JP2507385B2 - Plastic optical fiber with excellent heat resistance - Google Patents

Description

TECHNICAL FIELD The present invention relates to a plastic optical fiber having excellent heat resistance and hole permeability.

[Prior Art] Conventionally, as a plastic optical fiber industrially manufactured and sold, a core-sheath structure having polymethylmethacrylate as a core component and a fluorine-containing polymer having a refractive index lower than that of the core component as a sheath component Fibers are known. However, this conventional plastic optical fiber has its heat resistance, that is, the upper limit temperature at which it can be actually used is about 80 ° C., and it has a drawback that it cannot be applied to applications exposed to higher temperatures.

In order to improve the heat resistance of this plastic optical fiber, various proposals have been made to use a core component polymer having a higher glass transition point. That is, JP-A-60-32004 proposes a plastic optical fiber containing polycarbonate as a core component, and JP-A-58-34404 discloses.
A plastic optical fiber having a core component of a copolymer of a methacrylic acid ester having an alkyl group having 1 to 10 carbon atoms as an ester residue and an aryl methacrylate has been proposed. Further, JP-A-59-20020 proposes a plastic optical fiber having a core component of polymethyl methacrylate obtained by copolymerizing a methacrylic acid ester having an alicyclic hydrocarbon group such as bornyl methacrylate and adamantyl methacrylate. ing. However, these plastic optical fibers have not sufficiently improved their practicality. For example, in the case of the plastic optical fibers disclosed in JP-A-60-32004 and JP-A-58-34404, only colored fibers can be obtained, and compared with an optical fiber having polymethylmethacrylate as a core component. In addition, it has a low light-transmitting property and can transmit light only over a short distance. Further, when it is used at a high temperature for a long time, it is colored due to thermal deterioration and the light-transmitting property is rapidly lowered. Further, in the case of the plastic optical fiber disclosed in JP-A-59-20020, the copolymerization rate is increased,
When the glass transition point is set high, there is a problem that the mechanical properties of the obtained fiber are extremely deteriorated and the monomer cannot be sufficiently reduced because the boiling point of the copolymer component is high.

[Problems to be Solved by the Invention] An object of the present invention is to have excellent translucency and mechanical properties,
Another object of the present invention is to provide a plastic optical fiber having improved heat resistance.

[Means for Solving Problems] The object of the present invention can be achieved by adopting the following configuration.

What is claimed is: 1. A plastic optical fiber comprising a polymer containing an N-alkylmaleimide monomer unit as a core component and a fluorine-containing polymer as a sheath component, wherein the total amount of free carboxyl group and carboxylic acid anhydride of the core component polymer is 10 μeq. A plastic optical fiber with excellent heat resistance, characterized by being less than / g.

In the present invention, the core component polymer constituting the plastic optical fiber is not particularly limited as long as it is a polymer containing an N-alkylmaleimide monomer unit, but a methylmethacrylate copolymer is used in view of optical and mechanical properties of the obtained fiber. Is preferred.

A preferred composition is 5-70 N-alkylmaleimide.
%, Methyl methacrylate is a copolymer of 30 to 95%. More preferably, the N-alkylmaleimide is 10-
It is a copolymer of 50%.

The reason why the copolymerization rate of N-alkylmaleimide is preferably within the above range is that if it is less than 5%, sufficient heat resistance cannot be imparted, and if it exceeds 70%, the mechanical properties of the fiber are significantly deteriorated.

The core component polymer in the present invention may contain a copolymerizable monomer other than methyl methacrylate, for example, a third component such as methyl acrylate, ethyl acrylate, or styrene.

Preferred examples of the substituted alkyl group of N-alkylmaleimide include a hydrocarbon group having 1 to 6 carbon atoms,
Specific examples thereof include substituents such as methyl, ethyl, isopropyl, isobutyl, sec-butyl, t-butyl, 2,2-dimethylpropyl and cyclohexyl. Furthermore, considering the ease of purification in order to increase the purity of the monomer,
Especially preferred are isopropyl, isobutyl, sec-butyl, t-butyl, and 2,2-dimethylpropyl, which are liquid at room temperature.

An alkyl group having 7 or more carbon atoms is not preferable because it has a poor effect of improving heat resistance and it is difficult to purify a monomer. The N-arylmaleimide has colored monomers,
Also, the fiber obtained by copolymerization cannot be used because of its low translucency.

In the core component polymer of the plastic optical fiber of the present invention, the total of free carboxylic groups and carboxylic acid anhydride mainly derived from the synthetic raw material of N-alkylmaleimide monomer is 10 μeq / g (microequivalent / gram) or less. This is very important. When the total amount of the free carboxyl group and the carboxylic acid anhydride exceeds the above range, when the obtained plastic optical fiber is kept at a high temperature, the coloring is remarkably advanced and the translucency is deteriorated with time.

As means for obtaining a polymer having a reduced content of carboxyl groups and carboxylic acid anhydrides, the amounts of maleic acid and maleic anhydride, which are impurities in the maleimide monomer that is a raw material for producing the core component polymer, are extremely high. It is necessary to reduce the amount of the volatile components, and further to remove the volatile components of the polymer obtained by the copolymerization reaction before spinning to efficiently remove maleic acid and maleic anhydride.

The amount of maleic acid and maleic anhydride in the N-alkylmaleimide monomer is preferably less than 0.1 wt%. Specific methods for reducing the amount of maleic anhydride in the monomer include rectification, washing with water / treatment with activated alumina, or a combination of these.

The method for obtaining the core component polymer of the present invention is not particularly limited, but a bulk polymerization method or a solution polymerization method effective for obtaining a polymer having excellent light transmittance is preferable. The radical polymerization initiator used in the polymerization reaction may be a conventionally known compound, for example, azo compounds such as azo-t-butane and azo-t-octane, di-t-butyl peroxide, di-t-butyl peroxide. Examples thereof include organic peroxides such as benzoate. Among these polymerization initiators, azo-t-octane can be particularly preferably used.

Further, as a mercaptan used as a chain transfer agent, n-propyl, n-butyl, n-hexyl, n-dodecyl, i-butyl, i-pentyl, t-butyl, t-
Examples include mercaptans such as hexyl. Of these, n-butyl is particularly preferable.

The polymerization initiator and the chain transfer agent are supplied to the polymerization reaction tank, but they may be mixed in the monomer in advance or diluted with a solvent and supplied to the polymerization reaction tank.

The core component polymer of the present invention may contain other additives. For example, hindered phenol compounds, amines, sulfur compounds, phosphorus compounds and the like, which are generally used as antioxidants and heat deterioration inhibitors, may be added alone or in combination.

In the present invention, the polymer obtained by the polymerization reaction is supplied to the demonomerization step to remove impurities such as unreacted monomer and solvent. After that, the polymer is continuously supplied to the spinning machine in a molten state and merged with the low refractive index polymer of the sheath component to form a plastic fiber having a core-sheath structure.

The sheath component polymer used in the present invention is a fluorine-containing low refractive index polymer, fluoroalkyl acrylate,
Fluoroalkyl methacrylate, fluoroalkyl-
Examples thereof include polymers such as α-fluoroacrylate and fluoroalkyl trifluoromethacrylate, and polymers such as vinylidene fluoride, vinyl fluoride, fluoroolefins such as trifluoroethylene and tetrafluoroethylene.

[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples.

The measurement of translucency in the examples was performed by the cutback method. The heat resistance was evaluated by comparing the initial translucency with the translucency after heat treatment under predetermined conditions.

The contents of free carboxyl groups and carboxylic acid anhydrides in the polymer were measured by the following method. Dissolve 5 g of polymer in 95 g of ethyl acetate, add 5 g of water and heat at 70 ° C for 1 hour.
The carboxylic acid anhydride is hydrolyzed to the free carboxylic acid.
This solution is subjected to potentiometric titration according to a conventional method to quantify the concentration of free carboxyl group.

Example 1 N-isopropyl maleimide containing 0.03 wt% of maleic anhydride 75 parts / hour, methyl methacrylate 175 parts / hour,
While continuously filtering 0.38 parts of n-butyl mercaptan and 0.17 parts of azo-t-octane with a Teflon filter having a pore size of 0.05 μm, the polymer was fed to a polymerization reaction tank to carry out a continuous polymerization reaction. When the reaction temperature was 135 ° C. and the residence time was 4 hours, a polymer having a polymerization rate of 52% was obtained. This polymer is a five-stage vent extruder with the first vent at 190 ° C and 450 torr at the final vent of 25.
The temperature and pressure reduction conditions were gradually strengthened under the conditions of 0 ° C and 1 torr to demonomerize. The obtained polymer was introduced into a composite spinning machine, and α-fluoroacrylic acid trifluoroethyl / α-methyl methyl fluorocopolymer (85/15 molar ratio) was used as a sheath component, and the spinning temperature was 235 ° C and the take-up speed was 10 m / min. Spinning under the conditions,
A core-sheath composite yarn was obtained. The composite yarn was drawn at 180 ° C. by a factor of 2 and coated with polypropylene to form a cord.

The total content of free carboxyl groups and carboxylic acid anhydride in the core component polymer was a very low level of 3 μeq / g. In addition, the residual monomer in the core component polymer was gas chromatographically analyzed and found to contain 0.3 wt% of N-isopropylmaleimide,
It was 0.05 wt% of methyl methacrylate.

Transmitted loss of coded optical fiber is 220 dB / K at 660 nm.
m. Light loss after heat treatment at 125 ℃ for 500 hours is 2
There was almost no change at 35 dB / Km. The mechanical properties such as the flexibility of the fiber and the cord were satisfactory without problems.

Examples 2 to 4, Comparative Examples 1 to 2 Optical fibers were produced under the same conditions as in Example 1 except that the content of maleic anhydride or maleic acid in N-isopropylmaleimide was the value shown in Table 1. .

The characteristics of the obtained fiber and cord are shown in Table 1.

When the total amount of the carboxyl group and the carboxylic acid anhydride in the core component polymer is large, the heat resistance is poor.

[Effects of the Invention] The heat-resistant optical fiber of the present invention is an optical fiber having excellent translucency and mechanical properties, and improved long-term heat resistance and heat coloring resistance, and is resistant to high temperatures of 120 ° C or higher. It can be used in exposed environments.

Claims (1)

(57) [Claims] 1. A plastic optical fiber comprising a core component of a polymer containing an N-alkylmaleimide monomer unit and a sheath component of a fluorine-containing polymer, wherein a free carboxyl group and a carboxylic acid of the core component polymer. The sum of the anhydrides
A plastic optical fiber with excellent heat resistance, which is characterized by less than 10 μeq / g.