WO2012105246A1 - 光ファイバ心線 - Google Patents
光ファイバ心線 Download PDFInfo
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- WO2012105246A1 WO2012105246A1 PCT/JP2012/000661 JP2012000661W WO2012105246A1 WO 2012105246 A1 WO2012105246 A1 WO 2012105246A1 JP 2012000661 W JP2012000661 W JP 2012000661W WO 2012105246 A1 WO2012105246 A1 WO 2012105246A1
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- WIPO (PCT)
- Prior art keywords
- optical fiber
- coating layer
- coating
- fiber core
- modulus
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02395—Glass optical fibre with a protective coating, e.g. two layer polymer coating deposited directly on a silica cladding surface during fibre manufacture
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C25/00—Surface treatment of fibres or filaments made from glass, minerals or slags
- C03C25/10—Coating
- C03C25/48—Coating with two or more coatings having different compositions
- C03C25/50—Coatings containing organic materials only
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/44—Mechanical structures for providing tensile strength and external protection for fibres, e.g. optical transmission cables
- G02B6/4401—Optical cables
- G02B6/4403—Optical cables with ribbon structure
Definitions
- the present invention relates to an optical fiber core housed in an optical fiber cable.
- optical fiber core An optical fiber obtained by coating a glass optical fiber with some kind of coating is called an optical fiber core.
- the elution rate of the coating resin covering the optical fiber is 1.5 mass% or less.
- An optical fiber core wire is disclosed (see Patent Document 1).
- the saturation voltage of the coating covering the optical fiber is 0.2 kV to 0.7 kV, and the weight change rate in the hot water immersion test at 60 ° C. is less than 3% by weight with respect to the weight before immersion.
- the colored layer is formed of a resin having an elution rate of 3% or less when immersed in warm water at 60 ° C. for 30 days, and the primary coating layer of the colored optical fiber It is disclosed that Young's modulus is 0.5 MPa or more and 10 MPa or less (see Patent Document 3).
- an optical fiber core having a low Young's modulus of the first coating layer is immersed in water.
- voids 51 are partially generated in the first coating layer 31 as shown in FIG. 6, and the transmission loss of the optical fiber core 1 may increase.
- a second coating layer 32 is coated on the outside of the first coating layer 31, and the optical fiber core wire 1 includes a glass optical fiber 2, a first coating 31, and a second coating layer 32. Yes.
- the work of cleaning the surface and end face of the optical fiber with a solvent is generally performed.
- the jelly on the surface of the optical fiber is removed with a cable having a structure filled with a waterproof jelly or the like, the optical fiber is exposed to a solvent (mainly ethanol) for a long time. For this reason, the optical fiber core wire is required to have solvent resistance.
- the present invention has been made in view of the above, and an optical fiber core having resistance to solvent and micro-bending is unlikely to increase transmission loss even if the optical fiber is submerged and dried. It is to provide.
- One aspect of the present invention is an optical fiber core wire provided with a coating resin provided on the outer periphery of a glass optical fiber and laminated with at least two coating layers, and the most glass of the at least two coating layers
- the Young's modulus of the first coating layer provided on the optical fiber side is PY (MPa)
- the dissolution rate of the coating resin when the optical fiber core wire is immersed in 60 ° C. hot water for 168 hours is E (mass). %), PY ⁇ 0.55 MPa and 1.8 ⁇ E ⁇ 8.61 ⁇ PY + 1.40 are satisfied.
- an optical fiber core that hardly increases transmission loss even when the optical fiber core is immersed and dried, and has solvent resistance and microbend resistance.
- the optical fiber core wire 1 is obtained by coating a glass optical fiber 2 made of quartz glass with at least two layers of a coating resin 3.
- the first coating layer 31 of the coating resin 3 has a Young's modulus PY of 0.55 MPa or less, and the dissolution rate of the coating resin 3 when the optical fiber core wire 1 is immersed in warm water at 60 ° C. for 168 hours.
- E mass%
- the elution rate E of the coating resin satisfies the following formula (1).
- the lower limit of the Young's modulus PY is preferably 0.1 MPa or more, more preferably 0.14 MPa or more from the viewpoint of durability of the first coating layer against external forces such as side pressure and ironing applied during handling.
- E ⁇ 8.61 ⁇ PY + 1.40 in the above formula (1) indicates that the voids of the first coating layer 31 are generated and the first coating layer 31 is not dried when the optical fiber core wire 1 is dried after being submerged. This is derived by examining the relationship between Young's modulus PY and elution rate E. Although details will be described later, the generation of voids is suppressed when the elution rate E satisfies the relationship of E ⁇ 8.61 ⁇ PY + 1.40. Further, excellent solvent resistance (ethanol resistance) is obtained when the relationship of 1.8 ⁇ E in the above formula (1) is satisfied.
- the second coating layer 32 of the coating resin 3 has a Young's modulus of 500 MPa to 1500 MPa. In this way, by setting the Young's modulus of the second coating layer 32 high, sufficient mechanical strength required for the optical fiber core wire 1 is provided.
- an ultraviolet curable resin is mainly used.
- the ultraviolet curable resin includes an oligomer, a dilution monomer, and an additive.
- the additive include a photoinitiator, an antioxidant, a chain transfer agent, a light stabilizer, a plasticizer, a color pigment, a polymerization inhibitor, a sensitizer, and a lubricant.
- the oligomer urethane acrylate resins, epoxy acrylate resins, and polyester acrylate resins are mainly used.
- As the dilution monomer a monofunctional acrylate, a polyfunctional acrylate, or a vinyl monomer such as N-vinylpyrrolidone or N-vinylcaprolactam is used.
- the Young's modulus of the coating resin 3 can be adjusted by the molecular weight of the oligomer and the type of the diluted monomer. That is, as the molecular weight of the oligomer is increased, and the monofunctional monomer is increased as the diluting monomer rather than the polyfunctional monomer, the crosslinking density is lowered and a coating resin having a low Young's modulus is obtained. Therefore, in the first coating layer 31, the crosslinking density is increased by using an oligomer having a number average molecular weight of 500 to 10,000 and increasing the blending amount of a monofunctional monomer as a dilution monomer rather than a polyfunctional monomer.
- the second coating layer 32 has a high Young's modulus of 500 MPa or more and 1500 MPa or less by increasing the crosslinking density by increasing the blending amount of the polyfunctional monomer as the dilution monomer rather than the monofunctional monomer.
- the elution amount of the resin can be adjusted by the blending amount thereof. That is, the amount of resin elution can be increased as the amount of the non-reactive additive is increased.
- the affinity between these non-reactive additives and the molecular structure of the cross-linked part also affects the elution ease during water immersion. That is, since a strong electrostatic attractive force is generated between highly polar functional groups such as hydroxyl groups and esters, a non-reactive additive has a highly polar structure, and a coating layer having a structure in which the cross-linked portion has a low polarity.
- the electrostatic attractive force between the non-reactive additive and the water molecule becomes weak and the amount of elution increases. Conversely, if the polarity of the cross-linked portion is high, the amount of elution is reduced.
- a crosslinking reaction inhibitor such as a chain transfer agent
- the crosslinking density can be lowered, so that the first coating layer 31 can have a low Young's modulus. Ingredients increase. Therefore, considering them, the Young's modulus of each of the first coating layer 31 and the second coating layer 32, and the amount and type of the elution component, depending on the oligomer molecular weight, the type of dilution monomer, the amount of chain transfer agent, etc. Can be adjusted as appropriate.
- the Young's modulus PY of the first coating layer 31 is preferably 0.55 MPa or less, more preferably, a low Young's modulus resin of 0.50 MPa or less is used. The generation of microbend is suppressed, and excellent microbend resistance is obtained.
- the expression of E ⁇ 8.61 ⁇ PY + 1.40 is satisfied, voids are unlikely to be generated in the first coating layer 31 when the optical fiber core wire 1 is immersed and dried.
- the elution component from the coating resin 3 of the optical fiber core wire 1 comes out from the first coating layer 31 having a low crosslinking density. Therefore, the volume reduction amount of the first coating layer 31 increases as the elution rate E increases. In immersion, the first coating layer 31 absorbs water, so there is almost no effect of this volume change. However, the above-mentioned volume reduction caused by this elution component causes a tensile stress in the first coating layer 31 when dried. generate.
- the first coating layer 31 has a lower crosslink density, that is, a lower Young's modulus, so that the tensile strength becomes weaker.
- the solvent resistance (ethanol resistance) is good.
- the appearance change after immersing the optical fiber 1 in ethanol for 1 hour and immersing in hot water at 60 ° C. for 168 hours was 1. It was found that when the content was 8% by mass or more, no coating abnormality such as a crack or a crack occurred in the coating resin 3. This is for the following.
- the ethanol penetrates into the coating resin 3 of the optical fiber core wire 1 and the coating resin 3 swells. When the swelling is significantly increased, the coating resin 3 is destroyed and cracks and tears are generated.
- the optical fiber core wire 1 having a high elution rate E contains a large amount of low-molecular-weight uncrosslinked components in the coating resin 3, and these low-molecular-weight components when immersed in ethanol migrate to the outside of the coating layer. This is because the swelling of the coating resin 3 is thereby suppressed.
- the Young's modulus PY of the first coating layer 31 is constant, voids are more likely to occur as the elution rate E from the coating resin 3 at the time of water immersion is higher.
- the optical fiber core wire 1 having good solvent resistance can be obtained as long as the transmission loss is not easily increased and the range satisfies 1.8 ⁇ E in the formula (1).
- the optical fiber core wire 1 ⁇ / b> B is obtained by coating a glass optical fiber 2 with a coating resin 3 having three layers of a first coating layer 31, a second coating layer 32, and a colored layer 33.
- Each resin is an ultraviolet curable resin.
- the UV curable resin contains an oligomer, a dilution monomer, a photoinitiator, a chain transfer agent, an additive, and the like, but by changing its constituent material, a coating layer having a desired Young's modulus PY and elution rate E is obtained. Can do.
- the elution rate E is the elution rate of the entire coating resin including the colored layer 33.
- the outer diameter of the glass optical fiber 2 is 125 ⁇ m
- the outer diameter of the first coating layer 31 is 195 ⁇ m
- the outer diameter of the second coating layer 32 is 245 ⁇ m
- the outer diameter of the colored layer 33 is 255 ⁇ m.
- an optical fiber ribbon according to an embodiment of the present invention includes four optical fiber cores 1 ⁇ / b> B arranged in parallel in a flat shape, and a coating layer 5 made of an ultraviolet curable resin. It may be configured to cover the optical fiber ribbon 1C. In this case, the elution rate from both the colored resin and the coating resin of the optical fiber core wire can be measured by separating it from the optical fiber tape core wire 1C into a single core.
- the optical fiber core wire 1B is similar to the optical fiber core wire 1 described above in that the first coating layer 31 of the coating resin 3 has a Young's modulus PY Is equal to or less than 0.55 MPa, and the dissolution rate of the coating resin 3 when the optical fiber core wire 1 is immersed in warm water at 60 ° C. for 168 hours is defined as E (mass%), and the above equation (1) is satisfied. Yes.
- the optical fiber cores 1B and 1C like the optical fiber core wire 1, suppress the generation of voids when the elution rate E satisfies the relationship of E ⁇ 8.61 ⁇ PY + 1.40 in the above equation (1). it can. Moreover, when satisfy
- filling the relationship of 1.8 ⁇ E of said Formula (1), it has the outstanding solvent resistance (ethanol resistance). Furthermore, it has excellent microbend resistance when satisfying the relationship of PY ⁇ 0.55.
- the optical fiber core wire 1 having a different Young's modulus of the first coating layer 31 and the elution rate of the coating resin 3 is manufactured, whether voids are generated, solvent resistance, And the anti-microbend resistance properties were investigated.
- a glass optical fiber having an outer diameter (diameter) of about ⁇ 125 ⁇ m is used as the glass optical fiber 2, the first coating layer 31 is formed on the outer periphery, and the second layer is formed on the outer periphery.
- the coating layer 32 was formed, and the optical fiber core wire 1 was manufactured.
- the outer diameter of the first coating layer 31 was 195 ⁇ m, and the outer diameter of the second coating layer 32 was 245 ⁇ m.
- both urethane acrylate-based ultraviolet curable resins are used, and the Young's modulus and coating of each of the first coating layer 31 and the second coating layer 32 are used.
- the elution rate of resin 3 it adjusted suitably with the oligomer molecular weight, the kind of dilution monomer, the compounding quantity of a chain transfer agent, etc.
- the optical fiber core wire 1 having a different Young's modulus PY of the first coating layer 31 and elution rate E of the coating resin 3 is immersed in warm water at 60 ° C. for a predetermined time, taken out, and dried for one day (24 hours). And then observed with a microscope. In the microscopic observation, the case where a void was found in the first coating layer 31 was marked as x, and the case where no abnormality such as a void was found was marked as ⁇ . In this test, the elution rate is changed by changing the water immersion time even for the same optical fiber core.
- the Young's modulus PY of the first coating layer 31 was measured by an ISM (In Situ Modulus) test method described in Patent Document 4 and the like. Specifically, as shown in FIG. 4, a sample is prepared by leaving the coating only at one end of 10 mm, and removing the coating from the other part to expose the glass optical fiber 2, and coating the coated resin of the coated part. 3 is fixed with an adhesive or the like. Under a temperature of 23 ° C., a force is gradually applied so as to pull out the glass optical fiber 2 in the end direction where it is not fixed, and the displacement of the glass optical fiber 2 is measured.
- ISM In Situ Modulus
- the force applied to the unfixed end of the glass optical fiber 2 is F
- the displacement of the glass optical fiber 2 is u
- the radius of the glass optical fiber 2 is Rf
- the radius of the first coating layer 31 is Rp
- the coating is left.
- the shear elastic modulus Gp of the first coating layer 31 is calculated using the following equation (2).
- the Young's modulus PY of the first layer 31 is 3 Gp.
- the elution rate E was measured by the following method. 5 m long optical fiber 1 is 23 ° C. and 50% RH (RH is relative humidity, the amount of water vapor contained in the atmosphere at a certain temperature divided by the amount of saturated water vapor at that temperature (unit: %))) For 24 hours and then subtracting the mass of the glass optical fiber 2 from the mass of the optical fiber core 1 to measure the mass (w1) of the coating resin 3 portion. Next, the optical fiber core wire 1 is immersed in warm water heated to 60 ° C. for 168 hours, then taken out from the warm water and dried at 60 ° C. for 24 hours. Thereafter, the mass (w2) of the coating resin 3 portion is measured. From the measured w1 and w2, the elution rate E (mass%) was determined by the following formula (3).
- Optical Fiber Solvent Resistance Test Optical fiber solvent resistance test is performed by immersing a 10 cm long optical fiber core wire 1 in ethanol for 1 hour and then observing the appearance change with a microscope. ⁇ , when a covering abnormality such as a crack or a crack occurred, it was judged as x.
- microbend resistance test of optical fiber As the microbend resistance of optical fiber core wire 1, # 1000 sand paper specified by JIS is attached to the body part of a plastic bobbin (outer diameter: 28 cm). The optical fiber core wire 1 is wound around one layer (about 500 m). Then, within 30 minutes after winding, the transmission loss (L1) is measured at a measurement wavelength of 1550 nm by the cutback method. On the other hand, the transmission loss (L2) is measured at the measurement wavelength of 1550 nm by the same cutback method for the bundle state of the same optical fiber core wire 1 (about 1000 m when not wound around the bobbin).
- the cutback method is a method for obtaining a loss from the difference between the output from the test optical fiber core 1 and the output after the test optical fiber core 1 is cut into a cutback length (for example, 2 m). For this reason, since the loss of the connection point between the test optical fiber core 1 and the test apparatus is subtracted, the accurate loss of the glass optical fiber 2 of the test optical fiber core wire 1 can be measured. Then, L1-L2 is calculated and the value is set as the loss increment. When this value was 0.5 dB / km or less, it was marked with ⁇ , and when it was larger, it was marked with ⁇ . In addition, if the said loss increment is 0.5 dB / km or less, the optical fiber cable using this optical fiber core wire can be used suitably for a communication cable etc.
- Example 1-6 In Example 1 (Sample No. 2), urethane acrylate-based ultraviolet curable resin was used for the first coating layer 31 and the second coating layer 32, and each of the first coating layer 31 and the second coating layer 32 was used.
- the Young's modulus and the elution rate of the coating resin 3 are adjusted by adjusting the oligomer molecular weight, the type of dilution monomer, the blending amount of the chain transfer agent, etc., and the Young's modulus PY of the first coating layer 31 is 0.14 MPa. 3 is adjusted to 2.4 mass% at the elution rate E when immersed in 60 ° C. warm water for 168 hours.
- Example 2 (Sample No. 3), the Young's modulus PY of the first coating layer 31 is 0.20 MPa by adjusting the oligomer molecular weight, the type of dilution monomer, the blending amount of the chain transfer agent, and the like. It is the same as that of the above-mentioned Example 1 except having adjusted the elution rate E at the time of 168-hour warm water 60 degreeC to 1.8 mass%.
- Example 3 sample No.
- the Young's modulus PY of the first coating layer 31 is 0.22 MPa by adjusting the oligomer molecular weight, the type of dilution monomer, the blending amount of the chain transfer agent, and the like. It is the same as that of the above-mentioned Example 1 except having adjusted the elution rate E at the time of 168-hour hot water 60 degreeC adjustment to 2.9 mass%.
- the Young's modulus PY of the first coating layer 31 is 0.33 MPa, the oligomer molecular weight, the type of dilution monomer, the blending amount of the chain transfer agent, etc. are adjusted.
- Example 5 the Young's modulus PY of the first coating layer 31 is 0.49 MPa, the oligomer molecular weight, the type of dilution monomer, the blending amount of the chain transfer agent, etc. are adjusted. It is the same as Example 1 described above except that the elution rate E when immersed in 60 ° C. warm water for 168 hours is adjusted to 4.4 mass%.
- Example 6 Example No.
- the Young's modulus PY of the first coating layer 31 was 0.50 MPa, the oligomer molecular weight, the type of dilution monomer, the blending amount of the chain transfer agent, etc. were adjusted. It is the same as Example 1 described above except that the elution rate E when immersed in 60 ° C. warm water for 168 hours is adjusted to 3.8% by mass.
- Comparative Example 1-3 In Comparative Example 1 (Sample No. 18), the Young's modulus PY of the first coating layer 31 is 0.60 MPa and the coating resin 3 is adjusted by adjusting the oligomer molecular weight, the type of dilution monomer, the blending amount of the chain transfer agent, and the like. It is the same as that of the above-mentioned Example 1 except having adjusted the elution rate E at the time of 168 hour warm water 60 degreeC adjustment to 1.5 mass%. In Comparative Example 2 (Sample No.
- the Young's modulus PY of the first coating layer 31 is 0.81 MPa and the coating resin 3 is adjusted by adjusting the oligomer molecular weight, the type of dilution monomer, the blending amount of the chain transfer agent, and the like. It is the same as that of the above-mentioned Example 1 except having adjusted the elution rate E at the time of 168-hour warm water 60 degreeC to 1.8 mass%.
- the Young's modulus PY of the first coating layer 31 is 0.95 MPa by adjusting the oligomer molecular weight, the type of dilution monomer, the blending amount of the chain transfer agent, and the like. It is the same as that of the above-mentioned Example 1 except having adjusted the elution rate E at the time of 60 degreeC warm water 168 hour immersion to 1.4 mass%.
- FIG. 5 shows the measured values at the measurement points in FIG.
- the measurement points represented by black diamonds are the cases where no voids are generated (the test result is ⁇ )
- the measurement points represented by black rectangles are the cases where the occurrence of voids is observed (test The result is x).
- FIG. 5 shows that voids are more likely to occur as the elution rate E of the coating resin 3 increases and as the Young's modulus PY of the first coating layer 31 decreases.
- the elution rate E of the coating resin 3 is such that no voids are generated if the Young's modulus of the first coating layer 31 is PY and E ⁇ 8.61 ⁇ PY + 1.40 in the above formula (1). found.
- the right side of the above equation (1) was determined as follows. The slope and constant term of the line connecting the point of elution rate 2.4 mass% and Young's modulus 0.14 MPa at the upper limit where no void is generated, and the point of elution rate 5.5 mass% and Young's modulus 0.5 MPa Asked.
- the value of the gradient is 8.61, and the value of the constant term is 1.20.
- the term was sought.
- the value of the gradient is 8.61, and the value of the constant term is 1.59. Taking the middle of these values, the value of gradient was 8.61, the value of the constant term was 1.40, and the above equation of E ⁇ 8.61PY + 1.40 was derived.
- Example 2 The test conditions and results of Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 2 below. Further, the results of the solvent resistance test are shown in Table 2 below. From Table 2, after immersing in warm water at 60 ° C. for 168 hours and then drying for 24 hours, if the elution rate E is 1.8% by mass or more as in Examples 1 to 6 and Comparative Example 2, solvent resistance (Test result is ⁇ ).
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Abstract
Description
る。
光ファイバは、様々な外的応力やそれによって発生するマイクロベンドによって伝送損失が増加する。その外的応力から光ファイバを保護するために、一般的に光ファイバはガラス光ファイバに2層構造からなる樹脂被覆が施されている。なお、ガラス光ファイバに何らかの被覆を施した光ファイバを光ファイバ心線と呼ぶ。
また、光ファイバを被覆する被膜の飽和帯電圧が0.2kV~0.7kVであり、かつ60℃の温水浸漬試験における重量変化割合が、浸漬前の重量に対して3重量%未満である被膜を有する光ファイバが開示されている(特許文献2参照)。さらに、着色層を有する着色光ファイバにおいて、その着色層を60℃の温水に30日間浸水したときの溶出率が3%以下の樹脂で形成し、またその着色光ファイバの第一次被覆層のヤング率が0.5MPa以上10MPa以下であることが開示されている(特許文献3参照)。
図1に示すように、光ファイバ心線1は、石英ガラスからなるガラス光ファイバ2に少なくとも2層の被覆樹脂3を被覆したものである。被覆樹脂3の1層目被覆層31は、そのヤング率PYが0.55MPa以下であり、かつ、光ファイバ心線1を60℃の温水に168時間浸漬した際の被覆樹脂3の溶出率をE(質量%)としたとき、上記被覆樹脂の溶出率Eは下記(1)式を満たしている。また上記ヤング率PYの下限は、ハンドリング時に加わる側圧やしごきなどの外力に対する1層目被覆層の耐久性の観点から好ましくは0.1MPa以上、より好ましくは0.14MPa以上である。
被覆樹脂3のヤング率は、オリゴマーの分子量や希釈モノマーの種類により調整することができる。つまりオリゴマーの分子量を大きくするほど、また希釈モノマーとして多官能のモノマーよりも単官能のモノマーを多くすることにより、架橋密度が低くなり低ヤング率の被覆樹脂が得られる。したがって、1層目被覆層31では、数平均分子量が500ないし10000のオリゴマーを用いることにより、また希釈モノマーとして多官能のモノマーよりも単官能のモノマーの配合量を多くすることにより、架橋密度を低くして、好ましくは0.55MPa以下、より好ましくは0.50MPa以下という低いヤング率を得る。一方、2層目被覆層32は、希釈モノマーとして単官能モノマーよりも多官能モノマーの配合量を多くすることで架橋密度を高くして、500MPa以上1500MPa以下という高いヤング率を得ている。本明細書では、1分子中に反応基である二重結合(>C=C<)を1個持つものを単官能モノマーとし、2個以上持つものを多官能モノマーとする。
連鎖移動剤のような架橋反応抑制剤を用いた場合、架橋密度を低くすることができるので1層目被覆層31を低ヤング率化できるが、一方では低分子量成分も副生しやすく、溶出成分が増加する。したがってそれらを考慮して、オリゴマー分子量、希釈モノマーの種類、連鎖移動剤の配合量などにより、1層目被覆層31および2層目被覆層32のそれぞれのヤング率と溶出成分の量や種類とを適宜調整できる。
光ファイバ心線1の被覆樹脂3からの溶出成分は架橋密度の低い1層目被覆層31から出てくる。したがって、溶出率Eが高いほど1層目被覆層31の体積減少量が大きくなる。浸水中は1層目被覆層31が水を吸収することによりこの体積変化の影響はほとんどないが、乾燥するとこの溶出成分により発生する上述の体積減少が1層目被覆層31中に引張応力を発生させる。このため、溶出率Eが高いほど乾燥時に発生する引張応力が大きくなり、ボイドが発生しやすくなる。また1層目被覆層31は、架橋密度が低い、つまりヤング率が低いほど引張強度が弱くなるため、ボイドが発生しやすくなる。
光ファイバ心線1の耐溶剤性試験として、光ファイバ心線1をエタノールに1時間浸漬して外観の変化を観察したところ、60℃の温水に168時間浸漬した後の溶出率Eが1.8質量%以上であれば、被覆樹脂3に割れや裂け目などの被覆異常が発生しないことがわかった。これは以下のためである。エタノールに浸漬すると光ファイバ心線1の被覆樹脂3にエタノールが浸透し被覆樹脂3が膨潤する。膨潤が著しく大きくなると被覆樹脂3が破壊されて割れや裂け目が発生する。しかし溶出率Eが高い光ファイバ心線1は、被覆樹脂3中に低分子量の未架橋成分が多く含まれており、エタノール浸漬時のこれらの低分子量成分が被覆層外部に移行する。それにより被覆樹脂3の膨潤が抑制されるためである。
また、1層目被覆層31のヤング率PYが一定の場合、浸水時の被覆樹脂3からの溶出率Eが高いほど、ボイドが発生しやすくなる。
図2に示すように、光ファイバ心線1Bは、ガラス光ファイバ2に1層目被覆層31、2層目被覆層32、着色層33の3層を有する被覆樹脂3を被覆したものである。各樹脂には紫外線硬化型樹脂を用いている。紫外線硬化型樹脂は、オリゴマー、希釈モノマー、光開始剤、連鎖移動剤、添加剤等を含むが、その構成材料を変えることで、所望のヤング率PYおよび溶出率Eを有する被覆層とすることができる。この場合の溶出率Eは、着色層33を含む被覆樹脂全体の溶出率とする。またガラス光ファイバ2の外径を125μm、1層目被覆層31の外径を195μm、2層目被覆層32の外径を245μm、着色層33の外径を255μmとする。これらの値は一例であって適宜変更可能である。したがって、光ファイバ心線1Bは、着色層33以外、前述の第1実施形態の光ファイバ心線1と同様の構成である。このような構成の光ファイバ心線1Bは着色光ファイバ心線とも称する。
図3に示すように、本発明の一実施形態に係る光ファイバテープ心線は、上述の光ファイバ心線1Bを4本平面状に並行に並べ、紫外線硬化型樹脂からなる被覆層5で一括被覆して光ファイバテープ心線1Cとした構成であってもよい。この場合、光ファイバテープ心線1Cから単心に分離することで光ファイバ心線の着色樹脂および被覆樹脂の両方からの溶出率を測定することができる。
以下に前述の各実施形態で説明した光ファイバ心線の実施例について、以下に説明する。
1層目被覆層31のヤング率PYと被覆樹脂3の溶出率Eの異なる光ファイバ心線1を、60℃の温水に所定の時間浸水した後に取り出し、1日(24時間)乾燥させてから、顕微鏡で観察した。顕微鏡観察では、1層目被覆層31にボイドが見られた場合を×、ボイドなどの異常が見られなかった場合を○とした。なお、本試験では同一の光ファイバ心線に対しても、浸水時間をいくつか変化させることで溶出率を変化させている。
具体的には、図4に示すように、片端10mmのみ被覆を残し、それ以外の部分は被覆を除去してガラス光ファイバ2を露出させたサンプルを用意し、被覆している部分の被覆樹脂3を接着剤等で固定する。23℃の温度下で、固定されていない端方向にガラス光ファイバ2を引き抜くように徐々に力をかけ、ガラス光ファイバ2の変位を測定する。ガラス光ファイバ2の固定されていない端に加えられる力をF、ガラス光ファイバ2の変位をu、ガラス光ファイバ2の半径をRf、1層目被覆層31の半径をRp、被覆が残された部分の長さ(この場合は10mm)をLembすると、1層目被覆層31の剪断弾性率Gpは下記(2)式を用いて計算される。
長さ5mの光ファイバ心線1を23℃、50%RH(RHは相対湿度であり、ある気温で大気中に含まれる水蒸気の量を、その温度の飽和水蒸気量で割ったもの(単位は%)である。)の恒温室にて24時間放置した後、光ファイバ心線1の質量からガラス光ファイバ2の質量を差し引くことで被覆樹脂3部分の質量(w1)を測定する。次に、その光ファイバ心線1を60℃に加熱した温水に168時間浸漬した後に温水から取り出し、60℃で24時間かけて乾燥させる。その後、被覆樹脂3部分の質量(w2)を測定する。測定したw1とw2から、下記(3)式により溶出率E(質量%)を求めた。
光ファイバの耐溶剤性試験は、10cm長の光ファイバ心線1をエタノールに1時間浸漬してから外観の変化を顕微鏡により観察し、被覆樹脂3に変化が無ければ○、割れや裂け目などの被覆異常が発生したら×と判定した。
光ファイバ心線1の耐マイクロベンド特性としてプラスチックボビン(外径:28cm)の胴部分にJISで規定する#1000のサンドペーパを貼りつけ、ここに、100gの巻き付け張力で光ファイバ心線1を1層(約500m)巻き付ける。そして巻き付けてから30分以内にカットバック法により測定波長1550nmで伝送損失(L1)を測定する。一方、同じ光ファイバ心線1の束状態(ボビンに巻き付けていない状態で約1000m)につき同じくカットバック法により測定波長1550nmで伝送損失(L2)を測定する。
カットバック法は、試験用の光ファイバ心線1からの出力と、試験用の光ファイバ心線1をカットバック長(たとえば2m)に切断したあとの出力差から損失を求める方法である。このため,試験用の光ファイバ心線1と試験装置の接続点の損失は差し引かれるため、試験用の光ファイバ心線1のガラス光ファイバ2の正確な損失を測定できる。
そして、L1-L2を計算し、その値を損失増分とする。この値が0.5dB/km以下を○、それより大きい場合を×とした。なお、上記損失増分が0.5dB/km以下であれば、この光ファイバ心線を用いた光ファイバケーブルを通信用ケーブル等に好適に用いることができる。
実施例1(サンプルNo.2)は、1層目被覆層31、2層目被覆層32にウレタンアクリレート系紫外線硬化型樹脂を用い、1層目被覆層31、2層目被覆層32の各々のヤング率、被覆樹脂3の溶出率については、オリゴマー分子量、希釈モノマーの種類、連鎖移動剤の配合量などを調整して、1層目被覆層31のヤング率PYを0.14MPa、被覆樹脂3の60℃温水168時間浸漬時の溶出率Eを2.4質量%に調整したものである。なお、168時間としたのは、168時間を経過することで被覆樹脂からの溶出がほぼ飽和するからである。
実施例2(サンプルNo.3)は、オリゴマー分子量、希釈モノマーの種類、連鎖移動剤の配合量などを調整して、1層目被覆層31のヤング率PYを0.20MPa、被覆樹脂3の60℃温水168時間浸漬時の溶出率Eを1.8質量%に調整した以外前述の実施例1と同様のものである。
実施例3(サンプルNo.6)は、オリゴマー分子量、希釈モノマーの種類、連鎖移動剤の配合量などを調整して、1層目被覆層31のヤング率PYを0.22MPa、被覆樹脂3の60℃温水168時間浸漬時の溶出率Eを2.9質量%に調整した以外前述の実施例1と同様のものである。
実施例4(サンプルNo.12)は、オリゴマー分子量、希釈モノマーの種類、連鎖移動剤の配合量などを調整して、1層目被覆層31のヤング率PYを0.33MPa、被覆樹脂3の60℃温水168時間浸漬時の溶出率Eを3.8質量%に調整した以外前述の実施例1と同様のものである。
実施例5(サンプルNo.15)は、オリゴマー分子量、希釈モノマーの種類、連鎖移動剤の配合量などを調整して、1層目被覆層31のヤング率PYを0.49MPa、被覆樹脂3の60℃温水168時間浸漬時の溶出率Eを4.4質量%に調整した以外前述の実施例1と同様のものである。
実施例6(サンプルNo.16)は、オリゴマー分子量、希釈モノマーの種類、連鎖移動剤の配合量などを調整して、1層目被覆層31のヤング率PYを0.50MPa、被覆樹脂3の60℃温水168時間浸漬時の溶出率Eを3.8質量%に調整した以外前述の実施例1と同様のものである。
比較例1(サンプルNo.18)は、オリゴマー分子量、希釈モノマーの種類、連鎖移動剤の配合量などを調整して、1層目被覆層31のヤング率PYを0.60MPa、被覆樹脂3の60℃温水168時間浸漬時の溶出率Eを1.5質量%に調整した以外前述の実施例1と同様のものである。
比較例2(サンプルNo.19)は、オリゴマー分子量、希釈モノマーの種類、連鎖移動剤の配合量などを調整して、1層目被覆層31のヤング率PYを0.81MPa、被覆樹脂3の60℃温水168時間浸漬時の溶出率Eを1.8質量%に調整した以外前述の実施例1と同様のものである。
比較例3(サンプルNo.20)は、オリゴマー分子量、希釈モノマーの種類、連鎖移動剤の配合量などを調整して、1層目被覆層31のヤング率PYを0.95MPa、被覆樹脂3の60℃温水168時間浸漬時の溶出率Eを1.4質量%に調整した以外前述の実施例1と同様のものである。
図5から、被覆樹脂3の溶出率Eが高くなるほど、また1層目被覆層31のヤング率PYが低くなるほどボイドが発生し易いことがわかる。また被覆樹脂3の溶出率Eは、1層目被覆層31のヤング率をPYとして、上記の(1)式のE≦8.61×PY+1.40の範囲であればボイドが発生しないことが判明した。
上記(1)式の右辺は以下のようにして求めた。
ボイドが発生しない上限値の溶出率2.4質量%、ヤング率0.14MPaの点と、溶出率5.5質量%、ヤング率0.5MPaの点とを結んだ線の勾配と定数項を求めた。その勾配の値は8.61であり、定数項の値は1.20となる。また、ボイドが発生する下限値の溶出率2.8質量%、ヤング率0.14MPaの点と、溶出率5.9質量%、ヤング率0.5MPaの点とを結んだ線の勾配と定数項を求めた。その勾配の値は8.61であり、定数項の値は1.59となる。これらの値の中間をとって、勾配の値を8.61とし、定数項の値を1.40として、上記E≦8.61PY+1.40なる式を導出した。
さらに耐溶剤性試験の結果を下記表2に示す。
表2から、60℃の温水に168時間浸漬した後、24時間乾燥させて求めた溶出率Eが、実施例1から6および比較例2のように1.8質量%以上あれば耐溶剤性が得られる(試験結果は○)ことが判明した。
表2から、実施例1から6のように、1層目被覆層31のヤング率PYが0.55MPa以下、より好ましくは0.5MPa以下であれば、耐マイクロベンド特性が得られる(試験結果は○)ことが判明した。
Claims (3)
- ガラス光ファイバの外周に設けられ、少なくとも2層の被覆層が積層された被覆樹脂を備える光ファイバ心線であって、
前記少なくとも2層の被覆層の、最も前記ガラス光ファイバ側に設けられた1層目の前記被覆層のヤング率をPY(MPa)、
前記光ファイバ心線を60℃の温水に168時間浸漬した際の前記被覆樹脂の溶出率をE(質量%)としたとき、
PY≦0.55MPa、
かつ、
1.8≦E≦8.61×PY+1.40
なる式を満たすことを特徴とする光ファイバ心線。 - 前記被覆樹脂の最も外側の前記被覆層は、着色樹脂からなる着色層であることを特徴とする請求項1記載の光ファイバ心線。
- 請求項2に記載の光ファイバ心線を複数本並行に配置し、それらの光ファイバ心線を一括して被覆する被覆層をさらに備えることを特徴とする光ファイバテープ心線。
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