JPH0574049B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a novel copolymer used as an optical fiber sheath. Some optical fibers have a core and sheath made of plastic, others have a core made of glass and a sheath made of plastic, and some have both a core and sheath made of glass. It is applicable to both parties. In particular, optical fibers made of plastic have been recognized for their ease of use, and have become important as optical fibers for medium- and short-distance information communications and displays. [Prior art] Physical properties required for optical fiber sheath materials include a low refractive index, high transparency, high heat resistance, high adhesion to the core polymer, and high mechanical strength. The sheath material that has been conventionally used is the following described in Japanese Patent Publication No. 43-8978.

[Problem to be solved by the invention]

A particular problem that requires improvement concerns the softening temperature of the sheath material. According to the findings of the present inventors, in the case of fluoroalkyl methacrylate polymers, it has been found that when plastic optical fibers are left for a long time in an atmosphere several degrees above the softening temperature of the sheath material, the fibers begin to adhere to each other. . Particularly when a large number of fibers are used in a bundle, adhesion between the fibers can be fatal as it reduces the performance of the fibers. In order to increase the softening temperature, a monomer with a relatively high softening temperature such as methyl methacrylate may be copolymerized, but if the amount is too large, the refractive index will increase, so there is a limit to the amount added. Therefore, it has been considered to introduce unsaturated carboxylic acids with higher softening temperatures, such as methacrylic acid and acrylic acid. However, if these unsaturated carboxylic acids are copolymerized to a sufficiently high softening temperature, foaming will occur during molding, resulting in poor fluidity and brittleness of the polymer, so we cannot expect much from it. . The present inventors have been working to improve the heat resistance of polymers and develop sheath polymers that have excellent thermal stability and processability, and have finally achieved their goals and completed the present invention. [Means for solving the problem] The present invention uses 40% by weight or more of fluoroalkyl methacrylate having the following structure.

[C] (m=1 or 2, n=1 to 4, integer from 6 to 10, X
is F or H or Cl) A copolymer obtained by polymerizing a monomer consisting of 0.5 to 10% by weight of orthomethylphenylmaleimide and 1 to 59.5% by weight of other copolymerizable monomer components. This is an optical fiber sheath material made of a copolymer in which the content of unreacted orthomethylphenylmaleimide monomer is 0.1% by weight or less. Conventionally, methyl methacrylate-based and styrene-based polymers copolymerized with orthomethylphenylmaleimide have existed, but these were significantly colored. The present inventors actually copolymerized fluoroalkyl methacrylate and orthomethyl fermaleimide, and discovered that the optical fiber has superior heat resistance, thermal stability, and processability compared to fluoroalkyl methacrylate polymers. It was hopeless in terms of its colorless transparency, which is important as a sheath material. The inventors of the present invention have made extensive studies to solve this problem, and have finally discovered the cause of the coloring and a method for solving it. It was discovered that the coloring was mostly due to unreacted monomers of orthomethylphenylmaleimide. It was confirmed that the polymer from which orthomethylphenylmaleimide was removed to a sufficiently low concentration became colorless. In practice, removal of unreacted orthomethylphenylmaleimide from the polymer has been quite difficult. This is due to the low vapor pressure of orthomethylphenylmaleimide, and even when processed in multiple stages using a vented extruder, several thousand ppm remains, and the polymer is significantly colored. Therefore, the present inventors dissolved the polymer obtained by a batch polymerization method to complete the polymerization in a solvent, and then used a devolatilizing extruder to remove orthomethylphenylmaleimide along with the solvent. It was possible to reduce the residual concentration of maleimide to 0.05% by weight or less. Moreover, it was found that there was almost no coloring of the polymer. For example, the effect of copolymerizing orthomethylphenylmaleimide is that compared to a binary copolymer of fluoroalkyl methacrylate and methyl methacrylate, a ternary copolymer of fluoroalkyl methacrylate, orthomethylphenylmaleimide, and methyl methacrylate What was even more surprising was that as the softening temperature increased, the depolymerization phenomenon during thermoforming, which is characteristic of fluoroalkyl methacrylate components and methyl methacrylate components, could be suppressed. The fluoroalkyl methacrylate in the sheath polymer of the present invention is used to keep the refractive index sufficiently low.
It is necessary that the content be 40% by weight or more. Further, if the amount of orthomethylphenylmaleimide exceeds 10% by weight, the refractive index becomes high and the coloring becomes strong, which is not preferable. On the other hand, below 0.5% by weight, the effect of adding orthomethylphenylmaleimide is minimal. Unless the concentration of orthomethylphenylmaleimide remaining in the polymer is 0.1% by weight or less, coloring will be too strong. More preferably, it is 0.05% by weight or less. Other copolymerizable monomer components include methacrylic esters such as methyl methacrylate and ethyl methacrylate, acrylic esters such as methyl acrylate, ethyl acrylate, and butyl acrylate, and styrene. In particular, it has been found that when styrene is copolymerized in an amount of 0.5 to 2 times the amount of orthomethylphenylmaleimide, the amount of unreacted orthomethylphenylmaleimide is reduced and coloring is suppressed. The sheath polymer of the present invention can be used to manufacture a plastic optical fiber with a core-sheath structure by molding a methyl methacrylate-based polymer or styrene-based polymer as a core at 200 to 260°C using a composite spinning machine, or to manufacture a plastic optical fiber with a core-sheath structure. Optical fibers can be manufactured by coating the sheath material of the invention. The details of the invention are illustrated in Examples. Example 1 Fluoroalkyl methacrylate with the following structure
17FM

[Effects of the present invention]

To enumerate the excellent properties of the sheath copolymer of the present invention, the softening temperature is higher than that of conventionally used fluoroalkyl methacrylate sheath materials;
It has excellent thermal stability and is easy to mold. Moreover, it is a colorless and transparent copolymer with virtually no coloration. Therefore, the optical fiber coated with the sheath copolymer of the present invention can maintain high light guide performance and improve the heat resistance temperature of the optical fiber. In particular, it has become possible to increase the adhesion temperature between bare optical fibers.

Claims (1)

[Scope of Claims] 1 Fluoroalkyl methacrylate having the following structure: (m=1 or 2, n=1 to 4, an integer of 6 to 10, X
is a copolymer obtained by polymerizing monomers consisting of 40% by weight or more of F, H or Cl), 0.5 to 10% by weight of orthomethylphenylmaleimide, and 1 to 59.5% by weight of other copolymerizable monomer components. The content of unreacted orthomethylphenylmaleimide monomer remaining therein is 0.1% by weight.
An optical fiber sheath material made of the following copolymer. 2. Claim 1, wherein the other copolymerizable monomer component is styrene, methacrylic ester, acrylic ester, or a mixture thereof.
The optical fiber sheath material described in Section 1.