Process and apparatus for preparation of an optical fiber ribbon

Abstract: A sheet-shaped photoconductor composed of a plurality of optical fibers is prepared by melt-spinning a spinning dope into optical fibers and, before the as-spun fibers are completely solidified, bonding the fibers to one another along the entire length thereof. The melt-spinning is carried out using a nozzle having a plurality of annularly arranged orifices. The as-spun fibers are arranged linearly in parallel to but not in contact with one another by using a grooved guide, and then the optical fibers are brought into contact with and fusion-bonded to one another by using a fusion bonding guide having a concave curved face in the central portion thereof, and the thus-formed sheet-­ shaped photoconductor is taken up.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process and apparatus for the preparation of a plastics optical fiber ribbon that can be used for various image guides or as a photoconductive material. 2. Description of the Related Art An optical fiber ribbon comprising optical fibers is used as an element of an image guide or a photoconductor for various display devices. As the process for continuously preparing this optical fiber ribbon, there is known a process in which many optical fibers are arranged in the form of a ribbon by a comb-like guide and piano wires and then are bonded and fixed, as disclosed in Japanese Examined Patent Publication No. 52-38419. If, however, the optical fibers are forcibly passed through the guide, the outer surfaces of the optical fibers are damaged and the optical properties are lowered. Moreover, since the bonding step is indispensable, the operation is complicated and the manufacturing cost is increased. As a means for overcoming these problems, Japanese Unexamined Patent Publication No. 50-8540 proposes a process in which many optical fibers are melt-spun, and the spun optical fibers are fusion-bonded in parallel to one another while the as-spun fibers are maintained at a temperature higher than the glass transition temperature, whereby an optical fiber ribbon is prepared. According to this process, the post bonding treatment becomes unnecessary, but since the fibers are arranged in the form of a ribbon by a rod-shaped width-regulating guide arranged downstream of a spinning nozzle, the optical fibers spun cylindrically and concentrically must be immediately linearly arranged in parallel to one another. Moreover, since this width-regulating guide has a rod-like shape, the difference of the yarn tension of optical fibers spun from the central portion of the spinning nozzle from that of optical fibers spun from the peripheral portion of the spinning nozzle is large, and therefore, it is difficult to stably guide the optical fibers. Accordingly, yarn unevenness occurs or an overlapping of the optical fibers occurs locally in the ribbon-like arrangement of the optical fibers, with the result that it is difficult to obtain a ribbon having a uniform width, and an optical fiber ribbon not having uniform optical transmission characteristics is often formed. EP-A-131 058 discloses a process of manufacturing a plastics optical fiber ribbon comprising the following steps: melt-spinning a plurality of plastics optical fibers from a melt using a spinning nozzle having a plurality of orifices; arranging the fibers such that they are not in contact with one another; bringing the fibers into contact so that they fusion-bond to one another before they are cooled; and taking up the fiber ribbon. SUMMARY OF THE INVENTION Under this background, a primary object of the present invention is to provide a process and apparatus in which an optical fiber ribbon having excellent light transmission characteristics, a uniform width, and no overlapped portions, can be prepared at a high efficiency. In accordance with one aspect of the present invention, there is provided a process of manufacturing a plastics optical fiber ribbon comprising the following steps: spinning a plurality of optical fibers from a plastics melt using a spinning nozzle which has a plurality of spinning orifices annularly arranged; guiding the fibers over a grooved guide to arrange the fibers in parallel, but not in contact with each other; guiding the optical fibers around a fusion bonding guide which has a guiding surface concave in a direction transverse to the fiber transport direction to bring the optical fibers into contact with one another, so that the fibers fusion-bond to one another so as to form a fiber ribbon before they are cooled; taking up the fiber ribbon. In accordance with another aspect of the present invention, there is provided an apparatus for manufacturing a plastics optical fiber ribbon, said apparatus comprising: a spinning nozzle which comprises a plurality of annularly arranged orifices for melt-spinning a plurality of optical fibers; a grooved guide which has a plurality of guiding grooves for arranging the fibers in parallel, but not in contact with each other, said guide is disposed so that the axis thereof extends perpendicular to the spinning axis of the spinning nozzle: a fusion bonding guide, which has a guiding surface concave in a direction transverse to the fiber transport direction for bringing optical fibers guided around said fusion guiding member into contact with one another, so that the fibers fusion-bond to one another so as to form a fiber ribbon before they are cooled; a take-up roller for taking up the fiber ribbon. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic front view illustrating one embodiment of the apparatus for preparing an optical fiber ribbon according to the present invention; Fig. 2 is a bottom view illustrating the spinning nozzle shown in Fig. 1; Fig. 3 is a perspective view of the main parts of the apparatus viewed in the direction of an arrow R shown in Fig. 1; Fig. 4 is a partial enlarged section of the grooved guide shown in Fig. 1 and Fig. 2; Figs. 5A through 5C are front views showing examples of the fusion-bonding guide used in the present invention. Fig. 6 is a front view showing another example of the fusion-bonding guide; Figs. 7A and 7B are sectional views showing a part of the optical fiber ribbon obtained according to the present invention; and Figs. 8 through 10 are front views showing other embodiments of the preparation apparatus of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to embodiments illustrated in the accompanying drawings. Figure 1 is a schematic front view of the apparatus of the present invention. In Fig. 1, optical fibers F₁ are melt-spun from a spinning nozzle having many orifices 11 annularly arranged therein (shown in the bottom view of Fig. 2). A grooved guide 2 is arranged so that the axis thereof extends substantially in the perpendicular direction to the axis of the spinning nozzle 1 and has a number of grooves formed therein equal to or larger than the number of the orifices. The grooves extend in the peripheral direction of the grooved guide. To obtain an optical fiber ribbon having a superior performance, preferably the diameter S (in Fig. 2) of the circle along the circumference of which the orifices 11 are arranged is approximately equal to the sum T (in Fig. 3) of the widths of the grooves of the grooved guide 2 shown in Fig. 3. The shape of each groove the grooved guide 2 is not particularly critical, as long as contact between the optical fibers F₁ is prevented. For example, V-shaped grooves and U-shaped grooves can be used. Preferably, an auxiliary guide 3 is arranged so that the axis thereof is in parallel to the axis of the grooved guide 2 with a certain distance therebetween, as shown in Figs. 1 and 3, but to obtain a good parallel arrangement among the optical fibers F₂ , preferably the auxiliary guide 3 is located in a position such that the optical fibers F₂ traveling from the grooved guide 2 are slightly deviated whereby a certain tension is imposed on the optical fibers F₂. A fusion-bonding guide 4 has a concave curved face formed in the vicinity of the center thereof for arranging the optical fibers F₃ in parallel to one another and fusion-bonding them in this parallel state. The fusion-bonded optical fibers F₄ are taken up in the form of an optical fiber ribbon by a first nip roller 5 (shown in Fig. 1). The preparation process will now be described with reference to Figs. 1 through 10. Core and sheath components molten by melting devices not shown in the drawings are passed through predetermined flow paths and spun from the conjugate spinning nozzle 1. In this spinning nozzle 1, orifices 11 are annularly arranged to extrude optical fibers F₁ having a core-sheath structure. The spun fibers F₁ just after extrusion from the orifices 11 have a cylindrical shape having a diameter almost equal to the diameter S (Fig. 2) of the circle along the circumference of which the orifices 11 are arranged, but if the respective fibers F₁ are guided to the grooves of the grooved guide 2, the optical fibers F₁ can be linearly arranged in parallel to one another without contact thereamong (see Fig. 4). Since the optical fibers F₁ flow smoothly and substantially linearly in the grooves, no strain is imposed on the optical fibers F₁. Then a tension is applied to the optical fibers F₂ by the auxiliary guide 3 located downstream, to stabilize traveling of the optical fibers. At this point, the optical fibers F₂ are not fusion-bonded to one another and arrive independently at the fusion-bonding guide 4. Since the fusion-bonding guide 4 has a concave curved face in the central portion, the optical fibers F₃ are gathered and fusion-bonded to one another as shown in Fig. 3. The structures as shown in Figs 5A through 5C can be adopted for the fusion-bonding guide 4. More specifically, a structure having a curvature R₁ as shown in Fig. 5A, a structure having a curvature R₂ on both of the left and right sides as shown in Fig. 5B, and a structure having a V-shaped groove and a curvature R₃ at the center of the groove as shown in Fig. 5C can be adopted. The thus-combined optical fibers F₄ are substantially linearly arranged and fusion-bonded to one another and are taken up in this state by the nip roller 5 acting as the take-up roller. The optical fiber ribbon of the optical fibers can be prepared in the above-mentioned manner. In the present invention, since optical fibers spun from the nozzle 1 are guided by the grooved guide 2 to stabilize the flow of the optical fibers, a substantially equal tension is imposed on the respective optical fibers, and a fiber ribbon having a high uniformity with no local overlapping can be obtained. Figure 6 shows an embodiment of the fusion-bonding guide which is the same as the guide 4 shown in Figs. 1 and 3 except that the fusion-bonding guide in Fig. 6 is designed so that a plurality of optical fiber ribbons can be prepared by using one spinning nozzle. More specifically, the fusion-bonding guide having a structure as shown in Fig. 6 is arranged instead of the fusion-bonding guide 4 shown in Fig. 1 in the apparatus of the present invention. Thus, the as-spun optical fibers are divided into a plurality of groups and are linearly distributed and arranged in a plurality of concave curved faces by this fusion-bonding guide, and each group of fibers are fusion-bonded to one another in this state to obtain a plurality of optical fiber ribbons having different widths or the same widths. Figures 7A and 7B show the section of a part of the optical fiber ribbon prepared in the present invention; wherein Fig. 7A shows an example composed of optical fibers having a two-layer structure comprising a core Fa and a sheath Fb, and Fig. 7B shows an example composed of optical fibers having a three-layer structure comprising a core Fa, a sheath Fb, and a protecting layer Fc. Figure 8 illustrates another embodiment of the process for preparing an optical fiber ribbon by using the apparatus of the present invention. In this embodiment, a second take-up roller (nip roller) 6 is arranged downstream of the first take-up roller (nip roller) 5, and a heating device 7 is disposed between the two nip rollers 5 and 6. In this embodiment, the optical fiber ribbon can be subjected to hot drawing between the first and second nip rollers 5 and 6, whereby a high tenacity can be given to the optical fibers. Figure 9 illustrates still another embodiment in which a reeling winder 8 is arranged in the rear of the second nip roller 6 shown in Fig. 8. In this embodiment, the optical fiber ribbon is wound on the reeling winder 8 and is overlapped in multiple layers, and the laminate is fixed and cut at the respective corners to prepare optical fiber bands having a length corresponding to one side of the reeling winder 8. Figure 10 illustrates an embodiment in which an optical fiber ribbon F₅ having a certain length is obtained. In this embodiment, a cutter 9 is arranged behind the second nip roller 6 to cut the optical fiber ribbon to predetermined lengths, and the cut fiber ribbons are stored in a container case 10. The kind of optical fiber used in the present invention is not particularly critical, as long as melt spinning is possible, but plastic type optical fibers having a core composed of a thermoplastic resin such as an acrylic polymer, a polycarbonate or a polyallylate or a crosslinking-curing polymer such as a crosslinking silicone polymer, a crosslinking acrylate polymer, or an ion-crosslinking polymer and a sheath composed of a polymer having a refractive index smaller than that of the core polymer, such as a fluorine-containing polymer or an acrylic polymer, are preferably used. An appropriate protecting layer can be selected according to the intended use. Example 1 An optical fiber ribbon was prepared by using the preparation apparatus shown in Fig. 1. A conjugate spinning nozzle 1 having 100 orifices 11 arranged annularly was used, and polymethyl methacrylate was supplied as the core component at a rate of 1.07 g/min per orifice and a fluorine-containing methacrylate polymer was supplied as the sheath component at a rate of 0.08 g/min per orifice. Conjugate melt spinning was carried out at a spinning temperature of 255°C, and then the spun fibers were passed through a grooved guide 2, an auxiliary guide 3, and a fusion-bonding guide 4, and a formed optical fiber ribbon was taken up at a take-up speed of 120 m/min by a nip roller 5, The distance ℓ₁ between the spinning nozzle 1 and the grooved guide 2 was adjusted to 300 mm, the distance ℓ₂ between the grooved guide 2 and the auxiliary guide 3 was adjusted to 50 mm, and the distance ℓ₃ between the auxiliary guide 3 and the fusion-bonding guide 4 was adjusted to 50 mm. The grooved guide 2, auxiliary guide 3, and fusion-bonding guide 4 were forcibly cooled so that the surface temperature of these guides were maintained at the same level. In the obtained optical fiber ribbon, optical fibers, each having a diameter of 100 µm were uniformly arranged linearly in parallel to one another, and the width of the optical fiber ribbon was 10 mm. The single fiber diameter in the 100 optical fibers was within 100 µm ±1 µm, and the light transmission performance was as high as 285 dB/km ±30 dB/km. Example 2 An optical fiber ribbon was prepared by arranging a fusion-bonding guide having a structure as shown in Fig. 6 in the same apparatus as used in Example 1. Polymethyl methacrylate was supplied as the core component at a rate of 2.45 g/min per orifice, a fluorine-containing methacrylate polymer was supplied as the sheath component at a rate of 0.15 g/min per orifice, and polymethyl methacrylate was supplied as the protecting layer component at a rate of 0.13 g/min per orifice. Conjugate spinning was carried out at a spinning temperature of 250°C, the spun fibers were divided into 4 groups, each consisting of 25 fibers, by the fusion-bonding guide, the optical fibers were taken up at a speed of 50 m/min, and optical fiber ribbons were prepared by using a heating device 7 as shown in Fig. 8 (the inner temperature was adjusted to 200°C). Note, the take-up speed of the second nip roller 6 was adjusted to 51 m/min to draw the photoconductors at a draw ratio of 1.05. In each of the obtained optical fiber ribbons, the single fiber diameter was 250 µm and the ribbon width was 6.25 mm, and the single fiber diameter in the 100 fibers was within 250 µm ±2 µm and the light transmission performance was within 230 dB/km ±20 dB/km. None of the optical fiber ribbons had a meandering strain but were very pliable. According to the present invention, an optical fiber ribbon having good light transmission characteristics, and which is uniform without local overlapping or meandering strain, can be prepared at a high efficiency.

Claims: A process of manufacturing a plastics optical fiber ribbon comprising the following steps: spinning a plurality of optical fibers (F₁) from a plastics melt using a spinning nozzle (1) which has a plurality of spinning orifices (11) annularly arranged; guiding the fibers over a grooved guide (2) to arrange the fibers (F₂) in parallel, but not in contact with each other; guiding the optical fibers around a fusion bonding guide (4) which has a guiding surface concave in a direction transverse to the fiber transport direction to bring the optical fibers (F₄) into contact with one another, so that the fibers fusion-bond to one another so as to form a fiber ribbon before they are cooled; taking up the fiber ribbon. The process according to claim 1, wherein a tension is imposed on the optical fibers (F₂), which have been arranged in parallel to, but not fusion-bonded to one another yet, whereby travelling of the optical fibers is stabilized. The process according to claim 1, wherein the optical fibers which have been arranged in parallel to, but not in contact with one another, are divided into a plurality of groups of fibers and each group of fibers is brought into contact with and fusion-bonded to one another, whereby a plurality of fiber ribbons is formed. The process according to claim 1, wherein the formed optical fiber ribbon is subjected to hot drawing. An apparatus for manufacturing a plastics optical fiber ribbon, said apparatus comprising: a spinning nozzle (1) which comprises a plurality of annularly arranged orifices (11) for melt-spinning a plurality of optical fibers (F₁); a grooved guide (2) which has a plurality of guiding grooves for arranging the fibers (F₂) in parallel, but not in contact with each other, said guide (2) is disposed so that the axis thereof extends perpendicular to the spinning axis of the spinning nozzle (1); a fusion bonding guide (4), which has a guiding surface concave in a direction transverse to the fiber transport direction for bringing optical fibers guided around said fusion guiding member into contact with one another, so that the fibers fusion-bond to one another so as to form a fiber ribbon before they are cooled; a take-up roller (5) for taking up the fiber ribbon. The apparatus according to claim 5, wherein the number of the grooves formed in the grooved guide (2) is equal to or larger than the number of the orifices (11) of the nozzle (1), and the sum of the widths of the grooves is approximately equal to the diameter of the circle along the circumference of which the orifices (11) are arranged. The apparatus according to claim 5, which further comprises an auxiliary guide (3) arranged between the grooved guide (2) and the fusion-bonding guide (4) so that the axis of the auxiliary guide (3) is in parallel to the axes of the grooved guide (2) and the fusion bonding guide (4). The apparatus according to claim 7, wherein the auxiliary guide (3) is located in a position such that the optical fibers (F₂) travelling from the grooved guide (2) are slightly deviated whereby a tension is imposed on the optical fibers. The apparatus according to claim 5, wherein the fusion-bonding guide (4) has a plurality of concave curved faces whereby the optical fibers are divided into a plurality of groups and each group is formed into an optical fiber ribbon. The apparatus according to claim 5, which further comprises a second take-up roller (6) arranged downstream of the take-up roller (5), and a heating device (7) arranged between the two take-up rollers.

Inventors: HOSHIDE YOSHIHIKO, NIEDA YOSHIRO, OKAMOTO MASASHI, HOSHIDE, YOSHIHIKO, NIEDA, YOSHIRO, OKAMOTO, MASASHI
Applicants: MITSUBISHI RAYON CO, MITSUBISHI RAYON CO., LTD
Application year: 1989
Main classification: G02B6
IPC codes: G02B6