JP3208571B2 - Method of manufacturing plastic multifilament optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention has a large number of pixels of 50 to 30,000, and has a small number of deformed pixels. Especially, there is no deformed pixel at the center of the fiber, so that the image distortion is extremely small. And a plastic multifilament optical fiber having a wide effective field of view.

[0002]

2. Description of the Related Art A multifilament optical fiber in which quartz optical fibers having a fiber diameter of 200 μm or less are arranged in a good array and the fibers are bonded with an adhesive can transmit an image by light. The use of endoscopes is being promoted mainly in the field of medical equipment.

[0003] Glass-based optical fibers have been developed mainly for multi-filament optical fibers with a large number of pixels exceeding 3,000 because it is relatively easy to reduce the fineness compared to plastic-based optical fibers. However, since the glass-based optical fiber used here is extremely fine and has a low resistance to bending, this type of multi-filament type optical fiber requires a bending operation that is applied during its use. Therefore, it is a great difficulty that the wire breaks relatively easily and the portion becomes a pixel defect of the multifilament optical fiber.

A multifilament optical fiber made of a glass-based optical fiber cannot be prevented from being rigid due to its characteristics, and when used as an image scope, it is difficult to obtain a large bending angle. There is also a disadvantage that the surveillance field of view cannot be made very wide.

Therefore, conventionally, there has been attempted to develop a plastic-based multifilament optical fiber in which a plurality of plastic-based optical fibers having characteristics such that they are less likely to be broken and are more easily bent than glass-based optical fibers.

The present inventors have previously described a method for producing an excellent plastic multifilament type optical fiber by E. et al.
PO0207705. The present invention relates to a multi-filament sea-island multifilament type fiber manufacturing method in which a base plate having a large number of island component forming nozzle holes, a base plate having a sea component forming nozzle hole, and a base plate having a fiber collecting nozzle are stacked. The nozzle hole of the base plate located just above the bottom base plate of the base,
A large number of fibers which are provided with a trumpet-shaped opening toward the lower end surface of the base plate, and which are composite-spun using a base plate having a sea component flow path provided between two base plates provided immediately above the lower base plate. By assembling the strips with an assembling nozzle, a plastic multifilament optical fiber with an island component in a sea component cross-section is obtained in a bales arrangement structure. It has been found that a multifilament optical fiber can be made.

[0007]

By the way, the plastic multifilament optical fiber obtained in this way is provided with a multifilament optical fiber in a subsequent step in order to protect the optical fiber main body from damage when external force is applied and to prevent light leakage. It is general that the outer periphery of the optical fiber is covered with a cable material before it is put to practical use. In the cable-forming process, an extrusion die is usually used, but when a multifilament optical fiber passes through the extrusion die, the optical performance is degraded due to deformation of the cross section of the pixel arranged around the outside. The problem of doing so is likely to occur.

That is, the mechanical loss due to the contact between the optical fiber and the inner surface of the die due to the displacement of the optical fiber in the die, and the thermal damage to the optical fiber when the optical fiber is formed into a cable, the transmission loss of the outer island is reduced. It becomes remarkably large. As a result, the image transmitted using such a damaged optical fiber was bright at the center and dark at the periphery, and an image with uniform brightness could not be obtained.

In addition, the outer peripheral portion of the multifilament optical fiber is deformed into an elliptical shape because the nozzle wall and the island portion of the outer peripheral portion of the multifilament optical fiber come into contact with each other in the yarn production process. Is recognized.

In particular, when the degree of cross-sectional deformation of the island portion increases, not only the transmission image itself due to the multifilament optical fiber is distorted, but also the light transmission loss of the cross-sectional deformation pixel increases, so that the transmission from the island portion where the cross-section deformation is small is small. Since the brightness of the image is reduced and an image of uniform brightness cannot be obtained with the multifilament optical fiber, it is a step further improvement from this point to a plastic multifilament optical fiber with excellent image transmission performance Was needed.

[0011]

The inventors of the present invention have studied the purpose of obtaining a multifilament optical fiber made of plastic which is further excellent in image transmission, and have completed the present invention.

The gist of the present invention is that the optical transmission
Has a structure in which many islands with a substantially circular cross section are arranged in the main sea area
Manufactures multi-filament plastic optical fiber
In the method, a large number of
Assembling and unifying the melted yarn using a fiber bundle base plate
And the outer peripheral portion of
A protective layer with a thickness of 0.3 to 10 times the island diameter
By covering, the cross section of the island part shown by the following [Equation 2]
The number of islands with a deformation degree of 1.5 or more is 5 or less for 100 islands
Plastic multi-filler characterized by being below
In the method of manufacturing the optical fiber .

[0013]

(Equation 2)

In the present invention, the diameter of the light transmitting island portion is preferably a substantially circular cross section of 2 to 70 μm. An island portion having a cross-sectional diameter of less than 2 μm has an undesirably large transmission loss of 3 dB / m or more, resulting in a small brightness index I of a transmission image, which will be described later, and a dark transmission image.
On the other hand, in the case of an island portion having a cross-sectional diameter exceeding 70 μm, the cross-sectional diameter of a multifilament optical fiber having the same number of pixels and a small cross-sectional diameter of the island is larger than that of a multifilament optical fiber, and the flexibility of the multifilament optical fiber itself is reduced. Is not preferred. In addition, when a multifilament optical fiber having the same cross-sectional diameter is used, the number of islands that can be arranged there is reduced, and the resolution is undesirably reduced.

In the present invention, a substantially circular island cross section means a polygon having a hexagonal shape or more. In the case where the cross section of the light transmitting island is a polygon having a pentagon or smaller, a large difference occurs in the image transmission of each island, and the image transmission of the multifilament optical fiber is lost. Absent.

In the present invention, the structure of the light transmitting island portion is as follows:
It is composed of a core-sheath structure or a core only. When the island portion has a core-sheath structure, light is transmitted by repeating total reflection at the interface between the core-forming polymer and the sheath-forming polymer of each island.
In the case where the island portion is only the core, it is necessary to cause the sea portion to act as a sheath to perform optical transmission, and as the sea-forming polymer, a polymer having characteristics that the sheath-forming polymer should have,
That is, it is necessary to select a transparent polymer having a refractive index lower than that of the island-forming polymer. In the following description, for the sake of simplicity, unless otherwise specified, an example in which the structure of the island portion is a core-sheath structure will be described.

In the present invention, the deformation of the island section, that is, the deformation of the pixel section, is defined by the degree of deformation defined by [Equation 1]. Normally, the pixel cross section of the outer periphery of the multifilament optical fiber is easily deformed into an elliptical shape. Therefore, in [Equation 1], the “maximum value of the diameter of the island portion” is the value of the major axis of the deformed elliptical pixel. As the "minimum value of the diameter of the island portion", the value of the minor axis of the elliptical pixel is taken.

The island section deformation degree defined by [Equation 1] is 1.
A multifilament optical fiber composed of five or more islands has a distorted transmission image and cannot perform accurate image transmission. Further, in a pixel having a large cross-sectional deformation degree of 1.5 or more, the optical transmission loss is large, and the cross-sectional deformation degree is 1.
The transmitted image is darker than pixels of 5 or less islands. For this reason, a multifilament optical fiber including pixels having a large degree of cross-sectional deformation is not preferable because, when viewed as an entire image, the uniformity of the brightness of the image is impaired and the quality of the image is deteriorated.

When observing an image with a plastic multifilament optical fiber, the observation is performed mainly by capturing the object to be observed at the center of the visual field. Therefore, when the above-described image distortion or uneven image brightness, that is, a pixel having a large degree of cross-sectional deformation is located near the center of the visual field, this poses a particular problem in image observation. It is preferable that the amount of pixels having a large degree of island section deformation in the cross section of the multi-filament optical fiber is small. Desirably not present. In other words, in the multifilament optical fiber, a portion where there is no pixel formed of an island having a cross-sectional deformation of 1.5 or more is a portion that can be effectively used for observation (hereinafter referred to as an effective field of view). The larger the area of the effective field of view in the cross section of the multifilament optical fiber, the better the performance of the plastic multifilament optical fiber.The area of the effective field of view is the cross section of the fiber excluding the protective layer portion of the cross section of the multifilament optical fiber.
It is desirable that the area is at least 80%, preferably at least 90%, of the area of (f).

In order to obtain a plastic multi-filament optical fiber having a small degree of cross-sectional deformation of the island and a small number of such fibers, it is effective to provide a protective layer on the outer periphery of the optical fiber. Furthermore, it is imperative that the protective layer be integrally coated on the fiber in the spinning nozzle. And the thickness of the protective layer islands diameter of 0.3 times or more, preferably 0.8
The spinning is desirably carried out under such a condition that it is doubled, more preferably doubled.

In general, islands having a large degree of cross-sectional deformation are likely to occur on the outer periphery of a multifilament optical fiber. The reason for this is that the polymer forming the pixels (islands) on the outer periphery of the multifilament optical fiber is formed by the assembly of the fiber focusing die plate (39) based on the structure of the spinning nozzle shown in FIG. 3 and FIG. Since the polymer passes through a position very close to the outer peripheral surface of the mouth, it receives a greater shearing force than the polymer passing through the center of the multifilament optical fiber, and thus is easily deformed. In order to prevent this deformation, the polymer for island component formation should pass at a position as far as possible from the outer peripheral surface of the collecting port of the fiber collecting die plate (39) so that a large shear force is not applied to the polymer. This is an effective method. However, if the thickness of the protective layer is too large, the total area of the islands in the cross section of the multi-filament type optical fiber decreases, resulting in a disadvantage that the brightness of the image decreases. It is preferred that

[0022] The present inventors have results of various studies, the thickness of the protective layer islands diameter of 0.3 times or more multifilament type optical fiber in the cross section of the present invention, preferably 0.8 times or more,
More preferably, the deformation of the island at the outer peripheral portion of the multifilament optical fiber obtained so as to be about 2 to 10 times is very small, and the multifilament optical fiber of the present invention has a cross section of the island. Pixels having a deformation degree of 1.5 or more were successfully generated.

When the cross-sectional deformation of the island at the outer periphery of the multifilament optical fiber is 1.5 or less, the cross-sectional deformation of the island at the center is 1.2 or less. The distortion is small, and the unevenness of the image brightness is not a problem at all.

Further, in order to obtain a multifilament optical fiber having almost no islands whose cross-sectional deformation degree is 1.5 or more, the area of the effective field of view is reduced to the area of the fiber cross section (f) excluding the protective layer. On the other hand, it is preferably at least 80%, preferably at least 90%. Further, in a multifilament optical fiber having 50 or more pixels, even if a protective layer having an outer diameter of about 0.3 times the island diameter is provided, the cross-sectional area of the entire fiber is smaller than that in the case where no protective layer is provided. The brightness of the image can be maintained without being greatly reduced.

Further, as a component forming the protective layer, a polymer having a light shielding property is used, and by preventing external light from entering the multifilament type optical fiber, the contrast of a transmitted image is greatly improved. can do.

In the present invention, as the polymer for forming the light shielding protective layer, it is preferable to use an opaque but highly flexible polymer such as an ABS resin. More preferably,
It is desirable to use a material to which carbon black or the like having a light absorbing effect is added. The amount of carbon black added to the polymer should be 0.6 parts by weight or less based on 100 parts by weight of the polymer.
Moreover, preferably not more than 5 parts by weight. The protective layer formed with the addition amount of carbon black less than 0.6 parts by weight does not exhibit a light shielding effect. Also, over 5 parts by weight
The polymer composition added by the addition decreases its fluidity, spinning becomes unstable during spinning, and phenomena such as the diameter of the obtained fiber tend to fluctuate easily. The elastic modulus increases and the flexibility decreases.

The light shielding effect is proportional to the product of the amount of carbon black added and the thickness of the protective layer. Assuming that the added amount of carbon black per 100 parts by weight of the polymer is x parts by weight and the thickness of the protective layer is t μm, the value of x × t (unit is μm by weight) is 1 or more, more preferably 5 or more, and further preferably 10 or more. The above is desirable for obtaining a sufficient light shielding effect.

The light shielding effect is measured by measuring the contrast of an image. In the present invention, the contrast of the image is obtained when the image of line 4 of group 4 (the number of line pairs is 22.6 lp / mm) among the test targets of USAF (1951) is transmitted by a 1.5 m long multifilament optical fiber. Evaluated by MTF. A multifilament optical fiber whose MFT _B value is 70% or less measured by illuminating a 1-m-long portion of the fiber with an illuminance of 600 Lx compared to the MTF _D measured in a dark room is the light of the protective layer. It is determined that the shielding effect is insufficient. If the value of MTF _B / MTF _D is 0.7 or more, it is substantially determined that the protective layer of the multifilament optical fiber has sufficient light shielding properties.

The brightness index I of the transmission image of the multifilament optical fiber defined in the present invention is defined by [Equation 3].

[0030]

(Equation 3)

The brightness index I of the transmission image of the multifilament optical fiber of the present invention is preferably 4.5 × 10 ^-2 or more, and particularly when it is 5 × 10 ^-2 or more, an extremely bright transmission image is obtained. Optical fiber.

The ratio of the total area of the cross section of the optical transmission section in the cross section of the plastic-based multifilament optical fiber (hereinafter referred to as core occupation ratio) is less than 30%.
The brightness index I value of the transmitted image becomes 4.5 × 10 ^-2 or less, the brightness of the image transmitted through the image fiber sharply decreases, and the blurring of the transmitted image increases. From this viewpoint, the core occupancy in the image fiber of the present invention is 30% or more, particularly 40% or more, and furthermore,
It is preferably at least 50%.

The value of the numerical aperture NA is defined by the following equation [Equation 4], and is a factor contributing to the brightness of a transmitted image in the multifilament optical fiber of the present invention.

[0034]

(Equation 4)

[0035] [Equation 4] numerical aperture NA defined by the optical transmission member that forms the island component, in particular value determined by the refractive index n ₂ of the refractive index n ₁ and the sheath component of the core component plastic.

In the present invention, the difference between the refractive index n ₁ of the core component polymer forming the island component and the refractive index n ₂ of the sheath component polymer is not less than 0.01. It is necessary to prevent the transmission loss of the generated light from increasing. In the case of a multifilament type optical fiber made of a combination having an n ₁ -n ₂ value smaller than 0.01, a phenomenon in which light introduced into the core component leaks to the sheath layer is observed, and the multifilament as in the present invention is observed. In the type optical fiber, the sharpness of the transmitted image is significantly reduced.

Further, the numerical aperture NA value defined by [Equation 4] is 0.
It is desirable to select a core component polymer having a refractive index of n ₁ and a sheath component polymer having a refractive index of n ₂ so as to be in a range of 16 or more, particularly 0.3 or more. NA value is 0.
The value of the brightness index I of the transmission image of the multi-filament optical fiber made using the core polymer and the sheath polymer satisfying the refractive index relationship so as to be less than 16 is likely to be less than 4.5 × 10 ^-2, and it is clear and bright. However, it is not preferable because the multi-filament optical fiber cannot transmit images sufficiently.

The optical transmission loss α value of the multifilament optical fiber of the present invention is preferably 3 dB / m or less, particularly preferably 1.3 dB / m or less. When the α value exceeds 3 dB / m, even if an island component having a large numerical aperture is used, the brightness index I value of the transmission image of the multifilament optical fiber is 4.5.
× 10 ^-2 or more is difficult. In order to reduce the α value, it is particularly preferable to purify the polymer for forming the island component, particularly to purify the polymer from the raw material stage.

The value L in [Equation 3] is the working length (m) of the multifilament optical fiber of the present invention.
Value, NA value, and α value can be selected as appropriate, and it is usually preferable that the value be 0.1 to 20.

The cross section of the island portion of the multifilament optical fiber of the present invention is substantially circular, and the number of islands is 50.
It is preferably in the range of 30000 to 30000. If the number of islands is too large, it is difficult to maintain the uniformity of the obtained multifilament optical fiber. Further, in a multifilament optical fiber having less than 50 islands, the number of pixels in one multifilament optical fiber is too small, so that it is difficult to obtain a multifilament optical fiber capable of performing a transmission image with good resolution. In the present invention, it is particularly preferable to use a multifilament optical fiber having 150 to 12,000 islands.

FIG. 1 is a cross-sectional view of an example of the plastic multifilament optical fiber (11) of the present invention, in which a protective layer (12) coated at the time of spinning provides a peripheral island portion.
The cross-sectional shape of (13) is not different from the cross-sectional shape of the central island portion, and maintains sufficiently high optical performance. Although the cross section of the multifilament optical fiber is circular in shape, it may be rectangular, square, hexagonal or other polygonal shape.

In the plastic multifilament optical fiber of the present invention, the arrangement of the islands arranged in the sea section is preferably in a bale-stacked structure as shown in FIG. [Figure 2] (21) is the core section, (22)
Indicates a sheath component, and (23) indicates a sea component. By forming the array of island components in a sea component cross section in a bale-stacking structure, a high pixel density and high resolution multifilament optical fiber can be obtained.

FIG. 3 is a sectional view of an example of a spinneret preferably used for producing the plastic multifilament optical fiber of the present invention. This spinneret is a multi-filament optical fiber core forming base plate (31) serving as an island component, a sheath component forming base plate (32), a sea component forming base plate (33), a protective layer forming and This is a sea-island composite spinneret in which a multifilament optical fiber assembly die plate (39) and four die plates are stacked. (31a), (3
2a) and (33a) denote the core component spin hole and the sheath component spin hole and the sea component spin hole, respectively.

One of the features of this spinneret is a lower die plate, that is, a die plate installed immediately above the fiber assembly die plate (39). It is in the shape of the spinning hole (33a) of the sea component forming base plate (33). As shown in the figure, the sea-island component spinning hole (33a) is characterized in that it opens in a trumpet shape toward the lower surface of the sea component mouthpiece plate, and in particular, extends downward from the middle of the spinning hole (33a). It is preferable that the shape be a tapered hole. further,
It is preferable that the lower end of the spinning hole be the lower end of the sea-island component spinning hole adjacent to each other.

With the above-described base structure, the flow of the molten polymer at the junction between 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 is also substantially laminar. Therefore, the cross section of the island component can be maintained in a substantially circular shape close to a perfect circle, and the cross-sectional shape of the obtained multifilament optical fiber is compared with that of the related art [FIG. ] As shown in FIG.

When the spinning hole of the sea component forming die has a trumpet-shaped opening toward the lower end surface of the die as described above, the sea component of the plasticized yarn formed in a sea-island structure can be formed. Since the nozzle is well separated from the forming nozzle and does not meander or eccentric, it can efficiently prevent the occurrence of unevenness of fineness and the lack of circularity. Can be secured.

Next, a number of the yarns leaving the nozzle holes (33a) are covered on the outer periphery with the protective component supplied from the protective layer forming portion (38b) shown in FIG. According to this method, since the polymer is formed up to the protective layer at a stretch in the molten state during spinning, the fiber around the multifilament optical fiber is not damaged, and the central fiber and the peripheral fiber have uniform optical performance. It can be held.

Further, the threads are gathered and integrated below the gathering base plate (39) to obtain the plastic multifilament optical fiber of the present invention.

FIG. 4 shows another example of the spinneret used in the present invention. Here, the base plate (41) for forming the protective layer and the collecting base plate (39) are separate and independent base plates. With the nozzle having such a structure, the protective component polymer is mainly brought into contact with the protective layer forming base plate (41) and the collecting base plate (39), and the sea component forming base plate having a very complicated structure is formed. (3
Since the sea component spin hole (33a) in 3) is not touched, even when nozzle maintenance is required or when cleaning the nozzle, even if a polymer with high adhesiveness to the nozzle is used as a protective component, The polymer does not come into contact with the sea component forming base plate (33) which is difficult to clean because of its complicated structure, and the operability and simplicity of nozzle cleaning are extremely excellent.

As described above, in order to efficiently produce the plastic-based multifilament optical fiber of the present invention using the spinneret, a core component, a sheath component and a sea component are supplied to each nozzle and defined by the following equation (5). Spinning draft D is 30
Melt spinning under the above conditions, then 100-300
It is preferable to employ a spin drawing method in which a drawing treatment is performed at a temperature of ℃ and a draw ratio of 1.05 to 5.0 times.

[0051]

(Equation 5)

The plastic multifilament optical fiber obtained by melt-spinning under the condition that the spinning draft is less than 30 tends to be rigid and easily broken, and the take-up speed of the undrawn multifilament optical fiber is reduced. Is required, the shape retention stability of the fibrous polymer discharged from each nozzle hole tends to decrease. Therefore, in order to obtain a plastic-based multifilament optical fiber having good image transmission properties, the spinning draft D More than 30, especially
Spinning is preferably performed under the conditions of 60000 or less.

Another important property required for a multifilament optical fiber is transparency. The multifilament optical fiber of the present invention has a core having a substantially circular cross-section and a uniform shape, and is excellent in flexibility. In particular, a plastic-based multifilament optical fiber having sufficient flexibility is used. In order to achieve this, it is desirable to spin at a high draft. That is, after spinning under the condition that the spinning draft D defined by [Equation 5] is 30 or more, the multifilament optical fiber is drawn at 100 to 200 ° C., and the draw ratio is 1.05 to 5
This is to perform a hot stretching process at a factor of 2.

FIG. 5 is a drawing showing a drawing process suitably used for efficiently drawing the plastic multifilament optical fiber of the present invention. In the figure, (51) is a take-up roller of the undrawn yarn of the multifilament optical fiber discharged from the spinneret, (52) is a drawing heating device, (53) is a drawing roller, and (54) is It is a winding machine.

Specific examples of the plastic for forming the core component and the sheath component of the multifilament optical fiber of the present invention include polymethyl methacrylate (n = 1.49), a copolymer containing methyl methacrylate as a main component (n = 1.47 to 1.50),
Polystyrene (n = 1.58), styrene-based copolymer (n = 1.50 to 1.58), styrene acrylonitrile copolymer (n = 1.56), poly 4-methylpentene 1 (n = 1.46),
Ethylene / Vico vinegar (n = 1.46-1.50), polycarbonate (n = 1.50-1.57), polychlorostyrene (n = 1.6
1), polyvinylidene chloride (n = 1.63), polyvinyl acetate (n = 1.47), methyl methacrylate / styrene, vinyl toluene or α-methylstyrene / maleic anhydride terpolymer or quaternary copolymer (n = 1.50 to 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 systems of these fluorinated ethylenes Or ternary copolymer (n = 1.35-1.40), polyvinylidene fluoride and polymethyl methacrylate blend polymer (n = 1.42-1.46),
Copolymer containing fluorinated methacrylate represented by the general formula CH ₂ = C (CH ₃ ) COORf as the main component, wherein the group Rf is (CH ₂ ) _n (CF ₂ ) _n H (n = 1.37 to 1.42) , Rf is (CH ₂ ) _m (CF ₂ ) _n F (n = 1.37 to 1.40), and Rf is CH · (CF ₃ ) ₂ (n = 1.3
8), Rf is C (CF ₃ ) ₂ (n = 1.36), Rf is CH ₂ CF ₂ CHFCF
₃ (n = 1.40), Rf of CH ₂ CF (CF ₃ ) ₂ (n = 1.3
7), and copolymers of these fluorinated methacrylates (n = 1.36-1.40), and these fluorinated methacrylate and methyl methacrylate copolymers (n = 1.37-1.43),
Polymer having a fluorinated acrylate represented by the general formula CH ₂ = CH · COOR'f as the main component, where R'f is (CH ₂ ) _m (CF ₂ ) _n F (n = 1.37 to 1.40) , R′f of (CH ₂ ) _m (CF ₂ ) _n H (n =
1.37 to 1.41), where R'f is CH ₂ CF ₂ CHF.CF ₃ (n = 1.4
1) wherein R′f is CH (CH ₃ ) ₂ (n = 1.38), and these fluorinated acrylate copolymers (n = 1.36 to 1.41), and these fluorinated acrylates and the above-mentioned fluorinated methacrylate copolymer (n = 1.36) To 1.41), and these fluorinated acrylates, fluorinated methacrylates, and methyl methacrylate copolymers (n = 1.37 to 1.43), a polymer mainly composed of 2-fluoroacrylate represented by the general formula CH ₂ = CF · COOR "f,
And its copolymer (n = 1.37 to 1.42) [wherein R "
f is CH ₃ , (CH ₂ ) _m (CF ₂ ) _n F, (CH ₂ ) _m (CF ₂ ) _n H, CH ₂ CF ₂ CH
FCF ₃ and C (CF ₃ ) ₂ are shown].

Examples of the plastic which 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, poly-4-methylpentene 1, polyvinylidene fluoride Elastomers, ethylene / ethyl acrylate copolymers, ethylene / vinyl acetate copolymers, vinylidene fluoride copolymers, polymethyl methacrylate, polystyrene, ABS, polybutylene terephthalate, polyethylene, vinyl chloride and the like can be mentioned as specific examples. Choosing a polymer for forming the sea component and the protective layer component in which the fluidity is greater than the fluidity during spinning of the sheath-forming polymer, which is an island component, will result in clear and bright images. Preferable to make the multifilament type optical fiber for.

Further, carbon black, lead oxide, titanium oxide, an organic pigment, or the like is mixed with the polymer for forming the protective layer component, and the protective layer is colored to prevent leakage of light transmitted inside the fiber to the outside. The light shielding effect of preventing light from entering the interior of the fiber can be enhanced.

According to the present invention, it is possible to easily obtain a plastic multifilament optical fiber which has little deformation of islands and has no unevenness of brightness and which is extremely excellent in image transmission.

[0059]

The present invention will be further described with reference to the following examples. In the examples, the effective visual field ratio is a value measured by the following method.

The cross section of the multifilament optical fiber (f) except for the protective layer has a shape similar to that of the cross section of the optical fiber (f).
When the figure (a), which is X% of the area of the figure, is superimposed so that the center of gravity of the fiber cross section (f) and the center of gravity of the figure (a) coincide, When the degree of deformation was 1.5 or less, the effective visual field ratio was defined as X%.

[0061]

Example 1 A spinneret having a structure as shown in FIG. 3 was used, the number of holes was set to the number of holes shown in Table 1, and polymethyl having a refractive index of 1.492 was used as a core component constituting an island component. A methacrylate is compound-spun using a polyfluorinated methacrylate polymer having a refractive index of 1.415 as a sheath component, polymethyl methacrylate as a sea component, and polyethylene as a protective layer component, and has the properties shown in [Table 1]. A plastic multifilament optical fiber was obtained.

Experiment Nos. 1, 2, 3 and 4 in Table 1
The multifilament optical fiber made of plastic obtained as shown in FIG. 1 has an island component in a bale-stacked shape as shown in FIG. 1, has no pixels with a degree of deformation of 1.5 or more, and has an effective field ratio of 100. %Met. A clear and delicate image could be transmitted, and the transmitted image was extremely bright.

[0063]

[Table 1]

[0064]

Example 2 A spinneret having the structure shown in FIG. 4 was used, the number of holes was set to the number of holes shown in Table 2, and the core component constituting the island component was polymethyl having a refractive index of 1.492. Methacrylate, using a polyfluorinated methacrylate polymer having a refractive index of 1.415 as a sheath component, using polymethyl methacrylate as a sea component, using polyethylene as a protective layer component, and changing the thickness of the protective layer to perform composite spinning,
A plastic multifilament optical fiber having the characteristics shown in Table 2 was obtained.

The plastic multifilament optical fibers obtained as shown in Experiment Nos. 5, 6, 7 and 8 in [Table 2] had an island component in a bale stack as shown in FIG. As shown in Table 2, the number of pixels having a degree of deformation of 1.5 or more was small, and the effective visual field ratio was as large as 80% or more. And a clear and delicate image could be transmitted, and the brightness of the transmitted image was extremely bright.

[0066]

[Table 2]

[0067]

Comparative Example 1 The same spinneret, core polymer, sheath polymer, sea polymer and protective layer polymer as used in Example 2 were used, except that the thickness of the protective layer was outside the scope of the present invention.
The fibers shown in Table 2 were manufactured. In these fibers, since the thickness of the protective layer was too thin, the pixels at the outer periphery were greatly deformed, the number of pixels having a degree of deformation of 1.5 or more was large, and the effective visual field ratio was low.

[0068]

Example 3 A spinneret having a structure as shown in FIG. 4 was used, the number of holes was set to the number of holes shown in Table 3, polymethyl methacrylate having a refractive index of 1.492 as a core component, and a refractive index as a sheath component. Composite spinning was carried out in the same manner as in Example 1 using a poly (vinylidene fluoride) copolymer of 1.402, polymethyl methacrylate as a sea component, and ethylene / vinyl acetate copolymer as a protective layer component, and the results are shown in [Table 3]. A plastic multifilament optical fiber having the above characteristics was manufactured.

This multifilament optical fiber made of plastic has an island component in a bale-stack shape and a degree of deformation of 1.
There were no more than 5 pixels, and the effective visual field ratio was 100%. Further, as shown in Table 3, clear and delicate images could be transmitted, and the transmitted images were extremely bright.

[0070]

[Table 3]

[0071]

Comparative Example 2 A spinneret similar to that used in Example 1,
A plastic multifilament optical fiber having a core-sheath-sea three-layer structure was prepared by using a core polymer, a sheath polymer, and a sea polymer, but not using a protective layer polymer. Manufactured under the same conditions as Next, the outermost layers of these fibers were coated with polyethylene at a temperature of 150 ° C. using a commonly used cable coating apparatus. When an image was transmitted using these fibers, the image of the periphery of the cross section of the multifilament optical fiber was dark in each case, and the brightness unevenness of the center and the periphery became remarkable, as shown in [Table 2]. It was extremely difficult to obtain a clear image.

[0072]

Example 4 A spinneret having a structure as shown in FIG. 4 was used, the number of holes was set to the number of holes shown in Table 4, and the core component constituting the island component was polymethyl having a refractive index of 1.492. Methacrylate is used as a sheath component, a polyfluorinated methacrylate polymer having a refractive index of 1.415, a sea component is polyvinylidene fluoride, and a protective layer component is a particle size.
Using a mixture of 19 nm carbon black and 2.5 parts by weight with respect to 100 parts by weight of poly (vinylidene fluoride), changing the thickness of the protective layer and performing composite spinning, and a plastic multifilament having the properties shown in [Table 4] Type optical fiber was obtained.

Experiment numbers 12, 13, 14 and 15 in [Table 4]
The multifilament optical fiber made of plastic obtained as shown in FIG. 1 has an island component in a bale stack as shown in FIG. 1 and pixels having a degree of deformation of 1.5 or more are shown in Table 4. And the effective visual field ratio was as large as 80% or more. And a clear and delicate image could be transmitted, and the brightness of the transmitted image was extremely bright. The MTF showed a good value even when measured in a bright room, and the contrast of the transmitted image was also good.

[0074]

[Table 4]

[0075]

Comparative Example 3 The same spinneret, core polymer, sheath polymer, sea polymer and protective layer polymer as used in Example 4 were used, except that the thickness of the protective layer was outside the scope of the present invention.
The fibers shown in Table 4 were manufactured. In the obtained multifilament optical fiber, since the protective layer was too thin, the pixels at the outer periphery were greatly deformed, the number of pixels having a degree of deformation of 1.5 or more was large, and the effective visual field ratio was low. Further, the value of MTF _B / MTF _D , which is an index indicating the contrast of the image, was as poor as 0.7 or less.

[0076]

Example 5 Using the same conditions as those shown in Experiment No. 12 of Example 4, only the amount of carbon black to be mixed with the polymer forming the protective layer was changed to the value shown in Table 5 to obtain a multifilament type. An optical fiber was prepared, and the MTF _B / MTF _D of the obtained optical fiber was measured. The MTF _B / MTF _D of each of the multifilament optical fibers was 0.7 or more, and images with good contrast could be transmitted.

[0077]

[Table 5]

[0078]

Comparative Example 4 A multifilament optical fiber was manufactured in the same manner as in Example 5, except that the amount of carbon black added to the polymer for forming a protective layer was changed to 0.1 part by weight. Because the amount of carbon black in the protective layer of the obtained multifilament optical fiber was small,
The value of MTF _B / MTF _D was small, and transmission of images with good contrast was impossible.

[0079]

Comparative Example 5 An attempt was made to produce a multifilament optical fiber by the composite spinning method in the same manner as in Example 5 except that the amount of carbon black was changed to 6 parts by weight. However, the spinnability was unstable and satisfactory. A multifilament optical fiber with high performance could not be manufactured.

[0080]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a plastic multifilament optical fiber of the present invention.

FIG. 2 is a partially enlarged view of the multifilament optical fiber of the present invention.

FIG. 3 is a cross-sectional view of an example of a multifilament optical fiber manufacturing base.

FIG. 4 is a cross-sectional view of another example of a multifilament optical fiber manufacturing base.

FIG. 5 is a schematic diagram of a stretching apparatus used to carry out the present invention.

[Explanation of symbols]

11 optical fiber 12 protective layer 13 peripheral fiber 21 core 22 sheath component 23 sea component 31 core forming base plate 32 sheath component forming base plate 33 sea component forming base plate 39 fiber Assembling base plate 41 ... Base plate for forming protective layer 51 ... Taking-up roller 52 ... Stretching heating device 53 ... Stretching roller 54 ... Winding machine

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yoshihiko Hoshide 20-1, Miyukicho, Otake City, Hiroshima Prefecture Inside the Central Research Laboratory, Mitsubishi Rayon Co., Ltd. (72) Fumio Suzuki 20-1, Miyukicho, Otake City, Hiroshima Prefecture Inside Mitsubishi Rayon Co., Ltd. Central Research Laboratory (72) Inventor Toshinori Sumi 20-1, Miyukicho, Otake City, Hiroshima Prefecture Inside Mitsubishi Rayon Co., Ltd. Central Research Laboratory (72) Katsuhiko Shimada 20-1, Miyukicho, Otake City, Hiroshima Prefecture In the Central Research Laboratory of Mitsubishi Rayon Co., Ltd. (56) References JP-A-1-193703 (JP, A) JP-A-48-54952 (JP, A) Japanese Utility Model Showa 50-108452 (JP, U) Japanese Utility Model Showa 58 −98603 (JP, U)

Claims (3)

(57) [Claims] 1. A large number of islands having a substantially circular cross section having optical transmission properties
Multi-filament type plug having a structure arranged in a part
In the method of manufacturing a stick optical fiber, the sea component and the
A large number of melted yarns composed of island components
Using a metal plate to collectively integrate and assemble the molten yarn
In the case of integration, 0.3 to 10 times the island diameter
By integrally covering a protective layer with a thickness of
[1] The number of islands whose degree of deformation of the island section is 1.5 or more
Is set to 5 or less for 100 islands.
How to make a multifilament optical fiber made of plastic
Law . Degree of deformation of island cross section = maximum value of island diameter / minimum value of island diameter (However, the diameter of the island is a straight line connecting two points on the outer circumference of the island. It is the length that passes through the center of gravity of the island.) 2. A multi-filament optical fiber made of plastic according to claim 1, wherein a polymer having a light blocking property is used as the polymer component for forming the protective layer .
Construction method . 3. As a polymer component for forming a protective layer, 0.6 to 5 parts by weight of carbon black based on 100 parts by weight of the polymer.
3. A plastic multifilament optical fiber according to claim 2, wherein a polymer component to which a part is added is used.
Manufacturing method of ba .