KR20010088855A - water-resistant cable - Google Patents

Abstract

The present invention relates to a cable, in particular an optical fiber cable, having a low influence on the radial penetration of water and the longitudinal spreading. Such cable comprises a water soluble polymer material, characterized in that the material is water expandable and water soluble material. In particular, such a cable is prevented from spreading water due to the combination of the water-soluble material's water-soluble forming effect with a predetermined viscosity to prevent the expansion of the water-soluble material and the passage of the remaining water after water has penetrated the cable. It is characterized by. Preferably, the water soluble material is selected from polyacrylamide, modified polyvinyl alcohol, vinyl alcohol / vinyl acetate copolymers, polyirivinylpyrrolidone and mixtures thereof, wherein the material is preferably vinyl alcohol / vinyl acetate copolymer to be. The material is preferably extruded to form a tubular element comprising an optical fiber, for example an inner layer made of a water soluble material and an outer layer made of a bilayer tubular element made of conventional polymers such as PE, PP or PBT.

Description

Water-resistant cable

Cables, especially fiber optic cables, are used in atmospheric conditions which come into contact with both liquid and vapor water.

The presence of water molecules in the optical cable, especially near the optical fiber, results in a decrease in the fiber's transmission capacity.

The reason why the fiber's transfer capacity is reduced is, in particular, because water vapor diffuses into the ink secondary and primary coatings on the optical fiber followed by condensation of water on the ink secondary coating and glass primary coating interfaces. This condensation causes local separation between the ink and the secondary coating or between the glass and the primary coating, resulting in irregular mechanical stress ("microbending"), which causes attenuation of the transmission signal. Can be.

Contact between the optical fiber and liquid water can cause water to penetrate from poorly wrapped ends (during cable storage or device installation) or cause damage to the sheath.

The presence of water, especially liquid water, and the possibility of the water spreading longitudinally in the cable can also cause damage to the device to which the cable is connected. In view of the above observations, it is good to prevent water from spreading and limit the length of the cable to be cleaned after contact with water as long as possible.

Contact of the optical fiber in the cable with water in the vapor state occurs when this water seeps into the layers that make up the optical cable and thereby reaches the interior of where the optical fiber is located. Up to fairly high relative humidity values (usually about 75 to 80%), the optical fiber is not adversely affected by the presence of water vapor and can even remain under it for many years. Above these thresholds, high humidity in contact with the surface of the optical fiber may cause defects similar to those caused by contact with liquid water (eg, splitting into thin layers, local separation between glass and coatings, and / or between several coating layers). Separation, micro-bending phenomena), resulting in increased attenuation. Finally, prolonged contact of the surface of the fiber with water (liquid water or steamy water), such as occurs after the glass and primary coating split, can reduce the mechanical strength of the glass portion of the fiber. .

A range of solutions for restricting or preventing water from entering the cable is disclosed in the prior art.

For example, to limit the ingress of liquid water into an optical fiber cable, fluid barrier fillers, usually grease or thickened oil, are used to establish physical barriers to water passing into the cable. Methods of introducing into cable structures are known. The fillers are also known as "inert barriers" because they do not have a special physicochemical interaction with water.

Examples of such inert barriers are disclosed in EP 811,864, US 5,285,513, US 5,187,763 and EP 541,007.

Introducing the inert barrier filler into the structure of the optical cable during production is often difficult, such as in the manufacturing process of the ends ("top") of these cables which must be wrapped to prevent any loss of filler. In addition, during installation and / or maintenance of the cable, in order to be able to bond between the different parts of the cable, it is inevitable that the barrier filler must be flushed out of all components of the optical cable, due to the action of the solvent and friction This may damage the optical fiber.

Another known solution to limiting water entry into an optical cable may be to consider the use of water-swellable materials, ie materials capable of absorbing significant amounts of water. Is increased. In contrast to the materials described above, these materials are also known as "active barriers".

Typically, such water expandable material is distributed on a support made of fibrous plastic material, for example a tape or yarn, and these are installed close to the cable structure that is desired to prevent contact with water. .

For example, US Pat. No. 4,867,526 is a nonwoven material (especially polyester) impregnated with a water absorbent that can expand when contacted with water, especially a solution of polyacrylic acid made insoluble by crosslinking. The cable containing the tape made is described.

U. S. Patent No. 5,138, 685 describes a cable comprising a laminated tape consisting of two superimposed layers of nonwoven polymeric material and containing powdered water expandable material between the two layers.

U. S. Patent 5,642, 452 describes a cable comprising a water expandable material, in particular a yarn impregnated with polyacrylic acid. The yarn is wound around a central reinforcement element with tubular elements comprising an optical fiber filled with a conventional "inert" shield. According to the disclosure provided in this patent, this configuration prevents water from passing in the longitudinal direction in the star-shaped region formed by the spirally wound tubular elements around the central element.

U. S. Patent No. 4,767, 184 describes an optical cable with a grooved core, in which the grooves are arranged a plurality of strips of overlapping optical fibers, each coated with a thin film of resin containing water expandable or expanded material. With a strip of coated optical fiber containing the water expandable material, a coating of the same material as the one applied to the grooved core may be used, but a groove made of a water absorbing material may be used in the groove where the strip of optical fiber is not present. Should be used.

German patent DE 1,765,647 relates to a conventional metal-conductor telecommunication cable, which discloses a four-wire cable in which the cable core and wire are wrapped in a 100 μm thick foil made of low soapy high polymerization polyvinyl alcohol.

Applicants have found that if water expandable fibrous tape is used, it is necessary to include an additional wrapping process during the manufacture of the cable. Moreover, on the one hand the problem of release of water-expandable powders often occurs where the water barrier effect is lowered where necessary, and on the other hand, during installation / maintenance, the structure of the cable must be free of these powders. .

Moreover, once the water absorption effect is completed, known water expandable materials act like inert fillers by establishing a simple physical obstacle to the passage of water. Therefore, a sufficient amount of these materials should be provided for the structure of the cable to be protected. However, in certain optical cable structures, such as, for example, in plastic tubular elements containing loosely arranged optical fibers, conventional inert shields are used in this case because the amount of material used is excessive and uneconomical. In addition, due to the irregularly distributed pressure on the surface of the optical fiber, undesirable expansion of the water expandable material (even at relatively low relative humidity) caused attenuation of the transmitted signal, even under conditions that are otherwise harmful for the cable to function. There is a possibility that this may be generated.

In addition, as the inventors have observed, an optical fiber in contact with a material consisting of particles larger than about 1 μm in size may experience a microbending phenomenon, resulting in a strip or yarn containing water expandable powder in direct contact with the fiber. The process of inserting elements such as, represents a clear risk of increasing attenuation even in the presence of moisture.

In the case of an optical fiber strip coated with a thin film of water expandable material described in US Pat. No. 4,767,184, the Applicant has expanded, even at very little, at a relatively low relative humidity where the water expandable material used may not be harmful to the optical fiber. If there is a tendency to do so, this expansion may result in an irregular distribution of pressure on the fiber coated with the material or otherwise excessively ring the optical fiber, in both cases attenuation of the transmitted signal may occur. I found it to be a flaw.

Applicants also note that after the expansion material is expanded, the expansion material cannot fill all the gaps in the cable correctly, especially if the space to be filled is of a very irregular shape, for example, a star formed by winding it into a light tubular element. We found that we could not fill all the gaps correctly in the case of areas, spaces between optical fibers, etc. In this regard, even in these spaces, even after the expansion material is fully inflated, there is still a risk that channels, through which water can flow freely, remain in the structure of the cable.

In addition, the process of fully inflating the water expandable material generally requires considerable time, and during expansion the water flow is not completely blocked so that a considerable length of the cable is prevented by the longitudinal penetration of the water, in particular the voids involved in the cavity. If large, it may be affected.

As a result, all of the conventionally implemented solutions involve the insertion of additional elements (such as powder, tape, foil, etc.) into the cable structure. This generally allows for additional cumbersome steps in the cable fabrication process as well as for performing an annoying process that may be during the connection of the ends of the cable and / or while repairing the damaged portion of the cable.

The present invention relates to cables, in particular optical fiber cables, which are resistant to the phenomenon of radial penetration and longitudinal spreading.

The present invention also relates to a method of maintaining high resistance when water in both liquid and vapor phases passes in a cable, in particular an optical fiber cable.

1 is a schematic cross-sectional view of an optical fiber cable of one embodiment according to the invention of the type containing a tubular element with a central support.

2 is a cross-sectional view of a tubular element of a cable according to the invention with a double coating comprising an optical fiber.

3 is an identical cross-sectional view of the tubular element of FIG. 2 after the water has entered.

4 is a schematic cross-sectional view of an optical fiber cable of another embodiment according to the present invention of the type having a grooved core.

4A is an alternative embodiment for the cable depicted in FIG. 4.

5 is a graph of the viscosity of a water soluble polymer as a function of concentration in an aqueous solution.

According to the invention, a cable having no fluidic or powdery elements for blocking the flow of water is dissolved in infiltrating water and, together with this water, a solution that is sufficiently viscous to block the flow of water or at least to delay it. It can be made by combining the solid materials that can be formed with the cavities present in the cable. In particular, it may be advantageous that the solid material is formed from structural elements of an optical cable, such as a tube or slotted core that is easy to protect, including optical fibers.

Thus, one embodiment of the present invention provides a compact fiber in an optical fiber cable comprising a longitudinal cavity extending along the length of the cable, at least one optical fiber received within the longitudinal cavity and a solid compact element connected to the cavity. The element relates to an optical fiber cable comprising a water soluble polymer material capable of forming an aqueous solution having a predetermined viscosity to block the flow of water within 10 meters of the penetration point after water accidentally penetrates into the cable. Preferably, the solid compact element comprises at least about 30%, preferably at least about 50%, of the water soluble polymer material. According to a particularly preferred embodiment, the solid compact element is formed in an amount greater than about 75% by weight of the water soluble polymer material.

Preferably, the aqueous solution has a viscosity of at least about 10 ⁴ cP (centipoise) at 20 ° C.

In a preferred embodiment, the solid compact element is a structural element of a cable capable of protecting, including at least one optical fiber disposed in the longitudinal cavity. According to a preferred embodiment, said solid compact element comprising at least one optical fiber is a tubular element and said longitudinal cavity is defined by the interior volume of said tubular element. Preferably, the tubular element comprises a bilayer wall made of a polymer material whose inner layer is made of the water soluble solid material and whose outer layer is insoluble in conventional water. According to another preferred embodiment, the tubular element comprises a third outer layer made of a water soluble solid material. According to another embodiment, the tubular element is made of a single sheath of the water soluble material.

According to another embodiment, the structural element, which may include at least one optical fiber, is a grooved core comprising at least one groove longitudinally installed on an outer surface of the core, wherein the longitudinal cavity is defined by an internal volume within the groove. It is limited. According to an embodiment of the invention, at least the walls of the grooves are made of a water soluble solid polymer material. According to another embodiment, the grooved core is completely made of the water soluble solid polymer material.

According to another embodiment, the element made of water-soluble solid material included in the cable according to the invention is a tape.

According to another embodiment, the cable according to the invention comprises at least one sheath of a polymeric material arranged to form a cavity and at least one solid element of a water soluble material arranged within said sheath, the relative humidity outside said cavity Is at least about 75%, the relative humidity in the cavity is maintained at about 75% or less for a predetermined period of time. Preferably, the predetermined time period is at least 20 years.

Another preferred embodiment of the present invention provides an amount of water of less than about 25% of the amount of water that can be absorbed by the water-soluble solid material in saturation when the relative humidity is generally less than or about 80%. A cable as defined above, characterized in that it absorbs.

According to a preferred embodiment, the ratio between the cross section of the cavity and the perimeter of the cavity defined by the solid element made of water-soluble material is less than about 0.5 mm. Preferably, when the viscosity of the water soluble polymer is at least about 10 ⁴ cP, the ratio between the cross section of the cavity and the periphery of the cavity defined by the solid element made of water soluble material is less than about 0.4 mm.

According to another preferred embodiment, the cross section of the solid element made of water-soluble material is at least about 10% of the free cross section of the cavity to which the element is connected, preferably the cross section is at least 20% of the free cross section, in particular Up to about 40%.

According to another preferred embodiment, the cable according to the invention is also water soluble polymer material connected to the cavity of the cable is also expandable in water. Preferably, these materials expand by at least about 5% with respect to the volume of transportation when placed in contact with water for about 4 minutes.

According to a preferred embodiment, the water soluble material of the solid element associated with the longitudinal cavity has a water solubility of at least about 100 g / l. Preferably the material may form an aqueous solution having a viscosity of at least about 10 ⁴ cP at 20 ° C. Preferably, the aqueous solution comprises an amount of polymeric material between about 100 g / l and about 250 g / l.

Preferably, the water soluble polymer material included in the cable according to the invention has a fracture load greater than about 15 Mpa and an elastic modulus greater than about 100 Mpa.

According to a preferred embodiment, the water soluble polymer material included in the cable according to the invention is selected from the group consisting of polyacrylamide, modified polyvinyl alcohol, vinyl alcohol / vinyl acetate copolymers and polyvinylpyrrolidone and mixtures thereof. . Preferably, the material is vinyl alcohol / vinyl acetate copolymer.

According to a particularly preferred embodiment, the copolymer can be obtained by partial hydrolysis of acetate groups of the polyvinyl acetate homopolymer. Preferably, the degree of hydrolysis of the acetate groups of the polyvinyl acetate homopolymer is between about 50% and about 95%, more preferably between about 70% and 90%.

Preferably, the vinyl alcohol / vinyl acetate copolymer has a viscosity index of greater than about 5. Preferably, the viscosity index of the copolymer is between about 8 and about 40, with vinyl alcohol / vinyl acetate copolymer having a viscosity index between about 10 and about 30 being most preferred.

For the purposes of the present invention, the expression solid compact element is not fluid, fibrous or powdery at the working temperature of the cable (and in the absence of water), for example cores, sheaths or tubulars comprising optical fibers. It refers to an element consisting of a material having a mechanical property such as modulus of elasticity, breaking load, elongation at break, or a mixture of materials, similar to that of conventional polymer materials used to make structural elements of cables such as elements. The term " conventional material " refers to a material generally used in the description of the present invention to make such structural elements, and within the spirit of the invention, for example, polyethylene (high, medium and low density PE), polypropylene ( Polyolefins such as PP) or ethylene propylene copolymers (PEP), and polymer materials such as polybutylene terephthalate (PBT), polyvinylchloride (PVC) or polyamide (PA).

The expression “at least about 75% of the solid element of the water-soluble polymer material” refers to the presence of the solid element in an amount of less than about 25% by weight, preferably less than about 10%, eg, fillers, plasticizers, pigments, dyes, It is intended to mean mainly made of water-soluble polymer materials, with the addition of other minor ingredients such as processing agents, biocides or stabilizers.

In this description, the term water barrier material or water barrier property is intended to generally refer to a material that can prevent water from spreading longitudinally within a cable within a predetermined length of the cable. Preferably this length is less than or equal to 10 meters.

The term "water absorbent material" is intended to refer to a material that tends to absorb water in the surrounding environment.

In this description, the term “water expandable” or “expandable” material is intended to refer to a water absorbing material that, when placed in contact with water, absorbs a certain amount of water and then increases in volume while still maintaining a solid state. . This increase in volume depends on the type of material, the time of contact with the material and water, and the amount of water absorbed. This definition includes materials that, when in contact with water, show an increase of at least 5% over the original volume, in particular over 100% increase over the original volume for materials that absorb much water.

The term "water soluble material" is intended to mean that the water barrier material used in the cable according to the invention can at least partially dissolve when in contact with water, resulting in a water soluble having a predetermined viscosity value. In particular, the viscosity of the solution forming will be such as to disturb the flow of the solution in the cable. Preferably, such a solution has a viscosity that essentially blocks the flow of water penetrating into the cavity, within a distance of less than about 10 meters from the point of penetration of the water.

The present invention will be better understood from the following detailed description with reference to the accompanying drawings.

As shown in Fig. 1, a cable of the so-called tubular element type (especially a loose tube type) comprises a reinforcing element, in a radially innermost position, up to a given diameter, typically with a glass resin 5 It has a support element which is made and coated with a polymer layer 6.

The cable has one or more tubular elements or tubes (7) surrounding the support element (5) and the coating layer (6), arranged in the tubes one by one or in bundles of optical fibers, ribbons, small tubes ( That is, a fine sheath surrounding the fiber bundle) and the like.

The number of tubular elements present (these elements can also be arranged over a plurality of layers) and the dimensions of these tubular elements depend not only on the conditions of use of the cable, but also on the intended capacity of the cable.

For example, a cable with only one tubular element (in this case no central element 5 and its coating 6 present) is expected and six, eight, or more surrounded by one or more layers. It is envisioned that a cable having the above tubular element (eg up to 24 tubular elements surrounded by two layers).

The tubular elements 7 are in turn held together in the receiving layer 8, for example made by lapping, and are preferably combined with a reinforcing element 9, for example a layer of Kevlar fiber or a layer of glass yarn. The size of the reinforcement element depends on the mechanical strength requirements of the cable.

Two sheath-dividing filaments 10 separating the sheath are arranged longitudinally relative to the cable and can be included in the reinforcing layer 9.

Finally, the cable comprises a protective outer sheath 11 which is usually made of polyethylene. With regard to specific requirements, additional protective layers may also be present, for example metal layers may be present inside or outside the described structure.

According to one embodiment of the present invention, in the cable having the above-described structure, the tubular element 7 is made of a solid material having water blocking properties, and the outer layer 7a is made of polybutylene terephthalate (PBT). ), Polypropylene (PP), polyethylene (PE) or ethylene-propylene copolymers (PEP) can be made with double layer walls made of conventional materials.

2 shows a tubular element 7 having a two-layer wall (eg manufactured by co-extrusion), wherein the outermost layer 7a of the element is a conventional polymer material (eg PE, PP, PEP or PBT) and the innermost layer 7b is made of a solid water soluble polymer material. The space inside the tube not filled by the optical fiber is typically empty.

One or more of the optical fibers 3 are arranged in a tubular element, typically laid down, separated or gathered in a fiber ribbon, small tube or the like.

The material forming the inner layer 7b of the tubular element is a solid extrudable material having mechanical properties somewhat similar to the outer layer 7a, the property of which preferably is a tubular element having a single conventional layer with a thickness of the entire tubular element. Is not different from the typical thickness.

Typically a tubular element having an outside diameter of 3 mm, for example, may have a wall of about 0.6 to 0.7 mm in total thickness and divided into water soluble inner layers 7b and conventional outer layers 7a which are almost equal parts.

In case of accidental infiltration of water, the water-soluble polymer material of the two-layer tubular element inner layer 7b is at least partially infiltrated with water, starting from its original position (shown in dotted lines in the drawing), as shown in FIG. 3. It dissolves to form a viscous solution 4 that moves between fibers until the entire free cross section of the tubular element is blocked, thus filling the free space (generally irregular contour) regardless of the shape of the space.

The aqueous solution formed by appropriate selection of the properties of the water-soluble material of the layer 7b is sufficiently high to delay water spreading along the cable until it stops the water from spreading within a few meters from the point where the water enters. Has viscosity.

In this way, it is possible to block the spread of water accidentally penetrated into the cable, without introducing additional materials, such as powder, barrier fluid, etc., which have substantially increased the weight of the cable into the tubular element.

In addition to the free cross section in the tubular element 7, the cable structure described above is usually described as a star area and comprises an area 8a outside of the tubular element through which water accidentally penetrated into the cable can pass.

According to the invention, the polymer layer 6 for coating the central element 5 is preferably made of a solid, water-soluble material having the above mentioned properties, either completely or in the outer layer.

This coating layer 6 may be extruded (co-extrusion if a layer of solid water barrier polymer material is provided on the inside and a layer of solid water barrier polymer material on the outside) or a compact tape of solid water barrier polymer material (Longitudinal or helical) can be made by sticking on the central element 5 (which may optionally be already partially coated).

If appropriate, it is conceivable that the outer layer of the tubular element 7 is also made of a water barrier material, or alternatively the entire tubular element may be made of a water barrier material.

If desired, the receiving layer 8 according to the invention can be made by wrapping (either in whole or in part) with a compact tape of solid, water-blocking polymer material, or alternatively with an extruded layer of the same material.

The presence of the layer of solid water soluble polymer material in layers 6 and 8 and the size of the solid water soluble polymer material in these layers is dependent on the current free cross section (e.g. the star area 8a mentioned above) and This is determined by the requirement to block the flow of water in the cable in a rather narrow space.

Next, the reinforcing layer 9 comprises filaments or rods of the solid water-soluble polymer material of the above-mentioned type.

In addition, or in place of rods or filaments that may be included in the reinforcing layer 9, the coating 11 may be formed of two layers comprising an inner layer 11a made of a solid water-soluble material.

On the basis of the above mentioned principle, the present invention can also be applied to a cable having a grooved core.

As reported in FIG. 4, a cable with a grooved core has a reinforcing element 12 in the radially innermost position, for example made of glass resin, on which the solid water-soluble material according to the invention is made. There is a grooved core 13 made, which is typically extruded. The grooves 14 extend continuously in a continuous spiral or alternately along the s-z path along the entire outer surface of the core to receive the optical fiber 3 in the groove; In a manner similar to that mentioned above, the optical fibers 3 can be arranged individually or drooped (ie over the length) at the bottom face of the grooves or fit snugly into ribbons, small tubes and the like.

According to another embodiment, the grooved core may be made only partially of the water soluble polymer material, as shown in FIG. 4A. In this case, a double layer grooved core is produced (for example by double extrusion or coextrusion of two polymer layers), where the interior 13a of the core is made of a conventional polymer material (e.g. PE or PP). The outer grooved portion 13b is made of a water soluble material according to the invention.

Alternatively, the grooved core 13 may be entirely made of a conventional material such as PE or PP. In this case, a special U-shaped element 15 made of water-soluble material can be placed in the groove, for example by allowing the element to be coextruded with the grooved core or produced separately and then inserted into the groove.

By way of example, the grooved core may have a diameter between 4 and 12 mm and include 1 to 10 grooves, depending on the capacity of the given cable. The dimensions of the grooves themselves are determined by the number of fibers present in the grooves (which may be gathered with tapes of fibers) and by the degrees of freedom considered for these fibers.

The grooved core 13 is then coated with a layer 16 of a groove blocking polymer, preferably a polymer made of a solid water soluble material; Such coatings may be made in the form of extruded coatings or may be made as longitudinal or helical wrapping.

This layer may then be surrounded by an additional reinforcing tape 17 made of polyester, for example, followed by a reinforcement made of Kevlar, for example the trademark, which may comprise a filament or rod made of a solid water soluble material. It is surrounded by a layer or armoring 18.

An additional wrapping 19 made of polyester, for example, surrounds the sheath 18 and the wrapping itself is surrounded by an outer sheath 21 typically made of polyethylene; The layer of solid, water-soluble material 20 is installed just below the outer sheath 21 and wherever water may reach.

As mentioned above, for the purposes of the present invention, a solid element comprising a solid, water-soluble material is a component that is neither fluid, fibrous or powdery at the working temperature of the cable (and in the absence of water). When compared with those of the material used to make the elements of the cable, they should have mechanical properties such as modulus of elasticity, breaking load, elongation at break, and the like. Thus, optical cable elements made of the material can advantageously replace one or more structural elements (eg, covering sheaths, tubes, grooved cores, etc.) of an optical cable typically made of conventional polymer material. At the same time, the water solubility characteristics of these materials should be such as to block the flow of water under conceivable conditions to form an aqueous solution of sufficient viscosity. In particular, the highlighted characteristics will also be the case where the solid element is essentially (ie, at least about 75%) made of a water soluble polymer material.

In addition, it is preferred that the water soluble material according to the invention be one that can be easily extruded into one of the abovementioned compact elements of the solid.

The solid compact element connected to the longitudinal cavity in which the flow of water is to be blocked will comprise at least 30% by weight, and preferably at least 50% by weight of the water soluble polymer material. Thus, such solid elements having a water barrier function may, in addition to the above-mentioned water-soluble polymer materials, other materials which may be advantageously mixed with such water-soluble polymers, for example filling materials such as carbon black or inorganic fillers (eg Calcium carbonate or magnesium hydroxide), stabilizers, pigments or dyes and plasticizers such as conventional polymer additives or other compatible polymer materials. According to a preferred embodiment, these solid and compact elements consist essentially of at least about 75% by weight of a water soluble polymer material, with the remainder of the composition representing conventional additives for the polymer composition. Preferably, about 5% of the total weight of the composition is a plasticizer.

Applicants note that in the cable according to the invention, as the viscosity of a solution formed from a water-soluble material is increased, the dimensions of the cavity in which the blocking of water must occur can be increased and / or the time taken to block such flow of water can be reduced. I found out.

In particular, the Applicant has determined a viscosity value of about 10 ⁴ cP (centipoise), preferably 10, measured with a Hopler falling-sphere viscometer at a temperature of 20 ° C. in order to properly block the passage of water. It is particularly preferable to use a water-soluble material of a polymer which forms an aqueous solution which achieves a viscosity value of ⁴ to 10 ⁵ cP.

For this purpose, it is necessary to ensure that a sufficient amount of the water-soluble material of the layer 2 is dissolved in water and the solution so formed has the required viscosity.

In the case of a water soluble polymer forming a solution having a viscosity of about 10 ⁴ cP, during the testing of water spreading along a tubular element comprising an optical fiber of various water blocking and water soluble materials according to the invention, the first of the tubular elements To prevent water propagation within 10 meters (and within a few minutes), the cross section of the cavity (in mm ² ) and the part of the ambient length (in mm) (both in water) made of water-soluble material can be used It was found that the ratio between the measured in the absence of water should be less than or equal to about 0.3 mm.

For solutions with a viscosity of about 10 ⁵ cP, the ratio can increase to about 0.4 to 0.5 mm.

Advantageously, in order to reach a predetermined viscosity value, the polymeric material may be prepared at a concentration of between about 100 g / l and about 250 g / l, preferably between about 120 g / l and about 200 g / l, in which the aqueous solution is measured at 20 ° C. One having a viscosity of about 10 ⁴ cP at a concentration is used, with materials which form a solution having a viscosity of about 10 ⁴ cP at a concentration between about 130 g / l and 180 g / l.

For the purposes of the present invention, water-soluble polymer materials having a solubility in water of 20 ° C. of at least 100 g / l, preferably at least 200 g / l are thus preferred, and materials having a solubility of about 300 g / l or more in particular desirable.

The Applicant furthermore found that some water which interacts with the water soluble polymer to form a solution of the desired viscosity is included in the polymer, causing partial expansion of this polymer. Typically, within the usual time it takes to block or generally slow the flow of water, these water soluble polymers absorb from about 10% to about 25% by weight of water, resulting in expansion to about 5-10% of the original volume. Can be. This expansion of the polymer, although limited, nevertheless can reduce the cross section through which water passes and thus contribute to making the formed high viscosity polymer solution more easily block its flow. Thereafter, more contact between the polymer and the water present causes the polymer to expand further, thus further limiting the cross section through which the water passes, thereby increasing the blocking effect of the polymer solution. Among the water-soluble polymer materials which may be advantageous for use in the cable according to the invention, preferred is, as mentioned above, a material with water expandable properties, i.e. it can contain a significant amount of water therein, so that within a certain time In general, it will be a material that can cause a moderate expansion of at least 5% after about 4 minutes of contact with water, so that these materials can contribute to blocking the flow of water by the polymer solution.

In view of the above observations, in the case of a solid element consisting essentially of a water-soluble polymer material, assuming that the polymer material is completely dissolved in infiltrating water, the amount of material present per unit of length is such that It can be calculated that it should be at least about 10% of the free cross section of the cavity in order to form a solution with a concentration sufficient to obtain a viscosity of. For example, in the case of a tubular element having an inner diameter of about ² mm (cross section of about 3.14 mm ² ), the amount of water soluble material may be used to an extent that occupies at least about 0.314 mm ² cross section. Other such materials may be disposed in the cavity, for example as solid filaments of 0.63 mm in diameter, or preferably extruded into a thin polymer film, on the inner surface of the tubular element, to a thickness of about 0.05 mm. If one or more optical fibers are found in the tubular element, then the free inner cross section of this tubular element will be less, thus further limiting the amount of water soluble material used.

On the other hand, in some cases, it may be desirable to increase the amount of water soluble material per unit of length of the cable, since the concentration of material may be required up to 250 g / l to achieve the desired viscosity. In general, it may be advantageous to use an amount of water soluble material to such an extent that it occupies at least about 20% of the free cross section of the cavity through which water can flow, and about 40% of the free cross section. A way to further increase the amount of water soluble material may be contemplated in the case of certain cable designs where higher amounts of water barrier material are desired.

The Applicant has furthermore found that many of the water barrier materials chosen to make the cable of the present invention form water solubility that substantially increases viscosity over a long period of time until a gel is made which further contributes to maintaining long term water blocking conditions.

Applicants have found that to achieve the desired solubility it is desirable to ensure that the water soluble polymers are not crosslinked so that the various polymers are relatively unaffected by each other so that the water can dissolve a sufficient amount of the polymer.

Among the solid water soluble materials that can be used in the cables according to the invention, preference is given to the absorption of the material, typically only in a saturated state (RH = 100%), up to a relatively high relative humidity (RH) value of typically about 75 to 80%. It is a material that absorbs only a suitable amount of water in an amount less than about 25% by weight.

The material used in the cable according to the invention shows a weight increase (due to water absorption) of about 10%, for example when placed in an atmosphere of about 75% R.H. even after being tested for at least 1000 hours. The same material is 100% R.H. When placed in a valued atmosphere, it shows a weight gain of about 30% by weight after only about 100 hours of testing, and achieves an increase of 60% or more after about 800 hours of testing.

The optical fiber is particularly advantageous because it is relatively sensitive to the presence of water vapor up to a relative humidity value of less than about 75 to 80%, so that the water-soluble material hardly changes below this value.

The fact that the material does not actually react at these relatively low relative humidity values does not need to protect the material for atmospheric humidity, which is generally less than 75%, resulting in better processability and fewer problems in preserving the finished product. have.

Moreover, thanks to this property, some of these materials do not need to interact unnecessarily with water in the vapor state below the threshold for relative humidity, or even undesirably need to swell to squeeze the optical fiber. Almost all still help to block the water even in the case of infiltration of liquid water or an increase in relative humidity above the threshold.

The present application also relates to the use of water blocking and water soluble materials that can be used in the optical cable according to the present invention, when the material is placed in a housing comprising an optical fiber, which provides hygrostatic properties to the housing. I found it particularly beneficial. This is because according to the invention disposed in the cable structure in an appropriate amount when the environment outside the cable structure (eg tubular element of plastic material) in which the optical fiber is accommodated exceeds the relative humidity threshold (75-80%). This is because the material can maintain a relative humidity value below the threshold around the optical fiber.

For example, conventional tubular elements for containing optical fibers made of polybutylene terephthalate (PBT), polypropylene (PP) or polyethylene (PE), etc., when present in an atmosphere with high relative humidity (eg 95%), External humidity is likely to penetrate towards the center in these tubular elements where the optical fiber is received; Under these conditions, relative humidity values above 80% reach within the tubular element within months, with the possibility of the above mentioned defects occurring.

Conversely, if such a receiving tube element has a two-layer structure according to the invention made of a water absorbent material having an outer layer made of a conventional polymer material and an inner layer having the mentioned properties, the relative humidity in the tubular element is made entirely of conventional material. It was found to increase much more slowly than in the case of tubular elements.

Furthermore, if these tubular elements are contained in a container sheath made of a conventional type of polymer, then the relative humidity in the tubes can stay below the threshold for 20 to 25 years, corresponding to the expected average life of the optical cable. have.

Similar reactions are also found when the tubular element, including the optical fiber, consists of a single layer of water soluble material and the tubular element is housed in a container sheath made of conventional polymer material.

The presence of additional elements in the cable structure substantially made of the water-soluble material of the present invention, for example interstitial tapes or filaments (or other elements to be described in more detail below), may be counterparts. The time it takes to reach the humidity threshold can be further increased.

According to the invention, the polymers, which can preferably be used as water barrier materials, are typically solid at room temperature (or at the working temperature of the cable), can be extruded or otherwise processed, and dissolved in water to provide sufficient viscosity. It is a polymer that can form an excitation solution. Preferably these materials show reduced water uptake in the presence of relative humidity values of less than about 75 to 80% and / or have humidity control capability for the cavity containing or connected to the materials.

These polymers typically contain one or more hydrophilic groups in the polymer's structure, such as:

-Hydroxyl group (-OH)

Ether group (-COC-)

-Ester group (-CO-O-)

-Amine group (-NH ₂ )

-Carboxyl group (-COOH)

Amide group (-CO-NH-).

Examples of these polymers are esterified or etherified copolymers of polyacrylic acid, polyacrylamide, polyacrylamide / acrylic acid copolymers, methacrylic acid, polyvinylpyrrolidone and polyvinyl alcohols and in particular vinyl alcohol / vinyl Polymers derived from polyvinyl alcohols such as acetate copolymers.

Among the above-mentioned materials, it is particularly preferable to use polyacrylamide, modified polyvinyl alcohol, vinyl alcohol / vinyl acetate copolymer or polyvinylpyrrolidone.

The modified polyvinyl alcohol is not limited to the following:

a) by partial etherification of polyvinyl alcohol (e.g. by epoxidation incorporating a group such as (CH ₂ CH ₂ -O-) _n -OH) into the PVA homopolymer chain) ;

b) by partial esterification of the alcohol groups (similarly, suitable polyester homopolymers can be hydrolyzed to introduce hydroxyl group function into the homopolymers); or

c) obtained by block copolymerization, for example, by obtaining poly (vinyl alcohol-co-polyoxyethylene) from vinyl acetate, polyoxymethylene monomethyl ether and using diisocyanates or diepoxides as chain extenders Polymers.

For the purposes of the present invention, vinyl alcohol / vinyl acetate copolymers (hereinafter referred to as VA-VAc copolymers), which can be obtained by partial hydrolysis of the acetate groups of polyvinyl acetate (PVAc) homopolymers, are particularly preferred. .

In particular, the degree of hydrolysis of the PVAc homopolymer is between about 50% and about 95%, preferably between about 70% and about 90%.

Regarding the degree of hydrolysis of the copolymer, the Applicant has found that, when the degree of hydrolysis is zero, the solubility in water is not very high, such as about 0.01 g / l at 20 ° C.

As the degree of hydrolysis increases, the hydrophilicity of the material increases, with solubility, to about 300 g / l for about 88% degree of hydrolysis. However, the Applicant noted that further increase in the degree of hydrolysis decreases the solubility of the material in water accordingly. In fact, in the case of complete hydrolysis of acetate groups, the resulting polyvinyl alcohol homopolymers have extremely low solubility (1.43 g / l at 20 ° C.), although the material still has high hydrophilicity.

For the purposes of the present invention, it is desirable to use VA-VAc copolymers that are incomplete to ensure good solubility of the polymer in water and that have a degree of hydrolysis that is high enough so that the hydrophilicity of the polymer is sufficient to interact properly with water. .

In addition to the degree of hydrolysis of the PVAc homopolymers, one variable that may affect the water blocking action of the material is the molecular weight of the VA-VAc copolymer, in particular the viscosity index of the polymer.

The viscosity index of a polymer is defined here as the ratio between the viscosity of a 4% aqueous solution of the polymer (measured with a Hopler polling sphere viscometer at 20 ° C.) and the viscosity of water (measured with a Hopler polling sphere viscometer at 20 ° C.) ; In the case of the same degree of hydrolysis of the polymer, this viscosity index is proportional to the molecular weight of the polymer. Typically, for the same viscosity index, as the degree of hydrolysis of the VA-VAc copolymer increases, its molecular weight decreases.

In fact, Applicants have found that VA-VAc copolymers with low viscosity index react rapidly in the presence of water, absorbing more water and expanding more rapidly than copolymers with higher molecular weight.

Moreover, it has also been found that aqueous solutions of polymers having too low a viscosity index do not reach sufficiently fast enough to effectively block water from spreading in the longitudinal direction. According to the Applicant, this is probably due to the fact that such copolymers have a relatively high water solubility (in some cases similar to hydrolysis and higher than that of polymers with higher MW), in order to reach a predetermined viscosity This may be due to the fact that the concentration of polymer in solution should typically be high enough, typically at least 30% by weight. Thus, increasing the amount of polymer to be dissolved increases the time to form a solution with the desired viscosity, thereby increasing the cable length affected by the movement of water before blocking.

Applicants also note that if the viscosity index of the polymer used is too low, then in the presence of a relative humidity value of less than 75 to 80%, the surface of such polymer may be covered with a sticky coating film caused by partial absorption of water. Apart from the problems associated with the difficulty of handling these materials under these conditions, such surface stickiness is generally not necessary since such surfaces may cause attenuation when in contact with the optical fiber.

On the other hand, Applicants have found that VA-VAc copolymers with sufficiently high viscosity indexes have relatively high concentrations (e.g. between 10% and 20% by weight) with the required viscosity to block the flow of water within a certain time. It was found that a solution could be formed.

Moreover, in the presence of relative humidity percentages of less than 75 to 80%, although found in the case of low molecular weight copolymers, these copolymers do not exhibit surface stickiness caused by partial absorption of water.

However, VA-VAc copolymers with too high a viscosity index may dissolve at an extremely low rate upon contact with water, and as a result, the water may flow over an excessive distance (eg, many meters) in the cable before it is blocked. .

Applicants have therefore found that vinyl alcohol / vinyl acetate copolymers having a viscosity index of greater than about 5 are particularly suitable for the purposes of the present invention. Preferably, the viscosity index of the copolymer is between about 8 and about 40, and vinyl alcohol / vinyl acetate copolymers having a viscosity index between about 10 and about 30 are still more preferred. Advantageously, copolymers having different molecular weights Mixtures of polymers can be used to combine the particular advantages of each copolymer.

Examples of commercially available materials with the desired properties are those sold under the trade names Mowiol (Hoechst AG), Gohsenol (Nippon Gohsei), Elvanol (Du Pont) or Airvol (Air Products).

In order to evaluate the water soluble polymer material that can be used in the cable according to the present invention, the applicant has developed two simple experimental tests.

The first test, by extrusion, had a double layer covering 11 optical fibers of 250 μm diameter, consisting of an outer layer of about 0.35 mm polyethylene and an inner layer of a water-soluble polymer material about 0.3 mm thick, with an outer diameter of 3 mm. To produce a tubular element. This tubular element is connected to a water tank installed under the head of a meter of water. The Applicant has found that water-soluble polymer materials which are particularly suitable for producing cables according to the invention are those which can block the flow of water within 10 meters of the input point.

According to a second test, a plate of water soluble material (about 20 x 30 x 1 mm in size) is molded and immersed in about 1 liter of water for a defined time. Once in contact with water, some of the polymer material dissolves into a solution, some of the material forms a highly viscous solution at the surface of the plate and some of the material remains solid and partially expands after absorbing water. do. After that, the plate is removed from the water and gently shaken to remove the water on the surface. The viscous solution on the surface is removed, for example using a spatula, and the viscosity is measured. Applicants have found that particularly preferred polymeric materials are those which can form a solution having a viscosity of about 10 ⁴ cP or higher on these plate surfaces after immersion in water for about 4 minutes.

Water soluble polymer materials can be used in the various components that form the structure of the cable in several different ways to optimize the water barrier effect.

In addition to using a water soluble material to make or replace part of the structural elements of the cable, in order to provide such cable with water permeation barrier properties without increasing the weight of the material as described above, the flowable material, viscosity By introducing additional elements made of the same material without introducing these materials or powdered materials into the cable, the properties of the water-soluble materials that are effective in preventing the penetration of water into irregularly shaped cavities can be exploited.

For example, thin filaments of water soluble material (e.g., diameter ≤ 0.5 mm) can be produced, wherein a fiber bundle is wrapped around the filament or the filament, together with the bundle, is a star area during cable fabrication. (8a) is wrapped around a suitable rod or central support of suitable dimensions to be inserted into or into the groove 14.

In addition, it is also possible to make optical cables of different shape sizes, for example small tube cables, in which two or more optical fibers are preferably microcoated, which can be made of a water-soluble material according to the invention. microsheath (the thickness of the coating is about 0.07 to 0.15 mm), and then the plurality of small tubes are received in a large diameter buffer tube. In addition, a cable with a so-called tight core can also be produced, wherein the optical fiber is contained in a polymer core made of a partially or completely water soluble material.

It is particularly desirable to receive the optical fiber as a water soluble material so that when the material dissolves, the material comes into contact with the optical fiber, thereby preventing water from flowing along the cavity in which these fibers are housed.

Such a structure makes it possible to make a cable free of any conventional barrier material made of slippery or oily or powdery material in contact with the fibers.

However, with regard to specific structural and working characteristics, it is also possible in accordance with the invention to combine a part of the cable formed or coated with a water soluble material with another part including blocking grease or with a tape comprising water expandable powder. .

According to one embodiment of the present invention, as water accidentally enters the cable and the formed viscous solution fills the gap space, the fibers do not feel significant mechanical stress and the water flow is blocked.

This allows the cable to be repaired later, as the cable will remain functional without any particular drawback of signal attenuation even after water accidentally enters.

The preparation of the above-mentioned various elements made of or comprising a water soluble material can be carried out according to known techniques, preferably by extrusion.

In particular, the material may be a part of the cable structure (e.g. one, two and three layer tubular elements comprising optical fibers, the inner layer of the cable container sheath, the extrusion coating of the grooved core) and the individual elements to be inserted into the cable structure (e.g. optical fibers). Can be extruded directly into one of the rods to be wrapped with filaments, tubes, tapes or the like.

For this purpose, it is desirable to add an amount of plasticizer to these materials to improve processability and final flexibility. The amount of plasticizer may range from about 1% to about 30% of the weight of the water barrier material, preferably from about 5% to about 25%, particularly preferably from about 15 to 20%. Examples of suitable materials that can be used as plasticizers include low molecular weight polyglycols such as glycerol, sorbitol, trimethylolpropane, polyethylene glycol (e.g. di- or tri-ethylene glycol), pentaerythritol, neopentylglycol, triethanolamine, oxyethylate Hydrogenated phosphoric esters and water.

Applicants have furthermore found that the presence of plasticizers, in particular glycerol, in the amounts specified above can increase the water absorption of water soluble materials.

The mechanical properties (eg, modulus of elasticity, breaking load, elongation at break, etc.) of the water soluble polymer material are selected as a function of the particular use of the element in the cable structure. In order to change the mechanical properties according to special requirements, these properties can be obtained by appropriately selecting a material having desirable properties, or by appropriately changing the amount of plasticizer added to the polymer material, for example.

For example, because the polymer material can be used to make the entire wall of the fiber optic tubular element or to replace a portion of this wall thickness, alternatively compact wrapping tape or other components of the cable structure, In order to withstand the typical stresses these elements are subjected to, it would be desirable for the material to have mechanical properties similar to those of conventional materials (PET, PP, PE) used to make the elements.

Example 1

Absorption of water in the vapor state

Ten plates having a thickness of 1 mm were prepared using a VA-VAc copolymer sold under the trade name Mowiol (Hoechst AG). Table 1 gives the viscosity index and degree of hydrolysis of the polymers used and the plasticizer content in the mixture.

Characteristics of Water Blocking Materials Test number Registered trademark Mowiol, VA-VAc copolymer Glycerol Viscosity index Degree of hydrolysis (%) weight % weight % One 3 83 100 0 1a 3 83 95 5 1b 3 83 90 10 2 23 88 100 0 2a 23 88 95 5 3 10 74 100 0 3a 10 74 95 5 4 40 88 100 0 4a 40 88 95 5 4b 40 88 90 10

Weighed samples with 20 × 70 × 1 mm dimensions to be used for the water absorption test were obtained from plates placed for 7 days under atmospheric conditions (23 ° C., 40% relative humidity).

The test is performed in accordance with the method specified by ASTM D 570, instead of being immersed in water as indicated in the criteria above, the sample is in one case 100% (a value that is considered to be harmful to the fiber) and in other cases 75 It was performed with the difference when exposed to the atmosphere with relative humidity (RH) adjusted to% (value not considered harmful). The results are given in Table 1a below.

Test for Absorption of Vapor Water Test number % Of water absorbed over time At 100% RH At 75% RH One 33% 264 hours 9.9% 264 hours 1a 43% 264 hours 12% 264 hours 1b 53% 264 hours 14% 264 hours 2 47% 1400 hours 11% 1400 hours 2a 70% 1400 Hours 14% 1400 hours 3 49% 1400 hours 7% 1400 hours 3a 76% 1400 Hours 13% 1400 hours 4 38% 360 hours 9% 360 hours 4a 55% 360 hours 13% 360 hours 4b 68% 360 hours 16% 360 hours

From these data, the test material shows limited water absorption up to 75% RH, while this absorption is significantly increased at 100% RH.

It also indicates that the absorbency of the polymer increases with increasing the viscosity index; Moreover, it was found that the amount of water absorbed (both in saturated R.H and 75% R.H.) was increased by the presence of glycerol as a plasticizer.

Example 2

Humidity Control

One plate was hydrolyzed to 80% purchased from Aldrich, molded from fine particles of a commercial VA-VAc copolymer having a viscosity index of about 25, one plate was molded from MDPE, the thickness of both plates Were all about 0.2 mm.

Two disks with a working surface of 16 cm ² were obtained with MDPE plates, the two disks being measured by a suitable component, the Panametrics Hybrid-Cap sensor (approximately 2 mV) measuring the relative humidity. /% RH) into each cell and used to close the opening of two 30 cm ³ cells for testing water permeability according to ASTM E96, modified by inserting a wire for the sensor through a sealed slot. It became.

The cells were assembled in a glove bag infused with dry air (RH <1%). One of the cells was provided as a reference, with only a sensor in the empty state, and the other, along with the sensor, containing about 1 g of VA-VAc copolymer. This amount includes two layers of tubular elements (0.2 mm PE outer layer and 0.15 mm water-blocking copolymer inner layer) and a strip of water-blocking copolymer having a thickness of about 0.15 mm for a total of about 30 g / m water-soluble material. In proportion to the conceivable content of a typical cable according to the invention.

Subsequently, a sensor was provided to remove the assembled cells connected to the data logger from the glove bag and installed in a sealed container maintained at 100% relative humidity.

The results are given in Table 2 below.

Humidity Control city RH in container When polymer When empty 0 7% 7% 1000 35% 65% 2000 40% 77% 4000 50% 90% 5500 56% 100% 6500 60% 100% 8500 65% 100%

From these data it was found that after water penetrated the MDPE disk, the relative humidity of the two cells increased over time at an initial value of about 7%.

However, for cells containing VA-VAc copolymers at the expected rate, the relative humidity value slowly increases to 60% after 6500 hours, whereas for the empty cell the relative humidity is 80 at the end of 2000 hours. It increases more rapidly until it reaches the dangerous value of% relative humidity and reaches 100% relative humidity at about 5500 hours.

Based on the change in the line for the cell containing the water-soluble copolymer, it was estimated that after 20 years, the relative humidity would reach a value of about 75%.

Based on the experimental results obtained, it is believed that this test is a true depiction of the condition for cables with acceleration factor 10 due to the reduced thickness of the MDPE outer sheath (0.2 mm instead of 2 mm).

Thus, from this test, in an insulated cable containing elements made of solid, water-soluble material in an amount of about 30 g / m, and after 9 years, the internal relative humidity is still 60%, after about 9 years, about 20 years While only 75% is reached afterwards, the relative humidity in the case of the same cable of the conventional type already exceeds the threshold of 80% after three years.

Example 3

The ability to block the penetration of water from the tube

Using the commercially available Mowiol VA-VAc copolymer, a number of mixtures were prepared in a dry mixer, with the mixture, in the form of FIG. A two-layer tubular element with a VAc copolymer thickness of 0.3 mm and the remainder made of LDPE and containing 11 optical fibers was extruded.

The tubular element was then tested for longitudinal penetration of water.

The test was carried out according to the method provided in standard EIA / TIA-455-82B, differing from when the length of the tubular element used was 10 m.

The obtained results (average three tests) are as follows.

Longitudinal penetration of water into the tubular element ^★ test Water penetration (m) 1a > 10m 2a 7m 3a 4m 41 ~ 4m 4b 4m

^★ The properties of the polymers used in these various tests are as given in Table 1.

Three penetration tests were then repeated on the tubular element according to mixture 3a, giving an average value of 3.75 m, which was in good agreement with the test.

The test uses a VA-VAc copolymer as the solid water-soluble material for the interior, which spreads in the longitudinal direction of the water when two tubular elements without barrier material (especially those having a viscosity index of 3 or more) accidentally penetrate. The delay was supported to block this spread within a few meters at the point of infiltration.

Example 4

Ability to maintain delivery capacity when water enters

Two layer tubular elements were prepared as disclosed in Example 3, using Material 3a of Table 1 as the inner layer. The 5 m tubular element comprising 12 optical fibers was placed randomly and placed horizontally on a shelf in the climate chamber. One end of the tubular element is connected to a 1 m glass pipette by a hermetic connection, which is initially empty and installed vertically outside the climate chamber.

The twelve optical fibers were passed through the pipette.

Each fiber was then collected into a long merged optical fiber at one end outside the pipette and connected to the Fujikura FLU-312 LED light source via this path, the other end of the Fuji to provide a Fujikura FPM-01 optical power meter. It was connected to one of the entrances of the Kura FPM-Go1 optical power sensor.

The fiber is supplied with light of 1550 nm, which is the wavelength at which the fiber becomes particularly sensitive to microbending stress.

Fully assembled, the readings for all optical fibers are kept at a constant level, and then the readings are set to zero, from then on, at the time of zeroing with the instantaneous power transmitted by the fiber on each channel. The difference between the initial values is provided.

At this point, at a temperature of 20 ° C., the pipette is filled with water, which maintains a constant head of 1 m with respect to the surface on which the tubular element is placed casually. Once the flow of water was stopped (immediately this phenomenon occurred on an average of 3.75 m of tubular element), it began to record the change in transmitted power and the temperature was changed in steps of 20 to 24 hours each.

The lowest temperature achieved during the experiment was -40 ° C.

With an average of three repeated tests, the attenuation values obtained for the four fibers are given in Table 4 below.

Effect of temperature cycle on attenuation at 1550 nm after blocking of water city 0 0 20 21 23 25 26 28 30 Absolute temperature (℃) 20 20 ^★ 20 10 0 -15 -30 -40 20 fiber Attenuation Variation (dB) #One 0 0 -0.02 0.01 0 -0.01 -0.01 -0.03 0.03 #2 0 0 0 0.01 0.01 0.02 0.01 -0.01 0 # 3 0 0 -0.01 0 0 0 0 -0.02 -0.02 #4 0 0 -0.01 0.02 0.02 0.03 0.03 0.02 -0.03

^★ ingress of water

As can be seen, the action of the water-soluble material on the water penetrating the cable does not cause a large change in attenuation even if the temperature changes significantly.

After all, the system can be maintained in the normal mode of operation even after accidental ingress of water, and only if it is convenient to do so after the point of entry of the water is localized, for example by an accurate measurement of the attenuation, Essential repairs and / or replacements may be performed, for example, months later.

Example 5

The ability to block water ingress from the cable

This test exposes a fiber optic cable to a constant head of 1 meter of water over the entire cross section of the cable, corresponding to a pressure of 0.1 bar, and measures the time taken by the water before it is completely stopped in the cable.

The fiber optic cable used in this test essentially has the structure shown in Fig. 3 and consists in particular of:

A central glass-resin support 5 having a diameter of 3 mm;

-A VA-VAc copolymer tape that is 13 mm wide by 0.3 mm thick and spirally wound about 50% overlapping around the support to form the coating 6;

Seven tubular elements (7) having an outer diameter of 3 mm, spirally wound around the wrapped support, consisting of a 0.35 mm thick inner layer made of VA-VAc copolymer and a 0.4 mm thick outer layer made of low density polyethylene;

11 optical fibers having a diameter of about 250 μm coarsely disposed inside each tubular element;

A second tape of VA-VAc copolymer, 14 mm wide, 0.35 mm thick, spirally wrapped about 50% of the tubular element to form the lapping 8;

-Low density polyethylene outer sheath (11) about 1 mm thick.

In contrast to the cable shown in FIG. 3, the reinforcement layer or sheath 9 was absent.

The VA-VAc copolymer (Mowiol, Hoechst AG) used to make the various elements of the above mentioned cable has a viscosity index of 10, a degree of hydrolysis of 74, calcined with 5% glycerol, and in Table 1 3a. Is displayed.

A 1 m long glass column was filled with water containing dye (methylene blue) so that the front of the fluid inside the cable could be identified and connected to one end of the cable as described above.

The test was performed at ambient temperature for a 6 m long cable.

Table 5 shows the length of the cable along the front of the fluid and the time it takes for this movement.

Longitudinal penetration of water in the cable time Length (cm) 30 sec 116 60 sec 172 90 sec 198 120 sec 215 150 sec 226 180 seconds 237 24 o'clock 280 48 o'clock 280 7 days 280

As shown in Table 5, the cable was able to block the flow of fluid in the cable less than 3 m from the point of penetration of this liquid (only after 24 hours).

Example 6

Dissolution properties of the material

In order to evaluate the water-soluble polymer material, two plates were molded to dimensions of about 20 x 30 x 1 mm, using material 3a for the first plate and material 1b for the second plate. See Table 1 for characteristics. The plates were pre-weighed and then immersed in a test container filled with 1 liter of water at 25 ° C. for 4 minutes.

The sample with water removed was shaken to remove more liquid and weighed immediately.

The weighed sample was then rubbed with a spatula to remove the viscous solution adhering to the surface and reloaded.

Rubbed and weighed samples were placed in an oven and dried. The final dry weight of the test sample was obtained after drying.

The spatula and glassware used to remove the viscous solution from each sample were thoroughly washed with water and the water collected and dried in an oven. The weight of the dry residue, ie the weight of the polymer present in the viscous solution on the plate, was finally obtained.

Based on the measurements performed, it was found that after 4 minutes of immersion in water, the test sample of material 3a exhibited a polymer concentration in the viscous solution upon contact with about 17.5% by weight of the test sample. In line 51 of FIG. 5 representing the change in viscosity as a function of the concentration of a particular material, one reaches the viscosity of the relevant solution, ie about 2.7 × 10 ⁴ cP. Moreover, it was calculated that about 25 g of polymer per m ² of surface area of the test sample was dissolved in water in the test vessel. The total amount of polymer dissolved (in the viscous solution that was on the test sample and in the water in the container) was about 42 g / m ² of the test sample and the amount of water absorbed by the solid material was about 13% by weight.

In a similar manner, for a test sample of material 1b, it was found that the polymer concentration was about 29% by weight in the viscous solution buried in the test sample, based on the concentration / viscosity curve 52 in FIG. 5, respectively. This corresponds to a solution viscosity of about 650 cP. This test sample dissolves about 65 g of polymer per m ² of surface area of the test sample into water in the test vessel. The total amount of dissolved polymer was about 99 g / m ² and the amount of water absorbed by the solid material was about 12.5 wt%.

Referring to the embodiment described above, a material having suitable properties has been obtained, especially under test conditions, relatively quickly with a material exhibiting a viscosity value of at least about 10 ⁴ cP, i.e. a solution with sufficient viscosity to block the flow of water. The material which can be formed was obtained. Moreover, under test conditions, for materials that exhibit viscosity values of less than about 10 ³ cP, the reduced viscosity of these solutions entails an undesirable increase in blocking time and blocking distance in the test test.

Example 7

Mechanical properties of the material

Mechanical properties of water soluble polymer materials (vinyl alcohol / vinyl acetate copolymers sold under the name Mowiol by Hoechst) which can be used in cables according to the invention and conventional materials used in cables (high density polyethylene-HDPE and polybutylene terephthalate) The comparison between the corresponding properties of the -PBT) is given in the table below. The value of VA-Vac copolymer refers to the trademarked Mowiol 23/88 copolymer containing 18-20% (w / w) of pentaerythritol and 3-5% (w / w) of glycerin. In the case of the VA-Vac copolymer, the measurements of the mechanical properties were for buffer tubes placed at 0%, 10% and 30% relative humidity (RH), respectively. 0% RH was possible by leaving the test pieces at 60 ° C. in an oven under vacuum overnight. 10% and 30% RH were possible by placing the sample at room temperature at the respective RH value during the migration.

Mechanical properties are determined for materials extruded into a buffer tube (approximately 2.5 mm in outer diameter, about 1.8 mm in inner diameter and about 60 mm in length of the test piece), according to the following procedures, using an Ins. Measurements were made using an Instron model number 4501 dynamometer. Two metal rods (approximately 20 mm long) were inserted at each end of the tube to prevent the tube from breaking between the stationary grips. Then both ends of the tube were inserted into the stationary grip, with the grips having an initial distance of 25 mm. The grips were then separated from each other at a rate of 25 mm / minute. Tensile modulus was measured using an Instron Series ® Materials Testing System software.

Mechanical properties T.S. [MPa] E.B. [%] Coefficient E [MPa] HDPE (DGDK 3364) 19 580 350 PBT (Huls) 40 290 750 PVA 0% RH 67 120 1300 PVA 10% RH 60 150 720 PVA 30% RH 67 170 250

(T.S. = tensile strength, E.B. = elongation at break)

As shown in Table 6 above, the mechanical properties of the PVA are comparable to those of conventional materials used to make structural elements of the optical cable. Changes in mechanical properties that vary with exposure to different values of RH are within acceptable limits. In particular, since it is desirable to dry the material before it is extruded, the 0% RH condition generally corresponds to the RH humidity exposed during and after the material is extruded. If the water soluble material is coextruded with the outer layer of the conventional material, the outer layer will act as an obstacle to the outer RH and thus the mechanical properties of the material will remain unchanged for a relatively long period of time. On the other hand, the mechanical properties measured at 10% RH generally correspond to the mechanical properties of the extruded material exposed to circulating air (25 ° C., 40% RH) for about one week, the period of time being a normal buffer tube before being inserted into the cable structure. Is the maximum storage period. When a structural element made of or containing water expandable material is installed in the cable structure, the obstacle effect of the structure of the cable enclosed towards the external RH will almost limit the change in the mechanical properties of the material. In any case, it is necessary that the material possess mechanical properties comparable to those of conventional materials, especially when there is a possibility that the cable will be stressed and damaged during the manufacturing steps of the cable and during the laying process of the cable. You must be careful.

Included in the above.

Claims (29)

In a fiber optic cable comprising a longitudinal cavity extending along a length of a cable, at least one optical fiber received within the longitudinal cavity and a solid compact element connected to the cavity, the solid compact element is formed by accidental penetration of water into the cable. And a water-soluble polymer material capable of forming an aqueous solution having a predetermined viscosity to block water flow within 10 meters of the penetration point. The method of claim 1, Wherein said solid compact element comprises at least about 30% by weight of said water soluble polymeric material. The method of claim 1, And wherein said solid compact element comprises at least about 50% by weight of said water soluble polymeric material. The method of claim 1, And wherein said solid compact element comprises at least about 75% by weight of said water soluble polymer material. The method of claim 1, Wherein said solid compact element is a structural element of a cable that can be protected including at least one optical fiber disposed within said longitudinal cavity. The method of claim 5, Wherein said structural element is a tubular element and said longitudinal cavity is defined by an interior volume of said tubular element. The method of claim 6, Wherein said tubular element comprises a two-layered wall of an inner layer made of said water soluble solid material and an outer layer made of a polymeric material insoluble in conventional water. The method of claim 7, wherein Wherein the tubular element comprises a third outer layer made of a water soluble solid polymer material. The method of claim 6, And said tubular element is made of a single sheath of said water soluble material. The method of claim 5, Wherein the structural element, which may include at least one optical fiber, is a grooved core comprising at least one groove longitudinally installed on an outer surface of the core, wherein the longitudinal cavity is defined by an internal volume within the groove. The method of claim 10, At least the walls of the grooves are made of a water soluble solid polymer material. The method of claim 10, Wherein said grooved core is completely made of said water soluble solid polymer material. The method of claim 1, And said solid compact element made of water-soluble polymer material is a tape. The method of claim 1, And the water soluble polymer material has a water solubility of at least about 100 g / l. The method of claim 1, Said aqueous solution having a viscosity of at least about 10 ⁴ cP at 20 ° C. The method of claim 14, Wherein said aqueous solution comprises from about 100 g / l to about 250 g / l of water soluble polymer material. In an optical cable comprising at least one sheath of a polymeric material arranged to form a cavity and at least one solid element of a water soluble material arranged within the sheath, the relative inside the cavity if the relative humidity outside the cavity is at least about 75%. And humidity is maintained at about 75% or less for a predetermined time. In an optical cable comprising a cavity and a solid compact element connected to the cavity, the solid compact element comprises a water soluble polymer material, and when the relative humidity is generally less than or equal to about 80%, the water soluble polymer material is saturated. And absorbs less than about 25% of the amount of water that can be absorbed by the water-soluble solid material. In the cable according to any of the preceding claims, Wherein said water soluble polymer material is a water expandable material. In the cable according to any of the preceding claims, The water-soluble material is selected from polyacrylamide, modified polyvinyl alcohol, vinyl alcohol / vinyl acetate copolymer, polyvinylpyrrolidone and mixtures thereof. The method of claim 20, Wherein said water soluble material is a vinyl alcohol / vinyl acetate copolymer obtainable by partial hydrolysis of acetate groups of a polyvinyl acetate homopolymer. The method of claim 21, Wherein the degree of hydrolysis of the acetate groups of the polyvinyl acetate homopolymer is between about 50% and about 95%. The method of claim 21, And wherein said vinyl alcohol / vinyl acetate copolymer has a viscosity index greater than about five. The method according to any of the preceding claims, Wherein the water soluble polymer material has a fracture load greater than about 15 Mpa and an elastic modulus greater than about 200 Mpa. The method of claim 1, And the ratio between the cross section of the cavity and the peripheral length of the water soluble element upon contact of the cavity with the water soluble element is less than about 0.5 mm. The method of claim 25, When the water-soluble polymer forms an aqueous solution having a viscosity of about 10 ⁴ cP when in contact with water, the ratio is less than about 0.4 mm. The method of claim 1, Wherein the cross section of the solid element made of water-soluble material is at least about 10% of the free cross section of the cavity to which the element is connected. The method of claim 1, Wherein the cross section of the solid element made of water-soluble material is at least about 20% of the free cross section of the cavity to which the element is connected. The method of claim 1, The cross section of the solid element made of water-soluble material is at least about 40% of the free cross section of the cavity to which the element is connected.