JP2004523665A - Cellulose fibers with low water retention and low capillary discharge pressure - Google Patents

Abstract

The present invention provides cellulosic fibers with low median discharge pressure and low water retention value (WRV) that exhibit improved fluid drainage and liquid flow properties. These fibers are particularly suitable for use in uptake, distribution and uptake distribution layers, as well as in absorbent core structures. One embodiment of the present invention is a method for producing cellulose fibers by refining cellulose fibers to a freeness of about 300 to about 700 ml CSF and cross-linking the refined cellulose fibers. Another embodiment of the present invention is a fiber cross-linked by at least one cross-linking agent selected from saturated dicarboxylic acids, aromatic dicarboxylic acids, cycloalkyl dicarboxylic acids, difunctional monocarboxylic acids and amine carboxylic acids. . At the time of the crosslinking reaction, a crosslinking aid such as oxalic acid may be present in order to enhance the effect of the crosslinking agent. Yet another embodiment of the present invention is an absorbent core comprising fibers reversibly crosslinked with SAP particles.

Description

(式中、R¹、R²、R³およびR⁴は独立して水素、水酸基、C₁〜C₄アルコキシ、C₁〜C₄アルキル、アミノ、ハロゲン、またはニトロである)。好ましい芳香族ジカルボン酸はフタル酸である。
【００７１】
（シクロアルキルジカルボン酸架橋剤）
「シクロアルキルジカルボン酸」という用語は、カルボキシル基に対してαまたはβ位に炭素炭素二重結合を含まないシクロアルキルジカルボン酸を指す。1つの実施態様によれば、シクロアルキルジカルボン酸は次式を有する:
【化１０】

(式中、R⁶、R⁷、R¹⁰およびR¹¹は独立して水素、水酸基、ハロゲン、C₁〜C₄アルコキシ、C₁〜C₄アルキル、アミノまたはニトロであり;
R⁸およびR⁹は独立して水素、ハロゲン、C₁〜C₄アルコキシ、またはC₁〜C₄アルキルである)。好ましいシクロアルキルジカルボン酸は1,2,5,6-テトラヒドロフタル酸である。
【００７２】
（2官能性モノカルボン酸架橋剤）
「2官能性モノカルボン酸」は、(a)カルボキシル基を1個だけおよび(b)官能基(それはカルボキシル基でない)を有し、カルボキシル、カルボン酸、アミノ、またはポリマーの水酸基と反応し得る有機酸を指す。好ましくは、2官能性モノカルボン酸は、2個の官能基(つまりカルボキシル基ともう1つの官能基)のみを含む。
【００７３】
適当な2官能性モノカルボン酸は、アミノ酸、ハロ酢酸塩、ヒドロキシモノカルボン酸、ヒドロキシモノカルボン酸の酸誘導体(ヒドロキシモノカルボン酸の酸エステルなど)含むが、これらに限定されない。
【００７４】
好ましいハロ酢酸塩はクロロ酢酸ナトリウムである。特定の理論に拘束されるものではないが、クロロ酢酸ナトリウムとセルロース繊維との水性混合物を乾燥硬化させると、塩素を含むクロロ酢酸ナトリウム分子の炭素とセルロース水酸基との反応によってエーテルが形成されると信じられている。このエーテル化反応は塩酸分子を放出するが、これは新たに形成されたセルロースに基づく酸のナトリウム塩によって直ちに中和される。高い温度では、この酸は付随する水の放出と共に、繊維中で近接した水酸基のエステル化に利用可能である。エーテルおよびエステル形成後に、塩化ナトリウムが副産物として残る。
【００７５】
適当なヒドロキシカルボキシル酸およびその酸誘導体としては、グリコール酸、グリコール酸のメタンスルホン酸エステルおよびグリコール酸のパラトルエンスルホン酸エステルが挙げられるが、これらに限定されない。
【００７６】
（アミンカルボン酸架橋剤）
適当なアミンカルボン酸架橋剤は、1級、2級および3級アミンおよび芳香族アミンを含むが、これらに限定されない。好ましい1級アミンにはアミノ酸が含まれるが、これに限定されない。特に次式のアミノ酸がよい:
【化１１】

(式中、R¹²は結合、C₁〜C₁₂アルキルまたはカルボキシル基、水酸基、C₁〜C₄アルコキシ、C₁〜C₄アルキル、アミノもしくはニトロで置換されたC₁〜C₁₂アルキル基である)である。
【００７７】
好ましいアミノ酸は次式を有する
【化１２】

(式中、R⁵は線状または分岐鎖のC₁〜C₈アルキルである)ものであるが、これに限定されない。好ましい実施態様によれば、R⁵はC₂〜C₄アルキルである。これらに限定されるものではないが、他の適当なアミノ酸の例としてはアスパラギン酸およびグルタミン酸が挙げられる。
【００７８】
他の適当なアミンカルボン酸架橋剤としては、エチレンジニトリロ酢酸(EDTA)が挙げられるが、これに限定されない。
【００７９】
（架橋助剤）
本発明の架橋助剤は、架橋剤の効果を増加させる。好ましい架橋助剤はシュウ酸である。特定の理論に拘束されるものではないが、架橋剤のエステル化のための酸性触媒としてシュウ酸(pKa=1.23)が役立つと信じられている。あるいは、シュウ酸は架橋剤と混合無水物を形成し、次いで、これがセルロース繊維のエステル化を促進するのかもしれない。
【００８０】
（架橋の可逆性）
本発明の短い架橋剤(つまり、シュウ酸およびクロロ酢酸ナトリウムのように4個の炭素原子(たとえば、3個以下の炭素原子)を含むもの)により架橋された繊維は、脱架橋可能であり、しかも後に架橋することができる。こうした繊維の架橋は一般に、実質的に可逆的である、すなわち、架橋された繊維の少なくとも約50重量%は脱架橋することができる。1つの実施態様によれば、架橋された繊維の少なくとも約60、70、80、90、または95重量%を脱架橋できる。
【００８１】
架橋された繊維は、脱架橋に十分な時間、それらを水に浸漬することにより脱架橋できる。典型的には、架橋された繊維は、約0.5から約4時間浸漬する。好ましい実施態様によれば、繊維は約2時間浸漬する。架橋された繊維は、それらを、本願の実施例に記載されるような毛管吸収放出サイクルにさらすことにより脱架橋することができる(Burgeniら(上記)およびChatterjeeら(上記))。
【００８２】
繊維は乾燥または乾燥硬化により再架橋できる。この現象は、米国特許第5,137,537号、5,183,707号および5,190,563号に開示されている共有結合架橋繊維では観察されなかった。
【００８３】
特定の理論に拘束されるものではないが、架橋された繊維が水を吸収し膨潤するにつれて、セルロース・ポリマー鎖が吸収された水を収容しようと分かれだすため架橋部分が引っ張られると信じられている。シュウ酸またはクロロ酢酸ナトリウムなどで処理した繊維のように、架橋分子の長さが非常に短い場合(2個の炭素原子が、近接するセルロース・ポリマー鎖の上の水酸基を分離する)、膨潤した繊維における歪みは、繊維を架橋している2つの共有結合のうち1つの加水分解および分裂を促進するのに十分である。これとは対照的に、米国特許第5,137,537号; 第5,183,707号および第5,190,563号に開示されているようなクエン酸で架橋された繊維では、セルロース・ポリマー鎖間の空隙を橋懸けする分子の長さがはるかに長い(4個または5個の炭素原子が、近接するセルロース・ポリマー鎖の上の水酸基を分離する)。したがって、繊維が吸収し膨潤する際のより長い架橋分子に対する張力は架橋共有結合のうちの1つの開裂を促進するのには十分でない。
【００８４】
本発明の繊維を脱架橋することができるので、それらはバルクな状態や梱包した状態を取る代わりに、シート状にして乾燥させ輸送し、または保存できる。これは出荷コストおよび保存コストを低減する。繊維は目的地でまたは所望な任意の時点でたとえば分離硬化して再架橋できる。いったん繊維が再架橋されれば、これをたとえば吸収体構造と一体化できる。
【００８５】
「可逆的に架橋された繊維」「可逆的に架橋されたセルロース繊維」という用語は、本願では、架橋された繊維の約50、60、70、80、90、または95重量%が水中に4時間以下の浸漬で脱架橋され、脱架橋された繊維の約50、60、70、80、90、または95%が、105℃以上の温度での乾燥で再架橋できる架橋された繊維または架橋されたセルロース繊維を指す。
【００８６】
本発明の可逆的に架橋された繊維は、超吸収体ポリマー(SAP)粒子を含む吸収体コアで使用するに特にふさわしい。架橋された繊維はSAP粒子を分離し、吸収体コアの湿潤領域から乾燥領域に向けてSAP粒子周囲に流体の流路をもたらす。さらに、可逆的に架橋された繊維は、短時間(たとえば噴出)での多量の尿(または他の流体)の吸収を促進する。いったん尿または他の流体が吸収体コアに入ると、架橋された繊維は脱架橋を開始する。1つの実施態様によれば、尿その他の流体への0.5〜4.0時間さらされた後には、湿潤繊維の大半が脱架橋される。脱架橋された繊維は、永久に架橋された繊維よりも多量の尿その他の流体を保持して保つ。その結果、吸収体コアは、従来のフラフ繊維を含む吸収体コアと比較して改善された初期噴出容量を有し、永久に架橋された繊維を含む吸収体コアと比較して、改善された再湿潤性能を有する。
【００８７】
（吸収体構造）
本発明のセルロース繊維は、身体浸出物を吸収し保持する目的で、一般に着用者の身体に近接して配置されるか保持される任意の使い捨てまたは非使い捨て吸収体構造に組み込むことができる。こうした吸収体構造は、使い捨てまたは非使い捨て吸収体物品に広く用いられている。使い捨ての吸収体物品の例としては、幼児用おむつ、成人用失禁製品、躾用パンツ、生理用ナプキンその他の女性用衛生製品が挙げられるが、これらに限定されない。本発明のセルロース繊維を組み入れ得る吸収体構造の例としては、国際公開公報WO98/47456、WO99/63906、WO99/63922、WO99/63923、WO99/63925、WO00/20095、WO00/38607、WO00/41882、WO00/71790、およびWO00/74620ならびに米国特許第5,695,486号(これらはすべて参照によって本願に組み込まれる)に記載の例が挙げられるが、これらに限定されない。
【００８８】
（取込み分配層）
本発明のセルロース繊維は、取込み層、分配層または取込み-分配層に組み込むことができる。こうした層は、一般に、使い捨ての吸収体物品に含まれる吸収体構造で用いられている。取込みおよび/または分配層は、当技術分野で知られている任意の方法によって製造し、吸収体構造に組み込むことができる。1つの実施態様によれば、吸収体構造は、最上層(これは本発明の取込みおよび/または分配層を含む)と底部貯蔵層(吸収体コアとしても知られている)を含む。取込み層および分配層は、単一の層でもよいし2つの別個の層(つまりトップの取込み層とその下側の分配層)でもよい。下側の分配層は取込み層からの流体を迅速に排出し、貯蔵層に流体を分配する。
【００８９】
本発明の取込み層は、取込み層の全重量を100%として、通常、約90から約100重量%までの本発明のセルロース繊維を含む。取込み層の密度は、約0.04から約0.07g/cm³まで広い範囲に及ぶ。
【００９０】
（吸収体コア）
本発明のセルロース繊維、吸収体コア(貯蔵層としても知られている)に組み込むことができる。吸収体コアは、液体を吸収する当技術分野で知られている任意の材料を含み得る。適当な材料としては、繊維離解した、緩い、けば立った、および/もしくは親水性セルロース繊維または本発明の繊維から造られた繊維の中綿またはウェブ;超吸収性ポリマー(SAP)粒子、小粒、フレークまたは繊維(集団的に粒子);およびこれらのものの任意の組合せを含むが、限定されない。一般に、SAP粒子は、それ自体の重量よりも多くの倍率の重量の液体を吸収でき、実質的に層のかさばりを増加させずに、吸収体コアの吸収容量を著しく増加させる。
【００９１】
超吸収性物質ポリマー粒子またはSAP粒子という用語は、不規則な形の顆粒、球状粒子(ビーズ)、粉末、フレーク、短繊維および他の細長い粒子を含め任意形状の微粒子超吸収性ポリマーも含むものとする。SAPは、通常、架橋によって実質的に水不溶性にした水溶性ポリマーを指すが、一般に少なくともその重量の10倍、好ましくは少なくとも15倍の生理食塩類水を吸収することができる。SAP粒子は任意のサイズまたは形状でよい。超吸収性材料の多数の例およびそれらの製造方法は、たとえば、米国特許第4,102,340号;第4,467,012号;第4,950,264号;第5,147,343号;第5,328,935;第5,338,766号;第5,372,766号;第5,849,816号;第5,859,077号;およびRe.32,649に見ることができる。適当なSAP粒子の例としては、加水分解デンプン-アクリレート・グラフト・コポリマーなどのデンプン・グラフト・コポリマー共重合体;架橋カルボキシメチルセルロースおよびその誘導体;鹸化されたアクリル酸エステル・ビニル・コポリマー、中和化架橋ポリアクリル酸および架橋ポリアクリレート塩などの修正された親水性ポリアクリレートが挙げられるが、これらに限定されない。
【００９２】
好ましくは、SAP粒子は流体を吸収によりヒドロゲルを形成する。より好ましくは、SAP粒子は高いゲル・ボリュームまたはヒドロゲルの剛性率(shear modulus)による測定で高いゲル強度を有する。こうしたSAP粒子は、通常は合成尿(いわゆるエクストラクタブル(extractables))との接触によって抽出可能なポリマー材料を比較的少量含む。こうしたSAP粒子の例は、ヴァージニア州PortsmouthのHoechst-Celanese社からIM1000(登録商標)として入手できるデンプン・グラフト・ポリアクリレート・ヒドロゲルである。SAP粒子を含むヒドロゲルの他の例としては、SANWET(商標)(日本の三洋化成工業株式会社から入手可能);SUMIKA GEL(商標)(日本の住友化学株式会社から入手可能);Favor(商標)(ルイジアナ州GaryvilleのStockhausen社から入手可能);およびASAP(商標)(マサチューセッツ州AberdeenのBASFから入手可能)として販売されているものが挙げられるが、これらに限定されない。
【００９３】
1つの好ましい実施態様によれば、吸収体コアは(a)SAP粒子および(b)フラフ繊維、マトリックス繊維、本発明の繊維またはこれらのものの任意の組合せを含む。繊維は吸収体コアに構造上の一体性をもたらし、流体がコアを通り抜ける流路を提供する。
【００９４】
別の実施態様によれば、吸収体コアは、吸収体コアの全重量を100%として、約30重量%から約70重量%のSAP粒子と、約70重量%から約30重量%の本発明のセルロース繊維を含む。一般に、吸収体コアの体積密度は約0.15から0.25g/cm³まで変動する。
【００９５】
さらに別の実施態様によれば、吸収体コアは、本発明のSAP粒子および可逆的に架橋された繊維を含む。1つの好ましい実施態様によれば、可逆的に架橋された繊維は、シュウ酸、クロロ酢酸ナトリウムまたはそれらの混合物で架橋される。一般に、吸収体コアは、吸収体コアの全重量を100%として、約30重量%から約70重量%のSAP粒子と、約70重量%から約30重量%の本発明の可逆的に架橋された繊維を含む。別の好ましい実施態様によれば、取込み層および/または分配層ならびに吸収体コアは、シュウ酸で架橋された繊維を含む。
【００９６】
本発明の吸収体構造は、おむつ、成人用失禁パッドおよび女性用衛生用品などの使い捨ておよび非使い捨て吸収体物品に組み込むことができる。吸収体物品は、取込み層および/または分配層上に液体透過性トップシート(その機能は取込み層および/または分配層まで流体を通すことである)と液体不透過性のバックシート(その機能は流体を保持し、それが吸収体物品を通り抜けて吸収体物品の着用者の衣服に達するのを防止することである)を含むことができる。
【００９７】
1つの実施態様によれば、本発明の吸収体構造は、使い捨ての幼児のおむつに組み入れられる。これは、一般に正面のウエストバンド領域、後部ウエストバンド領域およびその間の股領域を含む。おむつの構造は、一般に液体透過性トップシート、液体不浸透性バックシート、吸収体構造、弾性部材および固定タブを含む。使い捨てのおむつの代表的な設計例は、たとえば、米国特許第4,935,022号および第5,149,335号に見ることができる。
【００９８】
別の実施態様によれば、本発明の吸収体構造は、米国特許第5,961,505号に開示されているような女性用衛生パッドに組み入れられる。
【００９９】
以下の実施例により本発明を説明するが、これは発明を限定するものではない。特に断らない限り、部およびパーセンテージはすべて重量で与えられる。例において使用されるすべての架橋剤、架橋助剤、および他の化学的試薬はすべて、ウィスコンシン州MilwaukeeのAldrich Chemical Companyから入手可能である。
【実施例】
【０１００】
毛管圧力および放出圧ならびに飽和容量の測定
毛管の吸収および放出圧力は、"Capillary Sorption Equilibria in Fiber Masses", A. A. Burgeni and C. Kapur, Textile Research Journal, 37:356-366 (1967)に記載の操作によって測定された。この操作の詳細は以下に記載する。
【０１０１】
個別化された繊維試料0.75gは、直径およそ55〜60mmのディスクで形成される。試料を150mlの粗フリットPyrex(登録商標)ガラス漏斗(Corning第36060番(ジョージア州SuwaneeのVWR社から入手可能))。試料の直径に匹敵する直径の、0.22psiの圧力を加えるのに十分な錘を試料の上に置く。漏斗の底は、減少する直径を備えたアダプターに取り付け、Tygon(登録商標)管No.R-3603(長さおよそ2フィート)がアダプターの一方の端に、他方の端には重さ0.01gを測定可能な電子秤に載せた流溜めに接続するように取り付けられる。管は液溜めの底部側面に取り付ける。液溜めは0.9%塩溶液を含む。液溜め中の塩溶液の高さは管取り付け位置の上およそ1インチである。漏斗をフリットより下にして、フリットが塩溶液で湿っているが塩溶液がフリットより上には出ないように、管を食塩水で満たす。液溜めからフリットまでの塩溶液の柱は柱内に空気を含まないように連続している。
【０１０２】
吸収サイクルは以下のとおりである。たとえば液溜めの食塩水のレベルの上20、30、または80cmの高さから始めて、試料に塩溶液を吸収させ平衡させて定常状態とする。定常状態は、液溜めの下の電子秤で1分間、0.04gを超える食塩水の重量変化がないものとして測定される。定常状態が達成されると、試料を液溜めの食塩水の液面に5cm接近するように低下させ、平衡が達成されるまでそこに保つ。試料をさらに5cm下げ、この操作を繰り返す。試料が液溜めの塩溶液面と同じ高さの平衡にある場合、操作を逆にすることにより(つまり、5cmの増分で上向きの試料を移動させることによって)試料を放出サイクルにさらす。
【０１０３】
液溜め中の食塩水と同じレベルにあるときの試料中の食塩水の重量が、試料の飽和容量である。下方への(吸収)サイクルで飽和容量の50%において液溜め中の塩溶液面からの試料の高さ(cmで報告する)(吸収圧力中央値)と上向きの(放出)カーブ(放出圧中央値)を外挿によって測定する。飽和容量の値は試料グラムあたりの食塩水のグラムとして表の中に報告する。
【０１０４】
実施例1〜8
表1中の実施例1〜8は以下のようにして製造した。
【０１０５】
740mlCSFの濾水度を有する未精砕のセルロース繊維(テネシー州MemphisのBuckeye Technologies Inc.からFoley Fluff (商標)として入手可能)を、水中でスラリーとし、環境温度および圧力でヴァリー(valley)叩解器によって適当な濾水度となるまで精砕した。繊維を遠心分離し、手で分離し、60%固形分になるまで風乾した。40%固形分のシートをもたらすのに十分な稀釈度を有するクエン酸水溶液を繊維に吹きかけることにより、適当な濃度のクエン酸(乾燥繊維基準)で繊維を架橋した。次いで、繊維を60%固形分まで風乾し、けば立たせ、一定重量になるまで乾燥し、表1の中に示す温度でさらに30分間加熱した。
【０１０６】
硬化したセルロース繊維の保水値、飽和容量、毛管吸収圧力および毛管放出圧を測定した。硬化したセルロース繊維の保水値は、TAPPI Useful Methods, UM 256に記載された操作によって測定した。毛管吸収圧および放出圧は上に記載された操作によって測定した。
【０１０７】
結果を表1に示す。
【０１０８】
比較例9
740mlCSFの濾水度を有する未精砕のセルロース繊維(テネシー州MemphisのBuckeye Technologies Inc.からFoley Fluff (商標)として入手可能)を、100℃で乾燥した。硬化したセルロース繊維の保水値、飽和容量、毛管吸収圧力および毛管放出圧を実施例1と同様にして測定した。
【０１０９】
結果を下記表1に示す。
【０１１０】
比較例10
740mlCSFの濾水度を有する未精砕のセルロース繊維(Buckeye Technologies Inc.からFoley Fluff (商標)として入手可能)に、40%固形分とするのに十分な水を吹きかけた。繊維を60%固形分となるように乾燥し、機械的にけば立て、150℃で一定の重量になるまで乾燥させた。次いで、繊維を同じ温度でさらに30分間加熱した。硬化したセルロース繊維の保水値、飽和容量、毛管吸収圧力および毛管放出圧を実施例1と同様にして測定した。
【０１１１】
結果を表1に示す。
【０１１２】
比較例11
740mlCSFの濾水度を有する未精砕のセルロース繊維(Buckeye Technologies Inc.からFoley Fluff (商標)として入手可能)をスラリー化し、ヴァリー(valley)叩解器によって濾水度がおよそ500mlCSFとなるまで精砕した。繊維を遠心分離し、手で分離し、60%固形分になるまで風乾し、150℃で一定の重量になるまで乾燥させた。次いで、繊維を150℃でさらに30分間加熱した。硬化したセルロース繊維の保水値、飽和容量、毛管吸収圧力および毛管放出圧を実施例1と同様にして測定した。
【０１１３】
結果を表1に示す。
【０１１４】
比較例12
740mlCSFの濾水度を有する未精砕のセルロース繊維(Buckeye Technologies Inc.からFoley Fluff (商標)として入手可能)をスラリー化し、ヴァリー(valley)叩解器によって濾水度がおよそ500mlCSFとなるまで精砕した。繊維を遠心分離し、手で分離し、60%固形分になるまで風乾した。クエン酸で処理した時、繊維と水の混合物のpHを実施例1において観察されたのと同じpHとするため、セルロース繊維にpH3の硫酸水溶液を固形分40%となるまで吹きかけた。繊維を60%固形分となるように乾燥し、機械的にけば立て、150℃で一定の重量になるまで乾燥させた。次いで、繊維を150℃でさらに30分間加熱した。硬化したセルロース繊維の保水値、飽和容量、毛管吸収圧力および毛管放出圧を実施例1と同様にして測定した。
【０１１５】
結果を表1に示す。
【０１１６】
比較例13
740mlCSFの濾水度を有する未精砕のセルロース繊維(Buckeye Technologies Inc.からFoley Fluff (商標)として入手可能)に、シートの固形分が40%となるように十分に希釈したクエン酸水溶液を吹きかけ、繊維を5%のクエン酸(乾燥繊維基準)で架橋した。繊維を60%固形分となるように乾燥し、機械的にけば立て、150℃で一定の重量になるまで乾燥させた。次いで、シートを150℃でさらに30分間加熱した。硬化したセルロース繊維の保水値、飽和容量、毛管吸収圧力および毛管放出圧を実施例1と同様にして測定した。
【０１１７】
結果を表1に示す。
【０１１８】
比較例14
5%のクエン酸の代わりに10%のクエン酸で繊維を架橋したこと以外は比較例13の操作を繰り返した。結果を表1に示す。
【０１１９】
【表１】

【０１２０】
表1の結果に示されるように精砕され架橋された繊維は、未精砕な他は同様の架橋された繊維よりも、より低いWRVおよび放出圧を示した。
【０１２１】
実施例15
Buckeye Technologies Inc.から入手可能な非乾燥Foley Fluff (商標)を2.75〜3.25重量%含む水性スラリーを調製した。水性スラリーを、環境温度および圧力で精砕器によりBauerモデルNo.444、24" (約61cm)ポンプを通した。Bauer精砕器プレートはNo.A24313とした。
【０１２２】
精砕器は、178倍(178 amps)流で、かつ毎分255ガロン(969リットル)のスラリー・フロー率で操作した。これらの条件は、繊維の絶乾米トン(約0.907t)当たり30〜60馬力時間の負荷を生じた。生産された繊維は、680mlCSFの濾水度を有していた。
【０１２３】
脱塩
精砕されたパルプ・スラリーを2.75〜3.25%のコンシステンシーとして二重底タンクに汲み入れた。パルプ・スラリーの撹拌中、名目pH2.0となるまで硫酸を添加した。少なくとも10分間撹拌した後に、水性スラリーを、最低3時間、二重底スクリーンを通して脱水した。次いで、スラリーを2.0%のコンシステンシーとなるまでナトリウム軟水で希釈し、pHを4.5〜5.0に調整した。
【０１２４】
シート形成
パルプのシート化は、ニューヨーク州Hudson FallsのSandy Hill Corporationから入手可能な抄紙機を用いて行った。デクル(シート幅)は最大36インチとした。2%パルプ・スラリーをスタッフ・ボックス(stuff box)および坪量バルブ(basis weight valve)を通して、白水サイロ内にコントロールされた流量で送り込んだ。直接に蒸気を当てることでサイロ温度を130〜150°Fに増加し、サイロ内のスラリーを1.0〜1.25%のコンシステンシーとなるまで白水で希釈した。
【０１２５】
次いで、スラリーを抄紙機ヘッドボックス(head box)に供給し、抄紙機の長網抄紙パート(Fordrinier section)の移動ワイヤー上に移した。形成されたシートが約32%のコンシステンシーでカウチ・プレス(couch press)を出るまで、自然排水および真空支援排水をほどこした。シート形成後カウチ・プレス前に、湿潤シートを、2つのジェット水で24インチ・デクルになるようにトリミングした。次いで、約32%のコンシステンシーを有する繊維シートを2台のウェット・プレスに通した(ここでは一層の水分除去およびシートの高密度化が生じた)。第2のウェット・プレスを出た後に、繊維シートはおよそ48%のコンシステンシーで第1乾燥機セクションに入った。第1乾燥機セクションでは、パルプ・シートはおよそ300〜325°Fの13台の回転蒸気缶上を通過した。次いで、パルプ・シートは、第2乾燥機・セクション中で8台の回転蒸気缶で通り、水分量4〜8%で乾燥機を出た。シートを約23インチのデクルでロール状に巻いた。このロール状シートの坪量は1平方フィートおよそ0.126ポンドであり、密度は1立方センチメートル当たりおよそ0.60グラムであった。
【０１２６】
スリッティング
パルプ・ロールを新しい芯上に巻き、スリッティングによってより小さなロール(幅10インチ)とした。
【０１２７】
化学的処理
10インチ幅のパルプ・シートをロールから解き、パドル・プレス(puddle press)をゆっくりと通した。パドル・プレスのニップ(nip:ロール間隙)には、クエン酸および次亜燐酸ナトリウム水溶液を満たした。次亜燐酸ナトリウムは、高温でのパルプ暗色化を抑える。液張りニップ(flodded nip)でのクエン酸および次亜燐酸ナトリウムの重量濃度は、それぞれおよそ14%および7%であった。パドル・プレスを通してシートは十分な量の水溶液を吸収し、約40%の含水率に達した。
【０１２８】
シート分解およびフラッフィング
パドル・プレスに続いて、シートをシュレッダ、プレブレーカおよびピッカを通してより細かな断片に分断した。次いで、分解したパルプを、5.5mmのギャップ値を設定して、Sunds Defibratorモデル3784 RO Fluffer (Sunds Defibrator(スウェーデンのSundsvall ABから入手可能)の導入口に吹き込んだ。この繊維離解器でパルプをフラッフィング(けば立たせ)し、分離された繊維の集塊とした。およそ380°Fで熱風の高い速度流を用いてフラッフ・パルプをRO Flufferから掃き出した。
【０１２９】
乾燥および硬化
RO Flufferからのフラフ(けば立てられた)繊維を運んだ熱風フローにさらにファンを用いフラッシュ・乾燥機を通し、ここで繊維中の全水分またはほとんどすべての水分を蒸発させた。乾燥パルプは、機械的インレット・コンベヤ上に落下してコンベヤ上に低密度の嵩高ベッド(high bulk bed)を形成した。次いで、繊維をペンシルヴェニア州HorshamのProctor & Schwartz, Inc.から入手可能なProctor & SchwartzK16476トンネル乾燥機に搬送した。一連の熱循環気流によって、乾燥機中の3つの部屋を通る際にフラフ繊維ベッドは加熱され、次いで冷却された。第1室では、ベッド温度が325〜330°Fに達した。第2室では、ベッド温度は385〜390°Fに増加させた。第3室では、ベッド温度は355〜360°Fまで減少した。トンネル乾燥機中の時間の合計はおよそ11.5分であった。
【０１３０】
梱包
架橋された繊維は、トンネル乾燥機の出口側においてコンベヤから落下し、梱包機モデルNo.3445(オハイオ州BellevueのAmerican Baler Companyから入手可能)に移り、ここで重さおよそ70〜80ポンドの梱包物に圧縮された。
【０１３１】
実施例16
以下のようにして表2の試料を製造した。
【０１３２】
Buckeye Technologies Inc.(テネシー州Memphis)からFoley Fluff (商標)として入手可能な740mlCSFの濾水度を有する未精砕セルロース繊維を水性スラリーとし、環境温度および圧力で精砕器によりBauerモデルNo.444、24" (約61cm)ポンプを通して適当な濾水度に達するまで精砕した。場合によっては、繊維を希硫酸で洗浄(酸洗)し、無機成分を除去した。精砕された繊維をシート化し乾燥した。
【０１３３】
1枚のシートを、架橋剤およびシュウ酸の溶液を含むトレーに沈めた。次いで、この紙片をひっくり返し、架橋剤およびシュウ酸の第2溶液に沈めた。これらの溶液は併せて架橋剤を10%(乾燥繊維基準)およびシュウ酸を5%(乾燥繊維基準)含んでいた。溶液は紙片を固形分40%とするに十分な希釈性を有していた。紙片を密封したポリエチレン・バッグ内に1時間置いた。繊維を60%固形分になるまで風乾し、けば立て、一定重量になるまで乾燥し、175℃でさらに30分間加熱した。
【０１３４】
硬化したセルロース繊維の保水値、飽和容量、毛管吸収圧力および毛管放出圧を測定した。硬化したセルロース繊維の保水値は、TAPPI Useful Methods, UM 256に記載された操作によって測定した。毛管吸収および放出圧は上に記載された操作によって測定した。
【０１３５】
結果を表2に示す。
【０１３６】
【表２】

【０１３７】
実施例17
以下のようにして表3の試料を製造した。
【０１３８】
Buckeye Technologies Inc.(テネシー州Memphis)からFoley Fluff (商標)として入手可能な740mlCSFの濾水度を有する未精砕セルロース繊維を水性スラリーとし、環境温度および圧力で精砕器によりBauerモデルNo.444、24" (約61cm)ポンプを通して適当な濾水度に達するまで精砕した。精砕繊維をシート化し乾燥した。繊維がウェット・ラップである場合は、次いで遠心分離した。
【０１３９】
1枚のシートを、架橋剤、次亜燐酸ナトリウム(および場合によってはシュウ酸)の溶液を含むトレーに沈めた。次いで、この紙片をひっくり返し、架橋剤、次亜燐酸ナトリウム(および場合によってはシュウ酸)の第2溶液に沈めた。これらの溶液は併せて、架橋剤を10%(乾燥繊維基準)、次亜燐酸ナトリウムを5%(乾燥繊維基準)およびシュウ酸を1%(乾燥繊維基準)含んでいた。溶液は紙片を固形分40%とするに十分な希釈性を有していた。紙片を密封したポリエチレン・バッグ内に1時間置いた。繊維を60%固形分になるまで風乾し、けば立て、一定重量になるまで乾燥し、175℃でさらに30分間加熱した。
【０１４０】
硬化したセルロース繊維の保水値、飽和容量、毛管吸収圧力および毛管放出圧を測定した。硬化したセルロース繊維の保水値は、TAPPI Useful Methods, UM 256に記載された操作によって測定した。毛管吸収および放出圧は上に記載された操作によって測定した。
【０１４１】
結果を表3に示す。
【０１４２】
【表３ａ】

【表３ｂ】

【表３ｃ】

【０１４３】
実施例18
下記表4に記載する試料を以下のようにして製造した。
【０１４４】
表4中に特定される架橋剤および架橋助剤のストック溶液を、蒸留水の22.5g中、表に示す量の架橋剤および架橋助剤を溶かすことにより製造した。
【０１４５】
試料は適当な溶液により以下のように処理した。Buckeye Technologies Inc.(テネシー州Memphis)からFoley Fluff (商標)として入手可能な740mlCSFの濾水度を有するシート化された未精砕セルロース繊維試料15g(乾燥基準)を架橋剤および架橋助剤を含む適当なストック溶液で処理した。これにより、混合物の繊維が固形分は40%に減少した。混合物を環境温度下密閉容器内に60分間置き、次いで60%固形分になるまで風乾した。繊維を機械的に分離し、個別化し、実験室用のけば立て機においてけば立て、一定重量になるまで175℃の強制循環空気オーブン中で乾燥した。同じ温度で30分間繊維を硬化させた。
【０１４６】
対照は以下のように製造した。Buckeye Technologies Inc.(テネシー州Memphis)からFoley Fluff (商標)として入手可能な740mlCSFの濾水度を有するシート化された未精砕セルロース繊維試料を40%固形分になるまで水で希釈した。混合物のpHを硫酸でpH3に調節した。上記操作で繊維に適用されたストック溶液は、典型的は3であった。次いで、この混合物を環境温度下密閉容器内に60分間置き、次いで60%固形分になるまで風乾した。繊維を機械的に分離し、個別化し、実験室用のけば立て機においてけば立て、一定重量になるまで175℃の強制循環空気オーブン中で乾燥した。同じ温度で30分間繊維を硬化させた。
【０１４７】
Pampers(登録商標)使い捨ておむつ(オハイオ州CincinnatiのProctor and Gamble社から入手可能)の取込み分配層から繊維を得て第2のコントロールとして使用した。
【０１４８】
繊維の保水値、飽和容量、毛管吸収圧力および毛管放出圧を測定した。セルロース繊維の保水値は、TAPPI Useful Methods, UM 256に記載された操作によって測定した。毛管吸収および放出圧は上に記載された操作によって測定した。
【０１４９】
結果を表4に示す。
【０１５０】
【表４ａ】

【表４ｂ】

【表４ｃ】

【０１５１】
実施例19
1.5gのクロロ酢酸ナトリウムを用い実施例18に記載の方法によって、架橋された繊維試料を製造した。第2の試料は、クロロ酢酸ナトリウムの代わりに1.5gのシュウ酸を用いて製造した。
【０１５２】
比較目的のために、10重量%クエン酸を含むストック溶液を使用し実施例18における操作によって架橋された繊維の試料を製造した。
【０１５３】
試料について上記操作による第1の毛管吸収放出サイクルを行った。次いで、試料について同じ操作による第2の毛管吸収放出サイクルを行った。両方のサイクルで観察された吸収および放出圧力を下記表5に示す。
【０１５４】
この試験を脱架橋されたFoley Fluff (商標)繊維でも繰り返した。
【０１５５】
【表５】

【０１５６】
実施例20
実施例19に記載の試料を製造し、2回の毛管吸収放出サイクルを施した。試料を105℃の強制循環空気オーブン中で夜通し乾燥させた。あるいは、試料は105℃で一定の重量になるまで乾燥させ、175℃でさらに30分間加熱(硬化)した。試料の飽和容量ならびに吸収および放出圧を測定した。
【０１５７】
結果を表6に示す。
【０１５８】
【表６】

【０１５９】
実施例21
化学的処理
10重量%シュウ酸溶液151ポンド、50重量%次亜燐酸ナトリウム溶液15ポンドおよび1ポンドの水を混合することにより、シュウ酸および次亜燐酸ナトリウムの水溶液を調製した。
【０１６０】
Buckeye Technologies Inc.からFoley Fluff (商標)として入手可能な10インチ幅のパルプ・シートをロールから解き、パドル・プレスをゆっくりと通した。パドル・プレスのニップは、シュウ酸および次亜燐酸ナトリウム水溶液で満たした。次亜燐酸ナトリウムは、高温でのパルプ暗色化を抑える。パドル・プレスを通してシートは十分な量の水溶液を吸収し、約47%(乾燥繊維の全重量を100%とする)の含水率に達した。処理したシートは、10重量%のシュウ酸および5%の次亜燐酸ナトリウムを含んでいた(乾燥繊維の全重量を100%とする)。
【０１６１】
シート分解およびフラッフィング
パドル・プレスに続いて、シートをシュレッダ、プレブレーカおよびピッカを通してより細かな断片に分断した。次いで、分解したパルプを、5.5mmのギャップ値を設定して、Sunds Defibratorモデル3784 RO Fluffer (Sunds Defibrator(スウェーデンのSundsvall ABから入手可能)の導入口に吹き込んだ。この繊維離解器でパルプをフラッフィング(けば立たせ)し、分離された繊維の集塊とした。およそ380°Fで熱風の高い速度流を用いてフラッフ・パルプをRO Flufferから掃き出した。
【０１６２】
乾燥および硬化
RO Flufferからのフラフ(けば立てられた)繊維を運んだ熱風フローにさらにファンを用いてフラッシュ乾燥機を通し、ここで繊維中の全水分を蒸発させた。乾燥パルプは、機械的インレット・コンベヤ上に落下してコンベヤ上に低密度の嵩高「ベッド」(high bulk "bed")を形成した。次いで、繊維をペンシルヴェニア州Horsham のProctor & Schwartz, Inc.から入手可能なProctor & SchwartzK16476トンネル乾燥機に搬送した。一連の熱循環気流によって、乾燥機中の3つの部屋を通る際にフラフ繊維ベッドは加熱され、次いで冷却された。第1室では、ベッド温度が330〜340°Fに達した。第2室では、ベッド温度は375〜385°Fに増加させた。第3室では、ベッド温度は355〜360°Fまで減少した。3つの加熱ゾーンを経た後、繊維ベッドを最後に、さらなる加熱は行わない断熱室(1室)に通した。トンネル乾燥機中の時間の合計はおよそ11.5分であった。
【０１６３】
梱包
架橋された繊維は、トンネル乾燥機の出口側においてコンベヤから落下し、梱包機モデルno.3445(オハイオ州BellevueのAmerican Baler Companyから入手可能)に移され、ここで重さおよそ85〜100ポンドの梱包物に圧縮された。
【０１６４】
本明細書で参照した文献はすべて本願に組み込まれる。本明細書と文献とで矛盾する部分については、本願の開示の文言に従うものとする。【Technical field】
[0001]
This application claims the benefit of U.S. Provisional Application No. 60 / 247,078 filed November 10, 2000 and U.S. Provisional Application No. 60 / 286,298 filed April 25, 2001. Both are incorporated herein by reference.
[0002]
The present invention relates to cellulosic fibers having a low water retention value and a low median release pressure as measured in a capillary absorption and release cycle, a method for producing these fibers, and an absorbent structure comprising these fibers.
[Background Art]
[0003]
Absorbent construction is important in a wide range of disposable absorbent articles, including infant diapers, adult incontinence products, sanitary napkins and other feminine hygiene products. These and other absorbent articles generally include an absorbent core that receives and retains bodily fluids. In conventional absorber structures, the absorber core consists of a liquid-permeable topsheet (its function is to pass fluid to the core) and a liquid-impermeable backsheet (its function is to retain the fluid, Between the article and the wearer's clothing of the absorbent article).
[0004]
Absorbent cores for diapers, adult incontinence pads, and feminine hygiene articles often include a batting or web of loose, fuzzy, hydrophilic cellulosic fibers. Filling of these fibers forms a matrix that can absorb and retain some liquid. However, their ability to perform such functions is limited. For this reason, the absorbent core contains superabsorbent polymer (SAP) particles, granules, flakes or fibers (collectively particles) capable of absorbing a liquid of a weight greater than its own weight, and substantially It is often practiced to increase the absorption capacity of the core without having to increase the bulk of the core. In an absorbent core comprising matrix fibers and SAP particles, the fibers physically separate the SAP particles, providing structural integrity to the absorbent core and providing a flow path for fluid to pass through the core.
[0005]
Although absorbent cores containing SAP particles have been successful, in recent years there has been an increasing market demand for thinner, more absorbent and more comfortable absorbent articles. As the core absorbency is improved, the ability of the core to quickly drain fluid from the absorbent article topsheet in order to maintain a dry environment between the absorbent article wearer's skin and the article topsheet. Has become important.
[0006]
The ability of the absorber core to drain fluid from the layer immediately above it in the absorber structure depends on gravity, the size and number of unoccupied volumes (voids or holes) and the spatial orientation in the absorber core, and It is controlled by the properties of the core component that affect fluid flow (such as how much the component gets wet by the captured fluid) and is indicated by the contact angle, surface tension of the captured fluid, and viscosity of the captured fluid. An uptake layer, distribution layer or uptake distribution layer can be included in the absorbent structure between the topsheet and the absorbent core to facilitate the outflow of fluid to the absorbent core.
[0007]
In order to optimize the performance of the absorbent structure with respect to fluid volume and core utilization, it is important that the fluid taken up by the absorbent core be rapidly transferred from the wet area of the core to the dry area of the core. The ability of the absorbent core to rapidly transfer fluid from the wet area of the core to the dry area of the core can be described by its permeability. The permeability of the absorbent core is defined as the ability of the liquid to flow through the absorbent core.
[0008]
The ability of a first substrate, such as an absorber core, to expel fluid by capillary forces primarily from a second substrate, such as an uptake and distribution layer, is known as the partition property of the substrate.
[0009]
It is known to those skilled in the art that an absorber structure including an absorber core with good fluid distribution properties will give poor results in fluid permeability. Similarly, an absorbent structure having good fluid permeability exhibits poor fluid distribution characteristics. Thus, the fibers used in the uptake layer have a higher toughness or elasticity (measured as dry compressibility) under the weight of the diaper wearer than conventional fibers used in the absorbent core. is important. This elasticity allows the diaper to quickly absorb fluid through the liquid permeable topsheet and into the absorbent structure of the diaper while retaining the interfiber voids or voids in the intake layer.
[0010]
It is also important that the density of the core fibers does not increase when wet, to the extent that fluid flow into and through the absorber core is limited. Must have sufficient physical integrity to maintain separation. This minimizes or eliminates gel blocking for particle swelling.
[0011]
One way to increase fiber tenacity and momentum is to crosslink them. Cellulose fibers can be strengthened by intra-fiber cross-linking (ie, cross-linking between two different parts of the same fiber), and to a lesser extent by inter-fiber cross-linking (ie, cross-linking between two different fibers).
[0012]
U.S. Pat.No. 5,190,563 issued to Herron et al. Discloses certain aliphatic and cycloaliphatic C _Two ~ C ₉ Disclose intra-fiber crosslinking with polycarboxylic acids. "C defined by Herron et al. _Two ~ C ₉ A "polycarboxylic acid" is an organic acid containing two or more carboxyl groups and 2 to 9 chain or cyclic carbon atoms to which the carboxyl groups are attached. Suitable C _Two ~ C ₉ The polycarboxylic acid contains at least three carboxyl groups or contains two carboxyl groups, and one or both carboxyl groups have a carbon-carbon double bond at the alpha and beta positions. If two carboxyl groups are separated by a carbon-carbon double bond or they are attached to the same ring, the two carboxyl groups must be in the cis configuration. Examples of such polycarboxylic acids include citric acid, 1,2,3-propanetricarboxylic acid, 1,2,3,4-butanetetracarboxylic acid (BTCA) and oxydisuccinic acid. Herron et al. Report that cellulose fibers cross-linked with an aliphatic alkane containing four carboxyl groups (i.e.BTCA) are those containing three carboxyl groups, i.e., citric acid, 1,2,3-propanetricarboxylic acid. It was found that the water retention value was lower than that of the acid. Typically, fibers with lower water retention values are stronger than those with higher water retention values.
[0013]
Unlike cellulosic fibers with intra-fiber crosslinks, cellulosic fibers with interfiber crosslinks, as found on most papers, are strong when dry but do not always maintain their firmness when wet. Inter-fiber crosslinked paper with citric acid and 1,2,3,4-butanetetracarboxylic acid, woven fabric crosslinked with maleic acid, citric acid and 1,2,3,4-butanetetracarboxylic acid Crosslinking is due to DF Caulfield, TAPPIJ., 77 (3): 205-212 (1994); D. Horie and CJ Biermann, TAPPIJ, 77 (8): 135-140 (1994); YJ Zhou, P. Luner and P Caluwe, J Appl. Polymer Sci., 58: 1523-1534 (1995); and DD Gagliardi and FB Shippee, Am. Dyestuff Reptr., 52: 300 (1963).
[0014]
Zhou et al. Previously studied the wet strength of paper cross-linked (inter-fiber) with certain polycarboxylic acids. Generally, inter-fiber crosslinking increases the wet strength of the paper fibers. Zhou et al. Have found that as the functionality of a polycarboxylic acid (ie, the number of carboxyl groups in the polycarboxylic acid) increases, the wet strength of the paper increases. For example, 1,2,3,4-butanetetracarboxylic acid (BTCA) (4 carboxyl groups) is more effective than tricarballylic acid (TCA) (3 carboxyl groups), while succinic acid (2 carboxyl groups) ) Was found to be significantly more effective. Paper treated with succinic acid showed little wet strength.
[0015]
HJ Campbell and T. Francis, Textile Res. J, 35: 260 (1965) crosslinked cotton cellulose with certain polycarboxylic acids. The reaction was catalyzed with trifluoroacetic anhydride (TFAA) and required the use of a non-aqueous solvent (benzene in this case) to prevent hydrolysis of TFAA. Campbell and Francis report that succinic and glutaric acids showed little reactivity with cotton cellulose. In addition, they report that esterification (ie, cross-linking) does not occur with oxalic acid. Malonic acid was found to react readily with cotton cellulose, producing a yellowed woven fabric depending on the degree of reaction.
[0016]
In many cases, crosslinked cellulosic fibers are manufactured at a location remote from where they are incorporated into the absorbent structure. Since the crosslinked fibers are bulky and there is little contact between the fibers, they do not bond well to each other. For this reason, the sheet formed from the crosslinked fibers easily disintegrates. For this reason, the crosslinked cellulose fiber is generally packed and shipped. As a result, crosslinked fibers increase shipping costs and costs in manufacturing the absorbent structure. Therefore, it would be desirable to produce a cellulosic fiber sheet containing a cross-linking agent.
[0017]
“Crosslinkable” cellulosic fibrous products formed in web or sheet form are disclosed in WO 00/65146. Crosslinkable products are obtained by applying a crosslinking agent to a mat of cellulosic fibers and then drying (without heating to a temperature sufficient to cure the crosslinking agent) the mat which has been treated so that there is substantially no crosslinking. The product is substantially free of crosslinks.
[0018]
U.S. Pat. No. 6,059,924 discloses a method for enhancing the dry compressive and wicking properties of fluff pulp. The method involves refining the chemical pulp slurry under mild conditions prior to forming the fluff pulp sheet.
DISCLOSURE OF THE INVENTION
[Problems to be solved by the invention]
[0019]
There is still a need for improved cellulosic fibers with low water retention and low median release pressure for incorporation in uptake, distribution and uptake-distribution layers. Fiber for the core or matrix that promotes fluid flow into and through the absorbent core and maintains sufficient physical integrity to minimize or eliminate gel blocking of swollen SAP particles Is also needed. Furthermore, there is a need for a method of producing a crosslinkable cellulose fiber sheet.
[Means for Solving the Problems]
[0020]
The present invention provides cellulosic fibers having a low median release pressure as measured by the capillary absorption and release cycle and having a low water retention value (WRV), which have improved drainage characteristics and fluid flow. Demonstrate the characteristics. These fibers are particularly suitable for use in uptake, distribution and uptake-distribution layers, and in absorbent core structures.
[0021]
According to one embodiment, the fibers of the present invention are crosslinked and have a median release pressure of 15 cm or less as measured in the sZ capillary absorption and release cycle. Preferably, the cellulosic fibers further have a WRV of 45% or less. These fibers can be made by refining cellulose fibers having a freeness in the range of about 300 to about 700 ml Canadian Standard Freeness Tester (CSF) and crosslinking the refined fibers. According to a preferred embodiment, after refining, the fibers are crosslinked with citric acid.
[0022]
Another embodiment of the present invention is a fiber cross-linked by at least one saturated dicarboxylic acid, aromatic dicarboxylic acid, cycloalkyldicarboxylic acid, bifunctional monocarboxylic acid or amine carboxylic acid. A crosslinking aid such as oxalic acid may be present during the crosslinking reaction to improve the effect of the crosslinking agent. According to one preferred embodiment, the cellulosic fibers are further comminuted prior to crosslinking to make them stronger.
[0023]
Another embodiment is (a) crosslinking cellulose fibers using at least one crosslinking agent selected from saturated dicarboxylic acids, aromatic dicarboxylic acids, cycloalkyl dicarboxylic acids, difunctional monocarboxylic acids and amine carboxylic acids. And (b) de-crosslinking the crosslinked cellulose fiber. Preferably, the crosslinking agent in this embodiment contains no more than 4 carbon atoms. Two preferred crosslinkers are oxalic acid and sodium chloroacetate. The crosslinkable fibers can be in sheet form, which facilitates transport. Further, the crosslinkable fibers can be recrosslinked by curing the decrosslinked cellulose fibers.
[0024]
Yet another embodiment of the present invention is an uptake layer, distribution layer or uptake distribution layer comprising the cellulose fibers of the present invention.
[0025]
Yet another embodiment is an absorbent core comprising cellulosic fibers. The absorbent core exhibits improved fluid flow characteristics into and through the core. According to one preferred embodiment, the absorber core comprises SAP particles and reversibly crosslinked fibers. The reversibly cross-linked fibers separate the SAP particles and provide a fluid flow path around the SAP particles from the wet area to the dry area of the absorbent core. In addition, reversibly crosslinked fibers promote the absorption of large amounts of urine (or other fluids) in a short period of time (eg, gushing). Once urine or other fluid enters the absorbent core, the crosslinked fibers begin to decrosslink. Decrosslinked fibers retain more urine and other fluids than fibers that remain permanently crosslinked. As a result, the absorbent core has an improved initial squirt volume as compared to an absorbent core containing conventional fluff fibers and is improved as compared to an absorbent core containing permanently crosslinked fibers. Has rewet performance.
[0026]
Yet another embodiment is an absorber structure comprising an uptake layer, distribution layer or uptake distribution layer of the invention and / or an absorber core of the invention. Preferably, the absorbent structure includes a top (uptake, distribution or uptake distribution) layer and a bottom (storage) layer that allows fluid communication with the top layer. The absorber structure exhibits superior distribution from the uptake and / or distribution layer to the storage layer as compared to conventional absorber structures.
[0027]
Still another embodiment is an absorbent article including the absorbent structure of the present invention.
[0028]
(Definition)
The term "capillary absorption-release cycle" (also known as the capillary sorption cycle or CSC) refers to the period during which liquid enters the absorber structure and subsequently drains fluid from the absorber structure. It refers to a method for measuring the relationship between the pore volume of the absorber structure and the capillary pressure. The capillary absorption-release cycle is a measure of the ability of the absorbent structure to attract, retain, and distribute fluid into the voids between the fibers of the absorbent structure. The absorber structure can be made to follow this cycle by systematically reducing and increasing the capillary pressure at short intervals, as shown in the method described in this example; "Capillary Sorption Equilibria in Fiber Masses", AA Burgeni. And C. Kapur, Textile Research Journal, 37: 356-366 (1967); and PK Chatterjee, Absorbency, Textile Science and Technology 7, Chapter 11, pp. 63-65, Elsevier Science Publishers (1985). The contents of which are incorporated herein by reference.
[0029]
The term "median release pressure" as measured in a capillary absorption and release cycle refers to the water release capacity of a water-swollen cellulose fiber. For example, a cellulosic fiber sample that strongly retains water will exhibit a much higher median release pressure than a swollen cellulosic fiber sample that readily releases water. The median release pressure discussed herein is determined by the method described in the Examples of this application; "Capillary Sorption Equilibria in Fiber Masses", AA Burgeni and C. Kapur, Textile Research Journal, 37: 356-366 (1967) ); And PK Chatterjee, Absorbency, Textile Science and Technology 7, Chapter 11, pp. 63-65, Elsevier Science Publishers (1985). The contents of which are incorporated herein by reference. This test method measures the ability of water-swollen cellulose fibers to retain water against hydrostatic pressure.
[0030]
The `` water retention value '' (WRV) of cellulose fibers is determined by the method described in TAPPI Useful Methods, UM 256 and PK Chatterjee, Absorbency, Textile Science and Technology Z, Chapter II, pp. 62-63, Elsevier Science Publishers (1985). Can be measured (both of which are incorporated herein by reference). The test measures the weight of water remaining in the sample after centrifuging the water-saturated cellulose fibers and expresses the amount as a weight percent based on the dry weight of the fibers. The WRV of cellulose fiber is related to its drainage capacity.
[0031]
Any "cellulosic fiber" known in the art, including any natural cellulosic fiber, such as from wood pulp, can be used as a starting material in the method of the present invention. Preferred cellulose fibers include digestive fibers such as kraft, pre-hydrolyzed kraft, soda, sulfite, chemi-thermal mechanical, and thermal mechanically-treated fibers derived from softwood, hardwood or cotton linters. It is not limited to these. More preferred cellulose fibers include, but are not limited to, kraft digested fibers (pre-hydrolyzed kraft digested fibers).
[0032]
In general, thick walled cellulose fibers are preferred because they are coarser and stiffer than similar thinner walled fibers. The fiber wall of the fiber is defined by the lumen of the fiber (ie, the hollow interior of the fiber) and the outer surface of the fiber. For example, since the fiber wall of the southern softwood is on average thicker than that of the northern softwood, fibers derived from the southern softwood are preferable. More preferably, the cellulosic fibers are derived from softwoods such as pine, fir and pine.
[0033]
Other suitable cellulosic fibers include those derived from African honeysuckle, bagasse, kemp, flax and other ligninous and cellulosic fiber sources. Cellulose fibers can be supplied in slurry or non-sheet or sheet form.
[0034]
The optimal fiber source utilized in the present invention will depend on the specific end use envisioned. Generally, the pulp fibers are preferably made by a chemical pulping process. Fully bleached, partially bleached and unbleached fibers can be used. Due to its superior brightness and appeal to consumers, it will often be desirable to utilize bleached pulp. For absorbent pads for paper towels, diapers and sanitary napkins, sanitary products and similar absorbent paper products, it is particularly preferred to use cellulose fibers derived from softwood pulp due to their particularly good absorption properties. .
[0035]
More preferred cellulosic fibers include, but are not limited to, bleached kraft pine pine fiber sold under Foley FlufffTM, which is available from Buckeye Technologies Inc. of Memphis, TN. .
[0036]
Cellulose fibers may have any fiber length. However, longer fibers typically produce crosslinked cellulosic fibers having lower release pressure and water retention values than those made from shorter fibers.
[0037]
(Refined crosslinked fiber)
Surprisingly and unexpectedly, when cellulosic fibers are refined and crosslinked, the resulting fibers have a low median release pressure and a low water retention value (WRV) as measured by the capillary absorption and release cycle. Was found. In addition, these fibers exhibit improved fluid drainage in the uptake and / or distribution layers as compared to similar fibers except that they are unrefined.
[0038]
Crosslinked cellulosic fibers have a median release pressure of 15 cm or less as measured in the capillary absorption and release cycle. Without being bound by a particular theory, the inventors believe that this property is the result of intra-fibrous cross-linking within the cellulosic fibers. More preferably, the cellulosic fibers of the present invention have a median release pressure of 14 cm or less as measured in the capillary absorption and release cycle; even more preferably, the fibers of the present invention have a median release pressure of 13 cm or less as measured in the capillary absorption and release cycle. More preferably, the fibers of the present invention as shown herein have a median release pressure of 12 cm or less as measured in the capillary absorption and release cycle.
[0039]
The refined and crosslinked cellulosic fibers typically have a WRV of no more than 45 percent; more preferably no more than 38 percent; even more preferably no more than 30 percent.
[0040]
Cellulose fibers can be produced by refining and crosslinking cellulosic fibers to about 300 to about 700 ml CSF freeness. According to one preferred embodiment, the starting cellulose fibers for refining are wet wraps. According to another preferred embodiment, the cellulosic fibers are bleached and / or brushed prior to refining. The refined fibers can be crosslinked by any method known in the art, for example, by reacting the fibers with a crosslinking agent.
[0041]
Fibers with improved median release pressure and water retention can be produced by first refining the fibers and then cross-linking the fibers with any of a variety of cross-linking agents. Suitable crosslinking agents include those described below and aliphatic and cycloaliphatic C <sub>Two</sub> ~ C <sub>9</sub> Other polycarboxylic acids, such as, but not limited to, polycarboxylic acids. In this application, "C <sub>Two</sub> ~ C <sub>9</sub> The term "polycarboxylic acid" refers to an organic acid that contains two or more carboxyl groups (COOH), and the chain or ring to which the carboxyl group is attached contains 2-9 carbon atoms. Carboxyl groups are not included in the number of carbon atoms in the chain or ring. For example, 1,2,3-propanetricarboxylic acid has a C containing three carboxyl groups. <sub>Three</sub> It will be considered a polycarboxylic acid. Also, 1,2,3,4-butanetetracarboxylic acid is a C containing four carboxyl groups. <sub>Four</sub> It would be considered a polycarboxylic acid.
[0042]
C suitable for use as a cellulose crosslinking agent in the present invention <sub>Two</sub> ~ C <sub>9</sub> The polycarboxylic acids have at least 3, preferably more, carboxyl groups per molecule (if a carbon-carbon double bond is present in alpha, beta for one or both carboxyl groups), saturated or olefinic. Includes unsaturated aliphatic and cycloaliphatic acids. Furthermore, to be reactive in the esterification of cellulose hydroxyl groups, a given carboxyl group in an aliphatic cycloaliphatic polycarboxylic acid has another carboxyl group at least two carbon atoms and at most three carbon atoms. It is preferred to be separated from Without being bound by any particular theory, in order for the carboxyl group to be reactive, it must be able to form a 5- or 6-membered anhydride ring with a nearby carboxyl group in the polycarboxylic acid molecule. Seems necessary. If two carboxyl groups are separated by a carbon-carbon double bond or both are connected to the same ring, then if they interact in this way, the two carboxyl groups will be in cis configuration with respect to each other. Must.
[0043]
(New crosslinked fiber)
Another embodiment of the present invention provides a low-capillary absorption-release cycle measured with at least one saturated dicarboxylic acid, aromatic dicarboxylic acid, cycloalkyldicarboxylic acid, bifunctional monocarboxylic acid or amine carboxylic acid. It is a cellulose fiber exhibiting a median release pressure and a low water retention value. These crosslinked fibers exhibit improved fluid drainage in the uptake and / or distribution layers and improved permeability in the absorbent core.
[0044]
Generally, these crosslinked cellulosic fibers have a median release pressure of 25 cm or less as measured in a capillary absorption and release cycle. Without being bound by a particular theory, it is believed that this property is the result of intra-fiber crosslinking within the cellulosic fibers.
[0045]
More preferably, the crosslinked cellulosic fibers have a median release pressure of less than or equal to 20 cm as measured in the capillary absorption and release cycle; even more preferably, the fibers of the present invention have a median release pressure of less than or equal to 18 cm as measured in the capillary absorption and release cycle. More preferably, the inventive fibers shown herein have a median release pressure of 15 cm or less as measured in a capillary absorption and release cycle; more preferably, the inventive fibers shown here have a capillary absorption and release It has a median discharge pressure of 14 cm or less as measured in the cycle; more preferably, the fibers of the present invention as shown herein have a median release pressure of 13 cm or less as measured in the capillary absorption and release cycle; more preferably The inventive fibers shown have a median release pressure of 12 cm or less as measured in the capillary absorption and release cycle. .
[0046]
Refined and crosslinked cellulosic fibers typically have a WRV of no more than 50 percent; more preferably no more than 45 percent; even more preferably no more than 38 percent; and even more preferably no more than 30 percent.
[0047]
Crosslinked cellulosic fibers generally have a saturation capacity (Burgeni et al. (Above); and Chatterjee et al. (Above)) measured by the procedure described in the Examples of the present application, which is equivalent to (g / g) saline per gram of sample. At least 10 grams. According to a preferred embodiment, the cross-linked cellulose fibers have a saturation capacity of at least 11, 12, 13, 14, or 15 g / g.
[0048]
The crosslinked cellulose fibers of the present invention are produced by crosslinking cellulose fibers with one or more crosslinkers of the present invention. The median release pressure and water retention of the crosslinked fibers can be reduced by refining the fibers prior to crosslinking. Further, to improve the effect of the crosslinking agent, the crosslinking reaction may be performed in the presence of one or more crosslinking aids of the present invention.
[0049]
(Refining)
Refining can be performed by any method known in the art, including mechanical refining. Pulp refining generally involves, but is not limited to, applying a load on fibers in the form of a water slurry. For example, the fibers can cut them, thereby reducing the average fiber length and refining. Alternatively, the fibers may be refined by rubbing the fibers together and against irregular surfaces under stress or pressure. This increases the external surface area of the fiber due to scoring and attrition of the surface. In addition, the load applied to the fibers during refining causes delamination of the inner walls and surfaces of the fibers. The result is a weakened fiber wall that absorbs more water and swells more than unrefined fibers. Refined fibers that are not dried are also more flexible than similar unrefined fibers that are not dried. Furthermore, drying the refined fibers into a sheet produces a sheet having greater strength and toughness than that produced by dry unrefined fibers.
[0050]
J. d'A.Clark, Pulp Technology and Treatment for Paper, 2nd Ed., Chapter 8, pp. 160-183, Chapter 12, pp. 277-305, Chapter 13, pp. 306-355, Chapter 14, pp. 356-407, Miller Freeman Pub., San Francisco (1985), including but not limited to the beating and fibrillating methods. A preferred method of refining cellulose fibers is fibrillation. Cellulose fibers can be refined using, for example, a disc refiner or a Valley refiner available from Valley Mill Corporation of Lee, Mass .. Refining is usually performed at ambient temperature and pressure. For example, cellulose fibers can be refined by passing an aqueous slurry of the cellulose fibers through a Valley beater at 15 minute intervals until the desired freeness is obtained.
[0051]
Generally, the fibers are wetted (ie, wetted) prior to refining. Nanogram did. According to one preferred embodiment, the cellulose fibers are bleached prior to refining.
[0052]
The cellulosic fibers are extensively refined to a freeness of about 300 to about 700 ml CSF, preferably to a freeness of about 500 to about 700 ml CSF. According to a preferred embodiment, the cellulose fibers are refined to a freeness of about 650 to about 700 CSF. The freeness of cellulose fibers discussed in this application is based on TAPPI method T-227.
[0053]
(Crosslinking)
Refined or unrefined cellulose fibers are strengthened by covalent crosslinks within the fibers. Preferably, the cellulosic fibers are wetted (ie, wetted) prior to reacting with the crosslinking agent and the crosslinking aid. Desirably, in some embodiments, the cellulose fiber is a never-dried cellulose fiber.
[0054]
The fibers are cross-linked by reacting them with a cross-linking agent and, optionally, a cross-linking aid of the present invention (eg, those described below). Preferably, the fibers are crosslinked in a highly twisted state. Normally the reaction process is under substantially unconstrained conditions, i.e. the individual fibers are free to move without interacting with neighboring fibers and are not under any substantial strain or pressure. Done in The fibers can be reacted with the crosslinking agent and optionally the crosslinking aid by curing in the presence of a crosslinking agent and optionally a crosslinking aid.
[0055]
Generally, the fibers are crosslinked by (i) mixing with a crosslinking agent and, optionally, a crosslinking aid, and (ii) curing the fibers under conditions sufficient to cause intrafiber crosslinking. Usually, an effective amount of a crosslinking agent and, optionally, a crosslinking aid to cause the formation of intra-fiber crosslinks is mixed with the cellulosic fibers. Preferably, an amount of crosslinking aid effective to increase the number or percentage of intra-fiber crosslinks formed by the reaction of the fiber with the crosslinking agent is mixed with the cellulose fibers. Generally, about 0.5 to about 40 mole percent, preferably about 1 to about 30 mole percent, of the crosslinker and coagent, calculated based on the number of moles of cellulose anhydrous glucose, are mixed with the fiber. When the crosslinker is a dicarboxylic crosslinker, generally about 5 to about 21 mole percent of the crosslinker, calculated based on moles of cellulose anhydroglucose, is mixed with the fiber. Generally, from about 1.8 to about 9 mole percent of the co-agent, based on the number of moles of cellulose anhydrous glucose, is mixed with the fiber. The mixture comprising the fibers and the crosslinker preferably comprises from about 5 to about 10% by weight of the crosslinker, based on the dry weight of the fibers.
[0056]
After the crosslinker is mixed with the fibers, the fibers are preferably separated and singulated, for example, by fluffing the fibers or by fluffing and disintegrating the fibers. Fiber separation minimizes cross-linking between fibers while maximizing intra-fiber cross-linking. Preferably, the fibers are cross-linked by formation of intra-fiber covalent bonds.
[0057]
Cellulose fibers supplied in wet wrap, dry wrap or other sheet form may be mechanically decomposed and separated into non-sheet forms. In the case of dry wrap, prior to mechanical degradation to plasticize the fiber and minimize fiber damage, e.g., 40% moisture (60% solids based on the total weight of fiber and water) It is advantageous to wet the fibers up to).
[0058]
If the crosslinking agent is applied to the fibers as an aqueous solution, the fibers are dried prior to curing. Preferably, the fibers are dried and cured to form intra-fiber crosslinks to remove any water in the fibers. Drying can be performed by any method known in the art. Drying is usually accomplished by heating the fibers to a temperature of about 50 ° C to about 225 ° C. Preferably, drying is performed at about 105 ° C to about 175 ° C. The fibers are usually dried to constant weight. Regardless of the temperature at which the fiber is dried, the fiber temperature in the drying process until all moisture evaporates from the fiber generally does not exceed 100 ° C. (the boiling point of water). As discussed in T. Lindstrom, Paper Structure and Properties, International Fiber and Technology Series 8, Chapter 5, pp 104-105, Marcel Dekker Inc., New York (1986), drying of cellulose fibers is typically Irreversibly reduces the swelling capacity of the fiber upon rewetting. This phenomenon is commonly called hornification. Without being bound by a particular theory, it is believed that the fibrils in the fiber wall bind together in the drying process, thereby reducing the size of the pores in the fiber wall. This makes the fibers stronger than the fibers before drying. A subsequent curing step promotes the formation of covalent bonds within the fiber, which fixes the firmness and positional relationship of the dried fiber.
[0059]
Curing is generally performed at a temperature sufficient to cause intra-fiber covalent bonding. Curing is generally performed at a temperature of about 105 ° C to about 225 ° C. Preferably, the cellulosic fibers are cured at a temperature of from about 150 ° C to about 190 ° C. More preferably, it is cured at a temperature from about 160 ° C to about 175 ° C. Curing can be performed for 15, 30, 45, or more minutes.
[0060]
According to one preferred embodiment, the fibers are contacted with an aqueous mixture of (i) a crosslinking agent, and optionally a co-agent, with an aqueous mixture comprising cellulose fibers, (ii) removing water from the aqueous mixture, (iii) The fibers are mechanically separated into substantially discrete forms, (iv) the fibers are dried, and (v) the fibers are reacted with a crosslinking agent to cause crosslinking in the fibers. Generally, step (ii) involves removing most of the water from the aqueous mixture. Preferably, sufficient water is removed from the aqueous mixture to obtain a mixture having about 40 to about 80% by weight solids based on 100% total weight of fiber and water. According to a more preferred embodiment, in step (ii), sufficient water is removed from the aqueous mixture to obtain a mixture having about 60% solids by weight based on 100% total weight of fiber and water. The water removal, separation and drying steps leave the fibers highly twisted. The twisted state is generally not permanently, but at least partially, permanently fixed by a crosslinking reaction.
[0061]
For example, the fibers may be crosslinked by the method described in U.S. Pat.No.5,190,563, which is incorporated herein by reference, replacing the crosslinker and coagent in the present invention with the crosslinker in U.S. Pat.No. 5,190,563. Good. In U.S. Pat.No. 5,190,563, cellulose fibers are C <sub>Two</sub> ~ C <sub>9</sub> Contact with a solution containing a polycarboxylic acid crosslinking agent. The fibers are then mechanically separated into substantially individual fiber forms, dried, and reacted with a crosslinking agent while maintaining substantially individual fiber forms to form intra-fiber crosslinks. The individualized cellulosic fibers are contacted with an effective amount of a cross-linking agent to cause the fibers to form intra-fiber cross-links. Preferably, from about 0.5 mole percent to about 6.0 mole percent of the crosslinker, calculated on the number of moles of cellulose anhydroglucose, is contacted with the fiber.
[0062]
If the crosslinker contains an amino or amine group to be reacted, the crosslinker is preferably activated prior to or simultaneously with the crosslinking reaction. As used herein, the term "activate" refers to modifying the cross-linking agent so that the nitrogen atom of the amino group or amine group becomes more reactive, that is, more reactive. The crosslinker may be activated by any method known in the art. For example, a crosslinking agent containing a nitrogen atom of an amine or an amino group may be activated by reacting it with nitrous acid.
[0063]
The fibers may be crosslinked in the presence of a reducing agent (antioxidant) that prevents the fibers from yellowing during the crosslinking reaction. Suitable reducing agents include, but are not limited to, hypophosphites such as sodium hypophosphite; sodium bisulfite; sodium phosphate; and any combination of any of these. The preferred reducing agent is sodium hypophosphite.
[0064]
Bleaching may be performed during or after the crosslinking reaction to improve the appearance of the fiber. For example, the fibers may be bleached by reacting with a bleach. Any bleach known in the art can be used. Suitable bleaches include, but are not limited to, hydrogen peroxide.
[0065]
For example, a bleach may be included in an aqueous solution containing a crosslinking agent applied to the fibers. Preferably, the aqueous solution of the fiber contains a sufficient amount of bleach such that the resulting mixture of the aqueous solution and the fiber contains about 2.5 to about 5% by weight bleach based on the dry weight of the fiber. .
[0066]
(Saturated dicarboxylic acid crosslinking agent)
The term "saturated dicarboxylic acid" refers to a dicarboxylic acid that contains no carbon-carbon double or triple bonds. Saturated dicarboxylic acids can include linear or branched aliphatic chains (ie, they are acyclic). Preferred saturated dicarboxylic acids are C <sub>Two</sub> ~ C <sub>8</sub> Including, but not limited to, saturated dicarboxylic acids. "C <sub>Two</sub> ~ C <sub>8</sub> The term "saturated dicarboxylic acids" refers to dicarboxylic acids having a total number of carbon atoms (including carboxyl group carbons) ranging from 2 to 8. C <sub>Two</sub> ~ C <sub>8</sub> Examples of saturated dicarboxylic acids include, but are not limited to, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, and suberic acid. Especially C <sub>Two</sub> ~ C <sub>6</sub> Saturated dicarboxylic acid and C <sub>Two</sub> ~ C <sub>Four</sub> Saturated dicarboxylic acids are preferred.
[0067]
According to one preferred embodiment, C <sub>Three</sub> ~ C <sub>8</sub> C such as saturated dicarboxylic acid <sub>Three</sub> The above saturated dicarboxylic acid is applied to a cellulose fiber together with a crosslinking aid such as oxalic acid.
[0068]
Another type of saturated dicarboxylic acid is a saturated hydroxy dicarboxylic acid. The term "saturated hydroxydicarboxylic acid" refers to a saturated dicarboxylic acid containing at least one hydroxyl group as a substituent. Suitable saturated hydroxy dicarboxylic acids include C <sub>Two</sub> ~ C <sub>8</sub> Include, but are not limited to, saturated hydroxydicarboxylic acids (ie, those containing 2-8 carbon atoms). Especially C <sub>Two</sub> ~ C <sub>8</sub> Saturated polyhydroxydicarboxylic acids are preferred. C <sub>Two</sub> ~ C <sub>8</sub> Examples of saturated polyhydroxydicarboxylic acids include, but are not limited to, tartaric acid, malic acid, sugar acids and mucus acids.
[0069]
(Aromatic dicarboxylic acid crosslinking agent)
The term "aromatic dicarboxylic acid" refers to an aromatic compound having the formula HOOC-R-COOH, where R is a substituted or unsubstituted phenyl group. As used herein, the term `` substituted '' refers to at least one of the following substituents (including but not limited to), hydroxyl, C ₁ ~ C _Four Alkoxy group, C ₁ ~ C _Four Includes alkyl, amino, halogen, and nitro.
[0070]
Preferred aromatic dicarboxylic acids have the formula:
Embedded image

(Where R ¹ , R ^Two , R ^Three And R ^Four Is independently hydrogen, hydroxyl, C ₁ ~ C _Four Alkoxy, C ₁ ~ C _Four Alkyl, amino, halogen, or nitro). The preferred aromatic dicarboxylic acid is phthalic acid.
[0071]
(Cycloalkyl dicarboxylic acid crosslinking agent)
The term “cycloalkyldicarboxylic acid” refers to a cycloalkyldicarboxylic acid that does not contain a carbon-carbon double bond in the α or β position relative to the carboxyl group. According to one embodiment, the cycloalkyl dicarboxylic acid has the formula:
Embedded image

(Where R ⁶ , R ⁷ , R ^Ten And R ¹¹ Is independently hydrogen, hydroxyl, halogen, C ₁ ~ C _Four Alkoxy, C ₁ ~ C _Four Alkyl, amino or nitro;
R ⁸ And R ⁹ Is independently hydrogen, halogen, C ₁ ~ C _Four Alkoxy, or C ₁ ~ C _Four Alkyl). The preferred cycloalkyldicarboxylic acid is 1,2,5,6-tetrahydrophthalic acid.
[0072]
(Bifunctional monocarboxylic acid crosslinking agent)
A “difunctional monocarboxylic acid” has (a) only one carboxyl group and (b) a functional group (which is not a carboxyl group) and can react with a carboxyl, carboxylic acid, amino, or hydroxyl group of a polymer Refers to organic acids. Preferably, the bifunctional monocarboxylic acid contains only two functional groups (ie, a carboxyl group and another functional group).
[0073]
Suitable bifunctional monocarboxylic acids include, but are not limited to, amino acids, haloacetates, hydroxymonocarboxylic acids, acid derivatives of hydroxymonocarboxylic acids (such as acid esters of hydroxymonocarboxylic acids).
[0074]
A preferred haloacetate is sodium chloroacetate. Without being bound by any particular theory, when an aqueous mixture of sodium chloroacetate and cellulose fibers is dried and cured, the reaction between the carbon of the sodium chloroacetate molecule containing chlorine and the cellulose hydroxyl groups forms an ether. Is believed. This etherification reaction releases hydrochloric acid molecules, which are immediately neutralized by the newly formed sodium salt of the cellulose-based acid. At higher temperatures, the acid is available for esterification of adjacent hydroxyl groups in the fiber, with the accompanying release of water. After ether and ester formation, sodium chloride remains as a by-product.
[0075]
Suitable hydroxycarboxylic acids and their acid derivatives include, but are not limited to, glycolic acid, methanesulfonic acid ester of glycolic acid, and paratoluenesulfonic acid ester of glycolic acid.
[0076]
(Amine carboxylic acid crosslinking agent)
Suitable amine carboxylic acid crosslinkers include, but are not limited to, primary, secondary and tertiary amines and aromatic amines. Preferred primary amines include, but are not limited to, amino acids. Particularly preferred are amino acids of the formula:
Embedded image

(Where R ¹² Is binding, C ₁ ~ C ₁₂ Alkyl or carboxyl group, hydroxyl group, C ₁ ~ C _Four Alkoxy, C ₁ ~ C _Four C substituted with alkyl, amino or nitro ₁ ~ C ₁₂ Which is an alkyl group).
[0077]
Preferred amino acids have the formula
Embedded image

(Where R ^Five Is a linear or branched C ₁ ~ C ₈ But not limited to). According to a preferred embodiment, R ^Five Is C _Two ~ C _Four Alkyl. Examples of other suitable amino acids include, but are not limited to, aspartic acid and glutamic acid.
[0078]
Other suitable amine carboxylic acid crosslinkers include, but are not limited to, ethylenedinitriloacetic acid (EDTA).
[0079]
(Crosslinking aid)
The crosslinking aid of the present invention increases the effect of the crosslinking agent. A preferred crosslinking aid is oxalic acid. Without being bound by a particular theory, it is believed that oxalic acid (pKa = 1.23) serves as an acidic catalyst for the esterification of the crosslinker. Alternatively, oxalic acid may form a mixed anhydride with the crosslinker, which in turn may promote esterification of the cellulose fibers.
[0080]
(Reversibility of crosslinking)
Fibers crosslinked with the short crosslinkers of the present invention (i.e., those containing 4 carbon atoms (e.g., 3 or fewer carbon atoms), such as oxalic acid and sodium chloroacetate) are decrosslinkable; Moreover, it can be crosslinked later. Crosslinking of such fibers is generally substantially reversible, ie, at least about 50% by weight of the crosslinked fibers can be decrosslinked. According to one embodiment, at least about 60, 70, 80, 90, or 95% by weight of the crosslinked fibers can be decrosslinked.
[0081]
Crosslinked fibers can be decrosslinked by immersing them in water for a time sufficient for decrosslinking. Typically, the crosslinked fibers are soaked for about 0.5 to about 4 hours. According to a preferred embodiment, the fibers are soaked for about 2 hours. Crosslinked fibers can be decrosslinked by exposing them to a capillary absorption and release cycle as described in the Examples herein (Burgeni et al. (Supra) and Chatterjee et al. (Supra)).
[0082]
The fibers can be recrosslinked by drying or dry curing. This phenomenon was not observed with the covalently crosslinked fibers disclosed in US Pat. Nos. 5,137,537, 5,183,707 and 5,190,563.
[0083]
While not being bound by any particular theory, it is believed that as the crosslinked fibers absorb and swell, the crosslinked portion is pulled as the cellulose polymer chains split off to accommodate the absorbed water. I have. When the length of the cross-linking molecules is very short, such as fibers treated with oxalic acid or sodium chloroacetate (two carbon atoms separate hydroxyl groups on adjacent cellulose polymer chains), they swell. The strain in the fiber is sufficient to promote hydrolysis and fission of one of the two covalent bonds cross-linking the fiber. In contrast, citric acid cross-linked fibers such as those disclosed in U.S. Patent Nos. 5,137,537; Much longer (four or five carbon atoms separate the hydroxyl groups on adjacent cellulose polymer chains). Thus, the tension on the longer cross-linking molecules as the fibers absorb and swell is not sufficient to promote the cleavage of one of the cross-linking covalent bonds.
[0084]
Because the fibers of the present invention can be decrosslinked, they can be dried, transported, or stored in sheets instead of in bulk or packed form. This reduces shipping and storage costs. The fibers can be re-crosslinked at the destination or at any desired time, for example, by separate curing. Once the fibers have been recrosslinked, they can be integrated, for example, with the absorbent structure.
[0085]
The terms `` reversibly crosslinked fiber '' and `` reversibly crosslinked cellulosic fiber '' are used herein to refer to about 50, 60, 70, 80, 90, or 95% by weight of the crosslinked fiber in water. Approximately 50, 60, 70, 80, 90, or 95% of the decrosslinked fibers that have been decrosslinked in less than or equal to immersion for less than or equal to Refers to cellulose fibers.
[0086]
The reversibly crosslinked fibers of the present invention are particularly suitable for use in an absorbent core comprising superabsorbent polymer (SAP) particles. The crosslinked fibers separate the SAP particles and provide a fluid flow path around the SAP particles from the wet area to the dry area of the absorbent core. In addition, reversibly crosslinked fibers promote the absorption of large amounts of urine (or other fluids) in a short time (eg, eruption). Once urine or other fluid enters the absorbent core, the crosslinked fibers begin to decrosslink. According to one embodiment, most of the wet fibers are decrosslinked after 0.5-4.0 hours of exposure to urine and other fluids. The decrosslinked fibers retain and retain more urine and other fluids than the permanently crosslinked fibers. As a result, the absorbent core has an improved initial squirt volume as compared to an absorbent core containing conventional fluff fibers and is improved as compared to an absorbent core containing permanently crosslinked fibers. Has rewet performance.
[0087]
(Absorber structure)
The cellulosic fibers of the present invention can be incorporated into any disposable or non-disposable absorbent structure generally positioned or retained in close proximity to the body of a wearer for the purpose of absorbing and retaining body exudates. Such absorbent structures are widely used in disposable or non-disposable absorbent articles. Examples of disposable absorbent articles include, but are not limited to, infant diapers, adult incontinence products, discipline pants, sanitary napkins, and other feminine hygiene products. Examples of the absorbent structure that can incorporate the cellulose fiber of the present invention include International Publication WO98 / 47456, WO99 / 63906, WO99 / 63922, WO99 / 63923, WO99 / 63925, WO00 / 20095, WO00 / 38607, WO00 / 41882. , WO00 / 71790, and WO00 / 74620, and U.S. Patent No. 5,695,486, all of which are incorporated by reference herein, without limitation.
[0088]
(Intake distribution layer)
The cellulosic fibers of the present invention can be incorporated into an uptake, distribution or uptake-distribution layer. Such layers are commonly used in absorbent structures included in disposable absorbent articles. The uptake and / or distribution layer can be manufactured by any method known in the art and incorporated into an absorber structure. According to one embodiment, the absorber structure includes a top layer (which includes the uptake and / or distribution layers of the present invention) and a bottom storage layer (also known as an absorber core). The uptake and distribution layers may be a single layer or two separate layers (ie, the top acquisition layer and the distribution layer below it). The lower distribution layer quickly drains fluid from the intake layer and distributes the fluid to the storage layer.
[0089]
The uptake layer of the present invention usually comprises from about 90 to about 100% by weight of the cellulose fibers of the present invention, with the total weight of the uptake layer being 100%. The density of the intake layer is from about 0.04 to about 0.07 g / cm ^Three Up to a wide range.
[0090]
(Absorber core)
The cellulose fibers of the present invention can be incorporated into an absorbent core (also known as a storage layer). The absorber core may include any material known in the art that absorbs liquids. Suitable materials include fiber defibrated, loose, fuzzy, and / or batting or webs made of hydrophilic cellulose fibers or fibers of the present invention; superabsorbent polymer (SAP) particles, granules, Flakes or fibers (collectively particles); and any combination thereof. In general, SAP particles are able to absorb more weight of liquid than their own weight and significantly increase the absorption capacity of the absorber core without substantially increasing the bulk of the layer.
[0091]
The term superabsorbent polymer particles or SAP particles is intended to also include particulate superabsorbent polymers of any shape, including irregularly shaped granules, spherical particles (beads), powders, flakes, short fibers and other elongated particles . SAP usually refers to a water-soluble polymer that has been rendered substantially water-insoluble by crosslinking, but is generally capable of absorbing at least 10 times, preferably at least 15 times, its weight of saline. The SAP particles can be of any size or shape. Numerous examples of superabsorbent materials and methods of making them are described, for example, in U.S. Patent Nos. 4,102,340; 4,467,012; 4,950,264; 5,147,343; 5,328,935; 5,338,766; 5,372,766; 5,849,816; No. 5,859,077; and Re.32,649. Examples of suitable SAP particles include starch-graft copolymer copolymers such as hydrolyzed starch-acrylate graft copolymers; cross-linked carboxymethylcellulose and its derivatives; saponified acrylate-vinyl copolymers, neutralized Modified hydrophilic polyacrylates such as, but not limited to, cross-linked polyacrylic acid and cross-linked polyacrylate salts.
[0092]
Preferably, the SAP particles form a hydrogel by absorbing the fluid. More preferably, the SAP particles have high gel strength as measured by high gel volume or the shear modulus of the hydrogel. Such SAP particles usually contain relatively small amounts of polymeric material that can be extracted by contact with synthetic urine (so-called extractables). An example of such SAP particles is a starch-graft polyacrylate hydrogel available as IM1000® from Hoechst-Celanese, Portsmouth, VA. Other examples of hydrogels containing SAP particles include SANWET (TM) (available from Sanyo Chemical Industries, Japan); SUMIKA GEL (TM) (available from Sumitomo Chemical Co., Japan); Favor (TM) (Available from Stockhausen, Garyville, Louisiana); and those sold as ASAP ™ (available from BASF, Aberdeen, Mass.).
[0093]
According to one preferred embodiment, the absorbent core comprises (a) SAP particles and (b) fluff fibers, matrix fibers, fibers of the invention or any combination thereof. The fibers provide structural integrity to the absorbent core and provide a flow path for fluid to pass through the core.
[0094]
According to another embodiment, the absorbent core comprises from about 30% to about 70% by weight of the SAP particles and from about 70% to about 30% by weight of the present invention, based on 100% by total weight of the absorbent core. Of cellulose fibers. Generally, the volume density of the absorber core is about 0.15 to 0.25 g / cm ^Three Fluctuate up to
[0095]
According to yet another embodiment, the absorbent core comprises the SAP particles of the invention and reversibly crosslinked fibers. According to one preferred embodiment, the reversibly crosslinked fibers are crosslinked with oxalic acid, sodium chloroacetate or a mixture thereof. Generally, the absorbent core is from about 30% to about 70% by weight of the SAP particles and from about 70% to about 30% by weight of the reversibly crosslinked inventive particles of the present invention, with the total weight of the absorbent core being 100%. Including fibers. According to another preferred embodiment, the uptake and / or distribution layers and the absorber core comprise oxalic acid crosslinked fibers.
[0096]
The absorbent structure of the present invention can be incorporated into disposable and non-disposable absorbent articles such as diapers, adult incontinence pads and feminine hygiene products. The absorbent article comprises a liquid-permeable topsheet (the function of which is to pass fluid to the intake and / or distribution layer) on the uptake and / or distribution layer and a liquid-impermeable backsheet (the function of which is To retain fluid and prevent it from passing through the absorbent article and reaching the wearer's clothing of the absorbent article).
[0097]
According to one embodiment, the absorbent structure of the present invention is incorporated into a disposable infant diaper. This generally includes a front waistband region, a rear waistband region and a crotch region therebetween. Diaper structures generally include a liquid permeable topsheet, a liquid impervious backsheet, an absorbent structure, an elastic member and a securing tab. Representative designs for disposable diapers can be found, for example, in U.S. Patent Nos. 4,935,022 and 5,149,335.
[0098]
According to another embodiment, the absorbent structure of the present invention is incorporated into a feminine hygiene pad as disclosed in US Pat. No. 5,961,505.
[0099]
The following examples illustrate the invention but do not limit the invention. Unless otherwise indicated, all parts and percentages are given by weight. All crosslinkers, coagents, and other chemical reagents used in the examples are all available from Aldrich Chemical Company, Milwaukee, Wisconsin.
【Example】
[0100]
Capillary and discharge pressure and saturation capacity measurements
Capillary absorption and release pressures were measured by the procedure described in "Capillary Sorption Equilibria in Fiber Masses", AA Burgeni and C. Kapur, Textile Research Journal, 37: 356-366 (1967). The details of this operation are described below.
[0101]
0.75 g of individualized fiber sample is formed on a disc approximately 55-60 mm in diameter. The sample was placed in a 150 ml coarse frit Pyrex® glass funnel (Corning No. 36060, available from VWR, Suwanee, Georgia). Place enough weight on the sample to apply a pressure of 0.22 psi of a diameter comparable to the diameter of the sample. The bottom of the funnel was attached to an adapter with decreasing diameter, Tygon® tubing No.R-3603 (approximately 2 feet long) at one end of the adapter and 0.01 g at the other end Is mounted to connect to a reservoir on an electronic balance that can be measured. The tube is attached to the bottom side of the reservoir. The reservoir contains a 0.9% salt solution. The height of the salt solution in the reservoir is approximately one inch above the tube mounting location. With the funnel below the frit, fill the tubing with saline so that the frit is wet with the salt solution but does not come out above the frit. The column of salt solution from the reservoir to the frit is continuous so that the column does not contain air.
[0102]
The absorption cycle is as follows. Starting at a height of 20, 30, or 80 cm above the level of the saline solution in the reservoir, for example, the salt solution is absorbed into the sample and allowed to equilibrate to a steady state. Steady state is measured on an electronic balance below the well for 1 minute assuming no weight change of more than 0.04 g of saline. Once steady state is achieved, the sample is lowered to 5 cm close to the level of the saline solution in the well and held there until equilibrium is achieved. Lower the sample by another 5 cm and repeat this procedure. If the sample is in equilibrium at the same height as the saline surface of the reservoir, expose the sample to a release cycle by reversing the procedure (ie, moving the sample upward in 5 cm increments).
[0103]
The weight of saline in the sample when it is at the same level as the saline in the reservoir is the saturation capacity of the sample. Sample height (reported in cm) above the saline surface in the reservoir (reported in cm) at the 50% saturation volume in the downward (absorption) cycle and the upward (release median) curve (median release pressure). Is measured by extrapolation. Saturation capacity values are reported in the table as grams of saline per gram of sample.
[0104]
Examples 1 to 8
Examples 1 to 8 in Table 1 were produced as follows.
[0105]
Unrefined cellulose fiber (available as Foley Fluff (TM) from Buckeye Technologies Inc., Memphis, TN) having a freeness of 740 ml CSF is slurried in water and valley beater at ambient temperature and pressure. To obtain a suitable freeness. The fibers were centrifuged, separated by hand and air dried to 60% solids. The fibers were crosslinked with an appropriate concentration of citric acid (on a dry fiber basis) by spraying the fibers with an aqueous solution of citric acid of sufficient dilution to provide a sheet of 40% solids. The fibers were then air dried to 60% solids, fluffy, dried to constant weight, and heated at the temperature shown in Table 1 for an additional 30 minutes.
[0106]
The water retention value, saturation capacity, capillary absorption pressure and capillary discharge pressure of the cured cellulose fibers were measured. The water retention value of the cured cellulose fiber was measured by the operation described in TAPPI Useful Methods, UM256. Capillary absorption and discharge pressures were measured by the procedure described above.
[0107]
Table 1 shows the results.
[0108]
Comparative Example 9
Unrefined cellulose fibers having a freeness of 740 ml CSF (available as Foley Fluff ™ from Buckeye Technologies Inc. of Memphis, TN) were dried at 100 ° C. The water retention value, saturation capacity, capillary absorption pressure and capillary discharge pressure of the cured cellulose fiber were measured in the same manner as in Example 1.
[0109]
The results are shown in Table 1 below.
[0110]
Comparative Example 10
Unrefined cellulose fibers having a freeness of 740 ml CSF (available as Foley Fluff ™ from Buckeye Technologies Inc.) were sprayed with sufficient water to achieve 40% solids. The fiber was dried to 60% solids, brushed mechanically and dried at 150 ° C. to constant weight. The fiber was then heated at the same temperature for another 30 minutes. The water retention value, saturation capacity, capillary absorption pressure and capillary discharge pressure of the cured cellulose fiber were measured in the same manner as in Example 1.
[0111]
Table 1 shows the results.
[0112]
Comparative Example 11
Unrefined cellulose fibers with a freeness of 740 ml CSF (available as Foley Fluff ™ from Buckeye Technologies Inc.) are slurried and refined with a valley beater to a freeness of approximately 500 ml CSF did. The fibers were centrifuged, separated by hand, air-dried to 60% solids, and dried at 150 ° C. to constant weight. The fiber was then heated at 150 ° C. for another 30 minutes. The water retention value, saturation capacity, capillary absorption pressure and capillary discharge pressure of the cured cellulose fiber were measured in the same manner as in Example 1.
[0113]
Table 1 shows the results.
[0114]
Comparative Example 12
Unrefined cellulose fibers with a freeness of 740 ml CSF (available as Foley Fluff ™ from Buckeye Technologies Inc.) are slurried and refined with a valley beater to a freeness of approximately 500 ml CSF did. The fibers were centrifuged, separated by hand and air dried to 60% solids. When treated with citric acid, cellulose fibers were sprayed with aqueous sulfuric acid at pH 3 until the solids content was 40%, in order to bring the pH of the mixture of fibers and water to the same pH as observed in Example 1. The fiber was dried to 60% solids, brushed mechanically and dried at 150 ° C. to constant weight. The fiber was then heated at 150 ° C. for another 30 minutes. The water retention value, saturation capacity, capillary absorption pressure and capillary discharge pressure of the cured cellulose fiber were measured in the same manner as in Example 1.
[0115]
Table 1 shows the results.
[0116]
Comparative Example 13
Unrefined cellulose fibers (available from Buckeye Technologies Inc. as Foley Fluff®) having a freeness of 740 ml CSF are sprayed with a sufficiently diluted aqueous citric acid solution to give a sheet solids content of 40%. The fibers were crosslinked with 5% citric acid (dry fiber basis). The fiber was dried to 60% solids, brushed mechanically and dried at 150 ° C. to constant weight. The sheet was then heated at 150 ° C. for another 30 minutes. The water retention value, saturation capacity, capillary absorption pressure and capillary discharge pressure of the cured cellulose fiber were measured in the same manner as in Example 1.
[0117]
Table 1 shows the results.
[0118]
Comparative Example 14
The procedure of Comparative Example 13 was repeated except that the fibers were crosslinked with 10% citric acid instead of 5% citric acid. Table 1 shows the results.
[0119]
[Table 1]

[0120]
The milled and crosslinked fibers, as shown in the results in Table 1, exhibited lower WRV and release pressures than unmilled but otherwise similar crosslinked fibers.
[0121]
Example 15
An aqueous slurry was prepared containing 2.75-3.25% by weight of the non-dried Foley Fluff ™ available from Buckeye Technologies Inc. The aqueous slurry was pumped through a Bauer Model No. 444, 24 "(about 61 cm) pump at ambient temperature and pressure with a Bauer Refiner plate No. A24313.
[0122]
The refiner was operated at 178 amps (178 amps) flow and a slurry flow rate of 255 gallons (969 liters) per minute. These conditions resulted in a load of 30-60 hp hours per ton of dry fiber (about 0.907 t) of fiber. The fiber produced had a freeness of 680 ml CSF.
[0123]
Desalination
The refined pulp slurry was pumped into a double bottom tank with a 2.75-3.25% consistency. During the stirring of the pulp slurry, sulfuric acid was added until a nominal pH of 2.0 was reached. After stirring for at least 10 minutes, the aqueous slurry was dewatered through a double bottom screen for a minimum of 3 hours. The slurry was then diluted with soft water sodium to a 2.0% consistency and the pH was adjusted to 4.5-5.0.
[0124]
Sheet formation
Pulp sheeting was performed using a paper machine available from Sandy Hill Corporation of Hudson Falls, NY. The declue (sheet width) was a maximum of 36 inches. A 2% pulp slurry was fed at a controlled rate into the white water silo through a stuff box and a basis weight valve. The silo temperature was increased to 130-150 ° F by direct steaming, and the slurry in the silo was diluted with white water to a consistency of 1.0-1.25%.
[0125]
The slurry was then fed to a paper machine head box and transferred onto a moving wire of a Fourdrinier section of the paper machine. Natural and vacuum assisted drainage was applied until the formed sheet exited the couch press at about 32% consistency. After sheet formation and prior to couch pressing, the wet sheet was trimmed with two jets of water to 24 inch decru. The fibrous sheet having a consistency of about 32% was then passed through two wet presses, which resulted in further moisture removal and densification of the sheet. After exiting the second wet press, the fiber sheet entered the first dryer section with approximately 48% consistency. In the first dryer section, the pulp sheet passed over 13 rotating steam cans at approximately 300-325 ° F. The pulp sheet then passed through eight rotating steam cans in the second dryer section and exited the dryer with a moisture content of 4-8%. The sheet was rolled into a roll with a decru of about 23 inches. The basis weight of the rolled sheet was approximately 0.126 pounds per square foot and the density was approximately 0.60 grams per cubic centimeter.
[0126]
Slitting
The pulp roll was wound onto a new core and slitted into smaller rolls (10 inches wide).
[0127]
Chemical treatment
The 10 inch wide pulp sheet was unwound from the roll and slowly passed through a puddle press. The paddle press nip was filled with aqueous citric acid and sodium hypophosphite. Sodium hypophosphite suppresses pulp darkening at high temperatures. The weight concentrations of citric acid and sodium hypophosphite in the flooded nip were approximately 14% and 7%, respectively. Through the paddle press, the sheet absorbed a sufficient amount of the aqueous solution to reach a water content of about 40%.
[0128]
Sheet disassembly and fluffing
Following the paddle press, the sheet was cut into smaller pieces through a shredder, pre-breaker and picker. The disintegrated pulp was then blown into the inlet of a Sunds Defibrator model 3784 RO Fluffer (available from Sundsvall AB, Sweden) with a gap value of 5.5 mm set. The luff was lumped to a mass of separated fibers, and fluff pulp was swept out of the RO Fluffer using a high velocity stream of hot air at approximately 380 ° F.
[0129]
Drying and curing
The hot air flow carrying the fluffed fibers from the RO Fluffer was further passed through a flash dryer using a fan to evaporate all or almost all of the moisture in the fibers. The dried pulp dropped onto the mechanical inlet conveyor to form a low bulky bulk bed on the conveyor. The fiber was then conveyed to a Proctor & Schwartz K16476 tunnel dryer available from Proctor & Schwartz, Inc. of Horsham, PA. The fluff fiber bed was heated and then cooled as it passed through the three rooms in the dryer by a series of thermal cycling airflows. In the first room, the bed temperature reached 325-330 ° F. In the second room, the bed temperature was increased to 385-390 ° F. In the third room, the bed temperature decreased to 355-360 ° F. The total time in the tunnel dryer was approximately 11.5 minutes.
[0130]
packing
The crosslinked fiber falls off the conveyor at the exit side of the tunnel dryer and travels to a baler model No. 3445 (available from the American Baler Company, Bellevue, Ohio), where it weighs approximately 70-80 pounds. Compressed into something.
[0131]
Example 16
The samples in Table 2 were manufactured as follows.
[0132]
Unrefined cellulose fibers having a freeness of 740 ml CSF, available as Foley Fluff (TM) from Buckeye Technologies Inc. (Memphis, TN), were made into aqueous slurries and Bauer Model No. , 24 "(approx. 61 cm) pump and refined to a suitable freeness. In some cases, the fibers were washed with dilute sulfuric acid (pickling) to remove inorganic components. And dried.
[0133]
One sheet was submerged in a tray containing a solution of the crosslinker and oxalic acid. The piece of paper was then turned upside down and submerged in a second solution of the crosslinker and oxalic acid. These solutions together contained 10% crosslinker (dry fiber basis) and 5% oxalic acid (dry fiber basis). The solution had sufficient dilutability to make the paper pieces 40% solids. The piece of paper was placed in a sealed polyethylene bag for one hour. The fiber was air-dried to 60% solids, fluffed, dried to constant weight and heated at 175 ° C. for an additional 30 minutes.
[0134]
The water retention value, saturation capacity, capillary absorption pressure and capillary discharge pressure of the cured cellulose fibers were measured. The water retention value of the cured cellulose fiber was measured by the operation described in TAPPI Useful Methods, UM256. Capillary absorption and release pressures were measured by the procedure described above.
[0135]
Table 2 shows the results.
[0136]
[Table 2]

[0137]
Example 17
The samples in Table 3 were manufactured as follows.
[0138]
Unrefined cellulose fibers having a freeness of 740 ml CSF, available as Foley Fluff (TM) from Buckeye Technologies Inc. (Memphis, TN), were made into aqueous slurries and Bauer Model No. , 24 "(approximately 61 cm) pump and refined until adequate freeness was achieved. The refined fibers were sheeted and dried. If the fibers were wet wrap, they were then centrifuged.
[0139]
One sheet was submerged in a tray containing a solution of the crosslinking agent, sodium hypophosphite (and optionally oxalic acid). The piece of paper was then turned upside down and submerged in a second solution of the crosslinking agent, sodium hypophosphite (and optionally oxalic acid). These solutions together contained 10% crosslinker (dry fiber basis), 5% sodium hypophosphite (dry fiber basis) and 1% oxalic acid (dry fiber basis). The solution had sufficient dilutability to make the paper pieces 40% solids. The piece of paper was placed in a sealed polyethylene bag for one hour. The fiber was air-dried to 60% solids, fluffed, dried to constant weight and heated at 175 ° C. for an additional 30 minutes.
[0140]
The water retention value, saturation capacity, capillary absorption pressure and capillary discharge pressure of the cured cellulose fibers were measured. The water retention value of the cured cellulose fiber was measured by the operation described in TAPPI Useful Methods, UM256. Capillary absorption and release pressures were measured by the procedure described above.
[0141]
Table 3 shows the results.
[0142]
[Table 3a]

[Table 3b]

[Table 3c]

[0143]
Example 18
The samples described in Table 4 below were produced as follows.
[0144]
Stock solutions of the crosslinker and coagent identified in Table 4 were prepared by dissolving the amounts of crosslinker and coagent shown in the table in 22.5 g of distilled water.
[0145]
The samples were treated with the appropriate solution as follows. 15 g (dry basis) of a sheeted unrefined cellulose fiber sample with a freeness of 740 ml CSF available as Foley Fluff (TM) from Buckeye Technologies Inc. (Memphis, TN) containing crosslinker and coagent Treated with the appropriate stock solution. This reduced the fiber content of the mixture to 40% solids. The mixture was placed in a closed container at ambient temperature for 60 minutes and then air-dried to 60% solids. The fibers were separated mechanically, singulated, fluffed in a laboratory flicker and dried in a forced air oven at 175 ° C. to constant weight. The fibers were cured at the same temperature for 30 minutes.
[0146]
Controls were made as follows. A sheeted unrefined cellulose fiber sample having a freeness of 740 ml CSF, available as Foley Fluff ™ from Buckeye Technologies Inc. (Memphis, TN), was diluted with water to 40% solids. The pH of the mixture was adjusted to pH 3 with sulfuric acid. The stock solution applied to the fibers in the above procedure was typically 3. The mixture was then placed in a closed vessel at ambient temperature for 60 minutes and then air dried to 60% solids. The fibers were separated mechanically, singulated, fluffed in a laboratory flicker and dried in a forced air oven at 175 ° C. to constant weight. The fibers were cured at the same temperature for 30 minutes.
[0147]
Fiber was obtained from the uptake distribution layer of Pampers® disposable diapers (available from Proctor and Gamble, Cincinnati, Ohio) and used as a second control.
[0148]
The fiber water retention, saturation capacity, capillary absorption pressure and capillary discharge pressure were measured. The water retention value of the cellulose fiber was measured by the operation described in TAPPI Useful Methods, UM256. Capillary absorption and release pressures were measured by the procedure described above.
[0149]
Table 4 shows the results.
[0150]
[Table 4a]

[Table 4b]

[Table 4c]

[0151]
Example 19
A crosslinked fiber sample was prepared by the method described in Example 18 using 1.5 g of sodium chloroacetate. A second sample was prepared using 1.5 g of oxalic acid instead of sodium chloroacetate.
[0152]
For comparative purposes, a sample of crosslinked fiber was prepared by the procedure in Example 18 using a stock solution containing 10% by weight citric acid.
[0153]
The sample was subjected to a first capillary absorption and release cycle according to the above procedure. The sample was then subjected to a second capillary absorption and release cycle with the same procedure. The absorption and release pressures observed for both cycles are shown in Table 5 below.
[0154]
This test was repeated with the decrosslinked Foley Fluff ™ fiber.
[0155]
[Table 5]

[0156]
Example 20
The sample described in Example 19 was prepared and subjected to two cycles of capillary absorption and release. The sample was dried overnight in a 105 ° C. forced air oven. Alternatively, samples were dried at 105 ° C. to constant weight and heated (cured) at 175 ° C. for another 30 minutes. The saturation capacity of the sample and the absorption and release pressure were measured.
[0157]
Table 6 shows the results.
[0158]
[Table 6]

[0159]
Example 21
Chemical treatment
An aqueous solution of oxalic acid and sodium hypophosphite was prepared by mixing 151 pounds of a 10% by weight oxalic acid solution, 15 pounds of a 50% by weight sodium hypophosphite solution and 1 pound of water.
[0160]
A 10 inch wide pulp sheet available from Buckeye Technologies Inc. as Foley Fluff ™ was unwound from the roll and passed slowly through a paddle press. The paddle press nip was filled with an aqueous solution of oxalic acid and sodium hypophosphite. Sodium hypophosphite suppresses pulp darkening at high temperatures. Through the paddle press, the sheet absorbed a sufficient amount of the aqueous solution to reach a water content of about 47% (100% of the total weight of the dry fiber). The treated sheet contained 10% by weight of oxalic acid and 5% of sodium hypophosphite (100% of the total weight of the dry fiber).
[0161]
Sheet disassembly and fluffing
Following the paddle press, the sheet was cut into smaller pieces through a shredder, pre-breaker and picker. The disintegrated pulp was then blown into the inlet of a Sunds Defibrator model 3784 RO Fluffer (available from Sundsvall AB, Sweden) with a gap value of 5.5 mm set. The luff was lumped to a mass of separated fibers, and fluff pulp was swept out of the RO Fluffer using a high velocity stream of hot air at approximately 380 ° F.
[0162]
Drying and curing
The hot air flow carrying the fluffed fibers from the RO Fluffer was further passed through a flash dryer using a fan to evaporate any moisture in the fibers. The dried pulp dropped onto the mechanical inlet conveyor to form a low density bulky "bed" on the conveyor. The fiber was then conveyed to a Proctor & Schwartz K16476 tunnel dryer available from Proctor & Schwartz, Inc. of Horsham, PA. The fluff fiber bed was heated and then cooled as it passed through the three rooms in the dryer by a series of thermal cycling airflows. In the first room, the bed temperature reached 330-340 ° F. In the second room, the bed temperature was increased to 375-385 ° F. In the third room, the bed temperature decreased to 355-360 ° F. After three heating zones, the fiber bed was finally passed through an insulated chamber (1 chamber) without further heating. The total time in the tunnel dryer was approximately 11.5 minutes.
[0163]
packing
The crosslinked fibers fall off the conveyor at the exit side of the tunnel dryer and are transferred to a baler model no. Compressed into packing.
[0164]
All documents referred to herein are incorporated herein. Inconsistent parts between the present specification and the literature shall be governed by the language of the disclosure of the present application.

Claims (138)

Cellulose fibers having a median release pressure of 15 cm or less as measured in a capillary absorption and release cycle. 2. The cellulose fiber according to claim 1, having a median release pressure of 14 cm or less. 2. The cellulose fiber according to claim 1, having a median release pressure of 13 cm or less. 2. The cellulose fiber according to claim 1, having a median release pressure of 12 cm or less. The cellulosic fiber according to any one of claims 1 to 4, having a water retention value of 45 percent or less. 5. Cellulose fiber according to any one of the preceding claims, having a water retention value of 38% or less. The cellulose fiber according to any one of claims 1 to 4, having a water retention value of 30% or less. The cellulose fiber according to any one of claims 1 to 7, wherein the cellulose fiber is cross-linked. An uptake distribution layer comprising the cellulose fibers according to any one of claims 1 to 8. An uptake layer comprising the cellulose fibers of any one of claims 1 to 8. A distribution layer comprising the cellulose fibers according to any one of claims 1 to 8. (a) a top layer comprising cellulose fibers having a median release pressure of 15 cm or less as measured in a capillary absorption and release cycle; and
(b) An absorber structure including a lowermost layer containing SAP particles, wherein the second layer is capable of flowing fluid with the first layer. 13. The absorbent structure according to claim 12, wherein the cellulose fibers have a median emission pressure of 14 cm or less. 14. The absorbent structure according to claim 13, wherein the cellulose fibers have a median emission pressure of 13 cm or less. 15. The absorbent structure according to claim 14, wherein the cellulosic fibers have a median emission pressure of 12 cm or less. The absorbent structure according to any one of claims 12 to 15, wherein the cellulosic fibers have a water retention value of 45 percent or less. 16. The absorbent structure according to any one of claims 12 to 15, wherein the cellulosic fibers have a water retention value of 38 percent or less. The absorbent structure according to any one of claims 12 to 15, wherein the cellulosic fibers have a water retention value of 30% or less. An absorbent structure comprising the cellulose fiber according to any one of claims 1 to 8. An absorber structure comprising the uptake distribution layer according to claim 9. An absorber structure comprising the uptake layer according to claim 10. An absorber structure comprising the distribution layer according to claim 11. A method for producing cellulose fibers, comprising: (a) refining cellulose fibers to have a freeness of about 300 to about 700 ml CSF; and (b) cross-linking the refined cellulose fibers. 24. The method according to claim 23, wherein the cellulosic fibers refined in step (a) are wet wraps. 24. The method of claim 23, wherein in step (a), the cellulose fibers are refined to a freeness of about 500 to about 700 ml CSF. 26. The method of claim 25, wherein in step (a) the cellulose fibers are refined to a freeness of about 650 to about 700 ml CSF. Step (b) is
(i) mixing the refined cellulose fibers with a crosslinking agent; and
24. The method of claim 23, comprising (ii) curing the cellulose fibers in the mixture. Step (b) is
(i) mixing the refined cellulose fibers with a crosslinking agent;
(ii) fluffing the cellulose fibers in the mixture; and
24. The method of claim 23, comprising (iii) curing the cellulosic fibers in the mixture. 29. The method of claim 28, wherein step (b) (iii) comprises drying the cellulose fibers and curing the dried cellulose fibers. 29. The method of claim 28, wherein curing is performed at a temperature ranging from about 150C to about 175C. Cellulose fiber produced by the method according to any one of claims 23 to 29. (a) producing a cellulose fiber by the method according to any one of claims 23 to 29; and
(b) A method for producing an absorbent structure, comprising a step of integrating the cellulose fibers into the absorbent structure. Crosslinked by at least one crosslinking agent selected from saturated dicarboxylic acids, aromatic dicarboxylic acids, cycloalkyldicarboxylic acids, difunctional monocarboxylic acids and amine carboxylic acids, and release of 25 cm or less as measured in a capillary absorption / release cycle Cellulose fibers having a median pressure. The cellulose fiber of claim 33, wherein the saturated dicarboxylic acid has 2 to 8 carbon atoms. 35. The cellulosic fiber of claim 34, wherein the saturated dicarboxylic acid has 2 to 6 carbon atoms. 36. The cellulosic fiber of claim 35, wherein the saturated dicarboxylic acid has 2 to 4 carbon atoms. 35. The cellulose fiber of claim 34, wherein the saturated dicarboxylic acid is selected from oxalic, malonic, succinic, glutaric, adipic, pimelic, suberic, and any combination thereof. The cellulose fiber according to claim 33, wherein the saturated dicarboxylic acid is a saturated hydroxycarboxylic acid. 39. The cellulosic fiber of claim 38, wherein the saturated hydroxy carboxylic acid has 2 to 8 carbon atoms. 40. The cellulosic fiber of claim 39, wherein the saturated hydroxy dicarboxylic acid is selected from glycolic acid, tartaric acid, malic acid, sugar acid, mucus acid, and any combination thereof. The aromatic dicarboxylic acid has the following formula:

Wherein R ¹ , R ² , R ³ and R ⁴ are independently hydrogen, hydroxyl, C ₁ -C ₄ alkoxy, C ₁ -C ₄ alkyl, amino, halogen, or nitro. Item 34. The cellulose fiber according to item 33. 42. The cellulose fiber according to claim 41, wherein the aromatic dicarboxylic acid is phthalic acid. The cycloalkyldicarboxylic acid has the following formula:

Wherein R ⁶ , R ⁷ , R ¹⁰ and R ¹¹ are independently hydrogen, hydroxyl, halogen, C ₁ -C ₄ alkoxy, C ₁ -C ₄ alkyl, amino or nitro;
R ⁸ and R ⁹ have hydrogen, halogen, a C ₁ -C ₄ alkoxy, or C ₁ -C ₄ alkyl) independently, cellulose fibers of claim 33. 44. The cellulose fiber according to claim 43, wherein the cycloalkyl dicarboxylic acid is 1,2,5,6-tetrahydrophthalic acid. 34. The cellulose fiber of claim 33, wherein the bifunctional monocarboxylic acid is selected from haloacetates, hydroxymonocarboxylic acids, acid derivatives of hydroxymonocarboxylic acids, and any combination thereof. 46. The cellulose fiber of claim 45, wherein the halo acetate is sodium chloroacetate. 34. The cellulose fiber according to claim 33, wherein the amine carboxylic acid is an amino acid. The amino acid has the formula:

(Wherein, R ¹² is a bond, C ₁ -C ₁₂ alkyl or one or more carboxyl, hydroxyl, C ₁ -C ₄ alkoxy, C ₁ -C ₄ alkyl, C ₁ ~ substituted by amino and nitro having a C ₁₂ alkyl group), cellulose fibers of claim 47. The amino acid has the formula:

(Wherein, R ⁵ is C ₁ -C ₈ alkyl linear or branched) having, cellulose fibers of claim 47. R ⁵ is C ₂ -C ₄ alkyl, cellulose fibers of claim 49. 50. The cellulosic fiber of claim 47, wherein the amino acid is selected from aspartic acid, glutamic acid, and any combination thereof. 34. The cellulose fiber according to claim 33, wherein the amine carboxylic acid is ethylene dinitrilotetraacetic acid. 53. The cellulosic fiber of any one of claims 33 to 52, wherein the cellulosic fiber is cross-linked with about 5 to about 21 mole percent of a cross-linking agent, calculated based on moles of cellulose anhydrous glucose. 54. The cellulose fiber according to any one of claims 33 to 53, wherein the cellulose fiber has been crosslinked in the presence of a crosslinking aid. 55. The cellulose fiber according to claim 54, wherein the crosslinking aid and the crosslinking agent are different. 56. The cellulose fiber according to claim 54 or 55, wherein the crosslinking aid is oxalic acid. The cellulose fiber of any one of claims 54 to 56, wherein the cellulose fiber has been crosslinked in the presence of about 1.8 to about 9 mole percent of a crosslinking aid, calculated based on the number of moles of cellulose anhydrous glucose. . The cellulosic fiber of any one of claims 54 to 57, wherein the cellulosic fiber is cross-linked with about 0.5 to about 40 mole percent of a cross-linking agent and a cross-linking aid, calculated based on the number of moles of cellulose anhydroglucose. . The cellulose fiber of any one of claims 54 to 58, wherein the cellulose fiber is cross-linked with about 1 to about 30 mole percent of a cross-linking agent and a cross-linking aid, calculated based on moles of cellulose anhydrous glucose. . The cellulose fiber according to any one of claims 33 to 59, wherein the cellulose fiber is derived from wood pulp. The cellulose fiber according to any one of claims 33 to 60, wherein the cellulose fiber has been refined prior to crosslinking. 62. The cellulosic fiber of claim 61, wherein the cellulosic fiber is refined to a freeness of about 300 to about 700 ml CSF prior to crosslinking. 63. The cellulosic fiber of claim 62, wherein the cellulosic fiber is refined to a freeness of about 500 to about 700 ml CSF prior to crosslinking. 64. The cellulosic fiber of claim 63, wherein the cellulosic fiber is refined to a freeness of about 650 to about 700 ml CSF prior to crosslinking. 65. The cellulosic fiber of any one of claims 33 to 64, wherein the cellulosic fiber has been cured at a temperature of from about 105 to about 225 <0> C. 66. The cellulosic fiber of claim 65, wherein the cellulosic fiber has been cured at a temperature of from about 150 to about 190 <0> C. 67. The cellulosic fiber of claim 66, wherein the cellulosic fiber has been cured at a temperature of from about 160 to about 175 <0> C. 68. The cellulose fiber according to any one of claims 33 to 67, wherein the cellulose fiber has been cured in the presence of a reducing agent. 69. The cellulosic fiber of claim 68, wherein the reducing agent is hypophosphite. 70. The cellulose fiber according to claim 69, wherein the reducing agent is sodium hypophosphite. 71. The cellulose fiber according to any one of claims 33 to 70, wherein the water retention value of the cellulose fiber is 50% or less. 72. The cellulose fiber of claim 71, wherein the water retention value of the cellulose fiber is 45 percent or less. 73. The cellulose fiber of claim 72, wherein the water retention value of the cellulose fiber is 38 percent or less. 74. The cellulose fiber according to claim 73, wherein the water retention value of the cellulose fiber is 30% or less. 75. The cellulose fiber of any one of claims 33 to 74, having a median release pressure of 20 cm or less as measured in a capillary absorption and release cycle. 76. The cellulose fiber of claim 75 having a median release pressure of 18 cm or less as measured in a capillary absorption and release cycle. 77. The cellulose fiber of claim 76 having a median release pressure of 15 cm or less as measured in a capillary absorption and release cycle. 78. The cellulosic fiber of any one of claims 33 to 77, wherein crosslinking is substantially reversible. 79. Cellulose fiber according to any one of claims 33 to 78, wherein the crosslinking agent is oxalic acid and the crosslinking is substantially reversible. A decrosslinked cellulose fiber produced by the step of decrosslinking a cellulose fiber according to any one of claims 33 to 79. 81. The decrosslinked cellulose fiber of claim 80, wherein the crosslinker contains no more than 4 carbon atoms. 83. The decrosslinked cellulose fiber of claim 81, wherein the crosslinking agent is oxalic acid. 83. The decrosslinked cellulose fiber of claim 81, wherein the crosslinking agent is sodium chloroacetate. 84. The decrosslinked cellulose fiber of any one of claims 80 to 83, wherein the decrosslinking step comprises immersing the cellulose fiber in water. 85. The decrosslinked cellulose fiber of claim 84, wherein the decrosslinking step comprises immersing the cellulose fiber in water for about 0.5 to about 4 hours. A sheet comprising the decrosslinked cellulose fibers of any one of claims 80 to 85. An absorbent structure comprising the fiber according to any one of claims 33 to 79. A method for producing a crosslinked cellulose fiber, comprising a step of cross-linking in a fiber with at least one of a saturated dicarboxylic acid, an aromatic dicarboxylic acid, a cycloalkyldicarboxylic acid, a bifunctional monocarboxylic acid or an amine carboxylic acid. 89. The method of claim 88, wherein the saturated dicarboxylic acid has 2 to 8 carbon atoms. 90. The method of claim 89, wherein the saturated dicarboxylic acid has 2 to 6 carbon atoms. 91. The method of claim 90, wherein the saturated dicarboxylic acid has 2 to 4 carbon atoms. 90. The method of claim 89, wherein the saturated dicarboxylic acid is selected from oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, and any combination thereof. 89. The method according to claim 88, wherein the saturated dicarboxylic acid is a saturated hydroxycarboxylic acid. 94. The method of claim 93, wherein the saturated hydroxy carboxylic acid has 2 to 8 carbon atoms. C ₂ -C ₈ saturated hydroxycarboxylic dicarboxylic acid, glycolic acid, tartaric acid, malic acid, saccharic acid, mucic acid, and is selected from any combination of these The method of claim 94. The aromatic dicarboxylic acid has the following formula:

Wherein R ¹ , R ² , R ³ and R ⁴ are independently hydrogen, hydroxyl, C ₁ -C ₄ alkoxy, C ₁ -C ₄ alkyl, amino, halogen, or nitro. Item 90. The method according to Item 88. 97. The method of claim 96, wherein the aromatic dicarboxylic acid is phthalic acid. The cycloalkyldicarboxylic acid has the following formula:

Wherein R ⁶ , R ⁷ , R ¹⁰ and R ¹¹ are independently hydrogen, hydroxyl, halogen, C ₁ -C ₄ alkoxy, C ₁ -C ₄ alkyl, amino or nitro;
R ⁸ and R ⁹ are independently hydrogen, halogen, C ₁ -C ₄ alkoxy or C ₁ -C ₄ alkyl), The method of claim 88. 100. The method according to claim 98, wherein the cycloalkyldicarboxylic acid is 1,2,5,6-tetrahydrophthalic acid. 89. The method of claim 88, wherein the bifunctional monocarboxylic acid is selected from a haloacetic acid salt, a hydroxymonocarboxylic acid, an acid derivative of a hydroxymonocarboxylic acid, and any combination thereof. The method of claim 100, wherein the haloacetate salt is sodium chloroacetate. 89. The method according to claim 88, wherein the amine carboxylic acid is an amino acid. The amino acid has the formula:

(Wherein, R ¹² is a bond, C ₁ -C ₁₂ alkyl or one or more carboxyl, hydroxyl, C ₁ -C ₄ alkoxy, C ₁ -C ₄ alkyl, C ₁ ~ substituted by amino or nitro the method of claim 102 is a C ₁₂ alkyl group). The amino acid has the formula:

(Wherein, R ⁵ is a linear or C ₁ -C ₈ branched alkyl) is a method according to claim 102. R ⁵ is C ₂ -C ₄ alkyl, The method of claim 104. 103. The method of claim 102, wherein the amino acid is selected from aspartic acid, glutamic acid, and any combination thereof. 89. The method according to claim 88, wherein the amine carboxylic acid is ethylene dinitriloacetic acid. 108. The method of claims 88-107, wherein the cellulosic fibers are crosslinked with about 5 to about 21 mole percent of a crosslinking agent, calculated based on moles of cellulose anhydrous glucose. 109. The method according to any one of claims 88 to 108, wherein the crosslinking step is performed in the presence of a crosslinking aid. 110. The method of claim 109, wherein the crosslinking agent is different from the crosslinking aid. 1 12. The method according to any one of claims 109 to 110, wherein the crosslinking aid is oxalic acid. 112. The method of any one of claims 109-111, wherein the cellulosic fibers are cross-linked in the presence of about 1.8 to about 9 mole percent of a cross-linking aid, calculated based on the number of moles of cellulose anhydrous glucose. 112. The method of any one of claims 109-112, wherein the cellulosic fibers are cross-linked with about 0.05 to about 40 mole percent of a cross-linking agent and a cross-linking aid, calculated based on the number of moles of cellulose anhydrous glucose. 114. The method of any one of claims 109-113, wherein the cellulosic fibers are cross-linked with about 1 to about 30 mole percent of a cross-linking agent and a cross-linking aid, calculated based on the number of moles of cellulose anhydrous glucose. The crosslinking process
(i) mixing the cellulose fibers with a crosslinking agent; and
115. The method of any one of claims 88-114, comprising (ii) curing the cellulose fibers in the mixture. The crosslinking process
(i) mixing a crosslinking agent and cellulose fibers;
(ii) fluffing the cellulose fibers in the mixture; and
115. The method of any one of claims 88-115, comprising (iii) curing the cellulose fibers in the mixture. 117. The method of claim 116, wherein step (iii) comprises drying the cellulose fibers and curing the dried cellulose fibers. 118. The method of any one of claims 115-117, wherein curing is performed at a temperature between about 150 and about 175 <0> C. 118. The cellulosic fiber according to any one of claims 88 to 118, wherein the fiber is crosslinked in the presence of a reducing agent. 120. The cellulosic fiber according to claim 119, wherein the reducing agent is hypophosphite. 121. The cellulose fiber according to claim 120, wherein the reducing agent is sodium hypophosphite. 122. The method of any one of claims 88-121, wherein the cellulosic fibers are refined prior to the crosslinking step. 133. The method of claim 122, wherein the cellulosic fibers are refined to a freeness of about 500 to about 700 ml CSF. 124. The method of claim 123, wherein the cellulosic fibers are refined to a freeness of about 650 to about 700 ml CSF. A cellulose fiber produced by the method according to any one of claims 88 to 124. The step of intracellularly crosslinking cellulose fibers with at least one of a saturated dicarboxylic acid, an aromatic dicarboxylic acid, a cycloalkyldicarboxylic acid, a bifunctional monocarboxylic acid or an amine carboxylic acid; and a step of decrosslinking the crosslinked cellulose fibers. A method for producing a decrosslinked fiber comprising: 127. The method of claim 126, wherein the crosslinker contains no more than 4 carbon atoms. 130. The method according to claim 127, wherein the crosslinking agent is oxalic acid. 130. The method according to claim 127, wherein the crosslinking agent is sodium chloroacetate. 130. The method of any one of claims 126 to 129, wherein the decrosslinking step comprises immersing the crosslinked cellulose fibers in water. 131. The method of claim 130, wherein the decrosslinking step comprises immersing the crosslinked cellulose fibers in water for about 0.5 to about 4 hours. A method of producing a decrosslinked cellulose fiber by the method according to any one of claims 126 to 131, and a step of forming the decrosslinked cellulose fiber into a sheet, comprising the steps of: How to make a sheet. (a) producing a decrosslinked cellulose fiber by the method of any one of claims 126 to 131; and
(b) A method for producing a crosslinked cellulose fiber, comprising a step of crosslinking the cellulose fiber. (a) producing cellulose fibers by the method of any one of claims 88-124 and 133; and
(b) A method for producing an absorbent structure, comprising a step of integrating cellulose fibers into the absorbent structure. An absorbent core comprising superabsorbent polymer particles and reversibly crosslinked cellulose fibers. 135. The absorbent core according to claim 135, wherein the reversibly crosslinked cellulosic fibers are crosslinked with oxalic acid, sodium chloroacetate, or a mixture thereof. 137. The absorbent core according to claim 136, wherein the reversibly crosslinked cellulose fibers are crosslinked with oxalic acid. The absorbent core comprising from about 30% to about 70% by weight of superabsorbent particles and from about 70% to about 30% by weight of reversibly crosslinked fibers, based on a total weight of 100%. Item 140. The absorbent core according to any one of items 135 to 137.