JPH09178958A - Production of preform for distributed refractive index plastic optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce a preform for a distributed refractive index plastic optical fiber suitable for high-speed transmission. SOLUTION: A layer of a clad part polymer is formed on the inside wall of a cylindrical vessel. A layer of a core part polymer contg. a compd. having a high refractive index is formed on the inner side of the clad part polymer. A gel of the core part polymer contg. the compd. having the high refractive index is then packed into the hollow part at the center and is solidified by polymn. or one end of the hollow part is sealed and while the pressure in the hollow part is reduced, the hollow part is closed by heating from the circumference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a preform for a gradient index plastic optical fiber,
More specifically, it relates to a method for manufacturing a preform for a gradient index plastic optical fiber suitable for high-speed transmission of light.

[0002]

2. Description of the Related Art As a method for producing a preform for a gradient index plastic optical fiber, Japanese Patent Application Laid-Open No. 60-1195.
No. 09 and JP-A-60-119510 disclose
A mixture of two or more kinds of monomers having different refractive index after polymerization or after polymerization and specific gravity before and after polymerization at a predetermined ratio, and while rotating a horizontally arranged cylindrical container, a cylindrical solution in order from a solution having a lower refractive index is used. Disclosed is a method of supplying the same to a cylindrical container and polymerizing them concentrically. According to this method, a refractive index distribution that changes stepwise is formed.

In this method, more layers must be stacked in order to form a continuous and smooth refractive index distribution. However, the more layers, the longer it takes to manufacture the preform. , The manufacturing cost rises. Further, the polymer used for each layer is prepared by copolymerization of two or more kinds of monomers having different refractive indexes. However, in the method of adjusting the refractive index by changing the charging ratio of the two or more kinds of monomers, the copolymer Phase separation occurs according to the chain distribution, and scattering loss increases.

Japanese Unexamined Patent Publication (Kokai) No. 4-29043 discloses a method for producing a plastic for a plastic optical fiber by polymerizing and solidifying a monomer solution serving as a core portion in a hollow tube. Two or more kinds of monomers having mutually different refractive indexes are used for the monomer solution forming the core portion, and the polymerization of the monomer solution proceeds from the inner wall surface of the hollow tube. This method utilizes the difference in reactivity ratios to form a continuously varying refractive index profile. That is, when a monomer having a low refractive index is used as a monomer having a high reactivity ratio and a monomer having a high refractive index is used as a monomer having a low reactivity ratio, a reaction occurs from the inner surface of the hollow tube, so that the reactivity ratio is close to the inner surface of the hollow tube. The high-refractive-index monomer with a high reactivity is preferentially polymerized, and the high-refractive-index monomer with a low reactivity ratio is gradually concentrated toward the center,
A refractive index distribution is formed as a whole. However, a monomer having a low reactivity ratio may remain as a monomer without being polymerized, and as a result, the residual monomer is vaporized in the next drawing step to generate bubbles. Bubbles increase the scattering loss of optical fibers, and such optical fibers are impractical.

Japanese Unexamined Patent Publication No. 5-173026 discloses a method for producing a preform for a plastic optical fiber by producing a hollow tube and polymerizing and solidifying a monomer solution to be a core portion therein. The point that the polymerization proceeds from the inner surface of the hollow tube toward the center to form a continuously changing refractive index distribution is the same as the method disclosed in Japanese Patent Laid-Open No. 4-29043. The same applies to the use of a mixture of two or more different monomers,
There are differences in the properties of the monomers used. That is, in the method disclosed in Japanese Patent Application Laid-Open No. 4-29043, the refractive index distribution is formed by utilizing the difference in reactivity ratio, whereas in this method, the reactivity ratio is almost the same, and The difference is used to form the refractive index. However, this method is also disclosed in JP-A-60-119509 and JP-A-60-1195.
It has the same drawbacks as the method described in Japanese Patent No.

[0006]

SUMMARY OF THE INVENTION The present invention is intended to provide a method of manufacturing a preform for a gradient index plastic optical fiber, which can solve the above-mentioned drawbacks of the prior art.

[0007]

A method of manufacturing a preform for a gradient index plastic optical fiber according to the present invention comprises forming a layer of a clad polymer on the inner wall of a cylindrical container and arranging the clad polymer layer inside the clad polymer layer. A layer of a core polymer containing a compound having a high refractive index is formed, and then the central hollow part is filled with a gel of a core polymer containing a compound having a high refractive index to polymerize or solidify the hollow part. And sealing the hollow portion at one end and heating the surrounding portion while reducing the pressure in the hollow portion to close the hollow portion.

With this, it is not necessary to prepare a plurality of monomer solutions whose concentrations and refractive indexes are adjusted, and the refractive index is not changed stepwise, so that the manufacturing time can be shortened and the refractive index can be gradually increased. It is not necessary to prepare a number of different solutions.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION An apparatus for polymerization used in the production method of the present invention is shown in FIG. This apparatus comprises a chuck portion 2 capable of holding a polymerization container 1, a motor 3 connected to the chuck portion 2,
A heating device 4 capable of heating the entire polymerization container may be provided. A speed change gear (not shown) may be provided between the motor 3 and the chuck portion 2 in order to control the rotation speed of the polymerization container. The polymerization vessel is usually made of glass, but may be made of other materials, such as metal. The size of the polymerization container may be appropriately selected according to the size of the preformer to be manufactured.

Using such a device, first, the core portion is formed on the inner wall of the polymerization container. As the polymer forming the core portion, a colorless and highly transparent plastic conventionally used for plastic optical fibers can be used. Examples of monomers that give such plastics include the following methacrylic acid esters, styrenic compounds, fluorinated acrylic acid esters, and fluorinated methacrylic acid esters: (a) Methacrylic acid ester Methyl methacrylate , Ethyl methacrylate, isopropyl methacrylate, t-butyl methacrylate, benzyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, diphenylmethyl methacrylate, etc .; (b) Styrene-based compounds Styrene, α-methylstyrene, chlorostyrene, bromo Styrene, dichlorostyrene, dibromostyrene, etc .; (c) Fluorinated acrylate ester 2,2,2-trifluoroethyl acrylate, etc .; (d) Fluorinated ethyl methacrylate 1,1,2-trifluoroethyl methacrylate, etc.

A polymerization initiator and, if desired, an additive (for example, a chain transfer agent) are added to such a monomer, and an appropriate amount is placed in a polymerization vessel. While the polymerization container is being rotated by a motor, the monomer is polymerized on the inner wall of the polymerization container by heating with a heating device to form a clad portion. The amount of the monomer may be determined based on the size of the polymerization container and the thickness of the clad portion. Alternatively, an excessive amount of monomer may be added, polymerization may be stopped when a clad portion having a desired thickness is formed, and unnecessary monomer may be discharged from the polymerization container.

The solution used as the raw material of the polymer forming the core portion is prepared by mixing the monomer used for forming the cladding portion with a compound having a refractive index higher than that of the polymer formed from the monomer. Such a compound can be easily selected according to the refractive index of the polymer in the clad portion in consideration of the following conditions. (1) The refractive index is larger than that of the polymer in the clad part. (2) The solubility parameter is almost equal to that of the polymer in the clad part. The greater the difference in solubility parameter, the easier the two will separate. When separated, it becomes cloudy and the light scattering loss increases.

For example, when polymethylmethacrylate is used as the polymer of the clad portion, a phthalate ester such as dioctyl phthalate, a sulfur compound, a benzoate ester, or a halogenated compound can be used as a compound having a high refractive index.

To form the core part, a polymerization initiator, a chain transfer agent, etc. are added to the mixture of the monomer and the high refractive index compound as described above, and the mixture is put into the polymerization container having the clad part and the polymerization container is rotated. While heating, heat to polymerize. The polymerization is terminated when a core having a predetermined thickness is formed.

At this point, the hollow portion remains inside the core portion. There are two methods for closing this hollow portion. One is a method of filling a gel of a polymer forming the core portion, and the other is a method of heating the collapsed portion / core portion composite while depressurizing the hollow portion to collapse the hollow portion.

In the method of filling the polymer gel, the monomer mixture for forming the core portion is separately polymerized to prepare a polymer gel, which is then filled in the hollow portion. In the method of closing the hollow portion by decompression, one end of the hollow portion is sealed and heated from the surroundings, and the hollow portion is deaerated under reduced pressure. The heating is preferably performed from the sealed end to the other end. The depressurization may be a pressure lower than the atmospheric pressure depending on other conditions such as the heating temperature and the type of plastic. There is no need to decompress excessively.

[0017]

According to the manufacturing method of the present invention, a gradient index plastic optical fiber preform suitable for high-speed transmission can be easily manufactured.

[0018]

EXAMPLES Hereinafter, the present invention will be described more specifically by showing examples. Example 1 (1) In a glass cylindrical container having an inner diameter of 19 mm and a length of 200 mm,
25 g of methyl methacrylate (MMA), 0.2% by weight of benzoyl peroxide as an initiator, and 0.2% by weight of a chain transfer agent were added, and after purging with nitrogen, both ends of the container were sealed. Using the apparatus shown in FIG. 1, while rotating the cylindrical container at 2500 rpm and heating at 90 ° C. for 24 hours for polymerization, the thickness is 2 mm.
Of PMMA was formed on the inner wall of the glass container. After this, the PMMA layer is kept in the glass tube at 110 ° C. for 24 hours.
Heat treated for hours.

(2) The solution used as the raw material for the core part was prepared by dissolving benzyl benzoate in MMA. Two types of solutions were prepared for forming the core portion. That is, the first solution was prepared by mixing 15% by weight of benzyl benzoate with MMA, 0.1% by weight of benzoyl peroxide as a polymerization initiator, and 0.2% by weight of a chain transfer agent. The solution is M
25% by weight of benzyl benzoate based on MA, 0.1% by weight of benzoyl peroxide as a polymerization initiator, 0.2 of a chain transfer agent
Prepared by mixing wt%.

30 g of the first solution was poured into a container, the atmosphere was replaced with nitrogen, and both sides of the container were sealed and attached to the apparatus shown in FIG. This was polymerized at a temperature of 80 ° C. and a rotation speed of 2500 rpm for 24 hours. Then, it heat-processed at 110 degreeC for 24 hours.
By polymerization, a hollow tube having an inner diameter of 6 mm having a two-layer structure was obtained. The refractive index distribution of the laminate was measured by an interference microscope.
The refractive index distribution is shown in FIG. Inner layer of hollow tube (core part)
Shows a GI type distribution morphology in which the refractive index changes continuously.

(3) In a separate container, add the second solution at 80 ° C. to 3
A gel that was polymerized for a period of time was prepared, poured into a hollow portion, sufficiently deaerated under vacuum, the container was closed, and the gel was polymerized and solidified at a temperature of 80 ° C. for 24 hours while rotating at 5 rpm. After that, heat treatment was performed at 110 ° C. for 24 hours to complete the polymerization. When the refractive index distribution of the preform thus manufactured was measured by an interference microscope, a refractive index distribution suitable for high speed transmission was formed as shown in FIG.

Example 2 One end of the hollow tube obtained in the step (2) of Example 1 was sealed, and the hollow part of the tube was depressurized from the other end by a rotary pump while being heated to 150 ° C. by a cylindrical heating device. Heated to. The heating was gradually performed from the closed end toward the open end, and was heated and melted without a gap. The diameter of the closed hollow is 18
It was a rod shape of mm. When the refractive index distribution was measured by an interference microscope, a refractive index distribution suitable for high speed transmission was formed as shown in FIG.

Example 3 A glass cylindrical container having an inner diameter of 19 mm and a length of 200 mm was charged with 15 g of methyl methacrylate (MMA), 0.2% by weight of benzoyl peroxide as an initiator and 0.2% by weight of a chain transfer agent, and charged with nitrogen. After replacement, both ends of the container were sealed. This is 2
By heating and polymerizing at 80 ° C. for 24 hours while rotating at 500 rpm, a PMMA tube can be produced in a glass container by centrifugal force. The thickness of the polymerized tube was 1 mm. This is heat-treated at 110 ° C. for 24 hours in a glass tube,
The solution of the core part was injected. The solution used as the raw material of the core part is
It is a mixture of MMA and a compound having a refractive index higher than PMMA. In this example, benzyl benzoate was used as the compound forming the refractive index profile.

Upon polymerization of the core part, a compound having a high refractive index was gradually added to MMA. Since the polymer is deposited on the inner wall of the tube as the polymerization progresses, if a compound having a high refractive index is continuously supplied, the concentration becomes higher toward the center. MMA solution contains 15% by weight of benzyl benzoate
Was gradually added over 8 hours until the concentration reached. The solution contains 0.1% by weight of benzoyl peroxide as a polymerization initiator,
A mixture of 0.2% by weight of a chain transfer agent was polymerized to prepare a hollow tube. 30 g of the MMA solution was poured into a container, the atmosphere was replaced with nitrogen, and both ends were sealed and attached to a rotating device. This was polymerized at a temperature of 80 ° C. and a rotation speed of 2500 rpm. At that time, a compound having a high refractive index was supplied at a rate of 0.56 g / hour. After 8 hours, supply was stopped and 1
The rotation and polymerization were continued for 2 hours (total 20 hours). After 20 hours, heat treatment was performed at 110 ° C. for 24 hours to produce a hollow tube.
By the polymerization, a hollow tube having an inner diameter of 6 mm having a two-layer structure was obtained, and the refractive index distribution of each layer was the same as in FIG. The refractive index distribution was measured with an interference microscope. The inner layer of the hollow tube showed a GI type distribution morphology in which the refractive index changed continuously.

After sealing one end of the hollow tube, a polymer gel was injected into it. The gel was prepared by using MMA and 25% by weight of benzyl benzoate based on MMA, 0.1% by weight of benzoyl peroxide as a polymerization initiator and 0.2% by weight of a chain transfer agent.
Were mixed and polymerized at 80 ° C. for 3 hours. The polymer gel prepared in a separate container was poured into the hollow portion, sufficiently deaerated under vacuum, then sealed, and the polymer gel was polymerized and solidified in the hollow portion while rotating at 5 rpm. The polymerization conditions are a temperature of 80 ° C.
Polymerization for 24 hours and then at 110 ° C to complete the polymerization.
And heat treated for 24 hours. When the refractive index distribution of the preform thus manufactured was measured by an interference microscope, a secondary distribution suitable for high speed transmission was formed as shown in FIG. As described above, a plastic optical fiber whose refractive index continuously changes, which is suitable for high-speed transmission, can be obtained by this manufacturing.

[Brief description of the drawings]

FIG. 1 is a schematic view of an example of an apparatus used in the manufacturing method of the present invention.

FIG. 2 is a diagram showing a refractive index distribution of a plastic optical fiber preform intermediate obtained in the step (3) of Example 1.

FIG. 3 is a diagram showing a refractive index distribution of a plastic optical fiber preform obtained in the final step of Example 1.

FIG. 4 is a diagram showing a refractive index distribution of the plastic optical fiber preform obtained in Example 2.

Claims (1)

[Claims] 1. A layer of a clad polymer is formed on an inner wall of a cylindrical container, and a layer of a core polymer containing a compound having a high refractive index is formed inside the clad polymer layer,
Then, in the central hollow portion, a gel of a core polymer containing a compound having a high refractive index is filled and polymerized or solidified,
Alternatively, a method of manufacturing a preform for a gradient index plastic optical fiber, which comprises sealing one end of the hollow portion and heating the surrounding portion while reducing the pressure of the hollow portion to close the hollow portion.