WO2001021706A1 - Extrusible thermoplastic material and fibre micromodule made from same - Google Patents

Abstract

The invention concerns a material for forming thin films. It consists of a composition containing an olefin polymer and a filler ratio ranging between 25 and 65 wt.% of the composition, said material in undivided state having a tensile strength ranging between 6 and 20 Mpa and an elongation at break ranging between 50 and 300 %.

Description

 EXTRUDABLE THERMOPLASTIC MATERIAL AND FIBER MICROMODULE MANUFACTURED FROM SUCH A MATERIAL

The present invention relates to an extrudable material making it possible to form thin films, comprising an olefinic polymer. The invention finds a particularly important, although not exclusive, application in the constitution of sheaths of sheathed optical fiber micromodules incorporable in a cable such as that described in document EP-A-0 468 878 to which reference may be made.

For a certain number of applications, and in particular for the constitution of micromodules having a bundle of optical fibers sheathed in mutual contact, enclosed with a sealing gel in an extruded support envelope, it is desirable to fulfill conditions which are in some contradictory measure. For example, we often look for both, especially in the case of the creation of micromodules:

- aptitude for extrusion in thin film (if possible around 0.1 mm),

- the compatibility of the material with the usual sealing gels,

- sufficient strength of the material in the form of a thin film, to allow handling during subsequent operations without risk of tearing,

the absence of bonding of the sheathing film of the micromodule on the fibers, during the heating which takes place due to the installation of the outer envelope of thermoplastic material,

- maintaining a correct cylindricity during the manufacture of the micromodule and the assembly of the micromodules to form a cable,

- a reduced shrinkage during the extrusion of the sheath to constitute the micromodule, and during cooling, this to avoid stresses on the optical fibers,

- easy coloring of the material, making it possible to identify the micromodules,

- limited extensibility making it possible to easily strip a micromodule in order to prepare the ends for joining the fibers,

- finally, high resistance to chemicals used during operations carried out on cables, for example cleaning solvent. In the case of the manufacture of optical fiber cables, some of the above characteristics are essential, in particular the mechanical strength, including during thermal aging, and the compatibility with the sealing gels and the cleaning solvents used to remove frost and dirt before connecting the optical fibers to a connector. However, the mechanical strength is unfavorable to the convenience of use, since a resistant sheathing film having a large elongation before rupture hinders the stripping of the micromodules to release the terminal parts of the fibers.

There is already known (GB - A - 2 110 696) an electrical insulating material comprising an alloy of at least partially crosslinked polymers, in particular containing an EVA (ethyl alkyl acetate) copolymer with more than 40% vinyl acetate, with inorganic fillers at a content sufficient to make the material flame retardant. Crosslinking is intended to allow a high charge rate.

The present invention aims in particular to provide an extrudable material in thin film representing a satisfactory compromise between the different results to be achieved. The invention notably proposes for this purpose a thin film extrudable material, consisting of a composition containing at least one (possibly several) practically non-crosslinked thermoplastic olefin polymer and a content of fillers of between 25 to 65% by weight of the composition, said material in the undivided state having a tensile strength of between 6 and 20 Mpa and an elongation at break of between 50 and 300%.

The term "practically non-crosslinked" will be understood to mean a polymer presented on the market as such, consequently having no appreciable degree of crosslinking and containing no crosslinking agent such as peroxides, except in the state of trace.

Thanks to the absence of crosslinking, the presence of “gels”, which is very harmful during a thin extrusion, is avoided, and post-extrusion shrinkage is reduced, which causes stress on the fibers.

The shore hardness of the material is advantageously between 35 and 55 D. The choice of a Shore D hardness exceeding 35 makes it possible, when the material is used to form a micromodule sheath, to ensure satisfactory cylindricity and to avoid the so-called "straw" effect, formed by the formation of a brutal bend during the flexions necessary for making the connections. Thanks to the limited elongation at break, due in particular to the presence of fillers, the strippability is sufficient so as not to require the use of special tools. The above minimum characteristics, in particular the tensile strength and the elongation at break, avoid excessive brittleness of the material during handling. In particular, these minima allow manipulation during the manufacture of a cable or connections without excessive risk of damage.

The minimum filler content indicated above makes it possible to reduce the expansion and retraction of the materials during temperature variations which occur during the manufacture of a cable. The presence of a sufficient content of fillers makes it possible to avoid the risk of bonding of the micromodules to each other, on sheathed fibers or on an external envelope.

The fillers will generally be mineral. It is possible in particular to use alumina (hydrated or not), chalk, kaolin, talc, silica, magnesium hydroxide and their mixtures. All these loads reduce the elongation at break and the expansion or retraction during temperature variations. In addition, they increase the thermal inertia and the heat capacity. The maximum level of fillers envisaged above makes it possible to maintain the viscosity at a level compatible with thin film extrusion.

The olefin polymers which can be used are substantially the same as those commonly used at present. In particular, the following products can be mentioned:

- PE: polyethylenes

- PP: polypropylenes

- EPR: Ethylene Propylene Rubber - EPDM: Ethylene propylene Diene Monomer

- EVA: ethylene-lower alkyl acetate copolymers (in particular vinyl acetate)

- EBA: ethylene copolymers - lower alkyl acrylate

- EEA: Ethylene Ethyl Acrylate

- EMA: Ethylene Methyl Acrylate - VLDPE: Very Low Density Polyethylene (very low density polyethylene)

- grafted polymers of acrylic acid or maleic anhydride

- PVC: polyvinyl chloride

- their mixtures and co-polymers. The different polymers are not fully equivalent to each other Often a mixture of olefin polymers will be used, one of the components of which is PE or PP and the other chosen from the other polymers mentioned above.

If the second polymer is EVA, a compound having no more than 30% of vinyl acetate co-monomer will be used in order to maintain sufficient hardness and mechanical characteristics. EBA, EEA or EMA have properties close to EVA. EPR and

EPDM will be used with sufficiently high levels of ethylene to prevent them from having properties that approximate those of an elastomer.

When using a polymer consisting on the one hand of PE or PP and on the other hand of an EVA copolymer, a composition having 40% to 80% EVA will advantageously be used.

The extrudable material will generally additionally contain plasticizers of low content, not exceeding a few percent by weight, such as aliphatic oils or phthalates (for example di-octyl or didecyl phthalate), adipates, trimellitates , etc.

Protective products against heat or ultraviolet rays are incorporated when exposure or solar radiation is to be feared.

In certain cases, one or more silanes or aminosilanes will be added, such as:

- vinyl trimethoxysilane - amino propylsilane

- amino trimethoxysilane

If a trialkoxy silane is used, it will be desirable not to go beyond a compound having more than five carbon atoms.

The silanes strengthen the bond between the fillers and the polymer. In the absence of crosslinking agent, the silane does not risk causing crosslinking which, moreover, would not be possible if the material were used to form optical fiber sheaths, the temperatures required for crosslinking not being then not reached during extrusion.

The invention also provides an optical fiber micromodule comprising a bundle of optical fibers and a sheath surrounding the bundle in a thin film of an extrudable material, characterized in that the sheath is made up of a composition containing a thermoplastic olefin polymer and a charge rate between 25 to 65% by weight of the composition, said material in the undivided state having a tensile strength of between 6 and 20 Mpa and an elongation at break of between 50 and 300%.

We will now give, by way of example, the properties of several materials in accordance with the invention, at the same time as a comparison with a control material conventionally used to date for constituting a micromodule sheath.

The following description refers to the single figure which shows a micromodule in a deformed state which it is likely to take when it is pressed against other micromodules by an external envelope.

The micromodule comprises several individually sheathed optical fibers 10 contained in a sheath 12 which must be easily tearable to allow the stripping of the ends of the fibers for connections. This sheath 12 is generally formed by extrusion on the bundle of optical fibers 10 during the drawing of the latter and then takes an approximately circular shape when the bundle of fibers itself has a periphery whose shape does not deviate too much from the circle. circumscribed. The sheath encloses the fibers and is indeed applied against them. Inside a cable, the pressure of the micromodules against each other can deform their cross-section and cause it, for example, to that illustrated.

The control material consists of polyethylene having a nominal density of 0.92 and a "melt flow index" of 0.3 g / 10 min at 190 ° C, under a pressure of 21.6 N. This material was used to form the sheath of a micromodule, by extrusion on a bundle of four optical fibers. The sheath 12 formed had a diameter of 1 mm and a thickness of 0.12 mm. Extrusion is done without difficulty and the sheath obtained is well cylindrical. But during the constitution of the cable, by extrusion of an external envelope based on polyethylene, the heat necessary for the extrusion of the envelope deforms the micromodules and the sheaths tend to stick together and to stick to the envelope exterior, imposing special precautions, such as interposing one or more separating tapes between the micromodules and the envelope.

These difficulties are eliminated during the use of a material according to the invention. Example 1:

In a mixer, a composition was prepared comprising, by weight:

- 50 parts of density 0.92 polyethylene having a Melt Flow Index at 190 ° C, under 21.6 N, of 1.8 g / 10 min - 50 parts of EVA copolymer contain 18% vinyl acetate - 130 parts of hydrate alumina

- 5 parts of lubricant (paraffinic oil)

- 5 parts of additives (antioxidants, silane, lubricant)

The ingredients are mixed for 10 minutes, up to 160 ° C. After calendering on a roller mixer, the material is cut, then molded at 180 ° C under pressure, in the form of plates making it possible to carry out measurements characterizing the material.

The mechanical characteristics obtained on the plates are as follows: Breaking strength = 11.4 Mpa Elongation at break = 125% Hardness = 45 Shore D

The composition was used to form micromodules. For this, it was put in the form of granules which are introduced into an extruder 45 mm in diameter, and 24 diameters in length. Extrusion temperatures are between 130 and 165 ° C, from the feed hopper to the extrusion head.

To characterize the sheath obtained, two operations were carried out.

The first was a shaping at a speed of 100m / min, to obtain a tube of 0.90 mm in external diameter, and 0.12 mm in radial thickness. For the second, the shaping was identical except that we introduce through the head of the extruder 4 colored optical fibers, and that we simultaneously inject a sealing gel to form a module which, after cooling of the extruded material, is collected in a tank where it freely winds up flat.

The characteristics obtained on the sheaths are as follows:

RT = Tensile strength, expressed in Newton AR = Elongation at break, expressed in% Va = Variation

These results indicate on the one hand the good thermal resistance, and on the other hand the good compatibility with the filling materials of the sheaths of the material according to the invention.

Example 2

The composition of the material is identical to Example 1, except that the filler based on hydrated alumina is replaced by a filler based on calcium carbonate. The mixing is carried out under the same conditions, and a micromodule with a diameter of 0.85 mm and a thickness of 0.11 mm is extruded at 100 m / min. The characteristics below show how modules with a correct chemical resistance are obtained with such a formulation, despite the small thickness of the sheath of the module.

Initial characteristics RT = 3.9N AR = 155%

After one hour in ethanol at 20 ° C Var RT = 1% Var AR = 3%

After one hour in isopropanol at 20 ° C Var RT = 5% Var AR = 3%

Example 3

A formulation identical to Example 1 is produced, except that the alumina-based filler is replaced by a kaolinic filler, and its concentration lowered to 65 parts. The paraffinic plasticizer is replaced by an oil of isononyl adipate type. The various ingredients are introduced in an internal mixer, mixed up to approximately 160 ° C., and granules. The characteristics of the material on the plate are as follows:

Initial mechanical characteristics Tensile strength RT = 10.5 Mpa AR = 157% Elongation at break

Aging 10 days at 70 ° C Var RT = + 1% Var AR = -13%

Aging 42 days at 80 ° C Var RT = + 7% Var AR = -19%

Compatibility with Macroplast CF 300 jelly Var RT = -15% Var AR = -18% 10 days at 70 ° C Mass variation ^: = 7%

Moist heat resistance 42 days at 40 ° C and 93% RH Var RT = -4% Var AR = + 2%

Immersion in kerdane 24 hours at 20 ° C Var RT = - 25% Var AR = -10%

Immersion in ethanol for 1 hour at 20 ° C Var RT = -4% Var AR = -10%

Immersion in isopropanol 1 hour at 20 ° C Var RT = -6% Var AR = -4%

Immersion in isopropanol 1 hour at 20 ° C Var RT = -4% VarAR = -10%

Hardness 45 Shore D From this formulation, a micromodule with four optical fibers with a sheath 0.11 mm thick is produced under the same conditions as above.

0.85 mm in diameter. The sealing gel is the "Macroplast CF 300" of the company

Henkel.

The characteristics obtained on the module are as follows:

Claims

1. Extrudable material making it possible to form thin films, comprising at least one olefinic polymer, characterized in that it consists of a composition containing at least one practically non-crosslinked thermoplastic olefin polymer and a content of fillers of between 25 to 65% by weight of the composition, said material in the undivided state having a tensile strength of between 6 and 20 Mpa and an elongation at break of between 50 and 300%. 2. Material according to claim 1, characterized in that it has a Shore D hardness between 35 and 55. 3. Material according to claim 1 or 2, characterized in that the polymer is chosen from the group consisting of: - PE: polyethylenes - PP: polypropylenes - EPR: Ethylene Propylene Rubber - EPDM: Ethylene propylene Diene Monomer - EVA: ethylene-lower alkyl acetate copolymers (in particular vinyl acetate) - EBA: ethylene copolymers - lower alkyl acrylate - EEA: Ethylene Ethyl Acrylate - EMA: Ethylene Methyl Acrylate - VLDPE: Very Low Density Polyethylene (very low density polyethylene) - grafted polymers of acrylic acid or maleic anhydride - PVC: polyvinyl chloride, their blends and co-polymers. 4. Material according to claim 1, 2 or 3, characterized in that the fillers are chosen from the group consisting of alumina (hydrated or not), chalk, kaolin, talc, silica, hydroxide of magnesia, and mixtures thereof. 5. Material according to any one of the preceding claims, characterized in that the polymer is a mixture of olefin polymers, one of the components is PE or PP and the other chosen from EVA at most 30% of vinyl acetate co-monomer. EBA, EEA or EMA, optionally in addition to a lubricant and additives. 6. Material according to any one of the preceding claims, characterized in that it comprises, in addition optionally a lubricant and additives other than crosslinking agents: - 50 parts of density 0.92 polyethylene having a Melt Flow Index at 190 ° C, under 21.6 N, of 1.8 g / 10 min - 50 parts of EVA copolymer containing 18% vinyl acetate 130 parts of hydrate d alumina 7. Material according to any one of claims 1 to 4, characterized in that it comprises, in addition to a lubricant and additives: 50 parts of polyethylene of density 0.92 having a Melt Flow Index at 190 ° C, under 21.6 N, 1.8g / 10 min 50 parts of EVA copolymer containing 18% vinyl acetate 130 parts of calcium carbonate. 8. Material according to any one of claims 1 to 4, characterized in that it comprises, in addition to a lubricant and additives: 50 parts of 0.92 density polyethylene having a Melt Flow Index at 190 ° C, under 21.6 N, of 1.8g / 10 min - 50 parts of EVA copolymer containing 18% vinyl acetate - 65 parts of kaolin. 9. Material according to any one of claims 1 to 7, containing one or more silanes or aminosilanes. 10. Micromodule of optical fibers comprising a bundle of optical fibers and a sheath surrounding the bundle in a thin film of an extrudable material, characterized in that the sheath is made up of a composition containing a thermoplastic olefin polymer and a content of fillers between 25 to 65% in weight of the composition, said material in the undivided state having a tensile strength of between 6 and 20 Mpa and an elongation at break of between 50 and 300%.