JP5108938B2 - Polyethylene naphthalate fiber and method for producing the same - Google Patents

Description

  The present invention relates to a polyethylene naphthalate fiber that is useful as a rubber reinforcing fiber for industrial materials, particularly tire cords and transmission belts, and has excellent heat resistance while being high modulus, and a method for producing the same.

Polyethylene naphthalate fibers exhibit high strength, high modulus and excellent dimensional stability, and are beginning to be widely applied in the industrial material field including rubber reinforcements such as tire cords and transmission belts. Among them, the conventional rayon fiber alternative is strongly expected because of its high modulus. This is because rayon fibers have a problem that they are difficult to process, mold and use because they have a large load during production and a large difference in wet and dry physical properties. However, rayon fiber has high dimensional stability and is easy to handle as a fiber for rubber reinforcement, whereas polyethylene naphthalate fiber has high strength and high modulus because its molecules are rigid and easily oriented in the fiber axis direction. However, there is a problem that it is difficult to achieve both dimensional stability, particularly dimensional stability against heat.
Therefore, for example, Patent Document 1 proposes a polyethylene naphthalate fiber excellent in heat resistance and dimensional stability by performing high-speed spinning. However, when the melting point is high, the strength is low, and when the strength is high, the melting point is low. That is, the strength and heat resistance cannot be satisfied at a high level.
Further, for example, in Patent Document 2, a heated spinning cylinder heated to 390 ° C. is installed immediately below a melt spinning base, and high-speed spinning and hot drawing of a draft of about 300 times are performed, thereby providing a dry heat shrinkage rate together with strength. And polyethylene naphthalate fibers having an excellent creep rate. However, the melting point of the obtained fiber is still as low as 288 ° C., the strength is insufficient as 8.0 g / de (about 6.8 N / dtex), and the heat resistance and dimensional stability are still satisfactory. It wasn't.
Unlike Patent Document 2, in Patent Document 3, a low draft undrawn yarn of about 60 times with a take-up speed of 1000 m / min or less is delayed-cooled using a spinning cylinder having a length of 20 to 50 cm and an ambient temperature of 275 to 350 ° C. After that, a polyethylene naphthalate fiber having high strength and excellent thermal stability has been proposed by stretching at a high magnification. In Patent Document 4, an undrawn yarn having a spinning draft ratio of 400 to 900 and a low birefringence of 0.005 to 0.025 is obtained, and this is high-strength and dimensioned by multistage drawing with a total draw ratio of 6.5 times or more. A polyethylene naphthalate fiber excellent in stability has been proposed.
However, by any of these methods, although the physical strength of the obtained fiber is high, its melting point is as low as 284 ° C. or less, and the heat resistance and dimensional stability are at a satisfactory level. Not reached.
Japanese Patent Laid-Open No. 62-155631 Japanese Patent Laid-Open No. 06-184815 Japanese Patent Laid-Open No. 04-352811 JP 2002-339161 A

  In view of such a current situation, the present invention is useful as a fiber for reinforcing rubber such as industrial materials, particularly tire cords and transmission belts, and is excellent in heat resistance while being high modulus, and as a result fatigue resistance under high temperature conditions. An object of the present invention is to provide a polyethylene naphthalate fiber having excellent properties and a method for producing the same.

［上の式中、Ｒ^１は炭素数６〜２０個の炭化水素基であるアリール基であり、Ｒ^２は水素原子又は炭素数の１〜２０個の炭化水素基であるアルキル基、アリール基又はベンジル基、Ｘは、水素原子または−ＯＲ^３基であり、Ｘが−ＯＲ^３基である場合、Ｒ^３は水素原子又は炭素数の１〜１２個の炭化水素基であるアルキル基、アリール基又はベンジル基、であり、Ｒ^２とＲ^３は同一であっても異なっていても良い。］
また、リン化合物が下記一般式（Ｉ’）であることが好ましく、特には、リン化合物がフェニルホスフィン酸またはフェニルホスホン酸であることが好ましい。

［上の式中、Ａｒは炭素数６〜２０個の炭化水素基であるアリール基であり、Ｒ^２は水素原子又は炭素数の１〜２０個の炭化水素基であるアルキル基、アリール基又はベンジル基、Ｙは、水素原子または−ＯＨ基である。］ The polyethylene naphthalate fiber of the present invention is a polyethylene naphthalate fiber whose main repeating unit is ethylene naphthalate, the crystal volume obtained from the X-ray wide angle diffraction of the fiber is 550 to 1200 nm ³ , and the crystallinity is 30. It is characterized by ˜60%.
Furthermore, it is preferable that the maximum peak diffraction angle of the X-ray wide angle diffraction is 25.5 to 27.0 degrees, or that the phosphorus atom is contained in an amount of 0.1 to 300 mmol% with respect to the ethylene naphthalate unit. . In addition, the polyethylene naphthalate fiber contains a metal element, and the metal element is at least one metal selected from the group consisting of a metal element of 4th to 5th period and 3 to 12 group metal and Mg in the periodic table. Preferably, the metal element is at least one metal element selected from the group consisting of Zn, Mn, Co, and Mg.
The exothermic peak energy ΔHcd under a temperature drop condition of 10 ° C./min under a nitrogen stream is 15 to 50 J / g, the strength is 4.0 to 10.0 cN / dtex, and the melting point is 285 to 285. It is preferable that it is 315 degreeC. The dry heat shrinkage at 180 ° C. is less than 0.5 to 4.0%, the peak temperature of tan δ is 150 to 170 ° C., the modulus E ′ (200 ° C.) at 200 ° C. and the modulus at 20 ° C. It is also preferable that the ratio E ′ (200 ° C.) / E ′ (20 ° C.) of E ′ (20 ° C.) is 0.25 to 0.5.
Method for producing polyethylene naphthalate fibers of another present invention is to melt the polymer main repeating unit is ethylene naphthalate, a method for producing a polyethylene naphthalate fiber for discharging from the spinneret, the polymer upon melting is A metal element, and the metal element is at least one metal element selected from the group consisting of a metal element of 4th to 5th period and a group 3-12 of the periodic table and Mg, and the following in the polymer at the time of melting: At least one phosphorus compound represented by the general formula (I ) is added directly to the polymer without previously reacting with other compounds and then discharged from the spinneret, and the spinning draft ratio after discharging from the spinneret is 500 to 5000. And immediately after the discharge from the spinneret, it passes through a heat-insulated spinning cylinder within ± 50 ° C of the molten polymer temperature. And characterized by stretching.

Wherein the above, R ¹ is 6 to twenty hydrocarbon radical der Rua aryl group carbon, the alkyl group R ² is 1-20 hydrogen atom or a hydrocarbon group carbon atoms, An aryl group or a benzyl group, X is a hydrogen atom or —OR ³ group, and when X is an —OR ³ group, R ³ is an alkyl group which is a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms. , An aryl group or a benzyl group, and R ² and R ³ may be the same or different. ]
Moreover, it is preferable that a phosphorus compound is the following general formula (I '), and it is especially preferable that a phosphorus compound is phenylphosphinic acid or phenylphosphonic acid.

[In the above formula, Ar is an aryl group which is a hydrocarbon group having 6 to 20 carbon atoms, and R ² is an alkyl group, an aryl group or a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms] Benzyl group, Y is a hydrogen atom or -OH group. ]

  According to the present invention, polyethylene which is useful as a rubber reinforcing fiber for industrial materials, particularly tire cords and power transmission belts, is excellent in heat resistance while being high modulus, and as a result is excellent in fatigue resistance under high temperature conditions. Naphthalate fibers and methods for their production are provided.

FIG. 1 is a wide-angle X-ray diffraction spectrum of Example 5 which is the product of the present invention.
FIG. 2 is a wide-angle X-ray diffraction spectrum of Comparative Example 1 which is a conventional product.
FIG. 3 is a wide-angle X-ray diffraction spectrum of Comparative Example 8.

1 Example 5
2 Comparative Example 1
3 Comparative Example 8

式中
ρ ：ポリエチレンナフタレート繊維の比重
ρａ：１．３２５（ポリエチレンナレフタレートの完全非晶密度）
ρｃ：１．４０７（ポリエチレンナレフタレートの完全結晶密度）
本発明のポリエチレンナフタレート繊維は、従来の高強力繊維と同様の高い結晶化度を維持しながら、従来に無い高い結晶体積を実現することにより高い熱安定性と高い融点を得ることができたものである。結晶体積が５５０ｎｍ^３（５５万オングストローム^３）未満では、このような高い融点を得ることができない。結晶体積は高くするほど熱安定性に優れ好ましいが、一般にその場合には結晶化度が低下し強度が低下するために１２００ｎｍ^３（１２０万オングストローム^３）程度が上限である。また結晶化度が３０％未満では高い引張強度やモジュラスを実現することができない。
結晶体積を大きくするためには、紡糸時の口金下温度を低く保ちながら、紡糸する方法が有効である。また、紡糸ドラフト比や延伸倍率等を高め、繊維を引き伸ばすことによっても大きい結晶体積を得ることができる。ただし、紡糸ドラフト比を高くすると剛直な繊維であるポリエチレンナフタレート繊維は断糸しやすくなるため、紡糸ドラフト比は１００〜５０００程度に留め、延伸倍率を高めることが特に有効である。もっとも、通常は紡糸時の口金下温度を低く保った状態で結晶体積を大きくするようなドラフトを行った場合には、紡糸時に断糸が発生し、繊維を製造することができない。しかし、本発明では特定のリン化合物を用いることによってこのような結晶体積を実現できるようになったのである。
結晶化度を高めるためには、結晶体積を大きくするのと同じく、紡糸ドラフト比や延伸倍率等を高め、繊維を高倍率に引き伸ばすことによって得ることができる。しかし結晶体積が大きくなるとともに結晶化度が高くなると剛直な繊維であるポリエチレンナフタレート繊維はますます断糸しやすくなる。そこで本発明では、結晶体積を５５０〜１２００ｎｍ^３（５５万〜１２０万オングストローム^３）の範囲内としながら、結晶化度を３０〜６０％とすることが重要となる。このためには紡糸前のポリマーの段階で、均一な結晶構造を形成させることが重要である。たとえば特有のリン化合物をポリマーに含有させることによってそのような均一な結晶構造を実現させることが可能となる。
さらに本発明のポリエチレンナフタレート繊維ではＸ線広角回折の最大ピーク回折角が２５．５〜２７．０度の範囲にあることが好ましい。理由は定かではないが、結晶面である（０１０）、（１００）、（１−１０）のうち、繊維軸上にこの（１−１０）面の結晶が大きく成長することにより耐熱性が大幅に向上される。このような繊維軸と平行な結晶の大きさは、特に繊維を一定方向に高倍率で引き伸ばすことによって高めることができ、たとえば紡糸ドラフト比や延伸倍率等を高めることによって得ることができる。
また本発明のポリエチレンナフタレート繊維としては、降温条件下での発熱ピークのエネルギーΔＨｃｄが１５〜５０Ｊ／ｇであることが好ましい。さらには２０〜５０Ｊ／ｇ、特には３０Ｊ／ｇ以上であることが好ましい。ここで降温条件下での発熱ピークのエネルギーΔＨｃｄとは、ポリエチレンナフタレート繊維を窒素気流下２０℃／分の昇温条件にて３２０℃まで加熱し５分溶融保持させた後、窒素気流下１０℃／分の降温条件にて示差走査熱量計（ＤＳＣ）を用いて測定したものである。この降温条件下での発熱ピークのエネルギーΔＨｃｄは、降温条件での降温結晶化を示しているものと考えられる。
さらに本発明のポリエチレンナフタレート繊維としては、昇温条件下での発熱ピークのエネルギーΔＨｃが１５〜５０Ｊ／ｇであることが好ましい。さらには２０〜５０Ｊ／ｇ、特には３０Ｊ／ｇ以上であることが好ましい。ここで昇温条件下での発熱ピークのエネルギーΔＨｃとは、ポリエチレンナフタレート繊維を３２０℃で２分間溶融保持させた後、液体窒素中で固化させ急冷固化ポリエチレンナフタレートとした後に、窒素気流下２０℃／分の昇温条件にて示差走査熱量計を用い測定したものである。この昇温条件下での発熱ピークのエネルギーΔＨｃは、繊維を構成するポリマーの昇温条件での昇温結晶化を示しているものと考えられる。一度溶融、冷却固化させることにより、繊維成形時の熱履歴の影響をより小さくすることができる。
このエネルギーΔＨｃｄまたはΔＨｃが低い場合には結晶性が低くなる傾向にあり好ましくない。またエネルギーΔＨｃｄまたはΔＨｃが高すぎる場合には、ポリエチレンナフタレート繊維の紡糸、延伸熱セット時に結晶化が進みすぎる傾向にあり、結晶成長が紡糸、延伸の工程を阻害し高強度の繊維となりにくい傾向にある。またエネルギーΔＨｃｄまたはΔＨｃが高すぎる場合には製造時に断糸、糸切れが多発する要因ともなる。
またこのような本発明のポリエチレンナフタレート繊維は、リン原子をエチレンナフタレート単位に対して０．１〜３００ｍｍｏｌ％含有するものであることが好ましい。さらには、リン原子の含有量が１０〜２００ｍｍｏｌ％であることが好ましい。リン化合物により結晶性をコントロールすることが容易になるからである。
また、本発明のポリエチレンナフタレート繊維は、通常触媒としての金属元素を含むものであるが、この繊維に含まれる金属元素が周期律表における第４〜５周期かつ３〜１２族の金属元素およびＭｇの群より選ばれる少なくとも１種以上の金属元素であることが好ましい。特には繊維に含まれる金属元素が、Ｚｎ、Ｍｎ、Ｃｏ、Ｍｇの群から選ばれる少なくとも１種以上の金属元素であることが好ましい。理由は定かではないが、これらの金属元素をリン化合物と併用した場合に特に結晶体積のばらつきが少ない均一な結晶が得られやすくなる。
このような金属元素の含有量としては、エチレンナフタレート単位に対して１０〜１０００ｍｍｏｌ％含有するものであることが好ましい。そして前述のリン元素Ｐと金属元素Ｍの存在比であるＰ／Ｍ比としては０．８〜２．０の範囲であることが好ましい。Ｐ／Ｍ比が小さすぎる場合には、金属濃度が過剰となり、過剰金属成分がポリマーの熱分解を促進し、熱安定性を損なう傾向にある。逆にＰ／Ｍ比が大きすぎる場合には、リン化合物が過剰のため、ポリエチレンナフタレートポリマーの重合反応を阻害し、繊維物性が低下する傾向にある。さらに好ましいＰ／Ｍ比としては０．９〜１．８であることが好ましい。
そして本発明のポリエチレンナフタレート繊維の強度としては４．０〜１０．０ｃＮ／ｄｔｅｘであることが好ましい。さらには５．０〜９．０ｃＮ／ｄｔｅｘ、より好ましくは６．０〜８．０ｃＮ／ｄｔｅｘであることが好ましい。強度が低すぎる場合にはもちろん、高すぎる場合にも耐久性に劣る傾向にある。また、ぎりぎりの高強度で生産を行うと製糸工程での断糸が発生し易い傾向にあり工業繊維としての品質安定性に問題がある傾向にある。
融点としては２８５〜３１５℃であることが好ましい。さらには２９０〜３１０℃であることが最適である。融点が低すぎる場合には耐熱性、寸法安定性が劣る傾向にある。一方高すぎても溶融紡糸が困難になる傾向にある。繊維が高い融点を有する場合には、繊維の耐熱強力維持率を高く保つことができ、高温雰囲気下で用いられる複合材料用の補強用繊維として最適である。
また１８０℃の乾熱収縮率は、０．５〜４．０％未満であることが好ましい。さらには１．０〜３．５％であることが好ましい。乾熱収縮率が高すぎる場合、加工時の寸法変化が大きくなる傾向にあり、繊維を用いた成形品の寸法安定性が劣るものとなりやすい。このような高融点、低乾熱収縮率は本発明の繊維を構成するポリマーの結晶体積を大きくすることにより達成されたものでである。
また、本発明のポリエチレンナフタレート繊維のｔａｎδのピーク温度は１５０〜１７０℃であることが好ましい。従来のポリエチレンナフタレート繊維のｔａｎδは通常１８０℃近辺であるが、本発明のポリエチレンナフタレート繊維は高配向結晶化に伴いｔａｎδの値が低温シフトしたもので、タイヤなどのゴム補強用繊維として疲労性の面で有利な特性を発揮することができる。
また高温条件でのモジュラスが高くなっていることが好ましい。例えば２００℃におけるモジュラスＥ’（２００℃）と２０℃におけるモジュラスＥ’（２０℃）の比Ｅ’（２００℃）／Ｅ’（２０℃）が０．２５〜０．５であることが好ましい。または、１００℃におけるモジュラスＥ’（１００℃）と２０℃におけるモジュラスＥ’（２０℃）の比Ｅ’（１００℃）／Ｅ’（２０℃）が０．７〜０．９であることが好ましい。このように高温でのモジュラスを高くすることにより、高温での寸法安定性を極めて高いレベルに保持することが可能となる。
本発明のポリエチレンナフタレート繊維の極限粘度ＩＶｆとしては０．６〜１．０の範囲であることが好ましい。極限粘度が低すぎると本発明の目的とする高強度、高モジュラス及び寸法安定性に優れたポリエチレンナフタレート繊維を得ることは困難である。一方極限粘度を必要以上に高めた場合、紡糸工程で断糸が多発し、工業的な生産は困難となる。本発明におけるポリエチレンナフタレート繊維の極限粘度ＩＶｆは０．７〜０．９の範囲であることが特に好ましい。
また本発明のポリエチレンナフタレート繊維の複屈折率（Δｎ_ＤＹ）としては、０．１５〜０．３５の範囲であることが好ましい。そして密度（ρ_ＤＹ）としては、１．３５０〜１．３７０であることが好ましい。複屈折率（Δｎ_ＤＹ）や密度（ρ_ＤＹ）が小さい場合には、十分発達した繊維構造が形成されておらず、本発明の目的である耐熱性、寸法安定性が得にくい傾向にある。一方、複屈折率（Δｎ_ＤＹ）や密度（ρ_ＤＹ）を上げ過ぎた場合、製造工程において延伸倍率を破断延伸倍率付近にまで高くするなどの条件を採用する必要があり、断糸が起こりやすく安定した繊維を得ることが困難な傾向にある。本発明におけるポリエチレンナフタレート繊維の複屈折率（Δｎ_ＤＹ）としては０．１８〜０．３２、密度（ρ_ＤＹ）としては１．３５５〜１．３６５の各範囲であることが、さらに好ましい。
本発明のポリエチレンナフタレート繊維の単糸繊度には特に限定は無いが、製糸性の観点から０．１〜１００ｄｔｅｘ／フィラメントであることが好ましい。特にタイヤコード、Ｖ−ベルト等のゴム補強用繊維や、産業資材用繊維としては、強力、耐熱性や接着性の観点から、１〜２０ｄｔｅｘ／フィラメントであることが好ましい。
総繊度に関しても特に制限は無いが、１０〜１０，０００ｄｔｅｘが好ましく、特にタイヤコード、Ｖ−ベルト等のゴム補強用繊維や、産業資材用繊維としては、２５０〜６，０００ｄｔｅｘであることが好ましい。また総繊度としては例えば１，０００ｄｔｅｘの繊維を２本合糸して総繊度２，０００ｄｔｅｘとするように、紡糸、延伸の途中、あるいはそれぞれの終了後に２〜１０本の合糸を行うことも好ましい。
さらに本発明のポリエチレンナフタレート繊維は、上記のようなポリエチレンナフタレート繊維をマルチフィラメントとし撚りを掛けてコードの形態としたものであることも好ましい。マルチフィラメント繊維に撚りを掛けることにより、強力利用率が平均化し、その疲労性が向上する。撚り数としては５０〜１０００回／ｍの範囲であることが好ましく、下撚りと上撚りを行い合糸したコードであることも好ましい。合糸する前の糸条を構成するフィラメント数は５０〜３０００本であることが好ましい。このようなマルチフィラメントとすることにより耐疲労性や柔軟性がより向上する。繊度が小さすぎる場合には強度が不足する傾向にある。逆に繊度が大きすぎる場合には太くなりすぎて柔軟性が得られない問題や、紡糸時に単糸間の膠着が起こりやすく安定した繊維の製造が困難となる傾向にある。
上記のような特徴を有する本発明のポリエチレンナフタレート繊維は、従来のポリエチレンナフタレート繊維に比べ融点が高く、高温条件下での使用の際にも充分に性能を発揮しうる補強用繊維となる。特に高温での耐久性が要求されるゴム補強用の繊維として最適である。
このような本発明のポリエチレンナフタレート繊維は、例えばもう一つの本発明であるポリエチレンナフタレート繊維の製造方法により得ることが可能である。すなわち、主たる繰り返し単位がエチレンナフタレートであるポリマーを溶融し、紡糸口金から吐出するポリエチレンナフタレート繊維の製造方法であって、溶融時のポリマー中に下記一般式（Ｉ）または（ＩＩ）であらわされる少なくとも１種類のリン化合物添加した後に紡糸口金から吐出し、紡糸口金から吐出後の紡糸ドラフト比が１００〜５０００であり、紡糸口金から吐出直後に溶融ポリマー温度のプラスマイナス５０℃以内の温度の保温紡糸筒を通過し、かつ延伸する製造方法により得ることできる。

［上の式中、Ｒ^１は炭素数１〜２０個の炭化水素基であるアルキル基、アリール基又はベンジル基であり、Ｒ^２は水素原子又は炭素数の１〜２０個の炭化水素基であるアルキル基、アリール基又はベンジル基、Ｘは、水素原子またはーＯＲ^３基であり、Ｘが−ＯＲ^３基である場合、Ｒ^３は水素原子又は炭素数の１〜１２個の炭化水素基であるアルキル基、アリール基又はベンジル基、であり、Ｒ^２とＲ^３は同一であっても異なっていても良い。］

［上の式中、Ｒ^４〜Ｒ^６は炭素数４〜１８個の炭化水素基であるアルキル基、アリール基又はベンジル基であり、Ｒ^４〜Ｒ^６は同一であっても異なっていても良い。］
本発明で用いられる主たる繰返し単位がエチレンナフタレートであるポリマーとしては、好ましくはエチレン−２，６−ナフタレート単位を８０％以上、特には９０％以上含むポリエチレンナフタレートであることが好ましい。他に少量であれば、適当な第３成分を含む共重合体であっても差し支えない。
適当な第３成分としては、（ａ）２個のエステル形成官能基を有する化合物や、（ｂ）１個のエステル形成官能基を有する化合物、さらには（ｃ）３個以上のエステル形成官能基を有する化合物など、重合体が実質的に線状である範囲内で使用可能である。また、ポリエチレンナフタレート中には、各種の添加剤が含まれていてもよいことはいうまでもない。
このような本発明のポリエステルは、従来公知のポリエステルの製造方法に従って製造することができる。すなわち、酸成分として、ナフタレン−２，６−ジメチルカルボキシレート（ＮＤＣ）に代表される２，６−ナフタレンジカルボン酸のジアルキルエステルとグリコール成分であるエチレングリコールとでエステル交換反応させた後、この反応の生成物を減圧下で加熱して、余剰のジオール成分を除去しつつ重縮合させることによって製造することができる。あるいは、酸成分として２，６−ナフタレンジカルボン酸とジオール成分であるエチレングリコールとでエステル化させることにより、従来公知の直接重合法により製造することもできる。
エステル交換反応を利用した方法の場合に用いるエステル交換触媒としては、特に限定されるものではないが、マンガン、マグネシウム、チタン、亜鉛、アルミニウム、カルシウム、コバルト、ナトリウム、リチウム、鉛化合物を用いることができる。このような化合物としては、例えばマンガン、マグネシウム、チタン、亜鉛、アルミニウム、カルシウム、コバルト、ナトリウム、リチウム、鉛の酸化物、酢酸塩、カルボン酸塩、水素化物、アルコラート、ハロゲン化物、炭酸塩、硫酸塩等を挙げることができる。
中でも、ポリエステルの溶融安定性、色相、ポリマー不溶異物の少なさ、紡糸の安定性の観点から、マンガン、マグネシウム、亜鉛、チタン、ナトリウム、リチウム化合物が好ましく、さらにマンガン、マグネシウム、亜鉛化合物が好ましい。また、これらの化合物は二種以上を併用してもよい。
重合触媒については、特に限定されるものではないが、アンチモン、チタン、ゲルマニウム、アルミニウム、ジルコニウム、すず化合物を用いることができる。このような化合物としては、例えばアンチモン、チタン、ゲルマニウム、アルミニウム、ジルコニウム、すずの酸化物、酢酸塩、カルボン酸塩、水素化物、アルコラート、ハロゲン化物、炭酸塩、硫酸塩等を挙げることができる。また、これらの化合物は二種以上を併用してもよい。
中でも、ポリエステルの重合活性、固相重合活性、溶融安定性、色相に優れ、かつ得られる繊維が高強度で、優れた製糸性、延伸性を有する点で、アンチモン化合物が特に好ましい。
本発明では、上記ポリマーを溶融し、紡糸口金から吐出して繊維とするのであるが、このとき溶融時のポリマー中に下記一般式（Ｉ）または（ＩＩ）であらわされる少なくとも１種類のリン化合物を添加した後に紡糸口金から吐出することを必須とする。

［上の式中、Ｒ^１は炭素数１〜２０個の炭化水素基であるアルキル基、アリール基又はベンジル基であり、Ｒ^２は水素原子又は炭素数の１〜２０個の炭化水素基であるアルキル基、アリール基又はベンジル基、Ｘは、水素原子または−ＯＲ^３基であり、Ｘが−ＯＲ^３基である場合、Ｒ^３は水素原子又は炭素数の１〜１２個の炭化水素基であるアルキル基、アリール基又はベンジル基、であり、Ｒ^２とＲ^３は同一であっても異なっていても良い。］

［上の式中、Ｒ^４〜Ｒ^６は炭素数４〜１８個の炭化水素基であるアルキル基、アリール基又はベンジル基であり、Ｒ^４〜Ｒ^６は同一であっても異なっていても良い。］
また、式中に用いられたアルキル基、アリール基、ベンジル基は置換されたものであっても良い。さらにはＲ^１およびＲ^２は、炭素数１〜１２個の炭化水素基であることが好ましい。
一般式（Ｉ）の好ましい化合物としては、例えばフェニルホスホン酸、フェニルホスホン酸モノメチル、フェニルホスホン酸モノエチル、フェニルホスホン酸モノプロピル、フェニルホスホン酸モノフェニル、フェニルホスホン酸モノベンジル、（２−ヒドロキシエチル）フェニルホスホネート、２−ナルフチルホスホン酸、１−ナフチルホスホン酸、２−アントリルホスホン酸、１−アントリルホスホン酸、４−ビフェニルホスホン酸、４−メチルフェニルホスホン酸、４−メトキシフェニルホスホン酸、フェニルホスフィン酸、フェニルホスフィン酸メチル、フェニルホスフィン酸エチル、フェニルホスフィン酸プロピル、フェニルホスフィン酸フェニル、フェニルホスフィン酸ベンジル、（２−ヒドロキシエチル）フェニルホスフィネート、２−ナルフチルホスフィン酸、１−ナフチルホスフィン酸、２−アントリルホスフィン酸、１−アントリルホスフィン酸、４−ビフェニルホスフィン酸、４−メチルフェニルホスフィン酸、４−メトキシフェニルホスフィン酸などを挙げることができる。
そして、一般式（ＩＩ）の化合物としてはビス（２，４−ジ−ｔｅｒｔ−ブチルフェニル）ペンタエリスリトールジホスファイト、ビス（２，６−ジ−ｔｅｒｔ−ブチル−４−メチルフェニル）ペンタエリスリトールジホスファイト、トリス（２，４−ジ−ｔｅｒｔ−ブチルフェニル）ホスファイトなどを挙げることができる。さらに、上記一般式（Ｉ）の化合物は、Ｒ^１はアリール基であり、Ｒ^２は水素原子又は炭化水素基であるアルキル基、アリール基又はベンジル基であり、Ｒ^３は、水素原子または−ＯＨ基であることが好ましい。
すなわち、本発明で用いられる特に好ましいリン化合物としては、下記一般式（Ｉ’）を挙げることができる。

［上の式中、Ａｒは炭素数６〜２０個の炭化水素基であるアリール基であり、Ｒ^２は水素原子又は炭素数の１〜２０個の炭化水素基であるアルキル基、アリール基又はベンジル基、Ｙは、水素原子または−ＯＨ基である。］
ちなみに式中で用いられているＲ^２の炭化水素基としては、アルキル基、アリール基、ベンジル基であることが好ましく、それらは未置換のもしくは置換されたものであっても良い。このときＲ^２の置換基としては立体構造を阻害しないのであることが好ましく、例えば、ヒドロキシル基、エステル基、アルコキシ基等で置換されているものを挙げることがきる。また上記（Ｉ’）のＡｒで示されるアリール基は、例えば、アルキル基、アリール基、ベンジル基、アルキレン基、ヒドロキシル基、ハロゲン原子で置換されていても良い。
さらには、本発明で用いられるリン化合物としては、下記一般式（ＩＩＩ）で表されたフェニルホスホン酸およびその誘導体あることが好ましい。

［上の式中、Ａｒは炭素数６〜２０個の炭化水素基であるアリール基であり、Ｒ^７は水素原子又は未置換もしくは置換された１〜２０個の炭素元素を有する炭化水素基である。］
本発明ではこれら特有のリン化合物を溶融ポリマー中に直接添加することにより、ポリエチレンナフタレートの結晶性が向上し、その後の製造条件の下で結晶化度を高く保ちながら、結晶体積の大きいポリエチレンナフタレート繊維を得ることができたのである。これはこの特有のリン化合物が、紡糸及び延伸工程で生じる粗大な結晶成長を抑制し結晶を微分散化させる効果であると考えられる。また従来ポリエチレンナフタレート繊維を高速紡糸することは非常に困難であったが、これらのリン化合物が添加されることにより、紡糸安定性が飛躍的に向上し、かつ断糸が起きない点から実用的な延伸倍率を高めることによって繊維を高強度化することができるようになった。
ちなみに式中で用いられているＲ^１〜Ｒ^７の炭化水素基としては、アルキル基、アリール基、ジフェニル基、ベンジル基、アルキレン基、アリーレン基を挙げることができる。またこれらは例えば、ヒドロキシル基、エステル基、アルコキシ基で置換されていることが好ましい。
かかる置換基で置換された炭化水素基としては好適には、下記官能基及びその異性体を例示することができる。
−（ＣＨ_２）ｎ−ＯＨ
−（ＣＨ_２）ｎ−ＯＣＨ_３
−（ＣＨ_２）ｎ−ＯＰｈ
−Ｐｈ−ＯＨ （Ｐｈ；芳香環）
［ｎは１〜１０までの整数を表す］
中でも結晶性を向上させるためには上記一般式（Ｉ）のリン化合物であることが、さらには上記一般式（Ｉ’）、特には上記一般式（ＩＩＩ）であることが好ましい。
また工程中の真空下での飛散を防止するためには、式（Ｉ）を例に説明すると、Ｒ^１の炭素数としては４個以上、さらには６個以上であることが好ましく、特にアリール基であることが好ましい。あるいは、Ｘが水素原子または水酸基である、例えば一般式（Ｉ’）であることが好ましい。Ｘが水素原子または水酸基である場合にも、工程中の真空下では飛散しにくい。
また、高い結晶性向上の効果を示すためには、Ｒ^１がアリール基であることが、さらにはベンジル基やフェニル基であることが好ましく、本発明の製造方法では、リン化合物がフェニルホスフィン酸またはフェニルホスホン酸であることが特に好ましい。中でもフェニルホスホン酸およびその誘導体であることが最適であり、作業性の面からもフェニルホスホン酸が最も好ましい。フェニルホスホン酸は水酸基を有するため、そうでは無いフェニルホスホン酸ジメチルなどのアルキルエステルに比べて沸点が高く、真空下で飛散しにくいというメリットもある。つまり、添加したリン化合物のうちポリエステル中に残存する量が増え、添加量対比の効果が高くなる。また真空系の閉塞が発生しにくい点からも有利である。
本発明で用いられるリン化合物の添加量としては、ポリエステルを構成するジカルボン酸成分のモル数に対して０．１〜３００ミリモル％であることが好適である。リン化合物の量が不十分であると結晶性向上効果が不十分になる傾向にあり、多すぎる場合には紡糸時の異物欠点が発生するために製糸性が低下する傾向にある。リン化合物の含有量はポリエステルを構成するジカルボン酸成分のモル数に対して１〜１００ミリモル％の範囲がより好ましく、１０〜８０ミリモル％の範囲がさらに好ましい。
また、このようなリン化合物と共に、周期律表における第４〜５周期かつ３〜１２族の金属元素およびＭｇの群より選ばれる少なくとも１種以上の金属元素が溶融ポリマー中に添加されていることが好ましい。特には繊維に含まれる金属元素が、Ｚｎ、Ｍｎ、Ｃｏ、Ｍｇの群から選ばれる少なくとも１種以上の金属元素であることが好ましい。理由は定かではないが、これらの金属元素を上記リン化合物と併用した場合に特に結晶体積のばらつきが少ない均一な結晶が得られやすくなる。これらの金属元素は、エステル交換触媒や重合触媒として添加しても良いし、別途添加することも可能である。
このような金属元素の含有量としては、エチレンナフタレート単位に対して１０〜１０００ｍｍｏｌ％含有するものであることが好ましい。そして前述のリン元素Ｐと金属元素Ｍの存在比であるＰ／Ｍ比としては０．８〜２．０の範囲であることが好ましい。Ｐ／Ｍ比が小さすぎる場合には、金属濃度が過剰となり、過剰金属成分がポリマーの熱分解を促進し、熱安定性を損なう傾向にある。逆にＰ／Ｍ比が大きすぎる場合には、リン化合物が過剰のため、ポリエチレンナフタレートポリマーの重合反応を阻害し、繊維物性が低下する傾向にある。さらに好ましいＰ／Ｍ比としては０．９〜１．８であることが好ましい。
本発明に用いるリン化合物の添加時期は、特に限定される物ではなく、ポリエステル製造の任意の工程において添加することができる。好ましくは、エステル交換反応又はエステル化反応の開始当初から重合終了する間である。さらに均一な結晶を形成させるためにはエステル交換反応又はエステル化反応の終了した時点から重合反応の終了時点の間であることがより好ましい。
また、ポリエステルの重合後に、混練機を用いて、リン化合物を練り込む方法を採用することもできる。混練する方法は特に限定されるものではないが、通常の一軸、二軸混練機を使用することが好ましい。さらに好ましくは、得られるポリエステル組成物の重合度の低下を抑制するために、ベント式の一軸、二軸混練機を使用する方法を例示できる。
この混練時の条件は特に限定されるものではないが、例えばポリエステルの融点以上、滞留時間は１時間以内、好ましくは１分〜３０分である。また、混練機へのリン化合物、ポリエステルの供給方法は特に限定されるものではない。例えばリン化合物、ポリエステルを別々に混練機に供給する方法、高濃度のリン化合物を含有するマスターチップとポリエステルを適宜混合して供給する方法などを挙げることができる。ただし溶融ポリマー中に本発明で用いられる特有のリン化合物を添加する際には、他の化合物とあらかじめ反応させることなく、直接ポリエステルポリマーに添加することが好ましい。リン化合物を他の化合物、例えばチタン化合物とあらかじめ反応させてできた反応生成物が粗大粒子となり、ポリエステルポリマー中で構造欠陥や結晶の乱れを誘起することを防ぐためである。
本発明で用いられるポリエチレンナフタレートのポリマーは、樹脂チップの極限粘度として、公知の溶融重合や固相重合を行うことにより０．６５〜１．２の範囲にすることが好ましい。樹脂チップの極限粘度が低すぎる場合には溶融紡糸後の繊維を高強度化させることが困難となる。また極限粘度が高すぎると固相重合時間が大幅に増加し、生産効率が低下するため工業的観点から好ましくない。極限粘度としては、さらには０．７〜１．０の範囲であることが好ましい。
本発明のポリエチレンナフタレート繊維の製造方法は、上記のポリエチレンナフタレートポリマーを溶融し、紡糸口金から吐出後の紡糸ドラフト比が１００〜５０００であり、紡糸口金から吐出直後に溶融ポリマー温度のプラスマイナス５０℃以内の範囲内に設定された保温紡糸筒を通過し、かつ延伸することを必須とする。
溶融時のポリエチレンナフタレートポリマーの温度としては２８５〜３３５℃であることが好ましい。さらには２９０〜３３０℃の範囲であることが好ましい。紡糸口金としてはキャピラリーを具備したものを用いることが一般的である。
そして紡糸ドラフトとしては１００〜５０００で行うことが必須である。さらには５００〜３０００のドラフト条件であることが好ましい。紡糸ドラフトとは、紡糸巻取速度（紡糸速度）と紡糸吐出線速度の比として定義され、下記の数式（２）で表されるものである。

（式中、Ｄは口金の孔径、Ｖは紡糸引取速度、Ｗは単孔あたりの体積吐出量を示す）
紡糸ドラフト比を大きくすることによって、ポリマー中の結晶体積や結晶化度を上げることができる。
このような高紡糸ドラフトとするためには、紡糸速度が高いことが好ましく、本発明の製造方法の紡糸速度としては１５００〜６０００ｍ／分であることが適切である。さらには２０００〜５０００ｍ／分であることが好ましい。
さらに本発明の製造方法では、紡糸口金から吐出直後に溶融ポリマー温度のプラスマイナス５０℃以内の範囲内に設定された保温紡糸筒を通過することを必須要件とする。さらには保温紡糸筒の設定温度は溶融ポリマー温度以下であることが好ましい。また、保温紡糸筒の長さとしては１０〜３００ｍｍであることが好ましく、さらには３０〜１５０ｍｍであることが好ましい。保温紡糸筒の通過時間としては、０．２秒以上であることが好ましい。
通常ポリエチレンナフタレート繊維の製造方法においては、本願のように高ドラフト条件を採用した場合、溶融ポリマー温度よりも数十度高い加熱紡糸筒を使用している。剛直なポリマーであるポリエチレンナフタレートポリマーは、紡糸口金から吐出された直後にすぐに配向しやすく、単糸切れを発生しやすいため、加熱紡糸筒をもちいて遅延冷却させる必要があるからである。紡糸筒温度が溶融ポリマー温度付近の場合には、吐出するポリマーの速度が速いために、遅延冷却状態とならないからである。
しかし本発明の製造方法では特定のリン化合物を用いて微小結晶を形成させることにより、同じ配向度であっても均一な構造とすることが可能となった。そして均一構造であるがゆえに加熱紡糸筒を用いなくても単糸切れが発生せず、高い製糸性を確保することが可能となったのである。また、このような低温の保温紡糸筒を用いることによりポリエチレンナフタレート繊維の結晶体積をより有効に大きくすることができるようになった。高温の紡糸筒ではポリマー中の分子運動が激しく、大きな結晶の生成が阻害されるためである。そして大きな結晶体積を有することにより、得られる繊維の融点や耐熱疲労性を有効に高めることができるようになったのである。
保温紡糸筒を通過した紡出糸条は、次いで３０℃以下の冷風を吹き付けて冷却することが好ましい。さらには２５℃以下の冷風であることが好ましい。冷却風の吹出量としては２〜１０Ｎｍ^３／分、吹出長さとしては１００〜５００ｍｍ程度であることが好ましい。次いで、冷却された糸状については、油剤を付与することが好ましい。
このようにして紡糸された未延伸糸は、複屈折率（Δｎ_ＵＤ）としては０．１０〜０．２８、密度（ρ_ＵＤ））としては１．３４５〜１．３６５の範囲であることが好ましい。複屈折率（Δｎ_ＵＤ）や密度（ρ_ＵＤ）が小さい場合には、紡糸過程での繊維の配向結晶化が不充分となり、耐熱性及び優れた寸法安定性が得られない傾向にある。一方、複屈折率（Δｎ_ＵＤ）や密度（ρ_ＵＤ）が大きすぎる場合、紡糸過程で粗大な結晶成長が発生していることが推測され、紡糸性を阻害し断糸が多発する傾向にあり、実質的に製造が困難となる傾向にある。また、その後の延伸性も阻害されるため高物性の繊維の製造が困難となる傾向にある。さらには紡糸された未延伸糸の複屈折率（Δｎ_ＵＤ）としては０．１１〜０．２６、密度（ρ_ＵＤ）としては１．３５０〜１．３６０の範囲であるこいとがより好ましい。
本発明は高紡糸ドラフトを行うことを特徴とするが、通常程度のドラフトを行った場合には、結晶体積が小さくなり融点も低く、本発明のように高い寸法安定性を得ることができない。一方、高紡糸ドラフトであっても加熱紡糸筒を用いて遅延冷却を行った場合には、同じく結晶体積が小さくなり融点も低く、本発明の保温紡糸筒を用いた場合と違い高い寸法安定性を得ることができない。
その後、本発明のポリエチレンナフタレート繊維の製造方法では、延伸を行う。本発明では均一な結晶を有する繊維に対し高紡糸ドラフトを行っているために、断糸が有効に防止される。そして結晶化度が高いにもかかわらず、大きい結晶体積の繊維を得ることができたのである。延伸は、引取りローラーから一旦巻取って、いわゆる別延伸法で延伸してもよく、あるいは引取りローラーから連続的に延伸工程に未延伸糸を供給する、いわゆる直接延伸法で延伸しても構わない。また延伸条件としては１段ないし多段延伸であり、延伸負荷率としては６０〜９５％であることが好ましい。延伸負荷率とは繊維が実際に断糸する張力に対する、延伸を行う際の張力の比である。延伸倍率や延伸負荷率を上げることによって、結晶体積や結晶化度を有効に大きくすることができる。
延伸時の予熱温度としては、ポリエチレンナフタレート未延伸糸のガラス転移点以上、結晶化開始温度の２０℃以上低い温度以下で行うことが好ましく、本発明においては１２０〜１６０℃が好適である。延伸倍率は紡糸速度に依存するが、破断延伸倍率に対し延伸負荷率６０〜９５％となる延伸倍率で延伸を行うことが好ましい。また、繊維の強度を維持し寸法安定性を向上させるためにも、延伸工程で１７０℃から繊維の融点以下の温度で熱セットを行うことが好ましい。さらには延神時の熱セット温度が１７０〜２７０℃の範囲であることが好ましい。このような高温での熱セットにより、有効に延伸倍率を上げることができ結晶体積を大きくすることができるようになる。
本発明の製造方法では、特定のリン化合物を用いることによって、高ドラフト率かつ保温紡糸筒による冷却条件を始めて採用することができ、高い製糸性の製造方法でありながら、高い寸法安定性と耐疲労性を有する繊維を得ることができたのである。ちなみに本発明の特定のリン化合物を用いない場合には、紡糸するためにドラフト率を下げるか、加熱紡糸筒を用いて遅延冷却させる必要があり、本発明のような寸法安定性や耐疲労性に優れた高融点の繊維を得ることはできないのである。
このような本発明のポリエチレンナフタレート繊維の製造方法にて得られたポリエチレンナフタレート繊維は、結晶体積が大きいと共に高い結晶化率を実現しており、高強度とともに高い融点と高い寸法安定性を有し、さらには優れた耐疲労性をも満たす繊維となる。
本発明のポリエチレンナフタレート繊維の製造方法では、さらに得られた繊維を撚糸したり、合糸することにより、所望の繊維コードを得ることができる。さらにはその表面に接着処理剤を付与することも好ましい。接着処理剤としてはＲＦＬ系接着処理剤を処理することが、ゴム補強用途には最適である。
より具体的には、このような繊維コードは、上記のポリエチレンナフタレート繊維に、常法に従って撚糸を加え、あるいは無撚の状態でＲＦＬ処理剤を付着させ、熱処理を施すことにより得ることができ、このような繊維はゴム補強用に好適に使用できる処理コードとなる。
このようにして得られた産業資材用ポリエチレンナフタレート繊維は、高分子と繊維・高分子複合体とすることができる。この時、高分子がゴム弾性体であることが好ましい。この複合体は、補強に用いられた本発明のポリエチレンナフタレート繊維が耐熱性や寸法安定性に優れているため、複合体としたときの成形性に非常に優れたものとなる。特に本発明のポリエチレンナフタレート繊維をゴム補強に用いた場合にその効果は大きく、例えばタイヤ、ベルト、ホースなどに好適に用いられる。
本発明のポリエチレンナフタレート繊維をゴム補強用コードとして使用する場合は、例えば次のような方法を使用することができる。すなわち、該ポリエチレンナフタレート繊維を撚係数Ｋ＝Ｔ・Ｄ^１／２（Ｔは１０ｃｍ当たりの撚数、Ｄは撚糸コードの繊度）が９９０〜２，５００で合撚して撚糸コードとなし、該コードを接着処剤処理に引き続き２３０〜２７０℃で処理する。
本発明のポリエチレンナフタレート繊維から得られる処理コードは、強力が８０〜１８０Ｎ、２ｃＮ／ｄｔｅｘ応力時の伸度（中間荷伸）と１８０℃乾熱収縮率の和で表す寸法安定性指数が４．５％以下であり、高モジュラスかつ耐熱性、寸法安定性に優れ、高度の耐疲労性を有する優れた処理コードを得ることができる。ここで、寸法安定性指数はその値が低いほどモジュラスが高く、乾熱収縮率が低いことを表す。さらに好ましくは、本発明におけるポリエチレンナフタレート繊維を用いてなる処理コードの強力は１００〜１６０Ｎ、寸法安定性指数は３．５〜４．５％である。   The polyethylene naphthalate fiber of the present invention is a fiber whose main repeating unit is ethylene naphthalate. Furthermore, a polyethylene naphthalate fiber containing 80% or more, particularly 90% or more of ethylene-2,6-naphthalate units is preferable. If it is a small amount, it may be a copolymer containing an appropriate third component. In addition, even if it is the same polyester, in the case of a polyethylene terephthalate, it does not have a clear crystal structure, and it does not become a fiber in which the high strength and the high elastic modulus of the present invention are compatible.
  In general, such polyethylene naphthalate fiber is made into a fiber by melt spinning a polymer of polyethylene naphthalate. The polymer of polyethylene naphthalate can be polymerized with naphthalene-2,6-dicarboxylic acid or a functional derivative thereof in the presence of a catalyst under appropriate reaction conditions. Moreover, copolymerization polyethylene naphthalate is synthesize | combined by adding the appropriate 1 type, or 2 or more types of 3rd component before completion | finish of superposition | polymerization of polyethylene naphthalate.
  Suitable third components include: (a) compounds having two ester-forming functional groups, for example, aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid; cyclopropanedicarboxylic acid, Cycloaliphatic dicarboxylic acids such as cyclobutanedicarboxylic acid and hexahydroterephthalic acid; aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, naphthalene-2,7-dicarboxylic acid, diphenyldicarboxylic acid; diphenyl ether dicarboxylic acid, diphenylsulfone dicarboxylic acid, Carboxylic acids such as diphenoxyethanedicarboxylic acid and sodium 3,5-dicarboxybenzenesulfonate; oxycarboxylic acids such as glycolic acid, p-oxybenzoic acid and p-oxyethoxybenzoic acid; propylene glycol, trimethylene glycol, and diethyl Glycol, tetramethylene glycol, hexamethylene glycol, neopentylene glycol, p-xylylene glycol, 1,4-cyclohexanedimethanol, bisphenol A, p, p'-diphenoxysulfone-1,4-bis (β- Oxy compounds such as hydroxyethoxy) benzene, 2,2-bis (p-β-hydroxyethoxyphenyl) propane, polyalkylene glycol and p-phenylenebis (dimethylcyclohexane), or functional derivatives thereof; Compounds having a high degree of polymerization derived from acids, oxy compounds or functional derivatives thereof, and (b) compounds having one ester-forming functional group such as benzoic acid, benzoylbenzoic acid, benzyloxybenzoic acid, methoxy Polyalkyle Glycol and the like. Furthermore, (c) compounds having three or more ester-forming functional groups, such as glycerin, pentaerythritol, trimethylolpropane, tricarballylic acid, trimesic acid, trimellitic acid, etc., are substantially linear in polymer. It can be used within the range.
  In the polyethylene naphthalate, various additives such as matting agents such as titanium dioxide, heat stabilizers, antifoaming agents, color modifiers, flame retardants, antioxidants, ultraviolet absorbers, infrared absorbers. Additives such as montmorillonite, bentonite, hectorite, plate-like iron oxide, plate-like calcium carbonate, plate-like boehmite, or carbon nanotubes as additives for fluorescent brighteners, plasticizers, impact agents, or reinforcing agents It may be.
  The polyethylene naphthalate fiber of the present invention is a fiber made of polyethylene naphthalate as described above, and has a crystal volume of 550 to 1200 nm obtained by X-ray wide angle diffraction.³(550,000-1.2 million angstroms³It is essential that the crystallinity is 30 to 60%. Furthermore, the crystal volume is 600 to 1000 nm.³(600,000 to 1 million angstroms³) Is preferable. The crystallinity is preferably 35 to 55%.
  Here, the crystal volume of the present application is a product of crystal sizes obtained from diffraction peaks having diffraction angles of 15 to 16 degrees, 23 to 25 degrees, and 25.5 to 27 degrees in wide-angle X-ray diffraction of fibers. Incidentally, each of these diffraction angles is due to surface reflection at the crystal planes (010), (100), and (1-10) of the polyethylene naphthalate fiber, and theoretically corresponds to each Bragg reflection angle 2θ. However, it has a peak slightly shifted due to a change in the entire crystal structure. Such a crystal structure is unique to polyethylene naphthalate fibers. For example, even if it is the same polyester fiber, it does not exist in polyethylene terephthalate fiber.
  The crystallinity (Xc) of the present application is a value obtained from the following formula (1) from the specific gravity (ρ), the complete amorphous density (ρa) and the complete crystal density (ρc) of polyethylene naphthalate. .

In the formula
  ρ: Specific gravity of polyethylene naphthalate fiber
  ρa: 1.325 (complete amorphous density of polyethylene naphthalate)
  ρc: 1.407 (complete crystal density of polyethylene naphthalate)
  The polyethylene naphthalate fiber of the present invention was able to obtain a high thermal stability and a high melting point by realizing an unprecedented high crystal volume while maintaining the same high crystallinity as the conventional high-strength fiber. Is. Crystal volume 550nm³(550,000 angstroms³If it is less than), such a high melting point cannot be obtained. The higher the crystal volume, the better the thermal stability and the better. However, in general, in that case, the crystallinity is lowered and the strength is lowered.³(1.2 million angstroms³) Is the upper limit. If the crystallinity is less than 30%, high tensile strength and modulus cannot be realized.
  In order to increase the crystal volume, a method of spinning while keeping the temperature below the die during spinning is effective. A large crystal volume can also be obtained by increasing the spinning draft ratio, the draw ratio, etc., and stretching the fiber. However, when the spinning draft ratio is increased, the polyethylene naphthalate fiber, which is a rigid fiber, is easily broken, and it is particularly effective to keep the spinning draft ratio at about 100 to 5000 and increase the draw ratio. However, normally, when drafting is performed to increase the crystal volume while keeping the temperature below the die during spinning, yarn breakage occurs during spinning, and fibers cannot be produced. However, in the present invention, such a crystal volume can be realized by using a specific phosphorus compound.
  In order to increase the degree of crystallinity, it can be obtained by increasing the spinning draft ratio, the draw ratio, etc., and stretching the fiber at a high ratio, as in the case of increasing the crystal volume. However, as the crystal volume increases and the degree of crystallinity increases, the polyethylene naphthalate fiber, which is a rigid fiber, is more likely to break. Therefore, in the present invention, the crystal volume is 550 to 1200 nm.³(550,000-1.2 million angstroms³), It is important to adjust the crystallinity to 30 to 60%. For this purpose, it is important to form a uniform crystal structure at the stage of the polymer before spinning. For example, such a uniform crystal structure can be realized by including a specific phosphorus compound in the polymer.
  Further, in the polyethylene naphthalate fiber of the present invention, the maximum peak diffraction angle of X-ray wide angle diffraction is preferably in the range of 25.5 to 27.0 degrees. The reason is not clear, but among the (010), (100), and (1-10) crystal planes, the (1-10) plane crystal grows greatly on the fiber axis, resulting in greatly improved heat resistance. To be improved. The size of the crystal parallel to the fiber axis can be increased by stretching the fiber in a certain direction at a high magnification, for example, by increasing the spinning draft ratio, the draw ratio, and the like.
  In addition, the polyethylene naphthalate fiber of the present invention preferably has an exothermic peak energy ΔHcd of 15 to 50 J / g under a temperature drop condition. Furthermore, it is preferable that it is 20-50 J / g, especially 30 J / g or more. Here, the exothermic peak energy ΔHcd under the temperature-decreasing condition means that the polyethylene naphthalate fiber is heated to 320 ° C. under a temperature rising condition of 20 ° C./min under a nitrogen stream and melted and held for 5 minutes, and then 10 It was measured using a differential scanning calorimeter (DSC) under a temperature drop condition of ° C / min. It is considered that the energy ΔHcd of the exothermic peak under the temperature lowering condition indicates the temperature lowering crystallization under the temperature lowering condition.
  Furthermore, the polyethylene naphthalate fiber of the present invention preferably has an exothermic peak energy ΔHc of 15 to 50 J / g under elevated temperature conditions. Furthermore, it is preferable that it is 20-50 J / g, especially 30 J / g or more. Here, the exothermic peak energy ΔHc under the temperature rising condition means that the polyethylene naphthalate fiber is melted and held at 320 ° C. for 2 minutes and then solidified in liquid nitrogen to form rapidly cooled solidified polyethylene naphthalate. It was measured using a differential scanning calorimeter under a temperature rising condition of 20 ° C./min. The exothermic peak energy ΔHc under this temperature rise condition is considered to indicate the temperature rise crystallization under the temperature rise condition of the polymer constituting the fiber. Once melted and cooled and solidified, the influence of thermal history during fiber forming can be further reduced.
  When this energy ΔHcd or ΔHc is low, the crystallinity tends to be low, which is not preferable. If the energy ΔHcd or ΔHc is too high, crystallization tends to proceed excessively during spinning and stretching heat setting of the polyethylene naphthalate fiber, and the crystal growth tends to hinder the spinning and stretching process, making it difficult to form a high-strength fiber. It is in. In addition, when the energy ΔHcd or ΔHc is too high, it becomes a factor that yarn breakage and yarn breakage occur frequently during production.
  In addition, the polyethylene naphthalate fiber of the present invention preferably contains 0.1 to 300 mmol% of phosphorus atoms with respect to the ethylene naphthalate unit. Furthermore, the phosphorus atom content is preferably 10 to 200 mmol%. This is because it becomes easy to control crystallinity by the phosphorus compound.
  Further, the polyethylene naphthalate fiber of the present invention usually contains a metal element as a catalyst, and the metal element contained in this fiber is a metal element of 4th to 5th period and 3-12 group metal element and Mg in the periodic table. It is preferably at least one metal element selected from the group. In particular, the metal element contained in the fiber is preferably at least one metal element selected from the group consisting of Zn, Mn, Co, and Mg. The reason is not clear, but when these metal elements are used in combination with a phosphorus compound, a uniform crystal with little variation in crystal volume is easily obtained.
  As content of such a metal element, it is preferable to contain 10-1000 mmol% with respect to an ethylene naphthalate unit. The P / M ratio, which is the abundance ratio of the phosphorus element P and the metal element M, is preferably in the range of 0.8 to 2.0. When the P / M ratio is too small, the metal concentration becomes excessive, and the excess metal component tends to accelerate the thermal decomposition of the polymer and impair the thermal stability. On the other hand, when the P / M ratio is too large, the phosphorus compound is excessive, so that the polymerization reaction of the polyethylene naphthalate polymer is inhibited and the fiber physical properties tend to be lowered. A more preferable P / M ratio is preferably 0.9 to 1.8.
  The strength of the polyethylene naphthalate fiber of the present invention is preferably 4.0 to 10.0 cN / dtex. Furthermore, it is preferably 5.0 to 9.0 cN / dtex, more preferably 6.0 to 8.0 cN / dtex. When the strength is too low, the durability tends to be inferior when the strength is too high. In addition, when production is performed with a very high strength, yarn breakage tends to occur in the yarn making process, and there is a tendency for quality stability as an industrial fiber.
  The melting point is preferably 285 to 315 ° C. Furthermore, it is optimal that it is 290-310 degreeC. When the melting point is too low, heat resistance and dimensional stability tend to be inferior. On the other hand, if it is too high, melt spinning tends to be difficult. When the fiber has a high melting point, the heat resistance and strength maintenance rate of the fiber can be kept high, which is optimal as a reinforcing fiber for a composite material used in a high temperature atmosphere.
  The dry heat shrinkage at 180 ° C. is preferably 0.5 to less than 4.0%. Furthermore, it is preferable that it is 1.0 to 3.5%. If the dry heat shrinkage is too high, the dimensional change during processing tends to be large, and the dimensional stability of a molded product using fibers tends to be poor. Such a high melting point and a low dry heat shrinkage ratio are achieved by increasing the crystal volume of the polymer constituting the fiber of the present invention.
  Moreover, it is preferable that the peak temperature of tan-delta of the polyethylene naphthalate fiber of this invention is 150-170 degreeC. The tan δ of conventional polyethylene naphthalate fibers is usually around 180 ° C, but the polyethylene naphthalate fibers of the present invention are those in which the value of tan δ is shifted at a low temperature due to high orientation crystallization. Can exhibit advantageous properties in terms of safety.
  Moreover, it is preferable that the modulus in high temperature conditions is high. For example, the ratio E ′ (200 ° C.) / E ′ (20 ° C.) of the modulus E ′ at 200 ° C. (200 ° C.) and the modulus E ′ at 20 ° C. (20 ° C.) is preferably 0.25 to 0.5. . Alternatively, the ratio E ′ (100 ° C.) / E ′ (20 ° C.) of the modulus E ′ at 100 ° C. (100 ° C.) and the modulus E ′ at 20 ° C. (20 ° C.) is 0.7 to 0.9. preferable. By increasing the modulus at high temperature in this way, it becomes possible to maintain the dimensional stability at high temperature at a very high level.
  The intrinsic viscosity IVf of the polyethylene naphthalate fiber of the present invention is preferably in the range of 0.6 to 1.0. If the intrinsic viscosity is too low, it is difficult to obtain a polyethylene naphthalate fiber excellent in high strength, high modulus and dimensional stability, which is an object of the present invention. On the other hand, when the intrinsic viscosity is increased more than necessary, fiber breakage occurs frequently in the spinning process, making industrial production difficult. The intrinsic viscosity IVf of the polyethylene naphthalate fiber in the present invention is particularly preferably in the range of 0.7 to 0.9.
  Also, the birefringence (Δn) of the polyethylene naphthalate fiber of the present invention._DY) Is preferably in the range of 0.15 to 0.35. And density (ρ_DY) Is preferably 1.350 to 1.370. Birefringence (Δn_DY) And density (ρ_DY) Is small, a sufficiently developed fiber structure is not formed, and heat resistance and dimensional stability, which are the objects of the present invention, tend to be difficult to obtain. On the other hand, the birefringence (Δn_DY) And density (ρ_DY) Is excessively high, it is necessary to adopt conditions such as increasing the draw ratio to the vicinity of the break draw ratio in the production process, and yarn breakage tends to occur, and it tends to be difficult to obtain stable fibers. Birefringence (Δn) of polyethylene naphthalate fiber in the present invention_DY) As 0.18 to 0.32, density (ρ_DY) Is more preferably in the range of 1.355 to 1.365.
  Although there is no limitation in particular in the single yarn fineness of the polyethylene naphthalate fiber of this invention, it is preferable that it is 0.1-100 dtex / filament from a viewpoint of yarn-making property. Particularly, rubber reinforcing fibers such as tire cords and V-belts, and industrial material fibers are preferably 1 to 20 dtex / filament from the viewpoint of strength, heat resistance and adhesiveness.
  The total fineness is not particularly limited, but is preferably 10 to 10,000 dtex, and particularly preferably 250 to 6,000 dtex for rubber reinforcing fibers such as tire cords and V-belts and fibers for industrial materials. . In addition, as the total fineness, for example, 2 to 10 yarns may be spun during spinning or drawing, or after the end of each, so that two fibers of 1,000 dtex are combined to a total fineness of 2,000 dtex. preferable.
  Furthermore, it is also preferable that the polyethylene naphthalate fiber of the present invention is a cord formed by twisting the polyethylene naphthalate fiber as described above into a multifilament. By twisting the multifilament fiber, the strength utilization rate is averaged and the fatigue property is improved. The number of twists is preferably in the range of 50 to 1000 turns / m, and it is also preferable that the cord is a combined yarn obtained by performing a lower twist and an upper twist. The number of filaments constituting the yarn before being combined is preferably 50 to 3000. By using such a multifilament, fatigue resistance and flexibility are further improved. When the fineness is too small, the strength tends to be insufficient. On the other hand, if the fineness is too large, it becomes too thick and flexibility cannot be obtained, and sticking between single yarns tends to occur during spinning, and it tends to be difficult to produce stable fibers.
  The polyethylene naphthalate fiber of the present invention having the above-mentioned characteristics has a higher melting point than conventional polyethylene naphthalate fiber, and becomes a reinforcing fiber that can sufficiently perform even when used under high temperature conditions. . In particular, it is optimal as a fiber for rubber reinforcement that requires durability at high temperatures.
  Such a polyethylene naphthalate fiber of the present invention can be obtained, for example, by another production method of polyethylene naphthalate fiber of the present invention. That is, a method for producing a polyethylene naphthalate fiber in which a polymer whose main repeating unit is ethylene naphthalate is melted and discharged from a spinneret, and represented by the following general formula (I) or (II) in the polymer at the time of melting. After the addition of at least one kind of phosphorus compound is discharged from the spinneret, the spinning draft ratio after discharge from the spinneret is 100 to 5000, and immediately after discharge from the spinneret, the molten polymer temperature is within plus or minus 50 ° C. It can be obtained by a production method of passing through a heat insulating spinning cylinder and drawing.

[In the above formula, R¹Is an alkyl group, aryl group or benzyl group which is a hydrocarbon group having 1 to 20 carbon atoms;²Is a hydrogen atom or an alkyl group, aryl group or benzyl group which is a hydrocarbon group having 1 to 20 carbon atoms, X is a hydrogen atom or —OR³A group and X is -OR³R is a group³Is a hydrogen atom or an alkyl group, aryl group or benzyl group which is a hydrocarbon group having 1 to 12 carbon atoms, and R²And R³May be the same or different. ]

[In the above formula, R⁴~ R⁶Is an alkyl group, aryl group or benzyl group which is a hydrocarbon group having 4 to 18 carbon atoms, and R⁴~ R⁶May be the same or different. ]
  The polymer in which the main repeating unit used in the present invention is ethylene naphthalate is preferably polyethylene naphthalate containing 80% or more, particularly 90% or more of ethylene-2,6-naphthalate units. If it is a small amount, it may be a copolymer containing an appropriate third component.
  Suitable third components include (a) a compound having two ester-forming functional groups, (b) a compound having one ester-forming functional group, and (c) three or more ester-forming functional groups. The polymer can be used within a range in which the polymer is substantially linear. Needless to say, the polyethylene naphthalate may contain various additives.
  Such polyester of this invention can be manufactured in accordance with the conventionally well-known manufacturing method of polyester. That is, after an ester exchange reaction between a dialkyl ester of 2,6-naphthalenedicarboxylic acid represented by naphthalene-2,6-dimethylcarboxylate (NDC) and ethylene glycol as a glycol component as an acid component, this reaction is performed. The product can be heated under reduced pressure and polycondensed while removing excess diol component. Alternatively, it can also be produced by a conventionally known direct polymerization method by esterifying with 2,6-naphthalenedicarboxylic acid as an acid component and ethylene glycol as a diol component.
  The transesterification catalyst used in the case of the method utilizing the transesterification reaction is not particularly limited, but manganese, magnesium, titanium, zinc, aluminum, calcium, cobalt, sodium, lithium, and lead compounds may be used. it can. Examples of such compounds include manganese, magnesium, titanium, zinc, aluminum, calcium, cobalt, sodium, lithium, lead oxide, acetate, carboxylate, hydride, alcoholate, halide, carbonate, sulfuric acid. A salt etc. can be mentioned.
  Of these, manganese, magnesium, zinc, titanium, sodium, and lithium compounds are preferable, and manganese, magnesium, and zinc compounds are more preferable from the viewpoints of melt stability of polyester, hue, small amount of insoluble foreign matter in the polymer, and spinning stability. Moreover, these compounds may use 2 or more types together.
  The polymerization catalyst is not particularly limited, and antimony, titanium, germanium, aluminum, zirconium and tin compounds can be used. Examples of such a compound include antimony, titanium, germanium, aluminum, zirconium, tin oxide, acetate, carboxylate, hydride, alcoholate, halide, carbonate, sulfate and the like. Moreover, these compounds may use 2 or more types together.
  Among them, an antimony compound is particularly preferable in that it has excellent polymerization activity, solid phase polymerization activity, melt stability, and hue of the polyester, and the obtained fiber has high strength, excellent spinning properties and stretchability.
  In the present invention, the polymer is melted and discharged from a spinneret to form fibers. At this time, at least one phosphorus compound represented by the following general formula (I) or (II) is contained in the polymer at the time of melting. It is essential to discharge from the spinneret after adding.

[In the above formula, R¹Is an alkyl group, aryl group or benzyl group which is a hydrocarbon group having 1 to 20 carbon atoms;²Is a hydrogen atom or an alkyl group, aryl group or benzyl group which is a hydrocarbon group having 1 to 20 carbon atoms, X is a hydrogen atom or -OR³A group and X is -OR³R is a group³Is a hydrogen atom or an alkyl group, aryl group or benzyl group which is a hydrocarbon group having 1 to 12 carbon atoms, and R²And R³May be the same or different. ]

[In the above formula, R⁴~ R⁶Is an alkyl group, aryl group or benzyl group which is a hydrocarbon group having 4 to 18 carbon atoms, and R⁴~ R⁶May be the same or different. ]
  In addition, the alkyl group, aryl group, and benzyl group used in the formula may be substituted. Furthermore, R¹And R²Is preferably a hydrocarbon group having 1 to 12 carbon atoms.
  Preferred compounds of the general formula (I) include, for example, phenylphosphonic acid, monomethyl phenylphosphonate, monoethyl phenylphosphonate, monopropyl phenylphosphonate, monophenyl phenylphosphonate, monobenzyl phenylphosphonate, (2-hydroxyethyl) Phenylphosphonate, 2-naphthylphosphonic acid, 1-naphthylphosphonic acid, 2-anthrylphosphonic acid, 1-anthrylphosphonic acid, 4-biphenylphosphonic acid, 4-methylphenylphosphonic acid, 4-methoxyphenylphosphonic acid, Phenylphosphinic acid, methyl phenylphosphinate, ethyl phenylphosphinate, propylphenylphosphinate, phenylphenylphosphinate, benzylphenylphosphinate, (2-hydroxyethyl) phenylphosphine 2-naphthylphosphinic acid, 1-naphthylphosphinic acid, 2-anthrylphosphinic acid, 1-anthrylphosphinic acid, 4-biphenylphosphinic acid, 4-methylphenylphosphinic acid, 4-methoxyphenylphosphinic acid, etc. Can be mentioned.
  The compounds of the general formula (II) include bis (2,4-di-tert-butylphenyl) pentaerythritol diphosphite, bis (2,6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphite. Examples thereof include phosphite and tris (2,4-di-tert-butylphenyl) phosphite. Furthermore, the compound of the above general formula (I) is R¹Is an aryl group and R²Is a hydrogen atom or a hydrocarbon group, an alkyl group, an aryl group or a benzyl group, and R³Is preferably a hydrogen atom or an —OH group.
  That is, as a particularly preferable phosphorus compound used in the present invention, the following general formula (I ′) can be exemplified.

[In the above formula, Ar is an aryl group which is a hydrocarbon group having 6 to 20 carbon atoms;²Is a hydrogen atom or an alkyl group, aryl group or benzyl group which is a hydrocarbon group having 1 to 20 carbon atoms, and Y is a hydrogen atom or —OH group. ]
  By the way, R used in the formula²The hydrocarbon group is preferably an alkyl group, an aryl group or a benzyl group, and these may be unsubstituted or substituted. At this time R²As the substituent, it is preferable that the three-dimensional structure is not inhibited, and examples thereof include those substituted with a hydroxyl group, an ester group, an alkoxy group or the like. The aryl group represented by Ar in the above (I ′) may be substituted with, for example, an alkyl group, an aryl group, a benzyl group, an alkylene group, a hydroxyl group, or a halogen atom.
  Furthermore, the phosphorus compound used in the present invention is preferably phenylphosphonic acid represented by the following general formula (III) and derivatives thereof.

[In the above formula, Ar is an aryl group which is a hydrocarbon group having 6 to 20 carbon atoms;⁷Is a hydrogen atom or an unsubstituted or substituted hydrocarbon group having 1 to 20 carbon elements. ]
  In the present invention, by adding these specific phosphorus compounds directly into the molten polymer, the crystallinity of polyethylene naphthalate is improved, and the polyethylene naphthalate having a large crystal volume is maintained while maintaining high crystallinity under the subsequent production conditions. A phthalate fiber could be obtained. This is considered to be due to the effect of this specific phosphorus compound to suppress coarse crystal growth that occurs in the spinning and stretching steps and to finely disperse the crystals. In addition, it has been very difficult to spin polyethylene naphthalate fibers at high speeds. However, the addition of these phosphorus compounds has greatly improved spinning stability and is practical because it does not break. It became possible to increase the strength of the fiber by increasing the stretch ratio.
  By the way, R used in the formula¹~ R⁷Examples of the hydrocarbon group include an alkyl group, an aryl group, a diphenyl group, a benzyl group, an alkylene group, and an arylene group. These are preferably substituted with, for example, a hydroxyl group, an ester group, or an alkoxy group.
  Preferable examples of the hydrocarbon group substituted with such a substituent include the following functional groups and isomers thereof.
-(CH₂N-OH
-(CH₂N-OCH₃
-(CH₂) N-OPh
-Ph-OH (Ph; aromatic ring)
[N represents an integer of 1 to 10]
  Among them, in order to improve the crystallinity, the phosphorus compound of the above general formula (I) is more preferable, the above general formula (I ′), particularly the above general formula (III) is preferable.
  In order to prevent scattering under vacuum during the process, the formula (I) will be described as an example.¹The number of carbon atoms is preferably 4 or more, more preferably 6 or more, and particularly preferably an aryl group. Or it is preferable that X is a hydrogen atom or a hydroxyl group, for example, general formula (I '). Even when X is a hydrogen atom or a hydroxyl group, it is difficult to scatter in a vacuum during the process.
  In order to show the effect of high crystallinity improvement, R¹Is preferably an aryl group, more preferably a benzyl group or a phenyl group, and in the production method of the present invention, the phosphorus compound is particularly preferably phenylphosphinic acid or phenylphosphonic acid. Of these, phenylphosphonic acid and its derivatives are optimal, and phenylphosphonic acid is most preferable from the viewpoint of workability. Since phenylphosphonic acid has a hydroxyl group, it has a higher boiling point than other alkyl esters such as dimethyl phenylphosphonate, and has the advantage that it is difficult to scatter under vacuum. That is, the amount of the added phosphorus compound remaining in the polyester is increased, and the effect of comparing the added amount is increased. It is also advantageous in that the vacuum system is less likely to be clogged.
  The addition amount of the phosphorus compound used in the present invention is preferably 0.1 to 300 mmol% with respect to the number of moles of the dicarboxylic acid component constituting the polyester. If the amount of the phosphorus compound is insufficient, the crystallinity improving effect tends to be insufficient. If the amount is too large, foreign matter defects are generated during spinning, so that the spinning property tends to be lowered. The content of the phosphorus compound is more preferably in the range of 1 to 100 mmol%, more preferably in the range of 10 to 80 mmol%, based on the number of moles of the dicarboxylic acid component constituting the polyester.
  In addition to such a phosphorus compound, at least one metal element selected from the group consisting of a metal element of 4th to 5th period and 3 to 12 group in the periodic table and Mg is added to the molten polymer. Is preferred. In particular, the metal element contained in the fiber is preferably at least one metal element selected from the group consisting of Zn, Mn, Co, and Mg. The reason is not clear, but when these metal elements are used in combination with the above phosphorus compound, it is easy to obtain a uniform crystal with little variation in crystal volume. These metal elements may be added as a transesterification catalyst or a polymerization catalyst, or may be added separately.
  As content of such a metal element, it is preferable to contain 10-1000 mmol% with respect to an ethylene naphthalate unit. The P / M ratio, which is the abundance ratio of the phosphorus element P and the metal element M, is preferably in the range of 0.8 to 2.0. When the P / M ratio is too small, the metal concentration becomes excessive, and the excess metal component tends to accelerate the thermal decomposition of the polymer and impair the thermal stability. On the other hand, when the P / M ratio is too large, the phosphorus compound is excessive, so that the polymerization reaction of the polyethylene naphthalate polymer is inhibited and the fiber physical properties tend to be lowered. A more preferable P / M ratio is preferably 0.9 to 1.8.
  The addition time of the phosphorus compound used for this invention is not specifically limited, It can add in the arbitrary processes of polyester manufacture. Preferably, the polymerization is completed from the beginning of the transesterification or esterification reaction. In order to form a more uniform crystal, it is more preferably between the time when the transesterification or esterification reaction ends and the time when the polymerization reaction ends.
  Further, a method of kneading the phosphorus compound using a kneader after polymerization of the polyester can also be employed. The method of kneading is not particularly limited, but it is preferable to use a normal uniaxial or biaxial kneader. More preferably, in order to suppress a decrease in the degree of polymerization of the resulting polyester composition, a method of using a vented uniaxial or biaxial kneader can be exemplified.
  The conditions during the kneading are not particularly limited. For example, the melting point is higher than the melting point of the polyester and the residence time is within 1 hour, preferably 1 minute to 30 minutes. Moreover, the supply method of the phosphorus compound and polyester to a kneading machine is not specifically limited. Examples thereof include a method of separately supplying a phosphorus compound and polyester to a kneader, and a method of appropriately mixing and supplying a master chip containing a high concentration phosphorus compound and polyester. However, when the specific phosphorus compound used in the present invention is added to the molten polymer, it is preferably added directly to the polyester polymer without reacting with other compounds in advance. This is because a reaction product obtained by previously reacting a phosphorus compound with another compound such as a titanium compound becomes coarse particles and prevents structural defects and crystal disturbances in the polyester polymer.
  The polyethylene naphthalate polymer used in the present invention preferably has a limiting viscosity of the resin chip in the range of 0.65 to 1.2 by performing known melt polymerization or solid phase polymerization. If the intrinsic viscosity of the resin chip is too low, it is difficult to increase the strength of the fiber after melt spinning. On the other hand, if the intrinsic viscosity is too high, the solid-state polymerization time is greatly increased and the production efficiency is lowered, which is not preferable from an industrial viewpoint. The intrinsic viscosity is further preferably in the range of 0.7 to 1.0.
  The method for producing the polyethylene naphthalate fiber of the present invention melts the above polyethylene naphthalate polymer, the spinning draft ratio after discharging from the spinneret is 100 to 5000, and the melt polymer temperature plus or minus immediately after discharging from the spinneret. It is essential to pass through a heat-insulated spinning cylinder set within a range of 50 ° C. and stretch.
  The temperature of the polyethylene naphthalate polymer at the time of melting is preferably 285 to 335 ° C. Furthermore, it is preferable that it is the range of 290-330 degreeC. In general, a spinneret having a capillary is used.
  And it is essential that the spinning draft is 100 to 5,000. Furthermore, it is preferable that it is a draft condition of 500-3000. The spinning draft is defined as a ratio between the spinning winding speed (spinning speed) and the spinning discharge linear speed, and is expressed by the following mathematical formula (2).

  (In the formula, D represents the hole diameter of the die, V represents the spinning take-up speed, and W represents the volume discharge amount per single hole)
  By increasing the spinning draft ratio, the crystal volume and crystallinity in the polymer can be increased.
  In order to obtain such a high spinning draft, it is preferable that the spinning speed is high, and the spinning speed of the production method of the present invention is suitably 1500 to 6000 m / min. Furthermore, it is preferable that it is 2000-5000 m / min.
  Furthermore, in the production method of the present invention, it is an essential requirement to pass through a heat-insulated spinning cylinder set within a range of plus or minus 50 ° C. of the molten polymer temperature immediately after discharging from the spinneret. Furthermore, it is preferable that the set temperature of the heat retaining spinning cylinder is not higher than the melt polymer temperature. Further, the length of the heat insulating spinning cylinder is preferably 10 to 300 mm, and more preferably 30 to 150 mm. The passing time of the heat-insulating spinning cylinder is preferably 0.2 seconds or longer.
  Usually, in the production method of polyethylene naphthalate fiber, when a high draft condition is adopted as in the present application, a heated spinning cylinder that is several tens of degrees higher than the molten polymer temperature is used. This is because the polyethylene naphthalate polymer, which is a rigid polymer, is easily oriented immediately after being discharged from the spinneret and is likely to cause single yarn breakage, so that it is necessary to delay cooling by using a heated spinning cylinder. This is because, when the spinning tube temperature is close to the molten polymer temperature, the polymer is discharged at a high speed, so that the delayed cooling state is not achieved.
  However, in the production method of the present invention, it is possible to form a uniform structure with the same degree of orientation by forming microcrystals using a specific phosphorus compound. And since it has a uniform structure, no single yarn breakage occurs without using a heated spinning cylinder, and it is possible to ensure high yarn production. Moreover, the crystal volume of the polyethylene naphthalate fiber can be increased more effectively by using such a low-temperature insulated spinning cylinder. This is because in a high-temperature spinning cylinder, the molecular motion in the polymer is intense and the formation of large crystals is hindered. By having a large crystal volume, the melting point and heat fatigue resistance of the resulting fiber can be effectively increased.
  The spun yarn that has passed through the heat-insulating spinning cylinder is preferably cooled by blowing cold air of 30 ° C. or lower. Furthermore, it is preferable that it is a cold wind of 25 degrees C or less. The cooling air blowing rate is 2 to 10 Nm³/ Minute, the blowing length is preferably about 100 to 500 mm. Next, it is preferable to apply an oil agent to the cooled thread form.
  The undrawn yarn spun in this way has a birefringence (Δn_UD) As 0.10 to 0.28, density (ρ_UD)) Is preferably in the range of 1.345 to 1.365. Birefringence (Δn_UD) And density (ρ_UD) Is small, orientational crystallization of fibers during the spinning process becomes insufficient, and heat resistance and excellent dimensional stability tend not to be obtained. On the other hand, the birefringence (Δn_UD) And density (ρ_UD) Is too large, it is presumed that coarse crystal growth has occurred in the spinning process, and the spinnability tends to be disturbed and the yarn breakage tends to occur frequently, and the production tends to be substantially difficult. Moreover, since the subsequent drawability is also inhibited, it tends to be difficult to produce fibers having high physical properties. Furthermore, the birefringence (Δn) of the spun undrawn yarn is_UD) As 0.11 to 0.26, density (ρ_UD) Is more preferably in the range of 1.350 to 1.360.
  The present invention is characterized by performing a high-spinning draft. However, when a normal draft is performed, the crystal volume is small and the melting point is low, and high dimensional stability cannot be obtained as in the present invention. On the other hand, when delayed cooling is performed using a heated spinning cylinder even with a high-spinning draft, the crystal volume is also small and the melting point is low, and the dimensional stability is high unlike the case of using the insulated spinning cylinder of the present invention. Can't get.
  Thereafter, the polyethylene naphthalate fiber production method of the present invention is stretched. In the present invention, since high-spinning drafting is performed on fibers having uniform crystals, yarn breakage is effectively prevented. In spite of the high degree of crystallinity, fibers with a large crystal volume could be obtained. Stretching may be performed by winding it once from a take-up roller and stretching it by a so-called separate stretching method, or by stretching it by a so-called direct stretching method in which undrawn yarn is continuously supplied from the take-up roller to the stretching process. I do not care. The stretching conditions are one-stage or multi-stage stretching, and the stretching load factor is preferably 60 to 95%. The drawing load factor is the ratio of the tension at the time of drawing to the tension at which the fiber actually breaks. By increasing the draw ratio and the draw load factor, the crystal volume and crystallinity can be effectively increased.
  The preheating temperature at the time of drawing is preferably carried out at a temperature not lower than the glass transition point of the polyethylene naphthalate undrawn yarn and not higher than 20 ° C. lower than the crystallization start temperature. The stretching ratio depends on the spinning speed, but it is preferable to perform stretching at a stretching ratio that gives a stretching load factor of 60 to 95% with respect to the breaking stretch ratio. Further, in order to maintain the strength of the fiber and improve the dimensional stability, it is preferable to perform heat setting at a temperature from 170 ° C. to the melting point of the fiber or less in the drawing process. Furthermore, it is preferable that the heat setting temperature at the time of Enjin is in the range of 170 to 270 ° C. By such heat setting at a high temperature, the draw ratio can be effectively increased and the crystal volume can be increased.
  In the production method of the present invention, by using a specific phosphorus compound, a cooling condition with a high draft ratio and a heat-retaining spinning cylinder can be employed for the first time, and while it is a production method with high yarn-spinning properties, it has high dimensional stability and resistance. A fiber having fatigue properties could be obtained. Incidentally, when the specific phosphorus compound of the present invention is not used, it is necessary to lower the draft rate for spinning or delay cooling using a heated spinning cylinder, and the dimensional stability and fatigue resistance as in the present invention. It is not possible to obtain a high melting point fiber having excellent resistance.
  The polyethylene naphthalate fiber obtained by the method for producing the polyethylene naphthalate fiber of the present invention has a large crystal volume and a high crystallization rate, and has a high melting point and high dimensional stability with high strength. In addition, the fiber has excellent fatigue resistance.
  In the method for producing polyethylene naphthalate fiber of the present invention, a desired fiber cord can be obtained by twisting or combining the obtained fibers. Furthermore, it is also preferable to apply an adhesive treatment agent to the surface. As the adhesion treatment agent, treatment with an RFL adhesion treatment agent is optimal for rubber reinforcement applications.
  More specifically, such a fiber cord can be obtained by adding a twisted yarn to the above polyethylene naphthalate fiber according to a conventional method, or attaching an RFL treatment agent in a non-twisted state and performing a heat treatment. Such a fiber becomes a treatment cord that can be suitably used for rubber reinforcement.
  The polyethylene naphthalate fiber for industrial material thus obtained can be made into a polymer and a fiber / polymer composite. At this time, the polymer is preferably a rubber elastic body. Since the polyethylene naphthalate fiber of the present invention used for reinforcement is excellent in heat resistance and dimensional stability, this composite has extremely excellent moldability when formed into a composite. In particular, when the polyethylene naphthalate fiber of the present invention is used for rubber reinforcement, the effect is great, and it is suitably used for tires, belts, hoses, and the like.
  When the polyethylene naphthalate fiber of the present invention is used as a rubber reinforcing cord, for example, the following method can be used. That is, the polyethylene naphthalate fiber is converted into a twist coefficient K = T · D.^1/2(T is the number of twists per 10 cm, D is the fineness of the twisted yarn cord) is twisted at 990 to 2,500 to form a twisted cord, and the cord is treated at 230 to 270 ° C. following the adhesive treatment.
  The treated cord obtained from the polyethylene naphthalate fiber of the present invention has a strength index of 80 to 180 N, a dimensional stability index represented by the sum of the elongation at the time of 2 cN / dtex stress (intermediate loading) and the 180 ° C. dry heat shrinkage rate. It is possible to obtain an excellent treated cord having a high modulus, heat resistance, dimensional stability, and high fatigue resistance. Here, the lower the value of the dimensional stability index, the higher the modulus and the lower the dry heat shrinkage rate. More preferably, the strength of the processing cord using the polyethylene naphthalate fiber in the present invention is 100 to 160 N, and the dimensional stability index is 3.5 to 4.5%.

式中ρ ：ポリエチレンナフタレート繊維の比重
ρａ：１．３２５（ポリエチレンナレフタレートの完全非晶密度）
ρｃ：１．４０７（ポリエチレンナレフタレートの完全結晶密度）
（５）複屈折（Δｎ）
浸漬液としてブロムナフタリンを使用し、ベレックコンペンセーターを用いてレターデーション法により求めた。（共立出版社発行：高分子実験化学講座 高分子物性１１参照）
（６）結晶体積、最大ピーク回折角
繊維の結晶体積、最大ピーク回折角はＢｒｕｋｅｒ社製Ｄ８ ＤＩＳＣＯＶＥＲ ｗｉｔｈ ＧＡＤＤＳ Ｓｕｐｅｒ Ｓｐｅｅｄを用いて広角Ｘ線回折法により求めた。
結晶体積は、繊維の広角Ｘ線回折において２Θがそれぞれ１５〜１６°、２３〜２５°、２５．５〜２７°に現れる回折ピーク強度の半価幅より、それぞれの結晶サイズをフェラーの式、

（ここで、Ｄは結晶サイズ、Ｂは回折ピーク強度の半価幅、Θは回折角、λはＸ線の波長（０．１５４１７８ｎｍ＝１．５４１７８オングストローム）を表す。）
より算出し、下式により結晶１ユニットあたりの結晶体積とした。
結晶体積（ｎｍ^３）＝結晶サイズ（２Θ＝１５〜１６°）×結晶サイズ（２Θ＝２３〜２５°）×結晶サイズ（２Θ＝２５．５〜２７°）
最大ピーク回折角は、広角Ｘ線回折において強度が最も大きいピークの回折角を求めた。
（７）融点Ｔｍ、発熱ピークエネルギーΔＨｃｄ、ΔＨｃ
ＴＡインスツルメンツ社製Ｑ１０型示差走査熱量計を用い、試料量１０ｍｇの繊維を窒素気流下、２０℃／分の昇温条件で３２０℃まで加熱して現れた吸熱ピークの温度を融点Ｔｍとした。
また引き続いて、３２０℃で２分間保持し溶融させた繊維試料を、１０℃／分の降温条件で測定し、現れる発熱ピークを観測し、発熱ピークの頂点の温度をＴｃｄとした。またピーク面積からエネルギーを計算し、ΔＨｃｄ（窒素気流下１０℃／分の降温条件下での発熱ピークエネルギー）とした。
他方、融点Ｔｍ測定後の繊維試料を引き続いて３２０℃で２分間保持し溶融させ、液体窒素中で急冷固化させた後、さらに窒素気流下、２０℃／分の昇温条件にて現れる発熱ピークを観測し、発熱ピークの頂点の温度をＴｃとした。またピーク面積よりエネルギーを計算し、ΔＨｃ（窒素気流下２０℃／分の昇温条件下での発熱ピークエネルギー）とした。
（８）製糸性
製糸性について、ポリエチレンナフタレート１トンあたりの紡糸工程あるいは延伸工程の断糸発生回数から以下の通り４段階評価した。すなわち、
＋＋＋：断糸発生回数０〜２回／トン、
＋＋：断糸発生回数３〜５回／トン、
＋：断糸発生回数≧６回／トン、
ｂａｄ：製糸不可、
とした。
（９）処理コードの作成
繊維に４９０回／ｍのＺ撚を与えた後、これを２本合わせて４９０回／ｍのＳ撚を与えて、１１００ｄｔｅｘ×２本の生コードとした。この生コードを接着剤（ＲＦＬ）液に浸漬し、２４０℃で２分間緊張熱処理した。
（１０）寸法安定性指数
前述の（２）、（３）項と同様にして、処理コードの荷重４４Ｎ応力時の中間伸度及び１８０℃乾熱収縮率を求め、それらを和して求めた。
処理コードの寸法安定性指数（％）
＝処理コードの４４Ｎ中間荷伸（％）＋１８０℃乾熱収縮率（％）
（１１）耐熱強力維持率
処理コードを加硫モールド中に埋め込み１８０℃、圧力５０ｋｇ／ｃｍ^２で１８０分間促進加硫した後処理コードを取り出し強力を測定し、加硫前の処理コード対比の強力維持率を求めた。
（１２）チューブ寿命
得られた処理コードとゴムからなるチューブを作成し、ＪＩＳ Ｌ１０１７−付属書１、２．２．１「チューブ疲労性」に準じた方法でチューブが破壊する時間を測定した。なお、試験角度は８５°とした。
（１３）ディスク疲労性
得られた処理コードとゴムからなる複合体を作成し、ＪＩＳ Ｌ１０１７−付属書１、２．２．２「ディスク疲労性」に準じた方法で測定した。なお、伸張率５．０％、圧縮率５．０％とし、２４時間連続運転後の強力維持率を求めた。
［実施例１］
２，６−ナフタレンジカルボン酸ジメチル１００重量部とエチレングリコール５０重量部との混合物に酢酸マンガン四水和物０．０３０重量部、酢酸ナトリウム三水和物０．００５６重量部を攪拌機、蒸留搭及びメタノール留出コンデンサーを設けた反応器に仕込み、１５０℃から２４５℃まで徐々に昇温しつつ、反応の結果生成するメタノールを反応器外に留出させながら、エステル交換反応を行い、引き続いてエステル交換反応が終わる前にフェニルホスホン酸（ＰＰＡ）を０．０３重量部（５０ミリモル％）を添加した。その後、反応生成物に三酸化二アンチモン０．０２４重量部を添加して、攪拌装置、窒素導入口、減圧口及び蒸留装置を備えた反応容器に移し、３０５℃まで昇温させ、３０Ｐａ以下の高真空下で縮合重合反応を行い、常法に従ってチップ化して極限粘度０．６２のポリエチレンナフタレート樹脂チップを得た。このチップを６５Ｐａの真空度下、１２０℃で２時間予備乾燥した後、同真空下２４０℃で１０〜１３時間固相重合を行い、極限粘度０．７４のポリエチレンナフタレート樹脂チップを得た。
このチップを、孔数２４９ホール、孔径０．７ｍｍ、ランド長３．５ｍｍの円形紡糸孔を有する紡糸口金からポリマー温度３１０℃で吐出し、紡糸速度２，５００ｍ／分、紡糸ドラフト９６２の条件で紡糸を行った。紡出した糸状は口金直下に設置した長さ５０ｍｍ、雰囲気温度３３０℃の保温紡糸筒を通じ、さらに、保温紡糸筒の直下から長さ４５０ｍｍにわたって、２５℃の冷却風を６．５Ｎｍ^３／分の流速で吹き付けて、糸状の冷却を行った。その後、油剤付与装置にて一定量計量供給した油剤を付与した後、引取りローラーに導き、巻取機で巻取った。
この未延伸糸は断糸や単糸切れの発生がなく製糸性良好に得ることができ、その未延伸糸の極限粘度ＩＶｆは０．７０、複屈折率（Δｎ_ＵＤ）０．１７９、密度（ρ_ＵＤ）１．３５７であった。
次いでこの未延伸糸を用い、以下の通り延伸を行った。なお延伸倍率は破断延伸倍率に対し延伸負荷率９２％となるように設定した。
すなわち、未延伸糸に１％のプリストレッチをかけた後、１３０ｍ／分の周速で回転する１５０℃の加熱供給ローラーと第一段延伸ローラーとの間で第一段延伸を行い、次いで１８０℃に加熱した第一段延伸ローラーと１８０℃に加熱した第二段延伸ローラーとの間で２３０℃に加熱した非接触式セットバス（長さ７０ｃｍ）を通し定長熱セットを行った後、巻取機に巻き取った。このときの全延伸倍率（ＴＤＲ）は１．０８であり、延伸時に断糸や単糸切れの発生なく製糸性は良好であった。製造条件を表１に示す。
得られた延伸糸は繊度１，０８０ｄｔｅｘ、結晶体積９５２ｎｍ^３（９５２０００オングストローム^３）、結晶化度４７％であった。この延伸糸のΔＨｃ、ΔＨｃｄはそれぞれ３８、３５Ｊ／ｇであり高い結晶性を示した。得られたポリエチレンナフタレート繊維の強度は７．４ｃＮ／ｄｔｅｘ、１８０℃乾収２．６％、融点２９７℃と高耐熱性かつ低収縮性に優れたものであった。
さらに、得られた延伸糸に４９０回／ｍのＺ撚を与えた後、これを２本合わせて４９０回／ｍのＳ撚を与えて、１１００ｄｔｅｘ×２本の生コードとした。この生コードを接着剤（ＲＦＬ）液に浸漬し、２４０℃で２分間緊張熱処理した。得られた処理コードの強度は１２３Ｎ、寸法安定性指数４．０％、耐熱強力維持率９３％と寸法安定性、耐熱性に優れたものであった。得られた物性を表３および５に示す。
［比較例１］
ポリエチレンー２，６−ナフタレートの重合において、エステル交換反応が終わる前にリン化合物であるフェニルホスホン酸（ＰＰＡ）の代わりに正リン酸を４０ｍｍｏｌ％添加したこと以外は、実施例１と同様に実施してポリエチレンナフタレート樹脂チップ（極限粘度０．７５）を得た。この該樹脂チップを用い実施例１と同様にして溶融紡糸を行ったが、紡糸での断糸が多発し満足に製糸することがでず、かろうじて広角Ｘ線回折のみ可能であった。製造条件を表１および２に示した。
［実施例２］
実施例１の紡糸速度を２５００ｍ／分から４７５０ｍ／分に、紡糸ドラフト比でいうと９６２から１２５１に変更するとともにその他の条件を変更した。すなわち得られる繊維の繊度をあわせるためにキャップ口金口径を０．７ｍｍから０．８ｍｍに変更し、口金直下の保温紡糸筒の温度を溶融ポリマーの融点よりも低い２６０度に、長さを１００ｍｍに変更して、未延伸糸を得た。またその後の延伸倍率を実施例１の１．０８倍から１．０５倍に変更し延伸糸を得た。若干製糸性に難があったが、製造は可能であった。
得られた延伸糸は結晶体積７８１ｎｍ^３（７８１０００オングストローム^３）、結晶化度４７％であった。得られたポリエチレンナフタレート繊維の強度は７．２ｃＮ／ｄｔｅｘ、１８０℃乾収２．７％、融点２９８℃と高耐熱性かつ低収縮性に優れたものであった。
さらにその延伸糸を実施例１と同様にして処理コードとした。製造条件を表１に、得られた物性を表３および５にそれぞれ示す。
［実施例３］
実施例２の口金直下の保温紡糸筒の長さを１３５ｍｍに長くし、温度を２３０℃から２８０℃に変更した以外は実施例２と同じ条件にてポリエチレンナフタレート繊維およびそれを用いたコードとした。
得られた繊維は高耐熱性及び低収縮性に優れたものであった。また製糸性も非常によく、断糸も見られなかった。
製造条件を表１に、得られた物性を表３および５にそれぞれ示す。
［実施例４］
実施例３の口金直下の保温紡糸筒の長さを２５０ｍｍに長くした以外は実施例３と同じ条件にてポリエチレンナフタレート繊維およびそれを用いたコードとした。
得られた繊維は高耐熱性及び低収縮性に優れたものであった。また製糸性も非常によく、断糸も見られなかった。
製造条件を表１に、得られた物性を表３および表５にそれぞれ示す。
［比較例２〜４］
ポリエチレンー２，６−ナフタレートの重合において、エステル交換反応が終わる前にリン化合物であるフェニルホスホン酸（ＰＰＡ）の代わりに正リン酸を４０ｍｍｏｌ％添加したこと以外は、実施例２〜４と同様に実施してポリエチレンナフタレート樹脂チップ（極限粘度０．７５）を得た。この該樹脂チップを用い実施例２〜４と同様にして溶融紡糸を行ったが、紡糸での断糸が多発し満足に製糸することができなった。詳細な製造条件を表１に示した。
［比較例５］
ポリエチレンー２，６−ナフタレートの重合において、エステル交換反応が終わる前にリン化合物であるフェニルホスホン酸（ＰＰＡ）の代わりに正リン酸を４０ｍｍｏｌ％添加したこと以外は、実施例４と同様に実施してポリエチレンナフタレート樹脂チップ（極限粘度０．７５）を得た。この該樹脂チップを用い実施例４の紡糸筒の温度を２８０度から３６０度に変更し、製糸性を改善して、未延伸糸を得た。またその後の延伸倍率は１．１９倍にし延伸糸を得た。リン化合物としてフェニルホスホン酸（ＰＰＡ）を添加しなかったため、若干製糸性に難があったが、比較例４と異なり何とか製造は可能であった。
得られた延伸糸は結晶体積４７４ｎｍ^３（４７４０００オングストローム^３）、結晶化度４４％であった。得られたポリエチレンナフタレート繊維の強度は５．９ｃＮ／ｄｔｅｘ、１８０℃乾収４．２％、融点２７９℃と耐熱性および収縮性に劣ったものであった。
さらにその延伸糸を実施例１と同様にして処理コードとした。
製造条件を表１に、得られた物性を表３および表５にそれぞれ示す。
［実施例５］
実施例１で用いたリン化合物をフェニルホスホン酸（ＰＰＡ）から、フェニルホスフィン酸に変更し、添加量を１００ｍｍｏｌ％とした以外は、実施例１と同様に繊維およびコードを得た。
得られた繊維は高耐熱性及び低収縮性に優れたものであった。また製糸性も非常によく、断糸も見られなかった。
製造条件を表２に、得られた物性を表４および５にそれぞれ示す。
［比較例６］
実施例１の紡糸速度を２５００ｍ／分から５５００ｍ／分に、紡糸ドラフト比でいうと９６２から２７００に変更するとともにその他の条件を変更した。すなわち得られる繊維の繊度をあわせるためにキャップ口金口径を０．７ｍｍから１．２ｍｍに変更し、そのままでは製糸が困難なために実施例１の口金直下の紡糸筒の温度を３３０度から４００度の溶融ポリマー温度よりも９０℃高い温度に、長さを５０ｍｍから３５０ｍｍに変更した加熱紡糸筒を用い、未延伸糸を得た。またその後の延伸倍率を１．２２倍に変更し強度の優れた延伸糸を得た。
得られた延伸糸は結晶体積１６３ｎｍ^３（１６３０００オングストローム^３）、結晶化度４８％であった。得られたポリエチレンナフタレート繊維の強度は８．５ｃＮ／ｄｔｅｘあったものの、１８０℃乾収６．３％、融点２８０℃と耐熱性および収縮性に劣るものであった。
さらにその延伸糸を実施例１と同様にして処理コードとした。
製造条件を表２に、得られた物性を表４および表５にそれぞれ示す。
［比較例７］
比較例６で用いたリン化合物をフェニルホスホン酸（ＰＰＡ）から、フェニルホスフィン酸に変更し、添加量を０．０６重量部（１００ミリモル％）とし、延伸倍率を１．１９倍にした以外は、比較例６と同様に繊維とコードを得た。
得られた繊維は耐熱性及び収縮性に劣るものであった。
製造条件を表２に、得られた物性を表４および表５にそれぞれ示す。
［比較例８］
実施例５の紡糸速度を２５００ｍ／分から４５９ｍ／分に、紡糸ドラフト比を９６２から８３とし、得られる繊維の繊度をあわせるためにキャップ口金口径を０．７ｍｍから０．５ｍｍに変更した。また口金直下の紡糸筒の温度を溶融ポリマー温度よりも９０℃高い温度である４００度に、長さを２５０ｍｍに変更した加熱紡糸筒を用い、未延伸糸を得た。またその後の延伸倍率を６．１０倍に変更し延伸糸を得た。
得られた延伸糸は結晶体積２９８ｎｍ^３（２９８０００オングストローム^３）、結晶化度４８％であった。得られたポリエチレンナフタレート繊維の強度は９．１ｃＮ／ｄｔｅｘあったものの、１８０℃乾収７．０％、融点２８０℃と耐熱性および収縮性に劣るものであった。
さらにその延伸糸を実施例１と同様にして処理コードとした。
製造条件を表２に、得られた物性を表４および表５にそれぞれ示す。
［比較例９］
正リン酸を用いた比較例５と同じポリエチレンナフタレート樹脂チップを固相重合で極限粘度０．８７に調整し、口金孔径を０．５ｍｍに、紡糸速度を５０００ｍ／分に、紡糸ドラフト比を３３０に変更した。そのままでは製糸性に難があるため、口金直下の紡糸筒の温度をポリマー溶融温度よりも８０℃高い３９０度の加熱紡糸筒とし、長さを４００ｍｍに変更して、未延伸糸を得た。またその後の延伸倍率は１．０７倍にし延伸糸を得た。リン化合物としてフェニルホスホン酸（ＰＰＡ）を添加しなかったため、製糸性に難があったが、何とか製造は可能であった。
得られた延伸糸は結晶体積５０２ｎｍ^３（５０２０００オングストローム^３）と小さく、結晶化度は４５％であった。得られたポリエチレンナフタレート繊維の強度は６．７ｃＮ／ｄｔｅｘ、１８０℃乾収２．５％、融点２８７℃と強度がやや劣ったものであった。
さらにその延伸糸を実施例１と同様にして処理コードとした。
製造条件を表２に、得られた物性を表４および表５にそれぞれ示す。得られた処理コードは強力、疲労性に劣るものであった。
［比較例１０］
正リン酸を用いた比較例５と同じポリエチレンナフタレート樹脂チップを固相重合で極限粘度０．９０に調整し、口金孔径を０．４ｍｍに、紡糸速度を７５０ｍ／分に、紡糸ドラフト比を６０に変更した。また口金直下の保温紡糸筒の温度を３３０度、長さを４００ｍｍに変更して、未延伸糸を得た。またその後の延伸倍率は５．６７倍にし延伸糸を得た。リン化合物としてフェニルホスホン酸（ＰＰＡ）を添加しなかったため、製糸性に難があり単糸切れが非常に多かったが、何とか製造は可能であった。
得られた延伸糸は結晶体積４４２ｎｍ^３（４４２０００オングストローム^３）と小さく、結晶化度は４８％であった。得られたポリエチレンナフタレート繊維の強度は８．８ｃＮ／ｄｔｅｘ、１８０℃乾収５．９％、融点２８０℃と強度は高いものの、耐熱性がやや劣ったものであった。
さらにその延伸糸を実施例１と同様にして処理コードとした。
製造条件を表２に、得られた物性を表４および表５にそれぞれ示す。得られた処理コードは寸法安定性、疲労性に劣るものであった。
［比較例１１］
正リン酸を用いた比較例５と同じポリエチレンナフタレート樹脂チップを固相重合で極限粘度０．９５に調整し、口金孔径を１．７ｍｍに、紡糸速度を３８０ｍ／分に、ただし繊度をあわせるために紡糸ドラフト比を５５０に変更した。また断糸を防ぐために口金直下の紡糸筒の温度を溶融ポリマー温度よりも６０℃高い３７０度の加熱紡糸筒とし、長さを４００ｍｍに変更して、未延伸糸を得た。またその後の延伸倍率は６．８５倍にし延伸糸を得た。リン化合物としてフェニルホスホン酸（ＰＰＡ）を添加しなかったため、製糸性に難があり、延伸での断糸が多発し、得られた延伸糸にも単糸切れが非常に多かった。
得られた延伸糸は結晶体積３７０ｎｍ^３（３７００００オングストローム^３）と小さく、結晶化度は４５％であった。得られたポリエチレンナフタレート繊維の強度は８．５ｃＮ／ｄｔｅｘ、１８０℃乾収５．６％、融点２７１℃と強度は高いものの、耐熱性が劣ったものであった。
さらにその延伸糸を実施例１と同様にして処理コードとした。
製造条件を表２に、得られた物性を表４および表５にそれぞれ示す。得られた処理コードは寸法安定性、疲労性に劣るものであった。

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by these. In addition, each characteristic value in an Example and a comparative example was measured with the following method.
(1) Intrinsic viscosity IVf
The resin or fiber was dissolved in a mixed solvent of phenol and orthodichlorobenzene (volume ratio 6: 4) and measured at 35 ° C. using an Ostwald viscometer.
(2) Strength, elongation, intermediate load elongation Measured according to JIS L1013. The intermediate unloading of the fiber was determined from the elongation at the time of 4 cN / dtex stress. The intermediate unloading of the fiber cord was determined from the elongation at a stress of 44N.
(3) Dry heat shrinkage rate Based on the JIS L1013 B method (filament shrinkage rate), the shrinkage rate was 180 ° C. for 30 minutes.
(4) Specific gravity and crystallinity Specific gravity was measured at 25 ° C. using a carbon tetrachloride / n-heptane density gradient tube. The crystallinity was calculated from the following specific gravity from the obtained specific gravity.

In the formula, ρ: specific gravity of polyethylene naphthalate fiber ρa: 1.325 (completely amorphous density of polyethylene naphthalate)
ρc: 1.407 (complete crystal density of polyethylene naphthalate)
(5) Birefringence (Δn)
Bromine naphthalene was used as the immersion liquid, and it was determined by a retardation method using a Berek compensator. (See Kyoritsu Publishing Co., Ltd .: Polymer Experimental Chemistry Course, Polymer Properties 11)
(6) Crystal Volume and Maximum Peak Diffraction Angle The crystal volume and maximum peak diffraction angle of the fiber were determined by wide-angle X-ray diffraction using a D8 DISCOVER with GADDS Super Speed manufactured by Bruker.
The crystal volume is determined from the half width of the diffraction peak intensity at which 2Θ appears at 15 to 16 °, 23 to 25 °, and 25.5 to 27 °, respectively, in the wide-angle X-ray diffraction of the fiber.

(Where D is the crystal size, B is the half width of the diffraction peak intensity, Θ is the diffraction angle, and λ is the X-ray wavelength (0.154178 nm = 1.54178 angstrom).)
The crystal volume per unit of crystal was calculated by the following formula.
Crystal volume (nm ³ ) = crystal size (2Θ = 15-16 °) × crystal size (2Θ = 23-25 °) × crystal size (2Θ = 25.5-27 °)
For the maximum peak diffraction angle, the diffraction angle of the peak having the highest intensity in wide-angle X-ray diffraction was determined.
(7) Melting point Tm, exothermic peak energy ΔHcd, ΔHc
Using a Q10 differential scanning calorimeter manufactured by TA Instruments, the temperature of the endothermic peak that appeared when a 10 mg sample fiber was heated to 320 ° C. under a nitrogen stream under a temperature rising condition of 20 ° C./min was defined as the melting point Tm.
Subsequently, the fiber sample held and melted at 320 ° C. for 2 minutes was measured under a temperature drop condition of 10 ° C./min, an exothermic peak that appeared was observed, and the temperature at the top of the exothermic peak was defined as Tcd. Further, energy was calculated from the peak area, and it was defined as ΔHcd (exothermic peak energy under a temperature drop condition of 10 ° C./min under a nitrogen stream).
On the other hand, the fiber sample after the melting point Tm measurement was continuously held at 320 ° C. for 2 minutes, melted, rapidly solidified in liquid nitrogen, and then exothermic peak appearing under a temperature rising condition of 20 ° C./min in a nitrogen stream. Was observed, and the temperature at the top of the exothermic peak was defined as Tc. Further, energy was calculated from the peak area, and ΔHc (exothermic peak energy under a temperature rising condition of 20 ° C./min under a nitrogen stream) was obtained.
(8) Spinnability The spinnability was evaluated according to the following four levels from the number of occurrences of yarn breakage in the spinning process or drawing process per ton of polyethylene naphthalate. That is,
+++: Number of occurrences of yarn breakage 0 to 2 times / ton,
++: Number of occurrences of yarn breakage 3 to 5 times / ton,
+: Number of occurrences of yarn breakage ≧ 6 times / ton,
bad: yarn cannot be made,
It was.
(9) Preparation of treated cords After applying 490 times / m Z twist to the fiber, two of them were combined to give 490 times / m S twist to obtain 1100 dtex × 2 raw cords. This raw cord was immersed in an adhesive (RFL) solution and subjected to tension heat treatment at 240 ° C. for 2 minutes.
(10) Dimensional stability index In the same manner as in the above items (2) and (3), the intermediate elongation and the 180 ° C. dry heat shrinkage rate of the treated cord at a load of 44 N were obtained and obtained by summing them. .
Dimensional stability index of processing code (%)
= 44N intermediate unloading (%) of processing cord + 180 ° C dry heat shrinkage (%)
(11) Heat resistance and strength maintenance rate The processing cord is embedded in a vulcanization mold and subjected to accelerated vulcanization for 180 minutes at 180 ° C. and a pressure of 50 kg / cm ^{2. After} that, the processing cord is taken out and measured for strength. The maintenance rate was determined.
(12) Tube life A tube made of the obtained treatment cord and rubber was prepared, and the time for the tube to break was measured by a method according to JIS L1017-Appendix 1, 2.2.1 “Tube fatigue”. The test angle was 85 °.
(13) Disc Fatigue A composite made of the obtained treated cord and rubber was prepared and measured by a method according to JIS L1017-Appendix 1, 2.2.2 “Disc Fatigue”. The strength retention after 24 hours of continuous operation was determined with an elongation rate of 5.0% and a compression rate of 5.0%.
[Example 1]
In a mixture of 100 parts by weight of dimethyl 2,6-naphthalenedicarboxylate and 50 parts by weight of ethylene glycol, 0.030 parts by weight of manganese acetate tetrahydrate and 0.0056 parts by weight of sodium acetate trihydrate were stirred, Charged to a reactor equipped with a methanol distillation condenser, the temperature was gradually raised from 150 ° C to 245 ° C, and the ester exchange reaction was carried out while distilling the methanol produced as a result of the reaction out of the reactor. Before the exchange reaction was completed, 0.03 part by weight (50 mmol%) of phenylphosphonic acid (PPA) was added. Thereafter, 0.024 parts by weight of diantimony trioxide is added to the reaction product, transferred to a reaction vessel equipped with a stirrer, a nitrogen inlet, a vacuum port and a distillation apparatus, heated to 305 ° C., and 30 Pa or less. A condensation polymerization reaction was performed under high vacuum, and a chip was formed according to a conventional method to obtain a polyethylene naphthalate resin chip having an intrinsic viscosity of 0.62. This chip was preliminarily dried at 120 ° C. for 2 hours under a vacuum of 65 Pa, and then subjected to solid phase polymerization at 240 ° C. for 10 to 13 hours under the same vacuum to obtain a polyethylene naphthalate resin chip having an intrinsic viscosity of 0.74.
This chip is discharged at a polymer temperature of 310 ° C. from a spinneret having a circular spinning hole having a hole number of 249 holes, a hole diameter of 0.7 mm, and a land length of 3.5 mm, under the conditions of a spinning speed of 2,500 m / min and a spinning draft 962. Spinning was performed. The spun yarn was passed through a heat-retaining spinning tube having a length of 50 mm and an atmospheric temperature of 330 ° C. installed immediately below the base, and further a cooling air of 25 ° C. was applied to the length of 450 mm from directly below the heat-retaining spinning tube to 6.5 Nm ³ / min. The filament was cooled by spraying at a flow rate. Thereafter, an oil agent that was metered and supplied by an oil agent applying device was applied, and the oil agent was guided to a take-up roller and wound by a winder.
This undrawn yarn can be obtained with good yarn production without occurrence of breakage or single yarn breakage. The intrinsic viscosity IVf of the undrawn yarn is 0.70, birefringence (Δn _UD ) 0.179, density ( ρ _UD ) 1.357.
Subsequently, the undrawn yarn was used for drawing as follows. The draw ratio was set so that the draw load factor was 92% with respect to the break draw ratio.
That is, after applying 1% pre-stretch to unstretched yarn, first-stage stretching is performed between a 150 ° C. heating supply roller rotating at a peripheral speed of 130 m / min and a first-stage stretching roller, and then 180 After performing a constant-length heat set through a non-contact type set bath (length 70 cm) heated to 230 ° C. between a first-stage drawing roller heated to ° C. and a second-stage drawing roller heated to 180 ° C., It was wound up on a winder. The total draw ratio (TDR) at this time was 1.08, and the yarn production was good without occurrence of yarn breakage or single yarn breakage during drawing. The manufacturing conditions are shown in Table 1.
The obtained drawn yarn had a fineness of 1,080 dtex, a crystal volume of 952 nm ³ (952000 angstrom ³ ), and a crystallinity of 47%. ΔHc and ΔHcd of the drawn yarn were 38 and 35 J / g, respectively, indicating high crystallinity. The strength of the obtained polyethylene naphthalate fiber was 7.4 cN / dtex, 180 ° C. dry yield 2.6%, melting point 297 ° C., and was excellent in high heat resistance and low shrinkage.
Furthermore, after giving Z twist of 490 times / m to the obtained drawn yarn, two of them were combined to give S twist of 490 times / m to obtain 1100 dtex × 2 raw cords. This raw cord was immersed in an adhesive (RFL) solution and subjected to tension heat treatment at 240 ° C. for 2 minutes. The obtained treated cord had a strength of 123N, a dimensional stability index of 4.0%, a heat resistant strength maintenance ratio of 93%, and excellent in dimensional stability and heat resistance. The obtained physical properties are shown in Tables 3 and 5.
[Comparative Example 1]
The polymerization of polyethylene-2,6-naphthalate was carried out in the same manner as in Example 1 except that 40 mmol% of regular phosphoric acid was added instead of phenylphosphonic acid (PPA), which is a phosphorus compound, before the transesterification reaction was completed. Thus, a polyethylene naphthalate resin chip (intrinsic viscosity 0.75) was obtained. Using this resin chip, melt spinning was carried out in the same manner as in Example 1. However, the yarn was spun frequently and could not be satisfactorily produced, and barely only wide-angle X-ray diffraction was possible. Production conditions are shown in Tables 1 and 2.
[Example 2]
In Example 1, the spinning speed was changed from 2500 m / min to 4750 m / min, and the spinning draft ratio was changed from 962 to 1251 and other conditions were changed. That is, in order to match the fineness of the obtained fiber, the cap base diameter was changed from 0.7 mm to 0.8 mm, the temperature of the heat-retaining spinning cylinder just below the base was set to 260 degrees lower than the melting point of the molten polymer, and the length was set to 100 mm. The undrawn yarn was obtained after modification. Further, the subsequent draw ratio was changed from 1.08 times of Example 1 to 1.05 times to obtain a drawn yarn. Although there was some difficulty in spinning, production was possible.
The obtained drawn yarn had a crystal volume of 781 nm ³ (781000 Å ³ ) and a crystallinity of 47%. The obtained polyethylene naphthalate fiber had a strength of 7.2 cN / dtex, 180 ° C. dry yield of 2.7%, a melting point of 298 ° C., and was excellent in high heat resistance and low shrinkage.
Further, the drawn yarn was treated as in the same manner as in Example 1. The production conditions are shown in Table 1, and the obtained physical properties are shown in Tables 3 and 5, respectively.
[Example 3]
A polyethylene naphthalate fiber and a cord using the same under the same conditions as in Example 2 except that the length of the heat-retaining spinning cylinder just below the base of Example 2 was increased to 135 mm and the temperature was changed from 230 ° C. to 280 ° C. did.
The obtained fiber was excellent in high heat resistance and low shrinkage. Further, the yarn forming property was very good, and no yarn breakage was seen.
The production conditions are shown in Table 1, and the obtained physical properties are shown in Tables 3 and 5, respectively.
[Example 4]
A polyethylene naphthalate fiber and a cord using the same were obtained under the same conditions as in Example 3 except that the length of the heat-retaining spinning cylinder just below the base of Example 3 was increased to 250 mm.
The obtained fiber was excellent in high heat resistance and low shrinkage. Further, the yarn forming property was very good, and no yarn breakage was seen.
The production conditions are shown in Table 1, and the obtained physical properties are shown in Table 3 and Table 5, respectively.
[Comparative Examples 2 to 4]
In the polymerization of polyethylene-2,6-naphthalate, the same as in Examples 2 to 4 except that 40 mmol% of normal phosphoric acid was added instead of phenylphosphonic acid (PPA), which is a phosphorus compound, before the transesterification reaction was completed. To obtain a polyethylene naphthalate resin chip (intrinsic viscosity 0.75). Using this resin chip, melt spinning was carried out in the same manner as in Examples 2 to 4, but it was not possible to produce the yarn satisfactorily due to frequent breakage in spinning. Detailed production conditions are shown in Table 1.
[Comparative Example 5]
The polymerization of polyethylene-2,6-naphthalate was carried out in the same manner as in Example 4 except that 40 mmol% of normal phosphoric acid was added instead of phenylphosphonic acid (PPA), which is a phosphorus compound, before the transesterification reaction was completed. Thus, a polyethylene naphthalate resin chip (intrinsic viscosity 0.75) was obtained. Using this resin chip, the temperature of the spinning cylinder of Example 4 was changed from 280 ° C. to 360 ° C. to improve the yarn forming property, and an undrawn yarn was obtained. The subsequent draw ratio was 1.19 times to obtain a drawn yarn. Since phenylphosphonic acid (PPA) was not added as a phosphorus compound, there was some difficulty in spinning, but unlike Comparative Example 4, production was possible somehow.
The obtained drawn yarn had a crystal volume of 474 nm ³ (474000 Å ³ ) and a crystallinity of 44%. The strength of the obtained polyethylene naphthalate fiber was 5.9 cN / dtex, 180 ° C. dry yield 4.2%, melting point 279 ° C., and was inferior in heat resistance and shrinkage.
Further, the drawn yarn was treated as in the same manner as in Example 1.
The production conditions are shown in Table 1, and the obtained physical properties are shown in Table 3 and Table 5, respectively.
[Example 5]
Fibers and cords were obtained in the same manner as in Example 1 except that the phosphorus compound used in Example 1 was changed from phenylphosphonic acid (PPA) to phenylphosphinic acid and the addition amount was 100 mmol%.
The obtained fiber was excellent in high heat resistance and low shrinkage. Further, the yarn forming property was very good, and no yarn breakage was seen.
The production conditions are shown in Table 2, and the obtained physical properties are shown in Tables 4 and 5, respectively.
[Comparative Example 6]
The spinning speed of Example 1 was changed from 2500 m / min to 5500 m / min, and the spinning draft ratio was changed from 962 to 2700, and other conditions were changed. That is, in order to match the fineness of the obtained fiber, the cap base diameter was changed from 0.7 mm to 1.2 mm, and it was difficult to produce the yarn as it was, so the temperature of the spinning cylinder just below the base of Example 1 was changed from 330 degrees to 400 degrees. An undrawn yarn was obtained by using a heated spinning cylinder whose length was changed from 50 mm to 350 mm at a temperature 90 ° C. higher than the molten polymer temperature. Further, the subsequent draw ratio was changed to 1.22 times to obtain a drawn yarn having excellent strength.
The obtained drawn yarn had a crystal volume of 163 nm ³ (163,000 angstrom ³ ) and a crystallinity of 48%. Although the strength of the obtained polyethylene naphthalate fiber was 8.5 cN / dtex, it was inferior in heat resistance and shrinkage at 180 ° C. dry yield 6.3% and melting point 280 ° C.
Further, the drawn yarn was treated as in the same manner as in Example 1.
The production conditions are shown in Table 2, and the obtained physical properties are shown in Table 4 and Table 5, respectively.
[Comparative Example 7]
The phosphorus compound used in Comparative Example 6 was changed from phenylphosphonic acid (PPA) to phenylphosphinic acid, the addition amount was 0.06 parts by weight (100 mmol%), and the draw ratio was 1.19 times. In the same manner as in Comparative Example 6, fibers and cords were obtained.
The obtained fiber was inferior in heat resistance and shrinkage.
The production conditions are shown in Table 2, and the obtained physical properties are shown in Table 4 and Table 5, respectively.
[Comparative Example 8]
In Example 5, the spinning speed was changed from 2500 m / min to 459 m / min, the spinning draft ratio was changed from 962 to 83, and the cap diameter was changed from 0.7 mm to 0.5 mm in order to match the fineness of the obtained fiber. Further, an undrawn yarn was obtained by using a heated spinning cylinder in which the temperature of the spinning cylinder just below the base was 400 ° C. which was 90 ° C. higher than the molten polymer temperature and the length was changed to 250 mm. Further, the subsequent draw ratio was changed to 6.10 times to obtain a drawn yarn.
The obtained drawn yarn had a crystal volume of 298 nm ³ (298000 Å ³ ) and a crystallinity of 48%. Although the strength of the obtained polyethylene naphthalate fiber was 9.1 cN / dtex, it was inferior in heat resistance and shrinkage at 180 ° C. dry yield of 7.0% and melting point of 280 ° C.
Further, the drawn yarn was treated as in the same manner as in Example 1.
The production conditions are shown in Table 2, and the obtained physical properties are shown in Table 4 and Table 5, respectively.
[Comparative Example 9]
The same polyethylene naphthalate resin chip as in Comparative Example 5 using normal phosphoric acid was adjusted by solid-phase polymerization to an intrinsic viscosity of 0.87, the die hole diameter was 0.5 mm, the spinning speed was 5000 m / min, and the spinning draft ratio was Changed to 330. Since the spinning performance is difficult as it is, the temperature of the spinning cylinder just below the die is set to a heated spinning cylinder of 390 degrees, which is 80 ° C. higher than the polymer melting temperature, and the length is changed to 400 mm to obtain an undrawn yarn. The subsequent draw ratio was 1.07 times to obtain a drawn yarn. Since phenylphosphonic acid (PPA) was not added as a phosphorus compound, there was a difficulty in spinning, but somehow production was possible.
The obtained drawn yarn had a crystal volume as small as 502 nm ³ (502000 angstrom ³ ) and the crystallinity was 45%. The strength of the obtained polyethylene naphthalate fiber was 6.7 cN / dtex, 180 ° C. dry yield 2.5%, melting point 287 ° C., and the strength was slightly inferior.
Further, the drawn yarn was treated as in the same manner as in Example 1.
The production conditions are shown in Table 2, and the obtained physical properties are shown in Table 4 and Table 5, respectively. The obtained treatment cord was strong and inferior in fatigue.
[Comparative Example 10]
The same polyethylene naphthalate resin chip as in Comparative Example 5 using orthophosphoric acid was adjusted to an intrinsic viscosity of 0.90 by solid phase polymerization, the diameter of the die hole was set to 0.4 mm, the spinning speed was set to 750 m / min, and the spinning draft ratio was set to Changed to 60. Further, the temperature of the heat insulating spinning cylinder just below the base was changed to 330 degrees and the length to 400 mm to obtain an undrawn yarn. The subsequent draw ratio was 5.67 times to obtain a drawn yarn. Since phenylphosphonic acid (PPA) was not added as a phosphorus compound, there was a difficulty in yarn production and there were very many single yarn breaks, but somehow production was possible.
The obtained drawn yarn had a crystal volume as small as 442 nm ³ (442000 angstrom ³ ), and the crystallinity was 48%. The obtained polyethylene naphthalate fiber had a strength of 8.8 cN / dtex, 180 ° C. dry yield of 5.9%, and a melting point of 280 ° C., but the strength was slightly inferior.
Further, the drawn yarn was treated as in the same manner as in Example 1.
The production conditions are shown in Table 2, and the obtained physical properties are shown in Table 4 and Table 5, respectively. The obtained treatment cord was inferior in dimensional stability and fatigue.
[Comparative Example 11]
The same polyethylene naphthalate resin chip as in Comparative Example 5 using normal phosphoric acid is adjusted to a limiting viscosity of 0.95 by solid phase polymerization, the diameter of the die hole is 1.7 mm, the spinning speed is 380 m / min, but the fineness is adjusted. Therefore, the spinning draft ratio was changed to 550. In order to prevent yarn breakage, the temperature of the spinning cylinder immediately below the die was set to a heated spinning cylinder of 370 degrees 60 ° C. higher than the melt polymer temperature, and the length was changed to 400 mm to obtain an undrawn yarn. The subsequent draw ratio was 6.85 times to obtain a drawn yarn. Since phenylphosphonic acid (PPA) was not added as a phosphorus compound, the yarn-making property was difficult, and many yarn breaks occurred during drawing, and the obtained drawn yarn also had many single yarn breaks.
The obtained drawn yarn had a crystal volume as small as 370 nm ³ (370000 angstrom ³ ) and the crystallinity was 45%. The polyethylene naphthalate fiber obtained had a strength of 8.5 cN / dtex, 180 ° C. dry yield of 5.6%, a melting point of 271 ° C., but a high strength but a poor heat resistance.
Further, the drawn yarn was treated as in the same manner as in Example 1.
The production conditions are shown in Table 2, and the obtained physical properties are shown in Table 4 and Table 5, respectively. The obtained treatment cord was inferior in dimensional stability and fatigue.

Claims (17)

A polyethylene naphthalate fiber whose main repeating unit is ethylene naphthalate, characterized in that the crystal volume obtained by X-ray wide-angle diffraction of the fiber is 550 to 1200 nm ³ and the crystallinity is 30 to 60%. Polyethylene naphthalate fiber.   The polyethylene naphthalate fiber according to claim 1, wherein the maximum peak diffraction angle of X-ray wide angle diffraction is 25.5 to 27.0 degrees.   2. The polyethylene naphthalate fiber according to claim 1, wherein the energy ΔHcd of an exothermic peak under a temperature drop condition of 10 ° C./min under a nitrogen stream is 15 to 50 J / g.   The polyethylene naphthalate fiber according to claim 1, which contains 0.1 to 300 mmol% of phosphorus atoms with respect to ethylene naphthalate units.   The polyethylene naphthalate fiber contains a metal element, and the metal element is at least one metal element selected from the group consisting of a metal element of 4th to 5th period and a group of 3 to 12 and Mg in the periodic table. The polyethylene naphthalate fiber according to claim 1.   The polyethylene naphthalate fiber according to claim 5, wherein the metal element is at least one metal element selected from the group consisting of Zn, Mn, Co, and Mg.   The polyethylene naphthalate fiber according to claim 1, which has a strength of 4.0 to 10.0 cN / dtex.   The polyethylene naphthalate fiber according to claim 1, which has a melting point of 285 to 315 ° C.   The polyethylene naphthalate fiber according to claim 1, which has a dry heat shrinkage of 180 ° C of less than 0.5 to less than 4.0%.   The polyethylene naphthalate fiber according to claim 1, wherein the peak temperature of tan δ is 150 to 170 ° C.   The ratio E '(200 ° C) / E' (20 ° C) of the modulus E 'at 200 ° C (200 ° C) and the modulus E' at 20 ° C (20 ° C) is 0.25 to 0.5. Polyethylene naphthalate fiber. A method for producing a polyethylene naphthalate fiber in which a polymer whose main repeating unit is ethylene naphthalate is melted and discharged from a spinneret , wherein the polymer at the time of melting contains a metal element, and the metal element is the fourth in the periodic table. And at least one phosphorus compound represented by the following general formula ( I) in a polymer at the time of melting: , Directly added to the polymer without reacting with other compounds in advance, then discharged from the spinneret, and the spinning draft ratio after discharging from the spinneret is 500 to 5000, and the temperature of the molten polymer immediately after discharging from the spinneret A polyethylene naphthalate fiber that passes through a heat-insulated spinning cylinder within 50 ° C and is drawn. Production method.

Wherein the above, ^{R 1} is 6 to twenty hydrocarbon radical der Rua aryl group carbon,
R ² is a hydrogen atom or an alkyl group, aryl group or benzyl group which is a hydrocarbon group having 1 to 20 carbon atoms,
X is a hydrogen atom or —OR ³ group,
When X is a -OR ³ group,
R ³ is a hydrogen atom or an alkyl group, aryl group or benzyl group which is a hydrocarbon group having 1 to 12 carbon atoms,
R ² and R ³ may be the same or different. ]   The method for producing polyethylene naphthalate fiber according to claim 12, wherein the spinning speed is 1500 to 6000 m / min.   The method for producing polyethylene naphthalate fiber according to claim 12, wherein the length of the heat-insulating spinning cylinder is 10 to 250 mm. The method for producing polyethylene naphthalate fiber according to claim 12, wherein the phosphorus compound is represented by the following general formula (I ').

[In the above formula, Ar is an aryl group which is a hydrocarbon group having 6 to 20 carbon atoms,
R ² is a hydrogen atom or an alkyl group, aryl group or benzyl group which is a hydrocarbon group having 1 to 20 carbon atoms,
Y is a hydrogen atom or —OH group. ]   The method for producing a polyethylene naphthalate fiber according to claim 15, wherein the phosphorus compound is phenylphosphinic acid or phenylphosphonic acid. The method for producing polyethylene naphthalate fiber according to claim 12 , wherein the metal element is at least one metal element selected from the group consisting of Zn, Mn, Co, and Mg.

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