WO2008101811A1 - Material comprising two improved adhesion layers - Google Patents

Abstract

The invention relates to a material including a first cross-linkable layer comprising an elastomer polymer matrix, and a second cross-linkable layer comprising a silicone compound, the first layer being in direct contact with the second layer, characterised in that the first layer includes at least 5 pcr of a silicone gum for 100 parts in weight of the elastomer polymer matrix, preferably at least 10 pcr.

Description

 Material comprising two layers with improved adhesion

The present invention relates to a material comprising two layers with improved adhesion, as well as an energy and / or telecommunication cable comprising said material. No. 3,988,496 discloses a process for improving the adhesion between cross-linked ethylene-vinyl acetate (EVA) resins and crosslinked silicone rubbers.

The crosslinked silicone rubbers have good electrical insulating properties, while the EVA resins have among other satisfactory mechanical properties that do not have said rubbers, including a tensile strength much greater than that of said rubbers.

Silicone rubbers are inorganic compounds that can not readily adhere to organic materials such as EVA. The object of this process is to obtain a bilayer type material having satisfactory insulating and mechanical properties by improving the mode of bonding EVA resins to crosslinked silicone rubber.

To do this, the process consists in mixing an EVA resin with a silane-type binding agent. However, this material does not have sufficient adhesion properties, and thus the synergy of mechanical and insulating properties provided by the two layers is limited or non-existent.

The technical problem to be solved, by the object of the present invention, is to propose a new material comprising a first crosslinkable layer comprising an elastomeric polymer matrix and a second crosslinkable layer comprising a silicone compound, the first layer being in direct contact with the second layer.

This new material thus makes it possible to avoid the problems of the state of the art by offering in particular a greatly improved adhesion while maintaining very good mechanical properties. The solution to the technical problem lies, according to the present invention, in that the first layer comprises at least 5 phr of a silicone gum per 100 parts by weight of the elastomeric polymer matrix, preferably at least 10 phr. In the present description, the term "bilayer material" is defined to mean that the first layer is directly in contact with the second layer.

Advantageously, the bilayer material, according to the present invention, once crosslinked, has an adhesion between the first and the second layer of at least 2N / cm when the amount of silicone gum is at least 5 phr in the first layer. layer.

In a particularly advantageous way, it makes it possible to satisfy the requirements of the international standard referenced BS7629-1, in particular for the type EI5 bilayers, by having an adhesion between the first and the second layer of up to 3N / cm or more, when the amount of silicone gum is at least 10 phr in the first layer.

The silicone gums are polyorganosiloxanes having a viscosity of at least 1,000,000 mPa.s at 25 ° C.

These silicone gums are generally linear polymers, whose diorganopolysiloxane chain consists essentially of units of formula R 2 SiO.

In other words, the main linear chain of the silicone gums is inorganic, whereas the main linear chain of the silanes is organic. This inorganic chain may be blocked at each end by a unit of formula RsSio.s and / or a radical of formula R ¹ O.

In these formulas, the R symbols, which are identical or different, represent monovalent hydrocarbon radicals such as alkyl radicals, for example methyl, ethyl, propyl, octyl or octadecyl radicals; aryl radicals, for example phenyl, tolyl, xylyl; aralkyl radicals such as for example benzyl, phenylethyl; cycloalkyl and cycloalkenyl radicals such as, for example, cyclohexyl and cycloheptyl radicals, cyclohexenyl; alkenyl radicals, for example vinyl radicals, allyl; alkaryl radicals, cyanoalkyl radicals such as, for example, a cyanoethyl radical; haloalkyl, haloalkenyl and haloaryl radicals, such as, for example, chloromethyl, 3,3,3-trifluoropropyl, chlorophenyl, dibromophenyl and trifluoromethylphenyl radicals.

The symbol R 'represents a hydrogen atom, an alkyl radical having 1 to 4 carbon atoms, the betamethoxy-ethyl radical.

Preferably, at least 60% of the R groups represent methyl radicals. On the other hand, the polyorganosiloxane may also contain from 0 to 4

% by weight of vinyl groups, preferably from 0.01 to 3% by weight.

In a preferred embodiment, the silicone gum contained in the first layer has a viscosity of about 1,000,000 mPa.s at 25 ° C.

In another preferred embodiment, the first layer comprises a silicone compound based on the silicone gum according to the present invention, said silicone compound having a Mooney viscosity ML (1 +4) of about 50 MU at 30 ^° C.

In a particular embodiment, the first layer comprises at most 30 phr of the silicone gum per 100 parts by weight of the elastomeric polymer matrix, preferably at most 26 phr.

These limit values are especially preferred when the silicone gum is incorporated as such in the elastomeric polymer matrix, that is to say when the silicone gum is not diluted in a silicone compound further comprising fillers and additives. The term "elastomeric polymer matrix" generally means a reversibly deformable polymer matrix comprising at least one elastomeric polymer.

It is preferable that the first layer remains of elastomer type by virtue of said matrix in order to guarantee the material mechanical properties, as well as adhesion properties of the first layer on the second layer, sufficient for its use in cabling. According to a preferred characteristic, the elastomeric polymer matrix comprises an ethylene copolymer, the ethylene copolymer being advantageously chosen from an ethylene vinyl acetate (EVA) copolymer, an ethylene butyl acrylate (EBA) copolymer, a ethylene methyl acrylate copolymer (EMA) and a copolymer of ethylene ethyl acrylate (EEA).

Of course, said elastomeric polymer matrix may typically comprise other non-elastomeric polymers such as polyolefins.

However, the addition of these non-elastomeric polymers to the matrix must not degrade the elastomeric nature of said matrix.

According to another preferred feature, the silicone compound of the second layer has a Mooney viscosity ML (1 +4) of about 50MU at 30 ^° C.

Another object of the present invention is an energy and / or telecommunication cable comprising said material, the latter being crosslinked. Whether electrical or optical, intended for energy transmission or data transmission, a cable is schematically constituted by at least one electrical or optical conducting element extending inside at least one insulating element. .

It should be noted that at least one of the insulating elements may also act as protection means and / or that the cable may also have at least one specific protective element forming a sheath, in particular for electrical cables.

In the present invention, the bilayer material may be an insulating member or a protective sheath of said cable. In a preferred embodiment and concerning the isolation of an electrical conductor, the latter is surrounded by a crosslinked bilayer material according to the present invention, so that the second layer is surrounded by the first layer.

Generally, this step is performed by extruding the bilayer material onto the electrical conductor.

After crosslinking, the insulation obtained makes it possible to guarantee very good resistance to abrasion and tearing. Other features and advantages of the present invention will emerge in the light of the examples which follow, said examples being given by way of illustration and in no way limiting.

In order to show the advantages obtained with the bilayer materials according to the present invention, Table 1 details various compositions of the first layer comprising an elastomeric polymer matrix as well as their mechanical properties such as tensile strength and elongation at break.

The compositions referenced EVA1 to EVA3 correspond to compositions of the prior art.

The compositions referenced EVA4 to EVA7 are those relating to compositions according to the present invention.

The mechanical properties of the second layer (Siliconel) are also mentioned in Table 1.

Table 1

The origin of the different compositions of Table 1 is as follows. Siliconel corresponds to a silicone compound having a Mooney viscosity ML (1 + 4) equal to 50 MU at 30 ^° C. This silicone compound is based on silicone gum (40 to 50% by weight of the silicone compound) and comprises an organic peroxide (0.4 to 2.5% by weight of the silicone compound) as well as well-known fillers and additives of the skilled person.

EVA1 corresponds to a composition as described in the Table

2.

Table 2

The elastomeric polymer matrix is a mixture based on 65% EVA and further comprises 35% polyolefins and / or elastomers, such as for example a polyethylene octene (POE) copolymer and / or a terpolymer of ethylene propylene (EPDM).

The fillers may be inorganic fillers, in particular flame retardant fillers such as calcium hydroxide, magnesium hydroxide, aluminum trihydroxide or calcium carbonate.

The additives may be, for example, plasticizers, antioxidants, dispersants, etc.

The crosslinking agent is typically a peroxide.

EVA2 corresponds to the mixture of EVAI with 4 pcr of 3-

(glycidoxypropyl) trimethoxy silane. Said silane has a viscosity of 3.5 mPa.s and is marketed by the company Degussa under the reference

Dynasylan GLYMO.

EVA3 corresponds to the mixture of EVAI with 10 phr of a polyorganosiloxane oil. Said oil has a viscosity of 100,000 mnrvVs (about 93.00OmPa. s) and is marketed by the company Rhodia SiI icon under the reference Rhodorsil H621V100000.

- EVA4 corresponds to the mixture of EVAI with 26 phr of Siliconel.

- EVA5 corresponds to the mixture of EVAI with 130 phr of Siliconel. EVA6 corresponds to the mixture of EVAI with 10 phr of Gommel silicone gum with a viscosity of 1,000.00OmPa. s at 25 ° C.

- EVA7 corresponds to the mixture of EVAI with 26 pcr of Gommel.

The amounts mentioned above are expressed in parts by weight (phr) per 100 parts by weight of the elastomeric polymer matrix in the composition EVA1.

In addition, the viscosities mentioned in the present invention are typically determined using equipment well known to those skilled in the art such as for example a dynamic rheometer or a Mooney viscometer. To study the adhesion properties between the first and second layers, the bilayer materials were prepared as follows.

Each composition, EVA1 to EVA7, is used in a first single-screw extruder at 110 ^° C.

In parallel, the Siliconel composition is used in a second single-screw extruder at 30 ^° C.

The first and second single-screw extruders meet at a common extrusion head.

Thus, we obtain 7 bilayer ribbons corresponding to a first layer respectively of each composition EVA1 EVA7 directly in contact with a second layer of Siliconel.

The said bilayer ribbons are then crosslinked by dipping each bilayer ribbon in a bath of salt without pressure at 220 ° C. for 4 minutes and then immersing them in a cold water bath.

The crosslinking process used in the context of the invention is in no way limiting.

For example, the crosslinking can also be done in a salt bath under pressure, or on a steam line. The bilayer ribbons are then cut into rectangular plates to perform a peel test.

The peel test consists in evaluating the adhesion force using a Monsanto 2000 type extensiometer. The rectangular plates are placed between the jaws of the extensiometer, the distance between the jaws being 30 mm.

The race of the cross is stopped after 150mm of movement, the crosshead speed of said extensometer being 50mm / min.

The Newton force (N) thus obtained is measured when a stable value is reached.

Table 3 summarizes the adhesion strength results obtained by the peel test on said cross-linked bilayer materials as previously described.

Table 3

The two-layer material EVA2-Silicone1, whose EVA-based layer comprises a silane compound, does not give sufficient adhesion results since the adhesion strength obtained is less than 2N / cm.

In addition, the silane compounds can alter the mechanical properties of the bilayer materials. It is therefore preferable to limit the introduction of silane compounds into the first layer comprising the composition based on an ethylene copolymer. Silicone oils also do not give satisfactory results since the adhesion values are less than 2 N / cm.

The two-layer EVA4-Silicone1 to EVA7-Silicone1 materials, whose EVA-based layer comprises a silicone rubber, have an adhesion of at least 2 N / cm.

More particularly, the two-layer materials EVA4-Silicone1 and

EVA5-Silicone1, containing a silicone compound having a viscosity of 50 MU at 30 ^° C. remarkably exhibits an optimized adhesion up to 3.3

N / cm with an amount of 130 phr of said polyorganosiloxane, combined with very good mechanical properties.

The two-layer materials EVA6-Silicone1 and EVA7-Silicone1, containing a silicone gum of viscosity equal to 1,000,000 mPa.s at

25 ° C show significantly improved adhesion reaching

10.3 N / cm with only 26 phr of said polyorganosiloxane, combined with very good mechanical properties.

It is interesting to note that with a minimal amount of 10 phr of the same polyorganosiloxane, the adhesion between the layers of the two-layer material EVA6-Silicone1 is of the order of 3N / cm.

Thus, the two-layer material EVA6-Silicone1 has a low cost since the amount of silicone gum as such, used in the EVA-based layer, is low, EVA-based compounds being half as much expensive than silicone gums.

Finally, it may be noted that the silicone compound, referred to as Siliconel, must be added in a larger quantity than the quantity of silicone gum itself, since the silicone compound is a mixture of a silicone gum with various additives and fillers.

The amount of the silicone compound added to the first layer is therefore not representative of the amount of silicone gum within said silicone compound, the final amount of silicone gum in the first layer remaining at least equal to at 5 phr according to the present invention. In addition, the additives and fillers in the silicone compound added with the EVA can alter the quality of the interface and decrease the adhesion with the second layer.

To check the good mechanical properties of the bilayer materials according to the present invention, an aging test according to BS 7629-1, referring to BS 7655 section 5.1, is carried out on the two-layer material EVA6-Silicone1.

Table 4 shows two bilayer materials, namely Isolanti and Isolant 2, with respective different thicknesses for the second crosslinked layer, that is to say the layer of silicone compound (Siliconel).

Tensile strength and elongation at break before and after the aging test of Isolanti and Insulator2 are also detailed in Table 4.

The aging test is carried out by placing the Isolanti and Isolant2 in an air oven for 168h at a temperature of 135 ° C.

Table 4

The initial mechanical properties (PMO) of Isolanti and Isolant2 are in accordance with the specifications of the international standard BS 7629-1 which imposes a minimum of 10 MPa for tensile strength and a minimum of 125% for elongation at break. Calculated variations between the initial mechanical properties

(PMO) and the mechanical properties after the aging test (PM1) are advantageously included in the specifications of said standard, ie the variations in tensile strength and elongation at break must be within a range of more or less 30%.

The present invention is not limited to the examples of compositions which have just been described and generally relates to all bilayer materials that can be envisaged from the general indications provided in the disclosure of the invention.

Claims

1. Material comprising: a first crosslinkable layer comprising an elastomeric polymer matrix, and a second crosslinkable layer comprising a silicone compound, the first layer being in direct contact with the second layer, characterized in that the first layer comprises at least 5 phr of an eraser. of silicone per 100 parts by weight of the elastomeric polymer matrix, preferably at least 10 phr. 2. Material according to claim 1, characterized in that the silicone gum has a viscosity of about 1,000,000 mPa.s at 25 ° C. 3. Material according to claim 1, characterized in that the first layer comprises a silicone compound based on said silicone gum, said silicone compound having a Mooney viscosity ML (1 +4) of about 50 MU at 30 ^° C. 4. Material according to any one of claims 1 to 3, characterized in that the first layer comprises at most 30 phr of the silicone gum per 100 parts by weight of the elastomeric polymer matrix, preferably at most 26 phr. 5. Material according to any one of claims 1 to 4, characterized in that the elastomeric polymer matrix comprises an ethylene copolymer. 6. Material according to claim 5, characterized in that the ethylene copolymer is chosen from a copolymer of ethylene vinyl acetate (EVA), a copolymer of ethylene butyl acrylate (EBA), a copolymer ethylene methyl acrylate (EMA) and a copolymer of ethylene ethyl acrylate (EEA). 7. Material according to any one of claims 1 to 6, characterized in that the silicone compound of the second layer has a viscosity Mooney ML (1 +4) of about 50MU at 30 ^° C. 8. Power cable and / or telecommunication, characterized in that it comprises a material as defined in claims 1 to 7, said material being crosslinked.