JP2004131381A - Optical fiber strand - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber strand having good fatigue resistance. <P>SOLUTION: This optical fiber strand (1) is obtained by forming a primary-coated layer (3) and a secondary-coated layer (4) both comprising an ultraviolet curing resin composition on a bare optical fiber (2). In this case, the resin composition forming the primary-coated layer (3) contains 0.01-5 mass% of a silane coupling agent, the organofunctional group of which is at least one of acryl and methacryl. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an optical fiber having improved reliability, particularly fatigue resistance, of the optical fiber.

The optical fiber is coated with a primary coating layer made of an ultraviolet curable resin (UV resin) having a relatively low Young's modulus of about 1 to 10 MPa, a silicone resin, or the like on a quartz optical fiber bare wire having an outer diameter of 125 μm, An outer coating having a diameter of 250 μm, on which a secondary coating made of an ultraviolet-curable resin (UV resin) having a relatively high Young's modulus of about 100 to 1000 MPa is provided on the primary coating, is generally used. The secondary coating layer has the effect of protecting the optical fiber from friction and external force by increasing the Young's modulus, and the primary coating layer has the effect of reducing external pressure and the like by reducing the Young's modulus. At present, UV resin is often used as a coating material from the viewpoint of manufacturability.
The usage form of the optical fiber is a single core, or a plurality of optical fibers are arranged in parallel, and the periphery thereof is covered with an ultraviolet curing type UV resin to form a tape core. In most cases, a plurality of tape cores are assembled and used as optical cables. This optical cable is used by being laid in an aerial, a cave, a duct, or the like. In the laid optical cable, a tensile force is constantly applied depending on the laid state, and a part of this tensile force also acts on the optical fiber constituting the optical cable, and a small load is continuously applied to the optical fiber for a long time. Over time. If such a relatively small load is continuously applied to the optical fiber, the optical fiber may suddenly break at a certain point, or may break only with a slight tensile force. There is. This problem is caused by the fatigue characteristics of the optical fiber, and in order to avoid this, it is necessary to provide the optical fiber with sufficient fatigue characteristics.
The fatigue properties of the bare optical fiber are closely related to the properties of the resin coating the bare optical fiber, particularly the resin constituting the primary coating layer 2. It is necessary to select and use an appropriate resin for 2.

Normally, a silane coupling agent is added to the primary coating layer in order to have an adhesion between the bare optical fiber and the primary coating layer. The silane coupling agent chemically combines an organic functional group having an affinity or reactivity with an organic resin and a hydrolyzable alkoxy group having an affinity or reactivity with an inorganic material such as a bare silica optical fiber. Is a silane compound bonded to. The UV resin is coated during the drawing, immediately after receiving the UV irradiation, cured, and wound on a bobbin. Because the UV resin is rapidly cured by UV irradiation, the silane coupling agent present near the interface between the bare fiber and the primary coating layer reacts with the primary coating material on the organic functional group side and the bare fiber on the alkoxy group side. This has the effect of improving the adhesion between the bare fiber and the primary coating layer interface. The higher the concentration of the silane coupling agent at the interface between the bare fiber and the primary coating layer, the higher the adhesion.

Examples of the silane coupling agent include γ-mercaptopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyl Methyldimethoxysilane, vinyltriethoxysilane and the like are commercially available, among which γ-mercaptopropyltrimethoxysilane is most commonly used.
Other than this, as silane coupling agents, β- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, γ-glucidoxypropyltrimethoxysilane, γ-glucidoxypropylmethyldiethoxysilane, γ-glucidoxysilane Examples of propyltriethoxysilane and the like are shown, and these are said to be effective in suppressing a decrease in optical fiber breaking strength under high temperature and high humidity. (For example, see Patent Document 1).
However, among these silane coupling agents, for example, γ-mercaptopropyltrimethoxysilane itself acts as a chain transfer agent, but reacts with the unsaturated double bond in the constituent material in the uncured resin, Along with the storage time of the resin, problems such as the Young's modulus at the time of curing becoming higher than the initial value adversely affect the stability of the resin, and furthermore, the silane coupling agent is deactivated in the resin and the storage time At the same time, it has been found that there is also a considerable phenomenon that the adhesion property of the resin to the glass decreases.

By the way, in the glass optical fiber generally made of quartz, when hydrogen gas is present, transmission loss is considered to be caused by absorption of the hydrogen gas. For this reason, ultraviolet curable resins used as coating materials are also required to have excellent long-term reliability without generation of hydrogen gas due to degradation and decomposition. Amine compounds have an excellent effect of suppressing generation of hydrogen from a resin (for example, Patent Document 2), and are generally used at present. Examples of the amine compound include a primary monoamine represented by R ₁ —NH ₂ , a primary diamine represented by NH ₂ —R ₂ —NH ₂ , a secondary amine represented by R ₃ R ₄ —NH, and R ₅ R ₆ And tertiary amines represented by R ₇ -N. The primary monoamine is an aliphatic alkylamine in which R ₁ is an alkyl group such as ethyl or propyl, for example, ethylamine or propylamine. When R ₁ is an aromatic amine such as a benzene ring, it is aniline, aminobenzophenone or the like. Primary In diamine R ₂ is an alkyl group aliphatic amines, such as ethylenediamine, 1,2-diaminopropane, 1,4-diaminobutane, and 1,6-hexamethylene diamine, R ₂ is from the benzene ring or the like Examples of the aromatic amine include toluenediamine, xylenediamine, and metaphenylenediamine. Examples of the secondary amine include dibutylamine, dipropylamine, 2-ethylhexylamine, N-methylaniline, and N-methylbenzylamine. Examples of the tertiary amine include tributylamine, trioctylamine, and N, N-dimethylaniline. All of these have an effect of effectively suppressing hydrogen generation.
JP 2000-86936 A JP-A-63-27503

However, it has been found that when an amine compound is added to a resin, the following problems occur in γ-mercaptopropyltrimethoxysilane, which is the most commonly used silane coupling agent. That is, the outer line curing resin is composed of an oligomer, a monomer, a photoinitiator, and an antioxidant, and additives such as a silane coupling agent, and γ-mercaptopropyltrimethoxysilane is an amine compound having a basic property. By addition, the mercapto group reacts with the acrylic double bond at the terminal of the oligomer or monomer in advance, and the mercapto group disappears, so the silane coupling agent itself already exists in a polymer state before curing in the resin. In other words, because of the polymer, it is difficult to move to the interface between the bare fiber and the primary coating layer during curing, and the concentration of the silane coupling agent on the glass surface is reduced. Has not been obtained, and good fatigue characteristics cannot be obtained.
In addition, although amine compounds are effective in suppressing hydrogen generation, they often show basicity, and have been found to affect the reduction in the breaking strength and fatigue resistance of the bare optical fiber itself.
Examples of the influence of the pH of the resin on the fatigue resistance of the fiber include a method in which the pH of the uncured resin of the coating layer is set to 8.0 or less as in JP-A-2001-064040, and a method as in JP-A-2003-004993. It is known that the cured resin of the coating layer directly in contact with the bare optical fiber has a resin pH of 4.5 or less.
However, even if the pH of the resin is 8.0 or less as described above or the pH of the resin directly in contact with the bare optical fiber is 4.5 or less, the inventors of the present invention have earnestly noted that the fatigue resistance does not increase. It became clear by examination.

The object of the present invention is to solve the above problems and to provide an optical fiber having good fatigue resistance.

As a means for solving the above-mentioned problems, the present invention is an optical fiber element wire provided with a primary coating layer and a secondary coating layer, comprising an ultraviolet-curable resin composition, on an optical fiber bare wire, The resin composition forming the primary coating layer contains 0.01 to 5% by mass of a silane coupling agent, and the organic functional group of the silane coupling agent is at least one selected from an acryl group and a methacryl group. An object of the present invention is to provide an optical fiber.
Further, the present invention is characterized in that the ultraviolet-curable resin constituting the primary coating layer contains an additive which is present alone even after ultraviolet-curing, and the additive is non-basic.
Further, the present invention is characterized by containing a phosphorus antioxidant.
Further, the ultraviolet-curable resin constituting the secondary coating layer contains an additive that exists alone even after ultraviolet-curing, and the additive is non-basic.

The optical fiber of the present invention has good fatigue resistance and excellent reliability. Therefore, the optical fiber of the present invention exhibits high reliability without breaking even when tension is continuously applied for a long period of time in use in a cable.

Hereinafter, the present invention will be described in more detail.
A preferred embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.
FIG. 1 is a sectional view showing an example of the bare optical fiber of the present invention. In the figure, an optical fiber 1 comprises a primary coating layer 3 coated on the outer peripheral surface of an optical fiber bare wire 2 and a secondary coating layer 4 coated on the outer circumference of the primary coating layer 3. .

(Primary coating layer)
Specific examples of the primary coating material forming the primary coating layer in the present invention include a resin composition containing a UV-curable resin such as a urethane acrylate or epoxy resin having a double bond at a terminal, a so-called oligomer. Is mentioned. In addition, a reactive monomer having a double bond at the terminal (hereinafter, also referred to as a reactive diluent monomer) and a photopolymerization initiator may be used as the diluent.
However, since the pH of the resin varies depending on the amount of a polar group such as an ester or a urethane group, a material in which the types of the urethane acrylate constituents, the monomers, and the type and amount of the photoinitiator are appropriately selected is used.
For example, the resin compositions described in Japanese Patent No. 1535199, Japanese Patent No. 2018841, Japanese Patent No. 2784339, Japanese Patent No. 2893135 and the like can be mentioned. These are preferably contained in the primary coating material in an amount of 40% by mass or more and less than 99.95% by mass.
To these resins, a silane coupling agent is added, and if necessary, an antioxidant, a chain transfer agent, a light stabilizer, a polymerization inhibitor, a sensitizer, and other additives are added.
The additive does not undergo a crosslinking reaction with the resin at the time of the crosslinking reaction by irradiation with ultraviolet rays, and is present alone after curing. The amount of the additive used is in the range of 0.005 to 3%. If the amount is small, there is no effect, and if it is too large, problems such as bleeding and discoloration are likely to occur.
The primary coating material is preferably applied to the outer peripheral surface of the bare optical fiber, cured by ultraviolet rays, and coated so as to have an outer diameter of 180 μm to 200 μm. In the present invention, the primary coating layer may be composed of multiple layers. The Young's modulus at the time of curing is preferably 0.8 MPa to 10 MPa, particularly preferably 1 MPa to 3 MPa. If the Young's modulus is too small, the coating layer is likely to be deformed by side pressure or the like, and if it is too large, an increase in loss due to the side pressure tends to occur.

The silane coupling agent contained in the primary coating material has a role of improving the adhesion between the bare optical fiber and the coating resin. The silane coupling agent chemically combines an organic functional group having an affinity or reactivity with an organic resin and a hydrolyzable alkoxy group having an affinity or reactivity with an inorganic material such as a bare silica optical fiber. Is a silane compound bonded to.
In the present invention, the amount of the silane coupling agent contained in the primary coating material is 0.01 to 5% by mass, and preferably 0.1 to 1% by mass. If the amount of the silane coupling agent is too small, the adhesion between the bare optical fiber and the primary coating layer is deteriorated, resulting in poor fatigue resistance. If the amount is too large, the curability is deteriorated.
The silane coupling agent used in the present invention has at least one of an acryl group and a methacryl group as an organic functional group. The number of organic functional groups may be at least one in one molecule. The silane coupling agent whose organic functional group is an acryl group or a methacryl group does not react with other components in the uncured resin and exists as it is in a stable state of a low molecular weight. It is considered that since it exists as a low molecular state, it can move to the bare fiber / primary coating layer interface during curing by UV irradiation. Further, these are an acrylic group or a methacryl group in which the organic functional group has a double bond and have the same constitution as the terminal of the oligomer or the monomer, so that the curing speed of the resin itself is not impaired. Preferred silane coupling agents include 3-acryloxypropyltrimethoxysilane (trade name KBM-5103, manufactured by Shin-Etsu Chemical Co., Ltd.), γ-methacryloxypropyl trimethoxysilane (trade name KBM-503, manufactured by Shin-Etsu Chemical Co., Ltd.), γ-methacryloxypropyltriethoxysilane (trade name: KBE-503, manufactured by Shin-Etsu Chemical Co., Ltd.), among which 3-acryloxypropyltrimethoxysilane is particularly preferable.
By the way, the pH of the ultraviolet curable resin greatly differs before and after the resin is cured, and the pH value is lowered by curing. This is because during the curing reaction of the urethane acrylate resin, acids such as carboxylic acid are generated as by-products.
The ultraviolet curable resin is used as a coating layer of the bare optical fiber in a cured state. Therefore, the pH of the cured resin has a greater effect on the fiber than the pH of the uncured resin.
Furthermore, the present inventors have conducted intensive studies and found that the crosslinking reaction with the resin does not undergo a crosslinking reaction at the time of the crosslinking reaction by ultraviolet irradiation, and that the additive present alone after curing greatly affects the increase in pH. .
That is, the present inventors have found that the additive added to the ultraviolet-curable resin composition used in the present invention is preferably non-basic.
For example, conventionally used amine compounds for suppressing the generation of hydrogen are basic, and the amount added is small compared to the main component, but the effect of increasing the pH of the resin is very large, Increase the value by about one.
Basic additives having a function of greatly increasing the pH even in such a small amount include primary amines such as ethylamine, propylamine, aniline and aminobenzophenone, ethylenediamine, 1,2-diaminopropane, and the like. Examples thereof include amine compounds such as primary diamines such as 1,4-diaminobutane, 1,6-hexamethylenediamine, toluenediamine, xylenediamine and metaphenylenediamine.
On the other hand, non-basic hindered phenol-based additives such as thiodiethylene-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) pyrionate] (trade name: Irganox1035, ciba Specialty Chemicals, Inc.) has been found to be effective in preventing long-term deterioration and suppressing hydrogen generation, and to function sufficiently as a substitute for an amine-based additive.
In addition, non-basic in the present specification means that the pH value does not increase even when it is added (specifically, the increase in pH value is less than 0.5 due to the addition) as in the above-mentioned amine compound. It means that.
In the present invention, the pH is measured by the following method.
An uncured resin is applied on a glass plate to a thickness of 0.2 mm, and cured in air at a radiation dose of 500 mJ / cm ² (using a metal halide lamp). From the obtained cured sheet, a 2.0 g mass was precisely weighed, then placed in a glass container such as a volumetric flask, and further added with 20 ml of pure water adjusted to pH 7.0 in advance, sealed, and heated at 80 ° C. for 18 hours. . After the container has cooled to room temperature, the water is transferred to another container and the pH is measured with a pH meter.
In order to confirm the influence of the most important additives on the present invention on the pH, the pH before and after the addition of each additive was measured, and the difference obtained by subtracting the pH value before the addition from the pH value after the addition was calculated as the pH increase amount. And
Further, the present inventors have found the following matters. That is, in the present invention, it is preferable that the additive is non-basic, but the uncured resin is stored for a long period of time compared to when a basic additive represented by some amine-based additives is added. It has been found that a new problem that the fatigue characteristics are reduced when the above is performed.
This is because the alkoxy group in the silane coupling agent reacts with a trace amount of water in the resin to form a silanol group, and the silanol groups react with each other to deactivate the alkoxy group. Is considered to decrease dynamic fatigue characteristics.
The urethane acrylate oligomer or monomer constituting the ultraviolet-curable resin contains impurities such as catalyst residues necessary for the synthesis. Generally, such impurities are removed at the time of purification.However, depending on the degree of purification, trace impurities are often left, and such catalyst residues may cause the presence of the alkoxy group of the silane coupling agent and the trace water in the resin. Has been found to promote and deactivate the reaction. This phenomenon is improved by adding a basic additive such as a part of an amine compound.
That is, as described above, the additive is preferably non-basic. However, when a basic additive such as some amine-based additives is not added, the resin adhesion to the glass and the storage time of the resin are increased. This causes a problem of lowering the force and also lowering the dynamic fatigue characteristics.
In order to solve such a problem, as a result of intensive studies, a specific antioxidant has the effect of retaining the dynamic fatigue characteristics that decrease with the storage time of the resin, which is the above problem, without increasing the pH of the resin. I found that it is new.
It is generally known that antioxidants include sulfur-based, phenol-based, phosphorus-based, and amine-based antioxidants.
The antioxidant used in the present invention is not particularly limited as long as it does not increase the pH of the resin, even if it is added in a small amount, but among the above antioxidants, phosphorus-based antioxidants, particularly 6 -[3- (3-t-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-t-butyldibenz [d, f] [1,3,2] dioxaphosphepin (Sumitomo It was newly found that Chemical Co., Ltd. (Sumilizer GP) is effective in suppressing a decrease in adhesion during long-term storage. In addition, as addition amount of this antioxidant, 0.05-3% is preferable and especially 0.5-2.0% is preferable.

(Secondary coating layer)
As the secondary coating layer material forming the secondary coating layer in the present invention, a resin composition containing an ultraviolet curable resin such as a polyether-based urethane acrylate resin or an epoxy acrylate resin having a double bond at a terminal Is mentioned. In addition, a reactive diluent monomer having a double bond at the terminal and a photopolymerization initiator may also be used. Examples include the resin compositions described in Japanese Patent Nos. 2021130, 2135130, 2525177, and 2601699. These are preferably contained in the secondary coating material in an amount of 35 to 100% by mass.
If necessary, various additives such as a chain transfer agent, an antioxidant, a light stabilizer, a plasticizer, a polymerization inhibitor, a sensitizer, and a lubricant are added. These additives do not undergo a crosslinking reaction with the resin at the time of the crosslinking reaction by ultraviolet irradiation, and are present alone after curing, and the amount of each additive is used in the range of 0.005 to 3%. . If the amount is small, there is no effect, and if it is too large, problems such as bleeding and discoloration are likely to occur.
Since the additive in the secondary coating layer is present alone in the resin, the additive migrates to the primary coating layer and increases the pH of the primary coating layer resin, which may reduce the fatigue resistance of the optical fiber. . Therefore, the additive added to the ultraviolet-curable resin composition used in the present invention is preferably non-basic.
For example, conventionally used amine compounds for suppressing the generation of hydrogen are slightly added in comparison with the main components, but have a very large effect of increasing the pH of the resin and increase the pH value by about one. Let it.
Additives having a function of greatly increasing pH even in such a small amount include primary monoamines such as ethylamine, propylamine, aniline and aminobenzophenone, ethylenediamine, 1,2-diaminopropane, 1,4 Amine compounds such as primary diamines such as diaminobutane, 1,6-hexamethylenediamine, toluenediamine, xylenediamine and metaphenylenediamine.
On the other hand, non-basic hindered phenol-based additives such as thiodiethylene-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) pyrionate] (trade name: Irganox1035, ciba Specialty Chemicals, Inc.) has been found to be effective in preventing long-term deterioration and suppressing hydrogen generation, and to function sufficiently as a substitute for amine-based additives.
Non-basic means that the pH does not increase even when added (specifically, the increase in pH value by addition is less than 0.5) as in the above-mentioned amine compound.
Therefore, it is preferable to use an additive which increases the pH value by adding less than 0.5, more preferably less than 0.3.
The secondary coating material is preferably applied to the outer peripheral surface of the primary coating material, cured by ultraviolet rays, and coated with an outer diameter of 240 to 250 μm. In the present invention, the secondary coating layer may be composed of multiple layers. The Young's modulus at the time of curing is preferably 100 to 1000 MPa, particularly preferably 500 to 800 MPa. If the Young's modulus is too low, the lateral pressure characteristics cannot be ensured. If the Young's modulus is too high, the rigidity is too high to cause bending loss and poor workability.

As the bare optical fiber in the present invention, a glass fiber having a core and a clad can be used, and although not particularly limited, for example, a silica-based glass fiber can be used. The bare optical fiber can be manufactured according to the method described in, for example, Tech. Dig. Fiber Communication 1994 Tul 1 PJ Lemaire et.al.
In this specification, the bare optical fiber is also referred to as a glass fiber, an optical fiber glass part, or simply a glass part.

Furthermore, the present inventors prefer that coating with a resin having a small change in contact angle before and after coating described below is preferable because the fatigue resistance of the optical fiber is improved, and conversely, coating with a resin having a large change in contact angle is preferred. Then, the fatigue resistance is found to decrease, especially in the optical fiber, the silane coupling agent concentration on the surface of the bare optical fiber has a great effect on the fatigue resistance, the greater the silane coupling agent concentration, It has been found that the fatigue resistance of the optical fiber is improved.

The contact angle change before and after coating will be described.
After coating and curing the resin on the glass plate, when peeled off, part of the resin remains on the surface of the glass plate. When the contact angle of pure water to the glass plate is measured in this state, the wettability with pure water is reduced due to the effect of the remaining resin, and the contact angle is increased as compared to before the coating. However, if a large amount of the silane coupling agent is present at the interface, many Si atoms of the alkoxy group also remain, and the wettability with pure water does not decrease so much, and the change in the contact angle before and after coating is small.
That is, if the measured value of the contact angle change before and after coating is small, a large amount of the silane coupling agent will be present at the interface.

The method for measuring the contact angle is as follows.
After measuring the contact angle of pure water (or ion-exchanged water) with an unused soda glass plate (manufactured by Suzuki Kogaku: main component SiO ₂ , CaO, Na ₂ O) whose surface has been wiped clean with alcohol, etc. The primary coating material is applied again on the glass plate to clean the surface, and then irradiated with ultraviolet rays of 100 mJ / cm ² under a nitrogen atmosphere to prepare a sheet having a thickness of 200 μm. Then, after leaving it to stand at room temperature for 7 days, the cured sheet is peeled off from the soda lime glass. The contact angle of pure water (or ion-exchanged water) to the glass surface after stripping is measured, and the difference from the contact angle before coating with the coating material is determined. This difference is defined as the contact angle change before and after coating.
In the resin composition forming the primary coating layer in the present invention, the contact change before and after the coating is preferably 30 ° or less. More preferably, it is 5 to 25 °. In order to obtain such a contact angle change amount, it is preferable that, for example, the type and content of the silane coupling agent are set as described above, and that a certain amount of moisture is present in the atmosphere.

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.
After melt-spinning a single-mode optical fiber bare wire having an outer diameter of 125 μm, a primary coating layer made of a urethane acrylate-type ultraviolet-curable resin of each of Examples and Comparative Examples whose properties after curing is shown in Table 1 was provided. Then, a secondary coating layer made of a urethane acrylate type ultraviolet curable resin was provided to manufacture an optical fiber having an outer diameter of 250 μm. The composition and characteristics of the coating materials of the examples and comparative examples are as shown in Table 1. In addition, the composition of the resin for the primary coating layer constituting the examples and the comparative examples was changed as shown in Table 1, by changing the type and amount of the silane coupling agent, and the combination of the additives, and all other compositions were the same. did. The same material was used for the secondary coating layer except for the additive.
In addition, three types of A, B, and C were prepared as combinations of additives for both the primary coating layer and the secondary coating layer. That is, A is a product obtained by adding a conventional basic additive (ethylenediamine). B is a non-basic additive (thiodiethylene-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) pyrionate] (trade name: Irganox1035, ciba Specialty Chemicals) in place of the basic additive , Inc.)). C is a phosphorus-based antioxidant (6- [3- (3-t-Butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra) in addition to the non-basic additive of B. -t-butyldibenz [d, f] [1,3,2] dioxaphosphepin (Sumilizer GP manufactured by Sumitomo Chemical Co., Ltd.)).

For the primary coating layer, a contact angle measurement test was performed as described above, and a change in the contact angle before and after coating the primary coating layer on the glass plate was measured.
Regarding the Young's modulus of both the primary coating layer and the secondary coating layer, about 200 μm thick, cured at a dose of 1.0 J / cm ² under air (using a metal halide lamp), and cut out to a width of 6 mm from the prepared sheet As a sample, the sample was pulled at 1 mm / min with a tensile tester, and the elastic modulus was calculated from the tensile strength at 2.5% elongation, and was defined as the Young's modulus.
Further, the fatigue resistance of the manufactured optical fiber sample was tested by a dynamic fatigue coefficient n.
The dynamic fatigue coefficient n was measured using a tensile tester according to a test method specified in TIA / EIA-455-76: Method for measuring Dynamic Fatigue of Optical Fibers by Tension. In the present invention, those having a dynamic fatigue coefficient n of 20 or more were judged to have good fatigue resistance.
As for the n value, both the fiber drawn using the primary resin untreated and the fiber drawn using the resin which had been subjected to heat aging for one week at 60 ° C. for 7 days were measured. did.
The results are shown in Table 1 below.

According to the results shown in Table 1 above, the optical fiber samples (Comparative Examples 1 and 2) in which the organic functional group of the silane coupling agent contained in the primary coating material was a mercapto group (Comparative Examples 1 and 2) had an n value of less than 20 and had a high resistance. Poor fatigue properties. In addition, the optical fiber sample of Comparative Example 3 in which the amount of the silane coupling agent contained in the primary coating material was too small was inferior in fatigue resistance, and in Comparative Example 4 in which the primary coating material was poor in curability, it was drawn. Could not be completed, and an optical fiber could not be produced.
On the other hand, the optical fiber sample of the present invention in which the organic functional group of the silane coupling agent is an acryl group or a methacryl group and the amount of the silane coupling agent is 0.01 to 5% by mass (Example 1) To 5) all have good fatigue resistance. It is understood that when the amount of change in the contact angle is 30 ° or less, excellent fatigue resistance is obtained, which is preferable.
In Examples 2 and 4, good results were obtained by adding a specific antioxidant and using an aged resin. Further, in Example 5, even better fatigue resistance was obtained by making the additive of the secondary material non-basic.

It is sectional drawing which shows an example of the optical fiber of this invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Optical fiber strand 2 Optical fiber bare wire 3 Primary coating layer 4 Secondary coating layer

Claims (4)

On the bare optical fiber, is an optical fiber element comprising an ultraviolet-curable resin, a primary coating layer and a secondary coating layer are provided, wherein the resin composition forming the primary coating layer contains a silane coupling agent. An optical fiber comprising 0.01 to 5% by mass, wherein the organic functional group of the silane coupling agent is at least one selected from an acryl group and a methacryl group. 4. The optical fiber according to claim 1, wherein the UV-curable resin constituting the primary coating layer contains an additive that is present alone after UV-curing, and the additive is non-basic. The optical fiber according to claim 2, wherein the additive contains a phosphorus-based antioxidant. 4. The optical fiber according to claim 3, wherein the UV-curable resin constituting the secondary coating layer includes an additive that exists alone even after UV-curing, and the additive is non-basic. 5. .

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