JP3102181B2 - Manufacturing method of optical fiber clad material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical fiber clad material which is excellent in colorless transparency, has a low residual monomer content, and has a low refractive index.

[0002]

2. Description of the Related Art An optical fiber is generally composed of a combination of two kinds of materials, a core and a clad having a lower refractive index than the core.

[0003] For the core, a polymer having excellent transparency such as typified by quartz, multi-component glass or polymethyl methacrylate is used.

On the other hand, the clad is required to have a lower refractive index than the core material in order to keep light inside the core, and fluorine-containing resins are widely used.

[0005] Conventionally, the fluorine-containing resin includes: a. Vinylidene fluoride / tetrafluoroethylene copolymer (JP-B-63-67164) and hexafluoroacetone / vinylidene fluoride copolymer (JP-A-61-22)
No. 305) and vinylidene fluoride copolymers, b. (Meth) acrylate / methyl methacrylate copolymer having a linear fluoroalkyl group (JP-B-43-197)
8978, JP-A-49-107790) and short-chain fluoroalkyl methacrylate copolymers; c. α-Fluoroacrylate copolymer (JP-A-59
No. 227908) has been proposed.

However, although vinylidene fluoride copolymers are excellent in mechanical properties and thermal stability, they are inferior in transparency due to crystallinity, and short-chain fluoroalkyl methacrylate copolymers have good colorless transparency. The refractive index is not so low and the mechanical properties are inferior.Although the α-fluoroacrylate copolymer has a low refractive index, it is easily colored by thermal desorption of the α-fluoro group and does not have sufficient colorless transparency. However, none of them had advantages and disadvantages and could sufficiently satisfy the requirements as cladding materials for optical fibers.

Accordingly, the following copolymers using a long-chain fluoroalkyl (meth) acrylate have been proposed as a material which can sufficiently satisfy all of these requirements as a cladding material.

D. A binary copolymer of a long-chain fluoroalkyl (meth) acrylate and methyl methacrylate, e. Ternary copolymer of long-chain fluoroalkyl (meth) acrylate, short-chain fluoroalkyl methacrylate and methyl methacrylate (JP-A-62-265606, 6
4-76003, 64-79704), f. Multi-component copolymers of long-chain fluoroalkyl (meth) acrylate, methyl methacrylate and a monomer having a high glass transition temperature (JP-A-63-180907, JP-A-4-204909) However, these long-chain fluoroalkyl (meth) Acrylate-containing (meth) acrylate-based copolymer,
Since it is produced by bulk polymerization in a batch system, the amount of residual monomers increases to about 3% or more. Such a copolymer containing a large amount of volatiles such as residual monomers, when used as it is as a clad material, is liable to foam due to the volatilization of the residual monomers at the time of melt extrusion,
Further, the variation in the diameter of the obtained optical fiber becomes large, and it is difficult to stably manufacture an optical fiber having high performance.

Therefore, after polymerization, it is necessary to remove volatiles by a demonomerization step or a drying step to reduce the amount of residual monomers. For example, after pulverizing a copolymer obtained by polymerization, Drying at ℃ (Japanese Unexamined Patent Publication No.
No. 2-265606), or 48 at 115 ° C.
A method of vacuum drying for a time has been proposed (JP-A-4-204909).

[0010]

However, in such low-temperature drying, it is difficult to sufficiently demonomerate a long-chain fluoroalkyl (meth) acrylate having a high boiling point.

A method of increasing the drying temperature for sufficient demonomerization is also conceivable. However, if the heat history is increased, a problem arises in that the copolymer becomes cloudy and the transparency deteriorates.

Accordingly, the present invention comprises a copolymer containing a long-chain fluoroalkyl (meth) acrylate, having a low refractive index, excellent colorless transparency, and having a sufficiently small amount of residual monomer in a well-balanced manner. It is a main object to provide a method for manufacturing an optical fiber clad material provided with the same.

That is, the present invention provides a method for sufficiently reducing the amount of residual monomer without impairing the colorless transparency of a copolymer containing a long-chain fluoroalkyl (meth) acrylate by improving the demonomerization method. The purpose is to do.

[0014]

In order to achieve this object, a method for manufacturing an optical fiber clad material according to the present invention comprises:
After polymerization, a copolymer containing 20% by weight or more of a fluoroalkyl (meth) acrylate unit represented by the following general formula [I] is transferred to a continuous demonomerization step, and the maximum temperature of the vent section is 280 ° C or less, and the extruding section is Temperature 200-250
° C, extrusion part temperature ≤ vent part maximum temperature, and by continuously discharging by passing within an average residence time of 30 minutes,
A colorless and transparent optical fiber cladding material having a residual monomer ratio of 0.5% or less is characterized.

[0015]

Embedded image (Where X 1 is CH ₃ , H, CF ₃ or F, n is 1
Or 2, m is an integer from 4 to 10, and X2 represents H or F. In the present invention, the copolymer used as the optical fiber cladding material is a fluoroalkyl (meth) acrylate unit represented by the above general formula [I]. (Hereinafter, simply referred to as long-chain fluoro units).

Since the long-chain fluoro unit has a high fluorine content, it is extremely effective in reducing the refractive index of the copolymer, and in order to exhibit the effect, the general formula [I]
M is 4 or more, and it is necessary to copolymerize at least 20% by weight. Further, the content is preferably 30% by weight or more, and at most about 90% by weight. In addition, m in the general formula [I] needs to be 10 or less so as not to impair the transparency of the copolymer.

On the other hand, since the long-chain fluoro unit has a large number of carbon atoms of a fluoroalkyl group of 4 or more, it has a higher boiling point and a higher copolymerization weight than a short-chain fluoro unit having 3 or less carbon atoms. Since the thermal decomposition of the coalesce, that is, the depolymerization, easily proceeds, the residual monomer ratio tends to increase, and as a result, viscosity reduction and foaming during melt extrusion tend to occur. On the other hand, even if the termination reaction is extremely slow and the polymerization initiator is decomposed and no longer exists, it has a contradictory property that the post-polymerization easily occurs with the residual monomer. In addition, in the copolymer containing the long-chain fluoro unit, the depolymerization and / or post-polymerization tends to become more intense as the heat history in the demonomerization step after the polymerization becomes higher. It is easy for the polymer to become cloudy.

Examples of the copolymer unit other than the long-chain fluoro unit include a short-chain fluoroalkyl (meth) acrylate unit represented by the following general formula [II] (hereinafter, simply referred to as a short-chain fluoro unit). (Meth) acrylic acid alkyl ester units (hereinafter, simply referred to as alkyl ester units) represented by the general formula [III], and N- (fluoro) alkylmaleimide units (hereinafter, simply maleimide) represented by the following general formula [IV] Unit).

[0019]

Embedded image (Where X 1 is CH ₃ , H, CF ₃ or F, n is 1
Or 2, m is an integer from 0 to 3, X2 is H or F
Which includes at least one F in the molecule)

Embedded image (Where X 1 represents CH ₃ or H, and n represents an integer from 1 to 10)

Embedded image (Where R1 is methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, hexyl,
This represents an alkyl group selected from the group of cyclohexyl or a fluoroalkyl group therefrom.) The short-chain fluoro unit (general formula [II]) has a low fluorine content in terms of the effect of reducing the refractive index of the copolymer. Although somewhat inferior, depolymerization and / or post-polymerization after polymerization can be suppressed, so that it can be partially used as a substitute for long-chain fluoro units. However, if the amount is too large, it becomes difficult to obtain a sufficiently low refractive index as a cladding material. Therefore, the short-chain fluoro unit is preferably set to 0 to 75% by weight, more preferably 0 to 59.8% by weight.

In order to suppress the depolymerization of the copolymer after polymerization, a small amount of the maleimide unit (general formula [IV]) may be copolymerized. In this case, the copolymerization ratio is preferably from 0.2 to 30% by weight. At least 0.2% by weight is necessary to exhibit the effect of copolymerizing the maleimide unit, and if it exceeds 30% by weight, the mechanical properties of the copolymer are greatly reduced, which is not preferable. .

The maleimito unit has the general formula [IV]
As represented by the formula, it may be an N-alkylmaleimide unit or an N-fluoroalkylmaleimide unit.

Particularly preferred N-alkyl substituents include propyl, isopropyl, butyl, sec-butyl, cyclohexyl and their fluorine-substituted ones, since the colorless and transparent properties of the copolymer are enhanced. On the other hand, N-substituted maleimide substituted with an aromatic group is not suitable for an optical fiber clad material because it has a high refractive index and is somewhat yellow.

The maleimide unit not only suppresses the depolymerization of the copolymer but also has a great effect of increasing the glass transition temperature of the copolymer.

In addition, the alkyl ester unit (general formula [III]) may be copolymerized. In this case, the copolymerization ratio is preferably 5 to 40% by weight.

When an alkyl acrylate such as methyl or ethyl is used as the alkyl ester unit, it is possible to suppress the depolymerization of the copolymer and improve the flexibility. The ester is adamantyl,
When an alicyclic methacrylate such as bornyl, tricyclodecanyl, or cyclohexyl is used, the glass transition temperature of the copolymer can be increased. Furthermore,
When the ester is an alkyl methacrylate such as methyl or ethyl, the copolymer can have flexibility and adhesion to the optical fiber core.

When a unit for increasing the glass transition temperature such as the maleimide unit or the alicyclic methacrylate is used, 10 to 30% by weight of methyl methacrylate is used.
It is preferred to contain. In this copolymer composition,
If the content of methyl methacrylate is less than 10% by weight, mechanical properties and adhesion are insufficient, and if it exceeds 30% by weight, it becomes difficult to obtain a sufficiently low refractive index, which is not preferable.

Further, as long as the effects of the present invention are not impaired, other monomers such as methacrylic acid, stabilizers such as antioxidants and ultraviolet absorbers, and plasticizers can be contained.

The polymerization method for obtaining this copolymer is as follows: as long as the composition distribution of the copolymer is small and does not become cloudy.
It may be any of bulk polymerization, suspension polymerization, emulsion polymerization or solution polymerization, and may be any of batch type and continuous type. In producing the copolymer, polymerization may be carried out using a general radical polymerization initiator such as an azo compound or a peroxide, and if necessary, a general molecular weight regulator.

The copolymer obtained by polymerization is transferred to a continuous demonomerization step, and demonomerized until the residual monomer ratio becomes 0.5% or less.

To prevent the copolymer from becoming cloudy in the demonomerization step, a continuous demonomerization step in which the copolymer is continuously supplied to remove volatiles and then continuously discharged is employed. is necessary. On the other hand, in the batch type demonomerization method and heating vacuum drying, the thermal history at the time of demonomerization increases as the scale increases, and it is not possible to avoid cloudiness, so a clad material with high colorless transparency and low residual monomer is industrially manufactured. It is difficult to obtain efficiently.

This continuous demonomerization step includes, in order, a preheating section for preheating the copolymer obtained by polymerization, a vent section for removing volatiles, and a discharge line having substantially no vent port. It is configured to include three parts of the extrusion part.

In this case, the temperature condition is set as follows:
80 ° C or less, extrusion section temperature 200 to 250 ° C, extrusion section temperature ≤ maximum temperature of the vent section, and an average residence time from the start of preheating of the copolymer in the preheating section to discharge from the extrusion section within 30 minutes. It is necessary to Further, the average residence time is preferably within 25 minutes. If the maximum temperature of the vent exceeds 280 ° C., the depolymerization becomes severe, and it is difficult to reduce the residual monomer. If the maximum temperature of the vent section is lower than the temperature of the extrusion section, sufficient demonomerization cannot be performed. If the temperature of the extruded portion is lower than 200 ° C., the copolymer melt viscosity is too high to stably extrude. On the other hand, if the temperature exceeds 250 ° C., the residual monomer increases due to depolymerization. On the other hand, if the average residence time exceeds 30 minutes, depolymerization and / or post-polymerization will become violent, resulting in cloudiness.

Further, by this demonomerization step, the monomer content in the copolymer, that is, the residual monomer ratio is reduced to 0.5.
% Is required to prevent foaming during melt extrusion, suppress fluctuations in the fiber diameter of the optical fiber, and obtain an optical fiber with high performance. Further, it is preferable to reduce the residual monomer ratio to 0.4% or less.

The clad material obtained by demonomerization in this manner is sent to an optical fiber spinning step, and is melt-coextruded with a core component to produce an optical fiber by an ordinary method.

Further, in the coating step, the obtained optical fiber is made of polyethylene, polypropylene or a copolymer or a blend thereof, an olefin polymer containing an organic silane group, ethylene-vinyl acetate, polyvinyl chloride, polyvinyl fluoride. The cord may be coated with a resin such as vinylidene chloride, nylon resin, polyester resin, nylon elastomer, polyester elastomer or polyurethane or polyurethane elastomer. Further, a cable may be formed by covering with a tension member such as Kevlar and further coating with the above resin.
If the coating temperature is 240 ° C. or lower, processing can be performed without impairing the light transmission performance of the optical fiber.

Further, after the clad material and the core material are melt-extruded, the clad material may be fused in a temperature range not lower than the glass transition temperature of the clad material to form a sheet-like optical fiber.

Alternatively, the core material is made of an island using a multi-core die,
The optical fiber may be extruded into a sea-island structure in which the clad material forms the sea.

Further, the clad material obtained by the method of the present invention is:
Since it has excellent solvent resistance, a coating solution can be formed by applying a resin solution having excellent heat resistance, a resin solution having high adhesiveness, or a solution containing a coloring dye or a fluorescent dye. Further, it is also possible to form a sheet heating element by using an optical fiber as a fabric.

[0039]

EXAMPLES The present invention will be described more specifically with reference to the following examples.

First, the structure of the fluoroalkyl (meth) acrylate used in the examples is shown below.

[0041]

Embedded image The characteristics of the cladding material and the optical fiber in the examples were measured as follows.

Refractive index: Measured with an Abbe refractometer according to ASTM D542-50.

Residual monomer ratio: The residual amount of each monomer in the clad material was determined by gas chromatography analysis, and the total of the monomer amounts was expressed as a ratio (% display) to the clad material.

Light Transmittance: According to JIS K6714, a thickness of 3.0 mm was measured with an integrating sphere light transmittance measuring device.
Of the test pieces.

Light transmission loss: 20 m / 2 m by a so-called cut-back method at 650 nm of a parallel halogen light.
Calculated from the difference in the light transmission loss values.

Wire diameter fluctuation width: 1 with a laser diameter measuring instrument
The time was measured and the difference between the maximum and minimum values was shown.

Example 1 The following ingredients: 17FM 70.0 parts by weight 3FM 12.0 parts by weight 4FM 12.0 parts by weight Methyl methacrylate 5.6 parts by weight Methacrylic acid 0.4 parts by weight Azobisisobutyro 0.1 part by weight of nitrile and 0.01 part by weight of n-butyl mercaptan were mixed, degassed under reduced pressure, and then heated at 80 ° C. for 15 hours for 110 hours.
C. for 3 hours. Obtained copolymer (copolymer
No.A) was pulverized and put into a vented extruder under a nitrogen atmosphere.
Demonomerization was performed under the condition of an average residence time of 15 minutes, and the mixture was discharged to form chips, which were used as clad materials.

As shown in Table 1, the obtained clad material had a small residual monomer ratio and was excellent in colorless transparency.

Using this copolymer as a cladding material and poly (methyl methacrylate) as a core material, composite spinning was carried out by an ordinary method to obtain an optical fiber having a diameter of 1000 μm.

As shown in Table 1, the obtained optical fiber had a sufficiently small light transmission loss and a small line diameter variation, and was an excellent optical fiber.

[Comparative Example 1] A copolymer (Copolymer No. A) obtained by polymerization in Example 1 was subjected to batchwise demonomerization at 130 ° C. for 12 hours by a vacuum drier to produce Example 1. In the same manner as in the above, a cladding material and an optical fiber were obtained.

The clad material obtained by demonomerization had a large amount of residual monomer, and the optical fiber had a large fluctuation in wire diameter.

Comparative Example 2 Example 1 was repeated except that the copolymer obtained by polymerization in Example 1 (Copolymer No. A) was batchwise demonomerized at 200 ° C. for 5 hours using a vacuum dryer. In the same manner as in the above, a cladding material and an optical fiber were obtained.

In the clad material obtained by demonomerization, the residual monomer was smaller than that in the case of Comparative Example 1, and the fluctuation of the optical fiber diameter was small. On the contrary, the copolymer became white and turbid. The light transmission of the fiber was poor.

Example 2 The following components: 17FM 41.0 parts by weight 17FA 9.0 parts by weight 3FM 30.0 parts by weight Methyl methacrylate 20.0 parts by weight Azobisisobutyronitrile 0.1 parts by weight n -Butyl mercaptan 0.04 parts by weight, and after degassing under reduced pressure, the mixture was heated at 70 ° C for 6 hours at 120 ° C.
For 2 hours. The obtained copolymer (copolymer N
o) B) was subjected to demonomerization in the same manner as in Example 1 to obtain a clad material, and further an optical fiber.

As shown in Table 1, the obtained clad material had a small residual monomer ratio and was excellent in colorless transparency. Also,
As shown in Table 1, the obtained optical fiber had a sufficiently small light transmission loss and a small variation in wire diameter, and was an optical fiber having excellent performance.

Comparative Example 3 A clad material and an optical fiber were obtained in the same manner as in Example 2, except that the average residence time was 38 minutes.

The obtained clad material was white and cloudy, and the optical fiber had poor light transmittance.

Comparative Example 4 The maximum temperature of the vent section was 260 ° C.
A clad material and an optical fiber were obtained in the same manner as in Example 2, except that the extruder temperature was set to 260 ° C. and the average residence time was set to 15 minutes.

The obtained clad material had a large amount of residual monomer, and the wire diameter of the optical fiber varied greatly.

Example 3 The following components: 17FM 30.0 parts by weight 3FM 50.0 parts by weight α-F, 3FA 10.0 parts by weight Methyl methacrylate 8.0 parts by weight Methacrylic acid 2.0 parts by weight Azo Bisisobutyronitrile 0.1 part by weight n-butyl mercaptan 0.03 part by weight was subjected to bulk polymerization in the same manner as in Example 2. The obtained copolymer (Copolymer No. C) was demonomerized into a clad material in the same manner as in Example 1 except that the average residence time in the demonomerization step was set to 21 minutes. did.

As shown in Table 1, the obtained clad material had a small residual monomer ratio and was excellent in colorless transparency. Also,
As shown in Table 1, the obtained optical fiber had sufficiently small transmission loss and small fluctuation in wire diameter, and was an optical fiber excellent in performance.

Example 4 The following components: 17FM 40.0 parts by weight 8FM 40.0 parts by weight Methyl methacrylate 11.0 parts by weight N-isopropylmaleimide 9.0 parts by weight Azobis-1,1,3,3 -Tetramethylbutane 0.003 parts by weight n-butyl mercaptan 0.0005
Parts by weight, degassed under reduced pressure, and continuously charged into a one-tank complete mixing type polymerization tank, while simultaneously polymerizing the resulting copolymer mixture (Copolymer No. D) using a gear pump. Discharged. The polymerization was performed at a polymerization temperature of 140 ° C., an average residence time of 4 hours,
The polymerization was carried out at a conversion of 48%.

The copolymer mixture obtained by the polymerization is discharged into chips at a maximum temperature of 270 ° C. in the vent portion of the thin-film type demonomerization tank, a temperature of 235 ° C. in the extruding portion, and an average residence time of 15 minutes.
A clad material was used.

As shown in Table 1, the obtained clad material had a small residual monomer ratio and was excellent in colorless transparency. Also,
As shown in Table 1, the obtained optical fiber had sufficiently small transmission loss and small fluctuation in wire diameter, and was an optical fiber excellent in performance.

[0066]

[Table 1]

[0067]

The cladding material obtained by the method of the present invention and comprising a low-refractive-index copolymer containing a long-chain fluoro unit is an optical fiber cladding material which is excellent in colorless and transparent and has a small amount of residual monomers. It has characteristics suitable for use and can be manufactured industrially stably.

Therefore, the numerical aperture is high, the translucency is good,
It is possible to industrially stably manufacture an optical fiber having a small variation in wire diameter.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-18608 (JP, A) JP-A-61-275705 (JP, A) JP-A-62-265606 (JP, A) JP-A-4- 204909 (JP, A) JP-A-6-235831 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/00-6/54

Claims (3)

(57) [Claims] 1. A copolymer containing 20% by weight or more of a fluoroalkyl (meth) acrylate unit represented by the following general formula [I] is transferred to a continuous demonomerization step after polymerization, and a maximum temperature of a vent portion is 280. ℃ or less, extrusion part temperature 2
A colorless and transparent optical fiber clad material having a residual monomer ratio of 0.5% or less and continuous discharge by passing the resin at a temperature of 00 to 250 ° C., an extruding part temperature ≦ the maximum temperature of the vent part, and an average residence time of 30 minutes or less. A method for producing an optical fiber clad material. Embedded image (Where X 1 is CH ₃ , H, CF ₃ or F, n is 1
Or 2, m is an integer from 4 to 10, and X2 represents H or F) 2. The copolymer comprises 20 to 90% by weight of a fluoroalkyl (meth) acrylate unit represented by the following general formula [I], and a fluoroalkyl (meth) acrylate unit represented by the following general formula [II]. Is a (meth) acrylate-based copolymer containing 0 to 75% by weight and 5 to 40% by weight of an alkyl (meth) acrylate represented by the following general formula [III]: 2. The method for producing an optical fiber clad material according to item 1. Embedded image (Where X 1 is CH ₃ , H, CF ₃ or F, n is 1
Or 2, m is an integer from 4 to 10, and X2 represents H or F. (Where X 1 is CH ₃ , H, CF ₃ or F, n is 1
Or 2, m is an integer from 0 to 3, X2 is H or F
Wherein at least one F is contained in the molecule. (Where X 1 represents CH ₃ or H, and n represents an integer from 1 to 10) 3. The (meth) acrylate copolymer contains 30 to 89.8% by weight of a fluoroalkyl (meth) acrylate unit represented by the following general formula [I], and is represented by the following general formula [II]. Fluoroalkyl (meth)
A copolymer containing 0 to 59.8% by weight of an acrylate unit, 10 to 30% by weight of methyl methacrylate, and 0.2 to 30% by weight of an N- (fluoro) alkylmaleimide unit represented by the following general formula [IV]: The method for producing an optical fiber clad material according to claim 2, wherein the optical fiber clad material is a polymer. Embedded image (Where X 1 is CH ₃ , H, CF ₃ or F, n is 1
Or 2, m is an integer from 4 to 10, and X2 represents H or F. (Where X 1 is CH ₃ , H, CF ₃ or F, n is 1
Or 2, m is an integer from 0 to 3, X2 is H or F
Represents: (Where R1 is methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, hexyl,
Represents an alkyl group selected from the group of cyclohexyl or a fluoroalkyl group therefrom)