CA2384842A1 - 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
MADE FROM SUCH MATERIAL
s The present invention relates to an extrudable material for constitute thin films, comprising a polymer olefinic.
The invention finds a particularly important application, although not exclusive, in the constitution of sheaths of sheathed optical fiber micromodules can be incorporated in a cable such as that described in document EP-A-0 468 io to which we can refer.
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 holding envelope, it East desirable to meet conditions which are to some extent is contradictory. For example, we often look for both, in the case of constitution 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 resistance of the material in the form of a thin film, in order to 2o allow handling during subsequent operations without risk of tear, - the absence of sticking of the sheath film of the micromodule on the fibers, during the heating which occurs due to the installation of the outer envelope in thermoplastic material, - maintaining correct cylindricity during the manufacture of the micromodule and 2s the assembly of the micromodules to constitute a cable, - a reduced shrinkage during the extrusion of the sheath to constitute the micromodule, and during cooling, this to avoid stresses on the fibers optical, - easy coloring of the material, making it possible to identify the micromodules, - limited extensibility allowing to easily strip a micromodule in order to 3o prepare the ends to connect the fibers, - finally, high resistance to chemicals used during operations performed on cables, for example with cleaning solvent.

2 In the case of fiber optic cable manufacturing, some of the above features are essential including strength mechanical, y understood during thermal aging, and compatibility with gels sealing and cleaning solvents used to remove frost and dirt before performing s the connection of optical fibers to a connector. But the resistance mechanical is unfavorable to the convenience of use, because a resistant sheathing film and having a large elongation before rupture hinders the stripping of the micromodules for release the terminal parts of the fibers.
There is already known (GB - A - 2 110 696) an electrical insulating material comprising io an alloy of at least partially crosslinked polymers, containing notably a EVA (ethyl alkyl acetate) copolymer with more than 40% vinyl acetate, with of inorganic fillers of sufficient content to make the material flame retardant.
The crosslinking is intended to allow a high charge rate.
The present invention aims in particular to provide an extrudable material is thin film representing a satisfactory compromise between different ies results to achieve. The invention proposes in particular for this purpose an extrudable material in thin film, consisting of a composition containing at least one (eventually several) substantially uncrosslinked thermoplastic olefin polymer and a rate fillers between 25 to 65% by weight of the composition, said material the state no 2o divided having a tensile strength between 6 and 20 Mpa and a elongation at break between 50 and 300%.
The term “practically non-crosslinked” will be understood to mean a polymer presented in the trade as such, consequently having no appreciable rate of crosslinking and not containing a crosslinking agent such as peroxides, except 2s the trace state.
Thanks to the absence of crosslinking, the presence of "gels" is avoided, very harmful during thin thickness extrusion, and shrinkage is reduced post-extrusion, which causes stress on the fibers.
The shore hardness of the material is advantageously between 35 and 55 D.
3o The choice of a Shore D hardness exceeding 35 allows, when using the material to constitute a micromodule sheath, to ensure a cylindricity satisfactory and to avoid the so-called "straw" effect, formed by the formation of an elbow brutal during the bending necessary to make the connections.

3 Thanks to the limited elongation at break, due in particular to the presence of charges, the strippability is sufficient to not require the use of tools special. The above minimum characteristics, including resistance to the tensile and elongation at break, avoid excessive brittleness of the material when s manipulation. In particular, these minima allow manipulations when manufacture of a cable or connections without excessive risk of damage.
The minimum filler content indicated above makes it possible to reduce the dilation and the shrinking of materials during temperature variations which intervene during the manufacture of a cable. The presence of a sufficient content of fillers allows 1o to avoid the risk of micromodules sticking together, on fibers sheathed or on an external envelope.
The fillers will generally be mineral. We can especially use alumina (hydrated or not), chalk, kaolin, talc, silica, hydroxide of magnesia and their mixtures. All these loads reduce the elongation at break and the expansion or retraction during temperature variations. In addition, they increase thermal inertia and heat capacity. The maximum rate of charges considered above makes it possible to maintain the viscosity at a compatible level with thin film extrusion.
The olefin polymers that can be used are substantially the same as those 2o commonly used at present. In particular, we can cite the products following - PE: polyethylenes - PP: polypropylenes - EPR: Ethylene Propylene Rubber 2s - EPDM: Ethylene propylene Diene Monomer - EVA: ethylene-lower alkyl acetate copolymers (especially acetate of vinyl) - EBA: ethylene copolymers - lower alkyl acrylate - EEA: Ethylene Ethyl Acrylate - EMA: Ethylene Methyl Acrylate 30 - 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.

4 Different polymers are not fully equivalent to each other Often a mixture of olefin polymers will be used, one of which components 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 s 30% of vinyl acetate co-monomer in order to maintain hardness and features sufficient mechanical. EBA, EEA or EMA have properties close to EVA. EPR
and EPDM will be used with ethylene levels high enough to avoid that they have properties that approximate those of an elastomer.
When using a polymer consisting on the one hand of PE or PP, on the other hand of io EVA copolymer, a composition having 40% is advantageously used at 80% of EVA.
The extrudable material will generally additionally include plasticizers to low content, not exceeding a few percent by weight, such as oils aliphatics or phthalates (e.g. di-octyl phthalate or didecyle), is adipates, trimellitates, etc.
Heat or ultraviolet protection products are incorporated when exposure or solar radiation is to be feared.
In some cases, add one or more silanes or aminosilanes, such as - vinyl trimethoxysilane 20 - amino propylsilane - amino trimethoxysilane If a trialkoxy silane is used, it will be desirable not to go beyond of a compound having more than five carbon atoms.
The silanes strengthen the bond between the fillers and the polymer.
2s In the absence of crosslinking agent, the silane is not likely to cause a crosslinking which, moreover, would not be possible if the material for constitute optical fiber sheaths, the temperatures required for reluctance then not being reached during extrusion.
The invention also provides a fiber optic micromodule comprising 3o a bundle of optical fibers and a sheath surrounding the bundle in one 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 charges between 25 to 65% by weight of the composition, said material in the state not divided s having a tensile strength between 6 and 20 Mpa and a elongation at failure between 50 and 300%.
We will now give, by way of example, the properties of several materials according to the invention, together with a comparison with a material witness s conventionally used to date to constitute a micromodule sheath.
The following description refers to the single figure which shows a micromodule in a deformed state that it is likely to take when is in a hurry against other micromodules by an external envelope.
The micromodule comprises several optical fibers 10 individually io sheathed contained in a sheath 12 which must be easily tearable for allow the stripping of the ends of the fibers for connections. This sheath 12 is generally formed by extrusion on the fiber bundle optics 10 at of the printing of these latter and then takes an approximate form circular when the fiber bundle itself has a perimeter whose shape does not deviates 1s not too much from the circumscribed circle. The sheath grips the fibers and is applied indeed against they. Inside a cable, the pressure of the micromodules against each other others can distort their section and bring it for example to the one that is illustrated.
The control material consists of polyethylene having a density nominal of 0.92 and a melt flow index of 0.3 g 110 min at 190 ° C, under a pressure of 20 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 constituted had a 1 mm diameter and 0.12 mm thickness. The extrusion is done without difficulty and the sheath obtained is well cylindrical. But during the constitution of the cable, by extrusion a polyethylene-based outer jacket, the heat needed to extrusion of 2s the envelope deforms the micromodules and the sheaths tend to stick together and to stick to the outer casing, imposing special precautions, like example the interposition of one or more separating tapes between the micromodules and the envelope.
These difficulties are eliminated when using a conforming material at 30 the invention.

Example 1 In a mixer, a composition was prepared comprising, by weight - 50 parts of 0.92 density polyethylene having a Melt Flow Index at 190 ° C, under 21.6 N, 1.8gI10 min s - 50 parts of EVA copolymer contain 18% vinyl acetate - 130 parts of alumina hydrate

- 5 parts of lubricant (paraffinic oil) - 5 parts of additives (antioxidants, silane, lubricant) The ingredients are mixed for 10 minutes, up to 160 ° C.
io After calendering on a roller mixer, the material is cut, then molded at 180 ° C under pressure, in the form of plates allowing to perform measures characterizing the material.
The mechanical characteristics obtained on the plates are as follows Breaking strength = 11.4 Mpa is Elongation at break = 125 Hardness = 45 Shore D
The composition was used to form micromodules. For that, we the granules which are introduced into a 45 mm extruder of diameter, and 24 diameters in length.
2o Extrusion temperatures are between 130 and 165 ° C, since the feed hopper, up to the extrusion head.
To characterize the sheath obtained, two operations were carried out.
The first one was a shaping at a speed of 100mlmin, to obtain a tube of 0.90 mm external diameter, and 0.12 mm radial thickness.
2s For the second, the formatting was identical except that we introduced to through the head of the extruder 4 colored optical fibers, which we inject simultaneously a sealing gel to form a module which, after cooling of the matter extruded, is collected in a tank where it freely wraps flat.
The characteristics obtained on the sheaths are as follows:
Module without gel Module with gel seal Initial characteristics RT = 4.5N AR = 138 RT = 4.6N AR = 112 %

WO 01/2170

6 PCT / FR00 / 02545

7 Winding on Correct Correct 6D chuck After 10 days 70C VaRT = 19% VarAR VarRT = 13% VarAR
= 15% = 13%

After 10 days 70C VarRT = 17% VarAR VarRT = 9% VarAR
= 20% = 11 + 42 days 80C

RT = Resistance to i raction, expnmee in wewton AR = Elongation at break, expressed in Va = Variation These results indicate on the one hand the good thermal resistance, and on the other go s good compatibility with the filling materials of the ducts of the material according to the invention.
Example 2 The composition of the material is identical to Example 1, except that the charge to io hydrated alumina base is replaced by a carbonate-based filler calcium. The mixture is produced under the same conditions, and is extruded to 100mlmin a micromodule with a diameter of 0.85 mm, and a thickness of 0.11 mm. The characteristics below show how we obtain with such a formulation of the modules having a correct chemical resistance, despite the small thickness of the sheath of is module.
Initial characteristics RT = 3.9N AR = 155 After one hour in ethanol Var RT = Var AR = 3 20C 1%

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

Example 3 We carry out a formulation identical to Example 1, except that the charge based 2o of alumina is replaced by a kaolinic filler, and its concentration lowered to 65 parts. The paraffinic plasticizer is replaced by an adipate type oil of isononyle.

8 The different ingredients are introduced in an internal mixer, mixed until about 160 ° C, and granules. The characteristics of the material on the plate are the following Initial mechanical characteristics Tensile strength RT = 10.5 AR = 157 Elongation at break Mpa Aging 10 days 70C Var RT = + Var AR = -13%
1%

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

Compatibility with MacroplastVar RT gel = -15%
CF 300 Var AR =
70C days -18%
Variation mass = 7%

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

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

Immersion in ethanol 1 hour Var RT = -4% Var AR = -10%

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

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

Duret 45 Shore D

9 From this formulation, we carry out under the same conditions as previously a micromodule with four optical fibers with a 0.11 mm thick sheath and 0.85 mm in diameter. The sealing gel is the "Macroplast CF 300" from the society Henkel.
s The characteristics obtained on the module are as follows Initial CM RT = 2.4 N AR = 105%

Variations CM after Var RT = 5% Var AR = 4%

70C days Variations CM after 10 days Var RT = 0 Var AR = 6%

in Macroplast CF 300 Variations CM after 42 days Var RT = 2% Var AR = 5%

Variations CM after 10 days Var RT = - 21 Var AR = - 6%
70C%

in CF 300, and 42 days Variations CM after 42 days Var RT = 5.4% Var AR = 0 40C and 93% RH

CM variations after 24h in Var RT = 11% Var = 25%
kerdane Variations after 24 hours Var RT = 8% Var AR = 12%
in fthanol Variations after 24 hours Var RT = 4% Var AR = 13%
in isopropanol io

Claims (10)

1. Extrudable material for forming films of low thickness, comprising at least one olefinic polymer, characterized in that it consists of a composition containing at least one olefinic polymer virtually non-crosslinked thermoplastic and a filler content of between 25 to 65 % by weight of the composition, said material in the undivided state having a resistance to tensile strength between 6 and 20 MPa and elongation at break included 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 selected from the group consisting of:
- PE: polyethylenes - PP: polypropylene - EPR: Ethylene Propylene Rubber - EPDM: Ethylene Propylene Diene Monomer - EVA: ethylene-lower alkyl acetate copolymers (in particular acetate vjnyl) - EBA: ethylene copolymers - lower alkyl acrylate - EEA: Ethylene Ethyl Acrylate - EMA: Ethylene Methyl Acrylate - VLDPE: Very Low Density Polyethylene (very low density polyethylene) - polymers grafted with acrylic acid or maleic anhydride - PVC: polyvinyl chloride their mixtures and co-polymers. 4. Material according to claim 1, 2 or 3, characterized in that the fillers are selected from the group consisting of alumina (hydrated or no), the chalk, kaolin, talc, silica, hydroxide of magnesia, and their mixtures. 5. Material according to any one of the preceding claims, characterized in that the polymer is a mixture of olefinic polymers of which one of the components is PE or PP and the other selected from EVA with a maximum of 30% co-monomer vinyl acetate. EBA, EEA or EMA, possibly in addition to a lubricant and of additives. 6. Material according to any one of the preceding claims, characterized in that it comprises, optionally in addition to a lubricant and additives others than crosslinking agents:
- 50 parts of polyethylene with a density of 0.92 having a Melt Flow Index of 190°C, under 21.6 N, 1.8g/10 mins - 50 parts EVA copolymer containing 18% vinyl acetate 130 parts alumina hydrate 7. Material according to any one of claims 1 to 4, characterized in this that it contains, in addition to a lubricant and additives:
50 parts of polyethylene with a density of 0.92 having a Melt Flow Index of 190°C, under 21.6 N, 1.8g/10 mins 50 parts EVA copolymer containing 18% vinyl acetate 130 parts of calcium carbonate. 8. Material according to any one of claims 1 to 4, characterized in this that it contains, in addition to a lubricant and additives:
50 parts of polyethylene with a density of 0.92 having a Melt Flow Index of 190°C, under 21.6 N, 1.8g/10 mins - 50 parts EVA copolymer containing 18% vinyl acetate - 65 parts of kaolin. 9. Material according to any one of claims 1 to 7, containing one or silanes or aminosilanes. 10. Fiber optic micromodule including fiber optic bundle and an sheath surrounding the bundle in a thin film of an extrudable material, characterized in that the sheath is made of a composition containing a thermoplastic olefinic polymer and a filler content of between 25 and 65% in weight of the composition, said material in the undivided state having a resistance to tensile between 6 and 20 Mpa and an elongation at break included between 50 and 300%.