JPH10221542A - Manufacture of preform for refraction index distribution type plastic optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the quantity of bubbles in a core and sufficiently suppress optical transmission loss by polymerizing a core part formation monomer, while pressurizing a cylindrical container and applying strain thereon, and forming the core part. SOLUTION: The inside of a cylindrical container of a polymer to become a clad is filled with monomer for forming a core part and the core part formation monomer is polymerized, while pressurizing the cylindrical container and applying strain thereon under such a temperature as deforming the cylindrical container, and formed into the core part. The ordinary formation method for the clad part is that monomer containing a non-polymerizing compound is put in the cylindrical polymerization container as desired so that the monomer is polymerized and formed into it, while rotating the polymerization container in such a state as being held horizontally. The polymerization temperature of the core formation monomer is set to such a temperature as sufficiently deforming the cylindrical container, preferably to be a glass-transition point ±60 deg.C of the polymer for constituting the cylindrical container, and more preferably within the temperature of glass-transition point ±20 deg.C.

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, the present invention relates to a method for manufacturing a preform for a gradient index plastic optical fiber that suppresses the amount of bubbles in a core to provide an optical fiber with low transmission loss.

[0002]

2. Description of the Related Art As a method for producing a preform for a gradient index plastic optical fiber, WO 93/08488 is known.
Discloses a method of forming a refractive index distribution by promoting polymerization of a monomer from the inner wall of a cylindrical container made of a polymer. Specifically, a polymethyl methacrylate (PMMA) tube is used as a cylindrical container, and a core is formed in a hollow portion of the PMMA tube. The PMMA tube is manufactured by heating and polymerizing a monomer tube containing a methyl methacrylate (MMA) monomer solution while rotating the glass tube, and the core is made of a PMM solution containing a non-polymerizable compound.
A preform having a refractive index distribution can be prepared by injecting into a tube A and performing heat polymerization while rotating. The obtained preform is drawn by heating and melting to obtain an optical fiber having a predetermined diameter.

The above-mentioned method is a method for producing a core having a continuously changing refractive index inside a polymer tube which itself becomes a clad. In order to form a refractive index distribution in the core, It is characterized by using a non-polymerizable compound. When a monomer solution as a raw material of a core is injected into a cylindrical polymer tube, the raw material monomer partially dissolves the inner wall surface of the polymer tube. The polymerization proceeds from the inner wall surface having increased viscosity toward the center of the cylinder due to the gel effect, so that the concentration of the non-polymerizable compound having a large refractive index increases toward the center.
Therefore, a continuous refractive index distribution is formed. Here, the polymer forming the cylindrical tube serving as the clad is a polymer obtained by polymerizing the same monomer as a part or most of the polymer serving as the core, provided that the polymer is soluble in a monomer solution which is a raw material of the core. is there.

JP-A-5-173026 discloses a method for producing a preform for a plastic optical fiber by producing a cylindrical tube which itself becomes a clad, and polymerizing and solidifying a monomer solution which becomes a core portion therein. doing. The point at which the polymerization proceeds from the inner surface of the hollow tube toward the center to form a continuously changing refractive index distribution is described in WO 93/084 described above.
88 is the same as the method 88, except that a polymerizable monomer having a different refractive index is used instead of a non-polymerizable compound as the second component for forming the refractive index distribution.

JP-A-61-130904 also discloses a method for producing a preform for a plastic optical fiber by producing a cylindrical tube which itself becomes a clad, and polymerizing and solidifying a monomer solution which becomes a core portion therein. Has been disclosed. The difference from the invention disclosed in the above publication is that the solution used for forming the core is, for example, when an MMA monomer is used, the reactivity ratio of the MMA monomer and the monomer having a lower refractive index than that of the MMA monomer is higher than that of the PMMA. It is a mixed solution. In the method described in JP-A-61-130904, as the polymerization of MMA having a high reactivity ratio proceeds from the inner wall of the polymer cylindrical tube, copolymerization of a monomer having a low reactivity ratio toward the center occurs. The ratio increases and a refractive index distribution is formed.

However, each of the above-mentioned prior art preform manufacturing methods has a problem that bubbles are generated during polymerization of the core-forming monomer. Such bubbles cause the internal solution to drop due to shrinkage (polymerization shrinkage) caused by polymerization of the monomer due to the monomer solution or gas dissolved in the cylindrical tube.
It is formed by foaming due to heating for polymerization or heat of polymerization. Further, decomposition by-products of the polymerization initiator, derivatives of the monomer, and the like contained in the monomer solution may be vaporized during polymerization to form bubbles.

When an optical fiber is manufactured by drawing a preform having a core portion containing air bubbles, air bubbles remain in the core of the optical fiber, but light transmitted at the air bubble interface in the core is scattered. Therefore, the optical transmission loss increases. In addition, if the bubbles are non-uniform in the length direction of the optical fiber, it is not possible to maintain uniform transmission performance in the length direction. Therefore, air bubbles wherever they are generated should be eliminated as much as possible.

Japanese Patent Application Laid-Open No. 8-170306 discloses a method for producing a preform that reduces the amount of air bubbles in the core.
A method has been proposed in which a heat-shrinkable tube is arranged around a polymer cylindrical container serving as a clad when a core-forming monomer is thermally polymerized. This method is intended to suppress the decrease in the internal pressure caused by the polymerization shrinkage of the core-forming monomer by shrinking the heat-shrinkable tube, thereby reducing the generation of bubbles. However, once shrinked tubing cannot be reused, increasing the amount of waste and environmentally unfriendly. Further, the heat-shrinkable tube is usually expensive because it is manufactured from a fluororesin. In addition, the use of a heat-shrinkable tube has the following problems. (1) It is difficult to uniformly shrink the heat-shrinkable tube in the length direction, so that the outer diameter of the obtained preform becomes uneven, and it is difficult to produce a preform of constant quality. is there. (2) The pressure applied to the cylindrical container cannot be controlled by the shrinkage of the heat-shrinkable tube. The polymerization conditions of the core-forming monomer are restricted, for example, it is necessary to set the polymerization temperature according to the state of the heat-shrinkable tube.

[0009]

An object of the present invention is to provide an optical fiber which can suppress the amount of bubbles in the core, which is a disadvantage of the above-mentioned prior art, without using a heat-shrinkable tube, and has a sufficiently low optical transmission loss. It is an object of the present invention to provide a method for producing a preform for a given gradient index plastic optical fiber.

[0010]

In order to solve the above-mentioned problems, the present invention provides a method in which a core-forming monomer is filled in a cylindrical container of a polymer serving as a clad, and a temperature at which the cylindrical container is deformed. And a method of producing a preform for a gradient index plastic optical fiber, comprising polymerizing the core-forming monomer to form a core while applying pressure to the cylindrical container to apply strain. I do.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the production method of the present invention, first,
A cylindrical cladding is formed. The method of forming the clad is not particularly limited, but usually, if necessary, a monomer containing a non-polymerizable compound is placed in a cylindrical polymerization vessel, and the monomer is polymerized while rotating while horizontally holding the polymerization vessel. Form. The polymerization vessel is usually made of glass,
It may be made from other materials, for example metal. The size of the polymerization container may be appropriately selected according to the size of the preform to be manufactured. The cylindrical clad portion can also be produced by hollowing out a cylindrical clad polymer mass. If desired, a polymer containing a non-polymerizable compound can be extruded to produce a cylindrical shape.

As the polymer forming the clad portion,
A colorless and highly transparent plastic conventionally used for a plastic optical fiber can be used. Examples of the monomer that provides such a plastic include methacrylates, styrene compounds, fluorinated acrylates, fluorinated methacrylates, and the like as follows: (a) Methacrylate and acrylic acid Esters Methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, t-butyl methacrylate, benzyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, diphenylmethyl methacrylate, etc .; methyl acrylate, ethyl acrylate, t-butyl acrylate (B) styrene-based compounds styrene, α-methylstyrene, chlorostyrene, bromostyrene, dichlorostyrene, dibromostyrene, etc .; (c) fluorinated acrylate 2,2,2-trifluoro B ethyl acrylate; (d) a fluorinated methacrylate ethyl 1,1,2-trifluoroethyl methacrylate.

To such a monomer, a polymerization initiator and, if desired, a non-polymerizable compound and an additive (for example, a chain transfer agent) are added, 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 from the size of the polymerization vessel and the thickness of the clad. 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 optional non-polymerizable compound is a liquid at or above room temperature,
A colorless and transparent compound that is compatible with the polymer used for the clad and the core, has a high boiling point, and is used. Examples of such compounds include the following compounds: benzoic acid esters such as benzyl benzoate; sebacic acid esters such as dibutyl sebacate; and other alkyl dibasic acid esters; phthalic acid esters such as dimethyl phthalate and dioctyl phthalate. And halogenated compounds such as bromobenzene, and sulfur compounds such as diphenyl sulfide.

The concentration of the non-polymerizable compound contained in the clad portion is 20% by weight or less, preferably 0.1% by weight or more,
In particular, it is in the range of 1 to 10% by weight and is set lower than the concentration of the non-polymerizable compound contained in the core portion. The solution serving as the raw material of the polymer forming the core portion is adjusted by mixing a non-polymerizable compound with the monomer used for forming the cladding portion.

To form the core portion, a polymerization initiator, a chain transfer agent, and the like are added to the mixture of the monomer and the non-polymerizable compound as described above, and the mixture is placed in a polymerization container having a clad portion formed therein. While heating, the mixture is heated and polymerized. A core having a predetermined thickness is formed, and one unreacted monomer is formed.
The polymerization is terminated when the content becomes 0% or less, preferably 5% or less. During the formation of the core, the non-polymerizable compound added as desired together with the polymer from the inner surface of the clad is dissolved in the monomer solution serving as the core. Become smooth.

One of the features of the production method of the present invention is that the cylindrical container is pressurized and strained during polymerization of the core-forming monomer. Pressurization is preferably performed with an inert gas, for example, a nitrogen gas, an argon gas, a helium gas, or the like. Unlike a heat-shrinkable tube, pressurization can apply uniform stress or strain to the entire cylindrical container, and the polymerization temperature, pressurization time and pressure can be freely controlled, so the preform has a length Since the fiber has uniform properties in the directions, the quality of the finally obtained optical fiber becomes constant.

The pressure of the inert gas is preferably from 0.8 to
It is 50 kgf / cm ² . When the pressure is less than 0.8 kgf / cm ² , the pressure is insufficient, the cylindrical container cannot be effectively shrunk, and bubbles are generated in the formed core portion. On the other hand, if it exceeds 50 kgf / cm ² , the cylindrical container is excessively shrunk, the cross-sectional area of the core portion of the preform becomes too small, and the core diameter of the finally obtained optical fiber becomes small, so that the light incidence Becomes difficult.

In the production method of the present invention, strain is preferably applied so that the cross-sectional area of the hollow portion of the cylindrical container is equal to or less than the volume of the core-forming monomer after polymerization shrinkage. For example, in the case of methyl methacrylate, the volume shrinkage due to polymerization is about 21%. Therefore, the pressure may be increased so that the volume of the hollow portion of the cylindrical container is 79% or less of that before polymerization. If the strain amount (shrinkage amount) is smaller than the polymerization shrinkage amount of the monomer, the inside of the container becomes a negative pressure, so that bubbles are easily generated. The polymerization shrinkage of styrene is 14%, and the polymerization shrinkage of ethyl acrylate is 17%.

The polymerization temperature of the monomer for forming the core is a temperature at which the cylindrical container can be sufficiently deformed, preferably the glass transition point of the polymer constituting the cylindrical container ± 60 ° C, more preferably ± 20 ° C. Temperatures in the range of ° C. When the polymerization temperature is low, the elastic modulus of the polymer constituting the cylindrical container is large, and a large pressure is required for deformation. on the other hand,
When the polymerization temperature is high, the cylindrical container is melted, fluidity appears, and the shape of the container becomes unstable. In addition, the polymer constituting the container is dissolved in the monomer.

If the monomer is degassed before the polymerization of the core-forming monomer, the generation of bubbles can be further reduced. Degassing is performed at a pressure lower than 300 Torr, preferably at a pressure lower than 0.3 Torr.
It is preferably performed at 0001 to 100 Torr. that time,
It is preferable to freeze the monomer solution with liquid nitrogen or the like so that the monomer, polymerization initiator, additives and the like do not evaporate.

[0022]

According to the present invention, the polymerization conditions can be easily controlled, the quality of the obtained preform is constant, and the amount of bubbles contained in the core of the preform can be reduced. The transmission loss of the optical fiber manufactured from the reform can be reduced.

[0023]

The present invention will be specifically described below with reference to examples. Example 1 Cylindrical polymerization of a solution prepared by blending methyl methacrylate (MMA) monomer with 0.1% by weight of benzoyl peroxide as an initiator and 0.15% by weight of n-butyl mercaptan as a chain transfer agent was performed. The mixture was sealed in a container, and while being held horizontally, the polymerization was carried out by heating at 80 ° C. while rotating the polymerization container at 2000 rpm. After polymerization for 20 hours, heat treatment was performed at 120 ° C. for another 20 hours. PM removed from polymerization vessel
The weight average molecular weight of the MA cylindrical tube is 120,000, the glass transition temperature is 106 ° C., the outer diameter of the cylindrical tube is 26 mm,
The inner diameter was 20 mm.

In the hollow part of the cylindrical tube, 1: 5 with respect to MMA
A solution containing benzyl benzoate at a ratio of (weight ratio) was injected. After injecting the core solution into the hollow portion of the cylindrical tube, 10 Torr at 1 Torr to remove dissolved gas in the solution.
Degassed for a minute. After the tube was sealed, the mixture was heated and polymerized at 110 ° C. for 40 hours while rotating at 5 rpm while being kept horizontal. The polymerization of the core-forming monomer is performed by nitrogen gas in a PMMA cylindrical tube in a pressurized chamber containing a heater and a gauge pressure of 5.9 kg.
Pressing was performed to f / cm ² . The cylindrical tube was supported by a stainless steel cylindrical mesh and rotated by a motor together with the mesh so that the PMMA cylindrical tube was not bent by heating. The outer diameter of the preform after polymerization was 23.2 mm, and the core diameter was 17.6 mm.

After the polymerization, the preform was drawn into a fiber having a diameter of 750 μm, and the transmission loss was measured by a cutback method. It was measured by cutting 50 m to 5 m. The transmission loss was 149 dB / km at a wavelength of 650 nm.

Example 2 A solution in which 0.1% by weight of benzoyl peroxide and 0.2% by weight of n-butylmercaptan were mixed with MMA monomer was sealed in a cylindrical polymerization vessel having an inner diameter of 26 mm and held horizontally. 8 while rotating the polymerization vessel at 2000 rpm
Heat polymerization was carried out at 0 ° C. After polymerization for 20 hours, heat treatment was performed at 120 ° C. for another 20 hours. PMM taken out of polymerization vessel
The weight average molecular weight of the cylindrical tube A was 100,000, the glass transition temperature was 105 ° C., and the cylindrical tube had an outer diameter of 26 mm and an inner diameter of 20 mm.

In the hollow portion of the cylindrical tube, 1: 5 with respect to MMA
A solution containing diphenyl sulfide at a ratio of (weight ratio) was injected. After injecting the core solution into the hollow portion of the cylindrical tube, 0.1 Torr was applied to remove dissolved gas in the solution.
For 10 minutes. At this time, the operation of freezing and melting was repeated with liquid nitrogen to remove gas dissolved in the solution. After sealing, rotate the tube at 5 rpm while keeping it horizontal.
Heat polymerization was carried out at 10 ° C. for 40 hours. This polymerization was performed according to Example 1.
In the same manner as described above, a gauge pressure of 5.2 kgf / cm ² was applied in a pressurized chamber. The outer diameter of the preform after polymerization is 2
3 mm and a core diameter of 17.2 mm. After the polymerization, the preform was drawn into a fiber having a diameter of 750 μm.
Transmission loss was measured in the same manner as described above. The transmission loss was 151 dB / km at a wavelength of 650 nm.

Example 3 A solution in which 0.1% by weight of benzoyl peroxide and 0.15% by weight of n-butylmercaptan were mixed with MMA monomer was sealed in a cylindrical polymerization vessel having an inner diameter of 26 mm, and held horizontally. 8 while rotating the polymerization vessel at 2000 rpm
Heat polymerization was carried out at 0 ° C. After polymerization for 20 hours,
Heat treated for hours. The PMMA cylindrical tube removed from the polymerization vessel had a weight average molecular weight of 120,000, a glass transition temperature of 120 ° C., an outer diameter of the cylindrical tube of 26 mm, and an inner diameter of 2 mm.
It was 0 mm. In the hollow part of the cylindrical tube,
A solution containing diphenyl sulfide at a ratio of 5 (weight ratio) was injected. After the solution serving as a core was injected into the hollow portion of the cylindrical tube, the solution was degassed at 1 Torr for 10 minutes in order to remove dissolved gas in the solution. At that time, to prevent the liquid from evaporating,
Frozen in liquid nitrogen.

After the tube was sealed, the mixture was heated and polymerized at 115 ° C. for 40 hours while rotating horizontally at 5 rpm. This polymerization was carried out in the same manner as in Example 1 by pressurizing a cylindrical tube of PMMA with a nitrogen gas to a gauge pressure of 3 kgf / cm ² in a chamber.
The outer diameter of the preform after polymerization was 23 mm and the inner diameter (core diameter) was 17.6 mm. After the polymerization, the preform is 75 mm in diameter.
A 0 μm fiber was drawn, and the transmission loss was measured in the same manner as in Example 1. The transmission loss was 148 dB / km at a wavelength of 650 nm.

Comparative Example 1 0.1% by weight of benzene peroxide and n
-A solution containing 0.15% by weight of butyl mercaptan was sealed in a cylindrical polymerization vessel having an inner diameter of 26 mm, and the polymerization vessel was rotated at 2,000 rpm while being held horizontally.
Heat polymerization was carried out at 0 ° C. After polymerization for 20 hours, additional 120 ° C
For 20 hours. PMM taken out of polymerization vessel
The weight average molecular weight of the cylindrical tube A was 120,000, the glass transition temperature was 106 ° C., the outer diameter of the cylindrical tube was 26 mm, and the inner diameter was 20 mm.

In the hollow portion of the cylindrical tube, 1: 5 with respect to MMA
A solution containing diphenyl sulfide at a ratio of (weight ratio) was injected. After injecting the core solution into the hollow portion of the cylindrical tube, 1 Torr at 1 Torr to remove dissolved gases in the solution.
Degassed for 0 minutes. After the tube was sealed, the mixture was heated and polymerized at 110 ° C. for 40 hours while rotating at 5 rpm while being kept horizontal. This polymerization was carried out at atmospheric pressure and without attaching a shrink tube or the like. 26 mm outer diameter of the preform after polymerization,
The core diameter was 18 mm. In the core of the preform,
Many bubbles were generated. After the polymerization, the preform was drawn into a fiber having a diameter of 750 μm, and the transmission loss was measured in the same manner as in Example 1. Transmission loss is 650nm
Was 1210 dB / km.

Comparative Example 2 0.1% by weight of benzene peroxide and n
-Solution containing 0.2% by weight of butyl mercaptan,
It is sealed in a cylindrical polymerization vessel having an inner diameter of 26 mm, and kept horizontally to 80 ° C. while rotating the polymerization vessel at 2000 rpm.
And heat polymerization. After polymerization for 20 hours, the mixture was further heated at 120 ° C for 2 hours.
Heat treatment was performed for 0 hours. The PMMA cylindrical tube removed from the polymerization vessel had a weight average molecular weight of 120,000, a glass transition temperature of 105 ° C, and an outer diameter of the cylindrical tube of 26 mm and an inner diameter of 20 mm.

In the hollow portion of the cylindrical tube, 1: 5 with respect to MMA
A solution containing benzyl benzoate at a ratio of (weight ratio) was injected. After injecting the core solution into the hollow portion of the cylindrical tube, 10 Torr at 1 Torr to remove dissolved gas in the solution.
Minutes. After the tube was sealed, the mixture was heated and polymerized at 115 ° C. for 40 hours while being rotated horizontally at 5 rpm while being held horizontally. This polymerization was carried out at atmospheric pressure and without attaching a shrink tube or the like. The outer diameter of the preform after polymerization was 26 mm, and the core diameter was 18 mm. Many bubbles were generated in the core of the preform. After the polymerization, the preform was drawn into a fiber having a diameter of 750 μm, and the transmission loss was measured in the same manner as in Example 1. The transmission loss was 1330 dB / km at a wavelength of 650 nm.

Comparative Example 3 0.1% by weight of benzene peroxide and n
-A solution containing 0.15% by weight of butyl mercaptan was sealed in a cylindrical polymerization vessel having an inner diameter of 26 mm, and the polymerization vessel was rotated at 2,000 rpm while being held horizontally.
Heat polymerization was carried out at 0 ° C. After polymerization for 20 hours, additional 120 ° C
For 20 hours. PMM taken out of polymerization vessel
The weight average molecular weight of the cylindrical tube A was 100,000, the glass transition temperature was 105 ° C., and the cylindrical tube had an outer diameter of 26 mm and an inner diameter of 20 mm.

In the hollow portion of the cylindrical tube, 1: 5 with respect to MMA
A solution containing diphenyl sulfide at a ratio of (weight ratio) was injected. After injecting the core solution into the hollow portion of the cylindrical tube, 1 Torr at 1 Torr to remove dissolved gases in the solution.
Degassed for 0 minutes. After the tube was sealed, the mixture was heated and polymerized at 110 ° C. for 40 hours while rotating at 5 rpm while being kept horizontal. The polymerization of the core was carried out in the same chamber as in Example 1 by applying a gauge pressure of 0.4 kgf / cm ² . The outer diameter of the preform after polymerization was 25.4 mm, and the core diameter was 18 mm. Many bubbles were generated in the core of the preform. After the polymerization, the preform was drawn into a fiber having a diameter of 750 μm, and the transmission loss was measured in the same manner as in Example 1. The transmission loss was 1160 dB / km at a wavelength of 650 nm.

Claims (6)

[Claims] 1. A core-forming monomer is filled in a cylindrical container of a polymer to be a clad, and the cylindrical container is pressurized and deformed at a temperature at which the cylindrical container is deformed. A method for producing a preform for a gradient index plastic optical fiber, comprising forming a core by polymerizing a core-forming monomer. 2. A cylindrical container serving as a clad is manufactured by putting a monomer containing a non-polymerizable compound into a cylindrical polymerization container and polymerizing the monomer while rotating the polymerization container while keeping the polymerization container horizontal. The manufacturing method according to claim 1. 3. The production method according to claim 1, wherein the polymerization of the core-forming monomer is carried out at a temperature of a glass transition point of the polymer forming the cylindrical container ± 60 ° C. 4. The method according to claim 1, wherein the cylindrical container is pressurized with an inert gas. 5. The pressure of the inert gas is 0.8 to 50 kg.
The production method according to claim 4, wherein f / cm ² is f / cm ² . 6. The method according to claim 1, wherein a strain is applied so that the cross-sectional area of the hollow portion of the cylindrical container is equal to or less than the cross-sectional area of the monomer for forming the core after polymerization shrinkage. .