JP3408697B2 - Manufacturing method of glass based optical fiber - 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 manufacturing a glass-based optical fiber, particularly a silica glass-based optical fiber.

[0002]

2. Description of the Related Art A glass-based optical fiber such as a silica glass-based optical fiber is generally manufactured by drawing its base material,
Immediately above it, a soft primary coating layer is generally applied. This primary coating layer is applied to prevent the generation of microcracks on the glass surface due to moisture and dust contained in the atmosphere and to prevent or reduce microbending of the optical fiber due to various external forces and internal stress. . A thermosetting resin, an ultraviolet curing resin, or the like is used as a constituent material of the primary coating layer. Soft UV-curable resins are obtained by curing various UV-curable resins by UV irradiation in the presence of a monofunctional monomer, and because of the use of a monofunctional monomer, there are few crosslinking points. Indicates softness. Regarding the conditions for irradiating the optical fiber coating layer with ultraviolet rays, Japanese Patent Publication No. 5-72339 discloses that an ultraviolet curable resin is 25
There is disclosed a method for forming a primary coating layer in which the elastic modulus is adjusted by maintaining a predetermined temperature within the range of up to 200 ° C. and irradiating with ultraviolet light. In addition, the Institute of Electronics, Information and Communication Engineers Autumn Meeting 1993,
No. 4 relates to the formation of a hard secondary coating layer, but the ultraviolet curable resin is kept at a predetermined temperature in the range of 20 to 100 ° C. and irradiated with ultraviolet rays of 30 to 100 mJ / cm ^2. It is disclosed. By the way, using urethane acrylate resin, which is one of the many UV-curable resins known for forming coating layers for optical fibers, and irradiating it with UV light under conventional irradiation conditions in the presence of a monofunctional monomer. When an optical fiber is manufactured, the obtained optical fiber often has a problem that its signal transmission performance changes or deteriorates with time.

The uncured or UV-curable urethane acrylate resin is produced by (1) an initiation reaction in which a photoinitiator incorporated in the resin is cleaved by ultraviolet rays to generate radicals, and (2) an initiation reaction. Via four reactions: a growth reaction in which the degree of polymerization of radicals increases gradually, (3) a chain transfer reaction in which radicals move to another molecule, and (4) a termination reaction in which radicals disappear and the radical reaction stops. It is generally considered to cure. As a result of various investigations for investigating the cause of the above problems based on these reaction mechanisms, the following was found. That is, when the UV-curable urethane acrylate resin is irradiated with UV light at a high temperature in the presence of a monofunctional monomer, the growth reaction is promoted at the early stage of the reaction to generate a growth radical with a slightly large molecular weight, but due to the high temperature of the surrounding environment. The degree of freedom of growing radicals increases, and the termination reaction becomes dominant. As a result, the reaction is completed without the growth reaction progressing sufficiently to obtain a cured product having an uncrosslinked portion. This uncrosslinked portion reacts or volatilizes away during use of the optical fiber, etc.
As a result, the characteristics of the primary coating layer are changed, and eventually the transmission characteristics of the optical fiber are changed.

[0004]

DISCLOSURE OF THE INVENTION The present invention, even when using a UV-curable urethane acrylate resin,
An object of the present invention is to provide a method capable of manufacturing an optical fiber having stable signal transmission performance by irradiating ultraviolet rays.

[0005]

The present invention has the following features. 1. An ultraviolet ray having an irradiation dose of at least 300 mJ / cm ² in the presence of a monofunctional monomer and a layer of an ultraviolet curable urethane acrylate resin coated on a glass optical fiber in the state where the layer is kept at a temperature of 50 ° C. or lower. A method for manufacturing a glass-based optical fiber, which comprises curing by irradiation. 2. 2. The method for producing a glass-based optical fiber according to 1 above, wherein the temperature of the ultraviolet-curable urethane acrylate resin layer is kept at 50 ° C. or lower by a cool air device. 3. UV curable urethane acrylate resin is polytetramethylene glycol, tolylene diisocyanate,
3. The method for producing a glass-based optical fiber as described in 1 or 2 above, which comprises hydroxyethyl acrylate.

[0006]

[Function] By irradiating an ultraviolet-curable urethane acrylate resin layer with ultraviolet rays in the presence of a monofunctional monomer and keeping the layer at a low temperature of 50 ° C. or lower, ultraviolet irradiation at the above-mentioned high temperature is performed. Unlike the above case, the diffusion of the monofunctional monomer, which is a low-molecular component, becomes dominant and the growth reaction is promoted. At least 30 in this situation
By irradiating with an ultraviolet ray as high as 0 mJ / cm ^{2, a} cured urethane acrylate resin layer having very few unreacted parts can be obtained.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The oligomer as the main component of the UV-curable urethane acrylate resin used in the present invention may have various chemical structures known for general coating, optical fiber production, etc., Generally, it is obtained from three kinds of materials of diisocyanate, polyol and hydroxyacrylate, and has a number average molecular weight of 500 to 2
Approximately 30,000, particularly about 1,000 to 7,000 is preferable.

The diisocyanate is, for example, tolylene diisocyanate, 4,4-diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, methylenebis (4-cyclohexylisocyanate), or the like, and one or more diisocyanates are used. .

Examples of polyols include polytetramethylene glycol, cyclic ethers other than tetrahydrofuran, copolymerized diols of at least one of propylene oxide and tetrahydrofuran with tetrahydrofuran, ethylene glycol, polyoxypropylene diamine, and the like. One or more polyols are used.

Examples of the hydroxy acrylate include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, pentaerythritol triacrylate, glycidyl methacrylate, and others, and one or two or more kinds of hydroxy acrylate are used.

A well-known photoinitiator and a monofunctional monomer are mixed and used in the UV-curable urethane acrylate resin. As the photoinitiator, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 1-hydroxycyclohexyl phenyl ketone, benzyl dimethyl ketal, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-propane- 1-one, benzophenone, benzoin ester, benzoin ether or others, in which one or more photoinitiators are used.

As the monofunctional monomer, various monomers used for photopolymerization of a UV-curable urethane acrylate resin, for example, one having one acryloyl group or methacryloyl group or one vinyl group in the molecule may be adopted. it can.

Examples of monofunctional monomers having one acryloyl group or methacryloyl group in the molecule include isobornyl acrylate, hexyl acrylate, 2-
Ethylhexyl acrylate, isooctyl acrylate, decyl acrylate, isodecyl acrylate, lauryl acrylate, stearyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, tetrahydrofurfuryl acrylate,
Butoxyethyl acrylate, ethyldiethylene glycol acrylate, cyclohexyl acrylate, dicyclopentadiene acrylate, polyethylene glycol acrylate, polypropylene glycol acrylate, methyltriethylene glycol acrylate, diethylaminoethyl acrylate, 7-amino-3,7-
Acrylic compounds such as dimethyloctylethyl acrylate, caprolactone-modified tetrafurfuryl acrylate, nonylphenoxy polyethylene glycol, hexyl methacrylate, 2-ethylhexyl methacrylate, isooctyl methacrylate, decyl methacrylate, isodecyl methacrylate, lauryl methacrylate, stearyl methacrylate, 2- Methacrylic compounds such as hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, polypropylene glycol methacrylate, and diethylaminoethyl methacrylate. Examples of monofunctional monomers having one vinyl group in the molecule include N-vinylcaprolactam and N-vinylcaprolactam.
Examples include vinylpyrrolidone, vinylphenol, acrylamide, vinyl acetate, vinyl ether and styrene.

Most of the urethane acrylate oligomers, which are the main components of the UV-curable urethane acrylate resin,
It is a highly viscous liquid at room temperature. Therefore, as the various monofunctional monomers described above, those capable of lowering the viscosity to such an extent that the high-viscosity oligomer can be dissolved and applied to the optical fiber by a usual method are preferable. Further, those which are excellent in terms of the curing rate with respect to the urethane acrylate oligomer, the crosslinking density, and the adhesion to the optical fiber are preferable. From the above viewpoints, particularly preferred monofunctional monomers include isobornyl acrylate, lauryl acrylate, 2-hydroxyethyl acrylate, caprolactone-modified tetrafurfuryl acrylate, nonylphenoxy polyethylene glycol, N-vinylcaprolactam, N-vinylpyrrolidone and the like. Is.

In the present invention, a UV-curable urethane acrylate resin containing a photoinitiator and a monofunctional monomer is coated on an optical fiber drawn from an optical fiber base material by a conventional method, and then coated. It is cured by being irradiated with ultraviolet rays at an irradiation dose of at least 300 mJ / cm ^{2 while} being kept at a temperature of 50 ° C. or lower, but particularly at least 350 mJ / cm 2 while being kept at a temperature of 40 ° C. or lower.
It is preferable to perform irradiation curing at an irradiation amount of ² .

The method of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a sectional view of an example of an apparatus used for carrying out the method of the present invention, in which 1 is an optical fiber preform P.
A heating furnace for drawing the coating material, 2 is a paint tank having a nozzle 21 containing a paint C made of an ultraviolet curable urethane acrylate resin composition, and 3 is a coating layer of the paint C applied on the optical fiber F with ultraviolet rays. It is a curing treatment tank for curing by irradiation. The curing treatment tank 3 includes an outer wall 31, a quartz glass tube 32 that serves as a passage for the optical fiber F, a tubular cold mirror 33 having an elliptical opening cross section, an ultraviolet lamp 34 installed in the cold mirror 33, and a ventilation introduction tube. Three
5, a ventilation lead-out pipe 36, and a cold air supply device 37 inserted into the lower end opening of the quartz glass pipe 32.
The quartz glass tube 32 is installed so as to penetrate through the curing treatment tank 3, and its upper end is open to the atmosphere in conformity with the opening provided on the upper wall of the outer wall 31. Quartz glass tube 3
The lower end of 2 penetrates the lower surface wall of the outer wall 31 and projects into the atmosphere. The cold mirror 33 has, over its entire length, a curved surface that collects the ultraviolet rays emitted from the ultraviolet lamp 34 on the surface of the optical fiber F passing through the quartz glass tube 32, and also the infrared rays emitted from the ultraviolet lamp 34. It also has the function of absorbing. Cold air supply device 3
7 includes a cold air supply pipe 371 and an annular gas distribution portion 372 connected to the cold air supply pipe 371. The gas distribution portion 372 has an annular gas outlet 373. Inside the annular gas distributor 372 is a passage for the optical fiber F.

The optical fiber F drawn from the optical fiber preform P descends as shown by the arrow and sequentially passes through the paint tank 2, the quartz glass tube 32, and the cool air supply device 37. The coating material C is applied to the optical fiber F in the coating material tank 2 to form a coating layer on the surface thereof, and the coating layer is irradiated with ultraviolet rays and cured while passing through the quartz glass tube 32. The temperature inside each of the hardening tank 3 and the quartz glass tube 32 rises due to the heat from the ultraviolet lamp 34. Since this temperature rise, especially that inside the quartz glass tube 32, is a bad thing in the practice of the present invention, in order to prevent this, cool air is supplied from the gas outlet port 373 of the cold air supply device 37 to the quartz glass tube 32. The coating layer on the optical fiber F is continuously discharged and kept at a low temperature of 50 ° C. or lower. As the cool air, an inert gas such as nitrogen, argon or helium is suitable. The temperature of the cold air required to realize the required cooling varies depending on the size and the linear velocity of the optical fiber F or the flow rate of the cold air itself, but generally about 5 to 25 ° C. is appropriate. During normal operation, the atmosphere is introduced from the ventilation inlet pipe 35 and exhausted from the ventilation outlet pipe 36 to prevent an excessive temperature rise of the curing treatment tank 3, but if necessary, increase this ventilation amount. It is also possible to indirectly assist the cooling inside the quartz glass tube 32.

[0018]

EXAMPLES The present invention will be described in more detail below with reference to Examples, and Comparative Examples will also be shown to show the remarkable effects of the present invention.

The following two types were prepared as the ultraviolet curable urethane acrylate resin. Resin 1: Polytetramethylene glycol, tolylene diisocyanate as urethane acrylate oligomer,
And 60 parts by weight of 2-hydroxyethyl acrylate, 10 parts by weight of caprolactone-modified tetrafurfuryl acrylate as a monofunctional monomer and 30 parts by weight of nonylphenoxy polyethylene glycol,
And 1 part by weight of 2,4,6-trimethylbenzoyldiphenylphosphine oxide as a photoinitiator. Resin 2: Polytetramethylene glycol, tolylene diisocyanate as urethane acrylate oligomer,
And 60 parts by weight of 2-hydroxyethyl acrylate, 10 parts by weight of caprolactone-modified tetrafurfuryl acrylate as a monofunctional monomer and 30 parts by weight of nonylphenoxy polyethylene glycol,
And a photoinitiator consisting of 0.5 parts by weight of 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 0.5 parts by weight of benzyl dimethyl ketal.

Example 1 The above resin 1 was applied onto an SM type silica glass optical fiber having an outer diameter of 125 μm which was continuously drawn from an optical fiber preform at a linear velocity of 600 m / min. The coating layer was cured in the same type of curing treatment tank as in Example ^{1 under} the irradiation conditions of an average temperature of 25 ° C. and an irradiation amount of 450 mJ / cm ² , and thus an optical fiber having an average thickness of the cured coating layer of 30 μm was obtained. Further, helium cooled to 15 ° C. was continuously supplied into the quartz glass tube at a flow rate of 10 liter / min to maintain the coating layer at the temperature as described above.

Example 2 An optical fiber having an average thickness of the cured coating layer of 30 μm was obtained by the same method and conditions as in Example 1 except that the irradiation amount of the coating layer was 350 mJ / cm ² .

Example 3 An optical fiber having an average thickness of the cured coating layer of 30 μm was obtained by the same method and conditions as in Example 1 except that the above resin 2 was used as the UV curable urethane acrylate resin.

Example 4 An optical fiber having an average thickness of the cured coating layer of 30 μm was obtained by the same method and conditions as in Example 3 except that the irradiation amount of the coating layer was 350 mJ / cm ² .

Comparative Example 1 The average temperature of the coating layer was 60 ° C., and the irradiation dose was 100 mJ / cm 2.
An optical fiber having an average thickness of the cured coating layer of 30 μm was obtained by the same method and conditions as in Example 1 except that the irradiation condition was ² .

Comparative Example 2 The coating layer has an average temperature of 60 ° C. and an irradiation dose of 100 mJ / cm 2.
An optical fiber having an average thickness of the cured coating layer of 30 μm was obtained by the same method and conditions as in Example 3 except that the irradiation conditions of ² were used.

Next, Examples 1 to 4 and Comparative Examples 1 and 2
With respect to each of the optical fibers obtained from the above, the gel fraction of the cured coating layer and the degree of change in signal transmission performance over time were measured by the methods described below. The measurement results are shown in Table 1.

[0027]

[Table 1]

Method for measuring the gel fraction of the cured coating layer: According to the Soxhlet extraction method using methyl ethyl ketone as the extraction solvent. The extraction was performed for 5 hours. Measuring method of the degree of change with time of signal transmission performance: 48 at 100 ° C
After heating for an hour, 10 heat cycles are performed between -40 ° C and + 70 ° C. Each holding time at −40 ° C. and + 70 ° C. is 120 minutes. The amount of change in transmission loss before and after this heating and heat cycle is measured.

From Table 1, the cured coating layer of the optical fiber produced by the method of the present invention not only has a high gel fraction,
It can be seen that the amount of change in transmission loss before and after heating the optical fiber itself is extremely small compared to those of the optical fiber obtained from the comparative example, and the signal transmission performance is stable.

[0030]

The optical fiber manufactured according to the present invention is suitable for various applications requiring high-performance signal transmission because the signal transmission performance is extremely stable over time.

[Brief description of drawings]

1 is a cross-sectional view of an exemplary apparatus used to carry out the method of the present invention.

[Explanation of symbols]

P Optical fiber base material F optical fiber 1 heating furnace 2 paint tanks 3 curing tank 32 quartz glass tube 33 Cold Mirror 34 UV lamp 37 Cold air supply device

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Claims (4)

(57) [Claims] 1. A state where and holding the said layer at a temperature of 50 ° C. below the layer of the coated UV-curable urethane acrylate resin in the presence of a monofunctional monomer on the glass optical fiber 3 mJ / cm ² A method for manufacturing a glass-based optical fiber, which is characterized in that it is cured by irradiation with the above-mentioned irradiation amount of ultraviolet rays. 2. Purple coated on a glass-based optical fiber
A layer of external ray curable urethane acrylate resin is used as a monofunctional monolayer.
And the layer was kept at a temperature below 50 ° C.
For UV irradiation with a dose of 300 mJ / cm ² or more
And the gel fraction of the layer is 94% by weight or more.
And a method for manufacturing a glass-based optical fiber . 3. A process according to claim 1 or 2 glass-based optical fiber according to maintain the temperature of the UV-curable urethane acrylate resin layer by cool air device 50 ° C. or less. 4. The method for producing a glass-based optical fiber according to claim 1, wherein the ultraviolet curable urethane acrylate resin comprises polytetramethylene glycol, tolylene diisocyanate, and hydroxyethyl acrylate.