JPH0436707A - Multifilament type optical fiber and productin thereof - Google Patents

Abstract

PURPOSE:To obtain the optical fiber having an excellent image transmission characteristic by disposing island parts each having an approximately circular shape and a specific diameter in piling structures of a specific number of pieces in a sea part in the relation of 1:1 to both end faces and providing a protective layer to prevent the infiltration of external light. CONSTITUTION:The sectional shape of the islands is approximately circular and the number of the island shaving 2 to 70 mum diameter is specified to a 50 to 20000 range. Maintaining of the uniformity is difficult if the number of the islands is too much. If the number of the islands is <50, the number of the picture elements in one piece of the fiber is too little and, therefore, the execution of the image transmission with the good resolution is difficult. Further, the fibers 13 of the peripheral part like the central part maintain high optical performance as the protective layer 12 consisting of the colored polymer coated integrally on the fiber at the time of spinning is formed. The arranging state of the islands disposed within the sea section is made into the piling structures or four-way stacking structures. The plastic multifilament type optical fiber having the excellent image transmission characteristic is obtd. if the fiber is formed in such a manner.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a plastic multifilament type optical fiber with a high pixel count of 50 to 20,000, and the transmission image is a glass multifilament type optical fiber. Extremely bright compared to optical fiber transmission image characteristics,
This invention relates to a plastic multifilament optical fiber that is less susceptible to external damage and external light.

[Prior art] Multifilament optical fibers, which are made by arranging quartz-based optical fibers with a fiber diameter of 200 μm or less and bonding the fibers together with adhesive, can transmit images by light, and are therefore used in gastrocameras. Its use as an endoscope is progressing mainly in the medical equipment field.

Glass optical fibers have been developed as multifilament optical fibers with more than 10,000 pixels because it is relatively easy to reduce the fineness of glass optical fibers compared to plastic optical fibers. The optical fiber used here is extremely fine and has low resistance to bending, so it is relatively easy to break during bending when using a multifilament type optical fiber, and the part in question is not a multifilament type optical fiber. A major drawback is that optical fibers have pixel defects.

Additionally, multifilament optical fibers made from glass-based optical fibers are inevitably rigid due to their characteristics, and when used as an image scope, it is difficult to bend the fibers at a large angle, making them difficult to monitor. There is also the drawback that it cannot be made very wide.

Therefore, attempts have been made to develop a plastic multifilament optical fiber, which is a collection of a plurality of plastic optical fibers that are less likely to break and easier to bend than glass optical fibers.

The present inventors have previously developed a method for making an excellent plastic multifilament optical fiber with E, P, 0.2
Proposed on 07705-A2. This invention is a composite material for manufacturing seabird-type multifilament fibers, which consists of stacking a cap plate with a large number of nozzle holes for forming island components, a cap plate with nozzle holes for forming sea components, and a cap plate with fiber aggregation nozzle holes. This method uses a spinneret, and the nozzle hole of the spinneret plate installed directly above the lowest spinneret plate has a trumpet-shaped opening toward the lower end surface of the spinneret plate. By using a spindle plate with a sea component flow path between two spindle plates, and assembling a large number of fibers compositely spun in a gathering nozzle, a structure was created in which the island component was piled up in bales within the sea component cross section. We succeeded in obtaining a plastic multifilament optical fiber. It has been revealed that this method can produce a plastic multifilament optical fiber with fairly good image transmission properties.

[Problems to be Solved by the Invention] By the way, the plastic multifilament optical fiber obtained in this way requires the cable material to be removed in a post-process in order to protect the main body from external damage and to reduce the influence of external light. Generally, it is coated before being used for practical use.

In the cable production process, an extrusion die is usually used, but when a multifilament optical fiber passes through the extrusion die, the island components around the fiber are damaged, resulting in a decrease in its optical performance. is likely to occur.

In other words, the transmission loss of the island component at the outer periphery becomes significantly large due to mechanical damage to the fiber itself caused by the optical fiber wobbling within the die and thermal damage during cable formation. The resulting image transmitted using a multifilament optical fiber is bright in the center and dark in the periphery, making it impossible to obtain an image with uniform brightness. In order to make this type of optical fiber, significant improvements were required.

[Means for Solving the Problems] The present inventors have completed the present invention as a result of studies aimed at obtaining a plastic multifilament optical fiber with even better image transmission properties.

The gist of the present invention is that a light-transmitting affected area having a substantially circular cross section and a diameter of 2 to 70 mm is located in the sea area of 50 to 20 mm.
000 pieces, with bale stacking structure or square stacking structure,
In addition, the positions of the affected areas on both end faces of the multifilament optical fiber are arranged in a one-to-one relationship, and a protective layer with a property of preventing external light from entering is integrated on the outer periphery. A multifilament optical fiber made of plastic is characterized in that it has an effect of preventing external light from entering the multifilament optical fiber.

In the present invention, the structure of the light transmitting affected area can be a core-sheath structure or only a core. The affected area is the core.
When configured with a sheath structure, light is transmitted through repeated total reflections at the interface between the core and sheath of the harmful bird. If the affected area consists only of the core, the sea part will act as a sheath.

For this reason, in the case of a multifilament optical fiber in which the affected part is a core-only structure, it is necessary to select a polymer having characteristics that a sheath-forming polymer should have as the sea-forming polymer. In the following description, unless otherwise specified, in order to simplify the explanation, the case where the structure of the affected area is a core-sheath structure will be used as an example.

When carrying out the present invention, examples of the colorant added to the polymer for forming the protective layer component for the purpose of blocking light from the outside include carbon black, lead oxide, titanium oxide, and organic pigments. A migratable coloring agent such as an organic dye is preferable because it will migrate from the protective layer-forming polymer to the light-transmitting high part-forming polymer while the fiber is left for a long time, significantly reducing the light transmitting performance of the fiber. do not have.

It is preferable to add as much as possible to the polymer for forming the protective layer for the coloring agent in order to enhance the effect of blocking external light, as long as it does not impair other properties.Usually, the amount of the polymer for forming the protective layer is 100. 0.1 parts by weight to 3 parts by weight
It is desirable to add 0 parts by weight, preferably 0.2 parts by weight to 20 parts by weight.

It is desirable to increase the thickness of the protective layer in order to block light from the outside, but increasing the thickness of the protective layer increases the outer diameter of the multifilament optical fiber and reduces the flexibility of the fiber. Not only that, but the area occupied by the core within the fiber cross section decreases, increasing the brightness index I of the transmitted image.
Therefore, it is preferable to make the thickness of the protective layer as thin as possible. It is desirable that it be 20% or less, preferably 10% or less, of the outer diameter (diameter) of a normal multifilament optical fiber.

The brightness index {circle around (2)} of a transmitted image of a multifilament optical fiber defined in the present invention is expressed as follows.

αL 1=S, NA”・1O−(IQ) (1) The brightness index 1 of the transmitted image of the multifilament optical fiber of the present invention is preferably 4.5 Xl0−” or more, particularly 5 Xl0 -'' or more, an extremely bright transmission image can be obtained.

If the ratio of the total area of the core cross section that plays the optical transmission function of a plastic multifilament optical fiber (hereinafter referred to as core occupancy) is less than 50%, the brightness index 1 value of the transmitted image is 4.5 × 101 or less As a result, the brightness of the image transmitted through this optical fiber suddenly becomes dark, and the blur of the transmitted image increases. From this point of view, the core occupancy rate in the image fiber of the present invention is 30%.
It is preferably at least 40%, more preferably at least 50%.

Further, the value of the numerical aperture NA is defined by the following equation (2), and is an element that contributes to the brightness of the transmitted image in the multifilament type optical fiber of the present invention.

NA=φpositive−n z (2) (in the formula, nl
is the refractive index of the core component, and fix is the refractive index of the sheath component.) The numerical aperture NA defined by (2) is the refractive index n of the core component plastic, which is the optical transmission body forming the island component, This value is determined by the refractive index n2 of the sheath component and the refractive index n2 of the sheath component.

In the present invention, the difference between the refractive index n1 of the core component polymer forming the island component and the refractive index n2 of the sheath component polymer is 0.
．． It is necessary to set the value to 01 or more in order not to increase the transmission loss of light transmitted through the island component. n
In the case of multi-optical fibers made by combinations with an l-J value of less than 0.01, a phenomenon in which light introduced into the core component leaks to the sheath layer is observed. In the case of fiber, the clarity of the transmitted image is significantly reduced.

Further, the numerical aperture NA value defined by formula (2) is in the range of 0.16 or more, particularly 0.3 or more, with a core component polymer having a refractive index of n and a sheath component having a refractive index of 02. A multifilament optical fiber made using a core polymer and a sheath polymer that satisfy the refractive index relationship such that the NA value is less than 0.16 has a brightness index of 1 for the transmitted image. is 4.5
This is not preferable because it tends to be less than

The optical transmission loss α value of the multifilament optical fiber of the present invention is preferably 3 dBZ- or less, particularly 1.3 dBZ- or less. When the α value exceeds 3 dB/-, it becomes difficult to make the brightness index (2) of the transmitted image 4.5×10 4 or more even with a multifilament optical fiber using an island component with a large numerical aperture. In order to lower this α value, it is particularly preferable to purify the polymer for forming the island component, particularly from the raw material stage.

The value in formula (1) is the length (m) of the multifilament optical fiber of the present invention, and the S value, NA value,
It can be selected appropriately by selecting the α value, and is usually 0.
The value is 1 to 20.

The cross-sectional shape of the islands of the multifilament optical fiber of the present invention is approximately circular, and the number of islands, that is, the number of pixels, is 50.
It is necessary that the number is in the range of 20,000 to 20,000. It is difficult to maintain uniformity in a multifilament optical fiber that has too many islands. Furthermore, in a multifilament optical fiber having fewer than 50 islands, it is difficult to transmit images with good resolution because the number of pixels in one multifilament optical fiber is too small. In the present invention, it is particularly preferable to use multifilament type optical fibers of 150 to 12,000 pieces.

FIG. 1 is a cross-sectional view of an example of the plastic multifilament optical fiber (11) of the present invention, in which the peripheral fiber (13) is also coated at the center by the protective layer (12) coated during spinning. It is possible to maintain sufficiently high optical performance without any change. In this example, the cross-sectional outer peripheral shape of the multifilament optical fiber is circular, but it can also be polygonal, such as a rectangle, square, or hexagon.

Furthermore, in the plastic multifilament optical fiber of the present invention, the arrangement state of the islands arranged within the sea cross section is second to none.
As shown in the figure, it is preferable to use a bale-stacked structure or a square-stacked structure. In Figure 2, (21) represents the core cross section, and (22)
indicates the sheath component, and (23) indicates the sea component.

By arranging the island components in a cross section of the sea component in a stacked-bale structure, a multifilament optical fiber with high pixel density and high resolution can be obtained.

FIG. 3 is a sectional view of an example of a spinneret preferably used in manufacturing the multifilament type optical fiber of the present invention. This spinneret consists of a spinneret plate (31) for forming the optical fiber core that will become the island component, a spinneret plate (32) for forming the sheath component, a spinneret plate (33) for forming the sea component, a spinneret plate for forming the protective layer, and a multifilament type light It is a seabird type composite spinneret in which a fiber collecting spinneret plate (39) and four spindle plates are stacked. In the same figure, (31a), (32a), and (33a) are the core component spinning holes, the sheath component spinning holes, and the sea component spinning holes, which become the island components, respectively.

One of the features of this spinneret is the lowermost spinneret plate, that is, the spinneret plate installed directly above the fiber gathering spinneret plate (39). It has the shape of the spinning hole (33a) of the sea component forming spinneret plate (33). As shown in the same figure, this seabird component spinning hole (33a) is characterized by its trumpet-shaped opening toward the lower surface of the marine component nozzle plate, and in particular, it widens upward from the middle of the spinning hole (33a). It is preferable to have a shape that provides a tapered hole. Furthermore,
The lower ends of the spinning holes are preferably the lower ends of adjacent seabird component spinning holes.

By adopting the above-mentioned spindle structure, the flow of the molten polymer at the junction of the island component and the sea component becomes extremely smooth, and the flow of the island component and the sea component in each spinning hole also becomes a laminar flow. Since the state can be secured, the island component can be maintained in a nearly circular shape that is close to a perfect circle.
The cross-sectional shape of the optical fiber component of the resulting multifilament type optical fiber can be made extremely uniform as shown in FIG.

In addition, if the shape of the spinning hole of the sea component forming nozzle is a trumpet-shaped opening toward the lower end surface of the nozzle as described above, the nozzle for forming the sea component of the thread in a plastic state formed in a seabird structure can be used. Since the nozzle distance from the fiber is good and meandering and eccentricity do not occur, unevenness in fineness and lack of roundness can be effectively prevented, ensuring uniformity of the sea-island fiber. It is possible.

Next, the large number of yarns that have left the nozzle hole (33a) are
The outer periphery is covered with a protective component supplied from the protective layer forming section (38b) shown in the figure. Unlike the conventional post-process cable forming method, the protective layer is formed all at once in the molten state of the polymer during spinning, so the island components at the periphery of the multifilament optical fiber are extremely unlikely to be damaged, and the island components at the center are , uniform optical performance can be maintained for both peripheral island components.

Further, at the bottom of the fiber gathering cap plate (39), the yarns are gathered and
This results in a plastic multi-optical fiber, which is the object of the present invention.

FIG. 4 shows another example of the spinneret used in the present invention.

Here, the protective layer forming cap plate (41) and the fiber gathering cap plate (39) are independent and separate cap plates. When the nozzle has such a structure, the protective component polymer is mainly applied to the protective layer forming cap plate (41) and the fiber gathering cap plate (39).
) without touching the sea component spinning hole (33a) of the sea component forming mouth plate (33), which has a very complicated structure.

Therefore, when cleaning the nozzle when nozzle maintenance is required, even if a polymer with high adhesiveness to the nozzle is used as a protective component, it is difficult to clean the sea component forming base plate (33) due to its complicated structure. Nozzle cleaning becomes extremely easy and convenient.

In order to efficiently produce the plastic multifilament optical fiber of the present invention using a spinneret as described above, a core component, a sheath component, and a sea component are supplied to each nozzle, and the spinning process defined by the following formula (3) is performed. It is preferable to adopt a spinning/drawing method in which melt spinning is carried out under conditions such that the draft D is 30 or more, and then drawing treatment is carried out under conditions such that the draft D is 30 or more, and then stretching is carried out at 100 to 300°C and a drawing ratio of 1.05 to 5.0 times.

Plastic multifilament optical fibers obtained by melt spinning under conditions where the spinning draft is less than 30 tend to be rigid and easily breakable, and the take-up speed of undrawn multifilament optical fibers is slowed down. As a result, the shape retention stability of the fibrous polymer discharged from each nozzle hole tends to decrease. Therefore, in order to produce a plastic multifilament optical fiber with good image transmission, the spinning draft D It is preferable to perform spinning under conditions of 30 or more, especially 60,000 or less.

Another important characteristic required of multifilament optical fibers is light transmission. Although the multifilament optical fiber obtained by the present invention has a substantially circular and uniform cross-sectional island shape and is excellent in flexibility, it is not desirable that the optical transmission loss tends to increase. .

In particular, in order to produce plastic multifilament optical fibers with sufficient flexibility, it is necessary to spin them at a high draft, but it has been observed that the resulting fibers tend to have significantly increased transmission loss. Therefore, it is preferable to treat the obtained undrawn multifilament optical fiber as follows.

That is, when manufacturing a plastic multifilament optical fiber in which an island component with a core-sheath structure is arranged in the sea part, the multifilament is The method is to heat-stretch the type optical fiber at 100 to 200°C and a stretching ratio of 1.05 to 5 times.

FIG. 5 is a diagram of a drawing process preferably used to efficiently produce the plastic multifilament type optical fiber of the present invention. In the figure, (51) is a reroller for taking up the undrawn multifilament optical fiber yarn discharged from the spinneret, (52) is a drawing heating device, (53) is a drawing roller, and (54) is a winding roller. It is a tori machine.

Specific examples of plastics for forming the core and sheath components of the multifilament optical fiber of the present invention include the following.

Polymethyl methacrylate (n=1.49) and a copolymer based on methyl methacrylate (n=1.49).
47-1.50), polystyrene (n=1.58) and styrene-based copolymers (n=1.50)
~1.58), styrene acrylonitrile copolymer (n=1.56), poly4-methylpentene 1 (n-
1,46), ethylene/vinyl acetate copolymer (n=1.4
6-1.50), polycarbonate (n=1.50-
1.57), polychlorostyrene (n=1.61)
, polyvinylidene chloride (n-1,63), polyvinyl acetate (n=1.47), methyl methacrylate/styrene, vinyltoluene or α-methylstyrene/maleic anhydride ternary or quaternary copolymer (n-1 ，
50-1.58), polydimethylsiloxane (n=1
．． 40), polyacetal (n=1.48), polytetrafluoroethylene (n=1.35), polyvinylidene fluoride (n=1.42), polytrifluoroethylene (n=1.40), perfluoropropylene (
n=1.34), and binary or ternary copolymers of these fluorinated ethylenes (n=1.35 to 1.40)
, polyvinylidene fluoride and polymethyl methacrylate blend polymer (n = 1.42 to 1.46), general 2 GHz = C (CHs) A copolymer mainly composed of fluorinated methacrylate represented by C00Rf,
A copolymer in which the group Rf is (CTo)-(CFz)-H (n=1.37-1.42), Rf is (cut),
(crt), IF (n=1.37-1.40
), Rf is CI・(CFI) z (n=1.3
8), where Rf is C(CFs)i (r+=1.36
), Rf is CH, CF2CHFCF3 (n=1.
40), where Rf is CHzCF(CF,)z (n=
1.37), and copolymers of these fluorinated methacrylates (n=1.36 to 1.40), and copolymers of these fluorinated methacrylates and methyl methacrylate (n=1.37 to 1.43), with general formula CIb =
A polymer whose main component is a fluorinated acrylate represented by CH-C0OR'f, provided that Rf' is (CHg)-(
CPz)-P (n=1.37-1.40), R
f' is (C1, (CF,), H (n= 1.3
7-1.41), Rf' is CHzCFzCHF-CP
s (n=1.41), Rf is C0(CI,)X
(n=1.38), these fluorinated acrylate copolymers (n=1.36 to 1.41), and these fluorinated acrylates and the above fluorinated methacrylate copolymers (n=1.36 to 1.41) , and these fluorinated acrylate, fluorinated methacrylate, and methyl methacrylate copolymers (n = 1.37 to 1.43)
, a polymer mainly composed of 2-fluoroacrylate represented by the general formula Cl(, = CF-COOR"f, and its copolymer (n = 1.37 to 1.42) (wherein R"f is CF8 , (CHffi), (CFril
IF, (CIri-(Ch)lIHSCToCFzCHF
Ch, C(CF s) z).

Plastics that can be used as the sea component and the protective layer component include, in addition to the above-mentioned plastics, polyamide, polyester elastomer, polyamide elastomer, polystyrene elastomer, polyolefin elastomer,
Boryl 4-methylpentene 1, polyvinylidene elastomer, ionomer, ethylene/ethyl acrylate copolymer, ethylene/vinyl acetate copolymer, polyvinylidene copolymer polymethyl methacrylate, polystyrene, ABS, polybutylene terephthalate,
Polyethylene, vinyl chloride, etc. can be mentioned as specific examples, and these polymers are used for forming the sea component and the protective layer component in which the fluidity of these polymers is greater than the fluidity during spinning of the shaft-forming polymer that becomes the island component. The selection of polymers is preferred for making multifilament optical fibers that transmit clear and bright images.

According to the present invention, a plastic multifilament type optical fiber with extremely excellent image transmission properties is produced without uneven brightness as seen in plastic multifilament type optical fiber cables manufactured by conventional post-process cable production methods. Fiber can be easily obtained.

[Example code] The present invention will be further explained below with reference to Examples.

Example 1 A spinneret having the structure shown in FIG. 3 was used, the number of holes was set as shown in Table 1, and polymethyl methacrylate having a refractive index of 1.492 was used as the core component constituting the island component. , a polyfluorinated methacrylate polymer with a refractive index of 1.415 is used as the sheath component, polymethyl methacrylate is used as the sea component, and polyethylene colored by mixing 5% by weight of Ketchen Black is used as the protective layer component, and composite spinning is performed. A plastic multifilament optical fiber having the characteristics shown in Table 1 was obtained.

The plastic multifilament optical fibers obtained as shown in Experiment Nos. 1.2.3 and 4 in Table 1 had island components in the shape of stacked bales as shown in Figure 1, and were clear.
It was also possible to transmit delicate images, and the brightness of the transmitted images was extremely bright.

Furthermore, even when images were transmitted through the fiber under illumination with an illuminance of 100 Lx, good contrast could be maintained.

Example 2 A spinneret having the structure shown in Fig. 4 was used, the number of holes was set as shown in Table 2, and the core component had a refractive index of 1.
．． 492 polymethyl methacrylate, using polyvinyl fluoride copolymer with a refractive index of 1.402 as the sheath component, using polymethyl methacrylate as the sea component,
Using polyethylene as the protective layer component and an ethylene/vinyl acetate copolymer mixed with 5% by weight of Ketchen black as the protective layer component, composite spinning was carried out in the same manner as in Example 1 to provide the properties shown in Table 2. A multifilament optical fiber was manufactured.

This optical fiber had a stacked island component, and was able to transmit a clear and delicate image, and the brightness of the transmitted image was extremely bright. Furthermore, even when the fiber was placed under illumination with an illuminance of 100 Lx, images could be transmitted while maintaining good contrast.

Table 1 Table 2 Comparative Example 1 The same spinneret, core polymer, sheath polymer, and sea polymer as in Example 1 were used except that the polymer for forming the protective layer was not used, and the three-layer structure of core-sheath and sea polymer was used. Plastic multifilament optical fibers were manufactured under the conditions of experiment numbers 1 to 4 as in Example 1. Next, these fibers were ketched at a temperature of 150°C using a commonly used cable coating device. The outermost layer was coated with enblacked polyethylene. When images were transmitted using these fibers, in each case the image at the periphery of the cross-section of the multifilament optical fiber was dark, and the brightness unevenness between the center and periphery was significant, making it impossible to obtain a clear image. It was extremely difficult.

Comparative Example 2 The same spinneret, core polymer, sheath polymer,
It was produced under the same conditions as in Example 2, except that a sea polymer and a protective layer polymer were used, but no colorant was added as the protective layer polymer. When these fibers were placed under illumination with an illuminance of 100 LX and images were transmitted, the contrast of the images was poor in all cases, making it difficult to obtain clear images.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the plastic multifilament optical fiber of the present invention, and FIG. 2 is a partially enlarged view of the same.
3 and 4 are partial sectional views of a spinneret used in the practice of the present invention, and FIG. 5 is a schematic diagram of a drawing device used in the practice of the present invention. 11... Optical fiber 12... Protective layer 13...
・Peripheral fiber 21...Core 22...Sheath component
23... Sea component 31... Core forming cap plate 32... Sheath component forming cap plate 33... Sea component forming cap plate 39... Fiber gathering cap plate 41... Protective layer formation Mouth plate 51...Take-off roller 52...Stretching heating device 5
3... Stretching roller 54... Winder patent applicant Mitsubishi Rayon Co., Ltd.

Claims (1)

[Claims] (1) In the sea area, there are 50 to 20,000 optically transmitting islands with a substantially circular cross section and a diameter of 2 to 70 μm,
Arranged in a bale-stacked structure or a square-stacked structure, and arranged so that the positions of the island parts arranged on both end faces of the multifilament optical fiber have a one-to-one relationship, and further,
This is a plastic multifilament optical fiber with a protective layer integrally coated on the outer periphery, and the protective layer is made of a colored polymer that has the effect of preventing external light from penetrating into the fiber. Plastic multifilament optical fiber.