JPS60222808A - Plastic optical fiber - Google Patents

Abstract

PURPOSE:To prevent deterioration of light transmission characteristics under high temp. and high humidity by forming at least one covering layer on a stretched plastic elemental optical fiber and using an ethylene-ethyl acrylate copolymer for the outermost layer. CONSTITUTION:The intended core 1a is made of the polymer essentially consisting of PMMA or the like, and its clad 1b is made of fluororesin or the like to form a pastic elemental optical fiber 1, and it is stretched longitudinally to reduce its breakability or brittleness. The covering layer 2 made of the ethylene- ethyl acrylate copolymer is formed on the outer circumference of the fiber 1 by using an extruder or the like to obtain the intended plastic optical fiber. As a result, when the fiber 1 is placed under conditions of high humidity and high temp., the fiber 1 tends to contrast, but since the contraction force is compensated with the heat expansion force, thus suppressing the contraction.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a plastic optical fiber having good moisture and heat resistance.

Prior art and its disadvantages Plastic optical fiber (hereinafter abbreviated as POF)
Generally, the core is composed of a polymer mainly composed of polymethyl methacrylate, and the cladding is composed of a polymer mainly composed of vinylidene fluoride/tetrafluoroethylene copolymer or fluorinated alkyl methacrylate. Since the polymethyl methacrylate that forms the core of this kind of POF is inherently prone to breakage, it is stretched in the length direction during manufacturing to make it less likely to break.For this reason, this type of POF is When heated to 120°C, it begins to shrink and its length shrinks by about 50%. Also, the POF with, for example 7
When placed under high temperature and high humidity conditions of 0 to 80° C. and 80 to 100% RH, it shrinks and has the drawback of increasing transmission loss.

Purpose of the Invention The present invention was made in view of the above circumstances, and an object thereof is to provide a POF whose transmission characteristics do not deteriorate even when placed under high temperature and high humidity conditions.

Structure of the Invention In the POF of the present invention, one or more coating layers are formed on the POF wire, and the outermost layer of these coating layers is made of ethylene.
It is made of ethyl acrylate copolymer.

Detailed structure of the invention and its operation FIG. 1 shows an example of the POF of the invention, and reference numeral 1 in the figure is a POF wire. This POF wire 1 has a core 1
It consists of a cladding 1b and a cladding 1b, and is drawn during production of the wire. A coating layer 2 is provided on the POF wire 1.

This coating layer 2 is made of ethylene/ethyl acrylate copolymer and has a thickness of about 0.1 to 1.0 mm.

The ethylene/ethyl acrylate copolymer used here has a content of ethyl acrylate, a copolymer component, of 9.
A content in the range of 22 wt% is preferably used. When the content of ethyl acrylate is less than 9 wt%, the adhesion between the coating layer 2 and the cladding lb of the POF wire 1 is low.
The shrinkage of the wire 1 cannot be sufficiently suppressed, and the melting temperature of the ethylene-ethyl acrylate copolymer becomes high, and the POF wire 1 is placed in a high temperature state during the formation of the coating layer 1, resulting in shrinkage. This causes a slight bend at the interface between the core 1a and the cladding 1b, which increases transmission loss and causes a disadvantage. On the other hand, if the content exceeds 22 wt%, although the effect of improving heat and humidity resistance can be obtained, the thermal softening point of the ethylene/ethyl acrylate copolymer is too low to be suitable for practical use. Furthermore, if the thickness of the coating layer 2 is less than [11,..., the thickness is too thin to resist the contractile force of the POF cable 1, and moist heat resistance cannot be obtained, and the thickness exceeds 1+i'e. However, the increase in the effect of improving heat and humidity resistance reaches a plateau, and it is also uneconomical.

This coating layer 2 is formed using an extruder equipped with a cross-layer Rad die. The extrusion temperature is about 120 to 150°C. In order to prevent the wire 1 from shrinking due to heat during extrusion coating, the feeding speed of the POF wire 1 is increased as well as the winding speed of the POF after extrusion coating, and a tensile force is constantly applied to the wire 1. It is preferable to
It is also preferable to carry out treatment such as cooling the mandrel portion of the die through which it passes with water.

In such a POF, the adhesion between the cladding lb of the POF wire 1 and the ethylene/field acrylate copolymer of the coating layer 2 is good, and the linear expansion coefficient of the ethylene/ethyl acrylate copolymer itself is good. is 1.7~Z6X10″-4
17) When the POF is placed under moist heat conditions, the POF strand 1 tends to shrink, but the coating layer 2 made of ethylene/ethyl acrylate copolymer on the strand 1 tends to shrink.
are in close contact with each other, the force that causes the wire 1 to shrink is canceled out by the thermal expansion force of the ethylene-ethyl acrylate copolymer, and the contraction of the POF wire 1 is effectively met.
Therefore, an increase in transmission loss can be prevented. Further, since shrinkage of the wire 1 is prevented, fluctuations at the interface between the core la and the cladding 1b do not occur, and an increase in transmission loss due to this fluctuation is also prevented.

Furthermore, since the coating layer 2 can be formed by an extrusion coating method, this POF can be obtained efficiently and at low cost.

Another Example of the Invention FIG. 2 shows another example of the POF of the invention. In the POF of this example, a first coating layer 3 made of ultraviolet curing resin is formed on the POF wire 1, and a second coating layer 3 made of ethylene-ethyl acrylate copolymer is formed on this @1 coating layer 3.
A covering layer 4 is provided. The ultraviolet curable resin constituting the first coating layer 3 is obtained by applying an ultraviolet curable resin liquid containing an unsaturated resin, a vinyl compound, and a photopolymerization initiator as main components to the wire 1, and curing it by irradiating it with ultraviolet rays. It is something. The above-mentioned unsaturated resin is a resin having a radically polymerizable double bond in the main chain or side chain of the resin molecule, such as unsaturated polyester, epoxy acrylate, urethane acrylate, polyester acrylate, polyether acrylate, Examples include acrylic type, oil/fatty acid type, unsaturated polybutadiene type, melamine acrylate type, and long side chain vinyl compound. The vinyl compound is used as a crosslinking agent and diluent for the unsaturated resin, and a vinyl monomer such as a styrene monomer having 1 to 4 unsaturated groups is used.

Furthermore, the above photopolymerization initiator is usually used in the near ultraviolet region (3
00 to 450 nm) to generate radicals, and examples include benzoin compounds, azo compounds, diphenyl sulfide compounds, organic peroxide compounds, organic dyes, and iron/phthalocyanine compounds. As a curing ultraviolet light source, a fluorescent chemical lamp, a high pressure mercury lamp, etc. are used. Specifically, a plurality of mercury lamps are arranged around the circumference, a predetermined amount of the above-mentioned ultraviolet curable resin is applied inside the lamp, and the nine I'OF strands 1 are run at a predetermined linear speed to irradiate the resin within a few seconds. Let it harden. Moreover, the film thickness of this first coating layer 3 is 5 to 200 mm.
It is considered to be within the ILIR range.

In the POF of this example, the ultraviolet curable resin forming the first coating layer 3 maintains appropriate hardness and strength and is in close contact with the POF wire 1, so when placed under moist heat, the first coating layer 3 acts like a tension member, and the contraction of the strand 1 is suppressed. In addition, since the first melting layer 3 made of ultraviolet curable resin strongly adheres to the 8g2 coated layer 4 made of ethylene/ethyl acrylate copolymer, the heat shrinkage force of the ethylene/ethyl acrylate copolymer is The strand IVc acts on the strand IVc through the ultraviolet curing resin, and similarly functions to suppress the shrinkage of the strand 1. Therefore, the POF of this example has extremely high moisture and heat resistance.

Further, FIGS. 3(a) to 3(l) show examples of application of the POF of the present invention. The example shown in Figure 3(a) is
This is a cable in which seven POF wires 1 are twisted together, and a coating layer 5 made of ethylene/ethyl acrylate copolymer is provided to cover the entire twisted wires. In addition, the example shown in FIG. 5 (+,) has five I'OF strands 1...
are arranged in parallel, and a coating layer 5 made of ethylene/ethyl acrylate copolymer is provided to cover them to form a parallel three-core cord.

In the example shown in Fig. 3 (0), six strands 1... are twisted together around a tension member 6 such as steel stranded wire or FRP cord, and a layer of ethylene-ethyl acrylate copolymer is placed on top of the strands 1... A cable is formed by forming a coating layer 5. Furthermore, in the example shown in FIG. 3(d), 1°l of POF wires are arranged in parallel on both sides of the tension member 6, and these are coated with a coating layer 5t made of ethylene-ethyl acrylate copolymer.
-It is set up.

Even with these POFKs, the coating layer 5 made of ethylene/ethyl acrylate copolymer effectively prevents the internal POF wires 1 from shrinking even when placed under moist heat, reducing transmission loss. There will be no increase.

Experimental Examples Experimental examples will be shown below to clarify the effects of the POF of the present invention.

[Experimental Example 1] A POF wire with a diameter of 1 whose core is made of polymethyl methacrylate polymer, whose cladding is made of fluorinated nalkyl methacrylate polymer, and whose transmission loss at a wavelength of 0.66 μm is 2656 B/lan. .0 y strand (
Esca Extra EK-40 (manufactured by Mitsubishi Rayon) was prepared. A coating layer consisting of five types of ethylene/ethyl acrylate copolymers having different ethyl acrylate contents was formed on this wire by an extrusion coating method. Extrusion temperature is 1
40°C, extruder die diameter “k 2.Otsrt
r, and the thickness of the coating layer was Q, 6 m1n.

After measuring the transmission loss of the nine POFs obtained at the same wavelength,
Moist heat treatment was performed at 0° C. and 95% RH for 60 days. Next, changes in transmission loss and shrinkage rate due to moist heat treatment were measured.

For comparison, strands with no coating layer and ethylene
The same heat-and-moisture treatment was also performed on the samples with coating layers made of vinyl acetate copolymer, polyester elastomer, and low-density polyethylene, and the same measurements were performed. The results are also shown in Table 1.

As is clear from the results in Table 1, when a coating layer made of ethylene/ethyl acrylate copolymer with an ethyl acrylate content of 9 to 22 wt% was formed, the transmission loss increased by 10 aB even after moist heat treatment. It can be seen that the shrinkage rate is about &5%, which is lower than those formed with a covering layer made of EVA, LDPE, or polyester elastomer, and has excellent heat and humidity resistance. In addition, if the ethyl acrylate content is, for example, 25%, the increase in transmission loss can be sufficiently suppressed, but the one-heat softening point is as low as 40°C, making it unsuitable for use at temperatures above this temperature. . In addition, +7% has a high thermal softening point of 70°C and has sufficient heat resistance, and the increase in transmission loss is slightly large at 22aB/7I2+, but in terms of the increase rate, it is compared to the POF wire. The increase is only 8 to 9%, which is sufficient for some uses.

[Experimental Example 2] A first coating layer with a thickness of 20 μm made of three kinds of ultraviolet curing resins was formed on the POF wire used in Experimental Example 1, and then an ethylene coating layer with a ethyl acrylate content of 1 Bvt% was formed.
Film thickness: 0.6m made of ethyl acrylate copolymer
A second coating layer of m was formed, and similar moisture and heat resistance was examined.

The results are shown in Table 2.

As is clear from the results shown in Table 2, it can be seen that the product in which the first coating layer made of the ultraviolet curable resin was also formed had extremely high heat and humidity resistance.

iqc and standing trees In the POF of the present invention, the outermost layer of the coating layer formed on the POF wire is composed of ethylene-ethyl acrylate copolymer, so the wire remains stable even when placed under high temperature and high humidity. Shrinkage is reliably suppressed, transmission loss does not increase, and heat and humidity resistance is good.

[Brief explanation of drawings]

1 and 2 are schematic cross-sectional views showing examples of the plastic optical fiber of the present invention, and FIGS.
4 is a schematic cross-sectional view showing an application example of the plastic optical fiber of the present invention, and FIG. 4 is a schematic perspective view showing a sample piece used in an experimental example. 1...POF wire, 2...covering layer, 4...
...Second coating layer, 5...Coating layer. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] A plastic optical fiber characterized in that one or more coating layers are formed on a stretched plastic optical fiber strand, and the outermost layer of the coating layers is made of ethylene-ethyl acrylate copolymer.