JPH10274716A - Plastic optical fiber high in numerical aperture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plastic optical fiber having high numerical aperture of >=0.52 and excellent and well-balanced in heat resistance, flexibility, and environmental resistance. SOLUTION: A plastic optical fiber comprising a clad, a 1st clad and 2nd clad with a composition different from the 1st core, has a configuration of the core consisting of copolymer of methylic methacrylate as a main component, the 1st clad consisting of co-polymer containing fluorinated vinylidene unit and hexafluoropropylene unit, and the 2nd clad consisting of (co-) polymer of fluorinated vinylidene unit as a main component. And, a high numerical aperture optical fiber can be made having high numerical aperture of >=0.52.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a plastic optical fiber which is as high as above and which has excellent heat resistance, bending resistance, environmental resistance and the like in a well-balanced manner.

[0002]

2. Description of the Related Art A plastic optical fiber (hereinafter abbreviated as POF) is superior to a glass-based optical fiber in terms of workability, handleability, manufacturing cost, and the like. Used in

In particular, in the field of light guides, it is desired to transmit a wide-angle light amount or an absolutely large amount of light, and a POF having a numerical aperture as high as about 0.50 is used. Is also required. The numerical aperture is represented by the difference between the refractive index of the core and the refractive index of the clad as in the following equation. Numerical aperture = [(refractive index of core) ² − (refractive index of cladding)
² ] ^1/2

[0004] The POF is composed of two kinds of polymers, a core and a clad. As the core, a polymer having excellent transparency and excellent weather resistance, such as polymethyl methacrylate (hereinafter abbreviated as PMMA), is generally used. On the other hand, the cladding needs to have a lower refractive index than the core in order to confine light inside the core, and fluorine-containing polymers are widely used.

[0005] As the fluorine-containing polymer for the cladding, the following three types are generally used. Each of them has advantages and disadvantages. Therefore, they can be selectively used from the viewpoints of numerical aperture, heat resistance, mechanical properties and the like. ing.

(1) Fluorination of vinylidene fluoride / tetrafluoroethylene copolymer (JP-B-63-67164), vinylidene fluoride / hexafluoroacetone copolymer (JP-A-61-22305), etc. Vinylidene copolymer. (2) Copolymer of fluoroalkyl methacrylate and methyl methacrylate (JP-B-43-8978). (3) Copolymer of long-chain fluoroalkyl methacrylate and methyl methacrylate (JP-A-62-265606)
No. JP-A-4-204909).

The vinylidene fluoride-based copolymer (1) has a P
It has good compatibility with polymers mainly composed of methyl methacrylate such as MMA.
OF has good interfacial adhesion to the core and good mechanical properties. However, the POF using these as the cladding has a low heat resistance of about 70 ° C., so that its use is also limited. Also,
Since all of these vinylidene fluoride copolymers are crystalline polymers, the vinylidene fluoride composition is substantially 70 to 70%.
It shows colorless transparency only within a limited range of 85 mol%. Therefore, in this case, the numerical aperture of the conventional PMMA-based POF is about 0.50, and it is not possible to further increase the numerical aperture.

The fluoroalkyl methacrylate copolymer (2) has excellent transparency and high glass transition temperature. Accordingly, POFs using these as claddings have excellent heat resistance of about 85 ° C., but are poor in mechanical properties such as bending resistance because they are brittle and have poor compatibility with polymers mainly composed of methyl methacrylate. . Moreover, as the composition ratio of fluoroalkyl methacrylate increases, the mechanical properties tend to be inferior. In this case, the numerical aperture of the conventional PMMA-based POF is about 0.47, and further increase in numerical aperture cannot be expected.

On the other hand, (3) a long-chain fluoroalkyl methacrylate copolymer may have improved mechanical properties and higher fluorine content and lower refractive index than (2). If the value is too high, there will be a problem that the film becomes cloudy or has poor thermal stability and foams to deteriorate the light transmittance. In this case, the numerical aperture of the conventional PMMA-based POF is about 0.49, and the numerical aperture is further increased. Can not hope.

As described above, in order to obtain a POF having a high numerical aperture, it is necessary to copolymerize a monomer having a lower refractive index and a higher fluorine content, and one of them is a vinylidene fluoride copolymer. In order to improve the transparency of POF, a non-crystalline polymer obtained by copolymerizing hexafluoropropylene as a third component and having a non-crystalline polymer is used for the cladding.
3401.

[0011]

This POF has a high numerical aperture and is excellent in translucency, but its copolymerization deteriorates bending resistance, and its glass transition temperature is within the operating temperature range, resulting in poor environmental resistance. Therefore, it was difficult to put it to practical use. Therefore, a main object of the present invention is to provide a POF having a high numerical aperture of 0.52 or more and having a good balance of heat resistance, bending resistance, environmental resistance, and the like.

[0012]

In order to achieve this goal, it is effective to use a clad having two layers and to specify a combination of polymers for the clad. be able to.

That is, according to the high numerical aperture POF of the present invention, in a plastic optical fiber comprising a core, a first clad, and a second clad having a composition different from that of the first clad, the core is mainly composed of methyl methacrylate. )
The first cladding is made of a copolymer containing vinylidene fluoride units and hexafluoropropylene units, the second cladding is made of a (co) polymer mainly containing vinylidene fluoride units, and It is characterized in that number ≧ 0.52.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The core (methyl) methacrylate (co) polymer of the present invention is a copolymer mainly composed of PMMA and methyl methacrylate (for example, (meth) acrylic acid ester, (meth) acrylic acid). , Substituted styrene, N-substituted maleimide, etc.), or modified polymers such as glutaric anhydride and glutarimide obtained by polymerizing them. The (meth) acrylate includes methyl acrylate, ethyl methacrylate, butyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, phenyl methacrylate, bornyl methacrylate, adamantyl methacrylate, and the like. Examples of N-substituted maleimides such as methylstyrene and α-methylstyrene include N-isopropylmaleimide, N-cyclohexylmaleimide, N-methylmaleimide, N-ethylmaleimide, and N-o-methylphenylmaleimide. These copolymer components may be used in plural,
A small amount of other components may be used. Further, a stabilizer such as an antioxidant may be contained in an amount that does not adversely affect the light transmittance. Among these polymers, it is most preferable that the polymer is substantially PMMA in terms of productivity, light transmittance, environmental resistance and the like.

The first clad of the present invention is made of a copolymer containing vinylidene fluoride and hexafluoropropylene as essential units, and the second clad is made of a (co) polymer containing vinylidene fluoride units as a main component. It must be 0.52. In addition, the second clad is a material in which a colorless and transparent composition different from the first clad is closely covered around the first clad. It is the clad diameter.

The reason why both the first clad and the second clad of the present invention require a vinylidene fluoride unit is to prevent mechanical properties such as bending resistance from being reduced by forming the clad into two thin layers. .

Further, it is necessary for the first clad to be copolymerized with hexafluoropropylene in order to lower the refractive index and to make the numerical aperture ≧ 0.52. Further, as other copolymer components, fluorinated vinyl ether, fluorinated polyether, tetrafluoroethylene, hexafluoroacetone, trifluoroethylene, vinyl fluoride, ethylene and the like may be copolymerized.

Preferred examples of the composition include a terpolymer of vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene and a terpolymer of vinylidene fluoride / hexafluoroacetone / hexafluoropropylene. A small amount of other copolymer components (5
Mol% or less). As a particularly preferred composition, hexafluoropropylene is 5 to 25 mol%, tetrafluoroethylene is 15 to 45 mol%, and vinylidene fluoride is 50 to 75 mol%. If the composition is out of this range, a low refractive index and low crystallization (low light transmission loss) cannot be achieved, the core has poor adhesion to a methyl methacrylate-based (co) polymer, bending resistance, etc. Or the mechanical properties of the material are greatly reduced.

The refractive index of the first cladding of the present invention is:
When the core is made of PMMA, it is preferable that the refractive index is less than 1.40 in order to make the numerical aperture ≧ 0.52.

Further, the second clad of the present invention is used for improving mechanical properties such as bending resistance.
Like the tetrafluoroethylene copolymer and the vinylidene fluoride / hexafluoroacetone copolymer, hexafluoropropylene is substantially free of the other components mentioned as the polymerizable component in the first clad component (5).
(Less than about mol%) vinylidene fluoride copolymers and blends thereof with PMMA are preferred. In order to further improve mechanical properties such as bending resistance, it is preferable that the copolymer is substantially a binary copolymer composed of 15 to 30 mol% of tetrafluoroethylene and 70 to 85 mol% of vinylidene fluoride.

The POF of the present invention may be manufactured in the same manner as a general manufacturing method. For example, the core material and the first and second clad materials are discharged from a composite die for concentric composite in a heated and melted state, and the core / first clad / second clad 3 is discharged.
A composite spinning method for forming a layer core-sheath structure is preferably used. Subsequently, a stretching process of about 1.2 to 3 times is generally performed for the purpose of improving the mechanical properties, and POF is obtained. The outer diameter of this POF is usually about 0.1 to 3 mm, and may be appropriately selected depending on the purpose.
Those having a size of 5 to 1.5 mm are preferable.

The POF of the present invention further comprises polyethylene, polypropylene or a copolymer or blend thereof, an olefin polymer containing an organic silane group,
The cord can be formed by coating a resin such as ethylene-vinyl acetate, polyvinyl chloride, polyvinylidene fluoride, nylon resin, polyester resin, nylon elastomer, polyester elastomer or urethane resin or fluorine resin. These coating materials may contain stabilizers such as antioxidants, antiaging agents, and UV stabilizers, in addition to flame retardants.

[0023]

The present invention will be described in more detail with reference to the following examples.

Refractive index: Measured at room temperature in an atmosphere of 25 ° C. using an Abbe refractometer as a measuring device.

Translucency: Halogen parallel light (wavelength 650n)
m) using the 30/2 m cutback method.

Number of continuous bending breaks: 5 at one end of fiber
A load of 00 g was applied, and the fiber was supported by a mandrel having a diameter of 30 mmφ.
And the number of times until the fiber was cut was measured (average value of n = 5).

Heat resistance: A fiber with a test length of 28 m (each end at 1 m outside the oven) was put into a high temperature oven (PHH-200 manufactured by Tabai Espec Co.) at 85 ° C. for 500 hours, and the light quantity before and after the test was measured. The amount of the change was used as an index (average value of n = 3; minus indicates a decrease in light amount).

Heat shock: A fiber with a test length of 28 m (each end at 1 m outside the oven) was put into a composite environmental tester, and the temperature was raised to -40 ° C. and 85 ° C. (heating or cooling in 5 minutes, 24 hours).
The change was measured as an index (average value of n = 3; minus indicates decrease in light amount).

Example 1 As a first clad material, a 2F / 4F / 6F copolymer (refractive index: 1.378) shown in Table 1 was used.
The 2F / 4F copolymer (refractive index: 1.402) shown in Table 1 was supplied to the composite spinning machine as a clad material. Further, PMMA ((refractive index: 1.492)) produced by continuous soul-like polymerization is supplied to a composite spinning machine as a core material, and the core, the first clad and the second clad are melt-spun into a three-layer core-sheath composite to obtain a fiber. Diameter 1000μm (core diameter 980μ
m, a first / second cladding thickness of 5.0 / 5.0 μm) was obtained. Furthermore, coating with polyethylene
The code was 2μ.

The POF thus obtained was evaluated by the above evaluation method, and the results are shown in Table 1. As can be seen from Table 1, the light-transmitting property, the repetitive bending property, the heat resistance, and the heat shock resistance were good, and were suitable as a high numerical aperture POF.

Examples 2 to 4 and Comparative Examples 1 to 4
A POF was obtained in the same manner as in Example 1 except that the copolymer of the clad material and the second clad material was changed as shown in Table 1. Further, a POF without the second clad was obtained in the same manner (Comparative Examples 1 and 2). The same evaluation as in Example 1 was performed using these POFs, and the results are shown in Table 1.

Examples 2 to 4 of the present invention were all excellent in translucency, repetitive flexibility, heat resistance and heat shock resistance. On the other hand, the one without the second clad as in Comparative Example 1 is inferior in bending resistance and environmental resistance, and the 2F / 4F copolymer having a numerical aperture ≧ 0.52 as in Comparative Example 2. Poor translucency, heat resistance and heat shock resistance.

When a fluoromethacrylate copolymer is used for the second clad as in Comparative Example 3, the bending resistance is extremely poor, and as in Comparative Example 4, the long chain fluoromethacrylate copolymer is used for the first clad. When used, the translucency and bending resistance were inferior.

[0034]

[Table 1]

[0035]

According to the present invention, a specific cladding material polymer is combined to form a two-layer clad, so that the numerical aperture is as high as 0.52 or more, and heat resistance, bending resistance, environmental resistance, etc. However, an excellent POF can be obtained in a well-balanced manner.

Claims (4)

[Claims] 1. A plastic optical fiber comprising a core, a first clad, and a second clad having a composition different from that of the first clad, wherein the core is made of a (co) polymer having methyl methacrylate as a main component. Is made of a copolymer containing vinylidene fluoride units and hexafluoropropylene units, the second cladding is made of a (co) polymer mainly containing vinylidene fluoride units, and the numerical aperture is 0.52 or more. A high numerical aperture plastic optical fiber. 2. A core comprising substantially only polymethyl methacrylate, wherein the first cladding has a refractive index of <1.40 and is substantially a vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene terpolymer or a fluoride. The second cladding is substantially composed of vinylidene / hexafluoroacetone / hexafluoropropylene terpolymer, and the second clad is substantially a vinylidene fluoride / tetrafluoroethylene binary copolymer or a vinylidene fluoride / hexafluoroacetone binary copolymer. 2. A high numerical aperture plastic optical fiber according to claim 1, wherein said optical fiber is made of only plastic. 3. The method according to claim 1, wherein the first clad comprises 5 to 25 mol% of hexafluoropropylene, 15 to
3. The high numerical aperture plastic optical fiber according to claim 2, wherein the terpolymer is 45 mol% and 50 to 75 mol% of vinylidene fluoride. 4. The high numerical aperture plastic according to claim 2, wherein the second cladding is a binary copolymer comprising 15 to 30 mol% of tetrafluoroethylene and 70 to 85 mol% of vinylidene fluoride. Optical fiber.