GB2170019A - Submarine optical fiber cable having graft polymer jacket - Google Patents

Abstract

A submarine optical fiber cable comprises a core collection of optical fibers 1, tension members 2, a pressure-resistant tube 3, and a jacket 4, wherein the jacket 4 is composed of a modified polyolefin which has been at least partially grafted with a vinyltrialkoxysilane. The polyolefin may be a polyethylene or copolymer thereof with a 3-10C alpha -olefin. The vinyltrialkoxysilane may be vinyltris( beta -methoxyethox)silane, vinyltriethoxysilane, vinyltrimethoxysilane, or gamma -methacryloxypropyltrimethoxysilane. <IMAGE>

Description

SPECIFICATION Submarine optical fiber cable Background of the invention (1) Field of the invention The present invention relates to a submarine optical fiber cable having a high resistance against a tension and bending forces.

(2) Description of the related art A submarine cable is normally used under severe conditions, and a jacketing material for the submarine cable must have a high resistance to low temperature brittleness, a high abrasion resistance, a high resistance to environmental stress cracking, and a high deterioration resistance (heat resistance and weatherability). From this viewpoint, polyolefins, especially polyethylene, are mainly used as the jacketing material.

Although the above characteristics are very important for jacketing materials of submarine optical fiber cables, because of the specific cable structure, these jacketing materials also must have the following new characteristic, i.e., a pressure-resistant structure. This structure is necessary for a submarine optical fiber cable to protect the optical fibers therein from sea water pressure at certain sea depths. The pressure resistance characteristic is greatly improved in a submarine optical fiber cable by arranging a pressure-resistant pipe outside of a core collection of optical fibers.

However, because of a poor adhesion between the metal tube (such as a copper tube) used as the pressure-resistant pipe and the jacket material, a conventional submarine optical fiber cable of this type has the following problems: (a) Since there is little or no adhesion between the pressure-resistant pipe and the jacket, when processing the terminal of the cable, the jacket shrinks upon cutting of the end face thereof and, consequently, the pressure-resistant pipe projects beyond the jacket, or at the molding step, the jacket shrinks under the application of heat and the dimensional precision is degraded.

(b) When a tension or bending forces are applied to the cable, the pressure-resistant pipe and the jacket move separately, and the cable jacket breaks at the molded portion of the cable terminal.

(c) If the cable is pulled by a lashing rod when the cable is laid, the jacket only is pulled and is broken.

A break in the jacket will lead to corrosion of the pressure-resistant pipe, and this becomes a serious problem in the optical transmission system.

Summary of the invention In view of the foregoing, it is a primary object of the present invention to solve the above problems and provide a submarine optical fiber cable having an excellent resistance to a tension or bending forces.

In accordance with the present invention, there is provided a submarine optical fiber cable comprising a core collection of optical fibers, tension members, a pressure-resistant tube, and a jacket, wherein the jacket is composed of a modified polyolefin which has been at least partially grafted with a vinyltrialkoxysilane.

Brief description of the drawings Figure 1 is a sectional view showing one example of the submarine optical fiber cable according to the present invention.

Description of the preferred embodiments Referring to Figure 1, the submarine optical fiber cable comprises a core collection 1 of optical fibers, tension members 2, a pressure-resistant tube 3, and a jacket 4. As the pressure-resistant tube 3, a tube made of a metal such as copper, iron aluminum, or an alloy of copper, iron or aluminum is used. Preferably, this metal tube is disposed as an outer pressure-resistant tube 3b, and an inner pressure-resistant tube 3a is disposed on the outside of the core collection 1 of optical fibers.

A two-layer structure comprising an insulator and an outer jacket may be adopted for the jacket 4.

In the present invention, it is indispensable that a modified polyolefin which has been at least partially grafted with a vinyltrialkoxysilane be used as the jacketing material. If this jacketing material is used, a high adhesion can be obtained between the pressure-resistant tube 3 and the jacket 4.

As the polyolefin, there are preferably used medium-pressure polyethylene, low-pressure polyethylene, high-pressure polyethylene, a copolymer of ethylene with an a-olefin having 3 to 10 carbon atoms (such as propylene, butene-1, hexene-1, 4-methylpentene-1 or octene-1), and a mixture thereof. In view of the resistance against low temperatures and the resistance against environmental stress cracking, preferably the melt index (MI) of the polyolefin is not larger than 2 g/10 minutes, more preferably, from 0.05 to 2 g/ 10 minutes.

As the vinyltrialkoxysilane, there can be mentioned vinyltris(ss-methoxyethox)silane, vinyltriethoxysilane, vinyltrimethoxysilane, and y-methacryloxypropyltrimethoxysilane.

As means for modifying the polyolefin, there is ordinarily adopted a method in which melt extrusion is carried out in the presence of an organic peroxide. This extrusion process can be carried out by an ordinary single screw extruder, a Banbury mixer, or other kneader.

As the organic peroxide, there can be mentioned, for example, t-butyl hydroperoxide, 2,5-dimethyl-2,5di(t-butylperoxy)hexane, 7,3-bis(t-butyl peroxyisopropyl) benzene, dicumyl peroxide, and benzoyl peroxide.

Preferably, the organic peroxide is added in an amount of 0.1 to 5 parts by weight, more preferably, 0.2 to 1 part by weight, per part by weight of the vinyltrialkoxysilane.

Preferably, the modified polyolefin (at least partially grafted with the vinyltrialkoxysilane) is a modified polyolefin or a blend thereof with an unmodified polyolefin. In view of the electric characteristics (dielectric loss and dielectric strength) when electricity is applied to the pressure-resistant tube, the adhesion property, and the gelation of the modified polyolefin with water with the lapse of time, preferably the amount of vinyltrialkoxysilane grafted is not larger than 0.1% by weight (1000 ppm), more preferably, from 0.001 to 0.05% by weight (10 to 500 ppm). Preferably, the melt index of the modified polyolefin is not larger than 2 g/10 minutes, more preferably, from 0.05 to 2 g/10 minutes.

An ordinary antioxidant is incorporated in the modified polyolefin used as the jacketing material in the present invention. Carbon black is not used when electricity is applied to the pressure-resistant tube such as a copper tube, but can be incorporated in other cases. Furthermore, a two-layer structure may be adopted in which the modified polyolefin is used as an inner insulator layer and an outer layer is formed thereon.

The submarine optical fiber cable of the present invention can be prepared according to a known method, for example, a method in which a modified olefin is melt-extruded onto a pressure-resistant tube, on the inner side of which a core collection of optical fibers and tension members are arranged, to form a covering tube having a uniform thickness, and the covering tube is then cooled.

The present invention will now be described in detail with reference to the following examples. In the examples, all of "parts" are by weight.

Example I To low-density polyethylene (MI = 0.12 9110 minutes and density = 0.923 g/cm3) were added 100 ppm of vinyltris(ss-methoxyethoxy)silane and 50 ppm of t-butyl hydroperoxide. The mixture was kneaded by a Banbury mixer and then reacted at 220"C. The reaction mixture was pelletized to obtain pellets of modified polyethylene.

The modified polyethylene was melt-extruded as a jacketing material at an extruded resin temperature of 200"C to 220"C onto a copper tube having a diameter of 13 mm, on the inner side of which a core collection of optical fibers and tension members were arranged in advance, to form a covering polyethylene layer having a jacket thickness of 5 mm. The jacketed tube was cooled at 55"C for 1 minute, at 25"C for 2 minutes, and at 150C for 35 minutes to form a cable having a covered jacket.

With respect to the thus-obtained covered sample, the adhesion, the low temperature brittle point, the environmental stress cracking ratio, and the absence or presence of protrusion at the time of cutting the covered pipe were determined according to the following methods.

Measurement of adhesion In a covered sample having a length of 25 cm, the covering layer was peeled on both ends of the sample for a distance of 10 cm and 5 cm, respectively, and the adhesion of the remaining covering layer having a length of 10 cm was measured at a pulling speed of 50 mm/min by a tensile testing machine.

Measurement of low temperature brittle point The temperature at which a 50% fracture occurred was determined according to the method of ASTM D-746.

Measurement of environmental stress cracking ratio Ten specimens were used for this test, and the cracking ratio was determined after 300 hours according to the method of ASTM D-1963 under the following conditions.

Temperature: 50"C i 0.5"C Test solution: aqueous solution containing 10% of Igepal Absence or presence of protrusion at time of cutting covered pipe The covered sample was cut and a check was made whether or not protrusion of the pipe was caused by shrinkage of the covering layer. The evaluation was carried out according to the following rating scale.

A: no protrusion B: slight protrusion C: conspicuous protrusion The obtained results are shown in Table 1.

Example 2 To linear low-density polyethylene (MI = 0.20 g/10 minutes and density = 0.930 g/cm3; containing butene-1) were added 200 ppm of vinyltriethoxysilane and 100 ppm of 2,5-dimethyl-2,5-di(t-butylperoxy)hexene-3, and the mixture was reacted at 200"C in an extruder and pelletized.

A sample of a covered cable was prepared in the same manner as described in Example 1 except that the thus-obtained pellet was used, as the jacketing material.

The obtained results are shown in Table 1.

Example 3 To linear low-density polyethylene (MI = 0.70 g/10 minutes and density = 0.920 g/cm3) were added 150 ppm of vinyltriethoxysilane and 50 ppm of 2,5-dimethyl-2,5-di(t-butylperoxy)hexene-3, and the mixture was pelletized at 220"C in an extruder.

A sample of a covered cable was prepared in the same manner as described in Example 1 except that the thus-obtained pellet was used as the jacketing material.

The obtained results are shown in Table 1.

Comparative Example 1 The procedures of Example 1 were repeated in the same manner except that low-density polyethylene (MI = 0.12 g/10 minutes and density = 0.923 g/cm3) was used as the jacketing material.

The obtained results are shown in Table 1.

Comparative Example 2 The procedures of Example 1 were repeated in the same manner except that linear low-density polyethylene (MI = 0.70 g/10 minutes and density = 0.20 g/cm3) was used as the jacketing material.

The obtained results are shown in Table 1.

TABLE 1 Jacketing material Adhesion Low Cracking Protrusion Synthetic (kg) tempera- ratio upon cutting evaluation ture (ESCR) pipe Poly- MI brittle (after ethylene Modifier Amount (ppm) (g/10 min) point 300 hours) Below Example 1 LDPE (1) Vinyl-tris (ss-methox- 0.11 250 -70 C Good A Good ethoxy)silane 100 Below Example 2 LDPE (1) Vinyl-triethoxysilane 200 0.19 200 -70 C Good A Good Below Example 3 LLDPE (2) - 150 0.60 170 -70 C Good A Good Below Comparative LDPE - 0 0.12 30 -70 C Good C Poor Example 1 Below Example 2 LLDPE - 0 0.70 25 -70 C Good C Poor LDPE (1): low density polyethylene, LLDEPE (2): linear low density polyethylene As is apparent from the foregoing description, the submarine optical fiber cable of the present invention has an excellent resistance to a tension or bending forces because the adhesion between the jacket and the pressure-resistant tube is high.

Claims (5)

1. A submarine optical fiber cable comprising a core collection of optical fibers, tension members, a pressure-resistant tube, and a jacket, wherein the jacket is composed of a modified polyolefin which has been at least partially grafted with a vinyltrialkoxysilane.

2. A submarine optical fiber cable as set forth in Claim 1, wherein the modified poloyolefin is medium-pressure polyethylene, low-pressure polyethylene, high-pressure polyethylene, a copolymer of ethylene with an os-olefin having 3 to 10 carbon atoms, or a mixture thereof, which has been at least partially grafted with a vinyltrialkoxysilane and has a melt index not larger than 2 g/10 minutes.

3. A submarine optical fiber cable as set forth in claim 1, wherein the modified polyolefin has not larger than 0.1% by weight of the vinyltrialkoxysilane grafted thereon.

4. A submarine optical fiber cable as set forth in claim 1, wherein the modified polyolefin is prepared by grafting the vinyltrialkoxysilane onto a polyolefin in the presence of 0.1 to 5 parts by weight of an organic peroxide per part by weight of the vinyltrialkoxysilane.

5. A submarine optical fiber cable substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.