JP4070548B2 - Fiber optic and liquid sensors - Google Patents

Description

【００２０】
実施例２
パーフルオロ樹脂をテトラフルオロエチレン−パーフルオロアルコキシエチレン共重合体（ＰＦＡ）（デュポン社製 ９５０ＨＰ−ｐｌｕｓ）に変えるとともに、延伸倍率を変えた点を除き、実施例１と同様にして光ファイバーを作製した。
得られた光ファイバーについて、測定光の波長０．８５μｍにおいて実施例１と同様に伝送損失を測定し、その結果を表２に示す。
【００２１】
【表２】

【００２２】
実施例３
実施例１で製造した光ファイバー（屈折率ｎ＝１．３２８）と、押出成形のみで延伸しなかった部材の、それぞれの長さ３００ｍｍを試料としてループ状にし、図１に示すように、光ファイバー１の一端を、波長６５０ｎｍの光源２、他端を光検出センサー３（オムロン製 Ｅ３Ｘ−ＤＡ−Ｎ）に取り付け、中央部Ａの２０ｍｍを、屈折率が異なる、水、メタノール、エタノールを入れた浸漬槽４へ浸漬した場合に、液体中への浸漬によって光量が５０％以上変化がしたものについては検出可能として表３に示す。
本発明の光ファイバーは、光の伝送損失が小さなものであるので、液体の付着によって光ファイバーの周囲から光が漏洩した場合には、検出器によって光量の変化を検出することが可能となった。
【００２３】
【表３】

【００２４】
【発明の効果】
本発明は、耐熱性、耐湿性、耐薬品性等の特性に優れたパーフルオロ樹脂からなる伝送損失が小さなプラスチック光ファイバーを提供することを可能としたものであり、とくに、表面への各種の有機溶剤の付着によって生じる伝送される光量の変化で、これらの有機溶剤の付着や、有機溶剤中へ直接浸漬することができる液体センサーを製造することができる。また、本発明のプラスチック光ファイバーを用いたセンサーは、従来のアクリル樹脂系のプラスチック光ファイバーに比べて、屈折率が低いので、たとえ被検出液体の屈折率が低くても被検出液体の付着、あるいは被検出液体の液面を容易に検出することができる。
【図面の簡単な説明】
【図１】本発明の一実施例を説明する図である。
【符号の説明】
１…光ファイバー、２…光源、３…光検出センサー、４…浸漬槽[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plastic optical fiber, and relates to an optical fiber that has large characteristics such as heat resistance, cold resistance, corrosion resistance, and friction resistance and a small transmission loss, and is particularly useful as a liquid sensor.
[0002]
[Prior art]
As the optical fiber, an optical fiber made of plastic is used together with a glass-based optical fiber made of quartz glass or the like. Plastic optical fiber has a larger transmission loss than quartz glass and is not suitable for long-distance signal transmission, but it is flexible and can handle large diameters. And the end portion is easy to process.
Taking advantage of these features, it is used in applications such as short-distance signal transmission, signal transmission in buildings or equipment such as automobiles, lighting, optical display devices, and various sensors. .
[0003]
As plastic optical fibers, there were provided those in which a clad layer was coated around a highly transparent resin core such as a polymer of methyl methacrylic acid. These acrylic resin-based optical fibers have a C structure in the chemical structure. -H bond causes an increase in transmission loss due to harmonic absorption of infrared vibration absorption of C-H bond, and heat resistance, moisture resistance, and chemical resistance are not sufficient. There is a problem that the acrylic resin deteriorates due to the use of the plasticizer or the action of the plasticizer of the vinyl chloride resin used for coating the optical fiber. Further, when the moisture resistance is not sufficient, an increase in transmission loss due to infrared vibration absorption cannot be avoided.
Therefore, an optical fiber made of amorphous fluororesin has been proposed instead of acrylic resin or the like. The amorphous fluororesin has a problem that it is not sufficient in terms of heat resistance and the like as compared with a crystalline synthetic resin although it has good transparency.
[0004]
On the other hand, it has been proposed to reduce the transmission loss of an optical fiber by stretching a partially crystallized fluororesin (see, for example, Patent Document 1), but the transmission loss is 30 dB / m or more, and the attenuation is The copolymer containing vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene, which are fluororesins mentioned as specific examples, that is, a thermoplastic fluororesin called THV has a melting point Is low, heat resistance is not sufficient, and since vinylidene fluoride is contained as a component of the copolymer, it has a C—H bond in the chemical structure like an acrylic resin optical fiber. Yes. For this reason, the influence of the increase in the transmission loss due to the harmonic absorption of the infrared vibration absorption of the C—H bond cannot be avoided.
[0005]
Various liquid level sensors using an optical fiber are known, and a sensor unit provided at the tip is coupled to an optical fiber (see, for example, Patent Document 2 and Patent Document 3). Alternatively, a liquid sensor that detects a liquid that is difficult to detect depending on a difference in refractive index from the clad by selecting a wavelength band of light has been proposed (for example, see Patent Document 4). Further, a liquid sensor has been proposed in which a resin layer having a refractive index larger than that of the clad on the optical fiber clad and outputting an output light corresponding to the difference in refractive index with respect to the liquid is provided (see, for example, Patent Document 5). . These were all detected by forming a clad in the core and utilizing the difference in refractive index from the clad.
[Patent Document 1]
Japanese Patent Publication No. 8-507876 [Patent Document 2]
Japanese Patent Laid-Open No. 2001-165751 [Patent Document 3]
JP-A-8-210897 [Patent Document 4]
JP 2000-97850 A [Patent Document 5]
JP-A-2001-91459 gazette
[Problems to be solved by the invention]
An object of the present invention is to provide a plastic optical fiber having good characteristics such as moisture resistance and heat resistance and having no transmission loss due to infrared vibration absorption of C—H bond, In particular, it is an object of the present invention to provide an optical fiber that is refracted and guided at an interface with a surrounding air layer without providing a cladding layer, and a sensor using the optical fiber.
[0007]
[Means for Solving the Problems]
An object of the present invention is a plastic optical fiber in which a molded product obtained by cooling a melt made of crystalline perfluorofluororesin is stretched by applying a tension at a temperature not lower than the glass transition point and not higher than the melting point. This can be solved by using a plastic optical fiber having a light guide property due to a difference in refractive index at the interface between the core material and air.
The method for producing an optical fiber according to the present invention, wherein the melt of the crystalline perfluoro resin is rapidly cooled after molding.
In the method for producing a plastic optical fiber, the crystalline perfluorofluororesin is a fluororesin selected from a tetrafluoroethylene-perfluoroalkoxyethylene copolymer and a tetrafluoroethylene-hexafluoropropylene copolymer.
[0008]
Moreover, in the liquid sensor, a molded product obtained by cooling a melt made of crystalline perfluorofluororesin is a core material that is stretched by applying tension at a temperature not lower than the glass transition point and not higher than the melting point, A light emitting means is provided at one end of a plastic optical fiber having a light guiding property due to a difference in refractive index at the interface between the core material and air, and a light receiving means having a light quantity change detecting function is provided at the other end. This can be solved by detecting the liquid sensor.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a semi-transparent tetrafluoroethylene-perfluoroalkoxy that has not been used as a light guiding material of an optical fiber, that is, a core, although it is conventionally used as a cladding or protective coating material of an optical fiber. Light transmittance is improved by stretching a molded body prepared from a melt of a crystalline perfluoro resin such as an ethylene copolymer or a tetrafluoroethylene-hexafluoropropylene copolymer to impart orientation in the axial direction. This is what we can do. The light-transmitting member can be used as a light guide material, and has a large heat resistance, cold resistance, moisture resistance, chemical resistance, solvent resistance, low friction, and the like that the crystalline perfluoro resin has. It has been found that it is possible to provide an optical fiber having a property, a flame resistance, a weather resistance, a non-water absorption property, a non-hygroscopic property, a smoke resistance, and the like.
[0010]
These light-guiding materials have been found to provide sufficient light-guiding characteristics due to the difference in refractive index formed at the interface with air without forming a cladding layer on the surface. Optical fibers without a cladding layer are limited to use in limited environments because the light guide characteristics change if the surface is contaminated by dust or other adhesion, but at the same time the amount of light changes due to surface changes. By using the characteristic of performing the above, it has a feature that it can be used as a liquid sensor for detecting that liquid or the like has adhered to the surface.
[0011]
Since the liquid sensor of the present invention can detect the adhesion of the liquid to the surface of the optical fiber, not only the immersion in the liquid but also a small amount of liquid adhered to the surface of the optical fiber as in the case of condensation from the atmosphere. It is also possible to detect cases. In particular, since the optical fiber of the present invention is made of crystalline perfluoro fluororesin with excellent chemical resistance, it provides a liquid sensor with excellent corrosion resistance against organic solvents that attack hydrocarbon plastics. can do. Further, the liquid sensor of the present invention is to detect by the difference in refractive index between the plastic optical fiber and the liquid attached to the surface of the optical fiber,
The method for producing the plastic optical fiber of the present invention will be described below.
[0012]
The manufacturing process of the plastic optical fiber of the present invention is formed from a monofilament molding process by extruding a melt of crystalline perfluoro fluororesin, a stretching process of a stretching material, and the like.
The optical fiber of the present invention, after forming a monofilament by extrusion or the like from a melt of crystalline perfluoro fluororesin, quickly cooled, and after producing a stretch material determined from the final product diameter and stretch ratio, It can be manufactured by applying a tension to the drawing material at a temperature not lower than the glass transition point and not higher than the melting point to produce a desired core material, and heat-fixing the core material by heating.
In addition, the optical fiber of the present invention may be stretched by adjusting the ratio between the feeding speed and the pulling speed so as to be stretched to a predetermined wire diameter by a single operation, or may be stretched in several times.
[0013]
The manufacturing process of a plastic optical fiber is generally required to be manufactured in an environment where the concentration of contaminants in the atmosphere is low. In particular, in the core material forming process, when the number of dusts in the atmosphere is large, the amount of dust is limited because the optical characteristics are greatly deteriorated as a result of the dust being mixed into the core material and the surface of the core material. It is preferable to manufacture in a clean environment.
[0014]
The crystalline perfluororesin that can be used in the optical fiber of the present invention includes polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), and tetrafluoroethylene-hexafluoropropylene copolymer. A polymer (FEP) can be mentioned, and among these, a thermoplastic perfluoro resin capable of producing a monofilament by a method such as extrusion molding after being heated and melted is preferable, and tetrafluoroethylene-perfluoroalkoxyethylene is preferable. A copolymer (PFA) and a tetrafluoroethylene-hexafluoropropylene copolymer (FEP) are preferred.
These resins can be molded by the same melt molding method as a general thermoplastic resin, and the resin can be melted and extruded from a die, and cooled by gas, liquid, etc. to produce a monofilament. The outer diameter of the monofilament is determined in consideration of the subsequent stretching rate.
In the molding of the melt, when it is slowly cooled at the time of cooling, crystals grow and the transparency is lowered. Therefore, cooling is preferably performed quickly, and it is preferable to immediately immerse in water or other cooling medium after melt extrusion. .
[0015]
The produced monofilament is stretched by applying tension in a state where the monofilament is heated to a temperature not lower than the glass transition temperature and not higher than the melting point of each resin. Stretching increases the degree of molecular orientation in the length direction and increases light transmittance. Therefore, it is preferable to increase the stretching ratio, and it is preferable to increase it as much as possible within the range where the monofilament is not cut.
[0016]
In addition, since crystalline perfluororesin changes in characteristics such as light transmittance depending on its polymerization method, it is preferable to use a fluororesin having large characteristics such as light transmittance. Further, as tetrafluoroethylene-perfluoroalkoxyethylene copolymer and tetrafluoroethylene-hexafluoropropylene copolymer, specifically, the content of impurities used for various devices such as a semiconductor manufacturing process, etc. Those having little transparency and preferable are preferable. Specifically, as the tetrafluoroethylene-perfluoroalkoxyethylene copolymer, AP-231SH (manufactured by Daikin) and 451HP-J (manufactured by Mitsui DuPont Fluorochemical) having good transparency are preferable. ), 950HP-plus (manufactured by DuPont), P-802UP (manufactured by Asahi Glass), and the like. Examples of the tetrafluoroethylene-hexafluoropropylene copolymer include NP-40 (manufactured by Daikin).
In the above description, the columnar member has been described, but a plate-like member may be used.
[0017]
【Example】
Hereinafter, the present invention will be described with reference to examples.
Example 1
Tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA) (450HP-J, made by Mitsui DuPont Fluorochemicals) was extruded from an extruder at a die temperature of 400 ° C in the transverse direction, and then cooled in water at 40 ° C for a diameter of 2 A 1 mm monofilament was produced.
Next, at 290 ° C. in air, tension was applied at a stretching speed of 0.8 m / min to stretch 4.5 times the original length to obtain a stretched material having a diameter of 1.0 mm.
Next, the fiber was optically fixed by holding it at 230 ° C. for 30 minutes in the air with the tension applied, and performing heat setting.
[0018]
The optical fiber obtained in a Class 10000 clean booth was subjected to ultrasonic cleaning in ethanol and then naturally dried, changing the wavelength of the measurement light to 1.3 μm, 0.85 μm, and white light to reduce transmission loss. It was measured. The results are shown in Table 1.
Transmission loss is measured by the cut-back method, where light from a stabilized light source (MG9001A manufactured by Anritsu) is incident on the optical fiber of the sample via a GI glass optical fiber, and the output light is an optical power meter (AQ-1135E manufactured by Ando Electric). To determine the transmission loss per unit length.
[0019]
[Table 1]

[0020]
Example 2
An optical fiber was prepared in the same manner as in Example 1 except that the perfluoro resin was changed to tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA) (950 HP-plus manufactured by DuPont) and the draw ratio was changed. .
For the obtained optical fiber, the transmission loss was measured in the same manner as in Example 1 at a wavelength of measuring light of 0.85 μm, and the results are shown in Table 2.
[0021]
[Table 2]

[0022]
Example 3
The optical fiber (refractive index n = 1.328) manufactured in Example 1 and a member that was not stretched only by extrusion molding were each formed into a loop shape with a length of 300 mm as shown in FIG. Attach one end of the light source 2 to the light source 2 with a wavelength of 650 nm, the other end to the light detection sensor 3 (E3X-DA-N manufactured by OMRON), and immerse 20mm in the center A with water, methanol, and ethanol with different refractive indexes. Table 3 shows that the amount of light changed by 50% or more due to immersion in the liquid when immersed in the tank 4 is detectable.
Since the optical fiber of the present invention has a small light transmission loss, when light leaks from the periphery of the optical fiber due to adhesion of liquid, it is possible to detect a change in the amount of light with a detector.
[0023]
[Table 3]

[0024]
【The invention's effect】
The present invention makes it possible to provide a plastic optical fiber having a small transmission loss made of a perfluoro resin having excellent heat resistance, moisture resistance, chemical resistance, and the like. Due to the change in the amount of light transmitted due to the adhesion of the solvent, it is possible to manufacture a liquid sensor that can adhere to these organic solvents or can be directly immersed in the organic solvent. In addition, the sensor using the plastic optical fiber of the present invention has a lower refractive index than that of a conventional acrylic resin-based plastic optical fiber. Therefore, even if the refractive index of the liquid to be detected is low, The liquid level of the detection liquid can be easily detected.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Optical fiber, 2 ... Light source, 3 ... Light detection sensor, 4 ... Immersion tank

Claims (2)

  In a plastic optical fiber, a molded product obtained by cooling a melt made of crystalline perfluorofluororesin is stretched by applying tension at a temperature not lower than the glass transition point and not higher than the melting point, and is used as a core material. A plastic optical fiber characterized in that it has light guiding properties due to a difference in refractive index at the interface between air and air.   In a liquid sensor, a core obtained by stretching a molded product obtained by cooling a melt made of crystalline perfluorofluororesin at a temperature not lower than the glass transition point and not higher than the melting point is used as a core material. A light emitting means is provided at one end of a plastic optical fiber having a light guide property due to a difference in refractive index at the interface between air and air, and a light receiving means having a light quantity change detecting function is provided at the other end to detect the liquid on the surface of the optical fiber. A liquid sensor characterized by that.

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