JPH01313506A - Photocurable resin composition and plastic-clad optical fiber prepared by using same - Google Patents

Abstract

PURPOSE:To obtain a photocurable resin excellent in mechanical strengths and optical transmission characteristics by mixing a compound having a plurality of unsaturated bonds with a photopolymerization initiator and a specified coupling agent. CONSTITUTION:This resin composition comprises a compound having at least two unsaturated bonds in the molecule, a photopolymerization initiator and a coupling agent which can form a chemical bond with quartz or an optical glass, and said coupling agent is one having no unsaturated bond. Examples of the coupling agents used include silane coupling agents such as methoxymethylsilane and tetramethoxysialne. More desirably, one containing a fluorine atom or an ester group in the molecule is desirable to improve the compatibility with other cladding material components. A plastic-clad optical fiber prepared by using this resin composition is advantageous in respect of the improved strength of optical fiber and the difficult occurrence of peeling between the core and the clad in attaching a pressure connector because it is improved in the wettability of the core with the clad and in the adhesiveness between the core and the clad.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to the production of optical splitters such as optical fiber star couplers and optical fiber taps using a photocurable resin composition and its cured product as a cladding material. The present invention relates to a plastic clad optical fiber suitable for

Conventional technology Conventionally, cladding materials for plastic clad optical fibers include polymeric resin (Japanese Patent Application Laid-Open No. 58-30703), polyfluoroalkyl methacrylate copolymer (
JP-A No. 61-66706), vinylidene fluoride/
Tetrafluoroethylene copolymer (Japanese Patent Publication No. 56-419
No. 66) is known. However, these cladding materials are no longer able to meet the diversifying demands of recent years, such as lower loss and higher strength of optical fibers, easier connector attachment by crimping, and formation of optical splitters.

For example, silicone resin is easy to separate from the core and is suitable for forming the mixing part of an optical splitter, but because the mechanical strength of the resin is low, the reliability of the connector part is poor, especially for crimp-type optical connectors. This would be impractical. Furthermore, since the coefficient of linear expansion is large, the NA (numerical aperture) of the fiber is highly dependent on temperature, and the low-temperature characteristics of transmission loss are poor. Since vinylidene fluoride/tetrafluoroethylene copolymer has poor transparency, it is impossible to reduce the loss of an optical fiber.

In addition, polyfluoroalkyl methacrylate copolymers are
Although it has excellent transparency, due to its low softening point, the fiber retention strength of crimp-type optical connectors is significantly reduced at high temperatures.
Furthermore, since the coefficient of linear expansion of the resin increases above the softening point, the NA of the fiber increases significantly, making it difficult to design an optical splitter to optimize insertion loss.

In contrast, in recent years, cladding materials using ultraviolet curable resin compositions have been proposed, as seen in Japanese Patent Application Laid-Open No. 62-250047 and US Pat. No. 4,707,076. Since these resin compositions take on a crosslinked structure through ultraviolet curing, they have advantages not found in conventional compositions, such as excellent mechanical strength and improved production speed of optical fibers. - proposed a cladding material in which a chemical bond is formed between the core and the cladding using a silane compound represented by a Nolan coupling agent, as seen in JP-A-6141106 and U.S. Patent No. 4.707.076. has been done. In this case, since the core and cladding are chemically bonded, the optical fiber has the advantage of high mechanical strength and little deterioration of optical transmission characteristics under high temperature and high humidity conditions.

However, the problem that the invention seeks to solve. Since the resin compositions found in these conventional techniques contain compounds (monofunctional acrylates, etc.) having only one unsaturated bond in the molecule, they do not have sufficient crosslink density, and therefore have low hardness. The optical fiber's heat resistance (softening temperature) is still not high enough for practical use, and the mechanical properties of the optical fiber deteriorate significantly at high temperatures. Furthermore, because the crosslinking density is insufficient, the resin softens significantly due to water swelling under high humidity. Particularly, the holding force between the optical fiber and the connector in the crimp type connector is significantly reduced at high temperatures or high temperatures and high humidity. Furthermore, the amount of core protruding from the connector tip is large after being left at high temperatures or under high temperature and high humidity, or after being subjected to heat cycles.
For example, the reliability of an optical splitter having a structure in which a plurality of optical fibers are fixed by a crimp method or a structure in which an optical splitter and an optical fiber cable are connected by a crimp type optical connector is disadvantageous. In addition to the above drawbacks,
A more detailed analysis shows that when a resin containing a compound that forms a chemical bond with the core is used for the cladding material, the cladding resin may peel off during the manufacturing process of the optical splitter because the cladding resin is chemically bonded to the core. Because it is difficult to remove and easily causes microcracks on the core surface when peeling,
The mechanical strength of the crut peeling portion decreases, making it difficult to manufacture a highly reliable optical splitter. On the other hand, if a compound that forms a chemical bond with the core is not mixed, the cladding can be easily peeled off and the optical splitter can be manufactured easily, but the adhesion between the core and the cladding is poor, so the optical fiber The mechanical properties are even worse, and peeling between the core and crut is likely to occur when installing crimp connectors. In particular, it has the disadvantage that the reliability including the connector part decreases after being left in high temperature or high temperature and high humidity conditions or after heat cycle load, and at the same time, the mismatch at the core-cladding interface increases and loss increases. are doing.

Means for Solving the Problems Among the drawbacks, ■The low softening temperature of the resin and the remarkable softening caused by swelling with water are caused by the fact that the resin composition contains a monofunctional unsaturated compound. This is thought to be a contributing factor. On the other hand, ■The requirements for cladding removability when manufacturing optical splitters, and ■The requirements for mechanical properties, optical properties, and crimp-type connector attachment under a wide temperature and humidity range provide optical fibers with excellent properties. The requirement for adhesion between the core and cladding for this purpose appears to be an impossible problem to satisfy upon inspection.

Therefore, the present invention provides a photocurable resin composition in which a photopolymerization initiator and a coupling agent having no unsaturated bonds are added to at least one resin compound containing at least two unsaturated bonds in the molecule. By using this method in the code, it is intended to simultaneously solve the problems (1), (2), and (2) above.

That is, the object of the present invention is to have excellent mechanical strength and reliable optical transmission characteristics, and to have mechanical properties, especially the holding force between a crimp-type optical connector and an optical fiber, which do not deteriorate even at high temperatures. In addition, the adhesion between the core and cladding is good, and when installing crimp connectors, it is difficult to cause peeling between the core and cladding, and at the same time, it is difficult to cause misalignment at the core-cladding interface in the longitudinal direction of the optical fiber. and,
An object of the present invention is to provide a plastic clad fiber whose cladding can be easily peeled off when assembling an optical splitter.

The present invention provides a composition that improves the mechanical strength and softening temperature by improving the crosslinking density of the composition, and also reduces the swelling amount of water under high humidity. By using a resin for the cladding material in which a coupling agent that does not form bonds and forms chemical bonds with the core is added to the composition, it is possible to maintain a practically sufficient adhesion between the core and the cladding while maintaining the optical branching part. During formation, the cladding is to be easily peeled off without damaging the core surface.

A photocurable resin composition comprising at least one compound containing two or more unsaturated bonds in the molecule, a photopolymerization initiator, and a coupling agent having no unsaturated bonds contains a monofunctional unsaturated compound. Compared to the composition, the hardness of the cured product at room temperature is higher and the softening point is higher. ), there is little loss in the holding force between the fiber and the connector due to crimp connectors, and the amount of fiber protruding from the connector tip after being left at high temperatures, high temperatures and high humidity, or after being subjected to negative heat cycles is also small. Furthermore, compared to a composition that does not contain a coupling agent that forms a chemical bond with the core, the wettability and adhesion between the core and cladding are improved, and the mechanical strength and transmission loss of the optical fiber immediately after drawing are improved. Not only does it have excellent initial properties, but the deterioration of mechanical strength and transmission loss after being left at high temperatures or high temperatures and high humidity and after heat cycles is small, and when a crimp connector is installed within the elastic limit of the crat material, the core - No clad separation occurs.

Furthermore, the coupling agent that forms a chemical bond with the core is
Since it does not have covalent bonds with other cladding material constituents, it is possible to partially remove the cladding without damaging the core.

In the present invention, the unsaturated bond refers to a carbon-carbon double bond, and includes vinyl groups, allyl groups, and acrylic and methacrylic groups with excellent reactivity. Further, in order for the composition to function as a cladding, the refractive index needs to be lower than the refractive index of the core material, and as a means for that purpose, the compound of the present composition can contain a fluorine atom.

The composition of the present invention can be applied uniformly to the core glass, and moreover,
Because it is applied to a thin wall of 00μm, the viscosity is 100~(
It is desirable that it be OOOOcps.

Therefore, the composition of the present invention contains not only monomers but also
It is desirable to contain prepolymerized polymers having an appropriate degree of polymerization. Such polymers are not particularly limited as long as they can be crosslinked by ultraviolet irradiation; Examples include (meth)acrylate copolymers having unsaturated bonds in side chains. R + R2 COORf COORx [wherein R1 and R2 are hydrogen or methyl group, 11
f represents a fluoroalkyl group, and RX represents a hydrocarbon group having an unsaturated bond in the molecule. ] Examples of RX include a hinyl group, an allyl group, an acrylic group, a methacryl group, an internal olefin, and the like.

This polymer may be copolymerized with a third component to improve heat resistance. Such third copolymerization components include isobornyl (meth)acrylate, synclopentanyl (
Examples include meth)acrylate, adamantyl (meth)acrylate, and the like.

Next, examples of compounds having two or more (meth)acryloyl groups in the molecule include the following compounds: 1.4-butanediol di(meth)acrylate, ethylene glycol di(meth)acrylate, glycerol di(meth)acrylate, Methacrylate, tetraethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, Glycerol diacrylate, 1,6-hexaneshiolno(meth)acrylate, tripropylene glycol noacrylate, Nippon Kayaku Co., Ltd. product name Kayalad MANDA, Kayalad r(-604, trimethylolpropane tri(meth)acrylate, Pentaerythritol triacrylate, pentaerythritol tetra(meth)acrylate, ditrimedylolpropane tetraacrylate, dipentaerythritol hexaacrylate.

Next, as a compound containing a fluorine atom, the formula is:

IRt CIlt=CCOO(CH-)a(CF-)b(Cll
*) aoOc; clIt [wherein R1 and R2 have the same meanings as surface notation, a is 1 or 2, and l) represents an integer of 2 to 6. ] Compounds shown in the following are exemplified.

In the formula, the numbers of a and b are selected according to the required physical properties of the composition, such as refractive index, toughness, and viscosity.

The types of compounds constituting these compositions and their composition ratios can be selected so as to provide the necessary cured physical properties. Preferably, the viscosity before curing is 00~+0000c
ps, the breaking strength after curing is 1.0 kg/mm' or more, the Young's modulus is 10 kg/mm' or more, the breaking elongation is 10% or more, the refractive index is 1.44 or less, and the transmittance of light at a wavelength of 850 nm. is preferably 90% or more (0°1 mm thickness).

Next, the photoinitiator is preferably a compound that easily generates radicals when irradiated with ultraviolet rays, and the following compounds may be mentioned: benzophenone, acetophenone, benzyl, benzoin, benzoin methyl ether, benzoin isobutyl ether, benzyl dimethyl ketal, α, α゛-azobisisobutyronitrile, benzoyl peroxide,
! -Hydroxycyclohequinulfenylketone, 2.2
-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one.

The preferred amount of photoinitiator added is 0.01 to 10% by weight.

The coupling agent having no unsaturated bond contained in the composition of the present invention refers to a compound that has a group capable of forming a chemical bond with quartz or optical glass and does not form a carbon-carbon double bond. means.

As mentioned above, the addition of this type of coupling agent improves the strength of the optical fiber, improves the holding force between the crimp type connector and the optical fiber under high temperature and high temperature, high humidity, and improves the strength of the optical fiber under high temperature and high temperature and high humidity. It is possible to reduce the amount of core protrusion from the tip of the connector after being left alone or subjected to a heat cycle.

Furthermore, since this type of coupling agent does not chemically bond to the cladding material components of the pond, it is possible to partially peel off the cladding without damaging the core.

The coupling agent is desirably one that has high compatibility with other cladding material components, is colorless and transparent, and preferably has a refractive index equivalent to that of the other cladding material components.

Such coupling agents include methoxytrimethylsilane, dimethoxydimethylsilane, methyltrimethoxysilane, tetramethoxysilane, ethoxytrimethylsilane, ethyltrimethoxysilane, n-propyltriethoxynolane, n-butyltrimethoxysilane,
Examples include silane coupling agents such as -pentyltriethquinsilane, n-pentyltrimethoxinesilane, n-drazyltriethylsilane, and n-octadecyltriethylsilane.

More preferably, it contains a fluorine atom or an ester group in the molecule in order to improve compatibility with the cladding material component of the pond. Examples of such coupling agents include nometquinemethyl-3,3.3-trifluoropropylsilane, 3゜3.3-trifluoropropyltrimethoxinelan, and 3-trifluoroacetoxypropyltrimethoquinosilane. can.

When the composition of the present invention is used as a cladding for a plus deck clad optical fiber, the composition is applied onto a core made of quartz or optical glass by a method such as die coating or spray coating, and active light such as ultraviolet rays is applied. It can be cured by irradiation. The irradiation amount can be determined as appropriate depending on the type and amount of the compound contained in the composition.

Example: Polymer (+), (■) or ([11)] is used as the polymer having two or more unsaturated bonds in the molecule, and the compounds shown in Table 1 are mixed therein at a predetermined ratio, A cladding material composition was prepared. Note that the values in Table 1 are parts by weight.

Immediately after drawing a quartz rod to have an outer diameter of 200 μm, these resin compositions were coated and exposed to UV2 under a nitrogen atmosphere to obtain an optical fiber with an outer diameter of 230 μm.

Furthermore, after extruding and coating these optical fibers with ethylenetetrafluoroethylene copolymer to an outer diameter of 500 μm, Kevlar (trademark: XKEVLAR) was attached vertically around the periphery.
Further, polyvinyl chloride was extruded loosely and coated thereon to an outer diameter of 2.2 mm to obtain an optical fiber cord.

In addition, after partially peeling off the cladding over the entire circumference of these optical fibers at the intermediate part in the cutting direction using a half-split die having a hole with a diameter approximately 5 μm larger than the core,
The cladding material remaining at the peeled portion was thoroughly removed using a case soaked in acetone to obtain an optical fiber sample with the core partially exposed. After arranging the exposed parts of these two optical fiber samples closely in parallel, a resin having the same composition as the cladding of each optical fiber sample is applied to the entire surface of the exposed part and fully cured with UV light. A number 2 optical splitter was obtained.

The physical properties when the crimp-type optical connector was attached to these optical fibers and optical fiber cords, the cladding removability during trial production of the optical splitter, and the physical properties of the optical splitter were as shown in Table 2.

In Tables 1 and 2, cladding material composition No. 1
-6 are photocurable resin compositions in which a photopolymerization initiator is blended with a resin composition containing a compound having only one unsaturated combination in the molecule; These are a photocurable resin composition consisting only of a compound having at least two unsaturated bonds therein and a photopolymerization initiator, and a resin composition in which a coupling agent is blended into the resin composition.

Comparison of physical property values such as pull-out strength and core protrusion between the connector and fiber shown in Table 2 shows that optical fibers having a cladding material made of a cured product of the latter composition group have excellent mechanical strength, especially It can be seen that the crimp-type optical connector has excellent retention characteristics between fibers.

In Tables 1 and 2, cladding material composition No.
-3 and 7-9 are resin compositions that do not contain a coupling agent that forms a chemical bond with the core, and cladding material composition Nos. 4-6 and 10-15 contain a coupling agent that forms a chemical bond with the core. It is a resin composition containing. Second
A comparison of the physical property values of connector-fiber pull-out strength and core protrusion amount shown in the table shows that optical fibers having a crat material made of a cured product of the latter composition group have excellent mechanical strength.

In other words, in Tables 1 and 2, fibers with a cladding made of a cured product of a resin composition with composition Nos. It can be seen that there is little decrease in holding power even at high temperatures.

Furthermore, in Tables 1 and 2, cladding material compositions Nos. 1 to 3 and 7 to 9 are resin compositions containing no coupling agent, and cladding material compositions Nos. 13 to 15 are coupling agents having no unsaturated bonds. Cladding material composition Nos. 4 to 6 and 10 to I2 are resin compositions containing a coupling agent having an unsaturated bond.

Comparison of the clad releasability shown in Table 2 and the physical property values when used in an optical splitter shows that when a resin composition containing a coupling agent with an unsaturated bond is used as a clad material, the clad peels after curing. If a resin composition containing a coupling agent without unsaturated bonds is used as a cladding material, other physical properties may be sacrificed. It turns out that you can solve this problem without doing anything.

As described in detail of the invention, an optical fiber using the photocurable resin composition of the invention for its cladding has excellent mechanical properties, and the physical properties are less likely to deteriorate, especially at high temperatures. That is, the pull-out force of the caulking type connector is less reduced even under high temperatures (85° C. or higher), and the amount of core protrusion from the connector tip is small after being left at high temperatures, high temperatures and high humidity, or after being subjected to a heat cycle.

In addition, by improving the wettability of the clad against the core and the adhesion between the core and the clad, the strength of the optical fiber is improved, and peeling between the core and the clad is less likely to occur when a crimp connector is attached.

Furthermore, a part of the cladding can be peeled off by a simple method without damaging the core surface. Therefore,
By using the optical transmission fiber according to the present invention, it becomes easy to form the mixing part of an optical splitter, and it becomes easier to manufacture highly reliable optical fiber star couplers and assemble optical fiber taps that connect branch fibers to main fibers. It becomes easier.

Patent applicant Sumitomo Electric Industries, Ltd. Representation: Patent attorney: Baka Aoyama, 1 person

Claims (1)

[Claims] 1. A photocurable compound comprising at least one compound having at least two unsaturated bonds in the molecule, a photopolymerization initiator, and a coupling agent that forms a chemical bond with quartz or optical glass. In the resin composition, the coupling agent is
A photocurable resin composition characterized by having no unsaturated bonds. 2. The photocurable resin composition according to claim 1, wherein the coupling agent is 3-trifluoroacetoxypropyltrimethoxysilane or n-pentyltriethoxysilane. 3. In an optical fiber having a core made of quartz-based or optical glass and a cladding made of plastic having a lower refractive index than the core, the cladding material described in claim 1 or 2
A plastic clad optical fiber characterized by using a cured product of the photocurable resin composition described in 1. 4. An optical splitter having a structure in which a mixing section is formed by optically coupling the cores of a plurality of optical fibers to each other by removing a part of the cladding of the optical fibers, as described in claim 3 as an optical fiber. An optical splitter characterized by using optical fibers.