JPH06222224A - Manufacture of optical fiber clad material - Google Patents

Abstract

PURPOSE:To prevent a copolymer from being made cloudy and reduce residual monomer amount sufficiently by specifying the conditions for polymerization and de-monomer in the copolymer containing a long chain fluoroalkylmetaacrylate and N-alkylmaleimid. CONSTITUTION:A copolymer-contains a fluoroalkyl (meta) acrylate unit in formulas I and II of 20 to 99.8% and 0 to 70% by weight, respectively, and an N-(fluoro) alkylmaleimid unit in formula III of 0.2 to 30% by weight. The polymerization part comprises a single tank type continuous polymerization tank. The polymerization is made so that polymerization temperature is 160 deg.C or below, polymerization rate is 35% or over, and the value of residual polymerization start agent density [1] to non-reactive monomer density [M] in the copolymer mixture is [1]/[M]<3.0X10<-5> and the demonomer is made to reduce a residual monomer rate to 0.5% or below. Where, in the formulas I to III, X1 is CH3, etc., n is 1 or 2, X2 is H, etc., and R1 is methyl, etc. Also m in the formula I is the integer of 4 to 10 and m in the formula II is the integer of 0 to 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method suitable for industrially and efficiently producing an optical fiber clad material which is excellent in colorless transparency, has a small amount of residual monomer, 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 refractive index lower than that of the core.

For the core, a polymer having excellent transparency such as quartz, multi-component glass or polymethylmethacrylate 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 resin is widely used.

As the fluorine-containing resin, a vinylidene fluoride / tetrafluoroethylene copolymer (Japanese Patent Publication No. 63-67164) and a hexafluoroacetone / vinylidene fluoride copolymer (Japanese Patent Laid-Open No. 61-22305) have hitherto been used. Vinylidene fluoride-based copolymers have been proposed. However, the vinylidene fluoride copolymer has
Although it has excellent thermal stability, it is inferior in transparency due to crystallinity,
Moreover, the operating temperature is as low as about 70 ° C.

Further, in order to raise the use temperature, a methacrylate / methyl methacrylate copolymer having a linear fluoroalkyl group (Japanese Patent Publication No. 43-8978, Japanese Patent Laid-Open No. 4978/1988).
9-107790), short-chain fluoroalkyl methacrylate copolymers, α-fluoroacrylate copolymers (JP-A-59-227908) and the like have been proposed.

However, the short-chain fluoroalkyl methacrylate copolymer has good colorless transparency, but the refractive index is not so low and the mechanical properties are poor, and the α-fluoroacrylate copolymer has a low refractive index. However, none of them can sufficiently satisfy the requirements as a clad material for an optical fiber, such as being easily colored by thermal desorption of α-fluoro group and not having sufficient colorless transparency.

Therefore, a method of using a long-chain fluoroalkyl methacrylate as a material capable of sufficiently satisfying all the required properties as these clad materials has been proposed (JP-A-62-265606, 64-76003).
Issue).

However, in this long-chain fluoroalkylmethacrylate, as the carbon number of the fluoroalkyl group increases, thermal decomposition of the copolymer is more likely to proceed, the amount of volatile matters such as residual monomers increases, and the viscosity during melt extrusion is increased. There is a problem that deterioration and foaming easily occur, and it is difficult to industrially stably produce an optical fiber.

In order to improve the thermal stability while maintaining the low refractive index, a method of copolymerizing a long-chain fluoroalkyl acrylate with a long-chain fluoroalkyl acrylate (JP-A-64-79704) has been tried. However, since the fluoroalkyl acrylate has a low glass transition temperature (Tg), the clad material is improved in thermal decomposability, but the operating temperature of the optical fiber is lowered, which is not preferable in practice.

Therefore, as a method capable of achieving both suppression of thermal decomposition and retention of the glass transition temperature, a method of copolymerizing N-alkylmaleimide with this long-chain fluoroalkylmethacrylate has been proposed (Japanese Patent Laid-Open No. 4-204). 204
909 publication).

[0012]

However, in the conventional method, although the copolymerizability of the long-chain fluoroalkyl methacrylate and the N-alkylmaleimide is different, this copolymer is produced by batch polymerization in bulk. Because
There is a problem that the composition distribution of the obtained copolymer becomes large and turbidity occurs. That is, when the copolymerizability is different as described above, white turbidity generally occurs in the whole copolymer obtained, but it is stirred in a glass ampoule as described in the above-mentioned JP-A-4-204909. When the polymer is polymerized without any treatment, the cloudy portion can be localized, and a partially transparent copolymer can be obtained. However, in this method, in order to obtain a colorless and transparent copolymer, a large amount of unnecessary cloudy parts must be simultaneously produced and discarded, which is extremely inefficient in industrial production and cannot be adopted.

Further, since this copolymer is produced by batch-wise bulk polymerization, the amount of residual monomer is as large as about 3% or more. When a copolymer containing a large amount of volatile substances such as residual monomers is used as it is as a clad material, foaming easily occurs due to volatilization of the residual monomers and the like during melt extrusion. Becomes large, and it is difficult to stably manufacture a high-performance optical fiber.

Therefore, in the conventional method, vacuum drying is carried out at 115 ° C. for 48 hours to obtain a clad material. However, since this long-chain fluoroalkyl methacrylate has a high boiling point, it is difficult to sufficiently demonomerize under such conditions. is there.
A method of increasing the drying temperature for sufficient demonomerization is also conceivable, but when the heat history is increased, another problem arises in which the copolymer becomes cloudy and the colorless transparency is impaired.

From the above, the present invention provides a copolymer containing long-chain fluoroalkyl methacrylate and N-alkylmaleimide as essential components, which has a low refractive index.
The main object of the present invention is to provide a method for industrially efficiently producing an optical fiber clad material that is excellent in colorless transparency and has a well-balanced characteristic that the amount of residual monomer is sufficiently small.

That is, according to the present invention, by specifying the production conditions in the polymerization and the demonomer, even in the case of the above-mentioned copolymer, white turbidity does not occur, and the amount of residual monomer can be sufficiently reduced in industrial practice. The purpose is to provide a suitable method.

[0017]

In order to achieve this object, a method for producing an optical fiber clad material according to the present invention is a polymerization / depolymerization part having a polymerization part, a demonomer part and a connecting part thereof.
Using a demonomerizer, the fluoroalkyl (meth) acrylate unit represented by the following general formula [I] is added to
99.8% by weight, 0 to 70% by weight of fluoroalkyl (meth) acrylate unit represented by the following general formula [II]
And a copolymer containing 0.2 to 30% by weight of an N- (fluoro) alkylmaleimide unit represented by the following general formula [III], followed by demonomerization to produce an optical fiber clad material. The polymerization section is composed of a single-tank continuous polymerization tank, and the polymerization temperature is 160 ° C. or lower and the polymerization rate is 35
% Or more and the value of the residual polymerization initiator concentration [I] (mol / l) with respect to the unreacted monomer concentration [M] (mol / l) in the copolymer mixture, which is expressed by the following formula (1): [ I] / [M] <3.0 × 10 ⁻⁵ (1) Polymerization is carried out, and then the connection part and the demonomer part are continuously passed to perform demonomerization and discharge. By doing so, a colorless and transparent optical fiber clad material having a residual monomer ratio of 0.5% or less is characterized.

[0018]

[Chemical 7] (Where X 1 is CH ₃ , H, CF ₃ or F, and n is 1
Or 2, m is an integer from 4 to 10, X2 represents H or F)

[Chemical 8] (Where X 1 is CH ₃ , H, CF ₃ or F, and n is 1
Or 2, m is an integer from 0 to 3, X2 is H or F
Represents)

[Chemical 9] (Where R1 is methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, hexyl,
The copolymer used for the optical fiber cladding material in the present invention is a long chain fluoroalkyl (meth) acrylate unit represented by the above general formula [I]. It is a copolymer containing. Since this long-chain fluoroalkyl (meth) acrylate unit has a high fluorine content, it is extremely effective in reducing the refractive index of the copolymer, and in order to exert its effect, the general formula [I] M in 4 is 4 or more, and 20 to 9
It is necessary to copolymerize 9.8% by weight. Above all, it is preferable to contain 50 to 95% by weight, 70 to 8
It is more preferable to contain 9.8% by weight. Further, m in the general formula [I] needs to be 10 or less so as not to impair the transparency of the copolymer. Further, X1 in the general formula [I] is CH ₃ from the viewpoint that the obtained copolymer has a relatively high glass transition temperature and a high colorless transparency.
That is, the long-chain fluoroalkyl methacrylate represented by the general formula [IV] is preferable.

[0019]

[Chemical 10] (Here, n represents 1 or 2, m represents an integer of 4 to 10, R represents H or F) The N- (fluoro) alkylmaleimide unit represented by the general formula [III] is as described above. The two major effects are to raise the glass transition temperature of the clad material and to suppress thermal decomposition. That is, the N- (fluoro) alkylmaleimide unit is an essential component for suppressing thermal decomposition of the long-chain fluoroalkyl (meth) acrylate unit, and by containing this component, the long-chain fluoroalkyl (meth) acrylate is contained.
It is possible to increase the amount of acrylate units. N in this N- (fluoro) alkylmaleimide unit
Among the alkyl substituents, propyl, isopropyl, butyl, sec-butyl, cyclohexyl, and fluorine-substituted products thereof are preferable in that the colorless transparency of the cladding material can be increased. The copolymerization ratio must be 0.2 to 30% by weight. If it exceeds 30% by weight, the mechanical properties of the clad material are significantly deteriorated, which is not preferable. A more preferable range is 0.2 to 20% by weight. On the other hand, aromatic N-substituted maleimides are not suitable for optical fiber clad materials because the refractive index of the clad material is high and the color is yellow to some extent.

The short-chain fluoroalkyl (meth) acrylate represented by the above general formula [II] is inferior in terms of the effect of reducing the refractive index of the copolymer by the low fluorine content,
It can be used as a partial replacement for the long-chain fluoroalkyl (meth) acrylate unit. This composition must be 70% by weight or less, and preferably 29.8% by weight or less, in order to sufficiently reduce the refractive index of the clad material. In addition, when the copolymerization ratio of the long-chain fluoroalkyl (meth) acrylate is high, it may be 0% by weight.

From the viewpoint of imparting flexibility to the clad material and adhesion to the optical fiber core, it is preferable to copolymerize methyl methacrylate in an amount of 29.8% by weight or less. When it exceeds 29.8% by weight, it is difficult to obtain a sufficiently low refractive index, which is not preferable. In order to fully bring out the effect by it, it is preferable to contain 10-29.8 weight%.

From the above, 70 to 89.8% by weight of the long-chain fluoroalkylmethacrylate unit represented by the general formula [IV], and the N- (fluoro) alkylmaleimide represented by the general formula [III] are contained. Unit is 0.2-2
0% by weight and 10 to 2 methyl methacrylate units
Most preferably, the clad material is a copolymer containing 9.8% by weight.

Further, other monomers such as (meth) acrylic acid ester and (meth) acrylic acid, stabilizers such as antioxidants and ultraviolet absorbers, plasticizers, etc. are contained within a range that does not impair the effects of the present invention. You may.

Now, the most important point of the present invention is that the copolymer having this copolymer composition has no white turbidity, is excellent in colorless transparency, and has a sufficiently low residual monomer ratio of 0.5% or less. It is an object of the present invention to provide a manufacturing condition capable of manufacturing a fiber clad material industrially efficiently and stably.

That is, as described above, it has been difficult to industrially efficiently produce the above clad material by the conventional method. Therefore, as a result of various studies, we have found that only the essential component, N- (fluoro) alkylmaleimide, has different reactivity, and the long-chain fluoroalkyl (meth) acrylate is thermally decomposed (depolymerized) due to its bulkiness. It is easy to be post-polymerized and easy to become cloudy, which is due to the characteristic properties of this copolymer composition, and those problems can be avoided by taking manufacturing conditions that satisfy all of the following requirements That is, the present invention has been completed.

In order to carry out the polymerization so that the composition distribution of the copolymer becomes uniform, the polymerization temperature is 1
It is necessary to carry out continuous polymerization at a temperature of 60 ° C. or lower so that the polymerization rate is 35% or higher.

Moreover, the value of the residual polymerization initiator concentration [I] (mol / l) with respect to the unreacted monomer concentration [M] (mol / l) in the copolymer mixture from the polymerized part is as follows (1)
Polymerization is carried out under the condition of the formula [I] / [M] <3.0 × 10 ⁻⁵ (1), and the copolymer mixture in this state in which the polymerization hardly progresses through the connecting part. Supply to the demonomerization part is necessary to suppress post-polymerization.

It is necessary to adopt a continuous demonomer method in which the monomer is continuously supplied to the demonomer part and continuously discharged in order to reduce the thermal history and suppress thermal decomposition and / or post-polymerization.

The respective conditions will be described below.

When containing monomers having different reactivity,
When batch polymerization is performed up to a high polymerization rate, the composition distribution becomes large. However, continuous polymerization in a one-tank complete mixing type polymerization tank is effective for suppressing the composition distribution during polymerization.
In a multi-tank type polymerization tank, a mixture of various compositions is formed, and a tube-type continuous polymerization without a tank is not suitable because the composition changes with passage of the tube and the composition distribution increases. Bulk polymerization is most preferable, but solution polymerization, suspension polymerization, or emulsion polymerization may be used.

When the polymerization temperature exceeds 160 ° C., the syndiotactic component in the stereoregularity of the copolymer is reduced, the glass transition temperature is lowered, and the copolymer is apt to be colored in the demonomer part. Not only that, even if the molecular weight modifier is not contained, the molecular weight of the copolymer does not increase sufficiently, which is not preferable. Further, if the polymerization rate is less than 35%, the productivity becomes extremely low, which is not preferable. Furthermore, the polymerization rate is 4
It is preferably 0% or more.

Since the long-chain fluoroalkyl (meth) acrylate unit is easily post-polymerized, if sufficient polymerization initiator remains in the linking portion and the demomerization portion, post-polymerization occurs and thermal decomposition also accompanies copolymerization. Whitening occurs in the coalescence. Therefore, it is necessary to make the concentration of the residual polymerization initiator in the copolymer mixture discharged from the polymerization tank sufficiently low so as not to be involved in the initiation of the polymerization in the linking portion and the demonomer portion. That is, the polymerization conditions such that the initiation of polymerization in the polymerization tank is sufficiently caused by the newly and continuously supplied polymerization initiator, and the residual polymerization initiator at the exit of the polymerization tank is at a concentration that hardly contributes to the initiation of polymerization. You have to choose. As a result of various studies, as shown in the formula (1), the condition that the value ([I] / [M]) of the residual polymerization initiator concentration with respect to the unreacted monomer concentration is less than 3.0 × 10 ⁻⁵ It has been found effective to meet.
More preferably, it is less than 2.0 × 10 ⁻⁵ .

[I] / [M] can be generally obtained by the following equation (2).

[I] / [M] = [I] ₀ / [M] / [A · exp (−E / R · T) · θ + 1] (2) (where [I] ₀ is Charged polymerization initiator concentration, A and E are constants (frequency factor and activation energy, respectively) determined by the type of polymerization initiator, and R is a gas constant (= 1.98).
7), T is the polymerization temperature ^(. K), ^θ is mean residence time (h
r) is represented. The values described in the literature may be used for A and E. Therefore, specifically, it is necessary to properly select the type of the polymerization initiator and its charging concentration, the polymerization temperature, and the average residence time, but the combination thereof is determined by considering the polymerization rate, the average molecular weight, etc. (2) You can select it according to the formula. As the polymerization initiator at this time, a general azo compound, a radical polymerization initiator such as a peroxide can be used, and in the case where the molecular weight is high, the polymerization can be carried out using a general molecular weight regulator. Also, it is not particularly limited as long as it does not impair the colorless transparency of the clad material.

By thus controlling the concentration of the polymerization initiator discharged from the polymerization tank, it is possible to suppress the post-polymerization in the connecting part and the demonomerizing part and suppress the white turbidity.

In order to prevent the turbidity of the copolymer during demonomerization, it is necessary to adopt a continuous demonomerization method in which the copolymer is continuously supplied to demonomerize and then continuously discharged. On the other hand, in the batchwise demonomerization method or the heating vacuum drying, the thermal history becomes large and thermal decomposition and / or post-polymerization is caused, so that the copolymer is apt to become cloudy.

Even in the case of continuous demonomerization, it is preferable to take the condition that the thermal history is made as small as possible. Specifically, the maximum temperature of the vent part in the demonomer part is 280 ° C., the extruded part including the discharge line which is not substantially demonomerized is 200 to 250 ° C., and the vent part maximum temperature ≧ extruded part temperature, and the average residence time is It is preferable to continuously pass the connecting part to the demomerizing part within 30 minutes (desirably within 25 minutes).

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

The clad material obtained by demonomerizing in this way is sent to the optical fiber spinning step and melted and coextruded together with the core component to produce an optical fiber by a usual method.

In the coating step, the obtained optical fiber is made of polyethylene, polypropylene or a copolymer thereof, or a blended product thereof, an olefin polymer containing an organic silane group, ethylene-vinyl acetate, polyvinyl chloride, polyvinyl fluoride. A cord can be formed by coating a resin such as vinylidene chloride, nylon resin, polyester resin, nylon elastomer, polyester elastomer, polyurethane or polyurethane elastomer. Further, it is possible to cover a tension member such as Kevlar and further coat it with the above resin to obtain a cable. If the coating temperature is 240 ° C. or lower, the optical fiber can be processed without impairing the light transmitting performance.

Alternatively, the clad material and the core material may be melt-extruded, and then 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.

Alternatively, the core material is an island using a multi-core die,
The clad material may be extruded into a sea-island structure forming the sea to form an optical fiber.

Further, since the clad material of the present invention has excellent solvent resistance, a resin solution having further excellent heat resistance or a resin solution having high adhesiveness or a solution containing a coloring dye or a fluorescent dye is applied to form a coating film. It can also be formed. Further, it is possible to fabricate the optical fiber into a sheet-like heating element.

[0044]

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

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

[0046]

[Chemical 11] The characteristics of the cladding material and the optical fiber used in the examples were measured as follows.

Refractive Index: Measured by Abbe's refractometer according to ASTM D542-50.

Residual monomer ratio: The residual amount of each monomer contained in the clad material was obtained by gas chromatography analysis, and the total amount of the residual monomers was calculated as a ratio (%) to the clad material.
Display).

Light transmittance: According to JIS K6714, an integrating sphere light transmittance measuring device has a thickness of 3.0 mm.
The test piece was measured.

Light transmission loss: Calculated from a light transmission loss value difference of 20 m / 2 m by a so-called cutback method in a halogen parallel light of 650 nm.

Line diameter fluctuation range: 1 with a razor wire diameter measuring instrument
The time was measured and the difference between the maximum and minimum values was shown.

Example 1 The following components were used: 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, and 1 mol of all these monomer mixtures. Di-tert-butyl peroxide 7.0 × 10 ^-5 n-butyl mercaptan 0.5 × 10 ^-5 was mixed in a molar ratio and degassed under reduced pressure, and then a one-tank type complete mixing type polymerization tank was started from the monomer supply tank. Was continuously charged. Polymerization is 155
As a result of setting the average residence time at 4 ° C for 4 hours, the polymerization rate was 5
Stable at 5%. The residual polymerization initiator concentration [I] (mol / l) with respect to the unreacted monomer concentration [M] (mol / l) in the copolymer mixture discharged from the polymerization part was 1.6 from the formula (2). It could be calculated as × 10 ^-5 .

The resulting copolymer mixture (Copolymer No.
A) was continuously fed to the thin film type demonomer by passing through a connecting part set at 150 ° C. by a gear pump, and then passed through a vent part set at 270 ° C. and an extruding part set at 235 ° C.,
The mixture was discharged at an average residence time of 15 minutes to be made into chips and used as a clad material.

As shown in Table 1, the obtained clad material had few residual monomers and was excellent in colorless transparency. In addition,
As a result of NMR analysis and elemental analysis, the composition of the obtained copolymer was 17FM / 8FM / methyl methacrylate / N-isopropylmaleimide = 41.0 / 40.7 / 11.1.
/7.2 (weight ratio).

Using this as a clad material and polymethylmethacrylate as a core, melt-composite spinning was carried out by an ordinary method to obtain an optical fiber having a diameter of 1000 μm. The results of these characteristics are shown in Table 1. Both transmission loss and wire diameter fluctuation are small,
An optical fiber with excellent performance was obtained.

Comparative Example 1 Azobisisobutyronitrile was used as a polymerization initiator (0.01 parts by weight), and the amount of n-butyl mercaptan was set to 0.005 parts by weight, without stirring in a glass ampoule. Monomers having the same composition as in Example 1 except for polymerization were mixed, degassed under reduced pressure, and then bulk polymerized at 60 ° C. for 16 hours and at 100 ° C. for 8 hours. The polymer obtained was crushed to give a colorless and highly transparent part (about 40% of the whole polymer).
Occluded) was taken out, and the monomer was removed by a vacuum dryer at 115 ° C. for 48 hours to obtain a clad material. The obtained clad material was excellent in colorless transparency as shown in Table 1, but the residual monomer was a little large.

Using this as a clad material and polymethylmethacrylate as a core, composite spinning was carried out to obtain an optical fiber having a diameter of 1000 μm. The results of these characteristics are shown in Table 1, and the wire diameter variation was large.

[Comparative Example 2] A clad material and an optical fiber were obtained in the same manner as in Comparative Example 1 except that the material was vacuum dried at 200 ° C for 3 hours. The obtained clad material was slightly clouded as shown in Table 1, and the translucency of the optical fiber was slightly poor.

[Comparative Example 3] A clad material and an optical fiber were obtained in the same manner as in Example 1 except that the polymerization temperature was 140 ° C. The polymerization rate is stable at 52%, and [M] / [I] is
From the above formula (2), it could be calculated as 5.3 × 10 ⁻⁵ . The obtained clad material was slightly clouded as shown in Table 1, and the translucency of the optical fiber was slightly poor.

[Comparative Example 4] A clad material was obtained in the same manner as in Example 1 except that n-butyl mercaptan was omitted and the polymerization temperature was changed to 170 ° C. The light transmittance was high but the material was slightly cloudy. An optical fiber could not be obtained because it turned yellow and the target molecular weight range was not reached. The polymerization rate was stable at 58%, and [M] / [I]
Was calculated to be 0.4 × 10 ⁻⁵ .

Example 2 Azobis-1,1,3,3-tetramethylbutane 3.0 × 10 3 in molar ratio to the total monomer mixture.
^-5 n-butyl mercaptan 1.0 x 10
^A clad material and an optical fiber were obtained in the same manner as in Example 1 except that ^-5 was mixed and the polymerization temperature was 140 ° C. The polymerization rate was stable at 46%, and [M] / [I]
Was calculated to be 0.8 × 10 ⁻⁵ .

Example 3 The following components: 17FM 41.0 parts by weight 17FA 9.0 parts by weight 3FM 25.0 parts by weight Methyl methacrylate 20.0 parts by weight N-cyclohexylmaleimide 5.0 parts by weight Azobis-1,1,3,3-tetramethylbutane 10.0 × 1 in molar ratio to 1 mol of total monomer mixture
0 ^-5 n-butyl mercaptan 0.8 × 1
0 ^-5 were mixed, polymerization temperature 0.99 ° C., an average residence time of 2.5
A clad material and an optical fiber were obtained in the same manner as in Example 1 except that the polymer (copolymer No. B) was polymerized as hr. The polymerization rate was stable at 56%, and [M] / [I] was 1.
It could be calculated as 6 × 10 ⁻⁵ .

[Comparative Example 5] A clad material and an optical fiber were obtained in the same manner as in Example 3 except that the polymerization temperature was 140 ° C. The polymerization rate is stable at 53%, and [M] / [I] is
It could be calculated as 3.8 × 10 ⁻⁵ . The obtained clad material is
As shown in Table 1, it was slightly clouded, and the optical transparency of the optical fiber was slightly poor.

Example 3 The following components: 17FM 74.0 parts by weight Methyl methacrylate 20.0 parts by weight N-isopropylmaleimide 6.0 parts by weight, and azobisiso in a molar ratio to 1 mol of all these monomer mixtures. Butyronitrile 10.0 × 10 ^-5 n-butyl mercaptan 3.0 × 10 ^-5 was mixed, the polymerization temperature was 110 ° C., and the average residence time was 2.0.
A clad material and an optical fiber were obtained in the same manner as in Example 1 except that (copolymer No. C) was polymerized as hr. The polymerization rate was stable at 45%, and [M] / [I] was 0.
It could be calculated as 5 × 10 ⁻⁵ .

[0065]

[Table 1]

[0066]

According to the present invention, when a clad material made of a low refractive index copolymer containing a long-chain fluoroalkyl (meth) acrylate unit and an N- (fluoro) alkylmaleimide unit is produced, it is colorless and transparent without clouding. It is possible to provide a characteristic suitable for an optical fiber clad material that is excellent in the amount and the amount of residual monomer is small.

Further, from the monomer mixture recovered in the demonomerization step, a high-boiling long-chain fluoroalkyl (meth)
Only the acrylate can be easily separated by distillation purification and reused.

From the above, according to the present invention, it is possible to produce a copolymer in which opaque portions do not coexist. Therefore, it is not necessary to remove the opaque portions as in the conventional method, and it is industrially efficient and stable. An optical fiber clad material can be manufactured.

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

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[Procedure amendment]

[Submission date] February 9, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0053

[Correction method] Change

[Correction content]

The resulting copolymer mixture (Copolymer No.
A) was continuously fed to the thin film type demonomer by passing through a connecting part set at 180 ° C. by a gear pump, and passed through a vent part set at 270 ° C. and an extruding part set at 235 ° C.,
The mixture was discharged at an average residence time of 15 minutes to be made into chips and used as a clad material.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0059

[Correction method] Change

[Correction content]

[Comparative Example 3] A clad material and an optical fiber were obtained in the same manner as in Example 1 except that the polymerization temperature was 140 ° C. The polymerization rate is stable at 52%, and [I] / [M] is
From the above formula (2), it could be calculated as 5.3 × 10 ⁻⁵ . The obtained clad material was slightly clouded as shown in Table 1, and the translucency of the optical fiber was slightly poor.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0060

[Correction method] Change

[Correction content]

[Comparative Example 4] N-butyl mercaptan was used.
And Example 1 except that the polymerization temperature was 170 ° C.
A clad material was obtained in the same manner, but had a high light transmittance.
The target molecule is slightly cloudy and yellowing
I didn't get an optical fiber because I didn't reach the quantity range
It was The polymerization rate is stable at 58%,[I] / [M]
Is 0.4 × 10^-FiveWas calculated.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0061

[Correction method] Change

[Correction content]

Example 2 Azobis-1,1,3,3-tetramethylbutane 3.0 × 10 3 in molar ratio to the total monomer mixture.
^-5 n-butyl mercaptan 1.0 x 10
^A clad material and an optical fiber were obtained in the same manner as in Example 1 except that ^-5 was mixed and the polymerization temperature was 140 ° C. The polymerization rate was stable at 46%, and [I] / [M]
Was calculated to be 0.8 × 10 ⁻⁵ .

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0062

[Correction method] Change

[Correction content]

Example 3 The following components: 17FM 41.0 parts by weight 17FA 9.0 parts by weight 3FM 25.0 parts by weight Methyl methacrylate 20.0 parts by weight N-cyclohexylmaleimide 5.0 parts by weight Azobis-1,1,3,3-tetramethylbutane 10.0 × 1 in molar ratio to 1 mol of total monomer mixture
0 ^-5 n-butyl mercaptan 0.8 × 1
0 ^-5 were mixed, polymerization temperature 0.99 ° C., an average residence time of 2.5
A clad material and an optical fiber were obtained in the same manner as in Example 1 except that the polymer (copolymer No. B) was polymerized as hr. The polymerization rate was stable at 56%, and [I] / [M] was 1.
It could be calculated as 6 × 10 ⁻⁵ .

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0063

[Correction method] Change

[Correction content]

[Comparative Example 5] A clad material and an optical fiber were obtained in the same manner as in Example 3 except that the polymerization temperature was 140 ° C. The polymerization rate is stable at 53%, and [I] / [M] is
It could be calculated as 3.8 × 10 ⁻⁵ . The obtained clad material is
As shown in Table 1, it was slightly clouded, and the optical transparency of the optical fiber was slightly poor.

[Procedure Amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0064

[Correction method] Change

[Correction content]

Example 4 The following components, 17FM 74.0 parts by weight methyl methacrylate 20.0 parts by weight N-isopropylmaleimide 6.0 parts by weight, and azobisiso in a molar ratio to 1 mol of all these monomer mixtures. Butyronitrile 10.0 × 10 ^-5 n-butyl mercaptan 3.0 × 10 ^-5 was mixed, the polymerization temperature was 110 ° C., and the average residence time was 2.0.
A clad material and an optical fiber were obtained in the same manner as in Example 1 except that (copolymer No. C) was polymerized as hr. The polymerization rate was stable at 45%, and [I] / [M] was 0.
It could be calculated as 5 × 10 ⁻⁵ .

Claims (2)

[Claims] 1. A fluoroalkyl (meth) acrylate unit represented by the following general formula [I] is used in an amount of 20 to 99.8 by using a polymerization / demomerization apparatus having a polymerization part, a demomerization part and a connecting part thereof. %, The following general formula [II]
0 to 70% by weight of a fluoroalkyl (meth) acrylate unit represented by and 0.2 to 3 of an N- (fluoro) alkylmaleimide unit represented by the following general formula [III].
A method for producing an optical fiber clad material by polymerizing a copolymer containing 0% by weight and subsequently demonomerizing, wherein the polymerizing section comprises a one-tank continuous polymerization tank, and a polymerization temperature of 160 ° C.
Below, the value of the residual polymerization initiator concentration [I] (mol / l) with respect to the unreacted monomer concentration [M] (mol / l) in the copolymer mixture having a polymerization rate of 35% or more was as follows: (1) Formula: Polymerization is performed so that [I] / [M] <3.0 × 10 ⁻⁵ (1), and then the connecting portion and the demonomer portion are continuously passed. A method for producing an optical fiber clad material, characterized in that a colorless and transparent optical fiber clad material having a residual monomer ratio of 0.5% or less is obtained by performing demonomerization and discharging. [Chemical 1] (Where X 1 is CH ₃ , H, CF ₃ or F, and 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, and 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 derived from them) 2. The copolymer has a fluoroalkyl methacrylate unit represented by the following general formula [IV] of 70 to 70:
89.8% by weight, a fluoroalkyl (meth) acrylate unit represented by the following general formula [II] is 0 to 29.8% by weight, a methyl methacrylate unit is 10 to 29.8% by weight, and the following general formula [III ] The manufacturing method of the optical fiber clad material according to claim 1, which is a copolymer containing 0.2 to 20% by weight of N- (fluoro) alkylmaleimide unit represented by the following formula. [Chemical 4] (Here, n is 1 or 2, m is an integer from 4 to 10, and R is H or F.) (Where X 1 is CH ₃ , H, CF ₃ or F, and 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 derived from them)