JPH10111414A - Multistep index type plastic optical fiber and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multistep index type plastic optical fiber which enables a cost effective mass production with stable quality. SOLUTION: A PMMA-based resin is used as a first component resin and an AS resin having refractive index nd 20 deg.C different by >=0.01 at the absolute value from the value of this PMMA resin is used as a second component resin. These independent component resins or the resin mixtures are arranged concentrically in >=5 layers in such a manner that the refractive index is highest at the central and decreases like a quadratic distribution toward its outer circumferential side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-step index plastic optical fiber having a multi-stage stepped refractive index distribution having a high bandwidth and a method for continuously producing the same according to a graded index plastic optical fiber.

[0002]

2. Description of the Related Art A graded index (GI) type optical fiber is an optical fiber in which the refractive index at the center of the fiber is high and the refractive index decreases in a quadratic distribution toward the outside, and the transmission band is wide. It is a feature.

[0003] Showa 4
Although many proposals have been made since the 0s, the most outstanding ones are those developed by Otsuka and Koike of Keio University.

[0004] In these GI POFs, a rod called a PMMA-based preform having a refractive index distribution is formed in advance by polymerization, and is stretched by heat to form a fiber. The point is that these preforms are polymerized in a PMMA pipe so that a refractive index gradient is formed well. Mainly, the MMA monomer and the high refractive index polymerizable monomer or non-polymerizable compound are allowed to stand or rotate. It is manufactured by polymerizing and solidifying in a long time while paying close attention to the above. The condition of this preform is
It determines important performance such as transmission loss and transmission band of the GI fiber.

[0005]

The advantage of the POF is that it has a large diameter and is easy to handle. However, the GI type POF by the conventional preform method has formed a refractive index distribution utilizing the diffusion state of molecules in the polymerization process. Therefore, it is difficult to manufacture a preform rod that is too large,
In order to maintain the advantages of F, the diameter is 0.5 mm to 1.
If a relatively large-diameter fiber of about 0 mm is drawn, the fiber length obtained from the preform is short, resulting in poor productivity. In fact, there is no prospect of mass-producing such preform rods with industrially stable quality and producing them economically.

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel GI-type POF which solves the drawbacks of the conventional preform method and enables economical mass production with stable quality and a method for producing the same.

[0007]

The structure of the present invention to achieve the above object is as follows.

That is, a first aspect of the present invention is that a transparent resin can be formed by mixing a PMMA-based resin mainly composed of methyl methacrylate as a first component resin and miscible with the resin, and has a refractive index nd of 20 ° C. Is a second component resin whose absolute value differs from the value of the PMMA-based resin by at least 0.01 in terms of the second component resin. The single component resin or the mixed resin has the highest refractive index at the center and the refractive index toward the outer circumference. Is multi-step index type plastic optical fiber characterized by being arranged concentrically in at least five or more layers so that is substantially reduced in a secondary distribution.

Further, a second aspect of the present invention is the method for producing a multi-step index type plastic optical fiber according to the first aspect of the present invention, wherein the first component resin in a molten state and the second
Using a gear pump with metering, mixing and transfer properties, adjust the mixing ratio of both component resins, adjust the refractive index, and supply them to at least five or more "super-multi-layer composite spinning dies". A multi-step index type plastic optical fiber in which a mixed resin having the highest refractive index is arranged at the center and concentrically arranged in multiple stages so that the refractive index decreases substantially in a secondary distribution toward the outer circumference. In a continuous production method.

The conventional method of manufacturing a graded-index type plastic optical fiber is one in which a refractive index gradient is provided by diffusion of a monomer during polymerization of a rod called a preform. The plastic optical fiber described above is formed by molding resins having different refractive indices into multiple layers and has mass productivity. However, the gradient of the refractive index of the fiber is stepped. Although this is not always desirable, it allows for a compromise in terms of cost performance. When the number of steps becomes infinite, the refractive index gradient becomes smooth, but 5
When the number of layers is equal to or more than the number of layers, the transmission band as a plastic optical fiber is improved.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As the first component resin according to the present invention, a homopolymer of methyl methacrylate or an acrylate, methacrylate or other copolymerizable component containing 50% by weight or more of methyl methacrylate is used. The preferred melt flow index of these PMMA-based resins is 2 mm in diameter and 8 mm in length at 230 ° C. under a load of 3.8 kg at 0.2 to 60 g / 10 minutes. It can be used, particularly preferably 1.0 to 40 g / 10 min.
In addition, as a measure to eliminate foreign substances contained in these PMMA-based resins as much as possible and to suppress coloring due to heat, the resin is manufactured by a continuous solution polymerization method or a continuous bulk polymerization method, and the resin mixing described below is performed. It is preferred that the spinning process is carried out by incorporating the process into a continuous process.

On the other hand, as the second component resin, the PMM
It is necessary to select a miscible resin that is well compatible with the A-based resin and can be mixed molecularly. The reason for this is that, besides the fact that the resin is mixed to produce layer resins with different refractive indices one after another, the compatibility of the resin on the surface where the resin of each layer comes into contact is good and the refractive index is smooth. This is important in that the distribution can be given. In addition, a resin that is miscible at 250 ° C. or less must be selected because it is mixed in a molten state or formed into a composite spin. Moreover, as another important property of these resins, it is necessary that the refractive index is different from that of the PMMA resin. The absolute value of the difference between the refractive indices needs to be 0.01 or more at a refractive index nd of 20 ° C. with respect to the sodium D line as a guide.

As the second component resin, for example, there is an AS resin which is a copolymer of acrylonitrile and styrene. Among them, copolymers having a styrene structural unit of 78 to 85% by weight and an acrylonitrile structural unit of 22 to 15% by weight can be treated by mixing an AS resin with a PMMA resin at 250 ° C. or lower. It is preferable because it can be completely miscible mixed. In addition, as an effective resin, an unsaturated vinylic acid such as methyl methacrylate and methacrylic acid or acrylic acid and an aromatic vinyl compound such as styrene or α-methylstyrene are copolymerized, and a 6-membered cyclic product is obtained by a thermal dehydration reaction. The contained copolymer is also a resin having excellent compatibility and is preferable. In addition, copolymers of methyl methacrylate, styrene and maleic anhydride are also available as PM
A transparent resin which is well compatible with the MA resin and is preferable.

The above-mentioned second component resin is a resin which can be produced by a continuous solution polymerization or a continuous bulk polymerization method. The first component resin and the second component resin are produced by a continuous polymerization method. Consistently performs devolatilization from the polymerization stage of the resin, and continues the mixing and spinning process in a continuous continuous process while keeping the resin in a molten state, optically excellent with little contamination and heat history This is preferred in that the resin composition is treated.

As the other second component resin, a vinylidene fluoride resin, for example, a copolymer of vinylidene fluoride and hexafluoroacetone or a copolymer of vinylidene fluoride and hexafluoroacetone is used.
Tertiary or higher copolymers obtained by further adding trifluoroethylene or tetrafluoroethylene to the base component are very preferable.
Further, a copolymer of vinylidene fluoride and hexafluoropropene, or a ternary or higher copolymer obtained by adding trifluoroethylene or tetrafluoroethylene to these binary components, and further, a copolymer of vinylidene fluoride and tetrafluoroethylene Is a resin that cannot be spun in an integrated process by continuous polymerization, but can be used as a second component resin. .

Hereinafter, the second component resin will be described in detail as an AS resin.

The AS resin has a different refractive index depending on the amount of the acrylonitrile component. The AS resin having an acrylonitrile component of 20% by weight has a refractive index nd20 ° C. of 1.5747, and the acrylonitrile component of 25% by weight has a refractive index nd20 ° C.
Is 1.5695.

On the other hand, the refractive index of the PMMA resin is nd 20 ° C.
Is about 1.492. When both resins are mixed, a transparent resin composition is obtained, and the refractive index can be adjusted in proportion to the blending.

For the mixing of these resins and the supply of the mixed resin to the composite spinning die, a feeding device having a mixing function such as a gear pump and having a quantitative property is convenient. As a more preferred method, the PMMA-based resin and the AS-based resin are each produced by a continuous polymerization method, devolatilize volatile components such as unreacted monomers and solvents in a continuous process, and use a measuring device in a molten state. The mixing ratio of the PMMA-based resin and the AS-based resin is adjusted in multiple stages to mix them in such a manner that the gradient of the refractive index becomes multiple stages, and the mixture is supplied to a composite spinning die via a mixing supply device such as a gear pump. Continuously manufacture plastic optical fiber in which a mixed resin with the highest AS concentration and the highest refractive index is arranged, and multi-stage concentrically arranged so that the refractive index decreases stepwise substantially in a secondary distribution around the resin. I do. At this time, the layer width in the fiber axial direction may or may not be uniform, but what is necessary is that the distribution of the refractive index in the axial direction is highest at the center and goes outward. Accordingly, the structure may be such that the relationship between the position and the refractive index at that location decreases in a secondary distribution.

The preferred melt flow index of the AS resin is 2 mm in diameter of the orifice, 8 mm in length, and 23
At a temperature of 0 ° C. and a load of 3.8 kg, those having a range of 0.2 to 60 g / 10 minutes can be used, and particularly preferably 1.0 to 40 g /
10 minutes is preferred.

Next, a specific example of a process from mixing of a PMMA resin and an AS resin to spinning will be described. First, a number of gear pumps corresponding to the number of resin layers are prepared, and the rotational speed of each gear pump is set to a value calculated in advance, and the melted PMMA resin is measured. On the other hand, the molten AS resin is mixed with the previously measured PMMA resin by each mixing gear pump connected to the discharge line of each PMMA-based gear pump. The number of revolutions of the mixing gear pump is controlled in proportion to the sectional area of each layer.

By the way, the method of setting the rotation speed of the PMMA resin gear pump is calculated from the refractive index and the amount of the mixed resin supplied by the mixed gear pump. That is, a mixed resin having the highest AS concentration at the center of the fiber and the highest refractive index is arranged, and a refractive index distribution is provided so that the refractive index decreases substantially in a quadratic distribution toward the outer circumference. The ratio of the AS resin and the PMMA resin is determined, and the quantity of the PMMA resin is determined from the total amount of the mixed resin. Of course, fine adjustments may be involved in the actual operation. Here, the quantity of the AS resin can be measured using a gear pump, but if anything, the AS resin is easily gelled or colored, so that it is preferable to avoid it.

The resin having the refractive index gradient designed in accordance with each layer in this manner is supplied to the “ultra-multilayer composite spinning die” by the designed sectional integral. Here, the “ultra-multi-layer composite spinning die” refers to a die having at least five layers including a central layer. The structure of the super-multi-layer composite spinning die has a die plate corresponding to the number of layers as shown in FIG. 2, and it is preferable that a pipe for guiding the resin of the corresponding layer is attached to the die plate. It is preferable that the number of layers of the die is larger, since the refractive index gradient becomes smoother.
Since the equipment cost increases and the amount of resin per layer is reduced, there is a disadvantage that the resin is easily deteriorated. Therefore, the number of layers is preferably about 5 to 20 layers. In this way, the resin supplied to the “ultra-multilayer composite spinning die” and having a multilayer structure is drawn down and stretched,
The fiber has a diameter of about 0.25 to 2.0 mm.

[0024]

An embodiment of the present invention will be described below.

FIG. 1 is a diagram showing a process of mixing and supplying PMMA resin and AS resin, and FIG. 2 is a diagram of a composite spinning die.

A copolymer of 98% by weight of methyl methacrylate and 2% by weight of methyl acrylate continuously polymerized in the absence of oxygen and having a ND of 20.degree. C. of 1.492 and a melt flow index of 9 g / 10 min. At ℃, it was supplied from a devolatilizing extruder to gear pumps P1 to P9. The discharge pipes of the gear pumps P1 to P9 are connected to the supply sides of the mixing gear pumps P11 to P19, respectively, and the PMMA resin measured by the gear pumps P1 to P9 is supplied to the mixing gear pumps P11 to P19. This gear pump P1
The discharge amount of P9 was as shown in Table 1.

On the other hand, a copolymer of 80% by weight of styrene and 20% by weight of acrylonitrile continuously polymerized in the absence of oxygen and having a nd of 20 ° C. of 1.575 and a melt flow index of 10 g / 10 min. The mixture was directly supplied from the devolatilizing extruder to the mixing gear pumps P11 to P19. The discharge amounts of P11 to P19, that is, the amount of mixed resin, were set as shown in Table 1.

The discharge pipes of the mixing gear pumps P11 to P19 were respectively connected to receiving ports H1 to H9 of the “super multi-layer composite spinning die” shown in FIG. During these steps, the resin temperature was kept at 210 ° C. Stretching the strand discharged from the outlet of the "super multi-layer composite spinning die", performing a stretching process,
A 1.0 mm diameter plastic optical fiber having a nine-layer structure was obtained. Then, the present plastic optical fiber was coated with black polyethylene to obtain a cable.

The refractive index nd of each layer constituting the plastic optical fiber is as shown in Table 1, which is shown in FIG. That is, in the present plastic optical fiber, the refractive index is highest at the center, and the refractive index decreases almost in a secondary distribution toward the outer circumference.

The transmission loss of the plastic optical fiber is 6
It was 300 dB / km at 50 nm. The transmission band of the present plastic optical fiber was 1 GHz / 50 m or more.

[0031]

[Table 1]

[0032]

As described above, according to the present invention,
A multi-step index type plastic optical fiber similar to a graded index type plastic optical fiber can be mass-produced economically with stable quality.

[Brief description of the drawings]

FIG. 1 is a view for explaining a mixed supply process of a PMMA resin and an AS resin according to an embodiment of the present invention.

FIG. 2 shows a “super multi-layer composite spinning die” according to an embodiment of the present invention.
It is sectional drawing which showed roughly.

FIG. 3 is a diagram showing a refractive index of each layer constituting a plastic optical fiber according to an example of the present invention.

Claims (4)

[Claims] 1. A PM mainly composed of methyl methacrylate
A MA-based resin is used as a first component resin, and can be mixed with the resin in a miscible manner to form a transparent resin.
20 ° C. is 0.0 in absolute value from the value of PMMA resin.
A resin that is at least one different from the second component resin is used as the second component resin, and these single component resins or the mixed resin are mixed such that the refractive index is the highest at the center and the refractive index decreases substantially in a secondary distribution toward the outer circumference. A multi-step index type plastic optical fiber, which is concentrically arranged in at least five layers. 2. The multi-step index type plastic optical fiber according to claim 1, wherein the second component resin is an AS resin mainly composed of styrene and acrylonitrile. 3. The AS resin mainly composed of styrene and acrylonitrile is a copolymer having a styrene structural unit of 78 to 85% by weight and an acrylonitrile structural unit of 22 to 15% by weight. Item 3. A multi-step index type plastic optical fiber according to item 2. 4. The method for producing a multi-step index type plastic optical fiber according to claim 1, wherein the first component resin and the second component resin in a molten state are measured with:
The mixing ratio of both components is adjusted by using a gear pump having mixing and transfer performance, the refractive index is adjusted, and at least 5
Multi-layer composite spinning die with more than one layer is supplied, and the mixed resin with the highest refractive index is placed at the center, and multi-step so that the refractive index decreases almost in a secondary distribution toward the outer circumference. ,
A method for continuously manufacturing concentrically arranged multi-step index type plastic optical fibers.