JPH03256014A - Optical cable - Google Patents

Abstract

PURPOSE:To form the optical cable which has excellent waterproofness and flame retardance and has a decreased transmission loss by sealing coated optical fibers by an intimate mixture contg. a silicone oil having a specific phenyl group concn. and a flame retarder. CONSTITUTION:The coated optical fibers 4 are sealed by the intimate mixture 8 contg. the silicone oil having >=0.2% phenyl group concn. (C) regulated by formula I and the flame retarder. In the formula I, S denotes the weight of polydimetyl-siloxane; F denotes the weight of polyphenyltyl-siloxane; P denotes the mol. wt. of the phenyl group; f denotes the average mol. wt. of the polyphenyltyl-siloxane. The transmission loss increases during long-term use if the phenyl group concn. is below 0.2% and the viscosity of the silicone oil is preferably 70 to 15,000cSt. The excellent fire retardance and waterproofness are obtd. in this way and the transmission loss by the hydrogen generated by the decomposition of water is decreased during long-term use.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a flame-retardant and waterproof optical cable with little transmission loss.

(Prior Art) In a conventionally known optical cable, an optical fiber is housed in the groove of a grooved spacer whose core material is a tensile strength member, and an optical fiber is placed on the outer peripheral surface of the spacer via a pressing layer or Many have a structure in which a metal shielding layer is directly provided, and a sheath is further provided on the outer peripheral surface of this metal shielding layer. and,
In such optical cables, the inside of the metal shielding layer is filled with dry nitrogen or inert gas in order to prevent an increase in transmission loss due to water intrusion.

In addition, optical cables used in places where maintenance and inspection of filled inert gas, etc. are difficult, are filled with sherry mixture so that there is no need to flow inert gas.

'Recently, there has been an increasing demand for such optical cables to be flame retardant, but this demand is generally solved by constructing the sheath with a flame retardant material. However, if the sherry mixture is flammable, the flame retardance of an optical cable filled with a sherry mixture will be reduced. Therefore, in the past, sherry mixtures mainly based on silicone oil mixed with flame retardants such as metal hydrates have been used.

(Problems to be Solved by the Invention) Optical cables using silicone oil-based sherry mixtures containing metal hydrates as flame retardants have the problem of causing transmission loss during long-term use. This is due to hydrogen generated due to moisture contained in the metal hydrate.

Therefore, in the case of an optical cable using such a Sherry mixture, it would be sufficient to remove hydrogen that causes transmission loss, but such an optical cable has not been found to date.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide an optical cable that has excellent waterproof and flame retardant properties and has low transmission loss.

(Means and Effects for Solving the Problems) In order to achieve the above object, the optical cable of the present invention has an optical fiber core having the following formula: % formula %) (wherein, S is the weight of polydimethylsiloxane. , F is the weight of the polyphenylmethylsiloxane, P is the molecular weight of the phenyl group, and f is the average molecular weight of the polyphenylmethylsiloxane). The composition is encapsulated by an admixture containing a flame retardant.

In the optical cable of the present invention, the optical fiber core is a mixture (hereinafter referred to as "admixture") containing silicone oil and a flame retardant having a phenyl group concentration (C) defined by the above formula of 0.2% or more. This includes all cables with a sealed structure, and the structure of the optical cable itself, such as the storage form of the optical fiber core, may be of any type. Also,
Encapsulation refers to a state in which the optical fiber core is wrapped in an admixture.

The silicone oil contained in the mixture is mainly composed of polydimethylsiloxane, and is further blended with a predetermined amount of polyphenylmethylsiloxane. Note that the silicone oil can also contain polyorganosiloxanes other than these.

The blending amount of polyphenylmethylsiloxane in silicone oil is such that the phenyl group concentration defined by the above formula is 0.2.
% or more. This phenyl group concentration is 0.2%
If it is less than that, there will be a lot of transmission loss during long-term use.

In addition, the viscosity of this silicone oil is 70 to 15.0.
Preferably, it is 00c S t. This viscosity is 70
If it is less than cSt, the admixture will flow out of the cable, which is not preferable. Also, the viscosity is 15.000c
If it exceeds S t , it is not preferable because it becomes difficult to encapsulate the optical fiber.

The flame retardant contained in the mixture is not particularly limited, and may be a hydrated substance such as a metal hydroxide, which has been difficult to use because it causes transmission loss.

Such flame retardants include, for example, aluminum hydroxide,
Mention may be made of metal hydroxides such as magnesium hydroxide, magnesium carbonate, red phosphorus, antimony trioxide, zinc borate and phosphoric acid esters.

These can be used alone or in combination of two or more.

The content of the flame retardant can be determined in consideration of imparting flame retardancy and filling workability of the mixture (viscosity of the mixture).

Additives such as flame retardant aids and viscosity modifiers can be added to the mixture used in the present invention, if necessary.

In addition, from the point of view of improving flame retardancy, the oxygen index of the mixture is 3.
It is preferable that it is 0 or more.

In the optical cable of the present invention, the waterproofness and flame retardance of the optical cable are improved by the action of the mixture, and the polyphenylmethylsiloxane contained in the mixture prevents the effects of flame retardant during long-term use. absorbs the hydrogen generated.

(Example) Examples 1 to 3 and Comparative Examples 1 to 3 Optical cables having the structure shown in FIG. 1 were manufactured. The following will explain based on the drawings.

First, a polyester non-woven fabric was wrapped once around a polyethylene spacer 2 in which an optical fiber core 4 was housed in a groove 3 in a 1/2 wrap to form a pressing layer 5. In addition, a total of four grooves 3 with a width of 1.5 mm and a depth of 2.5 mm are formed on the surface of the spacer 2 (diameter 9.0 mm). Core wire) 4 is stored. Next, a 1/2 wrap of aluminum tape is wrapped once around the holding layer 5, and the metal shielding layer 5 is wrapped around the metal shielding layer 5.
was formed. Thereafter, a sheath 7 was further formed around the metal shielding layer 6 using a composition (oxygen index: 31) containing ethylene-ethyl acrylate copolymer, magnesium hydroxide, and red phosphorus.

Next, the mixture 8 is filled into the groove 3 in which the optical fiber core 4 is housed from the end of the optical cable 1 having such a structure, and the optical fiber core 4 is encapsulated, thereby producing the optical cable of the present invention. l
I got it. This mixture 8 contains 50% by weight of the flame retardant shown in Table 1, and the remainder is silicone oil (polydimethylsiloxane and polyphenylmethylsiloxane) whose blending amount is set to have the phenyl group concentration shown in Table 1. It consists of a mixture of

The optical cable 1 was subjected to the following tests. The results are shown in Table 1.

Flame retardancy: Vertical tray test was performed according to the method specified in IEEE std, 383. Damage length due to combustion is 1
．． Those shorter than 8 m were considered acceptable, and those 1.8 m or more were rejected.

Waterproofness: First, a polyethylene pipe was connected to one end of an optical cable 1 cut to a total length of 1.5 m so as to cover it watertightly. Next, water is poured into this polyethylene pipe, and the end of the pipe opposite to the connection part is directed upward, the end of the optical cable opposite to the connection part (one end of the optical cable) is directed downward, and both ends of the pipe are directed upward. It was tilted and fixed so that the difference in height between the sections was 1 m. When the optical cable was left as it was for 24 hours, those in which water did not ooze out from one end of the optical cable were judged to be passed, and those in which water oozed out were judged to be rejected.

Transmission loss: First, optical cable 1 is
Transmission loss was measured when the film was wound on a 00m drum. Next, the transmission loss was measured after being left in an oven set at 80° C. for 30 days. Then, those with a transmission loss difference of less than 0.05 dB are accepted, and 0.05 dB
Anything above this was considered a failure.

(The following is a blank space) 4° (Effect of the invention) In the optical cable of the present invention, the phenyl group concentration is 0.
The optical fiber core is encapsulated in a mixture containing silicone oil and flame retardant at a content of 2% or more.

Therefore, the optical cable of the present invention has excellent flame retardant and waterproof properties due to the action of the above-mentioned mixture, and can reduce transmission loss due to hydrogen generated by water decomposition during long-term use. can.

[Brief explanation of drawings]

FIG. 1 is a circumferential cross-sectional view of the optical cable of the present invention.

Claims (1)

[Claims] The optical fiber core wire has the following formula: C(%)=[F+P/f]/[S+F]×100 (wherein, S is the weight of polydimethylsiloxane, and F is the weight of polyphenylmethylsiloxane. weight, P is the molecular weight of the phenyl group,
(f represents the average molecular weight of polyphenylmethylsiloxane) is characterized in that it is encapsulated by a mixture containing a silicone oil and a flame retardant having a phenyl group concentration (C) defined as 0.2% or more. optical cable.