JP4310564B2 - Inkjet recording method - Google Patents

Description

【００２４】
上記式は縦軸Ｈ、横軸ｔ^0.5でプロットすると、原点を通過する直線となるが、実際の系では図１に示すように、ある程度の浸透時間ｔ₀で折れ曲がる挙動を示すことが多い。
【００２５】
この切片（図中のＫｒ）を粗さ指数、傾き（図中のＫａ）を吸収係数、ｔ₀を濡れ時間と称することがある。この切片の命名は、インクが初期段階では用紙の表面凹凸に湿潤するのみで基体に浸透を開始するには一定時間（ｔ₀）を要するとの解釈に基づいている。本発明の吸収係数は図と同様のプロットにおいて、浸透深さ（インク吸収量）（縦軸）をｍｌ／ｍ²単位、浸透時間（横軸）を(ｍｓ)^0.5単位とした場合の傾き（Ｋａ）と定義される。
【００２６】
本発明は、上述の用紙条件において、吸収速度を１.５(ｍｌ／ｍ²)／(ｍｓ)^0.5以下、特に好ましくは０．９〜０．３ (ｍｌ／ｍ²)／(ｍｓ)^0.5とすることである。速度が０．９(ｍｌ／ｍ²)／(ｍｓ)^0.5を超えると浸透が過剰となり、インクは不要な裏移り（裏面にまでインクが達する）現象を生じ、本発明の非コート紙には実質的に使用出来ない。また、０.３(ｍｌ／ｍ²)／(ｍｓ)^0.5未満ではインクは浸透による乾燥（セット）に長時間を要し、特別の乾燥後処理工程を具備しない限り、実質的に高速の印刷は不可能である。
【００２７】
本発明の記録方法によれば、前述した吸収係数Ｋａの値と共に粗さ指数Ｋｒについても特定の範囲、特にＫｒが２０ｍｌ／ｍ²以下の領域が目的に合致している。インクジェット用専用紙を用いる等本発明の目的としない場合には、Ｋｒは２０ｍｌ／ｍ²を越すことが通例である。本発明の目的とする系においては、濡れ時間ｔ₀は通常極めて短く、５０ｍｓ以下と実際上ほぼ０に近いことが通例である。
【００２８】
なお、浸透速度の測定にはブリストー法、これを自動化した動的走査吸液測定法等がある。本発明の主旨は吸収係数で規定される物性とインクジェット記録の関係にあり、記録媒体は紙に限定されず、同様の特性を有する金属、プラスチック、その他可能な媒体全てに適用出来る。
【００２９】
本発明のインク組成物の表面張力は特に限定する必要はないが、本発明者は、多数のインクに関して上述の浸透速度とインク物性の相関性を調べた結果、特にインクの静的表面張力と浸透速度に顕著な相関性のあることを見出した。すなわち、２５℃の静的表面張力が３５mN/m以上のインクにおいて、特に好ましく浸透性と乾燥性の両立が図れる。３５mN/m未満のインクにおいては、浸透性が表面張力の低下と共に顕著に増大し、本発明の非コート紙に対しては、著しいにじみ、裏移りを生じて使用出来ない。前述のLucas−Washburnの式における表面張力γと浸透深さの関係と全く異なる相関である（γ大がＨ小）が、これはγの小さいインクの場合θが更に小さくなる（cosθ小）効果の方が大きいためと推定される。３５mN/mという特別のしきい値が出現する理由は明確ではないが、本発明の非コート紙の場合には紙を構成するセルロースの報告されている臨界表面張力値である４５mN/mに近いことと関係している可能性がある。本発明は静的表面張力に関してのみ記載したが、同様の事項が動的な表面張力の場合にも得られることも推定される。
【００３０】
本発明のインク組成物としては、限定なく各種の材料が使用される。一般的に着色剤、溶剤の主材料に、補助的に結着剤、粘度、表面張力、ｐＨ等の物性調整剤、防カビ剤、その他を添加して構成する。着色剤は染料又は顔料であり、溶剤は水、水溶性有機溶剤が主として使用されるが、非水系溶剤も可能である。これら溶剤は単に溶媒としての機能以外に乾燥防止剤（湿潤剤）、浸透剤（表面張力低下剤）、粘度、蒸発速度制御剤等の作用を有する場合もあり、様々な粘度、表面張力、溶解性、沸点、蒸発速度、引火点等を示す材料が使用される。
【００３１】
例えば、ジエチレングリコール、ポリエチレングリコール、グリセリン、ＮＭＰ、乳酸ナトリウム、ＤＭＳＯ、ポリオキシエチレンアルキルフェノール、ポリオキシエチレン脂肪酸エステル、エチレングリコールアルキルエーテル、ジエチレングリコールアルキルエーテル、エタノール、プロパノール等のアルコール等がある。物性調整剤としては、ＫＯＨ等の金属水酸化物、各種界面活性剤、ジエタノールアミン、トリエタノールアミン等のアルコールアミン類、りん酸、強酸のアルコールアミン塩、アンモニウム塩、低級カルボン酸、グリコール酸、乳酸等のヒドロキシカルボン酸、安息香酸ナトリウム、ソルビン酸カリウム、チアベンダゾール、ベンズイミダゾール等の防かび剤、キレート化剤、脱酸素剤、消泡剤、導電性付与剤等各種の添加剤が用途に応じて使用できる。本発明においては特に水、ポリエチレングリコール、グリセリン及び顔料を必須成分とするインク組成物が好適に使用出来る。
【００３２】
ポリエチレングリコール等の（ポリ）アルキレングリコールやグリセリン等の多価アルコールは蒸発速度が遅いことから、従来湿潤剤として用いられてきた。本発明では、粘度調整剤さらには水を主成分とする水性インクの粘度増加剤として平均分子量６００〜７００００のポリエチレングリコールが特に望ましいことを見出した。
【００３３】
本発明の目的を達成する成分としては平均分子量６００〜６０００のポリエチレングリコールを７．５〜４０重量％含有することが望ましい。平均分子量６００未満では主成分の水の粘度増加が少なく、良好な粘度範囲になるまで添加すると良好な印刷物が得られない。添加量４０重量％を越えると被記録材へのインクの浸透性が低下して乾燥性が悪くなり印刷品質が低下する。特に好ましいのは平均分子量６０００である。また、平均分子量２００００〜７００００のポリエチレングリコールを１〜１０重量％含有することが望ましい。平均分子量７００００を越えると、インクの粘度が著しく増加しインクの吐出量が減少して印字濃度の低下が生じる。
【００３４】
例えば、ポリエチレングリコール６００、１０００、１５４０、２０００、４０００、６０００、２００００、７００００（以上和光純薬製）、ＰＥＧ＃６００、ＰＥＧ＃６０００（以上、日本油脂）等が使用できる。
【００３５】
ポリエチレングリコールは少なくとも１種、または２種以上を混合して用いることができる。
【００３６】
さらに、本発明の目的を達成する成分としてはグリコールエーテルが適している。一般にグリコールエーテル類は、低粘度であるために記録液の粘度を上昇させずにボールペンのペン先やインクジェットのノズルの乾燥を防止する目的で添加された。しかし、水およびポリエチレングリコールと混合することにより安定した噴射が可能な粘度に調整できることを見出した。
【００３７】
具体的なグリコールエーテル類としては、メチルグリコール、メチルジグリコール、メチルトリグリコール、メチルポリグリコール、イソプロピルグリコール、ブチルグリコール、ブチルジグリコール、ブチルトリグリコール、イソブチルグリコール、イソブチルジグリコール（以上、日本乳化剤製）等のエチレングリコール系エーテルおよびメチルプロピレングリコール、メチルプロピレンジグリコール、メチルプロピレントリグリコール、プロピルプロピレングリコール、 プロピルプロピレンジグリコール、ブチルプロピレングリコール、ブチルプロピレンジグリコール、フェニルプロピレングリコール（以上、日本乳化剤製）等のプロピレングリコール系エーテルから選ばれるエーテルを０〜３０重量％含むことが望ましい。３０重量％を超えると表面張力が低下し、印刷品質が低下する。
【００３８】
さらに吐出性を良くする目的でグリセリン０〜２０重量％添加しても良い。田だし、２０重量％を越えると印刷物ににじみが生じやすくなる。
【００３９】
特性向上のために水溶性溶剤を添加しても良い。例えば、 アセトン、メチルエチルケトン、メチルイソブチルケトン、メタノール、エタノール、イソプロパノール等のケトンおよび低級アルコール類やエチレングリコール、プロピレングリコール、ジエチレングリコールおよびジプロピレングリコール等のグリコール類、アセテート類、チオジグリコール、 Ｎ−メチル−２−ピロリドン、１、３−ジメチルイミダゾリジノン、アミノアルコール等の含窒素化合物類を単独又は混合溶剤として使用しても良い。
【００４０】
本発明の目的を達成する成分である色材としては、特に有機顔料が望ましい。染料を色材とするインク組成物は製造は容易で多くの長所を有するものの、本発明の目的とする普通紙への高速印刷に関しては、画像の滲み、耐水性の不足等から使用は困難である。本発明に使用される顔料としては上記ビヒクルに良分散して耐候性に優れたものが望ましい。本発明に特に使用される顔料の発色性（添加濃度当たりの色濃度）は必ずしも高くなく、加えて均質の微粒子分散体の製造が困難なため、高濃度とすると過剰に溶融粘度が増大する現象があって、インクジェット用インクとしては従来実用化されていなかった。特に限定されるわけではないが、本発明には例えばカラーインデックスに記載される下記の番号の有機又は無機顔料が使用できる。顔料の色調はフルカラー印刷、スポット（部分的）カラー印刷、多色（マルチカラー）印刷等の種類により、適宜選択される。
【００４１】
赤あるいはマゼンタ顔料としては、Pigment Red 3、5、19、22、31、38、43、48：1、48：2、48：3、48：4、48：5、49：1、53：1、57：1、57：2、58：4、63：1、81、81：1、81：2、81：3、81：4、88、104、108、112、122、123、144、146、149、166、168、169、170、177、178、179、184、185、208、216、226、257、Pigment Violet 3、19、23、29、30、37、50、88、Pigment Orange 13、16、20、36、青またはシアン顔料としては、pigment Blue 1、15、15：1、15：2、15：3、15：4、15：6、16、17−1、22、27、28、29、36、60、緑顔料としては、Pigment Green 7、26、36、50、黄顔料としては、Pigment Yellow 1、3、12、13、14、17、34、35、37、55、74、81、83、93、94、95、97、108、109、110、137、138、139、153、154、155、157、166、167、168、180、185、193、黒顔料としては、Pigment Black 7、28、26などが目的に応じて使用できる。
【００４２】
具体的に商品名を示すと、例えば、クロモファインイエロー2080、5900、5930、AF−1300、2700L、クロモファインオレンジ3700L、6730、クロモファインスカーレット6750、クロモファインマゼンタ6880、6886、6891N、6790、6887、クロモファインバイオレット RE、クロモファインレッド6820、6830、クロモファインブルーHS−3、5187、5108、5197、5085N、SR−5020、5026、5050、4920、4927、4937、4824、4933GN−EP、4940、4973、5205、5208、5214、5221、5000P、クロモファイングリーン2GN、2GO、2G−550D、5310、5370、6830、クロモファインブラックA−1103、セイカファストエロー10GH、A−3、2035、2054、2200、2270、2300、2400（B）、2500、2600、ZAY−260、2700（B）、2770、セイカファストレッド8040、C405（F）、CA120、LR−116、1531B、8060R、1547、ZAW−262、1537B、GY、4R−4016、3820、3891、ZA−215、セイカファストカーミン6B1476T−7、1483LT、3840、3870、セイカファストボルドー10B−430、セイカライトローズR40、セイカライトバイオレットB800、7805、セイカファストマルーン460N、セイカファストオレンジ900、2900、セイカライトブルーC718、A612、シアニンブルー4933M、4933GN−EP、4940、4973（以上大日精化工業製）、KET Yellow 401、402、403、404、405、406、416、424、KET Orange 501、KET Red 301、302、303、304、305、306、307、308、309、310、336、337、338、346、KET Blue 101、102、103、104、105、106、111、118、124、KET Green 201（以上大日本インキ化学製）、Colortex Yellow 301、314、315、316、P−624、314、U10GN、U3GN、UNN、UA−414、U263、Finecol Yellow T−13、T−05、Pigment Yellow1705、Colortex Orange 202、Colortex Red101、103、115、116、D3B、P−625、102、H−1024、105C、UFN、UCN、UBN、U3BN、URN、UGN、UG276、U456、U457、105C、USN、Colortex Maroon601、Colortex BrownB610N、Colortex Violet600、Pigment Red 122、Colortex Blue516、517、518、519、A818、P−908、510、Colortex Green402、403、Colortex Black 702、U905（以上山陽色素製）、Lionol Yellow1405G、Lionol Blue FG7330、FG7350、FG7400G、FG7405G、ES、ESP−S（以上東洋インキ製）、Toner Magenta E02、Permanent RubinF6B、Toner Yellow HG、Permanent Yellow GG−02、Hostapeam BlueB2G（以上ヘキストインダストリ製）、カーボンブラック＃2600、＃2400、＃2350、＃2200、＃1000、＃990、＃980、＃970、＃960、＃950、＃850、MCF88、＃750、＃650、MA600、MA7、MA8、MA11、MA100、MA100R、MA77、＃52、＃50、＃47、＃45、＃45L、＃40、＃33、＃32、＃30、＃25、＃20、＃10、＃5、＃44、CF9、（以上三菱化学製）などが挙げられる。また、顔料を予め水や溶剤に高濃度分散した分散液を使用することもできる。例えば、MICROPIGMO WMBK-5、WMBE-5、WMRD-5、WMYW-5、AMBK-2、AMYW-2、AMBE-4（以上オリエント化学製）、JA Black 25W、GA Black 2821、GA Yellow 1、GA Magenta1、GA Cyan 2（以上御国色素製）CAB-O-JET200、 CAB-O-JET300（以上キャボットスペシャルティケミカルズ）などが挙げられ、顔料濃度が１０重量％以上の高濃度で分散されているものが特に望ましい。
【００４３】
添加量は顔料濃度１〜１０重量％が適量である。１重量％未満では画像品質が低下し、１０重量部より多いとインク粘度特性に悪影響を与える。また色の調整等で２種類以上の着色剤を適時混合して使用できる。本発明のインク組成物に更に機能性を発現するため、光安定化剤、表面処理剤、界面活性剤、粘度低下剤、酸化防止剤、老化防止剤、架橋促進剤、酸素吸収剤、可塑剤、防腐剤、防錆剤、蒸発促進剤、ｐＨ調整剤、消泡剤、保湿剤、分散剤、染料等を混合することができる。
上記した顔料及びその他の成分の混合、分散には、スターラー、ビーズミル、ホモジナイザが最適であるが周知の各種の撹拌、粉砕又は分散装置が特に制限無く使用できる。
【００４４】
本発明のインク組成物の蒸発速度は特に限定する必要はないが、オンデマンド型インクジェット記録方法に用いるインク組成物として、適当なインク蒸発速度を有することが好ましい。本発明者は各種のインクの蒸発速度（蒸発量）とインクジェット記録の安定性を比較検討した結果、２５℃／６０ＲＨ％の大気条件下での蒸発による重量減少が３０分で２〜２５重量％であるインク組成物が特に好ましいことを見出した。測定は、５０μｌのインク２滴（約１００ｍｇ）をスライドガラス上に滴下し、ほぼ無風状態で上記環境下に放置し、重量変化をミクロ天秤にて測定する方法をとった。本発明の蒸発速度はこの測定条件下で定義した。重量減少が２重量％未満では、インクジェット記録後のプリントの乾燥が不良で、例えば用紙重ね時に転写を生じやすく、又重量減少が２５重量％を超える場合にはインクの乾燥が著しくノズル詰まり、吐出不良を生じやすく記録工程の信頼性が低下する。
【００４５】
本発明のインク組成物の粘度は特に限定することはないが、２５℃の静的粘度は５〜１５ｍＰａ・ｓの範囲が安定な吐出特性を維持する上で好ましい。５ｍＰａ・ｓ未満の粘度では、インク滴の形状、周波数特性が不良となりやすく、１５ｍＰａ・ｓを超える粘度では吐出が困難で安定しにくい。本発明のインク組成物は使用する温度条件でニュートン流体挙動を示すことが望ましいが、通常測定に使用されるシェア速度（約１００ｒｐｍ前後）で上記条件に合致すれば、見かけの粘度が多少のシェア速度依存性が存在しても問題とはならない。
【００４６】
本発明の目的とする分野のプリンタの印刷速度は、従来のインクジェット記録より著しく高速であることが特徴である。速度に関して明瞭な限定はないが、本発明のインク組成物を効果的に使用するには、ノズル及び用紙の間の相対速度が１０ｉｐｓ（ｉｎｃｈ／ｓ）以上となる記録速度が特に好ましい。高速に記録するには、インク滴が記録媒体上に付着後直ちに定着（セット）することが必要であり、不十分の場合には、付着したインク溜が重ねられた他の用紙の裏面に転写する、記録装置中の送りロールに付着する、記録ドットが乱れる等の致命的な不具合を生じてしまう。記録速度１０ｉｐｓを実現するには、例えば記録後約１ｓ以内に記録が定着することが必要である。すなわち、本発明によれば、約１ｓ以内に実質的に記録は取り扱い可能（手が触ふれる等）となる。
【００４７】
圧電素子を用いたオンデマンド型インクジェット記録の記録ヘッドあるいは記録方法には、ライン型記録、シリアル型記録、転写型（シャトル型）記録等、様々な様式があるが、本発明はこれらに特に限定されることなく使用される。いずれにおいても、ノズル及び用紙（記録媒体）との相対的な移動速度が１０ｉｐｓ以上となる工程であり、例えばライン型記録の如く、ヘッド部分が固定され用紙のみ移動する場合は紙移動速度（紙送り速度）が上記相対速度に該当し、シリアル型記録、すなわちヘッドが紙送り方向に垂直に移動して順次記録し間欠的に紙送りが行われる場合は、ヘッド移動速度（キャリジ速度）が上記相対速度に該当する。用紙が回転するドラム等に設置されこれに記録を行う、あるいは一旦ドラムに記録し次いでこれを用紙に転写する転写型の場合は、移動する用紙ないしはドラム面とノズル間の相対位置の変化する速度と理解する。いずれの場合も、記録速度はノズル吐出周波数及び記録解像度に直接関係する。
【００４８】
例えば、ライン型記録の紙送り速度あるいはシリアル型のヘッド移動速度（すなわち記録速度）Ｖは、インク滴の吐出周波数ｆ、記録解像度Ｒにより、Ｖ＝ｆ×Ｒで示される。従来の５ｉｐｓ以下（通常は１ｉｐｓ以下）の記録においては従来報告されている多数のインク組成物がそのまま適用出来る。本発明は少なくとも５ｉｐｓ以上、特に好ましくは１０ｉｐｓ以上の高速度記録において、効果的に利用出来る。
【００４９】
本発明の高速度をより効果的に実施するために、加熱、乾燥工程等を付加することも可能である。しかしながら、本発明の効果は特にこれら乾燥加熱工程を用いなくとも十分実用的な印刷特性を実現出来る点に大きな特長がある。
【００５０】
本発明のインク組成物は、インクジェットプリンタに適用するために、周知の幾つかの要件を満足する。すなわち、このインクは室温で十分な安定性があり、印刷前の保管および印刷後の画質に信頼性がある。記録媒体に付着硬化後は十分な透明性と彩度を有し、かつ均一な薄膜を形成して良好な画質の印刷物を与える。印刷物を重ねておいた状態で、オフセットが発生しないこと、また、環境および人体に配慮した安全性が高い組成物であることが必要である。
【００５１】
更に、このインク組成物は、印刷を必要とするときのみインク小滴を噴射させる、従来公知のインクジェットプリンタ例えば、オフィス用プリンタ、工業用マーキングに使用されているプリンタ、ワイドフォーマット型プリンタ、刷版及び製版用プリンタ、ラベルプリンタおよびこの典型的操作を持つすべてのタイプの高速プリンタにも使用可能である。高速乾燥が可能であるため、記録媒体としては、上述した用紙以外にもプラスチックフィルム、カプセル、ジェル、金属箔、ガラス、木材、布等が使用できる。非接触印刷が可能なだけに媒体の形状は広範なものが使用できる。
【００５２】
次に本発明を実施例により具体的に説明するが、記載例に限定されるものではない。
〔実施例１〜６〕
６８重量部の精製水と平均分子量７０、０００のポリエチレングリコール（和光純薬製、商品名：ポリエチレングリコール７０、０００）を２重量部、グリセリン（和光純薬製）を２０重量部、及び表１に示す各種アルキレングリコールアルキルエーテル各々１０重量部を混合し、これに対して黒顔料水分散液（オリエント化学製Micropigmo、顔料含有量２０重量％）を１０重量部混合し、組成物全３００gをホモジナイザ（日立工機製ＨＧ３０）を用いて、回転数２,０００ｒｐｍで均質な混合物が得られるまで分散し、続いてろ過を行い不純物等を除去し、均質なインク組成物６種を得た。
【００５３】
インク組成物の吸収係数は動的走査吸液計（協和精工製、ＫＭ３５０−Ｄ）、粘度は回転粘度計（トキメック製ＥＤＬモデル）、表面張力は自動表面張力計（協和界面科学社製CVBP-Zモデル）、ベック平滑度は王研式透気度平滑度試験機（旭精工製KY-5）で測定した。いずれも測定温度は２５℃である。吸収係数Ｋａは、吸収量を縦軸浸透深さ（吸収量）Ｈ、横軸(浸透時間)^0.5でプロットした点を直線近似し、粗さ指数Ｋｒ（切片）及び吸収係数Ｋａ（勾配）を算定して求めた。
【００５４】
評価用に５５ｋｇ紙（小林記録紙製、ＮＩＰ紙）を記録媒体として、ダイレクト刷版作成機（日立工機製ＳＪ０２Ａ）のヘッド部分を摘出して固定した印刷試験機を使用し、インク吐出速度３ｋＨｚ、用紙送り速度を１０ｉｐｓとして、解像度３００（×６００）ｄｐｉで１０ｉｐｓの印刷を行った。該記録媒体のベック平滑度は４６.５ｓである。印刷結果は下記３項にて、簡易評価した。
（１）裏移り：インクが裏面に滲み出す状態を目視観察（インク滲み評価）
（２）転写：印刷後１ｓ以内に、別の用紙に圧着する工程により、インクが転写するかどうかを目視観察（セット性評価）
（３）耐水性：印刷後５ｓ以内に、流水に晒してインクの流出等の変化を目視観察表中、◎は優秀、○は良好、×は使用不可を意味している。実施例１〜６のインク組成物はいずれも吸収係数０．９〜０.３(ｍｌ／(ｍ²・ｍｓ^1/2))を示した。
【００５５】
表面張力は２５mN/m以上、粘度は５mPa・s以上である。印刷評価結果はいずれも優秀〜良好で、普通紙に対して良好な印刷が可能なことが判った。
【００５６】
以上の結果を表１に示す。
【００５７】
【表１】

【００５８】
〔実施例７〕
５０重量部の精製水、ジプロピレングリコール５０重量部及び実施例１と同様の黒顔料水分散液１０重量部を混合し、実施例１と同様にインク組成物を製造し、同様の評価を行った。結果は表１に記載した。
【００５９】
吸収係数は０．９(ｍｌ／(ｍ²・ｍｓ^1/2))、静的粘度は７.３mPa・s、表面張力は４０.３mN/mである。印刷結果は各評価とも問題無く、普通紙に良好な印刷が可能であった。
〔比較例１〜３〕
表１に示す組成の精製水６８重量部、ポリエチレングリコール７０、０００を２重量部、グリセリン２重量部、ジエチレングリコールモノブチルエーテル又はエチレングリコールイソブチルエーテル１０重量部を混合し、これに顔料水分散液を１０又は２０重量部添加したインク組成物３種を製造し、実施例１と同様の測定、評価を行った。
【００６０】
いずれの場合も吸収係数は２(ｍｌ／(ｍ²・ｍｓ^1/2))を超える値を示し、転写（乾燥性）、耐水性は優秀であったが、裏移り（インク滲み）は不良で多量のインクが裏面にドット状にしみ出し、普通紙印刷には使用不可能であった。これらのインク組成物の表面張力はいずれも３５mN/m未満であった。
〔実施例８〜１８〕
表２に示す組成で、精製水、ポリエチレングリコール（分子量６,０００）、ポリアルキレングリコールモノアルキルエーテル及び顔料分散液（キャボットスペシャルティケミカルズ製ＣＡＢ−Ｏ−ＪＥＴ３００）を用いて１１種の本発明のインク組成物を製造した。
【００６１】
そして、実施例１と同様の測定及び評価を行った結果を表２中に示した。
【００６２】
【表２】

【００６３】
いずれも０.３〜０．９(ｍｌ／(ｍ²・ｍｓ^1/2))の吸収係数を示し、印刷結果も各項目とも優秀〜良好であった。本発明のインク組成物が普通紙印刷に好適なことが判った。
〔実施例１９〜２０〕及び〔比較例４〜５〕
表３に示す組成で本発明のインク組成物１９、２０を製造した。更に比較のために市販のインクＡ及びＢを使用した。
【００６４】
実施例１と同様の測定及び評価結果を表３中に示した。
【００６５】
【表３】

【００６６】
本発明のインク組成物の吸収係数は実施例１９及び２０の順に０.５及び０．８(ｍｌ／(ｍ²・ｍｓ^1/2))であり、各項目とも優秀な印刷結果が得られた。
【００６７】
これら本発明のインク組成物２種及び比較インク２種を用いて、１１種類の市販用紙に印刷を行い、ドット面積及びドット形状係数（＝(周長)²／(２π・ドット面積)）を比較した（図２及び図３参照）。ドット形状の測定には倍率２０倍の顕微鏡からＣＣＤカメラにより取り込んだ画像を、自動画像品質評価ソフトウェア（Media Cybemetrics製Image Pro Plus）を用いて解析した。測定ドット数は３０〜１００個である。
【００６８】
結果を表４、表５に示す。
【００６９】
【表４】

【００７０】
インクジェット（ＩＪ）専用紙１〜５はいずれも表面にインク受容層が積層した構造であり、普通紙１〜６は非コート紙である。
【００７１】
表４に記載した通り、インクジェット専用紙はいずれもベック平滑度は８０ｓを超す値を示し、普通紙はいずれも８０ｓ以下の値を示すものである。表４にはドット面積の測定結果を示すが、比較例４、５に比べ、本発明のインク組成物１９、２０はいずれも顕著にドット径が小さいこと（すなわち滲みによるドット拡大が少ない）ことが判った。
【００７２】
【表５】

【００７３】
表５にはドット形状係数の測定結果を示すが、本発明のインク組成物は形状係数が小さく（すなわち形状がより真円形に近い）、インクドット形状の乱れが少ないことが判った。
【００７４】
インクジェット専用紙の場合はこれらの差違があるとは言え、いずれも微少なドット径（例えば１０、０００μｍ²以下）、ドット形状係数（例えば２以下）で両者ともにほぼ実用に供し得る。しかしながら、ベック平滑度８０ｓ以下の非コート紙の印刷結果を見ると、比較例のインクの場合ドット径は滲みにより１０、０００μｍ²を超す過大な拡大を示し、ドット形状係数も殆ど４を超える著しい乱れ（フェザリング等）を示して到底実用に供し得ない。これに反し、本発明のインク組成物１９、２０はこれら普通紙に対しても実用に供し得る特性を示す大きな長所を示した。
【００７５】
【発明の効果】
本発明のインクジェットプリンタ用インク組成物及び記録方法は、従来のインクジェット用インクでは不可能であった、非コート普通紙上に高速度で良好に印刷可能な方法を提示する。本発明のインク組成物により、平滑度の低い用紙上にドット滲み及び裏移りのない高画質の印刷が可能で、更にこの印刷物は高速度プリンタに適用できる程度の短時間で乾燥（セット）が終了する。
【図面の簡単な説明】
【図１】 記録媒体に浸透するインク組成物の浸透深さの時間経過を示すモデル図である。
【図２】 実施例１９、２０及び比較例４、５の実験結果を図示した図である。
【図３】 実施例１９、２０及び比較例４、５の実験結果を図示した図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an on-demand type ink jet recording apparatus using a piezoelectric element, and more particularly to a recording method of an ink jet recording apparatus that records on an uncoated paper at a high speed.
[0002]
[Prior art]
Conventionally, in inkjet recording, a special substrate (inkjet paper) is used to prevent excessive penetration and bleeding of ink droplets to achieve high density and saturation printing, and to improve water resistance and storage characteristics. ) Was customarily used. Many reports on this have already been made, for example, USP 5,854,649, USP 5,853,899, JP-A-11-192778, JP-A-11-129610, JP-A-11-078223, JP-A-11-078221, Japanese Patent Application Laid-Open No. 11-034485, Japanese Patent Application Laid-Open No. 11-028861, Japanese Patent Application Laid-Open No. 11-020300, Japanese Patent No. 2845832, Japanese Patent Application Laid-Open No. 11-506991, etc., ink adsorption by applying a specific water-soluble resin For example, USP 5,516,364, JP-A-11-192775, JP-A-11-157207, JP-A-11-129606, JP-A-11-048604, JP-A-11-034481 , Patent 2938917, Patent 2887098, Patent 2883299, Patent 2877740, etc. contain specific materials such as clay and alumina to improve ink adsorbability and perform high-quality printing. It is described.
[0003]
Many reports have been made on ink-jet ink compositions for realizing high-quality printing in parallel. For example, Patent 2136873, Patent 2116198, Patent 2037450, Patent 2037453, Patent 2894568, Patent 2710138, Patent 2792135, Patent 2841678, and Patent 1927399 have little blurring. Ink and the like that enable printing or water resistance are described.
[0004]
There have also been many reports on the relationship between the physical properties of paper and ink. JP 10-330666, JP 10-316915, JP 10-272828, JP 10-237370, JP 11-129460 No. 26618361, No. 2801295, No. 2529154, No. 2516218, No. 2525218, No. 2825224, etc. And reports on the evaporation rate of ink.
[0005]
General explanations on the above ink and paper (substrate) include, for example, “development of high-quality inkjet recording technology and related materials”, Technical Information Association, 1999 publication, “paper for printing and information recording” Characteristics and printability and analysis, evaluation ", Technical Information Association, 1999 publication.
[0006]
On the other hand, in recent years, there has been an increasing demand for high-quality printing on general paper (plain paper) instead of special paper specially manufactured for inkjet. This is not only for paper price reduction, but also in fields that have been processed by other printing methods (offset, flexographic printing and other ink printing fields, laser printers, non-impact printer fields such as thermal recording, impact printer fields, etc.). This is a problem inevitably encountered when applying the ink jet recording method. In particular, in the field of offices where a large number of office documents such as standard documents, slips, forms, etc. are printed at high speed, the use of plain paper and high-speed printing are indispensable requirements. In addition, the recording method is extremely difficult to realize.
[0007]
[Problems to be solved by the invention]
In an ink using water and a water-soluble solvent as a solvent, it is impossible in principle to prevent the phenomenon of deterioration of printing quality such as blurring and back-off (bleed-through) due to penetration and adsorption of paper into cellulose fibers. For this reason, as described above, as a basic measure, a method of maintaining print quality by processing paper (substrate) has been adopted, but it is suitable for plain paper (uncoated paper) printing intended by the present invention. do not do. In particular, the drying property (setting property) and the bleeding of plain paper are usually contradictory properties. When the bleeding is prevented, the drying property is lowered and high-speed printing becomes impossible. Similarly, there is a correlation between ink printing density and bleeding, and with an ink amount that achieves an appropriate high density, bleeding is excessive and offsetting easily occurs, and only poor-quality printing can be obtained.
[0008]
The present invention provides an ink-jet ink composition and a recording method that make it possible to achieve these previously impossible matters.
[0009]
[Means for Solving the Problems]
  The gist of the present invention for solving the above problems is as follows.TheAn on-demand type ink jet printer ejects ink droplets onto a recording medium which is uncoated paper with a Beck smoothness of 80 s or less to form recording dots. In the ink jet recording method in which recording is performed at a recording speed at which the relative speed is 10 ips or more, the viscosity at 25 ° C. is 5 to 15 mPa · s, and the absorption coefficient for the recording medium is 0.9 to 0.3 ( ml / m²) / (Ms)^0.5In other words, an ink composition using a pigment as a coloring material is used.
[0010]
  Preferably, an ink composition having a static surface tension at 25 ° C. of 35 mN / m or more is used. More preferably, an ink composition containing water, polyethylene glycol and a pigment as essential components, and preferably containing glycerin is used.It is in.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
As the paper classification, the method used for the production statistics of the Ministry of International Trade and Industry is often used. According to this, printing information paper, packaging paper, sanitary paper, and miscellaneous paper are broadly classified, and printing information paper includes uncoated paper, finely coated paper, coated paper, special printing paper, and information paper. is there. Paper for the purpose of the present invention belongs to a part of non-coated paper, special printing paper and information paper. The composition of the paper varies widely, and there are various types of pulp materials, types and amounts of paints, and production methods, and there are many methods for evaluating and classifying paper. For example, paper density, thickness, front / back difference, vertical / horizontal (stripping direction), pore porosity, air permeability, water / oil absorption, size, surface roughness, gloss, pH, surface strength, There are peel strength, stiffness, folding strength, chargeability, etc., each affecting print quality.
[0012]
Here, the present inventor paid attention to surface smoothness as a method for generally defining paper in the field intended by the present invention. These include Beck smoothness, smoother smoothness, Chapman smoothness, etc., and are defined in TAPPI-T479, JIS P8119, and the like. The Beck smoothness, smoother smoothness, and smoothness measured by the Oken type smoothness tester can be converted into each other by measuring air flow velocity or pressure change.
[0013]
The papers intended by the present invention are all uncoated paper and have a Beck smoothness of 80 s or less. Uncoated paper has a substantial amount of paint (filler) of 12 g / m on both sides²It means the following paper (below the fine coated paper in the above-mentioned production statistics definition). Inkjet printing relating to paper and the like not corresponding to these is outside the scope of the object of the present invention.
[0014]
Examples of the paper of the present invention include high-grade printing paper, intermediate-grade printing paper, lower-grade printing paper, thin-like printing paper, fine-coating printing paper, special printing paper such as fine-quality printing paper, form paper, PPC paper, and other information paper. Specifically, there are the following papers and various modified / processed papers using them, but the present invention is not particularly limited to these.
[0015]
OK fine paper, New OK fine paper, Sunflower, Phoenix, OK Royal White, Export fine paper (NPP, NCP, NWP, Royal White), OK Foam, OKH, NIP-N, OK Everlight, OK Everlight W, OK Starlight, OK Snowlight, White Birch Paper, OK New Light, OK Magazine Paper, OK Cream Everlight, OK High Parky, OK High Magazine Paper, OK Skylight, OK Fine Paper L, Everlight R, OK Bright, OK Royal Light S, Royal Light H, New Light R, New Light RS, Royal Light N, Clean Hit M, Cree Hit D, Clean Hit S, JJ, OKF, OKH, NIP, KS Form, 3800 Paper, KIP-N ( New Oji Paper), continuous transmission Paper, high quality NIP paper, Kim Wang, Toko, export high quality paper, special demand high quality paper, Pyrenees, Highland, Andes, Rocky, lightweight off-wheel, Alps, Himalayan, Seine, Hyceraster, Easter DX, Pyrenees DX, Super Pi Reine DX, Andes DX, Super Andes DX, Seine DX, Super Seine DX, Golden Foam, Silver Foam, Excellent Foam, Silver Recycled NIP, KRF Super, SKF, GOLF-NIP, PPC Paper (above Japan Paper), Pearl, Gold Rhyo, Diamond Form, Ruby Light O, Ruby Light, Ruby Light L, Mitsubishi NIP (Mitsubishi Paper), Kinpo V, Kinso SW, White Elephant, High Grade Publishing Paper, HNF Semi-quality Paper, Shiromari, Tokuginmari, Kinmari L, Alpha Super, Semi-Up KL, High , Beta Super, Shiromari L, High Gamma, Gamma Super, HNK, HNF (made by Hokuetsu Paper), Shirai, DSK, HAKURO, Sharon, Tokuyuki Yuzu, Shiriko, Libyan, Super Business Newspaper, AA Henry, BB Henry, CC Henry, DD Henry, EE Henry, EE Henry S, DSK, DSK38, DSK-N (made by Daishowa Paper), Silver Ring, Ring, Kimyang (W), Bridge, Capital, Excellent Form, Silver Foam, KRF, FPLB, KCR (Nippon Paper), Sendai MP fine paper, Kinko, Thunderbird fine, hanging paper, colored paper base paper, continuous slip paper, Chaton, Emine, RCP, Sendai foam, Thunderbird foam (Made by Chuetsu Pulp) , OP Kinzakura (above Chuetsu), gold sand, reference book paper, replacement certificate paper (white), Form printing paper, KRF, white form, color form, (K) NIP, fine PPC (made by Kishu Paper), Taiou, Bright Form, Kant, Kant White, Dante, CM Paper, Dante Comic, Heine, Bunko Paper, Heine S, New AD paper, Utrilo Excel, Excel Super A, Canto Excel, Excel Super B, Dante Excel, Heine Excel, Excel Super C, Excel Super D, AD Excel, Excel Super E, New Bright Form, New Bright NIP ( Daio Paper), Sun Ring, Moon Ring, Clouds, Galaxy, Baiyun, Weiss, Moon Ring Ace, Baiyun Ace, Clouds Ace (above Nippon Paper Industries), Taiou, Bright Foam, Brightnip (above Nagoya Pulp) ), Peony A, Golden Pigeon, Special Peony, White Peony A, White Peony C, Silver Pigeon, Super White Peony A, Light Cream White Peony, Special Medium Quality Paper, White Pigeon, Super Medium Quality Paper, Blue Pigeon, Red Pigeon, Gold Pigeon M Snow Vision, Snow Vision, Gold Pigeon Snow Vision, White Pigeon M, Super DX, Hamanasu O, Akabuchi M, HK Super Printing Paper (Honshu Paper), Starlinden (A / AW), Star Elm, Star Maple, Star Laurel, Star Poplar, MOP, Star Cherry I, Cherry I Super, Cherry II Super, Star Cherry III, Star Cherry IV, Cherry III Super, Cherry IV Super (made by Maruzumi Paper), SHF (made by Toyo Pulp), TRP (made by Tokai Pulp).
[0016]
As the recording medium, a paper having a sizing degree of 2 or more can be used without particular limitation according to JIS P8122 “Testing method for the paper sizing degree test”. Examples include high-quality paper and color high-quality paper such as 40 kg paper, 55 kg paper, 70 kg paper, 90 kg paper, and 135 kg paper, Xerox 4024, inkjet plain paper and special paper, recycled paper, and slip paper.
[0017]
The recording medium of the present invention can also be defined by the surface roughness coefficient. Although not exact, for example, paper having an average surface roughness Rz of 10 μm or more substantially corresponds to this.
[0018]
Although the film thickness of the recording medium of the present invention is not particularly limited, for example, paper having a film thickness of 80 to 200 μm is almost applicable. Paper having a film thickness of 95 to 115 μm, which is widely used as ordinary plain paper, is particularly preferable for the purpose of the present invention.
[0019]
The recording medium targeted by the present invention is preferably uncoated paper. For example, in terms of the ratio of elemental components of the paper (EDX measurement), the number of aluminum and silicon elements is 150 and 200, respectively, with respect to the carbon element 100. The following is desirable.
[0020]
As the specification of the paper of the present invention, it is possible to further define, for example, a Steecht size degree of 55 s or less.
[0021]
The gist of the present invention lies in the relationship between physical properties defined by Beck smoothness and ink jet recording. The recording medium is not limited to paper, and can be applied to all metals, plastics, and other possible media having similar characteristics.
[0022]
The penetration of liquid into paper is a complicated phenomenon in which capillary penetration into the voids of the fiber and swelling of the fiber itself are parallel, but the following Lucas-Washburn equation based on a cylindrical capillary model is widely used in the analysis. The penetration depth H of the liquid is expressed by the following equation using the surface tension γ, the viscosity η, the radius r of the capillary, the penetration time t, and the contact angle θ between the liquid and the capillary.
[0023]
[Expression 1]

[0024]
In the above formula, the vertical axis H and the horizontal axis t^0.5Is plotted as a straight line passing through the origin, but in an actual system, as shown in FIG.₀In many cases, it bends.
[0025]
The intercept (Kr in the figure) is the roughness index, the slope (Ka in the figure) is the absorption coefficient, t₀Is sometimes referred to as wetting time. The nomenclature for this section is a certain period of time (t) for the ink to start penetrating into the substrate simply by wetting the surface irregularities of the paper.₀). The absorption coefficient of the present invention is the same plot as in the figure, and the penetration depth (ink absorption amount) (vertical axis) is expressed in ml / m.²Unit, penetration time (horizontal axis) (ms)^0.5It is defined as the slope (Ka) in units.
[0026]
In the present invention, the absorption rate is 1.5 (ml / m²) / (Ms)^0.5Or less, particularly preferably 0.9 to 0.3 (ml / m²) / (Ms)^0.5It is to do. The speed is 0.9 (ml / m²) / (Ms)^0.5If it exceeds 1, the penetration becomes excessive, and the ink causes an unnecessary back-off phenomenon (the ink reaches the back surface), which cannot be substantially used for the uncoated paper of the present invention. In addition, 0.3 (ml / m²) / (Ms)^0.5Below, the ink takes a long time to dry (set) by permeation, and substantially no high-speed printing is possible unless a special post-drying processing step is provided.
[0027]
According to the recording method of the present invention, the roughness index Kr as well as the value of the absorption coefficient Ka described above is also in a specific range, in particular, Kr is 20 ml / m.²The following areas fit the purpose. When the purpose of the present invention is not used, such as using a dedicated ink jet paper, the Kr is 20 ml / m.²It is customary to go beyond. In the target system of the present invention, the wetting time t₀Is usually very short, typically less than 50 ms and practically close to zero.
[0028]
In addition, there are a Bristow method, a dynamic scanning liquid absorption measurement method that automates this, and the like for measuring the permeation rate. The gist of the present invention is the relationship between the physical properties defined by the absorption coefficient and ink jet recording. The recording medium is not limited to paper, and can be applied to all metals, plastics, and other possible media having similar characteristics.
[0029]
The surface tension of the ink composition of the present invention need not be particularly limited, but the present inventor investigated the correlation between the above-mentioned penetration rate and ink physical properties for a large number of inks. It was found that there is a significant correlation with the penetration rate. That is, in an ink having a static surface tension at 25 ° C. of 35 mN / m or more, both permeability and drying can be achieved particularly preferably. In the ink of less than 35 mN / m, the permeability increases remarkably with the decrease in surface tension, and the uncoated paper of the present invention cannot be used due to significant bleeding and set-off. This correlation is completely different from the relationship between the surface tension γ and the penetration depth in the above-mentioned Lucas-Washburn equation (γ large is H small), but this is the effect that θ becomes smaller (cos θ small) in the case of ink with small γ. This is presumed to be larger. The reason why the special threshold of 35 mN / m appears is not clear, but in the case of the uncoated paper of the present invention, it is close to 45 mN / m, which is the reported critical surface tension value of cellulose constituting the paper. May be related to this. Although the present invention has been described only with respect to static surface tension, it is presumed that similar considerations can be obtained in the case of dynamic surface tension.
[0030]
As the ink composition of the present invention, various materials are used without limitation. Generally, it is constituted by adding a binder, viscosity, surface tension, pH and other physical property adjusting agents, fungicides, and the like to the colorant and solvent main materials. The colorant is a dye or a pigment, and the solvent is mainly water or a water-soluble organic solvent, but a non-aqueous solvent is also possible. These solvents may have functions such as anti-drying agent (wetting agent), penetrating agent (surface tension reducing agent), viscosity, evaporation rate control agent, etc. in addition to the function as a solvent. Materials exhibiting properties, boiling point, evaporation rate, flash point, etc. are used.
[0031]
Examples thereof include alcohols such as diethylene glycol, polyethylene glycol, glycerin, NMP, sodium lactate, DMSO, polyoxyethylene alkylphenol, polyoxyethylene fatty acid ester, ethylene glycol alkyl ether, diethylene glycol alkyl ether, ethanol, and propanol. Physical property modifiers include metal hydroxides such as KOH, various surfactants, alcohol amines such as diethanolamine and triethanolamine, phosphoric acid, alcohol amine salts of strong acids, ammonium salts, lower carboxylic acids, glycolic acid, lactic acid Various additives such as anti-fungal agents such as hydroxycarboxylic acid, sodium benzoate, potassium sorbate, thiabendazole, benzimidazole, etc., chelating agents, oxygen scavengers, antifoaming agents, conductivity imparting agents, etc. Can be used. In the present invention, in particular, an ink composition containing water, polyethylene glycol, glycerin and a pigment as essential components can be preferably used.
[0032]
(Poly) alkylene glycols such as polyethylene glycol and polyhydric alcohols such as glycerin have conventionally been used as wetting agents because of their slow evaporation rate. In the present invention, it has been found that polyethylene glycol having an average molecular weight of 600 to 70000 is particularly desirable as a viscosity modifier and further as a viscosity increasing agent for water-based inks mainly composed of water.
[0033]
As a component for achieving the object of the present invention, it is desirable to contain 7.5 to 40% by weight of polyethylene glycol having an average molecular weight of 600 to 6000. If the average molecular weight is less than 600, the viscosity of the main component water is little increased, and if it is added until it reaches a good viscosity range, a good printed matter cannot be obtained. If the added amount exceeds 40% by weight, the ink permeability to the recording material is lowered, the drying property is deteriorated, and the printing quality is lowered. Particularly preferred is an average molecular weight of 6000. Further, it is desirable to contain 1 to 10% by weight of polyethylene glycol having an average molecular weight of 20000 to 70000. If the average molecular weight exceeds 70,000, the viscosity of the ink is remarkably increased, the ink discharge amount is decreased, and the printing density is lowered.
[0034]
For example, polyethylene glycol 600, 1000, 1540, 2000, 4000, 6000, 20000, 70000 (manufactured by Wako Pure Chemical Industries, Ltd.), PEG # 600, PEG # 6000 (manufactured by Nippon Oil & Fats) and the like can be used.
[0035]
Polyethylene glycol can be used by mixing at least one or two or more.
[0036]
Furthermore, glycol ether is suitable as a component that achieves the object of the present invention. In general, glycol ethers are added for the purpose of preventing drying of the tip of a ballpoint pen or an inkjet nozzle without increasing the viscosity of the recording liquid because of its low viscosity. However, it has been found that by mixing with water and polyethylene glycol, the viscosity can be adjusted to enable stable injection.
[0037]
Specific glycol ethers include methyl glycol, methyl diglycol, methyl triglycol, methyl polyglycol, isopropyl glycol, butyl glycol, butyl diglycol, butyl triglycol, isobutyl glycol, isobutyl diglycol ) And other ethylene glycol ethers and methylpropylene glycol, methylpropylene diglycol, methylpropylene triglycol, propylpropylene glycol, propylpropylene diglycol, butylpropylene glycol, butylpropylene diglycol, phenylpropylene glycol (above, manufactured by Nippon Emulsifier) It is desirable to contain 0 to 30% by weight of an ether selected from propylene glycol ethers. If it exceeds 30% by weight, the surface tension is lowered and the printing quality is lowered.
[0038]
Furthermore, you may add 0-20 weight% of glycerol for the purpose of improving discharge property. If it exceeds 20% by weight, bleeding tends to occur on the printed matter.
[0039]
A water-soluble solvent may be added to improve the characteristics. For example, acetone, methyl ethyl ketone, methyl isobutyl ketone, ketones such as methanol, ethanol, isopropanol and lower alcohols, glycols such as ethylene glycol, propylene glycol, diethylene glycol and dipropylene glycol, acetates, thiodiglycol, N-methyl- Nitrogen-containing compounds such as 2-pyrrolidone, 1,3-dimethylimidazolidinone and amino alcohol may be used alone or as a mixed solvent.
[0040]
An organic pigment is particularly desirable as the colorant that is a component that achieves the object of the present invention. Although the ink composition using a dye as a coloring material is easy to manufacture and has many advantages, it is difficult to use it for high-speed printing on plain paper, which is the object of the present invention, due to image blurring and insufficient water resistance. is there. The pigment used in the present invention is preferably a pigment that is well dispersed in the vehicle and has excellent weather resistance. The color development property (color density per added density) of the pigment used in the present invention is not necessarily high, and in addition, it is difficult to produce a homogeneous fine particle dispersion. Therefore, it has not been put into practical use as an inkjet ink. Although not particularly limited, for example, organic or inorganic pigments having the following numbers described in the color index can be used in the present invention. The color tone of the pigment is appropriately selected depending on the type of full color printing, spot (partial) color printing, multicolor printing, and the like.
[0041]
Examples of red or magenta pigments include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48: 1, 48: 2, 48: 3, 48: 4, 48: 5, 49: 1, and 53: 1. , 57: 1, 57: 2, 58: 4, 63: 1, 81, 81: 1, 81: 2, 81: 3, 81: 4, 88, 104, 108, 112, 122, 123, 144, 146 , 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88, Pigment Orange 13 16, 20, 36, blue or cyan pigments include pigment blue 1, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 17-1, 22, 27, 28, 29, 36, 60, as green pigment, Pigment Green 7, 26, 36, 50, as yellow pigment, Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 137, 138, 139, 153, 154, 155, 157, 166, 167, 168, 180, 185, 193, as a black pigment Pigment Black 7, 28, 26, etc. can be used according to the purpose.
[0042]
Specific product names include, for example, Chromo Fine Yellow 2080, 5900, 5930, AF-1300, 2700L, Chromo Fine Orange 3700L, 6730, Chromo Fine Scarlet 6750, Chromo Fine Magenta 6880, 6886, 6891N, 6790, 6877 , Chromofine Violet RE, Chromofine Red 6820, 6830, Chromofine Blue HS-3, 5187, 5108, 5197, 5085N, SR-5020, 5026, 5050, 4920, 4927, 4937, 4824, 4933GN-EP, 4940, 4973, 5205, 5208, 5214, 5221, 5000P, Chromo Fine Green 2GN, 2GO, 2G-550D, 5310, 5370, 6830, Chromo Fine Black A-1103, Seika Fast Yellow 10GH, A-3, 2035, 2054, 2200 , 2270, 2300, 2400 (B), 2500, 2600, ZAY-260, 2700 (B), 2770, Seika Fast Red 8040, C405 (F), CA120, LR-116, 1531B, 8060R, 1547, ZAW-262 , 1537B, GY, 4R-4016, 3820, 3891, ZA-215, Seikafast -Min 6B1476T-7, 1483LT, 3840, 3870, Seika Fast Bordeaux 10B-430, Seika Light Rose R40, Seika Light Violet B800, 7805, Seika Fast Maroon 460N, Seika Fast Orange 900, 2900, Seika Light Blue C718, A612, Cyanine Blue 4933M, 4933GN-EP, 4940, 4973 (manufactured by Daiichi Seika Kogyo), KET Yellow 401, 402, 403, 404, 405, 406, 416, 424, KET Orange 501, KET Red 301, 302, 303, 304 305, 306, 307, 308, 309, 310, 336, 337, 338, 346, KET Blue 101, 102, 103, 104, 105, 106, 111, 118, 124, KET Green 201 (above Dai Nippon Ink Chemical Made), Colortex Yellow 301, 314, 315, 316, P-624, 314, U10GN, U3GN, UNN, UA-414, U263, Finecol Yellow T-13, T-05, Pigment Yellow 1705, Colortex Orange 202, Colortex Red101 103, 115, 116, D3B, P-625, 102, H-1024, 105C, UFN, UCN, UBN, U3BN, URN, UGN, UG276, U456, U457, 105C, USN, Co lortex Maroon601, Colortex BrownB610N, Colortex Violet600, Pigment Red 122, Colortex Blue516, 517, 518, 519, A818, P-908, 510, Colortex Green402, 403, Colortex Black 702, U905 (manufactured by Sanyo dye), Lionol Yellow1405G, Lionol Blue FG7330, FG7350, FG7400G, FG7405G, ES, ESP-S (above Toyo Ink), Toner Magenta E02, Permanent RubinF6B, Toner Yellow HG, Permanent Yellow GG-02, Hostapeam BlueB2G (above Hoechst Industry), carbon Black # 2600, # 2400, # 2350, # 2200, # 1000, # 990, # 980, # 970, # 960, # 950, # 850, MCF88, # 750, # 650, MA600, MA7, MA8, MA11, MA100, MA100R, MA77, # 52, # 50, # 47, # 45, # 45L, # 40, # 33, # 32, # 30, # 25, # 20, # 10, # 5, # 44, CF9, (Mitsubishi Chemical). Further, it is also possible to use a dispersion liquid in which a pigment is dispersed in high concentration in water or a solvent in advance. For example, MICROPIGMO WMBK-5, WMBE-5, WMRD-5, WMYW-5, AMBK-2, AMYW-2, AMBE-4 (made by Orient Chemical), JA Black 25W, GA Black 2821, GA Yellow 1, GA Magenta1, GA Cyan 2 (above made by Gokoku Dye) CAB-O-JET200, CAB-O-JET300 (above Cabot Specialty Chemicals), etc., which have a pigment concentration dispersed at a high concentration of 10% by weight or more Particularly desirable.
[0043]
The appropriate amount of pigment added is 1 to 10% by weight of pigment. If it is less than 1% by weight, the image quality is deteriorated, and if it is more than 10 parts by weight, the ink viscosity characteristics are adversely affected. In addition, two or more kinds of colorants can be mixed as appropriate for color adjustment. In order to further develop functionality in the ink composition of the present invention, a light stabilizer, a surface treatment agent, a surfactant, a viscosity reducing agent, an antioxidant, an anti-aging agent, a crosslinking accelerator, an oxygen absorber, and a plasticizer , Antiseptics, rust inhibitors, evaporation accelerators, pH adjusters, antifoaming agents, humectants, dispersants, dyes, and the like can be mixed.
A stirrer, bead mill, or homogenizer is optimal for mixing and dispersing the pigment and other components described above, but various known stirring, pulverizing or dispersing devices can be used without any particular limitation.
[0044]
The evaporation rate of the ink composition of the present invention is not particularly limited, but it is preferable to have an appropriate ink evaporation rate as the ink composition used in the on-demand ink jet recording method. As a result of a comparative examination of the evaporation rate (evaporation amount) of various inks and the stability of inkjet recording, the present inventor found that the weight loss due to evaporation under atmospheric conditions of 25 ° C./60 RH% was 2 to 25% by weight in 30 minutes. It has been found that the ink composition is particularly preferable. The measurement was performed by dropping 2 drops (about 100 mg) of 50 μl of ink on a slide glass, leaving it in the above environment in a substantially windless state, and measuring the weight change with a microbalance. The evaporation rate of the present invention was defined under these measurement conditions. If the weight reduction is less than 2% by weight, drying of the print after ink jet recording is poor. For example, transfer tends to occur when the sheets are overlapped, and if the weight reduction exceeds 25% by weight, the ink drying is remarkably clogged and ejected. Defects are likely to occur and the reliability of the recording process is reduced.
[0045]
  The viscosity of the ink composition of the present invention is not particularly limited, but the static viscosity at 25 ° C is5A range of ˜15 mPa · s is preferable for maintaining stable ejection characteristics.5When the viscosity is less than mPa · s, the shape and frequency characteristics of ink droplets are likely to be poor, and when the viscosity exceeds 15 mPa · s, ejection is difficult and difficult to stabilize. The ink composition of the present invention desirably exhibits Newtonian fluid behavior under the temperature conditions to be used. However, if the above conditions are met at the shear rate (about 100 rpm) used for normal measurement, the apparent viscosity has a slight share. The presence of speed dependence does not matter.
[0046]
The printing speed of printers in the field of the present invention is characterized by being significantly faster than conventional ink jet recording. Although there is no clear limitation regarding the speed, in order to effectively use the ink composition of the present invention, a recording speed at which the relative speed between the nozzle and the paper is 10 ips (inch / s) or more is particularly preferable. In order to record at high speed, it is necessary to fix (set) ink droplets immediately after adhering to the recording medium. If insufficient, the adhering ink reservoir is transferred to the back of another sheet on which it is stacked. Such as sticking to the feed roll in the recording apparatus, and disturbing the recording dots. In order to realize the recording speed of 10 ips, for example, it is necessary that the recording is fixed within about 1 s after recording. In other words, according to the present invention, the recording can be handled substantially (touch the hand etc.) within about 1 s.
[0047]
There are various types of on-demand ink jet recording heads or recording methods using piezoelectric elements, such as line type recording, serial type recording, transfer type (shuttle type) recording, etc., but the present invention is particularly limited to these. Used without being. In either case, the relative moving speed between the nozzle and the paper (recording medium) is 10 ips or more. For example, when the head portion is fixed and only the paper moves as in line-type recording, the paper moving speed (paper Feed speed) corresponds to the above relative speed, and in the case of serial type recording, that is, when the head moves perpendicularly to the paper feed direction and sequentially records and paper feed is intermittently performed, the head movement speed (carriage speed) is Corresponds to relative speed. In the case of a transfer type where the paper is installed on a rotating drum or the like and records on this, or once recorded on the drum and then transferred to the paper, the moving speed of the moving paper or the relative position between the drum surface and the nozzle changes And understand. In either case, the recording speed is directly related to the nozzle discharge frequency and the recording resolution.
[0048]
For example, the paper feed speed of the line type recording or the serial type head moving speed (that is, the recording speed) V is represented by V = f × R by the ink droplet ejection frequency f and the recording resolution R. In conventional recording of 5 ips or less (usually 1 ips or less), a number of conventionally reported ink compositions can be applied as they are. The present invention can be effectively used in high-speed recording of at least 5 ips, particularly preferably 10 ips or more.
[0049]
In order to carry out the high speed of the present invention more effectively, it is also possible to add a heating and drying process. However, the effect of the present invention is particularly advantageous in that sufficiently practical printing characteristics can be realized without using these drying and heating steps.
[0050]
The ink composition of the present invention satisfies several well-known requirements for application to an inkjet printer. That is, this ink has sufficient stability at room temperature, and is reliable in storage before printing and image quality after printing. After adhering and curing on the recording medium, it has sufficient transparency and saturation, and forms a uniform thin film to give a printed matter with good image quality. It is necessary that the offset does not occur in a state where the printed materials are stacked, and that the composition is highly safe in consideration of the environment and the human body.
[0051]
Further, this ink composition ejects ink droplets only when printing is required, and conventionally known inkjet printers such as office printers, printers used for industrial marking, wide format printers, printing plates It can also be used in plate-making printers, label printers and all types of high-speed printers with this typical operation. Since high-speed drying is possible, a plastic film, capsule, gel, metal foil, glass, wood, cloth, etc. can be used as the recording medium in addition to the paper described above. As long as non-contact printing is possible, a wide variety of media shapes can be used.
[0052]
EXAMPLES Next, although an Example demonstrates this invention concretely, it is not limited to a description example.
[Examples 1 to 6]
68 parts by weight of purified water, 2 parts by weight of polyethylene glycol having an average molecular weight of 70,000 (trade name: polyethylene glycol 70,000), 20 parts by weight of glycerin (manufactured by Wako Pure Chemical), and Table 1 10 parts by weight of each of the various alkylene glycol alkyl ethers shown in Table 1 were mixed, and 10 parts by weight of a black pigment aqueous dispersion (Micropigmo manufactured by Orient Chemical Co., Ltd., pigment content 20% by weight) was mixed. Using HG30 manufactured by Hitachi Koki Co., Ltd., dispersion was performed at a rotational speed of 2,000 rpm until a homogeneous mixture was obtained, followed by filtration to remove impurities and the like to obtain six types of homogeneous ink compositions.
[0053]
The absorption coefficient of the ink composition is a dynamic scanning absorption meter (Kyowa Seiko, KM350-D), the viscosity is a rotational viscometer (EDL model manufactured by Tokimec), and the surface tension is an automatic surface tension meter (CVBP- manufactured by Kyowa Interface Science Co., Ltd.). Z model) and Beck smoothness were measured with Oken air permeability smoothness tester (KY-5 manufactured by Asahi Seiko). In either case, the measurement temperature is 25 ° C. Absorption coefficient Ka is the absorption amount vertical axis penetration depth (absorption amount) H, horizontal axis (penetration time)^0.5The points plotted in (1) were linearly approximated, and the roughness index Kr (intercept) and the absorption coefficient Ka (gradient) were calculated.
[0054]
Using 55 kg paper (manufactured by Kobayashi Recording Paper, NIP paper) as a recording medium for evaluation, a printing test machine in which the head portion of a direct plate making machine (SJ02A manufactured by Hitachi Koki) was extracted and fixed was used, and an ink ejection speed of 3 kHz. The paper feed speed was set to 10 ips, and printing was performed at 10 ips with a resolution of 300 (× 600) dpi. The Beck smoothness of the recording medium is 46.5 s. The printing results were simply evaluated in the following 3 items.
(1) Set-off: Visual observation of ink oozing out on back side (ink bleed evaluation)
(2) Transfer: Visual observation of whether or not ink is transferred in a process of pressure bonding to another sheet within 1 s after printing (set property evaluation)
(3) Water resistance: Within 5 s after printing, changes in ink spillage by exposure to running water in the visual observation table indicate that 、 is excellent, ○ is good, and × is unusable. Each of the ink compositions of Examples 1 to 6 has an absorption coefficient of 0.9 to 0.3 (ml / (m²・ Ms^1/2))showed that.
[0055]
The surface tension is 25 mN / m or more, and the viscosity is 5 mPa · s or more. The printing evaluation results were all excellent to good, and it was found that good printing was possible on plain paper.
[0056]
The results are shown in Table 1.
[0057]
[Table 1]

[0058]
Example 7
50 parts by weight of purified water, 50 parts by weight of dipropylene glycol and 10 parts by weight of the same black pigment aqueous dispersion as in Example 1 were mixed to produce an ink composition as in Example 1, and the same evaluation was performed. It was. The results are shown in Table 1.
[0059]
The absorption coefficient is 0.9 (ml / (m²・ Ms^1/2)), The static viscosity is 7.3 mPa · s, and the surface tension is 40.3 mN / m. The printing results were satisfactory for each evaluation, and good printing was possible on plain paper.
[Comparative Examples 1-3]
68 parts by weight of purified water having the composition shown in Table 1, 2 parts by weight of polyethylene glycol 70,000, 2 parts by weight of glycerin, 10 parts by weight of diethylene glycol monobutyl ether or ethylene glycol isobutyl ether are mixed, and 10% of the pigment aqueous dispersion is mixed therewith. Alternatively, three types of ink compositions added with 20 parts by weight were produced, and the same measurements and evaluations as in Example 1 were performed.
[0060]
In either case, the absorption coefficient is 2 (ml / (m²・ Ms^1/2)) Exceeding values, transfer (drying) and water resistance were excellent, but the back-off (ink bleeding) was poor and a large amount of ink oozed out into dots on the back, which was used for printing on plain paper It was impossible. All of these ink compositions had a surface tension of less than 35 mN / m.
[Examples 8 to 18]
11 inks of the present invention having the composition shown in Table 2 and using purified water, polyethylene glycol (molecular weight: 6,000), polyalkylene glycol monoalkyl ether and pigment dispersion (CAB-O-JET300 manufactured by Cabot Specialty Chemicals) A composition was prepared.
[0061]
And the result of having performed the measurement and evaluation similar to Example 1 was shown in Table 2.
[0062]
[Table 2]

[0063]
In either case, 0.3 to 0.9 (ml / (m²・ Ms^1/2)) And the printing results were excellent to good for each item. It has been found that the ink composition of the present invention is suitable for plain paper printing.
[Examples 19 to 20] and [Comparative Examples 4 to 5]
Ink compositions 19 and 20 of the present invention were produced with the compositions shown in Table 3. Further, commercially available inks A and B were used for comparison.
[0064]
Table 3 shows the same measurement and evaluation results as in Example 1.
[0065]
[Table 3]

[0066]
The absorption coefficient of the ink composition of the present invention was 0.5 and 0.8 (ml / (m²・ Ms^1/2)) And excellent print results were obtained for each item.
[0067]
Using these two types of ink compositions of the present invention and two types of comparative inks, printing was performed on 11 types of commercially available paper, and the dot area and dot shape factor (= (peripheral length))²/ (2π · dot area)) (see FIGS. 2 and 3). For the measurement of dot shape, an image captured by a CCD camera from a microscope with a magnification of 20 times was analyzed using automatic image quality evaluation software (Image Pro Plus manufactured by Media Cybemetrics). The number of measurement dots is 30 to 100.
[0068]
The results are shown in Tables 4 and 5.
[0069]
[Table 4]

[0070]
Inkjet (IJ) papers 1 to 5 all have a structure in which an ink receiving layer is laminated on the surface, and plain papers 1 to 6 are uncoated papers.
[0071]
As described in Table 4, all the inkjet papers have a Beck smoothness exceeding 80 s, and all the plain papers have a value of 80 s or less. Table 4 shows the measurement results of the dot area. Compared with Comparative Examples 4 and 5, the ink compositions 19 and 20 of the present invention have a remarkably small dot diameter (that is, less dot expansion due to bleeding). I understood.
[0072]
[Table 5]

[0073]
Table 5 shows the measurement results of the dot shape factor, and it was found that the ink composition of the present invention has a small shape factor (that is, the shape is closer to a true circle), and the ink dot shape is less disturbed.
[0074]
In the case of inkjet paper, although there is a difference between these, all have a small dot diameter (for example, 10,000 μm).²And the dot shape factor (for example, 2 or less), both of which can be practically used. However, when the printing result of uncoated paper with Beck smoothness of 80 s or less is seen, in the case of the ink of the comparative example, the dot diameter is 10,000 μm due to bleeding.²And the dot shape factor shows a significant disturbance (feathering or the like) almost exceeding 4 and cannot be put to practical use. On the other hand, the ink compositions 19 and 20 of the present invention showed great advantages that they can be used practically even for these plain papers.
[0075]
【The invention's effect】
The ink composition and recording method for ink jet printers of the present invention present a method that allows good printing at high speed on uncoated plain paper, which was impossible with conventional ink jet inks. The ink composition of the present invention enables high-quality printing without dot bleeding and set-off on low-smoothness paper, and the printed material can be dried (set) in a short time enough to be applied to a high-speed printer. finish.
[Brief description of the drawings]
FIG. 1 is a model diagram showing the passage of time of the penetration depth of an ink composition that penetrates a recording medium.
2 is a diagram illustrating experimental results of Examples 19 and 20 and Comparative Examples 4 and 5. FIG.
3 is a diagram illustrating experimental results of Examples 19 and 20 and Comparative Examples 4 and 5. FIG.

Claims (3)

An on-demand type ink jet printer ejects ink droplets onto a recording medium that is uncoated paper with a Beck smoothness of 80 s or less to form recording dots, and the nozzles of the on-demand type ink jet printer and the recording medium In the ink jet recording method in which recording is performed at a recording speed at which the relative speed is 10 ips or more,
Ink composition comprising a pigment having a viscosity at 25 ° C. of 5 to 15 mPa · s and an absorption coefficient of 0.9 to 0.3 (ml / m ² ) / (ms) ^0.5 for the recording medium. An ink jet recording method using an object. The ink jet recording method according to claim 1 Symbol mounting surface tension at 25 ° C. is characterized by using a 35 mN / m or more of the ink composition. 3. The ink jet recording method according to claim 1, wherein an ink composition containing water, polyethylene glycol and a pigment as essential components, and preferably containing glycerin is used.

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