JPH0226201B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a plastic optical fiber that uses a methyl methacrylate polymer as a core component, and the light transmission efficiency is improved by using a highly purified methyl methacrylate monomer as a raw material for the core component methyl methacrylate polymer. Regarding plastic optical fibers. Compared to inorganic glass, especially quartz glass fiber, plastic optical fiber has excellent flexibility even when made to a large diameter, is lightweight, and can easily be obtained with a high numerical aperture, so it has low connection loss with the light source. Moreover, it has the characteristic of being extremely inexpensive because it can be industrially mass-produced, and various technical efforts have been made to improve it. One of the factors that reduces the light transmission efficiency of plastic optical fibers whose core component is methyl methacrylate polymer is due to the difference in absorption in the visible light region and absorption in the ultraviolet region. We believe that these absorptions, which cause a decrease in optical transmission efficiency,
Core component methyl methacrylate polymer When trace amounts of impurities contained in the raw material monomers are not sufficiently removed by conventional purification methods and remain, or when the impurities themselves do not have the ability to absorb wavelengths in the visible and ultraviolet regions. We believe that this occurs during the process of forming polymers to form compounds and functional groups that absorb wavelengths in the visible and ultraviolet regions, and we have conducted extensive studies on various advanced purification methods for monomers, and have developed the method described in the present invention. The present invention was achieved by discovering the surprising fact that light transmission efficiency is dramatically improved by using highly purified methyl methacrylate monomers as raw materials for core methyl methacrylate polymers. be. That is, the gist of the present invention is that in plastic optical fibers using methyl methacrylate polymer as the core component, methyl methacrylate monomer pretreated with a reducing compound is used as a raw material for the core component methyl methacrylate polymer. This is a plastic optical fiber characterized by being used as a plastic optical fiber. This will be explained in detail below. Although the theory of the effect of pre-treating methyl methacrylate monomer with a reducing compound, which is the purification method of the present invention, is not fully clear, it is believed that trace amounts of oxidizing substances remaining in methyl methacrylate monomer may be absorbed during polymer formation. It is assumed that a side reaction occurs, forming a compound or functional group that absorbs visible and ultraviolet wavelength light, which causes a decrease in light transmission efficiency, and that oxidizing substances are reduced by treatment with a reducing compound. It is presumed that this material becomes an inert substance, thereby improving optical transmission efficiency. As the reducing compound used in the present invention, any generally known reducing compound can be used. Preferably, the reducing compound is a compound that generates hydrogen in the presence of water, and it is particularly preferable to use a hydrogenated compound as the reducing compound. Examples include lithium hydride, calcium hydride, magnesium hydride, barium hydride, and borohydride. The amount of reducing compound used is relative to the monomers being treated.
0.01-10% by weight, more preferably 0.1-5% by weight
is desirable. As a pretreatment method, methyl methacrylate monomer may be treated in the presence of a predetermined amount of reducing compound, stirring and mixing may be performed to improve treatment efficiency, or hydrogen may be generated in the presence of water. When a reducing substance is used, it is preferable to add a small amount of water for pretreatment. The methacrylic acid ester monomer pretreated in this manner is purified by vacuum distillation and used as a raw material for a methyl methacrylate polymer. The core component methyl methacrylate polymer used in the present invention may be a copolymer with other copolymerizable monomers such as methyl acrylate, ethyl acrylate, methyl methacrylate, butyl methacrylate, and in that case, The monomers to be copolymerized must also undergo the same purification treatment used in the present invention. In that case, it is desirable that the amount of monomer components other than methyl methacrylate in the polymer is 10% by weight or less. Although any polymerization method may be used, bulk polymerization is preferred in order to avoid contamination with dust, impurities, and the like. Polymerization is performed using an appropriate initiator and chain transfer agent under appropriate polymerization temperature conditions to obtain a polymer. Using the polymer obtained in this way, spinning is performed with a sheath component resin having a lower refractive index than the core component, and any method such as coating method or melt spinning method may be selected as the spinning method. From an industrial standpoint, melt spinning is preferred. The plastic optical fiber obtained as described above has dramatically improved optical transmission efficiency and excellent mechanical strength, making it possible to expand the scope of its application to short-distance transmission systems. be. The present invention will be explained below with reference to Examples. The optical transmission efficiency was automatically measured between 400 and 700 nm using an optical fiber loss spectrometer manufactured by Operax Co., Ltd., and was expressed in (dB/Km). Example 1 and Comparative Example 1 1000 c.c. of methyl methacrylate polymer and 5 g of calcium hydride were mixed in a 2000 c.c. glass container while stirring.
I did some time processing. After removing residual calcium hydride, vacuum distillation was performed to obtain purified methyl methacrylate monomer. Charge 500 g of purified monomer, 0.1 g of AIBN, and 1 g of n-butyl mercaptan in a completely closed system, and heat at 60℃ for 6 hours.
Polymerization was carried out at 100° C. for 1 hour to complete the polymerization. Composite melt spinning was performed using the thus obtained methyl methacrylate polymer as the core component and the fluorinated methacrylate copolymer as the sheath component to obtain a fiber. As a comparative example, methyl methacrylate monomer purified only by vacuum distillation without pretreatment was used, and polymerization and fiber formation were carried out in the same manner as in the examples.

[Table] As shown in Table 1, in the case of the example in which pretreatment was performed, the loss at the short wavelength side of 450 nm is significantly lower than that of the comparative example, and the loss value at 570 and 650 nm is also lower. are doing. Example 2 2000 c.c. of methyl methacrylate monomer and 10 g of lithium hydride were stirred in a 3000 c.c. glass container while maintaining the internal temperature at 5° C., and treated for about 5 hours. After converting the remaining lithium hydride, vacuum distillation is performed,
Purified methyl methacrylate monomer was obtained. Purified monomer 1000c.c. and tert-azobutane 0.5g, n
-Prepare 2g of butyl mercaptan in a completely closed system
After polymerizing at 130°C for 10 hours, polymerization was completed at 180°C for 5 hours. Performing composite melt spinning using the thus obtained methyl methacrylate polymer as a core component and the fluorinated methacrylate copolymer as a sheath component,
Got fiber. Table 2 shows the results.

[Table] As shown in Table 2, the loss on the short wavelength side of 450 nm is significantly reduced compared to the comparative example, and the loss value is also reduced at 570 and 650 nm. Example 3 1000 c.c. of methyl methacrylate monomer and 5 g of lithium hydride were treated in a 1000 c.c. glass container with stirring for about 5 hours, and then left at 0° C. overnight.
After removing residual lithium hydride, vacuum distillation was performed to obtain purified methyl methacrylate monomer. 500 c.c. of purified monomer, 0.1 g of azobisisovaleronitrile, and 1 g of n-butyl mercaptan were charged in a completely closed system, and polymerization was carried out at 60°C for 3 hours and at 90°C for 1 hour to complete the polymerization. Composite melt spinning is performed using the thus obtained methyl methacrylate polymer as a core component and the fluorinated methacrylate copolymer as a sheath component,
Got fiber. The results are shown in Table 3.

[Table] As shown in Table 3, as in Examples 1 and 2, the loss on the short wavelength side of 450 nm was significantly reduced compared to the comparative example, and the loss value also decreased on the short wavelength side of 570 and 650 nm. There is. Example 4 1000 c.c. of methyl methacrylate monomer and 5 g of calcium hydride were stirred in a 1000 c.c. glass container while maintaining the internal temperature at 5°C, and about 1 c.c. of water was gradually added. The treatment was carried out for 5 hours while dripping. After removing residual calcium, distillation was carried out under reduced pressure to obtain purified methyl methacrylate monomer. Purified monomer 500c.c. and tert-azobutane 0.5g, n
-Prepare 2g of butyl mercaptan in a completely closed system
Polymerization was carried out at 130°C for 10 hours and then at 180°C for 5 hours to complete the polymerization. Performing composite melt spinning using the thus obtained methyl methacrylate polymer as a core component and the fluorinated methacrylate copolymer as a sheath component,
Got fiber. Table 4 shows the results.

[Table] As shown in Table 4, when the monomer is treated by adding a small amount of water, a fiber with a further reduced loss value is obtained when compared to the comparative example as well as the other examples.

Claims (1)

[Scope of Claims] 1. In a plastic optical fiber using a methyl methacrylate polymer as a core component, a methyl methacrylate monomer pretreated with a reducing compound is used as a raw material for the core component methyl methacrylate polymer. A plastic optical fiber featuring: 2. The plastic optical fiber according to claim 1, wherein the reducing compound is a compound that generates hydrogen in the presence of water. 3. The plastic optical fiber according to claim 1, wherein the reducing compound is a hydrogenated compound.