EP2530684A1 - Cable comprising an insulating layer of non-polar material - Google Patents

Abstract

The electrically conducting cable comprises a conductor element surrounded by a first layer made of a non-polar material. The first layer is surrounded by a second layer made of ethylene and octene copolymer (50 wt.%) having a chemically reactive surface with grafted polar functions that adheres a third layer made of a polar material. Independent claims are included for: (1) a process for fabricating a cable; and (2) a junction box.

Description

The present invention relates to the field of cold adhesion of a polar material with an insulating layer of a cable made of a non-polar material.

In particular, the present invention relates to a cable having a polyolefin layer for improving the adhesion of a two-component polyurethane resin used in the junction boxes during electrical connection.

The present invention also relates to a method for manufacturing the above-mentioned cable, as well as the use of such a cable for making a sealed electrical junction box.

Polyolefins by their properties: low cost, durability, lightness etc ... are used in many consumer products and in particular for the manufacture of electrically conductive cables.

Such cables generally comprise and as shown in cross section on the figure 1 (see the electrical cable 1, shown on the figure 1 ), an elongated conductive element 2, such as aluminum or copper, which is surrounded by a first layer 3 of polyolefin, for example crosslinked polyethylene, this first layer being itself surrounded by a second layer 4 colored, by example polyethylene. This second layer 4 is called a surface layer or skin. The color of this surface layer corresponds to a specific function of the electric cable 1. For example, a yellow-green surface layer corresponds to a neutral cable and a blue layer to a protective cable.

However, polyolefins, such as polyethylene or polypropylene, because of their non-polar nature, exhibit relatively low adhesion and compatibility with most polar polymeric materials, such as polyurethanes.

By adhesion is meant the set of physicochemical phenomena that occur when two materials are brought into close contact in order to create a mechanical resistance to separation. A Once the contact is made, the energy required to achieve the separation is called adhesion energy.

However, in the field of electrical connection, and in particular in electrical junction boxes with casting resin, it is generally necessary to put in contact a polar insulating resin, such as polyurethane (PUR) bi-components, c ' that is composed of liquid polyurethane and a diphenylmethane diisocyanate hardener, with cables as described above (ie with cables having a polyolefin surface layer). However, this PUR resin is incompatible with a polyolefin surface, and is therefore incompatible with both the polyethylene thermoplastic surface layer and the crosslinked polyethylene bottom layer.

In the state of the art, in order to overcome this problem of adhesion between a polyurethane polar material and a non-polar material (an olefin), it is known to treat the surface of a flexible olefin thermoplastic sheet with a primer solution, containing one or more polar compounds, so that the sheet can adhere to a polyurethane surface. Generally, the primer solutions contain a halogenated polyolefin and an aromatic or aqueous solvent. However, such a surface treatment requires a large ventilation zone, equipped with a primer application mechanism, such as an immersion tank and drying means for evaporating water and other solvents. In addition, the flexible olefin thermoplastic sheet must adhere without voids to the polyurethane surface. Discontinuous application of a primer solution can indeed lead to the formation of voids between the olefin sheet and the polyurethane surface.

The document US2010 / 0055358 discloses a composition based on a multi-block interpolymer of olefin, a thermoplastic polyurethane, and a polydiol-based and / or polydiene-based polyurethane to promote adhesion between a polar material (such as polyester or polycarbonate) and a non-polar material. However, it is difficult to apply this technology to the field of electrically conductive cables. Indeed, it is not easy for a cable installer working on a construction site, to apply this composition, in particular to adhere a cable comprising a polyolefin surface layer with a polar material, such as a two-component polyurethane resin.

The present invention aims to propose a new cable that avoids all or part of the aforementioned drawbacks. In particular, the present invention aims to allow the adhesion of a polar material with an insulating layer of a cable made of a non-polar material and this, especially at room temperature (ie without it is necessary to (re) heat anything) and without the need for a special installation to adhere the two materials.

For this purpose, the subject of the invention is a cable comprising a conductive element surrounded by a first layer composed of a non-polar material, said first layer being itself surrounded by a second layer, characterized in that said second layer is composed of at least one copolymer of ethylene and octene (PEO) having, on the surface, grafted polar reactive chemical functions, said polar reactive chemical functions being able to adhere a third layer composed of a polar material.

The applicant has in fact surprisingly discovered that an ethylene-octene copolymer (PEO) surface layer having reactive polar chemical functions makes it possible to obtain a cable which is compatible with a polar material, such as a bi-component polyurethane resin as described above. The PEO layer is indeed both compatible with the lower layer of non-polar material, such as polyolefin and with the upper layer of polar material.

In an alternative embodiment, it is possible to add at least one intermediate layer between the conductive element and the first layer and / or between the first layer and the second PEO surface layer.

The layers comprising the cable are advantageously electrically insulating.

Preferably, the polar material of said third layer is diisocyanate-polyurethane.

Preferably, the polar reactive functions are chosen from among the functions: alcohol such as ⁺ CH ₂ -OH, CH ₃ -CH ⁺ -OH, CH ₃ -CH ₂ - ⁺ CH-OH; carbonyl such as CHO ⁺ , CH ₃ -CO ⁺ , (carboxyl) acid as CO ₂ H ⁺ and amine as NH ^- or a mixture thereof.

The PEO suitable for the present invention may for example be PEO ENGAGE ^® from DOW and in particular ENGAGE ^® 8003, ENGAGE ^® 8440, ENGAGE ^® 8540, ENGAGE ^® 8480, ENGAGE ^® 7086.01, ENGAGE ^® 7256, ENGAGE ^® 8556 and ENGAGE ^® 7380, or a mixture thereof.

Advantageously, the second layer also comprises polyethylene (PE). Even more advantageously, the polyethylene may be medium density polyethylene (MDPE). MDPE 28D780 sold by the company INEOS is suitable for the present invention.

Depending on its melting point, the PEO may optionally be mixed with PE or MDPE and this, for example, to obtain in addition a smoother surface that will promote better contact with the resin during molding and / or will allow to obtain an improved hardness.

In particular, the second layer comprises, by weight, relative to its total weight, 1% to 80% of polyethylene (PE) and 20% to 99% of ethylene-octene copolymer (PEO), preferably it comprises about 50% PE and about 50% PEO. For example, a composition suitable for the present invention is the use of 50% ethylene and octene copolymer of the brand ENGAGE ^® 8003 from DOW with 50% of medium density polyethylene having the reference 28D780 from INEOS .

According to one characteristic of the invention, the first layer of non-polar material is polyolefin.

In particular, the polyolefin is crosslinked. The crosslinking is carried out by techniques well known to those skilled in the art.

Even more particularly, the polyolefin is chosen from: polyethylene and polypropylene, or a mixture thereof.

Furthermore, the conductive element may be chosen from: bare copper, tinned copper, silver-plated copper, nickel-plated copper, nickel-plated copper and aluminum or any other conductive element known to those skilled in the art.

1. i) entourer l'élément conducteur par une première couche d'un matériau non polaire, de sorte que l'élément conducteur soit entouré de ladite première couche,
2. ii) entourer ladite première couche par une deuxième couche en copolymère d'éthylène et d'octène (PEO), de sorte à obtenir ladite deuxième couche,
3. iii) réaliser sur ladite deuxième couche lorsque le PEO est à l'état amorphe, un traitement de surface apte à fonctionnaliser en réactifs polaires la surface de la seconde couche en PEO.

The present invention also relates to a method for manufacturing a cable as described above, comprising the steps of:

1. i) surrounding the conductive element by a first layer of a non-polar material, so that the conductive element is surrounded by said first layer,
2. ii) surrounding said first layer with a second layer of ethylene-octene (PEO) copolymer, so as to obtain said second layer,
3. iii) performing on said second layer when the PEO is in the amorphous state, a surface treatment capable of functionalizing the surface of the second PEO layer with polar reagents.

Preferably, the surface treatment is carried out by atmospheric plasma in the air or by flame. When the treatment is carried out under atmospheric plasma, three plasma torches are generally arranged around the axis of the cable.

The present Applicant has surprisingly discovered and as will be demonstrated in the tests below, that when atmospheric plasma or oxidative flame surface treatment is performed when the PEO is still in the amorphous state, then we obtain a very good subsequent adhesion between the PEO layer and a polar material, even if the two materials are not adhered immediately after the surface treatment. Unexpectedly, the PEO must be processed in its molten state to retain its self-adhering property over time with a polar resin such as a two-component PUR resin. The cable thus manufactured can be stored without its ability to adhere too much over time. Amorphous state means that the PEO is substantially free of crystalline structure.

In addition, the choice of PEO is important because it reacts favorably to the surface treatment, compared to other polymers, such as linear polyethylene, radical polyethylene, polyethylene laden with chalk (for polarity), crosslinked polyethylene silane, chlorinated polyethylene, polypropylene or polyurethane. Indeed, as will be developed below during laboratory tests ( figure 3 ), the PEO allows to achieve exceptional adhesion results. This could be explained by the amorphous nature of the PEO material in the ambient state, as well as by its low degree of crystallinity. Better adhesion is obtained when the only polymer present in the surface layer is PEO. In this case, the adhesion can even be total, that is to say that one gets, during the peel test, a break in one or the other of the materials: namely PEO or polar material, without the interface being affected.

The adhesion according to the invention refers to the force required to apply to separate two materials in close contact, for example two materials bonded together. The technique used to separate the two materials will usually be peeling.

Preferably, steps i) and ii) are made by extrusion. Even more preferably, the first and second extrusions are performed at the same time (coextrusion of the first and second layers of the cable).

During an extrusion, the surface treatment is carried out right out of the extruder head (generally in the first meter and preferably in the first fifteen centimeters of the head). Indeed, towards the exit of the extruder head, the PEO is still in the amorphous state and this state makes it possible to graft perennial polar reactive chemical functions , despite hostile storage conditions (cold, frost, rain).

According to the invention, a plasma is an ionized gas which contains neutral and charged particles such as atoms, radicals, electrons and ions. When the pressure is low (P <133 Pa), the plasma used is considered "cold". Under these experimental conditions, the low density of excited molecules offsets the high temperatures of these species. Thus, the overall energy level is low and the chemistry of this plasma is at a temperature close to ambient temperature. The bombardment of the surface of the polymers by the energetic species created within the plasma leads to the rupture of the covalent bonds (cleavage of the macromolecular chains) and to the formation of free radicals. These react with the active species of plasma from which it results in the surface of materials the formation of functional chemical groups depending on the nature of the gas phase.

Advantageously, the gas used during the atmospheric plasma surface treatment is chosen from: compressed air, N ₂ , N ₂ / H ₂ , N ₂ / O ₂ , N ₂ / CO ₂ and N ₂ / N ₂ O, or a mixture thereof. In particular, the gas used is nitrogen, hydrogenated nitrogen at 3% maximum hydrogen or compressed air.

The use of plasma for surface treatment has many advantages. First, the action of the plasma is limited to the extreme surface, typically 100-200 Å. The properties of PEO at heart will thus be little altered. Then, this treatment takes place in a dry atmosphere (gas) which limits the contamination and removes the subsequent steps such as washing, necessary in the case of chemical processes. Processing times are short (usually between 5ms and 30ms). The plasma treatment is continuous online: during the extrusion phase of the polymer on the aluminum conductive element. The speed is on average 100m / min. The treatment is however effective from 20m / min (30ms of treatment time to treat 1cm of cable with three plasma torches) and can go up to 120m / min (5ms of treatment time to treat 1cm of cable with three torches plasma). To exceed these speeds and to observe an efficiency of the treatment, it is possible to add additional torches in order to treat several times the surface of the cable. In addition, the treatment takes place at not very high temperatures (around 70 ° C), which limits the thermal damage in the mass of the material.

The flame treatment can be done by oxidizing flame which is brought into contact with the surface of the PEO layer. Generally a contact time of 0.01 to 0.1 seconds is sufficient to oxidize the surface of about fifty Angstroms. The effect of the flame will mainly induce polar functions on the surface of PEO, such as carbonyl, carboxyl or hydroxyl groups.

The present invention also relates to the use of a cable as described above or obtained according to the aforementioned method, to realize cold sealing a junction box comprising at least said cable with a resin of polar material, such as diisocyanate / polyurethane.

An object of the present invention relates to a junction box comprising a resin of polar material, such as isocyanate / polyurethane, characterized in that it comprises at least one cable, preferably at least two cables to connect as described herein. above or obtained according to the aforementioned method.

The casting resin junction boxes allow the connection of several conductor to conductor cables. They are used in particular for junction, bypass or parallel bypass. They are particularly suitable for sealing and insulating low-voltage electrical connection accessories, which also require excellent dielectric strength. They also prevent water infiltration to the junction and the rest of the cable.

The resin joining material is generally composed of two components in liquid form: a resin on the one hand polyurethane and a hardener diphenylmethane diisocyanate on the other. These two components are, before use, in the form of two separate pockets, one containing the resin, the other containing the hardener. Once poured and cured, the resin joint material is watertight, transversely and longitudinally. These products therefore make it possible, safely, to use underground, inside and outside, in installation ducts.

Once the electrical connection of the cables made within the junction box, it is necessary to prepare the resin mixture by mixing together the two pockets. Once the mixture is well kneaded, the resulting mixture is introduced into the junction box which can be transparent and serves as a mold which has a very good mechanical strength and facilitates visual control. Accessories are necessary for mounting such as an insulating tape, a separator, a funnel, protective gloves ...

Thanks to the characteristics of the cables according to the invention or the method according to the invention, the electrical connection of the junction box can now include cables whose insulation comprises one or more polyolefin layers, such as crosslinked polyethylene coated with a PE / PEO surface layer, even if it is intended to pour two-component polyurethane resin into the junction box.

• La figure 1 a déjà été décrite précédemment, et est une vue de section transversale d'un câble selon l'art antérieur ;
• La figure 2 est un graphique montrant la moyennes des adhérences en N/mm au niveau de l'interface d'une couche en copolymère d'éthylène et d'octène (PEO) coloré et d'une résine PUR bi-composants pour 16 séries de câbles (une série comprenant 40 échantillons, et pour 4 couleurs différentes : vert/jaune, brun, noir et gris); et
• La figure 3 représente un tableau de synthèse des divers polymères testés lors des essais d'adhérence.

The present invention will be better understood and other objects, details, features and advantages thereof will appear more clearly in the light of the examples which follow with reference to the annotated figures, said examples and figures being given for illustrative and not limiting purposes. .

• The figure 1 has already been described above, and is a cross sectional view of a cable according to the prior art;
• The figure 2 is a graph showing the average adhesion in N / mm at the interface of a colored ethylene-octene (PEO) copolymer layer and a two-component PUR resin for 16 cable sets ( a series comprising 40 samples, and for 4 different colors: green / yellow, brown, black and gray); and
• The figure 3 represents a summary table of the various polymers tested during the adhesion tests.

EXAMPLES

For the quantitative tests below, the value of adhesion was measured according to HD603 part 5 Section G.

It is an attempt to separate the interface of two materials glued together, by peeling. For all tests 1 to 4 above, the plasma surface treatment is performed using a ULS type plasma from AcXys.

This standard specifies how to prepare samples. In addition, it requires cleaning after treatment with isopropanol. Therefore, from the qualitative tests below, the samples were cleaned or not with this alcohol to study the influence.

Qualitative tests: Trial 1:

For this first qualitative test, the adhesion was tested by several people by manual peeling. They compared the interfacial resistance of several materials with a two-component PUR resin by relative comparison.

The different parameters of this test 1 are shown in the table of the figure 3 . The various polymers tested are: MDPE medium density polyethylene (28D780 ^® ), PEO and MDPE blend (50% ENGAGE ^® 8003 + 50% 28D780), PEO blend and low density polyethylene (50% ENGAGE ^® 8003 + LD165 BW ^® Exxon Mobile), an ethylene / butyl acrylate copolymer comprising 8% butyl acrylate (B24D230), an ethylene / butyl acrylate copolymer comprising 15% butyl acrylate (B28N230), a low density polyethylene ( DFDK ^® -6050), PEO and other low density polyethylene (LD165).

The table of the figure 3 shows that very good adhesion results are obtained with the material PEO (ENGAGE ^® 8003) and with the material resulting from mixing PEO (ENGAGE ^® 8003) with a medium density polyethylene (28D780). Moreover, for these two materials, it should be noted that it is better to use an oven treatment step before cleaning with isopropanol in order not to impair their adhesion capacity too much.

Trial 2:

Several people believe this time the interface resistance of a PEO material and a two-component PUR resin. This adhesion test is also carried out by manual peeling. They thus estimate, by relative comparison, whether the adhesion is more or less strong during the manual separation of the PEO material and the resin.

PEO tested is the Engage ^® 8003 from Dow to which was added 1% by weight relative to the weight of PEO, a green colorant (2001-GN-50 reference PolyOne). The dye has the sole purpose of bringing the tested samples closer to the final composition of the colored topcoat a cable. Twelve plates or sheets of this PEO mixture with 1% dye are thus produced. At one end of each plate is disposed a ribbon serving as a starting point, ie a starting point to allow subsequent manual separation at the interface of the PEO with dye and the two-component PUR resin. After the processing step (samples 5 to 12) or non-treatment (control samples 1 to 4), a two-component PUR resin is poured onto the plates.

The experiments are summarized in Table I below. <i> Table I </ i> Samples treatments Adhesion result 1 no No adhesion 2 3 4 5 Plasma + IP * + wiping (cold) Adhesion between medium and good + white traces (adhesion marks) 6 7 8 9 Drying oven ** + plasma + IP * + wiping (hot) Medium to good adhesion with very difficult priming- Functionalization of the PEO surface lasts longer in time 10 11 12 * the samples were cleaned with iso-propan-1ol (IP) 1 hour before the start of each test.
** the samples were first placed in an oven at 195 ° C (measured temperature 182.9 ° C) for 5 minutes.

These different qualitative tests demonstrated that when the plasma was applied to the hot PEO, the adhesion was better compared to a cold plasma treatment (without oven) and that, in addition, the functionalization of the PEO surface was not too much affected by isopropanol, unlike cold treatment.

Indeed, in the hot treatment, the priming step is considered very difficult, which proves that the PEO material with dye had trouble detaching / peeling off the two-component PUR resin.

The cleaning step with isopropanol, required by the HD603 part 5 Section G, has the effect of taking away the chemical functions, especially the less grafted during the plasma treatment. Thus, during the hot-plasma treatment of PEO followed by the isopropanol cleaning step, a sufficient quantity of useful chemical functions at a sufficient level of adhesion for the application required remains, which is not the case. the case with cold processing. Thus, when the PEO is heat treated, it is not necessary to immediately proceed to "gluing". Therefore, the very good functionalization of the PEO surface layer, makes it possible to obtain cables that can adhere to the two-component PUR resin during their use on site, even a few months after plasma treatment. While cold-processed, cleaning with isopronaol destroys most of the polar functions induced by surface treatment and thus self-adhering property. Therefore, in cold processing, the "bonding" must be done immediately to obtain a suitable adhesion.

Quantitative tests : Trials 3

In the present case, it is an attempt to separate the polyethylene (PE) / ethylene-octene copolymer (PEO) surface layer from the two-component polyurethane resin as described above. All the tests below were carried out following the procedure of the HD60 part 5 Section G. This further describes how the results should be interpreted.

The results of the tests are curves representing the detachment force (in N) as a function of the separation distance (in mm).

The peel strength of a sample "s" is calculated as follows: $$P_s=\frac{F_s}{B}=\frac{{\mathit{F}}_{\mathit{smin}}\mathit{+}{\mathit{<figure-callout\; id="2"\; label="F\; smax"\; filenames="imgf0001.png"\; state="\{\{state\}\}">F\; </figure-callout>}}_{\mathit{smax}}}{2B}$$

Fs

force de décollement (en N)

F_Smin

force de décollement minimum (en N)

F_Smax

force de décollement maximum (en N)

B

largeur de l'échantillon « n »(en mm)

With,

fs

release force (in N)

F _Smin

minimum detachment force (in N)

F _Smax

maximum detachment force (in N)

B

sample width "n" (in mm)

If P _s gives the peel strength of a sample "n", the adhesion is defined by: $$\mathrm{AT}={\tilde{P}}_s={\displaystyle \underset{s=1}{\overset{40}{\Sigma }}}{P}_s$$

The objective of this test is to obtain an adhesion A ≥ 1N.mm ^-1 . This value is indeed satisfactory in the field of cables.

In 2010, 16 series of adhesion tests on cables having a section of 150mm ² were made, that is to say 16x40 peel tests (1 series = 40 samples). 10 samples per color and 4 colors were tested.

The cable for these tests included four aluminum conductors, each was coated with a crosslinked polyethylene layer, itself coated with a surface layer comprising MDPE 28D780 49,5% and 49,5% PEO ENGAGE ^® 8003 and about 1% dye (masterbach) for the color (one color for each driver): gray, brown, black, green / yellow. In particular, the green / yellow surface layer actually corresponds only to a partial green surface layer (green colored MDPE / PEO surface coating) which reveals in place the lower layer of crosslinked yellow polyethylene. Thus this green / yellow conductor is particular because not only the green part (MDPE / PEO) is treated but also the yellow part (XLPE) which moreover reacts less to the surface treatment, which explains slightly less adherence results. therefore.

On each sample tested is measured the force of separation in daN using a traction machine, the detachment to be performed over the length of the cable tested. In particular, the traction machine has the Zwick reference BZ1-MM14450.ZW04 and operates for the imposed displacement test of the crossbar at 100mm / min. In addition, for this test, the width of each sample (cable) was 10mm and the test length was 200mm.

The pulling machine provides a graph for each test. A peel strength P _s in N.mm ^-1 is then calculated.

This calculation is carried out on all the sample graphs, then by averaging we obtain the value of the adhesion A (see Table II).

$$A_{\mathit{Brun}}=4,68N\mathrm{.}m{m}^{-1}$$

$$A_{\mathit{Noir}}=5,35N\mathrm{.}m{m}^{-1}$$

$$A_{\mathit{Gris}}=6,08N\mathrm{.}m{m}^{-1}$$

$$A_{\mathit{Série}8}=\frac{A_{V/J}+A_{\mathit{Brun}}+A_{\mathit{Noir}}+A_{\mathit{Gris}}}{4}=4,76N\mathrm{.}m{m}^{-1}$$

Tableau II (valeur en N/mm) Série V/J Brun Noir Gris Adhérence 1 1,31 1,62 3,06 3,78 2,44 2 2,2 2,42 3,22 4,05 2,97 3 1,77 4,8 3,88 3,97 3,61 4 1,37 2,8 4,05 4,59 3,20 5 1,66 2,91 3,55 4,10 3,06 6 1,56 3,58 2,95 4,00 3,02 7 2,57 7,29 3,66 6,42 4,98 8 2,94 4,68 5,36 6,08 4,76 9 1,96 4,23 2,85 6,10 3,79 10 2,19 4,46 6,46 3,69 4,20 11 2,21 4,97 5,36 7,42 4,99 12 2,27 4,55 5,98 5,65 4,61 13 1,76 2,52 3,75 4,84 3,22 14 2,05 2,34 3,12 5,44 3,24 15 2,12 4,15 4,30 5,37 3,99 16 3,11 3,69 5,24 6,56 4,65 For example, for series 8 the following results are obtained and they are well above the target of 1 N / mm: $${\mathrm{AT}}_{V/J}=2,94\mathrm{NOT}\mathrm{.}m{m}^{-1}$$

$${\mathrm{AT}}_{\mathit{Brown}}=4,68\mathrm{NOT}\mathrm{.}m{m}^{-1}$$

$${\mathrm{AT}}_{\mathit{Black}}=5,35\mathrm{NOT}\mathrm{.}m{m}^{-1}$$

$${\mathrm{AT}}_{\mathit{Grey}}=6,08\mathrm{NOT}\mathrm{.}m{m}^{-1}$$

$${\mathrm{AT}}_{\mathit{Series}8}=\frac{{\mathrm{AT}}_{V/J}+{\mathrm{AT}}_{\mathit{Brown}}+{\mathrm{AT}}_{\mathit{Black}}+{\mathrm{<figure-callout\; id="4"\; label="AT\; Grey"\; filenames="imgf0001.png"\; state="\{\{state\}\}">AT\; </figure-callout>}}_{\mathit{Grey}}}{4}=4,76\mathrm{NOT}\mathrm{.}m{m}^{-1}$$

<i> Table II (value in N </ i> / <i> mm) </ i> Series G / Y Brown Black Grey adherence 1 1.31 1.62 3.06 3.78 2.44 2 2.2 2.42 3.22 4.05 2.97 3 1.77 4.8 3.88 3.97 3.61 4 1.37 2.8 4.05 4.59 3.20 5 1.66 2.91 3.55 4.10 3.06 6 1.56 3.58 2.95 4.00 3.02 7 2.57 7.29 3.66 6.42 4.98 8 2.94 4.68 5.36 6.08 4.76 9 1.96 4.23 2.85 6.10 3.79 10 2.19 4.46 6.46 3.69 4.20 11 2.21 4.97 5.36 7.42 4.99 12 2.27 4.55 5.98 5.65 4.61 13 1.76 2.52 3.75 4.84 3.22 14 2.05 2.34 3.12 5.44 3.24 15 2.12 4.15 4.30 5.37 3.99 16 3.11 3.69 5.24 6.56 4.65

As shown in Table II and the graphical figure of figure 2 the average adhesion for each series and for the 4 colors is well beyond the fixed target of 1N / mm.

It can also be observed that there are variations in adhesion values within the same series of the same sample. This must be explained by the fact that the grafting of reactive polar chemical functions is never identical each time. The number of groups of chemical functions must vary per mm ² .

The curve corresponding to the yellow / green color is the one which has an average of adhesion per test series the lowest compared to other colors. This is explained by the fact that, as previously stated, the surface layer of the cables of this color is irregular: the green PEO surface layer is twisted along the cable so as to reveal the bottom layer in yellow which is crosslinked polyethylene. Thus, the yellow / green cables have less functionalized PEO surface layer and therefore fewer polar chemical functions on their surface, which is why the adhesion is lower than with the cables having another color. Thus, this demonstrates the importance of the functionalized PEO surface layer to allow a good immediate or subsequent adhesion with a polar material, the crosslinked polyethylene lower layer not being able a priori to be functionalized as well.

Test 4: Sustainability of the functionalization of the PEO surface layer over time (Table III).

• 28 échantillons de câble présentant le revêtement de surface selon l'invention (49,5%de MDPE 28D780 et 49,5% de PEO ENGAGE^® 8003 et d'environ 1% de colorant (masterbach)) moulés dans la résine PUR bi-composants (2 premières colonnes) et,
• 28 échantillons pour lesquels le moulage a été réalisé 12 mois après la fabrication du câble revêtu du traitement de surface selon l'invention (49,5%de MDPE 28D780 et 49,5% de PEO ENGAGE^® 8003 et d'environ 1% de colorant (masterbach)) (deux dernières colonnes).
  Pour ces deux séries d'essais, les échantillons de câble présentent une section de 150mm².
  Le même mode opératoire que pour l'essai 3 a été réalisé en suivant de plus les conditions énoncées dans le tableau III.
  

Tests were carried out on 56 samples. Indeed 2 series of 28 samples were tested:

• 28 cable samples having the surface coating according to the invention (49.5% MDPE 28D780 and 49.5% PEO ENGAGE ^® 8003 and about 1% dye (masterbach)) molded in the dual-strength PUR resin; components (first 2 columns) and,
• 28 samples for which the molding was carried out 12 months after the manufacture of the cable coated with the surface treatment according to the invention (49.5% of MDPE 28D780 and 49.5% of PEO ENGAGE ^® 8003 and about 1% of dye (masterbach)) (last two columns).
  For these two series of tests, the cable samples have a section of 150mm ² .
  The same procedure as for test 3 was carried out by following the conditions set out in Table III.
  

As shown in Table III, after 12 months of molding, the PE / PUR interface remains solid, despite a slight decrease. In fact, on outgoing production cables, an adhesion value of (3 ± 1) N / mm on average was measured, and now a value of approximately (2 ± 1) N / mm is measured. It is not easy to describe this as a significant decrease given the dispersion of the results.

Similarly, a cable that would have been molded after 12 months still have sufficient reactive chemical functions to allow adhesion to the PUR resin greater than 1N / mm (column before molding).

Overall conclusion: We can conclude that this technique offers durable performance (> 12 months) of chemical adhesion between PE and PUR.

Although the invention has been described in connection with a particular embodiment, it is obvious that it is not limited thereto and that it comprises all the technical equivalents of the means described and their combinations if they are within the scope of the invention.

Claims (15)

A cable comprising a conductive element surrounded by a first layer composed of a non-polar material, said first layer itself being surrounded by a second layer, characterized in that said second layer is composed of at least one ethylene copolymer and octene (PEO) having on the surface grafted polar reactive chemical functions, said polar reactive chemical functions being able to adhere a third layer composed of a polar material. Cable according to claim 1, wherein the polar material of said third layer is diisocyanate-polyurethane. Cable according to one of the preceding claims, in which the polar reactive functions are chosen from among the functions: alcohol; carbonyl, carboxyl, and amine, or a mixture thereof. Cable according to one of the preceding claims, wherein the second layer also comprises polyethylene. The cable of claim 4, wherein the polyethylene is medium density polyethylene (MDPE). Cable according to one of claims 4 or 5, wherein the second layer comprises by weight, relative to its total weight, 1% to 80% of polyethylene (PE) and 20% to 99% of ethylene copolymer and octene (PEO), preferably of the order of 50% of polyethylene and 50% of copolymer of ethylene and octene. Cable according to one of the preceding claims, wherein the first layer of non-polar material is polyolefin. Cable according to claim 7, wherein the polyolefin is crosslinked. Cable according to one of claims 7 or 8, wherein the polyolefin is selected from: polyethylene and polypropylene, or a mixture thereof. A method for manufacturing a cable according to one of claims 1 to 9, comprising the steps of: i) surrounding the conductive element by a first layer of a non-polar material, so that the conductive element is surrounded by said first layer, ii) surrounding said first layer with a second layer of ethylene-octene (PEO) copolymer, so as to obtain said second layer, iii) performing on said second layer when the PEO is in the amorphous state, a surface treatment capable of functionalizing the surface of the second PEO layer with polar reagents. A method of manufacturing a cable according to claim 10, wherein the surface treatment is carried out by atmospheric plasma in the air or by flame. A method of manufacturing a cable according to claim 10 or 11, wherein steps i) and ii) are carried out by extrusion, preferably by coextrusion. A method for manufacturing a cable according to one of claims 11 or 12, wherein the gas used during the atmospheric plasma surface treatment is selected from: compressed air, N ₂ , N ₂ / H ₂ , N ₂ / O ₂ , N ₂ / CO ₂ and N ₂ / N ₂ O, or a mixture thereof. Use of a cable according to one of claims 1 to 9 or obtained according to the method according to one of claims 10 to 13, for cold sealing of a junction box comprising at least said cable with a resin in polar material, such as diisocyanate / polyurethane. Junction box comprising a resin made of polar material, such as diisocyanate / polyurethane, characterized in that it comprises at least one cable according to one of claims 1 to 9 or obtained according to the method according to one of claims 10 at 13.

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