JP2004059420A - Optical fiber with primary coating layer and secondary coating layer, optical fiber cable and their manufacturing methods - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a transmission loss of an optical fiber 1 caused by minute curving of fiberglass 3 by stabilizing the supporting condition of the fiberglass 3 with a primary coating layer 5. <P>SOLUTION: The optical fiber is comprised of the fiberglass, the primary coating layer composed of a soft curing resin directly covering the periphery of the fiberglass, and a secondary coating layer composed of a hard curing resin indirectly covering the periphery of the fiberglass through the primary coating layer. The Young's modulus of the soft curing resin is very lower than that of the hard curing resin; and the relational expression between the linear expansion coefficient α<SB>1</SB>of the soft curing resin and the linear expansion coefficient α<SB>2</SB>of the hard curing resin is denoted by the formula (wherein the fiberglass radius is R<SB>0</SB>; the outside radius of the primary coating layer is R<SB>1</SB>; the Poisson's ratio of the soft curing resin is ν<SB>1</SB>; the Poisson's ratio of the hard curing resin is ν<SB>2</SB>; and the temperature variation of the curing resins between during hardening and at the end of hardening is ΔT). <P>COPYRIGHT: (C)2004,JPO

Description

の線膨張係数の関係式が成立するように構成してなることを特徴とする。
【００１０】
本発明の更に他の様相によれば、光ファイバは、ファイバガラスと、軟質の硬化型樹脂により構成され、前記ファイバガラスの外周部を直接的に被覆する一次被覆層と、硬質の硬化型樹脂により構成され、前記ファイバガラスの外周部を前記一次被覆層を介して間接的に被覆する二次被覆層とを備えてあって、前記軟質の硬化型樹脂のヤング率が前記硬質の硬化型樹脂のヤング率に比べて極めて小さい場合であって、前記ファイバガラスの半径Ｒ_０、前記一次被覆層の外半径Ｒ_１、前記軟質の硬化型樹脂のポアソン比ν_１、前記硬質の硬化型樹脂のポアソン比ν_２、前記硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴを設定すると、前記軟質の硬化型樹脂の線膨張係数α_１と前記硬質の硬化型樹脂の線膨張係数α_２の間に、
【数５】

の線膨張係数の関係式が成立するように構成してなることを特徴とする。
【００１１】
本発明の更に他の様相によれば、光ファイバの製造方法は、ファイバガラスと、軟質の硬化型樹脂により構成されかつ前記ファイバガラスの外周部を直接的に被覆する一次被覆層と、硬質の硬化型樹脂により構成されかつ前記ファイバガラスを前記一次被覆層を介して間接的に被覆する二次被覆層とを備えてなる光ファイバの製造方法であって、前記軟質の硬化型樹脂のヤング率が前記硬質の硬化型樹脂のヤング率に比べて極めて小さい場合であって、前記ファイバガラスの半径Ｒ_０、前記一次被覆層の外半径Ｒ_１、前記軟質の硬化型樹脂のポアソン比ν_１、前記硬質の硬化型樹脂のポアソン比ν_２、前記硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴを設定すると、前記軟質の硬化型樹脂の線膨張係数α_１と前記硬質の硬化型樹脂の線膨張係数α_２の間に、
【数６】

の線膨張係数の関係式が成立するように前記軟質の硬化型樹脂と前記硬質の硬化型樹脂が選択されていることを特徴とする。
【００１２】
本発明の更に他の様相によれば、光ファイバは、ファイバガラスと、軟質の硬化型樹脂により構成され、前記ファイバガラスの外周部を直接的に被覆する一次被覆層と、硬質の硬化型樹脂により構成され、前記ファイバガラスの外周部を前記一次被覆層を介して間接的に被覆する二次被覆層とを備えてあって、前記軟質の硬化型樹脂のヤング率が前記硬質の硬化型樹脂のヤング率に比べて十分小さく、誤差範囲内で前記ファイバガラスの半径Ｒ_０を６２．　５μｍ、前記一次被覆層の外半径Ｒ_１を１２５μｍ、前記二次被覆層の外半径Ｒ_２を２００μｍ、前記軟質の硬化型樹脂のポアソン比ν_１、前記硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴとして、前記軟質の硬化型樹脂は、その線膨張係数が（１−２ν_１）／ΔＴ以下となるように選択されていることを特徴とする。
【００１３】
本発明の更に他の様相によれば、光ファイバは、ファイバガラスと、軟質の硬化型樹脂により構成され、前記ファイバガラスの外周部を直接的に被覆する一次被覆層と、硬質の硬化型樹脂により構成され、前記ファイバガラスの外周部を前記一次被覆層を介して間接的に被覆する二次被覆層とを備えてあって、前記軟質の硬化型樹脂のヤング率が前記硬質の硬化型樹脂のヤング率に比べて十分小さく、誤差範囲内で前記ファイバガラスの半径Ｒ_０を６２．　５μｍ、前記一次被覆層の外半径Ｒ_１を１２５μｍ、前記二次被覆層の外半径Ｒ_２を２００μｍ、前記軟質の硬化型樹脂のポアソン比ν_１、前記硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴとして、前記軟質の硬化型樹脂は、その線膨張係数α_１が、
（１−２ν_１）／１８０　＞　α_１　＞　（１−２ν_１）／２２５
を満たすように選択されていることを特徴とする。
【００１４】
本発明の更に他の様相によれば、光ファイバは、ファイバガラスと、軟質の硬化型樹脂により構成され、前記ファイバガラスの外周部を直接的に被覆する一次被覆層と、硬質の硬化型樹脂により構成され、前記ファイバガラスの外周部を前記一次被覆層を介して間接的に被覆する二次被覆層とを備えてあって、前記軟質の硬化型樹脂のヤング率が前記硬質の硬化型樹脂のヤング率に比べて十分小さく、誤差範囲内で前記ファイバガラスの半径Ｒ_０を６２．　５μｍ、前記一次被覆層の外半径Ｒ_１を１２５μｍ、前記二次被覆層の外半径Ｒ_２を２００μｍ、前記軟質の硬化型樹脂のポアソン比ν_１、前記硬質の硬化型樹脂のポアソン比ν_２、前記硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴとして、α_０　＝（１−２ν_１）／ΔＴとして、前記軟質の硬化型樹脂は、その線膨張係数α_１が、このα_０よりも大きく、且つ前記硬質の硬化型樹脂は、その線膨張係数α_２が
１５（α_１−α_０）／８（１＋ν_２）　＜　α_２　＜　９（α_１−α_０）／４（１＋ν_２）
を満たすように選択されていることを特徴とする。
【００１５】
本発明の更に他の様相によれば、光ファイバは、ファイバガラスと、軟質の硬化型樹脂により構成され、前記ファイバガラスの外周部を直接的に被覆する一次被覆層と、硬質の硬化型樹脂により構成され、前記ファイバガラスの外周部を前記一次被覆層を介して間接的に被覆する二次被覆層とを備えてあって、前記軟質の硬化型樹脂のヤング率が前記硬質の硬化型樹脂のヤング率に比べて十分小さく、誤差範囲内で前記ファイバガラスの半径Ｒ_０を６２．　５μｍ、前記一次被覆層の外半径Ｒ_１を９５μｍ、前記二次被覆層の外半径Ｒ_２を１２０μｍ、前記軟質の硬化型樹脂のポアソン比ν_１、前記硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴとして、前記軟質の硬化型樹脂は、その線膨張係数が（１−２ν_１）／ΔＴ以下となるように選択されていることを特徴とする。
【００１６】
本発明の更に他の様相によれば、光ファイバは、ファイバガラスと、軟質の硬化型樹脂により構成され、前記ファイバガラスの外周部を直接的に被覆する一次被覆層と、硬質の硬化型樹脂により構成され、前記ファイバガラスの外周部を前記一次被覆層を介して間接的に被覆する二次被覆層とを備えてあって、前記軟質の硬化型樹脂のヤング率が前記硬質の硬化型樹脂のヤング率に比べて十分小さく、誤差範囲内で前記ファイバガラスの半径Ｒ_０を６２．　５μｍ、前記一次被覆層の外半径Ｒ_１を９５μｍ、前記二次被覆層の外半径Ｒ_２を１２０μｍ、前記軟質の硬化型樹脂のポアソン比ν_１、前記硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴとして、前記軟質の硬化型樹脂は、その線膨張係数α_１が、
（１−２ν_１）／１２０　＞　α_１　＞　（１−２ν_１）／１５０
を満たすように選択されていることを特徴とする。
【００１７】
本発明の更に他の様相によれば、光ファイバは、ファイバガラスと、軟質の硬化型樹脂により構成され、前記ファイバガラスの外周部を直接的に被覆する一次被覆層と、硬質の硬化型樹脂により構成され、前記ファイバガラスの外周部を前記一次被覆層を介して間接的に被覆する二次被覆層とを備えてあって、前記軟質の硬化型樹脂のヤング率が前記硬質の硬化型樹脂のヤング率に比べて十分小さく、誤差範囲内で前記ファイバガラスの半径Ｒ_０を６２．　５μｍ、前記一次被覆層の外半径Ｒ_１を９５μｍ、前記二次被覆層の外半径Ｒ_２を１２０μｍ、前記軟質の硬化型樹脂のポアソン比ν_１、前記硬質の硬化型樹脂のポアソン比ν_２、前記硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴとして、α_０　＝（１−２ν_１）／ΔＴとして、前記軟質の硬化型樹脂は、その線膨張係数α_１が、このα_０よりも大きく、且つ前記硬質の硬化型樹脂は、その線膨張係数α_２が
｛０．８６６４／（１＋ν_２）｝（α_１−α_０）　＜　α_２　＜　｛１．０３９６８／（１＋ν_２）｝（α_１−α_０）
を満たすように選択されていることを特徴とする。
【００１８】
【発明の実施の形態】
以下、本発明の実施形態を図面に基づいて説明する。
【００１９】
図１は、本発明の実施の形態に係わるファイバガラス等の機械的要素を説明する図であって、図２は、本発明の実施の形態に係わる光ファイバの断面図であって、図４は、本発明の実施の形態に係わる材料強度試験装置の模式的な斜視図であって、図５は、本発明の実施の形態に係わる材料強度試験装置による強度試験を説明する図であって、図６は、図５（ｂ）における試験シートを上から見た図である。
【００２０】
ここで、「上」は、図４及び図５において上，図６において紙面に向かって表のことをいい、「下」は、図４及び図５において下，図６において紙面に向かって裏のことをいう。
【００２１】
図２に示すように、本発明の実施の形態に係わる光ファイバ１は、ファイバガラス３と、このファイバガラス３の外周部を直接的に被覆する一次被覆層５と、ファイバガラス３の外周部を一次被覆層５を介して間接的に被覆する二次被覆層７とを備えている。ここで、一次被覆層５は軟質の紫外線硬化型樹脂により構成され、二次被覆層７は硬質の紫外線硬化型樹脂により構成されている。
【００２２】
なお、前記軟質の硬化型樹脂や、前記硬質の硬化型樹脂は、所望の物理的な特性が得られるように紫外線硬化型樹脂等を光開始剤等と共に適宜配合して調整される。そのような紫外線硬化型樹脂としては、紫外線硬化型エポキシアクリレートや、紫外線硬化型ウレタンアクリレート樹脂や、その他のウレタン系樹脂といった、光重合性プレポリマーや光重合性モノマーが用いられる。
【００２３】
また、光ファイバ１は、図４に示すような材料強度試験装置９による材料強度試験の結果等に基づく構成を機械的要素としており、光ファイバ１の機械的要素について説明する前に、材料強度試験装置９の具体的構成及び材料強度試験装置９による強度試験について説明する。
【００２４】
図４に示すように、本発明の実施の形態に係わる材料強度試験装置９は、四角形状の第１ホルダ１１と四角形状の第２ホルダ１３を上下に対向して備えている。第１ホルダ１１が第２ホルダ１３に対して上下方向へ移動可能に支持されるようにするため、第２ホルダ１３には複数の固定突起１５が設けられており、複数の固定突起１５にはガイドピン１７が立設されてあって、第１ホルダ１１には対応するガイドピン１７に上下方向へ移動可能に案内される複数の可動突起１９が設けられている。
【００２５】
第１ホルダ１１の中央部には円形状の第１固定部材２１が設けられており、この第１固定部材２１は極めて薄い円板状の試験シートＳの表面が接着作用によって密着して固定される第１拘束面２１ｆ（図５参照）を有している。また、第２ホルダ１３の中央部には円形状の第２固定部材２３が第１固定部材２１に上下に対向して設けられており、この第２固定部材２３は試験シートＳの裏面が接着作用によって密着して固定される第２拘束面２３ｆ（図５参照）を有している。更に、第１固定部材２１及び第２固定部材２３は透明なガラスによりそれぞれ構成されている。
【００２６】
ここで、試験シートＳは、光ファイバ１における一次被覆層５を構成する軟質の紫外線硬化型樹脂と同じ軟質の紫外線硬化型樹脂からなるものであって、試験シートＳの厚みは、一次被覆層５の厚みと同じにしてある。
【００２７】
第１ホルダ１１には取付突起２５が設けられており、第２ホルダ１３には当接突起２７が取付突起２５に上下に対向して設けられている。第１固定部材２１を上方向（換言すれば、試験シートＳの厚み方向であって第２固定部材２３に対して離反する離反方向）へ微小変位させるため、取付突起２５にはつまみ２９の回転操作によって上下方向へ微小伸縮可能なスピンドル３１を備えたマイクロメータヘッド３３が設けられており、このスピンドル３１の先端部（下端部）は当接突起に当接可能である。
【００２８】
従って、スピンドル３１の先端部を当接突起２７に当接させて、つまみ２９を回転操作によってスピンドル３１を下方向へ微少量だけ伸ばすことにより、第１固定部材２１を第１ホルダ１１と一体的に上方向へ微小変位させることができる。このとき、複数の可動突起１９が複数のガイドピン１７に案内されて上方向へ変位するため、第１拘束面２１ｆと第２拘束面２３ｆは平行に保持した状態にある。
【００２９】
第１ホルダ１１の上方には第１固定部材２１の外側上方から試験シートＳを観察する顕微鏡３５が図示省略の支持アームを介して設けられている。なお、顕微鏡３５は適宜の機構を介して姿勢、位置等を変更することができる。
【００３０】
次に、材料強度試験装置９による強度試験について説明する。
【００３１】
図５に示すように、試験シートＳの表面を第１固定部材２１の第１拘束面２１ｆに接着作用により密着して固定すると共に、試験シートＳの裏面を第２固定部材２３の第２拘束面２３ｆに接着作用により密着して固定する（図５（ａ）参照）。これにより、試験シートＳの全領域のうち外周部付近を除く応力有効領域を径方向，周方向へ変位しないように拘束できる。
【００３２】
ここで、応力有効領域をより明確にすると、本発明の実施の形態にあっては、第１固定部材２１を上方向へ微小変位させると試験シートＳの外周面にＲ状の凹みＳｄが生じるが、応力有効領域とは、試験シートＳの全領域のうち外周部付近を除く領域であって、凹みＳｄが生じない領域のことをいう（図６参照）。
【００３３】
そして、顕微鏡３５により第１固定部材２１の外側から試験シートＳを拡大して観察しつつ、第１拘束面２１ｆと第２拘束面２３ｆを平行に保持した状態の下で、スピンドル３１の先端部を当接突起２７に当接させて、つまみ２９を回転操作してスピンドル３１を下方向へ微小変位させて、第１固定部材２１を上方向へ微小変位させる（図５（ｂ）参照）。これにより、試験シートＳは水平方向に収縮する傾向にあるが、第１拘束面２１ｆ及び第２拘束面２３ｆによって試験シートＳの応力有効領域の径方向，周方向の変位が拘束されることから、試験シートＳの応力有効領域に前記厚み方向（図５において上下方向）の引張応力の他に、前記径方向の引張応力と前記周方向の引張応力を付与することができ、換言すれば、試験シートＳの応力有効領域に３次元方向の引張応力を加えることができる。また、試験シートＳの厚さが極めて薄いことから、試験シートＳの応力有効領域において略均一に３次元方向の引張応力を加えることができる。
【００３４】
ここで、３次元方向の引張応力とは、前記径方向の引張応力σ_０ｒと、前記周方向の引張応力σ_{０ θ}、前記厚み方向の引張応力σ_０ｚのことをいう。
【００３５】
更に、第１固定部材２１の微小変位量が増えることよって、試験シートＳの応力有効領域の３次元方向の引張応力が徐々に高くなって、試験シートＳにボイドＶ又は亀裂（図示省略）が生じる（図５（ｃ）参照）。そして、試験シートＳにボイドＶ又は亀裂が生じたときにおける第１固定部材２１の変位量に基づいて、３次元方向の引張応力を加えた状態における前記軟質の紫外線硬化型樹脂の破損応力を求める。
【００３６】
ここで、第１固定部材２１の変位量に対する３次元方向の引張応力は、有限要素法による解析等を用いて求めることができ、試験シートＳの応力有効領域において第１固定部材２１の変位量と３次元方向の引張応力の間には線形の関係がある。また、３次元方向の引張応力を加えた状態における前記軟質の紫外線硬化型樹脂の破損応力とは、試験シートＳにボイドＶ又は亀裂が生じたときに試験シートＳに加えられた３次元方向の引張応力の平均引張応力（σ_０ｒ＋σ_{０ θ}＋σ_０ｚ）／３のことをいう。
【００３７】
前記軟質の紫外線硬化型樹脂の種類及び材料試験装置の環境温度を変更して、材料強度試験装置９による強度試験の結果を図８に示す。ここで、第１固定部材２１の半径及び第２固定部材２３の半径を５０ｍｍ、試験シートＳの半径を５０ｍｍ、試験シートの厚みを１００μｍとしている。
【００３８】
図８により明らかなように、円板状の試験シートＳにおいて略均一に３次元方向の引張応力（σ_０ｒ、σ_{０ θ}、σ_０ｚ）を加えて徐々に大きくすることによって、試験シートＳにボイドＶ又は亀裂が生じるときの３次元方向の引張応力の平均引張応力（σ_０ｒ＋σ_{０ θ}＋σ_０ｚ）／３、換言すれば３次元方向の引張応力を加えた状態における前記軟質の紫外線硬化型樹脂の破損応力が前記軟質の硬化型樹脂のヤング率よりも大きいということが判明した。
【００３９】
次に、材料強度試験装置９による材料強度試験の結果に基づく光ファイバ１の機械的要素及びその製造方法について説明する。
【００４０】
図１に示すように、前記軟質の紫外線硬化型樹脂の樹脂温度が、硬質の紫外線硬化型樹脂の硬化時から硬化終了時にかけて大きく低下することによって一次被覆層５において略均一に３次元方向の引張応力（σ_ｒ、σ_θ、σ_ｚ）を加えた場合に、
３次元方向の引張応力の平均引張応力（σ_ｒ＋σ_θ＋σ_ｚ）／３が一次被覆層５のヤング率Ｅ_１より小さくなるように、ガラスファイバ３の機械的要素、一次被覆層５の機械的要素、二次被覆層７の機械的要素を有するように選択して構成してある。
【００４１】
ここで、σ_ｒは一次被覆層５の径方向の引張応力であって、σ_θは一次被覆層５の周方向の引張応力であって、σ_ｚは一次被覆層５のファイバ軸方向（図１において紙面に向かって表裏方向）の引張応力である。また、ガラスファイバ３の機械的要素は、ファイバガラス３の半径Ｒ_０であって、一次被覆層５の機械的要素は、一次被覆層５の外半径Ｒ_１、前記軟質の紫外線硬化型樹脂のヤング率Ｅ_１，線膨張係数α_１，ポアソン比ν_１であって、二次被覆層７の機械的要素は、二次被覆層７の外半径Ｒ_２、前記硬質の紫外線硬化型樹脂のヤング率Ｅ_２，線膨張係数α_２，ポアソン比ν_２である。なお、硬化終了時とは、硬化終了直後の他に、硬化終了してから環境温度が変化した後も含むものである。
【００４２】
そして、前記軟質の紫外線硬化型樹脂と前記硬質の紫外線硬化型樹脂との特性を考慮しつつ、σ_ｒ、σ_θ、σ_ｚを計算によって求めると、次のようになる。
【００４３】
【数７】

なお、前記軟質の紫外線硬化型樹脂の樹脂温度の変化（低下した温度）をΔＴとする。そして、３次元方向の引張応力の平均引張応力（σ_ｒ＋σ_θ＋σ_ｚ）／３は、
【数８】

が成立するように、ガラスファイバ３の機械的要素、一次被覆層５の機械的要素、二次被覆層７の機械的要素を選択することが必要である。
【００４４】
次に、本発明の実施の形態の作用について説明する。
【００４５】
３次元方向の引張応力の平均引張応力（σ_ｒ＋σ_θ＋σ_ｚ）／３が一次被覆層５のヤング率Ｅ_１より小さくなるように、ガラスファイバ３の機械的要素、一次被覆層５の機械的要素、二次被覆層７の機械的要素を有するように選択して構成してあるため、硬化終了時において３次元方向の引張応力（σ_ｒ、σ_θ、σ_ｚ）によって一次被覆層５にボイドＶ又は亀裂が生じることがなくなる。
【００４６】
これは、前記軟質の紫外線硬化型樹脂からなる薄い円板状の試験シートＳにおいて略均一に３次元方向の引張応力（σ_ｒ、σ_θ、σ_ｚ）を加えて徐々に大きくすることによって、試験シートＳにボイドＶ又は亀裂が生じるときの３次元方向の引張応力の平均引張応力（換言すれば３次元方向の引張応力を加えた状態における前記軟質の紫外線硬化型樹脂の破損応力）が前記軟質の紫外線硬化型樹脂のヤング率Ｅ１よりも大きいという材料強度試験の結果（図８参照）に基づくものである。
【００４７】
以上のごとき、本発明の実施の形態によれば、硬化終了時において３次元方向の引張応力（σ_ｒ、σ_θ、σ_ｚ）によって一次被覆層５にボイドＶ又は亀裂が生じることがないため、一次被覆層５によるファイバガラス３の支持状態を安定させて、ファイバガラス３に微小な曲がりによる光ファイバ１の伝送損失を極力少なくして、光ファイバ１の品質を向上させることができる。
【００４８】
また、光ファイバ１を備えた光ファイバケーブル（図示省略）であっても、前記効果と同様の効果を奏する。ここで、前記光ファイバケーブルとは、狭義の光ファイバケーブルの他、光ファイバテープ心線、光ファイバコードも含むものである。
【００４９】
なお、本発明は、前述の発明の実施の形態の説明に限るものではなく、例えば、被覆層５，７を構成する材料を紫外線硬化型樹脂の代わりに別の硬化型樹脂に変更する等、その他種々の態様で実施可能である。
【００５０】
以下、本発明に係わる具体的な実施態様について簡単に説明する。
【００５１】
ファイバガラス３の半径Ｒ_０が６２．５μｍ、一次被覆層５の外半径Ｒ_１が１２５μｍ、二次被覆層７の外半径Ｒ_２が２００μｍであって、一次被覆層５のヤング率Ｅ_１が、−２０℃の環境温度で２．５ＭＰａ、０℃の環境温度で１．１ＭＰａ、２０℃の環境温度で１．０ＭＰａであって、二次被覆層７のヤング率Ｅ_２が、−２０℃の環境温度で１３００ＭＰａ、０℃の環境温度で１０００ＭＰａ、２０℃の環境温度で７００ＭＰａである場合に、硬化時の樹脂温度（硬化温度）を１００℃から２００℃の間で変えて６種類の光ファイバ（１Ａから１Ｆ）を製造し、６種類の光ファイバ（１Ａから１Ｆ）それぞれに環境温度を変化させて一次被覆層５のボイドＶ又は亀裂の発生の有無（破損の有無）を観察し、その観察結果は図９のようになる。
【００５２】
図９により明らかなように、一次被覆層５に働く３次元方向の引張応力の平均引張応力（σ_ｒ＋σ_θ＋σ_ｚ）／３が一次被覆層５のヤング率Ｅ_１より大きいと、一次被覆層５にボイドＶ又は亀裂が生じること、及び３次元方向の引張応力の平均引張応力（σ_ｒ＋σ_θ＋σ_ｚ）／３が一次被覆層５のヤング率Ｅ_１より小さいと、一次被覆層５にボイドＶ又は亀裂が生じないことがそれぞれ確認された。
【００５３】
次に、本発明の別の実施の形態を説明する。上記の通り、前記軟質の紫外線硬化型樹脂の樹脂温度の変化（低下した温度）をΔＴとする。そして、３次元方向の引張応力の平均引張応力（σ_ｒ＋σ_θ＋σ_ｚ）／３は、式（３）のようになる。この式が成立するように、ファイバガラス３の半径Ｒ_０、一次被覆層５の外半径Ｒ_１、前記軟質の紫外線硬化型樹脂のヤング率Ｅ_１，線膨張係数α_１，ポアソン比ν_１、二次被覆層７の外半径Ｒ_２、前記硬質の紫外線硬化型樹脂のヤング率Ｅ_２，線膨張係数α_２，ポアソン比ν_２を選択することになる。
【００５４】
更に、前記軟質の紫外線硬化型樹脂のヤング率Ｅ_１が前記硬質の紫外線硬化型樹脂のヤング率Ｅ_２に比べて極めて小さいという前提条件から、
【数９】

が成立する。式（５）及び式（６）から式（４）を簡略化すると、
【数１０】

となる。即ち、ファイバガラスの半径Ｒ_０、一次被覆層５の外半径Ｒ_１、軟質の硬化型樹脂のポアソン比ν_１、二次被覆層７の外半径Ｒ_２、前記硬質の硬化型樹脂のポアソン比ν_２、前記紫外線硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴを設定すると、
前記軟質の紫外線硬化型樹脂の線膨張係数α_１と前記硬質の紫外線硬化型樹脂の線膨張係数α_２の間に、線膨張係数の関係式（式（８）のこと）が成立するように、前記軟質の紫外線硬化型樹脂の線膨張係数α_１及び前記硬質の紫外線硬化型樹脂の線膨張係数α_２を選択している。
【００５５】
次に、本発明の実施の形態の作用について説明する。
【００５６】
前記軟質の紫外線硬化型樹脂の線膨張係数α_１と前記硬質の紫外線硬化型樹脂の線膨張係数α_２の間に、線膨張係数の関係式（式（８））が成立するように前記軟質の紫外線硬化型樹脂と前記硬質の紫外線硬化型樹脂を選択して構成してあるため、前記紫外線硬化型樹脂の樹脂温度が、硬質の紫外線硬化型樹脂の硬化時から硬化終了時にかけて大きく低下することによって一次被覆層５において略均一に３次元方向の引張応力（σ_ｒ、σ_θ、σ_ｚ）を加えた場合に、３次元方向の引張応力の平均引張応力（σ_ｒ＋σ_θ＋σ_ｚ）／３が一次被覆層５のヤング率Ｅ_１より小さくなり、硬化終了時において前記３次元方向の引張応力によって一次被覆層５にボイドＶ又は亀裂が生じることがなくなる。
【００５７】
これは、次の２つの点に基づくものである。
【００５８】
即ち、第１の点は、試験シートＳにおいて略均一に３次元方向の引張応力（σ_０ｒ、σ_{０ θ}、σ_０ｚ）を加えて徐々に大きくすることによって、試験シートＳにボイドＶ又は亀裂が生じるときの３次元方向の引張応力の平均引張応力（換言すれば３次元方向の引張応力を加えた状態における前記軟質の紫外線硬化型樹脂の破損応力）が前記軟質の紫外線硬化型樹脂のヤング率Ｅ_１よりも大きいという材料強度試験の結果（図８参照）である。
【００５９】
第２の点は、前記材料強度試験の結果から（σ_ｒ＋σ_θ＋σ_ｚ）／３が前記軟質の硬化型樹脂のヤング率Ｅ_１よりも小さくなるよう材料力学の関係式（式（４）のこと）を導き、前記軟質の紫外線硬化型樹脂のヤング率Ｅ_１が前記硬質の紫外線硬化型樹脂のヤング率Ｅ_２に比べて極めて小さいという前提条件から材料力学の関係式（式（４））を線膨張係数の関係式（式（８））に簡略化したことである。
【００６０】
以上のごとき、本発明の実施の形態によれば、硬化終了時において３次元方向の引張応力（σ_ｒ、σ_θ、σ_ｚ）によって一次被覆層５にボイドＶ又は亀裂が生じることがないため、一次被覆層５によるファイバガラス３の支持状態を安定させて、ファイバガラス３に微小な曲がりによる光ファイバ１の伝送損失を極力少なくして、光ファイバ１の品質を向上させることができる。
【００６１】
また、前記線膨張係数の関係式（式（８））は前記材料力学の関係式（式（４））を簡略化しているため、一次被覆層５にボイドＶ又は亀裂が生じないように、前記軟質の硬化型樹脂及び前記硬質の硬化型樹脂を選択することが容易になる。
【００６２】
更に、光ファイバ１を備えた光ファイバケーブル（図示省略）であっても、前記効果と同様の効果を奏する。ここで、前記光ファイバケーブルとは、狭義の光ファイバケーブルの他、光ファイバテープ心線、光ファイバコードも含むものである。
【００６３】
なお、本発明は、前述の発明の実施の形態の説明に限るものではなく、例えば、被覆層５，７を構成する材料を紫外線硬化型樹脂の代わりに別の硬化型樹脂に変更する等、その他種々の態様で実施可能である。
【００６４】
以下、本発明に係わる実施例について簡単に説明する。
【００６５】
図３は、線膨張係数の関係式に示される関係を示したグラフ図である。
【００６６】
ファイバガラス３の半径Ｒ_０が６２．５μｍ、一次被覆層５の外半径Ｒ_１が１２５μｍ、二次被覆層７の外半径Ｒ_２が２００μｍ、前記軟質の紫外線硬化型樹脂のポアソン比ν_１と前記硬質の紫外線硬化型樹脂のポアソン比ν_２が共に０．４６、前記紫外線硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴが１８０℃でそれぞれあって、前記線膨張係数の関係式（式（８））に示される関係をグラフ化すると、図３のようになる。
【００６７】
即ち、図３に描かれた選択直線よりも上側（図３において上側）の領域が、（σ_ｒ＋σ_θ＋σ_ｚ）／３が前記軟質の紫外線硬化型樹脂のヤング率Ｅ_１よりも小さくなって、一次被覆層５にボイドＶ又は亀裂が生じない領域である。また、前記選択直線よりも下側（図３において下側）の領域が、（σ_ｒ＋σ_θ＋σ_ｚ）／３が前記軟質の紫外線硬化型樹脂のヤング率Ｅ_１よりも大きくなって、一次被覆層５にボイドＶ又は亀裂が生じる領域である。
【００６８】
図１０に示すように、前記軟質の紫外線硬化型樹脂の線膨張係数α_１と前記硬質の紫外線硬化型樹脂の線膨張係数α_２の関係を変えて５種類の光ファイバ（ＡからＥ）を製造し、一次被覆層５のボイドＶ又は亀裂の発生の有無（破損の有無）を観察し、その観察結果は図９のようになる。
【００６９】
図１０により明らかなように、光ファイバＡ，Ｂ，Ｃは二種類の紫外線硬化型樹脂の線膨張係数（前記軟質の紫外線硬化型樹脂の線膨張係数α_１と前記硬質の紫外線硬化型樹脂の線膨張係数α_２）が前記選択直線よりも上側（図３において上側）の領域にあって、一次被覆層５にボイドＶ又は亀裂が生じないことが確認された。また、光ファイバＤ，Ｅは二種類の紫外線硬化型樹脂の線膨張係数α_１，α_２が前記選択直線よりも上側（図３において上側）の領域にあって、一次被覆層５にボイドＶ又は亀裂が生じることが確認された。
【００７０】
次に、この発明の実施の形態における光ファイバテープ心線を説明する。図７は、この発明の実施の形態における光ファイバテープ心線（８心テープ心線）の断面図である。
【００７１】
図７を参照するに、この実施の形態に係わる光ファイバテープ心線４１は、複数本の光ファイバ素線４３が並列に配列されて、その周囲に紫外線硬化型樹脂からなるテープ材としての二次被覆層４５が被覆されているものである。
【００７２】
光ファイバテープ心線４１を構成する光ファイバ素線４３は２以上の任意の数とすることができる。
【００７３】
上記の光ファイバ素線４３は、上記特性を持っている限り、特に限定されないが、例えば外径１２５μｍの裸光ファイバ４７に一次被覆層としての例えば紫外線硬化型樹脂４９で被覆して例えば外径２５０〜４００μｍとしたものが一般に用いられる。
【００７４】
硬質の紫外線硬化型樹脂からなる二次被覆層４５の外半径Ｒ_２は、裸光ファイバ４７の中心から最も近い二次被覆層４５の外表面までの距離とすれば、これまでの議論が近似的に成り立つ。従って、前記軟質の紫外線硬化型樹脂と前記硬質の紫外線硬化型樹脂の選択に関して、ここで詳しく述べられた内容は、光ファイバテープ心線においても有効である。
【００７５】
以下、具体的な実装例を示す。ファイバガラス３の半径Ｒ_０が６２．５μｍ、一次被覆層５の外半径Ｒ_１が１２５μｍ、二次被覆層７の外半径Ｒ_２が２００μｍ、前記硬質の紫外線硬化型樹脂のポアソン比ν２は０．４５〜０．４９とする。又、ファイバガラス３の半径Ｒ_０、一次被覆層５の外半径Ｒ_１、二次被覆層７の外半径Ｒ_２は、夫々０．３μｍの誤差を含むものとする。
【００７６】
この場合、図３に描かれた選択直線のｘ切片（α_０）は、前記紫外線硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴとポアソン比ν_１で決まり、α_０　＝（１−２ν_１）／ΔＴとなる。従って、樹脂温度の変化ΔＴとポアソン比ν_１の代わりに、このα_０を考慮すれば良い。前記軟質の紫外線硬化型樹脂のポアソン比ν_１は０．４２〜０．４７、前記紫外線硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴが高々１８０℃の場合、α_０は、約８．９〜３．３となる。一方、図３に描かれた選択直線の傾きは、Ｒ’＝（３／２）｛１＋（Ｒ_０／Ｒ_１）^２｝としてＲ’／（１＋ν_２）、即ち　（８／１５）／（１＋ν_２）となる。
【００７７】
以上のような状況で、ファイバ線膨張係数を選択する方法は以下の通りである。先ず、軟質の硬化型樹脂の線膨張係数α_１を、α_０以下に選択すべきである。即ち、（１−２ν_１）／ΔＴ　以下に選択すべきである。従って、ポアソン比ν_１の０．４２〜０．４７に応じて、約８．９〜３．３以下に選定しておけばよい。しかし、軟質の硬化型樹脂の線膨張係数α_１を、α_０以下に選択できなかった場合には、硬質の硬化型樹脂の線膨張係数α_２を、Ｒ’（α_１−α_０）／（１＋ν_２）、即ち、１５（α_１−α_０）／８（１＋ν_２）以上となるように選択すべきである。
【００７８】
本発明による恩恵は、線膨張係数の選択の幅が広がるという点にある。即ち、軟質の硬化型樹脂の線膨張係数α_１を、（１−２ν_１）／ΔＴ　以下に選択しておけば、硬質の硬化型樹脂の線膨張係数α_２を自由に選定しても、安全であることが保証される。又、軟質の硬化型樹脂の線膨張係数α_１や硬質の硬化型樹脂の線膨張係数α_２の安全な範囲が明確となり、これまで行われなかった組み合わせをも選択の範囲に組み込むことが可能となった。
【００７９】
従って、本発明の特徴が最も効果的なのは、α_０からα_０の８０パーセントの範囲に、軟質の硬化型樹脂の線膨張係数α_１を選択する場合である。即ち、線膨張係数α_１は
（１−２ν_１）／１８０　＞　α_１　＞　（１−２ν_１）／２２５．
を満たすべきである。通常、この範囲は、危険範囲に含まれているが、上記の通り安全であることが保証されている。又、軟質の硬化型樹脂の線膨張係数α_１を、α_０以下に選択できなかった場合には、硬質の硬化型樹脂の線膨張係数α_２を、Ｒ’（α_１−α_０）／（１＋ν_２）からＲ’（α_１−α_０）／（１＋ν_２）の１２０パーセントの範囲に選択する場合である。即ち、
Ｒ’（α_１−α_０）／（１＋ν_２）　＜　α_２　＜　（６／５）｛Ｒ’（α_１−α_０）／（１＋ν_２）｝
を満たすようにする。この例の場合、
１５（α_１−α_０）／８（１＋ν_２）　＜　α_２　＜　９（α_１−α_０）／４（１＋ν_２）
を満たすようにする。これも通常、危険範囲に含まれているが、上記の通り安全であることが保証されている。
【００８０】
例えば、上記の実装例の場合、前記軟質の紫外線硬化型樹脂のポアソン比ν_１を誤差範囲内で０．４２とした場合、α_０は、約８．９　ｘ　１０^{− ４}となる。その場合、軟質の硬化型樹脂の線膨張係数α_１を、８．９〜７．１の範囲で選定すると、従来にはなかった組み合わせが実現する。
【００８１】
ファイバガラス３の半径Ｒ_０が６２．５μｍ、一次被覆層５の外半径Ｒ_１が９５μｍ、二次被覆層７の外半径Ｒ_２が１２０μｍ、前記硬質の紫外線硬化型樹脂のポアソン比ν２は０．４５〜０．４９とする。又、ファイバガラス３の半径Ｒ_０、一次被覆層５の外半径Ｒ_１、二次被覆層７の外半径Ｒ_２は、夫々０．３μｍの誤差を含むものとする。
【００８２】
この場合も、図３に描かれた選択直線のｘ切片は、前記紫外線硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴとポアソン比ν_１で決まり、α_０　＝（１−２ν_１）／ΔＴとなる。やはり、樹脂温度の変化ΔＴとポアソン比ν_１の代わりに、このα_０を考慮すれば良い。前記軟質の紫外線硬化型樹脂のポアソン比ν_１は０．４２〜０．４７、前記紫外線硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴが高々１２０℃の場合、α_０は、約３．０〜２．２となる。一方、図３に描かれた選択直線の傾きは、Ｒ’＝（３／２）｛１＋（Ｒ_０／Ｒ_１）^２｝としてＲ’／（１＋ν_２）、即ち　０．８６６４／（１＋ν_２）となる。
【００８３】
以上のような状況で、ファイバ線膨張係数を選択する方法は以下の通りである。先ず、軟質の硬化型樹脂の線膨張係数α_１を、α_０以下に選択すべきである。即ち、（１−２ν_１）／ΔＴ　以下に選択すべきである。従って、ポアソン比ν_１の０．４２〜０．４７に応じて、約３．０〜２．２以下に選定しておけばよい。しかし、軟質の硬化型樹脂の線膨張係数α_１を、α_０以下に選択できなかった場合には、硬質の硬化型樹脂の線膨張係数α_２を、Ｒ’（α_１−α_０）／（１＋ν_２）、即ち、｛０．８６６４／（１＋ν_２）｝（α_１−α_０）以上となるように選択すべきである。
【００８４】
本発明による恩恵は、線膨張係数の選択の幅が広がるという点にある。即ち、軟質の硬化型樹脂の線膨張係数α_１を、（１−２ν_１）／ΔＴ　以下に選択しておけば、硬質の硬化型樹脂の線膨張係数α_２を自由に選定しても、安全であることが保証される。又、軟質の硬化型樹脂の線膨張係数α_１や硬質の硬化型樹脂の線膨張係数α_２の安全な範囲が明確となり、これまで行われなかった組み合わせをも選択の範囲に組み込むことが可能となった。
【００８５】
従って、本発明の特徴が最も効果的なのは、α_０からα_０の８０パーセントの範囲に、軟質の硬化型樹脂の線膨張係数α_１を選択する場合である。即ち、線膨張係数α_１は
（１−２ν_１）／１２０　＞　α_１　＞　（１−２ν_１）／１５０．
を満たすべきである。通常、この範囲は、危険範囲に含まれているが、上記の通り安全であることが保証されている。又、軟質の硬化型樹脂の線膨張係数α_１を、α_０以下に選択できなかった場合には、硬質の硬化型樹脂の線膨張係数α_２を、Ｒ’（α_１−α_０）／（１＋ν_２）からＲ’（α_１−α_０）／（１＋ν_２）の１２０パーセントの範囲に選択する場合である。即ち、
Ｒ’（α_１−α_０）／（１＋ν_２）　＜　α_２　＜　（６／５）｛Ｒ’（α_１−α_０）／（１＋ν_２）｝
を満たすようにする。この例の場合、
｛０．８６６４／（１＋ν_２）｝（α_１−α_０）　＜　α_２　＜　｛１．０３９６８／（１＋ν_２）｝（α_１−α_０）
を満たすようにする。これも通常、危険範囲に含まれているが、上記の通り安全であることが保証されている。
【００８６】
例えば、上記の実装例の場合、前記軟質の紫外線硬化型樹脂のポアソン比ν_１を誤差範囲内で０．４２とした場合、α_０は、（４／３）　ｘ　１０^{− ３}となる。その場合、軟質の硬化型樹脂の線膨張係数α_１を、１．３３　ｘ　１０^{− ３}　〜　１．０７　ｘ　１０^{− ３}　の範囲で選定すると、従来にはなかった組み合わせが実現する。
【００８７】
ファイバガラス３の半径Ｒ_０が６２．５μｍ、一次被覆層５の外半径Ｒ_１が９５μｍ、二次被覆層７の外半径Ｒ_２が１２０μｍ、前記硬質の紫外線硬化型樹脂のポアソン比ν２は０．４５〜０．４９とする。又、ファイバガラス３の半径Ｒ_０、一次被覆層５の外半径Ｒ_１、二次被覆層７の外半径Ｒ_２は、夫々０．３μｍの誤差を含むものとする。
【００８８】
この場合も、図３に描かれた選択直線のｘ切片は、前記紫外線硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴとポアソン比ν_１で決まり、α_０　＝（１−２ν_１）／ΔＴとなる。やはり、樹脂温度の変化ΔＴとポアソン比ν_１の代わりに、このα_０を考慮すれば良い。前記軟質の紫外線硬化型樹脂のポアソン比ν_１は０．４２〜０．４７、前記紫外線硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴが高々１８０℃の場合、α_０は、約８．９〜３．３となる。一方、図３に描かれた選択直線の傾きは、Ｒ’＝（３／２）｛１＋（Ｒ_０／Ｒ_１）^２｝としてＲ’／（１＋ν_２）、即ち　０．８６６４／（１＋ν_２）となる。
【００８９】
以上のような状況で、ファイバ線膨張係数を選択する方法は以下の通りである。先ず、軟質の硬化型樹脂の線膨張係数α_１を、α_０以下に選択すべきである。即ち、（１−２ν_１）／ΔＴ　以下に選択すべきである。従って、ポアソン比ν_１の０．４２〜０．４７に応じて、約８．９〜３．３以下に選定しておけばよい。しかし、軟質の硬化型樹脂の線膨張係数α_１を、α_０以下に選択できなかった場合には、硬質の硬化型樹脂の線膨張係数α_２を、Ｒ’（α_１−α_０）／（１＋ν_２）、即ち、｛０．８６６４／（１＋ν_２）｝（α_１−α_０）以上となるように選択すべきである。
【００９０】
本発明による恩恵は、線膨張係数の選択の幅が広がるという点にある。即ち、軟質の硬化型樹脂の線膨張係数α_１を、（１−２ν_１）／ΔＴ　以下に選択しておけば、硬質の硬化型樹脂の線膨張係数α_２を自由に選定しても、安全であることが保証される。又、軟質の硬化型樹脂の線膨張係数α_１や硬質の硬化型樹脂の線膨張係数α_２の安全な範囲が明確となり、これまで行われなかった組み合わせをも選択の範囲に組み込むことが可能となった。
【００９１】
従って、本発明の特徴が最も効果的なのは、α_０からα_０の８０パーセントの範囲に、軟質の硬化型樹脂の線膨張係数α_１を選択する場合である。即ち、線膨張係数α_１は
（１−２ν_１）／１８０　＞　α_１　＞　（１−２ν_１）／２２５．
を満たすべきである。通常、この範囲は、危険範囲に含まれているが、上記の通り安全であることが保証されている。又、軟質の硬化型樹脂の線膨張係数α_１を、α_０以下に選択できなかった場合には、硬質の硬化型樹脂の線膨張係数α_２を、Ｒ’（α_１−α_０）／（１＋ν_２）からＲ’（α_１−α_０）／（１＋ν_２）の１２０パーセントの範囲に選択する場合である。即ち、
Ｒ’（α_１−α_０）／（１＋ν_２）　＜　α_２　＜　（６／５）｛Ｒ’（α_１−α_０）／（１＋ν_２）｝
を満たすようにする。この例の場合、
｛０．８６６４／（１＋ν_２）｝（α_１−α_０）　＜　α_２　＜　｛１．０３９６８／（１＋ν_２）｝（α_１−α_０）
を満たすようにする。これも通常、危険範囲に含まれているが、上記の通り安全であることが保証されている。
【００９２】
例えば、上記の実装例の場合、前記軟質の紫外線硬化型樹脂のポアソン比ν_１を誤差範囲内で０．４２とした場合、α_０は、約８．９　ｘ　１０^−４となる。その場合、軟質の硬化型樹脂の線膨張係数α_１を、８．９〜７．１の範囲で選定すると、従来にはなかった組み合わせが実現する。
【００９３】
ファイバガラス３の半径Ｒ_０が６２．５μｍ、一次被覆層５の外半径Ｒ_１が１２５μｍ、二次被覆層７の外半径Ｒ_２が２００μｍ、前記硬質の紫外線硬化型樹脂のポアソン比ν２は０．４５〜０．４９とする。又、ファイバガラス３の半径Ｒ_０、一次被覆層５の外半径Ｒ_１、二次被覆層７の外半径Ｒ_２は、夫々０．３μｍの誤差を含むものとする。
【００９４】
この場合、図３に描かれた選択直線のｘ切片（α_０）は、前記紫外線硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴとポアソン比ν_１で決まり、α_０　＝（１−２ν_１）／ΔＴとなる。やはり、樹脂温度の変化ΔＴとポアソン比ν_１の代わりに、このα_０を考慮すれば良い。前記軟質の紫外線硬化型樹脂のポアソン比ν_１は０．４２〜０．４７、前記紫外線硬化型樹脂における硬化時と硬化終了時の樹脂温度の変化ΔＴが高々１２０℃の場合、α_０は、約３．０〜２．２となる。一方、図３に描かれた選択直線の傾きは、Ｒ’＝（３／２）｛１＋（Ｒ_０／Ｒ_１）^２｝としてＲ’／（１＋ν_２）、即ち　（８／１５）／（１＋ν_２）となる。
【００９５】
以上のような状況で、ファイバ線膨張係数を選択する方法は以下の通りである。先ず、軟質の硬化型樹脂の線膨張係数α_１を、α_０以下に選択すべきである。即ち、（１−２ν_１）／ΔＴ　以下に選択すべきである。従って、ポアソン比ν_１の０．４２〜０．４７に応じて、約３．０〜２．２以下に選定しておけばよい。しかし、軟質の硬化型樹脂の線膨張係数α_１を、α_０以下に選択できなかった場合には、硬質の硬化型樹脂の線膨張係数α_２を、Ｒ’（α_１−α_０）／（１＋ν_２）、即ち、１５（α_１−α_０）／８（１＋ν_２）以上となるように選択すべきである。
【００９６】
本発明による恩恵は、線膨張係数の選択の幅が広がるという点にある。即ち、軟質の硬化型樹脂の線膨張係数α_１を、（１−２ν_１）／ΔＴ　以下に選択しておけば、硬質の硬化型樹脂の線膨張係数α_２を自由に選定しても、安全であることが保証される。又、軟質の硬化型樹脂の線膨張係数α_１や硬質の硬化型樹脂の線膨張係数α_２の安全な範囲が明確となり、これまで行われなかった組み合わせをも選択の範囲に組み込むことが可能となった。
【００９７】
従って、本発明の特徴が最も効果的なのは、α_０からα_０の８０パーセントの範囲に、軟質の硬化型樹脂の線膨張係数α_１を選択する場合である。即ち、線膨張係数α_１は
（１−２ν_１）／１２０　＞　α_１　＞　（１−２ν_１）／１５０．
を満たすべきである。通常、この範囲は、危険範囲に含まれているが、上記の通り安全であることが保証されている。又、軟質の硬化型樹脂の線膨張係数α_１を、α_０以下に選択できなかった場合には、硬質の硬化型樹脂の線膨張係数α_２を、Ｒ’（α_１−α_０）／（１＋ν_２）からＲ’（α_１−α_０）／（１＋ν_２）の１２０パーセントの範囲に選択する場合である。即ち、
Ｒ’（α_１−α_０）／（１＋ν_２）　＜　α_２　＜　（６／５）｛Ｒ’（α_１−α_０）／（１＋ν_２）｝
を満たすようにする。この例の場合、
１５（α_１−α_０）／８（１＋ν_２）　＜　α_２　＜　９（α_１−α_０）／４（１＋ν_２）
を満たすようにする。これも通常、危険範囲に含まれているが、上記の通り安全であることが保証されている。
【００９８】
例えば、上記の実装例の場合、前記軟質の紫外線硬化型樹脂のポアソン比ν_１を誤差範囲内で０．４２とした場合、α_０は、（４／３）　ｘ　１０^{− ３}となる。その場合、軟質の硬化型樹脂の線膨張係数α_１を、１．３３　ｘ　１０^{− ３}　〜　１．０７　ｘ　１０^{− ３}　の範囲で選定すると、従来にはなかった組み合わせが実現する。
【００９９】
以上、本発明を実施例により詳細に説明したが、当業者にとっては、本発明が本願中に説明した実施例に限定されるものではないということは明らかである。本発明の装置は、特許請求の範囲の記載により定まる本発明の趣旨及び範囲を逸脱することなく修正及び変更態様として実施することができる。従って、本願の記載は、例示説明を目的とするものであり、本発明に対して何ら制限的な意味を有するものではない。
【０１００】
【発明の効果】
本発明の実施例によれば、硬化終了時において前記３次元方向の引張応力によって前記一次被覆層にボイド又は亀裂が生じることがないため、前記一次被覆層による前記ファイバガラスの支持状態を安定させて、前記ファイバガラスに微小な曲がりによる前記光ファイバの伝送損失を極力少なくして、前記光ファイバの品質を向上させることができる。
【０１０１】
また、前記線膨張係数の関係式は前記材料力学の関係式を簡略化しているため、前記一次被覆層にボイド又は亀裂が生じないように、前記軟質の硬化型樹脂及び前記硬質の硬化型樹脂を選択することが容易になる。
【図面の簡単な説明】
【図１】本発明の実施の形態に係わるファイバガラス等の機械的要素を説明する図である。
【図２】本発明の実施の形態に係わる光ファイバの断面図である。
【図３】線膨張係数の関係式に示される関係を示したグラフ図である。
【図４】本発明の実施の形態に係わる材料強度試験装置の模式的な斜視図である。
【図５】本発明の実施の形態に係わる材料強度試験装置による強度試験を説明する図である。
【図６】図５（ｂ）における試験シートを上から見た図である。
【図７】この発明の実施の形態における光ファイバテープ心線（８心テープ心線）の断面図である。
【図８】軟質の紫外線硬化型樹脂の種類及び材料試験装置の環境温度を変更して、材料強度試験装置による強度試験の結果を示す。
【図９】６種類の光ファイバ（１Ａから１Ｆ）それぞれに環境温度を変化させて一次被覆層のボイドＶ又は亀裂の発生の有無（破損の有無）を観察した結果を示す。
【図１０】５種類の光ファイバ（ＡからＥ）それぞれに環境温度を変化させて一次被覆層のボイドＶ又は亀裂の発生の有無（破損の有無）を観察した結果を示す。
【符号の説明】
１　光ファイバ
３　ファイバガラス
５　一次被覆層
７　二次被覆層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical fiber, an optical fiber cable having a primary coating layer and a secondary coating layer, and a method for manufacturing the same.
[0002]
[Prior art]
In general, the optical fiber is a fiber glass, a primary coating layer that directly covers the outer peripheral portion of the fiber glass, and a secondary coating layer that indirectly covers the outer peripheral portion of the fiber glass via the primary coating layer. It has.
[0003]
Here, the primary coating layer is made of a soft ultraviolet curing resin, and the secondary coating layer is made of a hard ultraviolet curing resin. This is because, when an external force is applied to the optical fiber, the deformation of the entire optical fiber is suppressed by the secondary coating layer, and the small deformation suppressed by the primary coating layer is absorbed, so that the deformation of the glass fiber due to the external force is minimized. This is because they do not tell.
[0004]
[Problems to be solved by the invention]
By the way, the primary coating layer tends to shrink three-dimensionally due to a significant decrease in the temperature of the UV-curable resin from the time of hardening of the hard UV-curable resin to the end of the hardening. Since the three-dimensional shrinkage of the primary coating layer is restrained by the coating layer, a substantially uniform three-dimensional tensile stress is generated in the primary coating layer. Here, the time at which the curing is completed includes not only immediately after the completion of the curing but also after the environmental temperature changes after the completion of the curing, and the three-dimensional tensile stress is defined as the radial stress of the primary coating layer in the radial direction. Tensile stress, tensile stress in the circumferential direction of the primary coating layer, and tensile stress in the fiber axis direction.
[0005]
Therefore, if the mechanical element of the glass fiber, the mechanical element of the primary coating layer, and the mechanical element of the secondary coating layer are inappropriate, the tensile stress of the three-dimensional direction applied to the primary coating layer at the end of curing is reduced. When the average tensile stress exceeds a predetermined breaking stress, voids or cracks occur in the primary coating layer. For this reason, the support state of the fiber glass by the primary coating layer becomes unstable, and a slight bending occurs in the fiber glass, which leads to transmission loss of the optical fiber and deteriorates the quality of the optical fiber.
[0006]
[Means for Solving the Problems]
According to one aspect of the present invention, the optical fiber is made of fiber glass and a soft curable resin, and a primary coating layer that directly covers an outer peripheral portion of the fiber glass, and a hard curable resin. And a secondary coating layer for indirectly coating the outer peripheral portion of the fiber glass via the primary coating layer, wherein the resin temperature of the curable resin is set at the time of curing of a hard ultraviolet curable resin. To the end of hardening, so that the primary coating layer has a substantially uniform three-dimensional tensile stress (σ) in the primary coating layer._r, Σ_θ, Σ_z) Is applied, the average tensile stress of the three-dimensional tensile stress (σ_r+ Σ_θ+ Σ_z) / 3 is smaller than the Young's modulus of the primary coating layer, the glass fiber mechanical element, the primary coating layer mechanical element, and the secondary coating layer mechanical element. .
[0007]
According to another aspect of the present invention, the optical fiber cable is an optical fiber cable composed of a plurality of optical fibers, each optical fiber being made of a fiber glass and a soft curable resin, A primary coating layer that directly covers the outer peripheral portion of the fiber glass, and a secondary coating layer that is formed of a hard curable resin and indirectly covers the outer peripheral portion of the fiber glass via the primary coating layer. The three-dimensional tensile stress (σ) in the primary coating layer is substantially uniform because the temperature of the hardening resin greatly decreases from the hardening of the hard ultraviolet hardening resin to the end of hardening._r, Σ_θ, Σ_z) Is applied, the average tensile stress of the three-dimensional tensile stress (σ_r+ Σ_θ+ Σ_z) / 3 is smaller than the Young's modulus of the primary coating layer, the glass fiber mechanical element, the primary coating layer mechanical element, and the secondary coating layer mechanical element. .
[0008]
According to still another aspect of the present invention, a method of manufacturing an optical fiber includes a fiber glass, a primary coating layer made of a soft curable resin and directly coating an outer peripheral portion of the fiber glass, and a hard coating. A method for manufacturing an optical fiber, comprising a curable resin and a secondary coating layer indirectly covering the fiber glass via the primary coating layer, wherein the resin temperature of the curable resin is hard. Greatly decreases from the time of curing to the time of completion of curing of the ultraviolet curable resin, whereby the three-dimensional tensile stress (σ) in the primary coating layer is substantially uniform._r, Σ_θ, Σ_z) Is applied, the average tensile stress of the three-dimensional tensile stress (σ_r+ Σ_θ+ Σ_zThe mechanical element of the glass fiber, the mechanical element of the primary coating layer, and the mechanical element of the secondary coating layer are selected such that (3) is smaller than the Young's modulus of the primary coating layer. And
[0009]
According to still another aspect of the present invention, the optical fiber is composed of fiber glass and a soft curable resin, and a primary coating layer that directly covers an outer peripheral portion of the fiber glass, and a hard curable resin. And a secondary coating layer for indirectly coating the outer peripheral portion of the fiber glass via the primary coating layer, wherein the Young's modulus of the soft curable resin is the hard curable resin. Is extremely small compared to the Young's modulus of₀, The outer radius R of the primary coating layer₁, The Poisson's ratio ν of the soft curable resin₁, The Poisson's ratio ν of the hard curable resin₂By setting a change ΔT in resin temperature between the time of curing and the time of completion of curing of the curable resin, the linear expansion coefficient α of the soft curable resin is set.₁And the linear expansion coefficient α of the hard curable resin.₂Between,
(Equation 4)

Wherein the relational expression of the linear expansion coefficient is satisfied.
[0010]
According to still another aspect of the present invention, the optical fiber is composed of fiber glass and a soft curable resin, and a primary coating layer that directly covers an outer peripheral portion of the fiber glass, and a hard curable resin. And a secondary coating layer for indirectly coating the outer peripheral portion of the fiber glass via the primary coating layer, wherein the Young's modulus of the soft curable resin is the hard curable resin. Is extremely small compared to the Young's modulus of₀, The outer radius R of the primary coating layer₁, The Poisson's ratio ν of the soft curable resin₁, The Poisson's ratio ν of the hard curable resin₂By setting a change ΔT in resin temperature between the time of curing and the time of completion of curing of the curable resin, the linear expansion coefficient α of the soft curable resin is set.₁And the linear expansion coefficient α of the hard curable resin.₂Between,
(Equation 5)

Wherein the relational expression of the linear expansion coefficient is satisfied.
[0011]
According to still another aspect of the present invention, a method of manufacturing an optical fiber includes a fiber glass, a primary coating layer made of a soft curable resin and directly coating an outer peripheral portion of the fiber glass, and a hard coating. A method of manufacturing an optical fiber, comprising a secondary coating layer composed of a curable resin and indirectly coating the fiber glass via the primary coating layer, wherein the Young's modulus of the soft curable resin is Is extremely smaller than the Young's modulus of the hard curable resin, and the fiber glass has a radius R₀, The outer radius R of the primary coating layer₁, The Poisson's ratio ν of the soft curable resin₁, The Poisson's ratio ν of the hard curable resin₂By setting a change ΔT in resin temperature between the time of curing and the time of completion of curing of the curable resin, the linear expansion coefficient α of the soft curable resin is set.₁And the linear expansion coefficient α of the hard curable resin.₂Between,
(Equation 6)

Wherein the soft curable resin and the hard curable resin are selected so that the relational expression of the linear expansion coefficient is satisfied.
[0012]
According to still another aspect of the present invention, the optical fiber is composed of fiber glass and a soft curable resin, and a primary coating layer that directly covers an outer peripheral portion of the fiber glass, and a hard curable resin. And a secondary coating layer for indirectly coating the outer peripheral portion of the fiber glass via the primary coating layer, wherein the Young's modulus of the soft curable resin is the hard curable resin. Is sufficiently smaller than the Young's modulus of the fiber glass, and the radius R of the fiber glass is within an error range.₀62. 5 μm, outer radius R of the primary coating layer₁125 μm, the outer radius R of the secondary coating layer₂Is 200 μm, the Poisson's ratio ν of the soft curable resin.₁As the change ΔT in resin temperature between the time of curing and the time of completion of curing of the curable resin, the soft curable resin has a linear expansion coefficient of (1-2ν).₁) / ΔT or less.
[0013]
According to still another aspect of the present invention, the optical fiber is composed of fiber glass and a soft curable resin, and a primary coating layer that directly covers an outer peripheral portion of the fiber glass, and a hard curable resin. And a secondary coating layer for indirectly coating the outer peripheral portion of the fiber glass via the primary coating layer, wherein the Young's modulus of the soft curable resin is the hard curable resin. Is sufficiently smaller than the Young's modulus of the fiber glass, and the radius R of the fiber glass is within an error range.₀62. 5 μm, outer radius R of the primary coating layer₁125 μm, the outer radius R of the secondary coating layer₂Is 200 μm, the Poisson's ratio ν of the soft curable resin.₁The soft curable resin has a coefficient of linear expansion α as a change ΔT in resin temperature between the time of curing and the time of completion of curing of the curable resin.₁But,
(1-2v₁) / 180> α₁> (1-2ν₁) / 225
Is selected to satisfy
[0014]
According to still another aspect of the present invention, the optical fiber is composed of fiber glass and a soft curable resin, and a primary coating layer that directly covers an outer peripheral portion of the fiber glass, and a hard curable resin. And a secondary coating layer for indirectly coating the outer peripheral portion of the fiber glass via the primary coating layer, wherein the Young's modulus of the soft curable resin is the hard curable resin. Which is sufficiently smaller than the Young's modulus of the₀62. 5 μm, outer radius R of the primary coating layer₁125 μm, the outer radius R of the secondary coating layer₂Is 200 μm, the Poisson's ratio ν of the soft curable resin.₁, The Poisson's ratio ν of the hard curable resin₂The change ΔT in resin temperature between the time of curing and the time of completion of curing of the curable resin is α₀= (1-2ν₁) / ΔT, the soft curable resin has a coefficient of linear expansion α₁But this α₀And the hard curable resin has a coefficient of linear expansion α₂But
15 (α₁−α₀) / 8 (1 + ν₂) <Α₂<9 (α₁−α₀) / 4 (1 + ν)₂)
Is selected to satisfy
[0015]
According to still another aspect of the present invention, the optical fiber is composed of fiber glass and a soft curable resin, and a primary coating layer that directly covers an outer peripheral portion of the fiber glass, and a hard curable resin. And a secondary coating layer for indirectly coating the outer peripheral portion of the fiber glass via the primary coating layer, wherein the Young's modulus of the soft curable resin is the hard curable resin. Is sufficiently smaller than the Young's modulus of the fiber glass, and the radius R of the fiber glass is within an error range.₀62. 5 μm, outer radius R of the primary coating layer₁95 μm, the outer radius R of the secondary coating layer₂Is 120 μm, the Poisson's ratio ν of the soft curable resin.₁As a change ΔT in the resin temperature between the time of curing and the time of completion of curing of the curable resin, the soft curable resin has a linear expansion coefficient of (1-2ν).₁) / ΔT or less.
[0016]
According to still another aspect of the present invention, the optical fiber is composed of fiber glass and a soft curable resin, and a primary coating layer that directly covers an outer peripheral portion of the fiber glass, and a hard curable resin. And a secondary coating layer for indirectly coating the outer peripheral portion of the fiber glass via the primary coating layer, wherein the Young's modulus of the soft curable resin is the hard curable resin. Is sufficiently smaller than the Young's modulus of the fiber glass, and the radius R of the fiber glass is within an error range.₀62. 5 μm, outer radius R of the primary coating layer₁95 μm, the outer radius R of the secondary coating layer₂Is 120 μm, the Poisson's ratio ν of the soft curable resin.₁The soft curable resin has a coefficient of linear expansion α as a change ΔT in resin temperature between the time of curing and the time of completion of curing of the curable resin.₁But,
(1-2v₁) / 120> α₁> (1-2ν₁) / 150
Is selected to satisfy
[0017]
According to still another aspect of the present invention, the optical fiber is composed of fiber glass and a soft curable resin, and a primary coating layer that directly covers an outer peripheral portion of the fiber glass, and a hard curable resin. And a secondary coating layer for indirectly coating the outer peripheral portion of the fiber glass via the primary coating layer, wherein the Young's modulus of the soft curable resin is the hard curable resin. Is sufficiently smaller than the Young's modulus of the fiber glass, and the radius R of the fiber glass is within an error range.₀62. 5 μm, outer radius R of the primary coating layer₁95 μm, the outer radius R of the secondary coating layer₂Is 120 μm, the Poisson's ratio ν of the soft curable resin.₁, The Poisson's ratio ν of the hard curable resin₂The change ΔT in resin temperature between the time of curing and the time of completion of curing of the curable resin is α₀= (1-2ν₁) / ΔT, the soft curable resin has a coefficient of linear expansion α₁But this α₀And the hard curable resin has a coefficient of linear expansion α₂But
｛0.8664 / (1 + ν)₂)｝ (Α₁−α₀) <Α₂<｛1.03968 / (1 + ν₂)｝ (Α₁−α₀)
Is selected to satisfy
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0019]
FIG. 1 is a diagram illustrating mechanical elements such as fiber glass according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of an optical fiber according to the embodiment of the present invention. FIG. 5 is a schematic perspective view of a material strength test device according to the embodiment of the present invention, and FIG. 5 is a diagram illustrating a strength test by the material strength test device according to the embodiment of the present invention. 6 is a view of the test sheet in FIG. 5B as viewed from above.
[0020]
Here, “upper” refers to the upper side in FIGS. 4 and 5 and the table in FIG. 6 toward the paper surface, and “lower” refers to the lower side in FIGS. 4 and 5 and the reverse in FIG. 6 toward the paper surface. Means
[0021]
As shown in FIG. 2, the optical fiber 1 according to the embodiment of the present invention includes a fiber glass 3, a primary coating layer 5 that directly covers an outer peripheral portion of the fiber glass 3, and an outer peripheral portion of the fiber glass 3. And a secondary coating layer 7 that indirectly coats through a primary coating layer 5. Here, the primary coating layer 5 is made of a soft UV-curable resin, and the secondary coating layer 7 is made of a hard UV-curable resin.
[0022]
The soft curable resin and the hard curable resin are adjusted by appropriately blending an ultraviolet curable resin or the like with a photoinitiator or the like so as to obtain desired physical characteristics. As such an ultraviolet curable resin, a photopolymerizable prepolymer or a photopolymerizable monomer such as an ultraviolet curable epoxy acrylate, an ultraviolet curable urethane acrylate resin, or another urethane resin is used.
[0023]
Further, the optical fiber 1 has a mechanical element based on a result of a material strength test or the like by the material strength test device 9 as shown in FIG. 4. Before describing the mechanical element of the optical fiber 1, A specific configuration of the test device 9 and a strength test by the material strength test device 9 will be described.
[0024]
As shown in FIG. 4, the material strength test device 9 according to the embodiment of the present invention includes a rectangular first holder 11 and a rectangular second holder 13 which are vertically opposed to each other. In order for the first holder 11 to be supported movably in the vertical direction with respect to the second holder 13, the second holder 13 is provided with a plurality of fixing protrusions 15, and the plurality of fixing protrusions 15 A guide pin 17 is provided upright, and the first holder 11 is provided with a plurality of movable projections 19 which are guided by the corresponding guide pin 17 so as to be movable in the vertical direction.
[0025]
A circular first fixing member 21 is provided at the center of the first holder 11, and the first fixing member 21 is fixed such that the surface of an extremely thin disk-shaped test sheet S is closely attached by an adhesive action. 1f (see FIG. 5). A circular second fixing member 23 is provided at the center of the second holder 13 so as to face the first fixing member 21 vertically, and the second fixing member 23 is bonded to the back surface of the test sheet S. It has a second constraining surface 23f (see FIG. 5) which is tightly fixed by the action. Further, the first fixing member 21 and the second fixing member 23 are each made of transparent glass.
[0026]
Here, the test sheet S is made of the same soft UV-curable resin as the soft UV-curable resin constituting the primary coating layer 5 in the optical fiber 1, and the thickness of the test sheet S is the same as that of the primary coating layer. 5 is the same as the thickness.
[0027]
The first holder 11 is provided with a mounting protrusion 25, and the second holder 13 is provided with a contact protrusion 27 that is vertically opposed to the mounting protrusion 25. In order to slightly displace the first fixing member 21 in the upward direction (in other words, in the thickness direction of the test sheet S and in the separating direction in which the first fixing member 21 is separated from the second fixing member 23), the knob 29 is rotated by the mounting protrusion 25. A micrometer head 33 provided with a spindle 31 that can be slightly expanded and contracted in the vertical direction by an operation is provided, and a tip end (lower end) of the spindle 31 can be brought into contact with a contact projection.
[0028]
Therefore, the first fixing member 21 and the first holder 11 are integrally formed by bringing the tip of the spindle 31 into contact with the contact protrusion 27 and rotating the knob 29 to slightly extend the spindle 31 downward by a small amount. Can be slightly displaced upward. At this time, since the plurality of movable protrusions 19 are guided by the plurality of guide pins 17 and are displaced upward, the first constraint surface 21f and the second constraint surface 23f are held in parallel.
[0029]
A microscope 35 for observing the test sheet S from above and outside the first fixing member 21 is provided above the first holder 11 via a support arm (not shown). Note that the posture, position, and the like of the microscope 35 can be changed via an appropriate mechanism.
[0030]
Next, a strength test by the material strength test device 9 will be described.
[0031]
As shown in FIG. 5, the front surface of the test sheet S is adhered and fixed to the first restraining surface 21 f of the first fixing member 21 by an adhesive action, and the back surface of the test sheet S is fixed by the second restraining member 23 of the second fixing member 23. The surface 23f is closely adhered and fixed by an adhesive action (see FIG. 5A). Thus, the stress effective area of the entire area of the test sheet S except for the vicinity of the outer peripheral portion can be restricted so as not to be displaced in the radial direction and the circumferential direction.
[0032]
Here, if the stress effective area is further clarified, in the embodiment of the present invention, when the first fixing member 21 is slightly displaced upward, an R-shaped depression Sd is generated on the outer peripheral surface of the test sheet S. However, the stress effective area is an area of the entire area of the test sheet S excluding the vicinity of the outer peripheral portion, and refers to an area where the depression Sd does not occur (see FIG. 6).
[0033]
Then, while observing the test sheet S from the outside of the first fixing member 21 with the microscope 35 in an enlarged manner, while holding the first constraint surface 21f and the second constraint surface 23f in parallel, the distal end of the spindle 31 Is brought into contact with the contact protrusion 27, the knob 29 is rotated to slightly displace the spindle 31 downward, and the first fixing member 21 is minutely displaced upward (see FIG. 5B). As a result, the test sheet S tends to contract in the horizontal direction. However, since the radial displacement and the circumferential displacement of the stress effective area of the test sheet S are restricted by the first constraint surface 21f and the second constraint surface 23f. In addition to the tensile stress in the thickness direction (vertical direction in FIG. 5), the tensile stress in the radial direction and the tensile stress in the circumferential direction can be applied to the stress effective area of the test sheet S. In other words, A three-dimensional tensile stress can be applied to the stress effective area of the test sheet S. Further, since the thickness of the test sheet S is extremely small, a three-dimensional tensile stress can be applied substantially uniformly in the effective stress region of the test sheet S.
[0034]
Here, the three-dimensional tensile stress refers to the radial tensile stress σ._0rAnd the circumferential tensile stress σ_{0 θ}, The tensile stress σ in the thickness direction_0zMeans
[0035]
Further, as the minute displacement amount of the first fixing member 21 increases, the tensile stress in the three-dimensional direction of the stress effective area of the test sheet S gradually increases, so that the test sheet S has voids V or cracks (not shown). Occurs (see FIG. 5C). Then, based on the displacement of the first fixing member 21 when the void V or the crack occurs in the test sheet S, the breaking stress of the soft ultraviolet-curable resin in a state where a three-dimensional tensile stress is applied is obtained. .
[0036]
Here, the tensile stress in the three-dimensional direction with respect to the displacement amount of the first fixing member 21 can be obtained using analysis by the finite element method or the like, and the displacement amount of the first fixing member 21 in the stress effective area of the test sheet S. And a three-dimensional tensile stress has a linear relationship. Further, the breaking stress of the soft ultraviolet-curable resin in a state where a three-dimensional tensile stress is applied refers to the three-dimensional direction applied to the test sheet S when a void V or a crack occurs in the test sheet S. Average tensile stress (σ_0r+ Σ_{0 θ}+ Σ_0z) / 3.
[0037]
FIG. 8 shows the results of a strength test performed by the material strength test device 9 by changing the type of the soft UV-curable resin and the environmental temperature of the material test device. Here, the radius of the first fixing member 21 and the radius of the second fixing member 23 are 50 mm, the radius of the test sheet S is 50 mm, and the thickness of the test sheet is 100 μm.
[0038]
As is clear from FIG. 8, the tensile stress (σ) in the three-dimensional direction is substantially uniform in the disc-shaped test sheet S._0r, Σ_{0 θ}, Σ_0z) To gradually increase the average tensile stress (σ) of the three-dimensional tensile stress when a void V or a crack occurs in the test sheet S._0r+ Σ_{0 θ}+ Σ_0z) / 3, in other words, it was found that the breaking stress of the soft ultraviolet-curable resin in a state where a three-dimensional tensile stress was applied was larger than the Young's modulus of the soft curable resin.
[0039]
Next, mechanical components of the optical fiber 1 based on the result of the material strength test by the material strength test device 9 and a method of manufacturing the same will be described.
[0040]
As shown in FIG. 1, the resin temperature of the soft UV-curable resin greatly decreases from the hardening of the hard UV-curable resin to the end of the hardening, so that the three-dimensional direction of the primary coating layer 5 is substantially uniform. Tensile stress (σ_r, Σ_θ, Σ_z),
The average tensile stress of three-dimensional tensile stress (σ_r+ Σ_θ+ Σ_z) / 3 is the Young's modulus E of the primary coating layer 5₁In order to make it smaller, it is selected to have a mechanical element of the glass fiber 3, a mechanical element of the primary coating layer 5, and a mechanical element of the secondary coating layer 7.
[0041]
Where σ_rIs the tensile stress in the radial direction of the primary coating layer 5 and σ_θIs the tensile stress in the circumferential direction of the primary coating layer 5 and σ_zIs the tensile stress of the primary coating layer 5 in the fiber axis direction (the front and back direction in FIG. 1 toward the paper surface). The mechanical element of the glass fiber 3 is a radius R of the fiber glass 3.₀And the mechanical element of the primary coating layer 5 is the outer radius R of the primary coating layer 5₁The Young's modulus E of the soft UV-curable resin₁, Linear expansion coefficient α₁, Poisson's ratio ν₁And the mechanical element of the secondary coating layer 7 is the outer radius R of the secondary coating layer 7₂The Young's modulus E of the hard UV-curable resin₂, Linear expansion coefficient α₂, Poisson's ratio ν₂It is. The term "end of curing" includes not only immediately after the end of the curing but also after the environmental temperature changes after the end of the curing.
[0042]
Then, considering the characteristics of the soft UV-curable resin and the hard UV-curable resin, σ_r, Σ_θ, Σ_zIs obtained by calculation as follows.
[0043]
(Equation 7)

The change (decreased temperature) in the temperature of the soft UV-curable resin is defined as ΔT. Then, the average tensile stress of the three-dimensional tensile stress (σ_r+ Σ_θ+ Σ_z) / 3 is
(Equation 8)

It is necessary to select the mechanical element of the glass fiber 3, the mechanical element of the primary coating layer 5, and the mechanical element of the secondary coating layer 7 so that the following holds.
[0044]
Next, the operation of the embodiment of the present invention will be described.
[0045]
The average tensile stress of three-dimensional tensile stress (σ_r+ Σ_θ+ Σ_z) / 3 is the Young's modulus E of the primary coating layer 5₁Since the mechanical elements of the glass fiber 3, the mechanical element of the primary coating layer 5, and the mechanical element of the secondary coating layer 7 are selected so as to be smaller, the mechanical elements 3 Dimensional tensile stress (σ_r, Σ_θ, Σ_z) Eliminates the occurrence of voids V or cracks in the primary coating layer 5.
[0046]
This is because, in the thin disk-shaped test sheet S made of the soft ultraviolet-curable resin, the tensile stress (σ_r, Σ_θ, Σ_z) To gradually increase the average tensile stress of the three-dimensional tensile stress when a void V or a crack occurs in the test sheet S (in other words, the soft tensile strength in the state where the three-dimensional tensile stress is applied). Is based on the result of a material strength test (see FIG. 8) that the softening UV-curable resin has a greater stress than the Young's modulus E1 of the soft UV-curable resin.
[0047]
As described above, according to the embodiment of the present invention, the three-dimensional tensile stress (σ_r, Σ_θ, Σ_z) Does not cause a void V or a crack in the primary coating layer 5, so that the support state of the fiber glass 3 by the primary coating layer 5 is stabilized, and the transmission loss of the optical fiber 1 due to the slight bending of the fiber glass 3 is minimized. By reducing the number, the quality of the optical fiber 1 can be improved.
[0048]
Further, even with an optical fiber cable (not shown) having the optical fiber 1, the same effects as those described above can be obtained. Here, the optical fiber cable includes an optical fiber cable and an optical fiber cord in addition to an optical fiber cable in a narrow sense.
[0049]
Note that the present invention is not limited to the description of the above-described embodiment of the present invention. For example, the material forming the coating layers 5 and 7 may be changed to another curable resin instead of the ultraviolet curable resin. The present invention can be implemented in various other modes.
[0050]
Hereinafter, specific embodiments according to the present invention will be briefly described.
[0051]
Radius R of fiber glass 3₀Is 62.5 μm, the outer radius R of the primary coating layer 5₁Is 125 μm, the outer radius R of the secondary coating layer 7₂Is 200 μm, and the Young's modulus E of the primary coating layer 5 is₁Is 2.5 MPa at an environmental temperature of −20 ° C., 1.1 MPa at an environmental temperature of 0 ° C., and 1.0 MPa at an environmental temperature of 20 ° C., and the Young's modulus E of the secondary coating layer 7 is₂However, when the ambient temperature of -20 ° C is 1300 MPa, the environmental temperature of 0 ° C is 1000 MPa, and the environmental temperature of 20 ° C is 700 MPa, the resin temperature during curing (curing temperature) is changed from 100 ° C to 200 ° C. To produce six types of optical fibers (1A to 1F), and changing the environmental temperature of each of the six types of optical fibers (1A to 1F) to determine whether the primary coating layer 5 has a void V or a crack (whether or not there is damage). ), And the observation result is as shown in FIG.
[0052]
9, the average tensile stress (σ) of the three-dimensional tensile stress acting on the primary coating layer 5 is apparent._r+ Σ_θ+ Σ_z) / 3 is the Young's modulus E of the primary coating layer 5₁If it is larger, voids V or cracks are formed in the primary coating layer 5 and the average tensile stress (σ_r+ Σ_θ+ Σ_z) / 3 is the Young's modulus E of the primary coating layer 5₁When it was smaller, it was confirmed that no void V or crack was generated in the primary coating layer 5.
[0053]
Next, another embodiment of the present invention will be described. As described above, the change (decreased temperature) in the resin temperature of the soft UV-curable resin is defined as ΔT. Then, the average tensile stress of the three-dimensional tensile stress (σ_r+ Σ_θ+ Σ_z) / 3 is expressed by Expression (3). The radius R of the fiber glass 3 is set so that this equation holds.₀, The outer radius R of the primary coating layer 5₁The Young's modulus E of the soft UV-curable resin₁, Linear expansion coefficient α₁, Poisson's ratio ν₁, The outer radius R of the secondary coating layer 7₂The Young's modulus E of the hard UV-curable resin₂, Linear expansion coefficient α₂, Poisson's ratio ν₂Will be selected.
[0054]
Further, the Young's modulus E of the soft UV-curable resin is₁Is the Young's modulus E of the hard UV-curable resin.₂From the premise that it is extremely small compared to
(Equation 9)

Holds. When Expression (4) is simplified from Expression (5) and Expression (6),
(Equation 10)

It becomes. That is, the radius R of the fiber glass₀, The outer radius R of the primary coating layer 5₁, The Poisson's ratio of soft curable resin ν₁, The outer radius R of the secondary coating layer 7₂, The Poisson's ratio ν of the hard curable resin₂When a change ΔT in the resin temperature between the time of curing and the time of curing of the ultraviolet curable resin is set,
Linear expansion coefficient α of the soft UV-curable resin₁And the linear expansion coefficient α of the hard UV-curable resin₂The linear expansion coefficient α of the soft UV-curable resin is set such that the relational expression of the linear expansion coefficient (formula (8)) is established between₁And the linear expansion coefficient α of the hard ultraviolet-curable resin.₂Is selected.
[0055]
Next, the operation of the embodiment of the present invention will be described.
[0056]
Linear expansion coefficient α of the soft UV-curable resin₁And the linear expansion coefficient α of the hard UV-curable resin₂Between the soft UV-curable resin and the hard UV-curable resin so that the relational expression of the linear expansion coefficient (Formula (8)) is established. Since the resin temperature of the resin significantly decreases from the hardening of the hard ultraviolet-curable resin to the end of the hardening, the tensile stress (σ) in the primary coating layer 5 is substantially uniform in the three-dimensional direction._r, Σ_θ, Σ_z) Is applied, the average tensile stress of the three-dimensional tensile stress (σ_r+ Σ_θ+ Σ_z) / 3 is the Young's modulus E of the primary coating layer 5₁When the curing is completed, the primary coating layer 5 does not have a void V or a crack due to the tensile stress in the three-dimensional direction at the end of the curing.
[0057]
This is based on the following two points.
[0058]
That is, the first point is that the tensile stress (σ) in the three-dimensional direction is substantially uniform in the test sheet S._0r, Σ_{0 θ}, Σ_0z) To gradually increase the average tensile stress of the three-dimensional tensile stress when a void V or a crack occurs in the test sheet S (in other words, the softness of the test sheet S in a state where the three-dimensional tensile stress is applied). Of the soft UV-curable resin is lower than the Young's modulus E of the soft UV-curable resin.₁FIG. 8 shows the result of a material strength test that is larger than that shown in FIG.
[0059]
The second point is that (σ_r+ Σ_θ+ Σ_z) / 3 is the Young's modulus E of the soft curable resin.₁A relational expression of the material mechanics (Equation (4)) is derived so as to be smaller than the above value.₁Is the Young's modulus E of the hard UV-curable resin.₂This is because the relational expression of the material mechanics (Equation (4)) is simplified to the relational expression of the linear expansion coefficient (Equation (8)) from the premise that the relation is extremely small as compared with the following.
[0060]
As described above, according to the embodiment of the present invention, the three-dimensional tensile stress (σ_r, Σ_θ, Σ_z) Does not cause a void V or a crack in the primary coating layer 5, so that the support state of the fiber glass 3 by the primary coating layer 5 is stabilized, and the transmission loss of the optical fiber 1 due to the slight bending of the fiber glass 3 is minimized. By reducing the number, the quality of the optical fiber 1 can be improved.
[0061]
In addition, since the relational expression of the linear expansion coefficient (Equation (8)) simplifies the relational expression of the material mechanics (Equation (4)), the primary coating layer 5 is prevented from having a void V or a crack. It becomes easy to select the soft curable resin and the hard curable resin.
[0062]
Further, even with an optical fiber cable (not shown) having the optical fiber 1, the same effects as those described above can be obtained. Here, the optical fiber cable includes not only an optical fiber cable in a narrow sense but also an optical fiber ribbon and an optical fiber cord.
[0063]
The present invention is not limited to the description of the embodiment of the invention described above. For example, the material forming the coating layers 5 and 7 may be changed to another curable resin instead of the ultraviolet curable resin. The present invention can be implemented in various other modes.
[0064]
Hereinafter, embodiments according to the present invention will be briefly described.
[0065]
FIG. 3 is a graph showing a relationship represented by a relational expression of a linear expansion coefficient.
[0066]
Radius R of fiber glass 3₀Is 62.5 μm, the outer radius R of the primary coating layer 5₁Is 125 μm, the outer radius R of the secondary coating layer 7₂Is 200 μm, the Poisson's ratio ν of the soft UV-curable resin.₁And the Poisson's ratio ν of the hard UV-curable resin₂Are both 0.46, and the change ΔT in the resin temperature between the time of curing and the time of the completion of curing of the ultraviolet curable resin is 180 ° C., respectively. FIG. 3 shows a graph.
[0067]
That is, the area above the selection straight line drawn in FIG._r+ Σ_θ+ Σ_z) / 3 is the Young's modulus E of the soft UV-curable resin.₁This is a region in which the primary coating layer 5 does not have a void V or a crack. Further, an area below the selection straight line (lower side in FIG. 3) is represented by (σ_r+ Σ_θ+ Σ_z) / 3 is the Young's modulus E of the soft UV-curable resin.₁This is a region in which the primary coating layer 5 has a void V or a crack.
[0068]
As shown in FIG. 10, the linear expansion coefficient α of the soft UV-curable resin is₁And the linear expansion coefficient α of the hard UV-curable resin₂Are manufactured by changing the relationship of (1) to (5), and the presence or absence of the void V or the crack (the presence or absence of breakage) of the primary coating layer 5 is observed. The observation result is as shown in FIG. Become.
[0069]
As is clear from FIG. 10, the optical fibers A, B, and C are made of two types of UV-curable resin (linear expansion coefficient α of the soft UV-curable resin).₁And the linear expansion coefficient α of the hard UV-curable resin₂) Is located above the selected straight line (the upper side in FIG. 3), and it was confirmed that no void V or crack was generated in the primary coating layer 5. The optical fibers D and E are the linear expansion coefficients α of the two types of ultraviolet curable resins.₁, Α₂In the region above the selected straight line (the upper side in FIG. 3), it was confirmed that the void V or the crack was generated in the primary coating layer 5.
[0070]
Next, an optical fiber ribbon according to an embodiment of the present invention will be described. FIG. 7 is a cross-sectional view of the optical fiber ribbon (8-core ribbon) according to the embodiment of the present invention.
[0071]
Referring to FIG. 7, an optical fiber ribbon 41 according to the present embodiment has a plurality of optical fiber wires 43 arranged in parallel, and has a two-sided tape material made of an ultraviolet curable resin around the optical fiber wires 43. The next coating layer 45 is covered.
[0072]
The number of the optical fibers 43 constituting the optical fiber ribbon 41 may be any number of 2 or more.
[0073]
The optical fiber 43 is not particularly limited as long as it has the above characteristics. For example, the bare optical fiber 47 having an outer diameter of 125 μm is coated with, for example, an ultraviolet-curable resin 49 as a primary coating layer to form, for example, an outer diameter. Those having a thickness of 250 to 400 μm are generally used.
[0074]
Outer radius R of secondary coating layer 45 made of hard UV-curable resin₂Assuming that is the distance from the center of the bare optical fiber 47 to the outer surface of the secondary coating layer 45 which is closest, the above discussion holds approximately. Therefore, the contents described in detail regarding the selection of the soft UV-curable resin and the hard UV-curable resin are also valid for the optical fiber ribbon.
[0075]
Hereinafter, a specific implementation example will be described. Radius R of fiber glass 3₀Is 62.5 μm, the outer radius R of the primary coating layer 5₁Is 125 μm, the outer radius R of the secondary coating layer 7₂Is 200 μm, and the Poisson's ratio ν2 of the hard UV-curable resin is 0.45 to 0.49. Also, the radius R of the fiber glass 3₀, The outer radius R of the primary coating layer 5₁, The outer radius R of the secondary coating layer 7₂Each include an error of 0.3 μm.
[0076]
In this case, the x-intercept (α) of the selected straight line drawn in FIG.₀) Is the resin temperature change ΔT and the Poisson's ratio ν at the time of curing and at the end of curing of the ultraviolet curable resin.₁Determined by α₀= (1-2ν₁) / ΔT. Therefore, the resin temperature change ΔT and Poisson's ratio ν₁Instead of this α₀Should be considered. Poisson's ratio ν of the soft UV-curable resin₁Is 0.42 to 0.47, and when the change ΔT in the resin temperature between the time of curing and the time of completion of curing of the ultraviolet curable resin is 180 ° C. at the most, α₀Is about 8.9 to 3.3. On the other hand, the inclination of the selection straight line drawn in FIG. 3 is R ′ = (3/2) ｛1+ (R₀/ R₁)²｝ As R '/ (1 + ν₂), That is, (8/15) / (1 + ν)₂).
[0077]
In the above situation, the method for selecting the fiber linear expansion coefficient is as follows. First, the linear expansion coefficient α of the soft curable resin₁And α₀The following should be selected: That is, (1-2ν₁) / ΔT. Therefore, Poisson's ratio ν₁May be selected to be about 8.9 to 3.3 or less in accordance with 0.42 to 0.47. However, the linear expansion coefficient α of the soft curable resin is₁And α₀If not selected below, the coefficient of linear expansion of the hard curable resin α₂Is R ′ (α₁−α₀) / (1 + ν)₂), That is, 15 (α₁−α₀) / 8 (1 + ν₂).
[0078]
An advantage of the present invention is that the range of choice of the coefficient of linear expansion is increased. That is, the linear expansion coefficient α of the soft curable resin₁To (1-2ν₁) / ΔT, the linear expansion coefficient α of the hard curable resin₂Even if you choose freely, it is guaranteed that it is safe. Also, the linear expansion coefficient α of the soft curable resin₁Linear expansion coefficient α₂The safe range has been clarified, and it has become possible to incorporate combinations that have not been done so far into the range of choice.
[0079]
Therefore, the feature of the present invention is most effective when α₀From α₀In the range of 80% of the linear curing coefficient α of the soft curable resin.₁Is selected. That is, the linear expansion coefficient α₁Is
(1-2v₁) / 180> α₁> (1-2ν₁) / 225.
Should be satisfied. Usually, this range is included in the danger range, but is guaranteed to be safe as described above. Also, the linear expansion coefficient α of the soft curable resin₁And α₀If not selected below, the coefficient of linear expansion of the hard curable resin α₂Is R ′ (α₁−α₀) / (1 + ν)₂) To R ′ (α₁−α₀) / (1 + ν)₂) Is selected in the range of 120%. That is,
R '(α₁−α₀) / (1 + ν)₂) <Α₂<(6/5) ｛R ’(α₁−α₀) / (1 + ν)₂)｝
To satisfy. In this case,
15 (α₁−α₀) / 8 (1 + ν₂) <Α₂<9 (α₁−α₀) / 4 (1 + ν)₂)
To satisfy. This is also usually included in the danger range, but is guaranteed to be safe as described above.
[0080]
For example, in the case of the above mounting example, the Poisson's ratio ν of the soft ultraviolet-curable resin₁Is set to 0.42 within the error range, α₀Is about 8.9 x 10^{− 4}It becomes. In that case, the linear expansion coefficient α of the soft curable resin₁Is selected in the range of 8.9 to 7.1, a combination that has not been achieved in the past is realized.
[0081]
Radius R of fiber glass 3₀Is 62.5 μm, the outer radius R of the primary coating layer 5₁Is 95 μm, and the outer radius R of the secondary coating layer 7 is₂And the hard UV-curable resin has a Poisson's ratio ν2 of 0.45 to 0.49. Also, the radius R of the fiber glass 3₀, The outer radius R of the primary coating layer 5₁, The outer radius R of the secondary coating layer 7₂Each include an error of 0.3 μm.
[0082]
Also in this case, the x-intercept of the selection straight line drawn in FIG.₁Determined by α₀= (1-2ν₁) / ΔT. Again, the resin temperature change ΔT and Poisson's ratio ν₁Instead of this α₀Should be considered. Poisson's ratio ν of the soft UV-curable resin₁Is 0.42 to 0.47, and when the change ΔT of the resin temperature between the time of curing and the time of curing of the ultraviolet curable resin is 120 ° C. at the most, α₀Is about 3.0 to 2.2. On the other hand, the inclination of the selection straight line drawn in FIG. 3 is R ′ = (3/2) ｛1+ (R₀/ R₁)²｝ As R '/ (1 + ν₂), That is, {0.8664 / (1 + ν)₂).
[0083]
In the above situation, the method for selecting the fiber linear expansion coefficient is as follows. First, the linear expansion coefficient α of the soft curable resin₁And α₀The following should be selected: That is, (1-2ν₁) / ΔT. Therefore, Poisson's ratio ν₁Should be selected to be approximately 3.0 to 2.2 or less in accordance with 0.42 to 0.47. However, the linear expansion coefficient α of the soft curable resin is₁And α₀If not selected below, the coefficient of linear expansion of the hard curable resin α₂Is R ′ (α₁−α₀) / (1 + ν)₂), That is, $ 0.8664 / (1 + ν)₂)｝ (Α₁−α₀).
[0084]
An advantage of the present invention is that the range of choice of the coefficient of linear expansion is increased. That is, the linear expansion coefficient α of the soft curable resin₁To (1-2ν₁) / ΔT, the linear expansion coefficient α of the hard curable resin₂Even if you choose freely, it is guaranteed that it is safe. Also, the linear expansion coefficient α of the soft curable resin₁Linear expansion coefficient α₂The safe range has been clarified, and it has become possible to incorporate combinations that have not been done so far into the range of choice.
[0085]
Therefore, the feature of the present invention is most effective when α₀From α₀In the range of 80% of the linear curing coefficient α of the soft curable resin.₁Is selected. That is, the linear expansion coefficient α₁Is
(1-2v₁) / 120> α₁> (1-2ν₁) / 150.
Should be satisfied. Usually, this range is included in the danger range, but is guaranteed to be safe as described above. Also, the linear expansion coefficient α of the soft curable resin₁And α₀If not selected below, the coefficient of linear expansion of the hard curable resin α₂Is R ′ (α₁−α₀) / (1 + ν)₂) To R ′ (α₁−α₀) / (1 + ν)₂) Is selected in the range of 120%. That is,
R '(α₁−α₀) / (1 + ν)₂) <Α₂<(6/5) ｛R ’(α₁−α₀) / (1 + ν)₂)｝
To satisfy. In this case,
｛0.8664 / (1 + ν)₂)｝ (Α₁−α₀) <Α₂<｛1.03968 / (1 + ν₂)｝ (Α₁−α₀)
To satisfy. This is also usually included in the danger range, but is guaranteed to be safe as described above.
[0086]
For example, in the case of the above mounting example, the Poisson's ratio ν of the soft ultraviolet-curable resin₁Is set to 0.42 within the error range, α₀Is (4/3) x 10^{− 3}It becomes. In that case, the linear expansion coefficient α of the soft curable resin₁Is 1.33 x 10^{− 3}～ 1.07 x 10^{− 3}Selecting within the range of realizes a combination that has never existed before.
[0087]
Radius R of fiber glass 3₀Is 62.5 μm, the outer radius R of the primary coating layer 5₁Is 95 μm, and the outer radius R of the secondary coating layer 7 is₂And the hard UV-curable resin has a Poisson's ratio ν2 of 0.45 to 0.49. Also, the radius R of the fiber glass 3₀, The outer radius R of the primary coating layer 5₁, The outer radius R of the secondary coating layer 7₂Each include an error of 0.3 μm.
[0088]
Also in this case, the x-intercept of the selection straight line drawn in FIG.₁Determined by α₀= (1-2ν₁) / ΔT. Again, the resin temperature change ΔT and Poisson's ratio ν₁Instead of this α₀Should be considered. Poisson's ratio ν of the soft UV-curable resin₁Is 0.42 to 0.47, and when the change ΔT in the resin temperature between the time of curing and the time of completion of curing of the ultraviolet curable resin is 180 ° C. at the most, α₀Is about 8.9 to 3.3. On the other hand, the inclination of the selection straight line drawn in FIG. 3 is R ′ = (3/2) ｛1+ (R₀/ R₁)²｝ As R '/ (1 + ν₂), That is, {0.8664 / (1 + ν)₂).
[0089]
In the above situation, the method for selecting the fiber linear expansion coefficient is as follows. First, the linear expansion coefficient α of the soft curable resin₁And α₀The following should be selected: That is, (1-2ν₁) / ΔT. Therefore, Poisson's ratio ν₁May be selected to be about 8.9 to 3.3 or less in accordance with 0.42 to 0.47. However, the linear expansion coefficient α of the soft curable resin is₁And α₀If not selected below, the coefficient of linear expansion of the hard curable resin α₂Is R ′ (α₁−α₀) / (1 + ν)₂), That is, $ 0.8664 / (1 + ν)₂)｝ (Α₁−α₀).
[0090]
An advantage of the present invention is that the range of choice of the coefficient of linear expansion is increased. That is, the linear expansion coefficient α of the soft curable resin₁To (1-2ν₁) / ΔT, the linear expansion coefficient α of the hard curable resin₂Even if you choose freely, it is guaranteed that it is safe. Also, the linear expansion coefficient α of the soft curable resin₁Linear expansion coefficient α₂The safe range has been clarified, and it has become possible to incorporate combinations that have not been done so far into the range of choice.
[0091]
Therefore, the feature of the present invention is most effective when α₀From α₀In the range of 80% of the linear curing coefficient α of the soft curable resin.₁Is selected. That is, the linear expansion coefficient α₁Is
(1-2v₁) / 180> α₁> (1-2ν₁) / 225.
Should be satisfied. Usually, this range is included in the danger range, but is guaranteed to be safe as described above. Also, the linear expansion coefficient α of the soft curable resin₁And α₀If not selected below, the coefficient of linear expansion of the hard curable resin α₂Is R ′ (α₁−α₀) / (1 + ν)₂) To R ′ (α₁−α₀) / (1 + ν)₂) Is selected in the range of 120%. That is,
R '(α₁−α₀) / (1 + ν)₂) <Α₂<(6/5) ｛R ’(α₁−α₀) / (1 + ν)₂)｝
To satisfy. In this case,
｛0.8664 / (1 + ν)₂)｝ (Α₁−α₀) <Α₂<｛1.03968 / (1 + ν₂)｝ (Α₁−α₀)
To satisfy. This is also usually included in the danger range, but is guaranteed to be safe as described above.
[0092]
For example, in the case of the above mounting example, the Poisson's ratio ν of the soft ultraviolet-curable resin₁Is set to 0.42 within the error range, α₀Is about 8.9 x 10^-4It becomes. In that case, the linear expansion coefficient α of the soft curable resin₁Is selected in the range of 8.9 to 7.1, a combination that has not been achieved in the past is realized.
[0093]
Radius R of fiber glass 3₀Is 62.5 μm, the outer radius R of the primary coating layer 5₁Is 125 μm, the outer radius R of the secondary coating layer 7₂Is 200 μm, and the Poisson's ratio ν2 of the hard UV-curable resin is 0.45 to 0.49. Also, the radius R of the fiber glass 3₀, The outer radius R of the primary coating layer 5₁, The outer radius R of the secondary coating layer 7₂Each include an error of 0.3 μm.
[0094]
In this case, the x-intercept (α) of the selected straight line drawn in FIG.₀) Is the resin temperature change ΔT and the Poisson's ratio ν at the time of curing and at the end of curing of the ultraviolet curable resin.₁Determined by α₀= (1-2ν₁) / ΔT. Again, the resin temperature change ΔT and Poisson's ratio ν₁Instead of this α₀Should be considered. Poisson's ratio ν of the soft UV-curable resin₁Is 0.42 to 0.47, and when the change ΔT of the resin temperature between the time of curing and the time of curing of the ultraviolet curable resin is 120 ° C. at the most, α₀Is about 3.0 to 2.2. On the other hand, the inclination of the selection straight line drawn in FIG. 3 is R ′ = (3/2) ｛1+ (R₀/ R₁)²｝ As R '/ (1 + ν₂), That is, (8/15) / (1 + ν)₂).
[0095]
In the above situation, the method for selecting the fiber linear expansion coefficient is as follows. First, the linear expansion coefficient α of the soft curable resin₁And α₀The following should be selected: That is, (1-2ν₁) / ΔT. Therefore, Poisson's ratio ν₁Should be selected to be approximately 3.0 to 2.2 or less in accordance with 0.42 to 0.47. However, the linear expansion coefficient α of the soft curable resin is₁And α₀If not selected below, the coefficient of linear expansion of the hard curable resin α₂Is R ′ (α₁−α₀) / (1 + ν)₂), That is, 15 (α₁−α₀) / 8 (1 + ν₂).
[0096]
An advantage of the present invention is that the range of choice of the coefficient of linear expansion is increased. That is, the linear expansion coefficient α of the soft curable resin₁To (1-2ν₁) / ΔT, the linear expansion coefficient α of the hard curable resin₂Even if you choose freely, it is guaranteed that it is safe. Also, the linear expansion coefficient α of the soft curable resin₁Linear expansion coefficient α₂The safe range has been clarified, and it has become possible to incorporate combinations that have not been done so far into the range of choice.
[0097]
Therefore, the feature of the present invention is most effective when α₀From α₀In the range of 80% of the linear curing coefficient α of the soft curable resin.₁Is selected. That is, the linear expansion coefficient α₁Is
(1-2v₁) / 120> α₁> (1-2ν₁) / 150.
Should be satisfied. Usually, this range is included in the danger range, but is guaranteed to be safe as described above. Also, the linear expansion coefficient α of the soft curable resin₁And α₀If not selected below, the coefficient of linear expansion of the hard curable resin α₂Is R ′ (α₁−α₀) / (1 + ν)₂) To R ′ (α₁−α₀) / (1 + ν)₂) Is selected in the range of 120%. That is,
R '(α₁−α₀) / (1 + ν)₂) <Α₂<(6/5) ｛R ’(α₁−α₀) / (1 + ν)₂)｝
To satisfy. In this case,
15 (α₁−α₀) / 8 (1 + ν₂) <Α₂<9 (α₁−α₀) / 4 (1 + ν)₂)
To satisfy. This is also usually included in the danger range, but is guaranteed to be safe as described above.
[0098]
For example, in the case of the above mounting example, the Poisson's ratio ν of the soft ultraviolet-curable resin₁Is set to 0.42 within the error range, α₀Is (4/3) x 10^{− 3}It becomes. In that case, the linear expansion coefficient α of the soft curable resin₁Is 1.33 x 10^{− 3}～ 1.07 x 10^{− 3}Selecting within the range of realizes a combination that has never existed before.
[0099]
Although the present invention has been described in detail with reference to the embodiments, it is apparent to those skilled in the art that the present invention is not limited to the embodiments described in the present application. The device of the present invention can be embodied as modifications and alterations without departing from the spirit and scope of the present invention defined by the appended claims. Therefore, the description of the present application is intended for illustrative purposes, and has no restrictive meaning to the present invention.
[0100]
【The invention's effect】
According to the embodiment of the present invention, at the time of completion of curing, the primary coating layer does not cause voids or cracks due to the tensile stress in the three-dimensional direction, so that the support state of the fiber glass by the primary coating layer is stabilized. Thus, the transmission loss of the optical fiber due to the slight bending of the fiber glass can be minimized, and the quality of the optical fiber can be improved.
[0101]
Further, since the relational expression of the coefficient of linear expansion simplifies the relational expression of the material mechanics, the soft curable resin and the hard curable resin do not cause voids or cracks in the primary coating layer. Is easier to select.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating mechanical elements such as fiber glass according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of the optical fiber according to the embodiment of the present invention.
FIG. 3 is a graph showing a relationship represented by a relational expression of a coefficient of linear expansion.
FIG. 4 is a schematic perspective view of a material strength test device according to an embodiment of the present invention.
FIG. 5 is a diagram illustrating a strength test by a material strength test device according to the embodiment of the present invention.
FIG. 6 is a view of the test sheet in FIG. 5B as viewed from above.
FIG. 7 is a cross-sectional view of an optical fiber ribbon (8-core ribbon) according to the embodiment of the present invention.
FIG. 8 shows the results of a strength test performed by a material strength test apparatus while changing the type of soft ultraviolet curable resin and the environmental temperature of the material test apparatus.
FIG. 9 shows the results of observing the presence or absence of a void V or a crack (presence or absence of a crack) in the primary coating layer by changing the environmental temperature for each of the six types of optical fibers (1A to 1F).
FIG. 10 shows the results of observing the presence or absence of voids V or cracks (presence or absence of breakage) in the primary coating layer by changing the environmental temperature for each of the five types of optical fibers (A to E).
[Explanation of symbols]
1 Optical fiber
3 fiber glass
5 Primary coating layer
7 Secondary coating layer

Claims (18)

Fiber glass,
A primary coating layer composed of a soft curable resin and directly coating the outer peripheral portion of the fiber glass,
It is constituted by a hard curable resin, and has a secondary coating layer that indirectly covers the outer peripheral portion of the fiber glass via the primary coating layer,
The resin temperature of the curable resin greatly decreases from the hardening of the hard UV-curable resin to the end of the hardening, so that the three-dimensional tensile stress (σ _r , σ _θ , σ _{z) in the} primary coating layer is substantially uniformly. ) Is added,
The mechanical element of the glass fiber and the mechanical element of the primary coating layer such that the average tensile stress (σ _r + σ _θ + σ _z ) / 3 of the three-dimensional tensile stress is smaller than the Young's modulus of the primary coating layer. An optical fiber, comprising a mechanical element of the secondary coating layer. The mechanical element of the glass fiber is a radius of the glass fiber, and the mechanical element of the primary coating layer is an outer radius of the primary coating layer, a Young's modulus of the soft curable resin, a coefficient of linear expansion, The Poisson's ratio, wherein mechanical elements of the secondary coating layer are an outer radius of the secondary coating layer, a Young's modulus of the hard curable resin, a linear expansion coefficient, and a Poisson's ratio. Item 2. The optical fiber according to item 1. The optical fiber according to claim 1, wherein the soft curable resin is a soft ultraviolet curable resin, and the hard curable resin is a hard ultraviolet curable resin. An optical fiber cable comprising a plurality of optical fibers, wherein each optical fiber is
Fiber glass,
A primary coating layer composed of a soft curable resin and directly coating the outer peripheral portion of the fiber glass,
It is constituted by a hard curable resin, and has a secondary coating layer that indirectly covers the outer peripheral portion of the fiber glass via the primary coating layer,
The resin temperature of the curable resin greatly decreases from the hardening of the hard UV-curable resin to the end of the hardening, so that the three-dimensional tensile stress (σ _r , σ _θ , σ _{z) in the} primary coating layer is substantially uniformly. ) Is added,
The mechanical element of the glass fiber and the mechanical element of the primary coating layer such that the average tensile stress (σ _r + σ _θ + σ _z ) / 3 of the three-dimensional tensile stress is smaller than the Young's modulus of the primary coating layer. An optical fiber cable comprising a mechanical element of the secondary coating layer. Fiber glass, a primary coating layer composed of a soft curable resin and directly covering the outer peripheral portion of the fiber glass, and a fiber curable resin composed of a hard curable resin and through the primary coating layer A method for manufacturing an optical fiber comprising a secondary coating layer for indirectly coating,
The resin temperature of the curable resin greatly decreases from the hardening of the hard UV-curable resin to the end of the hardening, so that the three-dimensional tensile stress (σ _r , σ _θ , σ _{z) in the} primary coating layer is substantially uniformly. ) If the applied, so that the average tensile stress in the three-dimensional directions of the tensile stress _{(σ r + σ θ + σ} z) / 3 is smaller than the Young's modulus of the primary coating layer, the mechanical components of the glass fiber, the A method of manufacturing an optical fiber, wherein a mechanical element of a primary coating layer and a mechanical element of the secondary coating layer are selected. The mechanical element of the glass fiber is a radius of the glass fiber, and the mechanical element of the primary coating layer is an outer radius of the primary coating layer, a Young's modulus of the soft curable resin, a coefficient of linear expansion, The Poisson's ratio, wherein mechanical elements of the secondary coating layer are an outer radius of the secondary coating layer, a Young's modulus of the hard curable resin, a linear expansion coefficient, and a Poisson's ratio. Item 6. The method for producing an optical fiber according to Item 5. The method according to claim 5, wherein the soft curable resin is a soft ultraviolet curable resin, and the hard curable resin is a hard ultraviolet curable resin. Fiber glass,
A primary coating layer composed of a soft curable resin and directly coating the outer peripheral portion of the fiber glass,
It is constituted by a hard curable resin, and has a secondary coating layer that indirectly covers the outer peripheral portion of the fiber glass via the primary coating layer,
When the Young's modulus of the soft curable resin is extremely smaller than the Young's modulus of the hard curable resin, the radius R _{0 of the} fiber glass, the outer radius R ₁ of the primary coating layer, and the soft By setting the Poisson's ratio ν ₁ of the curable resin, the Poisson's ratio ν ₂ of the hard curable resin, and the change ΔT in the resin temperature between the time of curing and the time of curing of the curable resin, the line of the soft curable resin is obtained. Between the expansion coefficient α ₁ and the linear expansion coefficient α ₂ of the hard curable resin,

An optical fiber characterized in that a relational expression of a linear expansion coefficient is satisfied. The optical fiber according to claim 1, wherein the soft curable resin is a soft ultraviolet curable resin, and the hard curable resin is a hard ultraviolet curable resin. Fiber glass,
A primary coating layer composed of a soft curable resin and directly coating the outer peripheral portion of the fiber glass,
It is constituted by a hard curable resin, and has a secondary coating layer that indirectly covers the outer peripheral portion of the fiber glass via the primary coating layer,
When the Young's modulus of the soft curable resin is extremely smaller than the Young's modulus of the hard curable resin, the radius R _{0 of the} fiber glass, the outer radius R ₁ of the primary coating layer, and the soft By setting the Poisson's ratio ν ₁ of the curable resin, the Poisson's ratio ν ₂ of the hard curable resin, and the change ΔT in the resin temperature between the time of curing and the time of curing of the curable resin, the line of the soft curable resin is obtained. Between the expansion coefficient α ₁ and the linear expansion coefficient α ₂ of the hard curable resin,

An optical fiber characterized in that a relational expression of a linear expansion coefficient is satisfied. Fiber glass, a primary coating layer composed of a soft curable resin and directly covering the outer peripheral portion of the fiber glass, and a fiber curable resin composed of a hard curable resin and through the primary coating layer A method for manufacturing an optical fiber comprising a secondary coating layer for indirectly coating,
When the Young's modulus of the soft curable resin is extremely smaller than the Young's modulus of the hard curable resin, the radius R _{0 of the} fiber glass, the outer radius R ₁ of the primary coating layer, and the soft By setting the Poisson's ratio ν ₁ of the curable resin, the Poisson's ratio ν ₂ of the hard curable resin, and the change ΔT in the resin temperature between the time of curing and the time of curing of the curable resin, the line of the soft curable resin is obtained. Between the expansion coefficient α ₁ and the linear expansion coefficient α ₂ of the hard curable resin,

Wherein the soft curable resin and the hard curable resin are selected so that the relational expression of the linear expansion coefficient is satisfied. The method according to claim 11, wherein the soft curable resin is a soft UV curable resin, and the hard curable resin is a hard UV curable resin. Fiber glass,
A primary coating layer composed of a soft curable resin and directly coating the outer peripheral portion of the fiber glass,
It is constituted by a hard curable resin, and has a secondary coating layer that indirectly covers the outer peripheral portion of the fiber glass via the primary coating layer,
The Young's modulus of the soft curable resin is sufficiently smaller than the Young's modulus of the hard curable resin,
The radius R _{0 of the} fiber glass is set within 62. 5 [mu] m, 125 [mu] m outer radius R ₁ of the primary coating layer, 200 [mu] m outer radius R ₂ of the secondary coating layer, the Poisson's ratio [nu ₁ of curable resin of the _soft, upon curing and end time of curing in the curable resin As the change ΔT in the resin temperature of
An optical fiber, wherein the soft curable resin is selected such that its coefficient of linear expansion is (1-2ν ₁ ) / ΔT or less. Fiber glass,
A primary coating layer composed of a soft curable resin and directly coating the outer peripheral portion of the fiber glass,
It is constituted by a hard curable resin, and has a secondary coating layer that indirectly covers the outer peripheral portion of the fiber glass via the primary coating layer,
The Young's modulus of the soft curable resin is sufficiently smaller than the Young's modulus of the hard curable resin,
The radius R _{0 of the} fiber glass is set within 62. 5 [mu] m, 125 [mu] m outer radius R ₁ of the primary coating layer, 200 [mu] m outer radius R ₂ of the secondary coating layer, the Poisson's ratio [nu ₁ of curable resin of the _soft, upon curing and end time of curing in the curable resin As the change ΔT in the resin temperature of
The soft curable resin has a linear expansion coefficient α ₁ ,
(1-2ν ₁ ) / 180> α ₁ > (1-2ν ₁ ) / 225
An optical fiber characterized in that it is selected to satisfy Fiber glass,
A primary coating layer composed of a soft curable resin and directly coating the outer peripheral portion of the fiber glass,
It is constituted by a hard curable resin, and has a secondary coating layer that indirectly covers the outer peripheral portion of the fiber glass via the primary coating layer,
The Young's modulus of the soft curable resin is sufficiently smaller than the Young's modulus of the hard curable resin,
The radius R _{0 of the} fiber glass is set within 62. 5 [mu] m, 125 [mu] m outer radius R ₁ of the primary coating layer, said secondary coating layer 200μm an outer radius R ₂ of the Poisson's ratio [nu ₁ of curable resin of the _soft, Poisson's ratio of the curable resin of the soft [nu ₂ As the change ΔT in the resin temperature between the time of curing and the time of completion of curing of the curable resin,
Assuming that α ₀ = (1-2ν ₁ ) / ΔT, the soft curable resin has a linear expansion coefficient α ₁ larger than α ₀ , and the soft curable resin has a linear expansion coefficient α ₂ is 15 (α ₁ −α ₀ ) / 8 (1 + ν ₂ ) <α ₂ <9 (α ₁ −α ₀ ) / 4 (1 + ν ₂ )
An optical fiber characterized in that it is selected to satisfy Fiber glass,
A primary coating layer composed of a soft curable resin and directly coating the outer peripheral portion of the fiber glass,
It is constituted by a hard curable resin, and has a secondary coating layer that indirectly covers the outer peripheral portion of the fiber glass via the primary coating layer,
The Young's modulus of the soft curable resin is sufficiently smaller than the Young's modulus of the hard curable resin,
62.5μm radius _{R 0} of said fiber glass within an error range, 95 .mu.m the outer radius _{R 1} of the primary coating layer, 120 [mu] m outer radius _{R 2} of the secondary coating layer, the Poisson's ratio of the curable resin of the soft ν ₁ , as a change ΔT in resin temperature between the time of curing and the time of completion of curing in the curable resin,
An optical fiber, wherein the soft curable resin is selected such that its coefficient of linear expansion is (1-2ν ₁ ) / ΔT or less. Fiber glass,
A primary coating layer composed of a soft curable resin and directly coating the outer peripheral portion of the fiber glass,
It is constituted by a hard curable resin, and has a secondary coating layer that indirectly covers the outer peripheral portion of the fiber glass via the primary coating layer,
The Young's modulus of the soft curable resin is sufficiently smaller than the Young's modulus of the hard curable resin,
62.5μm radius _{R 0} of said fiber glass within an error range, 95 .mu.m the outer radius _{R 1} of the primary coating layer, 120 [mu] m outer radius _{R 2} of the secondary coating layer, the Poisson's ratio of the curable resin of the soft ν ₁ , as a change ΔT in resin temperature between the time of curing and the time of completion of curing in the curable resin,
The soft curable resin has a linear expansion coefficient α ₁ ,
_{(1-2ν 1) / 120> α} 1> (1-2ν 1) / 150
An optical fiber characterized in that it is selected to satisfy Fiber glass,
A primary coating layer composed of a soft curable resin and directly coating the outer peripheral portion of the fiber glass,
It is constituted by a hard curable resin, and has a secondary coating layer that indirectly covers the outer peripheral portion of the fiber glass via the primary coating layer,
The Young's modulus of the soft curable resin is sufficiently smaller than the Young's modulus of the hard curable resin,
The radius R _{0 of the} fiber glass is set within 62. 5 [mu] m, 95 .mu.m the outer radius R ₁ of the primary coating layer, said secondary coating layer 120μm an outer radius R ₂ of the Poisson's ratio [nu ₁ of curable resin of the _soft, Poisson's ratio of the curable resin of the hard [nu ₂ As the change ΔT in the resin temperature between the time of curing and the time of completion of curing of the curable resin,
Assuming that α ₀ = (1-2ν ₁ ) / ΔT, the soft curable resin has a linear expansion coefficient α ₁ larger than α ₀ , and the soft curable resin has a linear expansion coefficient α ₂ is {0.8664 / (1 + ν ₂ )} (α ₁ −α ₀ ) <α ₂ <{1.03968 / (1 + ν ₂ )} (α ₁ −α ₀ )
An optical fiber characterized in that it is selected to satisfy

Images