JP4248007B2

JP4248007B2 - Steel cord for tire reinforcement

Info

Publication number: JP4248007B2
Application number: JP09038799A
Authority: JP
Inventors: 隆則小林
Original assignee: 金井宏彰
Priority date: 1999-03-31
Filing date: 1999-03-31
Publication date: 2009-04-02
Anticipated expiration: 2019-03-31
Also published as: JP2000280708A

Description

【０００１】
【発明の属する技術分野】
本発明は、自動車用タイヤの補強材として使用されるスチ−ルコ−ドに関し、特に４本〜１３本の素線を撚り合わせ、そのコ−ドの横断面が略楕円形状のスチ−ルコ−ドに関するものである。
【０００２】
【従来の技術】
一般にこの種のスチ−ルコ−ドは、多本数が平行に引揃えられた状態でゴム材に被覆されて、自動車用タイヤの補強材として使用されている。そして、スチ−ルコ−ドに要求される条件としては、機械的強度が優れていることは勿論のこと、ゴム材との化学的、物理的な接着が良好であること、およびスチ−ルコ−ド内部へのゴム浸入性が良好であること等があげられる。すなわち、スチ−ルコ−ドがタイヤ補強材としての役割を充分に果たすためにゴム材との完全な複合体となることが必要である。
【０００３】
とりわけ、トラック、バスなどの高重量の車両に用いられるタイヤにおいては、高強度でかつ柔軟性をもつスチ−ルコ−ドが求められており、その一つとして従来より１＋ｎ構成のスチ−ルコ−ドが使用されてきた。
【０００４】
しかし、従来の１＋ｎ構成のスチ−ルコ−ドの横断面構造は図６に示すようにクロ−ズ撚り構造で、かつ各素線９が相互に完全に密着して隙間がないため、空洞部Ｓがコ−ド内部に散在している。従って、このスチ−ルコ−ド８を２枚のゴムシ−トに挟んで複合体シ−トを形成した場合、ゴム材が上記空洞部Ｓまで浸入せず、ゴム材との完全な複合体を形成できない。
【０００５】
それゆえ、このゴムシ−トをタイヤに用いた場合、釘などの異物によりゴム被覆が一部分でも破れると、外部より浸入してきた水分が上記空洞部Ｓ内に伝播し、スチ−ルコ−ドが全面にわたり酸化を起こす。こうなると、ゴムとスチ−ルコ−ドの接着力が弱くなり、両者が剥離してしまい、スチ−ルコ−ドの補強材としての効果が非常に弱くなってしまう。
【０００６】
この問題を解決するため、図７に示すように芯素線１１にくせ付けを行ったスチ−ルコ−ド１０が提案されている。
【０００７】
【発明が解決しようとする課題】
図７のように芯素線１１にスパイラル状のくせ付けを行った、１＋ｎ構成のスチ−ルコ−ド１０は、断面形状が略真円の形状をしているため、スチ−ルコ−ドの剛性がどの方向に対しても同じである。従って、タイヤのコ−ナ−リング性能を上げるために剛性を高くすると、乗り心地まで悪くなるという問題がある。さらに、図７のスチ−ルコ−ドは、図６のようなクロ−ズ撚りのコ−ドに比べてコ−ド径が太くなり、カレンダ−（ゴム被覆工程）後のゴムシ−トが厚くなってしまい、加えてコ−ド径が太いためにゴムシ−トに所定本数のスチ−ルコ−ドを埋め込むことができず、シ−トの強力が弱くなる。従って、このゴムシ−トをタイヤに用いる場合、シ−トの重ね枚数を増やす必要が生じ、結果としてタイヤの重量が増加するという問題がある。さらにスチ−ルコ−ドの製造上の点からも図８のようにきれいに側素線１２を空間に配置するようなスチ−ルコ−ドは無理で撚りが非常に不安定となる。
【０００８】
本発明は、前記種々の従来のスチ−ルコ−ドの様々な問題点を解決するためになされたものであり、その課題は、補強材としてタイヤに用いた場合に、スチ−ルコ−ド内部へのゴム浸入性がよく、タイヤ回転方向の剛性を低くしながらタイヤ回転方向と直交する方向の剛性を高めることができ、圧縮および曲げに対する疲労性が良好で、しかも製造及び取扱作業性の優れたスチ−ルコ−ドを提供することにある。
【０００９】
【課題を解決するための手段】
上記目的を達成するために、本発明のタイヤ補強用スチ−ルコ−ドは、４本〜１３本の素線を、１本をコア素線、残りの素線を側素線とし、同一方向に撚りピッチＰで一度に撚り合わせたスチ−ルコ−ドであって、その横断面が長手方向に略同一向きで略楕円形状（長径Ｗ、短径Ｔ）であるタイヤ補強用スチ−ルコ−ドにおいて、側素線径ｄ₁ が０．１５〜０．２２ｍｍ、側素線径ｄ₂ が１．１ｄ₁ 〜２．０ｄ₁ ｍｍ（但し、ｄ₂ ≧０．２２ｍｍ）あり、かつコア素線が下記式（１）（２）を満足するくせピッチＰ₁ とコ−ド短径方向のくせ外径Ｄの略スパイラル状のくせを有し、また前記コア素線が前記略楕円の長径軸を挟む両側に位置する側素線の間に略ピッチＰ₁ 間隔で出現し、しかも前記略楕円形状の偏平率（Ｔ／Ｗの百分比）が３８％〜６０％であることを特徴とする。
Ｐ₁ ＝０．１Ｐ〜０．５Ｐ・・（１）
Ｔ−Ｄ＝０．０３〜０．３０・・（２）
Ｐ₁ ：くせピッチ（ｍｍ）
Ｐ：撚りピッチ（ｍｍ）
Ｔ：コ−ド短径（ｍｍ）
Ｄ：コ−ド短径方向のコア素線のくせ外径（ｍｍ）
【００１０】
本発明のスチ−ルコ−ドは、横断面が長手方向に略同一向きで偏平率の大きい略楕円形状であるため、スチ−ルコ−ドの短径方向と長径方向で大きく剛性が異なる。また、カレンダ−後のスチ−ルコ−ドは、ゴムシ−トの中において長径部を左右にして長手方向に略平行に並ぶため、曲げ剛性が上下方向に低く左右方向に高い。従って、このゴムシ−トを用いてタイヤとなしたとき、タイヤの回転方向の剛性は低いので乗り心地がよく、タイヤ回転方向と直交する方向の剛性は高いのでコ−ナ−リング性能を高めることが出来る。
【００１１】
また、本発明のスチ−ルコ−ドは横断面が略楕円形状をしているので、カレンダ−時はほとんど全てのスチ−ルコ−ドが長径部を左右にして長手方向に略平行に並ぶため、ゴムシ−ト厚はスチ−ルコ−ド短径部分に対応する厚みとなり、シ−トを薄くできる。そして、スチ−ルコ−ドの挿入本数を少なくできる。その結果タイヤの軽量化が進み、タイヤのコストダウン、自動車の燃費の改善が可能となった。さらに撚りの安定性の点においても、図７に示すようなスチ−ルコ−ドと比較して、撚りが安定しておりゴムシ−トに埋設した後でもほとんど同じ形状であり、製造上、取り扱い作業上も優れている。
【００１２】
ところで、本発明のスチ−ルコ−ドにおいて、側素線径ｄ₁ を０．１５〜０．２２ｍｍ、コア素線径ｄ₂ を１．１ｄ₁ 〜２．０ｄ₁ ｍｍ（但し、ｄ₂ ≧０．２２ｍｍ）としたのは、側素線径ｄ₁ が０．１５ｍｍ未満では、充分な強力が得られず、０．２２ｍｍを超えると、スチ−ルコ−ドの柔軟性が低下して疲労値が低下することによる。また、コア素線径ｄ₂ が側素線径ｄ₁ の１．１〜２．０倍で、かつ０．２２ｍｍ以上としたのは、０．２２ｍｍ未満では、スチ−ルコ−ドの低荷重伸びが大きくなり、以下の理由から、ゴム加硫後に偏平率が低下して本発明の効果が期待できないことによる。また、側素線径ｄ₁ の２．０倍を超えるとスチ−ルコ−ドの柔軟性が失われ、疲労値が低くなることによる。本発明のスチ−ルコ−ドは、柔軟性に富み、かつ低荷重時の伸びが小さく、ゴムに埋め込んでも偏平率が埋め込む前とほとんど変わらないスチ−ルコ−ドである。
【００１３】
ここで、低荷重伸びが大きいスチ−ルコ−ドは加硫後に偏平率が小さくなる（断面形状が丸くなる）理由を説明する。
カレンダ−工程において、スチ−ルコ−ドをゴムシ−トに挟む際、スチ−ルコ−ドには１ｋｇ程度の低張力がかけられるが、低荷重伸びが大きいスチ−ルコ−ドは、この張力で伸びて断面積が小さくなるように形状が変形した状態で挟まれる。その後の加硫処理でゴム材は加熱されて流動的になるので、ゴム中でこの形状は元に戻る（スプリングバック）。この時のスプリングバック量が短径側が大きいため、断面形状が丸くなるように形状が変化すると考えられる。
これに対し、低荷重伸びが小さいスチ−ルコ−ドは、張力に対する耐力が強いので、変形することなくシ−トで挟まれる。したがって、このシ−トを加硫してもスプリングバックは発生せず、よって加硫前の形状がそのまま残ると考えられる。
本発明のスチ−ルコ−ドは、コア素線径を太くして、低荷重伸びを小さく抑えたコ−ドであるので、ゴムに埋め込んでも埋め込む前と偏平率は変わらない。
【００１４】
スチ−ルコ−ドの撚りピッチは６ｍｍ〜２８ｍｍが好ましい。というのは、６ｍｍ未満とすると、極度に曲げ加工量が多くなるため断線が発生しやすくなり、またスチ−ルコ−ドの長さ当たりの撚り回数が多くなり、生産性が落ちるからである。さらに、本発明においては、コア素線のくせピッチが撚りピッチよりさらに小さいため、撚りピッチ６ｍｍ未満は適当ではない。一方、スチ−ルコ−ドの撚りピッチが２８ｍｍを越えると、スチ−ルコ−ドの柔軟性が失われるので疲労値が低くなり、また撚りが不安定となりフレア−も発生しやすくなり、実用的でない。
【００１５】
このスチ−ルコ−ドの撚りピッチをＰとしたとき、くせを有するコア素線のくせピッチＰ₁ を０．１Ｐ〜０．５Ｐとしたのは、Ｐ₁ が０．１Ｐ未満であると、素線が極度の塑性変形を受け、断線が多発するとともに生産性が悪くなり、一方、０．５Ｐを越えると、コア素線としての効果が果たせず、ゴムシ−ト成形時のゴムのフロ−による引張力、あるいはコ−ドに負荷されるしごき力によって素線間の隙間が減少し、ゴム浸入のための充分な隙間が素線間に生じなくなるからである。また、０．５Ｐを越えるとスチ−ルコ−ドの圧延が充分に出来ず、スチ−ルコ−ド横断面の短径（Ｔ）が大きくなり、ゴムシ−ト厚が小さく出来ない。
【００１６】
スチ−ルコ−ドの横断面の略楕円形の短径をＴとしたとき、くせを有するコア素線の前記短径方向のくせ外径Ｄを、Ｔ−Ｄ＝０．０３〜０．３０の式を満足する範囲としたのは、０．０３より小さい加工は実際上困難であり、また素線間に充分ゴム浸入を行うためにも０．０３以上の方がよいからである。また０．３０を越えると偏平の効果が少なくなり、ゴムシ−ト厚を小さくすることが出来ないことによる。よって、製造上、作用効果上この範囲が最も適している。
【００１７】
スチ−ルコ−ドの横断面における略楕円形状の偏平率（短径Ｔと長径Ｗとの比、Ｔ／Ｗの百分比）を３８％〜６０％としたのは、３８％未満とすると、撚りが不安定となると同時に各素線は長径端部での曲げ加工がきつくなり、取り扱いの作業性が悪く耐疲労性に劣ることによる。また、６０％を越える形状となっても撚りは不安定となり、また真円に近づくので本発明のスチ−ルコ−ドの効果は期待できなくなる。
【００１８】
本発明においては、くせを有するコア素線を前記略楕円形状の両端には出現させずに、かつまたコア素線を側素線の内側に完全に配置するという構造をとらず、長径軸を挟む両側では、コア素線を側素線の間に略ピッチＰ₁ 間隔で出現させ配置するようにし、結果的には一見してほぼ単層撚りのような構造にまで、スチ−ルコ−ドを偏平加工することにより本発明のスチ−ルコ−ドを完成することが出来た。そのため従来よりも撚りが安定し、かつ素線間に適当なる隙間を保ち、大きな偏平率のスチ−ルコ−ドが得られた。
【００１９】
本発明のスチ−ルコ−ドは、一本の素線にあらかじめ設定したくせを付けてコア素線とし、その周囲に側素線を撚り合わせた後、表面がフラットなロ−ラ−間を通過させ、かなり強い圧縮加工を施すことにより製造可能である。従来はこのような方法では、スチ−ルコ−ドの撚りがつぶれてしまって、コ−ドとして欠陥品ではないかと思われていたが、スチ−ルコ−ドを構成する素線それぞれに適当な張力をかけて、強い圧縮加工を施せば簡単に製造が可能であることも解った。
【００２０】
本発明のスチ−ルコ−ドはチュ−ブラタイプの撚線機でも製造できるが、バンチャ−タイプの撚線機で製造する方が、効率が良く実用的である。バンチャ−タイプの撚線機を用いた場合、素線に捻りが入るため、あらかじめ付けたくせとスチ−ルコ−ドでのくせとが異なるのでその点を考慮しておく必要がある。
【００２１】
上記構成のスチ−ルコ−ドを用いて、２枚のゴムシ−ト間に挟んで加圧加硫すると、各素線間にゴムが容易に浸入し、ゴム厚も薄くできる上、曲げ剛性も上下方向より左右方向が極端に高くなる。このときのスチ−ルコ−ド埋設方向は、シ−ト水平面に対してスチ−ルコ−ド長径部を左右方向とし、各スチ−ルコ−ドは長手方向に略平行に並んでいる。
【００２２】
【発明の実施の形態】
以下、本発明の実施の形態を図面を参照して説明する。
【００２３】
図１〜図３は本発明の各種実施の形態であるスチ−ルコ−ドの横断面を示す概略図で、図１に示すスチ−ルコ−ド１は、略スパイラル状のくせを有する１本のコア素線２と、コア素線２より線径が小さい４本の側素線３とから構成されている。
図２に示すスチ−ルコ−ド１は、同じく１本のコア素線２と８本の側素線３とから構成され、図３に示すスチ−ルコ−ド１は、同じく１本のコア素線２と１２本の側素線３とから構成されている。
【００２４】
図１〜図３に示した全てのスチ−ルコ−ド１で、側素線３の径ｄ₁ が０．１５〜０．２２ｍｍで、コア素線２の径ｄ₂ が、側素線３の径ｄ₁ の１．１倍から２．０倍である。但し、コア素線２の径ｄ₂ は、０．２２ｍｍ以上である。そして、スチ−ルコ−ド１の短径Ｔとコア素線２に施した略スパイラル状の小さなくせの短径方向のくせ外径Ｄとは、Ｔ−Ｄ＝０．０３〜０．３０の関係を満たしている。
また、コア素線２に施すスパイラル状くせのピッチは、撚りピッチの０．１倍から０．５倍で、このスパイラル状くせのピッチ間隔で、コア素線２が長径軸を挟む両側に位置する側素線３の間に出現する。
さらに、偏平率（Ｔ／Ｗ）は、３８〜６０％である。
【００２５】
【実施例】
本発明のスチ−ルコ−ドの特性を評価するために、素線本数Ｎ、撚りピッチＰ、側素線径ｄ₁ 、コア素線径ｄ₂ 、コア素線のくせのピッチＰ₁ 、外径Ｄ、スチ−ルコ−ド横断面の楕円形状の短径Ｔ、長径Ｗを本発明の範囲内でそれぞれ変化させたスチ−ルコ−ドを実施例１〜５とし、それらのうちのいずれかの構成要素の数値が本発明の範囲を外れるスチ−ルコ−ドを比較例１〜５とし、図６に示すような横断面形状を有するスチ−ルコ−ドを従来例１とし、図７に示すような横断面形状を有するスチ−ルコ−ドを従来例２とし、各スチ−ルコ−ドについて、ゴム加硫後の偏平率の変化、ゴム浸入率、耐疲労性、剛性比および取扱作業性について評価したところ、表１に示すような結果を得た。
【００２６】
【表１】

【００２７】
表１に示す各項目のテスト条件、評価方法は次の通りである。
【００２８】
偏平率の変化：カレンダ−工程前のスチ−ルコ−ド（生コ−ド）の偏平率Ａと、ゴム加硫後の偏平率Ｂを、Ｂ／Ａで比較した。この値が１より大きいものはゴム加硫後に断面形状が丸に近くなるように変化したことを示す。なお、加硫後の偏平率Ｂは、ゴムから取り出したサンプルを樹脂に埋め込み、投影機で以て長径ｗ・短径ｔを測定して求めた。
【００２９】
ゴム浸入率：各スチ−ルコ−ドに５ｋｇの引張加重をかけた状態でゴム中に埋め込み、加硫した後、スチ−ルコ−ドをゴム中から取り出し、そのスチ−ルコ−ドを分解して素線の一定長さを観察し、観察した長さに対してゴムと接触した形跡のある長さの比を％表示した。表中その値の大きい方がゴム浸入率が良いことを示している。
【００３０】
耐疲労性：複数本のスチ−ルコ−ドをゴムシ−トに埋め込んだ複合体シ−トを用いて３点プ−リ−曲げ疲労試験機により試験し、埋設したスチ−ルコ−ドがフレッティング磨耗、座屈等を経て破断するに至るまでの繰り返し回数を求め、従来例２の撚り構造のスチ−ルコ−ドの値を１００として指数表示した。表中その値が大きい方が耐疲労性に優れている。
【００３１】
剛性比：図４（ａ）に示すように、５本のスチ−ルコ−ド４を、１００％モジュラスが３５ｋｇ／ｃｍ² であるゴムシ−ト５に対して、スチ−ルコ−ドの横断面長径方向が横になるように一列に埋め込んだテストピ−ス６と、図４（ｂ）に示すように、５本のスチ−ルコ−ド４を、同ゴムシ−ト５に対して、スチ−ルコ−ドの横断面長径方向が縦になるように並列して埋め込んだテストピ−ス７を製作し、図５に示すように、テストピ−ス６または７を、スパンＳｐ＝２０ｍｍとした３点曲げ試験機に上架して、「テストピ−ス６を５ｍｍ押さえ込んだときの加重Ｇ」／「テストピ−ス７を５ｍｍ押さえ込んだときの加重Ｇ」を剛性比とした。
すなわち、「スチ−ルコ−ドの短径軸方向の曲げ剛性」／スチ−ルコ−ドの長径軸方向の曲げ剛性」を剛性比とした。表中その値の小さい方が曲げ剛性に差があることを示している。なお、テストピ−ス６または７の厚みは４ｍｍ、幅は１５ｍｍ、長さは１００ｍｍである。
【００３２】
取扱作業性：作業性良好なものを〇、作業性不良のものを×、その中間程度のものを△とした。
【００３３】
表１より以下の点が明らかである。
【００３４】
比較例１は、コア素線径ｄ₂ が本発明の下限より小さく、他は本発明の範囲内のスチ−ルコ−ドである。このスチ−ルコ−ドはコア素線の剛性が小さく、ゴム加硫後にスチ−ルコ−ドの断面が円に近くなり（Ｂ／Ａ）、剛性比が劣る。
【００３５】
比較例２は、比較例１とは逆に、コア素線径ｄ₂ が本発明の上限より大きいスチ−ルコ−ドである。このスチ−ルコ−ドは、コア素線の剛性が大きすぎ、柔軟性が劣るので耐疲労性が低い。また取扱作業性にもやや劣る。
【００３６】
比較例３は、コア素線径ｄ₂ が比較例１と同様小さく、コアのくせピッチＰ₁ も本発明の範囲を外れたスチ−ルコ−ドである。このスチ−ルコ−ドは隙間が小さく、ゴム浸入性に劣り、またゴム加硫後に断面が円に近くなり（Ｂ／Ａ）、剛性比が低い。
【００３７】
比較例４は、コア素線径ｄ₂ は本発明の範囲に入っているが、コア素線のくせピッチＰ₁ およびＴ−Ｄの値が本発明の上限より大きく、コ−ド横断面の略楕円形状の偏平率Ａが本発明の上限より大きいスチ−ルコ−ドである。このスチ−ルコ−ドは、素線間の隙間が小さく、ゴム浸入性に劣り、剛性も劣る。
【００３８】
比較例５は、コア素線径ｄ₂ 、コアのくせピッチＰ₁ ともに本発明の範囲に入っているが、Ｔ−Ｄの値は比較例４よりさらに大きく、本発明の上限を外れており、偏平率Ａも上限よりさらに大きいスチ−ルコ−ドである。このスチ−ルコ−ドは比較例４よりもさらにゴム浸入性に劣り、耐疲労性、剛性比、取扱作業性の全てが良くない。
【００３９】
従来例１のスチ−ルコ−ドは、ゴムがほとんど浸入していない。
【００４０】
従来例２のスチ−ルコ−ドは、横断面が楕円形状ではなくほぼ真円形状である。このためゴムシ−トでスチ−ルコ−ドを挟んだときゴムシ−トの厚みを薄くすることが出来ない。また実施例１〜５のスチ−ルコ−ドに比べて、ゴム浸入、耐疲労性、剛性比、取扱作業性において劣っている。
【００４１】
実施例１〜５のスチ−ルコ−ドは、上記のような欠点がなく、全てにおいて優れたスチ−ルコ−ドである。
【００４２】
【発明の効果】
本発明のタイヤ補強用スチ−ルコ−ドは、上記のとおり構成されているので、つぎの効果を奏する。
▲１▼スチ−ルコ−ド長手方向のほぼ全域にわたって空洞部がなく、かつ横断面形状の短径が極めて小さいため（いわゆる薄いため）スチ−ルコ−ド内部へのゴム浸入がよい。
▲２▼低荷重伸びが小さいので、ゴムに埋め込んでも偏平率が変化することがない。
▲３▼ゴムシ−ト厚を極端に薄くできるので、タイヤ重量を小さく抑えることができ、タイヤのコストダウン、自動車の燃費向上が可能となる。
▲４▼タイヤ回転方向の剛性を低くできるので、乗り心地を向上でき、一方、タイヤの回転方向と直交する方向の剛性を高くできるので、コ−ナ−リング性能を高めることができる。
▲５▼小さいくせを有するコア素線が、横断面の略楕円形状の長径両端部に出現せず、ほぼ中央部に位置し、かつ長径軸を挟む両側に位置する側素線の間に略ピッチＰ₁ 間隔で出現しているので、スチ−ルコ−ドとしての形状が非常に安定しており、かつ内部へのゴム浸入が非常によくなる。
▲６▼芯素線というような状態での素線が存在せず、全ての素線で単層撚りのような構造となるため、耐疲労性が良くなる。
▲７▼従来のチュ−ブラ−型、バンチャ−型のいずれの撚線機でも製造でき、撚り不良等のトラブルもないため、取扱作業性が優れている。
【図面の簡単な説明】
【図１】本発明のスチ−ルコ−ドの実施の形態を示す概略断面図である。
【図２】本発明のスチ−ルコ−ドの別の実施の形態を示す概略断面図である。
【図３】本発明のスチ−ルコ−ドのさらに別の実施の形態を示す概略断面図である。
【図４】３点曲げ試験に用いたテストピ−スを示し、（ａ）は短径方向の曲げ剛性測定用のテストピ−スの概略図、（ｂ）は長径方向の曲げ剛性測定用のテストピ−スの概略図である。
【図５】３点曲げ試験方法を示す説明図である。
【図６】従来のスチ−ルコ−ドの例を示す概略断面図である。
【図７】従来のスチールコードの別の例を示す概略断面図である。
【符号の説明】
１、４、８スチールコード
２、１１芯素線
３、９、１２側素線
５ゴムシ−ト
６、７テストピ−ス
ｄ₁ 側素線径
ｄ₂ 芯素線径
Ｄコア素線のくせ外径
Ｗスチ−ルコ−ド横断面の長径
Ｔスチ−ルコ−ド横断面の短径
Ｓ空洞部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel cord used as a reinforcing material for automobile tires, and in particular, four to thirteen strands are twisted together, and the cord has a substantially elliptical cross section. Is related to
[0002]
[Prior art]
In general, this type of steel cord is coated with a rubber material in a state in which a large number of steel cords are aligned in parallel, and is used as a reinforcing material for automobile tires. The conditions required for the steel code include not only excellent mechanical strength but also good chemical and physical adhesion to the rubber material, and the steel code. For example, rubber penetration into the inside of the door is good. That is, the steel cord needs to be a complete composite with the rubber material in order to sufficiently fulfill the role as a tire reinforcing material.
[0003]
In particular, steel cords having high strength and flexibility are required for tires used in heavy vehicles such as trucks and buses, and one of them is a steel cord having a 1 + n structure as a conventional one. Has been used.
[0004]
However, the cross-sectional structure of the conventional steel cord having the 1 + n configuration is a closed strand structure as shown in FIG. 6, and the strands 9 are completely in close contact with each other so that there is no gap. S is scattered inside the code. Therefore, when the steel sheet 8 is sandwiched between two rubber sheets to form a composite sheet, the rubber material does not enter the cavity S, and a complete composite with the rubber material is formed. It cannot be formed.
[0005]
Therefore, when this rubber sheet is used for a tire, if even a part of the rubber coating is broken by a foreign object such as a nail, moisture that has entered from the outside propagates into the cavity S, and the steel cord is entirely covered. Causes oxidation over time. If it becomes like this, the adhesive force of rubber | gum and a steel cord will become weak, both will peel, and the effect as a reinforcing material of a steel cord will become very weak.
[0006]
In order to solve this problem, a steel code 10 is proposed in which the core wire 11 is crushed as shown in FIG.
[0007]
[Problems to be solved by the invention]
The steel cord 10 having a 1 + n configuration in which the core wire 11 is spirally connected as shown in FIG. 7 has a substantially circular cross section. The stiffness is the same for any direction. Therefore, if the rigidity is increased in order to improve the cornering performance of the tire, there is a problem that the ride comfort is deteriorated. Further, the steel cord of FIG. 7 has a thicker cord diameter than that of the closed twisted cord as shown in FIG. 6, and the rubber sheet after the calendar (rubber coating step) is thicker. In addition, since the cord diameter is large, a predetermined number of steel cords cannot be embedded in the rubber sheet, and the strength of the sheet becomes weak. Therefore, when this rubber sheet is used for a tire, it is necessary to increase the number of sheets stacked, resulting in a problem that the weight of the tire increases. Further, from the viewpoint of manufacturing the steel cord, a steel cord in which the side wires 12 are neatly arranged in the space as shown in FIG. 8 is impossible and the twist becomes very unstable.
[0008]
The present invention has been made to solve the various problems of the various conventional steel codes, and the problem is that when used as a reinforcing material in a tire, the interior of the steel code is obtained. The rubber can easily penetrate into the tire, the rigidity in the direction perpendicular to the tire rotation direction can be increased while the rigidity in the tire rotation direction is lowered, the fatigue resistance against compression and bending is good, and the manufacturing and handling workability is excellent. Another object is to provide a steel code.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the steel reinforcing steel cord of the present invention has four to thirteen strands, one core strand and the remaining strands as side strands, in the same direction. A steel cord that is twisted at a time with a twist pitch P and has a transverse cross section that is substantially in the same direction in the longitudinal direction and is substantially elliptical (longer diameter W, shorter diameter T). The side element wire diameter d ₁ is 0.15 to 0.22 mm, the side element wire diameter d ₂ is 1.1 d _{1 to} 2.0 d ₁ mm (d ₂ ≧ 0.22 mm), and the core element The wire has a substantially spiral-shaped beak having a bend pitch P ₁ satisfying the following formulas (1) and (2) and a bevel outer diameter D in the direction of the minor axis of the code, and the core wire is a major axis of the substantially ellipse. found at substantially the pitch P ₁ spacing between the side strands positioned on both sides of the shaft, yet aspect ratio of the substantially elliptical shape (percentage of T / W) 38 Characterized in that it is a 60%.
P ₁ = 0.1 P to 0.5 P (1)
TD = 0.03 to 0.30 (2)
P ₁ : habit pitch (mm)
P: Twisted pitch (mm)
T: Code short diameter (mm)
D: Outer diameter of the core wire in the minor axis direction of the cord (mm)
[0010]
The steel cord of the present invention has a substantially elliptical shape in which the transverse section is substantially the same in the longitudinal direction and the flatness ratio is large, so that the rigidity is greatly different between the minor axis direction and the major axis direction of the steel cord. Further, since the steel cord after the calender is lined up substantially parallel to the longitudinal direction with the long diameter portion left and right in the rubber sheet, the bending rigidity is low in the vertical direction and high in the left and right direction. Therefore, when this rubber sheet is used to make a tire, the rigidity in the tire rotation direction is low, so the ride comfort is good, and the rigidity in the direction orthogonal to the tire rotation direction is high, so that the cornering performance is improved. I can do it.
[0011]
In addition, since the steel cord of the present invention has a substantially elliptical cross section, almost all of the steel cords are arranged substantially in parallel in the longitudinal direction with the long diameter portion on the left and right at the time of calendar. The rubber sheet thickness is a thickness corresponding to the steel cord minor axis portion, and the sheet can be thinned. And the number of steel codes inserted can be reduced. As a result, tires have become lighter, and tire costs can be reduced and automobile fuel consumption can be improved. Furthermore, in terms of twist stability, the twist is stable and almost the same after embedding in a rubber sheet as compared to a steel cord as shown in FIG. The work is also excellent.
[0012]
By the way, in the steel cord of the present invention, the side wire diameter d ₁ is 0.15 to 0.22 mm, and the core wire diameter d ₂ is 1.1 d ₁ to 2.0 d ₁ mm (provided that d ₂ ≧ 0.22 mm), when the side wire diameter d ₁ is less than 0.15 mm, sufficient strength cannot be obtained, and when it exceeds 0.22 mm, the flexibility of the steel cord decreases and fatigue occurs. Due to the drop in value. Also, in 1.1 to 2.0 times the core wire diameter d ₂ is the side wire diameter d _1, and was not less than 0.22mm, in less than 0.22mm, steel - Turkey - low load de The elongation increases, and the flatness decreases after rubber vulcanization for the following reasons, and the effect of the present invention cannot be expected. If it exceeds 2.0 times the side wire diameter d ₁ steel - Turkey - de flexibility is lost, due to the fatigue value is low. The steel cord of the present invention is a steel cord which is rich in flexibility, has a small elongation at low load, and is almost the same as before flattening even when embedded in rubber.
[0013]
Here, the reason why the steel cord having a large low load elongation has a small flatness after vulcanization (the cross-sectional shape becomes round) will be described.
In the calendering process, when the steel cord is sandwiched between the rubber sheets, a low tension of about 1 kg is applied to the steel cord, but the steel cord with a large low load elongation is applied with this tension. It is sandwiched in a state where the shape is deformed so that the cross-sectional area is reduced by extension. Since the rubber material is heated and fluidized by the subsequent vulcanization treatment, the shape of the rubber material returns to its original state (spring back). Since the amount of springback at this time is large on the short axis side, it is considered that the shape changes so that the cross-sectional shape becomes round.
On the other hand, a steel cord having a low low load elongation has a high resistance to tension, and is sandwiched between sheets without deformation. Therefore, even if this sheet is vulcanized, no springback occurs, and it is considered that the shape before vulcanization remains as it is.
Since the steel cord of the present invention is a cord in which the core wire diameter is increased and the low load elongation is suppressed, the flatness does not change even before embedding in rubber.
[0014]
The twist pitch of the steel cord is preferably 6 mm to 28 mm. This is because if the thickness is less than 6 mm, the amount of bending work becomes extremely large, so that disconnection is likely to occur, and the number of twists per length of the steel cord increases, resulting in a decrease in productivity. Furthermore, in the present invention, since the comb pitch of the core strand is further smaller than the twist pitch, a twist pitch of less than 6 mm is not appropriate. On the other hand, if the twist pitch of the steel cord exceeds 28 mm, the flexibility of the steel cord is lost, so the fatigue value becomes low, and the twist becomes unstable and flare is likely to occur. Not.
[0015]
When the twist pitch of this steel cord is P, the core pitch P ₁ of the core wire having a crack is 0.1 P to 0.5 P. When P ₁ is less than 0.1 P, The strands are subject to extreme plastic deformation, resulting in frequent disconnections and poor productivity. On the other hand, if the thickness exceeds 0.5 P, the effect as a core strand cannot be achieved, and the flow of rubber during rubber sheet molding This is because the gap between the strands is reduced by the pulling force due to or the squeezing force applied to the cord, and a sufficient gap for rubber penetration does not occur between the strands. On the other hand, if it exceeds 0.5 P, the steel cord cannot be sufficiently rolled, the short diameter (T) of the steel cord cross section becomes large, and the rubber sheet thickness cannot be reduced.
[0016]
When the minor axis of the substantially elliptical cross section of the steel cord is T, the outer diameter D in the minor axis direction of the core wire having a defect is defined as TD = 0.03 to 0.30. The reason why the above formula is satisfied is that processing smaller than 0.03 is practically difficult, and 0.03 or more is better for sufficient rubber penetration between the strands. On the other hand, if it exceeds 0.30, the flattening effect is reduced and the rubber sheet thickness cannot be reduced. Therefore, this range is most suitable in terms of manufacturing and operational effects.
[0017]
When the flatness of the substantially elliptical shape in the cross section of the steel cord (ratio of minor axis T to major axis W, percentage of T / W) is 38% to 60%, At the same time, each wire becomes hard to bend at the end of the long diameter, resulting in poor handling and poor fatigue resistance. Further, even if the shape exceeds 60%, the twist becomes unstable and approaches a perfect circle, so that the effect of the steel code of the present invention cannot be expected.
[0018]
In the present invention, the core wire without a warp does not appear at both ends of the substantially elliptical shape, and the core wire is not arranged completely inside the side wire, and the major axis is in the both sides, until the structure as a core element wire to arrange to appear at substantially the pitch P ₁ spacing between the side strands, resulting almost monolayer at first glance to twist, steel - Turkey - de The steel cord of the present invention was completed by flattening. For this reason, the steel cord has a higher flatness than that of the prior art, has a more stable twist and maintains an appropriate gap between the strands.
[0019]
In the steel cord of the present invention, a single strand is pre-set to a core strand, the side strands are twisted around it, and then between the rollers with flat surfaces. It can be manufactured by passing it through and applying a fairly strong compression process. Conventionally, in such a method, the twist of the steel cord was crushed, and it was thought that it was a defective product as a cord, but it was suitable for each strand constituting the steel cord. It was also found that it can be easily manufactured by applying a strong compression process under tension.
[0020]
The steel cord of the present invention can be manufactured with a tuber type twisting machine, but it is more efficient and practical to manufacture with a buncher type twisting machine. When a buncher-type twisting machine is used, the strands are twisted, so that the bends attached in advance are different from the beads in the steel cord, and this must be taken into consideration.
[0021]
Using the steel cord of the above configuration, when sandwiched between two rubber sheets and pressure vulcanized, the rubber can easily penetrate between the strands, the thickness of the rubber can be reduced, and the bending rigidity can be reduced. The horizontal direction is extremely higher than the vertical direction. The steel code burying direction at this time is such that the long diameter portion of the steel cord is in the left-right direction with respect to the sheet horizontal plane, and the steel cords are arranged substantially parallel to the longitudinal direction.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0023]
1 to 3 are schematic views showing cross sections of a steel code according to various embodiments of the present invention. The steel code 1 shown in FIG. 1 is a single one having a substantially spiral shape. Core wire 2 and four side strands 3 having a diameter smaller than that of the core wire 2.
The steel code 1 shown in FIG. 2 is similarly composed of one core wire 2 and eight side wires 3, and the steel code 1 shown in FIG. It consists of a

strand

2 and 12 side strands 3.
[0024]
In all the steel cords 1 shown in FIGS. 1 to 3, the side wire 3 has a diameter d ₁ of 0.15 to 0.22 mm, and the core wire 2 has a diameter d ₂ of the side wire 3. It is 1.1 times to 2.0 times the diameter d ₁ of the above. However, the diameter d ₂ of the core wire 2 is more than 0.22 mm. The short diameter T of the steel cord 1 and the outer diameter D in the short diameter direction of the substantially spiral shape formed on the core wire 2 are TD = 0.03 to 0.30. Satisfies the relationship.
Further, the pitch of the spiral bevel applied to the core strand 2 is 0.1 to 0.5 times the twist pitch, and the core strand 2 is located on both sides of the major axis with the spiral pitch interval. Appears between the side strands 3.
Further, the flatness ratio (T / W) is 38 to 60%.
[0025]
【Example】
In order to evaluate the characteristics of the steel cord of the present invention, the number N of strands, the twist pitch P, the side strand diameter d ₁ , the core strand diameter d ₂ , the core strand spider pitch P ₁ , the outer The steel cords in which the diameter D, the elliptical minor axis T, and the major axis W of the steel cord cross-section were changed within the scope of the present invention were designated as Examples 1 to 5, and any one of them. The steel cords whose numerical values are outside the scope of the present invention are referred to as Comparative Examples 1 to 5, the steel cord having a cross-sectional shape as shown in FIG. The steel cord having the cross-sectional shape shown in the figure is the conventional example 2, and for each steel cord, the change in flatness after rubber vulcanization, rubber penetration rate, fatigue resistance, rigidity ratio and handling work As a result, the results shown in Table 1 were obtained.
[0026]
[Table 1]

[0027]
The test conditions and evaluation methods for each item shown in Table 1 are as follows.
[0028]
Change in flatness: The flatness A of the steel code (raw code) before the calendar process and the flatness B after rubber vulcanization were compared by B / A. When this value is greater than 1, it indicates that the cross-sectional shape has changed to be close to a circle after rubber vulcanization. The flatness ratio B after vulcanization was obtained by embedding a sample taken out of rubber in a resin and measuring the major axis w and minor axis t with a projector.
[0029]
Rubber penetration rate: Each steel cord was embedded in rubber under a tensile load of 5 kg, vulcanized, and then the steel cord was taken out from the rubber and the steel cord was disassembled. A certain length of the wire was observed, and the ratio of the length of the trace that was in contact with the rubber to the observed length was displayed in%. The larger value in the table indicates that the rubber penetration rate is better.
[0030]
Fatigue resistance: Using a composite sheet in which a plurality of steel cords are embedded in a rubber sheet, a three-point pulley bending fatigue tester was used to test the embedded steel cord. The number of repetitions until rupture through ting wear, buckling, etc. was obtained, and the value of the steel cord of the twisted structure of Conventional Example 2 was taken as 100 and indicated as an index. The higher the value in the table, the better the fatigue resistance.
[0031]
Stiffness ratio: As shown in FIG. 4 (a), the cross-section of the steel code 4 with respect to the rubber sheet 5 having a 100% modulus of 35 kg / cm ² A test piece 6 embedded in a line so that the major axis direction is horizontal, and five steel cords 4 are connected to the rubber sheet 5 as shown in FIG. The test piece 7 embedded in parallel so that the major axis direction of the transverse direction of the cord is vertical is manufactured, and as shown in FIG. 5, the

test piece

6 or 7 has a span Sp = 20 mm. The rigidity ratio was set on the bending tester and “weight G when test piece 6 was pressed 5 mm” / “weight G when test piece 7 was pressed 5 mm” was used as the rigidity ratio.
That is, “the bending rigidity of the steel cord in the minor axis direction” / the bending rigidity of the steel cord in the major axis direction was defined as the rigidity ratio. The smaller value in the table indicates that there is a difference in bending rigidity. The

test piece

6 or 7 has a thickness of 4 mm, a width of 15 mm, and a length of 100 mm.
[0032]
Handling operability: Good workability is indicated by ◯, poor workability by x, and intermediate grade is indicated by △.
[0033]
From Table 1, the following points are clear.
[0034]
Comparative Example 1, the core wire diameter d ₂ is smaller than the lower limit of the present invention, other steel within the scope of the present invention - a de - Turkey. In this steel cord, the core wire has low rigidity, and after rubber vulcanization, the cross section of the steel cord becomes close to a circle (B / A) and the rigidity ratio is inferior.
[0035]
Contrary to Comparative Example 1, Comparative Example 2 is a steel code in which the core wire diameter d ₂ is larger than the upper limit of the present invention. This steel cord has low fatigue resistance because the rigidity of the core wire is too large and the flexibility is poor. In addition, the handling workability is slightly inferior.
[0036]
In Comparative Example 3, the core wire diameter d ₂ is as small as in Comparative Example 1, and the core pitch P ₁ is also a steel code outside the scope of the present invention. This steel cord has a small gap, is inferior in rubber penetration, has a cross-section close to a circle (B / A) after rubber vulcanization, and has a low rigidity ratio.
[0037]
In Comparative Example 4, the core wire diameter d ₂ is within the range of the present invention, but the values of the core strands' cut pitches P ₁ and TD are larger than the upper limit of the present invention, and the code cross section This is a steel code having a substantially elliptical flatness ratio A larger than the upper limit of the present invention. This steel cord has a small gap between the strands, is inferior in rubber penetration, and inferior in rigidity.
[0038]
In Comparative Example 5, both the core wire diameter d ₂ and the core pitch P ₁ are within the range of the present invention, but the value of TD is larger than that of Comparative Example 4, which is outside the upper limit of the present invention. The flatness ratio A is also a steel code that is larger than the upper limit. This steel cord is inferior to the rubber penetration property as compared with Comparative Example 4, and is not good in all of fatigue resistance, rigidity ratio and handling workability.
[0039]
In the steel cord of Conventional Example 1, rubber hardly penetrates.
[0040]
The steel cord of Conventional Example 2 has a substantially circular shape in cross section instead of an elliptical shape. For this reason, the thickness of the rubber sheet cannot be reduced when the steel cord is sandwiched between the rubber sheets. Moreover, compared with the steel cord of Examples 1-5, it is inferior in rubber penetration, fatigue resistance, rigidity ratio, and handling workability.
[0041]
The steel codes of Examples 1 to 5 do not have the above-mentioned drawbacks and are all excellent steel codes.
[0042]
【The invention's effect】
Since the steel reinforcing steel cord according to the present invention is configured as described above, the following effects can be obtained.
(1) Since there is no hollow portion over almost the entire length of the steel cord and the minor axis of the cross-sectional shape is extremely small (so-called thin), rubber penetration into the steel cord is good.
(2) Since the low load elongation is small, the flatness does not change even when embedded in rubber.
(3) Since the rubber sheet thickness can be made extremely thin, the tire weight can be kept small, the tire cost can be reduced, and the fuel efficiency of the automobile can be improved.
(4) Since the rigidity in the tire rotation direction can be lowered, the riding comfort can be improved, and on the other hand, the rigidity in the direction orthogonal to the tire rotation direction can be increased, so that the cornering performance can be improved.
(5) The core wire having a small habit does not appear on both ends of the major axis of the substantially elliptical shape in the cross section, but is located substantially between the side strands located on both sides of the major axis and located substantially in the center. since found at a pitch P ₁ interval, steel - Turkey - is extremely stable shape as de, and rubber penetration into the inside is very well.
{Circle around (6)} No strands in the state of core strands are present, and all strands have a single-layer twisted structure, so fatigue resistance is improved.
(7) It can be manufactured by any conventional twister type and buncher type twisting machines, and there is no trouble such as twisting failure, so that the handling workability is excellent.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an embodiment of a steel cord of the present invention.
FIG. 2 is a schematic cross-sectional view showing another embodiment of a steel cord of the present invention.
FIG. 3 is a schematic sectional view showing still another embodiment of the steel cord of the present invention.
4A and 4B show test pieces used in a three-point bending test, where FIG. 4A is a schematic diagram of a test piece for measuring bending stiffness in the minor axis direction, and FIG. 4B is a test piece for measuring bending stiffness in the major axis direction. FIG.
FIG. 5 is an explanatory diagram showing a three-point bending test method.
FIG. 6 is a schematic cross-sectional view showing an example of a conventional steel code.
FIG. 7 is a schematic cross-sectional view showing another example of a conventional steel cord.
[Explanation of symbols]
1, 4, 8

Steel cords

2, 11

Core strands

3, 9, 12 Side strand 5

Rubber sheet

6, 7 Test piece d ₁ Side strand diameter d ₂ Core strand diameter D Out of core strand Diameter W Long diameter of steel code cross section T Short diameter of steel code cross section S Cavity

Claims

A steel cord having 4 to 13 strands, one core strand and the remaining strands being side strands, twisted in the same direction at a twist pitch P at the same time. In a steel reinforcing steel cord having substantially the same surface in the longitudinal direction and a substantially elliptical shape (major axis W, minor axis T), the side strand diameter d ₁ is 0.15 to 0.22 mm, and the core strand The diameter d ₂ is 1.1d _{1 to} 2.0d ₁ mm (where d ₂ ≧ 0.22 mm), and the core strand satisfies the following formulas (1) and (2) and the pitch P ₁ and the core The core strand has a substantially spiral shape with a comb outer diameter D in the minor axis direction, and the core strand appears at a pitch P ₁ interval between the side strands located on both sides of the major axis of the substantially ellipse. In addition, the steel cord for reinforcing a tire is characterized in that the oblateness of the substantially elliptical shape (percentage of T / W) is 38% to 60%.
P ₁ = 0.1 P to 0.5 P (1)
TD = 0.03 to 0.30 (2)
P ₁ : habit pitch (mm)
P: Twisted pitch (mm)
T: Code short diameter (mm)
D: Outer diameter of core wire in the minor axis direction of the cord (mm)