JP2555576B2 - Plastic optical fiber with excellent thermal decomposition resistance - Google Patents

Description

TECHNICAL FIELD The present invention relates to a plastic optical fiber having excellent thermal decomposition resistance. More specifically, the present invention relates to a plastic optical fiber that has excellent thermal decomposition resistance near the molding processing temperature of a plastic optical fiber and suppresses thermal degradation, thereby improving the light transmission performance.

(Prior Art) Since a plastic optical fiber is more flexible than an inorganic optical fiber such as quartz, it can have a large diameter and is lightweight, and thus is excellent in workability and workability. In recent years, plastic optical fibers have been improved in light transmission performance in addition to the above advantages, and therefore, demand has rapidly increased in the field of short-distance communication such as terminal wiring of computers and mobile units.

However, the light transmission performance of the conventional plastic optical fiber is still not sufficient, for example, at a loss of 650 mm, which is about 200 dB / km, which is large compared to the theoretical value of 100 dB / km. For example, a plastic optical fiber obtained by a method of producing a polymer after thoroughly removing dust in the air mixed in a monomer as proposed in JP-A-58-68003, Although it is possible to suppress the scattering of foreign matter and reduce the light transmission loss to some extent, this is not yet sufficient. In other words, a thermal decomposition product is generated by the heat received during the molding process of the plastic optical fiber, so that the ultraviolet absorption loss increases and the light transmission performance deteriorates.

Further, the plastic optical fiber obtained by the method of removing oxygen and peroxide contained in the monomer as proposed in JP-A-58-193502 can suppress the ultraviolet absorption loss due to oxidative decomposition. Since the thermal decomposition resistance is not improved, it is impossible to suppress an increase in ultraviolet absorption loss due to thermal decomposition during molding of the plastic optical fiber.

Furthermore, as a method for suppressing thermal decomposition, it has been proposed to lower the molding temperature by lowering the molecular weight or adding a polymer melt viscosity reducing agent, but in that case, the decrease in mechanical strength of the plastic optical fiber is a problem. Becomes

(Problems to be Solved by the Invention) The object of the present invention is to suppress thermal decomposition during molding, which is a drawback of the conventional method, without deteriorating the mechanical strength of the plastic optical fiber, and to modify the thermal decomposition product. It is to provide a low loss plastic optical fiber with reduced ultraviolet absorption loss.

(Means for Solving Problems) The present invention has the following configurations.

A core-sheath composite plastic optical fiber, wherein the core component is a polymer containing at least 80% by weight of methyl methacrylate units, and the sheath component is a polymer having a refractive index smaller than that of the core component polymer by 2% or more, A plastic optical fiber excellent in thermal decomposition resistance, wherein the core component polymer contains a structural unit represented by the following formula (I).

(In the formula (I), R represents an alkylene group having 1 to 18 carbon atoms) Hereinafter, the constitution of the present invention will be described in detail.

The core component polymer in the present invention is not particularly limited as long as it contains 80% by weight or more of methyl methacrylate unit and contains the structural unit of the formula (I), and polymethyl methacrylate, It may be either a methyl methacrylate-based copolymer or a polymer mixture mainly composed of polymethyl methacrylate. At that time, the sub-monomer as the copolymer is not particularly limited as long as it can be copolymerized with methyl methacrylate, but from the viewpoint of transparency, mechanical properties and heat resistance, styrene and acrylic acid. Vinyl compounds such as methyl, ethyl acrylate, cyclohexyl methacrylate, phenyl methacrylate, bornyl methacrylate and adamantyl methacrylate are preferred. Further, as the polymer to be mixed with polymethylmethacrylate, a polymer such as polystyrene or polycarbonate is suitable from the viewpoint of transparency, but is not particularly limited.

Next, the sheath component polymer in the present invention is not particularly limited as long as it has a refractive index smaller than that of the core component polymer by 2% or more, but is a fluorinated olefin such as a tetrafluoroethylene unit or a fluorinated vinylidene unit. A polymer containing a compound, and further a polymer containing a methacrylic acid fluorinated alkyl ester compound such as a trifluoroethyl methacrylate unit and a pentafluoropropyl methacrylate unit are preferable.

Next, in the present invention, the relationship between the structural unit represented by the following formula (I) contained in the core component polymer and the thermal decomposition resistance of the polymer will be described.

(In the formula (I), R represents an alkylene group having 1 to 18 carbon atoms) The structural unit of the formula (I) is HS-R as a chain transfer agent.
-SH (R is an alkylene group having 1 to 18 carbon atoms) 2
It is produced by polymerizing methyl methacrylate with a functional alkylene mercaptan compound.

It is well known that in a polymer having a methyl methacrylate unit as a main component, thermal decomposition proceeds in a zipper form from the polymer end. It is also well known that the polymer contains a vinyl group at its end due to the polymerization termination mechanism of the polymer and the end of the vinyl group is easily decomposed by heat. Therefore, a chain transfer agent such as a mercaptan compound is used as a vinyl group-capping agent at the polymer terminal.

However, according to the studies by the present inventors, it was revealed that the thermal decomposability of the polymer when the chain transfer to the vinyl group at the terminal of the polymer was completely proceeded was largely different depending on the chain transfer agent used.

That is, as is clear from the comparison of the heating weight retention rate shown in Table 1, one of a monofunctional thioglycolic acid ester compound, a monofunctional alkyl mercaptan compound and a bifunctional alkylene mercaptan compound was selected as the chain transfer agent. In comparison, the polymer obtained by using the bifunctional alkylene mercaptan has a surprisingly high heating weight retention rate and excellent thermal decomposition resistance.

As a result of further study on this factor, the monofunctional mercaptan compound showed that the monofunctional mercaptan compound radical was newly added to the monomer after the chain transfer of hydrogen to the polymer terminal. Whereas the S-C bond is formed, when a bifunctional mercaptan is used, the S-C bond is present in the approximate center of the polymer chain, and the polymer ends are all functionalized with a vinyl group blocked by hydrogenation. It became clear that it was a group.

Here, in the bond dissociation energy of the methane derivative,
CH ₃ -H time of 102Kcal / mol, also CH ₃ in -CH ₃ 84.2Kcal / m
On the other hand, since CH ₃ S—CH ₃ has a small dissociation energy of 73.2 Kcal / mol, it can be considered that the thermal decomposition resistance decreases when it is generated at the terminal of the S—C bond polymer.

From this point of view, in order to achieve the object of the present invention, it is necessary that the core component polymer has a structural unit represented by the following formula (I).

(In the formula (I), R represents an alkylene group having 1 to 18 carbon atoms) Here, as the chain transfer agent forming the structural unit of the formula (I), dimercaptomethane, dimercaptoethane, dimercaptohexane, etc. However, it is not particularly limited as long as it is a bifunctional mercaptan having an alkylene group having 1 to 18 carbon atoms.

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

(Example) Example 1 Methyl methacrylate was bubble-treated with nitrogen having an oxygen content of 0.1 ppm or less, and then purified by distillation under a vacuum with an atmospheric pressure of 80 Torr. Subsequent 2.2'azobisoctane 1.7 x 10 ^-5 mol / distilled and purified as a radical initiator to the methyl methacrylate and 1 mol of feed methyl methacrylate monomer and dimercaptoethane 1.9 x previously distilled and purified as a chain transfer agent. 10 ⁻³ mol / feed of methyl methacrylate monomer (1 mol) was mixed and continuously supplied to the complete mixing reaction zone at a polymerization temperature of 130 ° C. After the polymerization was carried out with the residence time in the reaction zone being 3.5 hours, the reaction liquid was under the condition of 260 ° C / 1 Torr and the residence time calculated by the piston flow type flow
It was continuously fed to a de-monomer type extruder for 10 minutes. Furthermore, a pipe width with a residence time of 30 minutes calculated by the piston flow type flow from the extruder head to the yarn making head is transported under heating conditions of 260 ° C, and tetrafluoro is used at a spinning temperature of 260 ° C from the yarn making head. A plastic optical fiber was obtained by composite spinning with a sheath component polymer composed of a propyl methacrylate / methyl methacrylate copolymer. Analysis of poly (methyl methacrylate), which is the core component of the obtained plastic optical fiber, showed that the molecular weight (Mw) of the polymer collected by the de-monomer type extruder head was 88,000, the residual monomer ratio was 0.10%, and the dimer content was 30p
pm, and the residual monomer ratio of the polymer collected at the yarn making head is also
The 0.10% dimer content was also 30 ppm and no thermal deterioration was observed. The transmission loss of this plastic optical fiber is 400n
150 dB / km, 10 at m, 450 nm, 570 nm and 650 nm wavelengths
The light transmission performance was extremely excellent at 0 dB / km, 65 dB / km, and 135 dB / km.

Comparative Example 1 A plastic optical fiber was produced in the same manner as in Example 1 except that the chain transfer agent was normal butyl mercaptan. The residual monomer ratio of the core component polymer in the de-monomer type extruder head is 0.10%, and the residual monomer ratio in the yarn making head is 0.15%, while the dimer content is 70 ppm.
Thermal decomposition of 140ppm and about 0.05% was observed. Transmission loss of plastic optical fiber is 400nm, 450nm, 570nm, 650nm
270 dB / km, 190 dB / km, 90 dB / k at each wavelength of
Only m and 155 dB / km were obtained, especially those with poor light transmission performance in the near ultraviolet region.

Comparative Example 2 A plastic optical fiber was produced in the same manner as in Example 1 except that 2-ethylhexyl thioglycolate was used as the chain transfer agent. Residual monomer ratio of depolymerization type extruder head of core component polymer 0.12%, dimer content
180ppm, whereas the residual monomer ratio at the spinning head
It was 0.25% and the dimer content was 390 ppm, indicating that thermal deterioration had progressed considerably. The transmission loss of plastic optical fiber is 40
42 at each wavelength of 0 nm, 450 nm, 570 nm and 650 nm
Only 0 dB / km, 330 dB / km, 115 dB / km and 190 dB / km with further deteriorated light transmission performance were obtained.

(Effects of the Invention) The effects of the plastic optical fiber of the present invention are summarized as follows.

The core component polymer is extremely excellent in thermal decomposition resistance.

Since the thermal decomposition during plastic optical fiber molding is extremely small, the light transmission loss due to the thermal decomposition product is extremely small,
Excellent light transmission performance of plastic optical fiber.

Especially, the light transmission loss outside the near ultraviolet is small.

When polymethylmethacrylate is produced as the core component polymer, the chain transfer constant is close to 1, so that the molecular weight distribution of the core component polymer can be extremely narrowed.

Since the chain transfer constant is large, a small amount can be added when adjusting the molecular weight of the core component polymer.

Claims (1)

(57) [Claims] 1. A core-sheath composite type in which the core component is a polymer containing at least 80% by weight of methyl methacrylate units, and the sheath component is a polymer having a refractive index of 2% or more smaller than that of the core component polymer. In the plastic optical fiber, the core component polymer contains a structural unit represented by the following formula (I), which is excellent in thermal decomposition resistance. (In the formula (I), R represents an alkylene group having 1 to 18 carbon atoms)