JP7133290B2 - Plastic optical fiber and plastic optical fiber cable - Google Patents

Description

The present invention relates to plastic optical fibers and plastic optical fiber cables.

Multicore plastic optical fibers with polymethyl methacrylate resin (PMMA resin) as the core have been used for optical data communication, photoelectric sensors, etc. Plastic optical fiber sheaths used for these applications As for the resin of the layer, a binary copolymer composed of 80 mol % vinylidene fluoride and 20 mol % tetrafluoroethylene (see, for example, Patent Document 1), a copolymer composed of vinylidene fluoride, tetrafluoroethylene and hexafluoropropene. Coalescence (see, for example, Patent Document 2), carbonate-modified ethylene-tetrafluoroethylene-based copolymers (see, for example, Patent Document 3), fluoromethacrylate-based resins (see, for example, Patent Document 4), etc. have been put to practical use. .
These plastic optical fibers are mainly intended for optical data communication applications and photoelectric sensor applications, and are developed with the aim of reducing light transmission loss, so they are designed with a low resin ratio in the sheath layer. . As a result, crosstalk between pixels occurs. Crosstalk does not pose a practical problem in optical data communication applications and photoelectric sensor applications, but cannot be used in image transmission applications in which each core fiber acts as a pixel.

In view of the above circumstances, the plastic optical fiber for image transmission is designed differently from the plastic optical fiber for optical data communication.
Specifically, the number of cores is larger than that of the plastic optical fiber for optical data communication, and the cross-section of the plastic optical fiber is larger than that of the plastic optical fiber for optical data communication so that crosstalk does not occur between the core fibers. It is necessary to design the resin of the sheath layer to have a large proportion, and the resin of the sheath layer should have higher adhesion to the core resin than the resin of the sheath layer for the plastic optical fiber for optical data communication. It is made like this.
Therefore, the plastic optical fiber for image transmission is more complicated to design and manufacture than the plastic optical fiber for optical data communication, and only a limited number of resins for the sheath layer have been put into practical use. . For example, a binary copolymer composed of 80 mol % vinylidene fluoride and 20 mol % tetrafluoroethylene has been put into practical use as a resin for the sheath layer of a plastic optical fiber for image transmission (for example, Patent Documents 5 and 6). reference).

JP-A-5-134120 JP-A-11-95048 JP 2011-221384 A JP 2016-021019 A JP 2013-50646 A JP 2013-54241 A

Plastic optical fibers for image transmission are less expensive than glass fibers for image transmission, so they are expected to be used in disposable medical equipment. However, there are many pixel defects such as brown or black pixels. However, there is a problem that the image quality is inferior to that of the glass fiber for image transmission.
In addition, in medical applications, small-diameter fibers are preferred because they are less invasive, but if the plastic optical fiber for image transmission has a small diameter of 1 mm or less, the thickness of the sheath layer between the cores becomes thin, and crosstalk occurs. It has the problem of increasing and blurring the image.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a plastic optical fiber capable of transmitting clear images with few pixel defects, and which is particularly effective for image transmission.

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have solved the above-mentioned problems of the prior art by specifying the core resin, the sheath resin, and the resin of the protective layer in the multicore plastic optical fiber. We have found that the problem can be solved, and have completed the present invention.
That is, the present invention is as follows.

[1]
It has a plastic optical fiber bare wire consisting of 6000 or more and 7375 or less cores made of polymethyl methacrylate-based core resin and a sea-like sheath layer surrounding the entire core,
The sheath layer is made of a sheath resin having a refractive index smaller than that of the core resin by 0.1 or more,
Furthermore, on the outside of the sheath layer, a protective layer made of a resin different from the sheath resin is in close contact with the sheath layer.
Plastic optical fiber for image transmission.
[2]
The sheath resin is
[1] above, which is a resin containing a terpolymer consisting of vinylidene fluoride, tetrafluoroethylene and hexafluoropropene, or a terpolymer consisting of ethylene, tetrafluoroethylene and hexafluoropropene. Plastic optical fiber for image transmission.
[3]
The plastic optical fiber for image transmission according to the above [1] or [2], wherein the resin for the protective layer is a fluororesin.
[4]
The protective layer has a melting point of 120° C. or higher and a Vicat softening temperature (ASTM 1525
) is made of a resin composition containing a vinylidene fluoride resin having a temperature of 110 ° C. or higher,
The plastic optical fiber for image transmission according to the above [1] or [2].
[5]
The above [1] to [4], wherein the refractive index of the protective layer is 0.01 or more higher than the refractive index of the sheath resin
].
[6]
Outside the plastic optical fiber for image transmission according to any one of [1] to [5],
A plastic optical fiber cable, further comprising a coating layer made of a thermoplastic resin.

It is possible to provide a plastic optical fiber with few pixel defects and capable of transmitting clear images.

1 shows a schematic cross-sectional view of an example of a plastic optical fiber cable of the present embodiment; FIG.

Hereinafter, modes for carrying out the present invention (hereinafter simply referred to as "present embodiments") will be described in detail with reference to the drawings as necessary. It is not limited. The present invention can be carried out with various modifications within the scope of its gist.

[Plastic optical fiber]
The plastic optical fiber of this embodiment is
Having 1300 or more cores made of polymethyl methacrylate-based core resin,
The core is surrounded by a sheath layer made of a sheath resin having a refractive index smaller than that of the core resin by 0.1 or more,
Further, the plastic optical fiber is a plastic optical fiber in which a protective layer made of a resin different from the sheath resin is adhered to the sheath layer on the outside of the sheath layer.

The plastic optical fiber of this embodiment can be applied for illumination, optical data communication, sensors such as photoelectric sensors, and image transmission.
In particular, since the refractive index of the sheath layer of the plastic optical fiber of this embodiment is smaller than that of the core resin by 0.1 or more, the fiber NA becomes large and is excellent in the effect of transferring a bright image. It is suitable as an optical fiber.

FIG. 1 shows a schematic cross-sectional view of an example of a plastic optical fiber cable including the plastic optical fiber of this embodiment.
In FIG. 1, a plastic optical fiber cable 7 has a plastic optical fiber bare wire 5 consisting of a core 1 and a sheath layer 2 surrounding the core 1 .
A protective layer 3 is formed on the outer periphery of the plastic optical fiber bare wire 5 , and the plastic optical fiber bare wire 5 and the protective layer 3 form a plastic optical fiber strand 6 .
A coating layer 4 is formed on the outer periphery of the plastic optical fiber wire 6, and the plastic optical fiber wire 6 and the coated wire 4 form a plastic optical fiber cable.
Here, in the present specification, the term “plastic optical fiber” is a general term for forms including at least the plastic optical fiber strand 6 .

(core)
The plastic optical fiber of this embodiment has 1,300 or more cores made of polymethylmethacrylate-based core resin.
The diameter of the core is preferably 1-50 μm, more preferably 1-20 μm, still more preferably 3-10 μm.
If the diameter of the core is 1 μm or more, the pixel functions sufficiently and high resolution can be realized. Further, when the thickness is 50 μm or less, high resolution can be obtained when used for image transmission.

In the plastic optical fiber of this embodiment, the number of cores is 1300 or more, preferably 3000 or more, more preferably 3500 or more, and even more preferably 6000 or more, from the viewpoint of high resolution.
From the viewpoint of resolution, the number of cores is preferably as large as possible, but from the viewpoint of the practical thickness of bare wires, the number is preferably 30,000 or less, more preferably 14,000 or less.

In addition, the diameter of the plastic optical fiber bare wire 5 constituting the plastic optical fiber of the present embodiment is preferably 3000 μm or less, more preferably 250 to 1500 μm, more preferably 300 to 1000 μm, because it is easy to bend and can be used in a narrow space. is more preferred, and 300-750 μm is even more preferred.

The core resin used for the core of the plastic optical fiber of this embodiment is assumed to be polymethyl methacrylate resin (PMMA resin) because of its small attenuation of light.
As the PMMA-based resin, a methyl methacrylate homopolymer (PMMA) and a copolymer containing 50% by mass or more of methyl methacrylate are preferable.
Examples of copolymerizable components include, but are not limited to, acrylic acid esters such as methyl acrylate, ethyl acrylate, and butyl acrylate; ethyl methacrylate, propyl methacrylate, cyclohexyl methacrylate, and the like. methacrylic acid esters; maleimides such as isopropyl maleimide; acrylic acid, methacrylic acid, styrene, etc.;

(sheath layer)
In the plastic optical fiber of this embodiment, a core 1 is surrounded by a sheath layer 2 made of a sheath resin having a refractive index smaller than that of the core resin by 0.1 or more.
By using a resin having a refractive index smaller than that of the core resin by 0.1 or more as the sheath resin, the image is less likely to be blurred even if the diameter of the plastic optical fiber bare wire 5 is 1 mm or less.
Furthermore, with regard to pixel defects, it was conventionally thought that when the difference in refractive index between the core resin and the sheath resin increased, the adhesion between the core and the sheath layer decreased, resulting in an increase in pixel defects. Pixel defects were reduced rather than resins with a refractive index difference of less than 0.1. The reason for this is presumed to be that resins with a refractive index difference of 0.1 or more are more stable than resins with a refractive index difference of less than 0.1 when exposed to high temperatures during the manufacture of plastic optical fibers. .

The sheath resin used for the sheath layer 2 is not particularly limited as long as it has a refractive index smaller than that of the core resin by 0.1 or more, i.e., a difference in refractive index from the core resin of 0.1 or more. For example, a terpolymer of vinylidene fluoride, tetrafluoroethylene and hexafluoropropene; a carbonate-modified ethylene-tetrafluoroethylene copolymer; a terpolymer consisting of ethylene, tetrafluoroethylene and hexafluoropropene; can be used.
In addition, the vinylidene fluoride component is in the range of 30 to 92 mol%, the tetrafluoroethylene component is in the range of 0 to 55 mol%, and the hexafluoropropene component is in the range of 8 to 25 mol%, and the Shore D hardness at 23 ° C. is 30 to 55. Copolymers within this range are preferable because the flow characteristics of the resin are close to those of the PMMA resin used for the core resin, and the plastic optical fiber can be easily produced.
Furthermore, the vinylidene fluoride component is in the range of 40 to 62 mol%, the tetrafluoroethylene component is in the range of 28 to 40 mol%, and the hexafluoropropene component is in the range of 8 to 22 mol%. The modulus is in the range of 1.350 to 1.380, the value of Shore D hardness (ASTM D2240) at 23 ° C. is in the range of 35 to 45, the melt flow index (230 ° C., load 3.8 kg, orifice diameter 2 mm and 8 mm in length) is more preferably a resin exhibiting fluidity of 5 g/10 to 100 g/min.

The ratio of the core resin to the sheath resin is not particularly limited, but the more the core resin, the brighter the image. The thickness becomes thinner, crosstalk increases, and the image becomes blurry.
Therefore, a preferable ratio of core resin to sheath resin is selected according to the diameter of the bare wire 5 . When the diameter of the bare wire 5 is 1.2 mm or more, the core resin/sheath resin ratio is preferably 90/10 to 65/35, more preferably 80/20 to 70/30. When the diameter of the bare wire 5 is 0.8 mm to 1.2 mm, the core resin/sheath resin ratio is preferably 85/15 to 65/35, more preferably 80/20 to 70/30.
When the diameter of the bare wire 5 is 0.6 mm to 0.8 mm, the preferred ratio of the core resin to the sheath resin is 80/20 to 60/40, preferably 75/25 to 65/. 35 is more preferred.
When the diameter of the bare wire 5 is 0.6 mm or less, the ratio of core resin/sheath resin is preferably 75/25 to 50/50, more preferably 70/30 to 55/45.

The content of each component of the sheath resin can be measured by NMR. Specifically, a sample solution was prepared by dissolving an appropriate amount of the sheath resin sample in a mixed solvent of acetone ^{- d6} and α,α,α-trifluorotoluene. The frequency is 376 MHz, and ¹ H-NMR is converted to tetramethylsilane and ¹⁹ F-NMR is converted to trichlorofluoromethane as the standard for chemical shift. To calculate the concentration of each component from the spectrum, the mass% composition determined by the following formula is converted to mol%.
The vinylidene fluoride component was determined by calculating the molar ratio of ¹ H in the component to ¹ H in α,α,α-trifluorotoluene from the integrated value of ¹ H-NMR, and mol of the component in the sample was calculated from the molar ratio. Calculate the number and convert to mass ratio.
For the hexafluoropropene component, the molar ratio of the CF ₃ group in the component to the CF ₃ group in α,α,α-trifluorotoluene was calculated from the integrated value of ¹⁹ F-NMR, and from there the content of the component in the sample was determined. Calculate the number of moles and convert to mass ratio.
The tetrafluoroethylene component is calculated on the assumption that the vinylidene fluoride component and the hexafluoropropene component are excluded from the total.

The meanings of the symbols in the above formula are shown below.
A: Number of mmoles of trifluorotoluene in sample solution B: Sum of integrated values of 2.2 to 2.7 ppm and 3.0 to 3.8 ppm in ¹ H-NMR C: 7.0 to 8.0 ppm in ¹ H-NMR Integral value of 5 ppm D: Sample mg number in the sample solution E: Integrated value of -67 to -78 ppm in ¹⁹ F-NMR F: Integrated value of -62 to -66 ppm in ¹⁹ F-NMR

(protective layer)
In the plastic optical fiber of this embodiment, a protective layer 3 made of a resin different from the sheath resin is formed outside the sheath layer 2 so as to adhere to the sheath layer 2 .
The protective layer 3 has the function of protecting the plastic optical fiber bare wire 5 of the present embodiment and retaining its mechanical strength.
In general, the adhesion between the core resin and the sheath resin having a refractive index difference of 0.1 or more is poor, and in the absence of the protective layer 3, when the plastic optical fiber bare wire 5 is bent, the integrated core is easily separated. However, there is a possibility that the desired image transmission function cannot be exhibited. From this point of view, the protective layer 3 is effective for integrating the core 1 and the sheath layer 2 together.
Moreover, in the plastic optical fiber cable of this embodiment, the protective layer 3 is in close contact with the sheath resin of the sheath layer 2 forming the plastic optical fiber bare wire 5 .
Here, the adhesion state is determined by whether or not a gap is observed between the sheath layer 2 and the protective layer 3 when observed with a digital microscope with an image magnification of 200 times. can be determined.
Since the sheath layer 2 and the protective layer 3 are in close contact with each other, a sufficient function for maintaining mechanical strength can be obtained, and the aforementioned core separation phenomenon can be sufficiently prevented.

The thickness of the protective layer 3 is not particularly limited, but since the field of view is narrowed by the thickness of the protective layer 3, it is preferably 100 μm or less, more preferably 50 μm or less from the viewpoint of ensuring a sufficiently wide field of view. and more preferably 40 μm or less.
From the viewpoint of reducing the overall thickness of the plastic optical fiber of the present embodiment while maintaining the mechanical strength, the thickness is preferably 5 to 50 μm, more preferably 5 to 40 μm.

In the plastic optical fiber of this embodiment, the resin used for the protective layer 3 is different from the resin for the sheath layer 2 .
If the same resin as the sheath resin is used, it may completely fuse with the sheath layer during production and may not fulfill its role as a protective layer.
By using a resin different from that of the sheath layer, it is possible to prevent fusion between the sheath layer and the protective layer during the manufacturing process.

The resin for the protective layer 3 is not particularly limited as long as it is a resin different from the sheath resin, but a fluororesin is preferable in order to ensure stronger adhesion to the sheath resin.
Furthermore, a vinylidene fluoride resin is more preferable, and a resin composition containing a vinylidene fluoride resin having a melting point of 120° C. or higher and a Vicat softening temperature (ASTM 1525) of 110° C. or higher is It is preferable from the viewpoint that the flow property is close to that of the PMMA resin used for the core resin, and the plastic optical fiber can be easily manufactured.
Here, the Vicat softening temperature refers to the temperature when a needle is inserted to a depth of 1 mm under a load of 1.0 kg and a heating rate of 2° C./min according to ASTM D1525.

In the plastic optical fiber of this embodiment, if light is reflected at the interface between the sheath layer 2 and the protective layer 3, it causes blurring of the image. From this point of view, if the refractive index of the protective layer 3 is higher than the refractive index of the sheath layer 2, reflection is less likely to occur, which is desirable. More preferably, the refractive index of protective layer 3 is 0.01 or more, more preferably 0.03 or more, than that of sheath layer 2 .

In the plastic optical fiber of this embodiment, the core 1 , the sheath layer 2 and the protective layer 3 form the plastic optical fiber strand 6 .
Although the diameter of the plastic optical fiber strand 6 is not particularly limited, it is preferably 3 mm or less, more preferably 2.0 mm or less, from the viewpoint of maintaining flexibility. Since minimal invasiveness is required in medical applications, the thickness is more preferably 1.5 mm or less, even more preferably 1 mm or less, and even more preferably 0.8 mm or less.

(Method for manufacturing plastic optical fiber)
The method for manufacturing the plastic optical fiber of this embodiment is not particularly limited, and a known method can be applied. A manufacturing method, a method of spinning a plastic optical fiber bare wire, then coating and curing a protective layer, and a method of making a bare wire by adhering it to a sheath layer, and the like can be mentioned.

[Plastic optical fiber cable]
The plastic optical fiber cable of this embodiment further has a coating layer 4 made of a thermoplastic resin on the outer side of the plastic optical fiber strand 6 of this embodiment described above.
The method of manufacturing the plastic optical fiber cable of this embodiment is not particularly limited, and can be performed by a known method.
For example, polyethylene-based resin, polyvinyl chloride, polyvinylidene fluoride, tetrafluoroethylene/ethylene copolymer (ETFE), tetrafluoroethylene/perfluoroalkyl, melted by heat using a crosshead die may be applied to the outside of the plastic optical fiber strand. A method of forming a coating layer comprising a vinyl ether copolymer (PFA) and a silicone resin can be preferably used.
The thickness of the coating layer 4 is preferably 20 to 1000 μm, more preferably 50 to 900 μm, even more preferably 100 to 800 μm, from the viewpoint of protecting the plastic optical fiber and enabling use in narrow spaces.

EXAMPLES The present embodiment will be specifically described below with reference to specific examples and comparative examples, but the present embodiment is not limited to the following examples.
The physical property values used in this specification and the evaluation physical property values evaluated in Examples and Comparative Examples described later are based on the following measurement methods and evaluation methods, respectively.

[Evaluation of pixel defects]
For evaluation of pixel defects, an LED light panel ("A4G-L1316-SFR23" manufactured by Lumitechno Co., Ltd.) was prepared, 2 m of the produced plastic optical fiber was taken, the tip was brought into close contact with the LED light panel, and the other An output image output from the tip was observed by magnifying it 200 times with a digital microscope (manufactured by Keyence, VHX-5000).
Five samples were prepared for each fiber, and the number of pixels observed as brown or black was counted among the pixels excluding the outer periphery, and all five samples with 3 or less samples were accepted.
The evaluation results are shown in Table 1 below.

[Evaluation of resolution]
For evaluation of resolution, a target on which black lines with a thickness of 0.1 mm were drawn at intervals of 0.1 mm was prepared on a glass substrate of 5 cm square, and the same LED light as used in [Evaluation of pixel defects] was used. placed on the panel.
Next, 2 m of the produced plastic optical fiber was taken, the tip was brought into close contact with the target, and the output image output from the other tip was magnified 200 times with a digital microscope (manufactured by Keyence, VHX-5000). I made an observation.
Five samples were prepared for each fiber, and when black lines of 0.1 mm were clearly visible in all five samples, the samples were regarded as good, and when blurring or blurring was observed, the samples were regarded as unacceptable.
The evaluation results are shown in Table 2 below.

[Evaluation of mechanical strength]
As evaluation of mechanical strength, the fiber subjected to pixel defect evaluation was repeatedly bent 10 times at r 10 mm to ± 90 degrees, and then the above-described [pixel defect evaluation] was performed again, and pass/fail judgment was performed based on the same criteria. did.
The evaluation results are shown in Table 3 below.

[Example 1]
A plastic optical fiber was manufactured according to the configuration shown in FIG.
Polymethyl methacrylate (refractive index 1.491) as the resin (core resin) constituting the core 1, and a copolymer of vinylidene fluoride, tetrafluoroethylene and hexafluoropropene as the resin (sheath resin) constituting the sheath layer 2. (refractive index 1.37), and a copolymer of 72% by mass of vinylidene fluoride and 28% by mass of tetrafluoroethylene (refractive index 1.40) as a resin (protective layer resin) constituting the protective layer 3 is 7375, respectively. A core resin distribution chamber, a sheath resin distribution chamber and a protective layer distribution chamber of a core composite spinning die were put into a 7375 core plastic optical fiber strand 6 with a diameter of 1 mm to manufacture by composite spinning.
The refractive index was measured using an Abbe refractometer (manufactured by Atago Co., Ltd., "Abbe refractometer type 1") in a thermostatic chamber at 23°C using a sodium D line as a light source.

[Example 2]
A copolymer of ethylene, tetrafluoroethylene, and hexafluoropropene (refractive index: 1.39) was used as a resin (sheath resin) forming the sheath layer 2 . Other conditions were the same as [Example 1] to produce a plastic optical fiber 6 .

[Example 3]
The diameter was 0.75 mm. Other conditions were the same as [Example 1] to produce a plastic optical fiber 6 .

[Example 4]
The diameter was set to 0.5 mm. Other conditions were the same as [Example 1] to produce a plastic optical fiber 6 .

[Example 5]
The diameter was 0.75 mm. Other conditions were the same as [Example 2] to manufacture the plastic optical fiber strand 6 .

[Example 6]
The diameter was set to 0.5 mm. Other conditions were the same as [Example 2] to manufacture the plastic optical fiber strand 6 .

[Comparative Example 1]
Composite spinning was carried out without putting the protective layer resin in the protective layer distribution chamber. Other conditions were the same as [Example 1] to produce a plastic optical fiber 6 .

[Comparative Example 2]
A copolymer (refractive index: 1.40) of 72% by mass of vinylidene fluoride and 28% by mass of tetrafluoroethylene was used as the resin for the sheath layer 2 . Other conditions were the same as [Example 1] to produce a plastic optical fiber 6 .

[Comparative Example 3]
A copolymer (refractive index: 1.40) of 72% by mass of vinylidene fluoride and 28% by mass of tetrafluoroethylene was used as the resin for the sheath layer 2 . Other conditions were the same as [Example 3] to produce a plastic optical fiber 6 .

[Comparative Example 4]
A copolymer (refractive index: 1.40) of 72% by mass of vinylidene fluoride and 28% by mass of tetrafluoroethylene was used as the resin for the sheath layer 2 . Other conditions were the same as [Example 4] to produce a plastic optical fiber 6 .

Comprehensive evaluation is shown in Table 4 below.

The plastic optical fiber of the present invention has industrial applicability as medical endoscopes and industrial endoscopes.

REFERENCE SIGNS LIST 1 core 2 sheath layer 3 protective layer 4 coating layer 5 plastic optical fiber bare wire 6 plastic optical fiber bare wire 7 plastic optical fiber cable

Claims (6)

It has a plastic optical fiber bare wire consisting of 6000 or more and 7375 or less cores made of polymethyl methacrylate-based core resin and a sea-like sheath layer surrounding the entire core,
The sheath layer is made of a sheath resin having a refractive index smaller than that of the core resin by 0.1 or more,
Furthermore, on the outside of the sheath layer, a protective layer made of a resin different from the sheath resin is in close contact with the sheath layer.
Plastic optical fiber for image transmission. The sheath resin is
2. The image according to claim 1, which is a resin containing a terpolymer consisting of vinylidene fluoride, tetrafluoroethylene and hexafluoropropene, or a terpolymer consisting of ethylene, tetrafluoroethylene and hexafluoropropene. Plastic optical fiber for transmission. 3. The plastic optical fiber for image transmission according to claim 1, wherein the resin for said protective layer is a fluororesin. The protective layer has a melting point of 120° C. or higher and a Vicat softening temperature (ASTM 1525
) is made of a resin composition containing a vinylidene fluoride resin having a temperature of 110 ° C. or higher,
The plastic optical fiber for image transmission according to claim 1 or 2. 5. The plastic optical fiber for image transmission according to claim 1, wherein the protective layer has a refractive index greater than that of the sheath resin by 0.01 or more. Outside the plastic optical fiber for image transmission according to any one of claims 1 to 5,
A plastic optical fiber cable, further comprising a coating layer made of a thermoplastic resin.

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