JP2004523669A - Crosslinked cellulosic products formed by extrusion - Google Patents

Abstract

The present invention provides an extruded cellulosic fiber product. In one aspect, the product comprises in situ cross-linked cellulosic fibers. In another embodiment, the product further comprises a binder. The product can optionally include other fibers and absorbent materials. Methods for making cellulosic fiber products and absorbent materials containing the cellulosic fiber products are also described.

Description

【００６０】
上記表中のデータは、図６〜９に示されている細孔径分布のチャートに由来する。図６〜９は、それぞれ本押出法、フォーム形成法、エアレイド法およびウェットレイド法により形成された代表的複合体に関する細孔径分布のチャートを示す。各複合体は、３００ｇ／ｍ^２の標的坪量を有していた。これらの図において、吸収に関する細孔モード径を示す。脱着での細孔モード径には印を付けていないが、吸収の場合と同様に決定することができる。
【００６１】
毛管脱着圧（ＣＤＰ）に関する値が低いと、好ましい捕捉複合体であることが示されている。毛管脱着圧（ＣＤＰ）は、飽和試料中の液体の５０％が試料から排出された頭部圧力と定義される。流体の捕捉については、８〜４０ｃｍＨ_２Ｏ（典型的には８〜２５ｃｍＨ_２Ｏ）の毛管脱着圧の値が、流体を捕捉するための合成フォームに有利である（例えば、米国特許第５５７１８４９号；米国特許第５５５０１６７号；米国特許第５８５１６４８号参照）。流体の分配については、ＣＤＰに関する１２〜５０ｃｍＨ_２Ｏ（典型的には２０〜４０ｃｍＨ_２Ｏ）の値が、良好な性能に望ましい（米国特許第６０１３５８９号参照）。
【００６２】
上記のように、ＭｉｌｌｅｒおよびＴｙｏｍｋｉｎは、自動ポロシメーターから得られる飽和のパーセント対加えた圧力のプロットから、毛管脱着圧を決定できることを、示している。一定範囲の圧力にわたる吸収（取込み）および脱着（保持）曲線により、液体を捕捉および保持するための材料の能力の指標が得られる。乳児用おむつのような吸収性製品に用いるための捕捉材料は、迅速に液体を吸収するのと同様に、それを再びおむつのコアに効果的に放出しなければならない。自動ポロシメーターにより測定された毛管脱着圧を、中間脱着圧（ＭＤＰ）とよぶ。ＭＤＰは、捕捉材料として機能するための材料の能力の尺度として用いることができる。あらゆるパーセンテージの飽和を選択することができるのは明らかであるが、簡単にするために、変曲点に近いことから曲線の中点を選択した。本方法により形成された材料以外に、この時点までに１４ｃｍＨ_２Ｏ未満のＭＤＰ値を達成することができていないセルロース材料はない。このように、低いＭＤＰ値を示すセルロース含有材料は、改良された捕捉性能をもたらす。
【００６３】
一態様において、本発明の複合体は、約１４ｃｍＨ_２Ｏ未満のＭＤＰ値を有する。他の態様において、その複合体は、約１２ｃｍＨ_２Ｏ未満のＭＤＰ値を有する。他の態様では、その複合体は、約１０ｃｍＨ_２Ｏ未満のＭＤＰ値を有する。
【００６４】
セルロース系捕捉材料の現行の性能を示すために、サザンパイン繊維からなるエアレイド捕捉材料について検討する。ＴＲＩ自動ポロシメーターを用いて、ＭＤＰを４４ｃｍＨ_２Ｏであると決定した。このデータを図１０にあげ、自動ポロシメーターの出力を示す。
【００６５】
乳児用おむつなどのパーソナルケア用吸収性製品に架橋セルロース系繊維を用いることにより、市販されている現行のおむつの性能が改良された。２種の架橋繊維から作製されたいくつかのエアレイドパッドを、ＭＤＰについて試験した。クエン酸架橋繊維（化学品Ｂ）から作製されたパッドは、２４．２ｃｍＨ_２ＯのＭＤＰを有していた。ポリアクリル酸／クエン酸架橋繊維（化学品Ａ）は、１４．４〜１５．９ｃｍＨ_２ＯのＭＤＰを有していた。化学品Ｃは、ポリアクリル酸架橋繊維をさす。
【００６６】
本発明の方法は、向上したＭＤＰ値を有するウェブを提供する。例えば、Ｏａｋｅｓミキサー／フォーマーにより架橋化学(crosslinking chemistry)を用いることなく形成された押出パイン繊維ウェブは、１８．５ｃｍＨ_２ＯのＭＤＰを提供する（エアレイドでの４４ｃｍＨ_２Ｏと比較する）。ポリアクリル酸とクエン酸のブレンドで架橋された繊維から形成された押出ウェブ（予備架橋化学品Ａ）のＭＤＰ値は、１０．５ｃｍＨ_２Ｏと測定された（エアレイドでの１５．２ｃｍＨ_２Ｏと比較する）。クエン酸架橋繊維から形成された押出ウェブ（予備架橋化学品Ｂ）のＭＤＰ値は、１２．０ｃｍＨ_２Ｏと測定された（エアレイドでの２４．２ｃｍＨ_２Ｏと比較する）。
【００６７】
押出法は、ウェブの構造および表面張力作用に起因して、ＭＤＰの向上を提供する。表面張力は、Ｌａｐｌａｃｅの式に示されるように、差圧に相関する：
【００６８】
【化１】

【００６９】
［式中、ΔＰ＝差圧、σ＝表面張力、θ＝接触角、およびｒ＝半径］。
界面活性剤の存在により表面張力が低下した場合（本発明のフォーム押出法でのように）、一定半径において、差圧（事実上のＭＤＰ）も低下しなければならない。しかし、大部分の細孔は、潰れに対する抵抗がない限り、湿潤時に潰れる。繊維間架橋および／またはバインダー添加によって構造中の結合を増加させることにより、さらなる改良を得ることができる。結合および繊維のレジリエンスが増大すると、細孔半径は潰れなくなり、再びより低いＭＤＰ値をもたらす（細孔半径が潰れることに起因して圧力上昇が最小限に抑えられることにより）。ラテックスを添加すると接触角の値が増大し、したがってコサインは小さくなる。これにより、一定の細孔半径において、ＭＤＰの低下が求められる。
【００７０】
上記の改良を、図１１および１２にグラフで表す。図１１は、本方法に関し、架橋化学の関数として中間脱着圧の低下を実証する棒グラフである。パイン繊維、クエン酸架橋繊維、およびｉｎ ｓｉｔｕクエン酸架橋繊維（すなわち、クエン酸で処理されたが、硬化されていない繊維が、混合装置に加えられる）から形成された押出複合体は、それぞれ１８．５、１２．０および９．８ｃｍＨ_２ＯのＭＤＰ値を有していた。図１２は、ポリアクリル酸とクエン酸のブレンドで架橋された繊維（予備架橋化学品Ａ）、クエン酸架橋繊維（予備架橋化学品Ｂ）、ｉｎ ｓｉｔｕクエン酸架橋繊維（ｉｎ ｓｉｔｕ化学品Ｂ）、およびｉｎ ｓｉｔｕポリアクリル酸架橋繊維（ｉｎ ｓｉｔｕ化学品Ｃ）を含む押出複合体に関し、架橋剤増加のＭＤＰに対する効果を示すグラフである。架橋剤の量が増加すると、これらの繊維から作製された複合体に関するＭＤＰ値は低下する。予備架橋化学品Ｂの実線と比較した破線により、ＭＤＰにおける低下（１２ｃｍＨ_２Ｏから９．８ｃｍＨ_２Ｏへ）が示される。化学品Ｃは、ＭＤＰにおけるさらに大きな低下を示している。
【００７１】
ＨＢ Ｆｕｌｌｅｒ，Ｓｔ．Ｐａｕｌ ＭＮからのＰＤ８１６１のようなラテックスの添加（例えば、複合体の全重量に基づき５重量％）も、ＭＤＰに確実に影響を与え、捕捉性能を改良する。図１３は、ラテックス単独およびｉｎ ｓｉｔｕ架橋と組み合わせたラテックスが、ＭＤＰを低下させることを示している。さらに、予備架橋データから、対照がｉｎ ｓｉｔｕ架橋の影響（先に、１２〜９．８ｃｍＨ_２Ｏと実証されている）を示していると考えられる。ｉｎ ｓｉｔｕ架橋を含まないラテックスの影響は、ＭＤＰにおける１２から９．５ｃｍＨ_２Ｏまでの降下である。ｉｎ ｓｉｔｕ架橋とラテックス添加を組み合わせた影響は、ＭＤＰを９．８から８．３ｃｍＨ_２Ｏまで変化させる。より高いレベルのラテックスでは、さらに低いＭＤＰ値が得られる。一例として、１５％ラテックスを含む予備架橋化学品Ａ繊維のＭＤＰは、７．７ｃｍＨ_２Ｏであった。ＭＤＰ値の概要を表２にあげる。
【００７２】
【表２】

【００７３】
本発明に従い形成された押出複合体の捕捉速度を決定した。捕捉速度は、米国特許第５４６０６２２号および米国特許第４４８６１６７号（これらのそれぞれを、本明細書中で参考として援用する）に記載されているように決定した。手順の唯一の変更点は、全加重をおむつの全容量により近いものにして、試験をより厳密にするために、７５ｍＬの噴出流を用いた点である。
【００７４】
市販用おむつを購入し（Ｐｒｏｃｔｅｒ ＆ ＧａｍｂｌｅによるＰＡＭＰＥＲＳ）、指示された手順により４回目の噴出流の捕捉速度を試験した。その市販用おむつは、７５ｍＬの４回目の噴出流で０．４４ｍＬ／ｓｅｃの捕捉速度を示した。この性能は、当分野の現行の状況を表している。ｉｎ ｓｉｔｕ架橋捕捉パッチを、化学品Ｂ（クエン酸架橋繊維）およびＣ（ポリアクリル酸架橋繊維）の両方を用い、４および６％のレベルで製造した。その後、これらのパッチを、市販用おむつ（同じ大きさおよびタイプのＰＡＭＰＥＲＳを対照とする）中に挿入した。挿入は、以下のように成し遂げた。カバー素材をおむつの一端で慎重に切断してはがし、市販用捕捉パッチおよびキャリヤー用薄葉紙を露出させた。これらの材料を、おむつのコアを乱すことなく慎重に取り出した。市販用パッチと同じ寸法の代表的押出パッチを、そのおむつ中に挿入した。カバー素材を元の位置に戻し、封止した。
【００７５】
４％の架橋剤レベルにおいて、４回目の噴出流の捕捉速度は、化学品のタイプにより０．４８〜１．１３ｍＬ／ｓであった。第２の対照として、予備架橋繊維も試験した。６％のレベルにおいて、その速度は、坪量および化学品のタイプにより０．３６〜１．６０ｍＬ／ｓであった。これらのデータは、市販用おむつ対照、および予備架橋繊維から製造された捕捉材料に対する、押出複合体の補足速度の著しい改良を実証している。おむつの股領域が小さくなると、捕捉に利用可能な領域が少なくなるので、この改良は特に重要である。捕捉性能のデータを表３に要約する。
【００７６】
【表３】

【００７７】
本発明の押出複合体はまた、有利な引張強さを示す。被験試料の多くは非常に弱いので（例えば、エアレイド毛羽パッド）、引張強さは水平引張法により決定した。その方法では、Ｉｎｓｔｒｏｎにより提供されるような定速伸長引張試験機の下部クロスヘッドに固定された水平ジグを用いる。１０ｃｍ×１０ｃｍの試料を、そのジグ中にクランプする。各試料について、ロードセルをゼロに戻す。その後、試料を引張試験機で引張る。試験機で、各試料についての伸びおよび破壊加重を測定する。
【００７８】
ｉｎ ｓｉｔｕ架橋試料は、２種の異なる化学品を用い、３種のレベルで製造した。これらの試料からの引張強さのデータを、以下の表およびチャートに示す。ｉｎ ｓｉｔｕ化学品のレベルが高くなるにつれ、引張強さは上昇することが、明らかである。この上昇は、繊維間結合の増加の指標である。すべての試料（予備架橋と示されているものを除く）を、表４に示されているように化学品のタイプとレベルのみを変動させて、同じ方法で製造した。
【００７９】
【表４】

【００８０】
適用した架橋化学に応じて、ｉｎ ｓｉｔｕ架橋を用いた場合、引張強さは１０〜２０倍に上昇した。図１４に、押出複合体の引張強さに対するｉｎ ｓｉｔｕ架橋の影響を示す。
【００８１】
ラテックスを用いて、押出複合体の構造体およびウェブの強度を高めることができる。代表的押出複合体の強度に対するラテックスおよび繊維ブレンドの影響を、図１５に示す。代表的押出複合体の強度に対するラテックスおよび架橋化学の影響を、図１６に示す。図１５および１６を参照すると、６％の化学品を含む化学品Ｂ試料の強度は、３４ｇ／ｉｎである（ＢＷ＝２０５ｇ／ｍ^２）。５％のラテックスを含む予備架橋化学品Ｂ複合体は、９４ｇ／ｉｎである（ＢＷ＝１５７ｇ／ｍ^２）。５％のラテックスおよび６％のｉｎ ｓｉｔｕ架橋を含む複合体は、１０６５ｇ／ｉｎ（２０８ｇ／ｍ^２）の引張強さを有し、これは、いずれかの処理単独に比べ１０倍を超える強さである。
【００８２】
他の観点において、本発明は、架橋セルロース系繊維製品を含む吸収性材料を提供する。その製品を１以上の他の層と組み合わせて、吸収性物品、例えば、乳児用おむつ、成人用の失禁用製品、および女性用ケア製品中に組み込むことができる構造体を提供することができる。
【００８３】
実施例
実施例１
代表的二軸スクリュー押出装置および方法、ならびに代表的製品およびそれらの性能特性
本実施例では、代表的二軸スクリュー押出装置、その装置を用いた製品の形成方法、その装置を用いてその方法により形成された代表的製品、および代表的製品の性能特性について、記載する。
【００８４】
実験室試験により、フォーム媒体中で繊維ウェブを押し出すと、向上した性能の可能性を得られることが実証された。実験室での成功を考慮して、パイロット試験を実施した。Ｋｒｕｐｐ，Ｗｅｒｎｅｒ，ａｎｄ Ｐｆｌｅｉｄｅｒｅｒ（ＫＷ＆Ｐ）により製造された二軸スクリュー押出機を本発明の方法に用いて、本発明の代表的製品を提供することを、以下に記載する。
【００８５】
試験では、材料の連続ウェブを、幅広い範囲の坪量（約４００〜２０００ｇ／ｍ^２）で押し出した。二成分繊維（ＣＥＬＢＯＮＤ Ｔ１０５）を系中に供給して、より保全性の高い試料を製造した。界面活性剤濃度は、２つのレベル、すなわち全質量の１％および０．５％で試験した。両方のレベルで、適切なフォームが生じた。フォームの品質は、Ｏａｋｅｓの実験設備からの品質（プレートミキサー／フォーマー；空気含有率９４〜９９％；フォーム密度１０〜６０ｇ／Ｌ）と同様であった。繊維の開口部は、繊維長の点で繊維に損傷を与えなかった。製品の品質および性能は最適化しなかったので、Ｏａｋｅｓの系で調製された試料ほど十分なものではない。押出設備は小型であり、スクリューの直径によっては、足場および杭がなくてもコンクリートスラブ上に設置することができる。大きさが小さく、プロセスが簡素であるということは、典型的な製紙工業に比べ、資本的および工学的コストが少ないということである。乾燥した形状でＳＡＰを直接装備に添加できることが、有利である。
【００８６】
装備．９バレル型のＺＳＫ ５８ｍｍ二軸スクリュー押出機（ＫＷ＆Ｐ）を、試験に用いた。押出機設備の略図を図４に示す。４基のＡｃｒｉｓｏｎ一軸スクリューフィーダーを用いて、押出機へ原料を供給した。合計５種の異なるスクリュー設計を用いて、繊維を分散させてフォームを作製した。異なるスクリュー設計については、次の節に記載する。
【００８７】
図４に示されている装置は、いくつかの注目すべき特徴を示している。第一の特徴は、装備の相対的大きさである。押出機を、約２５’×２５’の領域に収納した。押出機をメインフロアに置き、フィーダーを第２フロアに置いた。各バレルの長さは、１フィート未満である。吸収性製品用の商業的設計では、９バレル型の系は必要とされていない（注：左から数えて１本目と最後のバレルは必要ない）。第３のバレルも、所望によるものであることができる。
【００８８】
他の重要な点は、簡素である点である。この系は、基本的に大量に入れ(mass in)、大量に出して（mass out）操作される。供給系は、公知の技術、すなわちロスウェイト式フィーダーを利用している簡素なものである。乾燥した形状にある吸収性材料（例えば、超吸収性ポリマー、ＳＡＰ）を、サイドフィーダーを通して直接的に、目詰まりすることなく湿潤繊維流に加えることができるとき、この点が強調される。この系により繊維およびＳＡＰを容易に加工することができ、最初の２つの試験目的が達成された。ＳＲ１００１（Ｓｔｏｃｋｈａｕｓｅｎから入手可能な軽く架橋されたポリアクリレート）を用いると、プロセスの一番最後に乾燥した形状でＳＡＰを添加すると、ＳＡＰの膨潤が最小限に抑えられた。Ｓｔｏｃｋｈａｕｓｅｎからの他のポリアクリレートであるＳＸＭ−７７は膨潤し、押出機内での保持時間５秒未満で乾燥したものを供給したとき、実験能力に影響を及ぼす。
【００８９】
実験の詳細．押出機の試験を、一連の実験で行った。これらの実験の要点を表７にまとめる。繊維を含まない場合、発泡に問題はなく、生じたフォームの空気含有率は９６〜９７％であった（ＰＣＴ／ＵＳ９９／２６５６０，Ｒｅｔｉｃｕｌａｔｅｄ Ａｂｓｏｒｂｅｎｔ ＣｏｍｐｏｓｉｔｅおよびＰＣＴ／ＵＳ９９／０５９９７，Ｍｅｔｈｏｄｓ Ｆｏｒ Ｆｏｒｍｉｎｇ Ａ Ｆｌｕｔｅｄ Ｃｏｍｐｏｓｉｔｅに記載されているフォーム形成法（フォームレイド）に関する理論最適値６７％と比較する。これらのそれぞれを、その全体を参考として本明細書中で特に援用する）。フォーム密度は、フォームレイド法では典型的に３５０ｇ／Ｌであるのに比べ、２９〜３０ｇ／Ｌであった。フォームの完成後、繊維の供給を開始した。繊維の分散を得るために、３種の異なるスクリュー形状を試した。第１の形状は、かなり多くの高剪断要素を有していた。これらの要素は剪断応力をもたらしたが、材料の流れが制限された（例えば、保持時間を増大させた）。この設計では熱が若干発生し、繊維が効率的に分散されなかった。第２の設計は、制限を伴わない低剪断設計であった。この設計により、著しい温度昇を伴わないで１０００ｒｐｍのスクリュー速度が可能になった。結果として、繊維の分散性は改善された。繊維のノットは、依然としてウェブ中に見られた。しかしながら、分散性は、第１のスクリュー設計に比べ良好であり、以下に１０５１−ＸＮＰとして識別しているこの試験で達成した分散性より良好であった。
【００９０】
第３の設計では、少数の高剪断要素を再挿入して、繊維化を改善した。これら少数の剪断要素により、温度が上昇した。
第４のスクリュー設計（第２の設計に似ているが、混練ブロックが多い）では、最高２２５ｌｂ．ＯＤ繊維／ｈｒ（２．５ｔ／日）の供給が可能であった。繊維のみを加工すると、このスクリュー設計では、繊維チャンクが粉砕されると思われた。繊維の分散をより容易に見ることができるように、供給量を０．５ｔ／日に減少させた。その後、スロットダイを取り付け、約５００ｇ／ｍ^２および０．０５ｇ／ｃｃ（２６．６％“クーチ(couch)”固体）のウェブを製造した。
【００９１】
試料および試験機のデータをとった後、ＳＲ１００１を約５０％のレベルで加えた。サイドフィーダーは完璧に機能し、ＳＡＰの供給に問題はなかった。この複合体（ＢＷ約１１００ｇ／ｍ^２、密度約０．１１ｇ／ｃｃ）をダイヘッドに通して押し出し、試料を採取した（３９％“クーチ”固体）。容量値は１６ｇ／ｇであった。ＳＸＭ−７７を試すと、すべての遊離水分が除去され、ＳＡＰおよび繊維の乾燥チャンクが生じた。これは、先の試験で見られた結果（１０５１−ＸＮＰ）と同様である。
【００９２】
ウェブをそのダイで製造することができたので、ＳＡＰを含む試料をより低い坪量で製造して、先に作製して試験したフォームレイド材料と比較した。保全性を向上させるために、二成分繊維ＣＥＬＢＯＮＤ Ｔ１０５も加えた。二成分繊維の代替として、湿潤紙力増強剤ＫＹＭＥＮＥを系に加えることもできる。低坪量の材料が得られた。界面活性剤レベルを、全質量の１％から０．５％に減少させたが、有害作用はなかった。実験的には、界面活性剤の総量に比べて、水分利用可能性の方が限定要因である。
【００９３】
ＣＥＬＢＯＮＤ Ｔ１０５を含むおよび含まない追加的な低坪量材料を、いくつかの三葉型要素を用いる第５のスクリュー設計で形成させた。その材料では、ノットが少ないようであった。押出量の試験を実施して、このスクリューでは繊維供給量が７００ｌｂ．／ｈｒ（そのまま）または全質量（４０％固形分および５０％ＳＡＰと仮定する）で約１１７０ｌｂ．／ｈｒに制限されることを決定した。
【００９４】
繊維の品質／分散の結果：スクリュー設計および押出量．いくつかのスクリュー軸設計からの材料試料を、ノットのパーセンテージおよび繊維長について試験した。典型的には、これら２種の試験は、ハンマーミルの効率を評価するために、毛羽実験室(fluff lab)で用いられる。これらの用具を用いて、異なるスクリュー設計を評価した。表５は、超音波分別データに基づき、設計５が設計４よりわずかに良好であると思われることを示している。どちらの設計においても、繊維長のデータにより証明されるように、繊維は切断されない。
【００９５】
【表５】

【００９６】
その他のデータは、設計２の効果が最も低く、それに続く設計では繊維の分散性が改善されたことを示した。
【００９７】
固形分．固体のパーセンテージを２５〜６５％で測定したが、物質収支に基づく予測値（１７〜４７％）に従っていない。１つを除くすべての測定値は、理論値より高い固形分を示している。これは、試料が完全に乾いていなかった可能性があることを示している。
【００９８】
容量の結果．荷重下での容量値の約１１〜１７ｇ／ｇを、３７〜４６％のＳＡＰ含有物を含有する試料で測定した。高い坪量と、ダイスロットの大きさが一定であることにより増大する密度を考慮すると、容量値は適当であった。
【００９９】
界面活性剤レベル．３種のレベルの界面活性剤（Ｃｒｏｄａから入手可能なＩｎｃｒｏｎａｍ ３０）を、５．０、７．５および１０．０（そのまま）ｌｂ．／ｈｒで用いた。水抽出物からの表面張力値は、界面活性剤が表面上に存在し、容易に除去されたことを示している。３種の界面活性剤レベル（５．０、７．５および１０．０ｌｂ．／ｈｒ）に関し、表面張力値は、４０．７、４０．４、および３５．５ｄｙｎ／ｃｍであった。すべてのレベルで発泡に成功したことと、このプロセスには“洗浄”工程がないことから、より低いレベルの界面活性剤を用いると、残留界面活性剤のレベルを低減させることができる。より低いレベルの界面活性剤により、製品の捕捉性能を高めることができる。Ｉｎｃｒｏｎａｍ ３０またはＤｅｈｙｔｏｎ Ｋを用いたフォームレイドウェブにおける典型的な抽出物の表面張力値は、４０〜４３ｄｙｎ／ｃｍであった。
【０１００】
捕捉性能／細孔径分布／中央脱着圧．捕捉性能は、Ｅｄａｎａ試験法の新規Ｍａｒｋｅｔ Ｐｕｌｐ Ｓｔａｎｄａｒｄにより測定した。Ｐｒｏｃｔｅｒ ＆ Ｇａｍｂｌｅ ＰＡＭＰＥＲＳ対照に関する捕捉時間は、１回目から３回目までの１００ｍＬの投与について、それぞれ２７秒、６０秒、および８５秒である。捕捉は、１回目から３回目までの１００ｍＬの投与について、それぞれ秒である。代表的試料の捕捉性能は、過剰な界面活性剤の存在を示した。１回目の投与の捕捉時間は、すべての試料に関し３０〜７０秒であった。一般に、２回目および３回目の投与では、３００秒（５分）を超える時間がかかった。
【０１０１】
代表的製品に関する細孔径分布および中央脱着圧を図に示す。
細孔径分布（ＰＳＤ）および中央脱着圧（ＭＤＰ）では、捕捉性能に関しては界面活性剤レベル以外の追加的洞察を得られない。上記図１７〜２０は、この試験中に製造された２種の低坪量試料に関するＰＳＤおよびＭＤＰを示している。図２１および２２と比較すると、１０５１−ＸＮＰ試料は、実施例２に記載されている実験室試験中にＯａｋｅｓで製造した試料に、非常によく似ている。ＭＤＰデータは、２種の試験のいずれも差異を示していない。試験１７および１９に関するＭＤＰ値はそれぞれ１７．２ｃｍＨ_２Ｏおよび１６．２ｃｍＨ_２Ｏと測定され、Ｏａｋｅｓ法での１００％パインに関する値は１６．５ｃｍＨ_２Ｏであった。
【０１０２】
同様のフォームレイド材料との比較．以下の表６は、本発明に従った材料と、フォームレイドで作製された材料との比較を示している。顕著な差があるのは、密度と、垂直吸上に対し得られる効果である。木材毛羽パルプ（サザンパイン）の含有率に差があるにもかかわらず、容量値は同様である。最適化しなくても、１０５１−ＸＮＰ材料は、フォームレイドで作製され材料と比較することができる。
【０１０３】
【表６】

【０１０４】
押出量．押出量の試験は、約４５０ＯＤ ｌｂ．／ｈｒ（５ｔ／日）の全質量を、５８ｍｍの試験機を通して加工できることを示している。
【０１０５】
【表７】

【０１０６】
【表８】

【０１０７】
【表９】

【０１０８】
【表１０】

【０１０９】
【表１１】

【０１１０】
実施例２
代表的プレートミキサー押出装置および方法、ならびに代表的製品およびそれらの性能特性
本実施例では、代表的プレートミキサー押出装置、その装置を用いた製品の形成方法、その装置を用いてその方法により形成された代表的製品、および代表的製品の性能特性について、記載する。
【０１１１】
プレートミキサー／押出法は、複合体コア材料の作製に用いられる従来の形成技術の代替法の１種である。本実施例では、Ｏａｋｅｓミキサー／フォーマー（Ｏａｋｅｓ ＣＯｎｔｉｎｕｏｕｓ Ｍｉｘｉｎｇ Ｈｅａｄ，Ｅ．Ｔ．Ｏａｋｅｓ Ｃｏｒｐｏｒａｔｉｏｎ，Ｈａｕｐｐａｕｇｅ，ＮＹ）を用いて、押し出し可能なフォームを作り、そのフォームから、簡単なダイヘッドを通す押出によりウェブを作製した。３種の繊維完成紙料を用いた：すなわち、サザンパインパルプ繊維（Ｃパイン）；クエン酸処理セルロース系繊維（ＸＬＡ）；および、これら２種の繊維の５０：５０ブレンドである。Ｈ．Ｂ．Ｆｕｌｌｅｒ ＣｏｍｐａｎｙからのＰＤ８１６１ラテックスを、結合およびレジリエンス助剤として５、１０、および１５重量％のレベルで用いた。
【０１１２】
本明細書中で用いる“ＥＸＰＲＯ”という用語は、本発明の押出法およびその方法により形成された製品をさす。
結果は以下のことを実証している。その装置および方法により、パインおよび処理繊維を、他の現行の方法より低密度でウェブにすることができる。押出ウェブの場合、これらの製品に関する平均細孔半径は、従来法により形成されたウェブより大きい。その製品は、現行の材料に比べて向上した捕捉性能を有する。その製品は、従来の方法で形成された現行の材料に比べて、はるかに低い中央脱着圧の値を示す。その押出法は、原料または製品の廃棄物が非常に少ない。
【０１１３】
一般．本実施例では、Ｃパイン、ＸＬＡ、およびＰＤ８１６１ラテックスを用いて、異なる繊維完成紙料およびラテックス含有率の試料を形成させた。試料の説明を表８に示す。
【０１１４】
【表１２】

【０１１５】
Ｏａｋｅｓ設備．図３−Ａ〜Ｃに示されている実験装置を用いて、これらの試料を製造した。具体的な試験機および実験の規格を以下に示す。
一般に、所望されるパルプ繊維を、スリップ助剤としての２重量％のＰｏｌｙｏｘ（分子量４００万のポリエチレンオキシド）と共に、３０％のコンシステンシーでピストンフィーダーを経由してミキサー／フォーマー中に供給した。空気、界面活性剤およびラテックスなど他の添加剤を、ピストンフィーダーを経由してＯａｋｅｓ装置上に位置する注入口へ加えた。現行の系は、大量に入れ、大量に出すことを基準に操作するバッチ式操作であり、実質的に廃棄物はなかった。試料の標的坪量（３００ｇ／ｍ^２）は、パルプの供給速度およびコンベヤーの速さによって制御した。
【０１１６】
細孔径分布．細孔径分布は、ＴＲＩ自動ポロシメーターで測定する。ここでは、いくつかの例について検討する。ここで選択する３種の試料は、３種の完成紙料に見られる差異を表している：パイン（試料２、図２３）、ＸＬＡ（試料６、図２４）、および５０：５０ブレンド（試料１０、図２５）。
【０１１７】
図２４では、曲線が、各曲線でより大きな平均半径にシフトしていることが認められる。これは、パインから架橋繊維への変化を示唆している。ブレンド試料である図２５は、図２３および２４に見られるモード値の中間のモード値を示している。より大きな平均半径は、より剛性の架橋繊維がより低密度のウェブを形成することに起因し、その構造による支持も一因である。曲線の下の面積は、試料の全容積、したがって試料の容量を示唆している。これは、ＰＳＤ曲線が、自動ポロシメーターから得られる累積容積チャートの導関数であるという事実に起因する。したがって、繊維完成紙料は、構造体の容積または容量に順次影響を与える、細孔径へのそれらの影響に基づき評価することができる。
【０１１８】
しかしながら、捕捉性能に関しては、細孔モード径のみに基づいて方法を比較することが最善である。これらの値を表１にあげる。これらのデータは、本発明の押出法により、試験した４種の方法のうちもっとも大きな細孔径が得られることを示している。
【０１１９】
捕捉性能．捕捉性能は、典型的には、複数回投与試験の結果に基づく。もっとも厳しい状態である４回目の噴出流の結果が、性能の指標としてしばしば用いられる。この試験における試料に関する４回目の噴出流の結果を、表９の概要データの表に示す。
【０１２０】
一般に、ＸＬＡの結果がもっとも有力であった。これらの結果を図２６にあげる。これらのデータは、現行のおむつの対照に比べてＸＬＡ単独で捕捉速度が向上していることを示している。ラテックスが存在していると、対照に比べ、そして１０１２−ＸＮＰの性能に比べ、結果はさらに向上する。４回目の噴出流の結果のみが向上しているわけではない。すべての噴出流（１〜４回）で、対照に対し向上した捕捉速度が示されている。
【０１２１】
中央脱着圧．捕捉材料が流体を迅速に捕捉することは重要であるが、その材料は直ちにそれを吸収性コアに放出できなければならない。流体を放出するこの能力は、中央脱着圧によって判定される。これは、自動ポロシメーターでの試験中に捕捉流体の５０％が試料から除去されたときの圧力である。
【０１２２】
クエン酸架橋繊維から形成された複合体は、約２０〜２２ｃｍＨ_２ＯのＭＤＰを有する。ＸＬＡなどの繊維から形成された複合体は、１６〜１９ｃｍＨ_２ＯのＭＤＰ値しか達成できなかった。図２９は、１０１２−ＸＮＰの試料の製造にＸＬＡが用いられている例を示す。ここで、ＭＤＰは１７ｃｍＨ_２Ｏであった。
【０１２３】
押出法を用いると、クエン酸架橋繊維のみから形成された複合体に関するＭＤＰ値が、１０．５ｃｍＨ_２Ｏに低下した（図２８参照）。ラテックスを加えると、ＭＤＰが７．７ｃｍＨ_２Ｏに向上した（図２７参照）。表９に示されている繊維完成紙料でのＭＤＰの範囲に基づき、これらの繊維、ラテックス、および押出法を用いると、ＭＤＰを８〜１７ｃｍＨ_２Ｏに制御することが可能であると思われる。
【０１２４】
これらの結果は、密度および細孔径分布の点において、異なる方法により異なる構造体が形成されることを示している。これらの構造的差異ならびに表面特性も、中央脱着圧に影響を与える。
【０１２５】
図２９、３０、および３１は、３種の異なる方法により形成された複合体のＭＤＰを示している。図３１は、ＸＬＡ繊維の２種のバッチから作製されたエアレイドパッドを示している。ここで、これらを４６−０１および４６−０２と識別する。これらのパッドは０．０６ｇ／ｃｍ^３の密度を有するが、ＭＤＰを妨害する界面活性剤を有さない（１４〜１６ｃｍＨ_２Ｏ）。先に言及したように、図２９は、フォーム形成複合体である。密度が低いにもかかわらず、ＭＤＰはエアレイド試料よりわずかに高い。図３０は、ウェットレイド複合体に関するＭＤＰを示している。この材料は、１８．５のＭＤＰおよびフォーム形成試料と同様の密度を有する。図２７および２８に見られるように、押出法により形成された試料は、はるかに小さなＭＤＰ値を示す。
【０１２６】
引張強さ．引張強さの変化は、予期した傾向に従っている：（１）パイン含有率が上昇するにつれ、引張強さは向上する；（２）架橋繊維含有率が上昇するにつれ、引張強さは低下する；そして（３）ラテックス含有率が上昇するにつれ、引張強さは向上する。これらの試料を、水平ジグを用いたＩｎｓｔｒｏｎで測定した。
【０１２７】
結果は、以下のように要約できる。パインまたは架橋繊維を用いた場合、押出ウェブの密度は他の吸収性ウェブ形成法より低い。押出ウェブでは平均細孔半径がより大きく、向上した捕捉性能が得られる。本押出法では、パインおよび架橋繊維を用いて、向上したＭＤＰを有するウェブを製造することができる。これは、この材料が、より容易に液体を貯蔵コアに放出するであろうことを示している。本押出法では、ラテックスおよび他の添加剤を、噴霧することなく、かつ廃棄物を出すことなく、ウェブに加えることができる。
押出複合体の強度に対するラテックスおよび繊維ブレンドの影響を、図１５に示す。
【０１２８】
【表１３】

【０１２９】
実施例３
代表的製品の性能特性
本実施例では、本発明に従い形成された代表的製品の性能特性について記載する。
中位取込み圧(medium uptake pressure)（ＭＵＰ）、中位脱着圧（ＭＤＰ）、および本発明の代表的製品の厚さを決定し、従来のエアレイドウェブと比較した。標準化した結果を表１０に示す。表１０において、ＸＬＡは、クエン酸で架橋されたセルロース系繊維のエアレイドウェブをさし；ＸＬＢは、クエン酸とポリアクリル酸繊維の組合わせで架橋されたセルロース系繊維のエアレイドウェブをさし；ＥＸＰＲＯ−Ｄは、クエン酸で架橋されたセルロース系繊維の複合体をさし；ＥＸＰＲＯ−Ｅは、クエン酸で処理されたセルロース系繊維から形成された本発明の製品をさし；そして、ＥＸＰＲＯ−Ｆは、クエン酸とポリアクリル酸の組合わせおよびラテックスで処理されたセルロース系繊維から形成された本発明の製品をさす。すべての試料を、３００ｇ／ｍ^２の坪量で試験した。
【０１３０】
【表１４】

【０１３１】
本発明の代表的製品の捕捉速度、および再湿潤(rewet)、および引張強さを決定し、従来のエアレイドウェブと比較した。標準化した結果を表１１に示す。表１１において、ＸＬＡは、クエン酸で架橋されたセルロース系繊維のエアレイドウェブをさし；ＸＬＢは、クエン酸とポリアクリル酸繊維の組合わせで架橋されたセルロース系繊維のエアレイドウェブをさし；ＥＸＰＲＯ−Ｄは、クエン酸で架橋されたセルロース系繊維のフォーム形成複合体をさし；そして、ＥＸＰＲＯ−Ｅは、クエン酸で処理されたセルロース系繊維から形成された本発明の製品をさす。すべての試料を、３００ｇ／ｍ^２の坪量で試験した。
【０１３２】
【表１５】

【０１３３】
本発明の好ましい態様を示し、記載してきたが、本発明の精神および範囲から逸脱することなく、その中にさまざまな変更を加えることができることは、理解されるであろう。
独占的な財産または特権を請求する本発明の態様を、上記のように定義する。
【図面の簡単な説明】
【０１３４】
【図１】それぞれ１３７ｇ／Ｌ、９５ｇ／Ｌ、６６ｇ／Ｌ、および４１ｇ／Ｌの密度を有するフォームに関し、フォームからの液体排出を時間の関数として示したグラフである。
【図２】本発明に従った押出複合体の代表的作製方法を示する流れ図である。
【図３−Ａ】本発明の方法に有用な代表的混合装置の像である。
【図３−Ｂ】図３−Ａに示されている混合装置のステーターの像である。
【図３−Ｃ】ローターを外した図３−Ａの混合装置の像である。
【図４】さまざまな材料を加えることができる位置を示す、本発明に有用な代表的押出装置の略図である。
【図５】（ａ）サザンパイン繊維、および（ｂ）４種の方法、すなわちフォームレイド、エアレイド、ウェットレイド、および本発明の押出法によりクエン酸とポリアクリル酸のブレンドで架橋された繊維、から作製された繊維複合体の密度を比較するグラフである。
【図６】ポリアクリル酸とクエン酸のブレンドで架橋されたセルロース繊維（繊維に基づき１３重量％架橋）を含み、本発明に従い形成された代表的押出複合体に関する、細孔径分布を示すグラフである。
【図７】ポリアクリル酸とクエン酸のブレンドで架橋されたセルロース繊維を含む代表的フォームレイド複合体に関する、細孔径分布を示すグラフである。
【図８】ポリアクリル酸とクエン酸のブレンドで架橋されたセルロース繊維を含む代表的エアレイド複合体に関する、細孔径分布を示すグラフである。
【図９】ポリアクリル酸とクエン酸のブレンドで架橋されたセルロース繊維を含む代表的ウェットレイド複合体に関する、細孔径分布を示すグラフである。
【図１０】サザンパイン繊維を含むエアレイド複合体に関し、自動ポロシメーターを用いて得られた吸収および脱着曲線を示すグラフである。
【図１１】本発明に従い形成された代表的押出複合体の中間脱着圧（ＭＤＰ）を比較するグラフである（“パイン繊維”は、サザンパイン繊維を含む複合体をさし；“予備架橋化学品Ｂ複合体”は、クエン酸架橋繊維を含む複合体をさし；“ｉｎ ｓｉｔｕ化学品Ｂ複合体”は、セルロース繊維を含む複合体であって、そのセルロース繊維が、クエン酸で処理されかつその複合体中で硬化されたものをさす）。
【図１２】本発明に従い形成された代表的押出複合体に関し、中間脱着圧に対する架橋化学の影響を示すグラフである（“予備架橋化学品Ａ”は、ポリアクリル酸とクエン酸のブレンドで架橋されたセルロース繊維を含む複合体をさし；“予備架橋化学品Ｂ”は、クエン酸架橋繊維を含む複合体をさし；“ｉｎ ｓｉｔｕ化学品Ｂ”は、セルロース繊維を含む複合体であって、そのセルロース繊維が、クエン酸で処理されかつその複合体中で硬化されたものをさし；“ｉｎ ｓｉｔｕ化学品Ｃ”は、セルロース繊維を含む複合体であって、そのセルロース繊維が、ポリアクリル酸で処理されかつその複合体中で硬化されたものをさす）。
【図１３】本発明に従い形成された代表的押出複合体に関し、中間脱着圧に対するラテックス含有率の影響を、架橋化学の関数として示すグラフである（“予備架橋化学品Ｂ”は、クエン酸架橋繊維を含む複合体をさし；“予備架橋化学品Ｂ＋５％ラテックス”は、クエン酸架橋繊維と５重量％のラテックスを含む複合体をさし；“ｉｎ ｓｉｔｕ化学品Ｂ”は、複合体であって、クエン酸で処理されかつその複合体中で硬化された繊維を含む複合体をさし；“ｉｎ ｓｉｔｕ化学品Ｂ＋５％ラテックス”は、複合体であって、クエン酸で処理されかつその複合体中で硬化された繊維と、５重量％のラテックスとを含む複合体をさす）。
【図１４】クエン酸架橋繊維およびポリアクリル酸架橋繊維を含み、本発明に従い形成された代表的押出複合体の引張強さに対する、ｉｎ ｓｉｔｕ架橋の影響を示すグラフである（“２％ ｉｎ ｓｉｔｕ”は、２重量％の架橋剤で処理された繊維を含む複合体をさし、“６％ ｉｎ ｓｉｔｕ”は、６重量％の架橋剤で処理された繊維を含む複合体をさし、“６％予備架橋”は、６重量％の架橋剤で架橋された繊維を含む複合体をさす）。
【図１５】本発明に従い形成された代表的複合体の強度に対する、ラテックスおよび繊維タイプの影響を示すグラフである（“パイン”は、サザンパイン繊維を含む複合体をさし、“ブレンド”は、サザンパイン繊維と、ポリアクリル酸およびクエン酸のブレンドで架橋された繊維との５０／５０ブレンドを含む複合体をさし、“化学品Ａ”は、ポリアクリル酸とクエン酸のブレンドで架橋された繊維を含む複合体をさす）。
【図１６】本発明に従い形成された代表的押出複合体の引張強さに対する、化学品のｉｎ ｓｉｔｕ架橋およびラテックスの影響を示すグラフである（“Ｃｈｅｍ Ｂ”は、クエン酸架橋繊維を含む複合体をさし、“Ｃｈｅｍ Ｃ”は、ポリアクリル酸架橋繊維を含む複合体をさす）。
【図１７】フォームレイド複合体に関する細孔径分布を示すグラフである。
【図１８】図１７の複合体に関する中間脱着圧を示すグラフである。
【図１９】フォームレイド複合体に関する細孔径分布を示すグラフである。
【図２０】図１９の複合体に関する中間脱着圧を示すグラフである。
【図２１】本発明に従い形成された代表的複合体（サザンパイン繊維を含む複合体）に関する細孔径分布を示すグラフである。
【図２２】図２１の複合体に関する中間脱着圧を示すグラフである。
【図２３】本発明に従い形成された代表的押出複合体（サザンパイン繊維および５％ラテックスを含む複合体）に関する細孔径分布を示すグラフである。
【図２４】本発明の代表的押出複合体（クエン酸とポリアクリル酸のブレンドで架橋された繊維と５％ラテックスとを含む複合体）に関する細孔径分布を示すグラフである。
【図２５】本発明の代表的押出複合体（サザンパイン繊維と、クエン酸およびポリアクリル酸のブレンドで架橋された繊維との５０：５０ブレンド、ならびに５％ラテックスを含む複合体）に関する細孔径分布を示すグラフである。
【図２６】本発明に従い形成された代表的押出複合体の４回目の噴出流の捕捉速度を、対照複合体と比較して示すグラフである。
【図２７】本発明に従い形成された代表的押出複合体（クエン酸およびポリアクリル酸架橋繊維のブレンドと１５％ラテックスを含む複合体）に関する中間脱着圧を示すグラフである。
【図２８】本発明に従い形成された代表的押出複合体（クエン酸およびポリアクリル酸架橋繊維のブレンドを含む複合体）に関する中間脱着圧を示すグラフである。
【図２９】フォームレイド複合体に関する中間脱着圧を示すグラフである。
【図３０】ウェットレイド複合体に関する中間脱着圧を示すグラフである。
【図３１】エアレイド複合体に関する中間脱着圧を示すグラフである。【Technical field】
[0001]
The present invention relates generally to cellulosic fiber products, and more particularly, to crosslinked cellulosic fiber products formed by extrusion.
[Background Art]
[0002]
Crosslinked cellulosic fibers are advantageously incorporated into a variety of fiber products to improve product bulk, resilience and dryness. Absorbent articles such as diapers are typically formed from fiber composites. The fiber composite includes absorbent fibers, such as wood pulp fibers, and may additionally include cross-linked cellulosic fibers. When incorporated into absorbent articles, such fiber composites provide products that offer the advantages of high liquid acquisition rate and high liquid wicking capacity provided by crosslinked and absorbent fibers, respectively. , Can be provided. However, fiber composites containing a relatively high percentage of crosslinked fibers have the disadvantage of low sheet strength.
[0003]
The relatively low strength of sheets containing crosslinked fibers is due in part to the loss of hydrogen bonding sites associated with the crosslinking of cellulose. As a result of their chemical modification, less hydroxyl groups are available in crosslinked cellulosic fibers to form hydrogen bonds between the fibers. Because of the low tendency of crosslinked fibers to form interfiber bonds, it is generally not possible to form them from any significant structural integrity of the sheet or web.
[0004]
Conventionally, a cellulose structure has been formed by an aqueous sheet forming method. Over the years, airlaid and foam forming methods have been developed, using new materials and providing improved properties of the resulting web. Foam forming methods have shown improved potential for utilizing long fibers of natural or synthetic origin, and have provided bulky webs. The airlaid method provided bulk and softness, but weak strength without high binder content. Crosslinked fibers have been used in the above methods to improve web properties such as resilience, bulk and capture performance. Heretofore, crosslinked fibers have only been available as individual crosslinked fibers packaged in bale. Numerous patents describe how to make and use individually crosslinked fibers. Therefore, there is a need to develop a method that eliminates the step of individually cross-linking cellulose fibers.
[0005]
Personal care absorbent products, such as infant diapers, adult incontinence products, and feminine care products include a liquid acquisition and / or distribution layer that is trapped after rapid acquisition. It serves to distribute the liquid to the holding storage core. To achieve rapid capture and distribution, these layers may include cross-linked cellulosic fibers that impart bulk and resilience to the layers. However, as mentioned above, webs containing a high proportion of crosslinked fibers suffer from lack of structural integrity. The problem of loss of structural integrity has traditionally been addressed by sandwiching webs containing crosslinked fibers between tissues or nonwoven sheets and securing them with an adhesive. In pursuit of such a structure, it is required to maintain the integrity of the web.
[0006]
Accordingly, there is a need for a cellulosic web that retains the advantageous properties of a web containing crosslinked cellulosic fibers and more advantageously maintains its structural integrity. The present invention seeks to meet these needs, and further provides related advantages.
DISCLOSURE OF THE INVENTION
[0007]
In one aspect, the present invention provides a crosslinked cellulosic fiber product comprising an in situ crosslinked cellulosic fiber. In one aspect, the product further comprises a binder. The product can optionally include other fibers alone, absorbent material alone, and other fibers and absorbent materials.
[0008]
In another aspect of the present invention, a method for forming a crosslinked cellulosic fiber product is provided. In one aspect, the product is formed using a screw extruder. In another aspect, the product is formed using a rotary mixing extruder.
[0009]
In another aspect, the present invention provides an absorbent article comprising the bound cellulosic textile. Structures can be provided in which the product can be combined with one or more other layers to incorporate into absorbent articles such as baby diapers, adult incontinence products, and feminine care products. .
[0010]
Detailed description of preferred embodiments
The above aspects and many attendant advantages of this invention will be more readily understood, as they become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings. Will be done.
[0011]
In one aspect, the invention provides a bonded cellulosic fibrous product comprising in situ cross-linked cellulosic fibers. As used herein, the term "in situ crosslinked cellulosic fibers" refers to cellulosic fibers that have been crosslinked during formation of the web. Thus, the products of the present invention are distinguished from conventional webs comprising cross-linked cellulosic fibers, which fibers are first formed and then introduced into the web during the web forming process. .
[0012]
The product includes in situ cross-linked cellulosic fibers. Because the fibers are cross-linked during the web forming process (ie, in situ), the products include intra-fiber cross-linked cellulosic fibers (ie, fibers having cross-links within each fiber) and inter-fiber cross-linked cellulosic fibers. (I.e., fibers having cross-links between fibers). The product has a bonded structure and includes intra-fiber cross-linked cellulosic fibers that are further cross-linked to adjacent fibers by inter-fiber cross-linking. The product retains the beneficial properties of bulk and resilience due to intra-fiber crosslinked fibers and the structural integrity benefits imparted to the structure by inter-fiber bonding. The product is a bonded web in which the cross-linked fibers and the bonded structure of the web itself provide the resilience and liquid trapping performance of the web.
[0013]
In one aspect, the product is formed into (1) a web of cellulosic fibers, wherein at least some of the fibers have been treated with a cross-linking agent and, if necessary, a cross-linking catalyst; Drying the web; and (3) heating the web at a temperature sufficient to effect crosslinking, for a sufficient time.
[0014]
Suitable fibers useful in forming the products of the present invention include cellulosic fibers that have been treated with a cross-linking agent and, if necessary, a cross-linking catalyst, and then dried without curing the cross-linking agent. These dried and treated fibers can be introduced into forming equipment for subsequent product formation.
[0015]
If desired, any one of a number of cross-linking agents and cross-linking catalysts can be used to provide the products of the present invention. The following is a representative list of useful crosslinkers and catalysts. Each of the following patents is specifically incorporated herein by reference in its entirety.
[0016]
Suitable urea-based crosslinkers include substituted ureas, for example, methylolated ureas, methylolated cyclic ureas, methylolated lower alkyl cyclic ureas, methylolated dihydroxy cyclic ureas, dihydroxy cyclic ureas, and lower alkyl substituted cyclic ureas. Specific urea-based crosslinking agents include dimethyldihydroxyurea (DMDHU, 1,3-dimethyl-4,5-dihydroxy-2-imidazolidinone), dimethylol dihydroxyethylene urea (DMDHEU, 1,3-dihydroxymethyl- 4,5-dihydroxy-2-imidazolidinone), dimethylol urea (DMU, bis [N-hydroxymethyl] urea), dihydroxyethylene urea (DHEU, 4,5-dihydroxy-2-imidazolidinone), dimethylol ethylene Urea (DMEU, 1,3-dihydroxymethyl-2-imidazolidinone) and dimethyldihydroxyethylene urea (DDI, 4,5-dihydroxy-1,3-dimethyl-2-imidazolidinone).
[0017]
Suitable crosslinkers include dialdehydes such as those described in U.S. Patent Nos. 4,822,453; 4,888,093; 4,889,595; 4,889,596; 4,889,597; and 4,889,642;₂-C₈Dialdehydes (eg glyoxal), C having at least one aldehyde group₂-C₈Includes dialdehyde acid analogs and oligomers of these aldehydes and dialdehyde acid analogs. Other suitable dialdehyde crosslinkers include those described in U.S. Patent Nos. 4,850,863; 4,900,324; and 5,840,306.
[0018]
Other suitable crosslinking agents include aldehyde and urea-formaldehyde adducts. See, for example, U.S. Patent Nos. 3,224,926; 3,241,533; 3,932,209; 4,035,147; 3,756,913; 4,689,118; 4,822,453; 3,344,135; 4,935,022; 3,819,470;
[0019]
Suitable crosslinkers include glyoxal adducts of urea, such as those in US Pat. No. 4,968,774, and US Pat. Nos. 4,285,690; 4,332,586; 4,396,391; 4,455,416; and 4,505,712. Glyoxal / cyclic urea adducts.
[0020]
Other suitable crosslinking agents include carboxylic acid crosslinking agents, such as polycarboxylic acids. Polycarboxylic acid crosslinkers (e.g., citric acid, propanetricarboxylic acid, and butanetetracarboxylic acid) and catalysts are described in U.S. Patent Nos. 3,526,048; 4,820,307; 4,936,865; 4,975,209; and 522,285. ing. C containing at least three carboxyl groups₂-C₉The use of polycarboxylic acids (eg, citric acid and oxydisuccinic acid) as crosslinkers is described in U.S. Patent Nos. 5,137,537; 5,183,707; 5,190,563; 5,562,740, and 5,873,979.
[0021]
Polymeric polycarboxylic acids are also suitable crosslinking agents. Suitable polymeric polycarboxylic acid crosslinkers are described in U.S. Patent Nos. 4,391,878; 4,420,368; 4,431,481; 5,049,235; 5,160,789; 5,442,899; 5,698,074; 5,496,476; 5,496,777; Nos. 5,287,771; 5,705,475; and 5,981,739. Polyacrylic acid and related copolymers as crosslinkers are described in U.S. Patent Nos. 6,306,251; 5,549,791; and 5,998,511. Polymaleic acid crosslinkers are described in U.S. Patent No. 5,998,511.
[0022]
Specific suitable polycarboxylic acid crosslinkers include citric acid, tartaric acid, malic acid, succinic acid, glutaric acid, citraconic acid, itaconic acid, tartrate monosuccinic acid, maleic acid, polyacrylic acid , Polymethacrylic acid, polymaleic acid, polymethylvinylether-co-maleate copolymers, polymethylvinylether-co-itaconate copolymers, copolymers of acrylic acid, and copolymers of maleic acid.
[0023]
Other suitable crosslinking agents are described in U.S. Patent Nos. 5,225,047; 5,366,591; 5,556,976; and 5,536,369.
Suitable catalysts can include acidic salts such as ammonium chloride, ammonium sulfate, aluminum chloride, magnesium chloride, magnesium nitrate, and alkali metal salts of phosphorus-containing acids. In one embodiment, the crosslinking catalyst is sodium hypophosphite.
[0024]
Mixtures or blends of crosslinkers and catalysts can also be used.
The cross-linking agent is applied to the cellulosic fibers in an amount sufficient to achieve intra- and inter-fiber cross-linking, as described above. The amount applied to cellulosic fibers can be from about 1 to about 10% by weight based on the total weight of the fiber. In one aspect, the crosslinker in an amount of about 4 to about 6% by weight based on the total weight of the fiber.
[0025]
Cellulosic fibers suitable for forming the products of the present invention include those known to those skilled in the art and include any fiber or fiber mixture that can be crosslinked, and then a fibrous web or sheet. Are included.
[0026]
Although available from other sources, cellulosic fibers are derived primarily from wood pulp. Wood pulp fibers suitable for use in the present invention can be obtained by well-known chemical methods such as the Kraft method and the sulfite method, with or without subsequent bleaching. Pulp fibers may be processed by a thermomechanical method, a chemithermomechanical method, or a combination thereof. Preferred pulp fibers are produced by a chemical method. Groundwood fibers, recycled or secondary wood pulp fibers, and bleached and unbleached wood pulp fibers can be used. Softwood and hardwood can be used. Details regarding the selection of wood pulp fibers are well known to those skilled in the art. These fibers are commercially available from a number of companies, including Weyerhaeuser Company, the assignee of the present invention. For example, suitable cellulosic fibers made from Southern pine that can be used in the present invention are available from Weyerhaeuser Company under the names CF416, NF405, PL416, FR516, and NB416.
[0027]
Wood pulp fibers useful in the present invention can also be pretreated before use. This pre-treatment may include a physical treatment, such as exposing the fibers to steam, or a chemical treatment.
Although not to be construed as limiting, examples of fiber pretreatment include the application of surfactants or other liquids that modify the chemistry of the fiber surface. Other pretreatments include the incorporation of antimicrobial substances, pigments, dyes and densification or emollients. Fibers pretreated with other chemicals such as thermoplastic and thermoset resins may also be used. A combination of pretreatments can also be used. Similar treatment can be applied after forming the textile in the post-treatment process.
[0028]
Cellulosic fibers treated with particulate binders and / or densification / softening aids known in the art can also be used in accordance with the present invention. The particulate binder serves to attach other materials, such as superabsorbent polymers as well as others, to the cellulosic fibers. Cellulosic fibers treated with suitable particulate binders and / or densification / softening aids, and methods for combining them with cellulosic fibers, are disclosed in the following U.S. patents: (1) "Polymeric Binders for Binding Particles to". Fibers "Patent No. 5543215 entitled; (2)" Non-Polymeric Organic Binders for Binding Particles to Fibers "Patent No. 5,538,783 entitled; (3)" Wet Laid Fiber Sheet Manufacturing With Reactivatable Binders for Binding Particles to Fibers With the title No. 5300192; (4) Patent No. 5352480 entitled "Method for Binding Particles to Fibers Using Reactable Binders"; Patent No. 5589256 entitled "Particle Binders that Enhance Fiber Densification"; (7) Patent No. 5672418 entitled "Particle Binders"; (8) "Particle Binding to No. 9; ) "Binders for Bind Patent No. 5,693,411 entitled "Winging Water Soluble Particles to Fibers"; (10) Patent No. 5574745 entitled "Particle Binders"; (11) Patent entitled "Particle Binding to Fibers"; No. 5308896 entitled "Particle Binders for High-Bulk Fibers"; (13) "No. Patent No. 5609727 (15) Patent No. 5557118 entitled "Reactive Binders for Binding Particles to Fibers"; (16) Patent entitled "Particle Binders for Highing Bulk Ingersin Birth Co., Ltd .; Nos. 5,614,570 entitled "Bulk Fibers"; (18) U.S. Pat. No. 5,789,326 entitled "Binder Treated Fibers"; and (19) U.S. Pat. No. 5,681,885 entitled "Particle Binders"; Incorporated as a reference in the book.
[0029]
In addition to natural fibers, synthetic fibers, including polymeric fibers, for example, polyolefins, polyamides, polyesters, polyvinyl alcohol, polyvinyl acetate fibers can also be incorporated into the product. Suitable synthetic fibers include, for example, polyethylene terephthalate, polyethylene, polypropylene, nylon and rayon fibers. Other suitable synthetic fibers include thermoplastic polymers, cellulosic fibers and other fibers coated with thermoplastic polymers, and multicomponent fibers wherein at least one of the components comprises a thermoplastic polymer. Are included. Mono- and multi-component fibers can be made from polyester, polyethylene, polypropylene, and other conventional thermoplastic fiber materials. Mono- and multi-component fibers are commercially available. Suitable bicomponent fibers include CELBOND fibers available from Hoechst-Celanese Company. The product may also include a combination of natural and synthetic fibers.
[0030]
In one aspect, the product further comprises a binder. Binders help to further increase the structural integrity of the product. Suitable binders include thermoplastic materials, such as bicomponent fibers and latex, and wet strength agents. If the binder is a thermoplastic fiber, the fiber can be combined with the cellulosic fiber, then made into a web and treated with a crosslinking agent. When the binder is a wet strength agent, the web can be subjected to fiber crosslinking conditions after the binder has been applied to the web.
[0031]
Suitable thermoplastic fibers include cellulosic fibers and other fibers coated with a thermoplastic polymer, as well as multicomponent fibers wherein at least one of the components comprises a thermoplastic polymer. Mono- and multi-component fibers can be made from polyester, polyethylene, polypropylene, and other conventional thermoplastic fiber materials. Mono- and multi-component fibers are commercially available. Suitable bicomponent fibers include CELBOND fibers available from Hoechst-Celanese Company.
[0032]
Suitable wet strength agents include cationically modified starches having a nitrogen-containing group (eg, an amino group), such as National Starch and Chemical Corp. Latex; wet-strength resins such as polyamide-epichlorohydrin resins (e.g., KYMENE 557LX, Hercules, Inc., Wilmington, Del.), And polyacrylamide resins (e.g., U.S. Pat. No. 3,569,932; also commercially available polyacrylamide traded under the trade name PAREZ631NC by American Cyanamid Co., Stanford, Conn.); Urea formaldehyde and melamine formaldehyde resins; and polyethyleneimine resins. . A general description of wet strength resins used in the papermaking art and generally applicable in the present invention can be found in TAPPI Monograph Series No. 29, "Wet Strength in Paper and Paperboard", Technical Association of the Pulp and Paper Industry (New York, 1965).
[0033]
In other aspects, the product can include other fibers. Other fibers include, for example, cellulosic fibers, particularly the wood pulp fibers described above, as well as hemp, bagasse, cotton, groundwood fibers, bleached and unbleached pulp, recycled fibers or secondary fibers.
[0034]
For embodiments of the product where retention of liquid is desired, the product may further include an absorbent material (eg, superabsorbent polymer particles). As used herein, the term "absorbent material" refers to a material that absorbs liquid and generally has an absorption capacity greater than the cellulosic fiber component of the composite. Preferably, the absorbent material is a water-swellable, generally water-insoluble polymeric material that is at least about 5 times its weight in saline (eg, 0.9% saline), desirably about 20%. And more preferably about 100 times or more. The absorbent material may be capable of swelling in the dispersion medium used in the method of forming the composite. In one embodiment, the absorbent material is untreated and can swell in the dispersion medium. In another aspect, the absorbent material is a coated absorbent material that is resistant to water absorption during the process of forming the article.
[0035]
The amount of absorbent material present in the product can vary widely depending on the intended use of the product. The amount of absorbent material present in an absorbent article, such as the absorbent core of a baby diaper, may range from about 2 to about 80% by weight, preferably from about 30 to about 60% by weight, based on the total weight of the composite. And is suitably present in the complex.
[0036]
Absorbable materials may include natural materials such as agar, pectin and guar gum, as well as synthetic materials such as synthetic hydrogel polymers. Synthetic hydrogel polymers include, for example, carboxymethylcellulose; alkali metal salts of polyacrylic acid; polyacrylamide; polyvinyl alcohol; ethylene maleic anhydride copolymer; polyvinyl ether; hydroxypropylcellulose; polyvinyl morpholinone; Polyacrylates; polyacrylamides; and especially polyvinylpyridine. In one aspect, the absorbent material is a superabsorbent material. As used herein, "superabsorbent material" refers to a polymeric material that can absorb large amounts of fluid by swelling and forming a hydrated gel (ie, a hydrogel). In addition to absorbing large volumes of fluid, superabsorbent materials can also retain significant amounts of bodily fluids at moderate pressures.
[0037]
Generally, superabsorbent materials fall into three classes: starch graft copolymers, crosslinked carboxymethylcellulose derivatives, and modified hydrophilic polyacrylates. Examples of such absorbent polymers include hydrolyzed starch-acrylonitrile graft copolymer, neutralized starch-acrylic acid graft copolymer, saponified acrylate-vinyl acetate copolymer, hydrolyzed acrylonitrile or acrylamide copolymer, modified Crosslinked polyvinyl alcohol, neutralized self-crosslinkable polyacrylic acid, crosslinked polyacrylate, carboxylated cellulose, and neutralized crosslinked isobutylene-maleic anhydride copolymer.
[0038]
Superabsorbent materials are commercially available, for example, polyacrylates from Clariant of Portsmouth, Virginia. These superabsorbent polymers are offered in various sizes, forms and absorption properties (available from Clariant under trade names such as IM3500 and IM3900). Other superabsorbent materials are commercially available under the trademarks SANWET (supplied by Sanyo Chemical Industries, Ltd.), and SXM77 (supplied by Stockhausen, Greensboro, North Carolina). Other superabsorbent materials are U.S. Pat. No. 4,16,0059; U.S. Pat. No. 4,676,784; U.S. Pat. No. 4,673,402; U.S. Pat. No. 5,002,814; U.S. Pat. No. 5,057,166; U.S. Pat. No. 4,102,340; And all are specifically incorporated herein by reference. Products such as diapers incorporating superabsorbent materials are described in U.S. Patent Nos. 3,699,103 and 3,670,731.
[0039]
Suitable superabsorbent materials useful for the product include superabsorbent particles and superabsorbent fibers.
In one aspect, the product swells relatively slowly for the purpose of product manufacture and at an acceptable rate such that it does not adversely affect the absorption properties of the product or any component containing the product. A swellable, superabsorbent material is included. Generally, the smaller the absorbent material, the faster it absorbs liquid.
[0040]
In another aspect of the present invention, a method is provided for forming a bonded cellulosic fiber product. The bound cellulosic fiber product can be formed by an extrusion method.
Generally, a method of forming a product involves the introduction of components, whereby the product is provided in a forming apparatus. Usually, the fibers are introduced into the apparatus as a pulp slurry (ie, a dispersion of the fibers in a dispersion medium). The pulp slurry can include dry pulp, never-dried pulp, treated pulp, or mixtures thereof. The pulp slurry can have a relatively high consistency, for example, from about 15 to about 50 weight percent solids in one aspect, and from about 20 to about 35 weight percent solids in another aspect. Thereafter, the pulp introduced into the mixing / extrusion device can be combined with other components. In embodiments that do not involve the introduction of the crosslinker-treated pulp into the apparatus, these components include a crosslinker and, if necessary, a crosslinker catalyst. For embodiments of the present invention that include a binder, the binder can be added to the pulp slurry in the apparatus. Surfactants and air can also be added to the pulp in the equipment to provide a foam-forming medium. Other components, such as absorbent materials, can be added as needed to provide the desired product.
[0041]
The components of the product are combined and mixed in the device and then extruded from the device. Thereafter, the extruded cellulosic material is dried, and finally a product is formed by heat treatment. This product is approximately 0.02 g / cm³Has an advantageous low density. Generally, the product will have about 0.02 to about 0.20 g / cm³Having a density of
[0042]
As mentioned above, the product of the present invention achieves cross-linking (ie, curing) and fiber bonding of a web comprising cellulosic fibers that include a cross-linking agent and, if necessary, a cross-linking catalyst and optionally a binder. It is formed by subjecting it to a sufficient temperature for a sufficient time. Curing of the crosslinker to obtain this product can be performed by several methods. Typically, crosslinking requires relatively high temperatures (180 ° C.) and long reaction times (greater than 4 minutes). In one aspect, the product is formed by heating in a curing oven where high temperatures and large volumes of air pass through the web. In another aspect, curing is performed after the web is placed in a shipping box. In this embodiment, the box containing the treated web is passed through a dryer (eg, a kiln dryer) to complete the crosslinking reaction.
[0043]
The product of the present invention winds and transports the fibrous web and forms it as an extended web or sheet having sufficient structural integrity and sheet strength to allow it to be used in a wound configuration in the next process. be able to.
[0044]
The products of the present invention can be supplied in fiber wound form and can be immediately incorporated into the next process. The product is suitable for a variety of absorbent articles, for example, diapers including disposable diapers and training pants; feminine care products including sanitary napkins, tampons, and panty liners; adult incontinence products; toweling; It can be advantageously incorporated into dental sponges; bandages; food tray pads and the like.
[0045]
In one aspect, the method of the present invention provides a bonded composite having intra-fiber and inter-fiber cross-linked fibers that provides improved performance of the resulting composite. As noted above, the present method is a foam forming method that allows for the formation of composites at high solids content (ie, high consistency), and does not require the use of forming wires and liquid drainage. In the present method, the air content and the foam density are characteristics of the foam of the present method. Foams can be classified as stable or unstable. However, overall, the foam is relatively thermodynamically unstable. Foam stability depends on many factors, such as surfactant type and concentration, temperature, stabilizer concentration, and the presence of solids. Foam collapse occurs when the liquid in the foam moves to the bottom of the foam cell by the force of gravity and the lamella at or above the cell thins to the point of failure. Porter, M .; R. See Handbook of Surfactants, 2nd Edition, Blackie Academic & Professional (Chapman & Hall), 1994, pp 65-69. In this method, the form is considered to be.
[0046]
To further understand the foams useful in the present method, consider a discussion of foam air content and foam density.
Wiggins-Teape teaches a foam having an air content of at least 65% by volume (see U.S. Patent Nos. 3,716,449 and 3,938,782). Foams having an air content of 55-75% by volume (see U.S. Pat. No. 3,871,952) or 50-70% by volume (see U.S. Pat. No. 3,937,273) to achieve dispersion. Outside this air content range (high or low), solids in the foam, such as glass fibers, cellulose fibers, synthetic fibers, fine particles, etc., agglomerate. However, foams provide better dispersibility than webs or handsheets made from aqueous slurries of the same solids content. Ahlstrom describes an improved process using an air content of 25-75% by volume (see US Pat. No. 5,904,809).
[0047]
However, at high air content (eg, above about 75% by volume), the foam viscosity is such that the liquid in the bubble lamellae cannot be further discharged from the mixture (eg, the foam is a stable foam) Ascending to the point, Wiggins-Teape states. Therefore, formation on a perforated support and draining liquid from the web, such as in a paper machine, is not practical. In the process of the present invention, the high air content foam is a stable foam that acts like a semi-solid and the liquid discharge is slow. Since very little liquid is available for discharge from within the foam (eg, a 1000 mL foam at 95% by volume air content contains only 50 mL liquid), the collapse of the foam due to liquid movement (gravity Or due to the applied suction) takes a very long time. The total ejection time can be demonstrated as exponentially decelerating, as seen in FIG. In fact, complete drainage is not fully achieved. As a result, this long drain time and foam stiffness or high viscosity make conventional liquid draining impractical. The process of the present invention utilizes a foam having a high air content, typically greater than about 75% by volume. In one aspect, the air content is greater than about 90% by volume, and in another aspect, greater than about 98% by volume. With such high air content foams, no production of a product that does not require a perforated support to drain the liberated liquid from the web has hitherto not been performed. In this method, the collapse of the foam is initiated by temperature and / or by a hygroscopic material in the system that absorbs enough liquid to achieve collapse of the foam cells.
[0048]
Foam density correlates closely with air content. The above references describe a foam density of 250-500 g / L at a pressure of 1 bar. By eliminating the need for liquid drainage, fibrous webs can be formed using lower foam densities (e.g., a foam density of about 20 to about 100 g / L translates to about 90 to about 98% air by volume). Content). Foam densities of about 20 to about 200 g / L at 1 bar are useful in the present invention. Eliminating the forming steps during the process significantly reduces the equipment requirements. Since no liquid is drained from the foam material during web formation, there is no typical white water or reclaimed liquid or foam that needs to be reworked and recycled. The reduced liquid / foam load also reduces the amount of liquid in the product, allowing for more economic drying. This is illustrated by testing the solids or consistency that forms during the process.
[0049]
The Ahlstrom patent states that a foaming process with a fiber consistency of up to 12% is possible with foams having an air content of 25 to 75% by volume. The method of the present invention utilizes a fiber consistency of about 15 to about 50% by volume. In certain embodiments, the fiber consistency is between about 30 and about 50%. In another aspect, the fiber consistency is from about 20 to about 35%. At such a high consistency, dehydration of the fibers can be achieved. The high solids fiber sludge can be further dewatered in the extruder with the addition of slip aids. Also, regenerated fibers can be extruded with high consistency with slip aids to regenerate fibers and fillers typically found on printing paper. In this method, the fibers are fluidized using a foam, rather than adding a slip aid. The foam is formed by the action of a high speed screw in a counter or co-rotating extruder or a high speed rotor of a rotary mixer / former or pump on a suitable surfactant. The foam used in the method includes a surfactant. Suitable surfactants are those that provide a foam density of about 100 g / L and an air content of about 90% at a surfactant concentration of about 0.01 to about 5% based on the weight of the composite. In one aspect, the surfactant is Incronam 30 manufactured by Croda.
[0050]
In the method of the present invention, high solids fibers are used. High solids fibers can be made from wet pulp that has been dewatered to greater than about 20% consistency, or from dry fibers obtained with a hammer mill plus water. Thus, in the method of the present invention, the high solids composition is formulated with suitable chemical additives such as binders, latexes, wet strength agents, dry strength agents, crosslinkers, acids, bases, dyes, powders. , Pigment and polymer in a mixing device and foamed.
[0051]
The method of the present invention employs high consistency fibers that are fluidized in a foam. A general flow diagram of a representative method of the present invention is shown in FIG.
The foaming and mixing operations can be achieved by a shear inducing mixing device. In one embodiment, the shear induction mixing device comprises a mixer / former, such as E.C. T. Model 8M Mixer / Former available from Oaks Corporation, Hauppauge, NY. This device is a rotary mixer, which is shown in FIGS. To fluidize the fiber, it is added to a device with a piston that pushes the fiber toward the rotor at about 30% solids. The surfactant is injected at the point of shear or mixing where the fiber contacts the rotor. The foamed fiber is discharged into a tube and supplied to a die. Referring to FIGS. 3-A-C, air and other chemicals can also be added along the radial axis of the rotor. Chemical addition can be made at the front or back of the rotor. The rotor and stator are shown in FIGS. 3-B and C. In that device, the path that the fiber must travel is tortuous, and the fiber clogs the rotor without foaming properly. A representative plate mixer extruder, method, representative product formed in accordance with the present invention, and performance characteristics of the representative product are described in Example 2.
[0052]
In another aspect, the shear induction mixing device is an extruder. One such extruder is ZSK 58, a very large compounder available from Coperion Corporation, Ramsey NJ. One possible shape of the extruder is shown in FIG. In this method, pulp is added to the extruder at about 20 to about 40% solids. Thereafter, a surfactant is added to initiate foaming. Additional chemicals are added downstream of foaming, but may be added before foaming. The crosslinking agent (eg, citric acid and catalyst) can be added and mixed with the fibers in an extruder making the fibers ready for crosslinking during subsequent drying of the product. Binders such as KYMENE (available from Hercules, Wilmington DE) and latex (available from DuPont, Midland MI or HB Fuller, St. Paul MN) can also be used. Chemicals and other binders in solid, liquid or gas form can be added. Air may be added if necessary to improve foaming and / or air content. A representative twin screw extruder, method, representative product formed in accordance with the present invention, and performance characteristics of the representative product are described in Example 1.
[0053]
Using any equipment (ie, a rotary mixer or a twin screw extruder), the foamed fibers and additives are extruded through a die to form a sheet or composite web. Other shapes can be made. The foam composite is extruded onto a solid conveyor belt, wire or nonwoven carrier fabric, and the web is transported to a dryer. The foam composite is then dried (and / or optionally cured) using techniques such as convection drying, through-air drying, impingement, microwave, radio frequency, and the like.
[0054]
Complexes formed by the methods of the present invention include capture and storage complexes. The method of the present invention allows for the formation of composites of any fiber, composites having a low density, and composites comprising in situ crosslinked fibers. For composites comprising in situ crosslinked fibers, a crosslinker can be added to the fibers before adding the fibers to the extruder. Alternatively, a cross-linking agent may be added to the mixing device during the extrusion process.
[0055]
To achieve adequate capture performance, the capture complex has a relatively low density. The capture complex also has appropriate absorption and desorption properties. This property is referred to herein as mid-point desorption pressure (MDP).
[0056]
As can be seen in FIG. 5, the density of the composite produced by the method of the present invention is much lower than the composite formed by the other methods mentioned. FIG. 5 illustrates the difference between the present method and the method for two fiber furnishes. Pine-only furnish is prepared using a foaming process to form a cellulosic composite described in PCT / US99 / 26560, Reticulated Absorbent Composite and PCT / US99 / 05997, Methods For Forming A Fluted Composite. Typically about 0.14 g / cm³Can be manufactured. In a conventional wetlaid system using papermaking fibers, the density is 0.1 to 1.4 g / cm depending on the grade.³(Handbook of Pulp and Paper Technology by K. Brit, 1970, p. 669). In this method, a composite from the same fiber (pine) is loaded with 0.037 g / cm³At a density of This density is lower than the foam laid or density at which a composite containing crosslinked fibers can be formed in a high dilution wet laid process.
[0057]
Density is related to pore size distribution. In this method, a web having a wide range of pore sizes is produced due to both the cohesive and dispersive properties of the foam. The pore size is measured with an automatic porosimeter and confirmed by the dimensions measured from a micrograph of the foam. An automatic porosimeter available from TRI / Princeton, Princeton, NJ can easily measure pore size distributions less than 750um. For a description of theory, applications and equipment, see Miller and Thomkin (162, 163-170, 1994) in The Journal of Colloid and Interface Science. In a porosimeter, a sample is tested by a cycle of absorption and desorption. Briefly, a pre-saturated sample is placed in the instrument. As the pressure in the sample chamber is increased, the liquid in the sample drains from the largest pores first, and then from the smaller pores. A computer connected to the balance monitors the amount of liquid desorbing from the sample at each applied pressure. If the system is reversed after testing the last pressure point, the sample can absorb liquid, which is tracked again with pressure. From this data, the pore size distribution and absorption / desorption hysteresis can be determined.
[0058]
Table 1 shows the pore mode radii (μm) for similar webs made in several ways. The mode is defined as the pore size having the highest volume with the highest occurrence frequency. These values indicate that the pore mode diameter (the pore diameter that provides the largest volume) in the composite formed by the present extrusion method is larger than that produced by other methods.
[0059]
[Table 1]

[0060]
The data in the above tables are derived from the pore size distribution charts shown in FIGS. 6-9 show charts of pore size distribution for representative composites formed by the present extrusion method, foam forming method, air laid method, and wet laid method, respectively. Each complex is 300 g / m²Of the target basis weight. In these figures, the pore mode diameter for absorption is shown. Although the pore mode diameter in desorption is not marked, it can be determined in the same manner as in the case of absorption.
[0061]
Low values for capillary desorption pressure (CDP) have been shown to be preferred capture complexes. Capillary desorption pressure (CDP) is defined as the head pressure at which 50% of the liquid in a saturated sample has exited the sample. For fluid capture, 8-40 cmH₂O (typically 8-25 cmH₂Capillary desorption pressure values of O) are advantageous for synthetic foams for trapping fluids (see, for example, US Pat. No. 5,571,849; US Pat. No. 5,550,167; US Pat. No. 5,851,648). For fluid distribution, 12-50 cmH for CDP₂O (typically 20-40 cmH₂A value of O) is desirable for good performance (see US Pat. No. 6,013,589).
[0062]
As noted above, Miller and Tyomkin show that capillary desorption pressure can be determined from a plot of percent saturation versus pressure applied from an automated porosimeter. Absorption (uptake) and desorption (retention) curves over a range of pressures provide an indication of the material's ability to capture and retain liquid. Capture materials for use in absorbent products such as baby diapers must effectively release the liquid back into the diaper core as well as absorb the liquid quickly. The capillary desorption pressure measured by the automatic porosimeter is called the intermediate desorption pressure (MDP). MDP can be used as a measure of a material's ability to function as a capture material. Obviously, any percentage of saturation could be chosen, but for simplicity, the midpoint of the curve was chosen because it was near the inflection point. In addition to the material formed by this method, 14 cmH₂No cellulosic material has been able to achieve MDP values below O. Thus, cellulose-containing materials that exhibit low MDP values result in improved capture performance.
[0063]
In one aspect, the conjugate of the invention comprises about 14 cmH₂It has an MDP value less than O. In another embodiment, the conjugate is about 12 cmH₂It has an MDP value less than O. In another aspect, the complex comprises about 10 cmH₂It has an MDP value less than O.
[0064]
In order to demonstrate the current performance of cellulosic capture materials, an airlaid capture material consisting of Southern pine fibers is discussed. Using a TRI automatic porosimeter, MDP is 44 cmH₂O was determined. This data is shown in FIG. 10 and shows the output of the automatic porosimeter.
[0065]
The use of crosslinked cellulosic fibers in personal care absorbent products, such as infant diapers, has improved the performance of current commercial diapers. Several airlaid pads made from the two crosslinked fibers were tested for MDP. A pad made from citric acid crosslinked fiber (Chemical B) has a 24.2 cmH₂Had an MDP of O. Polyacrylic acid / citric acid crosslinked fiber (Chemical product A) is 14.4 to 15.9 cmH₂Had an MDP of O. Chemical C refers to polyacrylic acid crosslinked fibers.
[0066]
The method of the present invention provides a web having an improved MDP value. For example, an extruded pine fibrous web formed by an Oakes mixer / former without using crosslinking chemistry is 18.5 cmH₂Provide MDP of O (44 cmH in airlaid)₂O). The extruded web formed from fibers cross-linked with a blend of polyacrylic acid and citric acid (pre-crosslinked chemical A) has an MDP value of 10.5 cmH₂O (15.2 cmH in airlaid)₂O). The MDP value of the extruded web (pre-crosslinked chemical B) formed from citric acid crosslinked fibers was 12.0 cmH₂O (24.2 cmH in airlaid)₂O).
[0067]
Extrusion provides improved MDP due to web structure and surface tension effects. Surface tension correlates to differential pressure, as shown in the Laplace equation:
[0068]
Embedded image

[0069]
Where ΔP = differential pressure, σ = surface tension, θ = contact angle, and r = radius.
If the surface tension is reduced due to the presence of the surfactant (as in the foam extrusion method of the present invention), at a constant radius, the differential pressure (effective MDP) must also be reduced. However, most pores collapse when wet unless they have resistance to collapse. Further improvements can be obtained by increasing the bonds in the structure by inter-fiber crosslinking and / or the addition of binders. As bond and fiber resilience increases, the pore radius no longer collapses, again resulting in lower MDP values (by minimizing pressure rise due to collapsed pore radius). The addition of latex increases the value of the contact angle and therefore reduces the cosine. This requires a decrease in MDP at a constant pore radius.
[0070]
The above improvement is graphically illustrated in FIGS. FIG. 11 is a bar graph demonstrating a decrease in intermediate desorption pressure as a function of crosslinking chemistry for the present method. Extruded composites formed from pine fibers, citric acid crosslinked fibers, and in situ citric acid crosslinked fibers (i.e., citric acid treated but uncured fibers are added to the mixing device) each have 18 .5, 12.0 and 9.8 cmH₂It had an MDP value of O. FIG. 12 shows fibers cross-linked with a blend of polyacrylic acid and citric acid (pre-crosslinked chemical A), citric acid cross-linked fibers (pre-crosslinked chemical B), in situ citric acid cross-linked fibers (in situ chemical B). 5 is a graph showing the effect of increasing crosslinker on MDP for extruded composites comprising, and in situ polyacrylic acid crosslinked fibers (in situ chemical C). As the amount of crosslinker increases, the MDP value for composites made from these fibers decreases. The decrease in MDP (12 cmH) is shown by the dashed line compared to the solid line of₂9.8cmH from O₂O) is indicated. Chemical C shows an even greater decrease in MDP.
[0071]
HB Fuller, St. Addition of a latex such as PD8161 from Paul MN (eg, 5% by weight based on the total weight of the conjugate) also reliably affects MDP and improves capture performance. FIG. 13 shows that latex alone and in combination with in situ crosslinking lowers MDP. In addition, from the pre-crosslinking data, the control indicates that the effect of in situ crosslinking (previously 12-9.8 cmH₂O (provided as O). The effect of latex without in situ cross-linking is from 12 to 9.5 cmH in MDP.₂It is a descent to O. The effect of combining in situ cross-linking and latex addition was to increase the MDP from 9.8 to 8.3 cmH.₂Change to O. Higher levels of latex result in lower MDP values. As an example, the MDP of the pre-crosslinked chemical A fiber containing 15% latex is 7.7 cmH₂O. Table 2 gives an overview of the MDP values.
[0072]
[Table 2]

[0073]
The capture rate of the extruded composite formed according to the present invention was determined. Capture rates were determined as described in US Pat. Nos. 5,460,622 and 4,486,167, each of which is incorporated herein by reference. The only change to the procedure is that a 75 mL effluent was used to bring the total weight closer to the full capacity of the diaper and to make the test more stringent.
[0074]
Commercial diapers were purchased (PAMPERS by Procter & Gamble) and the fourth effluent capture rate was tested according to the indicated procedure. The commercial diaper exhibited a capture rate of 0.44 mL / sec with a fourth 75 mL spout. This performance represents the current state of the art. In situ crosslinked capture patches were made at both 4 and 6% levels using both chemicals B (citric acid crosslinked fibers) and C (polyacrylic acid crosslinked fibers). These patches were then inserted into commercial diapers (controlling PAMPERS of the same size and type). Insertion was accomplished as follows. The cover stock was carefully cut off at one end of the diaper to expose the commercial acquisition patch and carrier tissue. These materials were carefully removed without disturbing the diaper core. A representative extruded patch of the same size as the commercial patch was inserted into the diaper. The cover material was returned to its original position and sealed.
[0075]
At a crosslinker level of 4%, the capture rate of the fourth effluent was 0.48 to 1.13 mL / s, depending on the type of chemical. As a second control, precrosslinked fibers were also tested. At the 6% level, the rate was 0.36-1.60 mL / s depending on basis weight and chemical type. These data demonstrate a significant improvement in the rate of capture of the extruded composite over commercial diaper controls and capture materials made from precrosslinked fibers. This improvement is particularly important because the smaller the crotch area of the diaper, the less area available for capture. Table 3 summarizes the capture performance data.
[0076]
[Table 3]

[0077]
The extruded composites of the present invention also exhibit advantageous tensile strength. Since many of the test samples are very weak (eg, airlaid fluff pads), the tensile strength was determined by the horizontal tensile method. The method uses a horizontal jig fixed to the lower crosshead of a constant speed tensile tester such as that provided by Instron. A 10 cm × 10 cm sample is clamped in the jig. Return the load cell to zero for each sample. Thereafter, the sample is pulled by a tensile tester. Measure the elongation and breaking load for each sample on the tester.
[0078]
In situ crosslinked samples were produced at three levels using two different chemicals. The tensile strength data from these samples are shown in the following tables and charts. It is clear that as the level of in situ chemicals increases, the tensile strength increases. This increase is indicative of an increase in interfiber bonding. All samples (except those indicated as precrosslinking) were prepared in the same manner, with only the chemical type and level varied as shown in Table 4.
[0079]
[Table 4]

[0080]
Depending on the crosslinking chemistry applied, the tensile strength increased 10- to 20-fold when using in situ crosslinking. FIG. 14 shows the effect of in situ crosslinking on the tensile strength of the extruded composite.
[0081]
Latex can be used to increase the strength of the extruded composite structure and web. The effect of latex and fiber blend on the strength of a representative extruded composite is shown in FIG. The effect of latex and crosslinking chemistry on the strength of a representative extruded composite is shown in FIG. Referring to FIGS. 15 and 16, the strength of the Chemical B sample containing 6% of the chemical is 34 g / in (BW = 205 g / m).²). The pre-crosslinked chemical B complex with 5% latex is 94 g / in (BW = 157 g / m2).²). The complex containing 5% latex and 6% in situ crosslinks was 1065 g / in (208 g / m²), Which is more than 10 times stronger than either treatment alone.
[0082]
In another aspect, the present invention provides an absorbent material comprising a crosslinked cellulosic fiber product. The product can be combined with one or more other layers to provide a structure that can be incorporated into absorbent articles, such as baby diapers, adult incontinence products, and feminine care products.
[0083]
Example
Example 1
Representative twin screw extruder and method, and representative products and their performance characteristics
In this example, a typical twin screw extruder, a method of forming a product using the device, a representative product formed by the method using the device, and performance characteristics of the representative product will be described.
[0084]
Laboratory tests have demonstrated that extruding a fibrous web in foam media offers the potential for improved performance. A pilot test was performed in consideration of laboratory success. It is described below that a twin screw extruder manufactured by Krupp, Werner, and Pfleiderer (KW & P) is used in the process of the invention to provide a representative product of the invention.
[0085]
In the test, a continuous web of material was tested for a wide range of basis weights (about²) Extruded. Bicomponent fibers (CELBOND T105) were fed into the system to produce more secure samples. Surfactant concentrations were tested at two levels: 1% and 0.5% of total mass. At both levels, the appropriate forms have arisen. Foam quality was similar to the quality from the Oakes laboratory facility (plate mixer / former; air content 94-99%; foam density 10-60 g / L). The fiber openings did not damage the fiber in terms of fiber length. Product quality and performance were not optimized, and are not as satisfactory as samples prepared with Oakes systems. Extrusion equipment is small and, depending on the diameter of the screw, can be installed on concrete slabs without scaffolds and piles. The small size and simplicity of the process means lower capital and engineering costs compared to the typical paper industry. Advantageously, the SAP can be added directly to the equipment in dry form.
[0086]
Equipment.A 9 barrel type ZSK 58 mm twin screw extruder (KW & P) was used for the test. A schematic diagram of the extruder equipment is shown in FIG. The raw materials were supplied to the extruder using four Acrison single screw feeders. A total of five different screw designs were used to disperse the fibers to make the foam. The different screw designs are described in the next section.
[0087]
The device shown in FIG. 4 shows some notable features. The first feature is the relative size of the equipment. The extruder was housed in an area of about 25 'x 25'. The extruder was placed on the main floor and the feeder was placed on the second floor. Each barrel is less than one foot long. The commercial design for absorbent products does not require a 9-barrel system (note: the first and last barrels from the left are not required). The third barrel can also be optional.
[0088]
Another important point is that it is simple. This system is basically operated in mass in and mass out. The supply system is a simple one utilizing a known technique, namely a loss-weight feeder. This is emphasized when absorbent material in dry form (eg, superabsorbent polymer, SAP) can be added to the wet fiber stream directly through the side feeder without clogging. This system allows easy processing of fibers and SAPs and has achieved the first two test objectives. With SR1001 (a lightly crosslinked polyacrylate available from Stockhausen), the addition of SAP in dry form at the end of the process minimized SAP swelling. SXM-77, another polyacrylate from Stockhausen, swells and affects laboratory performance when fed dry with less than 5 seconds retention time in the extruder.
[0089]
Experimental details.The extruder was tested in a series of experiments. Table 7 summarizes the points of these experiments. Without fibers, there was no problem with foaming and the resulting foam had an air content of 96-97% (PCT / US99 / 26560, Reticulated Absorbent Composite and PCT / US99 / 05997, Methods For Forming A Fused Composite). , Respectively, compared to a theoretical optimum of 67% for the foam forming method (foam raid), each of which is specifically incorporated herein by reference in its entirety). Foam density was 29-30 g / L, compared to typically 350 g / L for the foam laid method. After the foam was completed, the fiber supply was started. Three different screw configurations were tried to obtain fiber dispersion. The first configuration had a significant number of high shear elements. These elements introduced shear stress, but restricted material flow (eg, increased retention time). This design generated some heat and the fibers were not efficiently dispersed. The second design was a low shear design without restrictions. This design allowed a screw speed of 1000 rpm without significant temperature rise. As a result, the dispersibility of the fiber was improved. Fiber knots were still found in the web. However, the dispersibility was better than the first screw design and better than the dispersibility achieved in this test, identified below as 1051-XNP.
[0090]
In a third design, a small number of high shear elements were reinserted to improve fibrosis. These few shear elements raised the temperature.
The fourth screw design (similar to the second design but with more kneading blocks) can have up to 225 lb. Supply of OD fiber / hr (2.5 t / day) was possible. Processing only the fibers, this screw design appeared to shatter the fiber chunks. The feed rate was reduced to 0.5 t / day so that the fiber dispersion could be seen more easily. After that, a slot die is attached and about 500g / m²And a web of 0.05 g / cc (26.6% "couch" solids).
[0091]
After taking the sample and tester data, SR1001 was added at a level of about 50%. The side feeder worked perfectly and there was no problem with SAP supply. This complex (BW about 1100 g / m², A density of about 0.11 g / cc) was extruded through the die head and a sample was taken (39% "couches" solids). The capacity value was 16 g / g. When SXM-77 was tried, all free water was removed, resulting in dried chunks of SAP and fiber. This is similar to the result (1051-XNP) seen in the previous test.
[0092]
Since the web could be manufactured on the die, samples containing SAP were manufactured at lower basis weights and compared to previously made and tested foam laid materials. To improve the integrity, bicomponent fiber CELBOND T105 was also added. As an alternative to bicomponent fibers, a wet strength agent KYMENE can be added to the system. A low basis weight material was obtained. Surfactant levels were reduced from 1% of total mass to 0.5% with no adverse effects. Experimentally, the availability of water is a limiting factor compared to the total amount of surfactant.
[0093]
Additional low basis weight material with and without CELBOND T105 was formed in a fifth screw design using several trilobal elements. The material appeared to have less knots. A test of the throughput was carried out and this screw provided a fiber feed rate of 700 lb. / Hr (as is) or about 1170 lb. total weight (assuming 40% solids and 50% SAP). / Hr.
[0094]
Fiber quality / dispersion results: screw design and throughput.Material samples from several screw shaft designs were tested for knot percentage and fiber length. Typically, these two tests are used in a fluff lab to evaluate the efficiency of a hammer mill. Using these tools, different screw designs were evaluated. Table 5 shows that based on the ultrasonic fractionation data, design 5 appears to be slightly better than design 4. In both designs, the fibers are not cut, as evidenced by fiber length data.
[0095]
[Table 5]

[0096]
Other data indicated that Design 2 was the least effective, with subsequent designs having improved fiber dispersibility.
[0097]
Solid content.The percentage of solids was measured at 25-65% but did not follow the predicted value based on mass balance (17-47%). All measurements except one show solids higher than the theoretical value. This indicates that the sample may not have been completely dry.
[0098]
Capacity results.Approximately 11-17 g / g of the capacity value under load was measured on samples containing 37-46% SAP content. Considering the high basis weight and the increased density due to the constant size of the die slot, the capacity value was appropriate.
[0099]
Surfactant level.Three levels of surfactant (Incronam 30 available from Croda) were used at 5.0, 7.5 and 10.0 (as is) lb. / Hr. Surface tension values from the water extract indicate that the surfactant was present on the surface and was easily removed. For the three surfactant levels (5.0, 7.5 and 10.0 lb./hr), the surface tension values were 40.7, 40.4, and 35.5 dyn / cm. Because of the successful foaming at all levels and the lack of a "cleaning" step in this process, the use of lower levels of surfactant can reduce the level of residual surfactant. Lower levels of surfactants can enhance product capture performance. Typical extract surface tension values on foam laid webs using Incronam 30 or Dehyton K were 40-43 dyn / cm.
[0100]
Capture performance / pore size distribution / central desorption pressure.Capture performance was measured by a new Market Pulp Standard of the Edana test method. The capture time for the Procter & Gamble PAMPERS control is 27 seconds, 60 seconds, and 85 seconds for the first to third 100 mL doses, respectively. Capture is in seconds for each of the first to third 100 mL doses. Capture performance of a representative sample indicated the presence of excess surfactant. Capture time for the first dose was 30-70 seconds for all samples. Generally, the second and third doses took more than 300 seconds (5 minutes).
[0101]
The pore size distribution and central desorption pressure for representative products are shown in the figure.
Pore size distribution (PSD) and median desorption pressure (MDP) provide no additional insight into trapping performance other than surfactant levels. Figures 17-20 above show the PSD and MDP for the two low basis weight samples produced during this test. Compared to FIGS. 21 and 22, the 1051-XNP sample is very similar to the sample manufactured at Oakes during the laboratory test described in Example 2. The MDP data shows no differences between the two tests. The MDP values for tests 17 and 19 were each 17.2 cmH₂O and 16.2 cmH₂O and the value for 100% pine in the Oakes method is 16.5 cmH₂O.
[0102]
Comparison with similar foam laid materials.Table 6 below shows a comparison between the material according to the invention and a material made with foam laid. Notable differences are the density and the effect obtained on vertical wicking. Despite the difference in wood fluff pulp (Southern pine) content, the capacity values are similar. Without optimization, the 1051-XNP material can be made with foam laid and compared to the material.
[0103]
[Table 6]

[0104]
Extrusion amount.The throughput test is about 450 OD lb. It shows that a total mass of / hr (5 t / day) can be processed through a 58 mm tester.
[0105]
[Table 7]

[0106]
[Table 8]

[0107]
[Table 9]

[0108]
[Table 10]

[0109]
[Table 11]

[0110]
Example 2
Representative plate mixer extrusion equipment and methods, and representative products and their performance characteristics
In this example, a typical plate mixer extruder, a method of forming a product using the device, a representative product formed by the method using the device, and performance characteristics of the representative product will be described.
[0111]
The plate mixer / extrusion method is one of the alternatives to conventional forming techniques used to make composite core materials. In this example, an extrudable foam is made using an Oakes Mixer / Former (Oakes Continuous Mixing Head, ET Oakes Corporation, Hauppauge, NY), and the web is extruded from the foam by simple die head extrusion. Produced. Three fiber furnishes were used: Southern pine pulp fiber (C pine); citrated cellulosic fiber (XLA); and a 50:50 blend of these two fibers. H. B. PD8161 latex from Fuller Company was used as a binding and resilience aid at levels of 5, 10, and 15% by weight.
[0112]
The term "EXPRO" as used herein refers to the extrusion process of the present invention and the product formed by that process.
The results demonstrate the following: The apparatus and method allows the pine and treated fibers to be a lower density web than other current methods. In the case of extruded webs, the average pore radius for these products is larger than conventionally formed webs. The product has improved capture performance compared to current materials. The product exhibits a much lower central desorption pressure value compared to current materials formed by conventional methods. The extrusion process has very low raw material or product waste.
[0113]
General.In this example, samples of different fiber furnish and latex content were formed using C pine, XLA, and PD8161 latex. Table 8 shows the description of the sample.
[0114]
[Table 12]

[0115]
Oakes equipment.These samples were manufactured using the experimental apparatus shown in FIGS. The specific specifications of the tester and the experiment are shown below.
In general, the desired pulp fibers were fed into the mixer / former via a piston feeder at 30% consistency with 2% by weight of Polyox (polyethylene oxide with a molecular weight of 4 million) as slip aid. Other additives, such as air, surfactant and latex, were added via a piston feeder to the inlet located on the Oakes apparatus. The current system is a batch-type operation that operates on a large-volume and large-volume basis, and has substantially no waste. Target basis weight of sample (300 g / m²) Was controlled by the feed rate of the pulp and the speed of the conveyor.
[0116]
Pore size distribution.The pore size distribution is measured with a TRI automatic porosimeter. Here we consider some examples. The three samples selected here represent the differences found in the three furnishes: pine (sample 2, FIG. 23), XLA (sample 6, FIG. 24), and a 50:50 blend (sample 10, FIG. 25).
[0117]
In FIG. 24, it can be seen that the curves have shifted to a larger average radius in each curve. This suggests a change from pine to crosslinked fibers. FIG. 25, which is a blend sample, shows a mode value intermediate between the mode values found in FIGS. The larger average radius is due to the stiffer cross-linked fibers forming a lower density web, which is also due in part to its structural support. The area under the curve indicates the total volume of the sample, and thus the volume of the sample. This is due to the fact that the PSD curve is a derivative of the cumulative volume chart obtained from the automatic porosimeter. Thus, fiber furnishes can be evaluated based on their effect on pore size, which in turn affects the volume or volume of the structure.
[0118]
However, with respect to capture performance, it is best to compare methods based solely on pore mode diameter. Table 1 shows these values. These data indicate that the extrusion method of the present invention provides the largest pore size of the four methods tested.
[0119]
Capture performance.Capture performance is typically based on the results of a multiple dose test. The result of the fourth most severe jet is often used as an indicator of performance. The results of the fourth jet flow for the samples in this test are shown in the summary data table in Table 9.
[0120]
In general, the XLA results were the most powerful. FIG. 26 shows these results. These data indicate that XLA alone has an improved capture rate compared to current diaper controls. In the presence of latex, the results are further improved compared to the control and compared to the performance of 1012-XNP. It is not only the result of the fourth jet that has improved. All spouts (1-4 times) show improved capture rates relative to controls.
[0121]
Central desorption pressure.It is important that the capture material capture the fluid quickly, but the material must be able to release it immediately into the absorbent core. This ability to discharge fluid is determined by the central desorption pressure. This is the pressure at which 50% of the captured fluid has been removed from the sample during testing on the automated porosimeter.
[0122]
The composite formed from the citric acid cross-linked fibers is about 20-22 cmH₂It has an MDP of O. Composites formed from fibers such as XLA are 16-19 cmH₂Only the MDP value of O could be achieved. FIG. 29 shows an example in which XLA is used to manufacture a 1012-XNP sample. Here, MDP is 17 cmH₂O.
[0123]
Using the extrusion method, the MDP value for the composite formed from only the citric acid crosslinked fibers was 10.5 cmH₂O (see FIG. 28). When latex is added, MDP becomes 7.7 cmH₂O (see FIG. 27). Based on the range of MDP in the fiber furnish shown in Table 9, using these fibers, latex, and extrusion methods results in an MDP of 8-17 cmH₂It seems possible to control to O.
[0124]
These results indicate that different structures are formed by different methods in terms of density and pore size distribution. These structural differences as well as surface properties also affect central desorption pressure.
[0125]
Figures 29, 30, and 31 show the MDP of a complex formed by three different methods. FIG. 31 shows an airlaid pad made from two batches of XLA fibers. Here, they are identified as 46-01 and 46-02. These pads are 0.06 g / cm³But no surfactant to interfere with MDP (14-16 cmH₂O). As mentioned earlier, FIG. 29 is a foam-forming composite. Despite the lower density, the MDP is slightly higher than the airlaid sample. FIG. 30 shows the MDP for the wet laid composite. This material has an MDP of 18.5 and a similar density to the foamed sample. As seen in FIGS. 27 and 28, the samples formed by the extrusion method show much lower MDP values.
[0126]
Tensile strength.The change in tensile strength follows the expected trend: (1) tensile strength increases as pine content increases; (2) tensile strength decreases as crosslinked fiber content increases; And (3) as the latex content increases, the tensile strength increases. These samples were measured on an Instron using a horizontal jig.
[0127]
The results can be summarized as follows. When pine or crosslinked fibers are used, the density of the extruded web is lower than other absorbent web forming methods. Extruded webs have a larger average pore radius and provide improved capture performance. In the present extrusion method, webs having improved MDP can be produced using pine and crosslinked fibers. This indicates that this material will release liquid into the storage core more easily. In the present extrusion method, latex and other additives can be added to the web without spraying and without waste.
The effect of latex and fiber blend on the strength of the extruded composite is shown in FIG.
[0128]
[Table 13]

[0129]
Example 3
Performance characteristics of typical products
Example 1 This example describes the performance characteristics of a representative product formed in accordance with the present invention.
The medium uptake pressure (MUP), the medium desorption pressure (MDP), and the thickness of a representative product of the present invention were determined and compared to a conventional airlaid web. Table 10 shows the standardized results. In Table 10, XLA refers to an airlaid web of cellulosic fibers crosslinked with citric acid; XLB refers to an airlaid web of cellulosic fibers crosslinked with a combination of citric acid and polyacrylic fibers; EXPRO-D refers to a composite of cellulosic fibers cross-linked with citric acid; EXPRO-E refers to a product of the present invention formed from cellulosic fibers treated with citric acid; -F refers to the product of the present invention formed from a cellulosic fiber treated with a combination of citric acid and polyacrylic acid and latex. All samples were weighed at 300 g / m²The weight was tested.
[0130]
[Table 14]

[0131]
The capture rate, and rewet, and tensile strength of a representative product of the present invention were determined and compared to a conventional airlaid web. Table 11 shows the standardized results. In Table 11, XLA refers to an airlaid web of cellulosic fibers crosslinked with citric acid; XLB refers to an airlaid web of cellulosic fibers crosslinked with a combination of citric acid and polyacrylic fibers; EXPRO-D refers to a foam-forming composite of cellulosic fibers cross-linked with citric acid; and EXPRO-E refers to a product of the present invention formed from cellulosic fibers treated with citric acid. All samples were weighed at 300 g / m²The weight was tested.
[0132]
[Table 15]

[0133]
While the preferred embodiments of the invention have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.
Aspects of the invention in which an exclusive property or privilege is claimed are defined above.
[Brief description of the drawings]
[0134]
FIG. 1 is a graph showing liquid drainage from a foam as a function of time for foams having densities of 137 g / L, 95 g / L, 66 g / L, and 41 g / L, respectively.
FIG. 2 is a flowchart illustrating an exemplary method of making an extruded composite according to the present invention.
FIG. 3-A is an image of an exemplary mixing device useful in the method of the present invention.
FIG. 3-B is an image of a stator of the mixing device shown in FIG. 3-A.
FIG. 3-C is an image of the mixing device of FIG. 3-A with the rotor removed.
FIG. 4 is a schematic illustration of an exemplary extrusion apparatus useful in the present invention, showing locations where various materials can be added.
FIG. 5: (a) Southern pine fibers, and (b) fibers crosslinked with a blend of citric acid and polyacrylic acid by four methods: foam laid, air laid, wet laid, and the extrusion method of the present invention. 5 is a graph comparing the densities of the fiber composites prepared from the above.
FIG. 6 is a graph showing pore size distribution for a representative extruded composite formed according to the present invention comprising cellulose fibers cross-linked with a blend of polyacrylic acid and citric acid (13% by weight cross-linked based on fiber). is there.
FIG. 7 is a graph showing pore size distribution for a representative foam-laid composite comprising cellulose fibers cross-linked with a blend of polyacrylic acid and citric acid.
FIG. 8 is a graph showing pore size distribution for a representative airlaid composite comprising cellulose fibers cross-linked with a blend of polyacrylic acid and citric acid.
FIG. 9 is a graph showing pore size distribution for a representative wet laid composite comprising cellulose fibers cross-linked with a blend of polyacrylic acid and citric acid.
FIG. 10 is a graph showing absorption and desorption curves obtained using an automated porosimeter for an airlaid complex containing Southern pine fibers.
FIG. 11 is a graph comparing the median desorption pressure (MDP) of a representative extruded composite formed in accordance with the present invention (“pine fiber” refers to a composite containing Southern pine fiber; “pre-crosslinking chemistry”). "Product B composite" refers to a composite comprising citric acid cross-linked fibers; "in situ chemical B composite" is a composite comprising cellulose fibers wherein the cellulose fibers have been treated with citric acid. And cured in the composite).
FIG. 12 is a graph showing the effect of cross-linking chemistry on intermediate desorption pressure for an exemplary extruded composite formed in accordance with the present invention ("Pre-cross-linking chemistry A" is cross-linked with a blend of polyacrylic acid and citric acid). "Pre-crosslinked chemical B" refers to a composite comprising citric acid crosslinked fibers; "in situ chemical B" refers to a composite comprising cellulose fibers. Wherein the cellulose fibers are treated with citric acid and cured in the composite; "in situ chemical C" is a composite comprising cellulose fibers, wherein the cellulose fibers are: Treated with polyacrylic acid and cured in the composite).
FIG. 13 is a graph showing the effect of latex content on intermediate desorption pressure as a function of cross-linking chemistry for a representative extruded composite formed in accordance with the present invention ("Pre-cross-linking chemistry B" shows citrate cross-linking; "Pre-crosslinked chemical B + 5% latex" refers to a composite comprising citrate crosslinked fiber and 5% by weight latex; "in situ chemical B" refers to the composite A composite comprising fibers treated with citric acid and cured in the composite; "in situ chemical B + 5% latex" is a composite, treated with citric acid and A composite comprising fibers cured in the composite and 5% by weight of latex).
FIG. 14 is a graph showing the effect of in situ cross-linking on the tensile strength of a representative extruded composite comprising citric acid cross-linked fibers and polyacrylic acid cross-linked fibers and formed according to the present invention (“2% in situ”). "" Refers to a composite comprising fibers treated with 2% by weight of crosslinking agent, "6% in situ" refers to a composite comprising fibers treated with 6% by weight of crosslinking agent, "6% pre-cross-linked" refers to a composite comprising fibers cross-linked with 6% by weight cross-linking agent).
FIG. 15 is a graph showing the effect of latex and fiber type on the strength of a representative composite formed in accordance with the present invention (“pine” refers to a composite containing Southern pine fibers and “blend” , A composite comprising a 50/50 blend of Southern pine fibers and fibers cross-linked with a blend of polyacrylic acid and citric acid, wherein "Chemical A" is cross-linked with a blend of polyacrylic acid and citric acid. A composite comprising the treated fibers).
FIG. 16 is a graph showing the effect of chemical in situ cross-linking and latex on the tensile strength of a representative extruded composite formed in accordance with the present invention (“Chem B” indicates a composite comprising citric acid cross-linked fibers). "Chem C" refers to a composite comprising polyacrylic acid crosslinked fibers).
FIG. 17 is a graph showing the pore size distribution of the foam-laid composite.
FIG. 18 is a graph showing the intermediate desorption pressure for the composite of FIG.
FIG. 19 is a graph showing the pore size distribution for a foamlaid composite.
FIG. 20 is a graph showing the intermediate desorption pressure for the composite of FIG.
FIG. 21 is a graph showing the pore size distribution for a representative composite (composite containing Southern pine fibers) formed according to the present invention.
FIG. 22 is a graph showing the intermediate desorption pressure for the composite of FIG.
FIG. 23 is a graph showing pore size distribution for a representative extruded composite formed according to the present invention (composite comprising Southern pine fiber and 5% latex).
FIG. 24 is a graph showing the pore size distribution for a representative extruded composite of the present invention (a composite comprising fibers cross-linked with a blend of citric acid and polyacrylic acid and 5% latex).
FIG. 25: Pore size for a representative extruded composite of the present invention (50:50 blend of Southern pine fiber and fiber cross-linked with a blend of citric and polyacrylic acid, and a composite containing 5% latex). It is a graph which shows distribution.
FIG. 26 is a graph showing the capture rate of a fourth effluent of a representative extruded composite formed in accordance with the present invention, as compared to a control composite.
FIG. 27 is a graph showing intermediate desorption pressures for a representative extruded composite formed according to the present invention (a composite comprising a blend of citric acid and polyacrylic acid crosslinked fibers and 15% latex).
FIG. 28 is a graph showing the intermediate desorption pressure for a representative extruded composite formed according to the present invention (a composite comprising a blend of citric acid and polyacrylic acid crosslinked fibers).
FIG. 29 is a graph showing the intermediate desorption pressure for a foamlaid composite.
FIG. 30 is a graph showing the intermediate desorption pressure for a wet laid composite.
FIG. 31 is a graph showing the intermediate desorption pressure for the airlaid complex.

Claims (41)

A method for producing a cellulosic fiber composite,
(A) mixing the cellulosic fiber with a surfactant in a mixing device;
(B) forming a foam comprising cellulosic fibers, a surfactant, and air in the device;
(C) extruding the foam from the device to provide a cellulosic fiber composite;
A method comprising: The method of claim 1, wherein the cellulosic fibers mixed with a surfactant have a solids content of greater than about 15%. The method of claim 1, wherein the cellulosic fibers mixed with the surfactant have a solids content of less than about 50%. The method of claim 1, wherein the mixing device comprises a plate mixer extruder. The method according to claim 1, wherein the mixing device comprises a twin screw extruder. The method of claim 1, wherein the foam has an air content greater than about 75% by volume based on the volume of the foam. The method of claim 1, wherein the foam has an air content greater than about 90% by volume based on the volume of the foam. The method of claim 1, wherein the foam has an air content greater than about 98% by volume based on the volume of the foam. The method of claim 1, wherein the foam has a density greater than about 20 g / L. The method of claim 1, wherein the foam has a density of less than about 100 g / L. 2. The method of claim 1, wherein the surfactant is present in an amount from about 0.01 to about 5% by weight based on the weight of the conjugate. The method of claim 1, further comprising drying the extruded cellulosic fiber composite. The method of claim 1, wherein the foam further comprises a crosslinking agent. 14. The method of claim 13, further comprising heating the extruded composite to provide a bonded composite. The method of claim 1, wherein the foam further comprises a latex. 16. The method of claim 15, further comprising heating the extruded composite to provide a bonded composite. The method of claim 1, wherein the foam further comprises a thermoplastic fiber. 18. The method of claim 17, further comprising heating the extruded composite to provide a bonded composite. The method of claim 1, wherein the cellulosic fibers comprise cellulosic fibers treated with a crosslinking agent. 20. The method of claim 19, further comprising heating the extruded composite to provide a bonded composite. The method of claim 1, wherein the foam further comprises a wet strength agent. 22. The method of claim 21, further comprising heating the extruded composite to provide a bonded composite. 2. The method of claim 1, wherein the cellulosic fibers comprise cross-linked cellulosic fibers. The method of claim 1, wherein the foam further comprises an absorbent material. A cellulosic fiber composite comprising a cross-linking cellulosic fibers, the complex has an intermediate desorption pressure of less than about 14cmH 2 _O, the cellulose-based fiber composites. About 12cmH an intermediate desorption pressure of less than ₂ O, composite according to claim 25. About 10cmH an intermediate desorption pressure of less than ₂ O, composite according to claim 25. Having a density of less than about 0.10 g / cm ^3, the composite body according to claim 25. Having a density of greater than about 0.02 g / cm ^3, the composite body according to claim 25. 26. The conjugate of claim 25, having a fourth squirt liquid capture rate of greater than about 0.4 mL / sec. 26. The composite of claim 25, wherein the crosslinked cellulosic fibers comprise polyacrylic acid crosslinked fibers. 26. The composite of claim 25, wherein the cross-linked cellulosic fibers comprise cellulosic fibers cross-linked with a blend of citric acid and polyacrylic acid. 26. The composite of claim 25, wherein the crosslinked cellulosic fibers comprise cellulosic fibers pretreated with a crosslinking agent and cured during formation of the composite. 26. The composite of claim 25, wherein the crosslinked cellulosic fibers comprise cellulosic fibers that have been treated with a crosslinking agent during composite formation. 26. The composite of claim 25, wherein the cross-linked cellulosic fibers comprise intra- and inter-fiber cross-linked cellulosic fibers. 26. The composite of claim 25, further comprising a thermoplastic fiber. 37. The composite of claim 36, wherein the thermoplastic fibers comprise bicomponent fibers. 26. The conjugate of claim 25, further comprising a latex. 26. The composite of claim 25, further comprising a wet strength agent. 26. The composite of claim 25, further comprising an absorbent material. A foam comprising cellulosic fibers, a surfactant, and air, wherein the foam has an air content greater than about 75% by volume.

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