet recording material of the present invention. Examples of such a cationic compound include a cationic polymer and a water-soluble metal compound. As the cationic polymer, a polymer having a polyallylamine, an alkylamine polymer, a primary to tertiary amino group, a quaternary ammonium base, or a phosphonium base is preferably used.
[0049]
Examples of the water-soluble metal compound include the same water-soluble polyvalent metal salts as used in the above-mentioned dispersing aid. Among these water-soluble metal compounds, a water-soluble aluminum compound or a water-soluble compound containing a Group 4A element in the periodic table is particularly preferable. As the water-soluble aluminum compound, for example, as an inorganic salt, aluminum chloride or a hydrate thereof, aluminum sulfate or a hydrate thereof, ammonium alum and the like are known. Further, there is a basic polyaluminum hydroxide compound which is an inorganic aluminum-containing cationic polymer. Particularly, a basic polyaluminum hydroxide compound is preferable.
[0050]
The basic polyaluminum hydroxide compound has a main component represented by the following general formula 1, 2 or 3, and for example, [Al ₆ (OH) _Fifteen ] ³⁺ , [Al ₈ (OH) ₂₀ ] ⁴⁺ , [Al _Thirteen (OH) ₃₄ ] ⁵⁺ , [Al ₂₁ (OH) ₆₀ ] ³⁺ And water-soluble polyaluminum hydroxide stably containing a basic and high-molecular polynuclear condensed ion such as
[0051]
[Al ₂ (OH) _n Cl _6-n ] _m General formula 1
[Al (OH) ₃ ] _n AlCl ₃ General formula 2
Al _n (OH) _m Cl _{(3 nm)} 0 <m <3n General formula 3
[0052]
These are water treatment agents under the name of polyaluminum chloride (PAC) from Taki Kagaku Co., Ltd., and polyaluminum hydroxide (Paho) from Asada Kagaku Co., Ltd., and from Riken Green Co., Ltd. It is marketed under the name of Purachem WT and for the same purpose from other manufacturers, and various grades are readily available. In the present invention, these commercially available products can be used as they are, but some of them have an inappropriately low pH. In such a case, the pH can be appropriately adjusted and used.
[0053]
The water-soluble compound containing a Group 4A element of the periodic table used in the present invention is not particularly limited as long as it is water-soluble, but a water-soluble compound containing titanium or zirconium is preferable. For example, water-soluble compounds containing titanium include titanium chloride and titanium sulfate, and water-soluble compounds containing zirconium include zirconium acetate, zirconium chloride, zirconium oxychloride, zirconium hydroxychloride, zirconium nitrate, basic zirconium carbonate, zirconium hydroxide, Zirconium / ammonium carbonate, zirconium / potassium carbonate, zirconium sulfate, zirconium fluoride compounds and the like are known. Some of these compounds have an inappropriately low pH, and in such a case, the pH can be appropriately adjusted and used. In the present invention, the term "water-soluble" is intended to mean that 1% by mass or more is dissolved in water at normal temperature and normal pressure.
[0054]
In the present invention, the amount of the cationic compound used as a mordant in the ink is preferably 1 to 10% by mass based on the fumed silica. Two or more cationic compounds can be used in combination. When used as a mordant, it is preferable to use a cationic polymer and a water-soluble metal compound in combination.
[0055]
In the present invention, the pH of the film surface of the ink receiving layer containing fumed silica is preferably from 2 to 6, and particularly preferably from 3 to 5. The pH of the surface of the ink receiving layer is determined by the method described in J. Org. This is the surface pH measured after 30 seconds using distilled water according to the method described in TAPPI Paper Pulp Test Method N0.49.
[0056]
The pH of the ink receiving layer is preferably adjusted at the stage of the coating solution, but since the pH of the coating solution does not always coincide with the film surface pH in a state where the coating is dried, the relationship between the coating solution and the film surface pH is determined. Is required to be determined in advance by experiments or the like in order to obtain a predetermined film surface pH. The pH of the ink receiving layer coating solution is adjusted by appropriately combining an acid or an alkali. Examples of the acid include inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid, and organic acids such as acetic acid, citric acid, and succinic acid. Examples of the alkali include sodium hydroxide, ammonia water, potassium carbonate, and trisodium phosphate. Alternatively, as the weak alkali, an alkali metal salt of a weak acid such as sodium acetate is used.
[0057]
The ink receiving layer of the present invention may further contain various oil droplets for improving the brittleness of the film. Such oil droplets include hydrophobic high-boiling organic solvents having a solubility in water at room temperature of 0.01% by mass or less (for example, liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicone oil, etc.) and polymer particles ( For example, particles obtained by polymerizing one or more polymerizable monomers such as styrene, butyl acrylate, divinylbenzene, butyl methacrylate, and hydroxyethyl methacrylate) can be contained. Such oil droplets can be preferably used in the range of 10 to 50% by mass based on the hydrophilic binder.
[0058]
In the present invention, a surfactant can be added to the ink receiving layer. The surfactant used may be any of anionic, cationic, nonionic and betaine types, and may be of low molecular weight or high molecular weight. One or more surfactants are added to the ink-receiving layer coating solution. When two or more surfactants are used in combination, an anionic surfactant and a cationic surfactant are used in combination. It is not preferable. The addition amount of the surfactant is preferably 0.001 to 5 g, more preferably 0.01 to 3 g, per 100 g of the binder constituting the ink receiving layer.
[0059]
In the present invention, the ink-receiving layer further contains a coloring dye, a coloring pigment, a fixing agent for the ink dye, an ultraviolet absorber, an antioxidant, a dispersant for the pigment, a defoaming agent, a leveling agent, a preservative, and a fluorescent whitening agent. Various known additives such as a viscosity stabilizer and a pH adjuster can also be added.
[0060]
Examples of the support used in the present invention include water-absorbing supports such as general paper, art paper and coated paper, synthetic paper, polyester resins such as polyethylene terephthalate, diacetate resin, triacetate resin, acrylic resin, polycarbonate resin, and polychlorinated resin. Water-resistant supports such as plastic resin films such as vinyl, polyimide resin, cellophane and celluloid, and resin-coated paper in which a polyolefin resin is laminated on both sides of paper. Particularly, resin-coated paper is preferably used.
[0061]
The base paper constituting the resin-coated paper preferably used in the present invention is not particularly limited, and generally used paper can be used. More preferably, for example, a smooth base paper used for a photographic support is used. preferable. As the pulp constituting the base paper, natural pulp, recycled pulp, synthetic pulp or the like may be used alone or in combination of two or more. The base paper is blended with additives generally used in papermaking, such as a sizing agent, a paper strength enhancer, a filler, an antistatic agent, a fluorescent whitening agent, and a dye.
[0062]
Further, a surface sizing agent, a surface strength agent, a fluorescent whitening agent, an antistatic agent, a dye, an anchoring agent and the like may be applied on the surface.
[0063]
The thickness of the base paper is not particularly limited, but preferably has good surface smoothness, such as applying a pressure by a calender or the like during papermaking or after papermaking, and has a basis weight of 30 to 250 g / g. m ² Is preferred.
[0064]
As the resin of the resin-coated paper, a thermoplastic resin such as a polyolefin resin or a resin which is cured by an electron beam or ultraviolet light can be used. The polyolefin resin is a low-density polyethylene, high-density polyethylene, polypropylene, polybutene, a homopolymer of an olefin such as polypentene or a copolymer of two or more olefins such as an ethylene-propylene copolymer and a mixture thereof, Those having various densities and melt viscosity indices (melt index) can be used alone or in combination.
[0065]
Examples of the resin that can be used as a resin that can be cured by an electron beam or an ultraviolet ray include a compound having an ethylenically unsaturated bond, and more specifically, the following resins.
[0066]
(1) Aliphatic, alicyclic, aromatic, araliphatic polyhydric alcohols and poly (meth) acrylates of polyalkylene glycols
(2) Poly (meth) acrylate of polyhydric alcohol obtained by adding alkylene oxide to aliphatic, alicyclic, aromatic, or araliphatic polyhydric alcohol
(3) Polyester poly (meth) acrylate
(4) Polyurethane poly (meth) acrylate
(5) Epoxy poly (meth) acrylate
(6) Polyamide poly (meth) acrylate
(7) Poly (meth) acryloyloxyalkyl phosphate ester
(8) Vinyl or diene compounds having a (meth) acryloyloxy group at a side chain or at a terminal
(9) Monofunctional (meth) acrylate, vinylpyrrolidone, (meth) acryloyl compound
(10) Cyano compound having an ethylenically unsaturated bond
(11) Mono- or polycarboxylic acids having an ethylenically unsaturated bond, and their alkali metal salts, ammonium salts, amine salts, etc.
(12) Ethylenically unsaturated (meth) acrylamide or alkyl-substituted (meth) acrylamide and its multimer
(13) Vinyl lactam and polyvinyl lactam compound
(14) Polyether having an ethylenically unsaturated bond and its ester
(15) Ester of an alcohol having an ethylenically unsaturated bond
(16) Polyalcohol having ethylenically unsaturated bond and ester thereof
(17) Aromatic compounds having one or more ethylenically unsaturated bonds such as styrene and divinylbenzene
(18) A polyorganosiloxane compound having a (meth) acryloyloxy group on a side chain or at a terminal
(19) Silicone compound having an ethylenically unsaturated bond
(20) Multimers or oligoester (meth) acrylate modified products of the compounds described in (1) to (19) above
[0067]
These resins can be used alone or in combination with other resins. Further, it can be applied without solvent, or can be dissolved in an organic solvent and applied, or can be emulsified in water or an insoluble organic solvent, applied, dried and cured.
[0068]
Also, in the resin of the resin-coated paper, white pigments such as titanium oxide, zinc oxide, talc, calcium carbonate, fatty acid amides such as stearic acid amide and arachidic amide, zinc stearate, calcium stearate, aluminum stearate, stearin Fatty acid metal salts such as magnesium oxide, antioxidants such as Irganox 1010 and Irganox 1076, blue pigments and dyes such as cobalt blue, ultramarine blue, cecilian blue, phthalocyanine blue, and magenta such as cobalt violet, fast violet, and manganese purple It is preferable to add various additives such as pigments and dyes, fluorescent brighteners and ultraviolet absorbers in an appropriate combination.
[0069]
In the case of polyolefin resin on a running base paper, the resin-coated paper which is preferably used in the present invention is manufactured by a so-called extrusion coating method of casting a molten resin by heating, and both surfaces thereof are coated with the resin. You. In the case of a resin that is cured by an electron beam or ultraviolet light, the resin is applied by a commonly used coater such as a gravure coater, a microgravure coater, a roll coater, a comma coater, a blade coater, a cast coater, and then irradiated with an electron beam or ultraviolet light. Then, the resin is cured and coated. Further, it is preferable to perform an activation treatment such as a corona discharge treatment or a flame treatment on the base paper before coating the resin on the base paper. The surface (surface) of the support on which the ink receiving layer is applied has a glossy surface, a matte surface, and the like, depending on the intended use. It is not necessary to coat the back surface with a resin, but it is preferable to coat the resin from the viewpoint of curling prevention. The back surface is usually a matte surface, and the front surface or both front and back surfaces can be subjected to activation treatment such as corona discharge treatment and flame treatment as required. The thickness of the resin coating layer is not particularly limited, but is generally 5 to 50 μm thick on the surface or on both sides.
[0070]
The support in the present invention may be coated with various back coat layers for antistatic properties, transport properties, curling prevention properties, and the like. The back coat layer can contain an inorganic antistatic agent, an organic antistatic agent, a hydrophilic binder, a latex, a curing agent, a pigment, a surfactant and the like in an appropriate combination.
[0071]
In the present invention, an arbitrary method is used as a method for applying the ink receiving layer, and examples thereof include a slide lip system, a curtain system, an extrusion system, an air knife system, a roll coating system, and a rod bar coating system. It is. Since a uniform ink receiving layer independent of the surface shape of the support can be obtained by curtain coating, an ink jet recording material having a uniform surface and excellent ink absorption can be obtained.
[0072]
The coating liquid viscosity of the ink receiving layer coating composition applied by the curtain method in the present invention is generally 40 to 2500 mPa · s, preferably 100 to 2000 mPa · s. If it is lower than 40 mPa · s, the curtain film will be disturbed during stretching, and a uniform coating film cannot be obtained. If it is higher than 2500 mPa · s, the falling point of the curtain film moves downstream, so that uneven coating is likely to occur due to entrainment of air. The solid content of the coating liquid of the ink receiving layer coating composition is adjusted within the above viscosity range, but is generally 14 to 40% by mass. It is preferable to apply the coating solution at a high concentration, because the drying efficiency is improved and the surface roughness when water or the like evaporates can be suppressed.
[0073]
In the present invention, the ink jet recording material may be provided with another ink receiving layer, an ink fixing layer, an intermediate layer, a protective layer, and the like in addition to the ink receiving layer containing fumed silica.
[0074]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples, but the contents of the present invention are not limited to the examples. In addition, a part means a solid content mass part.
[0075]
Example 1
"Primary dispersion process of silica"
400 kg of a mixture of a cationic polymer (polydimethyldiallylammonium chloride, molecular weight 9000) containing 3.5 kg of a solid polymer as a dispersing aid and ion-exchanged water is charged into a batch type dispersion tank, and the mixed solution is batched. While circulating through a circulation path between the flow type dispersion tank and the flow type suction dispersion stirrer, a gas phase method silica having an average primary particle diameter of 7 nm (manufactured by Tokuyama Corporation, BET specific surface area 300 m ² / G) 100 kg was gradually charged. At the same time, a single-shaft rotary blade type stirrer having a saw-toothed blade provided in a batch type dispersion tank was operated at a peripheral speed of 20 m / sec. Dispersion was performed at a reduced pressure of 0.025 MPa for 30 minutes after all the fumed silica was charged, to obtain a crude dispersion of fumed silica having a fumed silica content of 20% by mass.
"Secondary dispersion process of silica"
The silica crude dispersion obtained in the primary dispersion step was dispersed twice with a high-pressure homogenizer under the conditions of a treatment amount of 1500 l / hour and a pressure of 40 MPa to obtain a target fumed silica dispersion.
[0076]
Example 2
In the “primary dispersion step of silica”, the same procedure as in Example 1 was carried out except that the rotating blade type stirrer having the saw-toothed blade was changed from one axis to two axes, and the dispersion time after charging the fumed silica was changed to 20 minutes. Thus, the desired fumed silica dispersion was obtained.
[0077]
Example 3
In the “primary dispersion step of silica”, except that the peripheral speed of the rotary impeller stirrer having a saw-toothed blade was changed from 20 m / sec to 18 m / sec, and the dispersion time after the addition of fumed silica was set to 50 minutes. A target fumed silica dispersion was obtained in the same manner as in Example 1.
[0078]
Example 4
In the "primary dispersion step of silica", a fumed silica dispersion was obtained in the same manner as in Example 1, except that the reduced pressure level was changed to 0.015 MPa.
[0079]
Example 5
The cationic polymer as a dispersing aid was changed from 3.5 kg to 4.2 kg, the fumed silica was changed from 100 kg to 120 kg, and the concentration of the fumed silica dispersion was changed to 24% by mass. A target fumed silica dispersion was obtained in the same manner as in Example 2 except that the dispersion time after the addition of silica was 35 minutes.
[0080]
Example 6
Example 1 Except that in the "secondary dispersion step of silica", treatment was performed three times with a treatment amount of 10 l / hour using an ultrasonic disperser (Nippon Seiki Seisakusho Co., Ltd., circulation ultrasonic homogenizer output 300 W) instead of the high-pressure homogenizer. In the same manner as described above, a target fumed silica dispersion was obtained.
[0081]
Example 7
In the "secondary dispersion step of silica", the purpose was the same as in Example 1 except that the high-pressure homogenizer was used instead of the high-pressure homogenizer, and processing was performed at a peripheral speed of 40 m / sec using a thin film revolving type disperser (manufactured by Tokushu Kika Kogyo Co., Ltd.). Was obtained.
[0082]
Example 8
In the “secondary silica dispersion step”, the same process as in Example 1 was carried out in the same manner as in Example 1 except that the high-pressure homogenizer was replaced with an ultrahigh-pressure homogenizer of an opposed collision type (Ultimizer, manufactured by Sugino Machine Co., Ltd.) once at 100 MPa. A phase method silica dispersion was obtained.
[0083]
Example 9
As fumed silica, fumed silica having an average primary particle diameter of 12 nm (Nippon Aerosil Co., Ltd., BET specific surface area 200 m ² / G) to obtain the target fumed silica dispersion in the same manner as in Example 1.
[0084]
Comparative Example 1
In the “primary dispersion process of silica”, gas-phase silica powder is directly supplied to a batch-type dispersion tank charged with a mixed solution of a cationic polymer and ion-exchanged water without using a flow-type suction / dispersion stirrer and a circulation path. Except for charging, a fumed silica dispersion was obtained in the same manner as in Example 1.
[0085]
Comparative Example 2
A fumed silica dispersion was obtained in the same manner as in Example 1 except that in the “silica primary dispersion step”, a rotor / stator mixer was used at 3000 rpm instead of the rotary blade type stirrer.
[0086]
Comparative Example 3
In the "silica primary dispersion step", a fumed silica dispersion was obtained in the same manner as in Example 1 except that primary dispersion was performed at atmospheric pressure without depressurization.
[0087]
Comparative Example 4
Primary dispersion was performed in the same manner as in Example 1, and a fumed silica dispersion was obtained without performing secondary dispersion.
[0088]
Example 10
As a support, a pulp blend of LBKP (50 parts) and LBSP (50 parts) of 120 g / m 2 ² 25 g / m 2 of a resin composition comprising low-density polyethylene (70 parts), high-density polyethylene (20 parts) and titanium oxide (10 parts) on the surface of ² After coating, a resin composition composed of high-density polyethylene (50 parts) and low-density polyethylene (50 parts) was applied to the back surface at 25 g / m2. ² A coated resin-coated paper was prepared. Using the fumed silica dispersion prepared in Example 1 on the support, an ink receiving layer coating liquid having a solid content concentration of 13% by mass having the following composition was prepared. 19g / m in minutes ² Was applied by a curtain coating apparatus and dried to prepare an ink jet recording material of Example 10. The pH of the ink receiving layer was adjusted to 4.2.
[0089]
<Ink receiving layer coating liquid>
100 parts of fumed silica dispersion (as solid content)
25 parts of polyvinyl alcohol
(Product name: PVA235, manufactured by Kuraray Co., Ltd., saponification degree 88%, average polymerization degree 3500)
Boric acid 4 parts
Amphoteric surfactant 0.3 part
(Product name: SWAM AM-2150, manufactured by Nippon Surfactant)
[0090]
Example 11
An ink jet recording material was prepared in the same manner as in Example 10, except that the fumed silica dispersion prepared in Example 2 was used instead of the fumed silica dispersion prepared in Example 1.
[0091]
Example 12
An ink jet recording material was prepared in the same manner as in Example 10, except that the fumed silica dispersion prepared in Example 3 was used instead of the fumed silica dispersion prepared in Example 1.
[0092]
Example 13
An ink jet recording material was prepared in the same manner as in Example 10, except that the fumed silica dispersion prepared in Example 4 was used instead of the fumed silica dispersion prepared in Example 1.
[0093]
Example 14
An ink jet recording material was prepared in the same manner as in Example 10, except that the fumed silica dispersion prepared in Example 5 was used instead of the fumed silica dispersion prepared in Example 1.
[0094]
Example 15
An ink jet recording material was prepared in the same manner as in Example 10, except that the fumed silica dispersion prepared in Example 6 was used instead of the fumed silica dispersion prepared in Example 1.
[0095]
Example 16
An ink jet recording material was prepared in the same manner as in Example 10, except that the fumed silica dispersion prepared in Example 7 was used instead of the fumed silica dispersion prepared in Example 1.
[0096]
Example 17
An ink jet recording material was prepared in the same manner as in Example 10, except that the fumed silica dispersion prepared in Example 8 was used instead of the fumed silica dispersion prepared in Example 1.
[0097]
Example 18
An ink jet recording material was prepared in the same manner as in Example 10, except that the fumed silica dispersion prepared in Example 9 was used instead of the fumed silica dispersion prepared in Example 1.
[0098]
Comparative Example 5
An ink jet recording material was prepared in the same manner as in Example 10, except that the fumed silica dispersion prepared in Comparative Example 1 was used instead of the fumed silica dispersion prepared in Example 1.
[0099]
Comparative Example 6
An ink jet recording material was prepared in the same manner as in Example 10, except that the fumed silica dispersion prepared in Comparative Example 2 was used instead of the fumed silica dispersion prepared in Example 1.
[0100]
Comparative Example 7
An ink jet recording material was prepared in the same manner as in Example 10, except that the fumed silica dispersion prepared in Comparative Example 3 was used instead of the fumed silica dispersion prepared in Example 1.
[0101]
Comparative Example 8
An ink jet recording material was prepared in the same manner as in Example 10, except that the fumed silica dispersion prepared in Comparative Example 4 was used instead of the fumed silica dispersion prepared in Example 1.
[0102]
For the fumed silica dispersions obtained in Examples 1 to 9 and Comparative Examples 1 to 4, the time required for primary dispersion, viscosity, change in viscosity over time, particle size distribution, and working environment were evaluated. Table 1 shows the results.
[0103]
<Primary dispersion time>
The time from the start of powder introduction to the end of primary dispersion was measured. The primary dispersion was terminated when the B-type viscosity of the primary dispersion became less than 2500 mPa · s. The shorter the time required, the better the industry.
[0104]
<Viscosity>
The viscosity of the fumed silica dispersion was measured at 25 ° C. using a B-type viscometer manufactured by Tokyo Keiki Co., Ltd. immediately after the dispersion was completed. Preferably it is 1000 mPa · s or less, more preferably 500 mPa · s or less.
[0105]
<Change in viscosity over time>
The viscosity of the fumed silica dispersion aged at 25 ° C. for 15 days was measured for viscosity in the same manner as described above, and the change in viscosity immediately after the completion of the dispersion was calculated. The smaller the value, the higher the stability of the dispersion.
[0106]
<Particle size distribution>
The measurement was performed with a laser scattering / diffraction type particle size distribution meter (LA-910, manufactured by Horiba, Ltd.), and the ratio (%) of particles having a size of 1 μm or more on a volume basis was determined. The larger the value, the more coarse particles remain.
[0107]
<Work environment>
During the series of dispersing operations, the presence or absence of powder scattering to the periphery was visually observed.
[0108]
With respect to the ink jet recording materials obtained in Examples 10 to 18 and Comparative Examples 5 to 8, ink absorbency and glossiness were evaluated. Table 2 shows the results.
[0109]
<Ink absorption>
Using an inkjet printer (PM-880C manufactured by Seiko Epson Corporation), C, M, and Y are printed at 120% each, and immediately after printing, the PPC paper is overlaid on the printing portion, lightly pressed, and transferred to the PPC paper. The extent of the amount was visually observed and evaluated according to the following criteria.
：: No transfer or slight transfer, but no problem in practical use.
Δ: Transfer, but lower limit of actual use.
×: Transfer.
[0110]
<Gloss>
It was measured according to the method described in JIS P-8142 (test method for 75 ° specular gloss of paper and paperboard).
[0111]
[Table 1]

[0112]
[Table 2]

[0113]
As is clear from the above results, according to the dispersion method of the fumed silica slurry according to the method proposed in the present invention as shown in Examples 1 to 9, the dispersion efficiency becomes extremely good and the primary dispersion step Agglomerated particles which have a great industrial significance that the required time is shortened and the working environment is good, and the obtained fumed silica dispersion has an appropriate viscosity and excellent stability over time, exceeding 1 μm Was not detected, or a slight amount of dispersion was obtained even if detected. However, as can be seen from the comparison between Examples 1 and 3, the peripheral speed of the rotary blade type stirrer is preferably 20 m / sec or more from the time required for the primary dispersion, and the particle size distribution as can be seen from the comparison between Examples 1 and 4. Therefore, the lower limit of the reduced pressure level is preferably 0.02 MPa or more. Further, as can be seen from a comparison between Examples 1 and 2, it is more efficient to use a rotary blade type stirrer with two shafts than with one shaft.
[0114]
In contrast, Comparative Example 1 did not use a flow-type suction-dispersion stirrer, Comparative Example 2 used a rotor / stator-type mixer instead of a rotary blade-type stirrer, and Comparative Example 3 depressurized. It is a case where the primary dispersion is performed at atmospheric pressure without, but in any case, the primary dispersion required time is longer industrially disadvantageous compared with the examples, and the viscosity of the obtained fumed silica dispersion is also low. The dispersion was higher than the examples and the stability over time of the viscosity was inferior to the examples, and the particles having a particle size distribution of more than 1 μm were larger. In addition, especially in Comparative Example 1, the working environment was inferior because a flow-type suction / dispersion stirrer was not used. In Comparative Example 4, the secondary dispersion was not performed, but the dispersion was inferior in viscosity, viscosity stability over time, and particle size distribution.
[0115]
Further, the ink jet recording materials of Examples 10 to 18 using the fumed silica slurries obtained in Examples 1 to 9 of the present invention had good ink absorbency and glossiness. On the other hand, the ink jet recording materials of Comparative Examples 5 to 8 using the fumed silica slurries obtained in Comparative Examples 1 to 4 were usable or at the lower limit of the ink absorption, but the glossiness was low. It was inferior to the examples.
[0116]
【The invention's effect】
According to the method for producing a fumed silica dispersion liquid proposed in the present invention, the time required for dispersion is reduced, the working environment is good, the handling properties are good, and the stability over time is excellent. A chemically dispersed fumed silica dispersion can be obtained at a high solids concentration. In addition, the ink jet recording material obtained by using the fumed silica dispersion obtained as described above has high ink absorption and gloss.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a primary dispersion step of the present invention.
[Explanation of symbols]
1 Flow type suction dispersion stirring
2 Batch type dispersion tank
3 Rotary impeller stirrer
4 circulation route
5 Powder supply route
6 fumed silica powder
7 Vacuum pump
Arrows indicate the flow direction of liquid or powder

Claims (12)

A method for producing a fumed silica dispersion, comprising a primary dispersion step of obtaining a coarse dispersion of fumed silica, and a secondary dispersion of finely dispersing the coarse dispersion obtained in the primary dispersion step to adjust the particle size distribution. It comprises a dispersion step, a flow-type suction dispersion stirrer for continuously supplying and dispersing fumed silica to a mixture of a dispersing aid and an aqueous dispersion medium in the primary dispersion step, and a rotary blade type stirrer. A method for producing a fumed silica dispersion using a batch type dispersion tank in combination and dispersing under reduced pressure. The method for producing a fumed silica dispersion according to claim 1, wherein the solid content concentration of the fumed silica dispersion is 17% by mass or more and 25% by mass or less. The method for producing a fumed silica dispersion according to claim 1 or 2, wherein the reduced pressure is a reduced pressure of 0.02 MPa or more and 0.07 MPa or less. The method for producing a fumed silica dispersion according to any one of claims 1 to 3, wherein the rotating blades of the rotating blade type stirrer are saw-toothed blades. The method according to any one of claims 1 to 4, wherein a peripheral speed of a rotary blade of the rotary blade type stirrer is 20 m / sec or more. The method for producing a fumed silica dispersion according to any one of claims 1 to 5, wherein the rotating blades of the rotating blade type disperser are biaxial. The method for producing a fumed silica dispersion according to any one of claims 1 to 6, wherein the fumed silica has an average primary particle size of 5 to 50 nm. The method for producing a fumed silica dispersion according to any one of claims 1 to 7, wherein the dispersing aid is cationic. The method for producing a fumed silica dispersion according to any one of claims 1 to 8, wherein the dispersing aid is a polydiallylamine derivative. In the secondary dispersion step, according to any one of claims 1 to 9, wherein at least one selected from a high-pressure homogenizer, an ultra-high-pressure homogenizer, an ultrasonic disperser, and a thin film disperser is used. The method for producing a fumed silica dispersion according to the above. An ink jet recording material obtained by applying a fumed silica dispersion produced according to the method for producing a fumed silica dispersion according to claim 1 to a support. The inkjet recording material according to claim 11, wherein the support is a water-resistant support.

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