JPS597310A - Optical transmission fiber - Google Patents

Abstract

PURPOSE:To form a plastic optical transmission fiber superior in performance with high productivity, by using as a clad component a fluoroalkyl methacrylate type polymer produced by using polyfunctional mercaptan as a chain transfer agent. CONSTITUTION:A fluoroalkyl methacrylate type polymer is prepd. by adding 0.01-0.5pt.wt. mercaptan (B) having >=2 mercapto groups in one molecule, such as triethylene glycol dithiol to 100pts.wt. fluoroalkyl methacrylate (A) optionally contg. copolymerizable vinyl monomer by <=30wt% of the total monomer, such as methyl methacrylate, and block polymerizing in the presence of a radical polymn. initiator. The present optical transmission fiber is obtained by using said polymer as a clad component, and polymethyl methacrylate as a core component, and melting and subjecting them to melt coextrusion molding.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flexible plastic optical transmission fiber comprising a core cladding.

In general, a step-index optical transmission fiber made of a core clad utilizes total internal reflection of light, so it has a structure in which a core with a high refractive index is surrounded by a clad with a low refractive index. The larger the difference in the refractive index of the cladding, the better the lightning transmission.

Conventionally, multicomponent glass or quartz glass has been mainly used as a base material for optical transmission fibers, and optical transmission fibers have been developed in which glasses having different refractive indexes or glass cores are coated with synthetic resins. However, glass is not flexible and may break.
Because of their ease of use, optical transmission fibers based on synthetic resins have also been developed, such as fibers with a core of polystyrene and cladding of acrylic resin such as polymethyl methacrylate, or fibers with a core of polymethyl methacrylate and a fluorine-containing fiber. Optical transmission fibers with polymer cladding are commercially available. Among these, dual optical transmission fibers that use polymethyl methacrylate as the core have excellent optical transmission properties and are superior to polystyrene in terms of flexibility and heat resistance, so they are used for applications such as short-distance optical communications. has been done.

However, the refractive index of polymethyl methacrylate is 149.
It belongs to the lowest class of general-purpose polymers, and the polymers that can be used as cladding when cored with polymethyl methacrylate are extremely limited. For example,
-8978, Special Publication No. 54-24502, Special Publication No. 1983
-49326, Special Publication No. 56-8621, Special Publication No. 1983
-8522, etc., discloses an optical transmission R fiber having a core of polymethacrylic acid alkyl and a cladding of the divine polyfluoroalkyl methacrylate. An optical transmission fiber clad with an ethylene copolymer has been disclosed.

The optical transmission performance of an optical transmission fiber is closely related to absorption and scattering of the core and cladding, light reflectance at the boundary between the core and the cladding, and the like.

The polyfluoroalkyl methacrylates that have been proposed as cladding materials have essentially very little absorption and scattering, so there should be little optical transmission loss due to these factors. Alkyl has poor thermal decomposition resistance, and has the drawback of increasing optical transmission loss when produced by melt coextrusion with polymethyl methacrylate as the core, which is commonly used in industry. This misaki effect is thought to be due to the depolymerization of the polyfluoroalkyl methacrylate during heating and melting during melt extrusion, resulting in foaming of the produced monomer and generation of carbides.

For example, when compared to esters of fluorinated alcohols such as methacrylic acid and non-fluorinated alcohols with the same number of carbon atoms, the density of double bonds that have radical polymerization ability is sparser, resulting in a molecular structure that is more susceptible to radical depolymerization. There is.

In this sense, the polymer properties during the production of fluorine-containing resin polymers deteriorate with repeated thermal shaping, the degree of polymerization decreases17, and the plasticizing effect of the fluorine-containing monomers produced after radical depolymerization decreases. However, the properties of fluorine-containing resins are significantly lower.

As a measure to prevent such thermal deterioration, a method of adding a deterioration inhibitor has been proposed, and hindered phenol is a typical deterioration inhibitor. However, although this method has good effects on heat resistance and prevention of depolymerization,
Problems arise with compatibility, dispersibility, and transparency with fluorine-containing resins, and because hindered phenol has molecular absorption in the visible and ultraviolet regions due to its molecular structure, it can have a fatal adverse effect on optical transmission fibers. have a defect.

On the other hand, a copolymer of vinylidene fluoride and tetrafluoroeburene as described in Japanese Patent Publication No. 53-42260 has excellent adhesion with methyl methacrylate, but is essentially crystalline and cloudy. Therefore, the disadvantage is that the transmission loss due to scattering is extremely large.

Based on this background, the present inventors essentially focused on absorption,
The idea was that by improving the thermal decomposition resistance of fluoroalkyl methacrylate, which is a transparent, low-refractive index polymer with very little scattering, it would be possible to provide plastic optical transmission fibers with excellent performance at low cost and with good productivity. As a result of intensive studies, the present invention was arrived at. That is,
The present invention uses polyfluoroalkyl methacrylate or fluoroalkyl methacrylate 70 as a core component mainly consisting of a polymer consisting of repeating methyl methacrylate.
A vinyl monodark body 6 that can be copolymerized with a gravity of 1-h or more
Optical transmission characterized in that the cladding component is a fluoroalkyl methacrylate polymer polymerized by adding a polymerization catalyst and a mercaptan having two or more mercapto groups in one molecule to a mixture of 0% by weight or less. It is a fiber.

As a result of intensive studies to improve the above-mentioned drawbacks, the present inventors found that
The mercaptan used as a chain transfer agent in the polymerization of the fluoroalkyl methacrylate polymer of the cladding component of the present invention has at least two mercapto groups in one molecule, and the radical species generated during depolymerization are absorbed by the mercaptan. By trapping it, radical depolymerization can be inhibited, and the heat resistance of the fluorine-containing resin can be improved. When a polyfunctional mercaptan containing two or more mercapto groups in one molecule is used as a chain transfer agent, when it is bonded to the end of the polymer to form a thioether type, the mercapto group exists bonded to the end. If so, it will effectively act as a radical scavenger generated during the overlapping thermoforming process and improve the heat resistance of the fluorine-containing resin.

When using mercapcoun containing two or more mercapto groups, one mercapto group undergoes chain transfer to the polymer terminal during radical depolymerization, and other mercapto groups become free at the polymer terminal and act as radical scavengers. It can be kept active at the end of the polymer.

Specific examples of mercaptans used include triethylene glycoldithiol, trimethylolpropane, lithioglycolate, pentaerythritol tetradioglyflate, trimedylolpropane tris, β-mercaptopropylene tris, and pentaerythritol tetrathioprobionate. -, mercaptoethyl borate, polyfunctional mercapto group-containing polymers produced from polyglycidyl meccrylate and thioglycolic acid, and the like.

In addition of the above mercaptan and 12, 100 parts by weight of the polymer is added, and V is optionally selected depending on the amount of the desired polymer. The preferred range is 0.01 to 0.05 parts by weight.

As a single ml unit of fluoroalkyl methacrylate used in the present invention, for example, the general formula % formula %) or the general formula CH3R+ CH2-CC-OC(CF2) l-Xl)1 R2 (wherein X(rjH, F or Ctl n11-6 is an integer, m is an integer of 1 to 10, t is an integer of 1 to 10, and R1 and crow represent H, CH,, CH, or CF. Specific examples of vinyl monomers copolymerizable with fluoroalkyl methacrylate in the invention include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, Schiff methacrylate, glycidyl acrylate, methacrylic acid, acrylic acid, and methyl acrylate. , ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethyl hequinyl acrylate,
Benzyl acrylate acrylate, styrene, α-methylstyrene, 2,4-)methylstyrene, P-chlorostyrene, 2,4-dichlorostyrene, P-methoxystyrene, acrylonitrile, methacrylatrile, vinyl acetate, methylhinyl ketone, Examples include hydroxypropyl acrylate, hydroxyethyl, acrylate, and the like. Among them, methyl methacrylate is particularly preferred from the viewpoint of strengthening the transparent copolymer. The content of these vinyl monomers in the copolymer can be 30% by weight or less of the fluorine-containing resin. If it exceeds 30% by weight, it is not preferable because it adversely affects the properties of the fluoroalkyl polymethacrylate, such as heat resistance, low refraction, and transparency.

As the polymerization catalyst, an ordinary radical polymerization initiator can be used, and specific examples include G-1, ert-
Butyl peroxide, dicumyl peroxide, methyl echalketone peroxide, tert-butyl perphthalate, tert-butyl perbennoe (., methylinobutyl ketone peroxide, lauroyl peroxide, cyclohexane peroxide, 2,5-dimethyl-2
, 5-tert-butylperoxyhexane, te
Organic peroxides such as rt-butyl peroctanoate, tert-butyl perisobutyrate, tert-butyl peroxyisopropyl carbonate, and methyl 2,2'
-Azohisisobutyrate, 1,1'-Azohiscyclohexylene carbonitrile, 2-phenylazo2,4
-Dimethyl-4-methoxyvaleronitrile, 2-carbamoyl-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylbereronitrile, 2,2'-azobisisobutyronitrile, etc. Examples include compounds.

Polymerization methods include emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization, but bulk polymerization is preferred in order to obtain a highly pure polymer.

The polymer mainly composed of repeating units of methyl methacrylate used as a core component in the present invention has at least 70% repeating units of methyl methacrylate.
Polymers of methyl methacrylate containing (-<, for example, homopolymers of methyl methacrylate or methyl methacrylate and ethyl methacrylate, propyl methacrylate, butyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate, or acrylic Copolymers with methyl acrylate, ethyl acrylate, 2-ethylhexol acrylate, and the like are useful.

Such polymethyl methacrylate and copolymers containing 70% or more of methyl methacrylate are preferred core components that are highly pure, extremely transparent, and readily available.

The optical transmission fiber of the present invention uses a core clad spinneret,
It is manufactured by melt-extruding the core component and cladding component into a composite filament.

The heat-resistant fluorine-containing resin composition of the present invention is used as a cladding component and is melt-coextruded together with the core component using a core clad spinneret. Abnormal phenomena such as foaming and whitening are observed in the cladding over a wide range of 653, and the numerical aperture, which is an important measurement value that is influenced by the interface state between the cladding and the core in optical transmission fibers, is the refraction of the core and the cladding. It has an extremely excellent feature of being close to the theoretical numerical aperture, which can be determined by the numerical aperture. This fact indicates that the fluoroalkyl methacrylate polymer of the present invention has extremely excellent heat decomposition resistance, and not only macroscopically suppresses foaming and whitening, but also microscopically shows extremely fine foaming and depolymerized monomers. It is thought that this suppresses the increase in scattering caused by the cladding and the disturbance at the cladding-core interface. Furthermore, the cladding of the present invention not only has improved heat resistance, but also has superior adhesion to the core compared to conventional cladding materials. Although the cause of this is not clear, it is thought that polyfunctional mercaptans play some role.

The present invention will be specifically explained below using Examples.

In addition, all parts in the examples indicate parts by weight, and all percentages indicate weight %.

In each Example and Comparative Example, the optical transmission performance was evaluated by the following method.

1. Evaluation of optical transmission loss The transmission loss of the obtained optical transmission fiber was measured using the apparatus shown in FIG.

Light emitted from a halogen lamp (102) driven by a stabilized power source (101) is collimated by a lens (10!+), then converted into a monochromatic light by an interference filter (104), and then passed through a light transmission fiber. It is focused at the focal point of a lens (105) with a numerical aperture equal to (100).

Adjustment is made so that the incident end surface (106) of the light transmission fiber is located at this focal point, and light is made to enter the light transmission fiber (100). The light incident from the input end face (106) is attenuated and exits from the output end face (107). This emitted light is converted into electric current by a photodiode (108) with a sufficiently large area.
After being amplified by a current-voltage conversion type amplifier (109), it is read as a voltage value by a voltmeter (110).

Measurement of transmission loss shall be carried out using the following procedure.

First, the optical transmission fiber (100) is made to have a length of 10.
Both end faces were cut at right angles to the fiber axis, finished to have a smooth surface, and the input end face (106) and the output end face (1o7) were placed in the above device.
) so that it does not move during measurement. Read the reading on the voltmeter in a dark room. Let this voltage level be 11.

Next, the room light is turned on, the emission end face (107) is removed from the device, and the optical transmission fiber (100) is cut from this end face at a point (111) of length t. Then, the end face of the optical fiber that is attached to the device is finished to a surface perpendicular to the fiber axis in the same way as the first one, and this is installed as a new output end face in the device. During these operations, to keep the amount of incident light constant,
Be careful not to move the entrance end face (106). Return to the dark room, read the reading on the voltmeter, and call this value ■.

The optical transmission loss (α) is expressed as 1′! by the following formula. :1. do.

Ko\det: Optical fiber long grass (km) II, I2: Light intensity (voltmeter reading) Note that the measurement conditions in the present invention are as follows.

Interference filter (dominant wavelength): 646 nm10 (total length of optical fiber): 15 m1 (cutting length of //): 10 m D (diameter of bobbin): 190 The bobbin is used to make the device compact. , entrance end face (10
The remaining optical fiber is wound around a bobbin (not shown) so that the distance between the optical fiber 6) and the output end face (107) is about 1 part.

2. Measuring the numerical aperture of an optical transmission fiber First, a device for measuring the numerical aperture of an optical transmission fiber will be explained with reference to FIG. (1) It is a parallel light source with a built-in 10-gen lamp.

The output light of this amount of light has a center wavelength of 650 nm and a half-width diameter of 141 nm.
After monochromating through a 5 nm interference filter (2), a lens with a numerical aperture larger than that of the light transmission fiber (
3), the parallel light beams are focused and made incident on one end surface (5) of the optical transmission fiber (4). The end face is cut 7 at right angles to the fiber axis of the optical transmission fiber, finished smooth, and fixed with a fixture (6) so that the fiber axis and optical axis (7) coincide.

After the incident light passes through a light transmission fiber with a total length of 15 m, it exits from the other end face (8). The end face (8), which has been finished into a smooth surface perpendicular to the fiber axis, is aligned with the central axis of the fixed shaft (9), and fixed by the fixture (10) so that the fiber axis and the central axis are perpendicular to each other. Fix it to the shaft (9). (11) is a rotating arm that rotates around the central axis of the fixed shaft (9) and can read the rotation angle θ. (12) is a photomultiplier tube for detecting light, which is placed in the case (13) and measures the amount of light passing through the hole (14) as a fij flow.The hole (14) is 15 pus in diameter and 125 pus from the central axis.
There is a position V in mm.

With the device configured as shown in Figure 2, the distribution of the emitted light is determined by the relationship between the rotation angle θ of the rotating arm and the current of the photomultiplier tube, and the distribution of the emitted light is determined by the relationship between the rotation angle θ of the rotating arm and the current of the photomultiplier tube. .Maximum current I
max, the numerical aperture (N , A , ) can be found from the angular width 2θW in which I max is reduced by 1/2e and the equation (2).

NA-sin θw --q) Example 1 2,2.2-1-lifluoroebur methacrylic acid 10
After mixing and dissolving 0 parts of methyl methacrylate, 2 parts of methyl methacrylate, and 05 parts of triethylene glycol dithiol, 0.05 parts of azohisinobutyronitrile was added as a polymerization catalyst, and 2 parts of methyl methacrylate were mixed and dissolved.
The mixture was placed in an autoclave for bulk polymerization, and the mixture was repeatedly degassed and replaced with nitrogen, and then sealed. After being immersed in hot water at 50°C for 10 hours and polymerized, the internal pressure became 10 Kg/cm2 gauge pressure. After further heating and polymerizing at 70°C for 5 hours, the polymerization was completed at 1 to 1, when the peak due to polymerization exotherm was completed, and a transparent polymer was formed. Obtained union. The polymerization conversion rate was 99%. The refractive index of the obtained It Bommer was 1.418.

This polymer is crushed by a crusher to give a
After separating into 8801 standard 16 mesh passes and 62 meshes A, extrusion was performed at 250°C using a core clad spinneret using polymethyl methacrylate as the core component and the above polymer as the cladding component, and winding was performed at 100 m/min. A composite filament with a diameter of 100 μ and a core diameter of 80 It was obtained.

Microscopic observation revealed that the core-clad interface was perfectly circular, with no air bubbles or foreign matter observed.

The transmission loss of this filament for light with a wavelength of 650 nm was 426 dB/km, for light of 570 nm it was 370 dB/km, and for light of 520 nm it was 41)7 dB/km.

Still, the numerical aperture of this filament is 0.42, the refractive index of the core, n, = 1.492, and the refractive index of the cladding, n
The theoretical aperture fjQ (N
, A, = rzi-] 噭-) o. The value was close to 46.

Examples 2 to 5, Comparative Examples 1 to 2 Polymerization was carried out in the same manner as in Example 1, except that mercaptan, which is not shown in Table 1, was used instead of triethylene glycoldithiol as a chain transfer example in Example 1. Further, the composite filament was processed into a V-shape in the same manner as in Example 1, and the transmission loss and numerical aperture were measured.

The evaluation results are shown in Table 1.

Examples 6 to 15 All procedures were carried out in the same manner as in Example 1, except that the types and amounts of fluoroalkyl methacrylate, copolymerized vinyl monomer, and chain transfer agent were changed as shown in Table 2. Polymerization and spinning were performed, and the transmission loss and numerical aperture of the obtained composite filament were measured. The results are shown in Table 2.

Comparative Examples 5 to 4 After pulverizing the polymer obtained in Comparative Example 1, it was mixed with a heat stabilizer (~
1. Mix and knead 1 part of the hindered phenol shown in Table 1. Perene 1- was obtained. Thereafter, a composite filament was obtained in the same manner as in the example, and the transmission loss and the number of open circuits were measured. Evaluation results

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an apparatus for measuring transmission loss of an optical transmission fiber, and Fig. 2 is a schematic diagram of an apparatus for measuring the opening number of an optical transmission fiber.
FIG. 6 is an explanatory diagram showing an example of numerical aperture measurement. 1. Light source Lens 4 Optical transmission fiber 5.8... Optical transmission fiber 12...
Photomultiplier tube OGjM 100...
Optical transmission fiber 106 ・Incidence end surface 107 ...
・Output end direction 55-

Claims (1)

[Claims] A mixture in which the core component is a polymer mainly composed of repeating units of methyl methacrylate, and polyfluoroalkyl meccrylate or fluoroalkyl methacrylate of 70% by weight or more and a vinyl monomer copolymerizable with it of 60% by weight or less 1. An optical transmission fiber comprising, as a cladding component, a fluoroalkyl methacrylate polymer polymerized by adding a polymerization catalyst and a mercaptan having two or more mercapto groups in one molecule.