JP4936237B2 - Positively charged hydrophobic titanium oxide fine powder and its production and use - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、正帯電性の疎水性酸化チタン微粉末に関するものであり、より詳しくは、粉体塗料や電子写真用トナー等において、それらの粉体の流動性改善、固結防止、帯電調整等の目的で添加される添加剤として用いられる正帯電性疎水性酸化チタン微粉末とその製造方法に関する。
【０００２】
【従来の技術】
最近、カラーレーザープリンタやカラーコピーマシンについて、そのデジタル化、高画質化が進められている。これまでのデジタル方式のカラープリンタやカラーコピーマシンのドラムは、ＯＰＣドラムが主に使用され、負帯電性のトナーが多く使用されており、外添剤も負帯電性のものが使用されていた。しかし、ＯＰＣドラムは耐久性や環境性に問題があり、これに代えてα-Ｓｉ用のドラムもよく用いられている。このシステムでは正帯電のトナーがよく用いられ、その外添剤として正帯電性のものが提案されている。
【０００３】
例えば、特公平１-３１４４号公報には正帯電性の外添剤として正帯電性シリカが提案されている。しかし、正帯電性シリカは外添したトナーの経時変化を生じやすく、環境安定性に問題があった。そこで、経時変化や環境安定性を改善する目的で、例えば、特開平１１−２７８８４５号公報には、気相で揮発性のチタン化合物を熱分解ないし加水分解して酸化チタン微粒子を生成させた後、オルガノシラン化合物で表面処理することによって得た疎水性の酸化チタン超微粒子が提案されている。しかし、この疎水性酸化チタン超微粒子は負帯電性を示すため、正帯電性トナーと混合した際に帯電性が変動すると云う問題がある。
【０００４】
一方、特開平８−２２０７９１号公報、特開平８−２２０７９５号公報および特開平８−２２０７９６号公報には、トナーの外添剤として湿式法で製造された酸化チタンを水系中で疎水化処理したものを用いる技術が提案されている。しかしながら、この酸化チタン微粉末は疎水化処理が水系中で行われているために乾燥工程や嵩密度が大きく、しかも凝集するため、これを解砕する工程が必要であるなどの問題点があった。また、このような方法で製造された酸化チタン微粉末は粒子の吸着水分が多く、温度および湿度といった環境に対して帯電特性が変動しやすいという問題もある。
【０００５】
また、特開昭６０−１３６７５５号公報には、負帯電性トナーに疎水性酸化チタンと疎水性シリカとを加えることによってトナーの流動性を高めることが記載されているが、ここで使用されている疎水性酸化チタンは平均粒径３０nm、ＢＥＴ比表面積５０m2/gのものであり、単独でトナーに添加しても良好な流動性を得ることができない。しかもこの酸化チタン粉末は高価であり、コストが嵩む問題がある。
【０００６】
【発明が解決しようとする課題】
近年、電子写真などにおいて高画質化が求められており、トナー粒子等が次第に微細化しており、従来よりトナー粒子等の流動性を高める必要が生じ、外添剤の添加量を増しても帯電安定性の高いものが求められている。本発明はこのような要請に応えるものであり、トナー粉末等に添加混合した際に、高い流動性と正帯電安定性を付与するトナー用外添剤を提供することを目的とし、特に疎水性を高めるだけでは得られない、経時変化に対する高い抵抗性を備えたトナー用外添剤の提供するものである。
【０００７】
【課題を解決するための手段】
本発明は、酸化チタン微粉末を正帯電付与剤と疎水化剤によって表面処理する際に、処理剤相互の量比、および酸化チタン微粉末表面のＯＨ基に対する量比についてその最適範囲内で処理することにより、環境変動に対して格段に安定な正帯電性を有する疎水性酸化チタン微粉末を提供する。
【０００８】
すなわち、本発明は以下の正帯電性疎水性酸化チタン微粉末に関する。
〔１〕（イ）温度４０℃および湿度８５％の高温高湿環境に２４時間放置した後の鉄粉との摩擦による帯電量（この帯電量をＨＨ環境下の帯電量と云う）と、温度１０℃および湿度２０％の低温低湿環境に２４時間放置した後の鉄粉との摩擦による帯電量（この帯電量をＬＬ環境下の帯電量と云う）について、（ＨＨ環境下の帯電量）／（ＬＬ環境下の帯電量）の比を摩擦帯電量の環境変動比とし、
（ロ）４５wt％メタノール水溶液の沈降体積と全沈した９０wt％のメタノール水溶液との体積比を疎水化率とし、
（ハ）孔径１５０μm、７５μm、４５μmの各スクリーンをおのおの振動させながら順次篩い分けし、各スクリーンを全て通過した割合を流動性とするとき、
ＢＥＴ比表面積５５〜１５０ｍ 2 /ｇ、摩擦帯電量の環境変動比が０.７以上〜１.０以下、疎水化率が１２％以下、および流動性が８７％以上であることを特徴とする正帯電性疎水性酸化チタン微粉末。
〔２〕ＢＥＴ比表面積５５〜１５０ｍ2/ｇの酸化チタン微粉末を原料とし、この酸化チタン微粉末を乾式下で正帯電付与剤と疎水化剤によって表面処理することにより正帯電性と疎水性を付与した酸化チタン微粉末であって、疎水化剤としてシランカップリング剤またはシリコーン化合物を用い、正帯電付与剤としてアミノシランまたはアミノ変性シリコーンオイルを用い、正帯電付与剤／疎水化剤のモル比が０.０１〜３０であって、両処理剤の総処理剤量と酸化チタン表面のＯＨ基のモル比、すなわち総処理剤量／ＯＨ基が０.１以上になるように表面処理してなる上記[１]に記載する正帯電性疎水性酸化チタン微粉末。
〔３〕全重量中、炭素量０.５wt％以上、窒素量５０ppm以上〜１００００ppm以下である上記[１]または上記[２]の何れかに記載する正帯電性疎水性酸化チタン微粉末。
【０００９】
また、本発明は以下の製造方法および用途に関する。
〔４〕ＢＥＴ比表面積５５〜１５０ｍ2/ｇの酸化チタン微粉末を原料とし、疎水化剤としてシランカップリング剤またはシリコーン化合物を用い、正帯電付与剤としてアミノシランまたはアミノ変性シリコーンオイルを用い、正帯電付与剤／疎水化剤のモル比が０.０１〜３０であって、両処理剤の総処理剤量と酸化チタン表面のＯＨ基のモル比、すなわち総処理剤量／ＯＨ基が０.１以上になるように、正帯電付与剤および疎水化剤を、不燃性ガス下で高速攪拌されている酸化チタン微粉末中に噴霧し、または蒸気と共に導入し、酸化チタン微粉末を乾式下で表面処理することによって、摩擦帯電量の環境変動比が０.７以上〜１.０以下、疎水化率が１２％以下、および流動性が８７％以上の正帯電性疎水性酸化チタン微粉末を製造することを特徴とする方法。
〔５〕上記[１]〜上記[３]の何れかに記載する正帯電性疎水性酸化チタン微粉末に、二酸化珪素および/または酸化アルミニウムを添加してなることを特徴とする電子写真用トナー組成物。
【００１０】
【発明の実施の形態】
以下、本発明を実施形態に基づいて具体的に説明する。
本発明の正帯電性疎水性酸化チタン微粉末は、電子複写機用トナーなどの粉体材料に混合して正帯電性混合物としたときに、高温高湿環境下での摩擦帯電量と低温低湿環境下での摩擦帯電量の比（環境変動比と云う）が０.７以上〜１.０以下であることを特徴とするものである。ここで、高温高湿環境とは、例えば温度４０℃および湿度８５％であり、低温低湿環境とは、例えば温度１０℃および湿度２０％の環境を云う。また、摩擦帯電量は鉄粉との摩擦による帯電量であり、摩擦帯電量の環境変動比は、上記高温高湿環境下および低温低湿環境下におのおの２４時間放置した後の摩擦帯電量比である。この環境変動比が１に近いほど環境変動に対して摩擦帯電量が安定である。従来の疎水性酸化チタン粉末における摩擦帯電量の環境変動比は概ね０.５以下であり、本発明の酸化チタン微粉末より大幅に低い。
【００１１】
本発明の正帯電性疎水性酸化チタン微粉末は、揮発性のチタン化合物をガス状で可燃性または不燃性ガスの存在下で高温分解して得たＢＥＴ比表面積が５５〜１５０ｍ2/ｇの酸化チタン超微粒子を原料として用いると良い。酸化チタン微粉末のＢＥＴ比表面積が５５ｍ2/ｇより小さいと均一に分散され難く、トナーの流動性が低下する。一方、ＢＥＴ比表面積が１５０ｍ2/ｇより大きいと酸化チタンの凝集力が非常に大きくなり、この場合にもトナーの流動性が低下する。
【００１２】
上記酸化チタン微粉末を乾式下で正帯電付与剤と疎水化剤によって表面処理することにより正帯電性と疎水性を付与する。疎水化剤としてはシランカップリング剤、および/またはシリコーン化合物が好適である。具体的には、疎水化剤として次式[Ｉ]または[II]に示すシランカップリング剤、または次式[III]、[IＶ]に示すシリコーン化合物が好ましい。
【００１３】
Ｘ4-nＳｉＲn ・・・…[Ｉ]
Ｒ3ＳｉＮＨＳｉＲ3 ・・・…[II]
上記式[Ｉ]、[II]において、Ｘは水酸基、アルコキシ基、ハロゲン原子から選択された基、Ｒは炭素数１〜１８のアルキル基、ｎは０〜３までの整数である。なお、炭素数が１８よりも大きい長鎖アルキルシランカップリング剤を用いると立体障害等のために表面改質が均一に行われ難く、しかも凝集しやすい。
【００１４】
上記式[III]、[IＶ]において、Ｒ'で表される置換基はメチル基またはエチル基から選択される基であり、Ｒ''はメチル基またはエチル基もしくは水素原子でありこの置換基の一部はビニル基またはフェニル基を含むアルキル基であってもよく、Ｘは水酸基、アルコキシ基、ハロゲン原子、またはアルキル基から選択された基、ｍは１〜５００までの整数である。なお、重合度５００以上の高分子のシリコーン化合物によって表面処理すると疎水性を有するが凝集しやすいので好ましくない。
【００１７】
正帯電付与剤としては、アミノシランおよび/またはアミノ変性シリコーンオイルが好ましい。具体的には、次式[Ｖ]、[ＶI]に示すアミノシラン化合物、あるいは上記式式[IＶ]に示すアミノ変性シリコーンオイルが好ましい。
【００１８】
ＸnＲ(n-3)Ｓｉ−(ＣＨ2)m−ＮＨ2 ・・・…[Ｖ]
式中、Ｘはクロロ基、アルコキシ基、アセトキシ基、ヒドロキシ基など加水分解可能な官能基であり、Ｒは水素基またはメチル基、エチル基などのアルキル基であり、ｎは１〜３の整数、ｍは１〜６の整数である。
【００１９】
ＸnＲ(n-3)Ｓｉ−(ＣＨ2)m−ＮＲ1Ｒ2 ・・・…[VI]
式中、Ｘはクロロ基、アルコキシ基、アセトキシ基、ヒドロキシ基など加水分解可能な官能基、Ｒは水素基またはメチル基、エチル基などのアルキル基、Ｒ1およびＲ2は水素基またはメチル基、エチル基、ブチル基などのアルキル基、またはフェニル基などのアリール基、または窒素原子、酸素原子、硫黄原子などの官能基を有するアルキル基などであり、Ｒ1＝Ｒ2＝Ｈの場合は除く。
【００２０】
以上の正帯電付与剤と疎水化剤とを、不燃性ガス下、高速攪拌されている酸化チタン微粉末中に乾式下で導入することにより表面処理する。乾式下で導入するとは、例えば、これらの正帯電付与剤と疎水化剤とを酸化チタン微粉末にスプレーにより噴霧し、または蒸気と共に導入する。この場合、正帯電付与剤／疎水化剤のモル比が０.０１〜３０であり、かつ両処理剤の総処理剤量と酸化チタン表面のＯＨ基のモル比（総処理剤量／ＯＨ基）が０.１以上となるように両処理剤の添加量を調整するのが好ましい。
【００２１】
処理剤のモル比(正帯電性付与剤／疎水化剤)が０.０１未満のとき、この疎水性酸化チタン微粉末は正帯電性を示さない。また、このモル比が３０を上回ると摩擦帯電量は正帯電性を示すものの、高疎水化を満足できず、外添したトナーが経時変化をおこしやすい。一方、総処理剤量と酸化チタン表面のＯＨ基のモル比（処理剤量／ＯＨ基）が０.１未満では正帯電性を示さず、しかも経時変化を生じやすい。
【００２２】
これらの表面改質剤は、同時に用いても良く、または個々に段階的に添加しても良い。また、表面改質を乾式で行えば酸化チタン微粉末の凝集を招かず、しかも排水処理が不要であるので環境汚染を生じることがない。また、乾式処理は比較的、安価に実施できる利点もある。
【００２３】
以上の表面処理によって、全重量中、炭素量が０.５wt％以上、窒素量５０ppm以上〜１００００ppm以下、疎水化率４０％以下であって、高温高湿環境下と低温低湿環境下での摩擦帯電量の環境変動比が０.７以上〜１.０以下の正帯電性疎水性酸化チタン微粉末を得ることができる。なお、炭素量が０.５wt％未満では高温高湿環境下で摩擦帯電量が不安定であるので好ましくない、一方、炭素量が０.５wt％以上であればこのような不都合を生じない。また、窒素量が５０ppm未満では低温低湿環境下において摩擦帯電量が不安定であり、１００００ppmより多いと高温高湿環境下において摩擦帯電量が不安定であるので好ましくない。窒素量が５０〜１００００ppmの範囲であれば何れの環境下でも摩擦帯電量が安定であり、また疎水化率が４０％以下である。
【００２４】
摩擦帯電量の環境変動比を求めるには、上記正帯電性疎水性酸化チタン微粉末を電子複写機用トナーにその混合物が正帯電となる割合で混合し、この混合物から二つの試料を分取し、一つを高温高湿環境下（温度＝４０℃、湿度＝８５％）に、他の一つを低温低湿環境下（温度＝１０℃、湿度＝２０％）において、おのおの２４時間放置した後、各試料について測定された鉄粉との摩擦帯電量の比を測定する。
【００２５】
本発明の上記正帯電性疎水性酸化チタン微粉末は電子複写機用トナーの添加剤として用いることができる。トナーは一成分磁性系、一成分非磁性系、二成分系の何れでも良い。またモノクロ用のトナー、あるいはカラー用のトナーの何れでも良い。さらに、正帯電性疎水性酸化チタン微粉末は一種のみでなく他の金属酸化物微粉末と共に用いても良い。例えば、本発明の正帯電性疎水性酸化チタン微粉末と表面改質した乾式シリカ微粉末、あるいは表面改質した湿式酸化チタン微粉末等と共に併用することができる。
【００２６】
【発明の効果】
本発明の正帯電性疎水性酸化チタン微粉末は疎水性と正帯電性が何れも高く、しかも帯電量の環境変動が少ない。従って、本発明の正帯電性疎水性酸化チタン微粉末を電子写真用トナーに用いた場合、長期間にわたって帯電安定性と高い流動性を得ることができる。
【００２７】
一般にシリコーンオイルなどによる疎水化処理とアミノシランなどによる正帯電化処理とはアミノ基が親水性であるために互いに打ち消し合う関係にあり、正帯電性と流動性とを何れも高くするのは難しい。本発明は酸化チタン微粉末を正帯電付与剤と疎水化剤によって表面処理する際に、処理剤相互の量比、および酸化チタン微粉末表面のＯＨ基に対する量比についてその最適範囲内で処理することにより、流動性と正帯電性とを何れも高く保つことができるようにしたものであり、しかもその正帯電性は環境変動に対して格段に安定である。
【００２８】
【実施例および比較例】
以下、実施例および比較例を示す。各例におけるトナー組成物の環境に対する帯電安定性、炭素量、窒素量、疎水化率、４５μmスクリーン通過率、摩擦帯電量、画像特性は以下の方法によって測定したものである。なお、実施例および比較例の結果を処理条件と共に表１に示した。
【００２９】
〔トナー組成物の環境に対する帯電安定性〕
ガラス容器(容積75ml)に正帯電性疎水性酸化チタン微粉末０.４ｇと負帯電性トナー(粒径８μm)４０ｇとを入れて、ミキサーで攪拌混合してトナー組成物とし、このトナー組成物２ｇに鉄粉キャリア４８ｇを入れ、高温高湿環境下(ＨＨ環境下と略記)および低温低湿環境下(ＬＬ環境下と略記)に各々２４時間放置する。ここで、ＨＨ環境下とは温度４０℃、湿度８５％、ＬＬ環境下とは温度１０℃、湿度２０％の雰囲気を云う。ＨＨ環境下およびＬＬ環境下に各々２４時間放置したトナー組成物と鉄粉キャリアの混合物をそれぞれターブラミキサーで５分間振とうした後、この混合物を０.２ｇ採取して帯電量を求め、両者の比（ＨＨ環境下の帯電量/ＬＬ環境下の帯電量）を環境変動比とした。この環境変動比が０.６以上のものを環境に対して安定であるとした。なお、帯電量はブローオフ帯電量測定装置（東芝ケミカル社製品:TB-200型）を用い、１分間窒素ブローした後の測定値をトナー組成物の帯電量とした。
【００３０】
〔炭素量〕
正帯電性疎水性酸化チタン微粉末を酸素雰囲気中で１１００℃に加熱し、熱分解した後に微量炭素分析装置（堀場社製品：EMIA-110型）によって炭素含有量を測定した。
〔窒素量〕
正帯電性疎水性酸化チタン微粉末を酸素雰囲気中で８００℃に加熱し、ＮＯｘに熱分解した後に微量炭素分析装置(三菱化学社製品：TN-10型)によって窒素含有量を測定した。
〔疎水化率〕
正帯電性疎水性酸化チタン微粉末０.２ｇを２００mlの遠沈管に計りとり、これに４５.９wt％のメタノール水溶液７mlを加えて栓をし、ターブラーミキサーで３０秒間振とうする。振とう後、遠心分離機を用い、２０００r.p.mの回転数で１０分間遠心分離する。分離後、沈降した正帯電性疎水性酸化チタン微粉末の体積を測定する。４５wt％メタノール水溶液の沈降体積と全沈した９０wt％のメタノール水溶液の体積比を疎水化率とした。
【００３１】
〔流動性〕
正帯電性疎水性酸化チタン微粉末０.４ｇと負帯電性トナー(粒径８μm)４０ｇとをミキサーで攪拌混合してトナー組成物とした。このトナー組成物をパウダテスタ（ホソカワミクロン社製品PT-N型）にて、１５０μm、７５μm、４５μmのスクリーンをおのおの振動させながら順次篩い分けを行ない、各スクリーンを全て通過した割合を流動性とし、この値が８０％以上を良好であるとした。
〔摩擦帯電量〕
ガラス容器(容積75ml)に鉄粉キャリア５０ｇと正帯電性疎水性酸化チタン微粉末０.１ｇを入れて混合し、ターブラミキサーで５分間振とうした後、この混合物０.１ｇを採取し、ブローオフ帯電量測定装置（東芝ケミカル社製品：TB-200型）で１分間窒素ブローした後の値を摩擦帯電量とした。
〔画像特性〕
市販の複写機を用いて５０,０００枚印刷を行い、画像特性(かぶり、画像濃度)を観察した。かぶりや画像濃度が低下した複写枚数を画像限界とした。
【００３２】
実施例１
乾式法で製造したBET比表面積５５ｍ2/ｇの酸化チタン微粉末１００重量部をミキサーに入れ、窒素雰囲気下、攪拌しながらｎ−ヘキシルトリメトキシシラン５重量部、３-アミノプロピルトリエトキシシラン３部を各々滴下し、２００℃で２時間加熱攪拌した後に冷却して正帯電性疎水性酸化チタン粉末を得た。この酸化チタン粉末について摩擦帯電量の環境変動比を測定したところ０.８であった。また疎水化率は１２％であり、画像限界は見られなかった。
【００３３】
実施例２
乾式法で製造したBET比表面積９０ｍ2/ｇの酸化チタン微粉末１００重量部をミキサーに入れ、窒素雰囲気下、攪拌しながらｉ−ブチルトリメトキシシラン１０部、３-アミノプロピルトリエトキシシラン５部を各々滴下し、２００℃で２時間加熱攪拌した後に冷却して正帯電性疎水性酸化チタン粉末を得た。この酸化チタン粉末について摩擦帯電量の環境変動比を測定したところ０.８であった。また疎水化率は０％であり、画像限界は見られなかった。
【００３４】
参考例
乾式法で製造したBET比表面積が１５０ｍ2/ｇの酸化チタン微粉末１００重量部をミキサーに入れ、窒素雰囲気下、攪拌しながらｎ−オクタデシルトリメトキシシラン５部、３-アミノプロピルトリエトキシシラン５部を各々滴下し、２００℃で２時間加熱攪拌した後に冷却して正帯電性の疎水性酸化チタン粉末を得た。この酸化チタン粉末について摩擦帯電量の環境変動比を測定したところ０.９であった。また疎水化率は０％であり、画像限界は見られなかった。
【００３５】
比較例１
トナーに外添剤を加えずに摩擦帯電量の環境変動比を測定した。この環境変動比は０.２であった。
比較例２
乾式法で製造したBET比表面積が５５ｍ2/ｇの酸化チタン微粉末１００重量部をミキサーに入れ、窒素雰囲気下、攪拌しながら３-アミノプロピルトリエトキシシラン８部を滴下し、２００℃で２時間加熱攪拌した後に冷却して正帯電性の疎水性酸化チタン粉末を得た。この酸化チタン粉末について摩擦帯電量の環境変動比を測定したところ０.３であった。また疎水化率は１２％であり、画像限界は３万枚であった。
【００３６】
比較例３
乾式法で製造したBET比表面積が９０ｍ2/ｇの酸化チタン微粉末１００重量部をミキサーに入れ、窒素雰囲気下、攪拌しながらi-ブチルトリメトキシシラン８重量部を滴下し、２００℃で２時間加熱攪拌した後に冷却し、負帯電性の疎水性酸化チタン粉末を得た。この酸化チタン粉末について摩擦帯電量の環境変動比を測定したところ０.４であった。また疎水化率は０％であり、画像限界は２５,０００枚であった。
【００３７】
比較例４
乾式法で製造したBET比表面積が１５０ｍ2/ｇの酸化チタン微粉末１００重量部をミキサーに入れ、窒素雰囲気下、攪拌しながらｎ−オクタデシルトリメトキシシラン０．５重量部、３-アミノプロピルトリエトキシシラン０．３部を各々滴下し、２００℃で２時間加熱熱攪拌した後に冷却し、正帯電性の疎水性酸化チタン粉末を得た。この酸化チタン粉末について摩擦帯電量の環境変動比を測定したところ０.５であった。また疎水化率は１００％であり、画像限界は２０５,０００枚であった。
【００３８】
【表１】
BACKGROUND OF THE INVENTION
The present invention relates to a positively chargeable hydrophobic titanium oxide fine powder, and more specifically, in powder coating materials, electrophotographic toners, etc., improvement of fluidity of those powders, prevention of caking, charge adjustment, etc. The present invention relates to a positively charged hydrophobic titanium oxide fine powder used as an additive to be added for the purpose and a method for producing the same.
[0002]
[Prior art]
Recently, color laser printers and color copy machines have been digitized and improved in image quality. The drums of digital color printers and color copy machines used so far have mainly used OPC drums, and many negatively charged toners have been used, and external additives have also been negatively charged. . However, the OPC drum has a problem in durability and environment, and a drum for α-Si is often used instead. In this system, a positively charged toner is often used, and a positively chargeable toner has been proposed as an external additive.
[0003]
For example, Japanese Patent Publication No. 1-3144 proposes positively chargeable silica as a positively chargeable external additive. However, the positively chargeable silica is liable to change with time in the externally added toner, and has a problem in environmental stability. Therefore, for the purpose of improving aging and environmental stability, for example, JP-A-11-278845 discloses a method in which titanium oxide fine particles are produced by thermally decomposing or hydrolyzing a volatile titanium compound in a gas phase. Hydrophobic titanium oxide ultrafine particles obtained by surface treatment with an organosilane compound have been proposed. However, since the hydrophobic titanium oxide ultrafine particles exhibit negative chargeability, there is a problem that the chargeability fluctuates when mixed with a positively chargeable toner.
[0004]
On the other hand, JP-A-8-220791, JP-A-8-22095, and JP-A-8-220796 were prepared by hydrophobizing titanium oxide produced by a wet method as an external additive for toner. Techniques that use things have been proposed. However, since the titanium oxide fine powder is hydrophobized in an aqueous system, there are problems such as a drying step and a large bulk density, and agglomeration, which requires a step of crushing it. It was. In addition, the fine titanium oxide powder produced by such a method has a problem that the adsorbed moisture of the particles is large and the charging characteristics are likely to fluctuate with respect to the environment such as temperature and humidity.
[0005]
Japanese Patent Laid-Open No. 60-136755 describes that the flowability of a toner is improved by adding hydrophobic titanium oxide and hydrophobic silica to a negatively chargeable toner. The hydrophobic titanium oxide having an average particle size of 30 nm and a BET specific surface area of 50 m 2 / g cannot provide good fluidity even when added alone to the toner. Moreover, this titanium oxide powder is expensive and has a problem of increasing costs.
[0006]
[Problems to be solved by the invention]
In recent years, there has been a demand for higher image quality in electrophotography and the like, and toner particles have become increasingly finer. As a result, it has become necessary to increase the fluidity of toner particles and the like. What has high stability is required. The present invention meets such a demand, and an object of the present invention is to provide an external additive for toner that imparts high fluidity and positive charge stability when added to and mixed with toner powder. It is an object of the present invention to provide an external additive for toner having high resistance to change over time, which cannot be obtained only by increasing the toner.
[0007]
[Means for Solving the Problems]
In the present invention, when titanium oxide fine powder is surface-treated with a positive charge imparting agent and a hydrophobizing agent, the amount ratio between the treatment agents and the amount ratio with respect to OH groups on the surface of the titanium oxide fine powder are treated within the optimum range. By doing so, a hydrophobic titanium oxide fine powder having positive chargeability that is remarkably stable against environmental fluctuations is provided.
[0008]
That is, the present invention relates to the following positively charged hydrophobic titanium oxide fine powder.
[1] (A) Charge amount due to friction with iron powder after being left in a high-temperature and high-humidity environment at a temperature of 40 ° C. and a humidity of 85% (this charge amount is referred to as a charge amount in an HH environment) and temperature Regarding the charge amount due to friction with iron powder after being left in a low-temperature and low-humidity environment at 10 ° C. and 20% humidity (this charge amount is called the charge amount in the LL environment) / (charge amount in the HH environment) / The ratio of (charging amount under LL environment) is the environmental fluctuation ratio of frictional charging amount,
(B) The volume ratio of the settling volume of 45 wt% aqueous methanol solution to the total precipitated 90 wt% aqueous methanol solution is defined as the hydrophobization rate,
(C) When each screen having a pore diameter of 150 μm, 75 μm, and 45 μm is sequentially sieved while vibrating, and the ratio of passing through each screen is made fluid,
The BET specific surface area is 55 to 150 m 2 / g, the environmental variation ratio of the triboelectric charge amount is 0.7 to 1.0, the hydrophobization rate is 12% or less, and the fluidity is 87% or more. Positively charged hydrophobic titanium oxide fine powder.
[2] Titanium oxide fine powder having a BET specific surface area of 55 to 150 m 2 / g is used as a raw material, and this titanium oxide fine powder is subjected to surface treatment with a positive charge imparting agent and a hydrophobizing agent under a dry process, thereby allowing positive chargeability and hydrophobicity. Titanium oxide fine powder provided with a silane coupling agent or a silicone compound as a hydrophobizing agent, aminosilane or amino-modified silicone oil as a positive charge imparting agent , and a positive charge imparting agent / hydrophobizing agent molar ratio The surface treatment was carried out so that the total amount of the treatment agents in both treatment agents and the molar ratio of the OH groups on the titanium oxide surface , that is, the total treatment agent amount / OH groups was 0.1 or more. The positively charged hydrophobic titanium oxide fine powder according to [1] above.
[3] The positively chargeable hydrophobic titanium oxide fine powder according to [1] or [2] above, wherein the carbon content is 0.5 wt% or more and the nitrogen content is 50 ppm to 10000 ppm in the total weight.
[0009]
Moreover, this invention relates to the following manufacturing methods and uses.
[4] Using titanium oxide fine powder having a BET specific surface area of 55 to 150 m 2 / g as a raw material, using a silane coupling agent or a silicone compound as a hydrophobizing agent, and using aminosilane or amino-modified silicone oil as a positive charge imparting agent, The charge imparting agent / hydrophobizing agent molar ratio is 0.01 to 30, and the total treatment agent amount of both treatment agents and the molar ratio of OH groups on the titanium oxide surface , that is, the total treatment agent amount / OH group is 0.1 . The positive charge imparting agent and the hydrophobizing agent are sprayed into a fine powder of titanium oxide that is stirred at high speed under a nonflammable gas or introduced together with steam so that the fine powder of titanium oxide is dry By subjecting to surface treatment, a positively chargeable hydrophobic titanium oxide fine powder having an environmental variation ratio of triboelectric charge amount of 0.7 to 1.0, a hydrophobization rate of 12% or less, and a fluidity of 87% or more is obtained. Manufacturing Wherein.
[5] An electrophotographic toner obtained by adding silicon dioxide and / or aluminum oxide to the positively chargeable hydrophobic titanium oxide fine powder according to any one of [1] to [3]. Composition.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be specifically described based on embodiments.
When the positively chargeable hydrophobic titanium oxide fine powder of the present invention is mixed with a powder material such as a toner for an electronic copying machine to form a positively chargeable mixture, the triboelectric charge amount in a high temperature and high humidity environment and the low temperature and low humidity. The ratio of the triboelectric charge amount under the environment (referred to as the environmental variation ratio) is 0.7 or more and 1.0 or less. Here, the high temperature and high humidity environment is, for example, a temperature of 40 ° C. and a humidity of 85%, and the low temperature and low humidity environment is, for example, an environment of a temperature of 10 ° C. and a humidity of 20%. The triboelectric charge amount is the triboelectric charge amount due to friction with the iron powder, and the environmental variation ratio of the triboelectric charge amount is the triboelectric charge amount ratio after being left for 24 hours in the high temperature and high humidity environment and the low temperature and low humidity environment. is there. The closer this environmental variation ratio is to 1, the more stable the triboelectric charge is against environmental variations. The environmental variation ratio of the triboelectric charge amount in the conventional hydrophobic titanium oxide powder is approximately 0.5 or less, which is significantly lower than the titanium oxide fine powder of the present invention.
[0011]
The positively chargeable hydrophobic titanium oxide fine powder of the present invention has a BET specific surface area of 55 to 150 m 2 / g obtained by high-temperature decomposition of a volatile titanium compound in the presence of a gaseous, flammable or nonflammable gas. Titanium oxide ultrafine particles are preferably used as a raw material. When the BET specific surface area of the titanium oxide fine powder is smaller than 55 m 2 / g, it is difficult to uniformly disperse and the fluidity of the toner is lowered. On the other hand, if the BET specific surface area is larger than 150 m 2 / g, the cohesive force of titanium oxide becomes very large, and the fluidity of the toner also decreases in this case.
[0012]
The titanium oxide fine powder is surface-treated with a positive charge imparting agent and a hydrophobizing agent under dry conditions to impart positive chargeability and hydrophobicity. As the hydrophobizing agent, a silane coupling agent and / or a silicone compound are suitable. Specifically, a silane coupling agent represented by the following formula [I] or [II] or a silicone compound represented by the following formula [III] or [IV] is preferable as the hydrophobizing agent.
[0013]
X 4-n SiR n ... [I]
R 3 SiNHSiR 3 ... [II]
In the above formulas [I] and [II], X is a group selected from a hydroxyl group, an alkoxy group and a halogen atom, R is an alkyl group having 1 to 18 carbon atoms, and n is an integer from 0 to 3. When a long-chain alkylsilane coupling agent having a carbon number greater than 18 is used, it is difficult to uniformly modify the surface due to steric hindrance and the like, and aggregation is likely to occur.
[0014]
In the above formulas [III] and [IV], the substituent represented by R ′ is a group selected from a methyl group or an ethyl group, and R ″ is a methyl group, an ethyl group or a hydrogen atom. May be an alkyl group containing a vinyl group or a phenyl group , X is a group selected from a hydroxyl group, an alkoxy group, a halogen atom, or an alkyl group, and m is an integer of 1 to 500. A surface treatment with a high molecular silicone compound having a polymerization degree of 500 or more is not preferable because it has hydrophobicity but tends to aggregate.
[0017]
As the positive charge imparting agent, aminosilane and / or amino-modified silicone oil is preferable. Specifically, an aminosilane compound represented by the following formulas [V] and [VI] or an amino-modified silicone oil represented by the above formula [IV] is preferable.
[0018]
X n R (n-3) Si- (CH 2) m -NH 2 ··· ... [V]
In the formula, X is a hydrolyzable functional group such as a chloro group, an alkoxy group, an acetoxy group or a hydroxy group, R is a hydrogen group or an alkyl group such as a methyl group or an ethyl group, and n is an integer of 1 to 3. , M is an integer of 1-6.
[0019]
X n R (n-3) Si- (CH 2) m -NR 1 R 2 ··· ... [VI]
In the formula, X is a hydrolyzable functional group such as a chloro group, an alkoxy group, an acetoxy group or a hydroxy group, R is a hydrogen group or a methyl group, an alkyl group such as an ethyl group, and R 1 and R 2 are a hydrogen group or a methyl group An alkyl group such as an ethyl group or a butyl group, an aryl group such as a phenyl group, or an alkyl group having a functional group such as a nitrogen atom, an oxygen atom, or a sulfur atom, and when R 1 = R 2 = H except.
[0020]
The surface treatment is performed by introducing the positive charge imparting agent and the hydrophobizing agent into a fine powder of titanium oxide that has been stirred at high speed in a nonflammable gas under a dry process. Introducing under a dry method means, for example, that these positive charge imparting agent and hydrophobizing agent are sprayed onto titanium oxide fine powder by spraying or introduced together with steam. In this case, the molar ratio of the positive charge imparting agent / hydrophobizing agent is 0.01-30, and the molar ratio of the total treatment agent amount of both treatment agents to the OH group on the titanium oxide surface (total treatment agent amount / OH group). ) Is preferably adjusted to be 0.1 or more.
[0021]
When the molar ratio of the treating agent (positive charge imparting agent / hydrophobizing agent) is less than 0.01, the hydrophobic titanium oxide fine powder does not exhibit positive chargeability. On the other hand, if the molar ratio exceeds 30, the triboelectric charge amount shows positive chargeability, but the high hydrophobicity cannot be satisfied, and the externally added toner is likely to change with time. On the other hand, when the molar ratio of the total treatment agent amount to the OH groups on the titanium oxide surface (treatment agent amount / OH group) is less than 0.1, positive chargeability is not exhibited, and a change with time is likely to occur.
[0022]
These surface modifiers may be used simultaneously or may be added stepwise individually. Further, if the surface modification is performed by a dry method, the titanium oxide fine powder is not aggregated and the waste water treatment is unnecessary, so that environmental pollution does not occur. In addition, the dry process has an advantage that it can be carried out relatively inexpensively.
[0023]
By the above surface treatment, the carbon content in the total weight is 0.5 wt% or more, the nitrogen content is 50 ppm to 10000 ppm, the hydrophobization rate is 40% or less, and the friction under high temperature and high humidity environment and low temperature and low humidity environment. A positively chargeable hydrophobic titanium oxide fine powder having an environmental variation ratio of the charge amount of 0.7 or more and 1.0 or less can be obtained. If the carbon content is less than 0.5 wt%, the triboelectric charge amount is unstable in a high temperature and high humidity environment, which is not preferable. On the other hand, if the carbon content is 0.5 wt% or more, such inconvenience does not occur. Further, if the nitrogen amount is less than 50 ppm, the triboelectric charge amount is unstable in a low temperature and low humidity environment, and if it exceeds 10000 ppm, the triboelectric charge amount is unstable in a high temperature and high humidity environment, which is not preferable. If the amount of nitrogen is in the range of 50 to 10,000 ppm, the triboelectric charge amount is stable in any environment, and the hydrophobization rate is 40% or less.
[0024]
In order to obtain the environmental fluctuation ratio of the triboelectric charge amount, the above-mentioned positively charged hydrophobic titanium oxide fine powder is mixed with the toner for an electronic copying machine in such a ratio that the mixture becomes positively charged, and two samples are collected from this mixture. One was left in a high-temperature and high-humidity environment (temperature = 40 ° C., humidity = 85%), and the other was left in a low-temperature, low-humidity environment (temperature = 10 ° C., humidity = 20%) for 24 hours. Thereafter, the ratio of the triboelectric charge amount to the iron powder measured for each sample is measured.
[0025]
The positively chargeable hydrophobic titanium oxide fine powder of the present invention can be used as an additive for toner for electronic copying machines. The toner may be one-component magnetic, one-component non-magnetic, or two-component. Further, either a monochrome toner or a color toner may be used. Further, the positively chargeable hydrophobic titanium oxide fine powder may be used not only with one kind but also with other metal oxide fine powders. For example, the positively chargeable hydrophobic titanium oxide fine powder of the present invention can be used in combination with a surface-modified dry silica fine powder or a surface-modified wet titanium oxide fine powder.
[0026]
【Effect of the invention】
The positively chargeable hydrophobic titanium oxide fine powder of the present invention has both high hydrophobicity and positive chargeability, and has little environmental fluctuation of the charge amount. Therefore, when the positively chargeable hydrophobic titanium oxide fine powder of the present invention is used for an electrophotographic toner, charging stability and high fluidity can be obtained over a long period of time.
[0027]
In general, the hydrophobic treatment with silicone oil or the like and the positive charge treatment with aminosilane or the like have a relationship of canceling each other because the amino group is hydrophilic, and it is difficult to increase both the positive chargeability and the fluidity. In the present invention, when titanium oxide fine powder is surface-treated with a positive charge imparting agent and a hydrophobizing agent, the amount ratio between the treatment agents and the amount ratio with respect to OH groups on the surface of the titanium oxide fine powder are treated within the optimum range. Thus, both fluidity and positive chargeability can be kept high, and the positive chargeability is remarkably stable against environmental fluctuations.
[0028]
Examples and Comparative Examples
Examples and comparative examples are shown below. The charging stability, carbon content, nitrogen content, hydrophobicity, 45 μm screen passage rate, triboelectric charge, and image characteristics of the toner composition in each example were measured by the following methods. The results of Examples and Comparative Examples are shown in Table 1 together with the processing conditions.
[0029]
[Charging stability of toner composition to environment]
In a glass container (volume 75 ml), 0.4 g of positively charged hydrophobic titanium oxide fine powder and 40 g of negatively charged toner (particle diameter 8 μm) are put and mixed by stirring with a mixer to obtain a toner composition. This toner composition 48 g of iron powder carrier is added to 2 g and left in a high temperature and high humidity environment (abbreviated as HH environment) and a low temperature and low humidity environment (abbreviated as LL environment) for 24 hours. Here, the HH environment means an atmosphere at a temperature of 40 ° C. and a humidity of 85%, and the LL environment means an atmosphere at a temperature of 10 ° C. and a humidity of 20%. The mixture of the toner composition and the iron powder carrier left in an HH environment and an LL environment for 24 hours, respectively, was shaken with a tumbler mixer for 5 minutes, and 0.2 g of this mixture was sampled to determine the charge amount. Ratio (charge amount under HH environment / charge amount under LL environment) was defined as the environmental variation ratio. Those having an environmental variation ratio of 0.6 or more were considered stable to the environment. The charge amount was determined by using a blow-off charge amount measuring device (Toshiba Chemical Co., Ltd. product: TB-200 type), and the measured value after nitrogen blowing for 1 minute was used as the charge amount of the toner composition.
[0030]
[Carbon content]
The positively charged hydrophobic titanium oxide fine powder was heated to 1100 ° C. in an oxygen atmosphere and thermally decomposed, and then the carbon content was measured by a trace carbon analyzer (Horiba product: EMIA-110 type).
[Nitrogen content]
The positively charged hydrophobic titanium oxide fine powder was heated to 800 ° C. in an oxygen atmosphere and thermally decomposed into NOx, and then the nitrogen content was measured with a trace carbon analyzer (product of Mitsubishi Chemical Corporation: TN-10 type).
[Hydrophobicization rate]
Weigh 0.2 g of positively charged hydrophobic titanium oxide fine powder into a 200 ml centrifuge tube, add 7 ml of a 45.9 wt% methanol aqueous solution, cap it, and shake it with a tumbler mixer for 30 seconds. After shaking, use a centrifuge to centrifuge for 10 minutes at 2000 rpm. After separation, the volume of the positively charged hydrophobic titanium oxide fine powder settled is measured. The volume ratio of the precipitation volume of 45 wt% methanol aqueous solution to the total precipitated 90 wt% methanol aqueous solution was defined as the hydrophobization rate.
[0031]
〔Liquidity〕
0.4 g of positively chargeable hydrophobic titanium oxide fine powder and 40 g of negatively chargeable toner (particle size: 8 μm) were stirred and mixed with a mixer to obtain a toner composition. This toner composition was screened with a powder tester (Model PT-N manufactured by Hosokawa Micron Corporation) while vibrating each screen of 150 μm, 75 μm, and 45 μm. Is 80% or more.
[Friction charge amount]
In a glass container (volume 75 ml), 50 g of iron powder carrier and 0.1 g of positively charged hydrophobic titanium oxide fine powder were mixed and shaken for 5 minutes with a Turbula mixer, and 0.1 g of this mixture was collected. The value obtained after nitrogen blowing for 1 minute with a blow-off charge measuring device (Toshiba Chemical Co., Ltd. product: TB-200 type) was taken as the friction charge amount.
(Image characteristics)
Using a commercially available copying machine, 50,000 sheets were printed, and image characteristics (fogging, image density) were observed. The number of copies with reduced fog or image density was defined as the image limit.
[0032]
Example 1
100 parts by weight of fine powder of titanium oxide having a BET specific surface area of 55 m 2 / g produced by a dry method is put in a mixer and stirred under a nitrogen atmosphere, 5 parts by weight of n-hexyltrimethoxysilane, and 3-aminopropyltriethoxysilane 3 Each part was added dropwise, heated and stirred at 200 ° C. for 2 hours, and then cooled to obtain a positively charged hydrophobic titanium oxide powder. The titanium oxide powder was measured for the environmental variation ratio of the triboelectric charge amount to be 0.8. The hydrophobization rate was 12%, and no image limit was observed.
[0033]
Example 2
100 parts by weight of fine powder of titanium oxide having a BET specific surface area of 90 m 2 / g produced by a dry method is put in a mixer and stirred under a nitrogen atmosphere, 10 parts of i-butyltrimethoxysilane, 3 parts of 3-aminopropyltriethoxysilane Were added dropwise, stirred at 200 ° C. for 2 hours and then cooled to obtain a positively charged hydrophobic titanium oxide powder. The titanium oxide powder was measured for the environmental variation ratio of the triboelectric charge amount to be 0.8. The hydrophobization rate was 0%, and no image limit was observed.
[0034]
Reference example: 100 parts by weight of titanium oxide fine powder having a BET specific surface area of 150 m 2 / g produced by a dry method was put in a mixer and stirred under a nitrogen atmosphere, 5 parts of n-octadecyltrimethoxysilane, 3- 5 parts of aminopropyltriethoxysilane was added dropwise, and the mixture was heated and stirred at 200 ° C. for 2 hours and then cooled to obtain a positively charged hydrophobic titanium oxide powder. The titanium oxide powder was measured for the environmental fluctuation ratio of the triboelectric charge amount to be 0.9. The hydrophobization rate was 0%, and no image limit was observed.
[0035]
Comparative Example 1
The environmental variation ratio of the triboelectric charge amount was measured without adding an external additive to the toner. This environmental variation ratio was 0.2.
Comparative Example 2
100 parts by weight of titanium oxide fine powder having a BET specific surface area of 55 m 2 / g produced by a dry method is put in a mixer, and 8 parts of 3-aminopropyltriethoxysilane are added dropwise with stirring in a nitrogen atmosphere. The mixture was heated and stirred for an hour and then cooled to obtain a positively charged hydrophobic titanium oxide powder. With respect to this titanium oxide powder, the environmental variation ratio of the triboelectric charge amount was measured and found to be 0.3. The hydrophobicity was 12%, and the image limit was 30,000.
[0036]
Comparative Example 3
100 parts by weight of titanium oxide fine powder having a BET specific surface area of 90 m 2 / g produced by a dry method was put in a mixer, and 8 parts by weight of i-butyltrimethoxysilane was added dropwise with stirring in a nitrogen atmosphere. After heating and stirring for a period of time, the mixture was cooled to obtain a negatively charged hydrophobic titanium oxide powder. The titanium oxide powder was measured for an environmental variation ratio of the triboelectric charge amount to be 0.4. The hydrophobicity was 0%, and the image limit was 25,000.
[0037]
Comparative Example 4
100 parts by weight of titanium oxide fine powder having a BET specific surface area of 150 m 2 / g produced by a dry method is put in a mixer and stirred under a nitrogen atmosphere, 0.5 parts by weight of n-octadecyltrimethoxysilane, and 3-aminopropyltri 0.3 parts of ethoxysilane was added dropwise, followed by heating and stirring at 200 ° C. for 2 hours, followed by cooling to obtain a positively charged hydrophobic titanium oxide powder. The titanium oxide powder was measured for the environmental fluctuation ratio of the triboelectric charge amount to be 0.5. The hydrophobicity was 100%, and the image limit was 205,000.
[0038]
[Table 1]
Claims (5)
（ロ）４５wt％メタノール水溶液の沈降体積と全沈した９０wt％のメタノール水溶液との体積比を疎水化率とし、
（ハ）孔径１５０μm、７５μm、４５μmの各スクリーンをおのおの振動させながら順次篩い分けし、各スクリーンを全て通過した割合を流動性とするとき、
ＢＥＴ比表面積５５〜１５０ｍ 2 /ｇ、摩擦帯電量の環境変動比が０.７以上〜１.０以下、疎水化率が１２％以下、および流動性が８７％以上であることを特徴とする正帯電性疎水性酸化チタン微粉末。 (A) Charge amount due to friction with iron powder after being left in a high-temperature and high-humidity environment at a temperature of 40 ° C. and a humidity of 85% (this charge amount is referred to as a charge amount in an HH environment), a temperature of 10 ° C. and Regarding the charge amount due to friction with iron powder after being left in a low-temperature and low-humidity environment with a humidity of 20% (this charge amount is called the charge amount under the LL environment) / (charge amount under the HH environment) / (LL environment) The ratio of the lower charge) is the environmental fluctuation ratio of the friction charge,
(B) The volume ratio of the settling volume of 45 wt% aqueous methanol solution to the total precipitated 90 wt% aqueous methanol solution is defined as the hydrophobization rate,
(C) When each screen having a pore diameter of 150 μm, 75 μm, and 45 μm is sequentially sieved while vibrating, and the ratio of passing through each screen is made fluid,
The BET specific surface area is 55 to 150 m 2 / g, the environmental variation ratio of the triboelectric charge amount is 0.7 to 1.0, the hydrophobization rate is 12% or less, and the fluidity is 87% or more. Positively charged hydrophobic titanium oxide fine powder.
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