JPH0469605A - Multifilament type optical fiber made of plastic - Google Patents

Abstract

PURPOSE:To decrease transmission losses and to allow the exact transmission of images by constituting the core parts of island parts of a methacrylate resin having a melt flow rate of a specific range. CONSTITUTION:The uniformity of the fibers is suitably adequately maintained if the island parts are arranged in the range of 100 to 30,000 pieces in a sea part. The thermal damages to be received by fiber components are decreased and the light transmission losses are decreased as well by specifying the melt flow rate of the fiber material to 5 to 4g/10 minutes and subjecting the resin to composite spinning in a 215 to 245 deg.C range at the time of spinning. The brightness of the images are insufficient unless the brightness index I of the optical fibers is >=2.5X10<-2>. The occupying rate of the fiber parts is, therefore, required to be >=25%. The deterioration by heat is lessened and the brightness of the image fiber is enhanced by using a polymer formed by copolymerizing >=70% or >=75% methyl methacrylate as the polymer for forming the fiber components.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides bright and clear image transmission in the range of 100 to 30,000 pixels and a brightness index of I≧2.5Xl0-”. The present invention relates to a plastic multifilament optical fiber that can be used as an image fiber for image transmission or a light guide.

[Prior Art] A multifilament type optical fiber, which is made by arranging quartz fibers with a fiber diameter of 200 mm or less and joining the fibers by bonding or fusing them, is capable of transmitting images by light. Its use is progressing mainly in the field of medical equipment as endoscopes such as gastrocameras.

Glass multifilament optical fiber has a fineness of 1ooo because it is relatively easy to make its fineness finer than the plastic multifilament optical fibers that have been developed so far.

The development of multifilament optical fibers with a number of pixels exceeding A major drawback of filament type optical fibers is that they are relatively easy to break due to bending operations during use, resulting in pixel defects.

In addition, 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. There is also the problem that the monitoring field of view cannot be very wide.

Therefore, compared to conventional glass-based optical fibers, breakage (
Attempts have been made to develop a plastic multifilament optical fiber, which is a collection of a plurality of plastic optical fiber cores that are flexible and easy to bend.
P-A2-0207705 discloses a method for manufacturing an excellent plastic multifilament optical fiber.

The present invention is a spinneret for manufacturing a multifilament optical fiber having a sea-island structure, which has a large number of nozzle holes for forming island components, and the nozzle holes of the nozzle plate installed directly above the lowermost die plate are located below the die plate. It is equipped with a trumpet-shaped opening toward the end surface, and a large number of composite spun fibers are assembled using a cap plate with a sea component flow path between two cap plates installed directly above the bottom cap plate. By aggregating them in a nozzle, it is possible to obtain a plastic multifilament optical fiber having a structure in which island components are stacked in bales within the cross section of the sea component.

[Problem to be solved by the invention] However, in the invention of EP-A2-0207705, the melt flow rate of the core component forming polymer is 1.2 g.
Since plastic multifilament optical fibers are obtained using polymethyl methacrylate, which has a low fluidity of 10 minutes, the temperature of the various polymers fed by the spinning device is kept extremely high to increase fluidity. A fixed quantity must be supplied to the cap. However, when the resin supplied to the spinning machine is heated to a high temperature, the fluidity of the resin improves, but due to thermal damage to the resin in the flow path inside the spinning machine, not only the core material but also the sheath material and groove material become pyrolyzed impurities. It is difficult to obtain an image transmitting body with clear image transmission properties and good brightness because of the occurrence of , gelation, or thermal coloring. On the other hand, when the temperature of the resin supplied to the spinning device is lowered, the fluidity of the resin is extremely poor, making it difficult to stably form a sea-island structure, and the distortion at the core-sheath interface becomes large, which is still a good result. Multifilament optical fibers with high brightness and excellent image transmission properties cannot be used, and in any case, it is difficult to transmit accurate images, especially when used as image fibers in medical endoscopes. There is a problem that must be solved that is difficult.

[Means for Solving the Problems] In view of the current situation as described above, the present inventors have developed a fiber that has lower transmission loss and can transmit accurate images, especially when used as an image fiber for medical endoscopes. As a result of intensive studies, we found that in a plastic multifilament optical fiber with a sea-island structure, the core part of the island was made of methacrylate resin with a melt flow rate within a specific range. The inventors have discovered that the object can be achieved, leading to the present invention.

The gist of the present invention is that the area is 30 to 1300
``It is a plastic multifilament optical fiber in which 100 to 30,000 high-vertical islands are arranged in a stack in the sea, and the core part of the islands, where light is mainly transmitted, is a melt-flow fiber. Rate (MFR) 5~4
This plastic multifilament optical fiber is made of a methyl methacrylate resin with a brightness index of 0 g/10 min and has a brightness index of ■≧2.5 Xl0-''.

The plastic multifilament optical fiber of the present invention has a sea-island structure, and the island part is 100 to 3
It is necessary that they are arranged in a range of 0,000.

If there are too many islands, the cross-sectional shape of the island portion may be deformed and the stacked arrangement structure of the islands may be disturbed, making it difficult to maintain the uniformity of the plastic multifilament optical fiber. In addition, for plastic multifilament optical fibers with less than 100 islands, it is difficult to reduce the island area to 750 m" or less due to handling reasons, and therefore, when used for image transmission, it is difficult to reduce the island area to 750 m" or less. On the other hand, if the number of islands is increased beyond 30,000, the cross-sectional shape of the islands will be insufficiently uniform, making it difficult to achieve multifilament type light with uniform brightness. Difficult to use as fiber.

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

The melt flow rate of the core material is 5 to 40 g/1 as described above.
By performing composite spinning by keeping the temperature of the resin in the range of 215 to 245"C during spinning, the core component receives less thermal damage, and the outer periphery within the cross section of the resulting multifilament type optical fiber is reduced. It is possible to obtain a plastic multifilament optical fiber in which there is no difference in the arrangement state between the island components in the central part and the island components in the central part, and the difference in optical transmission loss is extremely small. If the melt flow rate of methacrylate is less than 5,
Since it is necessary to raise the temperature of the resin that is passed through the spinning machine, the resin deteriorates and becomes colored, resulting in a decrease in the optical transmission performance of the resulting optical fiber. Melt flow rate is 40
Multifilament plastic optical fibers made of polymethyl methacrylate as a core material are brittle and easily break when handled.

In this publication, the outer shape of the fiber unit is circular, but it is also possible to take other polygonal shapes such as rectangular, square, and hexagonal shapes. In addition, the plastic multifilament optical fiber of the present invention requires that the island portions arranged in its sea cross section have a stacked structure as shown in Figure 1. By doing so, it is possible to prevent abnormal deformation of the island cross section within the multifilament type optical fiber, and it is possible to obtain a plastic multi-optical fiber with high image density and high resolution for image transmission.

As the polymer for forming the core material of the plastic multifilament optical fiber of the present invention, it is necessary to use a methyl methacrylate resin having a melt flow rate of 5 to 40 g/10 minutes.

By using a methyl methacrylate resin with such a melt flow rate, it is possible to melt and extrude at a relatively low temperature, suppressing thermal deterioration of the resin passing through the spinning machine, and as a result, coloring of the island component can be reduced. It is possible to use a plastic multifilament type optical fiber that is suppressed and has excellent transmission performance. The brightness index of the plastic multi-optical fiber in the present invention is expressed by the following equation.

! =S-NA"-10-(""0L--In the formula (1), S is made of plastic, the occupation rate of the core in the multifilament type optical fiber is N8, and the numerical aperture α is the plastic multifilament. Transmission loss per type optical fiber I11 (687 m) L indicates the usage length (m) of the plastic multifilament type optical fiber.

It is necessary that the brightness index I of the plastic multifilament type optical fiber of the present invention is 2.5 x 10-'' or more.In particular, the multifilament type optical fiber with an I value of 5 x 10-'' or more is required. When optical fibers are used for image transmission, they can transmit extremely bright images. If the occupancy rate of the core in the multifilament optical fiber is less than 25% as shown by the above formula (1), the brightness index of the transmitted image will be less than 2.5 × 101, and the multifilament optical fiber made of plastic The brightness of the image transmitted therein darkens rapidly, and the blur of the transmitted image also increases.

From this point of view, the occupancy rate of the core in the plastic multifilament optical fiber of the present invention is 25%.
It is preferable to set it above, especially 45% or more, and more preferably 55% or more. In addition, the value of the numerical aperture NA is given by the following formula (2), (
3) is a factor that contributes to the brightness of a transmitted image in the plastic multifilament optical fiber of the present invention.

NA-φW [over 7...(2) NA-φW [lower? ...In formula (3), n is the refractive index of the core material,
n2 represents the refractive index of the sheath component, n represents the refractive index of the warm material,
Equation (2) represents the numerical aperture when the island portion has a core-sheath structure, and Equation (3) represents the numerical aperture when the island portion is formed of only a core.

In the present invention, when the island portion has a core-sheath structure, the difference between the refractive index n of the core component and the refractive index n2 of the sheath component is 0.01.
As mentioned above, when the island component is formed only by the core, it is preferable that the difference between the refractive index n1 of the core component and the refractive index n3 of the sea component is 0.01 or more. n, -n2 or nl-n,
Plastic multifilament optical fibers made with a combination in which the This phenomenon is observed, and the sharpness of the image of the multifilament optical fiber is significantly reduced. Further, the numerical aperture NA value is 0.16 or more, especially 0.16 or more.
It is desirable to select a combination of a core component polymer, a sheath component polymer, and a sea component polymer that have a refractive index of 3 or more. The brightness index 1 value of the transmitted image of a multifilament optical fiber with NA less than 0°16 is 2.5X
Plastic multifilament I, which is difficult to make larger than 10", can transmit bright and clear images.
It is difficult to make a type optical fiber.

The optical transmission loss α value of the plastic multifilament optical fiber of the present invention is 3 dB/m or less, particularly 1.0 dB.
/m or less is preferable. If the α value exceeds 3 dB/m, it becomes difficult to set the brightness index T value to 2.5×10 −2 or more even if the numerical aperture NA value is increased.

L in equation (1) is preferably selected from various values depending on the intended use of the plastic multifilament optical fiber.

As the polymer for forming the core component of the plastic multifilament optical fiber of the present invention, a polymer copolymerized with methyl methacrylate in an amount of 70% or more, or 75% or more is used. Using a polymer with a lower copolymerization ratio of methyl methacrylate can lower its melting temperature, reduce thermal deterioration of the resin during spinning, and increase the brightness of the resulting multifilament optical fiber as an image fiber. However, since a problem arises in its heat resistance, the lower limit is substantially 70% by weight.

In the plastic multi-optical fiber of the present invention, a polymer for forming the shaft when the island portion has a core-sheath structure;
Alternatively, if the island is made up of only a core, a specific example of the sea-forming polymer is polymethylpentene (
n=1.46), ethylene/vinyl acetate copolymer (n-1,
46-1.50), polyvinyl acetate (n=1.47)
, polydimethylsiloxane (n=1.40), polyacetal (n=1.48), polytetrafluoroethylene (n=1.35), polyvinylidene fluoride (n-1
, 42), polytrifluoroethylene (n = 1
, 40), perfluoroethylene (n=1.34)
And, these binary or ternary copolymers of ethylene fluoride (n = 1.35 to 1.40), binary or ternary copolymers of vinylidene fluoride (n = 1.34 to 1)
．． 40) Blend polymer of polyvinylidene fluoride and polymethyl methacrylate (n = 1.42 to 1.46)
, general formula CI! = C(CH3) A copolymer mainly composed of fluorinated methacrylate represented by C00Rf, in which the groups Rf are (CHz), 1(CFz), and lH (n = 1.37 to 1.42), revised (CH
z)-(Ch)lIP (n=1.37-1.40)
, Rf is CL (CFi) z (n=1.38)
, Rf is C(CF3)3 (n=1.36), R
f is ChzChCHPCF+ (n=1.40),
Rf is CHzCF (Ch) 2 (n=1.37)
, and copolymers of these fluorinated methacrylates (
n=1.36-1.40), and methyl methacrylate copolymers of these fluorinated methacrylates (n-1
, 37-1.43), general formula CH= CH-C0OR
A polymer whose main component is fluorinated acrylate represented by 'f, provided that R'f is (C11□)-(CF2)-F (n = 1.37 to 1.40), R'f is ( CHt)
-(CF2) -HI3 (n = 1.37 to 1.41), R'f is CHz
CFzCHF-CP, + (n=1.41), R'
f is Cl1(CH3)Z (n=1.38), and these fluorinated acrylate copolymers (n-1, 36-1
．． 41), and these fluorinated acrylates and the fluorinated methacrylate copolymers (n=1.36 to 1.41
), and these fluorinated acrylate, fluorinated methacrylate, and methyl methacrylate copolymers (r+=1.
37-1.43), General 2C) lz-CP, C0OR
A polymer whose main component is 2-fluoroacrylate represented by 'f, and a copolymer thereof (n=1.37 to 1.
42) (However, in the formula, R"f is CH3, (CHJ),
(CFrifiF, (CHz) II (CF2), H1C
t■tCFtCHFCF+, C(CFs)z is shown. )
etc. can be shown as specific examples.

Further, specific examples of polymers for forming the sea component in the case of forming a multifilament optical fiber having a three-layer structure include polyamide, polyester elastomer, polyamide elastomer, polystyrene elastomer, polyolefin elastomer, poly-4-methylpentene elastomer, and polyfluoride. Vinylidene chloride, ionomer ethylene/ethyl acrylate copolymer, ethylene/vinyl acetate copolymer, vinylidene fluoride copolymer, polymethyl methacrylate, polycarbonate, polystyrene, ABS, polybutylene terephthalate, polyethylene, vinyl chloride, etc., but the flow of these polymers In order to obtain a plastic multifilament optical fiber capable of transmitting bright and clear images, it is preferable to select a polymer for forming the sea component whose properties are greater than the fluidity during spinning of the polymer forming the island component.

FIG. 2 shows a cross-sectional view of a spinneret that is effectively used in the present invention to manufacture a plastic multifilament optical fiber whose island portion has a core-sheath structure. In the figure, (1) is a cap for distributing the core, (2) is a cap for distributing the sheath,
(3) is the base for distributing the sea, (4) is the base for distributing each component, (
5) (6) (7) is a core component supply port, a sheath component supply port,
It is a sea component supply port, and (8) is a collective die for forming multi-fibers. (1a) is a core forming nozzle, (2a) is a shaft forming nozzle, and (3a) is a sea forming nozzle, each of which is characterized in that its lower end is a trumpet-shaped opening. (8) is the collecting nozzle, (9) is the collecting port, and (
6b) and (7b) are slits that respectively regulate the flow of the sheath component polymer and the sea component polymer within the mouthpiece.

A polymer for forming a core material is poured from (5) of the spinneret having such a structure, and distributed into a predetermined number of products at (1). Next, in (6), a polymer for forming a sheath material is poured, and in (2), a sheath part is formed around the core part.

Similarly, in step (7), a polymer for forming a sea portion is poured, and in step (3), a sea portion is formed around the sheath portion. After forming fibers each having a three-layer structure, each fiber is discharged independently in (3a), then fused and integrated in the collective nozzle in (8), and discharged from (9). The plastic multifilament optical fiber of the invention can be manufactured.

When producing the plastic multifilament optical fiber of the present invention using a spinneret as described above, the melt flow rate of the resin constituting the sheath and sea should be set higher than the melt flow rate of the methyl methacrylate resin of the core material. things are desirable. By increasing the difference in melt flow rate between the resins that make up the island portion and the sea portion, the island portion can be made to have a more stable circular cross section. By making the melt flow rate of the resin for forming the sea part close to the melt flow rate of the resin for forming the island part, the cross section of the island part can be made close to a hexagonal shape.

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

Example 1 Using a spinneret with a structure as shown in FIG. 2, the island component was composed of a core and a sheath, and a polymer for forming the core component had a refractive index n+=1.492 and a melt flow rate (MPR).
+=5.6 polymethyl methacrylate is used as the polymer for forming the sheath component, and polyfluorinated methacrylate with a refractive index n2-1.415 and melt flow rate (MFR) z=25 is used as the polymer for forming the sea component (CMPR) 3
Table 1 shows the characteristics of three types of multifilament optical fibers each having a pixel count of 1,500, which were obtained by spinning polymethyl methacrylate having a density of 26 and a spindle temperature of 245°C.

Table 1 Example 2 A spinneret device having the structure as shown in Fig. 2 was used, and the island component was composed of a core and a sheath, and the core component was formed into a rectangular shape, which caused poor image transmission and insufficient resolution. I couldn't get it either.

Table 2

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view showing an example of the multifilament optical fiber of the present invention, and FIG. 2 is a schematic cross-sectional view of a spinneret used to effectively produce the multifilament optical fiber of the present invention. rate n, -1,492
, melt flow rate CMPR) +30 and a refractive index jl, = 1, . 402, CMFR) Polyvinylidene fluoride of z = 40 was used as a polymer for forming the sea component using methyl methacrylate (MFR) 3 = 42, and a cap with the number of holes as shown in Table 2 was used. Three types of multifilament type optical fibers were obtained by spinning at a temperature of 225°C, and as a result, they had the characteristics shown in Table 2. Comparative Example Using the same spinneret as that used in Example 1, a refractive index n, -1,492, CMP was used as the polymer for forming the core component.
R), = 50 methyl methacrylate resin, the same polymer as that used in Example 1 as the polymer for forming the sheath component and the polymer for forming the sea component, and the temperature of the cap was 2.
Multifilament type optical fibers were manufactured by spinning at 40° C. in the same manner as in Experiment No. 1.2.3. The cross-sectional shapes of the island portions of the optical fibers obtained were all shown in Figure 6. Patent applicant Mitsubishi Rayon Co., Ltd.

Claims (1)

[Claims] 1 It is a plastic multifilament type fiber with a sea-island structure in which 100 to 30,000 islands are arranged in a stacked manner in the sea, and the core part of the islands where light is mainly transmitted is a melt flow fiber. Rate rate 5-40
A plastic multifilament optical fiber made of a methyl methacrylate resin having a brightness index of 1≧2.5×10^-^2.