JP2023137674A - optical cable - Google Patents

Abstract

To provide an optical cable capable of suppressing an increase in transmission loss at low temperature.SOLUTION: An optical cable is provided comprising multiple optical fibers, and a cable jacket surrounding an outer periphery of an assembly constituted by the multiple optical fibers, the cable jacket containing a flame retardant and having a shrinkage stress of 33 MPa or less.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to optical cables.

Optical cables are expected to be used for long periods of time under various usage environments. Under such usage environments, fire-resistant performance may be required, and therefore a flame-retardant resin composition is sometimes used as a material constituting the cable sheath of an optical cable. In particular, optical cables used indoors are required to be highly flame retardant, since in the event of a fire, the optical cables could become a fuse and spread the flames.
For example, Patent Document 1 discloses that a first resin component containing at least one of low density polyethylene and linear low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer and A flame-retardant resin composition is disclosed that includes a second resin component containing at least one member selected from the group consisting of low-density polyethylene, and a phosphinate metal salt. By using the flame-retardant resin composition for the cable jacket, it is highly flame-retardant and the cable has improved resistance to deterioration over time.

Japanese Patent Application Publication No. 2018-203949

It is known that the temperature characteristics of a cable jacket vary depending on the base resin constituting it, the type and content of flame retardants added to the base resin, and the like. Therefore, depending on the composition of the cable jacket, the cable jacket may shrink at low temperatures below 0°C, and lateral pressure will be applied to the optical fiber covered by the cable jacket, leading to an increase in the transmission loss of the optical cable. be.

An object of the present disclosure is to provide an optical cable that is highly flame retardant and can suppress an increase in transmission loss at low temperatures.

An optical cable according to the present disclosure includes a plurality of optical fibers and a cable sheath that covers the outer periphery of an aggregate made up of the plurality of optical fibers, and the cable sheath contains a flame retardant and has a shrinkage stress. It is 33 MPa or less.

According to the present disclosure, it is possible to achieve high flame retardancy and to suppress an increase in transmission loss of an optical cable at low temperatures.

FIG. 2 is a cross-sectional view of the optical cable according to the present embodiment in a direction perpendicular to the axis. It is an evaluation result of the shrinkage stress of the optical cable based on this embodiment, and the increment of transmission loss.

(Description of embodiments of the present invention)
An overview of an embodiment of the present invention will be described.
(1) Multiple optical fibers,
a cable jacket that covers the outer periphery of the aggregate made up of the plurality of optical fibers;
The optical cable, wherein the cable jacket contains a flame retardant and has a shrinkage stress of 33 MPa or less.

According to the above configuration, it is possible to achieve high flame retardancy and to suppress an increase in transmission loss of the optical cable at low temperatures. Note that the shrinkage stress is the product of the dimensional change rate of the cable jacket from 20°C to -40°C and the elastic modulus.

(2) The optical cable according to item (1), wherein the cable jacket contains ethylene-ethyl acrylate and linear low-density polyethylene.

According to the above configuration, since both ethylene-ethyl acrylate and linear low-density polyethylene have small shrinkage stress at low temperatures, it is possible to suppress an increase in transmission loss of the optical fiber at low temperatures.

(3) the ethylene-ethyl acrylate content of the cable jacket is 55% by mass or more,
The optical cable according to item (2), wherein the cable jacket has a linear low-density polyethylene content of 45% by mass or less.

Ethylene-ethyl acrylate has a lower glass transition temperature and less elastic force at low temperatures than linear low-density polyethylene. Therefore, according to the above configuration, by setting the ethylene-ethyl acrylate content to 55% by mass or more, shrinkage stress is reduced, and transmission loss of the optical fiber at low temperatures can be further suppressed. Note that the ethylene-ethyl acrylate content is the weight ratio of ethylene-ethyl acrylate in the material constituting the cable jacket. Similarly, the linear low-density polyethylene content is the weight proportion of the linear low-density polyethylene in the materials constituting the cable jacket.

(Details of embodiments of the present invention)
Embodiments of the present invention will be described below with reference to the drawings. Note that for the sake of convenience, the description of members having the same reference numbers as those already described in the description of this embodiment will be omitted. Further, the dimensions of each member shown in this drawing may differ from the actual dimensions of each member for convenience of explanation.

FIG. 1 is a cross-sectional view of an optical cable 1 according to the present embodiment in a direction orthogonal to the axis. As shown in FIG. 1, the optical cable 1 includes a plurality of optical fibers 2, a cable jacket 3, a slot rod 4, a tensile strength member 5, and a pressure wrapping tape 6.

The optical cable 1 has a cable outer diameter D of 25 mm, and is a so-called slot type optical cable in which a plurality of slot grooves 7 (six in this example) are provided for accommodating an optical fiber unit 8 consisting of a plurality of optical fibers 2. It is. The slot grooves 7 are open toward the outer circumferential side of the slot rod 4 and are provided at equal intervals in the circumferential direction of the slot rod 4. The slot groove 7 is formed in such a shape that both side wall portions 7a are gradually approached from the outer peripheral side of the slot rod 4 toward the center side. Further, the slot groove 7 has a bottom portion 7b having a curved surface that curves toward the center of the slot rod 4.

The slot rod 4 is made of, for example, a synthetic resin of polycarbonate (PC) and polybutylene terephthalate (PBT), or a hard resin material such as high-density polyethylene (HDPE).

The tensile strength member 5 has a circular cross-sectional view, and is embedded in the center of the slot rod 4 along the axial direction of the optical cable 1. The tensile strength member 5 is made of a wire having a strength against tension and compression during installation, such as steel wire or FRP (Fiber Reinforced Plastics).

Each slot groove 7 of the slot rod 4 accommodates an optical fiber unit 8 made up of a plurality of optical fibers 2. Each optical fiber unit 8 is composed of 288 optical fibers; for example, it may be a collection of 288 single optical fibers, or 24 12-fiber optical fiber tapes. It may be a collection. Optical fiber tape refers to a plurality of optical fibers arranged in parallel in a direction orthogonal to the longitudinal direction, with adjacent optical fibers being partially or completely disposed between the plurality of optical fibers. The present invention is an intermittent connection type optical fiber ribbon in which connection parts where wires are connected and non-connection parts where adjacent optical fibers are not connected are provided intermittently in the longitudinal direction.

The pressure-wrapping tape 6 is, for example, a tape made of a nonwoven fabric, or a tape made of a base material such as polyethylene terephthalate (PET) and a nonwoven fabric pasted together. Note that a water-absorbing agent (for example, water-absorbing powder) may be applied to the pressing tape 6. If the pressure-wrapping tape 6 functions as a water absorbing layer, water can be stopped from the optical fiber unit 8 and the like. The outside of the pressure winding tape 6 is covered with a cable sheath 3 containing a flame retardant, and is formed into, for example, a round shape.

The cable sheath 3 contains a flame retardant and covers the outer periphery of the plurality of optical fiber units 8 and the outside of the pressure wrapping tape 6.

The main component of the base resin constituting the cable jacket 3 is polyethylene resin. As the polyethylene resin, for example, ethylene-ethyl acrylate (EEA), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), low density polyethylene (LDPE), or a mixture thereof is used.
Furthermore, the cable jacket 3 is made by adding a flame retardant to these base resins. As the flame retardant, for example, a metal hydroxide such as magnesium hydroxide or aluminum hydroxide is used.

In this embodiment, the ease with which the cable jacket 3 contracts is expressed as "shrinkage stress." "Shrinkage stress" is defined as the product of "dimensional change rate" and "elastic modulus (Young's modulus)." "Dimensional change rate" is the rate of change in the dimension of the cable jacket 3 in the axial direction when the temperature changes from 20°C to -40°C. "Modulus" is the rate of change in stress and dimension during elastic deformation. "Shrinkage stress" therefore represents the stress that occurs when the cable jacket 3 changes dimensions.

Both EEA and LLDPE are polyethylene resins that have low shrinkage stress at low temperatures. Comparing the properties of EEA and LLDPE, EEA has a lower glass transition temperature and therefore has a lower elastic modulus at low temperatures. Therefore, EEA has smaller shrinkage stress and better temperature characteristics. On the other hand, LLDPE has higher rigidity and therefore has better mechanical properties.

FIG. 2 shows the evaluation results of the shrinkage stress and the increase in transmission loss of the optical cable according to this embodiment. The optical cable sample to be evaluated has the same configuration as the optical cable shown in FIG. 1.

Samples 1 to 3 are examples, in which EEA and LLDPE were used as the main components of the base resin constituting the cable jacket 3, and the contents of EEA and LLDPE were varied.
Sample 4 is a comparative example, in which HDPE and LDPE were used as the main components of the base resin constituting the cable jacket 3, and the HDPE content was 75% by mass and the LDPE content was 25% by mass.
Furthermore, a metal hydroxide as a flame retardant was added to each of Samples 1 to 4 so that the mass ratio to the main component resin was 0.50 or more and 1.50 or less.
Such optical cables of Samples 1 to 4 were manufactured, and their shrinkage stress and increase in transmission loss per 1 km (increment in transmission loss) were measured at -40°C.
Note that the shrinkage stress can be determined by determining the above-mentioned dimensional change rate and multiplying it by the elastic modulus at -40°C. Further, the increment in transmission loss per 1 km was defined as the difference in transmission loss at a wavelength of 1.55 μm between when the temperature was 20° C. and when the temperature was −40° C. Note that it was determined that the increase in transmission loss was good if it was 0.300 dB/km or less.

As shown in FIG. 2, in Samples 1 to 3, which are examples, as the main components of the base resin constituting the cable jacket 3, the content of EEA is 55% by mass or more, and the content of LLDPE is 45% by mass or less. By doing so, the shrinkage stress of the cable jacket 3 of the optical cable 1 was suppressed to 33.0 MPa or less. As a result, it was found that the increase in transmission loss could be suppressed to 0.300 dB/km or less, and good transmission characteristics at low temperatures could be obtained.

On the other hand, in Sample 4, which is a comparative example, by using HDPE and LDPE as the main components of the base resin constituting the cable jacket 3, the shrinkage stress of the cable jacket 3 of the optical cable 1 is greater than 33.0 MPa. became. As a result, it was found that the increase in transmission loss was larger than 0.300 dB/km, and good transmission characteristics at low temperatures could not be obtained.

Although the embodiments of the present invention have been described above, it goes without saying that the technical scope of the present invention should not be interpreted to be limited by the description of the present embodiments. This embodiment is merely an example, and those skilled in the art will understand that various modifications can be made within the scope of the invention as set forth in the claims. As described above, the technical scope of the present invention should be determined based on the scope of the invention described in the claims and the scope of equivalents thereof.

1: Optical cable 2: Optical fiber 3: Cable jacket 4: Slot rod 5: Tensile strength member 6: Pressure wrapping tape 7: Slot groove 7a: Both side walls 7b: Bottom 8: Optical fiber unit

Claims (3)

multiple optical fibers,
a cable jacket that covers the outer periphery of the aggregate made up of the plurality of optical fibers;
The optical cable, wherein the cable jacket contains a flame retardant and has a shrinkage stress of 33 MPa or less. The optical cable of claim 1, wherein the cable jacket comprises ethylene-ethyl acrylate and linear low density polyethylene. The ethylene-ethyl acrylate content of the cable jacket is 55% by mass or more,
The optical cable according to claim 2, wherein the linear low-density polyethylene content of the cable jacket is 45% by mass or less.

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